A STATISTICAL ANALYSIS OF A FUEL INJECTION RATE WAVEFORM BY THE BOSCH METHOD ACCORDING TO A PIEZOELECTRIC INJECTOR DRIVING PATTERN

To drive a diesel piezo injector, the charge and discharge of the current supplied to the piezo stack in the injector are controlled as a pair. The charge and discharge currents expand and contract the piezo stack, respectively. The expansion of the piezo stack causes an increase in the hydraulic pressure that presses the top of the injector needle, which results in the fuel injection. In contrast, the contraction of the piezo stack stops the fuel injection. The charge and discharge currents are controlled by a peak and hold method. The hold current is controlled by PWM (pulse width modulation) control of the driving power supplied to the injector. The duty ratios of the PWM signal used for the hold current control are 10%, 30%, and 100%. The injector driving voltage was 140V. A variety of charge and discharge current waveforms were generated by combining the duty ratio control of the PWM waveform with the driving power source. To measure the timeresolved injected mass under various current waveform conditions, the Bosch method was used in this study. An uncertainty analysis was performed on the Bosch injection rate waveform when it was measured 40 times for each fuel injection condition.