Method for Determining Thermal Resistances in Coupled Simulator: For Electric Valve Timing Control System

We developed a thermal calculation 1D simulator for an electric valve timing control system (VTC). A VTC can optimize the open and close timing of the intake and exhaust valves depending on the driving situation. Since a conventional VTC is driven hydraulically, the challenges are response speed and operation limit at low temperature. Our company has been developing an electric VTC for quick response and expansion of operating conditions. Currently, it is necessary to optimize the motor and reduction gear design to balance quicker response with downsizing. Therefore, a coupled simulator that can calculate electricity, mechanics, control, and thermo characteristics is required. In 1D simulation, a thermal network method is commonly used for thermal calculation. However, an electric VTC is attached to the end of a camshaft; therefore, determining thermal resistances is difficult. We propose a method of determining thermal resistances, using both theoretical and experimental approaches. Thermal resistances of convective heat transfer are calculated automatically by using the formula of the heat transfer coefficient while referring to the rotation speed of the electric VTC and engine. Thermal resistances of conduction are calculated based on heat conduction formula. Thermal resistances that cannot be calculated directly are determined through parameter identification by using test equipment that can measure the inner temperature of an electric VTC under driving conditions. The calculation and measured temperature were in agreement within less than 10°C under stable and transient conditions. This enables the coupled simulator to calculate the characteristics of an electric VTC including thermal behaviors.