Lithium battery heavy-duty forklift oil cylinder descending potential energy recovery hydraulic system and control method

Abstract

The application discloses a lithium battery heavy-duty forklift oil cylinder descending potential energy recovery hydraulic system and a control method, relates to the technical field of forklift oil cylinder potential energy recovery, and comprises a first speed reduction brake valve, a second speed reduction brake valve, an integrated main control valve group, a variable hydraulic motor, a generator, a pressure detection unit and a controller. The lithium battery heavy-duty forklift oil cylinder descending potential energy recovery hydraulic system and the control method directly drive the variable hydraulic motor to rotate by using high-pressure oil released during oil cylinder descending, drive the coaxial generator to generate electricity and store the electricity into a lithium battery, save the intermediate link of multiple energy form conversions in the accumulator scheme, and reduce invalid loss in the energy transmission process. Through adaptive switching of the displacement of the variable hydraulic motor and closed-loop regulation of the electromagnetic brake torque of the generator, the lithium battery heavy-duty forklift can adapt to the operation demand of heavy load and large lifting stroke without being limited by the volume and rated pressure of physical energy storage elements.

Description

Technical Field

[0001] This application belongs to the field of forklift cylinder potential energy recovery technology, and particularly relates to a hydraulic system and control method for recovering the descending potential energy of a lithium-ion heavy-duty forklift cylinder. Background Technology

[0002] With the rapid development of new energy industrial vehicle technology, lithium-ion battery-powered heavy-duty forklifts, with their core advantages of zero emissions, high torque, and low maintenance costs, have been widely used in heavy-duty operation scenarios such as port freight, heavy industrial warehousing, and large logistics stations. During the heavy-duty descent process, the mast lifting cylinder releases a large amount of gravitational potential energy. However, in existing conventional hydraulic systems, almost all of this potential energy is converted into heat dissipation through the main valve throttling orifice, resulting in significant energy waste. Therefore, cylinder descent potential energy recovery technology has become an important research and development direction for energy saving, consumption reduction, and performance improvement of lithium-ion battery-powered heavy-duty forklifts.

[0003] Currently, the mainstream potential energy recovery technology is mainly based on hydraulic accumulators, such as... Figure 6 As shown, this scheme stores the hydraulic energy released by the cylinder during descent through a hydraulic accumulator. When the forklift performs lifting or other operations, the stored hydraulic energy is released to assist in replenishing the hydraulic drive, thereby achieving the recovery and reuse of gravitational potential energy. However, this scheme has low recovery efficiency. The gravitational potential energy needs to undergo multiple energy form conversions: "hydraulic energy - accumulator internal energy - hydraulic energy". There are unavoidable energy losses in each conversion stage, and the proportion of energy that can be effectively utilized is low, resulting in limited actual energy saving effect. The energy storage capacity of the accumulator is strictly limited by its own size and rated working pressure, which cannot meet the operating requirements of heavy-duty forklifts with large loads and long lifting strokes. It is difficult to meet the requirements of large-capacity potential energy recovery under heavy-duty conditions. At the same time, the energy storage pressure of the accumulator fluctuates in real time during the charging and discharging process, which cannot provide a stable power output for the hydraulic system. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, this application provides a hydraulic system and control method for recovering the potential energy of the descent cylinder of a lithium-ion heavy-duty forklift.

[0005] This application provides a hydraulic system for recovering the potential energy of a lithium-ion battery-powered heavy-duty forklift cylinder during descent, including a first hydraulic cylinder, a second hydraulic cylinder, a first deceleration brake valve, a second deceleration brake valve, a confluence valve block, an integrated main control valve group, a variable hydraulic motor, a generator, a solenoid directional valve, a pressure detection unit, and a controller. The rodless chamber outlet of the first hydraulic cylinder is connected in series with the inlet of the first deceleration brake valve, and the rodless chamber outlet of the second hydraulic cylinder is connected in series with the inlet of the second deceleration brake valve; the outlets of the first and second deceleration brake valves are respectively connected to the corresponding inlets of the confluence valve block; the outlet of the confluence valve block is connected to the inlet of the integrated main control valve group. The integrated main control valve group internally integrates a first control valve, a second control valve, a first one-way sequence valve, a second one-way sequence valve, and an electro-proportional pilot control valve; the two oil outlets of the confluence valve block are respectively connected to the oil inlet of the first control valve and the oil inlet of the second control valve. The oil outlet of the first control valve is connected to the oil inlet of the first one-way sequence valve, and the oil outlet of the second control valve is connected to the oil inlet of the second one-way sequence valve; after the oil outlets of the first and second one-way sequence valves merge, they are connected to the oil inlet of the variable hydraulic motor; the output shaft of the variable hydraulic motor is connected to the input shaft of the generator. The oil outlet of the electro-proportional pilot control valve is connected to the external control terminals of the first control valve and the second control valve, respectively, and is used to drive the two control valves to switch from the lock-up mode to the throttling conduction mode. The variable displacement hydraulic motor has a displacement control branch connected in parallel to its oil inlet line. The displacement control branch is connected to the minimum displacement control terminal of the variable displacement hydraulic motor and the oil inlet terminal of the solenoid directional valve. The minimum displacement control terminal and the solenoid directional valve are connected in parallel. The oil outlet terminal of the solenoid directional valve is connected to the maximum displacement control terminal of the variable displacement hydraulic motor via a pilot-operated pressure relief valve. This connection is used to control the oil supply to the maximum displacement control terminal by switching the valve position on and off. The pressure detection unit is connected to the confluence valve block and the oil inlet pipe of the variable hydraulic motor, respectively, to collect the cylinder load pressure and the motor oil inlet pressure; the controller is electrically connected to the pressure detection unit, the electro-proportional pilot control valve, the solenoid directional valve and the generator, respectively, to adjust the loop flow and motor displacement in a closed loop according to the collected pressure parameters, and synchronously control the electromagnetic braking torque of the generator to realize potential energy recovery and power generation during the cylinder descent process.

[0006] Preferably, a parallel oil circuit is provided between the oil outlet of the first control valve and the oil outlet of the second control valve; a parallel oil circuit is also provided between the oil inlet of the first control valve and the oil inlet of the second control valve to balance the oil circuit pressure of the two cylinders and realize the synchronous descent of the first hydraulic cylinder and the second hydraulic cylinder.

[0007] Preferably, the oil inlet of the electro-proportional pilot control valve is connected to the system pilot pressure oil source through a pilot pressure interface, and the oil outlet of the electro-proportional pilot control valve is divided into three parallel branches. The first branch is connected to the pilot one-way valve, the second branch is connected to the external control end of the first control valve, and the third branch is connected to the external control end of the second control valve.

[0008] Preferably, a first branch check valve and a first filter are connected in series on the displacement control branch. The filtered oil is divided into three parallel branches: the first branch is directly connected to the minimum displacement control end of the variable hydraulic motor; the second branch is connected to the inlet end of the solenoid directional valve; and the third branch is connected to the return port of the variable hydraulic motor. A replenishment branch is provided on the return oil line of the variable hydraulic motor. The replenishment branch is connected to the displacement control branch after being filtered by the second branch check valve and the second filter. The outlet of the pilot-operated pressure relief valve is connected to the maximum displacement control end of the variable hydraulic motor. A branch oil line is provided on the connecting oil line between the outlet of the pilot-operated pressure relief valve and the maximum displacement control end, which is connected to the speed detection interface of the variable hydraulic motor. A first throttle valve is connected in series on the connecting oil line between the outlet of the pilot-operated pressure relief valve and the maximum displacement control end.

[0009] Preferably, the pressure detection unit includes a first pressure sensor and a second pressure sensor. The first pressure sensor is located on the confluence oil line of the first hydraulic cylinder and the second hydraulic cylinder, and is fixedly installed on the confluence valve block to collect the load pressure at the bottom of the cylinder. The second pressure sensor is fixedly installed on the oil inlet line of the variable hydraulic motor to collect the motor inlet oil pressure.

[0010] Preferably, the signal output terminals of both the first and second pressure sensors are electrically connected to the signal input terminal of the controller.

[0011] Preferably, the confluence valve block is provided with an oil supply interface, the oil supply interface oil circuit is connected to the oil inlet end of the first built-in check valve of the first deceleration brake valve, and the oil supply interface oil circuit is connected to the oil inlet end of the second built-in check valve of the second deceleration brake valve; the oil outlet end of the first built-in check valve is connected to the rodless chamber of the first hydraulic cylinder, and the oil outlet end of the second built-in check valve is connected to the rodless chamber of the second hydraulic cylinder.

[0012] Preferably, a second throttle valve is connected in series on the second branch of the electro-proportional pilot control valve; a third throttle valve is connected in series on the third branch of the electro-proportional pilot control valve; and a fourth throttle valve is connected in series on the oil line between the pilot pressure port and the oil inlet of the electro-proportional pilot control valve.

[0013] A method for controlling the recovery of potential energy during the descent of a lithium-ion battery-powered heavy-duty forklift cylinder includes the following steps: Step S1: The controller acquires the potential energy recovery descent mode selection signal from the forklift display screen and the cylinder bottom load pressure P1 collected by the pressure detection unit in real time. Step S2: When the controller determines that the potential energy recovery descent mode is not selected or the cylinder bottom load pressure P1 is less than the preset start pressure threshold P0, the system executes the normal descent procedure; when the controller determines that the potential energy recovery descent mode is selected and the cylinder bottom load pressure P1 is greater than or equal to the preset start pressure threshold P0, the potential energy recovery control procedure is started. Step S3: After starting the potential energy recovery control program, the controller collects the cylinder bottom load pressure P1 from the first pressure sensor, the motor inlet oil pressure P2 from the second pressure sensor, and the real-time variable hydraulic motor speed n collected by the speed detection interface in real time. At the same time, it acquires the target output current of the electro-proportional pilot control valve corresponding to the forklift lowering handle control signal. Step S4: The controller calculates the system target flow rate Q by combining the target output current of the electro-proportional pilot control valve; at the same time, it calculates the target operating displacement V and target output torque T of the variable hydraulic motor by combining the collected P1, P2 and real-time motor speed n. Step S5: The controller outputs a matching control signal to the solenoid directional valve. The solenoid directional valve adjusts the actual operating displacement of the variable hydraulic motor according to the control logic of its hydraulic circuit. At the same time, it outputs a control signal to the generator that matches the target output torque T, so that the generator generates the corresponding electromagnetic braking torque, drives the generator to generate electricity and stores the electrical energy in the lithium battery.

[0014] Preferably, the conventional descent procedure in step S2 specifically involves the controller energizing the electro-proportional pilot control valve solenoid to cut off the oil passage of the potential energy recovery hydraulic circuit, thus preventing the potential energy recovery power generation function from being activated. Specifically, the electromagnetic directional valve control logic in step S5 involves the controller initially controlling the electromagnetic directional valve to be in the off state, allowing hydraulic oil to enter the minimum displacement control terminal, maintaining the variable hydraulic motor in a high-efficiency power generation mode with minimum displacement and high speed. When the cylinder bottom load pressure P1 exceeds the preset heavy-load pressure threshold, the controller controls the electromagnetic directional valve to open, allowing hydraulic oil to enter the maximum displacement control terminal, switching the variable hydraulic motor to a smooth braking mode with maximum displacement and low speed.

[0015] The hydraulic system and control method for recovering the potential energy of the descending cylinder in a lithium-ion heavy-duty forklift disclosed in this application have the following advantages and positive effects: (1) The high-pressure oil released by the cylinder is lowered directly drives the variable hydraulic motor to rotate, which drives the coaxial generator to generate electricity and store it in the lithium battery. This eliminates the intermediate links of multiple energy form conversions in the energy storage scheme, reduces the ineffective loss in the energy transfer process, and realizes the maximum recovery and utilization of gravitational potential energy, effectively improving the actual energy saving effect.

[0016] (2) By adaptively switching the displacement of the variable hydraulic motor and adjusting the closed-loop regulation of the generator's electromagnetic braking torque, it is not limited by the size or rated pressure of the physical energy storage element and can adapt to the heavy load and long lifting stroke requirements of heavy forklifts: under medium and light load conditions, the minimum displacement high speed mode is adopted to maximize the power generation efficiency and energy recovery rate; under heavy load conditions, it switches to the maximum displacement low speed mode to significantly increase the motor output torque and braking resistance, and achieve smooth speed limiting of the cylinder descent under heavy load conditions. At the same time, this solution can provide stable and controllable braking resistance throughout the process, and there is no pressure fluctuation problem during the charging and discharging process of the accumulator, ensuring that the cylinder descent process is smooth throughout and the power output of the hydraulic system is stable and consistent. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of this application and constitute a part of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the hydraulic circuit of the hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift, as described in this application. Figure 2 This is a schematic diagram of the hydraulic circuit dual deceleration brake valve section of this application; Figure 3 This is a schematic diagram of the integrated main control valve assembly part of this application; Figure 4 This is a schematic diagram of the energy conversion section of the variable hydraulic motor in this application; Figure 5 This is a physical drawing of the hydraulic system of this application; Figure 6 This is a schematic diagram of a potential energy recovery scheme based on a hydraulic accumulator.

[0018] Explanation of reference numerals in the attached figures: 1-First hydraulic cylinder, 2-Second hydraulic cylinder, 3-First deceleration brake valve, 4-Second deceleration brake valve, 5-First built-in check valve, 6-Second built-in check valve, 7-First pressure sensor, 8-First control valve, 9-Second control valve, 10-First one-way sequence valve, 11-Second one-way sequence valve, 12-Electro-proportional pilot control valve, 13-Variable displacement hydraulic motor, 14-Generator, 15-First branch check valve, 16-First high-pressure filter, 17-Second branch check valve, 18-Second filter, 19-Solenoid directional valve, 20-Pilot-operated pressure relief valve, 21-Maximum displacement control terminal, 22-Minimum displacement control terminal, 23-Return port, 24-Speed ​​detection interface, 25-First throttle valve, 26-Second throttle valve, 27-Third throttle valve, 28-Fourth throttle valve, 29-Pilot pressure interface, 30-Pilot one-way valve. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0020] like Figures 1 to 4 As shown, the lithium-ion battery heavy-duty forklift hydraulic system for recovering potential energy during cylinder descent in this application includes a first hydraulic cylinder 1, a second hydraulic cylinder 2, a first deceleration brake valve 3, a second deceleration brake valve 4, a confluence valve block, an integrated main control valve group, a variable hydraulic motor 13, a generator 14, a solenoid directional valve 19, a pressure detection unit, and a controller.

[0021] Figure 5 In the middle, I is the confluence valve block, II is the deceleration brake valve integration, III is the integrated main control valve group, IV is the integration of variable hydraulic motor 13 and generator 14, and V is the return oil pipe integration.

[0022] The rodless chamber outlet of the first hydraulic cylinder 1 is connected in series with the inlet of the first deceleration brake valve 3, and the rodless chamber outlet of the second hydraulic cylinder 2 is connected in series with the inlet of the second deceleration brake valve 4; the outlets of the first deceleration brake valve 3 and the second deceleration brake valve 4 are respectively connected to the corresponding inlet of the confluence valve block; the outlet of the confluence valve block is connected to the inlet of the integrated main control valve group.

[0023] The first deceleration brake valve 3 and the second deceleration brake valve 4 are hydraulic balance valves with overspeed protection function. They have built-in check valves and overflow buffer structures. During the descent of the oil cylinder, if the descent speed exceeds the limit due to a sudden change in load, the deceleration brake valve will automatically close the valve opening to limit the return oil flow, thereby achieving overspeed protection for the descent of the oil cylinder, preventing the forks from falling and ensuring operational safety.

[0024] The first built-in check valve 5 and the second built-in check valve 6 provide independent oil inlet channels for the lifting operation of the hydraulic cylinder. During lifting, the hydraulic oil enters the rodless chamber of the hydraulic cylinder directly through the oil supply interface and the built-in check valve, without passing through the potential energy recovery circuit.

[0025] The integrated main control valve group internally integrates a first control valve 8, a second control valve 9, a first one-way sequence valve 10, a second one-way sequence valve 11, and an electro-proportional pilot control valve 12; the two oil outlets of the confluence valve block are respectively connected to the oil inlet of the first control valve 8 and the oil inlet of the second control valve 9.

[0026] The oil outlet of the first control valve 8 is connected to the oil inlet of the first one-way sequence valve 10, and the oil outlet of the second control valve 9 is connected to the oil inlet of the second one-way sequence valve 11. After the oil outlets of the first one-way sequence valve 10 and the second one-way sequence valve 11 merge, they are connected to the oil inlet of the variable hydraulic motor 13. The output shaft of the variable hydraulic motor 13 is connected to the input shaft of the generator 14.

[0027] The oil outlet of the electro-proportional pilot control valve 12 is connected to the external control terminals of the first control valve 8 and the second control valve 9, respectively, and is used to drive the two control valves to switch from the lock-up mode to the throttling conduction mode.

[0028] The oil inlet of the electro-proportional pilot control valve 12 is connected to the system pilot pressure oil source through the pilot pressure interface 29. The oil outlet of the electro-proportional pilot control valve 12 branches into three parallel branches. The first branch is connected to the pilot one-way valve 30, the second branch is connected to the external control end of the first control valve 8, and the third branch is connected to the external control end of the second control valve 9.

[0029] A second throttle valve 26 is connected in series on the second branch of the electro-proportional pilot control valve 12; a third throttle valve 27 is connected in series on the third branch of the electro-proportional pilot control valve 12; and a fourth throttle valve 28 is connected in series on the oil line between the pilot pressure port 29 and the oil inlet of the electro-proportional pilot control valve 12.

[0030] The first control valve 8 and the second control valve 9 are normally in a spring-reset locked state, cutting off the oil return channel of the oil cylinder and realizing the static locking of the oil cylinder to prevent cylinder slippage; the valve port will only be opened proportionally when the electro-proportional pilot control valve 12 outputs pilot control pressure.

[0031] The second throttle valve 26, the third throttle valve 27, and the fourth throttle valve 28 are used to buffer the impact of the pilot control pressure and avoid the hydraulic cylinder descent vibration caused by sudden pressure changes during the valve opening / closing process.

[0032] The oil inlet line of the variable hydraulic motor 13 is connected in parallel with a displacement control branch. The displacement control branch is connected to the minimum displacement control terminal 22 of the variable hydraulic motor 13 and the oil inlet of the solenoid directional valve 19. The minimum displacement control terminal 22 and the solenoid directional valve 19 are connected in parallel. The oil outlet of the solenoid directional valve 19 is connected to the maximum displacement control terminal 21 of the variable hydraulic motor 13 after passing through the pilot-operated pressure relief valve 20. It is used to control the oil supply to the maximum displacement control terminal 21 by the valve position.

[0033] The displacement control branch is connected in series with a first branch check valve 15 and a first filter 16. The filtered oil is divided into three parallel branches. The first branch is directly connected to the minimum displacement control terminal 22 of the variable hydraulic motor 13. The second branch is connected to the oil inlet of the solenoid directional valve 19. The third branch is connected to the oil return port 23 of the variable hydraulic motor 13. A replenishment branch is provided on the oil return line of the variable hydraulic motor 13. The replenishment branch is connected to the displacement control branch after being filtered by the second branch check valve 17 and the second filter 18. The oil outlet of the pilot-operated pressure relief valve 20 is connected to the maximum displacement control terminal 21 of the variable hydraulic motor 13. A branch oil line is provided on the connecting oil line between the oil outlet of the pilot-operated pressure relief valve 20 and the maximum displacement control terminal 21, which is connected to the speed detection interface 24 of the variable hydraulic motor 13. A first throttle valve 25 is connected in series on the connecting oil line between the oil outlet of the pilot-operated pressure relief valve 20 and the maximum displacement control terminal 21.

[0034] The first branch check valve 15 prevents the control oil from flowing back, and the first filter 16 filters impurities in the control oil to prevent impurities from entering the cavity of the minimum displacement control terminal 22 and causing jamming. The solenoid directional valve 19 is a two-position two-way solenoid switch valve. When normally energized, it is in the off state, and the control oil can only enter the minimum displacement control terminal 22, so that the variable hydraulic motor 13 is kept in the minimum displacement state. When de-energized, it is in the on state, and the control oil enters the maximum displacement control terminal 21 through the pilot-operated pressure relief valve 20, switching the variable hydraulic motor 13 to the maximum displacement state, realizing the rapid switching of displacement mode. The pilot-operated pressure relief valve 20 is used to set the rated control pressure of the maximum displacement control terminal 21 to avoid damage to the motor displacement adjustment mechanism due to excessive control pressure. The first throttle valve 25 is used to buffer the control pressure impact to ensure a smooth and vibration-free displacement switching process. The speed detection interface 24 has a built-in speed sensor that can collect the rotation speed of the variable hydraulic motor 13 in real time and provide speed parameters for the closed-loop control of the controller. After the variable hydraulic motor 13 performs its work, the hydraulic oil flows in two separate paths: one part of the oil flows directly back to the oil tank through the main return oil line, completing the main hydraulic circulation; the other part of the oil flows through the replenishment branch, is filtered by the second branch check valve 17 and the second filter 18, and then connected to the oil inlet of the displacement control branch, forming a closed-loop replenishment channel.

[0035] When the cylinder descends and starts, or under conditions such as sudden load changes, the pressure at the inlet of the variable hydraulic motor 13 drops, resulting in insufficient oil pressure in the displacement control branch. At this time, a portion of the oil returning from the variable hydraulic motor 13 is replenished to the displacement control branch through the oil replenishment branch, providing a stable control oil source for the minimum displacement control end 22 and the maximum displacement control end 21 of the variable hydraulic motor 13, thus avoiding the problem of jamming or adjustment failure of the displacement adjustment mechanism due to insufficient oil supply.

[0036] The pressure detection unit is connected to the confluence valve block and the oil inlet pipe of the variable hydraulic motor 13, respectively, to collect the cylinder load pressure and the motor oil inlet pressure; the controller is electrically connected to the pressure detection unit, the electro-proportional pilot control valve 12, the solenoid directional valve 19 and the generator 14, respectively, to adjust the loop flow and motor displacement in a closed loop according to the collected pressure parameters, and synchronously control the electromagnetic braking torque of the generator 14 to realize the potential energy recovery and power generation during the cylinder descent process.

[0037] The pressure detection unit includes a first pressure sensor 7 and a second pressure sensor. The first pressure sensor 7 is located on the confluence oil line of the first hydraulic cylinder 1 and the second hydraulic cylinder 2, and is fixedly mounted on the confluence valve block to collect the load pressure at the bottom of the cylinder. The second pressure sensor is fixedly mounted on the inlet oil line of the variable hydraulic motor 13 to collect the motor inlet oil pressure. The signal output terminals of both the first and second pressure sensors are electrically connected to the signal input terminals of the controller.

[0038] The controller is the VCU controller for the forklift vehicle, which can communicate directly with the forklift display screen, operating handle, and lithium battery BMS system to achieve real-time signal interaction.

[0039] Generator 14 is a permanent magnet synchronous generator, compatible with the forklift lithium battery charging system. The generated three-phase AC power is directly stored in the lithium battery after rectification. The electromagnetic braking torque of generator 14 is linearly related to the input control current. The braking torque can be precisely adjusted by the controller, thereby adjusting the rotational resistance of the motor and assisting in controlling the descent speed of the hydraulic cylinder.

[0040] A parallel oil circuit is provided between the oil outlet of the first control valve 8 and the oil outlet of the second control valve 9; a parallel oil circuit is also provided between the oil inlet of the first control valve 8 and the oil inlet of the second control valve 9, which is used to balance the oil circuit pressure of the two cylinders and realize the synchronous descent of the first hydraulic cylinder 1 and the second hydraulic cylinder 2.

[0041] The confluence valve block is provided with an oil supply interface. The oil supply interface is connected to the oil inlet of the first built-in check valve 5 of the first deceleration brake valve 3 and the oil supply interface is connected to the oil inlet of the second built-in check valve 6 of the second deceleration brake valve 4. The oil outlet of the first built-in check valve 5 is connected to the rodless chamber of the first hydraulic cylinder 1 and the oil outlet of the second built-in check valve 6 is connected to the rodless chamber of the second hydraulic cylinder 2.

[0042] Ports T, T1, and T2 are all connected to the return oil tank; port MX is a reserved external interface; port U is the oil drain port for the casing.

[0043] The oil outlet of the pilot one-way valve 30 is connected to the first branch of the electro-proportional pilot control valve 12. The oil inlet of the pilot one-way valve 30 is port B1. The external oil circuit can enter the first branch unidirectionally from the oil inlet of the pilot one-way valve 30.

[0044] This application provides a method for controlling the potential energy recovery during the descent of a lithium-ion battery-powered heavy-duty forklift cylinder, comprising the following steps: Step S1: The controller acquires the potential energy recovery descent mode selection signal from the forklift display screen and the cylinder bottom load pressure P1 collected by the pressure detection unit in real time. Step S2: When the controller determines that the potential energy recovery descent mode is not selected or the cylinder bottom load pressure P1 is less than the preset start pressure threshold P0, the system executes the normal descent procedure; when the controller determines that the potential energy recovery descent mode is selected and the cylinder bottom load pressure P1 is greater than or equal to the preset start pressure threshold P0, the potential energy recovery control procedure is started. Step S3: After starting the potential energy recovery control program, the controller collects the cylinder bottom load pressure P1 from the first pressure sensor 7, the motor inlet oil pressure P2 from the second pressure sensor, and the real-time speed n of the variable hydraulic motor 13 collected by the speed detection interface 24 in real time. At the same time, the forklift CAN bus obtains the target output current of the electro-proportional pilot control valve 12 corresponding to the forklift lowering handle control signal. Step S4: Based on the pre-stored current-orifice area characteristic curve of the electro-proportional pilot control valve 12, and combined with the target output current of the electro-proportional pilot control valve 12, the controller calculates the system target flow rate Q, which corresponds to the target descent speed of the cylinder controlled by the handle; simultaneously, it collects the load pressure P1 at the bottom of the rodless chamber of the cylinder, the inlet pressure P2 of the variable hydraulic motor 13, and the real-time speed n of the variable hydraulic motor 13, and performs a two-step closed-loop calculation: The first step is to match the flow rate, displacement, and speed of the hydraulic motor using the following formula: ; Combining the locked system target flow rate Q, the real-time collected motor speed n, and the pre-stored motor volumetric efficiency The target operating displacement V of the variable hydraulic motor 13 is calculated.

[0045] The second step involves using the inlet pressure P2 of the variable hydraulic motor 13 as its effective inlet and outlet pressure difference (the motor's return oil is directly connected to the oil tank, and the return oil pressure is approximately 0), and substituting the calculated target operating displacement V into the hydraulic motor torque calculation formula: Combined with pre-stored motor mechanical efficiency The target output torque T of the variable hydraulic motor 13 is calculated. The pressure difference between P1 and P2 is used as the verification value of the total pressure loss of the valve group. The closed-loop correction of the system target flow rate Q and the valve opening of the integrated main control valve group ensures that the actual descent speed of the oil cylinder is completely matched with the control command of the handle.

[0046] Step S5: Based on the target operating displacement V calculated in step S4, the controller outputs a matching on / off control signal to the solenoid directional valve 19. The solenoid directional valve 19 adjusts the actual operating displacement of the variable hydraulic motor 13 according to the control logic of its hydraulic circuit, and switches the control oil passage of the variable hydraulic motor 13 according to the valve position, so as to adjust the actual operating displacement V of the variable hydraulic motor 13 to the target value set in step S4. Under the premise of not changing the system target flow rate Q, the optimal operating mode is adapted to the current load condition. At the same time, based on the target output torque T calculated in step S4, the controller outputs a control signal matching the target output torque T to the generator 14, so that the generator 14 generates an electromagnetic braking torque corresponding to the target output torque T. This braking torque forms a dynamic balance with the hydraulic output torque of the variable hydraulic motor 13, which not only constrains the motor speed to be stable and prevents the cylinder from falling under heavy load, but also synchronously drives the generator 14 to generate electricity and store electrical energy in the lithium battery.

[0047] The conventional descent procedure in step S2 specifically involves the controller energizing the electro-proportional pilot control valve 12 to cut off the oil passage of the potential energy recovery hydraulic circuit, thus preventing the potential energy recovery power generation function from being activated. The control logic of the electromagnetic directional valve 19 in step S5 is as follows: initially, the controller controls the electromagnetic directional valve 19 to be in the off state, allowing hydraulic oil to enter the minimum displacement control terminal 22, enabling the variable hydraulic motor 13 to maintain a high-efficiency power generation mode with a minimum displacement and high speed. When the cylinder bottom load pressure P1 exceeds the preset heavy load pressure threshold, the controller controls the electromagnetic directional valve 19 to open, allowing hydraulic oil to enter the maximum displacement control terminal 21, switching the variable hydraulic motor 13 to a smooth braking mode with a maximum displacement and low speed.

[0048] The hydraulic circuit of this application can realize three major working conditions: cylinder lifting, normal lowering, and potential energy recovery lowering. The oil circuit routing and function implementation for each working condition are as follows: Hydraulic cylinder lifting operation When the forklift performs mast lifting operation, the hydraulic oil of the original hydraulic system enters the circuit through the oil supply interface of the confluence valve block and is divided into two paths: the first path enters the rodless chamber of the first hydraulic cylinder 1 through the first built-in check valve 5 of the first deceleration brake valve 3, pushing the piston rod to extend; the second path enters the rodless chamber of the second hydraulic cylinder 2 through the second built-in check valve 6 of the second deceleration brake valve 4, pushing the piston rod to extend, thereby realizing the lifting of the forks.

[0049] Under this condition, the controller energizes the electro-proportional pilot control valve 12, and the first control valve 8 and the second control valve 9 are locked. The potential energy recovery circuit is completely cut off. The one-way structure of the first deceleration brake valve 3 and the second deceleration brake valve 4 can realize unobstructed oil intake during the lifting process, ensuring lifting speed and power performance.

[0050] Normal descent conditions When the operator does not select the potential energy recovery descent mode on the display screen, or when the controller detects that the cylinder bottom load pressure P1 is less than the preset start pressure threshold P0 (corresponding to no-load / light-load conditions), the system executes the normal descent procedure.

[0051] Under this condition, the controller energizes the electro-proportional pilot control valve 12, cutting off the oil passage of the potential energy recovery hydraulic circuit. The first control valve 8 and the second control valve 9 remain locked, and the oil cylinder returns oil to the oil tank. The potential energy recovery power generation function is not activated, ensuring the operational flexibility of the cylinder descent under no-load / light-load conditions and avoiding the damping of the potential energy recovery circuit from affecting the descent response speed.

[0052] Potential energy recovery decline condition When the operator selects the potential energy recovery descent mode, and the controller detects that the cylinder bottom load pressure P1 is greater than or equal to the preset starting pressure threshold P0, the system starts the potential energy recovery control program. The oil circuit routing and function implementation in this working condition are divided into two stages: (1) High-efficiency power generation stage under medium and light loads When the hydraulic cylinder descends, the weight of the forks and the cargo pushes the piston rod of the hydraulic cylinder downward. The high-pressure oil in the rodless chambers of the first hydraulic cylinder 1 and the second hydraulic cylinder 2 enters the confluence valve block through the first deceleration brake valve 3 and the second deceleration brake valve 4 respectively. After confluence, the high-pressure oil is divided into two paths and enters the first control valve 8 (through port A) and the second control valve 9 (through port A1) respectively.

[0053] At this time, the controller outputs the corresponding target current to the electro-proportional pilot control valve 12 according to the control signal of the lowering handle. The electro-proportional pilot control valve 12 outputs pilot oil with the corresponding pressure. The oil enters from the pilot pressure port 29 (entering through port X) and enters the external control terminals of the first control valve 8 and the second control valve 9 respectively, driving the two control valves to open their valve ports. The high-pressure oil enters the first one-way sequence valve 10 and the second one-way sequence valve 11 after passing through the control valves. After merging, it enters the oil inlet of the variable hydraulic motor 13 (exiting through port B and entering the variable hydraulic motor 13 through port C), driving the variable hydraulic motor 13 to rotate and then flowing back to the oil tank (through port D).

[0054] During this stage, the controller keeps the solenoid directional valve 19 in the energized-off state. The control oil in the displacement control branch, after passing through the first branch check valve 15 and the first filter 16, only enters the minimum displacement control terminal 22 of the variable hydraulic motor 13, keeping the variable hydraulic motor 13 in the minimum displacement state. The high-pressure hydraulic drive motor achieves high-speed rotation at minimum displacement, driving the coaxially connected generator 14 to run at high speed. The controller outputs a matching control signal to the generator 14, causing the generator 14 to generate a corresponding electromagnetic braking torque, converting the rotational mechanical energy of the motor into electrical energy, which is then rectified and stored in the forklift's lithium battery, achieving efficient recovery of gravitational potential energy.

[0055] Simultaneously, the controller collects the real-time motor speed n from the first pressure sensor 7 (P1), the second pressure sensor (P2), and the speed detection interface 24, and adjusts the output current of the electro-proportional pilot control valve 12 and the electromagnetic braking torque of the generator 14 in a closed loop.

[0056] (2) Heavy-load smooth braking stage When the forklift is under heavy load, and the controller detects that the cylinder bottom load pressure P1 exceeds the preset heavy load pressure threshold, the controller controls the solenoid directional valve 19 to de-energize and conduct. The control oil of the displacement control branch enters the maximum displacement control terminal 21 of the variable hydraulic motor 13 after passing through the solenoid directional valve 19 and the pilot pressure relief valve 20, thus switching the variable hydraulic motor 13 to the maximum displacement state.

[0057] In this state, the high-pressure hydraulic fluid drives the variable displacement hydraulic motor 13 to rotate at low speed with maximum displacement. The motor's output torque is significantly increased, providing stronger braking resistance. Combined with the electromagnetic braking torque of the generator 14, this achieves smooth and speed-limited descent of the cylinder under heavy load conditions, avoiding the risk of falling under heavy load. At the same time, the controller adjusts the electromagnetic braking torque of the generator 14 in real time according to changes in load pressure, maximizing the recovery of gravitational potential energy while ensuring smooth descent, achieving a balance between safety and energy saving.

[0058] This application directly drives the high-pressure oil released during cylinder descent to rotate the variable hydraulic motor 13, which in turn drives the coaxial generator 14 to generate electricity and store it in a lithium battery. This eliminates the intermediate steps of multiple energy form conversions in the accumulator solution, reduces ineffective losses during energy transfer, and maximizes the recovery and utilization of gravitational potential energy, effectively improving the actual energy-saving effect. Through the adaptive switching of the displacement of the variable hydraulic motor 13 and the closed-loop adjustment of the electromagnetic braking torque of the generator 14, it is not limited by the size and rated pressure of physical energy storage elements and can fully adapt to the potential energy recovery needs of heavy-duty forklifts across the entire load range and lifting stroke: under medium and light load conditions, the minimum displacement high-speed mode is used to maximize power generation efficiency and energy recovery rate; under heavy load conditions, it switches to the maximum displacement low-speed mode to significantly increase the motor output torque and braking resistance, achieving smooth speed limiting of cylinder descent under heavy load conditions. At the same time, this solution can provide stable and controllable braking resistance throughout the entire process, eliminating the pressure fluctuation problem during the charging and discharging process of the accumulator, ensuring a smooth cylinder descent process and stable and consistent power output of the hydraulic system.

[0059] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A hydraulic system for recovering the potential energy of a lithium-ion battery-powered heavy-duty forklift cylinder during descent, characterized in that, It includes a first hydraulic cylinder (1), a second hydraulic cylinder (2), a first deceleration brake valve (3), a second deceleration brake valve (4), a confluence valve block, an integrated main control valve group, a variable hydraulic motor (13), a generator (14), an electromagnetic reversing valve (19), a pressure detection unit, and a controller; The rodless chamber outlet of the first hydraulic cylinder (1) is connected in series with the inlet of the first deceleration brake valve (3), and the rodless chamber outlet of the second hydraulic cylinder (2) is connected in series with the inlet of the second deceleration brake valve (4); the outlet of the first deceleration brake valve (3) and the outlet of the second deceleration brake valve (4) are respectively connected to the corresponding inlet of the confluence valve block; the outlet of the confluence valve block is connected to the inlet of the integrated main control valve group. The integrated main control valve group internally integrates a first control valve (8), a second control valve (9), a first one-way sequence valve (10), a second one-way sequence valve (11), and an electro-proportional pilot control valve (12); the two oil outlets of the confluence valve block are respectively connected to the oil inlet of the first control valve (8) and the oil inlet of the second control valve (9); The oil outlet of the first control valve (8) is connected to the oil inlet of the first one-way sequence valve (10), and the oil outlet of the second control valve (9) is connected to the oil inlet of the second one-way sequence valve (11). After the oil outlets of the first one-way sequence valve (10) and the second one-way sequence valve (11) merge, they are connected to the oil inlet of the variable hydraulic motor (13). The output shaft of the variable hydraulic motor (13) is connected to the input shaft of the generator (14) via a transmission. The oil outlet of the electro-proportional pilot control valve (12) is connected to the external control end of the first control valve (8) and the external control end of the second control valve (9) respectively, and is used to drive the two control valves to switch from the lock-up mode to the throttling conduction mode. The oil inlet pipe of the variable hydraulic motor (13) is connected in parallel with a displacement control branch. The displacement control branch is connected to the minimum displacement control terminal (22) of the variable hydraulic motor (13) and the oil inlet of the solenoid directional valve (19). The minimum displacement control terminal (22) and the solenoid directional valve (19) are connected in parallel. The oil outlet of the solenoid directional valve (19) is connected to the maximum displacement control terminal (21) of the variable hydraulic motor (13) after passing through the pilot-operated pressure relief valve (20), and is used to control the oil supply of the maximum displacement control terminal (21) by the valve position. The pressure detection unit is connected to the confluence valve block and the oil inlet pipe of the variable hydraulic motor (13) respectively, and is used to collect the cylinder load pressure and the motor oil inlet pressure; the controller is electrically connected to the pressure detection unit, the electro-proportional pilot control valve (12), the electromagnetic reversing valve (19) and the generator (14) respectively, and is used to adjust the loop flow and motor displacement in a closed loop according to the collected pressure parameters, and synchronously control the electromagnetic braking torque of the generator (14) to realize the potential energy recovery and power generation during the cylinder descent process.

2. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 1, characterized in that, A parallel oil circuit is provided between the oil outlet of the first control valve (8) and the oil outlet of the second control valve (9); a parallel oil circuit is provided between the oil inlet of the first control valve (8) and the oil inlet of the second control valve (9) to balance the oil circuit pressure of the two cylinders and realize the synchronous descent of the first hydraulic cylinder (1) and the second hydraulic cylinder (2).

3. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 1, characterized in that, The inlet of the electro-proportional pilot control valve (12) is connected to the system pilot pressure oil source through the pilot pressure interface (29). The outlet of the electro-proportional pilot control valve (12) is divided into three parallel branches. The first branch is connected to the pilot one-way valve (30), the second branch is connected to the external control end of the first control valve (8), and the third branch is connected to the external control end of the second control valve (9).

4. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 1, characterized in that, The displacement control branch is connected in series with a first branch check valve (15) and a first filter (16). The filtered oil is divided into three parallel branches. The first branch is directly connected to the minimum displacement control terminal (22) of the variable hydraulic motor (13). The second branch is connected to the oil inlet of the solenoid directional valve (19). The third branch is connected to the oil return port (23) of the variable hydraulic motor (13). A replenishment branch is provided on the oil return line of the variable hydraulic motor (13). The replenishment branch passes through the second branch check valve (17) and the second filter (18). After filtration, it is connected to the displacement control branch; the oil outlet of the pilot-operated pressure relief valve (20) is connected to the maximum displacement control terminal (21) of the variable hydraulic motor (13); on the oil line connecting the oil outlet of the pilot-operated pressure relief valve (20) and the maximum displacement control terminal (21), there is a branch oil line connected to the speed detection interface (24) of the variable hydraulic motor (13); a first throttle valve (25) is connected in series on the oil line connecting the oil outlet of the pilot-operated pressure relief valve (20) and the maximum displacement control terminal (21).

5. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 1, characterized in that, The pressure detection unit includes a first pressure sensor (7) and a second pressure sensor. The first pressure sensor (7) is located on the confluence oil line of the first hydraulic cylinder (1) and the second hydraulic cylinder (2). The first pressure sensor (7) is fixedly installed on the confluence valve block and is used to collect the load pressure at the bottom of the cylinder. The second pressure sensor is fixedly installed on the oil inlet line of the variable hydraulic motor (13) and is used to collect the motor oil inlet pressure.

6. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 5, characterized in that, The signal output terminals of the first pressure sensor (7) and the second pressure sensor are electrically connected to the signal input terminal of the controller.

7. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 1, characterized in that, The confluence valve block is provided with an oil supply interface. The oil supply interface is connected to the oil inlet of the first built-in check valve (5) of the first deceleration brake valve (3). The oil supply interface is connected to the oil inlet of the second built-in check valve (6) of the second deceleration brake valve (4). The oil outlet of the first built-in check valve (5) is connected to the rodless chamber of the first hydraulic cylinder (1). The oil outlet of the second built-in check valve (6) is connected to the rodless chamber of the second hydraulic cylinder (2).

8. The hydraulic system for recovering the potential energy of the descending cylinder of a lithium-ion heavy-duty forklift according to claim 3, characterized in that, A second throttle valve (26) is connected in series on the second branch of the electro-proportional pilot control valve (12); a third throttle valve (27) is connected in series on the third branch of the electro-proportional pilot control valve (12); and a fourth throttle valve (28) is connected in series on the oil line between the pilot pressure port (29) and the oil inlet of the electro-proportional pilot control valve (12).

9. A method for controlling the recovery of potential energy during the descent of a lithium-ion battery-powered heavy-duty forklift cylinder, characterized in that, The hydraulic system for recovering the potential energy during the descent of a lithium-ion heavy-duty forklift cylinder, as described in any one of claims 1 to 8, comprises the following steps: Step S1: The controller acquires the potential energy recovery descent mode selection signal from the forklift display screen and the cylinder bottom load pressure P1 collected by the pressure detection unit in real time. Step S2: When the controller determines that the potential energy recovery descent mode is not selected or the cylinder bottom load pressure P1 is less than the preset start pressure threshold P0, the system executes the normal descent procedure; when the controller determines that the potential energy recovery descent mode is selected and the cylinder bottom load pressure P1 is greater than or equal to the preset start pressure threshold P0, the potential energy recovery control procedure is started. Step S3: After starting the potential energy recovery control program, the controller collects the cylinder bottom load pressure P1 from the first pressure sensor (7), the motor inlet pressure P2 from the second pressure sensor, and the real-time speed n of the variable hydraulic motor (13) collected by the speed detection interface (24) in real time. At the same time, it acquires the target output current of the electro-proportional pilot control valve (12) corresponding to the forklift lowering handle control signal. Step S4: The controller calculates the target flow rate Q of the system by combining the target output current of the electro-proportional pilot control valve (12); at the same time, it calculates the target operating displacement V and target output torque T of the variable hydraulic motor (13) by combining the collected P1, P2 and the real-time speed n of the motor. Step S5: The controller outputs a matching control signal to the solenoid directional valve (19). The solenoid directional valve (19) adjusts the actual operating displacement of the variable hydraulic motor (13) according to the control logic of its hydraulic circuit. At the same time, it outputs a control signal matching the target output torque T to the generator (14), so that the generator (14) generates the corresponding electromagnetic braking torque, drives the generator (14) to generate electricity and stores the electrical energy in the lithium battery.

10. The method for controlling the recovery of potential energy during the descent of a lithium-ion battery-powered heavy-duty forklift cylinder according to claim 9, characterized in that, The conventional descent procedure in step S2 is specifically that the controller controls the electro-proportional pilot control valve (12) to energize the electromagnet, cut off the oil passage of the potential energy recovery hydraulic circuit, and does not start the potential energy recovery power generation function; the control logic of the electromagnetic directional valve (19) in step S5 is specifically that, initially, the controller controls the electromagnetic directional valve (19) to be in the off state, and the hydraulic oil enters the minimum displacement control terminal (22), so that the variable hydraulic motor (13) maintains the high-efficiency power generation mode of minimum displacement and high speed; when the cylinder bottom load pressure P1 exceeds the preset heavy load pressure threshold, the controller controls the electromagnetic directional valve (19) to be turned on, and the hydraulic oil enters the maximum displacement control terminal (21), switching the variable hydraulic motor (13) to the smooth braking mode of maximum displacement and low speed.

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