CN108298474B - Fork truck high-efficient economizer system with speed governing function - Google Patents

Abstract

The invention provides a forklift high-efficiency energy-saving system with a speed regulation function, which comprises a double-acting motor-generator, a double-acting pump-motor, a closed pressure oil tank, a hydraulic control oil supplementing valve, a bidirectional hydraulic lock valve, a lifting oil cylinder, a safety valve, a three-phase bridge inverter, an energy supply-energy storage device, a control device and an oil tank, wherein the double-acting motor-generator is connected with the double-acting pump-motor; the double-acting pump-motor is connected with the double-acting motor-generator; the double-acting motor-generator is connected with the three-phase bridge inverter; the three-phase bridge inverter is connected with the energy supply-energy storage device; the control device controls the working states of the three-phase bridge inverter and the energy supply-storage device; an oil discharge port and an oil suction port of the double-acting pump-motor are connected with a hydraulic control oil supplementing valve; the hydraulic control oil supplementing valve is connected with the bidirectional hydraulic lock valve, and the bidirectional hydraulic lock valve is connected with the rod cavity and the rodless cavity of the lifting oil cylinder; the lifting cylinder is provided with a rod cavity and a rodless cavity which are connected with a safety valve. The potential energy recovery system of the invention adjusts the descending speed of the fork by controlling the rotating speed of the double-acting motor-generator, eliminates the throttling loss of the hydraulic circuit, reduces the heating of hydraulic oil, improves the potential energy recovery efficiency, has simple and reliable system hardware and software, and can be realized to a high degree.

Description

A high-efficiency energy-saving system for forklifts with speed regulation function

Technical Field

The invention relates to a forklift energy-saving system, and in particular to a forklift high-efficiency energy-saving system with a speed regulation function.

Background Art

At present, in terms of potential energy recovery of electric forklifts, in addition to the current research hotspot, the use of energy storage devices to recover the descending potential energy, further, how to maximize the potential energy recovery efficiency based on the energy storage device is the current research focus and also the weak link in the research. Regarding the potential energy recovery efficiency of electric forklifts, the throttling loss of the electro-hydraulic servo valve that adjusts the fork descent speed in the hydraulic system not only directly causes the heating of the hydraulic system, but is also a key factor in potential energy loss and low potential energy recovery efficiency. Therefore, reducing throttling losses is of great significance to improving the potential energy recovery efficiency of forklifts. In addition, the energy storage device of electric forklifts mostly uses lead-acid batteries for energy storage, and the fork descent process of the forklift is usually between ten seconds and dozens of seconds. The lead-acid battery has a low power density and is difficult to charge quickly in a short period of time, and cannot efficiently recover the descending potential energy of the fork.

For the potential energy recovery system of electric forklifts, the existing technologies are as follows:

Taking Chinese patent 200610042603.3 as an example, the fork lowering speed is adjusted by the electro-hydraulic servo valve and the generator-motor pump control system. It is necessary to simultaneously control the motor, pump speed and the working position of the electro-hydraulic servo valve, that is, the real-time high-precision matching of the motor, pump and electromagnetic servo valve, which has high requirements on the system hardware and software equipment and high feasibility.

Taking Chinese patent 201210128114.5 as an example, energy regeneration and recovery is achieved through a multi-way valve, but the multi-way valve has a complex structure and many oil circuits. The forklift steering system and lifting system are designed in one hydraulic system, the hydraulic oil circuit is greatly modified and the operation is highly complicated.

Taking Chinese patent 201620398878.X as an example, potential energy recovery of electric forklifts is achieved through throttling speed regulation and variable speed volumetric speed regulation. However, the control accuracy of the manual reversing valve in the hydraulic system is low, the energy loss of throttling speed regulation is large, and it will also cause the hydraulic oil to heat up, reducing system efficiency.

Summary of the invention

In view of the above-mentioned deficiencies in the prior art, the present invention provides a high-efficiency energy-saving system for an electric forklift having a fork speed regulation function and having no throttling loss under normal working conditions.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a high-efficiency and energy-saving forklift system with speed regulation function, including a double-acting motor, a double-acting motor, a two-way hydraulic lock valve, a lifting cylinder, a three-phase bridge inverter, an energy supply and energy storage device and a control device; the double-acting motor is connected to the double-acting motor, and the oil discharge port and the oil suction port of the double-acting motor are connected to the two-way hydraulic lock valve; the two-way hydraulic lock valve is respectively connected to the rod cavity and the rodless cavity of the lifting cylinder; the control device includes a control chip and an auxiliary circuit, the double-acting motor is connected to the three-phase bridge inverter, the three-phase bridge inverter is connected to the energy supply and energy storage device, and the control device is respectively connected to the three-phase bridge inverter and the energy supply and energy storage device and controls the working status of the two.

Furthermore, the control device receives collected signals from the current sensor, voltage sensor and speed encoder, outputs a PWM signal, controls the on and off status of the MOS tube in the three-phase bridge inverter, controls the on and off status of the relay in the energy supply and storage device, the current sensor is installed on the U and V phases of the three-phase wires of the three-phase inverter, the voltage sensor is installed on the output end of the supercapacitor and the battery, and the speed encoder is installed on the output shaft of the double-acting motor.

Furthermore, the control chip is an ATMEGA328P-PU chip.

Furthermore, the system also includes a hydraulically controlled oil replenishing valve and a closed pressure oil tank. The closed pressure oil tank is connected to the hydraulically controlled oil replenishing valve. The hydraulically controlled oil replenishing valve is connected in parallel to the oil outlet and oil suction port of the double-acting motor. The hydraulic oil in the closed pressure oil tank can be supplied to the oil outlet and oil suction port of the double-acting motor respectively through two one-way valves of the hydraulically controlled oil replenishing valve.

Furthermore, the system includes a safety valve, which is composed of two overflow valves, and the two overflow valves are respectively connected to the rod chamber and the rodless chamber of the lifting cylinder.

Furthermore, the double-acting motor includes a motor and a generator, which outputs electrical energy when the double-acting motor rotates forward and generates electrical energy when the motor rotates reversely.

Further, the double-acting motor includes a motor and a pump, and generates attraction force when the double-acting motor rotates forward, and generates thrust force when the double-acting motor rotates reversely.

Furthermore, when the hydraulic oil flows into the hydraulically controlled one-way valve on the left side of the two-way hydraulic lock valve, the oil pressure controls the hydraulically controlled one-way valve on the right side of the two-way hydraulic lock valve to open in reverse, and the hydraulic oil entering the rodless chamber of the lifting cylinder pushes the hydraulic oil in the rod chamber of the lifting cylinder through the hydraulically controlled one-way valve on the right side of the two-way lock valve and flows back to the double-acting motor; when the hydraulic oil flows into the hydraulically controlled one-way valve on the right side of the two-way hydraulic lock valve, the oil pressure controls the hydraulically controlled one-way valve on the left side of the two-way hydraulic lock valve to open in reverse, and the hydraulic oil entering the rod chamber of the lifting cylinder pushes the hydraulic oil in the rodless chamber of the lifting cylinder through the hydraulically controlled one-way valve on the left side of the two-way lock valve and flows back to the double-acting motor.

Furthermore, when the fork is lowered too slowly, the current sensor and speed encoder on the generator transmit the generator working speed and torque state to the control device, and the control device compares the actual speed signal of the generator with the given speed, adjusts the switching order of the MOS tube, increases the speed of the double-acting motor-generator, reduces the torque of the double-acting motor-generator, reduces the torque of the double-acting pump-motor, reduces the descending resistance of the hydraulic system, and the hydraulic oil flows into the rod chamber of the lifting cylinder faster through the hydraulic-controlled one-way valve on the right side of the two-way hydraulic lock valve. At the same time, the hydraulic-controlled one-way valve on the left side of the two-way hydraulic lock valve is hydraulically controlled to open in the opposite direction, and the hydraulic oil in the rodless chamber of the lifting cylinder flows back to the double-acting pump-motor faster through the hydraulic-controlled one-way valve on the left side of the two-way hydraulic lock valve, thereby accelerating the descending speed of the fork.

The beneficial effects of the present invention are: 1. The present invention uses a pump control system composed of a double-acting motor and a double-acting motor, and utilizes direct torque technology to control the speed of the double-acting motor, thereby controlling the lowering speed of the fork, avoiding the complex speed regulation process of the valve control system, and the control device is simple, with low requirements on system hardware and software, and high feasibility. 2. The present invention replaces the electro-hydraulic servo valve for controlling the descending speed of the fork in the original system by a pump control system composed of a double-acting motor and a double-acting motor, thereby eliminating throttling losses under normal system conditions, improving potential energy recovery efficiency, further extending the single charge and discharge time of the battery, and extending the battery life of the forklift; 3. The present invention comprises a potential energy recovery system with a fork speed regulation function, which is composed of a two-way hydraulic lock valve, a hydraulically controlled oil replenishing valve, a double-acting motor, and a double-acting motor. The oil circuit is simple, the control is simple, the operation is convenient, and the feasibility is high; 4. In the present invention, the supercapacitor has a high power density, and the potential energy of the fork descent is recovered by the supercapacitor. Its fast charging and discharging performance can realize high-efficiency recovery of potential energy in a short time, and can provide instantaneous lifting power for the electric forklift lifting system, smooth the battery output power, and extend the battery life. 5. The present invention installs a current sensor in a three-phase inverter, installs a voltage sensor at the output end of a supercapacitor and a battery, and installs a speed encoder on the output shaft of a double-acting motor. The current signal of the three-phase inverter, the voltage signal of the supercapacitor and the battery, and the speed signal of the motor output shaft are collected in real time and sent to the control system. The control system can obtain the rising and falling speeds of the fork according to the above signals, and adjust the oil circuit by adjusting the switching sequence of the MOS tube, thereby achieving the purpose of adjusting the running speed of the fork. The present invention is simple to operate and accurate in control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall block diagram of the present invention.

FIG. 2 is a schematic diagram of the energy supply-energy storage device of the present invention.

3 is a schematic diagram of a three-phase bridge inverter of the present invention, wherein B4, B6, B8, B10, B12, and B14 are diodes, and B15, B16, and B17 are resistors.

FIG. 4 is a schematic diagram of a control device of the present invention.

DETAILED DESCRIPTION

The technical solution of the present invention is described in detail below in conjunction with embodiments. The embodiments are only used to further illustrate the present invention, but not to limit the present invention.

Referring to Figure 1, the present invention provides a forklift energy-saving system with speed regulation function, including a double-acting motor 1, a double-acting motor 2, a closed pressure oil tank 8, a hydraulically controlled oil replenishing valve 3, a two-way hydraulic lock valve 4, a lifting cylinder 5 safety valve 6, a three-phase bridge inverter, an energy supply-energy storage device, a control device, and an oil tank 7; the double-acting motor 2 is connected to the double-acting motor 1; the oil discharge port and the oil suction port of the double-acting motor 1 are connected to the two-way hydraulic lock valve 4; the two-way hydraulic lock valve 4 is respectively connected to the rod cavity and the rodless cavity of the lifting cylinder 5; the control device includes a control chip and an auxiliary circuit, the double-acting motor is connected to the three-phase bridge inverter, the three-phase bridge inverter is connected to the energy supply and energy storage device, and the control device is respectively connected to the three-phase bridge inverter and the energy supply and energy storage device and controls the working states of the two.

The output shaft of the double-acting motor 1 is equipped with a built-in bearing speed encoder to detect the motor rotor position and speed information, and the detection signal is transmitted to the I/O port of the ATMEGA328P-PU chip of the control device.

The closed pressure oil tank 8 is connected to the hydraulically controlled oil replenishing valve 3, and the hydraulically controlled oil replenishing valve 3 is connected in parallel to the oil outlet and oil suction port of the double-acting motor 2. The hydraulic oil in the closed pressure oil tank 8 can be supplied to the oil outlet and oil suction port of the double-acting motor respectively through the two one-way valves of the hydraulically controlled oil replenishing valve 3.

The safety valve 6 is composed of two overflow valves, and the two overflow valves are respectively connected to the rod chamber and the rodless chamber of the lifting cylinder 5. Since the weight of the forklift fork lifting heavy objects has a large uncertainty, when the fork is suddenly lowered by a large impact, the hydraulic oil of the lifting cylinder 5 does not have time to flow, and the cylinder is easily blocked. In order to prevent this from happening, when the pressure in the lifting cylinder reaches the set pressure of the overflow valve, the overflow valve opens to release the pressure in the lifting cylinder 5 to protect the lifting cylinder 5. The energy supply-energy storage device, referring to Figure 2, is composed of a battery A1 and a supercapacitor A2, and also includes a first relay A5, a second relay A6, and a first voltage sensor A3 and a second voltage sensor A4 respectively connected to the battery A1 and the supercapacitor A2. The battery A1 and the supercapacitor A2 are connected in parallel to the output end of the three-phase bridge inverter to provide an energy source for the forklift lifting system and to store the potential energy recovered by the fork descent. When the fork is lowered, the second voltage sensor A4 detects the voltage across the supercapacitor A2 at a detection frequency of 1KHZ. When the voltage across the supercapacitor A2 is lower than the rated voltage of 27V, the control device controls the second relay A6 to be turned on, and the potential energy of the fork's descent is used to power the supercapacitor A2 first; when the fork is lowered or the supercapacitor A2 is recovering potential energy for charging, when the voltage across the supercapacitor A2 is not lower than the rated voltage, the control device controls the second relay A6 to be turned off and the first relay A5 to be turned on, and the potential energy of the fork's descent is used to charge the battery A1; when the fork's descent stroke ends, the control device controls the first relay A5 and the second relay A6 to be turned off. When the fork is lifted, the second voltage sensor A4 detects the voltage across the supercapacitor A1. When the voltage across the supercapacitor A1 is not lower than the rated voltage, the control device controls the second relay A6 to be turned on, and the supercapacitor A2 provides power for the forklift to lift instantly. The power supply time is 1 to 2 seconds or until the voltage of the supercapacitor A2 is less than 20V. After that, the control device controls the second relay A6 to be turned off and the first relay A5 to be turned on, and the battery A1 supplies power to the forklift lifting system.

The voltage sensor uses the principle of resistor voltage division to reduce the port input voltage by five times, and transmits the detection value to the ATMEGA328P-PU chip I/O port to complete the voltage signal acquisition.

The three-phase bridge inverter mainly completes the AC-DC conversion of the current between the energy supply-energy storage device and the double-acting motor 1. The working current of the energy supply-energy storage device is direct current, and the working current of the double-acting motor 1 is three-phase alternating current. The structure of the three-phase bridge inverter is shown in Figure 3, which is mainly composed of six or six times MOS tubes and six free-switch diodes. The MOS tubes in the same vertical column are one phase. In order to avoid short circuit of the DC power supply, only one MOS in each phase is turned on at the same time. When the energy supply-energy storage device supplies power to the double-acting motor 1, the control device sends a PWM signal to control the conduction and shutdown of the six MOS tubes. By using the conduction delay of different MOS tubes between the three phases, the DC voltage can be converted into a voltage pulse sequence to drive the double-acting motor 1; because when multiple MOS tubes are connected in parallel in each driving bridge arm, the driving current can be increased, so the number of required MOS tubes is determined according to the rated current of the double-acting motor 1. When the double-acting motor 1 charges the energy storage device, the MOS tube stops working, and the free-switching diodes on each drive bridge are converted into traditional six-pulse rectifiers, converting the three-phase AC power into DC power to charge the battery. The first current sensor B1 and the second current sensor B2 detect the current of the U and V phases of the three-phase power respectively, and the detection signal is transmitted to the ATMEGA328P-PU chip. The W phase current can be obtained by using the three-phase current sum to be zero. The torque state of the current double-acting motor 1 can be determined by detecting the current.

The current sensor is an electromagnetically isolated Hall element. When current flows through the wire, an induced magnetic field is generated in the Hall element. The detected current signal is directly transmitted to the I/O port of the control device ATMEGA328P-PU chip to complete the current signal collection.

The control device is mainly composed of an ATMEGA328P-PU chip and an auxiliary circuit, as shown in Figure 4. The ATMEGA328P-PU chip is integrated in the Arduino board, including a digital I/O interface and an analog I/O interface, which can complete the data acquisition of current signals and voltage signals, and output a PWM signal to control the on-off of the relay. The control circuit diagram of the control device is shown in Figure 3. The ATMEGA328P-PU chip receives the lifting signal and the lowering signal of the fork, and collects the voltage sensor signal in the energy supply-energy storage device to control the on-off of the relay in the energy supply-energy storage device; the control device controls the speed of the double-acting motor 1 through direct torque control technology. The ATMEGA328P-PU chip receives the speed setting (command speed) in the programming program, judges the current working state of the three-phase bridge inverter through the Hall current sensor and the speed encoder, generates a torque command (torque current) to control the working state of the three-phase bridge inverter, and then controls the speed of the double-acting motor 1.

Embodiment 1, the first working state.

When the fork is lifted, the control device receives the fork lifting signal. At this time, the second voltage sensor A5 detects the voltage across the supercapacitor A2. If the voltage across the supercapacitor A2 is not lower than the rated voltage, the control device controls the second relay A6 to turn on. The supercapacitor A2 provides power for the forklift to lift instantly. The power supply time is 1 to 2 seconds or until the voltage of the supercapacitor A2 is less than 20V. After that, the control device controls the second relay A6 to turn off and the first relay A5 to turn on. The battery A1 supplies power to the forklift lifting system. At this time, the three-phase bridge inverter converts the DC power of the supercapacitor A2 or the battery A1. The control device controls the three-phase bridge inverter MOS tubes B3, B13, B7, B5, B11, and B9 to turn on in sequence, and controls the MOS tube switch timing between the three phases to differ by 120 degrees, so that the three phases U, V, and W output approximately sinusoidal waves, converting DC power into AC power to power the double-acting motor 1. At this time, the double-acting motor 1 works in the motor state. The double-acting motor 1 drives the double-acting motor 2 to rotate, and the double-acting motor 2 works in the pump state. The control device receives the current and speed signal of the double-acting motor 1 in real time, and compares it with the given speed in the control program, controls the PWM signal, and then changes the switching order of the MOS tube, so that the U, V, W three-phase output voltage amplitude and the load angle of the double-acting motor 1, thereby controlling the three-phase AC voltage to control the generator speed, and then controlling the pump speed. The pump drives the hydraulic oil to flow to the rodless chamber of the lifting cylinder 5 through the two-way hydraulic lock valve 4. When the fork needs to stay at a certain position to complete the loading and unloading action, the pump changes from the working state to the non-working state, and the two-way hydraulic lock valve 4 quickly cuts off the oil circuit to prevent the rodless chamber of the lifting cylinder 5 from returning oil, thereby locking the position of the fork. When the electric forklift lifting system encounters a heavy load, resulting in a large difference in pressure between the rod chamber and the rodless chamber of the lifting cylinder 5 or a sudden hydraulic oil shock, the safety valve 6 opens at this time to automatically adjust the pressure difference between the rod chamber and the rodless chamber of the lifting cylinder 5 to prevent the lifting cylinder 5 from being stuck. During the operation of the pump, if the pump does not absorb enough oil, resulting in insufficient hydraulic oil in the lifting oil circuit, the hydraulically controlled oil replenishing valve 3 automatically replenishes oil to the pump to ensure the normal operation of the hydraulic system.

Embodiment 2, second working state.

When the fork is lowered, the rodless chamber of the lifting cylinder 5 returns oil, the two-way hydraulic lock valve 4 opens, and the hydraulic oil flows through the two-way hydraulic lock valve 4 into the double-acting pump-motor 2, driving the double-acting motor 2 to reverse. At this time, the double-acting motor 2 works in the pump state. The pump drives the double-acting motor 1 to reverse, and at this time, the double-acting motor 1 works in the generator state, and the generator generates electricity to charge the super capacitor A2 or the battery A1 through the three-phase bridge inverter. When the fork descends too fast, the current sensor and speed encoder on the generator transmit the generator working speed and torque state to the control device. The control device compares the actual speed signal of the generator with the given speed, calculates the angle of the stator flux space vector, and selects the nearest MOS tube B3, B9, B11 or B5, B7, B13 or B5, B7, B11 or B5, B9, B11 to turn on, so that the stator flux of the double-acting motor 1 becomes larger, the generator torque is increased, the motor torque is increased, the hydraulic system descending resistance is increased, and the hydraulic oil slows down the flow into the rod chamber of the lifting cylinder 5 through the hydraulic control one-way valve on the right side of the two-way hydraulic lock valve 4. At the same time, the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve 4 is hydraulically controlled to open in the reverse direction, and the hydraulic oil in the rodless chamber of the lifting cylinder 5 slows down the flow back to the double-acting pump-motor through the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve 4, thereby slowing down the descending speed of the fork. When the fork descends too slowly, select and turn on the MOS tubes B3, B9, B13 or B3, B9, B11 or B3, B7, B11 or B5, B9, B13 nearby to reduce the stator magnetic flux of the double-acting motor 1, reduce the generator torque, reduce the motor torque, reduce the descending resistance of the hydraulic system, and the hydraulic oil flows into the rod chamber of the lifting cylinder 5 faster through the hydraulic control one-way valve on the right side of the two-way hydraulic lock valve 4. At the same time, the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve 4 is hydraulically controlled to open in the reverse direction, and the hydraulic oil in the rodless chamber of the lifting cylinder 5 flows back to the double-acting motor 2 faster through the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve 4, thereby accelerating the descending speed of the fork. When the generator charges the supercapacitor A2 or the battery A1, the second voltage sensor A4 detects the voltage across the supercapacitor A2. When the voltage across the supercapacitor A2 is lower than the rated voltage of 27V, the control device controls the second relay A6 to be turned on, and the potential energy of the fork's descent is used to charge the supercapacitor A2 first; when the fork is descending or the supercapacitor A2 is recovering potential energy for charging, when the voltage across the supercapacitor A2 is not lower than the rated voltage, the control device controls the second relay A6 to be turned off and the first relay A1 to be turned on, and the potential energy of the fork's descent is used to charge the battery A1; when the fork's descent stroke ends, the control device controls the first relay A5 and the second relay A6 to be turned off.

Claims (1)

1. A high-efficiency energy-saving system for forklifts with speed regulation function, characterized in that it includes a double-acting motor, a double-acting motor, a two-way hydraulic lock valve, a lifting cylinder, a three-phase bridge inverter, an energy supply and energy storage device and a control device; the double-acting motor is connected to the double-acting motor, and the oil discharge port and the oil suction port of the double-acting motor are connected to the two-way hydraulic lock valve; the two-way hydraulic lock valve is respectively connected to the rod chamber and the rodless chamber of the lifting cylinder; the control device includes a control chip and an auxiliary circuit, the double-acting motor is connected to the three-phase bridge inverter, the three-phase bridge inverter is connected to the energy supply and energy storage device, and the control device is respectively connected to the three-phase bridge inverter and the energy supply and energy storage device and controls the working states of the two; The energy supply and storage device is composed of a battery and a supercapacitor, and also includes a first relay and a second relay connected to the battery and the supercapacitor respectively, as well as a first voltage sensor and a second voltage sensor; the battery and the supercapacitor are connected in parallel at the output end of the three-phase bridge inverter to provide an energy source for the forklift lifting system and are used to store the potential energy recovered by the forklift descending. When the forklift descends, the second voltage sensor detects the voltage across the supercapacitor at a detection frequency of 1KHZ. When the voltage across the supercapacitor is lower than the rated voltage of 27V When the fork is lowered, the control device controls the second relay to be turned on, and the potential energy of the fork descent is used to power the supercapacitor first; when the fork is lowered or the supercapacitor is recovering potential energy for charging, when the voltage across the supercapacitor is not lower than the rated voltage, the control device controls the second relay to be turned off and the first relay to be turned on, and the potential energy of the fork descent is used to charge the battery; when the fork descent stroke ends, the control device controls the first relay and the second relay to be turned off, and when the fork is lifted, the second voltage sensor detects the voltage across the supercapacitor, and when the voltage across the supercapacitor is not lower than the rated voltage, the control device controls the second relay to be turned on, and the supercapacitor provides power for the forklift to lift instantly, and the power supply time is 1 to 2 seconds or until the supercapacitor voltage is less than 20V, after which the control device controls the second relay to be turned off and the first relay to be turned on, and the battery powers the forklift lifting system; The control device receives the collected signals from the current sensor, voltage sensor and speed encoder, outputs PWM signals, controls the on and off status of the MOS tube in the three-phase bridge inverter, controls the on and off status of the relay in the energy supply and energy storage device, the current sensor is installed on the U and V phases of the three-phase wires of the three-phase inverter, the voltage sensor is installed on the output end of the supercapacitor and the battery, and the speed encoder is installed on the output shaft of the double-acting motor; The system also includes a hydraulically controlled oil replenishing valve and a closed pressure oil tank, the closed pressure oil tank is connected to the hydraulically controlled oil replenishing valve, the hydraulically controlled oil replenishing valve is connected in parallel to the oil outlet and the oil suction port of the double-acting motor, and the hydraulic oil in the closed pressure oil tank can be supplied to the oil outlet and the oil suction port of the double-acting motor respectively through two one-way valves of the hydraulically controlled oil replenishing valve; The system includes a safety valve, which is composed of two relief valves, and the two relief valves are respectively connected to the rod chamber and the rodless chamber of the lifting cylinder; The double-acting motor includes a motor and a generator, which outputs electrical energy when the double-acting motor rotates forward and generates electrical energy when the motor rotates reversely; The double-acting motor includes a motor and a pump. When the double-acting motor rotates forward, it generates attraction, and when the double-acting motor rotates reversely, it generates thrust. When the hydraulic oil flows into the hydraulically controlled one-way valve on the left side of the two-way hydraulic lock valve, the oil pressure controls the hydraulically controlled one-way valve on the right side of the two-way hydraulic lock valve to open in the reverse direction, and the hydraulic oil entering the rodless chamber of the lifting cylinder pushes the hydraulic oil in the rod chamber of the lifting cylinder through the hydraulically controlled one-way valve on the right side of the two-way lock valve and flows back to the double-acting motor. When the hydraulic oil flows into the hydraulically controlled one-way valve on the right side of the two-way hydraulic lock valve, the oil pressure controls the hydraulically controlled one-way valve on the left side of the two-way hydraulic lock valve to open in the reverse direction, and the hydraulic oil entering the rod chamber of the lifting cylinder pushes the hydraulic oil in the rodless chamber of the lifting cylinder through the hydraulically controlled one-way valve on the left side of the two-way lock valve and flows back to the double-acting motor. When the fork descends too fast, the current sensor and speed encoder on the generator transmit the working speed and torque state of the generator to the control device. The control device compares the actual speed signal of the generator with the given speed, adjusts the switching sequence of the MOS tube, increases the stator magnetic flux of the double-acting motor, increases the torque of the generator, increases the torque of the motor, increases the descending resistance of the hydraulic system, and the hydraulic oil flows slowly into the rod chamber of the lifting cylinder through the hydraulic control one-way valve on the right side of the two-way hydraulic lock valve. At the same time, the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve is hydraulically controlled to open in the opposite direction, and the hydraulic oil in the rodless chamber of the lifting cylinder flows slowly back to the double-acting motor through the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve, thereby slowing down the descending speed of the fork; When the fork descends too slowly, the current sensor and speed encoder on the generator transmit the generator working speed and torque state to the control device, adjust the MOS tube switching sequence, reduce the stator magnetic flux of the double-acting motor, reduce the generator torque, reduce the motor torque, reduce the hydraulic system descending resistance, and the hydraulic oil flows into the rod chamber of the lifting cylinder faster through the hydraulic control one-way valve on the right side of the two-way hydraulic lock valve. At the same time, the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve is hydraulically controlled to open in the opposite direction, and the hydraulic oil in the rodless chamber of the lifting cylinder flows back to the double-acting motor faster through the hydraulic control one-way valve on the left side of the two-way hydraulic lock valve, thereby accelerating the fork descending speed.