Open type variable pump hydraulic system for large-dip-angle square bale picking and stacking machine

Abstract

The utility model relates to an open type variable pump hydraulic system for a large-dip-angle square bale picking and stacking machine, which comprises a main hydraulic system and an auxiliary hydraulic system, and the main hydraulic system controls square bale picking and stacking actions of the square bale picking and stacking machine. The auxiliary hydraulic system controls a pickup device mechanism of the square bale pickup stacker crane to ascend, descend and stretch out and draw back, the main hydraulic system comprises a plunger pump, an electric proportional multi-way valve and a plurality of actuators, the plunger pump has the pressure cutting-off and load sensing functions, the electric proportional multi-way valve is provided with an LS valve front pressure compensator, and the actuators are connected with the plunger pump. The electric proportional multi-way valve has the advantages that fixed difference adjustment of the plunger pump and stepless control of the electric proportional multi-way valve are achieved, efficiency of a hydraulic system is improved, heating is reduced, no other tedious valve sets exist, unnecessary pipeline connection is reduced, the whole system is high in integration, installation space is saved, and the weight of the whole system is reduced.

Description

Technical Field

[0001] This utility model relates to the technical field of hydraulic systems for palletizers, and in particular to an open variable pump hydraulic system for a large-angle square bale picking and palletizing machine. Background Technology

[0002] Currently, most of the hydraulic control systems used in commercially available bale palletizers employ a hydraulic system consisting of a fixed-displacement pump and a plate-type stacked valve. In this system, the fixed-displacement pump controls the speed and direction of each actuator through the stacked valve group. During operation, the gear pump continuously overflows at high pressure through the relief valve to adapt to the flow changes of the actuators, resulting in significant overflow losses. The actuators control their speed through the stacked throttle valve, which also causes significant throttling losses. These two phenomena result in the system's output power being far lower than its input power, leading to low palletizer efficiency, high workload, and poor palletizing quality.

[0003] Meanwhile, the power loss of the system will be converted into heat energy, causing the temperature of the oil and hydraulic components to rise. The square bale picker is a mobile machine. In order to reduce the weight of the hydraulic oil tank, the agricultural machinery system will not be equipped with a radiator. The square bale picker does not have a heat dissipation function. The rapid rise in hydraulic oil temperature will cause the hydraulic oil to deteriorate, accelerate the aging of hydraulic components, reduce the service life of the equipment, increase the maintenance frequency, and cause waste and increased costs when frequently changing hydraulic oil. The replacement and maintenance will also cause hydraulic oil to leak and pollute the environment.

[0004] Traditional square bale palletizers suffer from unstable flow rates in their hydraulic systems. The actuator speed in the metering pump system is affected by engine speed and load; the actuator speed increases with a smaller load and decreases or even stops with a larger load. Furthermore, the stacked valve assemblies are all controlled by solenoid directional valves, making it impossible to precisely control the actuator speed as designed. This results in poor performance of the pickup machine and makes it impossible to match the operating conditions to specific customer needs. Utility Model Content

[0005] To overcome the shortcomings of existing technologies, this utility model provides an open variable pump hydraulic system for a large-angle square bale picking and palletizing machine. The hydraulic system includes a main hydraulic system and an auxiliary hydraulic system. The main hydraulic system controls several actuators through a variable pump with load sensitivity and pressure cut-off function and an electro-proportional multi-way valve with pressure compensation before the plate-type LS valve. The actuators control the square bale picking and palletizing actions of the square bale picking and palletizing machine. The auxiliary hydraulic system controls the lifting and telescopic actions of the square bale picking and palletizing machine, realizing the constant differential adjustment of the plunger pump and the stepless control of the electro-proportional multi-way valve, improving the efficiency of the hydraulic system, reducing heat generation, eliminating other cumbersome valve groups, reducing unnecessary pipeline connections, and the whole system has high integration, saves installation space, and reduces the weight of the whole machine.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An open variable pump hydraulic system for a large-angle square bale picking and stacking machine includes a main hydraulic system and an auxiliary hydraulic system. The main hydraulic system controls the square bale picking and stacking actions of the square bale picking and stacking machine, and the auxiliary hydraulic system controls the lifting and extending actions of the picking mechanism of the square bale picking and stacking machine.

[0008] The main hydraulic system includes a piston pump, an electro-proportional multi-way valve, and several actuators. These actuators include a lifting and conveying motor, a front push plate cylinder, a platform cylinder, a loading platform cylinder, a guardrail cylinder, a rear push rod cylinder, and a forklift cylinder. The piston pump has pressure cut-off and load-sensing functions and is connected to the electro-proportional multi-way valve via a hydraulic circuit. The electro-proportional multi-way valve is equipped with an LS valve pre-pressure compensator. The electro-proportional multi-way valve has seven hydraulic circuits that connect to and control the lifting and conveying motor, the front push plate cylinder, the platform cylinder, the loading platform cylinder, the guardrail cylinder, the rear push rod cylinder, and the forklift cylinder, respectively. A hydraulically controlled check valve is installed on the hydraulic circuit between the electro-proportional multi-way valve and the rear push rod cylinder, and on the hydraulic circuit between the electro-proportional multi-way valve and the forklift cylinder. Electrically controlled shut-off valves are installed on the inlet and return pipes of the hydraulic circuit between the electro-proportional multi-way valve and the platform cylinder.

[0009] Furthermore, the auxiliary hydraulic system includes a lifting cylinder and a guard plate cylinder. The lifting cylinder controls the lifting and lowering of the picker mechanism of the bale picker, and the guard plate cylinder controls the extension and retraction of the picker mechanism of the bale picker and palletizer.

[0010] Furthermore, the open-type variable pump hydraulic system controls the large-angle square bale picking and stacking machine. The square bale picking and stacking machine includes a picker mechanism, a chain drive mechanism, a front push plate mechanism, a platform mechanism, a rear push rod mechanism, a collection platform mechanism, a guardrail mechanism, and a bale pressing fork mechanism. The picker mechanism is connected to the chain drive mechanism, which is connected to a lifting and conveying motor. The front push plate mechanism is connected to a front push plate cylinder. The platform structure is connected to a platform cylinder. The rear push rod mechanism is connected to a rear push rod cylinder. The collection platform mechanism is connected to a collection platform cylinder. The guardrail mechanism is connected to a guardrail cylinder. The bale pressing fork mechanism is connected to a bale pressing fork cylinder.

[0011] Furthermore, the plunger pump is a swashplate variable displacement plunger pump with pressure cut-off and load-sensing functions; a pressure difference of 22 bar is maintained between the outlet oil pressure of the plunger pump and the maximum load actuator oil pressure.

[0012] Furthermore, the electro-proportional multi-way valve is a seven-way parallel reversing valve with seven reversing links. Each reversing link is equipped with a proportional electromagnet on both sides. The proportional electromagnet controls the displacement of the reversing valve core in each reversing link by the magnitude of the input current, thereby controlling the hydraulic flow through the reversing valve core in each reversing link. An LS valve pre-pressure compensator is installed before the position of each reversing valve core. The outlet of the electro-proportional multi-way valve is connected to the hydraulic circuit of each of the seven actuators. A 9-bar differential pressure compensation is set between each reversing link through the LS valve pre-pressure compensator.

[0013] Furthermore, the lifting and conveying motors include two lifting motors and one horizontal conveying motor. The two lifting motors and the horizontal conveying motor are connected in series to an electro-proportional multi-way valve. Each motor has its own solenoid valve group with bypass shut-off function.

[0014] Furthermore, there are two forklift cylinders, which are connected in parallel and then connected to an electro-proportional multi-way valve.

[0015] Furthermore, the aforementioned loading platform has two hydraulic cylinders, which are connected in parallel and then connected to an electro-proportional multi-way valve.

[0016] Furthermore, the hydraulically controlled check valve and the electrically controlled shut-off valve are integrated into the electro-proportional multi-way valve.

[0017] Compared with the prior art, the beneficial effects of this utility model are:

[0018] 1) A variable displacement piston pump with load sensitivity and pressure cut-off function feeds back pressure and flow change signals to the piston pump to realize the control function; a pump displacement differential regulating valve is set to maintain a pressure difference of 22 bar between the oil pressure at the pump outlet and the oil pressure of the maximum load actuator to regulate the pump displacement. It has the characteristics of low standby pressure and fast response, which improves the working efficiency of the hydraulic system, the working efficiency of the square bale picking and palletizing machine, and the working effect of the square bale picking and palletizing machine.

[0019] 2) The LS valve is a pressure-compensated electro-proportional multi-way valve. The pressure-compensated flow control is unaffected by changes in load pressure and hydraulic pump flow. It is automatically controlled by a set 9-bar differential pressure value, achieving stepless control. It provides the exact amount of flow required by the bale picker and palletizer, ensuring accurate flow control, reducing power loss caused by overflow, improving the working efficiency of the bale picker and palletizer, and reducing system heat generation. This prevents the hydraulic oil temperature from rising rapidly, which can cause hydraulic oil deterioration and accelerated aging of hydraulic components, thus extending the lifespan of the bale picker and palletizer.

[0020] 3) The electro-proportional multi-way valve outlet has no other complicated valve groups between each actuator, reducing unnecessary pipeline connections; the hydraulic system has high integration, saves installation space, reduces the weight of the whole machine, has a simple structure, and the square bale picking and palletizing machine works accurately, with good picking and palletizing effect and high efficiency.

[0021] 4) The auxiliary hydraulic system controls the pickup mechanism of the bale picker to descend during operation and retract after operation. The operation is simple and has no performance requirements. The auxiliary hydraulic system is separated from the main system and connected to the hydraulic valve block on the tractor, which makes the layout of the main hydraulic system simpler and reduces costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the main hydraulic system described in this utility model.

[0023] Figure 2 This is a schematic diagram of the auxiliary hydraulic system described in this utility model.

[0024] Figure 3 This is a schematic diagram of the external structure of the square bale picking machine described in this utility model.

[0025] Figure 4 This is a schematic diagram of the electro-proportional multi-way valve structure described in this utility model.

[0026] Figure 5 This is a schematic diagram of the hydraulic system of the traditional square bale picker described in this utility model.

[0027] In the diagram: 1. Pickup mechanism; 2. Chain drive mechanism; 3. Hydraulic oil tank; 4. Front push plate mechanism; 5. Platform mechanism; 6. Rear push rod mechanism; 7. Loading platform mechanism; 8. Guardrail mechanism; 9. Hay-pressing fork mechanism; 10. Gear pump; 11. Stacking valve assembly; 12. Piston pump; 13. Electro-proportional multi-way valve; 14. Lifting and conveying motor; 15. Front push plate cylinder; 16. Hydraulic control check valve I; 17. Rear push rod cylinder; 18. Hydraulic control... 19. Check Valve II; 20. Hay-pressing Fork Cylinder; 21. Electrically Controlled Shut-off Valve; 22. Platform Cylinder; 23. Loading Platform Cylinder; 24. Guardrail Cylinder; 25. One-way Throttle Valve; 26. Relief Valve; 27. Sequence Valve; 28. Throttle Valve; 29. ​​Pickup Mechanism Telescopic Cylinder; 30. Pickup Mechanism Lifting Cylinder; 31. Horizontal Conveyor Motor; 32. Lifting Motor; 33. Emergency Handle; 34. Proportional Electromagnet; 35. LS Relief Valve. Detailed Implementation

[0028] The specific embodiments of this utility model will be further described below with reference to the accompanying drawings:

[0029] like Figures 1-5As shown, unlike the hydraulic system of a traditional square bale picker that uses a gear pump 10 and a plate-type stacked valve group 11, an open variable pump hydraulic system for a large-angle square bale picker and palletizer includes a main hydraulic system and an auxiliary hydraulic system. The main hydraulic system controls the square bale picking and palletizing work of the square bale picker and palletizer, while the auxiliary hydraulic system controls the lifting and retraction of the picker mechanism 1 of the square bale picker and palletizer.

[0030] like Figure 1 As shown, the main hydraulic system includes a piston pump 12, an electro-proportional multi-way valve 13, and several actuators. The actuators include a lifting and conveying motor 14, a front push plate cylinder 15, a platform cylinder 21, a loading platform cylinder 22, a guardrail cylinder 23, a rear push rod cylinder 17, and a grass-pressing fork cylinder 19. The piston pump 12 is connected to the electro-proportional multi-way valve 13 through pipelines. The electro-proportional multi-way valve 13 is divided into seven branches that are connected to the actuators respectively.

[0031] The plunger pump 12 is a variable pump with load sensitivity and pressure cut-off function. It feeds back pressure and flow change signals to the plunger pump 12 to realize the control function. A displacement differential regulating valve is set in the plunger pump 12 to maintain a pressure difference of 22 bar between the oil pressure at the outlet of the plunger pump 12 and the oil pressure of the maximum load actuator, thereby regulating the displacement of the plunger pump 12. It has the characteristics of low standby pressure and fast response. When the bale picker is not in operation, the plunger pump 12 is in a low-pressure, low-flow state (maintaining only the leakage flow of the hydraulic system); when the actuators such as the motor and cylinder move to the end of their stroke, the automatic variable pump maintains a high-pressure, low-flow state (maintaining only the leakage flow of the hydraulic system); improving the efficiency of the hydraulic system and reducing heat generation.

[0032] like Figure 4As shown, the electro-proportional multi-way valve 13 includes seven parallel reversing couplers with proportional solenoids 33, an LS valve pre-pressure compensator, an LS relief valve 34, and an emergency handle 32. Each reversing coupler of the electro-proportional multi-way valve is equipped with a proportional solenoid 33 on both sides, and each reversing coupler is equipped with a reversing valve core. Each channel of the electro-proportional multi-way valve is equipped with an emergency handle 32, which can manually control each hydraulic circuit individually. The proportional electromagnet 33 controls the displacement of each directional valve core by the magnitude of the input current, thereby controlling the flow rate through each directional valve core. An LS pre-valve pressure compensator is installed before each directional valve core position. Pressurized oil passes through the LS pre-valve pressure compensator before passing through the directional valve core. The LS pre-valve pressure compensator is set with a 9-bar pressure difference for pressure compensation, ensuring that the flow rate through the directional valve core is unaffected by load disturbances. The flow rate through each directional valve core is only affected by the 9-bar pressure difference set by the LS pre-valve pressure compensator and the magnitude of the input current of the proportional electromagnet, controlling the displacement of each directional valve core. It is unaffected by changes in load pressure or the flow rate of the plunger pump 12, and the output flow rate is linearly related to the valve core position. Flow control is automatically controlled by the set 9-bar pressure difference value, providing stepless control. The flow rate output by the plunger pump 12 is independent of load changes and engine speed. The electro-proportional multi-way valve 13 provides the required flow rate for each actuator of the bale picker and palletizer, improving the efficiency of the picker and palletizer and reducing heat generation.

[0033] like Figure 1As shown, the electro-proportional multi-way valve 13 is divided into seven hydraulic circuits that are respectively connected to control the lifting and conveying motor 14, the front push plate cylinder 15, the platform cylinder 21, the loading platform cylinder 22, the upright guardrail cylinder 23, the rear push rod cylinder 17, and the grass-pressing fork cylinder 19. A hydraulically controlled check valve I16 is installed on the hydraulic circuit between the electro-proportional multi-way valve 13 and the rear push rod cylinder 17, and a hydraulically controlled check valve II18 is installed on the hydraulic circuit between the electro-proportional multi-way valve 13 and the grass-pressing fork cylinder 19. Because the rear push rod cylinder... The rear push rod mechanism 6 and the pressing fork mechanism 9, connected to the pressing fork cylinder 19 and 17, are used to organize and stack square hay bales. Their positions cannot be changed by external forces; therefore, a hydraulically controlled check valve is used for pressure maintenance and locking to prevent the actuator from changing position due to its own weight or external forces. The selected hydraulically controlled check valve can be superimposed with the electro-proportional multi-way valve 13, resulting in a more compact structure and more accurate control, neatly stacking the square hay bales. The inlet and outlet pipes of the hydraulic circuit between the electro-proportional multi-way valve 13 and the platform cylinder 21 are... An electrically controlled shut-off valve 20 is installed on each oil pipe. The platform cylinder 21 is connected to the platform mechanism 5. The platform mechanism 5 flips to flip the bales of straw onto the loading platform mechanism 7. The platform cylinder 21 needs to have a position holding function during operation. An electrically controlled shut-off valve 20 is installed on the hydraulic circuit of the platform cylinder 21. The electrically controlled shut-off valve 20 is superimposed with the electro-proportional multi-way valve 13. When the electromagnet is energized, the platform cylinder 21 operates normally. When the electromagnet is de-energized, the platform cylinder 21 remains in the current position regardless of the system's operation, which facilitates maintenance and ensures safety. In this system, a piston pump 12 with a load-sensitive variable and the electro-proportional multi-way valve 13 form a load-sensitive system. By sensing and detecting load pressure, flow, and power change signals, the system provides feedback to the hydraulic system, achieving energy-saving control, flow and speed control, simultaneous action, and matching of prime mover power. There are no other complicated valve groups between the outlet of the electro-proportional multi-way valve 13 and each actuator, reducing unnecessary pipeline connections. The hydraulic system has high integration, saves installation space, and reduces the weight of the entire machine.

[0034] Instead of installing relief valves on the hydraulic circuits of the front push plate cylinder 15, the rear push rod cylinder 17, and the grass pressing fork cylinder 19, an LS relief valve 34 is installed in the return oil circuit of the pressure compensator before the LS valve of the corresponding reversing coupling of the electro-proportional multi-way valve 13 to limit pressure, reduce the power loss caused by overflow, and reduce the heat generation of the system.

[0035] like Figure 2As shown, the auxiliary hydraulic system includes a lifting cylinder 28 and a guard plate cylinder 29. The lifting cylinder 28 and the guard plate cylinder 29 are supplied with oil through two hydraulic circuits. One hydraulic circuit enters the auxiliary hydraulic system through port A. The hydraulic circuit at port A is divided into three oil lines. The first oil line is directly connected to the rod chamber of the lifting cylinder 28. The second oil line returns oil from another line through the relief valve 25 and the one-way throttle valve 24. The third oil line is connected to the throttle valve 27 and the rod chamber of the guard plate cylinder 29 through the one-way sequence valve 26. The other hydraulic circuit enters the auxiliary hydraulic system through port B. The hydraulic circuit at port B is also divided into three oil lines after passing through the one-way throttle valve 24. The first oil line is connected to the drain port of the relief valve 25. The second oil line is directly connected to the rodless chamber of the guard plate cylinder 29. The third oil line is connected to the rodless chamber of the lifting cylinder 28 through the one-way throttle valve 24. The auxiliary hydraulic system is mainly responsible for the lowering and retraction of the pickup mechanism of the bale picker after work. The lifting cylinder 28 of the auxiliary hydraulic system controls the lifting and lowering of the pickup mechanism, and the guard plate cylinder 29 controls the extension and retraction of the pickup mechanism. The operation is simple and has no performance requirements. The auxiliary hydraulic system is separated from the main hydraulic system and connected to the hydraulic valve block on the tractor, which makes the layout of the main hydraulic system simpler and reduces costs.

[0036] like Figure 3 As shown, further, the open variable pump hydraulic system controlling the large-angle square bale picking and stacking machine includes a picker mechanism 1, a chain drive mechanism 2, a hydraulic oil tank 3, a front push plate mechanism 4, a platform mechanism 5, a rear push rod mechanism 6, a loading platform mechanism 7, a guardrail mechanism 8, and a bale pressing fork mechanism 9. The picker mechanism is connected to the chain drive mechanism 2, which is connected to the lifting and conveying motor 14. The front push plate mechanism 4 is connected to the front push plate cylinder 15. The platform mechanism 5 is connected to the platform cylinder 21. The rear push rod mechanism 6 is connected to the rear push rod cylinder 17. The loading platform mechanism 7 is connected to the loading platform cylinder 22. The guardrail mechanism 8 is connected to the guardrail cylinder 23. The bale pressing fork mechanism 9 is connected to the bale pressing fork cylinder 19.

[0037] like Figure 1 As shown, the lifting and conveying motor 14 further includes two lifting motors 31 and a horizontal conveying motor 30. The lifting motors 31 and the horizontal conveying motor 30 are connected in series to an electro-proportional multi-way valve 13. Each motor has a separate solenoid valve group with bypass cut-off function. The action of each motor is controlled by the gain or loss of power of the solenoid valve.

[0038] like Figure 1As shown, there are two tumbler cylinders 19. The two tumbler cylinders 19 are connected in parallel to the electro-proportional multi-way valve 13. The tumbler cylinders 19 are located on both sides of the tumbler mechanism 9. The two tumbler cylinders 19 supply oil at the same time, which drives the tumbler mechanism 9 to move smoothly.

[0039] like Figure 1 As shown, there are two loading platform cylinders 22. The two loading platform cylinders 22 are connected in parallel to the electro-proportional multi-way valve 13. The loading platform cylinders 22 are arranged on both sides of the loading platform mechanism 7. The two loading platform cylinders 22 act simultaneously to support the loading platform mechanism 7 from both sides and smoothly and stably increase the tilting angle.

[0040] like Figure 4 As shown, the hydraulically controlled check valve I16, the hydraulically controlled check valve II18, and the electrically controlled shut-off valve 20 are further integrated on the electro-proportional multi-way valve 13.

[0041] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. An open center variable displacement pump hydraulic system for a large angle square bale pickup accumulator, comprising a main hydraulic system and an auxiliary hydraulic system, characterized in that, The main hydraulic system controls the square bale pickup and stacking action of the square bale pickup and stacking machine, and the auxiliary hydraulic system controls the lifting and stretching action of the pickup mechanism of the square bale pickup and stacking machine. The main hydraulic system comprises a plunger pump, an electric proportional multi-way valve and a plurality of actuators, the plurality of actuators comprises a lifting and conveying motor, a front push plate oil cylinder, a platform oil cylinder, a load collecting platform oil cylinder, a vertical fence oil cylinder, a rear push rod oil cylinder and a grass presser oil cylinder, the plunger pump is provided with a pressure cut-off and load sensitive function, the plunger pump is connected with the electric proportional multi-way valve through a hydraulic circuit, the electric proportional multi-way valve is provided with an LS valve front pressure compensator, the electric proportional multi-way valve is connected with the lifting and conveying motor, the front push plate oil cylinder, the platform oil cylinder, the load collecting platform oil cylinder, the vertical fence oil cylinder, the rear push rod oil cylinder and the grass presser oil cylinder through seven hydraulic circuits respectively, a hydraulic control check valve is arranged on the hydraulic circuit between the electric proportional multi-way valve and the rear push rod oil cylinder, a hydraulic control check valve is arranged on the hydraulic circuit between the electric proportional multi-way valve and the grass presser oil cylinder, and an electric control cut-off valve is arranged on the oil inlet pipe and the oil return pipe of the hydraulic circuit between the electric proportional multi-way valve and the platform oil cylinder.

2. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1, characterized in that, The auxiliary hydraulic system comprises a lifting oil cylinder and a guard plate oil cylinder, the lifting oil cylinder controls the lifting of the pickup mechanism of the square bale pickup machine, and the guard plate oil cylinder controls the stretching of the pickup mechanism of the square bale pickup and stacking machine.

3. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1, wherein, The open variable pump hydraulic system of the large-inclination square bale pickup and stacking machine controls the large-inclination square bale pickup and stacking machine, the square bale pickup and stacking machine comprises a pickup mechanism, a chain transmission mechanism, a front push plate mechanism, a platform mechanism, a rear push rod mechanism, a load collecting platform mechanism, a vertical fence mechanism and a grass presser mechanism, the pickup mechanism is connected with the chain transmission mechanism, the chain transmission mechanism is connected with the lifting and conveying motor, the front push plate mechanism is connected with the front push plate oil cylinder, the platform mechanism is connected with the platform oil cylinder, the rear push rod mechanism is connected with the rear push rod oil cylinder, the load collecting platform mechanism is connected with the load collecting platform oil cylinder, the vertical fence mechanism is connected with the vertical fence oil cylinder, and the grass presser mechanism is connected with the grass presser oil cylinder.

4. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1, wherein, The plunger pump is a swash plate variable plunger pump, and is provided with a pressure cut-off and load sensitive function; a pressure difference of 22 bar is kept between the oil pressure of the oil outlet of the plunger pump and the maximum load actuator oil pressure.

5. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1 wherein, The electric proportional multi-way valve is seven parallel seven-way reversing links, proportional electromagnets are arranged on both sides of each reversing link, the displacement of the reversing spool arranged in each reversing link is controlled by the size of the input current of the proportional electromagnet, so as to control the hydraulic flow through the reversing spool in each reversing link, an LS valve front pressure compensator is arranged in front of the position of each reversing spool, the outlet of the electric proportional multi-way valve is connected with the hydraulic circuits of seven actuators respectively, and a pressure difference pressure compensation of 9 bar is kept between each reversing link through the LS valve front pressure compensator.

6. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1 wherein, The lifting and conveying motor comprises two lifting motors and a horizontal conveying motor, the two lifting motors and the horizontal conveying motor are connected with the electric proportional multi-way valve in series, and each motor is separately provided with an electromagnetic valve group with bypass cut-off function.

7. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1 wherein, The grass presser oil cylinder has two, and the two grass presser oil cylinders are connected with the electric proportional multi-way valve in parallel.

8. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1 wherein, The two load collecting platform oil cylinders are connected with an electric proportional multi-way valve in parallel.

9. An open center variable displacement pump hydraulic system for a large angle square bale pickup and stacking machine according to claim 1 wherein, The hydraulic control one-way valve and the electric control stop valve are integrated on the electric proportional multi-way valve.

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