U.S. patent application number 09/171589 was filed with the patent office on 2001-05-24 for braking force controlling apparatus.
This patent application is currently assigned to KENYON & KENYON. Invention is credited to SHIMIZU, SATOSHI, YOSHIDA, HIROAKI.
Application Number | 20010001527 09/171589 |
Document ID | / |
Family ID | 14478029 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001527 |
Kind Code |
A1 |
YOSHIDA, HIROAKI ; et
al. |
May 24, 2001 |
BRAKING FORCE CONTROLLING APPARATUS
Abstract
A braking force controlling apparatus changes a magnitude of a
braking force produced by a braking operation based on a speed of
the braking operation. The braking force controlling apparatus is
directed to maintaining a brake-assisting control even when a
beginner unintentionally releases a braking operation force on a
brake pedal. A hydraulic pressure sensor (40) detects a master
cylinder pressure, and a maximum master cylinder pressure during
the braking operation of the brake pedal (30) is stored in an ECU
(10). When the master cylinder pressure is found to be below a
release-judgment level of the master cylinder pressure, which is
determined based on the maximum master cylinder pressure, the
brake-assisting control is terminated. When the master cylinder
pressure is found to be above the release-judgment level, the
brake-assisting control is maintained.
Inventors: |
YOSHIDA, HIROAKI;
(MISHIMA-SHI, JP) ; SHIMIZU, SATOSHI; (SUSONO-SHI,
JP) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
|
Assignee: |
KENYON & KENYON
|
Family ID: |
14478029 |
Appl. No.: |
09/171589 |
Filed: |
October 21, 1998 |
PCT Filed: |
April 24, 1997 |
PCT NO: |
PCT/JP97/01435 |
Current U.S.
Class: |
303/115.4 |
Current CPC
Class: |
B60T 7/12 20130101; B60T
8/4836 20130101; B60T 8/4854 20130101; B60T 8/3275 20130101; B60T
13/686 20130101; B60T 7/042 20130101 |
Class at
Publication: |
303/115.4 |
International
Class: |
B60T 008/42 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 1996 |
JP |
8-108180 |
Claims
1. A braking force controlling apparatus which selectively performs
one of a normal control to generate a braking force by a braking
operation and a brake-assisting control to generate an increased
braking force larger than the braking force generated during the
normal control, said apparatus comprising: an operation quantity
detection means (10, 40) for detecting a quantity of a braking
operation of a brake pedal; a maximum operation quantity storage
means (10, 112, 114) for storing a maximum quantity of the braking
operation during the braking operation of the brake pedal; and a
brake-assisting control termination judgment means (10, 122, 124)
for determining whether the brake-assisting control should be
terminated based on the braking operation quantity detected by the
operation quantity detection means and the maximum quantity stored
by the maximum operation quantity storage means.
2. The apparatus according to claim 1, characterized in that the
brake-assisting control termination judgment means (10, 122, 124)
terminates the brake-assisting control when the braking operation
quantity is smaller than a difference between the maximum quantity
and a decrease quantity.
3. The apparatus according to claim 1, characterized in that the
brake-assisting control termination judgment means (10, 122, 124)
terminates the brake-assisting control when the braking operation
quantity is smaller than a product of the maximum quantity and a
decrease ratio.
4. The apparatus according to claim 1, characterized in that the
brake-assisting control termination judgment means (10, 122, 124)
determines whether a brake releasing operation during the
brake-assisting control is an intentional operation based on the
braking operation quantity detected by the operation quantity
detection means and the maximum quantity stored by the maximum
operation quantity storage means, wherein, when the brake releasing
operation is determined as being not an intentional operation, the
brake-assisting control termination judgment means maintains the
brake-assisting control.
5. The apparatus according to claim 1, characterized in that the
apparatus further comprises a judgment means (10, 102) for
determining whether the brake-assisting control is currently being
performed, wherein, when the judgment means determines that the
brake-assisting control is currently being performed, the
brake-assisting control termination judgment means (122) determines
whether the brake-assisting control should be terminated.
6. The apparatus according to claim 2, characterized in that the
apparatus further comprises a maximum quantity judgment means (116,
118, 120) for determining whether the maximum quantity of the
braking operation is smaller than a predetermined quantity,
wherein, when the maximum quantity is determined as being smaller
than the predetermined quantity, the maximum quantity judgment
means sets the decrease quantity at a relatively large value, and,
when the maximum quantity is determined as being not smaller than
the predetermined quantity, the maximum quantity judgment means
sets the decrease quantity at a relatively small value.
7. The apparatus according to claim 3, characterized in that the
apparatus further comprises a maximum quantity judgment means (116,
218, 220) for determining whether the maximum quantity of the
braking operation is smaller than a predetermined quantity,
wherein, when the maximum quantity is determined as being smaller
than the predetermined quantity, the maximum quantity judgment
means sets the decrease ratio at a relatively large value, and,
when the maximum quantity is determined as being not smaller than
the predetermined quantity, the maximum quantity judgment means
sets the decrease ratio at a relatively small value.
8. The apparatus according to claim 1, characterized in that the
operation quantity detection means (10, 40) detects the quantity of
the braking operation of the brake pedal based on a master cylinder
pressure supplied by a master cylinder, and the maximum operation
quantity storage means (10, 112, 114) stores the maximum quantity
of the braking operation based on a maximum master cylinder
pressure supplied by the master cylinder.
9. The apparatus according to claim 1, characterized in that the
apparatus further comprises a judgment means (104, 106) for
determining whether the braking operation quantity detected by the
operation quantity detection means is smaller than a predetermined
first quantity, and for determining whether the braking operation
quantity is larger than a predetermined second quantity, wherein,
when the braking operation quantity is determined as being smaller
than the predetermined first quantity or determined as being larger
than the predetermined second quantity, the brake-assisting control
is maintained.
10. A braking force controlling apparatus which selectively
performs one of a normal control to generate a braking force by a
braking operation and a brake-assisting control to generate an
increased braking force larger than the braking force generated
during the normal control, said apparatus comprising: an operation
quantity detection means (10, 40) for detecting a quantity of a
braking operation of a brake pedal; a maximum operation quantity
storage means (10, 112, 114) for storing a maximum quantity of the
braking operation during the braking operation of the brake pedal;
and a brake-assisting control continuation judgment means (10, 122,
124) for determining whether a brake releasing operation during the
brake-assisting control is an intentional operation based on the
braking operation quantity detected by the operation quantity
detection means and the maximum quantity stored by the maximum
operation quantity storage means, wherein, when the brake releasing
operation is determined as being not an intentional operation, the
brake-assisting control continuation judgment means maintains the
brake-assisting control.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to a braking force
controlling apparatus, and more particularly to a braking force
controlling apparatus which changes a magnitude of a braking force
produced in response to a braking operation based on a speed of the
braking operation.
DESCRIPTION OF THE RELATED ART
[0002] As disclosed in Japanese Laid-Open Patent Application No.
4-121260, there is known a braking force controlling apparatus
which generates an increased braking force larger than a braking
force during a normal control, when it is detected that an
emergency braking operation is performed on an automotive vehicle.
The conventional apparatus of the above publication is provided
with a brake booster which generates a boosted pressure in response
to a braking operation force Fp on a brake pedal of the vehicle, or
the boosted pressure being equal to the braking operation force Fp
multiplied by a given magnification factor. The boosted pressure is
delivered from the brake booster to a master cylinder. The master
cylinder generates a master cylinder pressure Pmc in response to
the boosted pressure delivered from the brake booster, and the
master cylinder pressure Pmc is proportional to the braking
operation force Fp.
[0003] Further, the conventional apparatus of the above publication
is provided with a high-pressure source having a pump which
generates a brake-assisting pressure. The high-pressure source
generates a brake-assisting pressure in accordance with a drive
signal supplied by a control circuit. When a speed of the braking
operation of the brake pedal exceeds a reference speed, it is
determined that an emergency braking operation is performed by a
vehicle operator, and the control circuit supplies a drive signal
to the high-pressure source, the drive signal requesting a maximum
brake-assisting pressure to be generated by the high-pressure
source. Both the brake-assisting pressure generated by the
high-pressure source and the master cylinder pressure Pmc generated
by the master cylinder are supplied to a switching valve, and the
switching valve delivers a larger one of the brake-assisting
pressure and the master cylinder Pmc to wheel cylinders of the
vehicle.
[0004] In the conventional apparatus of the above publication, when
the speed of the braking operation is below the reference speed,
the master cylinder pressure Pmc, which is proportional to the
braking operation force Fp, is supplied to the wheel cylinders.
Hereinafter, the control that is performed to generate the braking
force by the braking operation under such a condition will be
called a normal control. On the other hand, when the speed of the
braking operation is above the reference speed, the brake-assisting
pressure, which is generated by the high-pressure source, is
supplied to the wheel cylinders. Hereinafter, the control that is
performed to generate an increased braking force larger than the
braking force generated during the normal control, under such a
condition, will be called a brake-assisting control.
[0005] In the conventional apparatus of the above publication, when
the braking operation of the brake pedal is performed at a normal
speed, the braking force is controlled to the magnitude that is
proportional to the braking operation force Fp, and, when the
emergency braking operation of the brake pedal is performed, the
braking force is quickly increased to be larger than the braking
force during the normal control.
[0006] When a condition that requires the emergency braking
operation is avoided, it is necessary to terminate the
brake-assisting control and restart the normal control. The vehicle
operator releases the braking operation force on the brake pedal
after the condition requiring the emergency braking is avoided. If
such a decrease of the braking operation force on the brake pedal
is detected, it is possible to determine the time of termination of
the brake-assisting control based on the detected braking operation
force decrease.
[0007] However, according to experiments performed by the inventors
of the present invention, it is concluded that beginners who are
less experienced in vehicle operation tend to unintentionally
release the brake pedal during the emergency braking operation. In
the conventional apparatus of the above publication, when the
decrease of the braking operation force on the brake pedal is
detected, the brake-assisting control is automatically terminated
even if a beginner unintentionally releases the brake pedal.
[0008] Therefore, when the beginner unintentionally releases the
braking operation force on the brake pedal during the emergency
braking operation, the conventional apparatus of the above
publication automatically terminates the brake-assisting control
and restarts the normal control based on the detected braking
operation force change. However, the condition requiring the
emergency braking still exists when the brake-assisting control is
terminated. In such a case, the termination of the
braking-assisting control is too early to ensure a vehicle running
stability. Hence, the capability of the conventional apparatus of
the above publication is inadequate to effectively achieve the
function of the brake-assisting control.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide an improved
braking force controlling apparatus in which the above-described
problems are eliminated.
[0010] Another, more specific object of the present invention is to
provide a braking force controlling apparatus which safely
maintains the brake-assisting control even if a beginner
unintentionally releases the braking operation force on the brake
pedal during the emergency braking operation.
[0011] The above-mentioned objects of the present invention are
achieved by a braking force controlling apparatus which selectively
performs one of a normal control to generate a braking force by a
braking operation and a brake-assisting control to generate an
increased braking force larger than the braking force generated
during the normal control, the apparatus comprising: an operation
quantity detection means which detects a quantity of a braking
operation of a brake pedal; a maximum operation quantity storage
means which stores a maximum quantity of the braking operation
during the braking operation of the brake pedal; and a
brake-assisting control termination judgment means which determines
whether the brake-assisting control should be terminated based on
the braking operation quantity detected by the operation quantity
detection means and the maximum quantity stored by the maximum
operation quantity storage means.
[0012] In the braking force controlling apparatus of the present
invention, the time of termination of the brake-assisting control
is determined based on the braking operation quantity detected by
the operation quantity detection means and the maximum quantity
stored by the maximum operation quantity storage means.
[0013] When the emergency braking is required, an experienced
vehicle operator intentionally maintains the braking operation
force on the brake pedal. After the condition requiring the
emergency braking is avoided, the vehicle operator intentionally
releases the braking operation force on the brake pedal. However,
the beginner tends to unintentionally release the brake pedal
during the emergency braking operation, which causes a decrease of
the braking operation force on the brake pedal.
[0014] Generally, a decrease of the quantity of the braking
operation of the brake pedal by an unintentional operation of the
beginner is smaller than a decrease of the quantity of the braking
operation by an intentional operation of the experienced vehicle
operator. It is possible to determine whether the braking operation
of the brake pedal is performed intentionally or not, by correctly
detecting the decrease of the quantity of the braking
operation.
[0015] Accordingly, it is possible for the braking force
controlling apparatus of the present invention to maintain the
brake-assisting control when the decrease of the quantity of the
braking operation is determined as being not caused by the
intentional operation, and to terminate the brake-assisting control
when the decrease of the quantity of the braking operation is
determined as being caused by the intentional operation.
[0016] In addition, the quantity of the braking operation of the
brake pedal during the emergency braking operation may differ
according to the individual vehicle operators. In the braking force
controlling apparatus of the present invention, a maximum quantity
of the braking operation during the braking operation is stored by
the maximum operation quantity storage means. The determination as
to whether the brake-assisting control should be terminated is made
based on the maximum quantity stored by the maximum operation
quantity storage means and the braking operation quantity detected
by the operation quantity detection means. It is possible to
determine the time of the termination of the brake-assisting
control with accuracy by eliminating the differences of the braking
operation quantity according to the individual vehicle
operators.
[0017] In a preferred embodiment of the present invention, the
braking force controlling apparatus may be constructed such that
the brake-assisting control termination judgment means terminates
the brake-assisting control when the braking operation quantity is
smaller than a difference between the maximum quantity and a
predetermined decrease quantity. Further, in another preferred
embodiment of the present invention, the braking force controlling
apparatus may be constructed such that the brake-assisting control
termination judgment means terminates the brake-assisting control
when the braking operation quantity is smaller than a product of
the maximum quantity and a decrease ratio.
[0018] In these embodiments of the present invention, it is
possible to determine the time of the termination of the
brake-assisting control with an increased accuracy by setting the
decrease quantity or the decrease ratio at an appropriate
value.
[0019] In a preferred embodiment of the present invention, the
braking force controlling apparatus may be constructed such that
the brake-assisting control termination judgment means determines
whether a brake releasing operation during the brake-assisting
control is an intentional operation based on the braking operation
quantity detected by the operation quantity detection means and the
maximum quantity stored by the maximum operation quantity storage
means, wherein, when the brake releasing operation is determined as
being not an intentional operation, the brake-assisting control
termination judgment means maintains the brake-assisting
control.
[0020] The above-mentioned objects of the present invention are
achieved by a braking force controlling apparatus which selectively
performs one of a normal control to generate a braking force by a
braking operation and a brake-assisting control to generate an
increased braking force larger than the braking force generated
during the normal control, the apparatus comprising: an operation
quantity detection means which detects a quantity of a braking
operation of a brake pedal; a maximum operation quantity storage
means which stores a maximum quantity of the braking operation
during the braking operation of the brake pedal; and a
brake-assisting control continuation judgment means which
determines whether a brake releasing operation during the
brake-assisting control is an intentional operation based on the
braking operation quantity detected by the operation quantity
detection means and the maximum quantity stored by the maximum
operation quantity storage means, wherein, when the brake releasing
operation is determined as being not an intentional operation, the
brake-assisting control continuation judgment means maintains the
brake-assisting control.
[0021] In the braking force controlling apparatus of the present
invention, the brake-assisting control continuation judgment means
determines whether a brake releasing operation during the
brake-assisting control is an intentional operation. When the brake
releasing operation is determined as being not an intentional
operation, the brake-assisting control continuation judgment means
maintains the brake-assisting control. Hence, when the emergency
braking is required, it is possible for the braking force
controlling apparatus of the present invention to quickly increase
the braking force to be larger than the level during the normal
control by maintaining the brake-assisting control.
[0022] In the braking force controlling apparatus of the present
invention, the brake-assisting control continuation judgment means
makes the determination as to whether the brake releasing operation
during the brake-assisting control is an intentional operation,
based on the braking operation quantity detected by the operation
quantity detection means and the maximum quantity stored by the
maximum operation quantity storage means. When the brake releasing
operation is determined as being an intentional operation, the
brake-assisting control continuation judgment means terminates the
brake-assisting control. However, when the brake releasing
operation is determined as being not an intentional operation, the
brake-assisting control continuation judgment means maintains the
brake-assisting control. Hence, the braking force controlling
apparatus of the present invention is effective in maintaining the
brake-assisting control even if a beginner unintentionally releases
the braking operation force on the brake pedal during the emergency
braking operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Other objects, features and advantages of the present
invention will be more apparent from the following detailed
description when read in conjunction with the accompanying drawings
in which:
[0024] FIG. 1 is a diagram of a first embodiment of a braking force
controlling apparatus of the present invention;
[0025] FIG. 2 is a diagram for explaining changes of a braking
operation force on a brake pedal with respect to the elapsed time
in various situations;
[0026] FIG. 3 is a diagram for explaining changes of a master
cylinder pressure with respect to the elapsed time when an
emergency braking operation is performed by various vehicle
operators;
[0027] FIG. 4 is a flowchart for explaining a braking force control
procedure performed by the braking force controlling apparatus of
FIG. 1;
[0028] FIG. 5 is a flowchart for explaining another braking force
control procedure performed by the braking force controlling
apparatus of FIG. 1; and
[0029] FIG. 6 is a diagram of a second embodiment of the braking
force controlling apparatus of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] A description will now be given of the preferred embodiments
of the present invention with reference to the accompanying
drawings.
[0031] FIG. 1 shows a first embodiment of the braking force
controlling apparatus of the present invention. The braking force
controlling apparatus of FIG. 1 is incorporated in an automotive
vehicle, and controlled by an electronic control unit 10
(hereinafter, called ECU 10).
[0032] In FIG. 1, input signal paths on which signals supplied by
certain elements of the braking force controlling apparatus are
sent to the ECU 10, and output signal paths on which signals
supplied by the ECU 10 are sent to certain elements of the braking
force controlling apparatus are indicated by the dotted-line arrows
in FIG. 1. Further, brake fluid paths on which brake fluid is
supplied between the elements of the braking force controlling
apparatus are indicated by the solid lines or the one-dot chain
lines in FIG. 1.
[0033] The braking force controlling apparatus includes a pump 12.
The pump 12 is provided with an actuating motor 14. The actuating
motor 14 actuates the pump 12 so that the pump 12 supplies a
high-pressure brake fluid. The pump 12 has an inlet port 12a which
is connected to a reservoir tank 16. The pump 12 has an outlet port
12b which is connected to an accumulator 20 via a check valve 18.
The pump 12 produces a high-pressure brake fluid from the brake
fluid received from the reservoir tank 16, and supplies the
high-pressure brake fluid from the outlet port 12b to the
accumulator 20 so that the accumulator 20 stores the high-pressure
brake fluid supplied by the pump 12. The check valve 18 allows only
a flow of the high-pressure brake fluid from the pump 12 to the
accumulator 20, and inhibits a counter flow of the brake fluid from
the accumulator 20 to the pump 12.
[0034] The accumulator 20 is connected through a high-pressure line
22 to a high-pressure port 24a of a regulator 24. The accumulator
20 is further connected through the high-pressure line 22 to a
regulator switching solenoid 26 (hereinafter, called STR 26). The
regulator 24 has a low-pressure port 24b which is connected through
a low-pressure line 28 to the reservoir tank 16. The regulator 24
has a controlled-pressure port 24c which is connected through a
controlled-pressure line 29 to the STR 26. The STR 26 is a
two-position solenoid valve which selectively opens one of the
high-pressure line 22 and the controlled-pressure line 29 and
closes the other. The STR 26 is normally set in a first position so
that the STR 26 opens the controlled-pressure line 29 and closes
the high-pressure line 22. When a drive signal is supplied to the
STR 26 by the ECU 10, the STR 26 is set in a second position so
that the STR 26 closes the controlled-pressure line 29 and opens
the high-pressure line 22. A brake pedal 30 is connected to the
regulator 24, and a master cylinder 32 is fixed to the regulator
24. The regulator 24 contains a pressure chamber therein, and the
controlled-pressure port 24c is open to the pressure chamber of the
regulator 24. In the regulator 24, one of the high-pressure port
24a and the low-pressure port 24b is selectively connected to the
pressure chamber in response to a condition (a speed or a quantity)
of the braking operation of the brake pedal 30.
[0035] The regulator 24 is arranged such that the internal pressure
of the pressure chamber is adjusted to a brake fluid pressure
proportional to the braking operation force Fp on the brake pedal
30. Hence, the brake fluid pressure proportional to the braking
operation force Fp is present at the controlled-pressure port 24c
of the regulator 24. Hereinafter, this brake fluid pressure will be
called the regulator pressure Pre.
[0036] The braking operation force Fp exerted on the brake pedal 30
is mechanically transmitted to the master cylinder 32 via the
regulator 24. In addition, a force proportional to the regulator
pressure Pre at the controlled-pressure port 24c of the regulator
24 is transmitted to the master cylinder 32. Hereinafter, this
force will be called the brake-assisting force Fa. Hence, when the
brake pedal 30 is depressed, a resultant force of the braking
operation force Fp and the brake-assisting force Fa is transmitted
to the master cylinder 32.
[0037] The master cylinder 32 includes a first pressure chamber 32a
("No. 1") and a second pressure chamber 32b ("No. 2") provided
therein. In the master cylinder 32, a master cylinder pressure Pmc,
which is proportional to the resultant force of the braking
operation force Fp and the brake-assisting force Fa, is produced in
both the first pressure chamber 32a and the second pressure chamber
32b. A proportioning valve 38 (hereinafter, called the P valve 38)
is connected to both the first pressure chamber 32a and the second
pressure chamber 32b of the master cylinder 32. Hence, both the
master cylinder pressure Pmc produced in the first pressure chamber
32a and the master cylinder pressure Pmc produced in the second
pressure chamber 32b are supplied to the P valve 34.
[0038] A first pressure line 36 and a second pressure line 38 are
connected to the P valve 34. When the master cylinder pressure Pmc
is below a reference pressure, the P valve 34 supplies the master
cylinder pressure Pmc to both the first pressure line 36 and the
second pressure line 38. When the master cylinder pressure Pmc is
above the reference valve, the P valve 34 supplies the master
cylinder pressure Pmc to the first pressure line 36 and supplies a
reduced pressure to the second pressure line 38. The reduced
pressure, supplied to the second pressure line 38 in this case, is
equal to the master cylinder pressure Pmc multiplied by a given
reduction ratio.
[0039] A hydraulic pressure sensor 40 is connected to the brake
fluid path between the P valve 34 and the second pressure chamber
32b of the master cylinder 32. The hydraulic pressure sensor 40
outputs a signal, indicative of the master cylinder pressure Pmc,
to the ECU 10. The ECU 10 detects the master cylinder pressure Pmc,
produced in the master cylinder 32, based on the signal supplied by
the hydraulic pressure sensor 40.
[0040] A third pressure line 42 is connected to the STR 26. As
described above, the STR 26 selectively opens one of the
high-pressure line 22 and the controlled-pressure line 29 and
closes the other. The brake fluid pressure from one of the
high-pressure line 22 and the controlled-pressure line 29 is
supplied to the third pressure line 42 according to the position of
the STR 26. In the present embodiment, the brake fluid pressure
from one of the first pressure line 36 connected to the P valve 34
and the third pressure line 42 connected to the STR 26, is supplied
to both a wheel cylinder 44FR and a wheel cylinder 44FL, which are
respectively provided on a front-right wheel ("FR") and a
front-left wheel ("FL") of the vehicle. Further, in the present
embodiment, the brake fluid pressure from one of the second
pressure line 38 connected to the P valve 34 and the third pressure
line 42 connected to the STR 26, is supplied to both a wheel
cylinder 44RR and a wheel cylinder 44RL, which are respectively
provided on a rear-right wheel ("RR") and a rear-left wheel ("RL")
of the vehicle.
[0041] A first pressure-assisting solenoid 46 (hereinafter, called
SA-1 46) and a second pressure-assisting solenoid 48 (hereinafter,
called SA-2 48) are connected to the first pressure line 36. A
front-right pressure-holding solenoid 50 (hereinafter, called SFRH
50), a front-left pressure-holding solenoid 52 (hereinafter, called
SFLH 52), and a third pressure-assisting solenoid 54 (hereinafter,
called SA-3 54) are connected to the third pressure line 42.
[0042] The SFRH 50 is a two-position solenoid valve which is
normally set in a valve-open position. The SFRH 50 is connected
through a pressure adjustment line 56 to both the SA-1 46 and a
front-right pressure-reducing solenoid 58 (hereinafter, called SFRR
58). A check valve 60 is provided in a bypass line between the
third pressure line 42 and the pressure adjustment line 56. The
check valve 60 allows only a flow of the brake fluid from the
pressure adjustment line 56 to the third pressure line 42, and
inhibits a counter flow of the brake fluid from the third pressure
line 42 to the pressure adjustment line 56.
[0043] The SA-1 46 is a two-position solenoid valve which
selectively connects one of the first pressure line 36 and the
pressure adjustment line 56 to the wheel cylinder 44FR. The SA-1 46
is normally set in a first position so that the SA-1 46 connects
the first pressure line 36 to the wheel cylinder 44FR. When a drive
signal is supplied to the SA-1 46 by the ECU 10, the SA-1 46 is set
in a second position so that the SA-1 46 connects the pressure
adjustment line 56 to the wheel cylinder 44FR. The SFRR 58 is a
two-position solenoid valve which disconnects the pressure
adjustment line 56 from or connects the pressure adjustment line 56
to the reservoir tank 16. The SFRR 58 is normally set in a
valve-closed position so that the SFRR 58 disconnects the pressure
adjustment line 56 from the reservoir tank 16. When a drive signal
is supplied to the SFRR 58 by the ECU 10, the SFRR 58 is set in a
valve-open position so that the SFRR 58 connects the pressure
adjustment line 56 to the reservoir tank 16.
[0044] The SFLH 52 is a two-position solenoid valve which is
normally set in a valve-open position. The SFLH 52 is connected
through a pressure adjustment line 62 to both the SA-2 48 and a
front-left pressure-reducing solenoid 64 (hereinafter, called SFLR
64). A check valve 66 is provided in a bypass line between the
third pressure line 42 and the pressure adjustment line 62. The
check valve 66 allows only a flow of the brake fluid from the
pressure adjustment line 62 to the third pressure line 42, and
inhibits a counter flow of the brake fluid from the third pressure
line 42 to the pressure adjustment line 62.
[0045] The SA-2 48 is a two-position solenoid valve which
selectively connects one of the first pressure line 36 and the
pressure adjustment line 62 to the wheel cylinder 44FL. The SA-2 48
is normally set in a first position so that the SA-2 48 connects
the first pressure line 36 to the wheel cylinder 44FL. When a drive
signal is supplied to the SA-2 48 by the ECU 10, the SA-2 48 is set
in a second position so that the SA-2 48 connects the pressure
adjustment line 62 to the wheel cylinder 44FL. The SFLR 64 is a
two-position solenoid valve which disconnects the pressure
adjustment line 62 from or connects the pressure adjustment line 62
to the reservoir tank 16. The SFLR 64 is normally set in a
valve-closed position so that the SFLR 64 disconnects the pressure
adjustment line 62 from the reservoir tank 16. When a drive signal
is supplied to the SFLR 64 by the ECU 10, the SFLR 64 is set in a
valve-open position so that the SFLR 64 connects the pressure
adjustment line 62 to the reservoir tank 16.
[0046] The second pressure line 38 at the output of the P valve 34
is connected to the SA-3 54. A rear-right pressure-holding solenoid
68 (hereinafter, called SRRH 68) and a rear-left pressure-holding
solenoid 70 (hereinafter, called SRLH 70) are connected to the
downstream side of the SA-3 54. The SRRH 68 and the SRLH 70 are
respectively provided for the wheel cylinder 44RR and the wheel
cylinder 44RL.
[0047] The SA-3 54 is a two-position solenoid valve which
selectively connects one of the second pressure line 38 and the
third pressure line 42 to the SRRH 68 and the SRLH 70. The SA-3 54
is normally set in a first position so that the SA-3 54 connects
the second pressure line 38 to the SRRH 68 and the SRLH 70. When a
drive signal is supplied to the SA-3 54 by the ECU 10, the SA-3 54
is set in a second position so that the SA-3 54 connects the third
pressure line 42 to the SRRH 68 and the SRLH 70.
[0048] The SRRH 68 is a two-position solenoid valve which is
normally set in a valve-open position. The downstream side of the
SRRH 68 is connected through a pressure adjustment line 72 to both
the wheel cylinder 44RR and a rear-right pressure-reducing solenoid
74 (hereinafter, called SRRR 74). The SRRR 74 is a two-position
solenoid valve which disconnects the pressure adjustment line 72
from or connects the pressure adjustment line 72 to the reservoir
tank 16. The SRRR 74 is normally set in a valve-closed position so
that the SRRR 74 disconnects the pressure adjustment line 72 from
the reservoir tank 16. When a drive signal is supplied to the SRRR
74 by the ECU 10, the SRRR 74 is set in a valve-open position so
that the SRRR 74 connects the pressure adjustment line 72 to the
reservoir tank 16. A check valve 76 is provided in a bypass line
between the SA-3 54 and the pressure adjustment line 72. The check
valve 76 allows only a flow of the brake fluid from the pressure
adjustment line 72 to the SA-3 54, and inhibits a counter flow of
the brake fluid from the SA-3 54 to the pressure adjustment line
72.
[0049] The SRLH 70 is a two-position solenoid valve which is
normally set in a valve-open position. The downstream side of the
SRLH 70 is connected through a pressure adjustment line 78 to both
the wheel cylinder 44RL and a rear-left pressure-reducing solenoid
80 (hereinafter, called SRLR 80). The SRLR 80 is a two-position
solenoid valve which disconnects the pressure adjustment line 78
from or connects the pressure adjustment line 78 to the reservoir
tank 16. The SRLR 80 is normally set in a valve-closed position so
that the SRLR 80 disconnects the pressure adjustment line 78 from
the reservoir tank 16. When a drive signal is supplied to the SRLR
80 by the ECU 10, the SRLR 80 is set in a valve-open position so
that the SRLR 80 connects the pressure adjustment line 78 to the
reservoir tank 16. A check valve 82 is provided in a bypass line
between the SA-3 54 and the pressure adjustment line 78. The check
valve 82 allows only a flow of the brake fluid from the pressure
adjustment line 78 to the SA-3 54, and inhibits a counter flow of
the brake fluid from the SA-3 54 to the pressure adjustment line
78.
[0050] In the braking force controlling apparatus of FIG. 1, a
brake switch 84 is provided in the vicinity of the brake pedal 30.
When the brake pedal 30 is depressed by the vehicle operator, the
brake switch 84 outputs an ON signal to the ECU 10. The ECU 10
determines whether the braking operation is performed by the
vehicle operator, based on the signal supplied by the brake switch
84.
[0051] In the braking force controlling apparatus of FIG. 1, a
wheel speed sensor 86FR, a wheel speed sensor 86FL, a wheel speed
sensor 86RR and a wheel speed sensor 86RL are provided in the
vicinity of the front-right wheel FR, the front-left wheel FL, the
rear-right wheel RR and the rear-left wheel RL of the vehicle,
respectively. Hereinafter, these wheel speed sensors will be
collectively referred to as the wheel speed sensors 86. Each of the
wheel speed sensors 86 outputs a signal, indicative of the wheel
speed of the related one of the wheels FR, FL, RR and RL, to the
ECU 10. The ECU 10 detects the respective wheel speeds of the
wheels FR, FL, RR and RL, based on the signals supplied by the
wheel speed sensors 86.
[0052] In the braking force controlling apparatus of FIG. 1, the
ECU 10 supplies the respective drive signals to the STR 26, the
SA-1 46, the SA-2 48, the SA-3 54, the SFRH 50, the SFLH 52, the
SFRR 58, the SFLR 64, the SRRH 68, the SRLH 70, the SRRR 74 and the
SRLR 80 in a controlled manner based on the signals supplied by the
hydraulic pressure sensor 40, the brake switch 84 and the wheel
speed sensors 86.
[0053] Next, a description will be given of the operation of the
braking force controlling apparatus of the present embodiment. When
the operating condition of the vehicle is found stable, the normal
control is performed by the braking force controlling apparatus of
the present embodiment to generate a braking force in accordance
with the braking operation force Fp on the brake pedal 30.
[0054] In order to perform the normal control by the braking force
controlling apparatus, the ECU 10 supplies no drive signals to the
STR 26, the SA-1 46, the SA-2 48, the SA-3 54, the SFRH 50, the
SFLH 52, the SFRR 58, the SFLR 64, the SRRH 68, the SRLH 70, the
SRRR 74 and the SRLR 80 so that the above solenoids are set in the
positions as shown in FIG. 1.
[0055] More specifically, when the above solenoids of the braking
force controlling apparatus are in the positions shown in FIG. 1,
the wheel cylinders 44FR and 44FL are connected to the first
pressure line 36, and the wheel cylinders 44RR and 44RL are
connected to the second pressure line 38. In this condition, the
master cylinder pressure Pmc from the master cylinder 32 is
supplied to and received by the wheel cylinders 44FR, 44FL, 44RL
and 44RR (hereinafter, these wheel cylinders will be collectively
called the wheel cylinders 44). Hence, in each of the respective
wheels FR, FL, RR and RL of the vehicle, the braking force in
accordance with the braking operation force Fp is generated.
[0056] In the braking force controlling apparatus of the present
embodiment, when it is found that any of the wheels of the vehicle
will be locked, it is determined that anti-lock braking system
(ABS) control execution conditions are satisfied. After this
determination is made, the execution of the ABS control of the
braking force controlling apparatus is started.
[0057] The ECU 10 calculates respective wheel speeds Vwfr, Vwfl,
Vwrr and Vwrl (hereinafter, these wheel speeds will be collectively
called the wheel speeds Vw) of the vehicle wheels based on the
signals supplied by the wheel speed sensors 86. By using a known
vehicle speed estimation method, the ECU 10 determines an estimated
vehicle speed Vso from the calculated wheel speeds Vw. If the
braking force is exerted on the vehicle by the braking operation,
the ECU 10 calculates a slip ratio S of each of the vehicle wheels
from the related wheel speed Vw and the estimated vehicle speed Vso
in accordance with the following formula:
S=(Vso-Vw).multidot.100/Vso (1)
[0058] Then, the ECU 10 determines whether the ABS control
execution conditions are satisfied based on the slip ratio S of
each of the vehicle wheels. When the slip ratio S is found to be
above a reference value, it is determined that the ABS control
execution conditions are satisfied. When this determination is
made, the ECU 10 supplies the drive signals to the SA-1 46, the
SA-2 48 and the SA-3 54. When the drive signal is supplied to the
SA1 46, the SA-1 46 is set in the second position so that the SA-1
46 connects the pressure adjustment line 56 to the wheel cylinder
44FR. The SA-1 46 closes off or disconnects the first pressure line
36 from the wheel cylinder 44FR. When the drive signal is supplied
to the SA-2 48, the SA-2 48 is set in the second position so that
the SA-2 48 connects the pressure adjustment line 62 to the wheel
cylinder 44FL. The SA-2 48 closes off or disconnects the first
pressure line 36 from the wheel cylinder 44FL. When the drive
signal is supplied to the SA-3 54, the SA-3 54 is set in the second
position so that the SA-3 54 connects the third pressure line 42 to
the SRRH 68 and the SRLH 70. The SA-3 54 closes off or disconnects
the second pressure line 38 from the SRRH 68 and the SRLH 70.
[0059] When the solenoids 46, 48 and 54 are set in the second
positions as described above, the SFRH 50, the SFLH 52, the SRRH 68
and the SRLH 70 (these solenoids will be called the
pressure-holding solenoids SH), as well as the SFRR 58, the SFLR
64, the SRRR 74 and the SRLR 80 (these solenoids will be called the
pressure-reducing solenoids SR) are connected to the respective
wheels cylinders 44, and the regulator pressure Pre from the
regulator 24 is supplied to the upstream sides of the
pressure-holding solenoids SH through the third pressure line 42
and the STR 26.
[0060] During the ABS control of the braking force controlling
apparatus of the present embodiment wherein the solenoids 46, 48
and 54 are set in the second positions as described above, the
pressure-holding solenoids SH and the pressure-reducing solenoids
SR may be controlled by the ECU 10 such that the pressure-holding
solenoids SH are set in the valve-open positions and the
pressure-reducing solenoids SR are set in the valve-closed
positions. When the ECU 10 performs this control procedure in the
braking force controlling apparatus, a wheel cylinder pressure Pwc
of the related one of the wheel cylinders 44 is increased up to the
regulator pressure Pre. This control procedure will be called (1) a
pressure-increasing control mode.
[0061] Alternatively, during the ABS control of the braking force
controlling apparatus of the present embodiment wherein the
solenoids 46, 48 and 54 are set in the second positions as
described above, the pressure-holding solenoids SH and the
pressure-reducing solenoids SR may be controlled by the ECU 10 such
that the pressure-holding solenoids SH are set in the valve-closed
positions and the pressure-reducing solenoids SR are set in the
valve-closed positions. When the ECU 10 performs this control
procedure in the braking force controlling apparatus, the wheel
cylinder pressure Pwc of the related one of the wheel cylinders 44
is held at the same level without increase or decrease.
Hereinafter, this control procedure will be called (2) a
pressure-holding control mode.
[0062] Alternatively, during the ABS control of the braking force
controlling apparatus of the present embodiment wherein the
solenoids 46, 48 and 54 are set in the second positions as
described above, the pressure-holding solenoids SH and the
pressure-reducing solenoids SR may be controlled by the ECU 10 such
that the pressure-holding solenoids SH are set in the valve-closed
positions and the pressure-reducing solenoids SR are set in the
valve-open positions. When the ECU 10 performs this control
procedure in the braking force controlling apparatus, the wheel
cylinder pressure Pwc of the related one of the wheel cylinders 44
is decreased. This control procedure will be called (3) a
pressure-decreasing control mode.
[0063] In the braking force controlling apparatus of the present
embodiment, the ECU 10 suitably performs one of (1) the
pressure-increasing control mode, (2) the pressure-holding control
mode and (3) the pressure-decreasing control mode so as to maintain
the slip ratio S of each of the vehicle wheels FR, FL, RR and RL
below the reference value, preventing all the vehicle wheels from
being locked during the braking operation.
[0064] It is necessary to quickly decrease the wheel cylinder
pressure Pwc of the related one of the wheel cylinders 44 after the
vehicle operator releases the braking operation force on the brake
pedal 30 during the ABS control. In the braking force controlling
apparatus of the present embodiment, the check valves 60, 66, 76
and 82 are provided in the brake fluid paths connected to the wheel
cylinders 44, so as to allow only the flow of the brake fluid from
the pressure adjustment lines 56, 62, 72 and 78 (connected to the
wheel cylinders 44) to the third pressure line 42. As the check
valves 60, 66, 76 and 82 function in this manner, it is possible
for the braking force controlling apparatus of the present
embodiment to quickly decrease the wheel cylinder pressure Pwc
after the vehicle operator releases the braking operation force on
the brake pedal 30 during the ABS control.
[0065] During the ABS control of the braking force controlling
apparatus of the present embodiment, the wheel cylinder pressure
Pwc of the related one of the wheel cylinders 44 is suitably
adjusted by supplying the regulator pressure Pre from the regulator
24 to the wheel cylinders 44. More specifically, when the brake
fluid from the pump 12 is delivered to the wheel cylinders 44, the
wheel cylinder pressure Pwc is increased, and, when the brake fluid
within the wheel cylinders 44 is returned to the reservoir tank 16,
the wheel cylinder pressure Pwc is decreased. If the increase of
the wheel cylinder pressure Pwc is performed by using the master
cylinder 32 as the only brake fluid pressure source, the brake
fluid contained in the master cylinder 32 is gradually decreased
through a repeated execution of the pressure-increasing control
mode and the pressure-decreasing control mode. In such a condition,
the master cylinder 32 may be malfunctioning due to a too small
amount of the brake fluid contained in the master cylinder 32.
[0066] In order to avoid the malfunction of the master cylinder 32
mentioned above, in the braking force controlling apparatus of the
present embodiment, the increase of the wheel cylinder pressure Pwc
is performed by selectively using one of the master cylinder 32 and
the pump 12 as the brake fluid pressure source. If the increase of
the wheel cylinder pressure Pwc is performed by using the pump 12
as the brake fluid pressure source, the present embodiment can
avoid the malfunction of the master cylinder 32. It is possible for
the braking force controlling apparatus of the present embodiment
to maintain a stable operating condition even when the ABS control
is continuously performed over an extended period of time.
[0067] As described above, the execution of the ABS control of the
braking force controlling apparatus of the present embodiment is
started when it is found that any of the wheels of the vehicle will
be locked. In other words, the prerequisite condition to start the
execution of the ABS control of the braking force controlling
apparatus of the present embodiment is that the vehicle operator
exerts an adequate braking operation force Fp on the brake pedal 30
so as to produce a large slip ratio S of any of the vehicle wheels
which can be detected by the braking force controlling
apparatus.
[0068] FIG. 2 shows changes of the braking operation force Fp on
the brake pedal 30 with respect to the elapsed time in various
situations. A change of the braking operation force Fp exerted on
the brake pedal 30 by an experienced vehicle operator who is
intended to perform an emergency braking operation, and a change of
the braking operation force Fp exerted on the brake pedal 30 by a
beginner who is intended to perform the emergency braking
operation, are indicated by the curve "A" and the curve "B" in FIG.
2, respectively. Generally, it is necessary that the braking
operation force Fp during the emergency braking operation is large
enough to start the execution of the ABS control of the braking
force controlling apparatus.
[0069] As indicated by the curve "A" of FIG. 2, in the case of the
experienced vehicle operator, when a condition requiring the
emergency braking has occurred, the braking operation force Fp on
the brake pedal 30 is quickly raised to an adequately large level,
and the braking operation force Fp is maintained at the adequately
large level over a certain period of time. In response to the
braking operation of the brake pedal 30, an adequately large master
cylinder pressure Pmc from the master cylinder 32 is supplied to
the wheel cylinders 44, and the ABS control of the braking force
controlling apparatus can be started.
[0070] However, as indicated by the curve "B" of FIG. 2, in the
case of the beginner, when the condition requiring the emergency
braking has occurred, the braking operation force Fp may not be
maintained at the adequately large level over a certain period of
time although the braking operation force Fp is initially raised to
the adequately large level. Hence, in response to the braking
operation of the brake pedal 30 by the beginner, an adequately
large master cylinder pressure Pmc from the master cylinder 32 may
not be supplied to the wheel cylinders 44, and the ABS control of
the braking force controlling apparatus cannot be started.
[0071] Generally, beginners who are less experienced in vehicle
operation tend to unintentionally release the brake pedal 30 during
the emergency braking operation. In the braking force controlling
apparatus of the present invention, a braking force control
procedure is performed by the ECU 10 when a brake releasing
operation of the brake pedal 30 is determined as being an
intentional operation, and this braking force control procedure
allows the adequately large master cylinder pressure Pmc of the
master cylinder 32 to be supplied to the wheel cylinders 44 even if
the braking operation force Fp is not raised to the adequately
large level as indicated by the curve "B" in FIG. 2. Hereinafter,
this braking force control procedure will be called a
brake-assisting control.
[0072] Before starting the brake-assisting control in the braking
force controlling apparatus of the present invention, it is
necessary to determine, with accuracy, whether a braking operation
of the brake pedal 30 is intended to perform the emergency braking
operation or not.
[0073] In FIG. 2, changes of the braking operation force Fp on the
brake pedal 30 (which is intended to perform a normal braking
operation) with respect to the elapsed time in various situations
are indicated by the curves "C" and "D". As indicated by the curves
"A" through "D", a rate of change of the braking operation force Fp
during the normal braking operation is smaller than a rate of
change of the braking operation force Fp during the emergency
braking operation. In addition, a convergence value of the braking
operation force Fp during the normal braking operation is smaller
than that of the braking operation force Fp during the emergency
braking operation.
[0074] The braking force controlling apparatus of the present
invention takes account of the differences between the braking
operation force Fp during the normal braking operation and the
braking operation force Fp during the emergency braking operation
as shown in FIG. 2. When a rate of change of the braking operation
force Fp during an initial period of the braking operation is above
a certain reference value and the braking operation force Fp is
raised to an adequately large level (which falls within a region
(I) above the borderline indicated by a dotted line in FIG. 2), the
ECU 10 of the braking force controlling apparatus of the present
invention determines that the braking operation of the brake pedal
30 is intended to perform the emergency braking operation.
[0075] On the other hand, when the rate of change of the braking
operation force Fp during the initial period of the braking
operation is not above the reference value, or when the braking
operation force Fp is not raised to the adequately large level
(which falls within a region (II) below the borderline indicated by
the dotted line in FIG. 2), the ECU 10 of the braking force
controlling apparatus of the present invention determines that the
braking operation of the brake pedal 30 is intended to perform the
normal braking operation.
[0076] In the braking force controlling apparatus of the present
invention, the ECU 10 makes a determination as to whether a speed
of the braking operation of the brake pedal 30 is above a reference
speed, and makes a determination as to whether a quantity of the
braking operation of the brake pedal 30 is above a reference
quantity. In accordance with the results of the determinations, the
ECU 10 can determine whether the braking operation of the brake
pedal 30 is intended to perform the emergency braking operation or
the normal braking operation.
[0077] In the braking force controlling apparatus of FIG. 1, the
speed and the quantity of the braking operation of the brake pedal
30 are detected by using the master cylinder pressure Pmc as the
parameter to define the braking operation speed or the braking
operation quantity. The master cylinder pressure Pmc is detected by
the ECU 10 based on the signal supplied by the hydraulic pressure
sensor 40. The master cylinder pressure Pmc varies in proportion
with the braking operation quantity, and a rate of change (dPmc) of
the master cylinder pressure Pmc is in correspondence with the
braking operation speed. Accordingly, before starting the
brake-assisting control, the braking force controlling apparatus of
the present embodiment can determine, with accuracy, whether the
braking operation of the brake pedal 30 is intended to perform the
emergency braking operation or not. Hereinafter, this function of
the braking force controlling apparatus of the present embodiment
will be called a brake-assisting control start judgment means. The
ECU 10 acts as the brake-assisting control start judgment
means.
[0078] Alternatively, in the braking force controlling apparatus of
the present invention, the brake-assisting control start judgment
means may be constituted by using another quantity of the braking
operation of the brake pedal 30 other than the master cylinder
pressure Pmc or the rate of change dPmc thereof described above
with the present embodiment.
[0079] Next, a description will be given of the operation of the
braking force controlling apparatus of the present embodiment after
it is determined that the brake-assisting control should be
started. As described above, in the present embodiment, when the
speed of the braking operation of the brake pedal 30 (or the rate
of change dPmc of the master cylinder pressure) is above the
reference speed and the quantity of the braking operation of the
brake pedal 30 (or the master cylinder pressure Pmc) is above the
reference quantity, the ECU 10 determines that the braking
operation of the brake pedal 30 is intended to perform the
emergency braking operation.
[0080] When it is determined that the braking operation of the
brake pedal 30 is intended to perform the emergency braking
operation, the ECU 10 supplies the drive signals to the STR 26, the
SA-1 46, the SA-2 48 and the SA-3 54.
[0081] When the drive signal is supplied to the STR 26 by the ECU
10, the STR 26 is set in the second position so that the STR 26
closes the controlled-pressure line 29 connected to the regulator
24, and connects the high-pressure line 22 to the third pressure
line 42. The accumulator pressure Pacc from the accumulator 20 is
supplied to the third pressure line 42 through the STR 26. When the
drive signal is supplied to the SA-1 46, the SA-1 46 is set in the
second position so that the SA-1 46 connects the pressure
adjustment line 56 to the wheel cylinder 44FR. The SA-1 46 closes
off or disconnects the first pressure line 36 from the wheel
cylinder 44FR. When the drive signal is supplied to the SA-2 48,
the SA-2 48 is set in the second position so that the SA-2 48
connects the pressure adjustment line 62 to the wheel cylinder
44FL. The SA-2 48 closes off or disconnects the first pressure line
36 from the wheel cylinder 44FL. When the drive signal is supplied
to the SA-3 54, the SA-3 54 is set in the second position so that
the SA-3 54 connects the third pressure line 42 to the SRRH 68 and
the SRLH 70. The SA-3 54 closes off or disconnects the second
pressure line 38 from the SRRH 68 and the SRLH 70.
[0082] Hence, when the drive signals are supplied to the STR 26,
the SA-1 46, the SA-2 48 and the SA-3 54, all the wheel cylinders
44 are connected to both the pressure-holding solenoids SH and the
pressure-reducing solenoids SR, and the accumulator pressure Pacc
is supplied to the upstream sides of the pressure-holding solenoids
SH through the STR 26.
[0083] Immediately when it is determined that the braking operation
of the brake pedal 30 is intended to perform the emergency braking
operation, the ECU 10 does not yet supply the drive signals to the
pressure-holding solenoids SH or the pressure-reducing solenoids
SR. The accumulator pressure Pacc is supplied to the wheel
cylinders 44 through the pressure-holding solenoids SH.
Consequently, the wheel cylinder pressure Pwc of each of the wheel
cylinders 44 is quickly increased to the accumulator pressure
Pacc.
[0084] Accordingly, it is possible for the braking force
controlling apparatus of the present embodiment to quickly increase
the wheel cylinder pressure Pwc of each of the wheel cylinders 44
when the emergency braking operation is performed, regardless of
the magnitude of the braking operation force Fp. Therefore, in the
braking force controlling apparatus of the present embodiment,
after the condition requiring the emergency braking has occurred,
it is possible to quickly generate an increased braking force
larger than that generated during the normal control, even if the
vehicle operator is a beginner.
[0085] After the accumulator pressure Pacc is continuously supplied
to the wheel cylinders 44, the increased braking force is generated
on the vehicle, and a relatively large slip ratio S of the vehicle
wheels FR, FL, RR and RL is produced. It is then determined that
the ABS control execution conditions are satisfied. After this
determination is made, the execution of the ABS control of the
braking force controlling apparatus of the present embodiment is
started. As described above, the ECU 10 suitably performs one of
(1) the pressure-increasing control mode, (2) the pressure-holding
control mode and (3) the pressure-decreasing control mode so as to
maintain the slip ratio S of each of the vehicle wheels FR, FL, RR
and RL below the reference value, preventing all the vehicle wheels
from being locked during the braking operation.
[0086] When the ABS control is performed following the emergency
braking operation, the wheel cylinder pressure Pwc of each of the
wheel cylinders 44 is increased by the supply of the accumulator
pressure Pacc from the pump 12 or the accumulator 20 to the wheel
cylinders 44, while the wheel cylinder pressure Pwc is reduced by
the returning flow of the brake fluid within the wheel cylinders 44
to the reservoir tank 16. It is possible to prevent the
malfunctioning of the master cylinder 32 even when the repeated
execution of the pressure-increasing mode control and the
pressure-reducing mode control is performed during the ABS
control.
[0087] When the vehicle operator starts releasing the brake pedal
30 after the brake-assisting control was started by the emergency
braking operation, it is necessary to terminate the brake-assisting
control. In the braking force controlling apparatus of the present
embodiment, during the execution of the brake-assisting control,
the ECU 10 supplies the drive signals to the STR 26, the SA-1 46,
the SA-2 48 and the SA-3 54. When the drive signals are supplied to
the solenoids 26, 46, 48, and 54 by the ECU 10, the solenoids 26,
46, 48 and 54 are set in the second positions as described above.
In this condition, the internal pressure chamber of the regulator
24 is isolated from the wheel cylinders 44 and the pump 12, and
both the first pressure chamber 32a and the second pressure chamber
32b of the master cylinder 32 are isolated from the wheel cylinders
44 and the pump 12.
[0088] Hence, in the braking force controlling apparatus of the
present embodiment, during the execution of the brake-assisting
control, the master cylinder pressure Pmc varies in proportion with
the braking operation force Fp on the brake pedal 30. By monitoring
the master cylinder pressure Pmc which is detected based on the
signal supplied by the hydraulic pressure sensor 40, the ECU 10 can
easily determine whether a brake releasing operation of the brake
pedal 30 is performed by the vehicle operator. When it is
determined that the brake releasing operation is performed, the ECU
10 stops supplying the drive signals to the STR 26, the SA-1 46,
the SA-2 48 and the SA-3 54. Hence, the brake-assisting control is
terminated and the normal control is restarted.
[0089] As described above, the beginners generally tend to
unintentionally release the brake pedal 30 during the emergency
braking operation. FIG. 3 shows changes of the master cylinder
pressure Pmc with respect to the elapsed time when the emergency
braking operation is performed by various vehicle operators. The
master cylinder pressure Pmc is in correspondence with the braking
operation force Fp exerted on the brake pedal 30. A change of the
master cylinder pressure Pmc with respect to the elapsed time when
the emergency braking operation is performed by an experienced
vehicle operator is indicated by the curve "A" in FIG. 3. Changes
of the master cylinder pressure Pmc with respect to the elapsed
time when the emergency braking operation is performed by the
beginners are indicated by the curves "B" and "C" in FIG. 3.
[0090] As indicated by the curve "A" of FIG. 3, in the case of the
experienced vehicle operator, when a condition requiring the
emergency braking has occurred, the master cylinder pressure Pmc is
quickly raised to an adequately large level by the braking
operation of the brake pedal 30. The master cylinder pressure Pmc
is maintained at the adequately large level over a certain period
of time.
[0091] However, as indicated by the curve "B" or "C" of FIG. 3, in
the case of the beginner, when the condition requiring the
emergency braking has occurred, the master cylinder pressure Pmc is
not maintained at an adequately large level over a certain period
of time after the master cylinder pressure Pmc is initially raised
to a maximum master cylinder pressure PmcMAX. In FIG. 3, the
adequately large level of the master cylinder pressure Pmc is
indicated by "Prl" in FIG. 3. In addition, the beginner
unintentionally releases the braking operation force Fp on the
brake pedal 30 during the emergency braking operation. In the case
of the beginner, there is a tendency that the master cylinder
pressure Pmc is gradually decreased from the maximum master
cylinder pressure PmcMAX. In the example indicated by the curve "B"
of FIG. 3, during a period from the time "T1" to the time "T2", the
beginner unintentionally releases the braking operation force Fp on
the brake pedal 30 so that the master cylinder pressure Pmc is
gradually decreased. The maximum master cylinder pressure PmcMAX is
produced at the time "T1". The beginner intentionally releases the
brake pedal 30 at the time "T2".
[0092] In the conventional apparatus of the afore-mentioned
publication, when a decrease of the braking operation force on the
brake pedal is detected, the brake-assisting control is
automatically terminated even if the beginner unintentionally
releases the brake pedal. Suppose that the level "Prl" is a fixed
release-judgment level of the master cylinder pressure Pmc in the
example of the curve "B" of FIG. 3. When the master cylinder
pressure Pmc is decreased to be below the release-judgment level
"Prl" shown in FIG. 3, the conventional apparatus automatically
terminates the brake-assisting control and restarts the normal
control based on the detected braking operation force change.
However, the condition requiring the emergency braking still exists
when the brake-assisting control is terminated. The capability of
the conventional apparatus is inadequate to effectively achieve the
function of the brake-assisting control.
[0093] The braking force controlling apparatus of the present
embodiment is directed to eliminating the above problem of the
conventional apparatus, and it is characterized in that a
release-judgment level of a braking operation quantity (or the
master cylinder pressure Pmc) is defined based on a maximum
quantity of the braking operation (or the maximum master cylinder
pressure PmcMAX) so as to safely maintain the brake-assisting
control even if the beginner unintentionally releases the braking
operation force on the brake pedal during the emergency braking
operation.
[0094] In the example of the curve "B" of FIG. 3, the beginner
effectively depresses the brake pedal 30 only in an initial period
of the emergency braking operation so that the master cylinder
pressure Pmc is initially raised to a maximum master cylinder
pressure PmcMAX. However, the beginner unintentionally releases the
brake pedal 30 during the emergency braking operation (or the
period between the time "T1" and the time "T2" in FIG. 3), and the
master cylinder pressure Pmc is not maintained at the adequately
large level over a certain period of time after the master cylinder
pressure Pmc is initially raised to the maximum master cylinder
pressure PmcMAX. A decrease quantity of the master cylinder
pressure Pmc during the period between the time "T1" and the time
"T2", which is caused by the brake releasing operation of the brake
pedal 30 by the beginner, is indicated by ".alpha." in FIG. 3.
[0095] In the present embodiment, the decrease quantity ".alpha."
is predetermined in accordance with the experiments of the
inventors. The release-judgment level of the master cylinder
pressure Pmc is defined by a difference between the maximum master
cylinder pressure PmcMAX and the decrease quantity .alpha.. That
is, when the master cylinder pressure Pmc is smaller than the
release-judgment level (PmcMAX-.alpha.), the braking force
controlling apparatus of the present embodiment makes a
determination that the brake-assisting control should be
terminated.
[0096] The change of the master cylinder pressure Pmc with respect
to the elapsed time during the emergency braking operation may
differ according to the individual vehicle operators. For example,
if it is assumed that the curve "C" in FIG. 3 indicates a change of
the master cylinder pressure Pmc with respect to the elapsed time
when the emergency braking operation is performed by a male
beginner or a beginner who has a certain pedal-depressing force,
then it can be assumed that the curve "B" in FIG. 3 indicates a
change of the master cylinder pressure Pmc with respect to the
elapsed time when the emergency braking operation is performed by a
female beginner or a beginner who has little pedal-depressing
force.
[0097] In the example of the curve "C" of FIG. 3, the male beginner
effectively depresses the brake pedal 30 only during an initial
period of the emergency braking operation so that the master
cylinder pressure Pmc is initially raised to a maximum master
cylinder pressure PmcMAX. This maximum master cylinder pressure
PmcMAX is larger than that in the example of the curve "B" of FIG.
3. However, similar to the female beginner in the example of the
curve "B", the male beginner in the example of the curve "C"
unintentionally releases the brake pedal 30 during the period
between the time "T1" and the time "T2" in FIG. 3. There is a
tendency that the master cylinder pressure Pmc is gradually
decreased during the period after the master cylinder pressure Pmc
is initially raised to the maximum master cylinder pressure PmcMAX.
A decrease quantity of the master cylinder pressure Pmc during the
period between the time "T1" and the time "T2", which is caused by
the brake releasing operation of the brake pedal 30 by the male
beginner, is indicated by ".alpha.1" in FIG. 3. As shown in FIG. 3,
the decrease quantity .alpha.1 in the example of the curve "C" (the
case of the male beginner) is slightly smaller than the decrease
quantity a in the example of the curve "B" (the case of the female
beginner). In the present embodiment, the decrease quantity .alpha.
is adjusted to a suitable value depending on the magnitude of the
maximum master cylinder pressure PmcMAX.
[0098] Therefore, in the braking force controlling apparatus of the
present embodiment, a maximum master cylinder pressure PmcMAX
during the braking operation is stored in the ECU 10, and the
determination as to whether the brake-assisting control should be
terminated is made based on the maximum master cylinder pressure
PmcMax stored in the ECU 10 and the master cylinder pressure Pmc
detected by the ECU 10. It is possible to determine the time of the
termination of the brake-assisting control with accuracy, so as to
eliminate the differences of the braking operation quantity
according to the individual vehicle operators.
[0099] In another preferred embodiment of the present invention,
the braking force controlling apparatus may be constructed such
that a maximum master cylinder pressure PmcMAX during the braking
operation is stored in the ECU 10, and the determination as to
whether the brake-assisting control should be terminated is made by
comparing the master cylinder pressure Pmc (detected by the ECU 10)
with a product of the maximum master cylinder pressure PmcMax
(stored in the ECU 10) and a decrease ratio
.beta.(0<.beta.<1).
[0100] In the present embodiment, the release-judgment level of the
master cylinder pressure Pmc is defined by the product
PmcMAX.times..beta.. That is, when the master cylinder pressure Pmc
is smaller than the release-judgment level PmcMAX.times..beta., the
braking force controlling apparatus of the present embodiment makes
a determination that the brake-assisting control should be
terminated.
[0101] In the present embodiment, the decrease ratio .beta. is
predetermined in accordance with the experiments of the inventors,
and the decrease ratio .beta. is adjusted (decreased or increased)
to a suitable value depending on the magnitude of the maximum
master cylinder pressure PmcMAX. It is possible for the present
embodiment to determine the time of the termination of the
brake-assisting control with accuracy, so as to eliminate the
differences of the braking operation quantity according to the
individual vehicle operators.
[0102] Accordingly, by making use of the above-described methods,
the braking force controlling apparatus of the present invention
can safely maintain the brake-assisting control even if a beginner
unintentionally releases the braking operation force on the brake
pedal during the emergency braking operation. Next, a description
will be given of a braking force control procedure performed by the
braking force controlling apparatus of FIG. 1.
[0103] FIG. 4 shows a braking force control procedure performed by
the ECU 10 of the braking force controlling apparatus of FIG. 1 in
order to make a determination as to whether the brake-assisting
control should be terminated. The control procedure shown in FIG. 4
is an interrupt-initiated routine which is periodically initiated
at intervals of a predetermined time.
[0104] In the control procedure of FIG. 4, steps 100 through 108
are performed to determine whether the brake-assisting control is
currently executed. As the control procedure of FIG. 4 is performed
to determine whether the brake-assisting control should be
terminated, the performance of the control procedure of FIG. 4 is
useless if the brake-assisting control is not currently executed.
Hence, before making a determination as to whether the
brake-assisting control should be terminated, the steps 100 through
108 are performed for this purpose.
[0105] As shown in FIG. 4, the ECU 10 at step 100 determines
whether the execution of the brake-assisting control is inhibited
because of a malfunction in the braking force controlling
apparatus. For example, when a break in a connection line between
the ECU 10 and any of the hydraulic pressure sensor 40, the brake
switch 84 and the wheel speed sensors 86 has occurred, or when a
malfunction of any of the hydraulic pressure sensor 40, the brake
switch 84 and the wheel speed sensors 86 has occurred, the
execution of the brake-assisting control is inhibited. When the
braking force controlling apparatus is malfunctioning, the
braking-assisting control cannot be properly performed. Therefore,
when the result at the step 100 is affirmative, the ECU 10 at step
124 terminates the brake-assisting control, and the subsequent
steps of the control procedure are not performed. If the normal
control is currently performed in the braking force controlling
apparatus, the ECU 10 at step 124 maintains the normal control.
[0106] When the result at the step 100 is negative, the ECU 10 at
step 102 determines whether the brake switch 84 is in an OFF state
based on the signal supplied by the brake switch 84. When the
result at the step 102 is affirmative, the brake pedal 30 is not
depressed by the vehicle operator. When the vehicle operator does
not depress the brake pedal 30, it is not necessary to perform the
brake-assisting control in the braking force controlling apparatus.
Therefore, when the result at the step 102 is affirmative, the ECU
10 at the step 124 terminates the brake-assisting control, and the
subsequent steps of the control procedure are not performed. If the
normal control is currently performed in the braking force
controlling apparatus, the ECU 10 at the step 124 maintains the
normal control.
[0107] When the result at the step 102 is negative, the ECU 10 at
step 104 determines whether the master cylinder pressure Pmc is
smaller than a given reference pressure P1. The reference pressure
P1 is preset to an adequately small value for the master cylinder
pressure Pmc produced in the master cylinder 32 during the
emergency braking operation of the brake pedal 30. When the master
cylinder pressure Pmc is smaller than the reference pressure P1, it
is not necessary to perform the brake-assisting control in the
braking force controlling apparatus. Therefore, when the result at
the step 104 is affirmative, the ECU 10 at the step 124 terminates
the brake-assisting control, and the subsequent steps of the
control procedure are not performed. If the normal control is
currently performed in the braking force controlling apparatus, the
ECU 10 at the step 124 maintains the normal control.
[0108] When the result at the step 104 is negative, the ECU 10 at
step 106 determines whether the master cylinder pressure Pmc is
larger than a given reference pressure P2. The reference pressure
P2 is preset to an adequately large value for the master cylinder
pressure Pmc produced in the master cylinder 32 when the emergency
braking operation of the brake pedal 30 is performed by the
beginner. The condition in which the master cylinder pressure Pmc
is larger than the reference pressure P2 may result in when the
emergency braking operation is performed by the experienced vehicle
operator. In this condition, it is not necessary to perform the
brake-assisting control in the braking force controlling apparatus.
Or, the condition in which the master cylinder pressure Pmc is
larger than the reference pressure P2 may result in when a
malfunction in the hydraulic pressure sensor 40 has occurred. In
this condition, the brake-assisting control cannot be properly
performed in the braking force controlling apparatus. Therefore,
when the result at the step 106 is affirmative, the ECU 10 at the
step 124 terminates the brake-assisting control, and the subsequent
steps of the control procedure are not performed. If the normal
control is currently performed in the braking force controlling
apparatus, the ECU 10 at the step 124 maintains the normal
control.
[0109] When the result at the step 106 is negative, the ECU 10 at
step 108 determines whether the estimated vehicle speed Vso is
smaller than a given low speed Vmin. The low speed Vmin is preset
to an adequately small value for the vehicle speed at which the
vehicle can be stopped without performing a sudden braking
operation. The ABS control is performed in the braking force
controlling apparatus in order to ensure a vehicle running
stability even when the braking operation is suddenly performed by
the vehicle operator. When the estimated vehicle speed Vso is
smaller than the low speed Vmin, it is not necessary to perform the
ABS control in the braking force controlling apparatus. Because of
the same reasons, when the estimated vehicle speed Vso is smaller
than the low speed Vmin, it is not necessary to perform the
brake-assisting control in the braking force controlling apparatus.
Therefore, when the result at the step 108 is affirmative, the ECU
10 at the step 124 terminates the brake-assisting control, and the
subsequent steps of the control procedure are not performed. If the
normal control is currently performed in the braking force
controlling apparatus, the ECU 10 at the step 124 maintains the
normal control.
[0110] When the result at the step 108 is negative, it is
determined that the brake-assisting control is currently executed
in the braking force controlling apparatus. Then, the ECU 10
performs the subsequent steps of the control procedure of FIG. 4 in
order to make a determination as to whether the brake-assisting
control should be terminated.
[0111] The ECU at step 112 determines whether the master cylinder
pressure Pmc (detected at the current cycle) is larger than the
maximum master cylinder pressure PmcMAX (stored at the preceding
cycle). When the result at the step 112 is affirmative
(Pmc>PmcMAX), the ECU 10 at step 114 substitutes the
previously-stored maximum master cylinder pressure PmcMAX by the
currently-detected master cylinder pressure Pmc (PmcMAX<--Pmc),
and stores the new maximum master cylinder pressure PmcMAX in a
memory (RAM) of the ECU 10. In this manner, the maximum master
cylinder pressure PmcMAX is renewed and stored in the ECU 10 every
time the step 114 is performed. For example, in the case of the
curve "B" of FIG. 3, the master cylinder pressure Pmc, detected at
the time T1, is stored as the maximum master cylinder pressure
PmcMAX in the ECU 10. After the step 114 is performed, the ECU 10
performs a next step 116. On the other hand, when the result at the
step 112 is negative, the ECU 10 does not perform the step 114 and
performs the step 116.
[0112] The ECU 10 at step 116 determines whether the maximum master
cylinder pressure PmcMAX (stored at the current cycle) is smaller
than a given reference pressure P3. In accordance with the
experiments of the inventors, the reference pressure P3 is preset
to a pressure larger than the maximum master cylinder pressure
PmcMAX produced in the master cylinder 32 when the braking
operation is performed by the beginner who has little
pedal-depressing force. The step 116 is performed in order to
adjust the decrease quantity .alpha. to a suitable value depending
on the magnitude of the maximum master cylinder pressure PmcMAX.
When PmcMAX<P3, it is determined that the braking operation is
performed by the beginner who has little pedal-depressing force.
When PmcMAX.gtoreq.P3, it is determined that the braking operation
is performed by the beginner who has a certain pedal-depressing
force.
[0113] When the result at the step 116 is affirmative, the ECU 10
at step 118 sets the decrease quantity a at a relatively large
value A1 (.alpha.<--A1). When the result at the step 116 is
negative, the ECU 10 at step 120 sets the decrease quantity a at a
relatively small value B1 (.alpha.<--B1). The values A1 and B1
are predetermined in accordance with the experiments of the
inventors such that the value A1 is larger than the value B1.
[0114] After the step 118 or the step 120 is performed, the ECU 10
at step 122 calculates a release-judgment level of the master
cylinder pressure Pmc by a difference between the maximum master
cylinder pressure PmcMAX and the decrease quantity a. Further, the
ECU 10 at step 122 determines whether the master cylinder pressure
Pmc (detected at the current cycle) is smaller than the
release-judgment level (PmcMAX-.alpha.).
[0115] When the result at the step 122 is affirmative
(Pmc<(PmcMAX-.alpha.)), it is determined that the vehicle
operator intentionally releases the brake pedal 30 after the
condition requiring the emergency braking is avoided. The ECU 10 at
the step 124 terminates the brake-assisting control. After the step
124 is performed, the control procedure of FIG. 4 ends.
[0116] On the other hand, when the result at the step 122 is
negative (Pmc.gtoreq.(PmcMAX-.alpha.)), it is determined that the
beginner unintentionally releases the brake pedal 30 during the
emergency braking operation. In this case, the ECU does not
performs the step 124 and the braking force control procedure of
FIG. 4 ends. Hence, the braking force controlling apparatus of the
present embodiment can safely maintain the brake-assisting control
when the beginner unintentionally releases the braking operation
force on the brake pedal 30 during the emergency braking
operation.
[0117] In the present embodiment, even if the beginner
unintentionally releases the braking operation force on the brake
pedal 30 during the emergency braking operation, the
braking-assisting control is safely maintained. The braking force
controlling apparatus of the present embodiment is effective in
matching the brake-assisting control with the intention of the
vehicle operator. It is possible to quickly increase the braking
force by the brake-assisting control when the condition requiring
the emergency braking has occurred. The steps 116-120 in the
control procedure of FIG. 4 are performed to adjust the decrease
quantity a to a suitable value depending on the magnitude of the
maximum master cylinder pressure PmcMAX. It is possible to
determine the time of the termination of the brake-assisting
control with accuracy by eliminating the differences of the braking
operation quantity according to the individual vehicle
operators.
[0118] Next, FIG. 5 shows another braking force control procedure
performed by the ECU 10 of the braking force controlling apparatus
of FIG. 1 in order to make a determination as to whether the
brake-assisting control should be terminated. The control procedure
shown in FIG. 5 is an interrupt-initiated routine which is
periodically initiated at intervals of a predetermined time.
[0119] In FIG. 5, the steps which are the same as corresponding
steps in FIG. 4 are designated by the same reference numerals, and
a description thereof will be omitted.
[0120] In the control procedure of FIG. 5, only steps 218 through
222 are different from the corresponding steps in the control
procedure of FIG. 4. As described above, in the control procedure
of FIG. 4, the release-judgment level of the master cylinder
pressure Pmc is calculated by the difference between the maximum
master cylinder pressure PmcMAX and the decrease quantity .alpha..
The determination as to whether the brake-assisting control should
be terminated is made by the comparison of the master cylinder
pressure Pmc and the release-judgment level (PmcMAX-.alpha.).
[0121] In the control procedure of FIG. 5, the ECU 10 at step 222
calculates a release-judgment level of the master cylinder pressure
Pmc by a product of the maximum master cylinder pressure PmcMAX and
the decrease ratio .beta. (0<.beta.<1). Further, the ECU 10
at step 222 determines whether the master cylinder pressure Pmc
(detected at the current cycle) is smaller than the
release-judgment level (PmcMAX.times..beta.).
[0122] When the result at the step 222 is affirmative
(Pmc<(PmcMAX.times..beta.)), it is determined that the vehicle
operator intentionally releases the brake pedal 30 after the
condition requiring the emergency braking is avoided. The ECU 10 at
the step 124 terminates the brake-assisting control. After the step
124 is performed, the control procedure of FIG. 5 ends.
[0123] On the other hand, when the result at the step 222 is
negative (Pmc.ltoreq.(PmcMAX.times..beta.)), it is determined that
the beginner unintentionally releases the brake pedal 30 during the
emergency braking operation. In this case, the ECU does not
performs the step 124 and the braking force control procedure of
FIG. 5 ends.
[0124] Similar to FIG. 4, in the control procedure of FIG. 5, when
the result at the step 116 is affirmative (PmcMAX<P3), it is
determined that the braking operation is performed by the beginner
who has little pedal-depressing force. In this case, the ECU 10 at
step 218 sets the decrease ratio .beta. at a relatively large value
A2 (.beta.<--A2). On the other hand, when the result at the step
116 is negative (PmcMAX.gtoreq.P3), it is determined that the
braking operation is performed by the beginner who has a certain
pedal-depressing force. In this case, the ECU 10 at step 220 sets
the decrease ratio .beta. at a relatively small value B2
(.beta.<--B2). The values A2 and B2 are predetermined in
accordance with the experiments of the inventors such that the
value A2 is larger than the value B2.
[0125] After the step 218 or the step 220 is performed, the ECU 10
performs the above-described step 222. When it is determined that
the vehicle operator intentionally releases the brake pedal 30
after the condition requiring the emergency braking is avoided, the
ECU 10 at the step 124 terminates the brake-assisting control.
After the step 124 is performed, the control procedure of FIG. 5
ends. On the other hand, when it is determined that the beginner
unintentionally releases the brake pedal 30 during the emergency
braking operation, the ECU does not performs the step 124 and the
braking force control procedure of FIG. 5 ends. Hence, the braking
force controlling apparatus of the present embodiment can safely
maintain the brake-assisting control when the beginner
unintentionally releases the braking operation force on the brake
pedal 30 during the emergency braking operation.
[0126] Similar to the control procedure of FIG. 4, in the present
embodiment, even if the beginner unintentionally releases the
braking operation force on the brake pedal 30 during the emergency
braking operation, the braking-assisting control is safely
maintained. The braking force controlling apparatus of the present
embodiment is effective in matching the brake-assisting control
with the intention of the vehicle operator. It is possible to
quickly increase the braking force by the brake-assisting control
when the condition requiring the emergency braking has occurred.
The steps 116, 218 and 220 in the control procedure of FIG. 5 are
performed to adjust the decrease ratio .beta. to a suitable value
depending on the magnitude of the maximum master cylinder pressure
PmcMAX. It is possible to determine the time of the termination of
the brake-assisting control with accuracy by eliminating the
differences of the braking operation quantity according to the
individual vehicle operators.
[0127] In the above-described embodiments, the determination as to
whether the braking operation of the brake pedal by the vehicle
operator is an intentional operation or not is made based on the
master cylinder pressure Pmc. However, the basic parameter for
making the determination according to the present invention is not
limited to the master cylinder pressure Pmc.
[0128] When the braking operation of the brake pedal 30 is
performed, not only the master cylinder pressure Pmc, but also the
braking operation force Fp on the brake pedal 30 or a stroke L of
the brake pedal 30 varies in accordance with a quantity of the
braking operation. Further, when the braking force is exerted on
the vehicle as a result of the braking operation of the brake pedal
30, a deceleration G of the vehicle is produced. By taking account
of these factors, the determination as to whether the braking
operation is an emergency braking operation or a normal braking
operation, and the determination as to whether the braking
operation is an intentional operation may be made based on any of
the basic parameters including: (1) the master cylinder pressure
Pmc; (2) the braking operation force Fp; (3) the brake pedal stroke
L; (4) the vehicle deceleration G; (5) the estimated vehicle speed
Vso; and (6) the wheel speed Vw.
[0129] Next, a description will be given of a second embodiment of
the preset invention with reference to FIG. 6. FIG. 6 shows the
second embodiment of the braking force controlling apparatus of the
present invention. For the sake of simplicity of description, a
configuration of the braking force controlling apparatus having
only one wheel cylinder provided for only one wheel of an
automotive vehicle is illustrated in FIG. 6.
[0130] As shown in FIG. 6, the braking force controlling apparatus
of the present embodiment is controlled by an electronic control
unit 200 (hereinafter, called ECU 200). The braking force
controlling apparatus of FIG. 6 includes a brake pedal 203. A brake
switch 203 is provided in the vicinity of the brake pedal 202. When
the brake pedal 202 is depressed by the vehicle operator, the brake
switch 203 outputs an ON signal to the ECU 200. The ECU 200
determines whether the braking operation is performed by the
vehicle operator, based on the signal supplied by the brake switch
203.
[0131] The brake pedal 202 is connected to a vacuum booster 204.
The vacuum booster 204 serves to increase the braking operation
force of the brake pedal 202 by using an intake pressure of air
into an internal combustion engine of the vehicle. A master
cylinder 206 is fixed to the vacuum booster 204. When the brake
pedal 202 is depressed, a resultant force of the braking operation
force Fp, exerted on the brake pedal 202, and a brake-assisting
force Fa, produced by the vacuum booster 204, is transmitted from
the vacuum booster 204 to the master cylinder 206.
[0132] The master cylinder 206 includes a pressure chamber provided
therein. A reservoir tank 208 is provided on the top of the master
cylinder 206. When the braking operation force on the brake pedal
202 is released by the vehicle operator, the reservoir tank 208 is
connected to or communicates with the pressure chamber of the
master cylinder 206. When the brake pedal 202 is depressed by the
vehicle operator, the reservoir tank 208 is disconnected from or
isolated from the pressure chamber of the master cylinder 206.
Hence, the pressure chamber of the master cylinder 206 is
replenished with brake fluid from the reservoir tank 208 every time
the braking operation force on the brake pedal 202 is released by
the vehicle operator.
[0133] A hydraulic pressure line 210 is connected to the pressure
chamber of the master cylinder 206. A hydraulic pressure sensor 212
is provided at an intermediate portion of the pressure line 210.
The hydraulic pressure sensor 212 outputs a signal, indicative of
the master cylinder pressure Pmc, to the ECU 10. The ECU 200
detects the master cylinder pressure Pmc, produced in the master
cylinder 206, based on the signal supplied by the hydraulic
pressure sensor 212.
[0134] A pressure-holding solenoid 216 (hereinafter called SH 216)
is provided in the pressure line 210. The SH 216 is a two-position
solenoid valve which is normally set in a valve-open position so as
to connect the master cylinder 206 to a wheel cylinder 213. When a
drive signal is supplied to the SH 216 by the ECU 200, the SH 216
is set in a valve-closed position so as to disconnect the master
cylinder 206 from the wheel cylinder 213.
[0135] The wheel cylinder 213 is connected on the downstream side
of the SH 216 to the pressure line 210. A pressure-reducing
solenoid 217 (hereinafter called SR 217) is also connected on the
downstream side of the SH 216 to the pressure line 210. The SR 217
is a two-position solenoid valve which is normally set in a
valve-closed position so as to inhibit a flow of the brake fluid
from the wheel cylinder 213 to a downstream portion of the pressure
line 210 via the SR 217. When a drive signal is supplied to the SR
217 by the ECU 200, the SR 217 is set in a valve-open position so
as to allow the flow of the brake fluid from the wheel cylinder 213
to the downstream portion of the pressure line 210 via the SR 217.
In addition, a check valve 215 is provided in a bypass line of the
pressure line 210 around the SH 216, and the bypass line is
connected to the wheel cylinder 213. The check valve 215 allows
only a flow of the brake fluid from the wheel cylinder 213 to the
pressure line 210, and inhibits a counter flow of the brake fluid
from the pressure line 210 to the wheel cylinder 213.
[0136] A wheel speed sensor 219 is provided in the vicinity of the
wheel of the vehicle for which the wheel cylinder 213 is provided.
The wheel speed sensor 219 outputs a signal, indicative of a wheel
speed of the vehicle, to the ECU 200. The ECU 200 detects the wheel
speed of the vehicle wheel based on the signal supplied by the
wheel speed sensor 219.
[0137] A reservoir 224 is connected to the pressure line 210 on the
downstream side of the SR 217. When the SR 217 is set in the
valve-open position, the brake fluid from the SR 217 flows into the
reservoir 224, and stored in the reservoir 224. In the reservoir
224, a certain amount of brake fluid is initially stored. A pump
226 is provided in the pressure line 210, and has an inlet port
226a which is connected to the reservoir 224. The pump 226 has an
outlet port 226b which is connected to a check valve 228 in the
pressure line 210. The check valve 228 is connected to the upstream
side of the SH 216 through the pressure line 210. The check valve
228 allows only a flow of the brake fluid from the outlet port 216b
of the pump 226 to the upstream side of the SH 216 in the pressure
line 210, and inhibits a counter flow of the brake fluid from the
upstream side of the SH 216 to the outlet port 226b of the pump
226.
[0138] An intake pressure line 230 and a pressure adjustment line
232 are connected to the vacuum booster 204. An intake pipe of the
engine or the like is connected to the intake pressure line 230,
and an intake pressure from the intake pipe is delivered through
the intake pressure line 230 to the vacuum booster 204. The
pressure adjustment line 232 is connected to both an intake
pressure valve 234 and an atmospheric pressure valve 236. The
intake pressure valve 234 is provided between the intake pressure
line 230 and the pressure adjustment line 232. The intake pressure
valve 234 is a two-position solenoid valve which is normally set in
a valve-open position so as to connect the intake pressure line 230
and the pressure adjustment line 2332. When a drive signal is
supplied to the valve 234 by the ECU 200, the valve 234 is set in a
valve-closed position so as to disconnect the pressure adjustment
line 232 from the intake pressure line 230. The atmospheric
pressure valve 236 is provided between the pressure adjustment line
232 and an atmospheric pressure line which is open to the
atmosphere. The atmospheric pressure valve 236 is a two-position
solenoid valve which is normally set in a valve-closed position so
as to disconnect the pressure adjustment line 232 from the
atmospheric pressure line. When a drive signal is supplied to the
valve 236 by the ECU 200, the valve 236 is set in a valve-open
position so as to connect the pressure adjustment line 232 and the
atmospheric pressure line.
[0139] The vacuum booster 204 includes an intake pressure chamber
and a pressure adjusting chamber both provided therein. In the
vacuum booster 204, the intake pressure chamber and the pressure
adjusting chamber are separated from each other by a diaphragm. The
intake pressure chamber is connected to the intake pressure line
230. When the vehicle is normally running, the intake pressure
chamber of the vacuum booster 204 is held at a vacuum pressure of
the intake pressure of the intake pressure line 230. The pressure
adjusting chamber of the vacuum booster 204 is connected to the
pressure adjustment line 232 through a valve device. The valve
device is provided in the vacuum booster 204 to adjust an internal
pressure of the pressure adjusting chamber in accordance with the
braking operation of the brake pedal 202.
[0140] The operation of the valve device of the vacuum booster 204
will now be described. When the intake pressure from the intake
pressure valve 234 is supplied to the pressure adjustment line 232,
the valve device connects the pressure adjusting chamber to the
pressure adjustment line 232 until a difference in pressure between
the pressure adjusting chamber and the intake pressure chamber is
produced in proportion to the braking operation force Fp on the
brake pedal 202 by the vehicle operator. An actuating force which
is proportional to the difference in pressure between the pressure
adjusting chamber and the intake pressure chamber (or in proportion
to the braking operation force Fp) is exerted on the diaphragm
between the pressure adjusting chamber and the intake pressure
chamber. Therefore, when the brake pedal 202 is depressed, the
brake-assisting force Fa is produced by the vacuum booster 204 in
accordance with the actuating force on the diaphragm, so that a
resultant force of the braking operation force Fp and the
brake-assisting force Fa is transmitted from the vacuum booster 204
to the master cylinder 206.
[0141] On the other hand, when the atmospheric pressure from the
atmospheric pressure valve 236 is supplied to the pressure
adjusting line 232, the valve device of the vacuum booster 204
connects the pressure adjusting chamber to the pressure adjustment
line 232 so that the atmospheric pressure is supplied to the
pressure adjusting chamber by the valve device, regardless of
whether the braking operation force Fp on the brake pedal 202. An
actuating force which is proportional to the difference in pressure
between the pressure adjusting chamber and the intake pressure
chamber is exerted on the diaphragm between the pressure adjusting
chamber and the intake pressure chamber. At this time, a maximum
brake-assisting force FaMAX is produced in accordance with the
actuating force on the diaphragm by the vacuum booster 204.
[0142] Next, a description will be given of the operation of the
braking force controlling apparatus of the present embodiment.
[0143] In the braking force controlling apparatus of the present
embodiment, when a normal control is performed by the ECU 200, the
ECU 200 supplies no drive signals to the intake pressure valve 234
and the valve 236 so that the valve 234 is set in the valve-open
position and the valve 236 is set in the valve-closed position. In
this condition, when the brake pedal 202 is depressed by the
vehicle operator, the brake-assisting force Fa is produced by the
vacuum booster 204 in accordance with the actuating force on the
diaphragm, so that a resultant force of the braking operation force
Fp and the brake-assisting force Fa is transmitted from the vacuum
booster 204 to the master cylinder 206.
[0144] When the vacuum booster 204 transmits the resultant force of
the braking operation force Fp and the brake-assisting force Fa to
the master cylinder 206, the master cylinder 206 produces a master
cylinder pressure Pmc which is equal to the braking operation force
Fp multiplied by a given magnification factor. Hence, when the
normal control is performed, the braking force controlling
apparatus of the present embodiment generates a braking force in
accordance with the braking operation force Fp on the brake pedal
202.
[0145] When the operating condition of the vehicle is found stable,
the normal control is performed by the ECU 200 of the braking force
controlling apparatus of the present embodiment. During the normal
control, the ECU 200 supplies no drive signals to the SH 216 and
the SR 217, so that the SH 216 is set in the valve-open position
and the SR 217 is set in the valve-closed position as shown in FIG.
6. The ECU 10 stops the operation of the pump 226 during the normal
control. When the hydraulic circuit related to the wheel cylinder
213 is placed in the above condition by the normal control, the
master cylinder pressure Pmc from the master cylinder 206 is
supplied to the wheel cylinder 213 through the SH 216. Hence,
during the normal control, the wheel cylinder 213 generates a
braking force on the vehicle wheel in accordance with the braking
operation force Fp on the brake pedal 202.
[0146] Similar to the first embodiment of FIG. 1, when the slip
ratio is found to be above a reference value after the braking
operation is performed in the braking force controlling apparatus
of the present embodiment, it is determined that the ABS control
execution conditions are satisfied. After this determination is
made, the execution of the ABS control of the braking force
controlling apparatus is started by the ECU 200. When the brake
pedal 202 is depressed, or when the master cylinder pressure Pmc
from the master cylinder 206 is increased to an adequately high
pressure, the ABS control is achieved by the ECU 200. That is,
during the ABS control, the ECU 200 starts the operation of the
pump 226, and controls the drive signals supplied to the SH 216 and
the SR 217 in the following manner.
[0147] During the ABS control of the present embodiment, if the
adequately increased master cylinder pressure Pmc is supplied by
the master cylinder 206, the ECU may control the SH 216 and the SR
217 such that the SH 216 is set in the valve-open position and the
SR 217 is set in the valve-closed position. When the ECU 200
performs this control procedure, the wheel cylinder pressure Pwc of
the wheel cylinder 213 is increased up to the master cylinder
pressure Pmc. Hereinafter, this control procedure will be called
(1) a pressure-increasing control mode.
[0148] Alternatively, during the ABS control of the present
embodiment, the ECU 200 may control the SH 216 and the SR 217 such
that the SH 216 is set in the valve-closed position and the SR 217
is set in the valve-closed position. When the ECU 200 performs this
control procedure, the wheel cylinder pressure Pwc of the wheel
cylinder 213 is held at the same level without increase or
decrease. Hereinafter, this control procedure will be called (2) a
pressure-holding control mode.
[0149] Alternatively, during the ABS control of the present
embodiment, the ECU 200 may control the SH 216 and the SR 217 such
that the SH 216 is set in the valve-closed position and the SR 217
is set in the valve-open position. When the ECU 200 performs this
control procedure, the wheel cylinder pressure Pwc of the wheel
cylinder 213 is decreased. Hereinafter, this control procedure will
be called (3) a pressure-decreasing control mode.
[0150] In the braking force controlling apparatus of the present
embodiment, the ECU 200 suitably performs one of (1) the
pressure-increasing control mode, (2) the pressure-holding control
mode and (3) the pressure-decreasing control mode so as to maintain
the slip ratio below the reference value, preventing the vehicle
wheel from being locked during the braking operation.
[0151] It is necessary to quickly decrease the wheel cylinder
pressure Pwc of the wheel cylinder 213 after the vehicle operator
releases the braking operation force on the brake pedal 202. In the
braking force controlling apparatus of the present embodiment, the
check valve 215 is provided in the bypass line connected to the
wheel cylinder 213 so as to allow only the flow of the brake fluid
from the wheel cylinder 213 to the pressure line 210. As the check
valve 215 functions in this manner, it is possible for the braking
force controlling apparatus of the present embodiment to quickly
decrease the wheel cylinder pressure Pwc after the vehicle operator
releases the braking operation force on the brake pedal 202 during
the ABS control.
[0152] During the ABS control of the braking force controlling
apparatus of the present embodiment, the wheel cylinder pressure
Pwc of the wheel cylinder 213 is suitably adjusted by supplying the
master cylinder pressure Pmc from the master cylinder 206 to the
wheel cylinder 213. When the brake fluid from the master cylinder
206 is delivered to the wheel cylinder 213, the wheel cylinder
pressure Pwc is increased, and, when the brake fluid within the
wheel cylinder 213 is delivered to the reservoir 224, the wheel
cylinder pressure Pwc is decreased. If the increase of the wheel
cylinder pressure Pwc is performed by using the master cylinder 206
as the only brake fluid pressure source, the brake fluid contained
in the master cylinder 206 is gradually decreased through a
repeated execution of the pressure-increasing control mode and the
pressure-decreasing control mode. However, in the present
embodiment, the brake fluid contained in the reservoir 224 is
returned back to the master cylinder 206 by the pump 226.
Therefore, it is possible to prevent the master cylinder 206 from
malfunctioning due to a too small amount of the brake fluid
contained therein even when the ABS control is continuously
performed over an extended period of time.
[0153] Next, a description will be given of the operation of the
braking force controlling apparatus of the present embodiment when
a brake-assisting control is performed by the ECU 200.
[0154] When the brake-assisting control is performed in the present
embodiment, the ECU 200 supplies the drive signals to the intake
pressure valve 234 and the atmospheric pressure valve 236 such that
the valve 234 is set in the valve-closed position and the valve 236
is set in the valve-open position.
[0155] In the braking force controlling apparatus of the present
embodiment, when the execution of the brake-assisting control is
started, the atmospheric pressure from the atmospheric pressure
valve 236 is supplied to the pressure adjustment line 232. As
described above, when the atmospheric pressure is supplied to the
pressure adjustment line 232, the atmospheric pressure is supplied
to the pressure adjusting chamber of the vacuum booster 206 by the
valve device thereof, and the vacuum booster 204 produces the
maximum brake-assisting force FaMAX. Hence, when the execution of
the brake-assisting control is started, a resultant force of the
braking operation force Fp and the maximum brake-assisting force
FaMAX is transmitted to the master cylinder 206 by the vacuum
booster 204.
[0156] During a period between from the start of the
brake-assisting control to the start of the ABS control, the ECU
200 maintains the hydraulic circuit connected to the master
cylinder 206 under the condition of the normal control. In this
condition, the master cylinder pressure Pmc from the master
cylinder 206 is supplied to the wheel cylinder 213 through the SH
216. Hence, after the start of the brake-assisting control, the
wheel cylinder pressure Pwc of the wheel cylinder 213 can be
quickly increased in accordance with a change of the force
transmitted to the master cylinder 206 from the resultant force
"Fa+Fp" to the resultant force "FaMAX+Fp".
[0157] In the braking force controlling apparatus of the present
embodiment, when an emergency braking operation of the brake pedal
202 is performed, it is possible to quickly increase the wheel
cylinder pressure Pwc of the wheel cylinder 213 to a level
adequately higher than a corresponding level for the braking
operation force Fp. Therefore, in the braking force controlling
apparatus of the present embodiment, after the condition requiring
the emergency braking has occurred, it is possible to quickly
generate an increased braking force larger than that generated
during the normal control even if the vehicle operator is a
beginner.
[0158] After the wheel cylinder pressure Pwc is quickly increased
as described above, the increased braking force is generated on the
vehicle, and a relatively large slip ratio of the vehicle wheel is
produced. It is then determined that the ABS control execution
conditions are satisfied. After this determination is made, the
execution of the ABS control of the braking force controlling
apparatus of the present embodiment is started. As described above,
the ECU 200 suitably performs one of (1) the pressure-increasing
control mode, (2) the pressure-holding control mode and (3) the
pressure-decreasing control mode so as to maintain the slip ratio
of the vehicle wheel below the reference value, preventing the
vehicle wheel from being locked during the braking operation.
[0159] In the braking force controlling apparatus of the present
embodiment, when the braking operation force Fp is exerted on the
brake pedal 202 by the vehicle operator after the start of the
brake-assisting control, the master cylinder pressure Pmc is
maintained at the level in accordance with the resultant force
"FaMAX+Fa" supplied by the vacuum booster 204. When the braking
operation force on the brake pedal 202 is released by the vehicle
operator after the start of the brake-assisting control, the master
cylinder pressure Pmc is decreased to the level in accordance with
the maximum brake-assisting force "FaMAX" supplied by the vacuum
booster 204.
[0160] The ECU 200 monitors the signal supplied by the hydraulic
pressure sensor 212, and determines whether the braking operation
force on the brake pedal 202 is released by the vehicle operator,
based on the signal supplied by the hydraulic pressure sensor 212.
When it is determined that the braking operation force on the brake
pedal 202 is released, the ECU 200 stops supplying the drive
signals to the valves 234 and 236 so as to terminate the
brake-assisting control.
[0161] In the braking force controlling apparatus of the present
embodiment, the ECU 200 performs either the braking force control
procedure of FIG. 4 or the braking force control procedure of FIG.
5 in a similar manner to the ECU 10 of the previous embodiment of
FIG. 1. Hence, in the present embodiment, even if the beginner
unintentionally releases the braking operation force on the brake
pedal during the emergency braking operation, the braking-assisting
control is safely maintained. The braking force controlling
apparatus of the present embodiment is effective in matching the
brake-assisting control with the intention of the vehicle operator.
It is possible to quickly increase the braking force by the
brake-assisting control when the condition requiring the emergency
braking has occurred. In addition, the steps 116-120 in the control
procedure of FIG. 4 are performed to adjust the decrease quantity a
to a suitable value depending on the magnitude of the maximum
master cylinder pressure PmcMAX. It is possible to determine the
time of the termination of the brake-assisting control with
accuracy by eliminating the differences of the braking operation
quantity according to the individual vehicle operators.
[0162] In the above-described embodiments, the ECU 10 or the ECU
200 can determine whether a brake releasing operation during the
brake-assisting control is an intentional operation or not, based
on the braking operation quantity and the maximum quantity. When
the brake releasing operation is determined as being not an
intentional operation, the ECU 10 or the ECU 200 maintains the
brake-assisting control. Hence, when the emergency braking is
required, it is possible for the braking force controlling
apparatus of the present invention to quickly increase the braking
force to be larger than the level during the normal control by
maintaining the brake-assisting control. On the other hand, when
the brake releasing operation is determined as being an intentional
operation, the ECU 10 or the ECU 200 terminates the brake-assisting
control. Hence, the braking force controlling apparatus of the
present invention is effective in maintaining the brake-assisting
control even if a beginner unintentionally releases the braking
operation force on the brake pedal during the emergency braking
operation.
[0163] Further, the present invention is not limited to the
above-described embodiments, and variations and modifications may
be made without departing from the scope of the present
invention.
* * * * *