Study Of Drive For The Control Of Needle Lift Of Direct Acting Piezoelectric Common Rail System

As the energy and environment problem becoming more and more serious, improving the efficiency of engine is becoming more and more important. Common rail system, as the main development direction of diesel engine, is what the main manufactures of common rail system want to improve the performance and update. As the update of common rail system, the performance of diesel has been improved and the exhaust has been reduced.The injection and spray characters of common rail system have great influence on the performance and exhaust of diesel. The injection characters include injection rate and injection time. Injection rate can be controlled through the control of injection pressure and needle lift. Injection pressure was the main method in the past years.Compared with traditional common rail system, direct acting piezoelectric common rail system has obvious advantages. This new common rail system responses more quickly, injects more accurate, costs less energy, what is more, it can control the needle lift proportionately, which makes it possible to control fuel injection characteristic through the control of needle lift.Based on the conclusion of advantages, designed a drive circuit of the piezoelectric actuator to control the needle lift and the injection rate. In order to control the current through the piezoelectric actuator, the control strategy of charge and discharge was analyzed to ensure the current is between the minimum value and the maximum value, which can get a high charge and discharge speed and prevent damage of the piezoelectric actuator.For the problems exist in existing voltage control manner, a closed loop voltage control manner was designed to realize the accurate control of the voltage of actuator. Through the study of the charge and discharge control strategies of the circuit, a variable feedback module was designed to realize the stair-like control of driving voltage by choosing the feedback resistance during the injection process.Using the existing piezoelectric actuator, the design was verified by simulation and experiment. Results show that the charge period and discharge period are both about 120μs. The change of driving voltage between different values is in 100μs, which meets the requirement of the needle lift. The drive circuit can control the injection rate by changing the driving voltage during the injection process. Using the piezo injector, the driving capability of the design was verified by injection test.