Electric balance forklift is a loading, unloading and handling vehicle powered by a DC power source (battery). According to foreign data statistics, the production of electric forklifts in Japan has exceeded one-third of the total number of forklifts. In some Western European countries such as Germany and Italy, the proportion of electric forklifts reaches about 50%. The rapid development of electric forklifts is mainly due to the continuous progress of various manufacturers. The product appearance mostly adopts streamlined design, which makes the shape more beautiful. The main manufacturers have achieved large-scale production and specialized production of components, as well as assembly line operations. The processing accuracy and automation level have been improved. In terms of new materials and processes, the most important manifestation is the application of transistor controllers (SCR and MOS transistors). Its appearance 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 point electric balance forklift with high sales in the market.
1. Vehicle body
The body of the forklift is the main structure, usually made of steel plates with a thickness of 5mm or more. Its characteristic is the absence of large beams, high body strength, and the ability to withstand heavy loads. There are two different manufacturing techniques for placing the battery on the forklift body, namely placing the battery between the front and rear axles or on the rear axle. These two technologies represent the two optimal choices for forklift design, each with its own advantages and disadvantages. They have good stability, but the available space inside the vehicle is relatively small, which limits the capacity of the battery. This is not particularly prominent for forklifts with a load capacity of no more than 3 tons, but it becomes serious for large tonnage forklifts with complex motion conditions and high battery capacity requirements within 8 hours of operation.
The use of high-capacity batteries to extend the continuous working time of electric forklifts and expand their range of use is a common goal pursued by forklift manufacturers.
For example, STILL's R60/40 system forklift, due to the use of the first technology, has a maximum battery capacity of 80V, 870A. h; 69.6kW.h, And CARER's R40 forklift, due to the use of the second technology, has a battery capacity of 960 A. h; 76.8kW. h (10.35% higher). The maximum capacity of batteries that can be installed on the E40 series forklifts using the first technology at LINDE company is 735A. h and 58.8kW. h. Due to the use of the second technology, the maximum capacity that can be installed with a battery has increased by 30.6% for CARER forklifts of the same specifications.
In the second scenario, when the battery is placed on the rear axle of the forklift, the center of gravity of the forklift increases and the stability of the entire machine is affected. Due to the increase in height of the forklift, the driver's seat is raised, so the driver's field of view is wider during operation, especially when handling large volumes of 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 foot pedal, the motor and hydraulic pump are clear at a glance. At present, most electric forklifts produced by domestic enterprises adopt the second technology, while foreign enterprises have both situations.
2. Door frame
At present, most electric forklifts at home and abroad have adopted a wide field of view gantry, and the lifting hydraulic cylinder has been changed from being placed in the middle to being placed on both sides. There are two types of placement positions for hydraulic cylinders: one is that the hydraulic cylinder is located behind the gantry, such as Fushun Forklift Factory and TOYOTA's electric forklifts; Another type is that the hydraulic cylinder is located outside the gantry, such as the Nanjing Huarui electric forklift and BALKANCAR forklift. The hydraulic cylinder of CARER's R40/45 series electric forklift is located on the outside of the gantry, while the hydraulic cylinder of R50/60/70 series forklift is located behind the gantry.
Door frames are generally divided into standard, double section, or triple section types. The lifting height of domestic forklifts is generally between 2 and 5 meters, with a majority of 3 meters and below. In contrast, the lifting height of foreign electric forklifts is generally between 2 and 6 meters. Due to the high degree of warehouse verticality, the demand for electric forklifts with a lifting height of 3 meters or more is much higher than in China.
3. Driver's cabin
Due to the fact that most electric forklifts are used for indoor handling, there is generally no enclosed cab and only a protective roof rack is installed. The world's most advanced electric forklifts, such as LINDE's E20 new forklift cab, have been developed based on advanced ergonomics principles. They feature comfortable hydraulic suspension seats that can be adjusted according to the driver's height and weight. The dual pedal acceleration system does not require steering when the forklift changes direction of travel, and the inclination angle of the steering wheel column can be adjusted according to the driver's requirements. The central hydraulic control lever integrates the lifting and front rear functions of the gantry. So these new designs greatly reduce the labor intensity of drivers.
4. Drive system
The drive system is one of the key components of an electric forklift. There are significant differences in the structure of the drive system among various forklifts, including differences in the arrangement of single motors. For example, some domestic forklifts have T-shaped motor shafts and drive axles, while foreign forklifts such as TOYOTA have compact motor shafts and drive axles. The front wheel drive of LINDE's E20 electric forklift and CARER's P50 forklift is achieved by two independent motors, which are placed parallel to the drive shaft and have a compact structure. Due to its dual motor drive, it has good acceleration and climbing performance, and strong traction. It adopts an electronic speed control system instead of the original mechanical differential system, which greatly improves its usability.
5. Hydraulic system
Electric forklifts generally use a separate motor to drive a gear pump, providing hydraulic power for the lifting and tilting of their gantry working system. At present, domestic forklifts, due to the lack of speed regulation of hydraulic motors, can only rotate at high speed after starting, and will not automatically adjust with changes in function and pressure. Excess flow can only flow back to the oil tank through the overflow valve, resulting in energy waste. New types of forklifts abroad, 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 reaction of the hydraulic circuit, thereby saving electricity. The advantages of this control are high power utilization, no voltage peak, low hydraulic system noise, and low wear of hydraulic components, greatly improving the reliability and service life of the entire vehicle.
6. Braking system
Typical electric forklifts mainly use mechanical parking brakes and hydraulic service brakes. Parking uses hand brakes, while driving uses foot brakes. The braking system of NISSAN BX series electric forklifts is equipped with a dominant vacuum booster, which ensures sufficient active pressure at all times, increasing braking safety and reducing driver labor intensity. The CARER electric forklift adopts a hydraulic braking system. Expansion type braking 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 electric forklifts. The energy regeneration process is also an electronic braking process, which occurs in the following three situations: (1) when the accelerator control pedal is released. (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 applied, the traction motor will become a generator, replenishing the electrical energy back to the battery, unlike typical forklifts that waste energy when braking. Hydraulic braking only truly works when further braking is applied. 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 also reduces the downtime for maintenance, thus reducing.
Balanced forklifts all use rear wheel steering, with a small working range and frequent steering movements. If mechanical steering is used, the driver's workload will be very high. If hydraulic power steering is used, the labor intensity will be greatly reduced. Therefore, forklifts sold on the market now have basically achieved power steering. The hydraulic steering of domestic electric forklifts generally involves the steering motor continuously running at full load during forklift operation, resulting in unnecessary energy waste and wear and tear on the motor and hydraulic system. However, the power steering of electric forklifts from companies such as LINDE and NISSAN has taken it a step further, that is, when the steering wheel is stationary, the steering motor does not work. This function not only saves energy, but also extends the working time after recharging, shortens the idle time of the steering motor, and thus reduces the wear and tear of the motor and hydraulic pump.
7. Electronic control, self diagnosis, and LCD display system
Electrical control is an important factor in demonstrating the technical level of electric forklifts. Therefore, with the development of electronic technology, the electronic control of electric forklifts is becoming increasingly sophisticated. The development of electric motor controllers has mainly gone through the following stages: (1) direct battery start-up, relying solely on complex adjustments or battery discharge control. (2) The resistor is activated. The control of energy loss is large and can only decompose at a limited speed. (3) Controlled by thyristor controller (also known as thyristor controller). Transistor control greatly improves reliability. (4) Bipolar transistor control. Compared with thyristors, it is simpler to use, but the reliability requirements of the circuit are higher. (5) MOS field-effect transistor (i.e. metal oxide semiconductor field-effect transistor) control. The gate drive current is small, the parallel control characteristics are good, the forward voltage drop is small, the switching loss is reduced, and MOS field-effect transistors have better control characteristics than bipolar transistors. Due to the reduction of components and the use of fully enclosed devices, reliability has been greatly improved. The socket voltage of SCR (silicon controlled rectifier) controllers is usually 1-1.5V, while the socket voltage of MOS field-effect transistor controllers is 0.25V. MOS field-effect transistors have higher working efficiency, allow for higher maximum speed, lower operating noise, and stronger protection measures. Therefore, user power supplies have anti short circuit protection devices and unique three safety protection measures, namely software automatic protection, hardware automatic protection, and hardware self diagnostic protection. The successful application of transistor chopper on forklifts not only achieves stepless speed regulation and regenerative braking, but also adds self fault diagnosis and LCD digital display functions.
