U.S. patent application number 09/725321 was filed with the patent office on 2001-07-05 for braking pressure control apparatus having device for diagnosing manually operated hydraulic system.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Kawahata, Fumiaki, Miyazaki, Tetsuya, Morikawa, Hirohiko, Otomo, Akihiro.
Application Number | 20010006308 09/725321 |
Document ID | / |
Family ID | 18490702 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006308 |
Kind Code |
A1 |
Kawahata, Fumiaki ; et
al. |
July 5, 2001 |
Braking pressure control apparatus having device for diagnosing
manually operated hydraulic system
Abstract
A braking pressure control apparatus for a hydraulically
operated brake, including a first hydraulic system having a first
hydraulic pressure source power-operated to pressurize a working
fluid and capable of controlling the fluid pressure, for operating
the brake, a second hydraulic system having a second hydraulic
pressure source operable by an operating force acting on a manually
operable brake operating member, to pressurize the working fluid to
a pressure higher than a level corresponding to the operating
force, for operating the brake, a switching device operable to
selectively establish a first state in which the brake is operated
with the pressurized fluid delivered from the first hydraulic
pressure source, and a second state in which the brake is operated
with the pressurized fluid delivered from the second hydraulic
pressure source, and a diagnosing device operable to diagnose the
second hydraulic system on the basis of the fluid pressure in the
second hydraulic system.
Inventors: |
Kawahata, Fumiaki;
(Toyota-shi, JP) ; Miyazaki, Tetsuya; (Toyota-shi,
JP) ; Morikawa, Hirohiko; (Toyota-shi, JP) ;
Otomo, Akihiro; (Toyota-shi, JP) |
Correspondence
Address: |
Oliff & Berridge PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
|
Family ID: |
18490702 |
Appl. No.: |
09/725321 |
Filed: |
November 29, 2000 |
Current U.S.
Class: |
303/122 |
Current CPC
Class: |
B60T 17/22 20130101;
B60T 8/441 20130101; B60T 8/4081 20130101; B60T 8/94 20130101; B60T
8/367 20130101 |
Class at
Publication: |
303/122 |
International
Class: |
B60T 008/88 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
11-367990 |
Claims
What is claimed is:
1. A braking pressure control apparatus for a hydraulically
operated brake, comprising: a first hydraulic system including a
first hydraulic pressure source which is power-operated to
pressurize a working fluid and capable of controlling a pressure of
the pressurized fluid, for operating said brake with the
pressurized fluid delivered from said first hydraulic pressure
source; a second hydraulic system including a manually operable
brake operating member, and a second hydraulic pressure source
which is operable by an operating force acting on said brake
operating member, to pressurize the working fluid to a pressure
higher than a level corresponding to said operating force, for
operating said brake with the pressurized fluid delivered from said
second hydraulic pressure source; a switching device operable to
selectively establish a first state in which said brake is operated
with the pressurized fluid delivered from said first hydraulic
pressure source, and a second state in which said brake is operated
with the pressurized fluid delivered from said second hydraulic
pressure source; and a diagnosing device operable to diagnose said
second hydraulic system on the basis of a pressure of the fluid in
said second hydraulic system.
2. A braking pressure control apparatus according to claim 1,
wherein said diagnosing device diagnoses said second hydraulic
system on the basis of the pressure of the fluid pressurized by
said second hydraulic pressure source and a pressure of the fluid
in said manually operable brake while said second state is
established by said switching device.
3. A braking pressure control apparatus according to claim 2,
wherein said diagnosing device includes a switching portion
operable when said first state is established, to change said first
state to said second state after the fluid pressure in said brake
has been controlled in said first state to a level close to the
fluid pressure in said second hydraulic pressure source.
4. A braking pressure control apparatus according to claim 2,
wherein said second hydraulic system comprises: a first pressure
sensing device for detecting the pressure of the fluid pressurized
by said second hydraulic pressure source; and a second pressure
sensing device for detecting the pressure of the fluid in said
brake, and wherein said diagnosing device includes a
sensor-diagnosing portion operable to diagnose at least one of said
first and second pressure sensing devices, on the basis of the
pressures detected by said first and second sensing devices.
5. A braking pressure control apparatus according to claim 4,
further comprising: a first braking pressure control device
operable while said first state is established by said switching
device, to control the pressure of the fluid in said brake on the
basis of the pressure of the fluid detected by said first pressure
sensing device; and a second braking pressure control device
operable when said sensor-diagnosing portion determines that said
first pressure sensing device is abnormal while said first state is
established by said switching device, said second braking pressure
control device controlling the pressure of the fluid in said brake
on the basis of an operating amount of said manually operable brake
operating member.
6. A braking pressure control apparatus according to claim 1,
wherein said second hydraulic system comprises: a hydraulic booster
including a power piston which is operatively connected to said
manually operable brake operating member and which partially
defines a booster chamber on a rear side of said power piston as
viewed in a direction of an advancing movement of said power piston
when said brake operating member is operated, said booster chamber
being arranged to receive a pressurized fluid whose pressure
corresponds to the operating force of said brake operating member;
and a booster pressure sensor for detecting the pressure of the
pressurized fluid in said booster chamber, and wherein said
diagnosing device diagnoses said second hydraulic system on the
basis of the pressure of the pressurized fluid in said booster
chamber detected by said booster pressure sensor.
7. A braking pressure control apparatus according to claim 6,
wherein said second hydraulic system comprises: a master cylinder
including a pressurizing piston which is operatively connected to
said power piston and which partially defines a pressurizing
chamber on one of opposite sides thereof remote from said power
piston; and a master-cylinder pressure sensor for detecting a
pressure of the fluid in said pressurizing chamber, and wherein
said diagnosing device diagnoses said second hydraulic system on
the basis of the fluid pressure detected by said master-cylinder
pressure sensor and the fluid pressure detected by said booster
pressure sensor.
8. A braking pressure control apparatus according to claim 7,
wherein said diagnosing device determines that said master cylinder
is normal while said hydraulic booster is abnormal, when the
pressure of the fluid in said pressurizing chamber detected by said
master-cylinder pressure sensor is not lower than a predetermined
threshold, while the pressure of the fluid in said booster chamber
detected by said booster pressure sensor is lower than a
predetermined threshold.
9. A braking pressure control apparatus according to claim 7,
wherein said hydraulic booster includes a pressure regulating
portion which is connected to a high-pressure source capable of
delivering a pressurized fluid whose pressure is higher than a
maximum pressure of the fluid pressurized by said second hydraulic
pressure source and which is operable to regulate the pressure of
the pressurized fluid received from said high-pressure source to a
level corresponding to the pressure of the fluid in said
pressurizing chamber, said hydraulic booster having a fluid passage
through which the pressurized fluid whose pressure has been
regulated by said pressure regulating portion is supplied to said
booster chamber, and wherein said diagnosing device determines that
said master cylinder is abnormal, when the fluid pressure in said
pressurizing chamber detected by said master-cylinder pressure
sensor is lower than a predetermined threshold while the fluid
pressure in said booster chamber detected by said booster pressure
sensor is lower than a predetermined threshold.
10. A braking pressure control apparatus according to claim 6,
further comprising: a first braking pressure control device
operable while said first state is established by said switching
device, to control the pressure of the fluid in said brake on the
basis of the pressure of the fluid detected by said first pressure
sensing device; and a second braking pressure control device
operable when said sensor-diagnosing portion determines that said
first pressure sensing device is abnormal while said first state is
established by said switching device, said second braking pressure
control device controlling the pressure of the fluid in said brake
on the basis of an operating amount of said manually operable brake
operating member, and wherein said second hydraulic system
comprises: a master cylinder including a pressurizing piston which
is operatively connected to said power piston and which partially
defines a pressurizing chamber on one of opposite sides thereof
remote from said power piston; and a master-cylinder pressure
sensor for detecting a pressure of the fluid in said pressurizing
chamber, and wherein said first braking pressure control device
includes a portion operable to control the pressure of the fluid in
said brake on the basis of the pressure of the fluid in said
pressurizing chamber detected by said master-cylinder pressure
sensor.
11. A braking pressure control apparatus according to claim 1,
wherein said second hydraulic system comprises: a pressure sensing
device for detecting the pressure of the fluid pressurized by said
second hydraulic pressure source; and an operating amount sensing
device for detecting an operating amount of said manually operated
brake operating member, and wherein said diagnosing device
diagnoses said second hydraulic system on the basis of the pressure
of the pressurized fluid detected by said pressure sensing device
and the operating amount of said brake operating member detected by
said operating amount sensing device.
12. A braking pressure control apparatus according to claim 11,
wherein said second hydraulic system includes a plurality of brake
cylinders for respective brakes, and fluid passages connecting said
brake cylinders to said second hydraulic pressure source, said
fluid passages including at least one main fluid passage connected
to said second hydraulic pressure source, and at lest one
connecting passage each of which is connected to one of said at
least two main fluid passage and connects at least two of said
plurality of brake cylinders to each other, said braking pressure
control apparatus further comprising: a communicating valve
provided in at least one of said at least one connecting passage
and is operable between an open state in which said at least two
brake cylinders are held in communication with each other, and a
closed state in which said at least two brake cylinders are
disconnected from each other, and wherein said diagnosing device
diagnoses said at least two brake cylinders for the presence of air
contained therein, on the basis of amounts of change of said
operating stroke of said brake operating member and the pressure of
the fluid pressurized by said second hydraulic pressure source
while said communicating valve is placed in said open state and
those while said communicating valve is placed in said closed
state.
13. A braking pressure control apparatus according to claim 1,
wherein said second hydraulic system includes a high-pressure
source capable of delivering a pressurized fluid whose pressure is
higher than a maximum pressure of the fluid pressurized by said
second hydraulic pressure source, and wherein said diagnosing
device diagnoses said second hydraulic system on the basis of the
pressure of the pressurized fluid of said high-pressure source as
well as the pressure of the fluid pressurized by said second
hydraulic pressure source.
14. A braking pressure control apparatus for a hydraulically
operated brake including a brake cylinder, comprising: a first
hydraulic system including a first hydraulic pressure source which
is power-operated to pressurize a working fluid and capable of
controlling a pressure of the pressurized fluid to be delivered to
said brake cylinder for operating said brake with the pressurized
fluid delivered from said first hydraulic pressure source; a second
hydraulic system including a manually operable brake operating
member, and a second hydraulic pressure source which is operable by
an operating force acting on said brake operating member, to
pressurize the working fluid to a pressure corresponding to said
operating force, so that the fluid pressurized by said second
hydraulic pressure source is delivered to said brake cylinder for
operating said brake; a switching device operable to selectively
establish a first state in which said brake cylinder is supplied
with the pressurized fluid delivered from said first hydraulic
pressure source, and a second state in which said brake is supplied
with the pressurized fluid delivered from said second hydraulic
pressure source; a stroke simulator device including a stroke
simulator connected to said second hydraulic pressure source, and a
simulator shut-off valve having a closed state in which said stroke
simulator is disconnected from said second hydraulic pressure
source, and an open state in which said stroke simulator is in
communication with said second hydraulic pressure source: and a
diagnosing device operable to diagnose said stroke simulator device
on the basis of an amount of change of an operating stroke of said
brake operating member and an amount of change of the pressure of
the fluid pressurized by said second hydraulic pressure source.
15. A braking pressure control apparatus according to claim 14,
wherein said diagnosing device diagnoses said stroke simulator
device while said second state is established by said switching
device.
16. A braking pressure control apparatus according to claim 15,
wherein said second hydraulic system includes a plurality of brake
cylinders for respective brakes, and fluid passages connecting said
brake cylinders to said second hydraulic pressure source, said
fluid passages including at least one main fluid passage connected
to said second hydraulic pressure source, and at lest one
connecting passage each of which is connected to said main fluid
passage and connects at least two of said plurality of brake
cylinders to each other, said braking pressure control apparatus
further comprising: a communicating valve provided in at least one
of said at least one connecting passage and is operable between an
open state in which said at least two brake cylinders are held in
communication with each other, and a closed state in which said at
least two brake cylinders are disconnected from each other, and
wherein said diagnosing device diagnoses said stroke simulator
device while said communicating valve is placed in said closed
state.
17. A braking pressure control apparatus according to claims 14,
wherein said diagnosing device has a releasing passage connected at
one end thereof to a low-pressure source and at the other end
thereof to a portion of said stroke simulator device which is
between said simulator shut-off valve and said stroke simulator,
said diagnosing device including a releasing valve provided in said
releasing passage and having an open state in which said stroke
simulator device is communicated at said portion thereof to said
low-pressure source, and a closed state in which said stroke
simulator device is disconnected at said portion thereof from said
low-pressure source, and wherein said diagnosing device diagnoses
said stroke simulator device on the basis of the amount of changes
of the operating stroke of said brake operating member and the
pressure of the fluid pressurized by said second hydraulic pressure
source while said releasing valve is placed in said open state.
18. A braking pressure control apparatus according to claim 14,
further comprising an alarming device operable to provide an alarm
when said diagnosing device has determined that said stroke
simulator device is abnormal.
19. A braking pressure control apparatus according to claim 1,
further comprising a controller for controlling said switch to
selectively establish said first and second states, depending upon
a result of a diagnosis by said diagnosing device.
20. A braking pressure control apparatus according to claim 14,
further comprising a controller for controlling said switch to
selectively establish said first and second states, depending upon
a result of a diagnosis by said diagnosing device.
21. A braking pressure control apparatus according to claim 1,
further comprising a first braking pressure control device operable
while no abnormality is detected by said diagnosing device, for
controlling the fluid pressure in said brake in a predetermined
normal manner, and a second braking pressure control device
operable while an abnormality of at least one of predetermined at
least one sensor is detected by said diagnosing device, for
controlling the fluid pressure in said brake in a manner different
from said predetermined normal manner, without using an output of
said at least one of said predetermined at least one sensor.
22. A braking pressure control apparatus according to claim 14,
further comprising a first braking pressure control device operable
while no abnormality is detected by said diagnosing device, for
controlling the fluid pressure in said brake in a predetermined
normal manner, and a second braking pressure control device
operable while an abnormality of at least one of predetermined at
least one sensor is detected by said diagnosing device, for
controlling the fluid pressure in said brake in a manner different
from said predetermined normal manner, without using an output of
said at least one of said predetermined at least one sensor.
23. A braking pressure control apparatus for a hydraulically
operated brake, characterized by comprising: a first hydraulic
system including a first hydraulic pressure source which is
power-operated to pressurize a working fluid and capable of
controlling a pressure of the pressurized fluid, for operating said
brake with the pressurized fluid delivered from said first
hydraulic pressure source; a second hydraulic system including a
manually operable brake operating member, and a second hydraulic
pressure source which is operable by an operating force acting on
said brake operating member, to pressurize the working fluid to a
pressure higher than a level corresponding to said operating force,
for operating said brake with the pressurized fluid delivered from
said second hydraulic pressure source; a switching device operable
to selectively establish a first state in which said brake is
operated with the pressurized fluid delivered from said first
hydraulic pressure source, and a second state in which said brake
is operated with the pressurized fluid delivered from said second
hydraulic pressure source; and a diagnosing device operable to
diagnose said second hydraulic system on the basis of an operating
state of said second hydraulic system.
24. A braking pressure control apparatus according to claim 1,
further comprising a device for restricting an amount of change of
at least one of an operating state of said brake operating member
and the fluid pressure in said brake when the operating state of
the apparatus is switched by said switching device between said
first and second states.
25. A braking pressure control apparatus according to claim 14,
further comprising a device for restricting an amount of change of
at least one of an operating state of said brake operating member
and the fluid pressure in said brake when the operating state of
the apparatus is switched by said switching device between said
first and second states.
26. A braking pressure control apparatus according to claim 21,
further comprising a device for restricting an amount of change of
at least one of an operating state of said brake operating member
and the fluid pressure in said brake when the operating state of
the apparatus is switched by said switching device between said
first and second states.
27. A braking pressure control apparatus according to claim 1,
further comprising a device for reducing a difference between the
fluid pressure in said brake and the pressure of the fluid
pressurized by said second hydraulic pressure source, when the
operating state of the apparatus is switched by said switching
device between said first and second states.
28. A braking pressure control apparatus according to claim 14,
further comprising a device for reducing a difference between the
fluid pressure in said brake and the pressure of the fluid
pressurized by said second hydraulic pressure source, when the
operating state of the apparatus is switched by said switching
device between said first and second states.
29. A braking pressure control apparatus according to claim 21,
further comprising a device for reducing a difference between the
fluid pressure in said brake and the pressure of the fluid
pressurized by said second hydraulic pressure source, when the
operating state of the apparatus is switched by said switching
device between said first and second states.
30. A braking pressure control apparatus according to claim 1,
further comprising a device for reducing an amount of flow of the
fluid between said second hydraulic pressure source and said brake
when the operating state of the apparatus is switched by said
switching device between said first and second states.
31. A braking pressure control apparatus according to claim 14,
further comprising a device for reducing an amount of flow of the
fluid between said second hydraulic pressure source and said brake
when the operating state of the apparatus is switched by said
switching device between said first and second states.
32. A braking pressure control apparatus according to claim 21,
further comprising a device for reducing an amount of flow of the
fluid between said second hydraulic pressure source and said brake
when the operating state of the apparatus is switched by said
switching device between said first and second states.
Description
[0001] This application is based on Japanese Patent Application No.
11-367990 filed Dec. 24, 1999, the contents of which are
incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a braking pressure control
apparatus including a diagnosing device.
[0004] 2. Discussion of Related Art
[0005] JP-A-10-100884 discloses an example of a braking pressure
control apparatus including a diagnosing device. The braking
pressure control apparatus disclosed in this publication includes
(1) a first hydraulic system including a first hydraulic pressure
source which is power-operated to pressurize a working fluid and
capable of controlling a pressure of the pressurized fluid, for
operating a brake with the pressurized fluid delivered from the
first hydraulic pressure source, (2) a second hydraulic system
including a second hydraulic pressure source in the form of a
master cylinder which is operable by an operating force acting on a
manually operated brake operating member, to pressurize the working
fluid to a pressure corresponding to the operating force, for
operating the brake with the pressurized fluid delivered from the
master cylinder, (3) a switching device for selectively
establishing a first state in which the brake is operated with the
pressurized fluid delivered from the first hydraulic pressure
source, and a second state in which the brake is operated with the
pressurized fluid delivered from the second hydraulic pressure
source, and (4) a diagnosing device operable to diagnose the second
hydraulic system for any abnormality on the basis of the pressure
of the fluid in the master cylinder and the pressure of the fluid
in the brake.
[0006] In the braking pressure control apparatus disclosed in the
publication identified above, the second hydraulic pressure source
is adapted to deliver the pressurized fluid on the basis of the
operating force of the brake operating member, but the pressure of
the pressurized fluid delivered from the second hydraulic pressure
source is not higher than a level corresponding to the operating
force of the brake operating member. Therefore, the diagnosing
device used in this conventional braking pressure control apparatus
may suffer from a drawback if the diagnosing device is used for a
second hydraulic system which includes a second hydraulic pressure
source adapted to deliver the working fluid to a pressure higher
than a level corresponding to the operating force of the brake
operating member.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a
braking pressure control apparatus including a diagnosing device
suitable for diagnosing a second hydraulic system which includes a
second hydraulic pressure source adapted to pressurize the working
fluid to a pressure higher than a level corresponding to the
operating force of the brake operating member.
[0008] The above object may be achieved according to any one of the
following modes of the present invention, each of which is numbered
like the appended claims and depends from the other mode or modes,
where appropriate, to indicate and clarify possible combinations of
elements or technical features. It is to be understood that the
present invention is not limited to the technical features or any
combinations thereof which will be described for illustrative
purpose only. It is to be further understood that a plurality of
elements or features included in any one of the following modes of
the invention are not necessarily provided all together, and that
the invention may be embodied without some of the elements or
features described with respect to the same mode.
[0009] (1) A braking pressure control apparatus for a hydraulically
operated brake, comprising:
[0010] a first hydraulic system including a first hydraulic
pressure source which is power-operated to pressurize a working
fluid and capable of controlling a pressure of the pressurized
fluid, for operating the brake with the pressurized fluid delivered
from the first hydraulic pressure source;
[0011] a second hydraulic system including a manually operable
brake operating member, and a second hydraulic pressure source
which is operable by an operating force acting on the brake
operating member, to pressurize the working fluid to a pressure
higher than a level corresponding to the operating force, for
operating the brake with the pressurized fluid delivered from the
second hydraulic pressure source;
[0012] a switching device operable to selectively establish a first
state in which the brake is operated with the pressurized fluid
delivered from the first hydraulic pressure source, and a second
state in which the brake is operated with the pressurized fluid
delivered from the second hydraulic pressure source; and
[0013] a diagnosing device operable to diagnose the second
hydraulic system on the basis of a pressure of the fluid in the
second hydraulic system.
[0014] In the braking pressure control apparatus according to the
above mode (1) of this invention, the second hydraulic system
provided to pressurize the fluid to a pressure level higher than a
level corresponding to the operating force of the brake operating
member can be diagnosed for any abnormality, by the diagnosing
device on the basis of the fluid pressure in the second hydraulic
system. As described in detail with respect to various specific
forms or modes of this invention, the time required for diagnosing
the second hydraulic system can be significantly reduced. In this
respect, it is noted that a difference between the fluid pressure
in the second hydraulic pressure source and the fluid pressure in
the brake is generally larger than a difference between the fluid
pressure in the master cylinder and the fluid pressure in the
brake. If the second hydraulic system were diagnosed on the basis
of the difference between the fluid pressure in the second
hydraulic pressure source and the fluid pressure in the brake, as
in the conventional braking pressure control apparatus wherein the
second hydraulic system is diagnosed on the basis of the difference
between the master cylinder pressure and the fluid pressure in the
brake, it would take a longer time for the fluid pressure in the
second hydraulic pressure source and the fluid pressure in the
brake to become equal to each other. The present braking pressure
control apparatus has a further advantage that a hydraulic booster
included in the second hydraulic pressure source can be diagnosed.
In the conventional braking pressure control apparatus, the
hydraulic booster cannot be diagnosed.
[0015] The fluid pressure in the second hydraulic system on which
the second hydraulic system is diagnosed may include a pressure of
the fluid in the second hydraulic pressure source, a pressure of
the fluid in a fluid passage connecting the second hydraulic
pressure source and a cylinder for the brake, and a pressure in the
brake during an operation of the brake with the pressurized fluid
delivered from the second hydraulic pressure source.
[0016] Abnormalities of the second hydraulic system that can be
detected by the diagnosing device include; abnormalities of
elements of the second hydraulic system (e.g., an abnormality of
the second hydraulic pressure source); and abnormalities of
detectors provided to detect the operating states of the
above-indicated elements (e.g., an abnormality of a pressure sensor
for detecting the fluid pressure in the second hydraulic pressure
source). Where the present braking pressure control apparatus is
adapted to control the pressure of the fluid pressurized by the
first hydraulic pressure source on the basis of the detectors
indicated above, these detectors may be considered to be elements
of the first hydraulic system. Since those detectors are used to
detect the operating states of the elements of the second hydraulic
system, however, the detectors are considered to be included in the
second hydraulic system, in the present application.
[0017] In the above mode (1), the "level corresponding to the
operating force" of the manually operable brake operating member is
typically a pressure linearly proportional to the operating force
of the brake operating member. However, the pressure level
corresponding to the operating force need not be linearly
proportional to the operating force, provided that the pressure
level in question is determined depending upon the operating
force.
[0018] (2) A braking pressure control apparatus according to the
above mode (1), wherein the diagnosing device diagnoses the second
hydraulic system on the basis of the pressure of the fluid
pressurized by the second hydraulic pressure source and a pressure
of the fluid in the manually operable brake while the second state
is established by the switching device.
[0019] In the braking pressure control apparatus according to the
above mode (2), the diagnosis of the second hydraulic system is
effected on the basis of the pressure of the fluid pressurized by
the second hydraulic pressure source and the fluid pressure in the
brake. In the second state, the second pressure source and the
hydraulic cylinder of the brake are held in communication with each
other, so that the fluid pressure in the brake must be
substantially equal to the pressure of the fluid pressurized by the
second hydraulic pressure source if the second hydraulic system is
normal. When the absolute value of a difference between the
pressure of the second hydraulic pressure source and the pressure
of the brake is larger than a predetermined threshold, for
instance, it indicates an abnormality of at least one of the
pressure sensors provided to detect the pressures of the second
hydraulic pressure source and the brake cylinder, or an abnormality
of at least one of the second hydraulic pressure source, a fluid
passage connecting the second hydraulic pressure source and the
brake cylinder, and the brake cylinder.
[0020] In the braking pressure control apparatus according to the
above mode (2), the second hydraulic system is diagnosed while the
brake operating member is operated and while the second state is
established by the switching device. Namely, the second hydraulic
system is diagnosed at an opportunity other than an initial check
of the apparatus prior to an operation of the brake. Thus, the
number of opportunities at which the second hydraulic system is
diagnosed is increased.
[0021] When a command to diagnose the second hydraulic system is
generated while the brake is operated in the first state, the
diagnosis is effected after the first state is switched to the
second state. Where the brake is used to brake a wheel of a
vehicle, the switching to the second state is preferably effected
while the vehicle is stationary. The switching from the first state
to the second state may cause a change in the braking force
generated by the brake. This change does not give an adverse
influence on the vehicle if the change takes place while the
vehicle is stationary. In this case, the diagnosis is effected
while the vehicle is stationary.
[0022] Where the diagnosis of the second hydraulic system is
effected after the operating or control state of the apparatus is
switched from the first state to the second state, it is desirable
to first control the first hydraulic pressure source in the first
state so that the fluid pressure in the brake is controlled to a
level that is to be established when the second state is
established, and then switch the operating state to the second
state. This arrangement makes it possible to reduce the amount of
change of the fluid pressure in the brake upon switching of the
operating state from the first state to the second state. In this
case, it is possible to rapidly increase the fluid pressure in the
brake cylinder to a level close to the level of the second
hydraulic pressure source. Accordingly, the time required for
diagnosing the second hydraulic system is reduced.
[0023] (3) A braking pressure control apparatus according to the
above mode (2), wherein the diagnosing device includes a switching
portion operable when the first state is established, to change the
first state to the second state after the fluid pressure in the
brake has been controlled in the first state to a level close to
the fluid pressure in the second hydraulic pressure source.
[0024] (4) A braking pressure control apparatus according to the
above mode (2) or (3), wherein the second hydraulic system
comprises:
[0025] a first pressure sensing device for detecting the pressure
of the fluid pressurized by the second hydraulic pressure source;
and
[0026] a second pressure sensing device for detecting the pressure
of the fluid in the brake,
[0027] and wherein the diagnosing device includes a
sensor-diagnosing portion operable to diagnose at least one of the
first and second pressure sensing devices, on the basis of the
pressures detected by the first and second sensing devices.
[0028] The sensor-diagnosing portion of the diagnosing device
provided according to the above mode (4) may be adapted to
determine that at least one of the first and second pressure
sensing devices is abnormal, if the absolute value of a difference
between the fluid pressures of the brake and the second hydraulic
pressure source which are detected by the respective first and
second pressure sensing devices is larger than a predetermined
threshold value.
[0029] (5) A braking pressure control apparatus according to the
above mode (4), further comprising:
[0030] a first braking pressure control device operable while the
first state is established by the switching device, to control the
pressure of the fluid in the brake on the basis of the pressure of
the fluid detected by the first pressure sensing device; and
[0031] a second braking pressure control device operable when the
sensor-diagnosing portion determines that the first pressure
sensing device is abnormal while the first state is established by
the switching device, the second braking pressure control device
controlling the pressure of the fluid in the brake on the basis of
an operating amount of the manually operable brake operating
member.
[0032] In the braking pressure control apparatus according to the
above mode (5), the fluid pressure in the brake is controlled by
the first braking pressure control device while the second
hydraulic system is diagnosed to be normal. Since the pressure of
the pressurized fluid corresponds to the operating force of the
brake operating member, the fluid pressure in the brake can be
controlled on the basis of the fluid pressure detected by the first
pressure sensing device, such that the braking force generated by
the brake is controlled as desired by the operator of an automotive
vehicle where the present braking pressure control apparatus is
used for braking the vehicle. For instance, the fluid pressure in
the brake is controlled so that the detected actual braking force
coincides with a desired value determined by the detected operating
amount of the brake operating member.
[0033] Where the first hydraulic system includes a power-operated
pressurizing device, and a pressure control valve device for
controlling the pressure of the fluid pressurized by the
pressurizing device, the fluid pressure in the hydraulically
operated brake can be controlled by controlling the pressure
control valve device. Where the first hydraulic system does not
include a pressure control valve device as described above, the
fluid-pressure in the brake can be controlled by controlling an
amount of power to be supplied to the pressurizing device.
[0034] When the second pressure sensing device of the second
hydraulic system is diagnosed to be abnormal, the fluid pressure in
the brake is controlled by the second braking pressure control
device, on the basis of the operating amount of the manually
operable brake operating member. The operating amount may be the
operating stroke or force of the brake operating member. By
controlling the fluid pressure in the brake on the basis of the
operating stroke or force of the brake operating member, the fluid
pressure in the brake can be controlled so as to generate the
braking force as desired by the vehicle operator, as in the case
where the fluid pressure in the brake is controlled on the basis of
the pressure of the fluid pressurized by the second hydraulic
pressure source.
[0035] As described later in detail in the DETAILED DESCRIPTION OF
THE PREFERRED EMBODIMENTS, the fluid pressure in the brake may be
controlled on the basis of the operating stroke of the brake
operating member, the fluid pressure of the second hydraulic
pressure source, and a predetermined weight of the operating stroke
and the fluid pressure of the second hydraulic pressure source with
respect to each other, while the second hydraulic system is normal,
and on the basis of only the operating stroke of the brake
operating member while the second hydraulic system is abnormal. In
the later case, that is, where the second hydraulic system is
abnormal, no weight is given on the fluid pressure of the second
hydraulic pressure source, and the weight or ratio of the operating
stroke with respect to the fluid pressure of the second hydraulic
pressure source is equal to "1".
[0036] (6) A braking pressure control apparatus according to any
one of the above modes (1)-(5), wherein the second hydraulic system
comprises:
[0037] a hydraulic booster including a power piston which is
operatively connected to the manually operable brake operating
member and which partially defines a booster chamber on a rear side
of the power piston as viewed in a direction of an advancing
movement of the power piston when the brake operating member is
operated, the booster chamber being arranged to receive a
pressurized fluid whose pressure corresponds to the operating force
of the brake operating member; and
[0038] a booster pressure sensor for detecting the pressure of the
pressurized fluid in the booster chamber,
[0039] and wherein the diagnosing device diagnoses the second
hydraulic system on the basis of the pressure of the pressurized
fluid in the booster chamber detected by the booster pressure
sensor.
[0040] In the braking pressure control apparatus according to the
above mode (6), the diagnosing device may be arranged to determine
that the second hydraulic pressure source is abnormal, if the fluid
pressure in the booster chamber of the hydraulic booster is lower
than a predetermined threshold value (lower limit). In this case,
it is considered that at least the hydraulic booster is not
normally functioning. The threshold value used by the diagnosing
device may be a value almost equal to the atmospheric pressure.
[0041] (7) A braking pressure control apparatus according to the
above mode (6), wherein the second hydraulic system comprises:
[0042] a master cylinder including a pressurizing piston which is
operatively connected to the power piston and which partially
defines a pressurizing chamber on one of opposite sides thereof
remote from the power piston; and
[0043] a master-cylinder pressure sensor for detecting a pressure
of the fluid in the pressurizing chamber,
[0044] and wherein the diagnosing device diagnoses the second
hydraulic system on the basis of the fluid pressure detected by the
master-cylinder pressure sensor and the fluid pressure detected by
the booster pressure sensor.
[0045] In the braking pressure control apparatus according to the
above mode (7) wherein the fluid pressure in the pressurizing
chamber of the master cylinder as well as the fluid pressure in the
booster chamber of the hydraulic booster is used by the diagnosing
device to diagnose the second hydraulic system, the second
hydraulic system can be diagnosed with a higher decree of accuracy
than when only the fluid pressure in the booster chamber is used
for the diagnosis. Further, the present arrangement has an
advantage of permitting a more detailed diagnosis of the second
hydraulic system, for instance, a diagnosis as to whether the
hydraulic booster or the master cylinder is abnormal.
[0046] The second hydraulic system is generally designed such that
the fluid pressure in the master cylinder and the fluid pressure in
the hydraulic booster are equal to each other. It is also noted
that the fluid in the pressurizing chamber is pressurized to a
level corresponding to a distance of the advancing movement of the
pressurizing piston, so that it is possible to determine that the
pressurizing piston has been advanced by only the operating force
of the brake operating member, or by both the operating force of
the brake operating member and an assisting force based on the
fluid pressure in the booster chamber, if the fluid pressure in the
pressurizing chamber of the master cylinder is higher than a
predetermined threshold or lower limit. It is also possible to
determine that the hydraulic booster is not normally functioning,
if the fluid pressure in the booster chamber is lower than the
predetermined threshold, as described above with respect to the
above mode (6).
[0047] Therefore, the use of the fluid pressure in the master
cylinder and the fluid pressure in the hydraulic booster improves
the accuracy or reliability of diagnosis of the second hydraulic
system by the diagnosing device, or permits the detailed diagnosis
of the second hydraulic system. For instance, the diagnosing device
may be arranged to determine that the second hydraulic system is
normal, when the fluid pressures of the master cylinder and the
hydraulic booster are equal to each other, and when these fluid
pressures are both higher than the respective threshold values.
Further, the diagnosing device may determine that the master
cylinder and the hydraulic booster are both normal, when the
conditions indicated above are satisfied. Other forms of diagnosis
by the diagnosing device will be described with respect to the
following modes (8) and (9).
[0048] (8) A braking pressure control apparatus according to the
above mode, wherein the diagnosing device determines that the
master cylinder is normal while the hydraulic booster is abnormal,
when the pressure of the fluid in the pressurizing chamber detected
by the master-cylinder pressure sensor is not lower than a
predetermined threshold, while the pressure of the fluid in the
booster chamber detected by the booster pressure sensor is lower
than a predetermined threshold.
[0049] In the above conditions in which the pressure in the
pressurizing chamber is not lower than the threshold while the
pressure in the booster chamber is lower than the threshold, it is
possible to determine that the fluid in the pressurizing chamber is
pressurized as a result of an advancing movement of the
pressurizing piston with the operating force of the brake operating
member, but not as a result of the assisting force based on the
fluid pressure in the booster chamber. In this case, it is possible
to determine that the master cylinder is normal while the hydraulic
booster is abnormal. It is desirable that the threshold for the
fluid pressure in the pressurizing chamber be higher than the
threshold for the fluid pressure in the booster chamber.
[0050] (9) A braking pressure control apparatus according to the
above mode (7) or (8), wherein said hydraulic booster includes a
pressure regulating portion which is connected to a high-pressure
source capable of delivering a pressurized fluid whose pressure is
higher than a maximum pressure of the fluid pressurized by the
second hydraulic pressure source and which is operable to regulate
the pressure of the pressurized fluid received from the
high-pressure source to a level corresponding to the pressure of
the fluid in the pressurizing chamber, the hydraulic booster having
a fluid passage through which the pressurized fluid whose pressure
has been regulated by the pressure regulating portion is supplied
to the booster chamber,
[0051] and wherein the diagnosing device determines that the master
cylinder is abnormal, when the fluid pressure in the pressurizing
chamber detected by the master-cylinder pressure sensor is lower
than a predetermined threshold while the fluid pressure in the
booster chamber detected by the booster pressure sensor is lower
than a predetermined threshold.
[0052] Where the fluid in the pressurizing chamber cannot be
pressurized due to an abnormality of the master cylinder, the
pressure of the pressurized fluid as regulated by the pressure
regulating portion of the hydraulic booster is substantially equal
to the atmospheric level, so that the pressure of the fluid in the
booster chamber is also substantially equal to the atmospheric
level. In this case, therefore, it is possible to determine that
the master cylinder is abnormal. Abnormalities of the master
cylinder include a sticking of the pressurizing piston at a certain
position in the cylinder bore of the master cylinder due to a
damage of the pressurizing piston and./or the cylinder bore.
[0053] The second hydraulic system may be diagnosed to be abnormal,
when the fluid pressure in the pressurizing chamber of the master
cylinder is lower than the fluid pressure in the booster chamber of
the hydraulic booster, even if the fluid pressures in the
pressurizing and booster chamber are both higher than the
respective threshold values.
[0054] (10) A braking pressure control apparatus according to any
one of the above modes (6)-(9), further comprising:
[0055] a first braking pressure control device operable while the
first state is established by the switching device, to control the
pressure of the fluid in the brake on the basis of the pressure of
the fluid detected by the first pressure sensing device; and
[0056] a second braking pressure control device operable when the
sensor-diagnosing portion determines that the first pressure
sensing device is abnormal while the first state is established by
the switching device, the second braking pressure control device
controlling the pressure of the fluid in the brake on the basis of
an operating amount of the manually operable brake operating
member,
[0057] and wherein the second hydraulic system comprises:
[0058] a master cylinder including a pressurizing piston which is
operatively connected to the power piston and which partially
defines a pressurizing chamber on one of opposite sides thereof
remote from the power piston; and
[0059] a master-cylinder pressure sensor for detecting a pressure
of the fluid in the pressurizing chamber,
[0060] and wherein the first braking pressure control device
includes a portion operable to control the pressure of the fluid in
the brake on the basis of the pressure of the fluid in the
pressurizing chamber detected by the master-cylinder pressure
sensor.
[0061] The fluid in the pressurizing chamber of the master cylinder
is pressurized to a level corresponding to the operating force of
the brake operating member, so that the fluid pressure in the brake
can be controlled to a level corresponding to the operating force
of the brake operating member, by controlling the fluid pressure in
the brake on the basis of the fluid pressure in the pressurizing
chamber. Although the fluid pressure in the brake can be controlled
to the level corresponding to the operating force of the brake
operating member, on the basis of the fluid pressure in the booster
chamber of the hydraulic booster, this control of the fluid
pressure in the brake cannot be effected if the hydraulic booster
is abnormal. In the braking pressure control apparatus according to
the above mode (10) wherein the fluid pressure in the brake is
controlled on the basis of the fluid pressure in the pressurizing
chamber, the fluid pressure in the brake can be controlled to the
level corresponding to the operating force of the brake operating
member, even when the hydraulic booster is abnormal. Thus, the
braking pressure control apparatus according to the above mode (10)
assures an increased degree of reliability of control of the fluid
pressure in the brake according to the brake operating force.
[0062] (11) A braking pressure control apparatus according to any
one of the above modes (1)-(10), wherein the second hydraulic
system comprises:
[0063] a pressure sensing device for detecting the pressure of the
fluid pressurized by the second hydraulic pressure source; and
[0064] an operating amount sensing device for detecting an
operating amount of the manually operated brake operating
member,
[0065] and wherein the diagnosing device diagnoses the second
hydraulic system on the basis of the pressure of the pressurized
fluid detected by the pressure sensing device and the operating
amount of the brake operating member detected by the operating
amount sensing device.
[0066] The fluid is pressurized by the second hydraulic pressure
source to a level corresponding to the operating amount of the
brake operating member. That is, there is a predetermined ideal or
normal relationship between the operating amount of the brake
operating member and the pressure of the fluid pressurized by the
second hydraulic pressure source. Accordingly, the second hydraulic
system can be diagnosed on the basis of a relationship between the
actually detected values of those two parameters as compared with
the normal relationship.
[0067] In the braking pressure control apparatus according to the
above mode (11), the diagnosing device is capable of diagnosing the
second hydraulic system while either of the first state and the
second state is established by the switching device. Usually, the
relationship between the brake operating amount of and the fluid
pressure of the second hydraulic pressure source in the first state
is different from that in the second state. In either of these two
states, however, the second hydraulic system can be diagnosed by
determining whether there exists the predetermined ideal or normal
relationship between the detected values of those two
parameters.
[0068] Further, the cylinder of the brake can be diagnosed for the
presence of air in the brake cylinder, on the basis of the
relationship between the operating stroke (as the operating amount)
of the brake operating member and the fluid pressure of the second
hydraulic pressure source in the second state of the apparatus. A
relatively low rate of increase of the fluid pressure in the brake
cylinder with an increase of the brake operating stroke indicates
the presence of air in the brake cylinder.
[0069] (12) A braking pressure control apparatus according to the
above mode (11), wherein the second hydraulic system includes a
plurality of brake cylinders for respective brakes, and fluid
passages connecting the brake cylinders to the second hydraulic
pressure source, the fluid passages including at least one main
fluid passage connected to the second hydraulic pressure source,
and at lest one connecting passage each of which is connected to
one of the at least one main fluid passage and connects at least
two of the plurality of brake cylinders to each other, the braking
pressure control apparatus further comprising:
[0070] a communicating valve provided in at least one of the at
least one connecting passage and is operable between an open state
in which the at least two brake cylinders are held in communication
with each other, and a closed state in which the at least two brake
cylinders are disconnected from each other,
[0071] and wherein the diagnosing device diagnoses the at least two
brake cylinders for the presence of air contained therein, on the
basis of amounts of change of the operating stroke of the brake
operating member and the pressure of the fluid pressurized by the
second hydraulic pressure source while the communicating valve is
placed in the open state and those while the communicating valve is
placed in the closed state.
[0072] While the communicating valve is placed in the open state,
the fluid pressurized by the second hydraulic pressure source is
delivered to all of the at least two brake cylinders through the
corresponding main fluid passage and connecting passage. While the
communication valve is placed in the closed state, the fluid
pressurized by the second hydraulic pressure source is not
delivered to the brake cylinder or cylinders which is/are connected
to the main fluid passage through the connecting passage. Based on
these facts, each of the brake cylinders can be diagnosed for the
presence of air contained therein, on the basis of the amounts of
change of the brake operating stroke and the fluid pressure of the
second hydraulic pressure source while the communicating valve is
in the open state and those while the communication valve is in the
closed sate.
[0073] For instance, the two brake cylinders are connected to the
second hydraulic pressure source such that one of the brake
cylinders is connected directly to the second hydraulic pressure
source through the main fluid passage, while the other brake
cylinder is connected to the second hydraulic pressure source
through the connecting passage and the main fluid passage. In this
instance, the fluid pressurized by the second hydraulic pressure
source is delivered to only one of the two brake cylinders and not
to the other brake cylinder while the communicating valve provided
in the connecting passage is placed in the closed state. If the
amount of change of the fluid pressure of the second hydraulic
pressure source with respect to the brake operating amount is
excessively small in the closed state of the communicating valve,
it indicates that air is contained in the above-indicated one brake
cylinder. If the amount of change of the fluid pressure of the
second hydraulic pressure source is normal in the closed state of
the communicating valve but is excessively small in the open state,
it indicates that air is contained in the other brake cylinder.
[0074] (13) A braking pressure control apparatus according to any
one of the above modes (1)-(12), wherein the second hydraulic
system includes a high-pressure source capable of delivering a
pressurized fluid whose pressure is higher than a maximum pressure
of the fluid pressurized by the second hydraulic pressure
source,
[0075] and wherein the diagnosing device diagnoses the second
hydraulic system on the basis of the pressure of the pressurized
fluid of the high-pressure source as well as the pressure of the
fluid pressurized by the second hydraulic pressure source.
[0076] The accuracy of diagnosis of the second hydraulic pressure
source can be improved when the diagnosis is based on the pressure
of the pressurized fluid delivered from the high-pressure source
and the pressure of the second hydraulic pressure source. When the
pressure of the high-pressure source is lower than a predetermined
threshold, the pressure of the fluid pressurized by the second
hydraulic pressure source may be abnormally lower or the fluid may
not be pressurized by the second hydraulic pressure source. When
the pressure of the second hydraulic pressure source is excessively
low while the pressure of the high-pressure source is in a normal
range, it means that the second hydraulic pressure source is
abnormal.
[0077] The high-pressure source of the second hydraulic system may
be separate from a high-pressure source of the first hydraulic
system. Alternatively, a single high-pressure source may be
commonly used for the first and second hydraulic systems. In the
latter case, the braking pressure control apparatus is simplified
and small-sized.
[0078] (14) A braking pressure control apparatus for a
hydraulically operated brake including a brake cylinder,
comprising:
[0079] a first hydraulic system including a first hydraulic
pressure source which is power-operated to pressurize a working
fluid and capable of controlling a pressure of the pressurized
fluid to be delivered to the brake cylinder for operating the brake
with the pressurized fluid delivered from the first hydraulic
pressure source;
[0080] a second hydraulic system including a manually operable
brake operating member, and a second hydraulic pressure source
which is operable by an operating force acting on the brake
operating member, to pressurize the working fluid to a pressure
corresponding to the operating force, so that the fluid pressurized
by the second hydraulic pressure source is delivered to the brake
cylinder for operating the brake;
[0081] a switching device operable to selectively establish a first
state in which the brake cylinder is supplied with the pressurized
fluid delivered from the first hydraulic pressure source, and a
second state in which the brake is supplied with the pressurized
fluid delivered from the second hydraulic pressure source;
[0082] a stroke simulator device including a stroke simulator
connected to the second hydraulic pressure source, and a simulator
shut-off valve having a closed state in which the stroke simulator
is disconnected from the second hydraulic pressure source, and an
open state in which the stroke simulator is in communication with
the second hydraulic pressure source: and
[0083] a diagnosing device operable to diagnose the stroke
simulator device on the basis of an amount of change of an
operating stroke of the brake operating member and an amount of
change of the pressure of the fluid pressurized by the second
hydraulic pressure source.
[0084] There is a know ideal or normal relationship between the
amount of change of the operating stroke of the brake operating
member and the amount of change of the pressure of the fluid
pressurized by the second hydraulic pressure source while the
stroke simulator device is normal. By comparing a relationship
between the detected actual amounts of change of those two
parameters with the normal relationship, the stroke simulator
device can be diagnosed for any abnormality.
[0085] Abnormalities of the stroke simulator device include a fluid
leakage from the stroke simulator, and an abnormality of the
simulator shut-off valve (sticking of a valve member in the open or
closed state of the valve).
[0086] If the amount of change of the fluid pressure of the second
hydraulic pressure source with respect to the amount of change of
the brake operating stroke while the simulator shut-off valve is
commanded to be placed in its closed state is abnormally small, it
indicates that the simulator shut-off valve is abnormally kept in
its open state due to sticking of its valve member.
[0087] If the amount of change of the fluid pressure of the second
hydraulic pressure source with respect to the brake operating
member while the simulator shut-off valve is commanded to be placed
in its open state is abnormally large, it indicates that the
simulator shut-off valve is abnormally kept in its closed state due
to sticking of its valve member.
[0088] If the amount of change of the fluid pressure of the second
hydraulic pressure source with respect to the brake operating
member while the simulator shut-off valve is placed in its open
state is extremely small, it indicates that the stroke simulator is
suffering from a fluid leakage.
[0089] (15) A braking pressure control apparatus according to the
above mode (14), wherein the diagnosing device diagnoses the stroke
simulator device while the second state is established by the
switching device.
[0090] The stroke simulator device can be diagnosed irrespective of
whether the first or second state is established by the switching
device. If the simulator shut-off valve is switched from the open
state to the closed state while the first state is established, the
brake operating stroke is reduced to a considerably small value,
unexpectedly to the operator of the present apparatus (e.g., the
operator of an automotive vehicle provided with the apparatus). In
the second state, however, the switching of the simulator shut-off
valve to the closed state will not cause a reduction of the brake
operating stroke since the pressurized fluid is delivered from the
second hydraulic pressure source to the brake cylinder.
[0091] The brake cylinder can be diagnosed for the presence of air
contained therein, on the basis of the amounts of change of the
brake operating stroke and the fluid pressure of the second
hydraulic pressure source while the second state is established by
the switching device. When the amount of change of the fluid
pressure of the second hydraulic pressure source with respect to
the brake operating stroke is abnormally small, however, it is not
possible to determine whether the simulator shut-off valve is
abnormally kept in its open state, or the brake cylinder contains
air. In this case, a diagnosis is repeated in the same manner after
the operating state of the apparatus is switched from the second
state to the first state. This diagnosis makes it possible to
determine whether the brake cylinder contains air or the simulator
shut-off valve is abnormal.
[0092] (16) A braking pressure control apparatus according to the
above mode (15), wherein the second hydraulic system includes a
plurality of brake cylinders for respective brakes, and fluid
passages connecting the brake cylinders to the second hydraulic
pressure source, the fluid passages including at least one main
fluid passage connected to the second hydraulic pressure source,
and at lest one connecting passage each of which is connected to
the main fluid passage and connects at least two of the plurality
of brake cylinders to each other, the braking pressure control
apparatus further comprising:
[0093] a communicating valve provided in at least one of the at
least one connecting passage and is operable between an open state
in which the at least two brake cylinders are held in communication
with each other, and a closed state in which the at least two brake
cylinders are disconnected from each other,
[0094] and wherein the diagnosing device diagnoses the stroke
simulator device while the communicating valve is placed in the
closed state.
[0095] The amount of the pressurized fluid to be delivered from the
second hydraulic pressure source to the plurality of brake
cylinders is smaller when the communicating valve is placed in the
closed state than when the communicating valve is placed in the
open state. Accordingly, the amount of change of the fluid pressure
of the second hydraulic pressure source with respect to the amount
of change of the brake operating stroke when the stroke simulator
device is normal is larger when the communicating valve is placed
in the closed state than in the open state. Accordingly, the
determination as to whether the stroke simulator device is normal
or not can be made with a higher degree of accuracy when the
communicating device is placed in the closed state.
[0096] It is also noted that the operating state of the brake
operating member while the stroke simulator device is diagnosed by
the diagnosing device in the second state of the apparatus is more
similar to the operating state when the communicating valve is
placed in the closed state than when it is placed in the open
state. That is, the second hydraulic pressure source is
disconnected from the brake cylinders and are held in communication
with the stroke simulator when the apparatus is in the first state.
In the second state in which the stroke simulator device is
diagnosed, the operating state of the brake operating member as
felt by the operator of the apparatus is more similar to that in
the first state when some of the brake cylinders are disconnected
from the second hydraulic pressure source by the communicating
valve, than when all of the brake cylinders are communicated with
the second hydraulic pressure source.
[0097] (17) A braking pressure control apparatus according to any
one of the above modes (14)-(16), wherein the diagnosing device has
a releasing passage connected at one end thereof to a low-pressure
source and at the other end thereof to a portion of the stroke
simulator device which is between the simulator shut-off valve and
the stroke simulator, the diagnosing device including a releasing
valve provided in the releasing passage and having an open state in
which the stroke simulator device is communicated at the portion
thereof to the low-pressure source, and a closed state in which the
stroke simulator device is disconnected at the portion thereof from
the low-pressure source,
[0098] and wherein the diagnosing device diagnoses the stroke
simulator device on the basis of the amount of changes of the
operating stroke of the brake operating member and the pressure of
the fluid pressurized by the second hydraulic pressure source while
the releasing valve is placed in the open state.
[0099] While the simulator shut-off valve is in the closed state,
the brake operating stroke will not be excessively large even when
the releasing valve is in the open state. While the simulator
shut-off valve is in the open state, however, the brake operating
member may be excessively large when the releasing valve is in the
open state.
[0100] Accordingly, the stroke simulator device can be accurately
diagnosed by suitably controlling the simulator shut-off valve and
the releasing valve, based on the phenomenon indicated above.
[0101] (18) A braking pressure control apparatus according to any
one of the above modes (14)-(17), further comprising an alarming
device operable to provide an alarm when the diagnosing device has
determined that the stroke simulator device is abnormal.
[0102] While the apparatus is in the first state, the operating
state of the brake is not necessarily influenced immediately after
the stroke simulator device becomes abnormal. However, an
abnormality of the stroke simulator device may cause an excessively
large amount of increase or decrease of the operating stroke of the
brake operating member. In this respect, the provision of the
alarming device is desirable for informing the operator of the
apparatus that the stroke simulator device has become abnormal.
[0103] (19) A braking pressure control apparatus according to any
one of the above modes (1)-(18), further comprising a controller
for controlling the switching device to selectively establish the
first and second states, depending upon a result of a diagnosis by
the diagnosing device.
[0104] Where the hydraulic booster or master cylinder of the second
hydraulic system is diagnosed to be abnormal, for instance, the
controller commands the switching device to establish the first
state so that the brake is operated with the pressurized fluid
delivered from the first hydraulic pressure source. When the
diagnosis is effected in the first state, the first state is
maintained. When the diagnosis is effected in the second state, the
operating state of the apparatus is switched from the second state
to the first state. In the first state, the braking force generated
by the brake is not reduced due to the abnormality of the second
hydraulic system.
[0105] Where any sensor used in the second hydraulic system is
diagnosed to be abnormal, the controller may be adapted to command
the switching device to establish the second state. The diagnosis
effected in the first state usually uses the output of the sensor
or sensors provided in the second hydraulic system. In this case,
the operating state of the apparatus may be changed from the first
state to the second state, only where there is/are not a sensor or
sensors that can be substituted for the sensor or sensors which
has/have been diagnosed to be abnormal, as described below with
respect to the following mode (20). The first state is changed to
the second state where a detected abnormality makes it difficult or
impossible to control the fluid pressure in the brake as
needed.
[0106] (20) A braking pressure control apparatus according to any
one of the above modes (1)-(19), further comprising a first braking
pressure control device operable while no abnormality is detected
by the diagnosing device, for controlling the fluid pressure in the
brake in a predetermined normal manner, and a second braking
pressure control device operable while an abnormality associated
with at least one of predetermined at least one sensor is detected
by the diagnosing device, for controlling the fluid pressure in the
brake in a manner different from the predetermined normal manner,
without using an output of the above-indicated at least one of the
predetermined at least one sensor.
[0107] The second hydraulic system may include a plurality of
sensors or detectors at least one of which is used to control the
fluid pressure in the brake in the first state. In this case, the
apparatus may include a sensor or sensors that can be substituted
for the above-indicated at least one sensor, when the latter is
diagnosed to be abnormal. For instance, the output of a
master-cylinder pressure sensor for detecting the pressure of the
master cylinder of the second hydraulic pressure source is used to
control the fluid pressure in the brake while the master-cylinder
pressure sensor is normal. If this master-cylinder pressure sensor
is found abnormal, the output of a stroke sensor for detecting the
operating stroke of the brake operating member may be used for
controlling the fluid pressure in the brake. In an alternative
arrangement wherein the fluid pressure in the brake is controlled
on the basis of the detected pressure of the master cylinder and
the detected brake operating stroke, the control of the fluid
pressure in the brake may be effected on the basis of only the
detected brake operating stroke where the sensor for detecting the
master cylinder pressure or the master cylinder per se is diagnosed
to be abnormal. In another alternative arrangement, the control of
the fluid pressure in the brake is effected on the basis of the
detected fluid pressure of the master cylinder and the detected
fluid pressure of the hydraulic booster. In this case, the control
may be effected on the basis of only the detected master cylinder
pressure where the sensor for detecting the pressure of the
hydraulic booster or the hydraulic booster per se is diagnosed to
be abnormal.
[0108] The "abnormality associated with at least one of
predetermined at least one sensor" may be an abnormality of the
sensor or sensors per se, or an abnormality of a device or devices
whose operating state or physical quantity is detected by the
sensor or sensors.
[0109] (21) A braking pressure control apparatus for a
hydraulically operated brake, characterized by comprising:
[0110] a first hydraulic system including a first hydraulic
pressure source which is power-operated to pressurize a working
fluid and capable of controlling a pressure of the pressurized
fluid, for operating the brake with the pressurized fluid delivered
from the first hydraulic pressure source;
[0111] a second hydraulic system including a manually operable
brake operating member, and a second hydraulic pressure source
which is operable by an operating force acting on the brake
operating member, to pressurize the working fluid to a pressure
higher than a level corresponding to the operating force, for
operating the brake with the pressurized fluid delivered from the
second hydraulic pressure source;
[0112] a switching device operable to selectively establish a first
state in which the brake is operated with the pressurized fluid
delivered from the first hydraulic pressure source, and a second
state in which the brake is operated with the pressurized fluid
delivered from the second hydraulic pressure source; and
[0113] a diagnosing device operable to diagnose the second
hydraulic system on the basis of an operating state of the second
hydraulic system.
[0114] In the braking pressure control apparatus according to the
above mode (21), the second hydraulic system is diagnosed on the
basis of its operating state.
[0115] (22) A braking pressure control apparatus according to any
one of the above modes (1)-(21), further comprising a device for
restricting an amount of change of at least one of an operating
state of the brake operating member and the fluid pressure in the
brake when the operating state of the apparatus is switched by the
switching device between the first and second states.
[0116] (23) A braking pressure control apparatus according to any
one of the above modes (1)-(22), further comprising a device for
reducing a difference between the fluid pressure in the brake and
the pressure of the fluid pressurized by the second hydraulic
pressure source, when the operating state of the apparatus is
switched by the switching device between the first and second
states.
[0117] (24) A braking pressure control apparatus according to any
one of the above modes (1)-(23), further comprising a device for
reducing an amount of flow of the fluid between the second
hydraulic pressure source and the brake when the operating state of
the apparatus is switched by the switching device between the first
and second states.
[0118] (25) A braking pressure control apparatus according to any
one of the above modes (1)-(24), further comprising a device for
restricting a rate of change of the fluid pressure in the brake
when the operating state of the apparatus is switched by the
switching device between the first and second states.
[0119] (26) A braking pressure control apparatus according to any
one of the above modes (1)-(25), wherein the switching device
switches the operating state of the apparatus from the first state
to the second state, when the brake operating member is not in
operation.
[0120] (27) A braking pressure control apparatus according to any
one of the above modes (1)-(26), further comprising a device for
restricting a change in control characteristic of the fluid
pressure in the brake, when the operating state of the apparatus is
switched by the switching device between the first and second
states.
[0121] (28) A braking pressure control apparatus according to the
above mode (27), wherein the above-indicated device for restricting
a change in control characteristic controls the fluid pressure in
the brake to a level which is expected to be established when the
operating state has been switched from one of the first and second
states to the other state.
[0122] (29) A braking pressure control apparatus according to any
one of the above modes (1)-(28), further comprising a device for
restricting a change in the operating state of the brake operating
member unexpectedly to the operator of the apparatus, when the
operating state of the apparatus is switched by the switching
device between the first and second states.
[0123] (30) A braking pressure control apparatus according to any
one of the above modes (1)-(29), further comprising a device for
controlling the fluid pressure in the brake in a manner different
from a predetermined normal manner, when the operating state of the
apparatus is switched by the switching device between the first and
second states.
[0124] (31) A braking pressure control apparatus according to any
one of the above modes (1)-(30), further comprising a device for
initiating an operation of restricting a change of at least one of
the operating state of the brake operating member and the fluid
pressure in the brake, when a symptom indicating that the operating
state of the apparatus is likely to be switched by the switching
device between the first and second states.
BRIEF DESCRIPTION OF THE INVENTION
[0125] The above and other objects, features, advantages and
technical and industrial significance of the present invention will
be better understood by reading the following detailed description
of presently preferred embodiments of the invention, when
considered in connection with the accompanying drawings, in
which:
[0126] FIG. 1 is a schematic view of a braking system including a
braking pressure control apparatus constructed according to one
embodiment of this invention;
[0127] FIG. 2 is an elevational view partly in cross section of a
linear valve device included in the braking pressure control
apparatus of FIG. 1:
[0128] FIG. 3 is a flow chart illustrating a braking pressure
control routine executed according to a control program stored in a
ROM of the braking pressure control apparatus;
[0129] FIG. 4 is a graph indicating a relationship between a
hydraulic pressure of a first hydraulic pressure source and a
desired braking force corresponding to a brake operating force,
which relationship is represented by a data table stored in the
ROM:;
[0130] FIG. 5 is a graph indicating a relationship between a brake
operating stroke and a desired braking force corresponding to the
brake operating stroke, which relationship is represented by a data
table stored in the ROM;
[0131] FIG. 6 is a graph indicating a relationship between a
desired braking force in the last control cycle and a ratio of
vehicle deceleration values corresponding to the brake operating
stroke and force, which relationship is represented by a data table
stored in the ROM;
[0132] FIGS. 7A, 7B and 7C are views showing a data table stored in
the ROM, which table indicates various treatments for dealing with
various kinds of abnormalities of a second hydraulic system of the
braking system;
[0133] FIG. 8 is a view showing a part of the data table of FIGS.
7A-7C;
[0134] FIGS. 9A and 9B are graphs indicating changes of hydraulic
pressures in the second hydraulic pressure source of the braking
pressure control apparatus;
[0135] FIG. 10 is a flow chart illustrating a pressure-sensor
diagnosing routine executed according to a control program stored
in the ROM of the braking pressure control apparatus;
[0136] FIG. 11 is a view showing changes of wheel brake cylinder
pressure upon detection of an abnormality of the braking
system;
[0137] FIG. 12 is a flow chart illustrating a simulator shut-off
valve abnormality detecting routine executed according to a control
program stored in the ROM of the braking pressure control
apparatus;
[0138] FIG. 13 is a graph indicating an abnormality detecting
relationship represented by a data table stored in the ROM;
[0139] FIG. 14 is a flow chart illustrating a routine for detecting
an abnormality of the second hydraulic system according to a
control program stored in the ROM of a braking pressure control
apparatus according to another embodiment of this invention;
[0140] FIG. 15 is a schematic view showing another braking system
according to a further embodiment of the invention, which includes
the braking pressure control apparatus of FIG. 1; and
[0141] FIG. 16 is a schematic view showing a further braking system
according to a still further embodiment of the invention, which
includes the braking pressure control apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0142] Referring first to FIG. 1, the hydraulically operated
braking system shown therein includes a manually operable brake
operating member in the form of a brake pedal 10, a pump device 12,
a second hydraulic pressure source 14, front wheel brakes 18 having
wheel brake cylinders 20 provided for respective front wheels 16,
rear wheel brakes 26 having wheel brake cylinders 28 provided for
respective rear wheels 24, and four linear valve devices 30
provided for the respective wheel brake cylinders 20, 28. In the
present embodiment, the pump device 12 and the linear valve devices
30 constitute a first hydraulic pressure source 31. The braking
system has a first control mode in which the wheel brake cylinder
20, 28 of each wheel 16, 24 is activated with a pressurized fluid
delivered from the first hydraulic pressure source 31, and a second
control mode in which the wheel brake cylinder 20, 28 is activated
with a pressurized fluid delivered from the second hydraulic
pressure source 14. The braking system is selectively placed in one
of the first and second control modes In the first control mode,
the fluid pressures in the individual wheel brake cylinders 20, 28
are controllable independently of each other by the respective
linear valve devices 30. The first and second control modes are
selectively established under the control of an electronic brake
control unit 32 (hereinafter referred to as "ECU 32"). In the
present invention, the linear valve devices 30 constitute a
solenoid-operated pressure control valve device.
[0143] The second hydraulic pressure source 14 includes a hydraulic
booster 78 and a master cylinder 80.
[0144] The master cylinder 80 has a housing 82, a pressurizing
piston 84 fluid-tightly and slidably received within the housing
82, and a pressurizing chamber 86. A working fluid in the
pressurizing chamber 86 is pressurized by an advancing movement of
the pressurizing piston 84.
[0145] The hydraulic booster 78 includes a pressure regulating
portion 88, and an input portion 92 including a power piston 90.
The pressure regulating portion 88 is arranged to regulate the
pressure of a pressurized fluid delivered from the pump device 12,
to a level corresponding to an operating force acting on the brake
pedal 10. The brake pedal 10 is connected through an operating rod
94 to the power piston 90. The power piston 90 partially defines a
rear pressurizing chamber (booster chamber) 98 on its rear side.
The pressurized fluid the pressure of which is regulated by the
pressure regulating portion 88 is supplied to the rear pressurizing
chamber 98, so that the power piston 90 is advanced (moved in the
left direction as seen in FIG. 1) by a force based on the fluid
pressure in the rear pressurizing chamber 98, whereby the operating
force of the brake pedal 10 is boosted by the hydraulic booster 78.
The force acting on the power piston 90 in its advancing direction
based on the fluid pressure in the booster chamber 98 will be
referred to as an "assisting force" where appropriate.
[0146] The pressure regulating portion 88 includes a pressure
regulating piston 100, a spool 102 and a reaction applying device
104. The pressure regulating piston 100 partially defines a
pressure regulating chamber 106 on its front side. The spool 102
functions to establish selective communication of the pressure
regulating chamber 106 with the pump device 12 or a master
reservoir 108, or disconnect the pressure regulating chamber 106
from both of the pump device 12 and the master reservoir 108. As a
result, the fluid pressure in the pressure regulating chamber 106
is regulated to the level corresponding to the operating force of
the brake pedal 10. The spool 102 is moved together with the
pressure regulating piston 100.
[0147] A return spring 110 is disposed between the spool 102 and
the housing 82, and a return spring 112 is disposed between the
pressure regulating piston 100 and the pressurizing piston 84. The
spool 102 is normally held in its fully retracted position
(rightmost position as seen in the figure) under a biasing action
of the return spring 110, while the pressurizing piston 84 is
normally held in its fully retracted position under a biasing
action of the return spring 112.
[0148] A preset load of the return spring 112 disposed between the
pressurizing piston 84 and the pressure regulating piston 100 is
larger than that of the return spring 110 disposed between the
spool 102 and the housing 82, so that while a drive force acting on
the pressurizing piston 84 in the advancing direction is smaller
than the preset load of the return spring 112 and larger than that
of the return spring 110, the pressurizing piston 84 is advanced so
as to advance the pressure regulating piston 100 together with the
spool 102. When the drive force acting on the pressurizing piston
84 becomes larger than the preset load of the return spring 112,
the pressurizing piston 84 is advanced relative to the pressure
regulating piston 100, so that the volume of the pressurizing
chamber 86 is reduced.
[0149] The housing 82 has a plurality of ports 114-118 formed
therein. Namely, the housing 82 has a high-pressure port 114
connected to the pump device 12, two low-pressure ports 115, 116
connected to the master reservoir 108, a brake-cylinder port 117
communicating with the booster chamber 98 and connected to the rear
wheel brake cylinders 28, and a brake-cylinder port 118
communicating with the pressurizing chamber 86 and connected to the
front wheel brake cylinders 20. The pressure regulating chamber 106
is connected through a fluid passage 120 to the booster chamber 98,
so that the pressurized fluid which is delivered from the pump
device 12 and the pressure of which is regulated by the pressure
regulating portion 88 is supplied to the rear wheel brake cylinders
28 through the booster chamber 98. The pressurized fluid delivered
from the pressurizing chamber 86 in response to an advancing
movement of the pressurizing piston 84 is supplied to the front
wheel brake cylinders 20.
[0150] A pressure chamber 122 is provided in communication with the
fluid passage 120. As described below, the reaction-force applying
device 104 is activated with the fluid pressure in the pressure
chamber 122.
[0151] When the spool 102 is placed in its fully retracted
position, the pressure regulating chamber 106 in front of the
pressure regulating piston 100 is held in communication with the
master reservoir 108 through the low-pressure port 115, so that the
fluid pressure in the pressure regulating chamber 106 is at the
atmospheric level, and the fluid pressure in the booster chamber 98
is accordingly at the atmospheric level.
[0152] When the spool 102 is advanced with an advancing movement of
the pressure regulating piston 100, the pressure regulating chamber
106 is disconnected from the master reservoir 108 and communicated
with the pump device 12 through the high-pressure port 114. As a
result, the fluid pressure in the pressure regulating chamber 106
is raised, and the thus pressurized fluid is delivered from the
pressure regulating chamber 106 to the booster chamber 98 through
the fluid passage 120. Accordingly, the power piston 90 receives
the assisting force in addition to the drive force based on the
operating force of the brake pedal 10, and is advanced to advance
the pressurizing piston 84. Thus, the operating force of the brake
pedal 10 is boosted by the hydraulic booster 78, and the fluid
pressure in the pressurizing chamber 86 is pressurized to a level
corresponding to the boosted force (sum of the drive force and the
assisting force). The pressure regulating piston 100 is eventually
held at a position of equilibrium between a force which acts on the
piston 100 in the advancing direction based on the fluid pressure
in the pressurizing chamber 86, and a sum of a force which acts on
the piston 100 in the retracting direction based on the fluid
pressure in the pressure regulating chamber 106 and the biasing
force of the return spring 110. Accordingly, the position of the
spool 102 is determined, and the fluid pressure in the pressure
regulating chamber 106 is regulated to a level corresponding to or
determined by the operating force of the brake pedal 10
(hereinafter referred to as a "brake operating force" where
appropriate).
[0153] As the force acting on the pressure regulating piston 100 in
the advancing direction is increased, the fluid pressure in the
pressure regulating chamber 106 is raised or increased, and the
fluid pressure in the pressure chamber 122 is accordingly raised.
As a result, a force based on the fluid pressure in the pressure
chamber 122 acts on a reaction disc 124 of the reaction-force
applying device 104 in the retracting direction, so that a reaction
force is applied from the reaction disc 124 to the spool 102
through a reaction rod 126, and to the brake pedal 10 through the
pressure regulating piston 100 and the pressurizing piston 84. As
the brake operating force is increased, the reaction force received
by the brake pedal 10 is accordingly increased, and the boosting
ratio of the hydraulic booster 78 is reduced.
[0154] The pump device 12 includes an accumulator 134, a pump 136,
an electric motor 138 for driving the ump 134, and a check valve
139. The pressurized fluid delivered from the pump device 12 is
detected by a hydraulic pressure sensor 140. Namely, the pressure
of the pressurized fluid stored in the accumulator 134 can be
detected by the pressure sensor 140. In this embodiment, the
electric motor 138 is controlled so as to hold the fluid pressure
in the accumulator 134 within a predetermined range, so that the
pressure in the accumulator 134 is held substantially within the
predetermined range. The pump 136 may be a plunger pump or a gear
pump.
[0155] A pressure relief valve 142 is provided in a fluid passage
connecting the delivery and suction sides (high-pressure and
low-pressure sides) of the pump 136. The pressure relief valve 142
functions to prevent an excessive rise of the pressure of the
pressurized fluid delivered from the pump 136, that is, an
excessive rise of the delivery pressure of the pump 136.
[0156] The second hydraulic pressure source 14 is arranged to
deliver a pressurized fluid when the brake pedal 10 is operated or
depressed. As the operating amount of the brake pedal 10 is
increased, the power piston 90 and the pressurizing piston 84 are
advanced to advance the pressure regulating piston 100 and the
spool 102, so that the fluid pressure in the pressure regulating
chamber 106 is increased by the pressurized fluid received from the
pump device 12, and is regulated by the pressure regulating portion
88, to a level corresponding to the brake operating force. The
pressurized fluid having the thus regulated pressure is supplied to
the booster chamber 98. As a result, the pressurizing piston 84 is
advanced by both the brake operating force and the assisting force
based in the fluid pressure in the booster chamber 98, so that the
fluid pressure in the pressurizing chamber 86 is increased. The
fluid pressurized in the booster chamber 98 is supplied to the rear
wheel brake cylinders 28, while the fluid pressurized in the
pressurizing chamber 86 is supplied to the front wheel brake
cylinders 20.
[0157] When the brake pedal 10 is released toward its non-operated
position, the brake operating force acting on the pressurizing
piston 84 is reduced, and the fluid pressure in the pressurizing
chamber 86 is lowered. As a result, the pressure regulating piston
100 is retracted with the spool 102, and the pressure regulating
chamber 106 is eventually communicated with the master reservoir
108, so that the fluid pressure in the chamber 106 is lowered. The
fluid discharged from the front wheel brake cylinders 20 is
returned to the master reservoir 108 through the pressurizing
chamber 86, a center valve 144 and the low-pressure port 116.
[0158] To the pressurizing chamber 86, there are connected the
front wheel brake cylinders 20 through a fluid passage 150. A
solenoid-operated shut-off valve 152 (hereinafter referred to as a
"master-cylinder shut-off valve 152", and represented by SMCF in
the drawings) is provided in the fluid passage 150. The two front
wheel brake cylinders 20 are connected to each other through a
connecting passage 153 in which is provided a solenoid-operated
shut-off valve 154 (hereinafter referred to as a "front
communicating valve 154", and represented by SCF in the drawings).
In the present embodiment, the fluid passage 150 functions as a
main fluid passage connected to the second hydraulic pressure
source 14, while the connecting passage 153 functions as a
connecting passage connected to the main fluid passage and
connecting the two front wheel brake cylinders 20 to each other. To
a portion of the fluid passage 150 between the master-cylinder
shut-off valve 152 and the brake-cylinder port 118, there is
connected a stroke simulator 156 through a solenoid-operated
shut-off valve 158 (hereinafter referred to as a "simulator
shut-off valve 158", and represented by SCSS in the drawings). The
stroke simulator 156 and the simulator shut-off valve 158
constitute a stroke simulator device 159.
[0159] To the booster chamber 98,, there are connected the rear
wheel brake cylinders 28 through a fluid passage 160. A
solenoid-operated shut-off valve 162 (hereinafter referred to as a
"master-cylinder shut-off valve 162", and represented by SMCR in
the drawings) is provided in the fluid passage 160. The two rear
wheel brake cylinders 28 are connected to each other through a
connecting passage 163 in which is provided a solenoid-operated
shut-off valve 164 (hereinafter referred to as a "front
communicating valve 164", and represented by SCR in the
drawings).
[0160] Each of the master-cylinder shut-off valves 152, 162 has a
solenoid coil, and is placed in its closed state when the solenoid
coil is energized. In the closed state, the corresponding wheel
brake cylinder 20, 28 is disconnected from the second hydraulic
pressure source 14. When the solenoid coil is de-energized, the
master-cylinder shut-off valve 152, 162 is placed in its open state
in which the corresponding wheel brake cylinder 20, 28 is
communicated with the second hydraulic pressure source 14. The
master-cylinder shut-off valves 152, 162 and the front and rear
communicating valves 154, 164 are normally open valves, while the
simulator shut-off valve is a normally closed valve.
[0161] To the pump device 12, there are connected the wheel brake
cylinders 20, 28 through a fluid passage 170 in which is provided a
pressure-increasing linear valve 172. Further, a pressure-reducing
linear valve 176 is provided in a fluid passage 174 connecting the
wheel brake cylinders 20, 28 and the master reservoir 108. These
pressure-increasing and pressure-reducing linear valves 172, 1766
constitute the linear valve device 30.
[0162] As shown in FIG. 2, the pressure-increasing and
pressure-reducing linear valves 172, 176 are both normally closed
valves, each of which is a seating valve including a solenoid
having a coil 188, a spring 190, a valve member 192, and a valve
seat 194.
[0163] When the coil 188 of the seating valve is in a de-energized
state, a biasing force of the spring 190 acts on the valve member
192 in a valve-closing direction that causes the valve member 192
to be seated on the valve seat 194, while at the same time a force
based on a pressure difference across the linear valve 172, 174
acts on the valve member 192 in a valve-opening direction that
causes the valve member 192 to be moved away from the valve seat
194. When the force based on the pressure difference is larger than
the biasing force of the spring 190, the valve member 192 is held
apart from the valve seat 194, that is, the linear valve 172, 176
is placed in the open position.
[0164] When the coil 188 is energized with an electric current, an
electromagnetic drive force acts on the valve member 192 in the
valve-opening direction. A sum of this electromagnetic drive force
and the force based on the pressure difference (hereinafter
referred to as a "pressure-difference force") acts on the valve
member 192 in the valve opening direction while the biasing force
of the spring 190 acts on the valve member 192 in the valve-closing
direction. The position of the valve member 192 relative to the
valve seat 194 is determined by a relationship between the
above-indicated sum and the biasing force of the spring 190. The
electromagnetic force is increased with an increase in the amount
of electric current to be applied to the coil 188.
[0165] When the electromagnetic force is increased with an increase
of the amount of electric current applied to the coil 188, the
force by which the valve member 192 has been forced against the
valve seat 194 is reduced, -so that the pressure-difference force
required to move the valve member 192 from the valve seat 194 is
accordingly reduced. The valve member 192 is moved apart from the
valve seat 194 when the sum of the pressure-difference force and
the electromagnetic force becomes larger than the biasing force of
the spring 190. The lower limit of the pressure difference across
the linear valve 172, 176 above which the valve member 192 is moved
apart from the valve seat 194 is referred to as a "valve-opening
pressure difference". The valve-opening pressure difference is
reduced with an increase in the electromagnetic force, that is,
with an increase in the amount of electric current to be applied to
the coil 188. In the pressure-increasing linear valve 172, the
pressure-difference force corresponds to a difference between the
pressure of the pressurized fluid delivered from the pump device 12
(fluid pressure in the accumulator 134) and the fluid pressure in
the wheel brake cylinder 20, 28. In the pressure-reducing valve
176, the pressure-difference force corresponds to a difference
between the fluid pressure in the master reservoir108 and the fluid
pressure in the wheel brake cylinder 20, 28. In both of the
pressure-increasing and pressure-reducing linear valves 172, 176,
the pressures of the fluid to be delivered to the wheel brake
cylinders 20, 28 can be controlled by controlling the
electromagnetic forces generated by the respective linear valves
172, 176, that is, by controlling the amounts of electric current
to be applied to the coils 188 of the respective linear valves 172,
176.
[0166] To a portion of the fluid passage 170 between the
pressure-increasing linear valve 172 and the pump device 12, there
is connected a hydraulic pressure sensor 196 provided for detecting
the pressure of the pressurized fluid to be supplied to the
pressure-increasing linear valve 172. The output signal of this
pressure sensor 196 more accurately represents the pressure of the
fluid as supplied to the linear valve 172, than that of the
pressure sensor 140, since the pressure detected by the pressure
sensor 196 reflects a pressure loss between the pump device 12 and
the linear valve 172. Accordingly, the use of the output signal of
the pressure sensor 196 assures improved accuracy of control of the
linear valve device 30.
[0167] To the operating rod 94, there is connected a stroke
simulator 200, which includes a spring 206 through which a
pedal-side rod 202 and a booster-side rod 204 of the operating rod
94 engage each other such that the pedal-side rod 202 is movable
relative to the booster-side rod 204.
[0168] In the present hydraulically operated braking system, the
stroke simulator 156 is provided in the fluid passage 150, in
addition to the stroke simulator 200. The stroke simulator 156 is a
wet-type stroke simulator, as distinguished from the stroke
simulator 200 which is a dry-type stroke simulator.
[0169] In the present hydraulically operated braking system,
hydraulic pressure sensors 210 and 211 are provided for detecting
the fluid pressures in the pressurizing chamber 86 and the booster
chamber 98 of the second hydraulic pressure source 14,
respectively, and hydraulic pressure sensors 212, 214, 216 and 218
are provided for detecting the fluid pressures in the respective
wheel brake cylinders 20, 28. Two stroke sensors 220, 221 are
provided for detecting the operating amount of the brake pedal 10,
more specifically, the operating stroke of the brake pedal 10.
Although the provision of the two stroke sensors 220, 221 is not
essential, it assures an improved degree of accuracy of detection
of the operating stroke of the brake pedal 10. The hydraulic
pressure sensor 210 for detecting the fluid pressure in the
pressurizing chamber 86 will be hereinafter referred to as a
master-cylinder pressure sensor, while the hydraulic pressure
sensor 211 for detecting the fluid pressure in the booster chamber
98 will be referred to as a booster pressure sensor. Although the
fluid pressure in the pressurizing chamber 86 (hereinafter referred
to as "master cylinder pressure") and the fluid pressure in the
booster chamber 98 (hereinafter referred to as "booster pressure")
are not necessarily exactly equal to each other, these master
cylinder pressure and the booster pressure correspond to the brake
operating force, and are considered to be equal to each other in
the present embodiment.
[0170] The output signals of the four sensors, namely, the
master-cylinder pressure 210, booster pressure sensor 211 and the
two stroke sensors 220, 221 are used to obtain a desired vehicle
braking torque or force. However, the use of these four sensors is
not essential, and the desired vehicle braking torque may be
obtained on the basis of the output signal of a single pedal force
sensor providing for detecting the operating force of the brake
pedal 10.
[0171] The present braking system further uses: a brake switch or
stop switch 224 for detecting an operation or a depressing action
of the brake pedal 10; wheel speed sensors 226 for detecting the
rotating speeds of the wheels 16, 24; a vehicle speed sensor 227
for detecting a running speed of the vehicle; and an
operating-state detecting device 228 for detecting the operating
states of manually operated members provided on a control panel,
for instance.
[0172] The slipping state or tendency of each wheel 16, 24 can be
detected on the basis of the output signal of the corresponding
wheel speed sensor 226. The operating states of the manually
operated members on the control panel can be detected by the output
signals of the operating-state detecting device 228. The manually
operated members include a braking-effect control selector switch
which is turned on by the vehicle operator when the operator
desires to control the braking system in a braking-effect control
mode in which the vehicle braking force is controlled on the basis
of a detected actual braking effect, which may be represented by
the detected deceleration value of the vehicle, for example.
[0173] The present braking system is controlled by the ECU 32,
which is principally constituted by a computer incorporating a
central processing unit (CPU) 240, a random-access memory (RAM)
242, a read-only memory (ROM) 244, an input portion 246 and an
output portion 248. To the input portion 246, there are connected
the above-indicated hydraulic pressure sensors 140, 196, 210, 211,
212-218, stroke sensors 220, 221, stop switch 224, wheel speed
sensors 226, vehicle speed sensor 227, and operating-state
detecting device 228. To the output portion 248, there are
connected control circuits for controlling the solenoid coils of
the above-indicated solenoid-operated shut-off valves 152, 154,
158, 162, 164 and the solenoid coils 188 of the linear valve
devices 30, and an alarming device 252. The ROM 244 stores various
control programs for executing a braking pressure control routine
illustrated in the flow chart of FIG. 3, a pressure-sensor
diagnosing routine illustrated in the flow chart of FIG. 10, a
simulator shut-off valve diagnosing routine illustrated in the flow
chart of FIG. 12, a data table of FIGS. 7 and 8 indicating various
remedies for dealing with various abnormalities of the second
hydraulic system 282, data tables of FIGS. 4-6 used for determining
the desired vehicle braking force. The ROM 244 stores other control
programs and data tables including a switching program for
selectively placing the braking system in the first control mode or
the second control mode, an anti-lock braking control program for
effecting the anti-lock braking control, a vehicle turning
stability control program for effecting a vehicle turning stability
control, a cooperative braking control program for effecting a
cooperative braking control, and a linear valve device control
program for controlling the linear valve devices 30. In the
cooperative braking control, the vehicle is braked by a
regenerative braking torque generated by a motor generator (not
shown), as well as a hydraulic braking torque generated by the
present braking system. The linear valve devices 30 are controlled
so that the actual fluid pressure in each wheel brake cylinder 20,
28 coincides with a desired value, in a feedback fashion on the
basis of the detected wheel brake cylinder pressure.
[0174] In the braking system constructed according to the present
embodiment of this invention, the pump device 12, linear valve
devices 30, fluid passage 170 and wheel brake cylinders 20, 28
cooperate to constitute a major portion of a first hydraulic system
280, while the second hydraulic pressure source 14, fluid passages
150, 160, master-cylinder shut-off valves 152, 162, wheel brake
cylinders 20, 28, stroke simulator device 159, stroke sensors 220,
221, stop switch 224, master-cylinder pressure sensor 210 and
booster pressure sensor 211 cooperate to constitute a major portion
of a second hydraulic system 282. The first hydraulic system 280
may be called a dynamic system, while the second hydraulic system
282 may be called a static system.
[0175] The linear valve devices 30 and the master-cylinder shut-off
valves 152, 162 constitute a switching device for switching the
control mode of the braking system between the first control mode
in which the first hydraulic system 280 is activated and the second
control mode in which the second hydraulic system 282 is activated.
It is also noted that the pump device 12 of the first hydraulic
system 280 is used also for the second hydraulic pressure source
14. In the present embodiment, the linear valve devices 30 are
controlled depending upon the operating state of the second
hydraulic system 282.
[0176] An operation of the hydraulically operated braking system
constructed as described above will be described.
[0177] In the first control mode of the braking system, the
master-cylinder shut-off valves 152, 162 are placed in the closed
state, so that the wheel brake cylinders 20, 28 are disconnected
from the second hydraulic pressure source 14. Further, the front
and rear communicating valves 154, 164 are placed in the closed
sate, while the simulator shut-off valve 158 is placed in the open
state. In this first control mode, the amounts of electric current
to be applied to the coils 188 of each linear valve device 30 are
controlled to control the pressure of the pressurized fluid
delivered from the pump 12, for thereby controlling the fluid
pressure in each wheel brake cylinder 20, 28.
[0178] In the second control mode of the braking system, the
master-cylinder shut-off valves 152, 162 are placed in the open
state, while the front and rear communicating valves 154, 164 are
placed in the open state, so that the wheel brake cylinders 20, 28
are communicated with the second hydraulic pressure source 14. In
this second control mode, a pressurized fluid is delivered from the
second hydraulic pressure source 14 to the wheel brake cylinders
20, 24 of the brakes 18, 26, in response to an operation of the
brake pedal 10.
[0179] In the second control mode, the simulator shut-off valve 158
is placed in the closed state, so that the stroke simulator 156 is
disconnected from the second hydraulic pressure source 14, to
prevent an unnecessary flow of the pressurized fluid into the
stroke simulator 156, for thereby avoiding an unnecessary
consumption of the pressurized fluid delivered from the second
hydraulic pressure source 14. In addition, the coils 188 of the
linear valve devices 30 are held in the de-energized state, and the
pressure-increasing and pressure-reducing valves 172, 176 of each
linear valve device 30 are held in the closed state, so that the
wheel brake cylinders 20, 28 are disconnected from the pump device
12.
[0180] In the second hydraulic pressure source 14 of the braking
system placed in the second control mode, the hydraulic booster 78
is activated with the pressurized fluid delivered from the pump
device 12. If the pressurized fluid is not supplied from the pump
device 12 to the hydraulic booster 78 due to any abnormality or
defect of the pump device 12, for instance, the hydraulic booster
78 is not operable. In this event, the second hydraulic pressure
source 14 functions simply as the master cylinder 80. Namely, the
pressurizing piston 84 is advanced by only the brake operating
force received from the brake pedal 10, without the assisting force
acting on the pressurizing piston 84. The fluid pressurized in the
pressurizing chamber 86 is delivered to the front wheel brake
cylinders 20 for activating the front brakes 18.
[0181] Normally, the braking system is placed in the first control
mode, and is controlled in the braking-effect control mode, in
which the vehicle braking force desired by the vehicle operator is
obtained on the basis of the output signals of the stroke sensors
220, 221, master-cylinder pressure sensor 210 and the booster
pressure sensor 211, and the amounts of electric current to be
applied to the coils 188 of the linear valve devices 30 are
controlled so that the actual fluid pressure in each wheel brake
cylinder 20, 28 coincides with a desired value corresponding to the
obtained desired vehicle braking force.
[0182] The braking system is switched to the second control mode
when the braking-effect control selector switch on the control
panel or any other appropriate manually operable member is turned
on to switch the control mode of the braking system from the first
control mode to the second control mode.
[0183] The control mode of the present braking system may be
switched between the first and second control modes, depending upon
whether the first and second hydraulic systems 280, 282 are
normally functioning or not. The second hydraulic system 282
includes the detecting device for detecting the operating state of
the brake pedal 10, that is, the stroke sensors 220, 221,
master-cylinder pressure sensor 210, booster pressure sensor 211,
etc. However, the output signals of the detecting device are used
in the first control mode, for controlling the fluid pressure in
the wheel brake cylinders 20, 28. Accordingly, the braking system
may be switched to the second control mode when the second
hydraulic system 282 is abnormal due to an abnormality or defect of
the detecting device. Thus, the control mode is switched from the
first control mode to the second control mode, when it is
impossible or difficult to control the fluid pressure in the wheel
brake cylinders 20, 28 due to some abnormality while the braking
system is placed in the first control mode. Where a portion of the
detecting device is abnormal but the other normal portion of the
detecting device can be substituted for the abnormal portion, the
braking system may be held placed in the first control mode in
which the first hydraulic system 280 is controlled on the basis of
the output signals of the normal portion of the detecting
device.
[0184] Where the vehicle on which the present braking system is
used includes an electric motor functioning as a vehicle drive
power source, the braking system is capable of effecting the
above-indicated cooperative braking control in which the hydraulic
braking force produced by the present braking system is controlled
so that a sum of the regenerative braking force produced by the
electric motor and the hydraulic braking force coincides with the
vehicle operator's desired vehicle braking force. The cooperative
braking control is effected when the operating speed of the
electric motor is higher than a predetermined lower limit and when
the amount of electric energy stored or left in a battery for the
electric motor is larger than a predetermined upper limit (when the
amount of electric energy that can be stored in the battery during
the regenerative braking operation of the electric motor is smaller
than a predetermined lower limit). The cooperative braking control
is terminated when the operating speed of the electric motor falls
below the lower limit, or when the amount of electric energy stored
in the battery has exceeded the upper limit. When the amount of
electric energy in the battery is larger than the upper limit,
there is a risk of excessive charging of the battery by the
electric motor. The cooperative braking control is effected while
the braking system is placed in the first control mode. When the
condition for terminating the cooperative braking control indicated
above is satisfied, or when it become difficult to obtain the
required hydraulic braking force in the first control mode, the
control mode of the braking system is changed from the first
control mode to the second control mode.
[0185] First, the operation of the braking system in the first
control mode will be briefly described.
[0186] In the first control mode, the fluid pressure in the wheel
brake cylinders 20, 28 is controlled by controlling the linear
valve devices 30. In the present embodiment, the braking system is
controlled in the braking-effect control mode in the first control
mode. Initially, an operator's desired fluid pressure P* in the
wheel brake cylinders 20, 28 is determined on the basis of the
detected operating stroke and operating force of the brake pedal
10. The operating stroke is detected on the basis of an average S
of the stroke values represented by the output signals of the two
stroke sensors 220, 221, while the operating force is detected on
the basis of an average of pressure values P.sub.M and P.sub.B
represented by the master-cylinder pressure sensor 210 and the
booster pressure sensor 211. The desired fluid pressure P* (desired
wheel brake cylinder pressure P*) is calculated according to the
following equation (1): 1 P * = K G ( 1 )
[0187] In the above equation (1), "G" represents a desired
deceleration value of the vehicle, which is represented by the
following equation (2); 2 G = Gpt + ( 1 - ) Gst ( 2 )
[0188] It will be understood from the above equation (1) that the
desired wheel brake cylinder pressure P* is proportional to the
desired vehicle deceleration value G. It will be understood from
the above equation (2) that the desired vehicle deceleration value
G is determined by a desired deceleration value Gpt which
corresponds to the brake operating force, and a desired
deceleration value Gst which corresponds to the brake operating
stroke. The desired deceleration value Gpt is determined on the
basis of the hydraulic pressure (P.sub.M+P.sub.B)/2 corresponding
to the brake operating force, and according to a predetermined
relationship between the value Gpt and the hydraulic pressure
(P.sub.M+P.sub.B)/2, as indicated in the graph of FIG. 4. This
relationship is represented by a data table stored in the ROM 244.
As indicated in FIG. 4, the value Gpt increases with an increase in
the hydraulic pressure (P.sub.M+P.sub.B)/2. Similarly, the desired
deceleration value Gst is determined on the basis of the brake
operating stroke S, and according to a predetermined relationship
between the value Gst and the operating stroke S, as indicated in
the graph of FIG. 5. This relationship is represented by a data
table stored in the ROM 244. As indicated in FIG. 5, the value Gst
increases with an increase in the brake operating stroke S. In the
above equation (1), "K" represents a predetermined coefficient, and
".alpha." represents a weight of the deceleration value
corresponding to the brake operating stroke with respect to the
deceleration value corresponding to the brake operating force. This
ratio .alpha. is determined by the desired vehicle deceleration
value G* used in the last control cycle, and according to a
predetermined relationship between the ratio .alpha. and the
deceleration value G*, as indicated in the graph of FIG. 6. This
relationship is represented by a data table stored in the ROM 244.
As indicated in FIG. 6, the ratio .alpha. increases with an
increase in the last value G*.
[0189] The amounts of electric current to be applied to the coils
188 of the linear valve devices 30 are controlled so that the
actual wheel brake cylinder pressure coincides with the determined
desired value P*. When the braking system is placed in the first
control mode, the wheel brake cylinder pressure is controlled
according to the braking pressure control routine illustrated in
the flow chart of FIG. 3.
[0190] The braking pressure control routine of FIG. 3 is initiated
with step S1 to determine whether any abnormality of the second
hydraulic system 282 has been detected. If any abnormality has been
detected (and an abnormality-processing control mode is not
established), a negative decision (NO) is obtained in step S1, and
the control flow goes to step S2 to determine whether the stop
switch 224 is in the ON state. If the brake pedal 10 is in
operation and the stop switch 244 is in the ON state, an
affirmative decision (YES) is obtained in step S2, and the control
flow goes to sep S3 to detect the operating stroke of the brake
pedal 10, and then to step S4 to detect the master-cylinder
pressure PM and the booster pressure PB. Step S4 is followed by
step S5 in which the desired wheel brake cylinder pressure P* is
calculated according to the above equations (1) and (2). Then, the
control flow goes to step S6 in which the linear valve devices 30
are controlled.
[0191] If the abnormality-processing control mode is established,
an affirmative decision (YES) is obtained in step S1, and the
control flow goes to step S7 to determine a treatment appropriate
for dealing with the abnormality, and then to step S8 to practice
the determined treatment. In the present embodiment, the ROM 244
stores a data table which indicates various treatments for dealing
with various kinds of abnormalities of the second hydraulic system
282. According to this data table, an appropriate treatment for
dealing with the particular abnormality of the second hydraulic
system 282 is determined.
[0192] While the present embodiment is adapted such that the
hydraulic pressure corresponding to the brake operating force is
determined to be an average of the master-cylinder pressure P.sub.M
and the booster pressure P.sub.B, the use of the average value is
not essential. Namely, the master-cylinder pressure P.sub.M or the
booster pressure P.sub.B may be used as the hydraulic pressure
corresponding to the brake operating force. Further, the desired
wheel brake cylinder pressure P* may be calculated according to the
following equation (3), rather than the above equation (1): 3 P * =
f s ( S , 1 / S 2 ) + f m { P , 1 - ( 1 / P 2 ) } ( 3 )
[0193] In the above equation (3), f.sub.s and f.sub.m are
functions. Where the desired wheel brake cylinder pressure P* is
determined according to the above equation (3), the weight of the
deceleration value corresponding to the brake operating stroke S is
increased with a decrease in the brake operating stroke S, and the
weight of the hydraulic pressure P corresponding to the brake
operating force is increased with an increase with the hydraulic
pressure P.
[0194] As indicated in FIGS. 7 and 8, the second hydraulic system
282 is diagnosed for any abnormality, on the basis of the output
signals of the stop switch 224, stroke sensors 220, 221,
master-cylinder pressure sensor 210, booster pressure sensor 211,
and accumulator pressure sensors 140, 196. The brake operating
stroke S is detected on the basis of the output signals of the two
stroke sensors 220, 221. For instance, the brake operating stroke S
is determined to be an average of the values represented by the
output signals of the two stroke sensors 220, 221. Similarly, the
pressure of the second hydraulic pressure source 14 may be
determined to be an average of the values represented by the output
signals of the master-cylinder pressure sensor 210 and the booster
pressure sensor 211, and the pressure of the accumulator 134 may be
determined to be an average of the values represented by the output
signals of the two accumulator pressure sensors 140, 196. However,
the ratio of the values represented by the output signals of the
two sensors as well as the values may be taken into account in
determining the brake operating stroke and the pressures of the
second hydraulic pressure source 14 and the accumulator 134.
[0195] In FIGS. 7 and 8, "NORMAL OUTPUTS" mean that is the output
signals of the appropriate two sensors are both normal, and
"ABNORMAL OUTPUTS" and "NO OUTPUTS" mean that at least one of the
output signals of the appropriate two sensors is abnormal or zero.
In the following description, the master-cylinder pressure and the
booster pressure will be collectively referred to as "pressure of
the second hydraulic pressure source 14", unless the
master-cylinder pressure and the booster pressure are required to
be distinguished from each other.
[0196] As indicated in FIGS. 7A-7C, the second hydraulic system 282
is diagnosed to be normal if an operating stroke of the brake pedal
10 is detected and if the pressure of the second hydraulic pressure
source 14 and the pressure of the accumulator 134 are both normal,
while the stop switch 224 is placed in the ON state. This state is
referred to as a state (A). In this state (A), the second hydraulic
pressure source 14 including the hydraulic booster 78 and the
master cylinder 80 is normally functioning in response to an
operation of the brake pedal 10.
[0197] Similarly, the second hydraulic system 282 is diagnosed to
be normal if an operating stroke of the brake pedal 10 is not
detected and if the pressure of the second hydraulic pressure
source 14 is zero, even if the pressure of the accumulator 134 is
held within a normal range, while the stop switch 224 is placed in
the OFF state. This state is referred to as a state (O). In this
state (O) wherein the brake pedal 10 is not in operation, neither
an operating stroke of the brake pedal 10 nor a pressure of the
second hydraulic pressure source 14 is detected.
[0198] When the second hydraulic system 282 is diagnosed to be
normal, the braking system is kept controlled in the first control
mode. The present invention does not directly relate to an
abnormality of the linear valve devices 30, and a description on
the diagnosis of the linear valve devices 30 is dispensed with.
However, it is noted that the control mode of the braking system
may be switched from the first control mode to the second control
mode when any abnormality of the linear valve devices 30 is
detected.
[0199] On the other hand, the second hydraulic system 282 is
diagnosed to have some abnormality which cannot be identified, if
the pressure of the accumulator 134 is abnormal even if an
operating stroke of the brake pedal 10 is detected and the pressure
of the second hydraulic pressure source 14 is normal, while the
stop switch 224 is in the ON state. This state is referred to as a
state (B). Where the pressure of the accumulator 134 is abnormally
low, the booster pressure detected by the booster-pressure sensor
211 must be abnormally low. In this sense, the state (B) wherein
the pressure of the accumulator 134 is normal does not
theoretically exist. Accordingly, the second hydraulic system 282
is diagnosed to have some abnormality that cannot be identified,
and the braking system is brought into an "impossible-to-diagnose
mode". That is, the control of the braking system in the first
control mode is terminated, and the control state is switched to
the second control mode. In the second control mode, either, the
brake operating force cannot be boosted by the hydraulic booster 78
since the pressure of the accumulator 134 is abnormally low, but
the wheel brake cylinders 20 can be activated by the brake
operating force, for operating the front wheel brakes 188.
[0200] In the state (B) wherein there exists an abnormality that
cannot be identified, it is impossible to correctly diagnose the
second hydraulic system 282. In this state, the braking system is
brought into the "impossible-to-diagnose" mode described above.
This mode is also established in other states, namely, in states
(F), (J) and (N) indicated in FIGS. 7A-7C. In the sate (F), the
brake operating stroke and the pressure of the accumulator 134 are
both normal even if the pressure of the second hydraulic pressure
source 14 is normal, while the stop switch 224 is placed in the ON
state. In the state (J), a brake operating stroke is detected, the
pressure of the hydraulic pressure source 14 is normal and the
pressure of the accumulator 134 is abnormal, even if the stop
switch 224 is placed in the OFF state. In the state (N), the
pressure of the second hydraulic pressure source 14 is normal even
if the brake operating stroke and the pressure of the accumulator
134 are abnormal, while the stop switch 224 is in the OFF
state.
[0201] The pump device 12 is diagnosed to be abnormal, if neither
the pressure of the second hydraulic pressure source 14 nor the
pressure of the accumulator 134 is normal even if the brake
operating stroke is normal, while the stop switch 224 is in the ON
state. This state is referred to as a state (D). In this state
wherein the pressure of the accumulator 134 is abnormally low, a
the second hydraulic pressure source 14 is not likely to be able to
deliver the pressurized fluid having a normal pressure level, when
the brake pedal 10 is operated. In this state (D), the control mode
of the braking system is switched to the second control mode.
[0202] The pump device 12 is also diagnosed to be abnormal, if
neither the pressure of the second hydraulic pressure source 14 nor
the pressure of the accumulator 134 is normal even if the brake
operating stroke is normal, while the stop switch 224 is placed in
the OFF state. This state is referred to as a state (L). In this
state, the pressure of the second hydraulic pressure source 14 can
be considered to be abnormal since the pressure of the accumulator
134 is abnormally low, and the booster 78 is not able to normally
function. Namely, the pump device 12 is considered to be abnormal.
In the state (L), at least one of the stroke sensors 220, 221 and
the stop switch 224 may be abnormal. In this case, however, it is
impossible to determine which one of the sensors 220, 221and stop
switch 224 is abnormal. Since it is not possible to determine
whether the brake pedal 10 has been operated, in the above case,
the pump device 12 is diagnosed to be abnormal. The abnormal state
(L) may be treated similarly to the above-indicated states (B),
(F), (J) and (L) in which it is impossible to diagnose the second
hydraulic system 282.
[0203] The pump device 12 is also diagnosed to be abnormal, if a
brake operating stroke is not detected and if neither the pressure
of the second hydraulic pressure source 14 and the pressure of the
accumulator 134 is normal, while the stop switch 224 is in the OFF
state. This state is referred to as a state (P).
[0204] The pump device 12 and the stop switch 224 are diagnosed to
be abnormal, if a brake operating stroke is not detected, and if
neither the pressure of the second hydraulic pressure source 14 nor
the pressure of the accumulator 134 is normal, even if the stop
switch 224 is detected to be in the ON state. This state is
referred to as a state (H). In this state, there is an extremely
low possibility that the brake pedal 10 is in operation.
[0205] The second hydraulic pressure source 14 is diagnosed to be
abnormal, if the pressure of the second hydraulic pressure source
14 is abnormal even if a brake operating stroke is detected and the
pressure of the accumulator 134 is in the normal range, while the
stop switch 224 is placed in the ON state. This state is referred
to as a state (C), which will be further described.
[0206] The stroke sensors 220, 221 are diagnosed to be abnormal, if
the brake operating stroke is abnormal even if the pressures of the
second hydraulic pressure source 14 and the accumulator 134 are
both normal, while the stop switch 224 is in the ON state. This
state is referred to as a sate (E). In this state, the braking
system is brought into an abnormal-stroke-sensor mode. Namely, the
braking system is kept in the first control mode, but the detected
brake operating stroke is not used to determine or calculate the
desired pressure P* of the wheel brake cylinders 20, 28. In this
case, the desired wheel brake cylinder pressure P* is determined on
the basis of the pressure of the second hydraulic pressure source
14. That is, the brake operating stroke S in the above equation (2)
is zeroed, and the weight ".alpha." is set to be "1".
[0207] The stroke sensors 220, 221 are also diagnosed to be
abnormal, if the pressure of the accumulator 134 is normal and if a
pressure of the second hydraulic pressure source 14 is not detected
even if a brake operating stroke is detected, while the stop switch
224 is in the OFF state. This state is referred to as a state (K).
In this state, the braking system is brought to the
abnormal-stroke-sensor mode, as in the state (E) described
above.
[0208] The stop switch 224 is diagnosed to be abnormal, if a brake
operating stroke is not detected and if the pressure of the
accumulator 134 is normal, even if the stop switch 224 is detected
to be placed in the ON state. This state is referred to as a state
(G). In this state, the braking system is brought into an
abnormal-stop-switch mode, in which the braking system is kept
controlled in the first control state, without depending upon the
operating state of the stop switch 224. Described in detail, the
control flow goes to step S3 while skipping step S2, when the
negative decision (NO) is obtained in step S1 in the braking
pressure control routine of FIG. 3. While the brake pedal 10 is not
in operation, the brake operating stroke and the pressure of the
second hydraulic pressure source 14 are both zero, and the desired
wheel brake cylinder pressure P* is also zero, so that the braking
system is not activated to apply an unnecessary hydraulic brake to
the vehicle. It is noted that a determination as to whether the
brake pedal 10 is in operation may be effected on the basis of the
output signals of the stroke sensors 220, 221 or the output signal
of the master-cylinder pressure sensor 210 or booster pressure
sensor 211, in place of the output signal of the stop switch 224.
An operation of the brake pedal 10 can be detected by determining
whether the detected operating stroke is larger than a
predetermined threshold or whether the master cylinder pressure is
higher than a predetermined threshold. In any event, the control of
the braking system in the first control mode is continued in the
above state (G).
[0209] The stop switch 224 is diagnosed to be abnormal if the brake
operating stroke, and the pressures of the second hydraulic
pressure source 14 and the accumulator 134 are all normal, even if
the stop switch 224 is detected to be in the OFF state. This state
is referred to as a state (I). In this state, the braking system is
brought into the abnormal-stop-switch mode, as in the above state
(G).
[0210] The stop switch 224 and the stroke sensors 220, 221 are both
diagnosed to be abnormal, if the pressure of the accumulator 134 is
normal even if the stop switch 224 is in the OFF state and a brake
operating stroke is not detected. This state is referred to as a
state (M). In this state, it is reasonable to consider that the
second hydraulic pressure source 14 is operated to generate a
normal pressure in response to an operation of the brake pedal 10
while the accumulator pressure is in the normal range. The pressure
of the second hydraulic pressure source 14 is detected based on the
output signals of the two pressure sensors 210, 211, and the
pressure of the accumulator 134 is also detected based on the
output signals of the two stroke sensors 220, 221, so that the
accuracy of diagnosis of those pressures is comparatively high. To
the contrary, the operation of the brake pedal 10 is detected based
on the output signal of only one stop switch 224. Accordingly, the
stop switch 224, and the stroke sensors 220, 221 whose output
signals do not match the output signals of the pressures of the
second hydraulic pressure source 14 and the accumulator 134 are
diagnosed to be abnormal, in the above state (M). In this case, the
braking system is brought into an abnormal-stop-switch,
abnormal-stroke-sensor mode, in which the braking system is
controlled in the first control mode, without depending upon the
output signal of the stop switch 224, and according to the desired
wheel brake cylinder pressure P* determined on the basis of the
pressure of the second hydraulic pressure source 14. Namely, the
brake operating stroke S used in step S5 is zeroed, and the weight
".alpha." is set to "1".
[0211] The abnormal state (C) indicated above will be described in
detail.
[0212] The state (C) is detected on the basis of the output signals
of the two pressure sensors 210, 211 (master-cylinder pressure
sensor 210 and booster pressure sensor 211). As described above,
the master-cylinder pressure sensor 210 is provided to detect the
fluid pressure in the pressurizing chamber 86, while the booster
pressure sensor 211 is provided to detect the fluid pressure in the
booster chamber 98. Theoretically, the fluid pressure in the
pressurizing chamber 98 is equal to the fluid pressure in the
booster chamber 98, as indicated in FIG. 9A, as long as the pump
device 12 and the second hydraulic pressure source 14 are normal.
In FIG. 9A, "AA" represents a pulsation of the pressure of the
pressurized fluid as detected by the master-cylinder pressure
sensor 210 upon initiation of an operation of the pressure
regulating portion 88 of the second hydraulic pressure source 14.
Except for this pressure pulsation, the fluid pressures as detected
by the two pressure sensors 210, 211 are equal to each other.
[0213] Where the pump device 12 or the pressure regulating portion
88 is abnormal, for instance, on the other hand, the pressures as
detected by the two pressure sensors 210, 211 are not equal to each
other. As indicated in FIG. 9B, the fluid pressures in the
pressurizing and booster chambers 86, 98 are both lowered, but the
fluid pressure in the booster chamber 98 is lowered down to a level
which is almost zero, but the fluid pressure in the pressurizing
chamber 86 is not lowered below a level corresponding to the brake
operating force. Where the fluid pressure in the pressurizing
chamber 98 is lowered (not down to zero) while the fluid pressure
in the booster chamber 98 is zero, therefore, the hydraulic booster
78 can be diagnosed to be abnormal. This state is referred to as a
state (C1), as indicated in FIG. 8. An example of this state (C1)
is a case where the spool 100 of the pressure regulating portion 88
is not movable. Where the fluid pressure in the pressurizing
chamber 98 is also zero, the cup of the pressurizing piston 84 may
be considered defective. This state is referred to as a state (C2),
as indicated in FIG. 8. The pressure regulating portion 88 is
arranged to regulate the pressure of the pressurized fluid received
from the accumulator 134, to a value corresponding to the fluid
pressure in the pressurizing chamber 86. If the fluid in the
pressurizing chamber 86 cannot be pressurized due to a damage of
the cup of the pressurizing piston 84, the pressure of the fluid
regulated by the pressure regulating portion 88 is extremely low.
Where the pressurization of the fluid in the booster chamber 98 is
detected while that in the pressurizing chamber 86 is not detected,
there appears to be some abnormality that cannot be identified.
This state is referred to as a state (C3), as also indicated in
FIG. 8.
[0214] When the abnormal state (C1) is detected, the braking system
is brought into an abnormal-pressure-regulating-portion mode, in
which the control of the braking system in the first control mode
is continued, and the desired wheel brake cylinder pressure P* is
determined on the basis of the output signals of the stroke sensors
220, 221, without depending on the output signals of the
master-cylinder pressure 210 and the booster pressure sensor 211.
In the above equation (2), the weight ".alpha." is zeroed. When the
abnormal state (C2) is detected, the braking system is brought into
an abnormal-piston mode, in which the control in the first control
mode is continued. In these states (C1) and (C2) wherein the pump
device 12 is normal, the braking system can be continuously
controlled in the first control mode. Where the abnormal state (C3)
is detected, the braking system is brought into the
impossible-to-diagnose mode, namely, is switched to the second
control mode.
[0215] As described above, the present embodiment is arranged not
to switch the braking system to the second control mode, but to
hold the braking system in the first control mode, as much as
possible, where the second hydraulic pressure source 14 is
diagnosed to be abnormal. Namely, the braking system is operated in
the braking-effect control mode as long as the braking-effect
control is possible in the presence of an abnormality of the second
hydraulic pressure source 14. This arrangement permits an improved
degree of controllability of the vehicle braking force. Where an
abnormality of the second hydraulic pressure source 14 is detected
while the braking system is placed in the cooperative braking
control mode, the cooperative braking control is not terminated
immediately after the detection of the abnormality of the hydraulic
braking system. Where the pump device 12 is normal, the control of
the braking system in the first control state can be continued even
in the presence of some abnormality of the second hydraulic
pressure source 14. Accordingly, the braking system is kept in the
first control mode, to control the hydraulic braking force based on
the pressurized fluid stored in the accumulator 134, with high
accuracy.
[0216] It is also noted that the two pressure sensors 210 and 211
are provided to detect the fluid pressures in the respective two
fluid chambers 86, 98. This arrangement permits an intricate
diagnosis of the second hydraulic pressure source 14 for any
abnormality at a specific location or portion thereof. Where the
diagnosis is effected on the basis of an average of the two values
represented by the two pressure sensors 210, 211, or on the basis
of one of these two values, the second hydraulic pressure source 14
can be diagnosed to be abnormal, but the abnormality cannot be
identified. Where the diagnosis is effected on the basis of the two
values represented by the two hydraulic pressure sensors, a
detected abnormality can be identified.
[0217] Although the present braking system is adapted to switch the
control mode from the first mode to the second mode where a
detected abnormality cannot be identified, as in the states (B),
(F), (J) and (N), the braking system can be kept in the first
control mode as long as the pressure of the fluid in the
accumulator 134 is higher than a predetermined threshold.
[0218] The master-cylinder pressure sensor 210 and the booster
pressure sensor 211 are diagnosed for any abnormality, according to
a pressure-sensor diagnosing routine illustrated in the flow chart
of FIG. 10. This routine is executed in this embodiment while the
vehicle is stationary.
[0219] The pressure-sensor diagnosing routine of FIG. 10 is
initiated with step S40 to determine whether the vehicle is
stationary. This determination is made by determining whether the
vehicle running speed is lower than a predetermined threshold. If
an affirmative decision (YES) is obtained in step S40, the control
flow goes to step S41 to determine whether the brake pedal 10 is in
operation. In the present embodiment, the determination in step S41
is made on the basis of the output signals of the stop switch 224
and the stroke sensors 210, 211. If the stop switch 224 is in the
ON state, and the average of the values represented by the output
signals of the two stroke sensors 210, 211 is larger than zero, it
is determined that the brake pedal 10 is in operation.
[0220] If the brake pedal 10 is in operation while the vehicle is
stationary, the control flow goes to sep S42 to determine whether a
TIME ELAPSE flag is set at "1". This flag is set to "1" when step
S45 has been implemented, and is reset to "0" in step S47 when a
predetermined time has elapsed. When step S42 is implemented for
the first time, a negative decision (NO) is obtained in this step,
and the control flow goes to step S43 to determine the desired
wheel brake cylinder pressure P**. The actual wheel brake cylinder
pressure is controlled by the linear valve devices 30, so as to
coincide with the determined desired value P**. The control of the
linear valve devices 30 in this case is different from the control
in the first control state described above, and is effected for the
purpose of diagnosing the pressure sensors 210, 211. Accordingly,
the desired wheel brake cylinder pressure P** is calculated
according to the following equation (3), which is different from
the equation (1). 4 P ** = ( P M + P B ) / 2 ( 3 )
[0221] The pressure P.sub.M and P.sub.B are the fluid pressures as
detected by the master-cylinder and booster pressure sensors 210,
211.
[0222] By controlling the actual wheel brake cylinder pressure so
as to coincide with the desired value P** determined according to
the above equation (2), as indicated in FIG. 11, an influence of
the opening actions of the master-cylinder shut-off valves 152, 162
on the operating state of the brake pedal 10 as felt by the vehicle
operator can be reduced.
[0223] Step S43 is followed by step S44 to determine whether the
absolute value of a difference between the actual value P.sub.WC
and the desired value P** of the wheel brake cylinder pressure is
equal to or smaller than a predetermined threshold .DELTA.P*. If an
affirmative decision (YES) is obtained in step S44, the control
flow goes to step S45 to de-energize the coils 188 of the linear
valve devices 30, so that the pressure-increasing and
pressure-reducing linear valves 162, 174 are closed. Further, the
master-cylinder shut-off valves 152, 162 are opened, in step S45.
As a result, the pressurized fluid delivered from the second
hydraulic pressure source 14 is supplied to the wheel brake
cylinders 20, 28.
[0224] Step S45 is followed by step S46 to determine whether the
predetermined time has passed after the pressure-increasing and
pressure-reducing linear valves 172, 176 have been placed in the
closed state. If an affirmative decision (YES) is obtained in step
S46, the control flow goes to step S47 to read in the output
signals of the master-cylinder pressure sensor 210, booster
pressure sensor 211 and the wheel brake cylinder pressure sensors
212-218. Then, the control flow goes to step S48 to determine
whether the absolute value of a difference between an average of
the pressure values as detected by the two pressure sensors 210,
211 and an average of the pressure values as detected by the four
wheel brake cylinder sensors 212-218 is smaller than a
predetermined threshold .DELTA.P. If an affirmative decision (YES)
is obtained in step S48, the control flow goes to step S49 to
determine that the master-cylinder pressure sensor 210 and the
booster pressure sensor 211 are normal. If a negative decision (NO)
is obtained in step S48, the control flow goes to step 50 to
determine that the pressure sensors 210, 211 are abnormal.
[0225] As described above, the braking pressure control apparatus
according to the present embodiment of the invention is arranged to
diagnose the second hydraulic pressure source 14 at an increased
number of opportunities. Conventionally, the sensors are usually
diagnosed only upon initial checking of the vehicle prior to an
operation of the braking system. On the other hand, the diagnosing
device included in the braking pressure control apparatus of the
present braking system is arranged to diagnose the pressure sensors
210, 211 during an operation of the brake pedal 10, so that the
number of opportunities at which the second hydraulic pressure
source 14 is diagnosed is accordingly increased.
[0226] Further, the fluid pressure in the wheel brake cylinders 20,
28 has been controlled to the desired value P** before step S45 is
implemented. Accordingly, the fluid pressure in the wheel brake
cylinders 20, 28 can be rapidly made equal to the pressure of the
second hydraulic pressure source 14 when the master-cylinder
shut-off valves 152, 162 are opened. Thus, the predetermined time
measured in step S46 can be reduced, making possible to reduce the
time required for diagnosing the second hydraulic pressure source
14.
[0227] However, controlling the actual wheel brake cylinder
pressure to the desired value P** before opening the
master-cylinder shut-off valves 152, 162 is not essential. The
master-cylinder shut-off valves 152, 162 may be opened provided the
wheel brake cylinder pressure is equal to the pressure of the
second hydraulic pressure source 14.
[0228] Further, the operation of controlling the actual wheel brake
cylinder pressure to the desired value P** is not essential in the
diagnosis of FIG. 10, provided the determination in step S48 is
effected after the pressure-increasing and pressure-reducing linear
valves 172, 176 have been closed and the master-cylinder shut-off
valves 152, 162 have been opened. In this case, too, the diagnosis
can be effected on the basis of the wheel brake cylinder pressure
and the pressure of the second hydraulic pressure source 14.
[0229] In the present embodiment, the simulator shut-off valve 158
is diagnosed according to a simulator shut-off valve diagnosing
routine illustrated in the flow chart of FIG. 12.
[0230] The simulator shut-off valve diagnosing routine is executed
when the operating stroke of the brake pedal 10 is increased while
the vehicle is stationary. The simulator shut-off valve 158 is
diagnosed to be abnormal, if the amount of change (increase) of the
operating stroke of the brake pedal 10 and the amount of change of
the fluid pressure in the pressurizing chamber 86 (master cylinder
pressure P.sub.M) do not have a normal relationship, upon
generation of a command to close the simulator shut-off valve 158.
If the shut-off valve 158 cannot be closed and is held in the open
state even after the command to closed the shut-off valve 158 is
generated (even after the solenoid coil of the shut-off valve 158
is de-energized), the amount of change of the master cylinder
pressure P.sub.M is smaller than that of the brake operating
stroke. In the present embodiment, the ROM 244 stores a data table
representing the predetermined relationship between the amounts of
change of the brake operating member and the master cylinder
pressure, as indicated in the graph of FIG. 13. The determination
as to whether the simulator shut-off valve 158 is abnormal or not
is effected by determining whether a point defined by the detected
two amounts of change is located on one side of the straight line
representing the relationship, or on the other side. When the
simulator shut-off valve 154 is diagnosed to be abnormal (kept in
the open state), the alarming device 252 is activated. The control
of the braking system in the first control mode is possible even
with the simulator shut-off valve 158 kept in the open state, as
long as the pump device 12 is normally functioning. However, the
brake operating stroke would be excessively increased if the
control mode is switched from the first mode to the second mode. In
this respect, it is not desirable to continue the control of the
braking system in the first control state. Further, the diagnosing
routine may be formulated to inhibit a running of the vehicle if
the simulator shut-off valve 158 is abnormally kept in its open
state and if the pressure of the accumulator 134 is lower than a
predetermined lower limit.
[0231] Although the simulator shut-off valve diagnosing routine of
FIG. 12 is formulated to diagnose the simulator shut-off valve 158
while the vehicle is stationary, this routine may be executed only
upon initial checking of the vehicle. For instance, the vehicle
operator is prompted to operate the brake pedal 10 or increase the
operating stroke when the ignition switch of the vehicle is turned
on while the vehicle is stationary. This arrangement assures a
diagnosis of the simulator shut-off valve 158 upon initial checking
of the vehicle.
[0232] The simulator shut-off valve diagnosing routine of FIG. 12
is initiated with step S81 to determine whether the vehicle is
stationary. If an affirmative decision (YES) is obtained in step
S81, the control flow goes to step S82 to determine whether the
operating amount of the brake pedal 10 is increased. If an
affirmative decision (YES) is obtained in step S82, the control
flow goes to step S83 to command the simulator shut-off valve 158
to be closed, and command the master-cylinder shut-off valves 152,
162 and the front and rear communicating valves 154, 164 to be
opened, so that the pressurized fluid delivered from the second
hydraulic pressure source 14 is supplied to the four wheel brake
cylinders 20, 28. Step S83 is followed by step S84 to detect the
amount of change of the brake operating stroke S and the amount of
change of the master cylinder pressure P.sub.M. Step S84 is
followed by step S85 to determine whether the point defined by the
detected amounts of change indicated above is located in an
abnormal area on one side of the straight line representing the
predetermined relationship of FIG. 13. If the point is not located
in the abnormal zone, a negative decision (NO) is obtained in step
S84, and the control flow goes to step S86 to determine whether the
simulator shut-off valve normal. If the point is located in the
abnormal zone, an affirmative decision (YES) is obtained in step
S85, and the control flow goes to step S87 to determine that the
simulator shut-off valve 158 is abnormal.
[0233] As described above, the present embodiment is arranged to
diagnose the simulator shut-off valve 158, so that it is possible
to inform the vehicle operator of an abnormality of the simulator
shut-off valve 158 if detected.
[0234] To diagnose the simulator shut-off valve 158 with an
improved degree of accuracy, it is desirable to obtain the ideal
relationship between the amount of change of the brake operating
stroke and the amount of change of the master cylinder pressure, on
the basis of data obtained experimentation, and store the obtained
ideal relationship in the ROM 244.
[0235] The arrangement to diagnose the simulator shut-off valve 158
can be utilized to diagnose the wheel brake cylinders 20, 28 for
the presence of air contained therein. That is, in the presence of
air in the wheel brake cylinders 20, 28, the amount of change of
the master cylinder pressure tends to be comparatively small with
respect to the amount of change of the brake operating stroke. In
this case, however, it is required to determine whether the
comparatively small amount of change of the master cylinder
pressure is caused due to a defect of the simulator shut-off valve
158 (e.g., its valve member being kept in the open state due to its
sticking) or due to the presence of air in the wheel brake
cylinders 20, 28. This determination may be made by effecting
another diagnosis according to the diagnosing routine of FIG. 12
while the master-cylinder shut-off valve 152 is held in the closed
state. The presence of air in the wheel brake cylinders 20, 28 can
be detected if the relationship between the amounts of change of
the brake operating stroke and the master cylinder pressure is
normal while the master-cylinder shut-off valve 152 is in the
closed state, but is abnormal while the shut-off valve 152 is in
the open state.
[0236] Similarly, the wheel brake cylinders 20, 28 can be diagnosed
for the presence of air therein, on the basis of a relationship
between the detected amounts of change of the brake operating
stroke and the master cylinder pressure while the front and rear
communicating valves 154, 164 are held in the open state, and that
while the valves 154, 164 are held in the closed state.
[0237] Further, the simulator shut-off valve 158 can be diagnosed
for an abnormality, on the basis of the above-indicated
relationship while the front and rear communicating valves 154, 164
are held in the closed state. In this closed state, the amount of
the pressurized fluid to be delivered from the second hydraulic
pressure source 14 to the wheel brake cylinders 20, 28 is reduced,
and the amount of change of the brake operating stroke is
accordingly reduced, so that the determination as to whether the
simulator shut-off valve 158 is in the closed state or not can be
effected with improved accuracy. In addition, an influence of the
diagnosis on the brake pedal 10 as felt by the vehicle operator can
be reduced. In this respect, it is noted that the relationship
between the amounts of change of the brake operating stroke and the
master cylinder pressure when the simulator shut-off valve 158 is
in the open state to diagnose the shut-off valve 158 with the front
and rear communicating valves 154, 164 are held in the closed state
is substantially the same as the relationship when the braking
system is placed in the first control state in which the simulator
shut-off valve 158 is in the open state with the master-cylinder
shut-off valve 152 is held in the closed state.
[0238] Further, the simulator shut-off valve 158 can be diagnosed
by first holding the master-cylinder shut-off valve 152 in the
closed state and the simulator shut-off valve 158 in the open
state, as in the normal control of the braking system in the first
control state during an increase of the brake operating stroke, and
then closing the simulator shut-off valve 158 while holding the
master-cylinder shut-off valve 152 in the closed state when the
brake operating stroke is reduced. If the master cylinder pressure
is rapidly lowered during a reduction of the brake operating
stroke, it means that the simulator shut-off valve 158 is in the
closed state. If the master cylinder pressure is gradually lowered,
it means that the simulator shut-off valve 158 is in the open
state.
[0239] It will be understood from the foregoing description of the
present embodiment that the various sensors indicated above and a
portion of the ECU 32 assigned to store and execute the diagnosing
routines of FIGS. 10 and 12 constitute a diagnosing device for
diagnosing the second hydraulic pressure source 14.
[0240] It will also be understood that a portion of the diagnosing
device assigned to store and execute the diagnosing routine of FIG.
10 constitutes a major part of a sensor diagnosing portion for
diagnosing the pressure sensors 210, 211, while a portion of the
diagnosing device assigned to store and execute the diagnosing
routine of FIG. 12 constitutes a major part of a simulator
diagnosing portion for diagnosing the stroke simulator 159.
[0241] It will further be understood that a portion of the ECU 32
assigned to store and execute the braking pressure control routine
of FIG. 3 constitutes a major part of a first braking pressure
control device operable while the braking system is normal. The
braking pressure control device includes a control portion for
controlling the wheel brake cylinder pressure to a value
corresponding to the master cylinder pressure. It will also be
understood that a portion of the ECU 32 assigned to store and the
data table of FIG. 7 and control the braking system according to
this data table constitutes a major part of a second braking
pressure control device operable while the second hydraulic
pressure source is abnormal, and that a portion of the ECU 32
assigned to switch the control mode of the braking system from the
first control mode to the second control mode upon detection of an
abnormality of the braking system according to the data table of
FIG. 7 constitutes a major part of a switching device for switching
the control mode between the first and second control modes.
[0242] In the above embodiment, the second hydraulic pressure
source 14 is diagnosed for any abnormality according to the data
table of FIG. 8. This diagnosis may be effected according to a
diagnosing routine illustrated in the flow chart of FIG. 14,
according to a second embodiment of this invention.
[0243] The diagnosing routine of FIG. 14 is initiated with step
S101 to determine whether the brake pedal 10 is in operation. If an
affirmative decision (YES) is obtained in step S101, the control
flow goes to step S102 to read in the master cylinder pressure
P.sub.M and the booster pressure P.sub.B on the basis of the output
signals of the master-cylinder pressure sensor 210 and the booster
pressure sensor 211. Step S102 is followed by step S103 to
determine whether the booster pressure P.sub.B is equal to or lower
than a predetermined threshold P.sub.SB (which is almost zero, in
this embodiment). If an affirmative decision (YES) is obtained in
step S103, it means that the second hydraulic pressure source 14 is
abnormal. The fluid pressure in the booster chamber 98 is not
pressurized directly by a depressing action of the brake pedal 10.
Therefore, the booster pressure lower than the threshold indicates
a defect of the second hydraulic pressure source 14. Although it is
not clear in this state whether the hydraulic booster 78 is
abnormal, it is at least evident that the pressure regulating
portion 88 is not able to generate a fluid pressure corresponding
to the brake operating force. On the other hand, the master
cylinder pressure (fluid pressure in the pressurizing chamber 86)
is increased directly by the depressing operation of the brake
pedal 10, so that the generated master cylinder pressure
corresponds to the brake operating force, even when the hydraulic
booster 78 is defective. Accordingly, the second hydraulic pressure
source 14 is desirably diagnosed on the basis of the booster
pressure as detected by the booster pressure sensor 211.
[0244] Although the second hydraulic pressure source 14 can be
diagnosed on the basis of the booster pressure, a further diagnosis
of the second hydraulic pressure source 14 is implemented in step
S104 and subsequent steps, after the second hydraulic pressure
source 14 has been diagnosed to be abnormal, on the basis of the
booster pressure lower than the threshold.
[0245] Step S104 is provided to determine whether the master
cylinder pressure P.sub.M as detected by the master-cylinder
pressure sensor 210 is equal-to or higher than a predetermined
threshold P.sub.SM. If the master cylinder pressure is equal to or
lower than the threshold, namely, if an affirmative decision (YES)
is obtained in step S104, the control flow goes to step S105 to
determine that the cup of the pressurizing piston 84 is damaged. If
a negative decision (NO) is obtained in step S104, it means that
the master cylinder pressure is normal. In this case, the control
flow goes to step S106 to determine whether the master cylinder
pressure is higher than the booster pressure. If the master
cylinder pressure is higher than the booster pressure, the control
flow goes to step S107 to determine that the pressure regulating
portion 88 is abnormal, and bring the braking system into the
abnormal-pressure-regulat- ing-portion mode, so that the fluid
pressure in the pressurizing chamber 86 can be pressurized to a
value corresponding to the operating force of the brake pedal 10 in
operation, even when the fluid pressure in the booster chamber 98
cannot be pressurized. If the master cylinder pressure lower than
the booster pressure, the control flow goes to step S108 to
determine that it is impossible to identify an abnormality of the
second hydraulic pressure source 14, and bring the braking system
into the impossible-to-diagnose mode described above.
[0246] If the booster pressure is higher than the predetermined
threshold, that is, if a negative decision (NO) is obtained in step
S103, the control flow goes to step S109 to determine whether the
master cylinder pressure is higher than the booster pressure. If an
affirmative decision (YES) is obtained in step S109, the control
flow goes to step S110 to determine that the second hydraulic
pressure source 14 is normal. If a negative decision (NO) is
obtained in step S109, the control flow goes to step S108 to bring
the braking system into the impossible-to-diagnose mode.
[0247] As described above, the second hydraulic pressure source 14
is diagnosed to be abnormal if the booster pressure is lower than
the threshold. Thus, the second hydraulic pressure source 14 can be
easily diagnosed.
[0248] The principle of the present invention is applicable to a
braking system constructed as shown in FIG. 15, as well as the
braking system of FIG. 1. In the embodiment of FIG. 15, a releasing
passage 300 is provided to connect the master reservoir 108 to a
fluid passage connecting the simulator shut-off valve 158 and the
stroke simulator 156 of the stroke simulator device 159. A
releasing valve 302 is provided in the releasing passage 300. This
shut-off valve 302 has an open position for fluid communication of
the stroke simulator 156 to the master reservoir 108, and a closed
position for inhibiting the fluid communication between the stroke
simulator 156 and the master reservoir 108. The releasing valve 302
permits accurate diagnosis of the simulator shut-off valve 158 as
to whether it is kept in its open state due to sticking of the
valve member.
[0249] In the third embodiment of FIG. 15, the simulator shut-off
valve 158 is diagnosed as to whether it is placed in the closed
state, as in the first embodiment. However, the diagnosis in the
present embodiment is effected while the shut-off valve 302 is held
in the open state. The amounts of change of the brake operating
stroke and the master cylinder pressure are detected when the
simulator shut-off valve 158 is commanded to be closed. If the
simulator shut-off valve 158 is kept in the open state, the
pressurized fluid is discharged from the pressurizing chamber 86
into the master reservoir 108 through the connecting passage 300
when the brake pedal 10 is operated. Accordingly, the brake
operating stroke is rapidly increased, and the amount of change of
the master cylinder pressure is comparatively small with respect to
the amount of change of the brake operating stroke. Thus, the
simulator shut-off valve 158 can be diagnosed with high accuracy
while the shut-off valve 302 is placed in the open state.
[0250] In the illustrated embodiments described above, the second
hydraulic pressure source 14 includes the hydraulic booster 78.
However, the second hydraulic pressure source 14 may include a
pressure-increasing device adapted to permit the pressure source 14
to generate a fluid pressure higher than a value corresponding to
the brake operating force. Further, the second hydraulic pressure
source 14 may not include the hydraulic booster 78 and a
pressure-increasing device as indicated above. An example of a
braking system incorporating this modification is shown in FIG. 16.
Namely, the braking system according to the fourth embodiment of
FIG. 16 include a second hydraulic pressure source 320, which
includes a master cylinder 322 but does not include a hydraulic
booster or a pressure-increasing device. In this braking system,
too, it is effective to diagnose the stroke simulator 159 and the
various sensors. Further, the second hydraulic pressure source may
include a vacuum booster. It is also noted that the stroke
simulator may be provided in a fluid passage connected to the fluid
passage 160 for the rear wheel brake cylinders 28, rather than the
fluid passage 150 for the front wheel brake cylinders 20.
Alternatively, the stroke simulator may be connected directly to
the pressurizing chamber 86 of the master cylinder 80. The
hydraulic pressure sensor 140 may be replaced by a pressure
switch.
[0251] While the stroke simulator 200 is provided as part of the
operating rod 94 in the illustrated embodiments, this stroke
simulator 200 is not essential, provided the stroke simulator 156
is provided.
[0252] Although the four linear valve devices 30 are provided for
the respective four wheel brake cylinders 20, 28, the use of the
four linear valve devices 30 is not essential. For instance, one
linear valve device 30 may be provided for all of the four wheel
brake cylinders, or each of the two pairs of the wheel brake
cylinders 20, 28. Further, the pressure-increasing and
pressure-reducing linear valves 172, 176 may be replaced by simple
solenoid-operated shut-off valves. It is also noted that the linear
valve devices 30 are not essential. In the absence of the linear
valve devices 30, the wheel brake cylinder pressure can be
controlled by controlling the pump device 12. The master-cylinder
shut-off valves 152, 162 and other shut-off valves may be replaced
by flow control valves capable of controlling a rate of fluid flow
therethrough with a variable cross sectional area of fluid
communication according to an electric current applied thereto.
[0253] It is to be understood that the present invention may be
embodied with various other changes, modifications and
improvements, such as those described in the SUMMARY OF THE
INVENTION, which may occur to those skilled in the art, without
departing from the spirit and scope of the invention defined in the
following claims:
* * * * *