CN100386254C - An energy recovery type electric forklift lifting control system - Google Patents

Abstract

The invention discloses an energy recovery type electric forklift lifting control system, the system includes a motor, a pump-motor, an oil supply device, an electro-hydraulic servo valve, a lifting cylinder, a control device, and a storage battery; the motor drives a pump in the hydraulic system - The motor, under the action of the control device, the electro-hydraulic servo valve controls the action of the lifting cylinder of the actuator. In addition to the drive control function of the lifting cylinder of the actuator, the control system makes the motor work in the regenerative braking mode during the rising and falling deceleration of the lifting cylinder, and the braking energy is recovered through the boost circuit and stored in the battery . In addition, when the heavy load is lowered, the potential energy of the heavy object drives the motor to reverse through the hydraulic pump-motor, so that the motor is in the state of generating electricity under the opposite working condition, and the potential energy of the heavy object is converted into electrical energy and stored in the battery. Therefore, the control system can not only realize the kinetic energy recovery of the electric forklift, but also realize the potential energy recovery of the falling weight. The utility model has the advantages of simple structure, low cost and great economic value.

Description

An energy recovery type electric forklift lifting control system

technical field

The invention belongs to the field of electric forklift lifting device control, and in particular relates to an energy recovery type electric forklift lifting control system, which can recycle and control the braking energy of the electric forklift lifting device during the braking process and the heavy object potential energy during the falling process of the heavy object.

Background technique

In recent years, with the development of industrial technology worldwide, the problems of energy shortage and environmental pollution have become increasingly serious. Electric forklifts, a product that integrates electronic technology and hydraulic technology, are changing rapidly. At present, electric forklifts account for 50% of the stock in foreign markets. ~60%, while the current holdings in my country account for about 15~20%, which has a broad market prospect. The electric forklift lifting device mostly adopts the drive mode of motor-hydraulic system-hydraulic cylinder, which has the disadvantages of low efficiency and high energy consumption. The energy-saving issue of electric forklifts has attracted widespread attention in the industry. The lifting cylinder of the electric forklift is characterized by frequent reciprocating motion, which requires repeated lifting and lowering of heavy objects, a large lifting force, and often bears negative loads. When the heavy object falls, its gravitational potential energy and kinetic energy are converted into throttling loss of the hydraulic system, which not only causes waste of energy, but also causes heat, noise and vibration of the hydraulic system. Even cause system failure and reduce system life and other hazards. In recent years, energy recovery technology has become a key research direction of hydraulic system energy saving. In addition, the ratio of the rated load to the minimum load of the lifting system is 6:1 to 8:1, so the no-load speed should be higher than the full-load speed. At present, most electric forklifts adopt throttling speed regulation to adjust the lifting speed, resulting in low operating efficiency of the hydraulic system and large energy loss. The power of the motor cannot be fully utilized, the no-load speed of the forklift is basically the same as the full-load speed, and the lifting efficiency needs to be improved.

Contents of the invention

Aiming at the defects and deficiencies in the above-mentioned prior art, the present invention provides an energy recovery type electric forklift lifting control system, which controls the motor to It works in the state of regenerative braking, and feeds back the electric energy generated by regenerative braking and stores it in the battery. When the heavy load is lowered, the potential energy of the heavy object drives the motor to reverse through the hydraulic pump-motor, so that the motor is in a state of generating electricity under the reverse working condition. The potential energy of the heavy object is converted into electrical energy and stored in the battery. In addition, in the driving control of the lifting cylinder of the actuator, the electric forklift realizes double speed regulation, and comprehensively utilizes the advantages of high response accuracy of the valve control system and high efficiency of the pump control system.

In order to achieve the above object, the technical solution adopted by the present invention is: an energy recovery electric forklift lifting control system, which is characterized in that the system includes a motor, a pump-motor, an oil supply device, an electro-hydraulic servo valve, and a lifting cylinder , control device, battery; the motor and displacement are connected to the pump-motor with the same area as the two chambers of the oil cylinder; the T port and P port of the electro-hydraulic servo valve are respectively connected to the oil discharge port and oil suction port of the pump-motor, and the electro-hydraulic servo valve Port A and port B of the valve are respectively connected to the rodless chamber and the rod chamber of the lift cylinder; the oil supply device is connected to the pump-motor oil discharge port and oil suction port, and is connected to the P port and T port of the electro-hydraulic servo valve ; The control device is connected to the storage battery and the lifting motor through electrical connection, and is respectively connected to the control signal interface of the electro-hydraulic servo valve, the second signal sensor set on the lifting cylinder and the first signal set on the motor through the control signal connection line. The sensor is connected.

The control device includes a control circuit board and a motor-driven DC/DC converter, wherein the control circuit board includes a filter circuit, a microprocessor, a photoelectric isolation circuit and a power drive circuit, and the control circuit board collects command signals and the first 1. The second sensor signal, the microprocessor performs data processing on the collected signal and then outputs the PWM signal through the photoelectric isolation circuit. One group is connected with the control signal interface of the electro-hydraulic servo valve, and the other group is driven by the motor through the power drive circuit. The control terminals of each power device of the DC/DC converter are connected.

The technical effect that the present invention brings is:

1) Double speed adjustment scheme is adopted. When the control signal is small, the control device adjusts the opening of the electro-hydraulic servo valve through PWM waveform to realize high-precision control of the valve control system. When the control signal is large, the control device adjusts the speed through PWM The speed of the motor is adjusted by the method, and the execution speed of the hydraulic cylinder is adjusted through the displacement of the pump-motor to achieve high-efficiency control of the pump control system. In this way, the constant torque adjustment can be realized at the rated speed, and the constant power adjustment can be realized when the rated power is exceeded, and the lifting speed at full load and no load can be adjusted respectively, so as to improve the operating efficiency of the forklift.

2) This system can realize the kinetic energy recovery of the actuator and the potential energy recovery of heavy objects without adding generators and energy storage components. During the deceleration process of lifting and lowering heavy objects by the lifting cylinder, the control device makes the motor work in the regenerative braking mode, and the braking energy is recovered by the DC/DC converter boost circuit driven by the motor and stored in the battery. In addition, when the lifting cylinder lowers a heavy load, the falling potential energy of the heavy object is recovered by using the feedback power generation braking principle of the motor, and stored in the battery. Since the feedback energy is stored in the storage battery, the service time of the storage battery is greatly increased, the throttling loss of the system is reduced, and the working efficiency of the system is improved.

Description of drawings

Fig. 1 is the structural diagram of the lifting control system of the energy recovery type electric forklift of the present invention, the system consists of a motor 1, a pump-motor 2, an oil supply device 3, an electro-hydraulic servo valve 4, a lifting cylinder 5, a control device 6, and a storage battery 7 composition.

Figure 2 is a schematic diagram of the control device;

Fig. 3 is a driving current direction diagram of the lifting cylinder for lifting heavy objects.

Fig. 4 is a direction diagram of the braking energy feedback current of the lifting cylinder lifting heavy objects.

Fig. 5 is the driving current direction diagram of the lifting cylinder for lowering lighter and heavier objects.

Fig. 6 is the current direction diagram of the braking energy feedback of the lifting cylinder for lowering the lighter weight and the potential energy feedback of the lowering of the heavier weight.

The present invention will be described in further detail below in conjunction with accompanying drawings and examples.

Detailed ways

The invention includes a permanent magnet brushless DC motor 1, a pump-motor 2, an oil supply device 3, an electro-hydraulic servo valve 4, a lifting oil cylinder 5, a control device 6, and a lead-acid storage battery 7. Its interconnection relationship is as follows:

1) The permanent magnet brushless DC motor 1 is connected to the pump-motor 2 whose displacement is equivalent to the area of the two cavities of the lifting cylinder.

2) The P port and the T port of the electro-hydraulic servo valve 4 are respectively connected with the oil discharge port and the oil suction port of the pump-motor 2, and the A port and the B port of the electro-hydraulic servo valve 4 are connected with the rodless chamber and the lift cylinder 5 respectively. There are rod cavities connected. The oil supply device 3 is connected to the oil discharge port and the oil suction port of the pump-motor 2, and is connected to the P port and the T port of the electro-hydraulic servo valve 4;

3) The control device 6 is respectively connected to the motor 1 and the storage battery 7 via electrical connecting wires. The control device 6 is respectively connected to the control signal interface of the electro-hydraulic servo valve 4 , the first signal sensor on the motor 1 and the second signal sensor on the lifting cylinder 5 via the control signal connection line.

The control device includes a control circuit board and a motor-driven DC/DC converter. As shown in Figure 2, the control circuit board includes a filter circuit, a microprocessor, a photoelectric isolation circuit and a power drive circuit. The microprocessor adopts DSP, the filter circuit adopts a typical filter circuit built by an operational amplifier, the photoelectric isolation circuit is realized by an optocoupler, and the power drive circuit adopts a modular design. The various levels required by the control device are powered by batteries, which are provided by matching with ordinary DC/DC switching power supplies. For permanent magnet brushless DC motors, the motor-driven DC/DC converter in the control device is composed of six power devices, power devices VT1 and VT4, VT3 and VT6, VT2 and VT5, which respectively form a drive half bridge to form a three-phase inverter bridge. , the two ends of the three-phase inverter bridge are connected in parallel with the storage battery, the middle of VT1 and VT4, VT3 and VT6, VT2 and VT5 are respectively connected with the motor winding.

The working principle of the present invention is as follows:

The control circuit board receives command signals and signals from the first and second sensors through the input filter circuit, and the signals include motor voltage, current signals, and hydraulic cylinder speed and displacement signals. The microprocessor performs data processing on the collected signals and outputs PWM signals through the photoelectric isolation circuit. A group of PWM signals are directly connected to the control signal interface of the electro-hydraulic servo valve to control the opening of the electro-hydraulic servo valve and realize high-precision control of the valve control system. The other group of PWM signals controls the action of each power device of the motor-driven DC/DC converter through the power drive circuit to realize the control of motor drive and braking. When the motor is driven, the DC/DC converter works in step-down mode, and the motor speed is adjusted by adjusting the duty cycle of the PWM signal. Since the motor and the pump-motor are coaxially connected, the displacement of the pump-motor is changed accordingly, so as to realize the high efficiency of the pump control system. efficiency control. When the motor brakes, the DC/DC converter works in boost mode, and adjusts the duty ratio of the PWM signal accordingly to adjust the braking torque of the motor, so as to realize regenerative braking of the motor and power generation braking under reverse working conditions. Therefore, on the one hand, this system can realize the dual speed control of the actuator, and comprehensively utilize the advantages of the high response accuracy of the valve control system and the high efficiency of the pump control system; on the other hand, it can realize the kinetic energy recovery of electric forklifts and the potential energy recovery of heavy objects .

When the actuator lifts the cylinder 5 to lift heavy objects, the DC/DC converter works in step-down mode, the motor 1 works in the first quadrant, and the current of the battery 7 flows into the motor 1 through the DC/DC converter in positive phase. The motor 1 is driven to rotate in the positive direction, and the current direction is shown in FIG. 3 . The control device 6 further adjusts the duty cycle of the PWM signal according to the instruction signal and the sensor signal to realize the dual speed regulation control of the lifting cylinder 5 .

When the lifting cylinder 5 of the actuator lifts the heavy object to brake, the DC/DC converter works in the boost mode, and the motor 1 works in the second quadrant. At this time, due to the freewheeling effect of the winding inductance of the motor 1, the regeneration of the motor 1 The kinetic energy is fed back to the battery 7 through DC/DC converter boost conversion, and the current direction is shown in FIG. 4 , and the braking torque is adjusted by adjusting the duty ratio of the PWM signal.

When the lifting cylinder 5 of the actuator lowers a lighter weight, since the load of the heavy object is not enough to overcome the system resistance to drive the pump-motor 2 to reverse, the load of the heavy object must be driven by the motor 1 to drive the pump-motor 2 to lower, at this time DC/DC The converter works in the step-down mode, and the motor 1 works in the third quadrant. The current of the battery 7 flows into the motor 1 in reverse phase through the DC/DC converter, driving the motor 1 to rotate in the opposite direction. The current direction is shown in Figure 5.

When the lifting cylinder 5 of the actuator is lowered to brake with a lighter weight, the DC/DC converter works in the boost mode, and the motor 1 works in the fourth quadrant. The kinetic energy is fed back to the storage battery 7 through the step-up conversion of the DC/DC converter, and the current direction is shown in FIG. 6 .

When the actuator lifts the cylinder 5 to lower the heavy object, the load of the heavy object is enough to overcome the system resistance, the hydraulic cylinder 5 drives the pump-motor 2 to rotate under the action of the heavy object load, and at the same time drives the motor 1 to reverse, so that the motor 1 works at In the power generation state of the reverse working condition, the electric energy is fed back to the storage battery 7 to realize the recovery of the potential energy of the heavy object. At this time, by controlling the conduction time of the power device of the DC/DC converter, the braking torque of the motor 1 and the magnitude of the feedback current can be controlled to ensure the lowering speed of the actuator. The current direction is shown in Figure 6.

Claims (4)

1. an electric regenerative electri forklift lifting control system is characterized in that, this system comprises motor (1), pump-motor (2), recharging oil device (3), electrohydraulic servo valve (4), elevating ram (5), control setup (6), storage battery (7); Motor (1) links to each other with the cooresponding pump-motor of two cavity areas (2) of oil cylinder with discharge capacity; The T mouth of electrohydraulic servo valve (4) links to each other with oil suction with the oil discharge outlet of pump-motor (2) respectively with the P mouth, and the A mouth of electrohydraulic servo valve (4) links to each other with rod chamber with the rodless cavity of elevating ram (5) respectively with the B mouth; Recharging oil device (3) is connected pump-motor (2) oil discharge outlet and oil suction, and links to each other with the T mouth with the P mouth of electrohydraulic servo valve (4); Control setup (6) links to each other with lifting motor (1) with storage battery (7) respectively through electrical cable, and links to each other with first signal transducer that motor (1) is gone up setting with the control signal interface of electrohydraulic servo valve (4), the secondary signal sensor that elevating ram (5) is gone up setting respectively by the control signal connection lead;

Described control setup (6) comprises control circuit board and motor-driven DC/DC changer, wherein control circuit board comprises filter circuit, microprocessor, photoelectric isolating circuit and power driving circuit, control circuit board is by input filter circuit acquisition instructions signal and first, second sensor signal, microprocessor carries out data handing after the photoelectric isolating circuit output pwm signal to the signal that collects, one group links to each other with the control signal interface of electrohydraulic servo valve, and another group links to each other through the control end of power driving circuit with each power device of motor-driven DC/DC changer.

2. electric regenerative electri forklift lifting control system as claimed in claim 1 is characterized in that described motor (1) is permanent-magnet brushless DC electric machine or permanent magnet brush DC machine.

3. the electri forklift lifting control system with energy recovery as claimed in claim 1 is characterized in that described storage battery (7) is lead-acid battery or lithium cell or Ni-MH battery.

4. electric regenerative electri forklift lifting control system as claimed in claim 4, it is characterized in that for permanent-magnet brushless DC electric machine, motor-driven DC/DC changer is made up of six power devices in the control setup, power device VT1 and VT4, VT3 and VT6, VT2 and VT5 form the driving half-bridge respectively and constitute three phase inverter bridge, the two ends and the storage battery of three phase inverter bridge are connected in parallel, VT1 and VT4, VT3 and VT6, the centre of VT2 and VT5 is connected with machine winding respectively.

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