Forklift hydraulic system and control method thereof

Abstract

The invention provides a forklift hydraulic system and a control method thereof. The forklift hydraulic system comprises a hydraulic oil tank, a hydraulic gear pump, a multi-way valve set, an electromagnetic reversing valve I, a lifting oil cylinder used for driving a pallet fork to ascend and descend and an inclined oil cylinder used for driving a portal to incline, and the hydraulic gear pump is used for conveying hydraulic oil in the hydraulic oil tank to the multi-way valve set; the hydraulic system further comprises an oil way switching control device, and the oil way switching control device can control the electromagnetic directional valve II and the electromagnetic directional valve I to drive the inclined oil cylinder to adjust the portal frame to be in a horizontal state. Meanwhile, when the lifting manipulator is in an ascending gear, the pallet fork can be controlled to ascend to a set ascending height and automatically stop ascending; when the lifting manipulator is in the descending gear, the pallet fork can be controlled to descend to the set descending height and automatically stop descending, and the working efficiency and flexibility of the forklift are effectively improved.

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 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 the specified end position. In actual operation, the starting point and end point of the goods are often set on a relatively fixed and usually horizontal table to facilitate the smooth loading and unloading and storage process. However, traditional forklift operators usually need to manually set the lifting height of the fork based on personal experience, and also need to rely on visual judgment to ensure that the fork remains horizontal. This operation 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 work efficiency largely dependent on the operator's professional skills and experience level, which seriously affects the operation 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, including 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 transport the hydraulic oil in the hydraulic oil tank to the multi-way valve group; The multi-way valve group includes an electromagnetic reversing valve II, a lifting reversing valve and a tilting reversing valve, wherein 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, and the second oil outlet of the electromagnetic reversing valve II is connected to the lifting reversing valve and the tilting reversing valve respectively, wherein 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; The hydraulic system also includes an oil circuit switching control device, which includes a controller, a start switch and a first displacement sensor arranged in the tilt cylinder. The start switch and the first displacement sensor are respectively connected to the controller signal, and the controller is connected to the electromagnetic reversing valve II and the electromagnetic reversing valve I by signal. 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 according to the signal transmitted by the start switch and the first displacement sensor.

[0004] 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, and the direct-acting overflow valve and the electromagnetic reversing valve III form an unloading circuit in parallel with the lifting circuit.

[0005] Furthermore, the multi-way valve group also includes a cartridge-type one-way valve and an electromagnetic reversing valve V which are arranged in parallel between the lifting reversing valve and the lifting cylinder, and the cartridge-type one-way valve and the electromagnetic reversing valve V constitute an OPS system.

[0006] Furthermore, the multi-way valve group also includes an electromagnetic reversing valve IV, and the electromagnetic reversing valve IV is connected in series between the lifting reversing valve and the electromagnetic reversing valve V.

[0007] Furthermore, the oil circuit switching control device also includes a lifting manipulator and a second displacement sensor arranged 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 by signal; when the lifting manipulator is in the lifting gear position, the controller can adjust the lifting cylinder to drive the fork to rise to a 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 position, the controller can adjust the lifting cylinder to drive the fork to descend to a set descending height through the electromagnetic reversing valve IV according to the signal transmitted by the starting switch and the second displacement sensor.

[0008] Furthermore, the automatic leveling circuit also includes a throttling 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 tilting cylinder.

[0009] 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.

[0010] A second aspect of the present application provides a control method for a forklift hydraulic system using the forklift hydraulic system, the method comprising: Select the control mode according to the signal of the start switch; If the start switch is turned on, the automatic adjustment mode is entered: 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 controlled to be energized to connect the automatic leveling circuit, and the electromagnetic reversing valve I is controlled to drive the tilt cylinder to restore the set stroke; If the start switch is turned off, the normal control mode is entered: the lifting reversing valve is controlled by the lifting manipulator to adjust the stroke of the lifting cylinder, and the tilting reversing valve is controlled by the tilting manipulator to adjust the stroke of the tilting cylinder.

[0011] Furthermore, the automatic adjustment mode also includes: When the lifting manipulator is in the lifting gear position, the second position sensor is used to determine whether the lifting cylinder is at the first displacement threshold M. If so, the electromagnetic reversing valve III is controlled to be energized, and the high-pressure oil flows back to the hydraulic oil tank through the unloading circuit, and the lifting cylinder stops moving; 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.

[0012] Further, the first position sensor is used to determine whether the tilt cylinder is at the tilt displacement threshold F, and if not, the electromagnetic reversing valve II is controlled to be electrically connected to the automatic leveling circuit, and the electromagnetic reversing valve I is controlled to drive the tilt cylinder to restore the set stroke, including: When the displacement value F of the tilt oil cylinder is greater than the tilt displacement threshold value F, the right control end of the control electromagnetic reversing valve I is energized, and the high-pressure oil enters the rod chamber of the tilt oil cylinder through the balance valve to drive the mast to tilt backward until the displacement value F of the tilt oil cylinder is equal to the tilt displacement threshold value F, and the control electromagnetic reversing valve II and the electromagnetic reversing valve I are both de-energized to keep the mast in a horizontal state; When the displacement value F of the tilt cylinder is less than the tilt displacement threshold F, the left control end of the control solenoid 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 control solenoid reversing valve II and the solenoid reversing valve I are both de-energized to keep the mast in a horizontal state.

[0013] Compared with the prior art, the beneficial effects of this application are: 1. The hydraulic system of the forklift provided in 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 goods are always kept horizontal and stable during the handling process. This not only greatly reduces the workload of the forklift operator, and effectively improves the work efficiency and flexibility of the forklift; it also improves the safety and accuracy of the operation and reduces the risk of goods falling. 2. The forklift hydraulic system provided in the embodiment of the present application can control the forklift to rise to the set lifting height and automatically stop rising when the lifting manipulator is in the lifting gear; and can control the forklift to descend to the set descending height and automatically stop descending when the lifting manipulator is in the descending gear. When the starting point and the end point of the cargo are set on a relatively fixed table, this technical solution greatly reduces the workload of the forklift operator, effectively improves the working efficiency and flexibility of the forklift; and also improves the safety and accuracy of the operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a hydraulic principle diagram of the forklift hydraulic system of the present application; Figure 2 It is a hydraulic principle diagram of the multi-way valve of the present application; Figure 3 It is a structural schematic diagram of the oil circuit switching control device of the present application; Description of reference numerals: 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 one-way valve; 409. Unloading screw plug; 410. Tilt reversing valve; 5. Tilt cylinder; 6. Solenoid reversing valve I; 7. Throttle speed regulating 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

[0015] In order to facilitate the understanding of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0016] The present application discloses a forklift hydraulic system for automatic adjustment of forklift attachments; the hydraulic system includes a hydraulic oil tank 11, a hydraulic gear pump 2, a multi-way valve group 4, an electromagnetic reversing valve Ⅰ6, a lifting cylinder 8 for driving the lifting of the cargo fork, and a tilting cylinder 5 for driving the mast to tilt. Among them, the electromagnetic reversing valve Ⅰ6 is a double-controlled three-position four-way electromagnetic reversing valve; the oil pump motor 1 is mechanically connected to the hydraulic gear pump 2, and is used to drive the hydraulic gear pump 2 to rotate; the multi-way valve group 4 includes an oil inlet P, a preferred oil outlet A1, a lifting oil port B1, a first tilting oil port A2, and a second tilting 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 group 4, and is used to transport the hydraulic oil in the hydraulic oil tank 11 to the multi-way valve group 4.

[0017] The multi-way valve group 4 also includes an electromagnetic reversing valve II 402, a lifting reversing valve 405 and a tilting reversing valve 410. In this embodiment, the electromagnetic reversing valve II 402 is a two-position three-way electromagnetic reversing valve, and the oil inlet of the electromagnetic reversing valve II 402 is connected to the oil inlet P of the multi-way valve group 4 through the main oil supply line 001; the first oil outlet of the electromagnetic reversing valve II 402 is connected to the priority oil outlet A1 of the multi-way valve group 4, the electromagnetic reversing valve I 6, and the tilting oil cylinder 5 in sequence through the leveling oil line 002 to form an automatic leveling circuit. 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 a manual reversing valve, and the first oil outlet of the lifting reversing valve 405 is connected to the lifting oil port B1 of the multi-way valve group 4 and the rodless chamber of the lifting oil cylinder 8 in sequence through the lifting oil line 005 to form a lifting 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 tilting circuit.

[0018] The hydraulic system also includes an oil circuit switching control device, which includes: a lifting manipulator 13, a start switch 14, a tilting manipulator 15, a first displacement sensor arranged in the tilting oil cylinder 5, and a second displacement sensor arranged in the lifting oil cylinder 8. Among them, the lifting manipulator 13 is mechanically connected to the lifting reversing valve 405, and the tilting manipulator 15 is mechanically connected to the tilting reversing valve 410; the start switch 14 is arranged on the lifting manipulator 13, the start switch 14 and the first displacement sensor are respectively connected to the controller signal, and the controller is connected to the electromagnetic reversing valve II 402 and the electromagnetic reversing valve I6 by signal. The controller can control the electromagnetic reversing valve II 402 and the electromagnetic reversing valve I6 according to the signal transmitted by the start switch 14 and the first displacement sensor to drive the tilting oil cylinder 5 to adjust the mast to a horizontal state.

[0019] 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 through the first position sensor, controls the electromagnetic reversing valve II 402 to be electrically connected to the automatic leveling circuit, and controls the electromagnetic reversing valve I6 to drive the tilt cylinder 5 to restore the set stroke; thereby automatically adjusting the mast to restore the horizontal state, ensuring that the goods are always horizontal and stable during the handling process. This not only greatly reduces the workload of the forklift operator, effectively improves the work efficiency and flexibility of the forklift; it also improves the safety and accuracy of the operation, and reduces the risk of goods falling.

[0020] In some embodiments, the multi-way valve group 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 in parallel with the lifting circuit. After the solenoid reversing valve III 404 is energized, it is connected to the unloading circuit, and the high-pressure oil flows back to the hydraulic oil tank 11 from the second oil outlet of the solenoid reversing valve II 402 through the unloading circuit.

[0021] In some embodiments, the multi-way valve group 4 further includes a cartridge check valve 408 and an electromagnetic reversing valve V407 disposed between the lifting reversing valve 405 and the lifting oil cylinder 8. Among them, the electromagnetic reversing valve V407 is a normally closed electromagnetic reversing valve; the oil inlet of the cartridge check valve 408 is connected to the lifting reversing valve 405, and the oil outlet of the cartridge check valve 408 is connected to the lifting oil cylinder 8, so that the high-pressure oil can only flow from the lifting reversing valve 405 to the lifting oil cylinder 8 through the cartridge check valve 408, but cannot flow from the lifting oil cylinder 8 to the lifting reversing valve 405 through the cartridge check valve 408. The cartridge check valve 408 and the electromagnetic reversing valve V407 are arranged in parallel to form an OPS system (operator presence sensing system).

[0022] When the operator does not sit on the seat, the electromagnetic reversing valve V407 is not energized, thereby cutting off the oil path from the lifting cylinder 8 to the lifting reversing valve 405 through the electromagnetic reversing valve V407; at the same time, the lifting cylinder 8 cannot flow to the lifting reversing valve 405 through the plug-in check valve 408. At this time, even if the lifting reversing valve 405 is pushed to switch to the lowering left position by the lifting manipulator 13, the fork cannot be lowered.

[0023] In some embodiments, the multi-way valve group 4 further includes an electromagnetic reversing valve IV406, which is connected in series between the lifting reversing valve 405 and the electromagnetic reversing valve V407. The electromagnetic reversing valve IV406 is a normally open electromagnetic reversing valve, which is connected to the controller signal. When the electromagnetic reversing valve IV406 receives the controller signal and is energized, the electromagnetic reversing valve IV406 cuts off the oil path from the lifting cylinder 8 to the lifting reversing valve 405 through the electromagnetic reversing valve V407. At the same time, the lifting cylinder 8 cannot flow to the lifting reversing valve 405 through the plug-in check valve 408. At this time, even if the lifting reversing valve 405 is pushed to switch to the lowering left position function by the lifting manipulator 13, the fork cannot be lowered.

[0024] In some embodiments, 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 IV406 and the electromagnetic reversing valve III404. When the lifting manipulator 13 is in the lifting gear, the controller can adjust the lifting cylinder 8 through the electromagnetic reversing valve III404 according to the signal transmitted by the starting switch 14 and the second displacement sensor to drive the fork to rise to the set lifting height; when the lifting manipulator 13 is in the descending gear, the controller can adjust the lifting cylinder 8 through the electromagnetic reversing valve IV406 according to the signal transmitted by the starting switch 14 and the second displacement sensor to drive the fork to descend to the set descending height.

[0025] The forklift hydraulic system provided in this embodiment can control the forklift to rise to the set lifting height and automatically stop rising when the lifting manipulator 13 is in the lifting gear; and can control the forklift to descend to the set descending height and automatically stop descending when the lifting manipulator 13 is in the descending gear. This greatly reduces the workload of the forklift operator, effectively improves the working efficiency and flexibility of the forklift, and also improves the safety and accuracy of the operation.

[0026] In some embodiments, the automatic leveling circuit also includes a throttle speed regulating valve 7 and a balance valve 12. The throttle speed regulating valve 7 is connected between the electromagnetic reversing valve II 402 and the electromagnetic reversing valve I6. The throttle speed regulating valve 7 is used to prevent the gantry from tilting too fast, so that the automatic leveling process of the gantry is 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 chamber of the tilt cylinder 5 is locked when the tilt manipulator 15 is not in action, to prevent the piston rod of the tilt cylinder 5 from being pulled out due to excessive weight of the cargo, to avoid the risk of cargo falling due to the forward tilt of the gantry caused by excessive weight of the cargo when the forklift is fully loaded, thereby improving the safety of the forklift. 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, so that the movement process of the fork is more stable and smooth.

[0027] The present application also discloses a control method for a forklift hydraulic system using the above method, the method comprising: Select the control mode according to the signal of the 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 I6 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.

[0028] Furthermore, the automatic adjustment mode also includes: 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. When the lifting manipulator 13 is in the descending gear, the second position sensor determines whether the lifting cylinder 8 is in the descending displacement threshold M2. If so, the electromagnetic reversing valve IV406 is energized to cut off the lifting circuit and stop the lifting cylinder 8 from moving.

[0029] Further, 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: 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 I6 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 II402 and the electromagnetic reversing valve I6 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 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 gantry 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 gantry horizontal.

[0030] 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.

[0031] The lifting reversing valve 405 is controlled by the tilt manipulator 15 to control the lifting and lowering of the lifting cylinder 8: 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.

[0032] When the lifting manipulator 13 is pushed forward, the lifting manipulator 13 is in the descending gear position, and the lifting reversing valve 405 is in the left position. When the operator sits on the seat, the electromagnetic reversing valve V407 is energized, and driven by the deadweight of the fork, the high-pressure oil sequentially passes through the rodless chamber of the lifting cylinder 8, and sequentially passes through the speed limiting valve 10, the electromagnetic reversing valve V407, and the lifting reversing valve 405 to return to the hydraulic oil tank 11, so that the fork is lowered. At this time, the height and speed of the fork's descent are determined by the opening degree of the lifting reversing valve 405.

[0033] Among them, the plug-in check valve 408 and the electromagnetic reversing valve V407 are arranged in parallel to form an OPS system (operator presence sensing system). When the operator does not sit on the seat, the electromagnetic reversing valve V407 is not energized, cutting off the oil path from the lifting cylinder 8 to the lifting reversing valve 405 through the electromagnetic reversing valve V407; at the same time, the lifting cylinder 8 cannot flow to the lifting reversing valve 405 through the plug-in check valve 408. At this time, even if the lifting reversing valve 405 is pushed to switch to the lowering left position function through the lifting manipulator 13, the fork cannot be lowered.

[0034] The tilt manipulator 15 controls the tilt reversing valve 410 to realize the forward and backward tilting of the tilt cylinder 5: When the tilt manipulator 15 is pushed backward, the tilt manipulator 15 is in the backward tilt gear position, and the tilt reversing valve 410 is in the right position function; at this time, the high-pressure oil enters the rod chamber of the tilt oil cylinder 5 through the electromagnetic reversing valve II 402 and the tilt reversing valve 410 in sequence, and the high-pressure oil in the rodless chamber of the tilt oil cylinder 5 flows back to the hydraulic oil tank 11 through the tilt reversing valve 410. The piston rod of the tilt oil cylinder 5 retracts to drive the mast to tilt backward.

[0035] When the tilt manipulator 15 is pushed forward, the tilt manipulator 15 is in the forward tilt gear position, and the tilt reversing valve 410 is in the left position function; at this time, the high-pressure oil enters the rodless chamber of the tilt oil cylinder 5 through the electromagnetic reversing valve II 402 and the tilt reversing valve 410 in sequence, and the high-pressure oil in the rod chamber of the tilt oil cylinder 5 flows back to the hydraulic oil tank 11 through the tilt reversing valve 410. The piston rod of the tilt oil cylinder 5 extends to drive the mast to tilt forward.

[0036] 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 tilting cylinder 5 from being pulled out due to excessive cargo, and avoids the risk of cargo falling due to the forward tilting of the mast caused by excessive cargo when the forklift is fully loaded, thereby improving the safety of the forklift.

[0037] Specifically, the automatic adjustment mode of the fork includes: setting the rising displacement threshold M1 of the lifting cylinder 8 according to the piston stroke of the lifting cylinder 8 when the fork is set to rise; setting the descending displacement threshold M2 of the lifting cylinder 8 according to the piston stroke of the lifting cylinder 8 when the fork is set to descend. 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.

[0038] 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.

[0039] When the displacement value F of the tilt cylinder 5 is greater than the tilt displacement threshold value F1, the mast is in a forward tilt state. The controller controls the right control end of the electromagnetic reversing valve I6 to be energized, and the electromagnetic reversing valve I6 is in the right position function. The high-pressure oil enters from the oil port D2 of the balance valve 12 and exits from the oil port U2, and enters the rod chamber of the tilt cylinder 5 through the first tilt oil circuit 008. At this time, the high-pressure oil in the rodless chamber of the tilt cylinder 5 passes through the second tilt oil circuit 009 to the balance valve 12, and the high-pressure oil enters from the oil port U1 of the balance valve 12 and exits from the oil port D1, and flows back to the hydraulic oil tank 11 through the electromagnetic reversing valve I6. The piston rod of the tilt cylinder 5 retracts to drive the mast to tilt backward until the displacement value F of the tilt cylinder 5 is equal to its tilt displacement threshold value F1. The controller controls the electromagnetic reversing valve II402 and the electromagnetic reversing valve I6 to lose power to keep the mast horizontal.

[0040] When the displacement value F of the tilt oil cylinder 5 is less than the tilt displacement threshold value F1, the mast is in a backward tilt state. The controller controls the left control end of the electromagnetic reversing valve I6 to be energized, and the electromagnetic reversing valve I6 is in the left position function. The high-pressure oil enters from the oil port D1 of the balance valve 12 and exits from the oil port U1, and enters the rodless chamber of the tilt oil cylinder 5 through the second tilt oil circuit 009. At this time, the high-pressure oil in the rod chamber of the tilt oil cylinder 5 passes through the first tilt oil circuit 008 to the balance valve 12, and the high-pressure oil enters from the oil port U2 of the balance valve 12 and exits from the oil port D2, and flows back to the hydraulic oil tank 11 through the electromagnetic reversing valve I6. The piston rod of the tilt oil cylinder 5 extends to drive the mast to tilt forward until the displacement value F of the tilt oil cylinder 5 is equal to its tilt displacement threshold value F1. The controller controls the electromagnetic reversing valve II402 and the electromagnetic reversing valve I6 to lose power to keep the mast in a horizontal state.

[0041] It is understandable that when the start switch 14 is pressed, the hydraulic system will give priority to the automatic leveling of the forklift mast. That is, no matter whether the lifting manipulator 13 is pushed forward or backward, the mast will be automatically leveled due to the presence of the electromagnetic reversing valve II 402, and the lifting and lowering of the mast will be determined according to the state of the lifting reversing valve 405.

[0042] If the operator wants to lift the fork 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 fork reaches the first preset height, that is, 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 overflow 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 supplies oil to the lifting cylinder 8 through the lifting circuit, but flows back to the hydraulic oil tank 11 through the unloading oil circuit, realizing the function of automatically stopping the lifting of the fork after it is lifted to the first preset height.

[0043] In some embodiments, when 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, 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 no lifting limit will occur, so as to meet the driver's operating needs under complex working conditions.

[0044] If the operator wants to lower the fork to the second preset height of the fork, he needs to press the start switch 14 and push the lifting manipulator 13 forward. At this time, the lifting manipulator 13 is in the descending gear position. After the mast is level, the lifting cylinder 8 starts to descend. When the fork reaches the second preset height, that is, the displacement value M of the lifting cylinder 8 is equal to the descending displacement threshold value M2. The controller controls the electromagnetic reversing valve IV406 to be energized, and the electromagnetic reversing valve IV406 cuts off the oil path from the lifting cylinder 8 to the lifting reversing valve 405 through the electromagnetic reversing valve V407. At the same time, the lifting cylinder 8 cannot flow to the lifting reversing valve 405 through the plug-in check valve 408. At this time, the fork cannot continue to descend, that is, the function of automatically stopping the fork from descending after it descends to the second preset height of the fork is realized.

[0045] In some embodiments, when 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, 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 descent limit will not appear, so as to meet the driver's operating needs under complex working conditions.

[0046] 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 by the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present application. Without departing from the spirit and scope of the present application, the present application may have various changes and improvements, which fall within the scope of the present application to be protected. The scope of protection claimed in the present application is defined by the attached claims and their equivalents.

Claims

1. A forklift hydraulic system, characterized in that: The invention 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 a fork to rise and fall, and a tilting cylinder (5) for driving a mast to tilt. The hydraulic gear pump (2) is used to deliver the hydraulic oil in the hydraulic oil tank (11) to the multi-way valve group (4); the multi-way valve group (4) comprises an electromagnetic reversing valve II (402), a lifting reversing valve (405) and a tilting reversing valve (410); the first oil outlet of the electromagnetic reversing valve II (402) is connected to the electromagnetic reversing valve I (6) and the tilting cylinder (5) in sequence to form an automatic leveling circuit; 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) and the tilting reversing valve (410) are connected to each other. The valve (405) is connected to the lifting cylinder (8) to form a lifting circuit, and the tilt reversing valve (410) is connected to the tilting cylinder (5) to form a tilting circuit; the hydraulic system also includes an oil circuit switching control device, the oil circuit switching control device includes a controller, a start switch (14) and a first displacement sensor provided in the tilting cylinder (5), the start switch (14) and the first displacement sensor are respectively connected to the controller signal, the controller is connected to the electromagnetic reversing valve II (402) and the electromagnetic reversing valve I (6) signal, and the controller can 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 tilting cylinder (5) to adjust the door frame to a horizontal state.

2. The forklift hydraulic system according to claim 1, characterized in that: The multi-way valve group (4) further comprises a direct-acting relief valve (403) and a solenoid reversing valve III (404) connected between the first 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 a load-unloading circuit connected in parallel with the lifting circuit.

3. The forklift hydraulic system according to claim 2, characterized in that: 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 cylinder (8); the plug-in check valve (408) and the electromagnetic reversing valve V (407) constitute an OPS system.

4. The forklift hydraulic system according to claim 3, characterized in that: The multi-way valve group (4) further comprises an electromagnetic reversing valve IV (406), wherein the electromagnetic reversing valve IV (406) is connected in series between the lifting reversing valve (405) and the electromagnetic reversing valve V (407).

5. The forklift hydraulic system according to claim 4, characterized in that: The oil circuit switching control device also includes a lifting manipulator (13) and a second displacement sensor provided in the lifting cylinder (8); the lifting manipulator (13) and the second displacement sensor are respectively connected to the controller by signal, and the controller is connected to the electromagnetic reversing valve IV (406) and the electromagnetic reversing valve III (404) by signal; when the lifting manipulator (13) is in a lifting gear position, the controller can adjust the lifting cylinder (8) through the electromagnetic reversing valve III (404) according to the signal transmitted by the starting switch (14) and the second displacement sensor, so that the fork is raised to a set lifting height; when the lifting manipulator (13) is in a descending gear position, the controller can adjust the lifting cylinder (8) through the electromagnetic reversing valve IV (406) according to the signal transmitted by the starting switch (14) and the second displacement sensor, so that the fork is lowered to a set descending height.

6. The forklift hydraulic system according to claim 1, characterized in that: The automatic leveling circuit further comprises a throttling 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 cylinder (5).

7. 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 cylinder (8) and the lifting reversing valve (405).

8. A control method for a forklift hydraulic system according to any one of claims 1 to 7, 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).

9. The control method of a forklift hydraulic system according to claim 8, 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 position, 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 stopping the movement of the lifting cylinder (8).

10. The control method of a forklift hydraulic system according to claim 8, characterized in that: The method of determining whether the tilt cylinder (5) is at the tilt displacement threshold value F1 by means of 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 cylinder (5) to restore the set stroke comprises: 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 electromagnetic reversing valve I (6) 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, 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 solenoid 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 solenoid reversing valve II (402) and the solenoid reversing valve I (6) are both de-energized to keep the mast in a horizontal state.

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