Working principle and structure of forklift truck
There are many kinds of forklifts, but no matter what type of forklifts, they are basically composed of four parts: power part, chassis, working part and electrical equipment. Due to the differences in structure and installation positions of these four parts, different types of forklifts are formed.
Balanced forklift is one of the most common forms of forklift. Taking this kind of forklift as an example, the composition of each part is discussed.
(1) Dynamic part
The role of forklift power device is to supply the power required for loading and unloading of forklift working device and tire chassis operation, generally.
Installed in the rear of forklift truck and play a balancing role.
The driving device of electric forklift is battery and DC series motor. Its driving characteristic is closest to the requirement of constant power soft characteristic, and its traction performance is better than internal combustion engine. In addition, smooth operation, no noise, no exhaust gas, easy maintenance, simple operation; The operating cost is lower and the service life of the vehicle is longer. Disadvantages are: the need for charging equipment, high basic investment, long charging time (generally 7~8h, quick charging 2~3h), a charge after the continuous working time is short, the battery is afraid of impact vibration, high requirements for the road surface. Due to the limitation of storage battery capacity, motor power is small, speed and climbing ability is low. Therefore, battery a motor driven battery forklift is mainly used in the narrow channel, the handling distance is not long, the road surface is good, the lifting weight is small, the speed is not required to be too fast in the warehouse and workshop. In inflammable warehouses or places requiring clean air, only battery forklifts can be used. It is difficult to start internal combustion engines in refrigerated warehouses. Battery forklifts should also be used.
The mechanical characteristics of internal combustion engine do not meet the requirement of constant power soft characteristics of forklift prime mover. Its output power increases with the increase of rotational speed. Therefore, the internal combustion engine must be equipped with mechanical transmission, hydraulic torque converter or hydraulic transmission device to increase the output torque before use. On the contrary, the main advantages of internal combustion forklift and battery forklift are: no need for charging equipment, long duration of operation, large power, strong climbing ability, low requirements for road surface, and less basic investment. If the proper transmission mode is adopted, the ideal traction performance can be obtained. Disadvantages are: running noise and vibration, exhaust gas, maintenance times, higher operating costs, the vehicle's service life is shorter. Therefore, the internal combustion forklift is superior. Generally, when the lifting weight is above medium tonnage, internal combustion forklift should be preferred.
In the internal combustion forklift, the use of diesel engine is the most common, lifting weight more than 3T forklift basically all use diesel engine. This is because diesel engines consume less fuel. But the diesel engine is bulky, noisy and vibratory. The forklift truck with small lifting weight can choose the gasoline engine, which is small in size and light in weight, but consumes much oil. Gasoline is expensive, and there are many harmful components in the exhaust fumes, which are easy to catch fire. In foreign countries, there are forklifts with LPG engines, which have low fuel prices and less exhaust gas.
In recent years, more and more domestic and foreign internal combustion forklifts use liquid petroleum gas as the power unit. Most of them are dual-fuel forklifts. Their power unit can use gasoline or diesel as fuel, or liquefied petroleum gas as fuel. The annual growth rate of LPG forklifts in Germany has reached 160%, and the number of LPG forklifts in the United States and Japan is also increasing. At present, the voice against vehicle exhaust pollution is getting higher and higher. Therefore, in the industrial vehicles driven by internal combustion engine, including forklifts, the use of liquid petroleum gas is more widespread. This is because the use of liquid petroleum engine, not only can avoid air pollution, reduce pollution and reduce engine wear. Prolong engine life. It also reduces fuel costs.
(2) Chassis
The chassis receives power from the power unit to power the forklift and ensure its normal movement. It is composed of transmission system, driving system, steering system and braking system.
Driveline is a device that receives power and transmits it to the driving train.
Mechanical transmission system is composed of friction clutch, gear transmission, universal transmission device and the main transmission device and differential mounted in the drive axle; The hydrodynamic mechanical drive system replaces the friction clutch with a torque converter and is the same as the former.
The driving system is the device that ensures the rolling operation of the forklift and supports the whole forklift. It is composed of bracket, axle, wheel and suspension device, etc. The front axle of forklift truck is the drive axle, which is to increase the axle load of the front axle when carrying, so as to improve the adhesion quality of the driving wheel and increase the adhesion of the ground, so as to ensure that the driving force of the engine can be fully played. Its rear bridge for the steering bridge. The steering device is located in front of the driver, and the gear lever and other control levers are placed on the right side of the driver seat.
The steering system is used to make the forklift truck walk in the direction determined by the driver's will. The steering system of forklift truck can be divided into mechanical steering system and power steering system according to the different energy required for steering. The former takes the driver's physical energy as the steering energy and consists of steering gear, steering transmission mechanism and steering mechanism. The latter is a steering device which uses both the driver's physical energy and the engine power as the steering energy. Under normal circumstances, only a small part of the energy required for forklift steering is provided by the driver, and most of it is provided by the engine through the steering afterburner. However, when the steering afterburner fails, the driver should be able to undertake the steering task independently. In forklift operation, steering and walking are changeable. In order to reduce the driver's control burden, internal combustion forklift truck mostly adopts power steering device. Commonly used power turning devices have integral power turning device, half integral power turning device and steering afterburner 3. The brake system is the system that slows or stops the forklift truck. It consists of a brake and a brake transmission mechanism. Braking system according to braking energy can be classified into human braking system, dynamic braking system and servo braking system. The former uses the driver's physical energy as the braking energy; The dynamic braking system relies entirely on the potential energy in the form of pressure or hydraulic pressure converted from the power of the engine as the braking energy. The latter is a combination of the first two.
The composition, function and working principle of forklift chassis and other parts are very similar to cars, so this part is generally the same content with cars, due to the limitation of space, forgive not to elaborate, and the content different from cars, will be introduced.
In the balance heavy forklift, the rear of the forklift is provided with a balance weight to balance the quality of the goods in the front of the forklift, and the power device (internal combustion engine) or battery of the forklift is generally installed in the rear of the forklift to play a partial balance role.
(3) The working part
The working part of forklift is a direct working mechanism that directly bears all the weight of the goods and completes the forklift, lifting, stacking and other processes of the goods. It is composed of the working device which directly carries out loading and unloading operation and the hydraulic transmission system which controls the action of the working device. From the design and manufacture and different working conditions two requirements, it has a variety of structural forms.
The fork is a fork component that directly carries the goods. It is mounted on the fork frame by hook. The distance between the two forks can be adjusted according to the needs of the operation and locked by the positioning device.
Fork frame is a structural part welded by steel plate, with a roller group, the inner side of the door frame has a groove track in the upper and lower direction, fork frame and the connection of the inner door frame is the same, also can only move up and down along the track of the outer door frame.
The inner frame is a frame structure welded by two grooves as columns and beams. Its lower part is hinged on the drive axle (front axle) of the forklift truck, and with the help of the inclined hydraulic cylinder, the door frame can be tilted at a certain Angle in the front and back direction. The door frame leans forward for the convenience of loading and unloading, and leans backward for the purpose of preventing the goods on the fork from slipping when the forklift is moving.
The lower end of the lifting hydraulic cylinder is on the outer door frame beam, and the upper end is connected with the inner door frame beam and sprocket. One end of the lifting chain is connected with the lower part of the outer door frame, and the other end is connected with the fork frame by bypassing the sprocket. When the pressure oil is passed into the hydraulic cylinder, the piston rod moves upward at the speed of V and drives the sprocket and the inner door frame to lift at the same speed of V. Due to the principle of moving pulley, the chain pulls the fork frame to lift at the speed of 2V. When the full stroke of the hydraulic cylinder ends, the inner frame is in the extreme position above the outer frame, and the fork frame is in the extreme position above the inner frame. When oil pressure is released, components such as cargo or forks fall by their own gravity.
1. Main types of forklift working devices
1) Classification by lifting form
(1) As long as the cargo fork is lifted without free lifting type, the inner door frame is also lifted at the same time, and H =2h '.
(2) Part of the free lifting type in the forklift from the ground to the maximum lifting height process can be divided into three stages: the first stage (free lifting stage) forklift to hydraulic cylinder 2 times the travel, the inner door frame does not move, forklift vehicle height unchanged. In the second stage, the cargo fork lifts twice the stroke of the hydraulic cylinder, and the inner door lifts synchronously with the stroke of the hydraulic cylinder. In stage 3, the inner door frame and the cargo fork lift synchronously at twice the hydraulic cylinder stroke to the maximum lifting height.
(3) The full free lifting is divided into two stages: the first stage is free lifting, the inner door frame does not move, the fork along it to the top of the inner door frame. In the second stage, the fork does not move relative to the inner frame and rises to the maximum lifting height with the inner frame. This is achieved by two sets of hydraulic cylinders (free lifting hydraulic cylinder and lifting hydraulic cylinder). Two sets of hydraulic cylinder oil lines are in parallel, and the free lifting hydraulic cylinder action pressure is low, so it is always up after down without free lifting device structure is the most simple, mostly in the open ground lifting weight relatively large forklift. Forklifts below 6T in and out of warehouses and workshops use part of the free lifting device. For forklifts below 3T in low barns and in containers for loading and unpacking, a fully free lifting device must be used.
2) According to the classification of the door frame
(1) single-stage frame it has only one frame, forklift along it, the hydraulic cylinder is short, the maximum lifting height is always lower than the forklift height, simple structure, good rigidity, only in the lifting height is very small forklift.
(2) Two-stage gantry added an inner gantry on the basis of single-stage gantry. Its lifting height can be higher than the forklift height, is the most used form of forklift.
(3) The three level door frame is added a middle door frame between the internal and external door frame, which forms the telescopic mechanism of the Vladivostok festival. Its lifting height is greatly different from the full height of forklift, which is adopted when the lifting height is required to be large or the full height of forklift is limited. Its structure is complex, and the driver's vision is poor.
