Development of diesel piezo injector driver using microcontrollers

A diesel piezo injector driver was developed using microcontrollers and MOSFETs. Fuel injection with a common rail injector is possible when controlling the magnitude of the hydraulic pressure acting on the nozzle needle. There are two types of solenoids and piezo-electric components to open and close the hydraulic passages acting on the nozzle needle. A solenoid-type injector is driven by controlling the current waveform supplied to the injector via a peak & hold approach. The solenoid-type injector driver can be implemented with a circuit that switches the driving power with one transistor which has a high current capacity. In contrast, a piezo-type injector is driven by the contraction and expansion of piezoelectric elements that open and close the hydraulic passages to control the movement of the nozzle needle. In order to control the contraction and expansion of the piezoelectric element in a piezo injector, charge and discharge control of the current supplied to the injector is required. For this purpose, a pair-switch circuit capable of charging and discharging the current supplied to the injector has been developed. The driving voltage of the piezo injector was in the range of 100 ~ 140V. High voltage and current switches were used for charging and discharging. Fuel injection at a high common rail pressure was possible with higher driving voltage supplied to the piezo injector. The control signal supplied to the MOSFET (IRF640N) is generated with the output pin or CCP pin of an 8-bit microcontroller PIC16F917. The common rail pressure was controlled by supplying square waves while varying the duty ratio of the control signal. The microcontroller's capture compares PWM (CCP) pins outputs the control signal. When the duty ratio of the PWM square wave supplied to the rail pressure controller is increased, the common rail pressure is decreased.