John. Deere (Jiamusi) Agricultural Machinery Co., Ltd. mainly produces combine harvesters. In order to meet the environmental protection requirements of the factory, all production and transportation vehicles (forklifts, tractors) operating in the workshop require battery power, and due to the limited factory area, its internal The space for designing and running the material racks and logistics vehicle access roads of the workshop is very compact, and the forklifts need to complete loading, steering, and correcting movements within a narrow range.

1. Problem description Based on the above requirements, a large number of small battery forklifts are used in the workshop as logistics transportation vehicles. Among them, the FB25-7 type 2.5T battery car accounts for 16% of the total number of logistics vehicles. In the EPS steering system of this model, the use of the ball screw for the transmission cycle Only 3 months to 5 months, each repair takes about 4 hours, and costs nearly 7,000 yuan, including spare parts and labor costs, which is time-consuming and labor-intensive.

2. The original structural steering part is controlled by the EPS electronic control system and the DC motor is controlled. After the gear is decelerated by the first gear, the nut is rotated and converted into the linear motion of the screw. The screw is connected with the triple plate to control the rear wheel steering; the EPS system passes the steering wheel angle The controlled potentiometer, output control signal, makes a feedback action via a steering torque feedback lever installed on the triple board, and constitutes a closed-loop feedback system. Due to the high transmission efficiency of the ball screw and the related torque feedback function, the steering At the time, the steering wheel has almost no sense and the operation is very labor-saving.

This closed-loop system is feasible in principle, but in practical application, it is found that when the rear wheel has turned to the mechanical limit position, the EPS system still controls the output torque of the motor after the hub has hit the top wire. After detailed analysis of the principle, it was found that in the EPS electronically controlled closed-loop system, only the steering signal and the motor output are controlled, and there is no output limitation of the limit position. This will inevitably lead to the system still continuing to output after the machine reaches the limit position. The bar will die at the top, and when the swift steering is performed, the sudden rotation of the nut in a sudden rotation due to the screw being stuck will cause a great impact on the ball screw and accelerate the damage of the screw. The most common form of failure is When it was stuck, the steel ball was suddenly stopped and the bead was damaged by the top of the steel ball. The beads were damaged and the screw was scrapped.

3. The improvement plan had communicated with the manufacturer's technical personnel on this issue, and discussed whether the EPS electronic steering could be changed to the transverse fuel tank type or the control circuit could be improved. However, because the internal structure of this model is very compact, there is no space for additional hydraulic pressure. Components or other mounting fixtures, and manufacturers do not provide technical support to improve the circuit.

The final decision was made to improve the EPS circuit in the factory. After analysis, a total of 2 sets of solutions were formulated:

(1) Control main loop: Design additional control circuit. When forward steering to the extreme position, use the proximity switch to control the additional circuit through the stopper and disconnect the forward current of the motor without disconnecting the reverse current, thus avoiding Kill the rudder without affecting the rudder;

(2) Control the input voltage of the EPS system: The original way to control the potentiometer of the steering wheel and adjust the voltage of the EPS signal is changed to additional circuit auxiliary control. When in the limit position, an additional circuit directly inputs a reference to the EPS system. The bit voltage causes the EPS motor output to be zero.

4. The program analysis and control of the main loop program found that if the rear wheel suspension test can achieve the intended purpose during the test, but the rear wheel touches the ground, and after normal use, the rear wheel swings back and forth in small amplitude after steering to the extreme position. Driving the steering wheel in reverse may cause harm to the operator. At the same time, the control relay is also rapidly picking up and opening. In the main circuit, nearly 20 A of the current is to be disconnected, and the relay is damaged after one day of trial operation. The reason is that the original car torque feedback system, the structure of the size of the three ball joints a total of nearly 15mm gap, and the rubber tire resilience: When close to the switch action, the motor loses power, because the tire rebound, it will In turn, the feedback system is activated to return the block, and the circuit recovers. The motor is re-powered, the proximity switch is activated, the motor is de-energized, and the cycle repeats, causing the above phenomenon.

Later changed to control the turn signal potentiometer of the EPS system. The total resistance of the potentiometer is 5K ohms, and the EPS output is controlled. The voltage at both ends is 5V. When it is in the middle position, the neutral voltage is 2.5V, the EPS output is 0, and the left and right deflection is Control EPS output current, so you can give a 2.5V voltage reference, when the steering to the extreme position, the neutral voltage is set to 2.5V, so that the EPS output is 0, consult the instructions that the voltage error The allowable value is ±0.4V, which is 16% of the full voltage. Now, use two 50K metal film resistors with a common 5% error to take the midpoint voltage in series. The actual voltage error is 10%, which is less than the allowable error of the system. The proximity switch is still used to control the relay. After the test run, it was found that this scheme can achieve the intended goal, and control the strong electric power with weak current, and the electric element parameters and volume of the circuit are reduced, which is easy to install.

5. Improvement results through the above improvements, due to avoiding the impact of the screw, the EPS ball screw can greatly extend the service life, reduce the failure rate of FB25-7 type battery forklift, reduce maintenance time and maintenance costs, make it more Good to meet production needs.