A study on the improvement of the cam phase control performance of an electric continuous variable valve timing system using a cycloid reducer and BLDC motor

Abstract

This paper discusses the control performance improvement for an electric-continuous variable valve timing (E-CVVT) system using a brushless direct current (BLDC) motor and cycloid reducer. Each component of the E-CVVT system was implemented with mathematical analysis, and the response performance of the E-CVVT system was determined based on the mathematical model of the cam shaft motion, cam profile, cycloid reducer, BLDC motor, and controller. To control the intake valve timing of the engine, a cycloid speed reducer with a high reduction ratio capable of amplifying the output torque of a small BLDC motor was implemented. The change in valve speed due to the rotation of the cam shaft was represented by the curves described by the vertical movement of the valve using the cam profile. A control performance test apparatus was constructed and the torque of the intake cam shaft was measured and applied to the analysis so that the phase of the cam shaft could be changed using the E-CVVT system. To analyze the operating characteristics of the E-CVVT system, the BLDC motors were modeled using Simulink. The E-CVVT system controls the phase angle of the intake cam shaft. When the E-CVVT system sets the target phase angle, the motor controller generates the optimal motor speed command. The intake cam phase response speed depends on the setting of each PID parameter that changes the phase of the cam shaft. Through analysis and vehicle-based experiments, we confirmed the improvement of the E-CVVT system response performance according to the change of the PID parameter.