Hitachi excavator EC motor fault case analysis two

Case two

Models: Hitachi EX200-5HHE

Fault phenomenon: the ignition key excavator on position, EC motor throttle pull arm can not be normal back to the starting position of the throttle, but the output of the EC motor shaft rotation angle is too large, even if the re adjustment of EC motor idling, the ignition key from the off to the on position, EC motor throttle pull arm is still not normal back to the starting position of the throttle, so that unable to start the engine.

Check:

(1) disconnect the EC motor control line connector. When the ignition key is transferred from off to on position, the MC control signal voltage waveform is detected by oscillograph, and the result is normal.

(2) measure the resistance value of two sets of coil of EC motor with multimeter. The result is normal.

(3) disconnect the EC motor position sensor line connector and use the high impedance digital multimeter to check the output voltage of the engine control panel unit when the ignition key is in the on position. The result is normal.

(4) use multimeter to check the resistance of EC motor position sensor, and the result is normal.

(5) the dismantling of EC motor, EC motor position sensor input shaft gear made of black rubber material, soft material, due to the use of time is too long, the rubber gear and the input shaft of the sensor with the pore radius, the gear cannot drive shaft synchronous rotation sensor.

Handling: change sensor, gear, assembly test run, trouble shooting.

Analysis: the EC motor position sensor is in fact a variable resistor. Excavator MC control rotation angle of EC motor size, by detecting the output voltage of the sensor to determine the value of the output voltage of the sensor, when the MC value is less than the set value, MC continues to lose control of the pulse voltage to the EC motor, EC motor continues to rotate, EC motor rotates to drive the sensor at the same time, a EC gear motor in gear. To rotate the sensor input shaft to rotate, change the sensor resistance, so that the sensor output voltage value changes. When the output voltage value of the sensor is equal to the MC setting value, the MC stops losing to the EC motor control signal so that the EC motor stops rotating. In this case EC motor position sensor gear and axle clearance is too large, EC motor rotates, the gear drives the sensor shaft cannot rotate synchronously, but rotate the sensor axis angle is smaller than the rotation angle of gear, so although MC has been sent to control the engine throttle signal to the starting position, but the sensor output voltage value was detected by MC less than the set value, so MC EC to control the motor rotation, when in fact EC motor has turned the engine to start position, the engine flameout position, so that the engine can't be started.

To be continued ---