Impact of Control Methods on Dynamic Characteristic of High Speed Solenoid Injectors

Accurate control of both the timing and quantity of injection events is critical for engine performance and emissions. The most serious problem which reduces the accuracy of the control operation in such systems is a time delay of the responsiveness for the opening and closing operation of the electromagnetic valve. Modern electronic control systems should be capable of driving high speed solenoid injectors at a very fast switch frequency with high efficiency and acceptable power requirements. In this paper, the dynamic characteristic of a high speed servo-hydraulic solenoid injector for diesel engine, with different driving circuits and control methods, is investigated. A pre-energizing control strategy based on a dual power supply is applied to speed up the opening response time of the injectors. The effect of free-wheeling circuit on the closing response time is experimentally studied and a reverse-energizing circuit is utilized for achieving a rapid extinction of the operating magnetic field. The solenoid current is measured to get the electrical delay of the injectors. Meanwhile, high-speed photography is employed to detect the total delay (electrical delay, hydraulic delay and mechanical delay) of the injection spray process. The results show that, there is a high correlation between the opening delay and the solenoid current, but the armature of the injector will not move until the current reaches a threshold value. The switching time (both the opening and the closing time) could be further optimized through the proposed driving circuits and control strategies without any change to the injectors. As a result, the interval between two injections can be significantly reduced, which can provide greater flexibility for multi-injections strategies.