Hitachi excavator EC motor fault case analysis

EC motor in excavator is used to control the engine throttle opening, it is actually a stepper motor, the excavator operator by turning the engine control dial potentiometer input signal, the main controller (MC), EC controlled by the master controller to control the motor, the engine throttle opening, engine to realize stepless speed regulation. In addition, the main controller of the excavator can automatically control the EC motor according to the working conditions, so as to control the automation practically. Figure 1 is a schematic diagram of the EC motor control system. EC motor and its control system structure principle is more complex, it is difficult to quickly repair after the failure, but as long as the maintenance personnel seriously analyze the fault phenomenon, check the steps clearly, the method is appropriate, the fault is not difficult to rule out. A few cases cited Hitachi motor and EC excavator fault control system the author contact to, for common reference and discussion.

Case 1

Models: Hitachi EX300-3HHE

Fault phenomenon: the engine can start normally, when starting the engine, the engine speed control panel gear button, EC motor throttle control arm pull severe jitter, while EC motor in a "KaKa" sound, EC motor can control the engine throttle.

Check:

(1) disconnect the EC motor control line connector, press the engine speed shift button at the same time, use the oscilloscope to measure the two sets of control voltage waveform from MC, and the measurement results are normal.

It should be pointed out that the control signal of the stepping motor (EC motor) is a pulse waveform, and it is inaccurate to test with any multimeter, so it must be observed by oscillograph. Only Carter, Sumitomo, Daewoo and other brands of excavators, EC motors with DC motors, control signals in order to use multimeter test.

(2) measure the resistance of the two sets of coils of the EC motor with a multimeter, a set of coils with a resistance value of 5 ohms, and a set of coil resistances of 0 ohms.

Handling: check the EC motor and find that a set of coils is burned at the access point to cause the coil to be shorted. After installation, the EC motor is controlled normally.

Analysis: the EC motor has two sets of winding coils. If a set of coils is short circuited or broken, the EC motor can not rotate under the control voltage of MC, which causes severe jitter. If the control line failure caused only a group of voltage to EC motor, the motor fault is above, so at the time of the inspection, you must first measure the MC control voltage waveform is normal, don't remove the indiscriminate dumping, the fault surface expansion.

To be continued ---