Structural and technical characteristics of electric forklift

Structural and technical characteristics of electric forklift

1. Car body

Electric balance forklift is loading, unloading, and handling vehicle powered by a DC power supply (battery). According to foreign statistics, Japanese electric forklift “The output has exceeded 1 / 3 of the total number of forklifts. In Germany, Italy and other Western European countries, the proportion of electric forklifts has reached about 50%. The rapid development of electric forklifts is mainly due to the continuous progress of various manufacturers. Most of the products adopt streamlined design and have a more beautiful appearance. The leading manufacturers have realized large-scale production and specialized parts and components Assembly line operation. The machining accuracy and automation have been improved. In terms of new materials and processes, the most critical embodiment is the application of transistor controller (SCR and MOS). Its appearance has dramatically improved the service performance of electric forklifts. Overall, electric forklifts’ durability, reliability, and applicability have been significantly improved, competing with internal combustion engine forklifts. This paper mainly reviews the structural characteristics and development of four fulcra electric balanced forklifts with significant sales in the market.

The car body is the main structure of the forklift, which is generally made of a steel plate of more than 5mm. It is characterized by no girder, high strength, and can bear a heavy load. As for the placement position of the battery on the forklift truck body, there are two different manufacturing technologies: the battery is placed between the front and rear axles or on the rear axle. These two technologies represent two optimal choices for forklift design, and each has advantages and disadvantages and good stability. However, the available space in the vehicle body is small, limiting the battery’s capacity, which is not prominent for forklifts with a load capacity of no more than 3T. However, it becomes serious for large tonnage forklifts with complex movement and high requirements for battery capacity within 8h working time.

The common goal of forklift manufacturers is to adopt high-capacity batteries to prolong the continuous working time of electric forklifts and expand the application range of electric forklifts.

For example, due to the adoption of the first technology, the R60 / 40 system forklift of the still company has a maximum battery capacity of 80V and 870a h; 69.6kW. h. The R40 forklift of the carer company adopts the second technology, and the battery capacity reaches 960A h; 76.8kW. H (10.35% higher). The maximum capacity of batteries installed on the E40 series forklift of Linde company adopting the first technology is 735a h,58.8kW. h。 For the forklift of carer company with the exact specification, due to the adoption of the second technology, the maximum capacity of the battery can be installed increased by 30.6%.

In the second case, when the battery is arranged on the forklift’s rear axle, the forklift’s centre of gravity is improved, and the stability of the whole machine is affected. Due to the increase of the height of the forklift and the improvement of the driver’s seat, the driver has a wider field of vision during operation, especially when handling large goods. The motor and hydraulic pump maintenance are more convenient when the battery is placed on the rear axle. After removing the battery and pedal, the motor and hydraulic pump can be seen. 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 view gantry, and the hydraulic lifting cylinder is placed on both sides instead of the middle. There are two positions for the hydraulic cylinder: the hydraulic cylinder is located behind the gantry, such as Fushun forklift factory and Toyota’s electric forklift; The other is that the hydraulic cylinder is located outside the gantry, such as Nanjing Huarui electric forklift and balance forklift. The hydraulic cylinder of the R40 / 45 series electric forklift of the carer company is located outside the gantry, and the hydraulic cylinder of the R50 / 60 / 70 series forklift is located behind the gantry.

Gantry is generally divided into standard, two-section, or three-section types. The lifting height of domestic forklift is generally between 2 ~ 5m, and most of them are 3M and below, while the lifting height of foreign electric forklift is generally between 2 ~ 6m. Due to the high three-dimensional degree of the warehouse, the lifting height is more than 3m, and the demand for electric forklifts is much higher than that in China.

3. Cab

Since most electric forklifts are used for indoor handling, there is generally no closed cab, and only the protective top frame is installed. The world’s more advanced electric forklifts, such as Linde’s E20 new forklift cab, are developed according to advanced ergonomic principles and adopt comfortable hydraulic damping suspension seats, which 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 wheel column can be adjusted according to the driver’s requirements. The central hydraulic control lever integrates the gantry’s lifting, front, and rear. Therefore, these new designs significantly reduce the labour intensity of drivers.

4. Drive system

The Drive system is one of the critical components of the electric forklift. There are great differences in the drive system structure of various forklifts, and there are also differences in the layout form of a single motor. For example, the motor shaft and drive axle are T-shaped structures for domestic forklifts, while the drive motor shaft and drive axle of foreign forklifts such as Toyota 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 placed parallel to the driveshaft and compact. Due to the dual-motor drive, good acceleration and climbing performance, and enormous traction, the whole electronic speed system is adopted to replace the original mechanical differential system, and the usability has been dramatically improved.

Electric forklifts generally use separate motors to drive gears to provide hydraulic power for the lifting and tilting their working gantry system. At present, the domestic forklift has not realized the speed regulation of the hydraulic motor. After starting, the hydraulic motor can only rotate at high speed and will not automatically adjust with the change of function and pressure. The excess flow can only flow back to the oil tank through the overflow valve, resulting in a waste of energy. New foreign forklifts, such as Linde’s E20 electric forklift, adopt 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 to save electric energy. The advantages of this control are:

Thus, the reliability and service life of the whole forklift is greatly improved.

5. Braking system

General electric forklift mainly adopts mechanical parking brake and hydraulic service brake. The hand brake is used for parking, and the foot brake is used for driving. Nissan BX series electric forklift braking system is equipped with a leading vacuum booster, which can ensure sufficient active pressure at any time, which increases braking safety and reduces drivers’ labour intensity. Carer electric forklift adopts a hydraulic braking system. The expansion brake has external control and adopts 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 in the following three cases: (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 Linde’s E20 and carer’s P50 electric forklifts, when the brake is pressed gently, or the first time, the traction motor will turn into a generator to supplement the electric energy back to the battery, rather than the battery wasting the energy when the forklift is braked. Only when further braking, hydraulic braking, will work. The advantage of this braking system is that it prolongs the working time after each charge, reduces the wear of the braking system and transmission components, and reduces the downtime of maintenance, reducing the cost.

The balance forklift adopts rear-wheel steering, with a small working range and frequent steering movement. The driver’s working intensity will be very high if mechanical steering is used. If hydraulic power steering is adopted, the labour intensity will be significantly reduced. Therefore, the forklifts sold on the market have realized power steering. The hydraulic steering of a domestic battery forklift is generally that the steering motor runs at full load continuously during the working process of forklift, resulting in unnecessary energy waste and wear of motor and hydraulic pressure. However, the power steering of the battery forklifts of Linde and Nissan takes a step further. When the steering wheel is stationary, the steering motor does not work. This function saves energy and prolongs the working time after recharging, shortens the idle time of the steering motor, and therefore reduces the wear of the motor and hydraulic pump.

6. Electric control and its self-diagnosis and liquid crystal display system

Electrical control is an essential factor in showing the electric forklift’s technical level. Therefore, with the development of electronic technology, the electric control of battery forklifts is becoming more and more perfect. The development of motor controller mainly goes through the following stages:

(1) The battery starts directly and only depends on complex adjustment or battery discharge control.

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

(3) Controlled by thyristor controller (also known as thyristor controller). Transistor control dramatically improves reliability.

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

(5) MOS FET (metal oxide semiconductor FET) control. The gate driving current is small, the parallel control characteristic is good, the forward voltage drop is small, the switching loss is reduced, and the control characteristic of MOS FET is better than that of the bipolar transistor. Due to the reduction of components and the use of the fully enclosed device, the reliability is greatly improved. Generally, the socket voltage of the SCR (silicon controlled rectifier) controller is 1 ~ 1.5V, while the socket voltage of the MOS FET Controller is 0.25V. MOS FET has higher working efficiency, higher allowable maximum speed, lower operating noise and more robust protection measures. Therefore, all user power supplies have anti short circuit protection devices and three special safety protection measures, namely software automatic protection measures, hardware automatic protection and hardware self-diagnosis protection. The successful application of transistor chopper in forklift realizes step-less speed regulation and regenerative braking and increases the functions of self fault diagnosis and LCD digital display.

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