A forklift hydraulic system and control method thereof

Abstract

The present application provides a forklift hydraulic system and control method thereof, comprising a hydraulic oil tank, a hydraulic gear pump, a multi-way valve group, an electromagnetic reversing valve I, a lifting cylinder for driving the lifting of the cargo fork, and a tilting cylinder for tilting the mast. The hydraulic gear pump is used to deliver hydraulic oil from the hydraulic oil tank to the multi-way valve group. The hydraulic system also includes an oil circuit switching control device, which can control the electromagnetic reversing valve II and the electromagnetic reversing valve I to drive the tilting cylinder to adjust the mast to a horizontal state. Simultaneously, when the lifting manipulator is in the lifting gear, the cargo fork can be controlled to rise to a set lifting height and automatically stop rising; when the lifting manipulator is in the lowering gear, the cargo fork can be controlled to descend to a set lowering height and automatically stop descending, effectively improving the operating efficiency and flexibility of the forklift.

Description

Technical Field

[0001] The present application relates to the technical field of engineering machinery, and in particular to a forklift hydraulic system and a control method thereof. Background Art

[0002] As an important piece of logistics equipment, the core function of a forklift is to efficiently carry out the handling and transfer of objects. Specifically, a forklift can accurately move goods from their original starting position to a designated end position. In actual operation, the starting and end points of the goods are often set on relatively fixed and usually horizontal surfaces to facilitate the smooth loading, unloading and storage processes. However, traditional forklift operators usually need to manually set the lifting height of the forks based on their personal experience, and also rely on visual judgment to ensure that the forks remain horizontal. This operating mode that relies on manual judgment and operation not only increases the uncertainty and risk in the operation process, but also makes the forklift's operating efficiency largely dependent on the operator's professional skills and experience level, seriously affecting the operating efficiency. Summary of the Invention

[0003] In order to solve the technical problems existing in the prior art, the first aspect of the present application provides a forklift hydraulic system, comprising a hydraulic oil tank, a hydraulic gear pump, a multi-way valve group, an electromagnetic reversing valve I, a lifting cylinder for driving the fork to lift and lower, and a tilting cylinder for driving the mast to tilt, wherein the hydraulic gear pump is used to deliver hydraulic oil in the hydraulic oil tank to the multi-way valve group;

[0004] The multi-way valve group includes an electromagnetic reversing valve II, a lifting reversing valve, and a tilting reversing valve. The first oil outlet of the electromagnetic reversing valve II is connected to the electromagnetic reversing valve I and the tilting oil cylinder in sequence to form an automatic leveling circuit. The second oil outlet of the electromagnetic reversing valve II is connected to the lifting reversing valve and the tilting reversing valve respectively. The lifting reversing valve is connected to the lifting oil cylinder to form a lifting circuit, and the tilting reversing valve is connected to the tilting oil cylinder to form a tilting circuit.

[0005] The hydraulic system also includes an oil circuit switching control device, which includes a controller, a start switch and a first displacement sensor provided in the tilt cylinder. The start switch and the first displacement sensor are respectively connected to signals from the controller, and the controller is connected to signals from the electromagnetic reversing valve II and the electromagnetic reversing valve I. The controller can control the electromagnetic reversing valve II and the electromagnetic reversing valve I to drive the tilt cylinder to adjust the mast to a horizontal state based on the signals transmitted by the start switch and the first displacement sensor.

[0006] Furthermore, the multi-way valve group also includes a direct-acting overflow valve and an electromagnetic reversing valve III connected between the first oil outlet of the electromagnetic reversing valve II and the hydraulic oil tank. The direct-acting overflow valve and the electromagnetic reversing valve III form an unloading circuit in parallel with the lifting circuit.

[0007] Furthermore, the multi-way valve group also includes a plug-in one-way valve and an electromagnetic reversing valve V arranged in parallel between the lifting reversing valve and the lifting cylinder. The plug-in one-way valve and the electromagnetic reversing valve V constitute an OPS system.

[0008] Furthermore, the multi-way valve group further includes an electromagnetic reversing valve IV, which is connected in series between the lifting reversing valve and the electromagnetic reversing valve V.

[0009] Furthermore, the oil circuit switching control device also includes a lifting manipulator and a second displacement sensor provided in the lifting cylinder. The lifting manipulator and the second displacement sensor are respectively connected to the controller signal, and the controller is connected to the electromagnetic reversing valve IV and the electromagnetic reversing valve III signal; when the lifting manipulator is in the lifting gear, the controller can adjust the lifting cylinder to drive the fork to rise to the set lifting height through the electromagnetic reversing valve III according to the signal transmitted by the starting switch and the second displacement sensor; when the lifting manipulator is in the descending gear, the controller can adjust the lifting cylinder to drive the fork to descend to the set descending height through the electromagnetic reversing valve IV according to the signal transmitted by the starting switch and the second displacement sensor.

[0010] Furthermore, the automatic leveling circuit further includes a throttle speed regulating valve connected between the electromagnetic reversing valve II and the electromagnetic reversing valve I, and a balancing valve connected between the electromagnetic reversing valve I and the tilt cylinder.

[0011] Furthermore, the lifting circuit also includes an explosion-proof valve and a speed limiting valve, and the speed limiting valve is connected between the lifting cylinder and the lifting reversing valve.

[0012] A second aspect of the present application provides a control method for a forklift hydraulic system, the method comprising:

[0013] Select the control mode according to the signal of the start switch;

[0014] If the start switch is turned on, the system enters the automatic adjustment mode: the first position sensor is used to determine whether the tilt cylinder is at the tilt displacement threshold F. If not, the electromagnetic reversing valve II is energized to connect to the automatic leveling circuit, and the electromagnetic reversing valve I is controlled to drive the tilt cylinder to restore the set stroke.

[0015] If the start switch is off, the normal control mode is entered: the lift reversing valve is controlled by the lift manipulator to adjust the stroke of the lift cylinder, and the tilt reversing valve is controlled by the tilt manipulator to adjust the stroke of the tilt cylinder.

[0016] Furthermore, the automatic adjustment mode also includes:

[0017] When the lifting manipulator is in the lifting gear position, the second position sensor determines whether the lifting cylinder is at the first displacement threshold M. If so, the electromagnetic reversing valve III is energized, and the high-pressure oil flows back to the hydraulic oil tank through the unloading circuit, and the lifting cylinder stops moving.

[0018] When the lifting manipulator is in the descending gear, the second position sensor is used to determine whether the lifting cylinder is at the second displacement threshold M. If so, the electromagnetic reversing valve IV is controlled to be energized, thereby switching the lifting circuit and stopping the lifting cylinder from moving.

[0019] Furthermore, the determining whether the tilt cylinder is at the tilt displacement threshold F by the first position sensor, and if not, controlling the electromagnetic reversing valve II to be electrically connected to the automatic leveling circuit, and controlling the electromagnetic reversing valve I to drive the tilt cylinder to restore the set stroke includes:

[0020] When the displacement value F of the tilt cylinder is greater than the tilt displacement threshold value F, the right control end of the control solenoid reversing valve I is energized, and high-pressure oil enters the rod chamber of the tilt cylinder through the balance valve, driving the mast to tilt backward until the displacement value F of the tilt cylinder is equal to the tilt displacement threshold value F, and the control solenoid reversing valve II and the solenoid reversing valve I are both de-energized to keep the mast in a horizontal state;

[0021] When the displacement value F of the tilt cylinder is less than the tilt displacement threshold F, the left control end of the electromagnetic reversing valve I is energized, and the high-pressure oil enters the rodless chamber of the tilt cylinder through the balance valve, driving the mast to tilt forward until the displacement value F of the tilt cylinder is equal to the tilt stroke threshold F, and the electromagnetic reversing valve II and the electromagnetic reversing valve I are both de-energized to keep the mast in a horizontal state.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The forklift hydraulic system provided by the embodiment of the present application, when the start switch is turned on, first determines whether the mast is in a horizontal state, and then automatically adjusts the mast to restore the horizontal state, ensuring that the cargo remains level and stable during the handling process. This not only greatly reduces the workload of the forklift operator and effectively improves the efficiency and flexibility of the forklift; it also improves the safety and accuracy of the operation and reduces the risk of cargo falling.

[0024] 2. The forklift hydraulic system provided in the embodiments of this application can control the forks to rise to a set height and automatically stop when the lift manipulator is in the up position; and can control the forks to descend to a set height and automatically stop when the lift manipulator is in the down position. When the load's starting and ending points are located on relatively fixed surfaces, this technical solution greatly reduces the workload of the forklift operator, effectively improving the forklift's operating efficiency and flexibility, and also enhancing the safety and accuracy of operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a hydraulic principle diagram of the forklift hydraulic system of the present application;

[0026] Figure 2 It is a hydraulic principle diagram of the multi-way valve of the present application;

[0027] Figure 3 It is a structural schematic diagram of the oil circuit switching control device of the present application;

[0028] Description of reference numerals:

[0029] 1. Oil pump motor; 2. Hydraulic gear pump; 3. Filter; 4. Multi-way valve group; 401. Main relief valve; 402. Solenoid reversing valve II; 403. Direct-acting relief valve; 404. Solenoid reversing valve III; 405. Lifting reversing valve; 406. Solenoid reversing valve IV; 407. Solenoid reversing valve V; 408. Insert-type check valve; 409. Unloading screw plug; 410. Tilt reversing valve; 5. Tilt cylinder; 6. Solenoid reversing valve I; 7. Throttle speed control valve; 8. Lifting cylinder; 9. Explosion-proof valve; 10. Speed ​​limiting valve; 11. Hydraulic oil tank; 12. Balance valve; 13. Lifting manipulator; 14. Start switch; 15. Tilt manipulator. DETAILED DESCRIPTION

[0030] To facilitate understanding of this application, the following will clearly and completely describe the technical solutions in the embodiments of this application in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] This application discloses a forklift hydraulic system for automatically adjusting forklift attachments. The hydraulic system includes a hydraulic oil tank 11, a hydraulic gear pump 2, a multi-way valve assembly 4, an electromagnetic reversing valve I6, a lift cylinder 8 for raising and lowering the forks, and a tilt cylinder 5 for tilting the mast. The electromagnetic reversing valve I6 is a dual-control, three-position, four-way electromagnetic reversing valve. The oil pump motor 1 is mechanically connected to the hydraulic gear pump 2 to drive its rotation. The multi-way valve assembly 4 includes an oil inlet P, a priority oil outlet A1, a lift oil port B1, a first tilt oil port A2, and a second tilt oil port B2. One end of the hydraulic gear pump 2 is connected to the hydraulic oil tank 11, and the other end is connected to the oil inlet P of the multi-way valve assembly 4, thereby transferring hydraulic oil from the hydraulic oil tank 11 to the multi-way valve assembly 4.

[0032] The multi-way valve assembly 4 also includes a solenoid reversing valve II 402, a lift reversing valve 405, and a tilt reversing valve 410. In this embodiment, the solenoid reversing valve II 402 is a two-position, three-way solenoid reversing valve. Its oil inlet is connected to the oil inlet P of the multi-way valve assembly 4 via the main oil supply line 001. The first oil outlet of the solenoid reversing valve II 402 is connected to the priority oil outlet A1 of the multi-way valve assembly 4, the solenoid reversing valve I 6, and the tilt cylinder 5 via the leveling oil line 002, forming an automatic leveling circuit. The second oil outlet of the solenoid reversing valve II 402 is connected to the lift reversing valve 405 and the tilt reversing valve 410, respectively. The lift reversing valve 405 is a manual reversing valve. Its first oil outlet is connected to the lift oil port B1 of the multi-way valve assembly 4 and the rodless chamber of the lift cylinder 8 via the lift oil line 005, forming a lift circuit. The tilt reversing valve 410 is a manual reversing valve. The first oil outlet of the tilt reversing valve 410 is connected to the first tilt oil port A2 of the multi-way valve group 4 and the rodless chamber of the tilt cylinder 5 in sequence. The second oil outlet of the tilt reversing valve 410 is connected to the second tilt oil port B2 of the multi-way valve group 4 and the rod chamber of the tilt cylinder 5 in sequence to form a tilt circuit.

[0033] The hydraulic system also includes an oil circuit switching control device, which includes: a lift manipulator 13, a start switch 14, a tilt manipulator 15, a first displacement sensor provided in the tilt cylinder 5, and a second displacement sensor provided in the lift cylinder 8. The lift manipulator 13 is mechanically connected to the lift reversing valve 405, and the tilt manipulator 15 is mechanically connected to the tilt reversing valve 410. The start switch 14 is provided on the lift manipulator 13. The start switch 14 and the first displacement sensor are respectively connected to the controller for signal transmission. The controller is signal-connected to the solenoid reversing valve II 402 and the solenoid reversing valve I 6. Based on the signals transmitted by the start switch 14 and the first displacement sensor, the controller can control the solenoid reversing valve II 402 and the solenoid reversing valve I 6 to drive the tilt cylinder 5 to adjust the mast to a horizontal state.

[0034] The forklift hydraulic system provided in this embodiment, when the start switch 14 is turned on, determines the displacement value F of the tilt cylinder 5 via the first position sensor and controls the electromagnetic reversing valve II 402 to connect to the automatic leveling circuit, thereby controlling the electromagnetic reversing valve I 6 to drive the tilt cylinder 5 to restore the set stroke. This automatically adjusts the mast to a horizontal state, ensuring that cargo remains level and stable during handling. This not only greatly reduces the workload of the forklift operator and effectively improves the forklift's operating efficiency and flexibility, but also enhances the safety and accuracy of operations and reduces the risk of cargo falling.

[0035] In some embodiments, the multi-way valve assembly 4 further includes a direct-acting relief valve 403 and a solenoid reversing valve III 404 connected between the second oil outlet of the solenoid reversing valve II 402 and the hydraulic oil tank 11. The direct-acting relief valve 403 and the solenoid reversing valve III 404 form an unloading circuit connected in parallel with the lifting circuit. When energized, the solenoid reversing valve III 404 connects to the unloading circuit, allowing high-pressure oil to flow from the second oil outlet of the solenoid reversing valve II 402 through the unloading circuit and back to the hydraulic oil tank 11.

[0036] In some embodiments, the multi-way valve assembly 4 further includes a cartridge-type check valve 408 and a solenoid-type reversing valve V 407, disposed between the lift reversing valve 405 and the lift cylinder 8. The solenoid-type reversing valve V 407 is a normally closed solenoid-type reversing valve. The oil inlet of the cartridge-type check valve 408 is connected to the lift reversing valve 405, and the oil outlet of the cartridge-type check valve 408 is connected to the lift cylinder 8. This ensures that high-pressure oil can only flow from the lift reversing valve 405 through the cartridge-type check valve 408 to the lift cylinder 8, but cannot flow from the lift cylinder 8 through the cartridge-type check valve 408 to the lift reversing valve 405. The cartridge-type check valve 408 and the solenoid-type reversing valve V 407 are arranged in parallel to form an OPS system (Operator Presence Sensing System).

[0037] When the operator is not sitting on the seat, the electromagnetic reversing valve V407 is de-energized, thereby cutting off the oil path from the lifting cylinder 8 through the electromagnetic reversing valve V407 to the lifting reversing valve 405. At the same time, the lifting cylinder 8 cannot flow through the plug-in check valve 408 to the lifting reversing valve 405. At this time, even if the lifting manipulator 13 is used to switch the lifting reversing valve 405 to the lowering left position, the forks cannot be lowered.

[0038] In some embodiments, the multi-way valve assembly 4 further includes a solenoid reversing valve IV 406, which is connected in series between the lift reversing valve 405 and the solenoid reversing valve V 407. The solenoid reversing valve IV 406 is a normally open solenoid reversing valve and is connected to the controller signal. When the solenoid reversing valve IV 406 receives power from the controller signal, it shuts off the oil flow from the lift cylinder 8 to the lift reversing valve 405 via the solenoid reversing valve V 407. Simultaneously, the lift cylinder 8 is unable to flow through the cartridge check valve 408 to the lift reversing valve 405. At this point, even if the lift manipulator 13 switches the lift reversing valve 405 to the lowering left position, the forks cannot be lowered.

[0039] In some embodiments, the lift manipulator 13 and the second displacement sensor are each connected to a controller by signal. The controller is then connected to the electromagnetic reversing valve IV 406 and the electromagnetic reversing valve III 404. When the lift manipulator 13 is in the raising position, the controller can, based on the signals transmitted by the starting switch 14 and the second displacement sensor, regulate the lift cylinder 8 via the electromagnetic reversing valve III 404 to raise the forks to a set raising height. When the lift manipulator 13 is in the lowering position, the controller can, based on the signals transmitted by the starting switch 14 and the second displacement sensor, regulate the lift cylinder 8 via the electromagnetic reversing valve IV 406 to lower the forks to a set lowering height.

[0040] The forklift hydraulic system provided in this embodiment can control the forks to rise to a set height and automatically stop when the lift controller 13 is in the up position. It can also control the forks to descend to a set height and automatically stop when the lift controller 13 is in the down position. This significantly reduces the workload of forklift operators, effectively improving the efficiency and flexibility of the forklift, and also enhances the safety and accuracy of operations.

[0041] In some embodiments, the automatic leveling circuit further includes a throttle control valve 7 and a balance valve 12. The throttle control valve 7 is connected between the electromagnetic reversing valve II 402 and the electromagnetic reversing valve I6. The throttle control valve 7 is used to prevent the gantry from tilting too quickly, making the automatic leveling process of the gantry more stable and smooth. The balance valve 12 is connected between the electromagnetic reversing valve I6 and the tilt cylinder 5. The balance valve 12 is used to ensure that the rod cavity of the tilt cylinder 5 is locked when the tilt manipulator 15 is not in operation, preventing the piston rod of the tilt cylinder 5 from being pulled out due to excessive weight of the cargo, and avoiding the risk of cargo falling due to the gantry tilting forward due to excessive weight of the cargo when the forklift is fully loaded, thereby improving the safety of the forklift.

[0042] In some embodiments, the lifting circuit also includes an explosion-proof valve 9 and a speed limiting valve 10. The speed limiting valve 10 is connected between the lifting cylinder 8 and the lifting reversing valve 405. The speed limiting valve 10 is used to limit the maximum descending speed of the fork, making the movement process of the fork more stable and smooth.

[0043] The present application also discloses a control method for a forklift hydraulic system using the above method, the method comprising:

[0044] Select the control mode according to the signal of the start switch 14;

[0045] If the start switch 14 is turned on, the system enters the automatic adjustment mode: the first position sensor determines whether the tilt cylinder 5 is at the tilt displacement threshold F1. If not, the electromagnetic reversing valve II 402 is controlled to be energized to connect the automatic leveling circuit, and the electromagnetic reversing valve I6 is controlled to drive the tilt cylinder 5 to restore the set stroke.

[0046] If the start switch 14 is turned off, the normal control mode is entered: the lift reversing valve 405 is controlled by the lift manipulator 13 to adjust the stroke of the lift cylinder 8, and the tilt reversing valve 410 is controlled by the tilt manipulator 15 to adjust the stroke of the tilt cylinder 5.

[0047] Furthermore, the automatic adjustment mode also includes:

[0048] When the lifting manipulator 13 is in the lifting gear position, the second position sensor determines whether the lifting cylinder 8 is at the lifting displacement threshold M1. If so, the electromagnetic reversing valve III 404 is energized, and the high-pressure oil flows back to the hydraulic oil tank 11 through the unloading circuit, and the lifting cylinder 8 stops moving.

[0049] When the lifting manipulator 13 is in the descending gear, the second position sensor determines whether the lifting cylinder 8 is at the descending displacement threshold M2. If so, the electromagnetic reversing valve IV406 is energized to cut off the lifting circuit and the lifting cylinder 8 stops moving.

[0050] Furthermore, the first position sensor is used to determine whether the tilt cylinder 5 is at the tilt displacement threshold F1. If not, the electromagnetic reversing valve II 402 is controlled to be electrically connected to the automatic leveling circuit, and the electromagnetic reversing valve I6 is controlled to drive the tilt cylinder 5 to restore the set stroke, including:

[0051] When the displacement value F of the tilt cylinder 5 is greater than the tilt displacement threshold value F1, the right control end of the control solenoid reversing valve I6 is energized, and the high-pressure oil enters the rod chamber of the tilt cylinder 5 through the balance valve 12, driving the mast to tilt backward until the displacement value F of the tilt cylinder 5 is equal to the tilt displacement threshold value F1. The control solenoid reversing valve II402 and the solenoid reversing valve I6 are both de-energized to keep the mast in a horizontal state;

[0052] When the displacement value F of the tilt cylinder 5 is less than the tilt displacement threshold value F1, the left control end of the control solenoid reversing valve I6 is energized, and the high-pressure oil enters the rodless chamber of the tilt cylinder 5 through the balance valve 12, driving the mast to tilt forward until the displacement value F of the tilt cylinder 5 is equal to the tilt displacement threshold value F1, and the control solenoid reversing valve II402 and the solenoid reversing valve I6 are both de-energized to keep the mast in a horizontal state.

[0053] Specifically, the normal control mode of the forklift includes: when the whole machine is powered on and the start switch 14 is not pressed, the solenoid reversing valve II 402, the solenoid reversing valve III 404, the solenoid reversing valve IV 406, and the solenoid reversing valve I 6 are all de-energized, the solenoid reversing valve II 402 is in the right position, and all functions of this forklift are normal functions of a traditional forklift.

[0054] The lifting reversing valve 405 is controlled by the tilt manipulator 15 to control the lifting and lowering of the lifting cylinder 8:

[0055] When the lifting manipulator 13 is pushed backward, the lifting manipulator 13 is in the lifting gear position, and the lifting reversing valve 405 is in the right position. At this time, the high-pressure oil enters the rodless chamber of the lifting cylinder 8 through the electromagnetic reversing valve II 402, the lifting reversing valve 405, the plug-in one-way valve 408, and the speed limiting valve 10 in sequence. The piston rod of the lifting cylinder 8 extends to drive the fork to rise. At this time, the lifting height and speed of the fork are determined by the opening degree of the lifting reversing valve 405.

[0056] When the lift control 13 is pushed forward, it is in the lowering position, and the lift reversing valve 405 is in the left position. When the operator sits on the seat, the solenoid reversing valve V 407 is energized. Driven by the deadweight of the forks, high-pressure oil flows sequentially through the rodless chamber of the lift cylinder 8, through the speed limiting valve 10, the solenoid reversing valve V 407, and the lift reversing valve 405, returning to the hydraulic oil tank 11, causing the forks to descend. The height and speed of the forks' descent are determined by the opening degree of the lift reversing valve 405.

[0057] The cartridge check valve 408 and solenoid reversing valve V407 are connected in parallel to form the OPS system (Operator Presence Sensing System). When the operator is not seated, the solenoid reversing valve V407 loses power, shutting off the oil flow from the lift cylinder 8 through the solenoid reversing valve V407 to the lift reversing valve 405. Simultaneously, oil from the lift cylinder 8 cannot flow through the cartridge check valve 408 to the lift reversing valve 405. At this point, even if the lift operator 13 switches the lift reversing valve 405 to the lowering left position, the forks cannot be lowered.

[0058] The tilt manipulator 15 controls the tilt reversing valve 410 to achieve the forward and backward tilting of the tilt cylinder 5:

[0059] When the tilt actuator 15 is pushed backward, it is in the rearward tilt position and the tilt reversing valve 410 is in the right position. High-pressure oil then flows through the solenoid reversing valve II 402 and the tilt reversing valve 410, entering the rod chamber of the tilt cylinder 5. The high-pressure oil in the rodless chamber of the tilt cylinder 5 then flows back through the tilt reversing valve 410 to the hydraulic oil tank 11. The piston rod of the tilt cylinder 5 retracts, driving the mast to tilt backward.

[0060] When the tilt actuator 15 is pushed forward, it is in the forward tilt position and the tilt reversing valve 410 is in the left position. High-pressure oil then flows through the solenoid reversing valve II 402 and the tilt reversing valve 410, entering the rodless chamber of the tilt cylinder 5. The high-pressure oil in the rod chamber of the tilt cylinder 5 then flows back through the tilt reversing valve 410 to the hydraulic oil tank 11. The piston rod of the tilt cylinder 5 extends, driving the mast to tilt forward.

[0061] In this embodiment, the tilt reversing valve 410 is a manual reversing valve with a built-in self-locking valve core, which prevents the piston rod of the tilt cylinder 5 from being pulled out due to excessive cargo, and avoids the risk of cargo falling due to the mast tilting forward due to excessive cargo when the forklift is fully loaded, thereby improving the safety of the forklift.

[0062] Specifically, the automatic adjustment mode for the forks includes: setting the lifting displacement threshold M1 of the lifting cylinder 8 according to the piston stroke of the lifting cylinder 8 when the forks are set to be raised; setting the lowering displacement threshold M2 of the lifting cylinder 8 according to the piston stroke of the lifting cylinder 8 when the forks are set to be lowered; and setting the tilt displacement threshold F1 of the tilt cylinder 5 according to the piston stroke of the tilt cylinder 5 when the mast is in a horizontal state.

[0063] When the whole machine is powered on and the start switch 14 is pressed, the controller first obtains the displacement value F of the tilt cylinder 5 through the first displacement sensor and determines whether the mast is in a horizontal state.

[0064] When the displacement value F of the tilt cylinder 5 exceeds the tilt displacement threshold F1, the mast is in a forward tilt state. The controller energizes the right control terminal of the solenoid reversing valve I6, placing it in the right position. High-pressure oil enters the rod chamber of the tilt cylinder 5 through port D2 and exits through port U2 of the counterbalance valve 12, then flows through the first tilt oil path 008. At this point, the high-pressure oil in the rodless chamber of the tilt cylinder 5 flows through the second tilt oil path 009 to the counterbalance valve 12. The high-pressure oil enters port U1 and exits through port D1 of the counterbalance valve 12, returning to the hydraulic tank 11 through the solenoid reversing valve I6. The piston rod of the tilt cylinder 5 retracts, driving the mast backward until the displacement value F of the tilt cylinder 5 equals the tilt displacement threshold F1. The controller then de-energizes both the solenoid reversing valve II402 and the solenoid reversing valve I6, maintaining the mast in a horizontal position.

[0065] When the displacement value F of the tilt cylinder 5 is less than the tilt displacement threshold F1, the mast is in a backward tilt state. The controller energizes the left control terminal of the solenoid reversing valve I6, placing it in the left position. High-pressure oil enters the rodless chamber of the tilt cylinder 5 through port D1 and exits through port U1 of the counterbalance valve 12, then flows through the second tilt oil circuit 009. At this point, the high-pressure oil in the rod chamber of the tilt cylinder 5 flows through the first tilt oil circuit 008 to the counterbalance valve 12, entering through port U2 and exiting through port D2 of the counterbalance valve 12. It then flows back through the solenoid reversing valve I6 to the hydraulic tank 11. The piston rod of the tilt cylinder 5 extends, driving the mast forward until the displacement value F of the tilt cylinder 5 equals its tilt displacement threshold F1. The controller then de-energizes both the solenoid reversing valve II402 and the solenoid reversing valve I6, maintaining the mast in a horizontal position.

[0066] As can be understood, when the start switch 14 is pressed, the hydraulic system prioritizes automatic leveling of the forklift mast. That is, regardless of whether the lift control 13 is pushed forward or backward, the presence of the solenoid valve II 402 prioritizes automatic leveling of the mast, and the mast's raising or lowering is then determined by the state of the lift reversing valve 405.

[0067] If the operator wants to lift the forklift to the first preset height, he needs to press the start switch 14 and push the lifting manipulator 13 backward. At this time, the lifting manipulator 13 is in the lifting gear position. After the mast is level, the lifting cylinder 8 starts the lifting action. When the forklift reaches the first preset height, that is, when the displacement value M of the lifting cylinder 8 is equal to the rising displacement threshold value M1. The controller controls the electromagnetic reversing valve III 404 to be energized and the control oil circuit 011 is connected, so that the direct-acting relief valve 403 can open the unloading circuit. At this time, although the lifting reversing valve 405 is in the right position, the high-pressure oil no longer flows through the lifting circuit to supply oil to the lifting cylinder 8, but flows back to the hydraulic oil tank 11 through the unloading oil circuit, realizing the function of automatically stopping the lifting of the forklift after it is raised to the first preset height.

[0068] In some embodiments, if the lifting cylinder 8 starts the lifting action, if the initial lifting height of the fork has exceeded the first preset height, that is, the displacement value M of the lifting cylinder 8 is greater than the rising displacement threshold M1, then the second displacement sensor cannot detect that the displacement value M of the lifting cylinder 8 is equal to the rising displacement threshold M1, and the lifting limit will not occur, so as to meet the driver's operating needs under complex working conditions.

[0069] If the operator wishes to lower the forks to the second preset height, they must press the start switch 14 and push the lift actuator 13 forward, which is now in the descending position. Once the mast is level, the lift cylinder 8 begins descending. When the forks reach the second preset height, i.e., when the displacement value M of the lift cylinder 8 equals the descending displacement threshold value M2, the controller energizes the solenoid valve IV 406, which shuts off the oil flow from the lift cylinder 8 to the lift reversing valve 405 via the solenoid valve V 407. Simultaneously, the oil flow from the lift cylinder 8 to the lift reversing valve 405 via the cartridge check valve 408 is also blocked. At this point, the forks cannot descend further, effectively achieving the automatic stop function after the forks reach the second preset height.

[0070] In some embodiments, if the lifting cylinder 8 starts to descend, if the initial descending height of the fork is already lower than the second preset height, that is, the displacement value M of the lifting cylinder 8 is less than the descending displacement threshold M2, then the second displacement sensor cannot detect the condition that the displacement value M of the lifting cylinder 8 is equal to the descending displacement threshold M2, and the descending limit will not appear, so as to meet the driver's operating needs under complex working conditions.

[0071] The above shows and describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. These changes and improvements are intended to fall within the scope of the present application. The scope of protection claimed in this application is defined by the appended claims and their equivalents.

Claims

1. A forklift hydraulic system, characterized in that: It comprises a hydraulic oil tank (11), a hydraulic gear pump (2), a multi-way valve group (4), an electromagnetic reversing valve I (6), a lifting cylinder (8) for driving the fork to lift and lower, and a tilting cylinder (5) for driving the mast to tilt, wherein the hydraulic gear pump (2) is used to transport the hydraulic oil in the hydraulic oil tank (11) to the multi-way valve group (4); The multi-way valve group (4) includes an electromagnetic reversing valve II (402), a lifting reversing valve (405) and a tilting reversing valve (410), wherein the first oil outlet of the electromagnetic reversing valve II (402) is connected to the electromagnetic reversing valve I (6) and the tilting oil cylinder (5) in sequence to form an automatic leveling circuit, and the second oil outlet of the electromagnetic reversing valve II (402) is connected to the lifting reversing valve (405) and the tilting reversing valve (410) respectively, wherein the lifting reversing valve (405) is connected to the lifting oil cylinder (8) to form a lifting circuit, and the tilting reversing valve (410) is connected to the tilting oil cylinder (5) to form a tilting circuit; The hydraulic system further comprises an oil circuit switching control device, the oil circuit switching control device comprising a controller, a start switch (14) and a first displacement sensor provided in the tilt oil cylinder (5), the start switch (14) and the first displacement sensor being respectively connected to the controller signal, the controller being connected to the electromagnetic reversing valve II (402) and the electromagnetic reversing valve I (6) signal, the controller being able to control the electromagnetic reversing valve II (402) and the electromagnetic reversing valve I (6) according to the signal transmitted by the start switch (14) and the first displacement sensor to drive the tilt oil cylinder (5) to adjust the mast to a horizontal state; The multi-way valve group (4) further includes a direct-acting overflow valve (403) and an electromagnetic reversing valve III (404) connected between the first oil outlet of the electromagnetic reversing valve II (402) and the hydraulic oil tank (11), wherein the direct-acting overflow valve (403) and the electromagnetic reversing valve III (404) form an unloading circuit connected in parallel with the lifting circuit; The multi-way valve group (4) further comprises a plug-in check valve (408) and an electromagnetic reversing valve V (407) which are arranged in parallel between the lifting reversing valve (405) and the lifting oil cylinder (8), wherein the plug-in check valve (408) and the electromagnetic reversing valve V (407) constitute an OPS system; The multi-way valve group (4) further includes an electromagnetic reversing valve IV (406), and the electromagnetic reversing valve IV (406) is connected in series between the lifting reversing valve (405) and the electromagnetic reversing valve V (407); The oil circuit switching control device also includes a lifting manipulator (13) and a second displacement sensor provided in the lifting oil cylinder (8), wherein the lifting manipulator (13) and the second displacement sensor are respectively connected to the controller signal, and the controller is connected to the electromagnetic reversing valve IV (406) and the electromagnetic reversing valve III (404) signal; when the lifting manipulator (13) is in the lifting gear, the controller can adjust the lifting oil cylinder (8) through the electromagnetic reversing valve III (404) according to the signal transmitted by the starting switch (14) and the second displacement sensor to drive the fork to rise to a set lifting height; when the lifting manipulator (13) is in the descending gear, the controller can adjust the lifting oil cylinder (8) through the electromagnetic reversing valve IV (406) according to the signal transmitted by the starting switch (14) and the second displacement sensor to drive the fork to descend to a set descending height.

2. The forklift hydraulic system according to claim 1, characterized in that: The automatic leveling circuit further includes a throttle speed regulating valve (7) connected between the electromagnetic reversing valve II (402) and the electromagnetic reversing valve I (6), and a balancing valve (12) connected between the electromagnetic reversing valve I (6) and the tilting oil cylinder (5).

3. The forklift hydraulic system according to claim 1, characterized in that: The lifting circuit further comprises an explosion-proof valve (9) and a speed limiting valve (10), wherein the speed limiting valve (10) is connected between the lifting oil cylinder (8) and the lifting reversing valve (405).

4. A control method for a forklift hydraulic system according to any one of claims 1 to 3, characterized in that: The method includes: Selecting a control mode according to a signal from a start switch (14); If the start switch (14) is turned on, the automatic adjustment mode is entered: the first position sensor is used to determine whether the tilt cylinder (5) is at the tilt displacement threshold F1. If not, the electromagnetic reversing valve II (402) is controlled to be electrically connected to the automatic leveling circuit, and the electromagnetic reversing valve I (6) is controlled to drive the tilt cylinder (5) to restore the set stroke. If the start switch (14) is turned off, the normal control mode is entered: the lifting reversing valve (405) is controlled by the lifting manipulator (13) to adjust the stroke of the lifting cylinder (8), and the tilting reversing valve (410) is controlled by the tilting manipulator (15) to adjust the stroke of the tilting cylinder (5).

5. The control method of a forklift hydraulic system according to claim 4, characterized in that: The automatic adjustment mode also includes: When the lifting manipulator (13) is in the lifting gear position, the second position sensor is used to determine whether the lifting cylinder (8) is at the lifting displacement threshold value M1. If so, the electromagnetic reversing valve III (404) is controlled to be energized, and the high-pressure oil flows back to the hydraulic oil tank (11) through the unloading circuit, and the lifting cylinder (8) stops moving; When the lifting manipulator (13) is in the descending gear, the second position sensor is used to determine whether the lifting cylinder (8) is at the descending displacement threshold value M2. If so, the electromagnetic reversing valve IV (406) is controlled to be energized, thereby switching the lifting circuit and the lifting cylinder (8) stops moving.

6. The control method of a forklift hydraulic system according to claim 4, characterized in that: The method of determining whether the tilt oil cylinder (5) is at the tilt displacement threshold value F1 by the first position sensor, and if not, controlling the electromagnetic reversing valve II (402) to be electrically connected to the automatic leveling circuit, and controlling the electromagnetic reversing valve I (6) to drive the tilt oil cylinder (5) to restore the set stroke includes: When the displacement value F of the tilt oil cylinder (5) is greater than the tilt displacement threshold value F1, the right control end of the control electromagnetic reversing valve I (6) is energized, and the high-pressure oil enters the rod chamber of the tilt oil cylinder (5) through the balance valve (12), driving the mast to tilt backward until the displacement value F of the tilt oil cylinder (5) is equal to the tilt displacement threshold value F1, and the control electromagnetic reversing valve II (402) and the electromagnetic reversing valve I (6) are both de-energized to keep the mast in a horizontal state; When the displacement value F of the tilt cylinder (5) is less than the tilt displacement threshold value F1, the left control end of the control electromagnetic reversing valve I (6) is energized, and the high-pressure oil enters the rodless chamber of the tilt cylinder (5) through the balance valve (12), driving the mast to tilt forward until the displacement value F of the tilt cylinder (5) is equal to the tilt stroke threshold value F1, and the control electromagnetic reversing valve II (402) and the electromagnetic reversing valve I (6) are both de-energized to keep the mast in a horizontal state.

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