Variable valve timing (VVT) systems can effectively improve engine performance. However, the common hydraulic VVT system driven by oil has negative effects on engine start and low-speed conditions because the low oil temperatures and pressures limit the advance of the camshaft. The Electric Variable Valve Timing (EVVT) systems overcome the cam phasing issues of oil-based systems according to a motor. However, there are few available EVVT control methods for the mass-production controller. It is difficult for classical controllers to balance the cam phase overshoot and response time. Complex methods are difficult to be applied in the engine control unit (ECU). In this paper, an EVVT system model included a 3-phase brushless direct current (BLDC) motor model, a cam phaser model and a Simplified Model-Based Control (SMBC) controller which can be applied in the ECU was constructed. The speed and load accuracy of the motor model was verified by experiments. In the SMBC controller, a motor speed planning model and a phase virtual sensing model were established according to the BLDC speed trajectory triangle and the phaser transmission ratio. Trajectory triangle was modeled based on max acceleration/deceleration performance. The phase virtual sensing model predicted the phase information with higher resolution. The model could be modified from the data which updated from camshaft position sensor. Therefore, the phase virtual sensing had almost the same accuracy compared with the sensor. The motor speed planning model used the phase prediction information and the trajectory triangle to calculate and predict the latest deceleration point without overshooting and thus maximized the motor performance. The EVVT control model converted the control of phase to planning the trajectory of BLDC and advanced/retarded camshaft of EVVT system finally. The simulation results showed that the proposed method was effective in improving the response performance and reducing overshoot of the EVVT system.
Electric Variable Valve Timing;Simplified Model-Based Control;motor speed planning;virtual sensing
第二届世界内燃机大会The 2nd World Congress on Internal Combustion Engines