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

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.

     

Aerodynamic drag reduction on a realistic vehicle using continuous blowing

The aerodynamic drag reduction of a realistic vehicle model through continuous blowing was numerically analyzed based on the open-source computational fluid dynamics (CFD) program, OpenFOAM. Simulations were performed on a realistic passenger vehicle model with available wind tunnel test data, DrivAer, at four different Reynolds numbers (Re). The aerodynamic drag coefficient decreased with increasing Re. The CFD technique was validated by comparing the aerodynamic drag coefficients at Re = 4.87 × 10⁶. Predicted drag coefficients of the DrivAer estate model show less than 3% difference from wind tunnel test data, whereas those of fastback and notchback vehicles showed less than 1% difference. Sectional pressure distributions agreed well with wind tunnel test data. The effect of continuous blowing was investigated using the DrivAer estate model with a blowing position at the end of the roof for vertical blowing and at the C-pillar for lateral blowing. Simulations were performed at Re = 4.87 × 10⁶ and 9.75 × 10⁶ and blowing speeds of 20%, 40%, 60%, and 100% of the vehicle driving speed. The effect of continuous blowing increased with Re. The drag reduction was more than 6% for roof blowing due to increasing rear pressure when the blowing speed equaled the vehicle driving speed. The maximum drag reduction was approximately 7.5% for simultaneous roof and lateral blowing. The results indicate that continuous blowing can efficiently reduce vehicle aerodynamic drag and consequently greenhouse gas emissions.

     

Optimum shape design of a BLDC motor for electric continuous variable valve timing system considering efficiency and torque characteristics

Microsystem Technologies - Recently, environmental problems caused by global warming and exhaust gas have been increasing, leading governments all over the world to implement strict environmental...