Hydraulic brake valve system

Abstract

A hydraulic brake valve system includes a main valve assembly actuatable by a first brake actuator and by a second brake actuator to control an outlet pressure. The hydraulic brake valve system further includes a first brake selector valve assembly that receives the outlet pressure, that selectively controls a first brake pressure supplied to a first brake, and that is actuatable by the first brake actuator. The hydraulic brake valve system further includes a second brake selector valve assembly that receives the outlet pressure, that selectively controls a second brake pressure supplied to a second brake, and that is actuatable by the second brake actuator. The first brake selector valve assembly and the second brake selector valve assembly may be positioned in respective open positions to respectively allow the first brake pressure and the second brake pressure to be substantially equal to the outlet pressure.

Description

HYDRAULIC BRAKE VALVE SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 618.741, filed January 8, 2024, the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION

[0002] The present invention relates to hydraulic systems, and more particularly to hydraulic brake systems.BACKGROUND OF THE INVENTION

[0003] A vehicle may include two or more wheels, spindles, and / or axles to be braked.SUMMARY OF THE INVENTION

[0004] The present disclosure provides, in one aspect, a hydraulic brake valve system including a main valve assembly that receives pressurized fluid from a hydraulic pressure source. The main valve assembly is actuatable by a first brake actuator and is actuatable by a second brake actuator. The main valve assembly is selectively positionable in an open position, a closed position, and a plurality of positions therebetween. A position of the main valve assembly controls an outlet pressure. A first brake selector valve assembly receives the outlet pressure from the main valve assembly. The first brake selector valve assembly is actuatable by the first brake actuator. The first brake selector valve assembly is positionable in an open position and in a closed position. The first brake selector valve assembly selectively controls a first brake pressure supplied to a first brake. The first brake selector valve assembly is positioned in the open position to allow the first brake pressure to be substantially equal to the outlet pressure. A second brake selector valve assembly receives the outlet pressure from the main valve assembly. The second brake selector valve assembly is actuatable by the second brake actuator. The second brake selector valve assembly is positionable in an open position and in a closed position. The second brake selector valve assembly selectively controls a second brake pressure supplied to a second brake. The second brake selector valve assembly is positioned in the open position to allow the second brake pressure to be substantially equal to the outlet pressure.

[0005] The present disclosure provides, in one aspect, a hydraulic brake valve system including a main valve assembly, a first brake selector valve assembly, and a second brake selector valve assembly. A first push rod is selectively positionable in a first default position, a first fully actuated position, and a plurality of positions between the first default position and the first fully actuated position. The first push rod actuates the main valve assembly and actuates the first brake selector valve assembly. A second push rod is selectively positionable in a second default position, a second fully actuated position, and a plurality of positions between the second default position and the second fully actuated position. The second push rod actuates the main valve assembly and actuates the second brake selector valve assembly. The second push rod is positionable in the second default position, and the first push rod is simultaneously positionable in a position other than the first default position, such that a position of the first brake selector valve assembly is determined by the position of the first push rod, and a position of the main valve assembly is determined by the position of the first push rod. The first push rod is positionable in the first default position, and the second push rod is simultaneously positionable in a position other than the second default position, such that a position of the second brake selector valve assembly is determined by the position of the second push rod, and a position of the main valve assembly is determined by the position of the second push rod. The first push rod is positionable in a position other than the first default position, and the second push rod is simultaneously positionable in a position other than the second default position, such that a position of the first brake selector valve assembly is determined by the position of the first push rod, a position of the second brake selector valve assembly is determined by the position of the second push rod, and a position of the main valve assembly is determined by whichever of the first push rod or the second push rod is displaced a farthest distance from the respective first default position or the second default position.

[0006] The present disclosure provides, in one aspect, a hydraulic brake valve system including a main body and a main valve assembly housed within the main body. The main valve assembly receives pressurized fluid from a fluid source at a pressure P and outputs fluid with a pressure B. The pressure B ranges between 0% and 100% of the pressure P. A first brake selector valve assembly is housed within the main body and receives an input of fluid at the pressure B from the main valve assembly. The first brake selector valve assembly is an on / off valve that is positionable in either an “on” position or in an “off” position. The first brake selector valve assembly outputs fluid at the pressure B in the “on” position, and thefirst brake selector valve assembly outputs fluid at a tank pressure in the “off’ position. A second brake selector valve assembly is housed within the main body and receives an input of fluid at the pressure B from the main valve assembly. The first brake selector valve assembly is an on / off valve that is positionable in either an “on"’ position or in an “off position. The second brake selector valve assembly outputs fluid at the pressure B in the “on” position, and the first brake selector valve assembly outputs fluid at the tank pressure in the “off’ position.

[0007] The present disclosure provides, in one aspect, a hydraulic brake valve system including a main body and a main valve assembly housed within the main body. The main valve assembly receives pressurized fluid from a fluid source at a pressure P and outputs fluid at a selected pressure. The main valve assembly includes a main spool that is biased into a closed position. A first brake selector valve assembly is housed within the main body and receives an input of fluid from the main valve assembly at the selected pressure. The first brake selector valve assembly includes a first brake selector valve that is biased into a closed position. The first brake selector valve is movable away from the closed position to output fluid from the first brake selector valve assembly at the selected pressure. The second brake selector valve assembly is housed within the main body and receives an input of fluid from the main valve assembly at the selected pressure. The second brake selector valve assembly includes a second brake selector valve that is biased into a closed position. The second brake selector valve is movable away from the closed position to output fluid from the second brake selector valve assembly at the selected pressure.

[0008] Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a perspective view of a hydraulic brake valve system.

[0010] FIG. 2 is another perspective view of the hydraulic brake valve system of FIG. 1.

[0011] FIG. 3 is yet another perspective view of the hydraulic brake valve system of FIG.1.

[0012] FIG. 4 is yet another perspective view of the hydraulic brake valve system of FIG. 1.

[0013] FIG. 5 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 5-5 shown in FIG. 4.

[0014] FIG. 6 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 6-6 shown in FIG. 4.

[0015] FIG. 7 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 7-7 shown in FIG. 2 with a first brake selector valve assembly positioned in a first default, closed position and a second brake selector valve assembly positioned in a second default, closed position.

[0016] FIG. 8 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 8-8 shown in FIG. 2.

[0017] FIG. 9 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 9-9 shown in FIG. 6.

[0018] FIG. 10 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 10-10 shown in FIG. 6.

[0019] FIG. 11 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 7-7 shown in FIG. 2 with the first brake selector valve assembly positioned in the first, default closed position and the second brake selector valve assembly positioned away from the second, default closed position.

[0020] FIG. 12 is a cross-sectional view of the hydraulic brake valve system of FIG. 1 along section line 7-7 shown in FIG. 2 with the first brake selector valve assembly positioned away from the first, default closed position and the second brake selector valve assembly positioned away from the second, default closed position.

[0021] FIG. 13 is a perspective view of a main valve assembly of the hydraulic brake valve system of FIG. 1.

[0022] FIG. 14 is a front elevation view of the hydraulic brake valve system of FIG. 1.

[0023] FIG. 15 is a side elevation view of the hydraulic brake valve system of FIG. 1.

[0024] FIG. 16 is another side elevation view of the hydraulic brake valve system of FIG.

[0025] FIG. 17 is a rear elevation view of the hydraulic brake valve system of FIG. 1.

[0026] FIG. 18 is a plan view of the hydraulic brake valve system of FIG. 1.

[0027] FIG. 19 is a bottom view of the hydraulic brake valve system of FIG. 1.

[0028] FIG. 20 is a cross-sectional view of a hydraulic brake system with a plunger valve in a location analogous to that shown in FIG. 6.

[0029] FIG. 21 is a cross-sectional view of a hydraulic brake system with a ball, seat, and pin valve in a location analogous to that shown in FIG. 6.

[0030] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the follow ing description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.DETAILED DESCRIPTION

[0031] Certain vehicles (e.g., certain off-road vehicles) include a first brake (e.g., a right brake) for braking a first wheel, axle, and / or spindle (e.g., a right wheel) and a second brake (e.g., a left brake) for braking a second wheel, axle and / or spindle (e.g.. a left wheel). The first and second brakes may be actuated separately and independently to cause the brakes to assist in turning the vehicle. The first and second brakes may be actuated at the same time to provide an even braking force to both brakes to assist in slowing the vehicle rather than turning the vehicle.

[0032] FIG. 1 illustrates a hydraulic brake valve system 10 for use with a vehicle such as an off-road vehicle or a vehicle suitable for both on-road and off-road conditions (e.g., a tractor, a truck, a skid steer, a utility vehicle, etc.). The hydraulic brake valve system 10 includes a first yoke 14a and a second yoke 14b. The first yoke 14a is threaded onto a firstthreaded push rod 18a. and the second yoke 14b is threaded onto a second threaded push rod 18b. Stop nuts 22a, 22b lock the respective yokes 14a, 14b into place relative to the respective threaded push rods 18a, 18b. As shown in Fig. 1, the first push rod 18a defines a first longitudinal axis Al along which the first push rod 18a is displaceable, and the second push rod 18b defines a second longitudinal axis A2 along which the second push rod 18b is displaceable. The first yoke 14a is coupled to a schematically illustrated first actuator 26a (e.g., a first brake pedal), and the second yoke 14b is coupled to a schematically illustrated second actuator 26b (e.g., a second brake pedal). The first actuator 26a may be connected to the first push rod 18a by means other than by a first yoke 14a, and the second actuator 26b may be connected to the second push rod 18b by means other than by a second yoke 14b.

[0033] With continued reference to FIG. 1, bushings 30a, 30b are made of a flexible material such as rubber and surround and protect respective push rods 18a, 18b. The push rods 18a. 18b pass through the respective bushings 30a. 30b, pass through respective sleeves 34a, 34b, and enter a main body 38 of the hydraulic brake valve system 10. The main body 38 is formed from a single casting as a monolithic piece (i.e., integrally formed). The sleeves 34a, 34b may include oil, dust, and / or grease seals that inhibit the passage of oil, dust, and / or grease between the push rods 18a, 18b and a respective one of the sleeves 34a, 34b. A first plate 42 is fixedly mounted to the main body 38 by fasteners 46. The fasteners 46 pass through a gasket 50 to anchor the first plate 42 and the gasket 50 to the main body 38. The first plate 42 includes mounting studs 54 for mounting the hydraulic brake valve system 10 to a frame such as a frame of a vehicle.

[0034] With reference to FIGS. 2 and 3, the hydraulic brake valve system 10 includes a pressure inlet port 58 that receives pressurized fluid from a pump at a pump pressure P and a low-pressure tank return port 62 that receives low-pressure fluid at a tank pressure T (FIG. 5). The hydraulic brake valve system 10 also includes a first brake outlet port 66a that selectively delivers pressurized fluid at a first brake pressure Bl and a second brake outlet port 66b that selectively delivers pressurized fluid at a second brake pressure B2. A position of the first push rod 18a along the first longitudinal axis Al controls whether pressurized hydraulic fluid is delivered to the first brake outlet port 66a and thereby to a schematically illustrated first brake 70a, and a position of the second push rod 18b along the second longitudinal axis A2 controls whether pressurized hydraulic fluid is delivered to the second brake outlet port 66b and thereby to a schematically illustrated second brake 70b.

[0035] With reference to FIG. 4. the hydraulic brake valve system 10 includes an AND gate outlet port 74 that delivers pressurized hydraulic fluid at an AND gate pressure G1 (FIG. 5). The AND gate outlet port 74 defines a longitudinal axis A5 that may be generally parallel to the longitudinal axes Al, A2, A3 (FIG. 5). The tank return port 62 defines a longitudinal axis A6 that may be generally perpendicular to the longitudinal axes Al, A2. A3, A5.

[0036] FIG. 5 is a cross-sectional view of the hydraulic brake valve system 10 along section line 5-5 shown in FIG. 4. A main valve assembly 78 is positioned within the main body 38 of the hydraulic brake valve system 10. A pressure inlet line 82 is provided within the main body 38 and is connected to the pressure inlet port 58. The pressure inlet line 82 connects to a pressure inlet 86 of the main valve assembly 78. A pressure outlet line 90 connects to a pressure outlet 94 of the main valve assembly 78. The main valve assembly 78 includes a main spool 98, a sleeve 102, a spring seat 106, a first main valve spring 110, a second main valve spring 114. a third main valve spring 118, and a plunger 122 having a plunger spring seat 126. The main spool 98 includes a narrow spool portion 99 (shown in FIG. 5 and in FIG. 7) that facilitates a flow of pressurized fluid around the main spool 98 when the main spool 98 is in an actuated position. The first and second main valve springs 110, 114 extend between the plunger 122 and the spring seat 106 and are compression springs that bias the main spool 98 away from the plunger 122. The third main valve spring 118 is provided inside the main spool 98 to bias the spool toward the plunger 122 and into a default, closed position. The main spool 98 defines a longitudinal axis A3 that may be parallel to the longitudinal axes Al, A2. The main spool 98 is movable along the longitudinal axis A3. An outlet pressure B is provided at the pressure outlet 94 and, accordingly, in the pressure outlet line 90 that is determined by a relative position of the main spool 98 along the longitudinal axis A3. For example, the main spool 98 may be positionable in a closed position in which the pressure outlet line 90 is disconnected from the pressure inlet line 82, in an open position in which the pressure outlet line 90 is fully connected to the pressure inlet line 82 such that the outlet pressure B is substantially equal to the pump pressure P, and a variety of positions therebetween. For example, the outlet pressure B may be proportional to a position of the main spool 98 along the longitudinal axis A3 relative to the closed position and the open position. The position of the main spool 98 along the longitudinal axis A3 is controlled by a position of the plunger 122 along the longitudinal axis A3. In this manner, the main valve assembly 78 functions as a pressure control valve assembly that determines the outlet pressure B, which may be referred to as a brake pressure B. The tank return port 62 isconnected to a low-pressure chamber 80 of the main valve assembly 78. The first main valve spring 1 10 and the second main valve spring 1 14 are provided within the low-pressure chamber 80. With reference to FIG. 13, the sleeve 102 includes a first narrow portion 123 including a first plurality of holes 124 and a second narrow portion 127 including a second plurality of holes 128. When the main spool 98 is moved such that the narrow spool portion 99 at least partially aligns with the narrow portions 123, 127 of the sleeve 102, the first and second narrow portions 123, 127 and the first and second pluralities of holes 124, 128 cooperate to allow fluid communication between the pressure inlet 86 and the pressure outlet 94. In other words, when the main spool 98 is moved along the longitudinal axis A3, the main spool 98 delivers a value of the brake pressure B at the pressure outlet 94 that depends upon how far the main spool 98 is moved along the longitudinal axis A3 (i.e., the brake pressure B increases as the distance that the main spool 98 is moved from a default, closed position, which is shown in FIGS. 5 and 7, increases).

[0037] With reference to FIG. 6, which is a cross-sectional view of the hydraulic brake valve system 10 along section line 6-6 shown in FIG. 4, a first brake selector valve assembly 130a receives the brake pressure B (FIGS. 5 and 9) from the main valve assembly 78 at a first pressure inlet 134a and selectively outputs the first brake pressure at a first pressure outlet 138a. The first brake selector valve assembly 130a functions analogously to a second brake selector valve assembly 130b (FIG. 7), which also receives the brake pressure B from the main valve assembly 78 at a second pressure inlet 134b and selectively outputs the second brake pressure B2 at an analogous second pressure outlet. The first brake selector valve assembly 130a includes a first spool 154a. a first spring seat 158a, a first brake selector first spring 162a, a first brake selector second spring 166a, a first brake selector third spring 170a, a first plunger 174a having a first plunger spring seat 178a, and a first plug 182a that holds the first brake selector valve assembly 130a in place by supporting the first brake selector third spring 170a. The first brake selector first and second springs 162a, 166a bias the first spool 154a away from the first plunger 174a, and the first brake selector third spring 170a biases the first spool 154a toward the first plunger 174a and toward a default, closed position. The first brake selector third spring 170a is provided within a first low-pressure chamber 132a that is connected to the tank pressure T through a first tank pressure inlet 136a. The first plunger 174a is connected to the first push rod 18a such that longitudinal motion of the push rod 18a along the longitudinal axis Al is transferred into longitudinal motion of the first plunger 174a along the longitudinal axis Al. Motion of the first plunger 174a along thelongitudinal axis Al accordingly results in motion of the first spool 154a along the longitudinal axis Al . The first and second brake selector valve assemblies 130a, 130b may be all-or-nothing valves (i.e., the first and second brake selector valve assemblies 130a, 130b may be “on / of ’ valves that are positionable either in an “on’" position or in an “off’ position). The first spool 154a is biased into the default, closed position as shown in FIG. 6 in which the first pressure inlet 134a is disconnected from the first pressure outlet 138a. By moving the push rod 18a, the first spool 154a is movable to an open position in which the first pressure inlet 134a is connected to the first pressure outlet 138a, thereby delivering the brake pressure B to the first pressure outlet 138a. Fluid pressure is communicated between the first pressure inlet 134a and the first pressure outlet 138a by aligning a first narrow portion 156a with both the first pressure inlet 134a and the first pressure outlet 138a. Therefore, the first brake selector valve assembly 130a may receive an input of the brake pressure B and provide an output of either a first brake pressure Bl that is substantially equal to the brake pressure B or a first brake pressure Bl that is substantially equal to zero. The first brake pressure Bl is delivered to the first brake outlet port 66a and to a first side of an AND gate valve assembly 186 through a first AND gate inlet 188a. Similarly, the second brake selector valve assembly 130b may transform the brake pressure B into either a second brake pressure B2 that is substantially equal to the brake pressure B or into a second brake pressure B2 that is substantially equal to zero. The second brake pressure B2 is delivered to the second brake outlet port 66b and to a second side of the AND gate valve assembly 186 through a second AND gate inlet 188b (FIG. 9). The AND gate valve assembly 186 defines a longitudinal axis A4 (FIG. 10) that is generally perpendicular to the longitudinal axes Al, A2, A3, A4, A5.

[0038] With reference to FIG. 7, a first low-pressure line 190a interconnects the low- pressure chamber 132a of the first brake selector valve assembly 130a and the low-pressure chamber 80 of the main valve assembly 74. A second low-pressure line 190b interconnects a low-pressure chamber 132b of the second brake selector valve assembly 130b and the low- pressure chamber 80 of the main valve assembly 74 through a second tank pressure inlet 136b. The second brake selector valve assembly 130b includes certain analogous components to the first brake selector valve assembly 130a (e.g., the second brake selector valve assembly 130b includes a second spool 154b having a second narrow portion 156b, a second spring seat 158b, a second brake selector first spring 162b, a second brake selector second spring 166b, a second brake selector third spring 170b, a second plunger 174b havinga second plunger spring seat 178b. and a second plug 182b that holds the second brake selector valve assembly 130b in place by supporting the second brake selector third spring 170b).

[0039] With continued reference to FIG. 7, the first plunger 174a includes a first lip 194a, and the second plunger 174b includes a second lip 194b. The first and second lips 194a, 194b extend from the respective plungers 174a, 174b to overlap with an end of the plunger 122 to interact with the plunger 122 such that movement of either the first plunger 174a or the second plunger 174b from the closed, default position causes a displacement of the plunger 122 and accordingly causes a displacement of the main valve assembly 78 (e.g., a displacement of the main spool 98). Whichever of the first plunger 174a or the second plunger 174b is displaced the farthest from the closed, default position determines the position of the plunger 122 and accordingly determines the position of the main valve assembly 78.

[0040] With reference to FIG. 8, the pressure inlet line 82 extends between the pressure inlet port 58 of the hydraulic brake valve system 10 and the pressure inlet 86 of the main valve assembly 74 to supply fluid pressure to the main valve assembly 74 and, in turn, to supply fluid pressure to the first and second brake selector valve assemblies 130a, 130b.

[0041] With reference to FIG. 9. the pressure outlet line 90 interconnects the first pressure inlet 134a of the first brake selector valve assembly 130a, the second pressure inlet 134b of the second brake selector valve assembly 130b, and the pressure outlet 94 of the main valve assembly 78. FIG. 5 shows a connection between the pressure outlet line 90 and the pressure outlet 94 of the main valve assembly 78, and FIG. 9 shows a connection between the pressure outlet line 90 and the first and second pressure inlets 134a. 134b. The pressure outlet line 90 is supplied with fluid from the main valve assembly 78 at the pressure B, which is determined by a displacement of the main spool 98 along the longitudinal axis A3 (FIG. 7).

[0042] With reference to FIG. 10, the AND gate valve assembly 186 includes a first chamber 198a that receives pressunzed fluid at the pressure Bl from the first pressure outlet 138a. The AND gate valve assembly 186 also includes a second chamber 198b that receives pressurized fluid at the pressure B2 from the second pressure outlet. A first shuttle valve 202a is provided within the first chamber 198a, and a second shuttle valve 202b is provided within the second chamber 198b. The first shuttle valve 202a is configured to seal against afirst valve seat 206a. and the second shuttle valve 202b is configured to seal against a second valve seat 206b. The first and second valve seats 206a, 206b are integrally formed with the main body 38. When both the first spool 154a and the second spool 154b are actuated away from their default, closed positions, the pressure Bl and the pressure B2 are substantially equal and are substantially equal to the pressure B, which is determined by the position of the main valve assembly 78. When only one of the first spool 154a or the second spool 154b is actuated away from the default, closed position (e.g., as shown in FIG. 11, in which the first spool 154a is actuated and the second spool 154b is not actuated, thereby providing a pressure Bl, which is equal to the pressure B, to the first chamber 198a and providing a pressure B2 of substantially zero to the second chamber 198b), then one of the first and second shuttle valves 202a, 202b is pressed against a respective one of the first and second valve seats 206a, 206b to seal a respective hydraulic fluid passageway 210a, 210b. The AND gate outlet port 74 may deliver pressurized hydraulic fluid at the AND gate pressure Gt, which may be substantially equal to the first brake pressure Bl and to the second brake pressure B2, to another brake such as a front axle brake or a trailer brake.

[0043] In operation, and with reference to FIGS. 7, 11, and 12, the main valve assembly 78 receives pressurized hydraulic fluid at the pump pressure P from the pressure inlet line 82 (FIG. 8). When neither push rod 18a, 18b is actuated, no braking pressure is supplied to the first and second brakes 70a, 70b. A user may actuate either of the push rods 18a, 18b independently (see FIG. 11, for example, which shows the push rod 18a in a default, closed position and the push rod 18b in an actuated position), or the user may actuate the push rods 18a, 18b simultaneously (FIG. 12). If the push rods 18a, 18b are actuated simultaneously, the push rods 18a, 18b may be actuated in equal amounts or in unequal amounts. For example, the first push rod 18a may be actuated such that the first push rod 18a moves a first distance along the first axis Al. and the second push rod 18b may be actuated such that the second push rod 18b moves a second distance along the second axis A2 that may be equal to, less than, or greater than the first distance. Because each push rod 18a, 18b is connected to a respective first or second plunger 174a, 174b of the first and second brake selector valve assemblies 130a, 130b, and because the plunger 122 is actuatable by either of the first or second plungers 174a, 174b (e.g., because the respective first and second lips 194a, 194b of the plungers 174a, 174b are positioned at an end of the plunger 122 to actuate the plunger 122 when either one of the first or second plungers 174a, 174b is moved from the default, closed position illustrated in FIG. 7), a movement of either of the push rods 18a, 18b from thedefault, closed position may result in a movement of the main valve assembly 78 in addition to a movement of one of the first or second brake selector valve assemblies 130a, 130b.

[0044] With continued reference to FIGS. 7, 11, and 12, the value of the pressure B that is delivered by the main valve assembly 78 is determined by a position of the main valve assembly 78. More specifically, an amount by which the main valve assembly 78 is moved from the default, closed position (shown in FIG. 7) determines a proportion of the pressure P that is delivered as the brake pressure B to both the first and second brake selector valve assemblies 130a. 130b through the pressure outlet line 90 (FIGS. 5 and 9). In this manner, the main valve assembly 78 delivers a substantially equal brake pressure B to both the first brake selector valve assembly 130a and the second brake selector valve assembly 130b. In this w ay, the main valve assembly 78 functions as a pressure control valve. When the first brake selector valve assembly 130a is positioned in the default, closed position, the first brake 70a receives a first brake pressure Bl of zero, and when the first brake selector valve assembly 130a is opened from the default, closed position, the first brake 70a receives a first brake pressure Bl that is substantially equal to the brake pressure B that is determined by the main valve assembly 78. When the second brake selector valve assembly 130b is positioned in the default, closed position, the second brake 70b receives a second brake pressure B2 of zero, and w hen the second brake selector valve assembly 130b is opened from the default, closed position, the second brake 70b receives a second brake pressure that is substantially equal to the brake pressure B that is determined by the main valve assembly 78.

[0045] With reference to FIGS. 14-19, side elevation views along with a top view and a bottom view of the hydraulic brake valve system 10 are provided.

[0046] In some embodiments, some or all of the valves described herein (e.g., the first brake selector valve assembly 130a and the second brake selector valve assembly 130b) may include a valve mechanism other than a spool (that is, a valve mechanism other than the first spool 154a and the second spool 154b). For example, with reference to FIG. 20, a hydraulic brake valve system 310 includes a first brake selector valve assembly 330a and may include an analogous second brake selector valve assembly. The first brake selector valve assembly 330a receives the brake pressure B (FIGS. 5 and 9) from the main valve assembly 78 at the first pressure inlet 134a and selectively outputs the first brake pressure Bl at the first pressure outlet 138a. The first brake selector valve assembly 330a includes a first brake selector valve including a plunger 354a that is connected to the first spring seat 158a such that longitudinalmotion of the first spring seat 158a along the longitudinal axis Al results in longitudinal motion of the plunger 354a along the longitudinal axis Al . A plurality of seals 362a, 366a, 370a surround the plunger 354a and provide respective sealing boundaries between the seals 362a, 366a, 370a and the main body 38. The seal 362a inhibits fluid from leaking past the seal 362a and into a low-pressure chamber 372a that houses the first spring seat 158a. The seals 366a, 370a define an inlet pocket 374a between the seals 366a, 370a, and the seals 362a, 366a define an outlet pocket 378a between the seals 362a, 366a. The plunger 354a is movable along the longitudinal axis Al such that the plunger 354a is positionable in a closed position in which the seal 366a (e.g., a middle seal 366a) is positioned between the first pressure inlet 134a and the first pressure outlet 138a to inhibit fluid communication between the first pressure inlet 134a and the first pressure outlet 138a to provide an output of the first brake pressure Bl to the first pressure outlet 138a that is substantially equal to zero. The plunger 354a is also movable along the longitudinal axis Al such that the plunger 354a is positionable in an open position in which the outlet pocket 378a is in fluid communication with both the first pressure inlet 134a and the first pressure outlet 138a to provide an output of the first brake pressure Bl to the first pressure outlet 138a that is substantially equal to the brake pressure B.

[0047] As another example, and with reference to FIG. 21, a hydraulic brake valve system 410 includes a first brake selector valve assembly 430a and may include an analogous second brake selector valve assembly. The first brake selector valve assembly 430a receives the brake pressure B (FIGS. 5 and 9) from the main valve assembly 78 at the first pressure inlet 134a and selectively outputs the first brake pressure Bl at the first pressure outlet 138a. The first brake selector valve assembly 430a includes a first brake selector valve that includes a pin 454a that is connected to the first spring seat 158a such that longitudinal motion of the first spring seat 158a along the longitudinal axis Al results in longitudinal motion of the pin 454a along the longitudinal axis Al. When the pin 454a is positioned in an unactuated position (e.g., positioned as shown in FIG. 21), a ball 462a is seated against a seat 466a to generate a seal between the ball 462a and the seat 466a to inhibit fluid communication between the first pressure inlet 134a and the first pressure outlet 138a to provide an output of the first brake pressure Bl to the first pressure outlet 138a that is substantially equal to zero. When the pin 454a is positioned in an actuated position (e.g., positioned to engage the ball 462a and thereby to displace the ball 462a from the seat 466a), fluid communication is permitted between the first pressure inlet 134a and the first pressure outlet 138a to provide anoutput of the first brake pressure Bl to the first pressure outlet 138a that is substantially equal to the brake pressure B. A seal 470a is positioned between the pin 454a and an inner bore of the seat 466a to inhibit fluid from leaking past the seal 470a and into the low-pressure chamber 372a that houses the first spring seat 158a.

[0048] The brake selector valve assemblies 130a, 130b, 330a, 430a and any analogous counterparts may include other types of on / off valves.

[0049] The disclosure presented herein may include the following aspects.

[0050] Aspect 1 : A hydraulic brake valve system comprises a main valve assembly configured to receive pressurized fluid from a hydraulic pressure source. The main valve assembly is actuatable by a first brake actuator and is actuatable by a second brake actuator. The main valve assembly is selectively positionable in an open position, a closed position, and a plurality of positions therebetween. A position of the main valve assembly controls an outlet pressure. The hydraulic brake valve system further comprises a first brake selector valve assembly that receives the outlet pressure from the main valve assembly. The first brake selector valve assembly is actuatable by the first brake actuator. The first brake selector valve assembly is positionable in an open position and in a closed position. The first brake selector valve assembly selectively controls a first brake pressure supplied to a first brake. The first brake selector valve assembly is positioned in the open position to allow the first brake pressure to be substantially equal to the outlet pressure. The hydraulic brake valve assembly further comprises a second brake selector valve assembly that receives the outlet pressure from the main valve assembly. The second brake selector valve assembly is actuatable by the second brake actuator. The second brake selector valve assembly is positionable in an open position and in a closed position. The second brake selector valve assembly selectively controls a second brake pressure supplied to a second brake. The second brake selector valve assembly is positioned in the open position to allow the second brake pressure to be substantially equal to the outlet pressure.

[0051] Aspect 2: The hydraulic brake valve system of aspect 1. wherein the main valve assembly, the first brake selector valve assembly, and the second brake selector valve assembly are housed within a main body that is formed as a monolithic piece.

[0052] Aspect 3: The hydraulic brake valve system of aspect 1. wherein the first brake selector valve assembly is an on / off hydraulic valve, and wherein the second brake selector valve assembly is an on / off hydraulic valve.

[0053] Aspect 4: The hydraulic brake valve system of aspect 1. wherein the first brake selector valve assembly includes a first spool. The first brake selector valve assembly defines a first longitudinal axis along which the first spool is longitudinally displaceable. The second brake selector valve assembly includes a second spool. The second brake selector valve assembly defines a second longitudinal axis along which the second spool is longitudinally displaceable. The main valve assembly includes a main spool. The main valve assembly defines a third longitudinal axis along which the main spool is longitudinally displaceable. The first longitudinal axis is parallel to both the second longitudinal axis and the third longitudinal axis.

[0054] Aspect 5: The hydraulic brake valve system of aspect 4, further comprising an AND gate operable along a fourth longitudinal axis. The fourth longitudinal axis is perpendicular to the first longitudinal axis, the second longitudinal axis, and the third longitudinal axis.

[0055] Aspect 6: The hydraulic brake valve system of aspect 5, further comprising an AND gate outlet port supplied by the AND gate. The AND gate outlet port defines a fifth longitudinal axis. The fifth longitudinal axis is parallel to each of the first longitudinal axis, the second longitudinal axis, and the third longitudinal axis.

[0056] Aspect 7: The hydraulic brake valve system of aspect 6, further comprising a tank return port that defines a sixth longitudinal axis. The sixth longitudinal axis is perpendicular to each of the first longitudinal axis, the second longitudinal axis, the third longitudinal axis, the fourth longitudinal axis, and the fifth longitudinal axis.

[0057] Aspect 8: The hydraulic brake valve system of aspect 1. wherein the first brake selector valve assembly includes a plunger connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the plunger. The first brake selector valve assembly further includes a first seal surrounding the plunger. The first seal provides a sealing boundary between the first seal and a main body of the hydraulic brake valve system and inhibits fluid from leaking past the first seal and into a low-pressure chamber that houses the first spring seat. The first brake selector valve assembly furtherincludes a second seal surrounding the plunger. The second seal at least partially defines an outlet pocket between the first seal and the second seal. The second seal provides a sealing boundary' between the second seal and the main body and inhibits fluid from leaking past the second seal and into the outlet pocket. The first brake selector valve assembly is positionable in the closed position such that the second seal is between a first pressure inlet and a first pressure outlet to inhibit fluid communication between the first pressure inlet and the first pressure outlet. The first brake selector valve assembly is positionable in the open position such that the outlet pocket is in fluid communication with both the first pressure inlet and the first pressure outlet.

[0058] Aspect 9: The hydraulic brake valve system of aspect 1, wherein the first brake selector valve assembly includes a pin that is connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the pin. The first brake selector valve assembly further includes a ball. The first brake selector valve assembly further includes a seat. The ball seals against the seat to inhibit fluid communication between a first pressure inlet and a first pressure outlet. The pin displaces the ball from the seat to permit fluid communication between the first pressure inlet and the first pressure outlet.

[0059] Aspect 10: The hydraulic brake valve system of aspect 1, further comprising a plate having mounting studs for mounting the hydraulic brake valve system to a frame.

[0060] Aspect 11 : The hydraulic brake valve system of aspect 1, further comprising an AND gate valve assembly that supplies an AND gate pressure to an AND gate outlet port. The AND gate pressure is equal to the first brake pressure and equal to the second brake pressure. The first brake selector valve assembly and the second brake selector valve assembly are simultaneously positionable in respective open positions such that the AND gate valve assembly supplies the AND gate pressure to the AND gate outlet port.

[0061] Aspect 12: A vehicle comprising the hydraulic brake valve system of aspect 1, wherein the first brake is a right brake that is selectively supplied with pressurized hydraulic fluid by the hydraulic brake valve system, and wherein the second brake is a left brake that is selectively supplied with pressurized hydraulic fluid by the hydraulic brake valve system.

[0062] Aspect 13: A hydraulic brake valve system comprises a main valve assembly, a first brake selector valve assembly, a second brake selector valve assembly, and a first push rod selectively positionable in a first default position, a first fully actuated position, and aplurality of positions therebetween. The first push rod is configured to actuate the main valve assembly and to actuate the first brake selector valve assembly. The hydraulic brake valve system further comprises a second push rod selectively positionable in a second default position, a second fully actuated position, and a plurality' of positions therebetween. The second push rod is configured to actuate the main valve assembly and to actuate the second brake selector valve assembly. The second push rod is positionable in the second default position and the first push rod is simultaneously positionable in a position other than the first default position such that a position of the first brake selector valve assembly is determined by the position of the first push rod, and a position of the main valve assembly is determined by the position of the first push rod. The first push rod is positionable in the first default position and the second push rod is simultaneously positionable in a position other than the second default position such that a position of the second brake selector valve assembly is determined by the position of the second push rod, and a position of the main valve assembly is determined by the position of the second push rod. The first push rod is positionable in a position other than the first default position and the second push rod is simultaneously positionable in a position other than the second default position such that a position of the first brake selector valve assembly is determined by the position of the first push rod, a position of the second brake selector valve assembly is determined by the position of the second push rod, and a position of the main valve assembly is determined by whichever of the first push rod or the second push rod is displaced a farthest distance from, respectively, the first default position or the second default position.

[0063] Aspect 14: The hydraulic brake valve system of aspect 13, wherein the main valve assembly, the first brake selector valve assembly, and the second brake selector valve assembly are housed within a main body that is formed as a monolithic piece. The main body has an open side that is covered by a plate.

[0064] Aspect 15: The hydraulic brake valve system of aspect 14, wherein the plate includes mounting studs for mounting the hydraulic brake valve system to a frame.

[0065] Aspect 16: The hydraulic brake valve system of aspect 13, wherein the main valve assembly is positioned between the first brake selector valve assembly and the second brake selector valve assembly.

[0066] Aspect 17: The hydraulic brake valve system of aspect 13, wherein the main valve assembly includes a main low-pressure chamber connected to a tank return port, the first brake selector valve assembly includes a first low-pressure chamber, the second brake selector valve assembly includes a second low-pressure chamber, the first low-pressure chamber and the main low-pressure chamber are interconnected by a first low-pressure line, and the second low-pressure chamber and the main low-pressure chamber are interconnected by a second low-pressure line.

[0067] Aspect 18: The hydraulic brake valve system of aspect 17, wherein the first brake selector valve assembly includes a first spool, a first pressure inlet, and a first pressure outlet. A first spring is positioned within the first low-pressure chamber to bias the first spool into a closed position in which the first pressure inlet is disconnected from the first pressure outlet. The second brake selector valve assembly includes a second spool, a second pressure inlet, and a second pressure outlet. A second spring is positioned within the second low-pressure chamber to bias the second spool into a closed position in which the second pressure inlet is disconnected from the second pressure outlet.

[0068] Aspect 19: The hydraulic brake valve system of aspect 18, wherein the main valve assembly, the first brake selector valve assembly, and the second brake selector valve assembly are housed within a main body. The first spring is accessible from an exterior of the main body by removing a first plug. The second spring is accessible from the exterior of the main body by removing a second plug.

[0069] Aspect 20: The hydraulic brake valve system of aspect 13, wherein the first brake selector valve assembly includes a first plunger surrounded by a first plurality' of seals, and wherein the second brake selector valve assembly includes a second plunger surrounded by a second plurality of seals.

[0070] Aspect 21 : The hydraulic brake valve system of aspect 13, wherein the first brake selector valve assembly includes a ball configured to seal against a seat. A pin is configured to selectively displace the ball from the seat.

[0071] Aspect 22: The hydraulic brake valve system of aspect 13, further comprising an AND gate valve assembly configured to supply an AND gate pressure to an AND gate outlet port. The AND gate pressure is equal to an outlet pressure of the main valve assembly. The first push rod is not positioned in the first default position and the second push rodsimultaneously is not positioned in the second default position such that the AND gate valve assembly supplies the AND gate pressure to the AND gate outlet port.

[0072] Aspect 23: The hydraulic brake valve system of aspect 22, wherein the first push rod is positionable in the first default position such that the AND gate pressure is equal to a tank pressure. The second push rod is positionable in the second default position such that the AND gate pressure is equal to the tank pressure.

[0073] Aspect 24: The hydraulic brake valve system of aspect 22, wherein the first push rod is positionable in the first default position such that the AND gate pressure is zero. The second push rod is positionable in the second default position such that the AND gate pressure is zero.

[0074] Aspect 25: A hydraulic brake valve system comprises a main body and a main valve assembly housed within the main body and configured to receive pressurized fluid from a fluid source at a pressure P and to output fluid with a pressure B. The pressure B ranges between 0% and 100% of the pressure P. The hydraulic brake valve system further comprises a first brake selector valve assembly housed within the main body and configured to receive an input of fluid at the pressure B from the main valve assembly. The first brake selector valve assembly is an on / off valve positionable in either an “on” position or in an “off position. The first brake selector valve assembly outputs fluid at the pressure B in the "on" position, and the first brake selector valve assembly outputs fluid at a tank pressure in the “off” position. The hydraulic brake valve system further comprises a second brake selector valve assembly housed within the main body and configured to receive an input of fluid at the pressure B from the main valve assembly. The first brake selector valve assembly is an on / off valve positionable in either an “on” position or in an “off’ position. The second brake selector valve assembly outputs fluid at the pressure B in the “on” position. The first brake selector valve assembly outputs fluid at the tank pressure in the “off’ position.

[0075] Aspect 26: A hydraulic brake valve system comprises a main body and a main valve assembly housed within the main body configured to receive pressurized fluid from a fluid source at a pressure P and to output fluid at a selected pressure. The main valve assembly includes a main spool biased into a closed position. The hydraulic brake valve system further comprises a first brake selector valve assembly housed within the main body and configured to receive an input of fluid from the main valve assembly at the selectedpressure. The first brake selector valve assembly includes a first brake selector valve biased into a closed position. The first brake selector valve is movable away from the closed position to output fluid from the first brake selector valve assembly at the selected pressure. The hydraulic brake valve system further comprises a second brake selector valve assembly housed within the main body and configured to receive an input of fluid from the main valve assembly at the selected pressure. The second brake selector valve assembly includes a second brake selector valve biased into a closed position. The second brake selector valve is movable away from the closed position to output fluid from the second brake selector valve assembly at the selected pressure.

[0076] Aspect 27 : The hydraulic brake valve system of aspect 26, wherein the first brake selector valve includes a first brake selector spool.

[0077] Aspect 28: The hydraulic brake valve system of aspect 26, wherein the first brake selector valve includes a plunger connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the plunger. The first brake selector valve further includes a first seal surrounding the plunger. The first seal provides a sealing boundary between the first seal and the main body and inhibits fluid from leaking past the first seal and into a low-pressure chamber that houses the first spring seat. The first brake selector valve further includes a second seal surrounding the plunger. The second seal at least partially defines an outlet pocket between the first seal and the second seal. The second seal provides a sealing boundary between the second seal and the main body and inhibits fluid from leaking past the second seal and into the outlet pocket. The first brake selector valve is positionable in the closed position such that the second seal is between a first pressure inlet and a first pressure outlet to inhibit fluid communication between the first pressure inlet and the first pressure outlet. The first brake selector valve is positionable away from the closed position such that the outlet pocket is in fluid communication with both the first pressure inlet and the first pressure outlet.

[0078] Aspect 29: The hydraulic brake valve system of aspect 26, wherein the first brake selector valve includes a pin that is connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the pin, a ball, and a seat. The ball seals against the seat to inhibit fluid communication between a first pressure inlet and a first pressure outlet. The pin displaces the ball from the seat to permit fluid communication between the first pressure inlet and the first pressure outlet.

[0079] Aspect 30: The hydraulic brake valve system of aspect 26, wherein the first brake selector valve is an on / off hydraulic valve, and the second brake selector valve is an on / off hydraulic valve.

[0080] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.

Claims

CLAIMSWhat is claimed is:

1. A hydraulic brake valve system comprising: a main valve assembly configured to receive pressurized fluid from a hydraulic pressure source, wherein: the main valve assembly is actuatable by a first brake actuator and is actuatable by a second brake actuator, the main valve assembly is selectively positionable in an open position, a closed position, and a plurality of positions therebetween, and a position of the main valve assembly controls an outlet pressure; a first brake selector valve assembly that receives the outlet pressure from the main valve assembly, the first brake selector valve assembly actuatable by the first brake actuator, wherein: the first brake selector valve assembly is positionable in an open position and in a closed position, the first brake selector valve assembly selectively controls a first brake pressure supplied to a first brake, and the first brake selector valve assembly is positioned in the open position to allow the first brake pressure to be substantially equal to the outlet pressure, and a second brake selector valve assembly that receives the outlet pressure from the main valve assembly, the second brake selector valve assembly actuatable by the second brake actuator, wherein: the second brake selector valve assembly is positionable in an open position and in a closed position, the second brake selector valve assembly selectively controls a second brake pressure supplied to a second brake, and the second brake selector valve assembly is positioned in the open position to allow the second brake pressure to be substantially equal to the outlet pressure.

2. The hydraulic brake valve system of claim 1, wherein the main valve assembly, the first brake selector valve assembly, and the second brake selector valve assembly are housed within a main body that is formed as a monolithic piece.

3. The hydraulic brake valve system of claim 1 , wherein the first brake selector valve assembly is an on / off hydraulic valve, and wherein the second brake selector valve assembly is an on / off hydraulic valve.

4. The hydraulic brake valve system of claim 1, wherein: the first brake selector valve assembly includes a first spool, the first brake selector valve assembly defining a first longitudinal axis along which the first spool is longitudinally displaceable, the second brake selector valve assembly includes a second spool, the second brake selector valve assembly defining a second longitudinal axis along which the second spool is longitudinally displaceable, the main valve assembly includes a main spool, the main valve assembly defining a third longitudinal axis along which the main spool is longitudinally displaceable, and the first longitudinal axis is parallel to both the second longitudinal axis and the third longitudinal axis.

5. The hydraulic brake valve system of claim 4, further comprising an AND gate operable along a fourth longitudinal axis, wherein the fourth longitudinal axis is perpendicular to the first longitudinal axis, the second longitudinal axis, and the third longitudinal axis.

6. The hydraulic brake valve system of claim 5, further comprising an AND gate outlet port supplied by the AND gate, the AND gate outlet port defining a fifth longitudinal axis, wherein the fifth longitudinal axis is parallel to each of the first longitudinal axis, the second longitudinal axis, and the third longitudinal axis.

7. The hydraulic brake valve system of claim 6, further comprising a tank return port that defines a sixth longitudinal axis, wherein the sixth longitudinal axis is perpendicular to each of the first longitudinal axis, the second longitudinal axis, the third longitudinal axis, the fourth longitudinal axis, and the fifth longitudinal axis.

8. The hydraulic brake valve system of claim 1, wherein the first brake selector valve assembly includes: a plunger connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the plunger, a first seal surrounding the plunger, the first seal providing a sealing boundary between the first seal and a main body of the hydraulic brake valve system and inhibiting fluid from leaking past the first seal and into a low-pressure chamber that houses the first spring seat, and a second seal surrounding the plunger, the second seal at least partially defining an outlet pocket between the first seal and the second seal, the second seal providing a sealing boundary betw een the second seal and the main body and inhibiting fluid from leaking past the second seal and into the outlet pocket, the first brake selector valve assembly positionable in the closed position such that the second seal is betw een a first pressure inlet and a first pressure outlet to inhibit fluid communication between the first pressure inlet and the first pressure outlet, the first brake selector valve assembly positionable in the open position such that the outlet pocket is in fluid communication with both the first pressure inlet and the first pressure outlet.

9. The hydraulic brake valve system of claim 1, wherein the first brake selector valve assembly includes: a pin that is connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the pin, a ball, and a seat, wherein the ball seals against the seat to inhibit fluid communication between a first pressure inlet and a first pressure outlet, and wherein the pin displaces the ball from the seat to permit fluid communication betw een the first pressure inlet and the first pressure outlet.

10. The hydraulic brake valve system of claim 1, further comprising a plate having mounting studs for mounting the hydraulic brake valve system to a frame.

11. The hydraulic brake valve system of claim 1, further comprising an AND gate valve assembly that supplies an AND gate pressure to an AND gate outlet port, wherein the ANDgate pressure is equal to the first brake pressure and equal to the second brake pressure, and wherein the first brake selector valve assembly and the second brake selector valve assembly are simultaneously positionable in respective open positions such that the AND gate valve assembly supplies the AND gate pressure to the AND gate outlet port.

12. A vehicle comprising the hydraulic brake valve system of claim 1, wherein the first brake is a right brake that is selectively supplied with pressurized hydraulic fluid by the hydraulic brake valve system, and wherein the second brake is a left brake that is selectively- supplied with pressurized hydraulic fluid by the hydraulic brake valve system.

13. A hydraulic brake valve system comprising: a main valve assembly; a first brake selector valve assembly; a second brake selector valve assembly; a first push rod selectively positionable in a first default position, a first fully actuated position, and a plurality of positions therebetween, the first push rod configured to actuate the main valve assembly and to actuate the first brake selector valve assembly; and a second push rod selectively positionable in a second default position, a second fully actuated position, and a plurality of positions therebetween, the second push rod configured to actuate the main valve assembly and to actuate the second brake selector valve assembly; wherein: the second push rod is positionable in the second default position and the first push rod is simultaneously positionable in a position other than the first default position such that a position of the first brake selector valve assembly is determined by the position of the first push rod, and a position of the main valve assembly is determined by the position of the first push rod, the first push rod is positionable in the first default position and the second push rod is simultaneously positionable in a position other than the second default position such that a position of the second brake selector valve assembly is determined by the position of the second push rod, and a position of the main valve assembly is determined by the position of the second push rod, and the first push rod is positionable in a position other than the first default position and the second push rod is simultaneously positionable in a position other than thesecond default position such that a position of the first brake selector valve assembly is determined by the position of the first push rod, a position of the second brake selector valve assembly is determined by the position of the second push rod, and a position of the main valve assembly is determined by whichever of the first push rod or the second push rod is displaced a farthest distance from, respectively, the first default position or the second default position.

14. The hydraulic brake valve system of claim 13, wherein the main valve assembly, the first brake selector valve assembly, and the second brake selector valve assembly are housed within a mam body that is formed as a monolithic piece, the main body having an open side that is covered by a plate.

15. The hydraulic brake valve system of claim 14. wherein the plate includes mounting studs for mounting the hydraulic brake valve system to a frame.

16. The hydraulic brake valve system of claim 13, wherein the main valve assembly is positioned betw een the first brake selector valve assembly and the second brake selector valve assembly.

17. The hydraulic brake valve system of claim 13, wherein: the main valve assembly includes a main low -pressure chamber connected to a tank return port. the first brake selector valve assembly includes a first low-pressure chamber. the second brake selector valve assembly includes a second low-pressure chamber, the first low -pressure chamber and the main low-pressure chamber are interconnected by a first low-pressure line, and the second low-pressure chamber and the main low-pressure chamber are interconnected by a second low-pressure line.

18. The hydraulic brake valve system of claim 17, wherein: the first brake selector valve assembly includes a first spool, a first pressure inlet, and a first pressure outlet,a first spring is positioned within the first low-pressure chamber to bias the first spool into a closed position in which the first pressure inlet is disconnected from the first pressure outlet, the second brake selector valve assembly includes a second spool, a second pressure inlet, and a second pressure outlet, and a second spring is positioned within the second low-pressure chamber to bias the second spool into a closed position in which the second pressure inlet is disconnected from the second pressure outlet.

19. The hydraulic brake valve system of claim 18. wherein: the main valve assembly, the first brake selector valve assembly, and the second brake selector valve assembly are housed within a main body, the first spring is accessible from an exterior of the main body by removing a first plug, and the second spring is accessible from the exterior of the main body by removing a second plug.

20. The hydraulic brake valve system of claim 13. wherein the first brake selector valve assembly includes a first plunger surrounded by a first plurality of seals, and wherein the second brake selector valve assembly includes a second plunger surrounded by a second plurality of seals.

21. The hydraulic brake valve system of claim 13. wherein the first brake selector valve assembly includes a ball configured to seal against a seat, wherein a pin is configured to selectively displace the ball from the seat.

22. The hydraulic brake valve system of claim 13. further comprising an AND gate valve assembly configured to supply an AND gate pressure to an AND gate outlet port, wherein the AND gate pressure is equal to an outlet pressure of the main valve assembly, and wherein the first push rod is not positioned in the first default position and the second push rod simultaneously is not positioned in the second default position such that the AND gate valve assembly supplies the AND gate pressure to the AND gate outlet port.

23. The hydraulic brake valve system of claim 22. wherein the first push rod is positionable in the first default position such that the AND gate pressure is equal to a tank pressure, and wherein the second push rod is positionable in the second default position such that the AND gate pressure is equal to the tank pressure.

24. The hydraulic brake valve system of claim 22, wherein the first push rod is positionable in the first default position such that the AND gate pressure is zero, and wherein the second push rod is positionable in the second default position such that the AND gate pressure is zero.

25. A hydraulic brake valve system comprising: a main body; a main valve assembly housed within the main body and configured to receive pressurized fluid from a fluid source at a pressure P and to output fluid with a pressure B, the pressure B ranging between 0% and 100% of the pressure P; a first brake selector valve assembly housed within the main body and configured to receive an input of fluid at the pressure B from the main valve assembly, wherein the first brake selector valve assembly is an on / off valve positionable in either an “on” position or in an “off’ position, wherein the first brake selector valve assembly outputs fluid at the pressure B in the “on” position, and wherein the first brake selector valve assembly outputs fluid at a tank pressure in the “off” position; and a second brake selector valve assembly housed within the main body and configured to receive an input of fluid at the pressure B from the main valve assembly, wherein the first brake selector valve assembly is an on / off valve positionable in either an “on” position or in an “off’ position, wherein the second brake selector valve assembly outputs fluid at the pressure B in the “on” position, and wherein the first brake selector valve assembly outputs fluid at the tank pressure in the “off’ position.

26. A hydraulic brake valve system comprising: a main body; a main valve assembly housed within the main body configured to receive pressurized fluid from a fluid source at a pressure P and to output fluid at a selected pressure, the main valve assembly including a main spool biased into a closed position;a first brake selector valve assembly housed within the main body and configured to receive an input of fluid from the main valve assembly at the selected pressure, the first brake selector valve assembly including a first brake selector valve biased into a closed position, wherein the first brake selector valve is movable away from the closed position to output fluid from the first brake selector valve assembly at the selected pressure; and a second brake selector valve assembly housed within the main body and configured to receive an input of fluid from the main valve assembly at the selected pressure, the second brake selector valve assembly including a second brake selector valve biased into a closed position, wherein the second brake selector valve is movable away from the closed position to output fluid from the second brake selector valve assembly at the selected pressure.

27. The hydraulic brake valve system of claim 26, wherein the first brake selector valve includes a first brake selector spool.

28. The hydraulic brake valve system of claim 26, wherein the first brake selector valve includes: a plunger connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the plunger, a first seal surrounding the plunger, the first seal providing a sealing boundary between the first seal and the main body and inhibiting fluid from leaking past the first seal and into a low-pressure chamber that houses the first spring seat, and a second seal surrounding the plunger, the second seal at least partially defining an outlet pocket between the first seal and the second seal, the second seal providing a sealing boundary between the second seal and the main body and inhibiting fluid from leaking past the second seal and into the outlet pocket, the first brake selector valve positionable in the closed position such that the second seal is between a first pressure inlet and a first pressure outlet to inhibit fluid communication between the first pressure inlet and the first pressure outlet, the first brake selector valve positionable away from the closed position such that the outlet pocket is in fluid communication with both the first pressure inlet and the first pressure outlet.

29. The hydraulic brake valve system of claim 26. wherein the first brake selector valve includes:a pin that is connected to a first spring seat such that longitudinal motion of the first spring seat results in longitudinal motion of the pin, a ball, and a seat, wherein the ball seals against the seat to inhibit fluid communication between a first pressure inlet and a first pressure outlet, and wherein the pin displaces the ball from the seat to permit fluid communication between the first pressure inlet and the first pressure outlet.

30. The hydraulic brake valve system of claim 26. wherein the first brake selector valve is an on / off hydraulic valve, and wherein the second brake selector valve is an on / off hydraulic valve.

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