A forklift pressure closed-loop control method and a control system using the same

Abstract

The present invention discloses a forklift pressure closed-loop control method and a control system using the same. A bypass return oil circuit is added to a three-piece type multi-way valve. A pressure sensor is connected at a position close to the oil outlet of the bypass return oil circuit on the bypass return oil pipe. A PI regulator is integrated in the forklift controller. The pressure sensor is used to collect the pressure data of the hydraulic oil in the bypass return oil pipe and transmit it to the PI regulator. The PI regulator outputs the control flow rate of the hydraulic oil. The forklift controller performs flow rate limiting on the control flow rate of the hydraulic oil. Then, according to the control flow rate of the hydraulic oil output after flow rate limiting, the rotational speed of the motor is controlled so that the gear pump outputs according to the control flow rate of the hydraulic oil output after flow rate limiting. This way of changing the flow rate output in real time according to the pressure data feedback reduces the flow rate and pressure loss leaked in the bypass return oil circuit, forms a closed-loop control of the oil circuit pressure, improves the working efficiency, achieves the energy-saving effect, and makes the working energy consumption of the forklift lower.

Description

Technical Field

[0001] The present invention relates to a forklift control technology, and particularly to a forklift pressure closed-loop control method and a control system using the same. Background Art

[0002] In recent years, as the country's requirements for energy conservation and emission reduction have become increasingly high, and it has promised to reach the peak carbon dioxide emissions before 2030 and achieve carbon neutrality before 2060, this will inevitably pose challenges to the existing working energy consumption of forklifts. To better achieve the dual-carbon goal, it is necessary to develop a more energy-efficient control system based on the existing working energy consumption of forklifts.

[0003] The existing forklift pressure control oil circuit includes a lifting cylinder, a tilt cylinder, a steering cylinder, a multi-way valve, a steering gear, a pump and a motor, a fuel tank, and connecting pipelines. The lifting cylinder is used to lift heavy objects by the forklift, the tilt cylinder is used to tilt heavy objects forward and backward by the forklift, the steering cylinder is used to steer the whole forklift, the multi-way valve is the core of the oil circuit control of the whole vehicle, and it distributes the flow rate to the lifting cylinder, the tilt cylinder, the steering cylinder, and the steering gear. The steering gear is connected to the steering wheel and provides hydraulic power for the whole vehicle to steer. This kind of forklift pressure control oil circuit has large flow losses and large pressure losses, resulting in still large working energy consumption of the forklift. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a forklift pressure closed-loop control method and a control system using the same, which can effectively reduce the flow loss and pressure loss, thereby reducing the working energy consumption of the forklift.

[0005] The technical solution adopted by the present invention to solve the above technical problem is as follows: a forklift pressure closed-loop control method, characterized by including the following steps:

[0006] Step 1: On the basis of the forklift pressure control oil circuit, add a bypass return oil circuit in the three-piece multi-way valve, and connect the inlet of the bypass return oil circuit to the outlet of the straight-through oil circuit that connects the first body, the second body, and the third body in the three-piece multi-way valve. The main return oil circuit in the three-piece multi-way valve is not connected to the outlet of the straight-through oil circuit that connects the first body, the second body, and the third body in the three-piece multi-way valve. The outlet of the bypass return oil circuit is connected to the fuel tank through a bypass return oil pipeline; then connect a pressure sensor near the outlet of the bypass return oil circuit on the bypass return oil pipeline, and connect the output end of the pressure sensor to the forklift controller; and then integrate a PI regulator in the forklift controller;

[0007] Step 2: When the forklift is working, the pressure sensor continuously collects the pressure of the hydraulic oil in the bypass return oil pipeline and transmits it to the PI regulator in the forklift controller;

[0008] Step 3: After the PI regulator receives the feedback pressure from the pressure sensor, it calculates the pressure difference between the given pressure and the feedback pressure, and then obtains the hydraulic oil control flow by linearly combining the proportion and integral of the pressure difference.

[0009] Step 4: The forklift controller performs flow limiting on the hydraulic oil control flow output by the PI regulator. If the hydraulic oil control flow output by the PI regulator is greater than the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow upper limit; if the hydraulic oil control flow output by the PI regulator is less than the set flow lower limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow lower limit; if the hydraulic oil control flow output by the PI regulator is greater than or equal to the set flow lower limit and less than or equal to the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the hydraulic oil control flow output by the PI regulator.

[0010] Step 5: The forklift controller controls the motor speed according to the hydraulic oil control flow output after flow limiting, so that the gear pump outputs according to the hydraulic oil control flow output after flow limiting.

[0011] In the said Step 3, the range of the given pressure is 2 - 5 kg / cm 2 。

[0012] In the said Step 3, the pressure difference is the given pressure minus the feedback pressure.

[0013] In the said Step 3, the hydraulic oil control flow obtained by linearly combining the proportion and integral of the pressure difference is denoted as u(t), where K p represents the proportional coefficient, T i represents the integral time, e(t) represents the pressure difference, and t represents the time variable.

[0014] In the said Step 4, the set flow lower limit is the hydraulic oil flow output by the gear pump when the motor speed is 200 rpm; when the forklift needs to lift, the set flow upper limit is the hydraulic oil flow output by the gear pump when the motor speed is 2500 rpm, when the forklift needs to tilt, the set flow upper limit is the hydraulic oil flow output by the gear pump when the motor speed is 1000 rpm, and when the forklift needs to turn, the set flow upper limit is the hydraulic oil flow output by the gear pump when the motor speed is 800 rpm. These data are obtained through a large number of experiments.

[0015] A control system using the above forklift pressure closed-loop control method, comprising a lifting oil circuit for lifting heavy objects by the forklift, a tilting oil circuit for tilting the heavy objects by the forklift in the forward and backward directions, a steering oil circuit for steering the whole forklift, a gear pump, a motor, a fuel tank, a forklift controller, and a three-piece multi-way valve for distributing the hydraulic oil flow to the lifting oil circuit, the tilting oil circuit, and the steering oil circuit. The three-piece multi-way valve has a first body, a second body, and a third body. A main return oil circuit is provided in the three-piece multi-way valve. It is characterized in that a bypass return oil circuit is additionally provided in the three-piece multi-way valve. The oil inlet of the bypass return oil circuit is connected to the oil outlet of a straight-through oil circuit that sequentially communicates with the first body, the second body, and the third body. The oil outlet of the bypass return oil circuit is connected to the fuel tank through a bypass return oil pipe. The main return oil circuit is not connected to the oil outlet of the straight-through oil circuit that sequentially communicates with the first body, the second body, and the third body. The oil outlet of the main return oil circuit is connected to the fuel tank through a main return oil pipe. A pressure sensor is connected to the bypass return oil pipe near the oil outlet of the bypass return oil circuit. The output end of the pressure sensor is connected to the forklift controller. A PI regulator is integrated in the forklift controller. The main return oil circuit controls the valve port of the third body to be in an open state or a closed state through the forklift controller. The bypass return oil circuit is in a normally open state.

[0016] The pressure sensor continuously collects the pressure of the hydraulic oil in the bypass return oil pipe and transmits it to the PI regulator. After receiving the feedback pressure fed back by the pressure sensor, the PI regulator calculates the pressure difference between the given pressure and the feedback pressure, and then linearly combines the proportion and integral of the pressure difference to obtain the hydraulic oil control flow. The forklift controller performs flow limiting on the hydraulic oil control flow output by the PI regulator. If the hydraulic oil control flow output by the PI regulator is greater than the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow upper limit; if the hydraulic oil control flow output by the PI regulator is less than the set flow lower limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow lower limit; if the hydraulic oil control flow output by the PI regulator is greater than or equal to the set flow lower limit and less than or equal to the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the hydraulic oil control flow output by the PI regulator. The forklift controller controls the rotation speed of the motor according to the hydraulic oil control flow output after flow limiting so that the gear pump outputs according to the hydraulic oil control flow output after flow limiting. Among them, the range of the given pressure is 2-5 kg / cm 2, the pressure difference is the given pressure minus the feedback pressure. The set lower flow limit is the hydraulic oil flow output by the gear pump when the motor speed is 200 rpm. When the forklift needs to lift, the set upper flow limit is the hydraulic oil flow output by the gear pump when the motor speed is 2500 rpm. When the forklift needs to tilt, the set upper flow limit is the hydraulic oil flow output by the gear pump when the motor speed is 1000 rpm. When the forklift needs to steer, the set upper flow limit is the hydraulic oil flow output by the gear pump when the motor speed is 800 rpm.

[0017] The lifting oil circuit consists of a lifting cylinder and a speed-limiting valve. The tilting oil circuit consists of a tilting cylinder. The steering oil circuit consists of a steering cylinder and a steering gear for providing hydraulic power for the vehicle to steer. The lifting cylinder is connected to the speed-limiting valve through a connecting oil pipe. The speed-limiting valve is connected to the second sheet through a connecting oil pipe. The tilting cylinder is connected to the third sheet through a connecting oil pipe. The steering cylinder is connected to the steering gear through a connecting oil pipe. The steering gear is connected to the first sheet through a connecting oil pipe. The first sheet, the second sheet, and the third sheet are respectively connected to the main return oil circuit. The gear pump is respectively connected to the first sheet and the fuel tank through a connecting oil circuit. The steering gear is connected to the steering wheel of the forklift. The motor is connected to the gear pump. The three-piece multi-way valve and the motor are respectively connected to the forklift controller.

[0018] The first sheet is a priority valve for preferentially supplying hydraulic oil to the steering oil circuit and supplying hydraulic oil to the three oil circuits simultaneously when the lifting oil circuit, the tilting oil circuit, and the steering oil circuit work simultaneously.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] 1) A bypass return oil circuit is added to the three-piece multi-way valve. A pressure sensor is connected near the oil outlet of the bypass return oil pipe of the bypass return oil circuit. A PI regulator is integrated in the forklift controller. The pressure sensor collects the pressure data of the hydraulic oil in the bypass return oil pipe and transmits it to the PI regulator. The PI regulator outputs the control flow of the hydraulic oil. The forklift controller performs flow limiting on the control flow of the hydraulic oil. Then, according to the control flow of the hydraulic oil output after flow limiting, the motor speed is controlled so that the gear pump outputs according to the control flow of the hydraulic oil output after flow limiting. This way of changing the flow output in real time according to the pressure data feedback reduces the flow and pressure loss leaked in the bypass return oil circuit, forms a closed-loop control of the oil circuit pressure, improves the work efficiency, achieves the energy-saving effect, and makes the working energy consumption of the forklift lower.

[0021] 2) Add a bypass oil return circuit to the three-piece multi-way valve, that is, use a three-piece multi-way valve with a main oil return circuit and a bypass oil return circuit to replace the traditional three-piece multi-way valve with only a main oil return circuit. Install a pressure sensor near the oil outlet of the bypass oil return circuit to check the pressure of the working oil circuit of the multi-way forklift. The multi-way oil circuit finally discovers flow and pressure losses in the bypass oil return circuit.

[0022] 3) According to the pressure data fed back by the pressure sensor, the forklift controller controls the output flow of the gear pump. When the forklift is idling and there is no action, it can automatically reduce the output flow to achieve a closed-loop effect of pressure balance, effectively reducing energy consumption.

[0023] 4) When the forklift is operating slowly and just starting up, the opening degree of the oil outlet valve of the three-piece multi-way valve is small, but the output flow is large. Using the traditional forklift pressure control oil circuit will cause a large amount of flow to directly return to the fuel tank through the main oil return circuit, resulting in large flow losses and high energy consumption losses. When using the present invention, when the opening degree of the oil outlet valve of the three-piece multi-way valve is small, the working oil circuit outputs pressure data through the pressure sensor installed near the oil outlet of the bypass oil return circuit. The forklift controller controls the motor and the gear pump to adjust the output flow to achieve oil circuit pressure balance, with very small flow losses.

[0024] 5) When the forklift is operating slowly and just starting up, the opening degree of the oil outlet valve of the three-piece multi-way valve is small, but the output flow is large. Using the traditional forklift pressure control oil circuit will cause a large amount of flow to directly return to the fuel tank through the main oil return circuit, resulting in large flow losses, low system pressure, no response or an unclear response during slow operation. Only by increasing the opening degree of the oil outlet valve of the three-piece multi-way valve, reducing the flow in the main oil return circuit, and increasing the flow in the working oil circuit can slow operation be achieved. In fact, this often results in unclear slow operation or directly rapid action without slow operation. When using the present invention, the bypass oil return circuit itself can pass through much less flow than the main oil return circuit. With the output flow unchanged, more flow can flow into the working oil circuit, truly realizing slow operation with high operation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the hydraulic schematic diagram of the forklift pressure closed-loop control system of the present invention;

[0026] Figure 2 is Figure 1 a partial schematic diagram;

[0027] Figure 3 is the schematic diagram of the main part implementation process of the forklift pressure closed-loop control method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be further described in detail below in conjunction with the embodiments of the drawings.

[0029] Embodiment 1:

[0030] A forklift pressure closed-loop control method proposed in this embodiment is as follows Figure 1 and Figure 3 shown, and it includes the following steps:

[0031] Step 1: Based on the forklift pressure control oil circuit, add a bypass return oil circuit R1 in the three-piece multi-way valve A, and connect the inlet of the bypass return oil circuit R1 to the outlet of the straight-through oil circuit connecting the first body A1, the second body A2, and the third body A3 in the three-piece multi-way valve A. The main return oil circuit R2 in the three-piece multi-way valve A is not connected to the outlet of the straight-through oil circuit connecting the first body A1, the second body A2, and the third body A3 in the three-piece multi-way valve A. The outlet of the bypass return oil circuit R1 is connected to the fuel tank F through the bypass return oil pipe R3; then connect a pressure sensor PT near the outlet of the bypass return oil circuit R1 on the bypass return oil pipe R3, and connect the output end of the pressure sensor PT to a forklift controller (not shown in the figure); then integrate a PI (proportional integral controller) regulator RE in the forklift controller.

[0032] The PI regulator RE is a linear controller. It forms a control deviation based on the given value and the actual output value, and forms a control quantity by linearly combining the proportion and integral of the control deviation to control the controlled object.

[0033] Step 2: When the forklift is working, the pressure sensor PT is used to collect the pressure of the hydraulic oil in the bypass return oil pipe R3 in real time and transmit it to the PI regulator RE in the forklift controller.

[0034] Step 3: After the PI regulator RE receives the feedback pressure fed back by the pressure sensor PT, calculate the pressure difference between the given pressure and the feedback pressure, and then obtain the hydraulic oil control flow by linearly combining the proportion and integral of the pressure difference.

[0035] In this embodiment, in step 3, the given pressure is the pressure allowed to be generated in the bypass return oil pipe R3. To reduce flow leakage, the range of the given pressure is set to 2 - 5 kg / cm 2 , for example, the given pressure is set to 3 kg / cm 2 ; the pressure difference is the given pressure minus the feedback pressure.

[0036] In this embodiment, in step 3, the hydraulic oil control flow obtained by linearly combining the proportion and integral of the pressure difference is denoted as u(t), where K p represents the proportionality coefficient, T i represents the integral time, e(t) represents the pressure difference, and t represents the time variable.

[0037] Step 4: The forklift controller performs flow limiting on the hydraulic oil control flow output by the PI regulator RE. If the hydraulic oil control flow output by the PI regulator RE is greater than the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow upper limit; if the hydraulic oil control flow output by the PI regulator RE is less than the set flow lower limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow lower limit; if the hydraulic oil control flow output by the PI regulator RE is greater than or equal to the set flow lower limit and less than or equal to the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the hydraulic oil control flow output by the PI regulator RE.

[0038] In this embodiment, in Step 4, the set flow lower limit is the hydraulic oil flow output by the gear pump B when the rotational speed of the motor C is 200 rpm; the set flow upper limit when the forklift needs to lift is the hydraulic oil flow output by the gear pump B when the rotational speed of the motor C is 2500 rpm, the set flow upper limit when the forklift needs to tilt is the hydraulic oil flow output by the gear pump B when the rotational speed of the motor C is 1000 rpm, and the set flow upper limit when the forklift needs to turn is the hydraulic oil flow output by the gear pump B when the rotational speed of the motor C is 800 rpm.

[0039] Step 5: The forklift controller controls the rotational speed of the motor C according to the hydraulic oil control flow output after flow limiting, so that the gear pump B outputs according to the hydraulic oil control flow output after flow limiting.

[0040] As described above, the given pressure and flow limiting are controlled by the IO responsible for the forklift operation.

[0041] Embodiment 2:

[0042] This embodiment proposes a control system using the forklift pressure closed-loop control method of Embodiment 1, as Figure 1 and Figure 2As shown in the figure, it includes a lifting oil circuit 1 for realizing the lifting of heavy objects by a forklift, a tilting oil circuit 2 for realizing the forward and backward tilting of heavy objects by the forklift, a steering oil circuit 3 for realizing the steering of the whole forklift, a gear pump B, a motor C, a fuel tank F, a forklift controller, and a three-piece multi-way valve A for distributing the hydraulic oil flow to the lifting oil circuit 1, the tilting oil circuit 2, and the steering oil circuit 3. The three-piece multi-way valve A has a first body A1, a second body A2, and a third body A3. A main return oil circuit R2 is provided in the three-piece multi-way valve A, and a bypass return oil circuit R1 is additionally provided in the three-piece multi-way valve A. The oil inlet of the bypass return oil circuit R1 is connected to the oil outlet of the straight-through oil circuit that sequentially communicates with the first body A1, the second body A2, and the third body A3. The oil outlet of the bypass return oil circuit R1 is connected to the fuel tank F through a bypass return oil pipe R3. The main return oil circuit R2 is not connected to the oil outlet of the straight-through oil circuit that sequentially communicates with the first body A1, the second body A2, and the third body A3. The oil outlet of the main return oil circuit R2 is connected to the fuel tank F through a main return oil pipe R4. That is, the main return oil circuit R2 and the bypass return oil circuit R1 are in a parallel state. A pressure sensor PT is connected near the oil outlet of the bypass return oil circuit R1 on the bypass return oil pipe R3. The output end of the pressure sensor PT is connected to the forklift controller. A PI regulator RE is integrated in the forklift controller. The main return oil circuit R2 controls the valve port of the third body A3 to be in an open state or a closed state through the forklift controller. The bypass return oil circuit R1 is in a normally open state and has a very small flow rate. The flow rate of the main return oil circuit R2 is much larger than that of the bypass return oil circuit R1.

[0043] As Figure 3 shown, the pressure sensor PT continuously collects the pressure of the hydraulic oil in the bypass return oil pipe R3 and transmits it to the PI regulator RE. After receiving the feedback pressure fed back by the pressure sensor PT, the PI regulator RE calculates the pressure difference between the given pressure and the feedback pressure, and then linearly combines the proportion and integral of the pressure difference to obtain the hydraulic oil control flow rate. The forklift controller performs flow rate limiting on the hydraulic oil control flow rate output by the PI regulator RE. If the hydraulic oil control flow rate output by the PI regulator RE is greater than the set flow rate upper limit, the hydraulic oil control flow rate output after flow rate limiting is made equal to the set flow rate upper limit; if the hydraulic oil control flow rate output by the PI regulator RE is less than the set flow rate lower limit, the hydraulic oil control flow rate output after flow rate limiting is made equal to the set flow rate lower limit; if the hydraulic oil control flow rate output by the PI regulator RE is greater than or equal to the set flow rate lower limit and less than or equal to the set flow rate upper limit, the hydraulic oil control flow rate output after flow rate limiting is made equal to the hydraulic oil control flow rate output by the PI regulator RE; the forklift controller controls the speed of the motor C according to the hydraulic oil control flow rate output after flow rate limiting so that the gear pump B outputs according to the hydraulic oil control flow rate output after flow rate limiting; wherein, the range of the given pressure is 2-5 kg / cm 2, the pressure difference is the given pressure minus the feedback pressure. The set lower flow limit is the hydraulic oil flow output by gear pump B when the rotational speed of motor C is 200 rpm. When the forklift needs to lift, the set upper flow limit is the hydraulic oil flow output by gear pump B when the rotational speed of motor C is 2500 rpm. When the forklift needs to tilt, the set upper flow limit is the hydraulic oil flow output by gear pump B when the rotational speed of motor C is 1000 rpm. When the forklift needs to steer, the set upper flow limit is the hydraulic oil flow output by gear pump B when the rotational speed of motor C is 800 rpm.

[0044] In this embodiment, the lifting oil circuit 1 is composed of a lifting cylinder E1 and a speed limiting valve D. The tilting oil circuit 2 is composed of a tilting cylinder E2. The steering oil circuit 3 is composed of a steering cylinder E3 and a steering gear G for providing hydraulic power for the vehicle to steer. The lifting cylinder E1 is connected to the speed limiting valve D through a connecting oil pipe. The speed limiting valve D is connected to the second plate A2 through a connecting oil pipe. The tilting cylinder E2 is connected to the third plate A3 through a connecting oil pipe. The steering cylinder E3 is connected to the steering gear G through a connecting oil pipe. The steering gear G is connected to the first plate A1 through a connecting oil pipe. The first plate A1, the second plate A2, and the third plate A3 are respectively connected to the main return oil circuit R2. The gear pump B is respectively connected to the first plate A1 and the fuel tank F through a connecting oil circuit. The steering gear G is connected to the steering wheel of the forklift (not shown in the figure). The motor C is connected to the gear pump B. The three-piece multi-way valve A and the motor C are respectively connected to the forklift controller.

[0045] In this embodiment, the first plate A1 is a priority valve for preferentially supplying hydraulic oil to the steering oil circuit 3 and supplying hydraulic oil to the three oil circuits simultaneously when the lifting oil circuit 1, the tilting oil circuit 2, and the steering oil circuit 3 work simultaneously.

[0046] In the above embodiment, the motor C can be selected as a common servo AC motor; the gear pump B can be selected as a common hydraulic gear pump; the three-piece multi-way valve A is the core of the vehicle's oil circuit control, which is improved on the basis of a commercially available three-piece multi-way valve, with a bypass return oil circuit R1 added and the main return oil circuit R2 not connected to the outlet of the straight-through oil circuit; the connection between the gear pump B and the first plate A1, the connection between the first plate A1 and the steering gear G, the connection between the steering gear G and the steering cylinder E3, the connection between the second plate A2 and the speed limiting valve D, the connection between the speed limiting valve D and the lifting cylinder E1, and the connection between the third plate A3 and the tilting cylinder E2 are all connected in the connection mode of the existing forklift pressure control oil circuit.

[0047] The working principle of this forklift pressure closed-loop control system is as follows:

[0048] The forklift controller controls the motor C and the gear pump B to work, and extracts hydraulic oil from the fuel tank F into the three-piece multi-way valve A.

[0049] When the forklift starts, the lifting cylinder E1, tilt cylinder E2, steering cylinder E3, steering gear G, and three-piece multi-way valve A do not perform any actions. The forklift controller controls the motor C to start the gear pump B to pump hydraulic oil at a set speed directly through the direct oil circuit and the bypass return oil circuit R1 in the three-piece multi-way valve A back to the fuel tank F. At this time, the pressure sensor PT can detect the pressure data of the hydraulic oil in the bypass return oil pipe R3 and feedback it to the PI regulator RE. The forklift controller initially sets a relatively high starting speed (in order to improve the response speed of the system, the initial starting speed is set to 80% to 100% of the upper limit of the corresponding action speed (for example, the upper limit of the action speed when tilting is 1000 rpm)). If there is no action within the specified time of the forklift, the forklift controller reduces the working speed of the motor C and the gear pump B through the pressure data detected by the pressure sensor PT, achieving the function of reducing flow loss and energy conservation.

[0050] When the lifting cylinder E1 works, the forklift controller controls the motor C to start the gear pump B to pump hydraulic oil at a set speed through the first body A1 of the three-piece multi-way valve A into the second body A2. As the opening degree of the oil outlet valve port of the second body A2 increases to the maximum, the flow rate originally passing through the bypass return oil circuit R1 gradually decreases and stops. At this time, the pressure sensor PT can detect the pressure data of the hydraulic oil in the bypass return oil pipe R3 and feedback it to the PI regulator RE. The forklift controller controls the motor C and the gear pump B to work, responding quickly and increasing the output flow rate so that the lifting cylinder E1 can work quickly; when the lifting cylinder E1 needs to work slowly, the opening degree of the oil outlet valve port of the second body A2 is maintained in a small opening state. At this time, the pressure sensor PT can detect the pressure data of the hydraulic oil in the bypass return oil pipe R3 and feedback it to the PI regulator RE. The forklift controller controls the motor C and the gear pump B to work, responding quickly and reducing the stable flow rate, maintaining the flow rate at the balance point so that the lifting cylinder E1 can work slowly; when the lifting cylinder E1 descends, the forklift controller controls the three-piece multi-way valve A, and the hydraulic oil returns to the fuel tank F through the main return oil circuit R2 and the main return oil pipe R4 to achieve a rapid descent.

[0051] When the tilt cylinder E2 works, the forklift controller controls the motor C to start the gear pump B, and the hydraulic oil enters the third body A3 of the three-piece multi-way valve A at a set speed through the first body A1 of the three-piece multi-way valve A. As the opening degree of the oil outlet valve port of the third body A3 increases to the maximum, the flow rate through the bypass return oil circuit R1 gradually decreases and stops. At this time, the pressure sensor PT can detect the pressure data of the hydraulic oil in the bypass return oil pipe R3 and feedback it to the PI regulator RE. The forklift controller controls the motor C and the gear pump B to work, responds quickly, increases the output flow rate, and enables the tilt cylinder E2 to work quickly; when the tilt cylinder E2 needs to work slowly, the opening degree of the oil outlet valve port of the third body A3 is maintained in a small opening state. At this time, the pressure sensor PT can detect the pressure data of the hydraulic oil in the bypass return oil pipe R3 and feedback it to the PI regulator RE. The forklift controller controls the motor C and the gear pump B to work, responds quickly, reduces the stable flow rate, and maintains the flow rate at the balance point, enabling the tilt cylinder E2 to work slowly; when the tilt cylinder E2 returns oil, the forklift controller controls the three-piece multi-way valve A, and the hydraulic oil returns to the fuel tank F through the main return oil circuit R2 and the main return oil pipe R4 to achieve quick action.

[0052] When the steering gear G works, the forklift controller controls the motor C to start the gear pump B, and the hydraulic oil preferentially enters the steering gear G through the first body A1 of the three-piece multi-way valve A at a set speed, and then enters the steering cylinder E3 through the steering gear G. Because the flow rate preferentially enters the steering gear G, the flow rate through the bypass return oil circuit R1 gradually decreases and stops. At this time, the pressure sensor PT can detect the pressure data of the hydraulic oil in the bypass return oil pipe R3 and feedback it to the PI regulator RE. The forklift controller controls the motor C and the gear pump B to work, responds quickly, increases the output flow rate, and enables the steering gear G and the steering cylinder E3 to work normally.

[0053] As described above, the opening degree of the oil outlet valve port of the second body A2 can be achieved by manually controlling the operating rod on the second body A2, and the opening degree of the oil outlet valve port of the third body A3 can be achieved by manually controlling the operating rod on the third body A3; the small opening state is below 50% of the maximum opening degree.

Claims

1. A forklift pressure closed-loop control method, characterized in that it includes the following steps: Step 1: On the basis of the forklift pressure control oil circuit, add a bypass return oil circuit in the three-piece multi-way valve, and connect the oil inlet of the bypass return oil circuit to the oil outlet of the straight-through oil circuit that connects the first body, the second body, and the third body in the three-piece multi-way valve. The main return oil circuit in the three-piece multi-way valve is not connected to the oil outlet of the straight-through oil circuit that connects the first body, the second body, and the third body. The oil outlet of the bypass return oil circuit is connected to the fuel tank through a bypass return oil pipe; then connect a pressure sensor near the oil outlet of the bypass return oil circuit on the bypass return oil pipe, and connect the output end of the pressure sensor to the forklift controller; then integrate a PI regulator in the forklift controller; Step 2: When the forklift is working, the pressure sensor continuously collects the pressure of the hydraulic oil in the bypass return oil pipe and transmits it to the PI regulator in the forklift controller; Step 3: After the PI regulator receives the feedback pressure fed back by the pressure sensor, calculate the pressure difference between the given pressure and the feedback pressure, and then obtain the hydraulic oil control flow by linearly combining the proportion and integral of the pressure difference; Step 4: The forklift controller performs flow limiting on the hydraulic oil control flow output by the PI regulator. If the hydraulic oil control flow output by the PI regulator is greater than the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow upper limit; If the hydraulic oil control flow output by the PI regulator is less than the set flow lower limit, the hydraulic oil control flow output after flow limiting is made equal to the set flow lower limit; if the hydraulic oil control flow output by the PI regulator is greater than or equal to the set flow lower limit and less than or equal to the set flow upper limit, the hydraulic oil control flow output after flow limiting is made equal to the hydraulic oil control flow output by the PI regulator; Step 5: The forklift controller controls the rotation speed of the motor according to the hydraulic oil control flow output after flow limiting, so that the gear pump outputs according to the hydraulic oil control flow output after flow limiting.

2. A forklift pressure closed-loop control method according to claim 1, characterized in that In the said step 3, the range of the given pressure is 2 to 5 kg / cm 2 .

3. A forklift pressure closed-loop control method according to claim 1 or 2, characterized in that In the said step 3, the pressure difference is the given pressure minus the feedback pressure.

4. A forklift pressure closed-loop control method according to claim 1, characterized in that In the described step 3, the hydraulic oil control flow rate obtained by linearly combining the ratio and integral of the pressure difference is denoted as u(t). where K p represents the proportionality coefficient, T i represents the integral time, e(t) represents the pressure difference, and t represents the time variable.

5. A forklift pressure closed-loop control method according to claim 1, characterized in that In the said step 4, the set flow lower limit is the hydraulic oil flow output by the gear pump when the motor speed is 200 rpm; when the forklift needs to lift, the set flow upper limit is the hydraulic oil flow output by the gear pump when the motor speed is 2500 rpm, when the forklift needs to tilt, the set flow upper limit is the hydraulic oil flow output by the gear pump when the motor speed is 1000 rpm, and when the forklift needs to turn, the set flow upper limit is the hydraulic oil flow output by the gear pump when the motor speed is 800 rpm.

6. A control system using the forklift pressure closed-loop control method described in claim 1, comprising a lifting oil circuit for lifting heavy objects by the forklift, a tilting oil circuit for tilting the heavy objects forward and backward by the forklift, a steering oil circuit for steering the whole forklift, a gear pump, an electric motor, a fuel tank, a forklift controller, and a three-piece multi-way valve for distributing the hydraulic oil flow to the lifting oil circuit, the tilting oil circuit, and the steering oil circuit. The three-piece multi-way valve has a first body, a second body, and a third body. A main return oil circuit is provided in the three-piece multi-way valve. Characterized in that: A side branch return oil circuit is additionally provided in the three-piece multi-way valve. The oil inlet of the side branch return oil circuit is connected to the oil outlet of a straight-through oil circuit that sequentially communicates with the first body, the second body, and the third body. The oil outlet of the side branch return oil circuit is connected to the fuel tank through a side branch return oil pipe. The main return oil circuit is not connected to the oil outlet of the straight-through oil circuit that sequentially communicates with the first body, the second body, and the third body. The oil outlet of the main return oil circuit is connected to the fuel tank through a main return oil pipe. A pressure sensor is connected near the oil outlet of the side branch return oil circuit on the side branch return oil pipe. The output end of the pressure sensor is connected to the forklift controller. A PI regulator is integrated in the forklift controller. The main return oil circuit controls the valve port of the third body to be in an open state or a closed state through the forklift controller. The side branch return oil circuit is in a normally open state.

7. A forklift pressure closed-loop control system according to claim 6, Characterized in that: The pressure sensor collects the pressure of the hydraulic oil in the branch oil return pipe in real time and transmits it to the PI regulator. After receiving the feedback pressure fed back by the pressure sensor, the PI regulator calculates the pressure difference between the given pressure and the feedback pressure, and then obtains the control flow rate of the hydraulic oil through linear combination of the proportion and integral of the pressure difference. The forklift controller performs flow limiting on the control flow rate of the hydraulic oil output by the PI regulator. If the control flow rate of the hydraulic oil output by the PI regulator is greater than the set flow rate upper limit, the control flow rate of the hydraulic oil after flow limiting is made equal to the set flow rate upper limit; if the control flow rate of the hydraulic oil output by the PI regulator is less than the set flow rate lower limit, the control flow rate of the hydraulic oil after flow limiting is made equal to the set flow rate lower limit; if the control flow rate of the hydraulic oil output by the PI regulator is greater than or equal to the set flow rate lower limit and less than or equal to the set flow rate upper limit, the control flow rate of the hydraulic oil after flow limiting is made equal to the control flow rate of the hydraulic oil output by the PI regulator. The forklift controller controls the rotation speed of the motor according to the control flow rate of the hydraulic oil after flow limiting so that the gear pump outputs according to the control flow rate of the hydraulic oil after flow limiting. Among them, the range of the given pressure is 2 to 5 kg / cm 2 , the pressure difference is the given pressure minus the feedback pressure, and the set flow rate lower limit is the hydraulic oil flow rate output by the gear pump when the rotation speed of the motor is 200 rpm; the set flow rate upper limit when the forklift needs to lift is the hydraulic oil flow rate output by the gear pump when the rotation speed of the motor is 2500 rpm, the set flow rate upper limit when the forklift needs to tilt is the hydraulic oil flow rate output by the gear pump when the rotation speed of the motor is 1000 rpm, and the set flow rate upper limit when the forklift needs to turn is the hydraulic oil flow rate output by the gear pump when the rotation speed of the motor is 800 rpm.

8. A forklift pressure closed-loop control system according to claim 6 or 7, Characterized in that: The lifting oil circuit consists of a lifting cylinder and a speed limiting valve. The tilting oil circuit consists of a tilting cylinder. The steering oil circuit consists of a steering cylinder and a steering gear for providing hydraulic power for the whole vehicle steering. The lifting cylinder is connected to the speed limiting valve through a connecting oil pipe. The speed limiting valve is connected to the second body through a connecting oil pipe. The tilting cylinder is connected to the third body through a connecting oil pipe. The steering cylinder is connected to the steering gear through a connecting oil pipe. The steering gear is connected to the first body through a connecting oil pipe. The first body, the second body, and the third body are respectively connected to the main return oil circuit. The gear pump is respectively connected to the first body and the fuel tank through a connecting oil circuit. The steering gear is connected to the steering wheel of the forklift. The electric motor is connected to the gear pump. The three-piece multi-way valve and the electric motor are respectively connected to the forklift controller.

9. A forklift pressure closed-loop control system according to claim 8, Characterized in that: The first body is a priority valve for preferentially supplying hydraulic oil to the steering oil circuit and supplying hydraulic oil to the three oil circuits simultaneously when the lifting oil circuit, the tilting oil circuit, and the steering oil circuit work simultaneously.

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