U.S. patent number RE28,890 [Application Number 05/433,510] was granted by the patent office on 1976-07-06 for actuator assemblies for hydraulic braking systems.
This patent grant is currently assigned to Girling Limited. Invention is credited to David Anthony Harries, Brian Ingram, Lancelot Phoenix.
United States Patent |
RE28,890 |
Ingram , et al. |
July 6, 1976 |
Actuator assemblies for hydraulic braking systems
Abstract
In an actuator assembly for an hydraulic braking system the
effective volume of a chamber through which hydraulic fluid under
pressure is supplied to a wheel brake is adapted to be varied
between a minimum and a maximum value by movement of a piston
assembly working in a bore in communication with the chamber. An
actuator piston having first and second different faces of
different areas normally holds the piston assembly in a position in
which the effective volume of the chamber is at a minimum until
equal hydraulic pressures are applied to the areas of the actuator
piston to cause the actuator piston to retract and permit the
piston assembly to be withdrawn whereby the effective volume of the
chamber is increased.
Inventors: |
Ingram; Brian (Lugamo,
AU), Harries; David Anthony (Solihull, EN),
Phoenix; Lancelot (Birmingham, EN) |
Assignee: |
Girling Limited (Birmingham,
EN)
|
Family
ID: |
27515661 |
Appl.
No.: |
05/433,510 |
Filed: |
January 15, 1974 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
073202 |
Sep 17, 1970 |
03694038 |
Sep 26, 1972 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Sep 17, 1969 [UK] |
|
|
45705/69 |
Jan 6, 1970 [UK] |
|
|
531/70 |
Mar 8, 1970 [UK] |
|
|
13117/70 |
|
Current U.S.
Class: |
303/113.1;
303/10; 188/181A |
Current CPC
Class: |
B60T
8/4233 (20130101); B60T 13/12 (20130101); B60T
13/14 (20130101); B60T 13/141 (20130101) |
Current International
Class: |
B60T
8/42 (20060101); B60T 13/14 (20060101); B60T
13/10 (20060101); B60T 13/12 (20060101); B60T
008/06 () |
Field of
Search: |
;303/21F,21AF,61-63,68-69,10 ;188/181A,181R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blix; Trygve M.
Assistant Examiner: Butler; Douglas C.
Attorney, Agent or Firm: Imirie, Smiley & Linn
Claims
We claim:
1. An actuator assembly for a vehicle hydraulic braking system
comprising a housing, means defining at least one first chamber in
said housing having a first inlet for connection to a fluid
pressure source and an outlet for connection to a slave cylinder of
a wheel brake, a piston assembly working in a first cylinder bore
in said housing in communication with said chamber and movable
between a first advanced position and a second retracted position,
an actuator piston working in a second cylinder bore in said
housing and normally acting on said piston assembly to urge said
piston assembly into said first advanced position in which the
effective volume of said first chamber is at a minimum value and
said inlet and outlet connections are open, said actuator piston
having a first area at an end of said actuator piston remote from
said piston assembly and a second area opposed to said first area,
a movable member .[.in said second cylinder bore.]. adjacent said
first area of said actuator piston, a compression spring urging
said movable member towards said actuator piston, means for
applying hydraulic fluid under pressure, between said movable
member and said first area of said actuator piston to urge said
piston assembly into said first advanced position, and a second
inlet connection in communication with said second cylinder bore
through which hydraulic fluid under pressure is adapted to be
admitted into said second bore when the deceleration of a braked
wheel controlled by a supply of hydraulic fluid from said outlet
exceeds a predetermined value, said supply of hydraulic fluid under
pressure admitted to said second bore acting over said second area
of said actuator piston to apply to said actuator piston a force to
move said actuator piston in a direction away from said piston
assembly and permit said piston assembly to be moved towards said
second retracted position in which said first inlet connection is
closed and the effective volume of said first chamber is increased
to reduce pressure in a line between said outlet connection and
said slave cylinder.
2. An actuator assembly as claimed in claim 1, incorporating a
valve for cutting off communication between said first inlet
connection and said chamber upon initial movement of said piston
away from said first advanced position.
3. An actuator assembly as claimed in claim 1, wherein said
actuator piston is of differential outline working in a stepped
bore and engages at its end of smaller diameter with said piston
assembly, said first area being located at the base of a recess in
the end of said piston of greater diameter, and said second area
being defined by a shoulder at a step in diameter between portions
of said stepped piston of different diameters.
4. An actuator assembly as claimed in claim 3 wherein said shoulder
on said actuator piston is spaced from a complementary shoulder at
a step at the change in diameter of said stepped bore when said
effective volume of the chamber is at said minimum value, and an
annular space between the shoulders and surrounding a portion of
said actuator piston of lesser diameter defines a second chamber
into which hydraulic fluid under pressure is adapted to be admitted
though through said second inlet connection.
5. An actuator assembly as claimed in claim 4, incorporating a
metering device for delaying the release of fluid pressure from
said second chamber when the supply of hydraulic fluid under
pressure to that chamber is terminated.
6. An actuator assembly as claimed in claim 5, wherein said
metering device comprising a cup-shaped piston located in said
second chamber and having an axially extending skirt and a spring
for urging said skirt into sealing engagement with said shoulder at
said step at the change in diameter in said stepped bore and
wherein said cup-shaped piston incorporates in a wall thereof at
least one orifice providing a restricted return path to said second
inlet connection for fluid actuator said second chamber after said
actuator piston has moved towards said first chamber by a distance
sufficient to enable said skirt to seat against said shoulder.
7. An actuator assembly as claimed in claim 6, wherein said
cup-shaped piston is slidable guided in a portion of said
differential piston of smaller diameter which projects into the
portion of said stepped bore of greater diameter, and there is a
clearance between an outer peripheral edge of said cup-shaped
piston and the wall of said portion of said stepped bore of greater
diameter.
8. An actuator assembly as claimed in claim 4, including a third
inlet connection in said housing leading to said second chamber,
wherein a one-way valve assembly is housed in each of said second
and third connections, each one-way valve assembly incorporating a
valve member, a seating surrounding an orifice and adapted to be
engaged by said valve member and spring means for urging said valve
member into engagement with said seating, said one-way valve
assemblies being constructed and arranged to operate in opposite
directions whereby high pressure fluid is adapted to be supplied to
both connections but is applied to said actuator piston only
through said one-way valve which opens in that direction, fluid
from said actuator piston being returned from said second chamber
upon re-application of a wheel brake through said other one-way
valve and said connection in which that one-way valve is located,
whereby the delay in the re-application of a wheel brake after the
deceleration of the wheel has been restored to a predetermined
value is controlled by the return of fluid from said actuator
piston .[.to the control valve.]. through said orifice in said
one-way valve in the return connection.
9. An actuator assembly is claimed in claim 8 wherein each orifice
is provided in a plate which is interchangeable with a series of
similar plates having orifices of different diameters whereby the
rate of flow fluid in each connection can be varied in accordance
with a desired braking characteristic.
10. An actuator assembly as claimed in claim 3, wherein the movable
member is a third piston working in said recess in said end of said
actuator piston of greater diameter and having an inner end,
wherein said inner end of said third piston defines with said base
of said recess forming the first area a third chamber into which
hydraulic fluid under pressure is admitted through an axial bore in
said third piston.
11. An actuator assembly as claimed in claim 1 incorporating means
for delaying re-application of a wheel brake following cut-off and
relief of the supply of fluid to a slave cylinder from said outlet
connection.
12. An actuator assembly as claimed in claim 1, wherein said piston
assembly comprises a single expander piston working in a bore in
said housing and controlled by a single actuator piston.
13. An actuator assembly as claimed in claim 1, wherein said piston
assembly comprises at least two expander pistons working in
separate parallel bores in said housing, said expander pistons
being controlled by single actuator piston, and each expander
piston being adapted to control the effective volume of a chamber
provided with separate inlet and outlet connections and operation
of a spring loaded valve means for controlling communication
between said inlet connection and said chamber of which the
effective volume is variable by that expander piston.
14. An actuator assembly as claimed in claim 1, wherein said piston
assembly comprises a two part axially separable assembly adapted to
regulate the effective volume of a first and second axially spaced
chamber, each provided with an inlet and an outlet connection.
15. An actuator assembly as claimed in claim 14, wherein said first
axially spaced chamber is located at the end of said bore in which
works said expander piston and into which a free end portion of a
first part of said separable assembly extends, and adjacent to the
opposite end of said first part is formed an axially extending
annular recess with which an adjacent end of a second part of said
separable assembly defines said second axially spaced chamber of
which the effective volume is variable upon relative axial movement
between said first and second parts of separable assembly.
16. An actuator assembly as claimed in claim 15 wherein
communication between said inlet and outlet connections with said
first axially spaced chamber is controlled by a valve operable by a
push-rod carried by the free end of said first part of said
separable assembly, and communication between said inlet and outlet
connections with said second axially spaced chamber is controlled
by a spring loaded tipping valve which is normally held in an open
position by the engagement of a stem of the tipping valve with a
shoulder at the end of said recess adjacent to said second part of
the separable assembly. .Iadd. 17. An actuator assembly for a
vehicle hydraulic braking system comprising a housing having first
and second opposite ends, means in said housing adjacent to said
first end defining at least one chamber having a first inlet for
connection to hydraulic fluid under pressure and an outlet for
connection to a slave cylinder of a wheel brake, a valve
controlling communication between said inlet and outlet, a piston
assembly working in a cylinder bore in said housing in
communication with said chamber and movable between an advanced
position in which said valve is held open and the effective volume
of said chamber is at a minimum value and a retracted position in
which said valve is shut and the effective volume of said chamber
is greater than the minimum, means in said housing for enabling
fluid from a high pressure source to urge said piston assembly to
said advanced position, means in said housing for enabling fluid to
move said piston assembly to said retracted position when the
deceleration of a braked wheel controlled by a supply of hydraulic
fluid from said outlet exceeds a predetermined value, a movable
member in said housing disposed between said piston assembly and
said second end of said housing and movable between a first
position in which said member permits said piston assembly to
assume said retracted position and a second position in which said
member maintains said piston assembly in said advanced position,
resilient means for constantly biassing said movable member to said
second position, and means in said housing for enabling the fluid
from said high pressure source to hold said movable member in said
first position in opposition to said resilient means, whereby, in
the event of the pressure of said high pressure source falling,
said resilient means can move said movable member to said second
position to maintain said piston assembly in said advanced
position. .Iaddend. .Iadd.18. An actuator assembly as in claim 17
wherein said piston assembly is adapted to be urged to said
advanced position by hydraulic fluid under pressure and wherein
said valve is separate from said piston assembly and movable away
from a fixed valve seat in said housing by said piston assembly.
.Iaddend..Iadd.19. An actuator assembly as in claim 118 wherein
said piston assembly comprises an expander piston working in a
first cyliner bore in the housing in communication with said
chamber, and an actuator piston working in a second cylinder bore
in said housing and acting on said expander piston, said movable
member being adapted to maintain said expander piston in said
advanced position. .Iaddend. .Iadd.20. An actuator assembly as in
claim 17 wherein said housing includes a plurality of said
chambers, and a plurality of said valves controlling communication
between said inlet and said outlet of each chamber, said piston
assembly actuating said valves. .Iaddend..Iadd.21. An actuator
assembly as in claim 20 wherein said piston assembly is adapted to
be urged to said advanced position by hydraulic fluid under
pressure and wherein said valves are held open by a mechanical
coupling between said piston assmbly and said valves. .Iaddend.
.Iadd. 22. An actuator assembly as in claim 21 wherein said piston
assembly comprises a plurality of expander pistons working in a
plurality of first cylinder bores, each of said first cylinder
bores being in communication with one of said chambers, and an
actuator piston working in a second cylinder bore in said housing
and acting on each of said expander pistons, said movable member
being adapted to maintain all of said expander pistons in said
advanced positions. .Iaddend..Iadd. 23. An actuator assembly for a
vehicle hydralic braking system comprising a housing having first
and second opposite ends, means in said housing adjacent to said
first end defining at least one chamber having a first inlet for
connection to hydraulic fluid under pressure and an outlet for
connection to a slave cylinder of a wheel brake, a valve in said
housing controlling said inlet, a piston assembly working in a
cylinder bore in said housing in communication with said chamber
and operating said valve, said piston assembly being movable
between an advanced position in which said valve is held open and
the effective volume of said chamber is at a minimum value, a first
retracted position in which said valve is shut, and a second
retracted position in which said valve is shut and the effective
volume of said chamber is at a maximum value, retraction of said
piston assembly first closing said valve and then progressively
increasing the volume of said chamber, means in said housing for
enabling fluid from a high pressure source to urge said piston
assembly to said advanced position, means in said housing for
enabling fluid to move said piston assembly to said retracted
positions when the deceleration of a braked wheel controlled by a
supply of hydraulic fluid from said outlet exceeds a predetermined
value, a movable member in said housing disposed between said
piston assembly and said second end of said housing and movable
between a first position in which said member permits said piston
assembly to assume said retracted positions and a second position
in which said member maintains said piston assembly in said
advanced position, resilient means for constantly biassing said
movable member to said second position, and means in said housing
for enabling the fluid from said high pressure source to hold said
movable member in said first position in opposition to said
resilient means, whereby in the event of the pressure of said high
pressure source falling, said resilient means can move said movable
member to said second position to maintain said piston assembly in
said advanced position. .Iaddend..Iadd. 24. An actuator assembly as
in claim 23 wherein said means for urging said piston assembly to
said advanced position and said means for holding said movable
member in said first position comprise an accumulator chamber
defined between said piston assembly and said movable member, and
an inlet leading into said accumulator chamber for connection to
said high pressure source, and wherein said means for moving said
piston assembly to said retracted position comprise a pressure
chamber defined between said piston assembly, on the opposite side
to said accumulator chamber, and said housing, and a port leading
into said pressure chamber for connection to a supply of hydraulic
fluid. .Iaddend..Iadd. 25. An actuator assembly for a vehicle
hydraulic braking system comprising a housing, means defining at
least one first chamber in said housing, said first chamber having
a first inlet for connection to a fluid pressure source and an
outlet for connection to a slave cylinder of a wheel brake, a
piston assembly working in a first cylinder bore in said housing in
communication with said chamber and movable between a first
advanced position and a second retracted position, a valve for
controlling communication between said first inlet connection and
said chamber, said valve being open when said piston assembly is in
said first advanced position and being closed upon initial movement
of said piston assembly away from said first advanced position, an
actuator piston working in a second cylinder bore in said housing
and normally acting on said piston assembly to urge said piston
assembly into said first advanced position in which the effective
volume of said first chamber is at a minimum value and said inlet
and outlet connections are open, said actuator piston having a
first area at an end of said actuator piston remote from said
piston assembly and a second area opposed to said first area, a
movable member sealingly engaging said actuator piston to define a
second chamber incorporating said first area of said actuator
piston, a second inlet connection for admitting hydraulic fluid
under pressure into said chamber to act on said first area of said
actuator piston to urge said piston assembly into said first
advanced position, a compression spring urging said movable member
towards said actuator piston, and a third inlet connection in
communication with said second cylinder bore through which
hydraulic fluid under pressure is adapted to be admitted into said
second bore when the deceleration of a braked wheel controlled by a
supply of hydraulic fluid from said outlet exceeds a predetermined
value, said supply of hydraulic fluid under pressure admitted to
said second bore acting over said second area of said actuator
piston to apply to said actuator piston a force to move said
actuator piston in a direction away from said piston assembly and
permit said piston assembly to be moved towards said second
retracted position in which said first inlet connection is closed
and the effective volume of said first chamber is increased to
reduce pressure in a line between said outlet connection and said
slave cylinder.
Description
This invention relates to improvements in actuator assemblies for
use in hydraulic braking systems for vehicles of the kind
comprising at least one chamber having an inlet for connection to a
fluid pressure source, for example a pedal-operated master
cylinder, and an outlet for connection to a slave cylinder of a
wheel brake.
According to our invention in an actuator assembly of the kind set
forth for use in an hydraulic braking system for a vehicle, the
effective volume of the chamber is adapted to be varied between a
normal minimum value, in which the inlet and outlet connections are
both open, and a maximum value, in which the inlet connection is
closed and the outlet connection is open, by movement of a piston
assembly working in a cylinder bore in a housing in communication
in the chamber, the piston assembly being normally urged in a
direction in which the effective volume of the chamber is at the
minimum value by an actuator piston working in a bore in the
housing and adapted to be subjected over a first area to an end
remote from the piston assembly to hydraulic fluid under pressure,
and the housing is provided with a further inlet connection for
admitting into the bore in which the actuator piston works, when
the deceleration of a braked wheel controlled by a supply of fluid
from the outlet connection exceeds a predetermined value, hydraulic
fluid under pressure which acts on the actuator piston over a
second area to retract the actuator piston away from the chamber
and permit the piston assembly to be withdrawn to increase the
effective volume of the chamber.
Initial retraction movement of the piston assembly enables a valve
to close thereby cutting off communication between the inlet
connection and the chamber, and further movement of the piston
assembly in the same direction reduces the pressure in a line
between the outlet connection and a slave cylinder of the wheel
brake to which the outlet connection is adapted to be
connected.
Preferably the actuator piston is of differential outline working
in a stepped bore and engages at its end of smaller diameter with
the piston assembly, the first area being located at the base of a
recess or blind bore in the end of the piston of greater diameter,
and the second area being defined by a shoulder at a step in
diameter between portions of the stepped piston of different
diameters.
In a normal operative position in which the effective volume of the
chamber is at its minimum value the shoulders on the actuator
piston is spaced from a complementary shoulder in the change in
diameter of the stepped bore and the annular space between the
shoulder and surrounding a portion of the actuator piston of lesser
diameter defines a second chamber into which hydraulic fluid under
pressure is adapted to be admitted through the said further
inlet.
Conveniently a third piston working in the recess or blind bore in
the end of the actuator piston of greater diameter is urged into
the recess or bore by a compression spring and the inner end of the
third piston defines with the inner end of the recess or bore
forming the first area a chamber into which hydraulic fluid under
pressure is admitted through an axial bore in the third piston.
Preferably the actuator assembly incorporates means for delaying
re-application of a wheel brake following cut-off and relief of the
supply of fluid to a slave cylinder. These means preferably
incorporate an orifice or other metering device which serves to
delay the release of pressure fluid from the second chamber when
the supply of hydraulic fluid under pressure to that chamber is
terminated.
The piston assembly may comprise a single expander piston working
in a bore in the housing and controlled by a single actuator
piston. Alternatively at least two expander pistons working in
separate parallel bores may be controlled by a single actuator
piston, in which each expander piston is adapted to control the
effective volume of a chamber provided with separate inlet and
outlet connections and operation of a spring loaded valve means for
controlling communication between the inlet connection and the
chamber of which the effective volume is variable by that expander
piston.
In other construction a single expander piston in the form of a two
part axially separable assembly is adapted to regulate the
effective volumes of a pair of chambers and provided with an inlet
and an outlet connection.
Some embodiments of our invention are illustrated in the
accompanying drawings in which:
FIG. 1 is a layout of an hydraulic braking system;
FIG. 2 is a layout of a braking system similar to the system
illustrated in FIG. 1 but showing some modifications;
FIG. 3 is a longitudinal section through a control valve for use in
the braking system of FIG. 1 or FIG. 2;
FIG. 4 is a longitudinal section through an actuator for use in the
braking system of FIG. 1 or FIG. 2;
FIG. 5 is a longitudinal section through an actuator similar to
that shown in FIG. 2 but of tandem construction incorporating a
pair of expander pistons arranged in parallel and adapted to be
actuated by a single piston;
FIG. 6 is a longitudinal section through an actuator similar to the
actuator of FIG. 5 but shown some modifications;
FIG. 7 is a longitudinal section of portion of an actuator shown
restrictor assemblies; and
FIG. 8 is a longitudinal section through an actuator incorporating
a single expander piston of two-part construction for controlling
the effective volume of a pair of chambers.
In the layout illustrated in FIG. 1, 1 is a pedal-operated tandem
master cylinder having two pressure spaces 2 and 3. The pressure
space 2 is connected through pipe-lines 4 and 5 to slave cylinders
6 for actuating brakes on the rear wheel of the vehicle, and
through pipe-lines 7 and 8 to slave cylinders 9 for actuating
brakes on the front wheels of the vehicle. The pressure space 3 is
also connected through pipe-lines 10 and 11 to separate slave
cylinders 12 for actuating the brakes on the front wheels of the
vehicle.
When the brakes are applied the deceleration of each front wheel is
sensed by an electrically inductive sensor 13, and the deceleration
of each rear wheel is sensed by an electrically inductive sensor
14.
When the deceleration of one or more wheels exceeds a predetermined
value the A.C. output from the sensor on that wheel or wheels in
question is fed to electronic control means which convert the A.C.
signal into a D.C. output. Specifically the output from each sensor
13 is fed to a separate electronic control module 15, and the A.C.
signals from the sensors 14 are fed to a common electronic control
module 16.
The system includes a supply circuit of hydraulic fluid under
pressure comprising a reservoir 17 for hydraulic fluid feeding an
electrically driven pump 18. The pump 18 pumps fluid under pressure
to an hydraulic accumulator 19. Fluid under pressure from the
hydraulic accumulator 19 is delivered through a first circuit to a
pair of control valves 20, and is then returned to the reservoir
17. Simultaneously fluid under pressure from the hydraulic
accumulator 19 is delivered through a second circuit to a third
control valve 21 and is then returned to the reservoir 17.
Each control valve 20 is adapted to regulate the supply of fluid
from the first circuit to an actuator 22 for controlling the
braking effort applied to one of the front wheels of the vehicle in
response to the D.C. output signal received from the control module
15 to which it is connected. The output signals from each control
module 15 are responsive to the deceleration of the front wheel
with which the module 15 is associated.
The control valve 21 is adapted to regulate the supply of fluid
from the second circuit to an actuator 24 for controlling the
braking effort applied to the rear wheels of the vehicle in
response to the D.C. output signal received from the control module
16. The output signals from the control module 16 is responsive to
the deceleration of the rear wheels of the vehicle.
.Iadd.Fluid from accumulator 19 is also delivered directly to
actuators 22, 26 to maintain them inoperative in a manner to be
described. .Iaddend.
A non-return valve 25 is located in the output side of the pump 18
to ensure that leak-back of pressure cannot occur in the system
which is maintained at substantially 300 p.s.i. by the pump. A
relief valve 26 is fitted in the line between the pump 18 and the
non-return valve 25 to protect the system from over-pressurization,
any overspill being returned to the reservoir through a by-pass
line 17.
The pump 18 is driven from the battery 28 of the vehicle, and the
accumulator 19 incorporates a pressure switch 29 of which the
contacts are held open when the system is fully pressurized. When
the pressure of the system falls, the contacts of the switch 29
close and energize a relay 30 to start up the pump 18 until the
system attains a normal working pressure when it is switched off by
the contacts of the pressure switch 29 which open automatically
again in response to the pressure attained in the hydraulic
accumulator 19.
The braking system shown in the layout of FIG. 2 is similar to that
illustrated in FIG. 1 and corresponding reference numerals
qualified by the suffix a have been used to indicate corresponding
parts.
In this embodiment the hydraulic accumulator 19 has been omitted
and the electrically driven pump 18a is supplied directly with
fluid from the reservoir 17a. The electrically driven pump 18a is
provided with two outlet lines 31 and 32. The line 31 delivers
fluid under pressure to the control valve 21a and, when the control
valve 21a is open, fluid is returned from the control valve 21a to
the reservoir 17a through a return line 33. Similarly the pump 18a
delivers fluid under pressure through the pipe-line 31 to the
control valves 20a which are connected in series by a pipe-line 34.
When the control valves 20a are open, fluid is returned from the
control valves 20a to the reservoir 17a through a return line
35.
Normally the control valves 20a and 21a are closed so that
hydraulic fluid under pressure is trapped in the lines 32 and 31
respectively on the downstream side of the non-return valve 18a
between the valve 18a and the control valves.
Each control valve 20, 20a and 21a is of the construction
illustrated in FIG. 3 of the drawings. As illustrated 36 is a
housing having a stepped cylindrical throughbore 37 of which
portions of the bore are separated by a partition member 38 having
a central opening 39. A chamber 40 between one face of the
partition member 38 and one end of the housing is formed with a
radial port 41 connected to the return line to the reservoir 17,
17a. The opposite face of the partition member 38 forms an abutment
for the inner end of a cup-shaped sleeve 42 which is formed in its
closed end with a central opening 43. The sleeve 42 is held in
engagement with the partition member 38 by a plug 44 screwed into
the opposite end of the bore 27 in a portion of enlarged diameter.
A spacer member 45 having a central opening 46 of substantial
diameter is clamped between the sleeve 42 and an adjacent face of
an annular member 47 of which the opposite face is in abutment with
the inner end of the plug 44.
The annular member 47 is provided with a central opening 48 of a
diameter substantially equal to that of the opening 43 and is in
communication with an axial passage 49 in the pump circuits.
A valve member in the form of a ball 50 is located in a chamber
between the sleeve 42 and the annular member 47 and is defined by
the opening 46. The ball 50 is adapted to engage with one of a pair
of axially spaced seatings surrounding the openings 43 and 48 to
prevent flow through that opening. The chamber 46 is connected by
the actuator 22, 22a or 24, 24a through a radial passage 51 in the
member 45 and a communicating radial port 52 in the cylinder
wall.
Normally the ball 50 is held against the seating surrounding the
opening 48 to cut-off communication between the high pressure
circuit and the actuator 22, 22a or 24, 24a by a push-rod assembly
53 located in the chamber 40 and extending through the opening 43
at its inner end. The push-rod assembly 53 is urged in this
direction by a pre-loaded spring 54 acting between an abutment
plate 55 and the inner end of the casing 56 of a solenoid assembly
57 adapted to be energized by D.C. supply from one of the
electronic control modules 15 or 16.
When the deceleration of one of the braked wheels exceeds a
predetermined value, the solenoid 57 of the control valve 22, 22a
or 24, 24a is energized by the D.C. supply from the module 15 or 16
associated with that wheel and the push-rod assembly 53 is
withdrawn against the force in the pre-loaded spring 54. The high
pressure fluid in the circuit acts on the ball 50 and urges it into
engagement with the seating surrounding the opening 43 to cut-off
communication with the reservoir 17, 17a through the port 41.
Simultaneously fluid under pressure passes to the corresponding
actuator 22, 22a or 24, 24a which operates in a manner to be
described.
When the deceleration of the wheel is reduced to a value at least
equal to the predetermined value, the solenoid 57 is de-energized
and the pre-loaded spring 54 acts on the push-rod assembly 53 to
urge the ball 50 into engagement with the seating surrounding the
opening 48. The high pressure fluid previously supplied to the
actuator 22, 22a or 24, 24a returns to the reservoir 17, 17a
through the opening 43, the chamber 40 and the port 41.
The actuator 24, 24a which is controlled by the control valve 21,
21a is illustrated in FIG. 4 of the accompanying drawings. The
actuator 24 comprises a body 58 in which is formed a through bore
having three stepped portions 59, 60 and 61 of constant
progressively increased diameter. The smallest diameter portion 59
of the bore leads into bore portion 62 of substantial diameter
terminating at one end of the body 58. A plug 63 having an axial
inlet passage 64 for connection in the pipe-line 4, 4a leading to
the rear wheel brakes is screwed in the outer end of the bore
portion 62. The inlet passage 64 at its inner end leads into a bore
65 which is counterbored at 66 at its opposite end to receive a
recessed annular member 67. The member 67 includes a forwardly
extending annular flange 68 which abuts against a shoulder 69 at
the step in diameter between the bore portions 59 and 62 and
projects inwardly beyond the inner end of the plug 63. A chamber 70
defined between the shoulder 69 and adjacent face of the member 67
and the plug 63 is connected to the slave cylinders 6, 6a of the
rear wheel brakes through radial openings 71 in the flange 68, and
a port 72 in the cylinder wall.
A stepped piston assembly works in the stepped bore and comprises a
differential actuator piston 73 working in the portions 60 and 61
of the bore. The piston is arranged such that when the outer end of
the portion 74 of lesser diameter is in abutment with a step 75 at
the change in diameter between the bore portions 60 and 59, the
portion 76 of greater diameter is spaced from a step 77 at the
change in diameter between the portions 61 and 60 to define a
chamber 78 connected through an inclined drilling 79 to the port 52
of the control valve 21, 21a. A cup-shaped piston 80 located within
the chamber 98 is slidably mounted on the piston portion 74 and is
normally urged into engagement with the step 77 by a spring 81. The
travel of the piston 80 relative to the portion 74 is limited by
the engagement with the piston 80 of a stop ring 82 carried by the
stepped piston portion 74.
An expander piston 83 works in the portion 59 of the bore and is of
such a length as to project into the chamber 70 when the portion 74
of the stepped piston assembly is in engagement with the step 75.
The end 81 of the expander piston 83 remote from the portion 74 is
in abutment with the inner end of a pair of concentric valve stems
85 and 86 which project into the bore 65 in the plug 63 through a
central opening 87 in the member 67. A clearance 88 is provided
between the outer stem 86 and the opening 87 and a bleed hole 89
also connects the chamber 65 to a clearance 88 between the stem 85
and 86, so that fluid from the master cylinder 1, 1a can pass to
the slave cylinders 6 of the rear wheel brakes when the brakes are
applied normally. The inner stem 65 is longer than the outer stem
86, and each stem carries a valve head 90 and 91 respectively at
its outer end. The inner ends of the valve stems 85 and 86 are
normally urged into engagement with the outer end of the expander
piston 83 by concentric compression springs 92 and 93 in abutment
with a centrally apertured plate 94 in engagement with the end of
the bore 65 remote from the expander piston 83.
The larger diameter portion 76 of the actuator piston 73 is formed
in its outer end with an axially extending recess or blind bore of
an area less than the area 96 of the step in diameter between the
portions 76 and 74 of the piston 73. A piston 97 works the bore 95
and is urged towards the base of the recess by a spring 98 which
acts as a stop. The spring 98 is located between the inner end of a
cage 99 surrounding the portion of the body containing at least a
part of the portion 61 of the bore and engaging with the piston 97.
An abutment plate 100 is secured to the body 58 and is held in a
fixedly spaced relationship thereto by an axially extending cage or
shroud 101.
The piston 97 has an axial passage 102 leading into the recess 95
to which fluid under pressure is supplied from the hydraulic
accumulator 19 or the pump 18a for applying to the piston a force
in opposition to and greater than the force in the spring 98. The
valves 90 and 91 are normally held in open positions when the brake
is applied by a force acting on the pistons 73 and 88 which is
greater than the force in the springs 92 and 93 plus the force
exerted on the expander piston 83 by the fluid pressure from the
master cylinder 1, 1a.
For normal operation of the system fluid under pressure is supplied
from the master cylinder 1, 1a to the slave cylinders 6, 6a, 9, 9a
and 12, 12a of the wheel brakes to apply the brakes.
When the deceleration of one of the rear wheels exceeds a
predetermined value the solenoid 57 of the control valve 21, 21a is
energized as described above to deliver fluid under pressure from
the accumulator 19 or pump 17a to the chamber 78 in the bore
portion 61. The pressure acts on the area 96 between the piston
portions 74 and 76 to move the actuator piston 73 rearwardly from
the step 75. Due to the loading in the springs 92 and 93 and the
master cylinder pressure in the chamber 65 the expander piston 83
follows this movement to increase progressively the effective
volume of the chamber 70 and permit the valve head 91 to cut off
flow through the clearance 88, and subsequently permit the valve
head 90 to seat on the head 91 and cut-off flow through a clearance
between the concentric valve stems 85 and 86. Thus the supply of
braking fluid from the master cylinder 1, 1a to the slave cylinders
of the rear wheel brakes is cut-off. Thereafter further rearward
movement of the actuator piston 73 and the expander piston 83 serve
to increase still further the effective volume of the chamber 70 to
relieve the pressure applied to the rear wheel brakes thus
decreasing the rate of decleration of the wheels. During this
movement the piston 80 is initially held in engagement with the
step 77 by the force in the spring 81 until the piston 80 is
carried rearwardly by the piston 73 due to the engagement with the
piston 80 of the stop ring 82.
When the deceleration of the wheel is reduced to the predetermined
value and the solenoid 66 is de-energized to close the control
valve 21, 21a the supply of fluid from the accumulator 19 or pump
17a to the chamber 78 is cut-off and the chamber 78 is placed in
communication through the control valve 21, 21a with the reservoir
17, 17a. Initially, fluid is returned rapidly to the reservoir 17,
17a until the piston 80 again engages return of fluid is less rapid
as it is accomplished by a bleed through an orifice 103 in the
piston 80. Thus there is a delay until a point is reached in which
the valves 90 and 91 open sequentially to permit re-application of
the brakes in the normal manner and at the original pressure as
described above. However, before the point of re-application
referred to above is reached, in any case the brakes are re-applied
progressively at an intermediate pressure less than that of the
master cylinder 1, 1a due to the progressive insertion of the outer
end of the expander piston 83 into the chamber 70 to reduce the
effective volume of the chamber and pressurize the trapped volume
of fluid contained therein.
The delay in relieving the pressure in the chamber 78 due to the
provision of the orifice 103 has the advantage that a sufficient
interval of time is available for the sensors 14 to sense what is
occuring during the progressive re-application of the brakes by the
movement of the expander piston 83 into the chamber 70.
Specifically movement of the actuator piston in a direction to
permit the valves 90 and 91 to close it faster than in the opposite
direction to open the valve.
Reciprocation of the expander piston 83 may occur a number of times
to affect re-application of the brakes in response to wheel
acceleration or deceleration before the valve 90 and 91 are
re-opened. Such reciprocation of the expander piston 83 is
controlled by movement of the actuator piston 73 which in turn are
dictated by operation of the control valve 21, 21a regulating the
supply of fluid under pressure to the chamber 78 as described
above. Reopening of the valves 90 and 91 occurs only when the
braked wheel contacts a surface of a co-efficient of friction
higher than the surface with which that wheel was previously in
contact and capable of accepting a braking force corresponding to
the fluid pressure trapped in the line between the actuator 24, 24a
and the slave cylinder 6, 6a in accordance with the position of the
expander piston 83. Alternatively, re-opening of the valves 90 and
91 occurs when the pedal pressure applied to the master cylinder 1,
1a is reduced by a sufficient amount.
The actuator described above with reference to FIG. 4 is suitable
for use when only the pressure in a single line to a wheel brake or
brakes is/are to be regulated.
Where the brakes on wheels of a vehicle are cross-connected, that
is to say when separate slave cylinders of the same brakes are
supplied with fluid from different pressure spaces of a master
cylinder, as for example the front wheel brakes of the layout
illustrated in FIGS. 1 and 2 of the drawings, it is necessary for
the pressure in each supply line to the slave cylinders of the same
brake to be regulated simultaneously.
This can be achieved by a pair of expander pistons 83 arranged in
separate bores in the body of the actuator and operated
simultaneously by a single actuator piston assembly. Such a tandem
actuator assembly is illustrated in FIG. 5 of the drawings and
corresponding reference numerals qualified by the suffix b have
been used to indicate the parts which correspond to and are
identical with those in the actuator described above with reference
to FIG. 4.
It will be seen from FIG. 5 of the drawings that two expander
pistons 83b are provided and each piston regulates the effective
volume of a chamber 70b at the outer end of bore portion 59b in
which that piston works. The plugs 63b are each connected in the
pipe-lines 11, 11a and 8, 8a to the separate slave cylinders 12,
12a, 9, 9a of the brakes on one front wheel of the vehicle, and the
passages 72b leading from the chambers 70b are connected in
corresponding pipe-lines on the downstream slave cylinder side.
An actuator as illustrated in FIG. 5 is provided for each of the
front wheels of the vehicle and each actuator is controlled by a
separate control valve 20, 20a responsive to the deceleration
sensed by the sensor 13, 13a of the wheel supplying a signal to the
control module 15 of that control valve.
When the brakes are applied by operation of the master cylinder 1,
1a the slave cylinders 12, 12a and 9, 9a are operated by the supply
of fluid under pressure through the inlet ports 64b the chambers
71b and the outlet passages 72b.
When the deceleration of one of the front wheels exceeds a
predetermined value, the control valve responsive to deceleration
of that wheel supplies high pressure fluid to the chamber 78b as
described above with reference to FIG. 4 and the subsequent
sequence of operation is as described above except that both
expander pistons 83b are operated simultaneously to regulate the
supply of fluid pressure through the pipe-line 8, 8a and 11, 11a
simultaneously.
The advantage of the construction illustrated in FIG. 5 is that
only half the stroke is required as compared with that of in-line
assembly. Furthermore normal braking performance is available in
the event of failure of one of the expander pistons 83b or its
associated braking system. That is to say the total force applied
by the actuator piston 73b is then applied to one expander piston
area resulting in twice the output pressure being applied to its
associated braking circuit.
In the embodiments described above the single actuator 24, 24a and
each tandem actuator 22, 22a may each be embodied into a single
unit with the control valve 21, 21a or 20, 20a by which it is
controlled.
In the braking systems described above with reference to FIGS. 1
and 2 the brakes on the front wheels of the vehicle are applied
from separate pairs of slave cylinders 9, 9a and 12, 12a.
Preferably, each pair of slave cylinders actuates a single disc
brake. When the slave cylinders of each pair are of equal diameters
and cross-section the expander pistons 83b are of equal
cross-section. However, when the slave cylinder of each pair are of
different diameter, the cross-section areas of the expander pistons
83b are different to compensate for the differencd in cross-section
area between the slave cylinders as shown in the actuator
illustrated in FIG. 6 of the drawings.
The actuator illustrated in FIG. 6 of the drawings is substantially
identical with the actuator ilustrated in FIG. 4 and corresponding
reference numerals, qualified by the suffix c have been applied to
corresponding parts.
In the actuator illustrated in FIG. 6 of the drawings the spaced
parallel bore portions 72c in which the expander pistons 83c work,
are of different diameters, in total less than that of the actuator
piston 73c. The outer end of each bore portion 72c leads into a
bore 65c through an opening 103 in an annular partition 104 through
which projects a stem 105 at the inner end of the expander piston
83c working in the bore 65c with which that bore 72c is in
communication. Each stem 105 is adapted to engage a valve member
106 in the form of a ball which is normally urged towards a seating
surrounding the opening 103 in the partition by means of a spring
107 acting between the ball 106 and a plug 108 screwed into the
outer end of that bore 65c. The bores 65c which are of equal
diameters, are connected to the master cylinder 1, 1a through
radial ports 109.
In the position shown in the drawings, the expander pistons 83c are
in positions in which the chambers defined by the bore portions 70c
are of minimum effective volumes. In this position hydraulic fluid
is supplied to the slave cylinders of the brake circuits through
the radial ports 72c in the cylinder wall at pressures commensurate
with the capacities of the slave cylinders so that each slave
cylinder applies an equal force to the brake.
When the deceleration of a braked wheel exceeds a predetermined
value, and the actuator piston 73c is retracted due to the force in
the springs 107 and the balls 106 engage with their seatings and
cut off communication between the bores 65c and the chambers 70c.
Thereafter, further movement of the expander pistons 83c in the
same direction increases the effective volumes of the chambers 70c
but at different rates to compensate for the differences in the
volumes of hydraulic fluid supplied to the slave cylinders in
accordance with their respective capacities. This ensures that,
although the braking pressure supplied to the brakes of the
separate braking circuits is relieved, the rate at which this is
achieved is chosen to maintain equal braking efforts on the brakes
of the circuit.
In the actuators described above with reference to FIGS. 4 and 5 of
the drawings means are incorporated to delay re-application of a
wheel brake following cut-off in the supply of braking fluid to the
brakes and subsequent reduction in the pressure of the braking
fluid when the deceleration of the braked wheel has exceeded a
predetermined value.
The actuator illustrated in FIG. 7 of the drawings comprises a
modified form of the actuator illustrated in FIG. 4 but the
modifications illustrated in FIG. 7 could also be embodied in the
construction of the FIG. 5. In the embodiment of FIG. 7 reference
numerals qualified by the suffix d have been applied to parts which
correspond to those in FIG. 4.
In fact the actuator illustrated in FIG. 7 is identical with that
illustrated in FIG. 4 except that the piston 80 and the spring 81
have been omitted, and the valve stems 86 and 85 and the heads 91
and 90 which they carry have been replaced by a modified valve
assembly.
In FIG. 7 the body 58d of the actuator is provided with a pair of
inclined drillings 79d leading into the chamber 78d. Each drilling
79d is provided at its outer end with an internally screw-threaded
counterbore 110 into which is screwed one end of a one-way valve
assembly 111. Each one-way valve assembly 111 comprises a pair of
complementary housing members 112, 113. Each housing member 112,
113 is provided with an axial through bore 114 and 115 respectively
which is counterbored at 116 and 117 respectively for a substantial
portion of its length. The housing member 112 is reduced in
external diameter for substantially the length of the counterbore
116, and that portion of the housing member 112 is screwed into
engagement in the counterbore 117 of the housing member 111.
An annular washer 118 of deformable material, suitably copper is
located between the outer end of the housing member 13 and a
shoulder at the step in diameter of the external surface of the
housing member 112. The shoulder is stepped at 119 so that when the
housing members are clamped together, the material of the washer
118 is deformed over the step to form an effective seal between the
housing members.
A plate 120 having a central orifice 121 is clamped between the
base of the counterbore 117 in the housing member 113 and the inner
end of the housing member 112, and a resilient annular sealing ring
122 interposed between the housing member 112 and the plate 120
forms a seal between the housing members 112, 113 and the plate
120.
A valve member 123 in the form of a ball located within a chamber
defined by the counterbore 116 is normally urged into engagement
with a valve seating surrounding the orifice 121 by means of a
compression spring 127 acting between the ball 123 and the base of
the counterbore 116.
The one-way valve assemblies are mounted in the counterbores 110 in
opposite directions so that for fluid flows in the same direction
one valve assembly is open and the other remains closed. The free
outer end of each valve asembly 111 is connected to a pipe-line
leading to one of a pair of outlet ports in the control valve 21,
21a (FIGS. 1 and 2).
A single valve member in the form of a ball 124 is housed within a
chamber defined by the bore 65d and an adjacent end of the member
67d. The ball 124 is urged towards a seating surrounding the
central opening 87d in the member 67d by a compression spring 125
but normally, the ball 124 is held away from the seating by a rod
or extension 126 integral with or carried by the adjacent end of
the expander piston 83d. The rod or extension 126 is of a diameter
less than that of the opening 87d through which it normally
projects into bore 65d.
The operation of the actuator in accordance with our present
invention is substantially identical with that of the actuator
described above with reference to FIG. 4. That is to say, for
normal operation of the system, fluid under pressure is supplied
from the master cylinder 1, 1a to the slave cylinders of the wheel
brakes. The slave cylinders of at least one wheel brakes are
supplied with fluid from the outlet port 72d which receives fluid
from the bore 65d through the clearance between the rod or
extension 126 and the opening 87d in the member 67d, since the ball
124 is held away from its seating.
However, when the deceleration of one of the rear wheels exceeds a
predetermined value and the solenoid of the control valve 21, 21a
is energized to deliver fluid under pressure from the accumulator
19 or pump 18a to the chamber 78d, the fluid pressure is delivered
to the chamber 78d through the one-way valve assembly 111 at the
foot of the drawings. That is to say, the pressure fluid pressure
acts on the ball 123 to move it away from the seating against the
force in the compression spring 117 to permit fluid to enter the
chamber 78d through the counterbore 117, the bore 114 and the
drilling 79d. The other one-way valve remains closed due to
pressure from the accumulator or pump acting on it in an opposite
direction. As the expander piston 83d moves rearwardly, the rod 126
is progressively withdrawn through the opening 87d to permit the
ball 124 to engage with its seating and cut off the supply of
braking fluid to the rear wheel brakes through the opening 87d.
When the deceleration of the wheel attains the predetermined valve
the supply of fluid from the accumulator or pump is cut off and,
since there is no pressure acting on the uppermost one-way valve
111, as illustrated in the drawings, the pressure of fluid with the
chamber 78d is returned to the reservoir 17, 17a through that
one-way valve 111 as the expander piston 83d moves forwardly to
decrease the effective volume of the chamber 70d. During this
forward movement of the expander piston 83d, the rod 126 may engage
with the ball 124 to urge it away from its seating and permit the
wheel brakes to be re-applied at full pressure as described
above.
The damping characteristics of the actuator may be adjusted by
altering the diameters of the orifices 121 in the plates 120 within
the one-way valves 111. This is achieved by replacing an existing
plate 120 with an interchangeable plate provided with an orifice of
a different diameter.
In a modification each ball 123 is adapted to engage a seating
surrounding a central opening in a plate interposed between the
ball 123 and the plate 120. The orifice 121 in each plate 120 is of
a diameter smaller than that of the opening in the plate forming
the seating to provide restriction for the flow of fluid through
the one-way valve assembly 111 in which that plate 120 is
incorporated.
In the embodiments of actuator described above with reference to
FIGS. 5 and 6 a pair of expander pistons working in spaced parallel
bores are adapted to be operated by a single actuator piston. As
illustrated in the embodiment of FIG. 8 where corresponding
reference numerals qualified by the suffix e have been applied to
corresponding parts a single expander piston 83e working in a bore
59e is adapted to control the pressure applied to a pair of
separate slave cylinders when the deceleration of a wheel brake or
brakes actuated by those slave cylinders exceeds a predetermined
value.
In the embodiment of FIG. 8 the bore 59e is of substantial length
and the wall of the bore 59e, at an intermediate point in its
length accomodates a spring loaded tipping valve 130 controlling
the supply of fluid under pressure from the master cylinder 1, 1a
to a slave cylinder through an outlet port 131 in the wall. The
stem 132 of the tipping valve 130 extends into the bore 59e and is
received in an axially extending recess 133 of substantial length
in the expander piston 83e. Normally the tipping valve 130 is held
in a tipped-open position by the engagement with its stem of one
end of the recess 133. In this position a ball 134 housed in a bore
135 in the plug 63e is held away from a seating surrounding a
central opening 136 in the member 67e by a rod or extension 137
carried by the expander piston 83e and projecting through the
opening 136 to engage the ball 134.
When the deceleration of the braked wheel or wheels exceeds the
predetermined value and the actuator piston 73e is retracted, the
expander piston 83e also retracts due to the provision of a return
spring 138 acting between the free end of the expander piston 83e
and the member 67e. This allows the valves 134 and 130 to close and
cut off the supply of braking fluid to the slave cylinders. Further
retraction of the expander piston 83e increases the effective
volume of the chamber 70e as described above.
The expander piston 83e comprises a two part assembly. The port 139
in abutment with the actuator piston 73e is then withdrawn further
with respect to the other part. This increases the effective volume
of a chamber in communication with the other slave cylinder and
defined within the bore 59e between the end of the part 139 remote
from the actuator piston 73e and the end of the recess 133 which is
remote from the end of the part 140 which normally engages with the
part 139. Thereafter successive re-application and release of the
brakes controlled by the slave cylinders takes place as described
above with reference to the preceding embodiments.
* * * * *