Evaluation and Validation of Viscous Oil Cavitation Model Used in Torque Converter

Meng Guo,Wei Wei,Cheng Liu,Zhifang Ke,Juan Li,Qingdong Yan

doi:10.3390/app11083643

Abstract

Hydraulic torque converter is widely used in transmission units as it is able to provide variable speed and torque ratio, isolate vibration, and absorb shock. The pursuit of a highly packed power unit requires a high capacity/speed torque converter, consequently resulting in a higher risk for cavitation and severe performance degradation, noise, vibration, and even failure. Existing cavitation models generally focus on water, and the empirical parameters are not suitable for the cavitation prediction of torque converter which utilizes high viscosity oil as its working medium. This paper focused on the influence of parameters on the performance and cavitation characteristics of torque converter. A full flow passage geometry and different computational fluid dynamics (CFD) models with cavitation were developed to predict torque converter fluid behavior by resolving Reynolds-averaged Navier–Stokes equations using finite volume method (FVM). The numerical results indicated that nuclei volume fraction, vaporization coefficient, mean nucleation site radius, and maximum density ratio have great influences on the cavitation behavior. These parameters altered the degree of cavitation and the pressure distribution on the surface of stator blades, and affected the stall performance such as stall capacity factor and torque ratio. The cavitation model was then modified to improve calculation accuracy. The test results showed that the prediction error under stall operating condition was decreased from 6.7% to 2%. This study provides insight on the influences of the empirical parameters on both internal cavitation behavior as well as overall hydrodynamic performance.

Highlights

Hydraulic torque converter is a closed-loop fluid machinery which transfers power by the conversion between fluid kinetic energy and mechanical energy, and it serves as a core component of automatic transmission and hydraulic transmission (Figure 1).Hydraulic torque converters are widely used in transmission systems of passenger cars, offroad vehicles, commercial vehicles and construction machinery because it is able to provide continuously variable transmission, self-adaption to load, and absorb vibration from the engine [1]
Guo investigated the dynamic cavitating flows inside a torque converter using transient computational fluid dynamics (CFD) model and Zwart cavitation model, the results indicated that stator domain was the main place where cavitation occurred, and it brought about over 20%
The mass flow rate (MF) was extracted from the simulation results to reveal the influence of cavitation

Summary

Introduction

Hydraulic torque converter is a closed-loop fluid machinery which transfers power by the conversion between fluid kinetic energy and mechanical energy, and it serves as a core component of automatic transmission and hydraulic transmission (Figure 1).Hydraulic torque converters are widely used in transmission systems of passenger cars, offroad vehicles, commercial vehicles and construction machinery because it is able to provide continuously variable transmission, self-adaption to load, and absorb vibration from the engine [1]. The increasing demand for higher power density leads to higher flow velocity and lower local pressure, which makes the flow inside the torque converter more prone to cavitation. Cavitation will occur when the local pressure is lower than the vapor pressure of the working fluid, and it will reduce the performance of torque converter, and cause vibration, noise, and a series of unfavorable issues [2,3]. The periodic growth and collapse of cavitation will cause vibration and noise of torque converter, and the high local pressure is generated during cavitation collapse, all of these will lead to poor performance, short service life, and cavitation damage or even damage the torque converter in severe cases. As the development of hydraulic torque converter is toward high capacity, high speed, and high power–weight ratio, cavitation in torque converters has become one of the key issues affecting performance and reliability

Methods

Results

Conclusion