A speed-sensitive power control hydraulic system and control method for skid steer loaders

Abstract

This invention discloses a speed-sensitive power control hydraulic system and control method for a skid steer loader, including an engine assembly, a travel hydraulic system, and a pilot hydraulic control system. The travel hydraulic system includes a variable displacement pump and a travel motor. The pilot hydraulic control system includes a pilot pump, a control handle, and a variable displacement control pushrod. The pilot pump supplies oil to the variable displacement control pushrod via the control handle; the variable displacement control pushrod controls the variable displacement pump. A power limiting valve connected to an oil tank is installed on the oil line between the control handle and the variable displacement control pushrod. The engine assembly includes a speed sensor connected to the machine controller. The machine controller is connected to the power limiting valve. The control method calculates the engine output power by measuring the engine speed, obtains the power of the working hydraulic system, and limits the upper limit of the power of the travel hydraulic system to ensure that the power demand of the working hydraulic system is prioritized. Beneficial effect: This invention achieves anti-stalling effect in the skid steer loader through the power limiting valve.

Description

Technical Field

[0001] This invention relates to a hydraulic system and control method for engineering equipment, and particularly to a hydraulic system and control method for a skid steer loader with speed-sensitive power control, belonging to the field of engineering machinery technology. Background Technology

[0002] A skid steer loader is a small wheeled or tracked loading device that uses the speed difference between its two wheels to achieve steering. Its most distinctive feature is that it has no steering wheel or differential; it steers by the skid friction generated by the speed difference between the left and right wheels and has the ability to turn 360° on the spot.

[0003] The skid steer loader uses a closed hydrostatic travel system with dual pumps and dual motors to drive the machine's movement. The output flow of the travel pump is controlled by a handle, which controls the speed of the motors on both sides, enabling different machine speeds and differential skid steering.

[0004] Currently, the mainstream technologies in the market include two operating modes: ISO mode, where a single handle controls the machine's forward and turning directions in four directions; and H mode, where the left and right handles control the forward and backward movement of the left and right tires respectively. In ISO mode, the machine's travel pump is typically equipped with a DA valve to control the pressure at the travel handle inlet, thus controlling the pump's power. In H mode, there is usually no power setting, which often leads to the machine stalling when simultaneously traveling and operating under heavy loads, severely impacting work efficiency.

[0005] When the machine is controlled in H mode, there is usually no power setting, which often causes the machine to stall, severely impacting work efficiency. In this mode, pushing and pulling the left and right handles forward and backward control the left and right tires respectively, while the left and right movements of the handles control the main control valve of the machine, which in turn controls the operation of the upper actuator. Using the traditional solution of using a DA valve for power control through the handle's oil inlet will cause abnormal upper actuator movements, making the machine unable to operate normally.

[0006] For example, Chinese patent CN113819103B discloses a power control hydraulic system and control method for a skid steer loader. It controls proportional solenoid directional valves I and II via a speed-sensing control valve. These valves, through a pilot pressure connected to a multi-way valve working device, control the output flow of the working device, thereby controlling the hydraulic system power until it matches the engine power. This technical solution uses a DA valve to limit the flow rate of the working hydraulic system to achieve power control. However, the load changes constantly during operation, causing the pressure of the working hydraulic system to also change continuously. Controlling the hydraulic system power by controlling the flow rate of the working hydraulic system can lead to abnormal operation of the working device, preventing the machine from operating normally and even causing safety accidents. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to address the technical problems existing in the prior art by providing a speed-sensitive power control hydraulic system and control method for skid steer loaders. By sensing the engine speed, the pilot control flow output by the control handle is controlled to control the displacement of the travel pump, thereby realizing the anti-stalling function of the H-mode skid steer loader.

[0008] Technical Solution: A speed-sensitive power control hydraulic system for a skid steer loader includes an engine assembly, a left-side travel hydraulic system, a right-side travel hydraulic system, and a pilot hydraulic control system. The left-side travel hydraulic system includes a left-side variable displacement pump and a left-side travel motor, which are connected via pipelines to form a closed-loop hydraulic circulation system. The right-side travel hydraulic system includes a right-side variable displacement pump and a right-side travel motor, which are also connected via pipelines to form a closed-loop hydraulic circulation system. The engine assembly drives both the left and right variable displacement pumps. The pilot hydraulic control system includes a pilot pump, a left control lever, and a right control lever. The engine assembly includes a left-side variable displacement control pushrod and a right-side variable displacement control pushrod. The engine assembly drives a pilot oil pump. The pilot oil pump supplies oil to the left-side variable displacement control pushrod via a left-side control lever, while the right-side control lever supplies oil to the right-side variable displacement control pushrod. The left-side variable displacement control pushrod controls the displacement of the left-side variable displacement pump and the flow direction of the hydraulic oil, and the right-side variable displacement control pushrod controls the displacement of the right-side variable displacement pump and the flow direction of the hydraulic oil. Power limiting valves connected to the oil tank are installed in the oil passages between the left-side control lever and the left-side variable displacement control pushrod, as well as in the oil passages between the right-side control lever and the right-side variable displacement control pushrod. The engine assembly includes a speed sensor connected to the engine controller. The engine controller is controlled by the power limiting valve.

[0009] This invention controls the displacement of the left and right variable pumps by setting a power limiting valve connected to the oil tank in the oil circuit of the pilot hydraulic control system, thereby controlling the opening of the power limiting valve and thus controlling the travel hydraulic system, achieving the anti-stalling effect of the H-mode skid steer loader.

[0010] The working principle of this invention is that the machine controller monitors the engine assembly speed through a speed sensor to determine whether the hydraulic system power matches the current output power of the engine assembly during machine operation. When the engine assembly reaches its maximum output power or the hydraulic system pressure suddenly increases during operation, the engine assembly may slow down or even stall. To ensure the safety of machine operation, the oil supply to the working hydraulic system is prioritized. The machine controller reduces the flow rate of the traveling hydraulic system through a power limiting valve, thereby reducing the overall hydraulic system power and achieving the anti-stalling power for the H-mode skid steer loader.

[0011] In a preferred embodiment, to precisely and quickly control the power of the walking hydraulic system, the power limiting valve includes an electro-proportional relief valve. The inlet and outlet oil circuits of the left and right variable control push rods are connected in parallel through check valves and then connected to the inlet of the electro-proportional relief valve. The outlet of the electro-proportional relief valve is connected to the oil tank. The check valves provide unidirectional flow to the inlet side of the electro-proportional relief valve. The control terminal of the electro-proportional relief valve is connected to the signal of the overall machine controller.

[0012] The overall controller controls the opening of the electro-proportional relief valve based on the engine assembly speed and the pressure and flow values ​​of the walking hydraulic system and the working hydraulic system. The check valve can prevent oil from flowing back to the pilot oil circuit, and the electro-proportional relief valve can directly guide the pilot oil in the pilot oil circuit back to the oil tank without the need for the control handle, thereby improving the response speed of the power limit and avoiding abnormal operation of the working device due to the lag in response.

[0013] In a preferred embodiment, to conform to operating habits and meet the control needs of the entire machine, the left and right control handles have the same structure; self-resetting switch valves are respectively set in the four directions of front, back, left, and right, and are initially connected to the oil tank. Pushing the control handle opens one or two adjacent self-resetting switch valves simultaneously; the self-resetting switch valves located in the front and back directions are located in the pilot hydraulic control oil circuit of the walking hydraulic system; the oil ports of the self-resetting switch valves located in the left and right directions are connected to the main control valve of the working hydraulic system.

[0014] By installing self-resetting switch valves connected to the hydraulic system controlling the travel mechanism at the front and rear positions of the left and right handles, pushing the left handle forward or backward will cause the left travel motor to drive the left wheel forward or backward, and similarly, pushing the right handle will cause the right travel motor to drive the right wheel. Pushing both handles simultaneously will cause both travel motors to drive both wheels. The greater the pull of the handle, the higher the speed of the travel motor. When the speeds on both sides are equal, the machine travels; when the speeds are unequal, it steers towards the side with the slower speed. Simultaneously opening two adjacent self-resetting switch valves by pushing the handles enables the machine to travel while operating.

[0015] In a preferred embodiment, to ensure stable control pressure and provide appropriate control oil pressure for the pilot hydraulic control system, a pilot relief valve is provided in the oil line between the pilot oil pump and the control lever of the pilot hydraulic control system. The pilot relief valve allows for the establishment of suitable control oil pressure for controlling the variable displacement push rod in the pipeline of the pilot hydraulic control system.

[0016] In a preferred embodiment, to ensure the normal operation of the closed-loop hydraulic circulation system and to promptly replenish oil losses in the system, the pilot oil pump is connected to both the left-side and right-side travel hydraulic systems via one-way relief valves. The pilot oil pump also functions as a replenishment pump for the travel hydraulic system, saving costs and making the entire hydraulic system more compact.

[0017] In a preferred embodiment, to facilitate oil replenishment of the travel hydraulic system, four one-way relief valves are provided, with their inlets connected to the outlet of the pilot pump and their outlets connected to the oil lines on both sides of the variable pump's inlet and outlet. Since the oil flow direction changes in a closed-loop hydraulic circulation system, oil replenishment is typically performed on the back pressure side. To ensure the travel hydraulic system can be replenished at any time, one-way relief valves are used in the inlet and return lines of both travel hydraulic systems for oil replenishment.

[0018] A control method for a speed-sensitive power control hydraulic system of a skid steer loader. Step 1: Collect engine speed. The speed sensor collects the current speed of the engine assembly and transmits the speed signal to the engine controller. Step 2: Calculate the engine output power. The engine controller calculates the maximum power that the engine assembly can output based on the engine power curve and the current engine speed collected by the speed sensor. Step 3: Obtain the power of the working hydraulic system. The whole machine controller calculates and obtains the power value of the working hydraulic system based on the pressure and flow values ​​of the working hydraulic system. Step 4: Calculate the available power of the walking hydraulic system. The machine controller subtracts the working hydraulic system power value obtained in Step 3 from the maximum power value calculated in Step 2 to obtain the available power value of the walking hydraulic system. Step 5: Obtain the flow threshold of the walking hydraulic system, collect the current pressure value of the walking hydraulic system, and combine it with the available power value of the walking hydraulic system obtained in Step 4 to obtain the current maximum flow threshold. Step 6: Set the power limit of the walking hydraulic system. Based on the current maximum flow threshold of the walking hydraulic system obtained in Step 5, the whole machine controller sets the opening threshold of the power limiting valve. When the current power of the walking hydraulic system does not exceed the available power of the walking hydraulic system, the power limiting valve does not work. When the current power of the walking hydraulic system reaches the upper limit of the available power of the walking hydraulic system, the power limiting valve opens. Based on the current pressure value of the walking hydraulic system, the power limiting valve controls the output flow of the variable pump.

[0019] This invention sets a power threshold for the walking hydraulic system. Under the premise of meeting the power requirements of the working hydraulic system, it limits the power of the walking hydraulic system to ensure the normal operation of the engine and prevent the engine assembly from stalling.

[0020] To improve the machine's self-adaptability, in step one, when the engine assembly's current speed, collected by the speed sensor, suddenly drops, the power limiting valve immediately opens, reducing the output flow of the variable pump. When the engine assembly's speed suddenly drops, it indicates that the machine has encountered an emergency, and the required power increases instantaneously. Since the engine assembly cannot instantly increase its power output, reducing the power of the travel hydraulic system can quickly reduce the required power. This manifests as a decrease in the machine's travel speed, while the operation of the working mechanism remains unaffected.

[0021] To control the power of the travel hydraulic system, the method for controlling the output flow of the variable pump using the power limiting valve in step six is ​​as follows: The overall controller controls the opening of the electro-proportional relief valve. The oil output from the pilot pump of the pilot hydraulic control system is split after passing through the left and / or right control handles. Part of the oil returns to the oil tank through the electro-proportional relief valve, and the other part controls the extension and retraction of the left and / or right variable control push rods. The left variable control push rod drives the displacement of the left variable pump, and the right variable control push rod drives the displacement of the right variable pump.

[0022] Since the pressure value of the travel hydraulic system is determined by the load and road conditions, the power of the travel hydraulic system can only be controlled by adjusting the flow rate. With the engine assembly speed remaining constant, the power is controlled by adjusting the displacement.

[0023] Beneficial effects: This invention achieves the control of the displacement of the left and right variable pumps by setting a power limiting valve connected to the oil tank in the oil circuit of the pilot hydraulic control system and controlling the opening of the power limiting valve, thereby achieving the control of the travel hydraulic system and realizing the anti-stalling effect of the H-mode skid steer loader. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is a hydraulic schematic diagram of the present invention; Figure 2 This is a hydraulic schematic diagram of the control handle of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention 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. Therefore, they should not be construed as limitations on this invention.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0029] like Figure 1 As shown, a speed-sensitive power control hydraulic system for a skid steer loader includes an engine assembly 1, a left-side travel hydraulic system 2, a right-side travel hydraulic system 3, and a pilot hydraulic control system 4. The left-side travel hydraulic system 2 includes a left-side variable pump 21 and a left-side travel motor 22, which are connected by pipelines to form a closed-loop hydraulic circulation system. The right-side travel hydraulic system 3 includes a right-side variable pump 31 and a right-side travel motor 32, which are connected by pipelines to form a closed-loop hydraulic circulation system. The engine assembly 1 drives the left variable pump 21 and the right variable pump 31 to work respectively; The pilot hydraulic control system 4 includes a pilot oil pump 41, a left control handle 42, a right control handle 43, a left variable control push rod 44, and a right variable control push rod 45; the engine assembly 1 drives the pilot oil pump 41 to work; the pilot oil pump 41 supplies oil to the left variable control push rod 44 through the left control handle 42, while the right control handle 43 supplies oil to the right variable control push rod 45; the left variable control push rod 44 drives the displacement of the left variable pump 21 and the flow direction of the hydraulic oil, and the right variable control push rod 45 drives the displacement of the right variable pump 31 and the flow direction of the hydraulic oil; A power limiting valve 5 connected to the oil tank is provided in the oil circuit between the left control handle 42 and the left variable control push rod 44 and in the oil circuit between the right control handle 43 and the right variable control push rod 45. The engine assembly 1 includes a speed sensor 11 that is signal-connected to the engine controller 6; the engine controller 6 is control-connected to the power limiting valve 5.

[0030] This invention achieves the control of the displacement of the left variable pump 21 and the right variable pump 31 by setting a power limiting valve 5 connected to the oil tank in the oil circuit of the pilot hydraulic control system 4, and controlling the opening of the power limiting valve 5, thereby achieving the control of the travel hydraulic system and realizing the anti-stalling effect of the H-mode skid steer loader.

[0031] The working principle of this invention is that the machine controller 6 monitors the rotational speed of the engine assembly 1 through the speed sensor 11 to determine whether the power of the hydraulic system matches the current output power of the engine assembly 1 during operation. When the maximum output power of the engine assembly 1 is reached or the hydraulic system pressure suddenly increases during operation, the engine assembly 1 may slow down or even stall. To ensure the safety of the machine operation and prioritize the oil supply to the working hydraulic system, the machine controller 6 reduces the flow rate of the travel hydraulic system through the power limiting valve 5, thereby reducing the power of the overall hydraulic system and achieving the power to prevent stalling of the H-mode skid steer loader.

[0032] To precisely and quickly control the power of the walking hydraulic system, the power limiting valve 5 includes an electro-proportional relief valve 51. The inlet and outlet oil passages of the left variable control push rod 44 and the right variable control push rod 45 are connected in parallel through check valves 52 and then connected to the inlet of the electro-proportional relief valve 51. The outlet of the electro-proportional relief valve 51 is connected to the oil tank. The check valve 52 conducts unidirectionally to the inlet side of the electro-proportional relief valve 51. The control terminal of the electro-proportional relief valve 51 is connected to the signal of the whole machine controller 6.

[0033] The overall controller 6 controls the opening of the electro-proportional relief valve 51 according to the speed of the engine assembly 1 and the pressure and flow values ​​of the walking hydraulic system and the working hydraulic system. The one-way valve 52 can prevent the oil from flowing back to the pilot oil circuit. The electro-proportional relief valve 51 can directly guide the pilot oil in the pilot oil circuit back to the oil tank without the need for the control handle, thereby improving the response speed of the power limit and avoiding abnormal operation of the working device due to the lag in response.

[0034] like Figure 2 As shown, in order to conform to operating habits and meet the control needs of the whole machine, the left control handle 42 and the right control handle 43 have the same structure; self-resetting switch valves 431 are respectively set in the front, back, left and right directions, and are all connected to the oil tank in the initial state. Pushing the control handle opens one or two adjacent self-resetting switch valves 431 at the same time; the self-resetting switch valves 431 located in the front and back directions are located in the pilot hydraulic control oil circuit of the walking hydraulic system; the oil ports of the self-resetting switch valves 431 located in the left and right directions are connected to the main control valve 7 of the working hydraulic system.

[0035] By installing self-resetting switch valves 431 connected to the hydraulic system controlling the travel mechanism at the front and rear positions of the left and right handles, the left travel motor 22 can drive the left wheel forward or backward when the left handle is pushed forward or backward; similarly, the right travel motor 32 drives the right wheel when the right handle is pushed. Simultaneously pushing both handles causes both travel motors to drive both wheels. The greater the amplitude of the handle push, the higher the speed of the travel motors. When the speeds on both sides are equal, the machine travels smoothly; when the speeds are unequal, it steers towards the side with the slower speed. Simultaneously opening two adjacent self-resetting switch valves 431 by pushing the handles enables the machine to travel while operating.

[0036] like Figure 1 As shown, to ensure stable control pressure and provide appropriate control oil pressure for the pilot hydraulic control system 4, a pilot relief valve 46 is provided in the oil line between the pilot oil pump 41 and the control handle of the pilot hydraulic control system 4. The pilot relief valve 46 allows the establishment of a suitable control oil pressure for controlling the variable displacement push rod in the pipeline of the pilot hydraulic control system 4.

[0037] like Figure 1 As shown, to ensure the normal operation of the closed-loop hydraulic circulation system and to replenish the oil lost in the system in a timely manner, the pilot oil pump 41 is connected to the left-side travel hydraulic system 2 and the right-side travel hydraulic system 3 in one direction via a one-way relief valve 47. The pilot oil pump 41 also functions as a replenishment pump for the travel hydraulic system, saving costs and making the entire hydraulic system more compact.

[0038] To facilitate oil replenishment in the travel hydraulic system, four one-way relief valves 47 are provided. The inlets of all four valves are connected to the outlet of the pilot pump 41, and the outlets of the one-way relief valves 47 are connected to the oil lines on both sides of the variable pump's inlet and outlet. Since the flow direction of the oil changes in a closed-loop hydraulic system, oil replenishment is typically performed on the back pressure side. To ensure that the travel hydraulic system can be replenished at any time, one-way relief valves 47 are used to replenish the oil inlet and return lines of both travel hydraulic systems.

[0039] A control method for a speed-sensitive power control hydraulic system of a skid steer loader. Step 1: Collect engine speed. The speed sensor 11 collects the current speed of the engine assembly 1 and transmits the speed signal to the engine controller 6. Step 2: Calculate the engine output power. The engine controller 6 calculates the maximum power value that the engine assembly 1 can output based on the engine power curve and the current speed of the engine assembly 1 collected by the speed sensor 11. Step 3: Obtain the power of the working hydraulic system. The whole machine controller 6 calculates and obtains the power value of the working hydraulic system based on the pressure value and flow value of the working hydraulic system. Step 4: Calculate the available power of the walking hydraulic system. The whole machine controller 6 subtracts the working hydraulic system power value obtained in step 3 from the maximum power value calculated in step 2 to obtain the available power value of the walking hydraulic system. Step 5: Obtain the flow threshold of the walking hydraulic system, collect the current pressure value of the walking hydraulic system, and combine it with the available power value of the walking hydraulic system obtained in Step 4 to obtain the current maximum flow threshold. Step 6: Set the power limit of the walking hydraulic system. Based on the current maximum flow threshold of the walking hydraulic system obtained in Step 5, the whole machine controller 6 sets the opening threshold of the power limiting valve 5. When the current power of the walking hydraulic system does not exceed the available power of the walking hydraulic system, the power limiting valve 5 does not work. When the current power of the walking hydraulic system reaches the upper limit of the available power of the walking hydraulic system, the power limiting valve 5 opens. Based on the current pressure value of the walking hydraulic system, the power limiting valve 5 controls the output flow of the variable pump.

[0040] To improve the machine's self-adaptability, in step one, when the speed sensor 11 detects a sudden drop in the current speed of engine assembly 1, the power limiting valve 5 immediately opens, reducing the output flow of the variable pump. When the speed of engine assembly 1 suddenly drops, it indicates that the machine has encountered an emergency and the required power increases instantaneously. Since engine assembly 1 cannot instantly increase its power output, the required power can be quickly reduced by decreasing the power of the travel hydraulic system. This manifests as a decrease in the machine's travel speed, while the operation of the working mechanism remains unaffected.

[0041] To control the power of the walking hydraulic system, the power limiting valve 5 controls the output flow of the variable pump in step six as follows: The machine controller 6 controls the opening of the electro-proportional relief valve 51. The oil output by the pilot oil pump 41 of the pilot hydraulic control system 4 is split after passing through the left control handle 42 and / or the right control handle 43. Part of the oil returns to the oil tank through the electro-proportional relief valve 51, and the other part controls the extension and retraction of the left variable control push rod 44 and / or the right variable control push rod 45. The left variable control push rod 44 drives the displacement of the left variable pump 21, and the right variable control push rod 45 drives the displacement of the right variable pump 31.

[0042] Since the pressure value of the travel hydraulic system is determined by the load and road conditions, the power of the travel hydraulic system can only be controlled by adjusting the flow rate. With the engine assembly speed remaining constant, the power is controlled by adjusting the displacement.

[0043] This invention sets a power threshold for the walking hydraulic system to limit the power of the walking hydraulic system while meeting the power requirements of the working hydraulic system, thereby ensuring the normal operation of the engine and preventing engine assembly 1 from stalling.

[0044] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A speed-sensitive power control hydraulic system for a skid steer loader, comprising an engine assembly (1), a left-side travel hydraulic system (2), a right-side travel hydraulic system (3), and a pilot hydraulic control system (4). The left-side walking hydraulic system (2) includes a left-side variable pump (21) and a left-side walking motor (22), which are connected by pipelines to form a closed-loop hydraulic circulation system. The right-side walking hydraulic system (3) includes a right-side variable pump (31) and a right-side walking motor (32), which are connected by pipelines to form a closed-loop hydraulic circulation system. The engine assembly (1) drives the left variable pump (21) and the right variable pump (31) to work respectively; The pilot hydraulic control system (4) includes a pilot oil pump (41), a left control handle (42), a right control handle (43), a left variable control push rod (44), and a right variable control push rod (45); the engine assembly (1) drives the pilot oil pump (41) to work; the pilot oil pump (41) supplies oil to the left variable control push rod (44) through the left control handle (42), while the right control handle (43) supplies oil to the right variable control push rod (45); the left variable control push rod (44) drives the displacement of the left variable pump (21) and the flow direction of the hydraulic oil, and the right variable control push rod (45) drives the displacement of the right variable pump (31) and the flow direction of the hydraulic oil; characterized in that: The oil circuit between the left control handle (42) and the left variable control push rod (44) and the oil circuit between the right control handle (43) and the right variable control push rod (45) are provided with a power limiting valve (5) connected to the oil tank. The engine assembly (1) includes a speed sensor (11) that is signal-connected to the engine controller (6); the engine controller (6) is control-connected to the power limiting valve (5).

2. The speed-sensitive power control skid steer loader hydraulic system according to claim 1, characterized in that: The power limiting valve (5) includes an electro-proportional relief valve (51). The inlet and outlet oil paths of the left variable control push rod (44) and the right variable control push rod (45) are connected in parallel through a check valve (52) and then connected to the oil inlet of the electro-proportional relief valve (51). The oil outlet of the electro-proportional relief valve (51) is connected to the oil tank. The check valve (52) unidirectionally guides to the oil inlet side of the electro-proportional relief valve (51). The control terminal of the electro-proportional relief valve (51) is connected to the whole machine controller (6) via a signal.

3. The speed-sensitive power control hydraulic system for skid steer loaders according to claim 1, characterized in that: The left control handle (42) and the right control handle (43) have the same structure; self-resetting switch valves (431) are respectively set in the front, back, left and right directions. In the initial state, they are all connected to the oil tank. Pushing the control handle opens one or two adjacent self-resetting switch valves (431) at the same time; the self-resetting switch valves (431) located in the front and back directions are located in the pilot hydraulic control oil circuit of the walking hydraulic system; the oil ports of the self-resetting switch valves (431) located in the left and right directions are connected to the main control valve (7) of the working hydraulic system.

4. The speed-sensitive power control hydraulic system for skid steer loaders according to claim 1, characterized in that: The pilot hydraulic control system (4) has a pilot relief valve (46) installed on the oil line between the pilot oil pump (41) and the control handle.

5. The speed-sensitive power control hydraulic system for skid steer loaders according to claim 1 or 4, characterized in that: The pilot oil pump (41) is connected in one direction to the left travel hydraulic system (2) and the right travel hydraulic system (3) through a one-way relief valve (47).

6. The speed-sensitive power control hydraulic system for skid steer loaders according to claim 5, characterized in that: There are four one-way relief valves (47), and their inlets are all connected to the outlet of the pilot oil pump (41). The outlets of the one-way relief valves (47) are connected to the oil circuits on both sides of the inlet and outlet of the variable pump.

7. A control method for a skid steer loader hydraulic system with speed-sensitive power control, characterized in that: Step 1: Collect engine speed. The speed sensor (11) collects the current speed of the engine assembly (1) and transmits the speed signal to the engine controller (6). Step 2: Calculate the engine output power. The engine controller (6) calculates the maximum power value that the engine assembly (1) can output based on the engine power curve and the current speed of the engine assembly (1) collected by the speed sensor (11). Step 3: Obtain the power of the working hydraulic system. The whole machine controller (6) calculates and obtains the power value of the working hydraulic system based on the pressure value and flow value of the working hydraulic system. Step 4: Calculate the available power of the walking hydraulic system. The whole machine controller (6) subtracts the working hydraulic system power value obtained in step 3 from the maximum power value calculated in step 2 to obtain the available power value of the walking hydraulic system. Step 5: Obtain the flow threshold of the walking hydraulic system, collect the current pressure value of the walking hydraulic system, and combine it with the available power value of the walking hydraulic system obtained in Step 4 to obtain the current maximum flow threshold. Step 6: Set the power limit of the walking hydraulic system. Based on the current maximum flow threshold of the walking hydraulic system obtained in Step 5, the whole machine controller (6) sets the opening threshold of the power limiting valve (5). When the current power of the walking hydraulic system does not exceed the available power of the walking hydraulic system, the power limiting valve (5) does not work. When the current power of the walking hydraulic system reaches the upper limit of the available power of the walking hydraulic system, the power limiting valve (5) opens. Based on the current pressure value of the walking hydraulic system, the power limiting valve (5) controls the output flow of the variable pump.

8. The control method for the speed-sensitive power control hydraulic system of a skid steer loader according to claim 7, characterized in that: When the engine speed of the engine assembly (1) suddenly drops, the power limiting valve (5) immediately opens, reducing the output flow of the variable pump.

9. The control method for the speed-sensitive power control hydraulic system of a skid steer loader according to claim 8, characterized in that, The method for controlling the output flow of the variable pump using the power limiting valve (5) in step six is ​​as follows: The whole machine controller (6) controls the opening of the electro-proportional relief valve (51). The oil output by the pilot oil pump (41) of the pilot hydraulic control system (4) is split after passing through the left control handle (42) and / or the right control handle (43). Part of it returns to the oil tank through the electro-proportional relief valve (51), and the other part controls the extension and retraction of the left variable control push rod (44) and / or the right variable control push rod (45). The left variable control push rod (44) drives the displacement of the left variable pump (21), and the right variable control push rod (45) drives the displacement of the right variable pump (31).

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