When the ignition key of a Hitachi ex200-3 excavator is set to the on position, the EC motor throttle arm cannot normally return to the starting throttle position, but the rotation angle of the EC motor output shaft is too large. Even if the EC motor idle speed is readjusted and the ignition key is turned from off to on position, the EC motor throttle arm cannot normally return to the starting throttle position, so that the engine cannot be started.
Fault analysis:
The EC motor position sensor is actually a variable resistor The excavator MC controls the rotation angle of the EC motor by detecting the sensor output voltage value. When the sensor output voltage value is less than the MC set value, the MC continues to send the EC motor control pulse voltage to make the EC motor continue to rotate. At the same time, the EC motor rotates, it drives the sensor gear located in the EC motor. The gear rotation makes the sensor input shaft rotate, and changes the sensor resistance value, so that the sensor output voltage value changes When the sensor output voltage value is equal to the MC set value, MC stops sending control signals to EC motor to stop the rotation of EC motor.
Inspection steps:
1 first disconnect the EC motor control line connector. When the ignition key is turned from off to on, use an oscilloscope to detect the voltage waveform of the MC control signal, and the result is normal Check the coil resistance of EC motor with a multimeter, and the result is normal.
2. Disconnect the EC motor position sensor wire connector. When the ignition key is set to the on position, use a high impedance digital multimeter to detect the output voltage of the engine control dial unit. The result is normal Check the resistance value of EC motor position sensor with a multimeter, and the result is normal.
3. The EC motor was disassembled and inspected. It was found that the transmission gear of the input shaft of the EC motor position sensor was made of black rubber material, which was soft. Due to the long service time, the matching hole between the rubber gear and the sensor input shaft became larger, and the gear could not drive the sensor shaft to rotate synchronously.
4. Troubleshooting: replace the sensor gear, assemble and test run, and eliminate the fault.
In this case, the fitting clearance between gear and shaft of EC motor position sensor is too large When the EC motor rotates, the gear cannot drive the sensor shaft to rotate synchronously, but the sensor shaft rotation angle is smaller than the gear rotation angle. Therefore, although the MC has sent a signal to control the engine throttle to the starting position, the sensor output voltage value detected by the MC is smaller than the set value, so the MC continues to control the EC motor to rotate. In fact, at this time, the EC motor has turned to the engine starting position and reached the engine flameout position, Therefore, the engine cannot be started.
