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Ratcheting Devices are often used in automatic transmissions to provide a unidirectional power flow to achieve specific gear functions. These devices consist of two members that rotate relative to each other and a locking mechanism between these two rotating parts. In order to meet certain gearshift needs, the ratcheting device performs a combined overrun and engagement function. In both modes the components experience high-speed rotation and are subjected to significant impact forces. The high impact forces between the components may cause damage on the parts and the device may fail to function as intended. It is important to understand the dynamic behaviors of these ratcheting devices and the key design factors affecting their performances under various operating conditions. Vehicle tests and/or laboratory tests are often conducted to investigate the dynamic performance of these devices.

Due to complexities of interaction among gears and crescent-shaped island, a crescent oil pump is one of the most difficult auto components to model using three dimensional Computational Fluid Dynamics(CFD) method. This paper will present a novel approach to address the challenges inherent in crescent oil pump modeling. The new approach is incorporated into the commercial pump design tool PumpLinx from Simerics, Inc.. The new method is applied to simulate a production crescent oil pump with inlet/outlet ports, inner/outer gears, irregular shaped crescent island and tip leakages. The pump performance curve, cavitation effects and pressure ripples are studied using this tool and will be presented in this paper. The results from the simulations are compared to the experiment data with excellent agreement. The present study shows that the proposed computational model is very accurate and robust and can be used as a reliable crescent pump design tool.