U.S. patent number RE44,677 [Application Number 09/939,509] was granted by the patent office on 2013-12-31 for electronic brake management system with manual fail safe.
This patent grant is currently assigned to Kelsey-Hayes Company. The grantee listed for this patent is Gregory P. Campau, Robert L. Ferger, Blaise J. Ganzel, Andrew W. Kingston, Mark S. Luckevich, Salvatore Oliveri, Thomas Weigert. Invention is credited to Gregory P. Campau, Robert L. Ferger, Blaise J. Ganzel, Andrew W. Kingston, Mark S. Luckevich, Salvatore Oliveri, Thomas Weigert.
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United States Patent |
RE44,677 |
Campau , et al. |
December 31, 2013 |
Electronic brake management system with manual fail safe
Abstract
An improved electro-hydraulic brake system having features for
improving the pedal feel of the system, while further having design
features which contribute to the economy of manufacture of certain
components of the system. The system provides for an electrically
powered normal source of pressurized hydraulic brake fluid, and a
manually powered backup source of pressurized hydraulic brake fluid
to the vehicle brakes in the event of failure of the normal source.
During normal braking, fluid from the backup source is redirected
from the vehicle brakes to a pedal simulator. The pedal simulator
preferably includes arrangements of spring loaded pistons,
expansion volumes, and damping orifices, together with valves
selectively controlling the flow of fluid to and from the pedal
simulator which provides for an improved pedal feel during vehicle
braking. The brake system of the invention further includes a
relatively low cost fluid separator unit which is provided which
prevents intermixing of pressurized fluid between the backup source
and the normal source. The fluid separator unit acts to permit the
normal source to act upon the hydraulic brake fluid of the backup
source to operate the vehicle brakes. The fluid separator unit is
preferably embodied as a piston having two working faces, each of
the same diameter.
Inventors: |
Campau; Gregory P. (Plymouth,
MI), Kingston; Andrew W. (Waldesch, DE), Ferger;
Robert L. (Vaihingen an der Enz, DE), Weigert;
Thomas (Sulzbach, DE), Oliveri; Salvatore
(Filsen, DE), Ganzel; Blaise J. (Ann Arbor, MI),
Luckevich; Mark S. (Austin, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Campau; Gregory P.
Kingston; Andrew W.
Ferger; Robert L.
Weigert; Thomas
Oliveri; Salvatore
Ganzel; Blaise J.
Luckevich; Mark S. |
Plymouth
Waldesch
Vaihingen an der Enz
Sulzbach
Filsen
Ann Arbor
Austin |
MI
N/A
N/A
N/A
N/A
MI
TX |
US
DE
DE
DE
DE
US
US |
|
|
Assignee: |
Kelsey-Hayes Company (Livonia,
MI)
|
Family
ID: |
27533531 |
Appl.
No.: |
09/939,509 |
Filed: |
August 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60038043 |
Mar 6, 1997 |
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60032595 |
Dec 2, 1996 |
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60018814 |
May 31, 1996 |
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60013005 |
Mar 7, 1996 |
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Reissue of: |
08813146 |
Mar 7, 1997 |
5941608 |
Aug 24, 1999 |
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Current U.S.
Class: |
303/113.4;
303/115.4; 303/84.2; 303/DIG.3 |
Current CPC
Class: |
B60T
8/3255 (20130101); B60T 13/16 (20130101); B60T
8/4827 (20130101); B60T 13/74 (20130101); B60T
13/686 (20130101); B60T 8/4081 (20130101); B60T
17/221 (20130101); B60T 7/042 (20130101); B60T
8/267 (20130101); Y10S 303/03 (20130101) |
Current International
Class: |
B60T
8/34 (20060101) |
Field of
Search: |
;303/3,10,15,113.4,113.5,122.09,122.11,122.13,155,166,115.1,116.1,116.2 |
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Other References
Abstract of patent document DE3423944 printed from the EPO internet
site
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|
Primary Examiner: Schwartz; Christopher
Attorney, Agent or Firm: MacMillan, Sobanski & Todd,
LLC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
No. 60/038,043 filed Mar. 6, 1997, U.S. Provisional Application No.
60/032,595 filed Dec. 2, 1996, U.S. Provisional Application No.
60/018,814 filed May 31, 1996, and U.S. Provisional Application No.
60/013,005 filed Mar. 7, 1996, the disclosures of which are hereby
incorporated by reference.
Claims
What is claimed is:
1. A brake system comprising: a normal source of pressurized
hydraulic brake fluid; a backup source of pressurized hydraulic
brake fluid; a vehicle brake which is operated by application of
pressurized hydraulic brake fluid thereto; a valve for selectively
preventing the flow of hydraulic brake fluid between the backup
source and said vehicle brake; .Iadd.a fluid conduit in fluid
communication with said backup source; a pedal simulator in fluid
communication with said backup source via said fluid conduit, said
pedal simulator including a spring and a piston acting to compress
said spring under the influence of pressurized hydraulic fluid from
said backup source exceeding a first pressure; .Iaddend.and a fluid
separator unit for maintaining the integrity of said backup source
of pressurized fluid and preventing intermixing of the hydraulic
brake fluid of said normal source and the hydraulic brake fluid of
said backup source and having a movable pressure boundary which
enables, through movement thereof, said normal source of
pressurized hydraulic brake fluid to selectively act upon said
vehicle brake via a portion of said backup source when said valve
is shut.
2. The brake system of claim 1, further including a brake system
brake demand detection arrangement comprising: a manually operated
master cylinder .Iadd.comprising at least a portion of said backup
source.Iaddend.; .[.a.]. .Iadd.said .Iaddend.fluid conduit
.Iadd.being .Iaddend.in fluid communication with said master
cylinder; .[.a pedal simulator in fluid communication with said
master cylinder via said fluid conduit, said pedal simulator
including a spring and a piston acting to compress said spring
under the influence of pressurized hydraulic fluid from said master
cylinder exceeding a first pressure;.]. a pressure transducer
generating a signal representative of the pressure of said fluid
flowing between said master cylinder and said pedal simulator; and
an expansion volume unit in fluid communication with said master
cylinder and said pedal simulator via said fluid conduit, said
expansion volume unit permitting fluid to flow from said master
cylinder into said expansion volume unit when said fluid exceeds a
second pressure less than said first pressure.
3. The brake system of claim 2 wherein said pedal simulator further
includes a housing defining a bore having a first end adapted to be
connected in fluid communication with said backup source, said bore
further having a second end, said piston being slidably disposed in
said bore and having a first face and a second face, said spring
engaging said second face of said piston and acting between said
piston and a portion of said housing to urge said first face of
said piston toward said first end of said bore, and a damping
circuit hydraulically interposed between said first end of said
bore and said backup source to present a first cross sectional flow
area to fluid flowing from said backup source through said damping
circuit into said housing, and presenting a second cross sectional
flow area to fluid flowing from said housing through said damping
circuit, the ratio of said second cross sectional flow area to said
first cross sectional flow area being greater than unity.
4. The brake system of claim 3 wherein said ratio is less than
10:1.
5. The brake system of claim 4 wherein said ratio is in the range
of 2:1 to 4:1.
6. The brake system of claim 3 further including a relief valve
opening above a predetermined pressure to permit fluid flow through
said relief valve from said brake system to said housing.
7. The brake system of claim 6 wherein said predetermined pressure
is in the range of about 5 bar to about 30 bar.
8. The brake system of claim 3 further including a relief valve
opening above a predetermined pressure to permit fluid flow through
said relief valve from said brake system to said housing.
9. The brake system of claim 8 wherein said predetermined pressure
is in the range of about 5 bar to about 30 bar.
10. The brake system of claim 2 wherein said fluid separator unit
has a housing defining a cylinder bore and a piston slideably
disposed therein, said piston having a first working face in fluid
communication with said normal source and a second working face in
fluid communication with said backup source, said first and second
working faces having substantially similar areas.
11. The brake system of claim 2, further including: a brake pedal
for operating said master cylinder; a pedal travel sensor for
generating a stroke signal representative of the stroke of said
brake pedal; said signal from said pressure transducer being
related to the brake application force applied by a driver to said
brake pedal; .Iadd.and .Iaddend. a control unit responsive to a
demand signal for controlling said brake system actuator, said
demand signal being generated as a blended function of both said
stroke signal and said signal from said pressure transducer
wherein, during an initial movement of said brake pedal, said
stroke signal is weighted greater than said signal from said
pressure transducer, and wherein, during a subsequent movement of
said brake pedal, said signal from said pressure transducer is
weighted greater than said stroke signal.
12. The brake system of claim 1 .[.further including a pedal
simulator.]., said pedal simulator comprising: a housing defining a
bore having a first end adapted to be connected in fluid
communication with said backup source, said bore further having a
second end; .[.a.]. .Iadd.said .Iaddend.piston .Iadd.being
.Iaddend.slidably disposed in said bore and having a first face and
a second face; .[.a.]. .Iadd.said .Iaddend.spring engaging said
second face of said piston and acting between said piston and a
portion of said housing to urge said first face of said piston
toward said first end of said bore; and a damping circuit
hydraulically interposed between said first end of said bore and
said backup source to present a first cross sectional flow area to
fluid flowing from said backup source through said damping circuit
into said housing, and presenting a second cross sectional flow
area to fluid flowing from said housing through said damping
circuit, the ratio of said second cross sectional flow area to said
first cross sectional flow area being greater than unity.
13. The brake system of claim 12 wherein said ratio is less than
10:1.
14. The brake system of claim 13 wherein said ratio is in the range
of 2:1 to 4:1.
15. The brake system of claim 12 further including a relief valve
opening above a predetermined pressure to permit fluid flow through
said relief valve from said brake system to said housing.
16. The brake system of claim 15 wherein said predetermined
pressure is in the range of about 5 bar to about 30 bar.
17. The brake system of claim 1 wherein said fluid separator unit
has a housing defining a cylinder bore .[.and a.]..Iadd., said
.Iaddend.piston .Iadd.being .Iaddend.slideably disposed therein,
said piston having a first working face in fluid communication with
said normal source and a second working face in fluid communication
with said backup source, said first and second working faces having
substantially similar areas.
18. A brake system comprising: a brake pedal for operating a brake
system actuator; a pedal travel sensor for generating a stroke
signal representative of the stroke of said brake pedal; a brake
system sensor for generating a force signal representative of the
brake application force applied by a driver to said brake pedal; a
control unit responsive to a demand signal for controlling said
brake system actuator, said demand signal being generated as a
blended function of both said stroke, signal and said force signal
wherein, during a first part of the stroke of said brake pedal,
said stroke signal is weighted greater than said force signal, and
wherein, during a second part of the stoke of said brake pedal,
said force signal is weighted greater than said stroke signal.
19. An electro-hydraulic brake system comprising: a reservoir of
hydraulic brake fluid; a pump having a suction port and a discharge
port, said suction port being connected in fluid communication with
said reservoir; a first fluid conduit being connected in fluid
communication with said discharge port of said pump; a fluid
separator unit having a housing with a bore defined therethrough,
said bore having a first end and a second end, said first end of
said bore being connected in fluid communication with said
discharge port of said pump via said first fluid conduit, said
fluid separator unit further including a piston slidingly disposed
in said bore and a spring disposed to urge said piston toward said
first end of said bore; a second fluid conduit connected in fluid
communication with said second end of said fluid separator unit; a
vehicle brake connected in fluid communication with said second end
of said fluid separator unit via said second fluid conduit; a third
fluid conduit connected in fluid communication with said vehicle
brake; a hydraulic master cylinder connected in fluid communication
with said vehicle brake via said third fluid conduit; an
electrically-operated valve disposed in said third fluid conduit,
said valve preventing the flow of hydraulic brake fluid between
said master cylinder and said vehicle brake when closed, said valve
being open to permit the flow of hydraulic brake fluid between said
master cylinder and said vehicle brake when said valve is
electrically deenergized; a fourth fluid conduit connected in fluid
communication with said master cylinder and said third fluid
conduit; a pedal simulator connected in fluid communication with
said master cylinder via said fourth fluid conduit; an second
electrically-operated valve disposed in said fourth fluid conduit,
said second valve being closed to prevent the flow of hydraulic
brake fluid between said master cylinder and said pedal simulator
when said second valve is deenergized, said second valve permitting
the flow of hydraulic brake fluid between said master cylinder and
said pedal simulator when said second valve is open; and a damping
circuit hydraulically interposed between said master cylinder and
said pedal simulator, said damping circuit comprising, in parallel
flow paths, an orifice and a check valve such that said damping
circuit presents a first cross sectional flow area to fluid flowing
from said master cylinder through said damping circuit into said
pedal simulator, and presenting a second cross sectional flow area,
different from said first cross sectional flow area, to fluid
flowing from said pedal simulator to said master cylinder through
said damping circuit.
20. The electro-hydraulic brake system of claim 19 further
including a third electrically-operated valve disposed in said
first fluid conduit, said third valve preventing fluid
communication between said pump and said fluid separator unit when
said third valve is closed, said third valve permitting fluid
communication between said pump and said fluid separator unit when
said third valve is open, the electro-hydraulic brake system
further including fifth fluid conduit having a first end connected
in fluid communication with said first fluid conduit and said fluid
separator unit and having a second connected in fluid communication
with said reservoir, the electro-hydraulic brake system further
including a fourth electrically-operated valve disposed in said
fifth fluid conduit, said fourth valve preventing fluid
communication between said fluid separator unit and said reservoir
when said fourth valve is closed, said fourth valve permitting
fluid communication between said fluid separator unit and said
reservoir when said fourth valve is open.
.Iadd.21. A hydraulic brake system for a vehicle comprising: wheel
brakes for four wheels, in which the wheels are distributed with a
first and a second wheel brake on a first vehicle axle and a third
and a fourth wheel brake on a second vehicle axle; a normal
hydraulic energy source, having electrically controllable brake
valve devices disposed between said energy source and said wheel
brakes; a brake pedal; a sensor generating a first signal
indicative of the position of said brake pedal; a second sensor
generating a second signal indicative of the force exerted by a
driver on said brake pedal; a master cylinder supplying two brake
circuits, said master cylinder being actuated by said brake pedal
and being intended for carrying out a backup brake operation by
muscle-powered energy via said brake pedal, each brake circuit
being in fluid communication with a respective one of said first
and second wheel brakes; a respective normally open isolation valve
being disposed between said master cylinder and said wheel brakes
in each of said two brake circuits, each of said isolation valves
being switched into a closed position when said wheel brakes are
supplied with fluid from said normal hydraulic energy source; a
respective fluid separator unit being interposed between each of
said first and second wheel brakes of said first vehicle axle and
an associated one of the electrically controllable brake valve
devices, said fluid separator units having movable components
forming a pressure boundary that enables said normal source to
selectively act upon said vehicle brake via a portion of said
backup source, said first and second wheel brakes being connected
to a respective one of said isolation valves associated with said
two brake circuits of said master cylinder; and a control unit for
controlling said normal hydraulic energy source and said isolation
valves, said control unit responding as a blended function of both
said first signal and said second signal, with the contribution of
the second signal relative to the first signal generally varying as
a function of the first signal..Iaddend.
.Iadd.22. The hydraulic brake system of claim 18, further
comprising: wheel brakes for two wheels, in which the wheels are
distributed at each end of a front vehicle axle; a normal source of
pressurized hydraulic brake fluid, having electrically controllable
brake valve devices disposed between said normal source and said
wheel brakes, a master cylinder comprising at least a portion of
said brake system actuator and supplying two brake circuits, said
master cylinder being actuated by said brake pedal and being
intended for carrying out a backup brake operation by
muscle-powered energy via said brake pedal, each of said brake
circuits being in fluid communication with a respective one of said
wheel brakes; and a respective normally open isolation valve being
disposed between said master cylinder and said respective one of
said wheel brakes in each brake circuit, each of said isolation
valves being electrically switched into a closed position when said
wheel brakes are supplied with fluid from said normal source, and
wherein at least the electrically controllable brake valve devices
are controlled by said control unit..Iaddend.
.Iadd.23. The hydraulic brake system of claim 22, said normal
source including a motor driven pump for pumping hydraulic brake
fluid from a reservoir, wherein said electrically controllable
brake valve devices are arranged to block a respective flow path
from said normal source to said wheel brakes and to open a
respective flow path from said wheel brakes to said reservoir when
no braking is being demanded..Iaddend.
.Iadd.24. The hydraulic brake system of claim 22, said normal
source including a motor driven pump for pumping hydraulic brake
fluid from a reservoir, wherein said electrically controllable
brake valve devices are arranged to block a respective flow path
from said normal source to said wheel brakes and to open a
respective flow path from said wheel brakes to said reservoir when
no braking is being demanded..Iaddend.
.Iadd.25. The brake system of claim 18, further comprising: an axle
of a vehicle; a first wheel brake mounted on said axle; a second
wheel brake mounted on said axle; a normal source of pressurized
hydraulic brake fluid adapted to selectively supply hydraulic brake
fluid to said first wheel brake and said second wheel brake; a
backup source of pressurized hydraulic brake fluid comprising a
master cylinder; a first backup fluid conduit extending between
said master cylinder and said first wheel brake to selectively
provide fluid communication between said backup source and said
first wheel brake; and a second backup fluid conduit extending
between said master cylinder and said second wheel brake to
selectively provide fluid communication between said backup source
and said second wheel brake..Iaddend.
.Iadd.26. The hydraulic brake system of claim 25, wherein said
normal source is under the control of said control
unit..Iaddend.
.Iadd.27. The brake system of claim 18, further comprising: wheel
brakes for two wheels, in which the wheels are distributed at each
end of a front vehicle axle; a normal source of pressurized
hydraulic brake fluid, having electrically controllable brake valve
devices disposed between said normal source and said wheel brakes,
said electrically controllable brake valve devices being controlled
by a control unit in response to a braking demand signal; a master
cylinder supplying two brake circuits, said master cylinder being
actuated by said brake pedal and being intended for carrying out a
backup brake operation by muscle-powered energy via said brake
pedal, each of said brake circuits being in fluid communication
with a respective one of said wheel brakes; and a respective
normally open isolation valve being disposed between said master
cylinder and said respective one of said wheel brakes in each brake
circuit, each of said isolation valves being electrically switched
into a closed position when said wheel brakes are supplied with
fluid from said normal source..Iaddend.
.Iadd.28. The hydraulic brake system of claim 27, said normal
source including a motor driven pump for pumping hydraulic brake
fluid from a reservoir, wherein said electrically controllable
brake valve devices are arranged to block a respective flow path
from said normal source to said wheel brakes and to open a
respective flow path from said wheel brakes to said reservoir when
no braking is being demanded..Iaddend.
.Iadd.29. The hydraulic brake system of claim 18, further
comprising: wheel brakes for two wheels, in which the wheels are
distributed at each end of a front vehicle axle; a hydraulic fluid
reservoir; a normal source of pressurized hydraulic brake fluid,
having a motor-driven pump for pumping hydraulic brake fluid from
said reservoir; a master cylinder comprising at least a portion of
said brake system actuator and supplying two brake circuits, said
master cylinder being actuated by said brake pedal and being
intended for carrying out a backup brake operation by
muscle-powered energy via said brake pedal, each of said brake
circuits being in fluid communication with a respective one of said
wheel brakes; and a respective electrically controllable brake
valve device associated with each of said wheel brakes, said
electrically controllable brake valve devices being arranged to
block a respective flow path from said normal source to said wheel
brakes and to open a respective flow path from said wheel brakes to
said reservoir when no braking is being demanded..Iaddend.
.Iadd.30. The brake system of claim 18, further comprising: wheel
brakes for four wheels, in which the wheels are distributed with a
first and second wheel brake on a first vehicle axle and a third
and a fourth wheel brake on a second vehicle axle; a normal
hydraulic energy source, having electrically controllable brake
valve devices disposed between said energy source and said wheel
brakes; said brake system sensor actuated by said brake pedal, for
carrying out brake operations by operation of the electrically
controllable brake valve devices; a master cylinder supplying two
brake circuits, said master cylinder being actuated by said brake
pedal and being intended for carrying out a backup brake operation
by muscle-powered energy via said brake pedal, each brake circuit
being in fluid communication with at least one of said wheel
brakes; a respective normally open isolation valve being disposed
between said master cylinder and said wheel brakes in each of said
two brake circuits, each of said isolation valves being switched
into a closed position when said wheel brakes are supplied with
fluid from said normal hydraulic energy source, and wherein at
least the electrically controllable brake valve devices are
controlled by a control unit; and a respective fluid separator unit
being interposed between each of said first and second wheel brakes
of said first vehicle axle and an associated one of the
electrically controllable brake valve devices, said first and
second wheel brakes being connected to a respective one of said
isolation valves associated with said two brake circuits of said
master cylinder..Iaddend.
.Iadd.31. The brake system of claim 18, further comprising: wheel
brakes for two wheels, in which the wheels are distributed at each
end of a front vehicle axle; a hydraulic fluid reservoir; a normal
source of pressurized hydraulic brake fluid, having a motor-driven
pump for pumping hydraulic brake fluid from said reservoir; a
master cylinder supplying two brake circuits, said master cylinder
being actuated by said brake pedal and being intended for carrying
out a backup brake operation by muscle-powered energy via said
brake pedal, each of said brake circuits being in fluid
communication with a respective one of said wheel brakes; and a
respective electrically controllable brake valve device associated
with each of said wheel brakes, said electrically controllable
brake valve devices being arranged to block a respective flow path
from said normal source to said wheel brakes and to open a
respective flow path from said wheel brakes to said reservoir when
no braking is being demanded..Iaddend.
.Iadd.32. The brake system of claim 1, further comprising: a second
vehicle brake, each of said vehicle brake and said second vehicle
brake comprising respective wheel brakes for two wheels, in which
the wheels are distributed at each end of a front vehicle axle;
electrically controllable brake valve devices disposed between said
normal source and said wheel brakes, said electrically controllable
brake valve devices being controlled by a control unit in response
to a braking demand signal; a brake pedal; said backup source
comprising a master cylinder supplying two brake circuits, said
master cylinder being actuated by said brake pedal and being
intended for carrying out a backup brake operation by
muscle-powered energy via said brake pedal, each of said brake
circuits being in fluid communication with a respective one of said
wheel brakes; and a respective normally open isolation valve being
disposed between said master cylinder and said respective one of
said wheel brakes in each brake circuit, each of said isolation
valves being electrically switched into a closed position when said
wheel brakes are supplied with fluid from said normal source, one
of said normally open isolation valves comprising said valve for
selectively preventing the flow of hydraulic brake fluid between
the backup source and said vehicle brake..Iaddend.
.Iadd.33. The brake system of claim 32, said normal source
including a motor driven pump for pumping hydraulic brake fluid
from a reservoir, wherein said electrically controllable brake
valve devices are arranged to block a respective flow path from
said normal source to said wheel brakes and to open a respective
flow path from said wheel brakes to said reservoir when no braking
is being demanded..Iaddend.
.Iadd.34. The brake system of claim 1, further comprising: a second
vehicle brake, said vehicle brake and said second vehicle brake
being mounted on an axle of a vehicle, said normal source of
pressurized hydraulic brake fluid adapted to selectively supply
hydraulic brake fluid to said vehicle brake and said second vehicle
brake, said backup source of pressurized hydraulic brake fluid
comprising a master cylinder; a first backup fluid conduit
extending between said master cylinder and said first vehicle brake
to selectively provide fluid communication between said backup
source and said first vehicle brake; and a second backup fluid
conduit extending between said master cylinder and said second
vehicle brake to selectively provide fluid communication between
said backup source and said second vehicle brake..Iaddend.
.Iadd.35. The brake system of claim 1, further comprising: a second
vehicle brake, said vehicle brake and said second vehicle brake
distributed on a first vehicle axle; a third and a fourth vehicle
brake on a second vehicle axle; electrically controllable brake
valve devices disposed between said normal source of pressurized
hydraulic brake fluid and said vehicle brakes; a brake pedal; a
first brake system sensor that is actuated by said brake pedal, for
carrying out brake operations by operation of the electrically
controllable brake valve devices; a master cylinder supplying two
brake circuits, said master cylinder being actuated by said brake
pedal and being intended for carrying out a backup brake operation
by muscle-powered energy via said brake pedal, each brake circuit
being in fluid communication with at least one of said vehicle
brakes; a respective normally open isolation valve being disposed
between said master cylinder and said vehicle brakes in each of
said two brake circuits, each of said isolation valves being
switched into a closed position when said vehicle brakes are
supplied with fluid from said normal hydraulic energy source, and
wherein at least the electrically controllable brake valve devices
are controlled by a control unit; and a respective one of said
fluid separator unit and a second fluid separator unit being
interposed between each of said first and second vehicle brakes of
said first vehicle axle and an associated one of the electrically
controllable brake valve devices, said first and second vehicle
brakes being connected to a respective one of said isolation valves
associated with said two brake circuits of said master
cylinder..Iaddend.
.Iadd.36. The brake system of claim 1, further comprising: a second
vehicle brake, each of said vehicle brake and said second vehicle
brake comprising respective wheel brakes for two wheels, in which
the wheels are distributed at each end of a front vehicle axle; a
hydraulic fluid reservoir; said normal source of pressurized
hydraulic brake fluid having a motor-driven pump for pumping
hydraulic brake fluid from said reservoir; a brake pedal; said
backup source of pressurized hydraulic fluid comprising a master
cylinder supplying two brake circuits, said master cylinder being
actuated by said brake pedal and being intended for carrying out a
backup brake operation by muscle-powered energy via said brake
pedal, each of said brake circuits being in fluid communication
with a respective one of said wheel brakes; and a respective
electrically controllable brake valve device associated with each
of said wheel brakes, said electrically controllable brake valve
devices being arranged to block a respective flow path from said
normal source to said wheel brakes and to open a respective flow
path from said wheel brakes to said reservoir when no braking is
being demanded..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates in general to brake systems for ground
vehicles, and in particular to electro-hydraulic brake systems with
normal braking pressure supplied by an electrically driven
pump.
Electro-hydraulic braking systems with manually powered backup
systems have been shown in some publications. For example, German
Patent Application DE 4413579A1 illustrates a system having a
manually powered master cylinder connected through isolation valves
to brakes at a vehicle's wheels. When the isolation valves are
shut, pressurized brake fluid from the master cylinder is delivered
to a pedal simulator. Pressure transducers are used to develop a
signal representative of a desired braking effort, which is fed to
an electronic control unit. The electronic control unit controls
the operation of motor operated braking pressure generators (pumps)
to correspondingly deliver pressurized hydraulic brake fluid to the
vehicle brakes.
SUMMARY OF THE INVENTION
While certain general principles of electro-hydraulic braking are
known, the known equipment has been relatively expensive, and has
had relatively poor functionality in such important areas as "pedal
feel", the tactile feedback a driver feels when operating the brake
pedal of such a brake system.
This invention relates to an improved electro-hydraulic brake
system having features for improving the pedal feel of the system,
while further having design features which contribute to an economy
of manufacture of certain components of the system. The system
provides for an electrically powered normal source of pressurized
hydraulic brake fluid, and a manually powered backup source of
pressurized hydraulic brake fluid to the vehicle brakes in the
event of failure of the normal source. During normal braking, fluid
from the backup source is redirected from the vehicle brakes to a
pedal simulator. The pedal simulator preferably includes
arrangements of spring loaded pistons, expansion volumes, and
damping orifices, together with valves selectively controlling the
flow of fluid to and from the pedal simulator which provide for an
improved pedal feel during vehicle braking. The brake system of the
invention further includes a relatively low cost fluid separator
unit which is provided to prevent intermixing of pressurized fluid
between the backup source and the normal source. The fluid
separator unit acts to permit the normal source to act upon the
hydraulic brake fluid of the backup source to operate the vehicle
brakes. The fluid separator unit is preferably embodied as a piston
having two working faces, each of the same diameter.
Various objects and advantages of this invention will become
apparent to those skilled in the art from the following detailed
description of the preferred embodiment, when read in light of the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a first embodiment of a vehicle brake
system.
FIG. 2 is partial schematic view of the brake system of FIG. 1.
FIG. 3 is a graph of Pedal Force vs. Pedal Travel for an
electro-hydraulic brake system having an expansion volume unit and
for an electro-hydraulic brake system not having an expansion
volume unit.
FIG. 4 is a schematic view of a second embodiment of a vehicle
brake system
FIG. 5 is a schematic view of a third embodiment of a vehicle brake
system.
FIG. 6 is a sectional view of specific embodiments for a master
cylinder and a pedal simulator which can be used for the brake
systems of the present invention.
FIG. 7 is an enlarged cross-sectional view of a fluid separator
piston which may be used in the fluid separator units of FIG.
1.
FIG. 8 is an end elevational view of a piston which may be used in
the fluid separator units of FIG. 1, showing a groove formed in the
working face thereof.
FIG. 9 is a view taken along the line 9-9 of FIG. 8.
FIG. 10 is a schematic view of a vehicle brake system having an
electro-hydraulic normal source and a backup source of pressurized
hydraulic brake fluid for the front brakes and individual power
cylinder for supplying pressurized hydraulic brake fluid to a
respective rear wheel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There is shown in FIG. 1, a first embodiment of a vehicle brake
system, indicated generally at 2, in accordance with the invention.
The brake system 2 may suitably be used on a ground vehicle such as
an automotive vehicle having four wheels and a brake for each
wheel. The brake system 2 includes a normal source of pressurized
hydraulic brake fluid, indicated at 4, and a backup source of
pressurized hydraulic brake fluid, indicated at 6. The normal
source 4 includes an electronic control module 10. The control
module 10, as will be discussed below, receives various signals,
processes these signals, and controls the operation of various
components of the brake system 2 based on these signals. In this
manner, the control module 10 causes the normal source 4 to
cooperate with a portion of the hydraulic circuitry of the backup
source 6 to provide hydraulic brake fluid at electronically
controlled pressures to four vehicle brakes 11a, b, c, and d. The
vehicle brakes 11a, b, c, and d each include a respective brake
actuation member (such as a slave cylinder) and friction member
actuatable by the actuation member for engaging a rotatable braking
surface of the vehicle wheel.
The backup source 6 provides for manual backup braking for,
preferably, two of the vehicle brakes 11a and 11b, as will be
discussed in detail below. Generally, since the forward or front
brakes of a vehicle provide most of the braking resistance in an
automotive vehicle in the majority of braking situations, it is
envisioned that the front brakes will be connected to the backup
supply of pressurized hydraulic brake fluid. However, this
invention could be easily adapted to function with any combination
of brakes, and is not limited to the configuration shown.
The source of pressurized hydraulic brake fluid for the backup
source 6 is a manually operated master cylinder 12. The master
cylinder 12 is operated by a brake pedal 14 to supply pressurized
hydraulic brake fluid to a first manual backup brake circuit via a
conduit 16 and a second manual backup brake circuit via a conduit
17. As shown, the master cylinder 12 is preferably a tandem master
cylinder, having two service pistons, but the master cylinder 12
may be of any suitable design, such as a single piston or triple
piston design. The brake pedal 14 may be provided with a brake
pedal detector 18 to detect the movement of the brake pedal 14. The
brake pedal detector 18 may be a switch which actuates the brake
lights (not shown), or acts as an input to a control module 10 to
indicate that the brake pedal 14 is depressed. The brake pedal 14
is also preferably coupled to a displacement transducer 19
producing a signal indicative of how far the brake pedal 14 is
depressed, which is indicative of brake demand by the operator,
which signal can be an input to the control module 10. As is
common, a reservoir 20 is provided which communicates with the
first and second brake circuits through the master cylinder 12 in
the ordinary manner. The reservoir 20 may be a single, dual or
triple chamber design, as appropriate, and indeed may have any
suitable number of chambers.
The conduit 16 is connected via a first electrically operated
isolation valve 22a with a first hydraulically operated vehicle
brake 11a. The conduit 17 is connected via a second electrically
operated isolation valve 22b with a second hydraulically operated
vehicle brake 11b. When an isolation valve 22a or 22b is
electrically de-energized, the valve is open, as shown in FIG. 1,
allowing pressurized brake fluid from the master cylinder 12 to be
applied to the associated vehicle brake 11a or 11b to brake the
vehicle. In normal operation, the isolation valves 22a and 22b are
deenergized open when no braking is occurring. The isolation valves
22a and 22b are energized shut during vehicle braking, isolating
the master cylinder 12 from the vehicle brakes 11a and 11b. In this
condition, the pressurized brake fluid developed in the master
cylinder 12 is routed instead to a pedal simulator 26 via a conduit
27. Located in the conduit 27 is a simulator valve 28 for
selectively allowing the passage of fluid flowing into and out of
the pedal simulator 26. When the isolation valves 22a and 22b are
energized shut, the simulator valve 28 is energized open. When the
isolation valves 22a and 22b are deenergized open, the simulator
valve 28 is deenergized shut. The isolation valves 22a and 22b and
the simulator valve 28 may be pulse width modulated to
electronically command the operation of the valves.
As shown in detail in FIG. 6, the pedal simulator 26 includes a
housing 26a having a bore 26b. A piston 26c is slideably disposed
within the bore 26b. The piston 26c is coupled to a cupped flanged
member 26d. Rightward movement of the piston 26c from the position
illustrated in FIG. 6 compresses a conical spring 26e against a
plate 26f. The pedal simulator 26 also includes an adjustable stop
member 26g threaded into the plate 26f which restricts the travel
of the piston 26c and the flanged member 26d. The plate 26f is held
in place against the force of the spring 26e by a snap ring 26h
engaging a groove formed in the housing 26a. An elongate member 26i
couples the piston 26c and the cupped flanged member 26d to keep
the piston 26c and the cupped flanged member 26d in alignment and
to transfer forces therebetween.
The pedal simulator 26 is connected to the conduit 16 so that when
the brake pedal 14 is depressed, pressurized brake fluid from the
master cylinder 12 is directed through the conduit 16 to the pedal
simulator 26 to drive the piston 26c to compress the spring 26e. As
the spring 26e compresses, the spring 26e exerts increased
resistance to further movement of the piston 26c. As will be
explained in detail below, the spring 26e preferably has a
progressive rate, resulting in a greater resistance to further
movement, per unit of displacement of the brake pedal 14, when the
brake pedal 14 is near the end of the pedal stroke than when the
brake pedal 14 is first depressed. In this manner, the pedal
simulator 26 can mimic the progressively greater incremental
resistance to pedal movement felt in conventional braking systems.
One way of causing the spring 26e to have a progressive spring rate
is to form the spring 26e as a conical helical spring with a
varying pitch, that is, with each wrap of the spring 26e being
inclined differently relative to a plane (not shown) defined
perpendicular to a central axis 26j of the spring 26e.
As the spring 26e of the pedal simulator 26 exerts greater
resistance, pressure in the conduit 16 is increased due to the
resistance to further movement by the spring loaded piston 26c.
This resistance to movement is fed back to the pedal 14 through the
increased pressure of the conduit 16 reacting in the master
cylinder 12, so that the operator of the brake pedal feels an
increasing resistance as the brake pedal 14 is depressed, similar
to the resistance felt when the master cylinder 12 is hydraulically
coupled to the vehicle brakes 11a and 11b. The pressure in the
conduit 17 will rise along with the pressure in the conduit 16 in
the ordinary manner For example, if the master cylinder 12 is a
tandem axial master cylinder, increased pressure in the primary
chamber (not shown) of the master cylinder 12 and the conduit 16 is
fed to the secondary chamber (not shown) of the master cylinder 12
and the conduit 17 by movement of the master cylinder secondary
piston (not shown).
While the pedal simulator 26 preferably is embodied as the piston
26c acting against a single metal coil spring 26e, as shown in
FIGS. 1 and 6, other designs of pedal simulators are contemplated
for use as part of the invention. For example, the pressurized
hydraulic brake fluid in the pedal simulator 26 may act against any
suitable spring arrangement such as a plurality of coiled springs
arranged to act in series or parallel to each other, and may
suitably interact to deliver the desired progressive spring rate.
Furthermore, the spring of the pedal simulator 26 may be made of
any suitable material. For example, the spring may be an
elastomeric spring
The piston 26c of the pedal simulator 26 may be replaced by a
diaphragm acting against a spring, or some other flexible or
movable fluid separator. As a further example, the pedal simulator
26 could include a piston, diaphragm, or bladder as a fluid
separator, a first side of which is acted upon by the pressurized
brake fluid from the master cylinder 12, and a second side of which
is acted upon by a fluid, the pressure of which may increase
naturally as the pressure in the brake circuits increase (such as a
fixed volume of gas), or which may be selectively controlled. It is
specifically contemplated that the pressure of the fluid on the
second side of such a fluid separator in the pedal simulator 26
could be controlled to selectively adjust the damping and spring
rate characteristics of the pedal simulator 26. Such pressure
control could be achieved by any desired means, such as pressure
feedback, electronic control of suitable pumps or valves or other
mechanical actuators, or actuators achieving displacement
principally due to a material therein undergoing a phase
change.
It is also contemplated that such a fluid separator in the pedal
simulator 26 could be acted on directly by a selectively operated
mechanical actuator By controlling the spring rate and damping
characteristics of the pedal simulator 26, the pedal feel
experienced by the operator of the vehicle can be controlled when
the brake pedal 14 is depressed and released. In yet another design
variation, the pedal simulator 26 could be embodied as a chamber in
which is situated an amount of a suitable material, such as a block
of an elastomeric material, having a desired set of physical
characteristics. The material is elastically compressed as the
pressure of the brake fluid in the pedal simulator 26 increases.
The material could contain internal chambers filled with a gas.
The brake system 2 preferably includes an optional dampening
circuit, shown schematically as block 29 in FIG. 1, and an optional
expansion volume unit, shown schematically as block 31 in FIG. 1.
As will be discussed in detail below, the dampening circuit 29 and
the expansion volume unit 31 cooperate with the pedal simulator 26
to provide for improved brake pedal feel, which as indicated above,
is the response characteristic experienced by the operator of the
vehicle while operating the brake pedal 14.
The pressure in the conduit 16 between the master cylinder 12 and
the isolation valve 22a is monitored by a pressure transducer 30
which supplies a signal representative of the sensed pressure to
the control module 10 as a brake demand signal. Note that the
signal from the brake pedal displacement transducer 19 may be used
instead of the pressure signal from the pressure transducer 30 as
the brake demand signal, or may be used as a backup or check signal
to verify proper operation of the pressure transducer 30. If
desired, the pressure in the conduit 17 can also be monitored by a
pressure transducer (not shown).
Preferably, however, the displacement signal from the pedal
transducer 19 and the pressure signal from the pressure transducer
30 are blended together in a suitable fashion to create a system
brake demand signal. For example, during the first portion of pedal
travel, pressure measured by the pressure transducer 30 does not
increase greatly compared to the amount of pedal travel. It may be
difficult to accurately determine the desired braking demand from
the pressure signal produced by the pressure transducer 30, as the
increase in the pressure signal may be difficult to differentiate
from normal electronic background "noise". Thus, in the first part
of pedal travel, the signal from the pedal transducer 19 can be a
better indicator of desired braking, and can be given increased
weight in determining the brake demand signal. However, in the
latter part of the pedal stroke, the pressure monitored by the
pressure transducer 30 can change significantly with only a small
change in position of the brake pedal 14, and thus a relatively
small change in the brake pedal signal produced by the pedal
transducer 19. Thus, in this region, the signal from the pressure
transducer 30 may be a more accurate determinator of the desired
braking, and thus given greater weight in determining the brake
demand signal. In an intermediate portion of the pedal stroke, the
signal from the pressure transducer 30 and the signal from the
pedal transducer 19 can be given equal weight in determining the
brake demand signal.
The pressure signal from the pressure transducer 30 is proportional
to the force exerted by the driver on the pedal 14. Instead of
using a pressure transducer to measure pressure resulting from the
force exerted by the driver on the brake pedal 14, it is
contemplated that a direct measurement of the force upon the brake
pedal may be obtained by use of a strain gauge suitably positioned
in the linkage extending from the brake pedal 14 to the pistons of
the master cylinder 12. This measure may be used in developing a
brake demand signal instead of the signal from the pressure
transducer 30.
One preferred embodiment of an algorithm for a brake demand signal
develops a signal P.sub.BBW, which represents the pressure at which
the normal source 4 is being commanded by the driver to deliver
hydraulic fluid pressure to the brakes 11a, b, c, and d. This
signal may be overridden by such automatic controls as collision
avoidance signals or antilock braking control signals. P.sub.BBW is
developed from a travel command component,
P.sub.CMD.sub.--.sub.TRAVEL, and a force command component,
P.sub.CMD.sub.--.sub.FORCE. The force command component
P.sub.CMD.sub.--.sub.FORCE is developed from the pressure signal
from the pressure transducer 30 (or a force sensor, as discussed
above). P.sub.CMD.sub.--.sub.TRAVEL and P.sub.CMD.sub.--.sub.FORCE
are conditioned for backlash (hysterisis) and subjected to limits
prior to being input to develop P.sub.BBW.
P.sub.CMD.sub.--.sub.Travel has both proportional and squared
functions, as indicated by the following equation:
P.sub.CMD.sub.--.sub.TRAVEL=P.sub.T.times.k.sub.1+P.sup.2.sub.T.times.k.s-
ub.2 (1)
where P.sub.T is the conditioned signal from the displacement
transducer 19, and k.sub.1 and k.sub.2 are gain factors constants
which may be suitably adjusted to further condition
P.sub.CMD.sub.--.sub.TRAVEL. P.sub.CMD.sub.--.sub.FORCE also has
both proportional and squared functions, as indicated by the
following equation:
P.sub.CMD.sub.--.sub.FORCE=P.sub.F.times.k.sub.3+P.sup.2.sub.F.times.k.su-
b.4 (2)
where P.sub.F is the conditioned signal from the pressure
transducer 30, and k.sub.3 and k.sub.4 are gain factors constants
which may be suitably adjusted to further condition
P.sub.CMD.sub.--.sub.FORCE.
P.sub.CMD.sub.--.sub.FORCE and P.sub.CMD.sub.--.sub.TRAVEL as
developed in equations 1 and 2 above are blended to develop
P.sub.BBW according to the following two equations (3 and 4):
W.sub.BLEND=P.sub.F.times.k.sub.BLEND-P.sub.BLEND.sub.--.sub.OFFSET|.sup.-
high.sub.lowlimit (3)
P.sub.BBW=P.sub.CMD.sub.--.sub.TRAVEL.times.(1-W.sub.BLEND)+P.sub.CMD.sub-
.--.sub.FORCE.times.W.sub.BLEND (4)
With this system, one measures the drivers intent through pedal
travel and force "electrically". These signals are electrically
blended to provide a desired command to the normal source 4. The
output is applied through a resolution circuit (not shown) which
sets a limitation on the signal to control the minimum step of
change to limit hunting and noise. The signal is further
conditioned in a slew circuit to limit the rate of commanded
pressure apply. The signal is further subjected to limits in terms
of the maximum pressure which can be commanded. If pedal travel and
force are both at minimum, a default negative pressure command
signal is preferably switched in to force P.sub.BBW to a negative
valve. This insures that the pressure control valve of the normal
source 4 (discussed in detail below) smoothly transitions to a zero
pressure out condition during a pressure reduction cycle before the
spool of the pressure control valve is "parked", and avoiding
"hunting" or "simmering" of the control valve due to noise in the
circuitry when there is no actual demand signal.
As the operator of the vehicle depresses the brake pedal 14, the
master cylinder 12 is actuated, thereby causing an increase in
pressure within the conduits 16 and 17. The increase pressure
within the conduit 16 compresses the spring of the pedal simulator
26, and the pressure in the conduit 16 is sensed by the pressure
transducer 30. The pedal simulator 26 is provided so that the
operator of the vehicle experiences a consistent pedal feel,
whether or not the isolation valves 22a and 22b are closed. It is
also contemplated that the simulator valve 28 may be omitted. If
the simulator valve 28 is omitted, the master cylinder 12 should
pressurize a sufficient volume of brake fluid to supply both the
pedal simulator 26 and actuate the vehicle brakes 11a and 11b with
adequate pressure in the event of a failure of the normal source
4.
The pressure in the conduits 16 and 17 between each isolation valve
22a and 22b, and the respective vehicle brake 11a and 11b, is
sensed by respective pressure transducers 36a and 36b, which supply
signals representative of the respective sensed pressures to the
control module 10. The control module 10 utilizes the pressure
signals produced by the pressure transducers 36a and 36b for
purposes which will be described below. As also will be further
described below, the control module 10 controls the operation of
the simulator valve 28 and the isolation valves 22a and 22b.
As indicated above, the isolation valves 22a and 22b are energized
and shut during normal operation of the brake system 2. Only in an
abnormal situation, such as a loss of electrical power, will the
isolation valves 22a and 22b remain open after the driver initiates
a brake demand signal by depressing the brake pedal 14. In such a
situation, the master cylinder 12 acts to supply pressurized
hydraulic brake fluid to the vehicle brakes 11a and 11b through the
open isolation valves 22a and 22b. However, absent some type of
failure, it is intended that the normal source 4 should supply
pressurized hydraulic brake fluid for actuating the vehicle brakes
11a, b, c, and d.
The normal source 4 includes a pump 42 which is capable of pumping
hydraulic brake fluid from the reservoir 20 to actuate the vehicle
brakes 11a, b, c, and d. The pump 42 is preferably electrically
driven by a motor 43 under the control of the control module 10.
However, the pump 42 may be driven by any suitable means, with the
output of the pump 42 being controlled by the control module 10.
The normal source 4 is provided with over-pressure protection by a
relief valve 44 which opens when a preset pressure is exceeded to
direct pressurized brake fluid from the discharge of the pump 42
back to the reservoir 20.
Pressurized hydraulic brake fluid from the pump 42 is supplied to a
high pressure accumulator 46 through a check valve 47. The check
valve 47 allows brake fluid to flow from the discharge of the pump
42 and restricts brake fluid from flowing into the pump 42 through
the discharge port. The accumulator 46 is conventional, including a
piston movable with a sliding seal within the cylinder of the
accumulator 46, and a pre-charge of nitrogen acting as a spring
element. Other suitable spring elements which are contemplated
include a compressible volume of any other suitable gas, a metallic
or elastomeric spring, or other spring arrangement. The pre-charge
of nitrogen contained in the accumulator 46 biases the piston
toward the fluid connection of the accumulator 46. Of course, any
suitable accumulator design may be used, and the accumulator 46
need not be of the piston design depicted. For example, the
accumulator 46 may be of the diaphragm type, with a diaphragm or
bellows made of metal, rubber, or plastic or other elastomer.
As pressurized hydraulic brake fluid flows into the accumulator 46
through the fluid connection, the piston of the accumulator 46 is
moved to further compress the nitrogen gas precharge. In this
condition, the accumulator 46 contains a reservoir of hydraulic
brake fluid which is pressurized by the piston under the influence
of the compressed nitrogen gas, which may be used to actuate the
vehicle brakes 11a, b, c, and d whether or not the pump 42 is
running. The pressure of the hydraulic brake fluid in the
accumulator 46 is sensed by a pressure transducer 49, which
supplies a corresponding signal to the control module 10.
The normal source 4 also includes a pressure isolation valve 48.
The pressure isolation valve 48 is controlled by the control module
10 to move between a de-energized position, shown in FIG. 1, in
which pressurized brake fluid in the accumulator 46 is prevented
from discharging from the accumulator 46, and an energized position
in which pressurized brake fluid can flow out of the accumulator
46. The pressure isolation valve 48 will normally be deenergized
closed to prevent discharge of the accumulator 46 due to system
leakage past various other system valves. Note that the high
pressure relief valve 44 and the check valve 47 cooperate with the
pressure isolation valve 48 to prevent the fluid within the
accumulator 46 from discharging when the pressure isolation valve
48 is shut. When braking is required, the pressure isolation valve
48 is energized open to allow the pressurized hydraulic brake fluid
in the accumulator 46 to be used to apply the vehicle brakes 11a,
b, c, and d. The location of the pressure isolation valve 48 in the
brake system 2 provides for over-pressure protection for the
accumulator 46 by the relief valve 44.
Through the pressure isolation valve 48, the outlet of the pump 42
and the accumulator 46 are in fluid communication with a fluid
conduit 50. The fluid conduit 50 is in fluid communication with
proportional control valves 51a, b, c, and d. A filter 52 is
preferably provided in the fluid conduit 50 between the sources of
pressurized hydraulic brake fluid (the pump 42 and the accumulator
46) and the proportional control valves 51a, b, c, and d to remove
contaminating particles from the hydraulic brake fluid supplied to
the proportional control valves 51a, b, c, and d.
The illustrated proportional control valve 51 a has a port which is
in fluid communication with a fluid separator unit 54a. The
proportional control valve 51b has a port which is in fluid
communication with a fluid separator unit 54b. The fluid separator
unit 54b is similar in structure and function to the fluid
separator unit 54a. As shown in more detail in FIG. 7, the fluid
separator unit 54a includes a housing 55 with a cylindrical bore
55a therethrough. A first end 55b of the bore 55a is in fluid
communication with the proportional control valve 51a. A second end
55c of the bore 55a is in fluid communication with the vehicle
brake 11a.
A fluid separator piston 56 is slideably disposed within the
cylindrical bore 55a between the first end 55b and the second end
55c of the bore 55a. The piston 56 is generally cylindrical, having
a first piston face 56a in fluid communication with the normal
source 4 via the first end 55b of the bore 55a and a second piston
face 56b in fluid communication with the backup source 6 via the
second end 55c of the bore 55a. The piston 56 is preferably formed
with a pair of axially spaced apart, circumferentially extending
grooves 56c and 56d. The groove 56c is formed near the first piston
face 56a, while the groove 56d is formed near the second piston
face 56b. The piston 56 is further formed with a reduced diameter
projection 56e extending axially from the second piston face 56b.
Preferably the piston 56 is also formed with a raised boss 56f on
the first piston face 56a. The boss 56f assists in preventing a
hydraulic lock between the piston 56 and the adjacent end wall of
the bore 55a when the piston 56 is in the unactuated position shown
in FIG. 7
A first seal 57a, which is preferably a lip seal, is disposed in
the first groove 56c formed in the piston 56 and oriented to
slidingly seal between the piston 56 and the wall of the bore 55a
against pressurized hydraulic brake fluid from the normal source 4
supplied to the first end 55b of the bore 55. The first seal 57a
and the piston face 56a cooperate to define a first working face of
the piston 56.
Similarly, a second seal 57b, which is also preferably a lip seal,
is disposed in the second groove 56d formed in the piston 56. The
second seal 57b is oriented to slidingly seal between the piston 56
and the wall of the bore 55a against pressurized hydraulic brake
fluid from the backup source 6 at the second end 55c of the bore
55. The second seal 57b and the piston face 56b, including the
extension 56e, cooperate to define a second working face of the
piston 56.
It will be appreciated from FIG. 7 that the diameter of the piston
56 is the same in the region of the seal 57a as it is in the region
of the seal 57b. Thus, the cross-sectional area of the first
working face of the piston 56 (the area acted upon by the adjacent
volume of hydraulic brake fluid) is the same as the cross-sectional
area of the second working face of the piston 56. Furthermore, the
bore 55a is of constant diameter. These features .[.of the
invention.]. are believed to simplify construction of the fluid
separator unit 54a and reduce costs compared to a possible
alternate construction having a stepped bore and stepped piston
sliding therein. In the fluid separator unit 54a, pressurized fluid
from the .[.backup source 6.]. .Iadd.normal source 4
.Iaddend.actuates the piston 56 of the fluid separator unit 54a to
pressurize the trapped hydraulic brake fluid between the isolation
valve 22a and the wheel brake 11a to substantially the same
pressure as the pressure at which the hydraulic brake fluid is
supplied to the fluid separator unit 54a from the .[.backup source
6.]. .Iadd.normal source 4.Iaddend.. Any differences due to the
compression of the spring 58 of the fluid separator unit 54a and
friction are generally negligible fractions of the pressures of the
hydraulic brake fluid acting in the fluid separator unit 54a during
braking.
The fluid separator unit 54a permits pressure in the hydraulic
brake fluid on one side of the piston 56 (acting on one of the
first and second working faces of the piston 56) to be transferred
to the hydraulic brake fluid on the other side of the fluid
separator piston 56 (acting on the other of the first and second
working faces of the piston 56) through movement of the fluid
separator piston 56 within the bore 55a. The fluid separator unit
54a is sealed to the wall of the bore 55a by the seals 57a and 57b
to prevent intermixing of the hydraulic brake fluids on either side
of the piston 56. As will become apparent, a primary purpose of the
fluid separator unit 54a (and of the fluid separator unit 54b) is
to maintain the integrity and operability of the backup source 6 of
hydraulic brake fluid even in the event of a malfunction or rupture
of the normal source 4.
A spring 58 is provided which biases the fluid separator piston 56
toward the unactuated position of the piston 56, at the first end
55b of the bore 55a of the fluid separator unit 54a. The fluid
separator piston 56 is constrained to remain in the bore 55a, and
thus a complete loss of hydraulic brake fluid and pressure on one
side of the fluid separator piston 56 of the fluid separator unit
54a will not result in loss of fluid or complete loss of pressure
on the other side of the fluid separator piston 56. As pressurized
hydraulic brake fluid flows into the fluid separator unit 54a from
the proportional control valve 51a, the fluid separator piston 56
is moved to an actuated position, compressing the spring 58. The
piston 56 acts on the hydraulic brake fluid in the second end 55c
of the bore 55, thereby pressurizing the hydraulic brake fluid
trapped between the energized isolation valve 22a and the vehicle
brake 11a and causing the vehicle brake 11a to be applied. The
normal source 4 also includes a fluid separator unit 54b connected
(in an arrangement similar to that of the fluid separator unit 54a,
the control valve 51 a and the brake 11a) between the control
.[.valves.]. .Iadd.valve .Iaddend.51b and the vehicle brake 11b.
The fluid separator unit 54b is similar in construction and
operation to the fluid separator unit 54a.
FIGS. 8 and 9 illustrate a piston 59 which is an alternate
embodiment of a piston which can be used in the fluid separator
units 54a and 54b in lieu of the piston 56. As shown therein, the
piston 59 is a generally cup-shaped cylindrical piston, having a
first piston face 59a in fluid communication with the normal source
4 via the first end 55b of the bore 55a and a second piston face
59b in fluid communication with the backup source 6 via the second
end 55c of the bore 55a. The piston 59 is preferably formed with a
pair of axially spaced apart, circumferentially extending grooves
59c and 59d. The groove 59c is formed near the first piston face
59a, while the groove 59d is formed near the second piston face
59b. The piston 59 is further formed with a recess 59e extending
axially into the piston 59 from the second piston face 59b.
If .[.desire.]. .Iadd.desired.Iaddend., a groove 59f may be defined
in the first piston face 59a of the piston 59. The groove 59f, like
the boss 56f, assists in preventing hydraulic locking of the piston
59 at the unactuated position thereof. The groove 59f may be formed
to extend only partially across the first face 59a of the piston
59, and still be effective in preventing hydraulic locking of the
piston 59.
A first seal (not shown), which is preferably an o-ring, is
disposed in the first groove 59c formed in the piston 59. The first
seal slidingly seals between the piston 59 and the wall of the bore
55a, scaling against pressurized hydraulic brake fluid from the
normal source 4 supplied to the first end 55b of the bore 55. The
first seal and the piston face 59a cooperate to define a first
working face of the piston 59.
Similarly, a second seal (not shown), which is also preferably an
o-ring, is disposed in the second groove .[.56d.]. .Iadd.59d
.Iaddend.formed in the piston .[.56.]. .Iadd.59.Iaddend.. The
second seal slidingly seals between the piston 56 and the wall of
the bore 55a, sealing against pressurized hydraulic brake fluid
from the backup source 6 at the second end 55c of the bore 55. The
second seal and the piston face .[.56b.]. .Iadd.59b.Iaddend.,
including the recess .[.56e.]. .Iadd.59e.Iaddend., cooperate to
define a second working face of the piston .[.56.].
.Iadd.59..Iaddend.
A spring 60 is disposed partially in the recess 59e and acts
between the piston 59 and the end wall at the second end of the
bore 55a to urge the piston 59 to a retracted position thereof at
the first end 55b of the bore 55a. In operation, the piston 59 acts
similarly to the piston 56.
Each of the proportional control valves 51a, b, c, and d are
electrically positioned by the control module 10. In a first
energized position, the apply position, the proportional control
valve 51a or b directs the pressurized hydraulic brake fluid
supplied to the proportional control valve 51 a or 51b from the
fluid conduit 50 to the associated fluid separator unit 54a or 54b.
In a second energized position, the maintain position, the
proportional control valve 51a or 51b closes off the port thereof
which is in communication with the associated fluid separator unit
54a or 54b, thereby hydraulically locking the associated fluid
separator piston of the fluid separator unit 54a or 54b in a
selected position. In a de-energized position, the release
position, the spool of the proportional control valve 51a or 51b is
moved by a spring to the position illustrated in FIG. 1, where the
proportional control valve 51a or 51b provides fluid communication
between the associated fluid separator unit 54a or 54b and the
reservoir 20. This vents pressure from the associated fluid
separator unit 54a or 54b, allowing the piston 56 thereof to move
back to the unactuated position thereof under the urging of the
associated spring 58, thereby reducing pressure at the associated
vehicle brake 11a or 11b. The proportional control valves 51c and
51d generally operate in the same manner as the proportional
control valves 51a and 51b, except that there is not a fluid
separator unit positioned between the proportional control valves
51c and 51d and the respective vehicle brakes 11c and 11d since the
backup source 6 does not supply the vehicle brakes 11c and 11d. The
pressures in the conduits between each proportional control valve
51c and 51d, and the respective vehicle brake 11c and 11d, is
sensed by respective pressure transducers 36c and 36d, which supply
signals representative of the respective sensed pressures to the
control module 10.
Preferably, the positions of the proportional control valves 51a,
b, c, and d are controlled so that the controlled pressures are
proportional to the current of the energizing electrical signal.
The controlled pressure for the proportional control valves 51a or
51b is the fluid pressure in the fluid conduit between the
respective proportional control valve 51a or 51b and the associated
fluid separator unit 54a or 54b. The controlled pressure for the
proportional control valves 51c or 51d is the fluid pressure in the
fluid conduit between the respective proportional control valve 51c
or 51d and the associated vehicle brake 11c or 11d. A respective
pressure feedback conduit 61a, b, c, or d is provided to the
associated proportional control valve 51a, b, c, or d, so that
controlled pressure opposes the movement caused in the proportional
control valve 51a, b, c, or d caused by increasing energization of
the solenoid thereof.
It may be desirable, however, to control the position of the
proportional control valves 51a, b, c, and d, such that the exact
position of a proportional control valve 51a, b, c, or d is
proportional to the energizing electrical signal from the control
module 10. Thus, the proportional control valves 51a, b, c, or d
may be positioned at an infinite number of positions rather than
just the three positions described above. In other words, the
proportional valves 51a, b, c, or d may be positioned in the apply
position, the maintain position, or the release position; the
proportional valves 51a, b, c, or d may also be positioned to any
position between the apply and maintain position to provide a
throttled path for directing the pressurized hydraulic brake fluid
to the associated fluid separator unit 54a, b, c, or d, and the
proportional valves 51a, b, c, or d may be positioned to any
position between the release position and the maintain position to
provide a throttled path for venting the pressurized hydraulic
brake fluid from the associated fluid separator unit 54a, b, c, or
d to the reservoir 20. If it is desired to rapidly apply
pressurized hydraulic brake fluid to the associated vehicle brake
11a, b, c, or d, the proportional control valve 51a, b, c, or d is
moved fully to the first energized (apply) position. However, if it
is desired to more slowly apply hydraulic brake fluid to the
associated vehicle brake 11a, b, c, or d, the proportional control
valve 51a, b, c, or d is moved to a position between the first
(apply) and second (maintain) energized positions described above,
so that pressurized hydraulic brake fluid can be applied to the
associated vehicle brake 11a, b, c, or d at less than the maximum
rate possible because the proportional control valve 51a, b, c, or
d is throttled. Similarly, the proportional control valve 51a, b,
c, or d may be moved to a position between the second (maintain)
energized position and the de-energized position to vent
pressurized hydraulic brake fluid from the associated vehicle
brakes 11a, b, c, or d at less than the rate possible when the
proportional control valve 51a, b, c, or d is in the de-energized
(release) position.
The brake system 2 further includes a pair of normally open balance
valves 62 and 64 which are electrically controlled by the control
module 10. The balance valve 62 selectively isolates the fluid
communication between the outlet ports of the proportional control
valves 51a and 51b. The balance valve 64 selectively isolates the
fluid communication between the vehicle brakes 11c and 11d. As will
be discussed in detail below, another function of the balance
valves 62 and 64 is to provide for calibration between the vehicle
brakes 11a and 11b, and between the vehicle brakes 11c and 11d,
respectively.
During normal braking, the control module 10 maintains the
isolation valves 22a and 22b energized shut and the simulator valve
28 energized open, thereby isolating the master cylinder 12 from
the vehicle brakes 11a and 11b, and hydraulically connecting the
pedal simulator 26 to the master cylinder 12. Fixed volumes of
hydraulic brake fluid are trapped between the isolation valve 22a
and the vehicle brake 11a, and between the isolation valve 22b and
the vehicle brake 11b. The pump 42 is suitably run to cooperate
with the accumulator 46 to supply sufficient quantities of
pressurized hydraulic brake fluid to meet the brake demand.
Generally, the pump 42 is shut off by the control module 10 when a
sufficient quantity of suitably pressurized hydraulic brake fluid
has been generated to meet brake demand. In this manner, the fluid
conduit 50 is pressurized up to the proportional control valves 5a,
b, c, and d.
The pressure transducer 49 monitors the pressure in the accumulator
46 and the fluid conduit 50 (when the pressure isolation valve 48
is energized open), providing input to the control module 10. The
control module 10 controls the operation of the pump 42 as needed
to maintain pressure of the hydraulic brake fluid of the normal
source 4. Suitably the control module 10 may be designed to alert
the vehicle operator if the pressure response is not as
expected.
In the event that an abnormal loss of pressure in the normal source
4, or other failure of the normal source 4, the control module 10
monitors the pressure transducer 49, 36a, 36b, 36c, 36d and 30 to
attempt to determine the extent of the abnormality. Pre-programmed
degraded control schemes are preferably programmed into the control
module 10. As will be discussed below, the control module 10 may
maintain braking control from the normal source 4 in certain
degraded conditions. In certain other conditions, the control
module 10 may cause pressurized hydraulic brake fluid for operation
of the vehicle brakes 11a and 11b to be supplied from the manual
backup source 6, from the master cylinder 12. In this case, the
isolation valves 22a and 22b, the simulator valve 28, and the
proportional control valves 5a, b, c, and d are deenergized,
thereby connecting the vehicle brakes 11a and 11b to the master
cylinder 12 for manual control. Note that even a rupture of the
fluid conduit 50 of the normal source 4, and a complete draining of
hydraulic brake fluid from the normal source 4, will not prevent
the operation of the vehicle brakes 11a and 11b by the master
cylinder 12, since the fluid separator units 54a and 54b will
prevent any loss of hydraulic brake fluid from the conduit 16 or
the conduit 17 of the backup source 6 to the piping of the normal
source 4.
During normal braking, however, with the normal source 4 available,
the operator of the vehicle generates a manual brake demand signal
by depressing the brake pedal 14. Depressing the brake pedal 14
sends pressurized hydraulic brake fluid to the pedal simulator 26.
The pressure of the hydraulic brake fluid in the pedal simulator 26
increases as the brake pedal 14 is further depressed, owing to
further compression of the spring 26e of the pedal simulator 26.
The resultant rise in pressure in the conduit 16 is monitored by
the pressure transducer 30. As indicated above, the output signal
of the pressure transducer 30 is a brake demand signal sent to the
control module 10. The more the brake pedal 14 is depressed, the
greater the brake demand signal developed by the pressure
transducer 30. Similarly, the more the brake pedal 14 is depressed,
the greater the brake demand signal generated by the brake pedal
displacement transducer 19 which is sent to the control module 10.
As described above, the brake demand signals generated by the
displacement transducer 19 and the pressure transducer 30 are
combined to generate a system brake demand signal.
Various automated brake demand signals and brake modulation signals
may be supplied to the control module 10. For example, it may be
desired to actuate one or more of the vehicle brakes 11a, b, c, and
d for purposes of traction control, coordinated vehicle stability
control, hill hold, or automated collision avoidance control
schemes, even when the vehicle operator is not depressing the brake
pedal 14. Similarly, it may be desired to temporarily decrease the
braking force of one or more of the vehicle brakes 11a, b, c, and d
for the purposes of antilock braking even if the operator is
depressing the brake pedal 14. Signals which may be supplied to the
control module 10 for the purposes of such automated control
schemes may include wheel speed of each of the vehicle's wheels,
vehicle deceleration, steering angle, vehicle yaw rate, vehicle
speed, vehicle roll rate, and signals from radar, infrared,
ultrasonic, or similar collision avoidance systems, cruise control
systems (including AICC--Autonomous Intelligent Cruise Control
Systems), and the like. It may also be desirable to actuate one or
more of the vehicle brakes 11a, b, c, and d for purposes of panic
brake assist when the vehicle operator is depressing the brake
pedal 14.
When braking is demanded at one or more of the vehicle brakes 11a,
b, c, and d, the pressure isolation valve 48 is opened, and the
appropriate proportional control valve(s) 51a, b, c, and d are
energized to an apply position. The balance valves 62 and 64 are
normally actuated to a closed position during braking, thereby
isolating the vehicle brakes 11a, b, c, and d from each other. For
the vehicle brakes 11a and 11b, pressurized hydraulic brake fluid
from the normal source 4 is applied to the fluid separator
piston(s) 56 of the respective fluid separator unit(s) 54a and 54b,
causing the fluid separator piston(s) 56 to move toward the second
end 55c of the bore 55a, compressing the spring 58, and forcing
pressurized hydraulic brake fluid out of the second end 55c of the
fluid separator unit(s) 54a and 54b. Since there is already a
trapped volume of hydraulic brake fluid between the vehicle brakes
11a and 11b and the associated isolation valve 22a and 22b, the
pressurized hydraulic brake fluid from the fluid separator unit(s)
54a and 54b causes the associated vehicle brake(s) 11a and 11b to
be applied. Since there are no fluid separator units associated
with the vehicle brakes 11c and 11d, pressurized hydraulic brake
fluid from the proportional control valves 51c and 51d,
respectively, is applied to the associated vehicle brakes 11c and
11d. Of course, fluid separator units could suitably be added
between the proportional control valves 51c and 51d and the
associated vehicle brakes 11c and 11d together with selective fluid
communication with the master cylinder 12 if it is desired to
provide manual braking to the rear vehicle brakes 11c and 11d.
The pressure of the hydraulic brake fluid applied to the vehicle
brakes 11a, b, c, and d is monitored by the associated pressure
transducers 36a, b, c, and d. When a desired brake pressure is
reached in a vehicle brake 11a, b, c, or d, the control module 10
will cause the associated proportional control valve 51a, b, c, or
d to move to the maintain position, to hold the desired pressure.
If the accumulator 46 is unable to supply sufficient pressure and
volume of pressurized hydraulic brake fluid to the proportional
control valves 5a, b, c, and d, the pump 42 is started to supply
the needed pressurized hydraulic brake fluid.
When the pressure at the vehicle brake 11a, b, c, or d is no longer
the desired pressure, the control module 10 will position the
associated proportional control valve 51a, b, c, or d to apply more
pressurized fluid to increase the pressure applied, or to vent
pressurized brake fluid to the reservoir 20 to decrease or release
the pressure applied, as appropriate, in response to the varying
brake and modulation demand signals and the control scheme
programmed into the control module 10.
After installation of the brake system 2 or during periodic
intervals, the brake system 2 can be calibrated to determine the
zero point reading for each of the pressure transducers 36a, b, c,
and d. During a non-braking situation, in which the brake pedal 14
is not depressed and the master cylinder 12 and the normal source 4
are not actuated, the balance valves 62 and 64 are left in their
unactauted open position. A first reading is taken of each pressure
transducer 36a, b, c, and d to determine a zero reference value.
After the first reading has been recorded, the balance valves 62
and 64 are actuated to a closed position. The normal source 4 is
then actuated and the proportional valves 51a, b, c, and d are
energized to an apply position to increase the pressure within the
fluid conduits from the proportional control valves 51a, b, c, and
d to the associated vehicle brakes 11a, b, c, and d. The normal
source 4 and the proportional control valves 51a, b, c, and d can
be actuated by a calibrating command signal from the control module
10 or by depressing the brake pedal 14 to actuate the brake system
2 as described above. A second reading is taken of each pressure
transducer 36a, b, c, and d to determine a signal gain. Preferably,
the second reading is taken after the pressure increase generally
levels out so that the fluid flow effects of the brake fluid
through the brake system 2 do not adversely affect the reading. If
desired, several pressure readings can be taken at different
pressure levels to check the linearity of the response for each of
the pressure transducers 36a, b, c, and d.
The calibration method described above operates under the
assumption that the proportional control valves 51a, b, c, and d
are functioning properly. This assumption can be generally verified
by checking that the pressure readings of the pressure transducers
36a, b, c, and d are within an expected value range. If the
readings of the pressure transducers 36a, b, c, and d are not
within an expected value range, the brake system 2 can be further
analyzed by first deenergizing the balance valves 62 and 64 to an
open position. The proportional control valves 51a, b, c, and d are
then operated individually and the readings of the pressure
transducers 36a, b, c, and d are monitored to determine which wheel
fluid circuit may be faulty.
The balance valves 62 and 64 are normally in a non-actuated open
position during a non-braking condition, thereby conserving or
reducing current consumption of the brake system 2.
The balance valves 62 and 64 also provide fail-safe backup in
certain conditions of system failure. If a proportional control
valve 51a, b, c, or d is not properly supplying the required
pressure to its associated vehicle brake 11a, b, c, or d, the
associated balance valve 62 or 64 can be opened so that the other
proportional control valve 51a, b, c, or d of an associated pair
can actuate the vehicle brake 11a, b, c, or d. For example, if the
vehicle brake 11a was not receiving pressure from the normal source
4, such as by failure of the proportional control valve 51a or a
rupture within the piping from the normal source 4 to the vehicle
proportional control valve 51a, the balance valve 62 can be
deenergized to an open position. The proportional control valve 51b
can then be used to supply pressurized fluid to both of the vehicle
brakes 11a and 11b. Similarly, if the vehicle brake 11b failed, the
proportional control valve 51a can be used to supply pressure to
the vehicle brake 11b. Likewise, for the pair of vehicle brakes 11c
and 11d, the balance valve 64 can be deenergized to an open
position so that the unfailed proportional control valve 51c or 51d
can supply pressure to both vehicle brakes 11c and 11d.
In another failure scenario, if a pressure transducer 36c or 36d
senses a pressure drop (such as caused by a rupture in one of the
fluid lines connected to the vehicle brake 11c or 11d), the balance
valve 64 can be actuated to remain in a closed position even when
no braking is in progress so that air cannot enter both of the
fluid lines supplying pressurized fluid to the remaining operable
vehicle brake 11c or 11d. In the event that an abnormal pressure
drop is detected between one of the fluid separator units 54a or
54b and the respective pressure control valve 51a or 51b, the
balance valve 62 can be actuated to a closed position during
periods of braking and non-braking so that air cannot enter both of
the fluid lines supplying pressurized fluid to the remaining
operable vehicle brake 11a or 11b. Note, if an abnormal pressure
drop is detected on the other side of a fluid separator unit 54a or
54b (in the fluid lines between a fluid separator unit 54a or 54b
and the respective vehicle brake 11a or 11b), the appropriate
isolation valve 22a or 22b is actuated to a closed position.
Note that even a rupture of the fluid conduit 50 of the normal
source 4, and a complete draining of hydraulic brake fluid from the
normal source 4 will not prevent the operation of the vehicle
brakes 11a and 11b by the master cylinder 12, since the fluid
separator units 54a and 54b will prevent any loss of hydraulic
brake fluid from the conduit 16 or the conduit 17 to the normal
source 4.
It should be noted that many of the components described and
illustrated as discrete components may be easily combined in a
single compact housing. For example, the master cylinder 12, the
isolation valves 22a and 22b, the simulator valve 28, the pedal
simulator 26 and one or more travel transducers and one or more
pressure transducers 30, could be integrated into one unit with or
without the reservoir 20 included therein. Similarly, the fluid
separator units 54a and 54b, the proportional control valves 51a,
b, c, and d, the balance valves 62 and 64, the pressure transducers
36a, b, c, and d, the filter 52, and the relief valve 44 could be
integrated into a single unit. The accumulator 46, the pressure
isolation valve 48, the relief valve 44, the pump 42 with motor,
and the pressure transducer 49 could be incorporated into one unit.
The control module 10 (also known as an ECU--Electronic Control
Unit) could be integrated into the unit containing the pump 42.
Indeed, it is contemplated that any or all of the components
discussed in this paragraph could be highly integrated into one
unit.
It is also contemplated that the fluid separator units 54a and 54b
can be integrated into their respective vehicle brake 11a and 11b
(for example, in the caliper of a disc brake or the actuator of a
drum brake).
The brake pedal detector 18 and pedal displacement transducer 19
may be integrated into a package with the brake pedal 14 or the
master cylinder 12. It may also be desired to provide a pedal
simulator 26 for each of the conduits 16 and 17.
It should also be noted that it is generally desirable to use
compact components to allow the brake system 2 to fit within the
space constraints of modem vehicle designs. Therefore, it would be
desirable to use a relatively compact master cylinder 12, with the
brake system 2. It is expected that power assist (e.g., vacuum or
hydraulic boost) of fluid pressure in the master cylinder is 12
will not be required, since the master cylinder 12 is not the
normal source of pressurized brake fluid for actuating the vehicle
brakes 11a, b, c, and d. However, if desired, vacuum or hydraulic
boosters, or other suitable arrangements for increasing the force
applied to operate the master cylinder 12, may be used.
FIG. 2 illustrates a preferred embodiment of the damping circuit
29. The damping circuit 29 is hydraulically positioned between the
pedal simulator 26 and the simulator valve 28. The dampening
circuit 29 has three parallel fluid branches 80, 82, and 84. The
fluid branch 80 includes an orifice 86 and a check valve 88. The
check valve 88 restricts the flow of fluid through the fluid branch
80 in a direction from the simulator valve 28 to the pedal
simulator 26 (referred to as the "apply direction"). The fluid
branch 82 includes an orifice 90. Fluid is free to flow through the
branch 82 in either the apply direction or in a direction from the
pedal simulator 26 to the simulator valve 28 (referred to as the
"release direction"). The fluid branch 84 includes a relief valve
94 which prevents the flow of fluid through the fluid branch 84 in
the apply direction until a predetermined pressure is reached. When
the predetermined pressure is reached, the relief valve 94 opens,
thereby allowing fluid to travel through the fluid branch 84 in the
apply direction. It will thus be apparent that when fluid is
flowing in the release direction ("release direction flow"), the
fluid can flow through both the fluid branches 80 and 82. In
contrast, of the fluid branches 80 and 82, fluid can only s flow
into the pedal simulator 26 ("apply direction flow") through the
fluid branch 82.
Referring to FIGS. 1 and 2, as the operator of the vehicle
depresses the brake pedal 14 and actuates the master cylinder 12,
the pressure within the conduit 16 is increased. During normal
braking, in which brake failure has not occurred, the simulator
valve 28 is open and the isolation valves 22a and 22b are closed.
Fluid flows through the dampening circuit 29 via the fluid branch
82 into the pedal simulator 26. As long as the pressure within the
conduit 16 is less than the predetermined pressure which opens the
relief valve 94, all of the fluid traveling through the dampening
circuit 29 will be directed through the fluid branch 82. As the
fluid travels through the restricted cross-sectional area of the
orifice 90, the operator of the brake pedal will feel a resistance
to this fluid movement. Of course, the operator of the vehicle will
also feel a resistance force acting on the brake pedal 14 due to
such factors as the compression of the spring 26e within the pedal
simulator 26, and friction of the moving components of the brake
system 2. The combination of the dampening circuit 29 and the pedal
simulator 26, and the other factors mentioned above, create a pedal
feel characteristic which can closely mimic that of a conventional
brake system or other desired pedal feel.
If during brake apply the pressure within the conduit 16 is greater
than the predetermined pressure which opens the relief valve 94,
such as during a panic brake situation, the relief valve 94 will
open, thereby allowing a greater amount of fluid to travel through
the dampening circuit 29 in the apply direction.
Upon release of the brake pedal 14, the fluid will flow out of the
pedal simulator 26 and through the dampening circuit 29 via the
fluid branches 80 and 82. Unlike the case during brake apply, fluid
flows through both the orifice 90 and the orifice 86. Thus, the
pedal response felt by the operator is different in the brake
release direction than in the brake apply direction.
For the brake apply direction, the pressure difference between the
master cylinder 12 and the pedal simulator 26 depends upon the flow
of fluid through the orifice 90 and possibly through the relief
valve 94. For the brake release direction, the pressure difference
between the master cylinder 12 and the pedal simulator 26 depends
upon the flow through the orifices 86 and 90. The flow volume is
related to the actuation speed of the brake pedal 14. Thus, the
resistance characteristic is dependent on the actuation speed of
the brake pedal as well as the pressure difference between the
master cylinder 12 and the pedal simulator 26. The resistance
characteristic can be altered by adjusting the predetermined
pressure which opens the relief valve 94 and by adjusting the
cross-sectional areas of the orifices 86 and 90. Preferably, the
orifices 86 and 90 are sized or adjustable so that actuation of the
brake pedal 14 (apply direction flow) creates more of a resistance
than when the brake pedal 14 is released (release direction
flow).
The total cross sectional area for apply direction flow through the
branches 80 and 82 during normal brake apply situations (in which
the relief valve 94 remains shut) is less than the cross sectional
area for release direction flow. This has been found to be a
significant factor to achieving a good pedal feel. Generally, a
preferred ratio of cross section area for release flow to the cross
sectional area for apply direction flow through the branches 80 and
82 has been found to be greater than unity (1:1) and less than
about 10:1, and most preferably in the range of about 2:1 to
4:1.
As previously stated above, the fluid branch 84 includes the relief
valve 94 which prevents the flow of fluid through the fluid branch
84 in the apply direction until a predetermined pressure is
reached. When the predetermined pressure is reached, the relief
valve 94 opens, thereby allowing fluid to travel through the fluid
branch 84 in the apply direction. This serves to limit the pedal
reaction force a driver of the vehicle experiences during a panic
stop situation. The value of the suitable predetermined pressure is
dependent upon the area of the working face of the piston in the
master cylinder 12. If the working face area of the piston in the
master cylinder is larger, for a given pressure seen at the master
cylinder 12 as a result of pressure drop across the damping circuit
29, the reaction force on the brake pedal 14 is correspondingly
larger. However, for vehicles such as light trucks and passenger
cars, with the master cylinder 12 being of a size typically
supplied on such vehicles, a preferred range (for good pedal feel)
for the predetermined pressure setpoint for operating the relief
valve 94 has been found to be from about 5 bar to about 30 bar.
Although FIG. 2 illustrates a specific example of a dampening
circuit 29, it should be understood that any suitable configuration
can be used.
There is also shown schematically in FIG. 2 an example of an
expansion volume unit 31 which is in fluid communication with the
pedal simulator 26. The expansion volume unit 31 preferably
includes a flexible membrane disposed within a cylinder. The
membrane is preferably made of an elastomeric material. As the
brake pedal 14 is depressed, pressurized fluid from the master
cylinder 12 is directed into the expansion volume unit 31, thereby
expanding the membrane in an outwardly direction. Preferably, the
membrane expands into a caged housing ultimately which limits the
expansion of the membrane. As the membrane expands, the membrane
provides increasing resistance to further expansion, resulting in a
gradually increasing pressure in the conduit 16 as fluid flows from
the master cylinder 12 into the expansion volume unit 31. This
resistance to expansion is fed back to the brake pedal 14 through
the increase in pressure of the conduit 26 reacting in the master
cylinder 12, so that the operator of the brake pedal 14 feels an
increased resistance. The membrane will continue to expand
outwardly until the membrane expands to the boundaries of the caged
member. The resistance force caused by the expansion of the
membrane is dependent on the various design criteria of the
expansion volume unit 31, such as the stiffness of the membrane
material and the shape of the membrane and caged housing
Although FIG. 2 illustrates a specific example of an expansion
volume unit 31, it should be understood that any suitable
configuration can be used. For example, the expansion volume unit
can be designed without a caged housing, and instead include a
sealed chamber. The sealed chamber can be filled with air or other
suitable gases to provide for a reactionary spring force acting
against the membrane. The sealed chamber can then be provided with
a valve arrangement to seal air within the sealed chamber. The
expansion volume unit 31 can also be provided with a mechanical
spring element to supplement the force exerted by the membrane. In
a preferred embodiment, the expansion volume unit includes a
housing (not shown) defining a cylinder which is vented at first
end (preferably to the reservoir 20, although the cylinder may be
vented to atmosphere). The second end of the cylinder of the
expansion volume unit is in fluid communication with the pedal
simulator 26. A piston (not shown) is slideably disposed in the
cylinder of the expansion volume unit and seals against the wall of
the cylinder. A first end of the piston is in fluid communication
with the pedal simulator 26. A spring (not shown) extends between a
second end of the piston of the expansion volume unit, and a spring
seat formed at the second (vented) end of the cylinder. A membrane
is fixed to the first end of the piston with an air volume formed
between the membrane and the first end of the piston. A vent hole
is formed through the piston to vent the air volume to the second
(vented) end of the cylinder. As pressure increases in the pedal
simulator, the membrane in the expansion volume unit first distorts
against the piston to collapse the air volume As pressure continues
to rise, the piston in the expansion volume unit (which is
relatively lightly spring-loaded compared to the piston of the
pedal simulator 26) begins to move, compressing the spring of the
expansion volume unit. As the piston in the expansion volume unit
nears the end of travel, the pressure in the pedal simulator 26
rises to the pressure required for the piston in the pedal
simulator 26 to begin moving. This arrangement, in a manner similar
to the expansion volume unit 31, results in improved pedal feel, as
will be explained below with reference to the illustrated expansion
volume unit 31.
The expansion volume unit 31 provides for improved pedal feel
during initial stroke movement of the brake pedal 14. FIG. 3 is a
graph which plots the input force acting on the pedal 14 by the
operator of the vehicle (Pedal Force) vs. the travel length or
stroke of the brake pedal 14 (Pedal Travel). The plot for a typical
electro-hydraulic brake system without an expansion volume unit 31
is shown in a solid line. The plot for an electro-hydraulic brake
system with an expansion volume unit 31 is shown in broken
line.
Referring now to the solid line plot for a typical
electro-hydraulic brake system without an expansion volume unit 31,
the initial stroke of the brake pedal 14, labeled "A" in FIG. 3,
involves taking up the slack in the mechanical pedal linkages. For
a conventional master cylinder having compensation ports, the
initial stroke "A" of the brake pedal 14 also involves the movement
of the pistons within the master cylinder 12 prior to the closing
of the compensation ports by the piston seals. During the closing
of the compensation ports, indicated by the reference letter "B",
the pedal force increases relatively rapidly over a relatively
small pedal travel distance. The static friction of the piston of
the pedal simulator 26 and the preload of the spring 26e of the
pedal simulator 26 cause a generally rapid rise in pedal force with
little or no pedal travel, as indicated by the reference letter
"C". Once the static friction and spring preload of the pedal
simulator are overcome and the piston 26c in the pedal simulator 26
begins to move (break-free pressure), continued movement of the
brake pedal 14 results in the characteristic curve of the
piston/spring arrangement of the pedal simulator 26, as indicated
by the reference letter "D".
The expansion of the membrane of the expansion volume unit 31
provides a resistance which is felt by the operator of the brake
pedal 14. Preferably, the expansion volume unit 31 is designed so
that the operator of the brake pedal 14 feels this gradually
increasing resistance during the beginning stages of brake pedal
movement as the compensating ports close on the master cylinder 12
and pressure rises to the break-free pressure to get the pedal
simulator piston 26c moving, thereby increasing the pedal travel
required for a given pressure rise, and "smoothing" the Pedal Force
vs. Pedal Travel curve, such as that indicated by the broken line
of FIG. 3.
Note that the dampening circuit 29 and the expansion volume unit 31
are preferably both included in the brake systems .[.of the present
invention.]. .Iadd.described herein.Iaddend.. However, it is
contemplated that either or both of the dampening circuit 29 and
the expansion volume unit 31 can be suitably omitted. The expansion
volume unit 31 can also be designed to provide a progressively
larger resistance to movement throughout the pedal stroke, thereby
acting as a pedal simulator and eliminating the need for the pedal
simulator 14 from the brake system.
FIG. 4 is a schematic view illustration of another vehicle brake
system, indicated generally at 200, according to the present
invention. The components of the brake system 200, and their
function, are in many instances identical in function and structure
to the components disclosed in the above embodiment of the brake
system 2 shown in FIG. 1. Such components will be referred to using
the same reference numbers as in the brake system 2. Unless
otherwise indicated, where a similarly numbered component is shown
in FIG. 4 but not specifically discussed, its function and
structure may be taken to be similar to that of the similarly
numbered component of the brake system 2 of FIG. 1. Similarly, if a
component is discussed or implied and not specifically shown, its
structure and function may also be taken to be similar to the
previously disclosed, similarly situated component of FIG. 1.
The vehicle brake system 200 may suitably be used on an automotive
vehicle having four wheels and a brake for each wheel. .[.This
invention provides.]. .Iadd.The vehicle brake system 200 is
.Iaddend.an electronically controlled brake system for the four
wheels with manual backup braking to two of the vehicle brakes 11a
and 11b. One of the differences between the brake systems 2 and
200, is that the balance valve 62 provides communication between
the vehicle brakes 11a and 11b instead of communications between
the outlets of the pressure control valves 51a and 51b. Thus, the
balance valve 62 of the brake system 200 is hydraulically connected
on the other side of the fluid separator units 54a and 54b from the
balance valve 62 in the vehicle brake system 2. This arrangement
presents different testing capabilities for the control module 10
by permitting direct cross connection of the wheel brake 11a and
the pressure transducer 36a with the other front wheel brake 11b
and the pressure transducer 36b, for example.
FIG. 5 is a schematic view illustration of another vehicle brake
system, indicated generally at 300, according to the present
invention. The components of the brake system 300, and their
function, are in many instances identical in function and structure
to the components disclosed in the above embodiments of the brake
systems 2 and 200 as shown in FIGS. 1 and 4, respectively. Such
components will be referred to using the same reference numbers as
in the brake systems 2 and 200. Unless otherwise indicated, where a
similarly numbered component is shown in FIG. 5 but not
specifically discussed, its function and structure may be taken to
be similar to that of the similarly numbered component of the brake
systems 2 or 200. Similarly, if a component is discussed or implied
and not specifically shown, its structure and function may also be
taken to be similar to the previously disclosed, similarly situated
component of FIG. 1 or FIG. 4.
The vehicle brake system 300 may suitably be used on an automotive
vehicle having four wheels and a brake for each wheel. One of the
differences between the brake systems 2 and 300 is that the brake
system 300 is an electronically controlled brake system for the
four wheels with manual backup for all four of the vehicle brakes
11a, b, c, and d. The brake system 300 includes a primary circuit
conduit 302 which is in fluid communication with the vehicle brakes
11a and 11b through an isolation valve 306. The brake system 300
also includes a secondary circuit conduit 304 which is in fluid
communication with the vehicle brakes 11c and 11d through an
isolation valve 308. The brake system 300 further includes a
balance valve 310 which selectively isolates the fluid
communication between the vehicle brakes 11a and 11b. A balance
valve 312 selectively isolates the fluid communication between the
vehicle brakes 11c and 11d. The brake system 300 also includes four
fluid separator units 54a, b, c, and d, positioned between the
proportional control valves 5a, b, c, and d and the vehicle brakes
11a, b, c, and d, respectively.
If desired, the brake systems 200 and 300 can further include a
suitable dampening circuit 29 and a suitable expansion volume unit
31, either separately or in combination.
FIG. 6 illustrates a specific embodiment of the master cylinder 12
and the pedal simulator 26 which can be used in the brake systems
2, 200, and 300 of the present invention. The master cylinder 12 is
a tandem master cylinder, having two service pistons 12a and 12b.
The master cylinder 12 is in fluid communication with the pedal
simulator 26 via a conduit, such as the conduit 16. The isolation
valve, indicated by the block 28, is located within the conduit 16
between, and thus in fluid communication with the master cylinder
12 and the pedal simulator 26. The optional dampening circuit,
indicated by the block 29, is also shown in fluid communication
with the pedal simulator via the conduit 16. Although not shown,
the expansion volume unit 31 is preferably also in fluid
communication with the pedal simulator 26 through the conduit
16.
FIG. 10 is a schematic view illustration of a vehicle brake system,
according to the present invention, which is indicated generally at
350. Many of the components of the brake system 350 are similar to
the components disclosed in the brake systems 2, 200, and 300, and
function in a similar manner. Such components will be assigned the
same reference numbers as in the previous brake systems 2, 200, and
300. Where a component is shown in FIG. 10 but not specifically
discussed, its function and structure may be taken to be similar to
that of components similarly situated in the brake systems 2, 200,
and 300. Similarly, if a component is discussed or implied and not
specifically shown, its existence and function may also be taken to
be similar to the previously disclosed similarly situated
components.
The vehicle brake system 350 may suitably be used on an automotive
vehicle having four wheels and a brake for each wheel. The vehicle
brake system 350 is comprised of two separate brake systems, a
front brake system shown generally at .[.351.]. .Iadd.352
.Iaddend.and a rear brake system shown generally at 354. The front
brake system .[.351.]. .Iadd.352 .Iaddend.is comprised of two
sub-systems: an electrically powered front brake system which
includes a motor operated, electronically controlled normal source
of pressurized brake fluid 4; and a manual supply of pressurized
hydraulic brake fluid, embodied as a master cylinder 12. The rear
brake system 354 is comprised of two electronically controlled
power cylinders 210 and 212 for supplying pressurized hydraulic
brake fluid to individual wheel brake units. The power cylinder 210
uses a linear actuator 214 to drive a spring loaded piston 218 a
controlled distance into a cylinder 226. The operation of the power
cylinder 210 is controlled by the control module. The cylinder 226
is filled with hydraulic brake fluid, which may be pressurized and
urged from the cylinder 226 of the power cylinder 210 into the
brake unit 11d to generate a controlled amount of braking force
with the vehicle brake 11d. The linear actuator 214 may be any
suitable device for accurately controlling the position of the
piston 218 with respect to the cylinder 226. A pressure transducer
222 provides a signal to the control module representative of the
pressure developed by the power cylinder 210. Preferably, this
pressure signal is used by the control module as a pressure
feedback loop for controlling the operation of the power cylinder
210. The control module can modulate the pressure by positioning
the linear actuator 214 of the power cylinder 210. The power
cylinder brake unit 212 is preferably identical in configuration to
the power cylinder brake unit 210. The power cylinder 212 uses a
linear actuator 216 controlled by the control module to drive a
piston 220 a controlled distance into a cylinder 228. The cylinder
228 is filled with hydraulic brake fluid, to selectively effect a
controlled amount of braking force in the vehicle brake 11c. The
linear actuator 216 may be any suitable device for accurately
controlling the position of the piston 220 with respect to the
cylinder 228. The pressure transducer 224 provides a pressure
feedback signal to the control module representative of the
pressure developed by the power cylinder 212. Preferably, this
pressure signal is used by the control module as a pressure
feedback loop for controlling the operation of the power cylinder
212. The control module can modulate the pressure by positioning
the linear actuator 216 of the power cylinder 212.
The front brake system .[.351.]. .Iadd.352 .Iaddend.of the present
invention differs from the front brake units disclosed above, in
that there is a single proportional control valve 51 that controls
the hydraulic brake fluid pressure to both front vehicle brakes 11a
and 11b. The hydraulic brake fluid is then selectively applied to
the vehicle brakes 11a and 11b through electrically operated
solenoid isolation valves 70a, 70b, 72a, and 72b, as will be
described below. Additionally, a pressure isolation valve 348 is
provided which acts to isolate only the accumulator 46 and not the
pump 42. Suitable overpressure protection (not shown) should be
provided for the accumulator 46. The pressure transducer 49
reflects the discharge pressure of the pump only when the discharge
pressure is at least as high as the pressure in the accumulator 46
when the pressure isolation valve 348 is shut. However the pressure
isolation valve 348 is energized open during normal braking,
enabling the pressure transducer 49 to reflect the pressure of the
hydraulic brake fluid being supplied to the proportional control
valve 51.
Note that two damping circuits 29 are provided, one for each of two
pedal simulator 26a and 26b connected, respectively to the conduits
16 and 17 out of the master cylinder 12. Only one expansion volume
unit 31 is shown, in fluid communication with the pedal simulator
26a. If desired, an expansion volume unit 31 could be provided in
fluid communication with the pedal simulator 26b.
Referring to FIG. 10, the normal source of pressurized hydraulic
brake fluid to the front vehicle brakes 11a and 11b is shown
generally at 4. A proportional control valve 51 modulates the
pressure of the hydraulic brake fluid provided to vehicle brakes
11a and 11b according to instructions received from a control
module (not shown). The hydraulic brake fluid is supplied to the
vehicle brakes 11a and 11b through electrically operated isolation
valves 70a and 70b, respectively. During normal operation, the
isolation valves 70a and 70b are de-energized and in the open
position, as shown in FIG. 10. The isolation valves 70a and 70b
thereby allow passage of the hydraulic brake fluid from the
proportional control valve 51 to the fluid separator units 54a and
54b. The fluid separator units 54a and 54b function identically to
the fluid separator units in the brake system 2, in that the fluid
separator units 54a and 54b prevent the hydraulic brake fluids of
the normal source 4 and the backup source 6 from mixing, thereby
preventing a leak from the piping of the normal source 4 from
disabling the backup source 6 of hydraulic brake fluid, while
allowing pressure from the normal source of pressurized hydraulic
brake fluid 4 to be operatively hydraulically connected to the
vehicle brakes 11a and 11b. The proportional control valve 51
controls the pressure of the hydraulic brake fluid to be supplied
to the vehicle brakes 11a and 11b for foundation braking. In
response to various driver demands, as signaled by the pressure
sensed at the pressure transducers 30 and 32, the proportional
control valve 51 will be positioned to apply pressurized fluid to
the vehicle brakes 11a and 11b, to hold pressure on the brakes 11a
and 11b, or to vent pressure from the brakes 11a and 11b. Only the
one pressure control valve 51 is used to control the pressure for
both of the brakes 11a and 11b. Such an arrangement may prove to be
less expensive than a separate proportional control valve 51 for
each of the brakes 11a and 11b of the brake system 2, for
example.
The isolation valves 70a and 70b cooperate with the dump valves 72a
and 72b to provide digital brake control for antilock braking,
vehicle stability control, or traction control functions. For
example, a traction control scenario might involve, in a
front-wheel drive vehicle, a left front wheel which is losing
traction during heavy acceleration. In such a situation, it may be
desired to apply the brake 11a, while not applying the brake 11b.
To accomplish this, the isolation valve 70b is shut while the
isolation valve 70a remains open. The pressure isolation valve 348
is opened, and pressurized hydraulic brake fluid from the
accumulator 46 is regulated by the pressure control valve 51 to a
desired pressure. The pressurized hydraulic brake fluid is blocked
from being applied to the brake 11b by the isolation valve 70b, but
is allowed, by the open valve 70a to actuate the brake 11a, slowing
the individual wheel until the associated wheel slows and regains
traction. The dump valve 72a can then be opened, or the control
valve 51 can then be deenergized, or both, to bleed pressure from
the brake 11a back to the reservoir 40, as directed by the control
module. The pressure isolation valve 348 is then shut, and the pump
42 stopped, if the pump 42 was running.
Other control schemes may also be suitably used. For example, if
both front wheels were slipping under acceleration, but not at the
same rate, both the isolation valves 70a and 70b may be shut, the
proportional control valve 51 opened to regulate pressure higher
than is to be needed at either wheel, and then the isolation valves
70a and 70b pulsed open to achieve independently controlled
pressures needed to slow down the respective wheel. The braking
force at each wheel would be controlled by cooperative modulation
of the respective isolation valves 70a and 70b, and the dump valves
72a and 72b. In another control arrangement which is contemplated,
the isolation valves 70a and 70b would not be initially closed, but
would be closed when the associated wheel began to slow, or when
the desired brake pressure was reached. In yet another control
scheme which is contemplated, the proportional control valve 51
would modulate pressure in the brakes as needed to achieve the
pressure needed for both of the brakes 11a and 11b, with both the
isolation valves 70a and 70b remaining open at all times, and both
of the dump valves 72a and 72b remaining shut. This would be simple
control, but may result in a brake 11a or 11b which did not need as
high a brake pressure as the other of the brakes 11a and 11b being
braked with greater pressure than needed to prevent wheel spin.
Therefore it is also contemplated that the proportional control
valve 51 would be modulated to control the wheel spin on the wheel
operating on the surface with the lower coefficient of friction,
while the isolation valves 70a or 70b and the dump valves 72a or
72b would be modulated to control the brake pressure of the other
wheel, on a surface with higher coefficient of friction, at the
appropriate lower pressure needed to stop the wheel spin. Thus it
is apparent that the arrangement of the brake system 350 provides
for great flexibility in a traction control situation. The same is
true in other braking situations, such as when antilock braking is
required.
As an example, if a need was detected for pulsing the vehicle
brakes 11a and b such as would be required to prevent locking up
the brakes, or for braking in slippery road conditions, the
isolation valves 70a and 70b and the dump valves 72a and 72b could
be pulsed open and closed. The digital (either on or off) nature of
control of the isolation valves 70a and 70b and the dump valves 72a
and 72b allows the isolation valves 70a and 70b and the dump valves
72a and 72b to cooperate to rapidly increase, decrease, or hold
pressure for antilock braking. Other non-modulated or digital
applications of the front brake system 351 could be effected as
needed with the arrangement of the isolation and dump valves 70a,
70b, 72a, and 72b as shown. Note that it is anticipated that the
isolation valves 70a and 70b and the dump valves 72a and 72b may be
suitably constructed to provide proportional control of hydraulic
brake fluid passing through the respective valve, thereby
permitting finer control of the hydraulic pressure in the brakes
11a and 11b. For example, the isolation valves 70a and 70b may be
constructed to enable the valve to operate in a stable manner when
the valve is partially open, allowing a more gradual pressure rise
in the associated brake 11a and 11b, which may be desired if the
wheel is near lock-up. The dump valves 72a and 72b could similarly
be constructed to modulate flow of hydraulic brake fluid
therethrough.
As in the previous embodiments of the brake system 2, 200 and 300,
upon failure of the normal source of pressurized hydraulic brake
fluid 4 to the vehicle brakes 11a and 11b, or upon failure of the
control module, the backup source 6 of pressurized hydraulic brake
fluid supplied by the master cylinder 12, will be an available
source of pressurized hydraulic brake fluid to be applied to the
brakes of the brake system 350, preferably to the front brakes 11a
and 11b as illustrated in FIG. 10. The vehicle brakes 11a and 11b
supplied by the master cylinder 12 can be designed to provide
sufficient braking force to safely operate the vehicle with the
pressure supplied from the master cylinder 12. Of course, although
not illustrated in FIG. 10, it is contemplated that the master
cylinder 12 can be operatively connected to selectively supply
pressurized hydraulic brake fluid to the power cylinders 210 and
212, if desired. It is also contemplated that separate power
supplies may by used to power the motors of the power cylinders 210
and 212 to provide an additional level of redundancy and safety to
the brake system 350. Of course redundant, independently powered,
and cross-checking control modules may be utilized to control the
operation of the power cylinders 210 and 212, and of the
proportional control .[.valves 51a and 51b.]. .Iadd.valve
51.Iaddend.. It is also contemplated that all four of the vehicle
brakes 11a, b, c, and d could be supplied from a respective power
cylinder similar to the power cylinder 210. The backup source 6
could be connected to two or four of the vehicle brakes 11a, b, c,
and d. A suitable fluid separator unit 54a is preferably provided
between the power cylinder and the connection of the backup source
6 in communication with the vehicle brakes 11a, b, c, and d.
The principle and mode of operation of this invention have been
explained and illustrated in its preferred embodiment. However, it
must be understood that this invention may be practiced otherwise
than as specifically explained and illustrated without departing
from its spirit or scope.
* * * * *
References