When the ignition key of a Hitachi EX200-3 excavator is set to the on position, the throttle arm of the EC motor cannot return to the starting throttle position normally, but the rotation angle of the output shaft of the EC motor is too large, even if the idle speed of the EC motor is readjusted, the ignition key is turned off After turning to the on position, the throttle arm of the EC motor cannot return to the starting throttle position normally, so that the engine cannot be started.
Failure analysis:
The EC motor position sensor is actually a variable resistor. The excavator MC controls the rotation angle of the EC motor, which is determined by detecting the sensor output voltage value. When the sensor output voltage value is less than the MC set value, MC continues to input The pulse voltage is controlled for the EC motor, so that the EC motor continues to rotate. At the same time, the EC motor drives the sensor gear located in the EC motor. The gear rotation rotates the sensor input shaft and changes the sensor resistance, thereby changing the sensor output voltage value. When the output voltage value of the sensor is equal to the set value of MC, MC stops sending the control signal to the EC motor, so that the EC motor stops rotating.
Inspection steps:
1 First disconnect the connector of the EC motor control line. When the ignition key is turned from off to on, the voltage waveform of the MC control signal is detected with an oscilloscope. The result is normal. The resistance of the two sets of coils of the EC motor is detected with a multimeter.
2. Disconnect the EC motor position sensor cable connector. When the ignition key is on, use a high-impedance digital multimeter to detect the output voltage of the engine control dial unit. The result is normal. Use a multimeter to detect the resistance value of the EC motor position sensor. The result is normal.
3. Disassembly and inspection of the EC motor and found that the transmission gear of the input shaft of the EC motor position sensor is made of black rubber material, which is relatively soft. Due to the long use time, the hole for the rubber gear and the sensor input shaft becomes larger, and the gear cannot drive the sensor shaft. Rotate synchronously.
4. Troubleshooting method: replace the sensor gear, assemble the test drive, and eliminate the fault.
In this case, the gap between the EC motor position sensor gear and the shaft is too large. When the EC motor rotates, the gear cannot drive the sensor shaft to rotate synchronously, but the shaft rotation angle of the sensor is smaller than the gear rotation angle, so MC occurs although the engine throttle has been issued to control The signal of the starting position, but the output voltage value of the sensor detected by MC is less than the set value, so MC continues to control the rotation of the EC motor, but in fact the EC motor has already turned to the engine start position and reached the engine stall position, so it is unable to Start the engine.
