Battery maintenance knowledge.

2022-10-09

Electric balanced forklift is a loading, unloading and handling vehicle powered by DC power (battery). According to foreign statistics, the output of electric forklifts in Japan has exceeded 1/3 of the total number of forklifts. In some Western European countries such as Germany and Italy, the proportion of electric forklifts has reached about 50%. The rapid development of electric forklift mainly benefits from the continuous progress of various manufacturers. The product shape is mostly streamlined design, which makes it more beautiful. The major manufacturers have realized large-scale production, specialized production of parts and assembly lines. The machining accuracy and automation have been improved. In terms of new materials and new processes, the most important embodiment is the application of transistor controllers (SCR and MOS tubes). Its appearance has greatly improved the use performance of electric forklifts. On the whole, the durability, reliability and applicability of electric forklifts have been significantly improved, which can completely compete with diesel forklifts. This paper mainly reviews the structural characteristics and development of the four fulcrum electric balanced forklift truck with 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 5 mm. It is characterized by no girder, high strength and can withstand heavy loads. As far as the storage battery is placed on the forklift body, there are two different manufacturing technologies, namely, the storage battery is placed between the front and rear axles or on the rear axle. These two technologies represent two optimal choices for forklift design, each with advantages and disadvantages and good stability. However, the available space in the vehicle body is small, which limits the capacity of the battery. This is not prominent for forklifts with a load capacity of no more than 3t, but it is serious for those large tonnage forklifts with complex movement conditions that require high battery capacity within 8h working time. It is the common goal of all forklift manufacturers to adopt large capacity batteries to extend the continuous working time of electric forklifts and thus expand the use range of electric forklifts. 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. As the height of the forklift increases, the driver's seat is improved, so the driver has a wider vision during operation, especially when handling large goods. When the battery is placed on the rear axle, the maintenance of the motor and hydraulic pump is more convenient, because the motor and hydraulic pump can be seen at a glance after the battery and pedal are removed. At present, most electric forklifts produced by domestic enterprises use the second technology, while foreign enterprises have both.

2. Gantry

At present, most electric forklifts at home and abroad have adopted wide field of view gantry, and the lifting hydraulic cylinders are placed on both sides instead of in the middle. The hydraulic cylinder can be placed in two positions: one is located behind the gantry; The other is that the hydraulic cylinder is located outside the gantry. The portal frame is generally divided into standard type, two section type or three section type. The lifting height of domestic forklift trucks is generally 2~5m, and most of them are 3m or less, while the lifting height of foreign electric forklift trucks is generally 2~6m. Due to the high degree of three-dimensional warehouse, the lifting height is more than 3m, and the demand for electric forklift trucks is much higher than that in China.

3. Cab

As most electric forklifts are used for indoor handling, there is generally no closed cab, and only a protective roof frame is installed. The world's more advanced electric forklift is developed according to advanced ergonomic principles. It uses comfortable hydraulic damping suspension seats and can be adjusted according to the driver's height and weight. The dual pedal acceleration system does not need to turn 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 control lever integrates the lifting, front and back of the mast. Therefore, 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 drive system structure of various forklifts, and there are also differences in the single motor layout. Due to the dual motor drive, good acceleration and climbing performance, and large traction, the electronic speed regulating system is adopted to replace the original mechanical differential system, and the usability has been greatly improved.

5. Hydraulic system

Electric forklift generally adopts a separate motor to drive the gear pump, so as to provide hydraulic power for the lifting and tilting of its gantry working system. At present, the domestic forklift does not realize the speed regulation of the hydraulic motor. After starting, the hydraulic motor can only rotate at a high speed and will not automatically adjust with the change of function and pressure. Excess flow can only flow back to the oil tank through the overflow valve, causing energy waste. New foreign forklift trucks, such as the E20 electric forklift of LINDE, have adopted 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, so as to save electric energy. The advantages of this control are high power utilization, no voltage peak, low noise of the hydraulic system, and low wear of hydraulic components, thus greatly improving the reliability and service life of the whole vehicle.

6. Brake system

General electric forklift mainly adopts mechanical parking brake and hydraulic service brake. Hand brake is used for parking and foot brake is used for driving. The brake system of BX series electric forklift is equipped with a leading vacuum booster, which can ensure that there is sufficient active pressure at any time, which not only increases the safety of braking, but also reduces the labor intensity of the driver. Electric forklift adopts hydraulic braking system. The expansion brake has external control and uses power assisted braking (the same power form as the power steering system). The use of SCR and MOS tubes makes it possible to regenerate the braking energy of the battery forklift. The energy regeneration process is also an electronic braking process. The electronic braking is generated under the following three conditions:

(1) When the accelerator control pedal is released.

(2) When the reverse accelerator pedal is depressed.

(3) When the first stage of the hydraulic brake pedal is depressed.

For E20 and CARER P50 electric forklifts, when the brake is applied for the first time or lightly, the traction motor will become a generator to supplement the electric energy back to the battery, instead of wasting the energy when braking ordinary forklifts. Only when the brake is further applied can the hydraulic brake really work. The advantage of this braking system is that it prolongs the working time after each charging, reduces the wear of the braking system and transmission components, and also reduces the downtime for maintenance, thus reducing.

Balanced forklifts all adopt rear wheel steering, with small working range and frequent steering movement. If mechanical steering is adopted, the working intensity of the driver will be high. If hydraulic power steering is adopted, the labor intensity will be greatly reduced. Therefore, forklift trucks sold on the market have basically achieved power steering. The hydraulic steering of domestic battery forklift is generally that the steering motor runs continuously at full load during the operation of the forklift, resulting in unnecessary energy waste and wear of the motor and hydraulic reducer. However, the power steering of battery forklifts from LINDE, NISSAN and other companies is further improved, that is, when the steering wheel does not move, the steering motor does not work. This function not only saves energy, but also prolongs the working time after recharging, shortens the idling time of the steering motor, and therefore reduces the wear of the motor and hydraulic pump.

7. The electric control and its self diagnosis and the electric control of the LCD display system are important factors for displaying the technical level of the electric forklift. Therefore, with the development of electronic technology, the electric control of battery forklift is becoming more and more perfect. The development of motor controller mainly goes through the following stages:

(1) The battery can be started directly only by complex adjustment or battery discharge control.

(2) The resistor is activated. The control energy loss is large, and the speed can only be limited.

(3) Thyristor controller (also called silicon controlled controller) control. The transistor control greatly improves the reliability.

(4) Bipolar transistor control. Compared with the thyristor, it is simpler to use, but the reliability of the circuit is relatively high.

(5) MOS FET (metal oxide semiconductor FET) control. 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 FET 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. Generally, the socket voltage of SCR (silicon controlled rectifier) controller is 1~1.5V, while that of MOSFET controller is 0.25V. MOS FET has higher working efficiency, higher allowable maximum speed, lower operating noise and stronger protection measures. All user power supplies are equipped with short circuit protection devices, and have three unique safety protection measures, namely, software automatic protection measures, hardware automatic protection and hardware self diagnosis protection. The successful application of transistor chopper on forklift truck not only realizes stepless speed regulation and regenerative braking, but also adds self fault diagnosis and LCD digital display functions.

Previous: Operation method of electric tractor. Next: Type and use of lifting table