Forklift electro-hydraulic control system and method

Abstract

This application provides an electro-hydraulic control system and method for a forklift, including a first motor, a first hydraulic pump, a second hydraulic pump, a second motor, a solenoid valve group, a multi-way valve group, a tilting cylinder, a lifting cylinder, and a hydraulic oil tank. During mast lifting operation, the hydraulic oil output by the first and second hydraulic pumps collects at the right working position of the lifting valve plate and provides a high-pressure oil source for the lifting cylinder. During mast lowering operation, the high-pressure oil generated by the potential energy of the load enters the left working position of the lifting valve plate through port A of the multi-way valve group and flows back to the hydraulic oil tank through the solenoid valve group and the second hydraulic pump.

Description

Technical Field

[0001] This application relates to the field of forklift technology, specifically to an electro-hydraulic control system and method for forklifts. Background Technology

[0002] Driven by the accelerated pace of electrification, electric counterbalance forklifts are facing increasingly stringent technical requirements regarding ride comfort and overall performance. Currently, with the continuous increase in maximum no-load and full-load lifting speeds, system energy loss is significantly increasing. This leads to higher overall vehicle energy consumption and reduced range; furthermore, it causes higher hydraulic system oil temperatures, which can damage hydraulic component seals, causing oil leaks and severely impacting component lifespan. Simultaneously, users are demanding more precise control over the lifting and lowering speeds of large-tonnage forklift masts. Therefore, achieving performance improvements and effectively reducing system energy consumption with a low-cost solution has become a pressing technical challenge in the field of large-tonnage electric counterbalance forklifts. Summary of the Invention

[0003] To address the problems in the prior art, the first aspect of this application provides a forklift electro-hydraulic control system, including a first motor, a first hydraulic pump, a second hydraulic pump, a second motor, a solenoid valve group, a multi-way valve group, a tilting cylinder, a lifting cylinder, and a hydraulic oil tank. The second hydraulic pump is a bidirectional hydraulic pump, and the multi-way valve group includes a lifting valve plate and a tilting valve plate, wherein the lifting valve plate is connected to the lifting cylinder. One end of the first hydraulic pump is connected to the hydraulic oil tank, and the other end is connected to the lifting valve plate. One end of the second hydraulic pump is connected to the hydraulic oil tank, and the other end is connected to the lifting valve plate via the solenoid valve group. During the gantry lifting operation, the hydraulic oil output by the first hydraulic pump and the second hydraulic pump is collected at the right working position of the lifting valve plate and provides a high-pressure oil source for the lifting cylinder. During the gantry descent, the high-pressure oil generated by the potential energy of the heavy object enters the left working position of the lifting valve plate through the A port of the multi-way valve group, and flows back to the hydraulic oil tank through the solenoid valve group and the second hydraulic pump.

[0004] Furthermore, the lifting valve plate adopts a three-position five-way reversing valve, and the lifting valve plate is equipped with a displacement sensor for detecting the displacement of the valve core; the vehicle controller controls the speed of the first motor and the second motor according to the signal value of the displacement sensor, so as to achieve precise control of the lifting and lowering speed of the mast.

[0005] Furthermore, the solenoid valve assembly includes a solenoid directional valve and a pressure compensator. The V port of the solenoid directional valve is connected to the left end of the pressure compensator, and the V port is connected to the right end of the pressure compensator.

[0006] Furthermore, during the gantry lifting operation, the vehicle controller controls the electromagnetic reversing valve to fully open, at which time the valve core of the pressure compensator is in the right working position and the throttle port is fully open; During the gantry descent, the vehicle controller controls the opening of the electromagnetic directional valve based on the signal value of the displacement sensor to control the descent speed. At the same time, the pressure compensator's valve core is subjected to forces that tend to balance on both sides, thereby maintaining a fixed pressure difference between the inlet and outlet ports V and V of the electromagnetic directional valve.

[0007] Furthermore, the C port of the solenoid valve assembly is connected to a pressure sensor, which is used to detect the pressure signal at the C port and feed it back to the vehicle controller; the second motor is an electric generator, and when the mast is lowered, the vehicle controller controls the second motor of the second hydraulic pump to output the reverse torque at the corresponding pressure value, so that the second motor is in the generator state.

[0008] Furthermore, when the vehicle controller detects that a person has left the seat via the seat-integrated pressure sensor, it controls the solenoid directional valve to remain closed, cutting off the mast descent oil circuit.

[0009] A second aspect of this application provides a control method based on the electro-hydraulic control system of a forklift as described in any of the above claims, comprising the following steps: The displacement signal of the lifting valve disc core is monitored in real time, and the current working condition of the forklift is determined based on the displacement signal. If the condition is determined to be a mast lifting operation, the vehicle controller adjusts the speed of the first motor and the second motor according to the displacement signal, so that the hydraulic oil output by the first hydraulic pump and the second hydraulic pump merges in the lifting valve plate and drives the lifting cylinder to move. At the same time, the controller controls the electromagnetic reversing valve in the electromagnetic valve group to be in a fully open state, so that the pressure sensor is in the right working position with the throttle port fully open. If the gantry is determined to be in a descent condition, the vehicle controller controls the first motor to stop rotating and adjusts the opening of the solenoid valve group according to the displacement signal. The pressure sensor is used to maintain a constant pressure difference between the inlet and outlet of the solenoid valve group. At the same time, the pressure signal of port C of the solenoid valve group is collected, and the second motor is controlled to output reverse torque according to the pressure signal, so that the second motor is in a power generation state to recover the descent potential energy of the gantry.

[0010] Furthermore, if the condition is determined to be a non-gantry working condition, the second motor is kept off and the first motor is controlled to idle, providing a high-pressure oil source for gantry tilting operations or vehicle operation.

[0011] Furthermore, it also includes: real-time monitoring of seat pressure sensor signals; if a person is detected leaving the seat, the electromagnetic reversing valve is closed and the operation of the first and second motors is stopped, thus blocking the mast descent oil circuit.

[0012] Furthermore, after receiving the lifting displacement signal, the vehicle controller sets a delay control for the opening process of the electromagnetic reversing valve to prevent the mast from descending unexpectedly due to the lag in pressure build-up under heavy load conditions.

[0013] Compared with the prior art, the beneficial effects of this application are: The electro-hydraulic control system of this application does not generate additional energy loss of the solenoid valve assembly during the lifting operation; during the lowering operation, the opening degree of the solenoid directional valve is controlled according to the signal value of the displacement sensor. Regardless of whether the forklift is in an unloaded or fully loaded lowering state, the solenoid valve assembly can accurately control the speed of the mast lowering, thereby improving the forklift's handling performance.

[0014] The forklift electro-hydraulic control system of this application controls the second motor to output reverse torque during descent, achieving precise and controllable recovery of descent potential energy. Simultaneously, it reduces energy loss caused by high-pressure oil flowing directly back to the hydraulic tank, lowers the oil temperature of the hydraulic system, and ensures the reliability and service life of hydraulic components. Attached Figure Description

[0015] Figure 1 This is a hydraulic schematic diagram of the forklift electro-hydraulic control system of this application; Figure 2 This is a hydraulic schematic diagram of the multi-way valve assembly of this application; Figure 3 This is a hydraulic schematic diagram of the solenoid valve assembly of this application; In the picture: 1. First motor; 2. First suction filter; 3. First hydraulic pump; 4. Second suction filter; 5. Second hydraulic pump; 6. Second motor; 7. Return filter; 8. Solenoid valve assembly; 81. Solenoid directional valve; 82. Pressure sensor; 83. Pressure compensator; 9. Multi-way valve assembly; 91. Main relief valve; 92. First check valve; 93. Displacement sensor; 94. Lifting valve plate; 95. Ball valve; 96. Second check valve; 97. Tilting valve plate; 10. Tilting cylinder; 11. Lifting cylinder; 12. Explosion-proof valve; 13. Hydraulic oil tank; 110. Oil circuit I; 120. Oil circuit II; 130. Oil circuit III; 140. Oil circuit IV; 150. Oil circuit V; 160. Oil circuit VI; 170. Oil circuit VII; 180. Oil circuit VIII. Detailed Implementation

[0016] To facilitate understanding of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] refer to Figures 1 to 2 As shown, this application provides a forklift electro-hydraulic control system, including a first motor 1, a first hydraulic pump 3, a second hydraulic pump 5, a second motor 6, a solenoid valve group 8, a multi-way valve group 9, a tilting cylinder 10, a lifting cylinder 11, and a hydraulic oil tank 13. Among them, the second hydraulic pump 5 is a bidirectional hydraulic pump, and the multi-way valve group 9 includes a lifting valve plate 94 and an tilting valve plate 97. The lifting valve plate 94 is connected to the lifting cylinder 11. One end of the first hydraulic pump 3 is connected to the hydraulic oil tank 13, and the other end is connected to the lifting valve plate 94. One end of the second hydraulic pump 5 is connected to the hydraulic oil tank 13, and the other end is connected to the lifting valve plate 94 via the solenoid valve group 8. During the gantry lifting operation, the hydraulic oil output by the first hydraulic pump 3 and the second hydraulic pump 5 is collected in the right working position of the lifting valve plate 94 and provides a high-pressure oil source for the lifting cylinder 11. During the gantry descent, the high-pressure oil generated by the potential energy of the heavy object enters the left working position of the lifting valve plate 94 through the A1 port of the multi-way valve group 9, and flows back to the hydraulic oil tank 13 through the solenoid valve group 8 and the second hydraulic pump 5.

[0018] In some embodiments, the lifting valve plate 94 is a three-position five-way directional valve, and the lifting valve plate 94 is equipped with a displacement sensor 93 for detecting the displacement of the valve core; the displacement signal value of the displacement sensor 93 reflects the driver's demand for the mast lifting speed, i.e., the hydraulic system flow rate. The vehicle controller controls the speed of the first motor 1 and the second motor 6 according to the displacement signal value of the displacement sensor 93, so as to achieve precise control of the mast lifting and lowering speed.

[0019] refer to Figure 3 As shown, in some embodiments, the solenoid valve assembly 8 includes a solenoid directional valve 81 and a pressure compensator 83. The solenoid directional valve 81 is a two-position two-way directional valve. The V1 port of the solenoid directional valve 81 is connected to the left end of the pressure compensator 83, and the V2 port is connected to the right end of the pressure compensator 83.

[0020] During the mast lifting operation, the vehicle controller fully opens the solenoid directional valve 81. Because the high-pressure oil source flowing through the solenoid directional valve 81 generates a certain pressure loss, the pressure at port V2 of the solenoid directional valve 81 is higher than the pressure at port V1. That is, the pressure feedback value of oil circuit VII170 is lower than the signal feedback value of oil circuit VIII180 during mast lifting. Since the pressure compensator 83, i.e., the constant pressure differential valve core, has a spring at its right end to maintain a constant pressure difference between ports V1 and V2 of the solenoid directional valve 81 during mast descent, the force at the left end of the pressure compensator 83 valve core is less than the force at the right end. At this time, the pressure compensator 83 valve core is in the right working position, maintaining a fully open valve port to avoid energy loss caused by the lower valve core throttling during lifting.

[0021] During the mast descent, the lifting valve plate 94 is in the left-hand position. High-pressure oil generated by the gravitational potential energy of the mast flows through the multi-way valve assembly 9 to oil line V150, and then enters the solenoid valve assembly 8 through port C1. The vehicle controller controls the opening of the solenoid directional valve 81 based on the signal value from the displacement sensor 93, thereby controlling the descent speed. Simultaneously, the pressure compensator 83's valve core experiences forces that tend towards equilibrium on both sides, thus maintaining a fixed pressure difference between the inlet and outlet ports V1 and V2 of the solenoid directional valve 81.

[0022] Specifically, the high-pressure oil source generated by gravitational potential energy flows through oil circuit VI160 to the left-position function of the lifting valve plate 94, then to oil circuit V150, and enters the solenoid valve group 8 through port C1. At this time, the vehicle controller outputs a corresponding current to adjust the throttle opening of the solenoid directional valve 81. The pressure compensator 83 provides feedback on the pressure values ​​of ports V1 and V2 of the solenoid directional valve 81 through oil circuits VII170 and VIII180. To maintain the forces at both ends of the pressure compensator 83 valve core in a balanced state, the pressure at the left end of the pressure compensator 83 valve core needs to be higher than the pressure at the right end by a pressure difference equal to the spring force.

[0023] According to the basic principle of hydraulic speed control technology, the greater the flow through the throttle orifice, the higher the pressure loss. Therefore, the pressure compensator 83 automatically adjusts the pressure difference between the V1 and V2 ports of the solenoid directional valve 81 by adjusting its valve opening, that is, maintaining the feedback pressure of oil circuit VII170 as always higher than the feedback pressure of oil circuit VIII180 by a valve core spring force. This ensures that the inlet and outlet pressure difference of the solenoid directional valve 81 remains constant during the descent process. This constant value is the right-end spring force of the pressure compensator 83, which is generally assumed to be a fixed value. According to the flow characteristics of the hydraulic system, when the throttle orifice pressure difference is fixed, the flow rate through the throttle orifice is directly proportional to the flow area of ​​the throttle orifice. Under other unchanged conditions, the fixed pressure difference and the flow rate through the fixed throttle orifice are unique values. The opening degree of the solenoid directional valve 81 is controlled according to the signal value of the displacement sensor 93. Regardless of whether the forklift is descending under no-load or full-load conditions, the solenoid valve group 8 can precisely control the speed of mast descent. Compared to traditional forklift hydraulic systems, this solution eliminates the need for a speed limiting valve to limit the maximum descent speed of the mast and improves the forklift's maneuverability.

[0024] In some embodiments, a pressure sensor 82 is connected to port C1 of the solenoid valve assembly 8. The pressure sensor 82 detects the pressure signal at port C1 and feeds it back to the vehicle controller. The second motor 6 is an electric generator. During the mast descent, the vehicle controller controls the second motor 6 of the second hydraulic pump 5 to output a reverse torque corresponding to the pressure value, thus putting the second motor 6 into a generator state. Simultaneously, the generator power varies with the feedback signal value from the pressure sensor 82. Whether the forklift is unloaded or heavily loaded, precise and controllable recovery of descent potential energy can be achieved. This solution significantly reduces energy loss caused by the direct return of high-pressure oil to the hydraulic tank 13, lowers the oil temperature of the hydraulic system, and ensures the reliability and service life of hydraulic components.

[0025] In some embodiments, when the vehicle controller detects that a person has left the seat via the seat-in-seat pressure sensor, it controls the solenoid directional valve 81 to remain closed, cutting off the mast descent oil circuit.

[0026] To ensure operational safety, the forklift hydraulic system must strictly adhere to a mandatory safety constraint: the mast must not descend on its own when the operator leaves the seat. This is to prevent the mast from accidentally falling due to the driver's temporary absence, thus avoiding crushing injuries to surrounding personnel, goods, or equipment. Existing technologies typically integrate an OPS operator presence sensor solenoid valve within the multi-way valve, directly cutting off the descent oil circuit by detecting the seat signal. However, this method is limited by the valve body structure, and repairs are complex and costly if the solenoid valve fails. The technical solution of this invention is as follows: when the vehicle controller detects that a person has left the seat through the pressure sensor built into the seat, it closes the control solenoid directional valve 81 and stops the operation of the first motor 1 and the second motor 6, blocking the mast descent oil circuit. This eliminates the possibility of the mast descending under its own weight. Compared to traditional solutions, this invention uses a solenoid valve group 8 in conjunction with electrical program control to achieve OPS safety protection during forklift descent. Simultaneously, the multi-way valve group 9 integrates a ball valve 95. When the vehicle's electrical system malfunctions, the ball valve 95 can be manually opened to achieve emergency mast descent, further improving system redundancy and safety.

[0027] This application also provides a control method based on the above-mentioned forklift electro-hydraulic control system, including the following steps: The displacement signal of the lifting valve plate 94 valve core is monitored in real time, and the current working condition of the forklift is determined based on the displacement signal. If the condition is determined to be a mast lifting operation, the vehicle controller adjusts the speed of the first motor 1 and the second motor 6 according to the displacement signal, so that the hydraulic oil output by the first hydraulic pump 3 and the second hydraulic pump 5 merges in the lifting valve plate 94 and drives the lifting cylinder 11 to move. At the same time, it controls the solenoid directional valve 81 in the solenoid valve group 8 to be in a fully open state, so that the pressure sensor 82 is in the right working position with the throttle port fully open. If the gantry is determined to be in a descent condition, the vehicle controller controls the first motor 1 to stop rotating and outputs a command to adjust the opening of the solenoid valve group 8 according to the displacement signal. The pressure sensor 82 is used to keep the pressure difference between the inlet and outlet of the solenoid valve group 8 constant. At the same time, the pressure signal of the C1 oil port of the solenoid valve group 8 is collected, and the second motor 6 is controlled to output reverse torque according to the pressure signal, so that the second motor 6 is in the power generation state to recover the descent potential energy of the gantry.

[0028] In some embodiments, the system further includes: if a non-mast operating condition is determined, keeping the second motor 6 off and controlling the first motor 1 to idle, providing a high-pressure oil source for mast tilting operations or vehicle operation. Since the flow requirements of the tilting system or other functions are relatively low, the second motor 6 is not needed when there is no signal feedback from the displacement sensor 93. By using only the idling speed of the first motor 1 to achieve forklift tilting or other functional actions, this scheme can further reduce system energy consumption. When lifting, tilting, and other functions are not in operation, the oil generated by the first motor 1 driving the first hydraulic pump 3 at idle speed flows through pipeline I110 to the T-port of the multi-way valve group 9 and back to the hydraulic oil tank 13 via the return oil filter 7.

[0029] In some embodiments, the method further includes: real-time monitoring of seat pressure sensor signals; if a person is detected leaving the seat, closing the control solenoid reversing valve 81 and stopping the operation of the first motor 1 and the second motor 6, thereby blocking the mast descent oil circuit.

[0030] In some embodiments, after receiving the lifting displacement signal, the vehicle controller sets a delay control for the opening process of the electromagnetic reversing valve 81 to prevent the mast from falling unexpectedly due to the pressure build-up lag under heavy load conditions; in addition, the multi-way valve group 9 adds a one-way valve 92 in the oil circuit IV140, which is also used to realize the above-mentioned anti-fall protection function.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the appended claims and their equivalents.

Claims

1. A forklift electro-hydraulic control system, characterized in that, It includes a first motor (1), a first hydraulic pump (3), a second hydraulic pump (5), a second motor (6), a solenoid valve group (8), a multi-way valve group (9), a tilting cylinder (10), a lifting cylinder (11), and a hydraulic oil tank (13). Among them, the second hydraulic pump (5) is a bidirectional hydraulic pump, and the multi-way valve group (9) includes a lifting valve plate (94) and a tilting valve plate (97). The lifting valve plate (94) is connected to the lifting cylinder (11). One end of the first hydraulic pump (3) is connected to the hydraulic oil tank (13), and the other end is connected to the lifting valve plate (94). One end of the second hydraulic pump (5) is connected to the hydraulic oil tank (13), and the other end is connected to the lifting valve plate (94) via the solenoid valve group (8). In the gantry lifting condition, the hydraulic oil output by the first hydraulic pump (3) and the second hydraulic pump (5) is collected at the right working position of the lifting valve plate (94) and provides a high-pressure oil source for the lifting cylinder (11); During the gantry descent, the high-pressure oil generated by the potential energy of the heavy object enters the left working position of the lifting valve plate (94) through the A1 port of the multi-way valve group (9), and flows back to the hydraulic oil tank (13) through the solenoid valve group (8) and the second hydraulic pump (5).

2. The forklift electro-hydraulic control system according to claim 1, characterized in that, The lifting valve plate (94) adopts a three-position five-way reversing valve, and the lifting valve plate (94) is equipped with a displacement sensor (93) for detecting the displacement of the valve core; the vehicle controller controls the speed of the first motor (1) and the second motor (6) according to the signal value of the displacement sensor (93) to achieve precise control of the lifting and lowering speed of the mast.

3. The forklift electro-hydraulic control system according to claim 2, characterized in that, The solenoid valve assembly (8) includes a solenoid directional valve (81) and a pressure compensator (83). The V1 port of the solenoid directional valve (81) is connected to the left end of the pressure compensator (83), and the V2 port is connected to the right end of the pressure compensator (83).

4. The forklift electro-hydraulic control system according to claim 3, characterized in that, When the gantry is lifted, the vehicle controller controls the electromagnetic reversing valve (81) to open completely. At this time, the valve core of the pressure compensator (83) is in the right working position and the throttle port is fully open. During the gantry descent, the vehicle controller controls the opening of the electromagnetic directional valve (81) based on the signal value of the displacement sensor (93) to control the descent speed. At the same time, the valve core of the pressure compensator 83 is subjected to forces at both ends to balance, thereby maintaining the pressure difference between the inlet and outlet ports V1 and V2 of the electromagnetic directional valve 81 at a fixed value.

5. The forklift electro-hydraulic control system according to claim 3, characterized in that, The C1 port of the solenoid valve group (8) is connected to a pressure sensor (82). The pressure sensor (82) is used to detect the pressure signal of the C1 port and feed it back to the vehicle controller. The second motor (6) is an electric generator. When the mast is lowered, the vehicle controller controls the second motor (6) of the second hydraulic pump (5) to output the reverse torque at the corresponding pressure value, so that the second motor (6) is in the generator state.

6. The forklift electro-hydraulic control system according to claim 3, characterized in that, When the vehicle controller detects that a person has left the seat via the seat-integrated pressure sensor, it controls the solenoid directional valve (81) to remain closed, cutting off the mast descent oil circuit.

7. A control method based on the electro-hydraulic control system of a forklift according to any one of claims 1 to 6, characterized in that, Includes the following steps: The displacement signal of the valve core of the lifting valve plate (94) is monitored in real time, and the current working condition of the forklift is determined based on the displacement signal. If the condition is determined to be a mast lifting condition, the vehicle controller adjusts the speed of the first motor (1) and the second motor (6) according to the displacement signal, so that the hydraulic oil output by the first hydraulic pump (3) and the second hydraulic pump (5) merges in the lifting valve plate (94) and drives the lifting cylinder (11) to move. At the same time, the electromagnetic reversing valve (81) in the electromagnetic valve group (8) is controlled to be in a fully open state, so that the pressure sensor (82) is in the right working position with the throttle port fully open. If the gantry is determined to be in a descent condition, the vehicle controller controls the first motor (1) to stop rotating and adjusts the opening of the solenoid valve group (8) according to the displacement signal output command. The pressure sensor (82) is used to keep the pressure difference between the inlet and outlet of the solenoid valve group (8) constant. At the same time, the pressure signal of the C1 port of the solenoid valve group (8) is collected, and the second motor (6) is controlled to output reverse torque according to the pressure signal, so that the second motor (6) is in the power generation state to recover the descent potential energy of the gantry.

8. The forklift electro-hydraulic control method according to claim 7, characterized in that, If it is determined to be a non-gantry working condition, the second motor (6) is kept off and the first motor (1) is controlled to be in an idling state to provide a high-pressure oil source for gantry tilting operation or vehicle operation.

9. The forklift electro-hydraulic control method according to claim 7, characterized in that, Also includes: The seat pressure sensor signal is monitored in real time. If a person leaves the seat, the electromagnetic reversing valve (81) is closed and the first motor (1) and the second motor (6) are stopped, blocking the mast descent oil circuit.

10. The forklift electro-hydraulic control method according to claim 8, characterized in that, After receiving the lifting displacement signal, the vehicle controller sets a delay control for the opening process of the electromagnetic reversing valve 81 to prevent the mast from descending unexpectedly due to the lag in pressure build-up under heavy load conditions.

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