Forklift electric proportional control hydraulic system

Abstract

The application discloses a forklift electric proportional control hydraulic system, which comprises an oil tank, an oil pump, an electric proportional multi-way valve, a lifting oil cylinder, an inclination oil cylinder, an accessory oil cylinder, a hydraulic steering gear and a steering oil cylinder. The electric proportional multi-way valve comprises a priority valve. An oil inlet of the priority valve is connected with the oil pump. One oil outlet of the priority valve is connected with an oil supply oil way of the electric proportional multi-way valve. Another oil outlet of the priority valve is connected with an oil inlet of the hydraulic steering gear. A control signal input of the priority valve is connected with a control signal output of the hydraulic steering gear. When the hydraulic steering gear controls steering action, the priority valve is controlled to act to adjust the opening degree of the two oil outlets of the priority valve. The electric proportional control hydraulic system realizes accurate automatic control in remote control or unmanned driving. The priority valve is arranged to integrate the steering priority function. When steering, the oil supply for other oil cylinders is reduced to provide sufficient pressure oil for steering, thereby ensuring smooth steering and improving the safety and reliability of the system.

Description

Technical Field

[0001] This invention relates to the field of forklift control systems, and in particular to an electro-proportional control hydraulic system for forklifts. Background Technology

[0002] Forklifts are widely used in various technical fields. Their control systems include lifting cylinders, tilting cylinders, and steering cylinders. By hydraulically controlling the extension and retraction of each cylinder, the mast can be raised, lowered, tilted, and steered normally.

[0003] In existing technologies, mechanical valves in control systems achieve multi-way valve switching via mechanical levers. This approach suffers from problems such as high operating force, long idle travel, poor micro-motion performance, and significant impact during the opening and closing of multi-way valves, making remote automated control impossible. Furthermore, during vehicle steering, insufficient hydraulic pressure cannot be provided to the steering gear, resulting in unsmooth steering maneuvers.

[0004] Therefore, providing a forklift electro-proportional control hydraulic system that can be remotely and automatically controlled and prioritizes steering is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide an electro-proportional control hydraulic system for forklifts. The valves in the electro-proportional multi-way valve are proportionally controlled by electrical signals to achieve precise operation of the forklift hydraulic system. It can realize intelligent remote control and, by setting a priority valve, provides sufficient pressure oil for steering to ensure smooth steering.

[0006] To solve the above-mentioned technical problems, the present invention provides an electro-proportional control hydraulic system for forklifts, including an oil tank, an oil pump, an electro-proportional multi-way valve, a lifting cylinder, a tilting cylinder, an attachment cylinder, a hydraulic steering gear, and a steering cylinder. The oil pump is connected to the inlet of the electro-proportional multi-way valve, and the return port of the electro-proportional multi-way valve is connected to the oil tank. Multiple working ports of the electro-proportional multi-way valve are respectively connected to the lifting cylinder, the tilting cylinder, the attachment cylinder, and the hydraulic steering gear. The electro-proportional multi-way valve includes a priority valve. The inlet of the priority valve is connected to the oil pump, one outlet of the priority valve is connected to the oil supply circuit of the electro-proportional multi-way valve, and the other outlet of the priority valve is connected to the inlet of the hydraulic steering gear. The control signal input port of the priority valve is connected to the control signal output port of the hydraulic steering gear. When the hydraulic steering gear controls the steering action, it controls the priority valve to adjust the opening of the two outlets of the priority valve.

[0007] Preferably, a steering safety valve connected to the oil tank is provided in the control oil circuit of the priority valve.

[0008] Preferably, the electro-proportional multi-way valve further includes a lifting proportional solenoid valve and a lowering proportional solenoid valve. The lifting proportional solenoid valve is connected to the oil supply circuit and the rodless chamber of the lifting cylinder, respectively. The lowering proportional solenoid valve is connected to the rodless chamber of the lifting cylinder and the return oil circuit of the electro-proportional multi-way valve, respectively.

[0009] Preferably, a check valve is provided at the outlet of the lifting proportional solenoid valve, and a descent compensator is provided at the outlet of the lowering proportional solenoid valve, with the control port of the descent compensator connected to the inlet of the lowering proportional solenoid valve.

[0010] Preferably, the system further includes an unloading valve core, a lifting shuttle valve, and a main safety valve. The unloading valve core is connected to the oil supply circuit and the oil return circuit, respectively. The first inlet of the lifting shuttle valve is connected to the inlet of the check valve through a damping orifice. The outlet of the lifting shuttle valve is connected to the pilot port of the unloading valve core and the inlet of the main safety valve. The outlet of the main safety valve is connected to the oil return circuit.

[0011] Preferably, it also includes a manual emergency lowering valve, which is connected to the rodless chamber of the lifting cylinder and the return oil passage, respectively.

[0012] Preferably, the electro-proportional multi-way valve further includes a tilting electro-proportional directional valve, a tilting compensator, and a tilting shuttle valve. The inlet of the tilting electro-proportional directional valve is connected to the oil supply circuit through the tilting compensator. The return port of the tilting electro-proportional directional valve is connected to the return oil circuit. The two working ports of the tilting electro-proportional directional valve are respectively connected to the rodless chamber and the rod chamber of the tilting cylinder. The pilot port of the tilting compensator is connected to the tilting shuttle valve and the load signal port of the tilting electro-proportional directional valve. A balance valve is provided at one working port of the tilting electro-proportional directional valve, and the pilot port of the balance valve is connected to the other working port.

[0013] Preferably, the electro-proportional multi-way valve further includes a first attachment electro-proportional directional valve and a second attachment electro-proportional directional valve arranged in parallel; the inlet of the first attachment electro-proportional directional valve is connected to the oil supply circuit through a first compensator, the return port of the first attachment electro-proportional directional valve is connected to the return oil circuit, the two working ports of the first attachment electro-proportional directional valve are respectively connected to the two ends of the first attachment cylinder, and the pilot port of the first compensator is connected to the first shuttle valve and the load signal port of the first attachment electro-proportional directional valve; the inlet of the second attachment electro-proportional directional valve is connected to the oil supply circuit through a second compensator, the return port of the second attachment electro-proportional directional valve is connected to the return oil circuit, the two working ports of the second attachment electro-proportional directional valve are respectively connected to the two ends of the second attachment cylinder, and the pilot port of the second compensator is connected to the second shuttle valve and the load signal port of the second attachment electro-proportional directional valve.

[0014] Preferably, the two working ports of the second accessory electro-proportional directional valve are connected to the return oil circuit through a first overload valve and a second overload valve, respectively.

[0015] Preferably, the electro-proportional multi-way valve is further provided with an auxiliary oil inlet and a pressure test port, the auxiliary oil inlet and the pressure test port being connected to the oil supply circuit.

[0016] This invention provides an electro-proportional control hydraulic system for forklifts, including an oil tank, an oil pump, an electro-proportional multi-way valve, a lifting cylinder, a tilting cylinder, an attachment cylinder, a hydraulic steering gear, and a steering cylinder. The oil pump is connected to the inlet of the electro-proportional multi-way valve, and the return port of the electro-proportional multi-way valve is connected to the oil tank. Multiple working ports of the electro-proportional multi-way valve are respectively connected to the lifting cylinder, the tilting cylinder, the attachment cylinder, and the hydraulic steering gear. The electro-proportional multi-way valve includes a priority valve. The inlet of the priority valve is connected to the oil pump, one outlet of the priority valve is connected to the oil supply circuit of the electro-proportional multi-way valve, and the other outlet of the priority valve is connected to the inlet of the hydraulic steering gear. The control signal input port of the priority valve is connected to the control signal output port of the hydraulic steering gear. When the hydraulic steering gear controls the steering action, it controls the priority valve to adjust the opening of the two outlets of the priority valve.

[0017] By using an electro-proportional multi-way valve to proportionally control each valve with an electrical signal, mechanical control is replaced. This reduces the operating force and improves micro-motion performance, enabling precise automatic control during remote control or unmanned driving. Furthermore, by setting a priority valve, a steering priority function is integrated, reducing the oil supply to other cylinders during steering to provide sufficient pressure oil for steering, ensuring smooth steering and improving system safety and reliability. Attached Figure Description

[0018] Figure 1 A hydraulic schematic diagram of a specific embodiment of the electro-proportional control hydraulic system for forklifts provided by the present invention;

[0019] Figure 2 This is a hydraulic schematic diagram of an electro-proportional multi-way valve in one specific embodiment of the electro-proportional control hydraulic system for forklifts provided by the present invention.

[0020] The components include: oil tank 1, oil suction filter 2, oil pump 3, electro-proportional multi-way valve 4, speed limiter valve 5, lifting cylinder 6, tilting cylinder 7, hydraulic steering gear 8, steering cylinder 9, priority valve 10, steering safety valve 11, descent compensator 12, descent proportional solenoid valve 13, unloading valve core 14, lifting proportional solenoid valve 15, check valve 16, manual emergency descent valve 17, lifting shuttle valve 18, tilting shuttle valve 19, tilt compensator 20, tilt electro-proportional directional valve 21, balance valve 22, first shuttle valve 23, first compensator 24, first attachment electro-proportional directional valve 25, second shuttle valve 26, second compensator 27, second attachment electro-proportional directional valve 28, first overload valve 29, second overload valve 30, and main safety valve 31. Detailed Implementation

[0021] The core of this invention is to provide an electro-proportional control hydraulic system for forklifts. Each valve in the electro-proportional multi-way valve is proportionally controlled by electrical signals to achieve precise operation of the forklift hydraulic system. It can realize intelligent remote control and, by setting a priority valve, provides sufficient pressure oil for steering to ensure smooth steering.

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Please refer to Figure 1 and Figure 2 , Figure 1 A hydraulic schematic diagram of a specific embodiment of the electro-proportional control hydraulic system for forklifts provided by the present invention; Figure 2 This is a hydraulic schematic diagram of an electro-proportional multi-way valve in one specific embodiment of the electro-proportional control hydraulic system for forklifts provided by the present invention.

[0024] This invention provides an electro-proportional hydraulic control system for forklifts, including an oil tank 1, an oil pump 3, an electro-proportional multi-way valve 4, a lifting cylinder 6, a tilting cylinder 7, an attachment cylinder, a hydraulic steering gear 8, and a steering cylinder 9. The oil pump 3 can be a gear pump or other types of pumps. The oil inlet of the oil pump 3 is connected to the oil tank 1 through an oil suction filter. When the oil pump 3 is working, it outputs the hydraulic oil in the oil tank 1 to the electro-proportional multi-way valve 4. The electro-proportional multi-way valve 4 is equipped with multiple oil ports, including an inlet port P, a return port T, a steering working port CF, a signal transmission port LS, and multiple working oil ports. The output port of the oil pump 3 is connected to the inlet port P of the electro-proportional multi-way valve 4. The return port T of the electro-proportional multi-way valve 4 is connected to the oil tank 1. The internal return oil circuit of the electro-proportional multi-way valve 4 is connected to the return port T, so that the return oil circuit is connected to the oil tank 1. The multiple working oil ports of the electro-proportional multi-way valve 4 are respectively connected to the lifting cylinder 6, the tilting cylinder 7, the attachment cylinder, and the hydraulic steering gear 8. Among them, the lifting cylinder 6 is equipped with a speed limit valve at the inlet and outlet, and the hydraulic steering gear 8 is connected to the steering cylinder 9.

[0025] Furthermore, the electro-proportional multi-way valve 4 includes a priority valve 10, which has an inlet, two outlets, and a control signal input port. The inlet of the priority valve 10 is connected to the inlet P of the electro-proportional multi-way valve 4, and is connected to the oil pump 3 through the inlet P. One outlet of the priority valve 10 is connected to the oil supply circuit of the electro-proportional multi-way valve 4, and the other outlet of the priority valve 10 is connected to the steering working port CF of the electro-proportional multi-way valve 4, and is connected to the inlet of the hydraulic steering gear 8 through the steering working port CF. The control signal input port of the priority valve 10 is connected to the signal transmission port LS of the electro-proportional multi-way valve 4, and is connected to the control signal output port of the hydraulic steering gear 8 through the signal transmission port LS. The outlet of the hydraulic steering gear 8 is connected to the oil tank 1.

[0026] When the system is only performing non-steering operations such as lifting, the outlet of the priority valve 10 connected to the oil supply circuit has its maximum opening. The hydraulic oil output by the oil pump 3 enters the oil supply circuit through the priority valve 10, providing sufficient hydraulic oil to the oil supply circuit of the electro-proportional multi-way valve 4. When the steering wheel is turned, the control signal output port of the hydraulic steering gear 8 transmits the pressure oil signal through the oil pipe to the signal transmission port LS of the electro-proportional multi-way valve 4. The pressure signal is fed back to the control signal input port of the priority valve 10, causing the priority valve 10 to switch directions and adjust the opening of the two outlets of the priority valve 10. The outlet connected to the steering working port CF is increased, and the opening of the other outlet is decreased. The hydraulic oil output by the oil pump 3 passes through the priority valve 10 and reaches the steering working port CF first, entering the hydraulic steering gear 8 to provide sufficient hydraulic oil for the steering action of the entire vehicle, realizing the steering priority function.

[0027] Furthermore, a steering safety valve 11 connected to the oil tank 1 is provided on the control oil circuit of the priority valve 10. The inlet of the steering safety valve 11 is connected to the control signal input port of the priority valve 10, and the outlet of the steering safety valve 11 is connected to the return oil circuit. When the pressure on the control oil circuit is too high, the pressure is relieved through the steering safety valve 11 to ensure the maximum steering pressure.

[0028] The valves within the electro-proportional multi-way valve 4 are controlled proportionally by electrical signals, replacing mechanical control. This reduces operating force and improves micro-motion performance, enabling precise automatic control during remote control or unmanned driving. Furthermore, by setting a priority valve 10, a steering priority function is integrated, reducing the oil supply to other cylinders during steering to provide sufficient pressure oil for steering, ensuring smooth steering and improving system safety and reliability.

[0029] In the forklift electro-proportional control hydraulic system provided in the specific embodiment of the present invention, in order to realize the lifting and lowering functions of the mast, a lifting working port A is provided on the electro-proportional multi-way valve 4. The electro-proportional multi-way valve 4 also includes a lifting proportional solenoid valve 15 and a lowering proportional solenoid valve 13. The inlet of the lifting proportional solenoid valve 15 is connected to the oil supply line, and the outlet of the lifting proportional solenoid valve 15 is connected to the lifting working port A. The lifting working port A is connected to the rodless chamber of the lifting cylinder 6 through the speed limiter valve 5. The inlet of the lowering proportional solenoid valve 13 is connected to the lifting working port A, and the outlet of the lowering proportional solenoid valve 13 is connected to the return oil line. The opening degree of the lifting proportional solenoid valve 15 and the lowering proportional solenoid valve 13 can be adjusted proportionally by electrical signal to control the lifting and lowering of the lifting cylinder 6.

[0030] Furthermore, to improve the reliability and safety of the lifting operation, a check valve 16 is provided at the outlet of the lifting proportional solenoid valve 15. The inlet of the check valve 16 is connected to the outlet of the lifting proportional solenoid valve 15, and the outlet of the check valve 16 is connected to the lifting working oil port A. The check valve 16 allows hydraulic oil to flow from the lifting proportional solenoid valve 15 to the speed limiting valve 5, and the check valve 16 will not affect the operation of the lowering proportional solenoid valve 13. A lowering compensator 12 is provided at the outlet of the lowering proportional solenoid valve 13. The inlet of the lowering compensator 12 is connected to the outlet of the lowering proportional solenoid valve 13, and the outlet of the lowering compensator 12 is connected to the return oil circuit. The control port of the lowering compensator 12 is connected to the inlet of the lowering proportional solenoid valve 13.

[0031] When the gantry is lifted, the controller outputs an electrical signal proportional to the opening degree of the thumb switch to the lifting proportional solenoid valve 15. The coil b is energized, generating a corresponding electromagnetic force, which drives the valve core of the lifting proportional solenoid valve 15 to open to the corresponding valve core opening. The hydraulic oil supplied by the oil supply circuit passes through the lifting proportional solenoid valve 15 and the check valve 16 to output the corresponding oil flow to the lifting working oil port A, which is then supplied to the gantry lifting cylinder 6, realizing the lifting function that can proportionally control the lifting speed.

[0032] When the gantry descends, the controller outputs an electrical signal proportional to the opening degree of the thumb switch to the descent proportional solenoid valve 13. Coil a is energized, generating a corresponding electromagnetic force that drives the valve core of the descent proportional solenoid valve 13 to open to the corresponding valve core opening. The oil in the lifting cylinder 6 reaches the lifting working port A, flows back to the oil passage through the descent proportional solenoid valve 13 and the descent compensator 12, and finally returns to the oil tank 1. When the descent speed is high, the inlet and outlet pressure of the descent proportional solenoid valve 13 increases, entering the control port of the descent compensator 12. The descent compensator 12 actuates, reducing its opening and decreasing the descent speed. The combined action of the descent proportional solenoid valve 13 and the descent compensator 12 achieves the function of proportionally controlling the descent speed.

[0033] It also includes an unloading valve core 14, a lifting shuttle valve 18, and a main safety valve 31. The inlet and outlet of the unloading valve core 14 are connected to the oil supply circuit and the oil return circuit, respectively. The first inlet of the lifting shuttle valve 18 is connected to the inlet of the check valve 16 through a damping orifice, which is connected to the outlet of the lifting proportional solenoid valve 15. The outlet of the lifting shuttle valve 18 is connected to one pilot port of the unloading valve core 14 and the inlet of the main safety valve 31. The other pilot port of the unloading valve core 14 is connected to the inlet of the lifting proportional solenoid valve 15. The second inlet of the lifting shuttle valve 18 is connected to the control oil circuit of the subsequent valves. The outlet of the main safety valve 31 is connected to the oil return circuit. During lifting operation, the unloading valve core 14 can detect the pressure difference between the inlet and outlet of the lifting proportional solenoid valve 15 and adjust the opening of the unloading valve core 14 according to the change of pressure difference to achieve unloading adjustment. Furthermore, when the pressure at the outlet of the lifting proportional solenoid valve 15 is too high, the hydraulic oil passes through the lifting shuttle valve 18 to the main safety valve 31 and flows back to the oil return circuit.

[0034] To enable manual emergency descent, a manual emergency descent valve 17 can be installed. The manual emergency descent valve 17 is connected to the rodless chamber of the lifting cylinder 6 and the return oil passage. Specifically, one end of the manual emergency descent valve 17 is connected to the lifting working oil port A and the return oil passage. When manual emergency descent is required, the manual emergency descent valve 17 is opened manually, and the hydraulic oil in the rodless chamber of the lifting cylinder 6 flows out through the manual emergency descent valve 17 to achieve manual descent.

[0035] In the forklift electro-proportional control hydraulic system provided in the specific embodiment of the present invention, in order to realize the tilting function of the mast, the electro-proportional multi-way valve 4 also includes a tilt electro-proportional directional valve 21, a tilt compensator 20, and a tilt shuttle valve 19. The oil inlet of the tilt electro-proportional directional valve 21 is connected to the oil supply circuit through the tilt compensator 20, and the oil return port of the tilt electro-proportional directional valve 21 is connected to the oil return circuit. The two working ports of the tilt electro-proportional directional valve 21 are respectively connected to the first tilt working port A1 and the second tilt working port B1 of the electro-proportional multi-way valve 4. The first tilt working port A1 and the second tilt working port B1 are respectively connected to the rodless chamber and the rod chamber of the tilt cylinder 7. The pilot port of the tilt compensator 20 is connected to the load signal port of the tilt electro-proportional directional valve 21, and the first inlet of the tilt shuttle valve 19 is connected to the pilot port of the tilt compensator 20. The second inlet of the tilt shuttle valve 19 is connected to the control oil circuit of the subsequent valve, and the outlet of the tilt shuttle valve 19 is connected to the second inlet of the lifting shuttle valve 18. When the load changes, the opening degree of the tilt compensator 20 is controlled to control the hydraulic oil flow. A balance valve 22 is installed at one working port of the tilting electro-proportional directional valve 21, and the pilot port of the balance valve 22 is connected to the other working port.

[0036] When the system performs the gantry tilting function, the controller outputs an electrical signal proportional to the opening degree of the thumb switch to the tilting proportional directional valve 21. The coil a1 is energized, generating a corresponding electromagnetic force, which drives the valve core of the tilting proportional directional valve 21 to open to the corresponding valve core opening. The first tilting working port A1 outputs the corresponding oil flow rate and supplies it to the gantry tilting cylinder 7. At the same time, the pressure signal of the first tilting working port A1 is fed back to the balance valve 22 of the second tilting working port B1, causing the balance valve 22 to open. The oil in the second tilting working port B1 returns to the oil tank 1, realizing the tilting function with proportional control of the lifting speed.

[0037] When the system performs the gantry tilting function, the controller outputs an electrical signal proportional to the opening degree of the thumb switch to the tilting proportional directional valve 21. The coil b1 is energized, generating a corresponding electromagnetic force, which drives the valve core of the tilting proportional directional valve 21 to open to the corresponding valve core opening. The second tilting working oil port B1 outputs the corresponding oil flow rate, which is supplied to the gantry tilting cylinder 7, thereby realizing the tilting function with proportional control of the tilting speed.

[0038] In the forklift electro-proportional control hydraulic system provided in a specific embodiment of the present invention, the electro-proportional multi-way valve 4 further includes a first attachment electro-proportional directional valve 25 and a second attachment electro-proportional directional valve 28 arranged in parallel. The inlet of the first attachment electro-proportional directional valve 25 is connected to the oil supply circuit via the first compensator 24, and the return port of the first attachment electro-proportional directional valve 25 is connected to the return oil circuit. The two working ports of the first attachment electro-proportional directional valve 25 are respectively connected to the first attachment working port A2 and the second attachment working port B2 of the electro-proportional multi-way valve 4. The first attachment working port A2 and the second attachment working port B2 are respectively connected to the two ends of the first attachment cylinder. The pilot port of the first compensator 24 is connected to the load signal port of the first attachment electro-proportional directional valve 25, and the first inlet of the first shuttle valve 23 is connected to the pilot port of the first compensator 24. The second inlet of the first shuttle valve 23 is connected to the control oil circuit of the subsequent valve, and the outlet of the first shuttle valve 23 is connected to the second inlet of the tilting shuttle valve 19. The opening degree of the first compensator 24 is controlled when the load changes, thereby controlling the hydraulic oil flow.

[0039] When the system performs the attachment function, the controller outputs an electrical signal proportional to the opening degree of the thumb switch to the first attachment electro-proportional directional valve 25. The coil a2 or b2 is energized, generating a corresponding electromagnetic force, which drives the valve core of the first attachment electro-proportional directional valve 25 to open to the corresponding valve core opening. The first attachment working port A2 and the second attachment working port B2 output the corresponding oil flow rate, which is supplied to the corresponding attachment cylinder of the mast, realizing the action function of proportionally controlling the attachment speed.

[0040] Similarly, the inlet of the second attachment electro-proportional directional valve 28 is connected to the oil supply circuit through the second compensator 27, and the return port of the second attachment electro-proportional directional valve 28 is connected to the return oil circuit. The two working ports of the second attachment electro-proportional directional valve 28 are respectively connected to the third attachment working port A3 and the fourth attachment working port B3 of the electro-proportional multi-way valve 4. The third attachment working port A3 and the fourth attachment working port B3 are respectively connected to the two ends of the second attachment cylinder. The pilot port of the second compensator 27 is connected to the load signal port of the second attachment electro-proportional directional valve 28, and the first inlet of the second shuttle valve 26 is connected to the pilot port of the second compensator 27. The second inlet of the second shuttle valve 26 is connected to the control oil circuit of the subsequent valve or directly connected to the return oil circuit. The outlet of the second shuttle valve 26 is connected to the second inlet of the first shuttle valve 23. When the load changes, the opening of the second compensator 27 is controlled to control the hydraulic oil flow.

[0041] When the system performs the attachment function, the controller outputs an electrical signal proportional to the opening degree of the thumb switch to the second attachment electro-proportional directional valve 28. The coil a3 or b3 is energized, generating a corresponding electromagnetic force, which drives the valve core of the second attachment electro-proportional directional valve 28 to open to the corresponding valve core opening. The third attachment working oil port A3 and the fourth attachment working oil port B3 output the corresponding oil flow rate, which is supplied to the corresponding attachment cylinder of the gantry, realizing the action function of proportionally controlling the attachment speed.

[0042] Furthermore, the two working ports of the second accessory electro-proportional directional valve 28 are connected to the return oil circuit through the first overload valve 29 and the second overload valve 30, respectively.

[0043] In this specific embodiment, only two attachment cylinders are controlled. However, the number of attachment cylinders can be increased according to actual needs, and corresponding attachment electro-proportional directional valves can be configured. The structure and connection method are similar, and all are within the protection scope of this invention.

[0044] Based on the forklift electro-proportional control hydraulic system provided in the above specific embodiments, the electro-proportional multi-way valve 4 is also equipped with an auxiliary oil inlet P1 and a pressure measuring port M. The auxiliary oil inlet P1 is connected to the oil supply circuit, enabling the system to achieve dual-pump confluence function. The pressure measuring port M is connected to the oil supply circuit, enabling pressure measurement of the working device. The electro-proportional multi-way valve 4 integrates steering priority function, proportional adjustment function corresponding to forklift mast movement, load sensitivity function, pressure compensation function, forward tilt self-locking function, and manual emergency lowering function. The lowering and lifting functions adopt an independent oil circuit design to achieve better micro-motion performance, while also avoiding noise and vibration problems caused by shared oil circuits. The use of load sensitivity technology improves system efficiency, reduces losses, and is more energy-efficient compared to traditional hydraulic systems.

[0045] The forklift electro-proportional control hydraulic system provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A forklift electro-proportional control hydraulic system, comprising an oil tank (1), an oil pump (3), an electro-proportional multi-way valve (4), a lifting cylinder (6), a tilting cylinder (7), an attachment cylinder, a hydraulic steering gear (8), and a steering cylinder (9), wherein the oil pump (3) is connected to the oil inlet of the electro-proportional multi-way valve (4), the oil return port of the electro-proportional multi-way valve (4) is connected to the oil tank (1), and multiple working ports of the electro-proportional multi-way valve (4) are respectively connected to the lifting cylinder (6), the tilting cylinder (7), the attachment cylinder, and the hydraulic steering gear (8), characterized in that, The electro-proportional multi-way valve (4) includes a priority valve (10). The oil inlet of the priority valve (10) is connected to the oil pump (3). One oil outlet of the priority valve (10) is connected to the oil supply circuit of the electro-proportional multi-way valve (4). The other oil outlet of the priority valve (10) is connected to the oil inlet of the hydraulic steering gear (8). The control signal input port of the priority valve (10) is connected to the control signal output port of the hydraulic steering gear (8). When the hydraulic steering gear (8) controls the steering action, it controls the priority valve (10) to adjust the opening of the two oil outlets of the priority valve (10). The control oil circuit of the priority valve (10) is provided with a steering safety valve (11) connected to the oil tank (1). The electro-proportional multi-way valve (4) also includes a lifting proportional solenoid valve (15) and a lowering proportional solenoid valve (13). The lifting proportional solenoid valve (15) is connected to the oil supply circuit and the rodless chamber of the lifting cylinder (6) respectively. The lowering proportional solenoid valve (13) is connected to the rodless chamber of the lifting cylinder (6) and the return oil circuit of the electro-proportional multi-way valve (4) respectively. A one-way valve (16) is provided at the outlet of the lifting proportional solenoid valve (15), and a descent compensator (12) is provided at the outlet of the descent proportional solenoid valve (13). The control port of the descent compensator (12) is connected to the inlet of the descent proportional solenoid valve (13). It also includes an unloading valve core (14), a lifting shuttle valve (18), and a main safety valve (31). The unloading valve core (14) is connected to the oil supply circuit and the oil return circuit respectively. The first inlet of the lifting shuttle valve (18) is connected to the inlet of the check valve (16) through a damping hole. The outlet of the lifting shuttle valve (18) is connected to the pilot port of the unloading valve core (14) and the inlet of the main safety valve (31). The outlet of the main safety valve (31) is connected to the oil return circuit. It also includes a manual emergency lowering valve (17), which is connected to the rodless chamber and the return oil passage of the lifting cylinder (6).

2. The forklift electro-proportional control hydraulic system according to claim 1, characterized in that, The electro-proportional multi-way valve (4) also includes a tilt electro-proportional directional valve (21), a tilt compensator (20), and a tilt shuttle valve (19). The inlet of the tilt electro-proportional directional valve (21) is connected to the oil supply circuit through the tilt compensator (20). The return port of the tilt electro-proportional directional valve (21) is connected to the return oil circuit. The two working ports of the tilt electro-proportional directional valve (21) are respectively connected to the rodless chamber and the rod chamber of the tilt cylinder (7). The pilot port of the tilt compensator (20) is connected to the load signal port of the tilt shuttle valve (19) and the tilt electro-proportional directional valve (21). A balance valve (22) is provided at one working port of the tilt electro-proportional directional valve (21). The pilot port of the balance valve (22) is connected to the other working port.

3. The forklift electro-proportional control hydraulic system according to claim 2, characterized in that, The electro-proportional multi-way valve (4) further includes a first attachment electro-proportional directional valve (25) and a second attachment electro-proportional directional valve (28) arranged in parallel; the oil inlet of the first attachment electro-proportional directional valve (25) is connected to the oil supply circuit through a first compensator (24), the oil return port of the first attachment electro-proportional directional valve (25) is connected to the oil return circuit, the two working ports of the first attachment electro-proportional directional valve (25) are respectively connected to the two ends of the first attachment cylinder, and the pilot port of the first compensator (24) is connected to the first shuttle valve (23). The first attachment electro-proportional directional valve (25) and the load signal port of the first attachment electro-proportional directional valve (28) are connected to the oil supply circuit through the second compensator (27). The return port of the second attachment electro-proportional directional valve (28) is connected to the return oil circuit. The two working ports of the second attachment electro-proportional directional valve (28) are respectively connected to the two ends of the second attachment cylinder. The pilot port of the second compensator (27) is connected to the second shuttle valve (26) and the load signal port of the second attachment electro-proportional directional valve (28).

4. The forklift electro-proportional control hydraulic system according to claim 3, characterized in that, The two working ports of the second accessory electro-proportional directional valve (28) are connected to the return oil circuit through the first overload valve (29) and the second overload valve (30), respectively.

5. The forklift electro-proportional control hydraulic system according to any one of claims 1 to 4, characterized in that, The electro-proportional multi-way valve (4) is also provided with an auxiliary oil inlet and a pressure test port, which are connected to the oil supply circuit.

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