FB25-7 battery forklift steering system improvement overview
John Deere (Jiamusi) Agricultural Machinery Co., Ltd. mainly produces combine harvesters. All production and transportation vehicles (forklifts, tractors) operating in the workshop require battery power to meet the environmental requirements of the factory, and because of the limited factory area, The material racks and logistics vehicles in the internal workshops are designed to run very tightly. The forklifts need to be loaded, steered, and squared in a narrow range. 1. Description of the problem Based on the above requirements, a large number of small battery forklifts are used as logistics vehicles in the workshop. Among them, the FB25-7 2.5T battery car accounts for 16% of the total number of logistics and transportation vehicles. In the EPS steering system of this model, the use of the ball screw for transmission is only used. 3 months to 5 months, each maintenance takes about 4 hours, and costs nearly 7,000 yuan including spare parts and labor costs, which is time-consuming and labor-intensive and costly. 2. Original structure The steering part is controlled by the EPS electronic control system. After the first gear is decelerated, the nut rotates and transforms into the linear motion of the screw. The screw is connected to the triple plate to control the rear wheel steering. The EPS system controls the potential through the steering wheel angle. Output control signal, through the steering torque feedback rod installed on the triple plate, to make feedback action, constitute a closed-loop feedback system, due to the high transmission efficiency of the ball screw and the related torque feedback function, the steering wheel is almost turned No feeling, the operation is very labor-saving. This closed-loop system is feasible in principle, but in practical applications, it is found that the EPS system still controls the output torque of the motor when the rear wheel has turned to the mechanical limit position and the hub has hit the top wire. After analyzing the principle in detail, it is found that in the closed-loop system of EPS electronic control, only the steering signal and the motor output are controlled, and there is no output limit of the limit position, which inevitably leads to the system still continuing to output when the machine reaches the limit position. The bar will die, and when the rudder is quickly steered, the quick rotation of the nut will be stuck due to the screw in place, which will cause a great impact on the ball screw and accelerate the damage of the screw. The most common failure mode is When the card is stuck, the steel ball suddenly stops circulating, and the ball returner is broken by the steel ball, the beads are damaged, and the screw is scrapped. 3. Improvement plan I have communicated with the manufacturer's technicians on this issue to discuss whether the EPS electronic steering can be changed to the horizontal cylinder or improve the control circuit, but because the internal structure of the model is very compact, there is no room for additional hydraulic components or It is another mounting fixed structure, and the manufacturer does not provide technical support for improved circuit. Finally, it was decided to improve the EPS circuit in the factory. After analysis, two sets of plans were formulated: (1) Control the main circuit: design an additional control circuit. When the rudder is forwarded to the limit position, the additional circuit is controlled by the proximity switch through the stop, and the forward current of the motor is disconnected without breaking the reverse current, thereby avoiding Kill the rudder without affecting the rudder; (2) Control the input signal voltage of the EPS system: change the mode of the EPS signal voltage from the steering wheel control potentiometer to the additional circuit auxiliary control. When in the limit position, the additional circuit directly inputs a reference to the EPS system. The bit voltage makes the EPS motor output zero. 4. Program analysis In the scheme of controlling the main circuit, it is found that if the rear wheel suspension test can achieve the intended purpose, but the rear wheel touches the ground, in normal use, after the rudder is pushed to the limit position, the rear wheel will swing back and forth in a small amount, and the reverse drive The steering wheel swings, which may cause damage to the operator. At the same time, the control relay is also quickly pulled in and out, and nearly 20A of current is disconnected in the main circuit. The relay is damaged after one day of trial operation. The reason is that in the torque feedback system of the original car, the three ball heads in the structural size chain have a gap of nearly 15 mm, and the resilience of the rubber tire: when the proximity switch is actuated, the motor loses power, because the tire rebounds, In turn, the feedback system is actuated, the block returns, and then the circuit is restored, the motor is powered again, the proximity switch is re-actuated, the motor is de-energized, and the cycle reciprocates, causing the above phenomenon. After changing to the EPS signal steering potentiometer, the potentiometer has a total resistance of 5K ohms, controls the EPS output, and the voltage at both ends is 5V. When it is in the middle position, the neutral line voltage is 2.5V, the EPS output is 0, and the left and right deflection sizes Control the EPS output current, so you can give a 2.5V voltage reference. When steering to the limit position, set the voltage of the neutral line to 2.5V, so that the EPS output is 0. Refer to the manual for the voltage error. The allowable value is ±0.4V, which is 16% of the full voltage. The current 50V metal film resistor with 5% error is used to take the midpoint voltage in series. The actual voltage error is 10%, which is less than the system tolerance. The proximity switch is still used to control the relay. After the test run, it was found that this scheme can achieve the intended target, and the strong electric power is controlled by the weak current, and the electrical component parameters and volume of the circuit are reduced, which is convenient for installation. 5. Improve the results Through the above improvement, the service life of the ball screw of the EPS system can be greatly prolonged by avoiding the impact on the lead screw, reducing the failure rate of the FB25-7 battery forklift, reducing the maintenance time and maintenance cost, and making it better. Meet production needs. Conductor Bar,Bus Bar,Rail System Conductor Bar Crane Machinery Import&Export Co., Ltd. , http://www.cnliftmachine.com