가변형 베인펌프의 성능특성에 관한 해석적 연구

Abstract

Recently, most automatic transmission vehicles use a gear pump where the discharge flow rate increases as engine speed rises. The discharge flow rate increases excessively when the gear pump rotating speed goes beyond a certain range, and cavitation occurs at the suction port due to an increase in the low-pressure region leading to a power loss. When the cavitation occurs, the performance of the pump is reduced dramatically with vibration and noise, indicating an unstable state. Therefore, research is actively underway on preventing power loss due to excessive oil discharge flow of the gear pump and minimizing cavitation generation by using flow control of the oil pump in the automatic transmission at high rotating speed. Few cases have applied variable displacement vane pumps to engines. However, it cannot be applied directly to the automatic transmission oil pump because of high operating pressure. Therefore, it must be re-designed in consideration of the working pressure. In order to make it possible for the flow control of the vane pump to be applied in an automatic transmission, it is very necessary to analyze the variation in pressure ripples, cavitation generation, and flow rate, which are really important for flow control and vane pump design, according to operating temperature and rotation speed. However, the financial and time costs are high in figuring out performance characteristics under variable operating conditions through experimentation. Therefore, time and money can be saved by using computational fluid dynamics (CFD) to analyze the variations in performance under different operation conditions. In a previous study, research on the variations in pressure ripples and cavitation occurrences was hardly found. As well, the study of cavitation generation is still lacking compared to that of the pressure ripple. Many existing studies of cavitation focus on single blades or vanes. The performance and fluid flow study for whole vane pumps is not enough, especially for automatic transmissions, which are operated under high pressure. In the present work, the variation of discharge flow rate, Driving torque, cavitation generation, and the pressure field of the flow-control vane pump are applied to automatic transmissions and analyzed using the simulation model. In order to understand the performance due to change in variable amounts, were analyzed discharge mass flow rate, pressure ripples, cavitation amount and cam ring movement while changing the rotational speed, operating temperature and feedback pressure. Discharge flow rate showed up to decreases with rise of operating temperature and bigger clearance and fixed by 38 l/m with chamber displacement angle. Driving torque decreased with operating temperature and clearance increases and in inverse proportional to the variation amount. Flow and pressure ripples were increased by an increase in viscosity due to lowering of the operating temperature and higher discharge flow rate with increasing rotational speed. Cavitation show a tendency to occur in the suction section, disappear by collapse rapidly discharge portion.