History of forklifts - main components of electric forklifts (IV)
Forklift history is divided into seven parts, this period for the fourth part of the main components of an electric forklift.
1. Forklift Motor
It is well known that the motor provides direct power to the electric forklift. At present, the world electric forklift industry without exception shows that the use of an AC motor has become an inevitable trend. However, it wasn't until the 1990s. Electric forklifts have always been powered by DC motor. Given the technology at the time, there was no alternative.
After 1990, two new types of motors entered the industrial production of forklifts almost simultaneously: the low-voltage AC Motor and the separated Motor, SEM. His exciter belongs to DC motor, which means that the excitation coil and armature winding of the motor is separate motors, and the excitation current is provided independently of the armature current. The field windings and Armature windings of his exciter are respectively powered by two power sources. Due to the use of a separate excitation power supply, the equipment is more complex. But this kind of motor is widely used in the main engine driving because of its wide operating range. His exciter has no directional contactor. There is no need to weaken the incentive to accelerate, the brake is regenerative. In Manufacturing, the individual field motors are a little different from conventional DC motor.
Therefore, in the traditional forklift manufacturing industry, the AC motor to a certain extent subject to technology. Since the late 1990s, however, designers have paid renewed attention to the design of electric drives. In fact, Since the AC motor has no forward/backward commutator, there is no brush or commutator. It's smaller, lighter and it spins faster. There is no longer a need to check and replace carbon brushes regularly. The most critical problem is that the forklift motor requires little maintenance throughout its life. Therefore, the forklift truck is more reliable and stable. In addition, the forklift is designed without maintenance space because the motor is completely enclosed in the pile body, making the forklift more compact. Non-contact braking allows the brake to reduce wear and tear and is much simpler than conventional braking. In addition, when the forklift driver uses the brake to slow down or stop the vehicle or change direction, the motor acts as a generator, converting the electromagnetic torque into the braking torque. This means that the wear on the brake pads will be minimal. This greatly reduces maintenance costs and minimizes operating costs. In addition, the operation and braking efficiency of the AC motor is higher. When braking or changing direction, energy is generated. The powerful braking action will generate more regenerative energy. Energy will be returned to the battery to extend its working time. Although some DC drive forklifts also have regenerative braking, they only start during very powerful braking processes. This means that during a lot of regenerative braking, energy is transferred to the heat. However, the AC inverter can generate renewable energy in almost all operating conditions and continue until the forklift has come to a complete stop. Obviously, energy regeneration efficiency is higher than the DC motor.AC motor is technologically advanced and has many specific advantages.
In addition, the use of high-frequency control, so that the AC motor can provide the best power feedback (recovery). The engine is the first to be used on a counterweight forklift truck by a leading German forklift company, Still.
2. Electronic System
Engine Control Technology has also changed completely. From the 1920s to the 1950s, forklifts were produced using carbon stacks -- a control system consisting of several carbon rings as resistors, which in turn were incorporated into the power supply circuit of a moving engine. When you push down on the speed pedal, the carbon ring is pushed down, reducing the resistance and increasing the machine speed.
Engine Control Technology has also changed completely. From the 1920s to the 1950s, forklifts were produced using carbon stacks -- a control system consisting of several carbon rings as resistors, which in turn were incorporated into the power supply circuit of a moving engine. When you push down on the speed pedal, the carbon ring is pushed down, reducing the resistance and increasing the machine speed.
In the 1980s, another important step was taken: the introduction of microprocessors, invented by Faggin, Hoff, and Mazor in 1971. With the introduction of microprocessors, control became more compact and faster. The microprocessor can also quickly detect anomalies in the engine and make the necessary adjustments more quickly. Also created is a load switch-bipolar transistor. Normally, the transistor was invented by Bardeen, Brattain, and Shockley in 1947. But until then, he can't switch the high voltage of the traction battery. The new load switch is easier to operate than the SCR control and requires no complex circuitry to connect to the main transistor. Control Systems with bipolar junction transistors are also smaller and cheaper.
Not only is the microprocessor easier to use, but it also runs very fast and has no power loss. And it can be connected in parallel, and it can even adjust a lot of voltage, which means it can be used on heavy-duty forklifts. The MOSFET switch is suitable for regulating battery voltages up to 96V. Currently, another technology based on the IGBT (integrated gate bipolar transistor) insulated-gate bipolar transistor is switching this high voltage. It works almost as easily as a MOSFET and is as reliable as an SCB control.
As these technological innovations are introduced, control systems become more compact, efficient, powerful, reliable, and less costly. Because of the high-frequency technology used in the battery charger, the battery can be charged to the maximum possible current in the shortest possible time. In particular, the Pitstop method allows the forklift to be recharged during the lunch break and other breaks, which means the battery can last longer. Conversely, smaller batteries can be selected to perform the material handling tasks that match them.
When the control system on the electronic equipment received abnormal data will be issued a warning message. The use of electronic systems on forklifts with internal combustion engines (ICE) mainly increases productivity, making the forklift safer, more comfortable and easier to handle. Examples of such systems include "reduced curvilinear speed" (a safety feature that improves machine rollover stability by reducing speed according to Steering Angle) developed by Jungheinrich of Germany or Toyota's active safety system (SAS) of Japan. In SAS systems, electronic control is based on data from sensors, such as the height of the load, the speed of the machine, and the angle of rotation. Once the value of any parameter or its combination reaches a critical value, the system alarms.
Today's cable connections also have a radically different look. Because of the new development in the electronic field, the serial communication scheme has been used. At the end of the 20th century, this led to the creation of the Can-bus data bus, which replaced the usual multi-core cable, there are only two wires for communication and transmission of digital information and two wires for power supply (when using external power sources). The data is received by the electronic system of the forklift truck and transmitted digitally through the communication channel. Each packet has its own, immutable address code, which is identified by the "smart" external station to get the information to the required loader system or unit, where the lights are turned on to speed up the engine, etc.
These data buses have become the overall industry standard. A typical example of using electronic equipment on ICE forklifts is an engine control system based on the Can-bus system and electronic control, which is standard on heavy forklifts.
3. Forklift Chassis
"If you give me a Fulcrum, " says Archimedes, "I will move the earth. " Indeed, the Fulcrum is the basis of any correlation, and this applies equally to forklifts: their load capacity and maximum allowable load depend directly on their frontal and lateral stability. The necessary dynamic stability can be achieved if the forklift chassis and superstructure are designed so that the wheels of the forklift truck are always in contact with the road surface. This requires maximum wheelbase and minimum center of gravity. As a result, some modern forklift models have the same chassis as previous models. An electric forklift truck in which the battery is located directly on the chassis between the wheelbase. They have a very low center of gravity, so they are very stable. According to the 1990s statistics, about 25.3 percent of all deaths related to forklift operations were caused by overturning, while only 14.4 percent were caused by falling cargo. This is why the EU standard for forklifts (EN 1726) imposes very stringent requirements on manufacturers: In order to reduce the risk of side and front overturning during normal operation, forklifts must pass standard stability tests, and must not be permanently deformed.
The highest safety requirements are for heavy-duty forklifts used in open areas. For them, a rigid welded one-piece chassis is an essential standard. In this case, the engine, gearbox, and differential should be installed as low as possible. The SAS (active Stabilization System) active stabilization system equipped with Toyota Series VII forklift has made significant progress in ensuring the stability of the forklift. SAS is active when the forklift is facing aside, forward or backward tilt.
The SAS system uses signals from sensors to analyze whether a forklift is in a potentially dangerous state and to activate safety functions when necessary. The touch sensors used to measure the deviation from the vehicle's side face work in the same way as satellite navigation systems.
4. Rechargeable battery
In the process of improving electric forklifts, forklift manufacturers began to equip them with heavier batteries in order to increase capacity. As a result, with each new model, the performance of the machine is constantly improving. Previous generations of forklifts were equipped with batteries with a capacity of 200A H. Today, forklifts with rechargeable batteries with a capacity of 600 to 750ah are common. This increases the carrying capacity of the forklift and allows it to work long hours without needing to be recharged. So far there has been no special breakthrough on the working principle of the traditional lead-acid battery. But the battery itself is bigger and more powerful. Progress has been noted in reducing charging time and in organizing the circulation of liquid in the battery. Electronic devices are used for battery preventative monitoring, allowing monitoring of battery temperature, battery level, battery failure, and battery charge.
Acid cycle batteries have been on the market since the 1990s. Thanks to advances in battery repair technology, the forklift trucks can now run longer. As a result, the batteries can now work for up to eight hours. Back in the 1980s, Steele created a system that returns the energy released during forklift braking back to the battery. Therefore, a considerable amount of battery power can be saved.
In the 1970s, Clark, the world's first forklift manufacturer, realized the choice between two voltage values for electric forklifts. If the operator chooses the maximum power mode or the energy-saving mode with reduced energy consumption, it can move as needed.
Since 2000, new energy power batteries, such as lithium battery and hydrogen fuel cell, have been used in the forklift industry. With the development of society and technology, forklift trucks are developing towards new energy in the future.
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