Electric forklift electronic steering system principles outlined

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John Deere (Jiamusi) Agricultural Machinery Co., Ltd., mainly produces combine harvesters to meet the plant

requirements of environmental protec tion, all running in the workshop production of transport vehicles

(forklifts, tractors) all require battery power,skid steer attachment plate
and the factory area is limited, internal frame of workshop

materials and logistics vehicles to the access road design and operation of space is very tight, forklift in a

narrow range to complete load, steering, straighten such action.
(1) Description of the problem
Based on the above requirements, the extensive use of small battery forklift workshop as logistics transport

vehicles, which accounted for 16% of the total number of logistics and transport vehicles FB25-7 the 2.5T

battery car, this model of EPS steering system, drive the ball screw life cycle is only 3 -5 months, every

time maintenance need about four hours and cost, including spare parts costs, used skid steer buckets
labor costs nearly one thousand

yuan, time consuming and costly.
(2) the original structure
Turn to the part of the DC motor controlled by the EPS electronic control system, through a gear reducer after

the wire mother rotation into linear motion of the screw, the screw connection triple board, control, rear-

wheel steering; EPS system through the steering wheel angle control potentiometer, the output control signals

via installed in the steering torque feedback lever triple board, make a feedback action, constitutes a closed

loop feedback system, due to the high transfer efficiency of the ball screw, and torque feedback function,

steering The steering wheel is almost no sense, the operation is very labor-saving.
The principle of closed-loop system is feasible, but in practical applications, when the rear wheel has been

transferred to the mechanical limit position, the wheels have come across the top wire, the EPS system is

still to control the motor in the output torque. Detailed analysis of its principle, the closed-loop system,

EPS electronic control, just control the turn signals and motor output, and limit the output of the limit

positi on, which will inevitably lead to the machinery reaches the limit position, the system still will

continue to output wire would bar top dead quickly to fight the rudder in the rapid rotation of the wire

mother suddenly screw in place to be stuck, give the ball screw to a very great impact, accelerated screw

damage, the most common form of failure when the stuck state, the ball suddenly stop the cycle, leaving the

back bead ball top bad, broken beads, screw scrapped.
3 improvement program
Communication issue with manufacturers and technical personnel, to explore whether the EPS electronic steering

changed to the form of transverse fuel tanks, or to improve its control circuitry, but this model the internal

structure design is very compact space with additional hydraulic components or other mounting structure, and

th e manufacturers do not provide technical support to improve the circuit.
Final decision on the factory to improve its own EPS circuit, analysis, developed two sets of programs:
(1) control the main circuit: design an additional control circuit, when the forward to play the rudder to the

limit position, through the block, using proximity switches to control the additional circuit, disconnect the

forward current of the motor rather than disconnect the reverse current, thereby avoiding killed rudder,

without affecting the back rudder;
(2) control of the EPS system input signal voltage: the original potentiometer is controlled by the steering

wheel, adjust the way of the EPS signal voltage instead of the additional circuit auxiliary control, when in a

limit position by the additional circuit directly to the EPS system, enter a reference bit voltage, so that

the EPS motor output is 0.
(4) program analysis
Program to control the main circuit, the test if the rear wheel floating test, you can achieve the desired

purpose of the rear wheels touch the ground during normal use, after playing the position of the rudder to the

limit, the rear wheels will be a slight swing back and forth, anti-driven swing the steering wheel damage,

might be the operator, control relays are fast pull, disconnect the main circuit near 20A of current you want

to disconnect, test run the day after the relay is damaged. It reasons for the original car\\ s torque feedback

system, the chain of structural size three ball head nearly 15mm of clearance, as well as the resilience of

the rubber tires, electrical power failure: When the proximity switch action, because the tire rebound, it

will in turn driven by the feedback system action block to return, and then restore the circuit to the motor

re-energized, close to the switch and then the action, the motor lost power, the cycle, resulting in the above

phenomenon.
Later changed to control the EPS system turn signal potentiometer total resistance of this potentiometer 5K

ohm control EPS output, both ends of the point voltage 5V, when in the middle of the center line voltage of

2.5V, EPS output, left and right deflection size control the size of the EPS output current, so you can give a

2.5V voltage reference when playing the position of the rudder to the limit, to the center line of the voltage

strong-enacted as 2.5V, so the EPS output is 0, check the manual to know the voltage error allowable value of

± 0.4V, 16% of the full voltage are two common 5% error in the 50K metal film resistors in series to take the

midpoint voltage, actual voltage error of 10%, less than the allowable error. Still use the proximity switches < br />
control relays. After the test run, this program can achieve the target, and weak control the strong electric

circuit of the electrical component parameters and volume are reduced, and easy to install.
(5) to improve results
By the above improvements, the impact of screw ball screw enable EPS system greatly extended service life,

reduce the failure rate of the FB25-7 battery forklift, reducing maintenance time and maintenance costs make

it better to meet production needs.