Note: Descriptions are shown in the official language in which they were submitted.
~2S~8(~
The present invention relates generally to a control
valve for use in a vehicle s~id control system and, in
particular, to a control valve for use in a vehicle skid
control system wherein the braking of a predetermined
number of wheels of a multi-wheeled vehicle is controlled
and at least one braked wheel of the vehicle is not
controlled by the skid control system, and to a brake
control system employing such a valve.
Braking a vehicle in a controlled manner under
adverse conditions such as rain, snow, or ice generally
requires precise application of the brakes by the vehicle
driver. Under these conditions, or in panic stop
situations, a driver will often apply excessive brake
pressure, thus causing the wheels to lock such that
excessive slippage between the wheels and the road surface
takes place. Wheel lockup conditions can lead to loss of
directional stability and, possibly, uncontrolled vehicle
spinout.
In a continuing effort to improve the operational
safety of vehicles, many companies have been involved in
the development of skid control braking systems. While
typically such systems are adapted to control the braking
of each braked wheel of a vehicle, some systems have been
developed for controlling the braking of only a portion of
the braked wheels. Examples of prior art skid control
systems are disclosed in United States Patent Nos.
3,515,440, 3,870,376 and 3,880,474~
Generally, prior art skid control systems include a
central control unit for monitoring the speed of the
controlled wheels to determine the deceleration of the
controlled wheels. When the brakes of the vehicle are
applied and the wheel deceleration of the monitored wheels
exceeds a predetermined deceleration threshold, indicating
that there is wheel slippage and the wheels are
approaching a lockup condition, the central control unit
functions to control the application of hydraulic pressure
through a suitable valve means to the associated brakes to
~- prevent lockup of the controlled wheels. Typically, the
~S~3 ~80
skid control system includes means for cyclically
relieving and reapplying pressure to the associated brakes
to limit wheel slippage to a safe level while continuing
to produce adequate brake torque to decelerate the vehicle
as desired by the driver. In these systems, the means for
reapplying pressure is generally a separate hydraulic
power source.
Despite the tremendous advantages a skid control
system can provide in stopping a vehicle in a controlled
manner under adverse braking conditions, very few vehicles
are ac-tually provided with such control systems. One of
the chief reasons for this is that the control units and
associated valving of such systems are somewhat
sophisticated and expensive, and are therefore typically
only found on more expensive vehicles.
The present invention concerns a unique con-trol valve
for use with a vehicle anti-lock braking system.
Basically, the anti-loc~ braking system is adapted to
control, via the control valve, the application of brake
fluid pressure to at least one selected braked wheel of an
associated vehicle. When an incipent wheel loc~ condition
of the controlled wheels is detected, further application
of fluid pressure to the controlled wheel brake is cut off
by the control valve and the fluid pressure to the
controlled wheel brakes at that time is held at a
relatively constant level, and is maintained at that level
during the completion of the wheel stop unless certain
conditions are present. For example, if after the brake
pressure is held, the controlled wheel deceleration
exceeds the predetermined amount, the control valve is
operated to selectively reduce the brake pressure to the
controlled wheel to reduce excessive wheel slippage.
Also, after a wheel slip condition has been
corrected, the system is designed to detect when the
vehicle travels from a relatively low friction surface
(i.e. ice) to a relatively high friction surEace (i.e.
concrete). In these instances, the brake wheels not
- con-trolled by this skid control system will cause the
.J_
. .
lZS84t30
vehicle to decelerate at a greater rate. Under these
conditions, the brake pressure applied to the controlled
wheels can generally be increased without causing a lock
up condition. The braking system detects such an increase
in deceleration and operates the control valve to
selectively cause additional pressure to be supplied to
the controlled wheel brakes.
The control valve of the present invention is
specifically useful in a skid control system for a vehicle
having first and second sets of wheel brakes. In such a
system, a brake pedal is operable by the vehicle operator
and is connected to actuate a master cylinder for
supplying pressurized brake fluid. The pressurized brake
fluid is supplied to a first brake pressurizing circuit to
actuate the first set of wheel brakes, and is also
supplied to a second brake pressuring circuit to actuate
the second set of wheel brakes. The control valve of the
present invention is connected in the second brake
pressurizing circuit, and is operable by a computer
control means.
More specifically, the present invention provides a
control valve for use in a vehicle anti-lock braking
system adapted to control the application of pressurized
brake fluid to at least one selected vehicle brake, the
valve comprising, an outer housing having an inlet for
receiving pressurized brake fluid and an outlet for
supplying pressurized brake fluid to the selected vehicle
brake, the housing having a passageway formed therein for
connecting the inlet to the outlet, normally open
isolation valve means located in the passageway for
controlling the flow of fluid through the passageway
between the inlet and the outlet, the valve means movable
between a normally open position wherein fluid can flow
from the inlet to the outlet and a closed position wherein
fluid is prevented from flowing from the inlet to the
outlet, means for exerting a biasing force to urge the
valve means toward the normally open position, solenoid
means responsive to a control signal for moving the valve
~'',
~ZS8~8~
means from the open position to the closed position, the
valve means and the housing means cooperating to define a
chamber for containing brake fluid, the chamber varying in
volume as the valve means i5 moved from the closed
position to the open position, and hydraulic damping means
associated with the valve means for restricting fluid flow
between the passageway and the chamber for damping the
movement oE the valve means as the valve means is moved
from the closed position to the open position whereby the
opening of the valve means is precisely controlled.
The present invention further provides a brake
control system for a wheeled vehicle having first and
second sets of wheels provided with first and second sets
of wheel brakes, a brake pedal operable by the vehicle
operator, a master cylinder connected with and actuated by
the brake pedal to supply pressurized bra~e fluid in a
first brake pressurizing circuit to actuate the first set
of wheel brakes and to supply pressurized brake fluid in a
second brake pressurizing circuit to actuate the second
set of wheel brakes, the second brake pressurizing circui-t
including a control valve for controlling the application
of fluid to the second set of wheel brakes and a con-trol
means for operating the control valve, the control valve
comprising, an outer housing having an inlet coupled to
receive pressurized brake fluid from the master cylinder
and an outlet coupled to supply pressurized brake fluid to
the second set of wheel brakes, the housing having a
passageway formed therein for connecting the inlet to the
outlet, normally open isolation valve means located in the
passageway for controlling the flow of fluid through the
passageway between the inlet and the outlet, the valve
means being movable between an open position wherein fluid
can flow ~rom the inlet to the outlet and a closed
position wherein fluid is preven-ted from flowing from the
inlet to the outlet, means for exerting a biasing force to
urge the valve means toward the normally open position,
solenoid means responsive to a first control signal from
the control means for closing the isolation valve means to
~;~ '
1~2S8~80
hold the fluid pressure to the second set of brakes at a
relatively constant level, the solenoid means responsive
to a second control signal from the control means for
momentarily opening the isolation valve means for a
predetermined time period after the valve means has been
closed to selectively reapply pressure from the master
cylinder to the second set of wheel braXes, the valve
means and the housing means cooperating to define a
chamber for containing brake fluid, the chamber adapted to
vary in volume as the valve means is moved from the closed
position to the open position, and hydraulic damping means
associated with the valve means for restricting fluid flow
between the passageway and the chamber for damping the
movement oE the valve means as the valve means is moved
from the closed position to the open position whereby the
opening of the valve means and the selective reapplication
of master cylinder pressure to the second set of wheel
brakes is precisely controlled.
The present invention will become more readily
zo apparent to those skilled in the art when the following
detailed description of an embodiment of the invention is
read in conjunction with the attached drawings, in which:
Figure 1 is a schematic diagram illustrating the skid
control system which utilizes a control valve embodying
the present invention;
Figures 2 and 3 are perspective views of the
preferred embodiment of the control valve of the present
invention;
Figure 4 is a sectional view, taken along the line 4-
4 of Figure 3 and illustrating the positions of theisolation valve, the dump valve, and the accumulator
within the control valve;
Figure 5 is a sectional view taken along the line 5-
5 of Figure 2 and illustrating the position of the
pressure differential switch within the control valve;
Figure 6 is an exploded perspective view illustrating
the individual components of the isolation valve and dump
valve;
~ 258~8o
Figure 7 is an exploded perspective view illustrating
the individual components of the pressure differential
switch;
Figure 8 is an enlarged sectional view of the
isolation valve as illustrated in Figure 4;
Figure 9 is an enlarged sectional view of the dump
valve as illustrated in Figure 4; and
Figure 10 is an enlarged sectional view of the
pressure differential switch as illustrated in Figure 5.
Referring to the drawings, and particularly to Figure
1, there is shown a schematic diagram of an anti-skid
control system which utilizes a control valve 10 embodying
the features of the present invention. The anti-skid
control system is specifically adapted to monitor and
control the braking of a predetermined number of wheels of
a multi-wheeled vehicle having at least one braked wheel
which is not connected to the anti-skid control system.
For example, as illustrated in Figure 1, the anti-skid
control system can be utilized to control the braking of
the rear wheels of a four wheeled vehicle wherein the
front brakes of the vehicle are not controlled by the
anti-skid control system. Such a system is especially
desirable for a vehicle such as a small truck, for
example, wherein the weight supported by the rear wheels
can vary greatly due to the wide range of payloads the
truck may be transporting.
As shown in Figure 1, the anti-skid control system is
installed on a vehicle having a hydraulic braking system
consisting of a brake pedal 12 coupled to operate a dual
-reservoir master cylinder 14. When the vehicle operator
depresses the brake pedal 12, the master cylinder 14
supplies hydraulic fluid under pressure from a front
reservoir 14a through a hydraulic line 16a and from a rear
reservoir 14b through a hydraulic line l~b to a
conventional combination valve 18. The combination valve
18 includes a first output line 18a adapted to supply
hydraulic fluid at a first predetermined pressure to
actuate the vehicle front brakes l9a and l9b and a second
~....
~Z58480
~ 7
output line 18b which supplies fluid ~t a second
predetermined pressure to actuate the vehicle rear brakes
20a and 20b. While not shown in the drawings, the
combination valve 18 is typically provided with an
integral pressure differential switch for detecting a
predetermined pressure difference between the fluid in the
lines 16a and 16b, which difference is indicative of a
partial brake failure.
The anti-lock control valve 10 is provided with a
normally open isolation valve 22 connected between the
line 18b and a line 24 which supplies the pressurized
brake fluid to the rear brakes 20a and 20b. As will be
discussed, the isolation valve 22 is solenoid operated and
is closed in the event impendin~ rear wheel lockup is
detected to hold the pressure in the line 24 and thus
prevent any further increase in pressure in the line 18b
from being supplied to the line 24.
Also, the anti-lock control valve 10 includes a
normally closed dump valve 26 connected between the line
24 and a line 27 which is connected to an accumulator 28.
The accumulator 28 includes a variable volume fluid
reservoir 28a for containing hydraulic fluid which is
maintained at a slightly elevated pressure by a slidable
piston 28b biased by a spring 28c. More specifically, the
spring 28c maintains the fluid in the accumulator at a
pressure slightly above the non-actuated pressure of the
fluid in the line 24. As will be discussed, when the
isolation valve 22 has been closed and the pressure held
in the line 24 continues to cause excessive slippage of
the rear wheels, the dump valve 26 is selectively opened
to direct fluid into the accumulator 28 to reduce the
pressure in the line 24 and prevent lockup of the rear
brakes. After the brake pedal 12 has been released, the
dump valve 26 can be momentarily opened to return fluid in
the accumulator 28 to the line 24.
The operation of the isolation valve 22 and the dump
valve 26 is controlled by a computer control module 30.
The isolation valve 22 and the dump valve 26 are solenoid
..
i258~80
7a
operated valves wh~ch can be connected to the computer
control module by means of electric lines 32 and 34
respectively. In order to determine whether the vehicle
operator is in the process of braking the vehicle, the
computer control 30 is connected to a brake light switch
36 by a line 38 to monitor whether of the brake pedal 12
is depressed. The computer control module 30 is also
connected to a speed sensor 40 by a line 42 to monitor the
speed of the vehicle rear wheels.
In addition to monitoring the position of the brake
pedal 12 via the brake light switch 36 and the rear wheel
speed via the speed sensor 40 r the computer control module
:.. - ....
,~
",
~;258~80
30 is connected to a pressure difference switch 44 by a
line 46. The pre~sure differential switch 44 is coupled to
monitor the pressure difference between the fluid in the
lines 18b and 24 and i5 adapted to close when the pressure
in the line 18b is greater than the pressure in the line
24. When the pressure differential switch is in the on
state, this indicates that the isolation valve has closed
and that the pressure in the line 18b is greater than the
pressure in the line 24 and, when the ~witch is in the off
state, this indicates that the pressure in the line 18b is
equal to or has dropped below the pressure in the line 24.
In instances wherein the switch 44 has turned on, and
has subsequently turned off, this indicates a situation
wherein the operator has initially applied a relatively
heavy braking effort to the brake pedal to cause the
isolation valve to close to prevent lockup of ~he rear
wheels and, subsequently, has reduced braking effort to the
pedal without necessarily completely releasing the pedal.
It is in this situation where it is desirable to release
the anti-lock mode and return the braking Fystem to the
normal operating mode. Thus, if the system senses that the
pressure differential switch 44 has at one point turned on,
but is now off, the system will return to the normal
braking mode and the beginning of the loop. Typically,
there is 60me hysteresis associated with the operation of
the pressure differential switch 44 such that the switch 44
does not chatter between an on and off condition when the
pressure in the line 18b remains xelatively equal to the
pressure in the line 24. Also, the control module 30 is
connected to a brake warning light 48 which is activated in
the event a failure in the anti-lock brake system is
detected.
Basically, the anti-lock brake system monitors the
rear wheel speed and deceleration and, during a vehicle
stop, functions to control the application of hydraulic
pressure to the vehicle rear brakes via the control valve
lZS8q~80
10 in order to prevent a lockup condition o~ the brakes.
In the event a wheel slip condition is detected,
indicating the rear brakes are approaching a lockup
condition, the control module 30 closes the isolation
valve 22 to hold the pressure in the line 24 at its
present value. If, after the isolation valve 22 has been
closed, the rear wheel deceleration rate exceeds a
predetermined amount, the dump valve 26 can be selectively
opened to reduce the pressure in the line 24 to prevent a
lockup condition of the brakes.
Also, after an impending lockup condition has been
corrected, the rate of change of deceleration of the rear
wheels is monitored to detect instances wherein the
vehicle travels from a road surface such as ice wherein
the coefficient of friction (mu) between the vehicle and
the road surface is relatively low (low mu surface) to a
road surface such as concrete wherein the coefficient of
friction between the vehicle and the road surface is
relatively high (high mu surface). In these instances,
when the vehicle front wheels contact the higher mu
surface, the uncontrolled front brakes will cause an
increase in the rate of deceleration of the vehicle as the
vehicle travels from the low mu surface to the high mu
surface. Under these conditions, the pressure held in the
line 24 to the rear brakes can generally be increased to
provide further braking without causing a lockup condition
of the rear brakes. This is accomplished by momentarily
opening the isolation valve 22 to permit the higher
pressure fluid in the line 18b to be supplied to the line
24. Due to the continued braking effort by the driver on
the vehicle brake pedal under a hard braking condition,
the pressure in the line 18b will generally be higher than
the pressure in the line 24. As will be discussed, the
isolation valve 22 is provided with damping means which
enables the momentary opening of the valve to be precisely
controlled to regulate the pressure increase to the rear
brakes.
iZS8~80
The specific construction of the control valve 10 will
now be discussed in more detail. Referring to F$gs. 2 and
3, there are shown perspective views of a preferred
embodiment of the anti-lock control valve 10. The control
valve 10 includes an outer two-piece housing S0 which, as
viewed in the drawings, consists of a left end housing
portion 50a and a right end housing portion 50b. An
intermediate gasket member 52 (a perspective view of which
is shown in Fig. 7) is positioned between the facing ena
surfaces of the housing portions 50a and 50b and, as shown
in Fig. 4, ~unctions to seal a longitudinally extending
inner cavity 54 formed in the housing 50. The housing end
portions 5~0a and 50b are fastened together by means of a
plurality of elongated bolts 55 extending through apertures
formed in the right end housing portion 50b and threaded
into cooperating internally threaded apertures formed in
the left end housing portion 50a.
The valve 10 includes an inlet fitting 56 which, as
shown in Fig. 4, is threaded into the side wall of the
right end housing portion 50b and is sealingly connected
thereto by means of an O-ring 56a. The inlet fitting 56 i5
adapted to be connected to the line 18b to receive
pressurized brake fluid from the combination valve 18. An
outlet fitting 58 extends through an opening 52a (see Fig.
7) formed in the gasket member 52 and is adapted to be
connected to the line 24 to supply pressurized fluid to the
rear brakes. A conventional bleed screw 60 is threaded
into the side wall of the left end housing portion 50a and
is utilized during installation or service of the brake
system to bleed the associated fluid passageways contained
within the valve 10. Further, a plurality of internally
threaded mounting holes 62 can be provided in the housing
portions 5Da and 50b for attaching the valve ~o the vehicle
body (not shown).
As previously mentioned, the control valve 10 includes
the isolation valve 22, the dump valve 26, the accumulator
'" i ., '~,"Y ~ ` ' " ~ ' "~
lZS8~30
11
28, and the pressure differential switch 44, all of which
are shown in individual boxes in Fig. 1. As shown in Fig.
4, the components of the isolation valve 22 and the dump
valve 26 are housed within the longitudinally extending
cavity 54 defined by the cooperation of the left end
housing portion 50a, the gasket member 52, and the right
end housing portion 50b. The isolation valve components
and the dump valve components are separated within the
housing cavity 54 by an intermediate core member 66.
As will be discussed, the core member 66 is provided
with a number of internal passageways for directing fluid
flow through the valve. For example, as shown in Fig. 4,
pressurize~ brake fluid having entered the valve 10 through
the inlet 56 and having passed the normally open isolation
valve 22 enters a longitudinally extending passageway 66a
formed through the core member 66 and is supplied to the
outlet fitting 58 through an outlet passageway 66b
extending transversely to the passageway 66a. The outlet
fitting 58 is threaded into the passageway 66b and is
sealingly connected thereto by an O-ring 58a. As shown in
Fig. 4, a pair of solenoid coils 64a and 64b are positioned
within the housing cavity 54 and are maintained in axially
spaced apart relationship by means of the core member 66.
The solenoid coil 64a is adapted to actuate the
isolation valve 22, while the solenoid coil 64b is operable
to actuate the dump valve Z6. The components of the
accumulator 28 are located within a cavity 50c formed in
the outer end of the housing portion 50a. The outer open
end of the 50c cavity is sealingly closed by means of an
externally threaded plug 68 and a cooperating O-ring 68a.
As shown in Fig. 5, the components of the pressure
differential switch 44 are positioned within an aperture
66c in the core member 66 which intersects and extends
transversely relative to the longitudinal passageway 66a.
Referring now to Figs. 4, 6, and 8, the individual
components which comprise the isolation valve 22 and the
lZS8480
12
operation thereof will be discussed in more detail. The
components of the isolation valve 22 are individually
shown in the exploded perspective view of Figure 6. More
specifically, the isolation valve 22 includes an axially
shiftable armature 70 constructed of a suitable
ferromagnetic material and having a cylindrical end 71
which is slidably received within a sleeve 72. One end of
the sleeve 72 is slipped over an axially extending,
reduced diameter portion 66d of the core member 66, while
the opposite end of the sleeve 72 is inserted into a
reduced diameter bore hole 54a (best shown in Figure 8)
formed in the right end housing portion 50b. The inner
wall of the sleeve 72 is sealingly connected to the outer
annular surface of the reduced diameter portion 66d of the
core member 66 by an O-ring 74l while the outer wall of
the sleeve member 72 is sealingly connected to the inner
wall of the bore hole 54a by an O-ring 76.
As shown in Figure 8, a sealing ball 78 is pressed
into and frictionally held within a cavity 70a formed in
an end face 70b of the isolation valve armature 70. The
sealing ball 78 is adapted to project axially outwardly
past the end face 70b. When the solenoid coil 64a is
energized, the magnetic field generated thereby urges the
armature 70 toward the core member 66 and the ball 78 will
sealingly engage a ball seat 66e formed in an end face 66f
of the core member 66 to prevent fluid flow into the
passageway 66a.
The isolation valve armature 70 is maintained in a
normally open position by means of a tapered helical
spring 80 which, as shown in Figure 8, is coaxially
positioned about an intermediate reduced diameter portion
70c of the armature 70. One end of the spring 80 seats
against one face of a washer 82 having an opposite face
abutting the outer end of the sleeve 72, while the
opposite end of the spring seats against a shoulder 70d
provided on the outer end of the isolation valve armature
70. When the isolation
,~;
~' ~ 'J.,
~z~ 8~
13
valve i 5 not energized, the spring 80 urges the outer end
face 70e of the armature against the end wall 54b of the
housing cavity 54, as shown in Figs. 4 and 8. As will be
discussed, in accordance with the present invention, the
outer end of the isolation valve armature 70 is provided
with a damping ring 84 which surrounds the outer end of the
armature and is utilized to dampen the movement of the
armature when the valve is moved from its closed to its
open position.
As previously mentioned, the isolation valve 22 is
normally maintained in the open position such that brake
fluid pressure supplied to the rear brakes via the outlet
58 is the ~ame pressure as the pressure present at the
inlet 56. More specifically, the brake fluid flows from
the inlet 56 into a passageway 88 formed in the side wall
of the housing portion 50b. A filter screen 90 can be
positioned in the passageway 88 to provide filtering for
fluid entering the valve. From the passageway 88, fluid
flows into a chamber 92 surrounding the reduced diameter
portion 70c of the armature 70. The fluid then flows
axially through longitudinally extending slots 70f formed
in the armature 70 and into a gap between the end face 66f
of the core member 66 and the inner end face 70b of the
armature 70. As shown in Fig. 8, this gap is set to a
predetermined distance G1 such that, after the isolation
valve has been closed, and it is desired to reapply
pressure to the rear brakes by momentarily opening the
isolation valve, the amount of pressure increase to the
rear brakes can be precisely controlled. After having
entered the gap Gl, fluid can flow past the ball 78 and
into the longitudinalLy extending passageway 66a where
fluid is supplied to the outlet fitting 58 via the outlet
port 66b (shown in Fig. 4).
When the solenoid coil 64a is energized, the magnetic
force generated thereby urges the armature 70 axially
against the force of the spring 80 and causes the ball 78
~Z~8~80
to sealingly engage the associated ball seat 66e, thereby
blocking fluid flow from the inlet 56 to the outlet 58 to
maintain the pressure to the rear bra~es at a constant
level. As previously mentioned, in some instances, it is
desirable to selectively open the isolation valve to
provide a predetermined amount of pressure increase to the
rear brakes. In order to accurately control the pressure
increase to the rear brakes, it has been discovered that
the selective opening of the isolation valve must be
precisely controlled. To achieve such control, the
present invention includes damping means associated with
the isolation valve for controlling the opening of the
isolation valve, thereby regulating the pressure increase
to the rear brakes.
More specifically, this damping is provided by the
damping ring 84 positioned within an annular groove formed
in the outer end of the isolation valve armature. The
damping ring 84 is specifically designed to prevent fluid
flow between an outer annular surface 84a of the ring 84
and an inner annular surface of the cavity 54 when the
valve is moved from the open to the closed position, but
will allow fluid flow between the annular surfaces 84a and
54c when the valve is moved from its open to its closed
position.
When the valve is moved from its open to its closed
position, fluid will flow between the ring surface 84a and
the inner annular cavity surface 54c to fill the resulting
chamber between the end face 70e of the armature and the
inner end wall 54b of the cavity. Additionally, fluid
will flow into this chamber by way of a transversely
extending bore hole 70i formed in the armature 70 which
communicates with an axially extending passageway 70g
having a reduced diameter portion 70h. However, when the
valve is moved from its closed to its open position, since
the damping ring 84 is designed to prevent fluid flow
across its exterior surface 84a as the armature 70 is
moved toward the
.
1~8~80
right from its closed to itR open position, fluid located
in the chamber between the end face 70e of the armature 70
and the end wall 54b of the cavity must flow through the
reduced diameter portion 70h of the passageway 70g before
the valve can be moved toward the right. In accordance
with the present invention, the diameter D1 of the portion
70h is selected to partially restrict the fluid flow from
the chamber, thus damping the opening movement of the
armature 70. It has been found that such damping enables
the reapplication of pressure to the rear brakes to be more
precisely controlled.
Referring to ~igs. 4, 6, and 9, the specific
constructi~n and operation of the dump valve 26 will now be
discussed in more detail. As previously mentioned, the
dump valve is normally maintained in a closed state, but
can be selectively opened after the isolation valve has
been closed to dump fluid into an accumulator 28 to
~electively reduce the pressure to the rear brakes. The
components of the dump valve 26 are individually shown in
the exploded perspective view of ~ig. 6. The dump valve 26
includes an armature 100 constructed of a ferromagnetic
material which is axially shiftable upon actuation of the
solenoid coil 64b. As shown in Figs. 4 and 9, the armature
100 is biased in a normally closed position by means of a
compressed helical spring 101 having one end rec~ived
within an opening in the inner end of the armature 100 and
an opposite end which engages a filter 102 positioned in
the core passageway 66a. The armature 100 is slidably
mounted within a sleeve member 103 having one end which is
slipped over a reduced diameter end portion S6g of the core
member 66 and is sealingly connected thereto by means of an
O-ring 104, and has an opposite end which is inserted into
a reduced diameter portion 54d of the cavity 54 and is
~ealingly connected thereto by means of an O-ring 106.
The dump valve armature 100 is provided with a
central, axially extending passageway lOOa. A sealing ball
lZ58~BO
16
108 is pressed into and frictionally held within the outer
end of the passageway lOOa, and is adapted to sealingly
engage a ball seat llOa formed in an end face llOb of a
floating piston 110. The spring 101 compressed between
the dump valve armature 100 and a filter element 102
maintains the dump valve armature in a normally closed
position. The piston 110 includes a central, axially
extending passageway llOc having a reduced diameter
portion llOd adjacent the ball seat llOa. The passageway
llOc is in axial alignment with a passageway 50d formed in
the end wall of the cavity 54 which, when the dump valve
is open, supplies brake fluid into the accumulator 28. An
annular sealing ring 111 surrounds the piston 110 and
sealing engages an annular wall 54e of the cavity 54.
The accumulator 28 includes a piston 112 (which
corresponds to the piston 28b of Figure 1) slidably
mounted within the cavity 50c formed in the one end of the
housing portion 50a and closed by the plug 68. An O-ring
114 is positioned within an annular groove formed in the
cavity 50c to sealingly engage the outer cylindrical wall
of the piston 112. Normally, the piston 112 is urged
axially inwardly by means of a helical spring 120 ~which
corresponds to the spring 28c schematically shown in
Figure 1) such that the end surface 112a of the piston 112
abuts an inner end wall 50e of the cavity 50c. When the
dump valve is momentarily opened to selectively reduce
pressure to the rear brakes, brake fluid will be supplied
into the cavity 50c to urge the piston 112 axially toward
the left and compress the spring 120. In accordance with
the present invention, the annular sealing ring 111
surrounding the floating piston 110 is adapted to prevent
fluid flow between the exterior walls of the piston 110
and into the accumulator but, when the pressure in the
rear brake circuit falls below the pressure in the
accumulator, fluid can be returned to the rear brake
circuit by flowing past the annular sealing ring 111, and
into a chamber 122 surrounding the outer end of the
armature 100.
f~ :
~;Z 58~80
17
As previously mentioned, the dump valve is normally
closed such that fluid having passed through the filter
102, into the longitudinal armature passage lOOa, and then
through transversely extending armature passageways lOOb
enters a chamber 122 surrounding the outer end of the
armature 100, but will not enter the accumulator 2B due to
the sealing of the ball 108 and the ring 111. When it iB
desired to reduce the fluid pressure supplied to the rear
brakes, the solenoid coil 64b is momentarily actuated to
shift the armature 100 and disengage the ball 108 from the
ball seat llOa. This enables fluid to enter the
accumulator via the passageway 110c. After completion of
a controlled stop and a release of the brake pressure to
the rear wheels, fluid contained in the accumulator will
automatically be returned to the system in a manner as
described above. It should be noted that, by properly
selecting the diameter D2 of the passageway llOd and the
dimension G2 of the gap between an end face lOOc of the
armature 100 and an end face 66h of the core member 66, the
amount of pressure reduction can be precisely controlled.
Referring to Figs. 5, 7, and 10, the specific
construction and operation of the pressure differential
switch 44 will now be discussed. As previously mentioned,
the pressure differential switch 44 monitors the difference
in pressure between the pressure received from the
combination valve 18 of Pig. 1 and the pressure supplied to
the rear brakes. Normally, if the pressure supplied to the
rear brakes is less than or eyual to the pressure received
from the iso~ation valve on a line 18b, the switch is in an
open state. However, when the pressure supplied by the
combination valve on the line 18b is greater than the
pressure supplied to the rear brake, indicating that the
system has entered the anti-lock mode, the swi~tch closes.
Basically, the components of the switch are positioned
within the aperture 66c formed in the core member 65 which
intersects and extends transversely to the a~ial
' ~ ' ~ ~ I ' , ' !'
i'~S84~30
passageway. ~he individual components of the pressure
differential switch 44 are shown in more detail in the
exploded perspective view of Fig. 7. More ~pecifically,
the pressure differential ~witch 44 includes a differential
valve 130, a biasing helical ~pring 132, and O-ring6 134a,
134b and 134c which function to sealingly surround selected
portions of the valve 130 and to sealingly engage selected
outer annular surfaces of the cavity 66c in which the valve
130 is positioned. Also, the switch 44 includes an
externally threaded plug 136 which, as shown in Fig. 10, is
threaded into the upper end of the aperture 66c and is
sealingly connected thereto by means of an O-ring 136a.
Normally, the helical spring 132 which, as shown in Fig.
10, has one end which engages the lower end of the plug 136
and a lower end which engages a ~houlder 130a formed on the
valve 130, urges the valve downwardly to maintain the
contact tip 130b of the valve in spaced apart, unconnected
relationship with a contact terminal 138 located in the
upper end of the plug and surrounded by an insulating
member 140. An intermediate portion of the valve is
exposed to the rear brake pressure via the passageway 66a,
while a lower shoulder 130c of the valve 130 is exposed to
the pressure received from the combination valve via a
passageway 66j which is in communication with the fluid
surrounding the isolation valve armature 70.
When the isolation valve is closed, and the upward
force exerted in the valve 130 by the fluid pressure
on the shoulder 130c is greater than the resultant downward
force of the helical spring 132 and the pressure exerted on
the valve via the fluid in the passageway 66a, the valve
~ill be urged upwardly (as viewed in Fig. 10) such that the
upper tip 130b of the valve contacts the termlnal 138,
causing a ground potential signal to be gener~ted in the
associated electrical line 46. When the pressure in the
passageway 66j has fallen such that the resultant upward
force on the differential valve is less than the resultant
3L'~S8480
19
downward force cau~ed by the helical spring and the rear
brake pressure in the passageway 66a, the differential
valve will move downwardly, thereby opening the
differential ~witch 44.
In accordance with the provisions of the Patent
Statutes, the principle and ~ode of operation of the
invention have been illustrated and described in what is
considered to represent its preferred embodiment. However,
it should be noted that the invention may be practiced
otherwise than as specifically illustrated and described
without departing from the 6pirit of the following claims.
