FIELD OF THE INVENTION

[0001] The present invention relates to hydraulic brake systems for off-highway vehicle, for example agricultural vehicles, construction vehicles, and material handling vehicles.

BACKGROUND OF THE INVENTION

[0002] Hydraulic brake systems for off-highway vehicles may include a master cylinder and a pressure modulating valve. Master cylinders are often configured as single-piston, straight bore type hydraulic cylinders having a fluid reservoir. The fluid reservoir contains hydraulic fluid and is open to a piston chamber through an equalizing port. Movement of a piston into the piston chamber causes fluid to enter a pilot line, which is connected to a pressure modulating valve (e.g., a full power brake valve) for achieving a braking demand.

[0003] Master cylinders require a minimum amount of fluid volume on reserve. The fluid must generally have a temperature characteristic that maintains its fluidity throughout a temperature range. Prior solutions have included a heating element and thermostatic control system to keep the master cylinder warm. However, this solution requires a heating element, thermostat, and wire harness, claiming space and consuming electrical power. Alternative solutions include engineering the hydraulic fluid to flow easily even at very low temperatures. However, this solution requires an additional fluid, separate from the braking fluid, and requires isolation from braking fluid to prevent cross-contamination of fluids and seal failure.

[0004] Accordingly, there remains a continued need for a hydraulic braking system that maintains a desired temperature within the master cylinder reservoir. In addition, there remains a continued need for a hydraulic braking system for correcting an imbalance in split braking systems in an integrated package with reductions in physical footprint and installation time.

SUMMARY OF THE INVENTION

[0005] An improved hydraulic brake system is provided. In one embodiment of the invention, the hydraulic brake system uses the same fluid in the brake system as the master cylinder and automatically routes fluid from a modulating brake valve up through the pilot lines to the master cylinder. The hydraulic brake system uses less space and simplifies installation when compared to routing warm fluid to the master cylinder or adding a thermostat and a heating element. The hydraulic brake system requires no special fluid, does not need to be filled or maintained, and does not require a system to keep fluids from each other.

[0006] In this embodiment, the hydraulic brake system includes a modulating brake valve, an isolation check valve, and a back pressure valve. The modulating brake valve is coupled to a master cylinder pilot line and includes a pressure port, a brake port, and a tank port. The isolation check valve is connected between the tank port and the master cylinder pilot line, such that back pressure at the tank port causes warmed brake fluid to flow through the isolation check valve to the master cylinder. The back pressure valve is spring biased and is connected between the tank port and a vehicle reservoir. Back pressure at the master cylinder pilot line can be released to the vehicle reservoir to prevent damage to the master cylinder.

[0007] In another embodiment of the invention, the hydraulic brake system includes a balancing piston between two pilot lines from dual master cylinders. The balancing piston is self-centered by a centering spring on each side of the balancing piston. The displacement of the balancing piston is slightly larger than needed to compensate for the expected variation between unequal applications of two brake pedals. The force of the centering springs can be high enough to always return the balancing piston to its center position when the brake pedals are released, but not so high as to appreciably affect balancing of the left and right pilot pressures.

[0008] In this embodiment, the hydraulic brake system includes a first modulating valve coupled to a first master cylinder and a second modulating valve coupled to a second master cylinder. The balancing piston is movable within a cylinder bore defining a first chamber on a first side of the balancing piston and defining a second chamber on a second side of the balancing piston. A left centering spring and a right centering spring on opposing sides of the balancing piston equalizes a fluid pressure differential between first and second pilot lines.

[0009] In still another embodiment, the present invention includes an integrated valve for a dual full power brake system. The integrated valve combines the functionality of a dual relay valve, an accumulator charge valve, and an electrohydraulic brake valve. By combining these valves into a single hardware design, the present invention reduces the mounting brackets for different valve assemblies. The integrated valve includes a manifold block having a left pilot port and a right pilot port. The manifold block houses an internal balancing piston, left and right modulating brake valves, left and right isolation check valves, and left and right back pressure check valves. An electrohydraulic brake valve is optionally housed within the manifold block. The electrohydraulic brake valve can control braking on front brakes, can control secondary braking, and/or can control parking brake control.

[0010] These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanying drawings and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of a hydraulic brake system in accordance with one embodiment.

[0012] Figure 2 is the schematic diagram of a hydraulic brake system including a balancing piston for equalizing brake pressure for dual master cylinders.

[0013] Figure 3 is a perspective view of an integrated valve for full power braking of an off-highway vehicle.

DETAILED DESCRIPTION OF THE CURRENT EMBODIMENT

[0014] Referring to Figure 1, a hydraulic brake system in accordance with one embodiment is illustrated and generally designated 10. The hydraulic brake system 10 uses the same fluid in the brake system as the master cylinder and automatically routes fluid from a modulating brake valve to the master cylinder. The hydraulic brake system 10 is described below in connection with an agricultural tractor, but can be used with other vehicles as desired.

[0015] More specifically, the hydraulic brake system 10 is self-contained within a single manifold block 12. The manifold block 12 includes a pilot port 14 for connection to a master cylinder 16, a pressure port 18 for connection to a pressurized supply of brake fluid, a tank port 20 for connection to a vehicle reservoir, and a brake port 22 for connection to vehicle brakes. The manifold block 12 houses a number of power components, including a modulating brake valve 24 (also referred to as a full power brake valve), a pressure reducing valve or priority valve 26 (not shown in this embodiment), a charge rate orifice 27, a check valve 29, an inverted shuttle valve 28, an accumulator charging valve 30, a relief valve 32, and an electrohydraulic brake valve 34. The modulating brake valve 24 includes a tank port 36, a pressure port 38, and a brake port 40, as distinguished from the tank port 20, pressure port 18, and brake port 22 of the manifold block 12.

[0016] As shown in Figure 1, the hydraulic brake system 10 also includes an insolation check valve 42 and a spring-biased back pressure check valve 44. The isolation check valve 42 is connected between the pilot port 14 of the manifold block 12 and the tank port 36 of the modulating brake valve 24. The spring-biased back pressure check valve 44 is connected between the tank port 36 of the modulating brake valve 24 and the tank port 20 of the manifold block 12. The modulating brake valve 24 includes an internal spool that is movable between a neutral, closed, and open position in a conventional manner. In the neutral position, the spool blocks the pressure port 38, while the brake port 40 is open to the tank port 36. In the closed position, the spool blocks the pressure port 38, the brake port 40, and the tank port 36. In the open position, the spool blocks the tank port 36, while the brake port 40 is open to the pressure port 38. The internal spool allows a small amount of brake fluid to leak from the pressure port 38 to the tank port 36 whenever there is pressure at the pressure port 38. This back pressure is required to force brake fluid into the master cylinder pilot line 46 to top off a fluid reservoir 48 within the master cylinder, warm the pilot line 46, warm the master cylinder 16, and bleed the brake fluid out of the pilot line 46. As discussed below, this continues until the brake pedal is depressed.

[0017] In the closed position as shown in Figure 1, sufficient back pressure at the tank port 36 causes warmed brake fluid to flow through the isolation check valve 42 to the master cylinder pilot line 46. When the operator of the vehicle depresses a brake pedal 50, the master cylinder 16 displaces fluid down through the pilot line 46 and into the pilot section of the modulating brake valve 24. The isolation check valve 42 then closes and normal operation of the brake system occurs. When the operator releases the brake pedal 50, fluid volume in the brakes must return to the vehicle reservoir to release the brakes. Brake pressure is available to push fluid to the vehicle reservoir. Most of this volume passes through the back pressure check valve 44 to release the brakes as quickly as possible. Brake pressure continues to decay to a level where the back pressure check valve 44 closes. At this point, normal operation of the hydraulic brake system resumes, and the master cylinder 16 is again warmed with brake fluid.

[0018] In braking systems having two master cylinders, the hydraulic braking system of the present invention can also include a balancing piston to equalize a fluid pressure differential between first and second pilot lines. More particularly, and as shown in Figure 2, a hydraulic brake system in accordance with a second embodiment is illustrated and generally designated 60. The hydraulic braking system 60 of Figure 2 is structurally and functionally similar to the hydraulic braking system 10 of Figure 1, except that the hydraulic braking system 60 of Figure 2 now includes a second modulating brake valve 62, a second isolation check valve 64, and a second back pressure check valve 66. In addition, a piston assembly 67 is coupled between a first pilot line 46 and a second pilot line 68. The piston assembly 67 includes a balancing piston 70 that is moveable within a cylinder housing 72 defining a first chamber on a first side of the balancing piston 70 and a second chamber on a second side of the balancing piston 70. The piston assembly 67 further includes a left centering spring 74 and a right centering spring 76 on opposing sides of the balancing piston 70, such that the piston assembly 67 equalizes a fluid pressure differential between the first and second pilot lines 46, 68. Each centering spring 74, 76 is seated at one end against the cylinder housing 72 and seated at another end against the balancing piston 70. As optionally shown in Figure 2, the first brake pedal 50 and first master cylinder 16 controls left vehicle braking, and the brake pedal 80 and second master cylinder 82 controls right vehicle braking.

[0019] The balancing piston 70 is self-centered from each side, and the displacement of the balancing piston 70 is selected to be slightly larger than needed to compensate for expected variations between unequal application of the brake pedals. The force of each centering spring 74, 76 is selected to be high enough to return the balancing position 70 to its center position when the left and right brake pedals 50, 80 are released, but not so high as to appreciably affect balancing of the left and right pilot pressures. As a result, the comfort of the operator is improved, as the vehicle has a reduced tendency to react to an imbalanced brake pressure when both brake pedals 50, 80 are applied together. In addition, drivetrain wear is reduced because the brake pressure on each side of the vehicle is closer to equal when both pedals are applied together. Other advantages include the reduction in noise due to the take-up of slack between sides of a drive train and the reduction of unequal wear in brake systems when both left and right pedals are applied together.

[0020] To reiterate, the embodiment of Figure 2 provides a hydraulic brake system 60 for a vehicle having two master cylinders 16, 82, where each master cylinder is operated by its own brake pedal 50, 80. In other embodiments, the master cylinder can be the tandem type and include two sections for controlling a front wheel brake and a rear wheel brake. Each master cylinder can have two supply connections and two delivery connections. Braking of the left front wheel is controlled by a hydraulic branch that is separate from the hydraulic branch for the left rear wheel, but both sections of the left master cylinder are operated simultaneously be the left brake pedal. Similarly, braking of the right front wheel is controlled by a hydraulic branch that is separate from the hydraulic branch for the right rear wheel, and both sections of the right master cylinder are operated simultaneously be the right brake pedal.

[0021] The hydraulic brake systems 10, 60 of Figures 1 and 2 can be self-contained within a single manifold block for dual systems or electrohydraulic control for braking on the front axle and/or secondary braking. As shown in Figure 3, the manifold block 12 includes a rigid housing 90 and a plurality of fluid ports for communicating fluid pressure signals to vehicle brakes. The rigid housing 90 can be a machined block of metal or metal casting, for example aluminum or an aluminum alloy. The rigid housing 90 is a cuboid in the present embodiment, having six planar faces, each with a subset of the plurality of fluid ports. As shown in Figure 3 for example, a top face 92 includes the left pilot port 14 (referred to as pilot port 14 in relation to Figs. 1 and 2) and a right pilot port 15 (shown representatively in Figure 2), and a right face 94 includes a right brake port 23 (shown representatively in Figure 2). The manifold block 12 houses an internal balancing piston assembly 70 (shown representatively in Figure 2), left and right modulating brake valves 24, 62 left and right isolation check valves 42, 64, and left and right back pressure check valves 44, 66. An electrohydraulic brake valve 34 is also housed within the manifold block, partially protruding from a front face 96 of the manifold block 90. The electrohydraulic brake valve 34 can control braking on front brakes, can control secondary braking, and/or can control parking brake control. Additional ports include a pressure port 18, a tank port 20, and left and right brake ports 22, 23, with only the right brake port 23 being visible in Figure 3.

[0022] The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements by ordinal terms, for example “first,” “second,” and “third,” are used for clarity, and are not to be construed as limiting the order in which the claim elements appear. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.