Structural characteristics and analysis of electric forklifts at home and abroad
The electric balance forklift is a loading and unloading and transportation vehicle powered by a DC power supply (battery). According to statistics from foreign sources, the output of electric forklifts in Japan exceeded 1/3 of the total volume of forklifts in 1992. In some Western European countries such as Germany and Italy, electric forklifts account for about 50%. The rapid development of electric forklifts is mainly due to the continuous progress of various manufacturers. Most of the appearance of the product adopts streamlined design, the shape is more beautiful. Major manufacturers have realized large-scale production and specialized production of parts and components and assembly line operations. Processing accuracy and automation have been improved. In terms of new materials and new processes, the most important manifestation is the application of transistor controllers (SCR and MOS tubes). The emergence of it has greatly improved the performance of electric forklifts. Overall, the durability, reliability and applicability of electric forklifts have been significantly improved, and they can fully compete with internal combustion engine forklifts.
This article mainly reviews the structural characteristics and development of the four-pivot electric balance forklift, which has a large sales volume in the market.
1 Car body
The car body is the main structure of the forklift, which is generally made of steel plates of more than 5mm. It is characterized by no girders, the car body has high strength and can withstand heavy loads.
As far as the placement of the battery on the forklift body is concerned, there are two different manufacturing techniques. That is, the battery is placed between the front and rear axles or on the rear axle.
These two technologies represent the two optimal choices for forklift design, and each has advantages and disadvantages and good stability, but the available space in the car body is small, so the capacity of the battery is limited, which is less than 3t Forklifts are not outstanding, but for those with complex movements, large-tonnage forklifts with high battery capacity requirements within 8 hours of work have become serious.
The use of large-capacity batteries to extend the continuous working time of electric forklifts and thereby expand the use of electric forklifts is the goal pursued by all forklift manufacturers.
For example, the R60/40 system forklift of Still Company, due to the adoption of the first technology, its maximum battery capacity is 80V, 870A.h; 69.6kW.h, while the R40 forklift of CARER Company adopts the second technology, the battery The capacity reaches 960A.h; 76.8kW.h (10.35% higher). The maximum capacity of the battery that can be installed on the E40 series forklift that Linde adopts the first technology is 735A.h, 58.8kW.h. The CARER forklift of the same specification, due to the use of the second technology, the maximum capacity of the battery can be increased by 30.6%.
In the second case, when the battery is arranged on the rear axle of the forklift, the center of gravity of the forklift is increased, and the stability of the whole machine is affected. Due to the height of the forklift, the driver's seat is increased, so the driver's vision is wider during operation, especially It is more suitable for handling bulky goods. When the battery is placed on the rear axle, the maintenance of the motor and hydraulic pump is more convenient, because after removing the battery and the foot pedal, the motor and hydraulic pump can be seen at a glance.
At present, most of the electric forklifts produced by domestic companies use the second technology, while foreign companies have both cases.
2 Door frame
At present, most of the electric forklifts at home and abroad have adopted wide-view gantry, and the lifting hydraulic cylinders have been placed from the middle to both sides. There are two types of hydraulic cylinder placement: one is the hydraulic cylinder is located behind the gantry, such as the electric forklift of Fushun Forklift Factory and Toyota; the other is the hydraulic cylinder is located outside the gantry, such as Nanjing Huarui Electric Forklift and BALKANCAR Forklift . The hydraulic cylinders of CARER's R40/45 series electric forklifts are located on the outside of the gantry, and the hydraulic cylinders of the R50/60/70 series forklifts are located behind the gantry.
The portal is generally divided into standard type, two-section type or three-section type. The lift height of domestic forklifts is generally between 2 and 5m, and most of them are below 3m and 3m, while the lift height of foreign electric forklifts is generally between 2 and 6m. Due to the high degree of three-dimensional warehouse, the lift Above 3m in height, the demand for electric forklifts is much higher than domestic ones.
3 Cab
Since most electric forklifts are used for indoor transportation, there is generally no closed cab, and only protective roof racks are installed. The world's most advanced electric forklifts, such as: LINDE's E20 new forklift cab, is developed according to advanced ergonomic principles. It adopts a comfortable hydraulic shock-absorbing suspension seat that can be adjusted according to the height and weight of the driver. . The double-pedal acceleration system does not require steering when the forklift changes the driving direction, and the inclination of the steering column can be adjusted according to the driver's requirements. The central hydraulic joystick integrates the lifting and front and rear of the mast. So these new designs have greatly reduced the driver's labor intensity.
4 Drive system
The drive system is one of the key components of the electric forklift. There are great differences in the structure of the drive system of various forklifts, and there are also differences in the arrangement of single motors. For example, the forklift produced in Fushun in China has a T-shaped structure for the motor shaft and drive axle, while foreign TOYOTA and BALKANCAR forklifts The drive motor shaft and drive axle are arranged and compact. The front wheel drive of LINDE's E20 electric forklift and CARER's P50 forklift is completed by two independent motors, which are placed parallel to the drive shaft and have a compact structure. Because it is driven by dual motors, it has good acceleration and climbing performance, and large traction. It uses an electronic full-speed system to replace the original mechanical differential system, and its usability has been greatly improved.
5 Hydraulic system
Electric forklifts generally use a separate motor to drive the gear pump, thereby providing hydraulic power for the lifting and tilting of its gantry working system. At present, for domestic forklifts, since the speed adjustment of the hydraulic motor is not achieved, the hydraulic motor can only rotate at a high speed after starting, and will not automatically adjust with the change of function and pressure, and the excess flow can only flow back to the tank through the overflow valve. Cause energy waste. New foreign forklifts, such as LINDE's E20 electric forklift, use advanced hydraulic pulse control technology. The hydraulic pump pulse controller can automatically balance the motor speed and oil consumption according to the response of the hydraulic circuit, thereby saving electrical energy. The advantages of this control It is high power utilization, no voltage peak, low noise of hydraulic system, and low wear of hydraulic components, thus greatly improving the reliability and service life of the vehicle.
6 Braking system
The general electric forklift mainly uses mechanical parking brake and hydraulic service brake. Hand brake is used for parking, and foot brake is used for driving.
NISSAN BX series electric forklift braking system is equipped with a leading vacuum booster, which can ensure that there is enough active pressure at any time, which not only increases the safety of braking, but also reduces the labor intensity of the driver.
CARER electric forklift adopts hydraulic brake system. The expansion brake has external control and uses power-assisted braking (same as the power form of the power steering system).
The use of SCR and MOS tubes makes it possible to regenerate the braking energy of battery forklifts. The energy regeneration process is also an electronic braking process. Electronic braking is generated under the following three conditions:
(1) When releasing the accelerator control pedal.
(2) When stepping on the reverse accelerator pedal.
(3) When stepping on the first stage of the hydraulic brake pedal.
For LINDE's E20 and CARER's P50 electric forklifts, when the brake is first or lightly depressed, the traction motor will become a generator, which will supply electrical energy back to the battery, unlike the ordinary forklift that will be in vain when braking. Wasted. Only when further braking, the hydraulic brake really works. The advantage of this braking system is to extend the working time after each charge, reduce the wear of the brake system and transmission elements, and also reduce the downtime of maintenance, thus reducing the cost of use.
7 Steering system
Balance forklifts use rear wheel steering, and the working range is small, and the steering movement is frequent. If mechanical steering is used, the driver's work intensity will be high. If hydraulic power steering is used, the labor intensity will be greatly reduced. Therefore, the forklifts currently on the market have basically achieved power steering. The hydraulic steering of domestic battery forklifts is generally the steering motor running at full load during the work of the forklift, thus causing unnecessary energy waste and reduced wear of the motor and hydraulic pressure. However, battery forklifts of companies such as LINDE and NISSAN have taken power steering even further. That is, when the steering wheel is not moving, the steering motor does not work. This function not only saves energy, but also prolongs the working time after recharging and shortens the idle time of the steering motor, so it also reduces the wear of the motor and hydraulic pump.
The battery forklift of Komatsu Japan uses EPS speed sensor power steering. The system is a "load-sensing" steering with a servo brake and power hydraulic steering type priority distribution valve. The power steering system uses the power of the lifting motor to automatically select the best force required for steering.
8 Electronic control and self-diagnosis and LCD display system
Electrical control is an important factor that shows the technical level of electric forklifts. Therefore, with the development of electronic technology, the electric control of battery forklifts is becoming more and more perfect. The development of the motor controller has mainly experienced the following stages:
(1) The battery starts directly, only relying on complicated adjustment or battery discharge control.
(2) The resistor starts. The control energy loss is large, and the decomposition speed can only be limited.
(3) Controlled by thyristor controller (also called thyristor controller).
Transistor control greatly improves reliability.
(4) Bipolar transistor control. Compared with the thyristor, the use is simpler, but the reliability of the circuit is relatively high.
(5) Control of MOS field effect tube (ie metal-oxide-semiconductor field effect tube). The gate drive current is small, the parallel control characteristics are good, the forward voltage drop is small, and the switching loss is reduced. The MOS field effect transistor has better control characteristics than the bipolar transistor. Due to the reduction of components and the use of fully enclosed devices, the reliability is greatly improved. Usually the socket voltage of SCR (silicon controlled) controller is 1~1.5V, while the socket voltage of MOS field effect transistor controller is 0.25V. MOS tube field effect tube has higher working efficiency, greater maximum speed allowed, less operation noise and stronger protection measures, so the user power supply has anti-short circuit protection device, and has three unique safety protection measures, namely Software automatic protection measures, hardware automatic protection and hardware self-diagnosis protection.
The successful application of the transistor chopper in the forklift, in addition to achieving stepless speed regulation and regenerative braking, also added self-fault diagnosis and liquid crystal digital display functions.
Japan Komatsu Electric Forklift is equipped with a liquid crystal display controller, represented by various symbols, with readability. The indicator warns the driver of possible errors, including releasing and locking the parking brake, safety neutral interlock and excessive discharge of the battery, showing various data including battery discharge, electrolyte amount, working time and driving Speed, etc., can report the possible faults to the driver at any time, which greatly facilitates the maintenance and repair of the forklift. At the same time, it can provide the driver with parameters such as driving speed and forklift weight, and also provide a basis for the driver's scientific operation, thereby extending the service life of the forklift.
