Hydraulic steering brake system, electro-hydraulic steering brake system and bulldozer

Abstract

The invention discloses a hydraulic steering brake system, an electro-hydraulic control steering brake system and a bulldozer. The hydraulic steering brake system comprises an oil tank, an oil pump, a steering brake control valve, a parking brake valve, a service brake valve, a steering brake valve, a steering clutch and a brake clutch. The oil pump supplies oil to each control valve, and a port A of the steering brake control valve and a port A of the service brake valve can control a pilot port of the steering brake valve; the parking brake valve controls a main oil source of the steering brake valve, an oil way of the steering brake valve is cut off during parking, and the brake clutch is normally closed to realize reliable locking; in the running process, by adjusting the opening degree of a steering brake control valve or a service brake valve, a steering clutch is controlled to be combined and a brake clutch is controlled to be pressed tightly in a linkage mode, and flexible steering and composite braking are achieved. Particularly, under the high-torque working condition, the problem that traditional spring braking is insufficient is effectively solved, operation safety and flexibility are remarkably improved, fuel economy is remarkably improved, and the service life of the whole machine is remarkably prolonged.

Description

Technical Field

[0001] This application relates to the field of engineering machinery technology, and in particular to a hydraulic steering and braking system, an electro-hydraulic steering and braking system, and a bulldozer. Background Technology

[0002] Hydraulic bulldozers are widely used in earthmoving, mining, and infrastructure construction due to their reliable structure, ease of operation, and strong adaptability. Among them, hydraulic steering systems are widely used in small and medium horsepower hydraulic bulldozers because of their simple structure, low manufacturing cost, and relatively relaxed requirements on hydraulic oil cleanliness.

[0003] Currently, hydraulic bulldozers with normally closed braking systems generally employ a service braking method: without cutting off power output from the engine to the transmission system, the operator depresses the foot brake pedal, releasing the control oil pressure of the brake clutch through the hydraulic control circuit. At this time, the return spring inside the brake clutch pushes the friction plates and steel plates together, thereby generating braking torque and achieving deceleration or stopping of the entire machine. This braking mechanism can effectively achieve braking function and meet basic operational requirements under low output torque conditions such as low engine speed or high gear transmission.

[0004] However, under high-torque conditions with high engine speeds and the transmission in low gears (such as 1st or 2nd gear), the above braking method has significant drawbacks: due to the continuous output of large torque from the power system, relying solely on spring force to press the brake clutch is insufficient to overcome the driving torque transmitted by the transmission system, resulting in insufficient braking force and inability to effectively decelerate or stop. This not only poses serious safety hazards but also forces the brake clutch to operate in a slipping state for extended periods, leading to a series of negative effects, including but not limited to: accelerated abnormal wear of the brake band, increased transmission system oil temperature, accelerated oxidation and deterioration of hydraulic oil, and increased oil contamination. Furthermore, the slipping power consumption generated during ineffective braking also causes unnecessary energy waste, reducing the overall fuel economy of the engine. Summary of the Invention

[0005] The purpose of this application is to provide a hydraulic steering and braking system, an electro-hydraulic steering and braking system, and a bulldozer, which not only improves the operational flexibility, safety, and economy of the bulldozer, but also effectively solves the shortcomings of the traditional hydraulic bulldozer braking method under high output torque conditions, and significantly improves the overall working efficiency and service life of the machine.

[0006] The embodiments of this application can be implemented as follows: In a first aspect, the present invention provides a hydraulic steering and braking system, comprising an oil tank, an oil pump, a steering brake control valve, a parking brake valve, a service brake valve, a steering brake valve, a steering clutch, and a braking clutch; The inlet of the oil pump is connected to the oil tank, and the P port of the steering brake control valve, the P port of the parking brake valve, and the P port of the service brake valve are all connected to the outlet of the oil pump. The A port of the steering brake control valve and the A port of the service brake valve are both connected to the pilot port of the steering brake valve. The parking brake valve's port A is connected to the steering brake valve's port P, the steering brake valve's port A1 is connected to the steering clutch's inlet, and the steering brake valve's port A2 is connected to the steering clutch's inlet. The T-port of the steering brake control valve, the T-port of the service brake valve, the T-port of the steering brake valve, the outlet of the steering clutch, and the outlet of the brake clutch are all connected to the oil tank. In the case that the P port and A port of the parking brake valve are blocked, the P port of the steering brake valve is blocked from the A1 port and connected to the A2 port. When the parking brake valve's P port and A port are connected, the conduction area between the steering brake control valve's P port and A port, as well as the conduction area between the service brake valve's P port and A port, are both positively correlated with the conduction area between the steering brake valve's P port and A1 port, and both are negatively correlated with the conduction area between the steering brake valve's P port and A2 port.

[0007] In an optional embodiment, the service brake valve includes a two-position three-way electro-hydraulic valve, a first brake check valve, and a second brake check valve. The P port of the two-position three-way electro-hydraulic valve is connected to the outlet of the oil pump, the T port of the two-position three-way electro-hydraulic valve is connected to the oil tank, and the A port of the two-position three-way electro-hydraulic valve is connected to the A port of the first brake check valve and the A port of the second brake check valve. Both port B of the first brake check valve and port B of the second brake check valve are connected to the pilot port of the steering brake valve. The conduction area between the P port and A port of the two-position three-way electro-hydraulic valve is positively correlated with the proportional current signal.

[0008] In an optional embodiment, the steering brake control valve includes a left steering brake control valve and a right steering brake control valve, wherein the P port of the left steering brake control valve and the P port of the right steering brake control valve are both connected to the outlet of the oil pump. The T-port of the left turn brake control valve and the T-port of the right turn brake control valve are both connected to the oil tank. Port A of both the left steering brake control valve and the right steering brake control valve is connected to the pilot port of the steering brake valve.

[0009] In an optional embodiment, the parking brake valve includes a two-position three-way hydraulic control valve and an electro-hydraulic control valve; The P port and pilot port of the two-position three-way hydraulic control valve and the P port of the electro-hydraulic control valve are all connected to the outlet of the oil pump. The A port of the two-position three-way hydraulic control valve is connected to the P port of the steering brake valve. The T port of the two-position three-way hydraulic control valve and the T port of the electro-hydraulic control valve are both connected to the oil tank. When the electro-hydraulic control valve is open, the P port and A port of the two-position three-way hydraulic control valve are blocked; when the electro-hydraulic control valve is closed, the P port and A port of the two-position three-way hydraulic control valve are connected.

[0010] In an optional embodiment, the parking brake valve further includes a parking relief valve, the P port of which is connected to the outlet of the oil pump. The P port of the two-position three-way hydraulic control valve, the P port of the electro-hydraulic control valve, and the pilot port of the two-position three-way hydraulic control valve are all connected to the T port of the parking relief valve.

[0011] In an optional embodiment, the steering brake valve includes a steering valve and a brake valve, wherein the pilot port of the steering valve and the pilot port of the brake valve are both connected to the A port of the steering brake control valve and the A port of the service brake valve. The P port of the steering valve and the P port of the brake valve are both connected to the A port of the parking brake valve. The T-port of the steering valve and the T-port of the brake valve are both connected to the oil tank. The A port of the steering valve is connected to the inlet of the steering clutch, and the A port of the brake valve is connected to the inlet of the brake clutch. The conduction area between the P port and A port of the steering valve is positively correlated with the oil inlet pressure of the steering valve pilot port; the conduction area between the P port and A port of the brake valve is negatively correlated with the oil inlet pressure of the brake valve pilot port.

[0012] In an optional embodiment, the steering valve includes a left steering valve and a right steering valve, the brake valve includes a left brake valve and a right brake valve, the steering clutch includes a left steering clutch and a right steering clutch, and the brake clutch includes a left brake clutch and a right brake clutch. The A port of the left steering valve is connected to the left steering clutch, the A port of the right steering valve is connected to the right steering clutch, the A port of the left brake valve is connected to the left brake clutch, and the A port of the right brake valve is connected to the right brake clutch.

[0013] In an optional embodiment, the hydraulic steering and braking system further includes a coarse filter, a fine filter, an overflow valve, and an accumulator; The coarse filter, the oil pump, the fine filter, and the accumulator are connected in series. The P port of the steering brake control valve and the P port of the service brake valve are both connected to the accumulator. The P port of the overflow valve is connected to the outlet of the oil pump, and the T port of the overflow valve is connected to the oil tank.

[0014] In a second aspect, the present invention provides an electro-hydraulic steering and braking system, including a controller, a parking brake controller, a service brake pedal, a steering brake controller, and a hydraulic steering and braking system as described in any of the foregoing embodiments; The parking brake controller, the service brake pedal, and the steering brake controller are all electrically connected to the controller. The controller is electrically connected to the steering brake control valve, the parking brake valve, and the service brake valve. When the parking brake controller is in the locked state, the controller controls the P port and A port of the parking brake valve to be blocked; when the parking brake controller is in the unlocked state, the controller controls the P port and A port of the parking brake valve to be open. When the parking brake controller is in the unlocked state, the steering brake controller can control the conduction area between the P port and A port of the steering brake control valve through the controller, and the service brake pedal can control the conduction area between the P port and A port of the service brake valve through the controller.

[0015] Thirdly, the present invention provides a bulldozer including the electro-hydraulic steering and braking system described in the foregoing embodiments.

[0016] Compared with the prior art, the beneficial effects of the embodiments of this application include, for example: 1. Parking Lock Function: When the P and A ports of the parking brake valve are blocked, this system ensures that both the steering clutch and the brake clutch remain normally closed, allowing the brake clutch to generate maximum braking force while the steering clutch does not transmit power, thus locking the bulldozer in place. This design guarantees the safety and stability of construction machinery or vehicles when parked.

[0017] 2. Starting and driving control: When the P port and A port of the parking brake valve are connected, the hydraulic oil flows to the steering brake valve. If there is no electrical signal input between the steering brake control valve and the service brake valve, the P port and A1 port of the steering brake valve are blocked and the A2 port is connected. The brake clutch is supplied with hydraulic oil at maximum pressure to release the brake. The steering clutch is not supplied with oil to maintain maximum engagement force, and the power is transmitted completely, allowing the bulldozer to engage gear and start driving quickly.

[0018] 3. Flexible service brake adjustment: By pressing the service brake pedal, the oil flow of the service brake valve 8 can be controlled. The braking force and power transmission of the traveling mechanism (track or wheel) can be flexibly adjusted as needed, thereby achieving precise deceleration or stopping, improving safety and avoiding the brake clutch from working in a slipping state for a long time.

[0019] 4. Efficient Steering Operation: When turning is required during driving, the driver can operate the steering brake control device to change the conduction area between the steering brake control valve port and port A corresponding to left or right turn, thereby adjusting the power difference between the left and right sides of the travel mechanism and achieving turning operations of different radii. In particular, by maximizing the oil flow of the steering brake control valve, the steering clutch on one side can be fully disengaged and the braking force of the brake clutch can be maximized, thus achieving the smallest turning radius.

[0020] 5. By connecting the steering brake control valve and the service brake valve to the pilot port of the steering brake valve, a high-efficiency hydraulic control architecture with hydraulic logic to achieve functional coordination is constructed. This architecture not only inherits the advantages of hydraulic control systems such as simple structure, low cost, and resistance to contamination, but also realizes dynamic decoupling and intelligent coordination of braking and steering through pilot control.

[0021] In summary, this hydraulic steering and braking system not only improves the operational flexibility, safety, and economy of bulldozers, but also effectively solves the shortcomings of traditional hydraulic bulldozer braking methods under high output torque conditions, significantly improving the overall working efficiency and service life of the machine. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the electro-hydraulic steering and braking system according to an embodiment of this application.

[0024] Icons: 1-Fuel tank; 2-Coarse filter; 3-Fuel pump; 4-Fine filter; 5-Relief valve; 6-Accumulator; 7-Steering brake control valve; 7A-Left steering brake control valve; 7B-Right steering brake control valve; 8-Service brake valve; 8A-Two-position three-way electro-hydraulic valve; 8B-First brake check valve; 8C-Second brake check valve; 9-Steering brake valve; 9A-Left steering valve; 9B-Left brake valve; 9C-Right brake valve; 9D-Right steering valve; 10-Parking brake valve; 10A-Parking relief valve; 10B-Electro-hydraulic control valve; 10C-Two-position three-way hydraulic control valve; 11-Left steering clutch; 12-Left brake clutch; 13-Right brake clutch; 14-Right steering clutch; 15-Parking brake controller; 16-Controller; 17-Service brake pedal. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0027] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0028] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0029] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," not that the structure must be completely horizontal, but can be slightly tilted.

[0030] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0031] The following is combined Figure 1 This application provides a detailed description of some embodiments. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0032] This application discloses an electro-hydraulic steering and braking system, including a controller 16, a parking brake controller 15, a service brake pedal 17, a steering brake controller, and a hydraulic steering and braking system. The parking brake controller 15, the service brake pedal 17 and the steering brake controller are all electrically connected to the controller 16. The controller 16 is electrically connected to the steering brake control valve 7, the parking brake valve 10 and the service brake valve 8. The steering brake control valve 7 can be a control handle or button (mechanical button or virtual button) in the cab of a bulldozer, tractor or other construction machinery vehicle, mainly used to control the steering of the equipment.

[0033] The service brake pedal 17 is used to realize the service braking of construction machinery or vehicles. The service brake is the main braking system used to decelerate or stop construction machinery or vehicles during operation.

[0034] The parking brake controller 15 can be a parking brake lever or a button (mechanical button or virtual button) used to realize the parking brake of the vehicle. The parking brake is a braking system used to prevent the vehicle from rolling when it is parked for a long time. It is usually a mechanical locking type and is independent of the service brake (foot brake). It is an important safety guarantee.

[0035] The hydraulic steering and braking system includes an oil tank 1, an oil pump 3, a steering brake control valve 7, a parking brake valve 10, a service brake valve 8, a steering brake valve 9, a steering clutch, and a brake clutch; The inlet of oil pump 3 is connected to oil tank 1, and the P port of steering brake control valve 7, the P port of parking brake valve 10 and the P port of service brake valve 8 are all connected to the outlet of oil pump 3. Port A of steering brake control valve 7 and port A of service brake valve 8 are both connected to the pilot port of steering brake valve 9. The A port of the parking brake valve 10 is connected to the P port of the steering brake valve 9, the A1 port of the steering brake valve 9 is connected to the inlet of the steering clutch, and the A2 port of the steering brake valve 9 is connected to the inlet of the brake clutch. The T-port of the steering brake control valve 7, the T-port of the service brake valve 8, the T-port of the steering brake valve 9, the outlet of the steering clutch, and the outlet of the brake clutch are all connected to the oil tank 1. Among them, when the P port and A port of the parking brake valve 10 are blocked, the P port and A1 port of the steering brake valve 9 are blocked and the A2 port is connected. When the P port and A port of the parking brake valve 10 are connected, the conduction area between the 7 port and A port of the steering brake control valve, and the conduction area between the 8 port and A port of the service brake valve are both positively correlated with the conduction area between the 9 port and A1 port of the steering brake valve, and both are negatively correlated with the conduction area between the 9 port and A2 port of the steering brake valve.

[0036] When the parking brake control device 15 is in the locked state, the controller 16 controls the P port and A port of the parking brake valve 10 to block. When the parking brake control device 15 is in the unlocked state, the controller 16 controls the P port and A port of the parking brake valve 10 to open. When the parking brake controller 15 is in the unlocked state, the steering brake controller can control the conduction area between the steering brake control valve 7 port and port A through the controller 16, and the service brake pedal 17 can control the conduction area between the service brake valve 8 port and port A through the controller 16.

[0037] In this way, when the P port and A port of the parking brake valve 10 are blocked, hydraulic oil will not flow to the steering brake valve 9. At this time, both the steering clutch and the brake clutch are not supplied with oil and remain normally closed. The brake clutch brakes to the maximum extent so that the bulldozer remains parked and locked.

[0038] After the P port and A port of the parking brake valve 10 are connected, the hydraulic oil will flow to the steering brake valve 9. When there is no control electrical signal input to the steering brake control valve 7 and the service brake valve 8, the P port and A port of the steering brake control valve 7 and the P port and A port of the service brake valve 8 are blocked. Correspondingly, the P port and A1 port of the steering brake valve 9 are blocked and connected to the A2 port. At this time, the brake clutch is supplied with hydraulic oil at maximum pressure, the steering clutch remains engaged, and the power transmission from the engine to the traveling mechanism is maintained. When the brake clutch is released, the bulldozer can be put into gear and start driving. During the operation of construction machinery or vehicles, if it is necessary to decelerate or stop the vehicle by braking, the driver can control the oil flow of the service brake valve 8 by pressing the service brake pedal 17. That is, control the conduction area between the P port and A port of the service brake valve 8. The greater the depth of pressing the service brake pedal 17, the greater the conduction area between the P port and A port of the service brake valve 8, and the greater the oil pressure supplied to the pilot port of the steering brake valve 9. The conduction area between the P port and A1 port of the steering brake valve 9 increases and the conduction area between the P port and A2 port decreases. This results in a smaller oil flow of the brake clutch, a larger braking force on the traveling mechanism (tracks or wheels), and thus deceleration or stopping. Moreover, when the service brake pedal 17 is pressed, the increased oil flow of the steering clutch reduces the corresponding engagement force, thereby actively weakening the driving force transmitted from the engine to the traveling mechanism. Compared to the traditional method that relies solely on springs to press the friction pair, this application realizes a composite braking mechanism of "power cut-off + mechanical braking", which significantly enhances the overall machine torque, ensures reliable deceleration or stopping under high output torque conditions, reduces safety hazards, and avoids the brake clutch working in a slipping state for a long time.

[0039] If turning is required during driving, the driver can operate the steering brake control device to open ports P and A of the steering brake control valve 7 corresponding to left or right turn. This reduces the braking force of the steering clutch and increases the braking force of the brake clutch, creating a difference in power between the left and right sides of the driving mechanism, thus achieving a large-radius turn. As the driver operates the steering brake control valve 7, the conduction area between ports P and A increases to the maximum oil flow, at which point the steering clutch releases the brake, and the brake clutch reaches its maximum braking force, thus achieving a small-radius turn. Upon completion of the turn, releasing the steering brake control device engages the steering clutch to output power, and the brake clutch disengages, resuming straight-line driving.

[0040] Furthermore, since the steering brake control valve 7 and the service brake valve 8 are connected to the pilot port of the steering brake valve 9, they form a pilot-controlled hydraulic system. Pilot control utilizes a small flow rate and low pressure control oil to drive the main valve core, allowing the driver to achieve precise control of the high-pressure main oil circuit with only a small operating force (such as lightly pressing the pedal or lightly pulling the lever). This significantly reduces operator fatigue and improves driving comfort. Simultaneously, steering and service braking are controlled by two independent pilot signals (from the steering brake control valve 7 and the service brake valve 8) superimposed on the steering brake valve. Compared to electronically controlled proportional valves or high-speed switching valves, pilot-operated hydraulic valves are less sensitive to hydraulic oil contamination, making them more suitable for the use of small and medium-horsepower bulldozers in harsh working environments such as mining and earthmoving, and resulting in lower maintenance costs. Additionally, the oil circuit to the steering brake valve is only opened by the pilot signal when needed, avoiding energy loss caused by continuous high-pressure overflow. The energy-saving effect is particularly noticeable under conditions of frequent start-stop or fine-tuning of steering.

[0041] Based on the above, the hydraulic steering and braking system of this embodiment has the following main effects: 1. Parking Lock Function: When the P and A ports of the parking brake valve 10 are blocked, this system ensures that both the steering clutch and the brake clutch remain normally closed, allowing the brake clutch to generate maximum braking force while the steering clutch does not transmit power, thus locking the bulldozer in place. This design guarantees the safety and stability of construction machinery or vehicles when parked.

[0042] 2. Starting and driving control: When the P port and A port of the parking brake valve 10 are connected, the hydraulic oil flows to the steering brake valve 9. At this time, if there is no electrical signal input to the steering brake control valve 7 and the service brake valve 8, the P port and A1 port of the steering brake valve 9 are blocked and connected to the A2 port. The brake clutch is supplied with hydraulic oil at the maximum pressure to release the brake. The steering clutch is not supplied with oil to maintain the maximum engagement force, and the power is transmitted completely, so that the bulldozer can be engaged and started driving quickly.

[0043] 3. Flexible service brake adjustment: By pressing the service brake pedal 17, the oil flow of the service brake valve 8 can be controlled. The braking force and power transmission of the traveling mechanism (track or wheel) can be flexibly adjusted as needed, thereby achieving precise deceleration or stopping, improving safety and avoiding the brake clutch from working in a slipping state for a long time.

[0044] 4. Efficient Steering Operation: When turning is required during driving, the driver can operate the steering brake control device to change the conduction area between port 7 and port A of the steering brake control valve corresponding to left or right turn, thereby adjusting the power difference between the left and right sides of the travel mechanism and achieving turning operations of different radii. In particular, by maximizing the oil flow of the steering brake control valve 7, the steering clutch on one side can be fully disengaged and the braking force of the brake clutch can be maximized, thus achieving the smallest turning radius.

[0045] 5. By connecting the steering brake control valve 7 and the service brake valve 8 to the pilot port of the steering brake valve 9, a high-efficiency hydraulic control architecture with hydraulic logic to achieve functional coordination is constructed. This architecture not only inherits the advantages of hydraulic control system such as simple structure, low cost and pollution resistance, but also realizes dynamic decoupling and intelligent coordination of braking and steering through pilot control.

[0046] In summary, this hydraulic steering and braking system not only improves the operational flexibility, safety, and economy of bulldozers, but also effectively solves the shortcomings of traditional hydraulic bulldozer braking methods under high output torque conditions, significantly improving the overall working efficiency and service life of the machine.

[0047] In detail, the steering brake valve 9 includes a steering valve and a brake valve. The pilot port of the steering valve and the pilot port of the brake valve are both connected to the A port of the steering brake control valve 7 and the A port of the service brake valve 8. The P port of the steering valve and the P port of the brake valve are both connected to the A port of the parking brake valve 10. The T-port of the steering valve and the T-port of the brake valve are both connected to the oil tank 1; The A port of the steering valve (i.e., the A1 port of the entire steering brake valve 9) is connected to the inlet of the steering clutch, and the A port of the brake valve (i.e., the A2 port of the entire steering brake valve 9) is connected to the inlet of the brake clutch. The conduction area between the P port and A port of the steering valve is positively correlated with the oil inlet pressure of the steering valve pilot port; the conduction area between the P port and A port of the brake valve is negatively correlated with the oil inlet pressure of the steering valve pilot port.

[0048] Thus, since the pilot ports of the steering valve and the brake valve are both connected to the same pilot oil circuit, this circuit supplies oil to both port A of the steering brake control valve 7 and port A of the service brake valve 8. This means that when the driver operates the steering handle (controlling the steering brake control valve 7) or depresses the brake pedal (controlling the service brake valve 8), the oil pressure at the pilot port will change. In other words, the pilot pressure is a unified control variable for steering and braking actions. By using a single pilot pressure signal to simultaneously regulate steering release and braking application, the operating logic is simplified.

[0049] As the conduction area between the P port and A port of the steering valve increases with the increase of pilot pressure, the oil pressure of the steering clutch increases accordingly, and the braking force decreases (clutch releases), thus achieving steering. On the other hand, the conduction area between the P port and A port of the brake valve decreases with the increase of pilot pressure, so the oil pressure of the brake clutch decreases and the spring presses the friction plate, thereby increasing the braking force. This reverse design of one increasing and the other decreasing constitutes the hydraulic interlock mechanism of braking and steering, which ensures a smooth transition between braking and steering actions, avoids abrupt switching, and improves handling comfort and safety.

[0050] It is understandable that for tracked construction machinery or vehicles, steering is usually achieved by controlling the different speeds of the left and right walking mechanisms (tracks). For example, braking and decelerating the left track achieves a left turn, and braking and decelerating the right track achieves a right turn. Therefore, in this embodiment, for tracked construction machinery or vehicles, the steering valve includes a left steering valve 9A and a right steering valve 9D, the braking valve includes a left braking valve 9B and a right braking valve 9C, the steering clutch includes a left steering clutch 11 and a right steering clutch 14, and the braking clutch includes a left braking clutch 12 and a right braking clutch 13. The A port of the left steering valve 9A is connected to the left steering clutch 11, the A port of the right steering valve 9D is connected to the right steering clutch 14, the A port of the left brake valve 9B is connected to the left brake clutch 12, and the A port of the right brake valve 9C is connected to the right brake clutch 13.

[0051] In this way, since the left and right steering clutches 14 and the left and right braking clutches 13 are controlled by their respective independent hydraulic valves, the system can apply different driving / braking states to the two sides of the traveling mechanism. When one side of the steering clutch is released (oil is supplied) while the other side remains engaged (or the braking clutch is pressed), a speed difference is generated between the two tracks, thereby achieving smooth and controllable differential steering and avoiding slippage or steering lag of the whole machine.

[0052] When a turn is required, the driver can operate the left or right steering brake control valve independently via the steering brake controller to precisely adjust the pilot pressure on the corresponding side, thereby continuously controlling the opening of the steering valve and brake valve on that side. This enables a full range of adjustment from large-radius gradual turns (wide turns) to small-radius sharp turns (narrow turns), significantly enhancing the equipment's maneuverability and operational accuracy in narrow spaces, trench edges, or complex terrain.

[0053] The left and right brake clutches 13 are independently controlled by the left and right brake valves 9C, which can ensure that the braking force on both sides is applied synchronously during the braking process, avoiding deviation, fishtailing or skidding caused by the lag or insufficiency of braking force on one side. Especially on slopes or slippery surfaces, it effectively improves the braking stability and driving safety of the whole vehicle.

[0054] In this embodiment, the service brake valve 8 includes a two-position three-way electro-hydraulic valve 8A, a first brake check valve 8B, and a second brake check valve 8C; The P port of the two-position three-way electro-hydraulic valve 8A is connected to the outlet of the oil pump 3, the T port of the two-position three-way electro-hydraulic valve 8A is connected to the oil tank 1, and the A port of the two-position three-way electro-hydraulic valve 8A is connected to the A port of the first brake check valve 8B and the A port of the second brake check valve 8C. The B port of the first brake check valve 8B and the B port of the second brake check valve 8C are both connected to the pilot port of the steering brake valve 9. That is, the B port of the first brake check valve 8B is connected to the pilot ports of the left steering valve 9A and the left brake valve 9B, and the B port of the second brake check valve 8C is connected to the pilot ports of the right steering valve 9D and the right brake valve 9C. The conduction area between port A and port A of the 2-position 3-way electro-hydraulic valve is positively correlated with the proportional current signal.

[0055] In this way, since the conduction area between the P and A ports of the two-position three-way electro-hydraulic valve 8A is positively correlated with the input proportional current signal, the electrical signal generated when the driver depresses the driving brake pedal 17 (e.g., via the pedal position sensor) can linearly adjust the valve opening, thereby continuously and precisely controlling the control oil pressure output to the steering valve pilot port and the brake valve pilot port. This allows the braking force to be steplessly adjusted according to the operating intention, avoiding the shock or response lag caused by traditional on / off braking.

[0056] The first brake check valve 8B and the second brake check valve 8C respectively direct the control oil from the service brake valve 8 to the pilot port of the steering brake valve 9. Their one-way conduction characteristic effectively blocks reverse oil flow interference from the steering brake control valve 7 or other circuits, preventing crosstalk of the brake pilot pressure caused by steering operation. At the same time, the parallel structure of the two check valves ensures that the left and right brake control signals reliably merge in the pilot chamber, providing a unified and stable pilot pressure source for the subsequent left / right brake valves 9C. Moreover, the presence of the check valves not only isolates reverse flow but also limits the spread of faults in the event of local pipeline leakage or valve core jamming. The electro-hydraulic valve only needs to control a small flow of pilot oil, and the main braking action is still completed by the large flow of steering brake valve 9, reducing the stringent requirements on the diameter and cleanliness of the electro-hydraulic valve.

[0057] The pilot pressure generated by the service brake enters the steering brake valve 9 via a one-way valve. On the one hand, it reduces the oil supply to the brake clutch (increasing braking force), and on the other hand, it increases the oil supply to the steering clutch (reducing the power transmission efficiency on the steering side). This mechanism, driven by the same pilot pressure to link braking and power transmission in opposite directions, can improve handling safety under complex operating conditions.

[0058] Electro-hydraulic proportional control replaces traditional mechanical linkages or pure hydraulic foot valves, eliminating mechanical backlash and frictional hysteresis. Combined with the low-flow characteristics of pilot control, it significantly accelerates braking response speed. At the same time, the proportional current signal can be integrated with controller 16, facilitating the implementation of intelligent functions such as hill-start assist braking and anti-skid control, and reserving interfaces for future electronic control upgrades.

[0059] In driving mode, the two-position three-way electro-hydraulic valve 8A can be switched to the T port for unloading (P-T conduction), so that the output of the oil pump 3 returns directly to the oil tank 1, avoiding energy loss caused by continuous high-pressure overflow; while during braking, it only outputs pilot flow as needed, reducing unnecessary hydraulic power consumption and helping to improve the fuel economy of the whole machine.

[0060] In this embodiment, the steering brake control valve 7 includes a left steering brake control valve 7A and a right steering brake control valve 7B. The P port of the left steering brake control valve 7A and the P port of the right steering brake control valve 7B are both connected to the outlet of the oil pump 3. The T port of the left turn brake control valve 7A and the T port of the right turn brake control valve 7B are both connected to the oil tank 1. Port A of the left turn brake control valve 7A and port A of the right turn brake control valve 7B are both connected to the pilot port of the turn brake valve 9. That is, port A of the left turn brake control valve 7A is connected to the pilot port of the left turn valve 9A and the pilot port of the left brake valve 9B. Port A of the right turn brake control valve 7B is connected to the pilot port of the right turn valve 9D and the pilot port of the right brake valve 9C.

[0061] In this way, the left steering brake control valve 7A and the right steering brake control valve 7B control the hydraulic pilot signals of the left and right travel mechanisms respectively, without interfering with each other. When the driver operates the left turn button on the steering brake control device (pressing or moving it to the left), only the left steering brake control valve 7A outputs pilot pressure, acting on the left steering valve 9A and the left brake valve 9B; the right travel system remains in its original state. The reverse is also true. This independent control architecture ensures the accuracy and symmetry of steering actions, avoiding steering deviation or response imbalance caused by cross-interference. Moreover, the driver only needs to use the left and right buttons on the handle to control the left and right steering respectively, without the need for additional operating commands. The steering intention is directly converted into the corresponding hydraulic pilot signal, and the system automatically completes the linkage of steering clutch release and brake clutch engagement, reducing operational complexity, especially suitable for long-term, high-intensity operation scenarios, and reducing operator fatigue.

[0062] For either side, the pilot pressure output by the same control valve simultaneously acts on the steering valve (positive correlation: pressure ↑ → steering clutch oil flow ↑ → weakened transmission) and the brake valve (negative correlation: pressure ↑ → brake clutch oil flow ↓ → spring-loaded braking). Therefore, when operating the left (or right) steering handle, the system automatically achieves a coordinated action of "power cut-off on this side + track braking on this side," creating a significant speed difference. This allows for efficient small-radius or even stationary turning under high torque conditions, improving operational flexibility.

[0063] In addition, since the left and right steering brake control valves 7B and the service brake valve 8 share the same pilot control chamber (which is fed in through their respective check valves), when the driver simultaneously presses the brake pedal and operates the steering handle, the pilot pressure is superimposed, which can enhance the braking effect on the steering side while decelerating, thus achieving composite working condition control of "braking and steering at the same time". This is suitable for high-risk operation scenarios such as emergency obstacle avoidance and slope turning.

[0064] In this embodiment, the parking brake valve 10 includes a two-position three-way hydraulic control valve 10C and an electro-hydraulic control valve 10B; The P port and pilot port of the two-position three-way hydraulic control valve 10C and the P port of the electro-hydraulic control valve 10B are all connected to the outlet of the oil pump 3. The A port of the two-position three-way hydraulic control valve 10C is connected to the P port of the steering brake valve 9. The T port of the two-position three-way hydraulic control valve 10C and the T port of the electro-hydraulic control valve 10B are both connected to the oil tank 1. When the electro-hydraulic control valve 10B is open, the P port and A port of the two-position three-way hydraulic control valve 10C are blocked; when the electro-hydraulic control valve 10B is closed, the P port and A port of the two-position three-way hydraulic control valve 10C are connected.

[0065] Thus, when the machine needs to be parked, the driver operates the parking brake controller 15, which in turn energizes the electro-hydraulic control valve 10B to open. This releases the pressure in the pilot chamber of the two-position three-way hydraulic control valve 10C to the oil tank 1, causing its valve core to switch to the P-T connected and P-A blocked position under the action of the spring. At this time, the hydraulic supply to the main oil circuit (P port) of the steering brake valve 9 is completely cut off, and both the left / right steering clutch 14 and the brake clutch are pressed by the return spring due to the loss of pressure, entering the fully locked braking state. This design not only relies on spring force but also ensures parking reliability through active oil cut-off, avoiding accidental movement caused by system leakage or residual pressure.

[0066] When normal driving or operation is required, the electro-hydraulic control valve 10B is de-energized and closed, and the pressure of the oil pump 3 acts simultaneously on the P port and pilot port of the two-position three-way hydraulic control valve 10C, so that its valve core is kept in the P-A conducting position, and continuously provides a stable working oil pressure to the steering brake valve 9.

[0067] Optionally, the parking brake valve 10 also includes a parking relief valve 10A, the P port of which is connected to the outlet of the oil pump 3. The P port of the two-position three-way hydraulic control valve 10C, the P port of the electro-hydraulic control valve 10B, and the pilot port of the two-position three-way hydraulic control valve 10C are all connected to the T port of the parking relief valve 10A.

[0068] In this way, the parking relief valve 10A pre-regulates the high-pressure oil from the oil pump 3 and outputs it to its T port, which serves as the working oil port (P port) of the two-position three-way hydraulic control valve 10C, the pilot control port, and the oil inlet of the electro-hydraulic control valve 10B. This means that no matter how the main system pressure fluctuates (such as due to sudden load changes or pump flow variations), the pressure supplied to the parking brake logic circuit is always limited to below the set value of the parking relief valve 10A, thereby ensuring that the operating pressure of the two-position three-way hydraulic control valve 10C is stable and that the electro-hydraulic control valve 10B operates within a safe pressure range, thus ensuring that the pilot control response is linear and reliable.

[0069] In this embodiment, the hydraulic steering and braking system also includes a coarse filter 2, a fine filter 4, an overflow valve 5, and an accumulator 6; The coarse filter 2, oil pump 3, fine filter 4 and accumulator 6 are connected in series. The P port of steering brake control valve 7 and the P port of service brake valve 8 are both connected to accumulator 6. The P port of the overflow valve 5 is connected to the outlet of the oil pump 3, and the T port of the overflow valve 5 is connected to the oil tank 1.

[0070] Thus, the hydraulic oil enters the oil pump 3 after being initially removed by the coarse filter 2 to remove large particulate contaminants, and then undergoes further filtration by the fine filter 4 to ensure that the oil entering the accumulator 6 and subsequent control valves (steering, parking, and service brake valves 8) has a high degree of cleanliness. Since these valves are mostly precision pilot components (such as electro-hydraulic valves and hydraulic control valves), they are extremely sensitive to contamination. The two-stage filtration significantly reduces the risk of jamming, wear, or malfunction, and improves the long-term reliability of the system.

[0071] Both the steering brake control valve 7 and the service brake valve 8 draw oil from the accumulator 6 at their P ports, rather than directly from the oil pump 3 outlet. The accumulator 6 absorbs pressure fluctuations caused by output pulsations and sudden load changes from the oil pump 3, providing a more stable pilot pressure for the steering brake control valve and the service brake valve, thus improving the linearity and consistency of braking and steering operations. When the driver quickly operates the steering lever or urgently presses the brake pedal, the accumulator 6 can immediately release the stored high-pressure oil to compensate for the response lag of the oil pump 3, ensuring millisecond-level control response. In addition, even if the engine is briefly turned off or the pump stops working, the accumulator 6 can still support several critical operations (such as emergency parking), improving safety.

[0072] The relief valve 5 is directly connected to the outlet of the oil pump 3, forming the first-level overload protection of the system. When the accumulator 6 is full, the control valve is closed, or the pipeline is blocked, causing the system pressure to rise abnormally, the relief valve 5 will automatically open to release the excess flow back to the oil tank 1, preventing damage to the pump, pipeline or valve body due to overpressure, and ensuring that the system operates within the safe pressure range.

[0073] This embodiment also discloses a bulldozer that includes the electro-hydraulic steering and braking system described in the above embodiment.

[0074] The working principle of the electro-hydraulic steering and braking system in this embodiment is explained by way of example below: 1. Parking brake When the driver operates the parking brake control 15 (such as pressing the parking button or pulling the parking handle) to enter the locked state, the controller 16 outputs a signal to block the P port and A port of the parking brake valve 10, cutting off the hydraulic supply to the main oil circuit of the steering brake valve 9. At this time, both the steering clutch and the brake clutch lose pressure and remain normally closed under the action of the return spring—the steering clutch cuts off power transmission, and the brake clutch applies maximum braking force, achieving reliable parking and locking of the entire machine and preventing the vehicle from rolling.

[0075] 2. Steering control: With the parking brake released, the driver presses the left or right turn button on the steering brake control: During light operation, the left or right turn button has a small travel, and the steering brake control valve 7 on the corresponding side (left or right) outputs a small pilot pressure, which makes the steering clutch part on that side energized (partially engaged) and the brake clutch part depressurized (partially braked), resulting in a small speed difference between the two tracks, thus achieving a large-radius smooth turn. When operating with large movements, the left or right turn button reaches its maximum travel, the pilot pressure increases to the maximum, the corresponding side steering clutch is completely depressurized and disengaged (power cut off), and at the same time the braking clutch is fully engaged (power braking), the track on that side stops rotating, and the other side drives normally, thus achieving small-radius or even stationary turning.

[0076] 3. Service brakes: When the vehicle is in motion, the driver depresses the service brake pedal 17. The controller 16 adjusts the opening of the service brake valve 8 according to the pedal travel and inputs control oil with corresponding pressure into the pilot port of the steering brake valve 9. Increased pilot pressure leads to reduced oil supply to the brake clutch and increased clamping, generating braking force. At the same time, the increased oil supply to the steering clutch makes engagement more reliable, maintaining power transmission stability and assisting in steering ease. The deeper you press the pedal, the greater the braking force, achieving linear and controllable deceleration or stopping.

[0077] In summary, the hydraulic steering and braking system, the electro-hydraulic steering and braking system, and the bulldozer used in this embodiment have at least the following advantages: 1. Significantly improved braking reliability: It adopts a composite braking mechanism of "power cut-off + active mechanical braking", which can still provide sufficient braking force under high output torque conditions such as high engine speed and low gear. It effectively solves the problems of brake failure and slippage caused by traditional methods that rely solely on spring compression, and greatly improves driving safety.

[0078] 2. Parking lock is safer and more reliable: When parked, the main oil circuit is cut off by electronic control, so that the steering and braking clutches are completely locked under the action of the spring, realizing dual mechanical braking to prevent slippage or accidental movement, which is in line with the safety principle of "braking upon loss of pressure" for construction machinery.

[0079] 3. Flexible and precise steering operation: It supports independent control on the left and right sides. By adjusting the travel of the steering controller, it can achieve stepless adjustment from large radius slow turn to small radius turn on the spot, meeting the high mobility operation requirements in narrow spaces and complex terrains.

[0080] 4. Easy to operate and user-friendly: With a pilot-operated hydraulic control structure, the driver only needs a small amount of operating force (lightly pull the handle or lightly press the pedal) to accurately control the high-pressure main oil circuit, which greatly reduces operator fatigue and improves operating comfort.

[0081] 5. Strong ability to adapt to harsh working conditions: Compared to pure electronic proportional control systems, the combination of electronic control and pilot hydraulic control has lower requirements for hydraulic oil cleanliness, stronger anti-pollution capabilities, and is more suitable for field operation environments with high dust and vibration, such as mines and earthmoving, with lower maintenance costs.

[0082] 6. Energy-efficient and highly effective: The main oil circuit is opened only when needed by a pilot signal to avoid continuous high-pressure overflow; the accumulator 6 and the overflow valve 5 work together to optimize energy utilization, reduce system temperature rise and fuel consumption, and improve the overall economy of the machine.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A hydraulic steering and braking system, characterized in that, Includes fuel tank (1), fuel pump (3), steering brake control valve (7), parking brake valve (10), service brake valve (8), steering brake valve (9), steering clutch and brake clutch; The inlet of the oil pump (3) is connected to the oil tank (1), and the P port of the steering brake control valve (7), the P port of the parking brake valve (10) and the P port of the service brake valve (8) are all connected to the outlet of the oil pump (3). The A port of the steering brake control valve (7) and the A port of the service brake valve (8) are both connected to the pilot port of the steering brake valve (9). The A port of the parking brake valve (10) is connected to the P port of the steering brake valve (9), the A1 port of the steering brake valve (9) is connected to the inlet of the steering clutch, and the A2 port of the steering brake valve (9) is connected to the inlet of the brake clutch. The T-port of the steering brake control valve (7), the T-port of the service brake valve (8), the T-port of the steering brake valve (9), the outlet of the steering clutch, and the outlet of the brake clutch are all connected to the oil tank (1). In the case that the P port and A port of the parking brake valve (10) are blocked, the P port of the steering brake valve (9) is blocked from the A1 port and connected to the A2 port. When the P port and A port of the parking brake valve (10) are connected, the conduction area between the P port and A port of the steering brake control valve (7) and the conduction area between the P port and A port of the service brake valve (8) are both positively correlated with the conduction area between the P port and A1 port of the steering brake valve (9) and negatively correlated with the conduction area between the P port and A2 port of the steering brake valve (9).

2. The hydraulic steering and braking system according to claim 1, characterized in that, The service brake valve (8) includes a two-position three-way electro-hydraulic valve (8A), a first brake check valve (8B), and a second brake check valve (8C). The P port of the two-position three-way electro-hydraulic valve (8A) is connected to the outlet of the oil pump (3), the T port of the two-position three-way electro-hydraulic valve (8A) is connected to the oil tank (1), and the A port of the two-position three-way electro-hydraulic valve (8A) is connected to the A port of the first brake check valve (8B) and the A port of the second brake check valve (8C). The B port of the first brake check valve (8B) and the B port of the second brake check valve (8C) are both connected to the pilot port of the steering brake valve (9); The conduction area between port P and port A of the two-position three-way electro-hydraulic valve (8A) is positively correlated with the proportional current signal.

3. The hydraulic steering and braking system according to claim 1, characterized in that, The steering brake control valve (7) includes a left steering brake control valve (7A) and a right steering brake control valve (7B). The P port of the left steering brake control valve (7A) and the P port of the right steering brake control valve (7B) are both connected to the outlet of the oil pump (3). The T-port of the left steering brake control valve (7A) and the T-port of the right steering brake control valve (7B) are both connected to the oil tank (1). The A port of the left steering brake control valve (7A) and the A port of the right steering brake control valve (7B) are both connected to the pilot port of the steering brake valve (9).

4. The hydraulic steering and braking system according to claim 1, characterized in that, The parking brake valve (10) includes a two-position three-way hydraulic control valve (10C) and an electro-hydraulic control valve (10B). The P port and pilot port of the two-position three-way hydraulic control valve (10C) and the P port of the electro-hydraulic control valve (10B) are all connected to the outlet of the oil pump (3). The A port of the two-position three-way hydraulic control valve (10C) is connected to the P port of the steering brake valve (9). The T port of the two-position three-way hydraulic control valve (10C) and the T port of the electro-hydraulic control valve (10B) are both connected to the oil tank (1). When the electro-hydraulic control valve (10B) is open, the P port and A port of the two-position three-way hydraulic control valve (10C) are blocked; when the electro-hydraulic control valve (10B) is closed, the P port and A port of the two-position three-way hydraulic control valve (10C) are connected.

5. The hydraulic steering and braking system according to claim 4, characterized in that, The parking brake valve (10) also includes a parking relief valve (10A), the P port of which is connected to the outlet of the oil pump (3); The P port of the two-position three-way hydraulic control valve (10C), the P port of the electro-hydraulic control valve (10B), and the pilot port of the two-position three-way hydraulic control valve (10C) are all connected to the T port of the parking relief valve (10A).

6. The hydraulic steering and braking system according to claim 1, characterized in that, The steering brake valve (9) includes a steering valve and a brake valve. The pilot port of the steering valve and the pilot port of the brake valve are both connected to the A port of the steering brake control valve (7) and the A port of the service brake valve (8). The P port of the steering valve and the P port of the brake valve are both connected to the A port of the parking brake valve (10). The T-port of the steering valve and the T-port of the brake valve are both connected to the oil tank (1); The A port of the steering valve is connected to the inlet of the steering clutch, and the A port of the brake valve is connected to the inlet of the brake clutch. The conduction area between the P port and A port of the steering valve is positively correlated with the oil inlet pressure of the steering valve pilot port; the conduction area between the P port and A port of the brake valve is negatively correlated with the oil inlet pressure of the brake valve pilot port.

7. The hydraulic steering and braking system according to claim 6, characterized in that, The steering valve includes a left steering valve (9A) and a right steering valve (9D), the brake valve includes a left brake valve (9B) and a right brake valve (9C), the steering clutch includes a left steering clutch (11) and a right steering clutch (14), and the brake clutch includes a left brake clutch (12) and a right brake clutch (13). The A port of the left steering valve (9A) is connected to the left steering clutch (11), the A port of the right steering valve (9D) is connected to the right steering clutch (14), the A port of the left brake valve (9B) is connected to the left brake clutch (12), and the A port of the right brake valve (9C) is connected to the right brake clutch (13).

8. The hydraulic steering and braking system according to claim 1, characterized in that, The hydraulic steering and braking system also includes a coarse filter (2), a fine filter (4), an overflow valve (5), and an accumulator (6). The coarse filter (2), the oil pump (3), the fine filter (4) and the accumulator (6) are connected in series. The P port of the steering brake control valve (7) and the P port of the service brake valve (8) are both connected to the accumulator (6). The P port of the overflow valve (5) is connected to the outlet of the oil pump (3), and the T port of the overflow valve (5) is connected to the oil tank (1).

9. An electro-hydraulic steering and braking system, characterized in that, Includes a controller (16), a parking brake control unit (15), a service brake pedal (17), a steering brake control unit, and the hydraulic steering brake system according to any one of claims 1-8; The parking brake controller (15), the service brake pedal (17) and the steering brake controller are all electrically connected to the controller (16). The controller (16) is electrically connected to the steering brake control valve (7), the parking brake valve (10) and the service brake valve (8); When the parking brake controller (15) is in the locked state, the controller (16) controls the P port and A port of the parking brake valve (10) to be blocked. When the parking brake controller (15) is in the unlocked state, the controller (16) controls the P port and A port of the parking brake valve (10) to be open. When the parking brake controller (15) is in the unlocked state, the steering brake controller can control the conduction area between the P port and the A port of the steering brake control valve (7) through the controller (16), and the service brake pedal (17) can control the conduction area between the P port and the A port of the service brake valve (8) through the controller (16).

10. A bulldozer, characterized in that, Includes the electro-hydraulic steering and braking system as described in claim 9.

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