Braking system anti-lock modulator configuration

A control valve assembly for use in an anti-lock braking system wherein a 3-way isolation valve normally connects a wheel cylinder to a master cylinder and isolates that wheel cylinder(s) from the master cylinder and simultaneously connects the wheel cylinder to the common connection of a pressure modulating unit when the anti-lock system has been energized. The assembly enables use of a three channel anti-lock system in a dual circuit cross split brake system and increases the protection of the normal brake circuit from leakage in the modulating unit.

The present invention relates to anti-lock braking systems and more 
particularly to a solenoid actuated modulating valve configuration which 
improves certain failure modes of such a system and enables use of the 
system with cross-split braking systems with little or no increase in 
hardware. 
Anti-lock braking systems continue to develop and gain acceptance. In 
contemporary systems, it has become accepted to use up to three solenoid 
actuated valves for each control channel of the system. One of these 
valves effects isolation of the wheel cylinders of a channel from the 
normal brake pressure modulator such as, for example, a master cylinder or 
a manually modulated hydraulic booster, a second solenoid valve for 
reducing or "decaying" brake pressure in the system in response to control 
signals generated in response to rotational behavior of the vehicles 
wheels, and a third solenoid valve, also responsive to the control signals 
for increasing brake pressure, pressurized brake fluid for this purpose 
being obtained from another fluid source such as a motor-driven pump or 
booster. It is further a common practice in such systems to connect the 
isolation valve in series between the source of pressurized brake fluid 
and the wheel cylinder. With such a configuration, a leak in a decay valve 
can cause a decrease or loss of normal braking. It is also possible to 
trap bubbles in the system between the isolation valve and the wheel 
cylinder. This configuration is further not well suited for use in a 
cross-split braking system which is further provided with a three-channel 
anti-lock system, that is, a system in which two front wheels of a vehicle 
are controlled separately and the rear wheels are controlled as a pair. 
Such a cross-split system requires individual modulators for each rear 
brake. There therefore exists a need for an improved control or modulating 
valve configuration for use in anti-lock braking systems which eliminates 
the afore-mentioned problems. 
In its broader aspects, the present invention is a modulating valve 
configuration for use in an anti-lock braking system wherein isolation of 
the anti-lock channel is effected by means of a three-way valve which 
connects the build and decay valves of a channel in parallel with the 
standard braking system of the vehicle. 
More specifically, the invention is a modulating valve configuration for 
use in an anti-lock braking system which includes a source of pressure 
fluid such as a master cylinder or hydraulic booster and at least one 
wheel cylinder. The control valve assembly includes an isolation valve for 
interrupting fluid communication between the master cylinder and wheel 
cylinder and connecting the wheel cylinder to a common connection of an 
anti-lock brake pressure modulating device. In this configuration, bubbles 
in the system occurring between the build valve and a wheel cylinder 
isolation valve are not trapped in the normal braking system. In this 
configuration, it is also possible to adapt a cross-split braking system 
to a three channel anti-lock braking system with the addition of a second 
rear isolation valve. Each rear isolation valve connects its respective 
rear wheel cylinder normally to its respective master cylinder chamber, 
and to the common anti-lock pressure modulating device when in its second 
operating position. 
It is therefore an object of the invention to provide an improved 
modulating valve configuration for use in anti-lock braking systems. 
It is another object of the invention to provide such a valve configuration 
which obviates trapping of bubbles in the system occurring between the 
pressure build valve and a wheel cylinder that will affect normal braking. 
It is another object of the invention to provide a valve configuration for 
an anti-lock braking system that protects the system against leakage from 
the anti-lock pressure decay modulating valve to the low pressure return. 
Still another object of the invention is to provide a valve configuration 
which enables the use of a three channel anti-lock braking system in a 
cross-split brake system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, there is shown in schematic a two channel 
braking system which includes a dual circuit master cylinder 12 which 
receives braking fluid from a reservoir 14 through a pair of shut off 
valves 16, 18. The two master cylinder pistons 20, 22 produce pressurized 
brake fluid at master cylinder output ports 24, 26 in response to 
pressurized braking fluid in boost chamber 28. The fluid in chamber 28 in 
turn is manually modulated by means of an actuating rod 30 which 
mechanically modulates a hydraulic control valve 32. Valve 32 is, in turn, 
connected to receive pressurized braking fluid by a conduit 34 connected 
to a motor driven pump and accumulator assembly 36. In now conventional 
manner, failure of one or the other of the two braking channels I, II, is 
detected by a pressure differential switch 38 connected between output 
conduits 40, 42 and mechanical actuation of the pistons 20, 22 is effected 
via control rod 30. 
Four wheel brake cylinders 44, 46, 48, and 50 are provided. In the 
illustrated embodiment, it will be seen that these are connected in a 
cross-split configuration with one front and an oppositely disposed 
rear-wheel cylinder comprising each of channels I and II. Cylinders 44, 46 
are commonly connected at 52, a proportioning valve 54 being interposed 
between connection 52 and left rear cylinder 44 to balance or proportion 
pressure between the front and rear cylinders. The connection 52 is 
coupled through a 3 way isolation valve 56 to the conduit 40 through its 
normally open circuit. The normally closed circuit of isolation valve 56 
extends between the conduit 52 and an output conduit 58. Conduit 58, in 
turn, is connected to a common connection 60 connected to the inputs 62, 
64 of a pair of normally closed 2 way valves 66, 68. 
Valve 66 connects intersection 60 to the reservoir 14 and valve 68 connects 
connection 60 to chamber 28 to provide for decay and build of pressure and 
are accordingly designated the "decay" and "build" valves, respectively. 
A 3 way isolation valve 70, build valve 72 and decay valve 74 are 
identically connected in control channel II in cooperation with wheel 
cylinders 48 and 50 associated with the right rear and left front wheels 
of the vehicle, respectively. 
In operation, during normal braking, valve 56 is in its normal state 
whereby wheel cylinders 44, 46 are operated in conventional fashion from 
the piston 20. In the event that the anti-lock control system senses an 
incipient lock condition by means of a wheel sensor 78 and electronic 
control 80, it will output control signals via output lines as at 82 to 
operate the solenoid actuators of the valves 56, 66, and 68. Initially, 
isolation valve 56 is actuated thereby interrupting fluid communication 
between master cylinder 12 (piston 20) and wheel cylinders 44, 46. 
Simultaneously, 3 way isolation valve 56 connects the wheel cylinders 44, 
46 to output conduits 58 and 60 and through the valve 68 to conduit 84 
connected to the chamber 28. This connects the valves 56, 66, and 68 to 
the fluid pressure source 36 or to the reservoir 14. Decay and building of 
brake pressure can now be performed in accordance with well known 
anti-lock brake systems. Control channel II is identical and operates in 
the same manner. Typically, a pressure differential switch 88 will also be 
provided in the system to sense a failure of boost pressure to deactivate 
the anti-lock system and convert the system to manual operation. It will 
be apparent that the system in FIG. 1 can be applied to any two channel 
anti-lock system whether of the cross-split type as shown, or conventional 
front rear split. 
Referring now to FIG. 2, there is shown a three channel anti-lock braking 
system applied to a cross-split brake system. 
In this embodiment, master cylinder 12, reservoir 14, shut off valves 16, 
18 and the pump 36 are identical in configuration and function to that 
disclosed in FIG. 1 and the like numerals apply to like elements. Channel 
I is coupled to piston 20 via conduit 102. Conduit 102 splits and is 
connected to right rear wheel cylinder 48 and left front wheel cylinder 50 
through a pair of 3 way valves 104, 106, respectively, this connection 
being through the normally open ports of the valves. The normally closed 
ports 108, 110 are connected to the common connections 112, 114 of 
normally closed pairs of build and decay valves 116, 118 and 120, 122. The 
outputs of the decay valves 116, 122 are connected via return conduits 
124, 126 to the reservoir 14. 
Similarly, left rear cylinder 44 and right front cylinder 46 are connected 
to piston 22 via conduit 130 through the normally open ports of 3 way 
isolation valves 132, 134, respectively. The normally closed port 137 of 
valve 134 is connected to the common connection 136 of another pair of 
build and decay valves 138, 140 the other ports of which are connected to 
the boost chamber 28 and reservoir 14, respectively. The normally closed 
port 142 of 3 way isolation valve 132 is connected to the common 
connection 112 of the build decay valve pair 116, 118. Thus configured it 
will be seen that in a normal operating mode the braking system is 
connected as a conventional cross-split braking system having two channels 
I and II. When the anti-lock system is energized, and on command each of 
the four 3 way valves 104, 106, 134 and 132 will isolate their respective 
wheel cylinders 48, 50, 46 and 44 from the master cylinder 12 and 
simultaneously connect the right front and left front wheel cylinders 46, 
50 to respective pairs of build and decay valves 120, 122 and 138, 140 and 
further connect left rear and right rear cylinders 44, 48 as a pair to the 
build decay valve pair 116, 118. It will thus be seen that in this state 
the system operates as a conventional three channel anti-lock system with 
individual control of the front wheels and joint control of the two rear 
wheels. This is further accomplished with the addition of only a single 
additional isolation valve 132 compared to a similar 3-channel vertical 
split system. That is, a conventional cross-split dual channel braking 
system can be converted to a three channel anti-lock braking system with 
the addition of only one additional isolation valve 132. 
Referring briefly to FIG. 3, there is shown for contrast, a typical prior 
art valve configuration wherein the isolation valve 150 is provided as a 
standard normally open 2 way valve and the build and decay valves 152, 154 
are connected fluidly downstream from the isolation valve 150 to a wheel 
cylinder 156. This is distinguishable with the configuration of the 
present invention wherein the build and decay valves are in effect 
connected in parallel with the master cylinder circuit and are alternately 
switched into the circuit by means of 3 way isolation valves. 
This novel configuration of valves enables adaptation of a three channel 
anti-lock braking system to a cross-split braking system. Leaks through 
the decay valve will not affect normal braking because of the isolation of 
the decay circuit by the isolation valve during normal brake operation. 
Additionally, with the configuration of the present invention the flow 
path of the decay and build valves may be made smaller without affecting 
normal braking flow thereby allowing use of smaller solenoids in the 
anti-lock system. 
Although the present invention has been illustrated and described in 
connection with example embodiments, it will be understood that this is 
illustrative of the invention, and is by no means restrictive, thereof. It 
is reasonable to be expected that those skilled in the art can make 
numerous revisions and additions to the invention and it is intended that 
such revisions and additions will be included in the scope of the 
following claims as equivalents of the invention.