Abstract
Hydraulic torque converter is a kind of high speed rotating machine using viscosity hydraulic oil as working medium, and its internal flow field is very complex. Thereby cavitation can occur easily in the working process, resulting in severe degradation of torque converter performance, noise, vibration and even failure. In order to reveal the effect of rotating speeds on the cavitation characteristics, a full flow passage geometry and a computational fluid dynamics (CFD) model with cavitation were developed to analyze the flow behavior in the torque converter. The results show that cavitation occurs when the speed difference between pump and turbine exceeds 1400 rpm for the basic model torque converter, which could be used as a useful indicator for the occurrence and degree of severity of flow cavitation. The increase of pump rotating speed or the decrease of speed ratio will intensify cavitation, which reduces the hydraulic transmission capacity and efficiency by over 20%, and seriously alters the shape, size, vapor volume fraction and region of cavitation bubbles. In extreme cases, more than 80% of the area on the suction side of the stator blade could be covered by cavitation bubbles. Moreover, the increase of pump rotating speed also changes the critical cavitation number and extends the cavitation range towards high speed ratio conditions not previously affected. These findings can provide guidance on how to choose the operating conditions of the hydraulic torque converter and how to improve its hydrodynamic performance and stability.
Highlights
Hydraulic torque converter is a closed-loop fluid machine that transfers power by the conversion between fluid kinetic energy and mechanical energy, and it serves as a core component of an automatic transmission and hydraulic transmission since it is able to provide continuously variable transmission, self-adaption to load, and absorption of vibration from the engine [1]
The increasing demand for higher power density and higher speed leads to higher flow velocity and lower local pressure, which makes the flow inside the torque converter more prone to cavitation
ANSYS CFX was employed to resolve the Reynolds-averaged Navier–Stokes equation of the full three-dimensional flow field based on the following assumptions [2]: (1) The flow is incompressible and the heat transfer is ignored in the torque converter
Summary
Hydraulic torque converter is a closed-loop fluid machine that transfers power by the conversion between fluid kinetic energy and mechanical energy, and it serves as a core component of an automatic transmission and hydraulic transmission since it is able to provide continuously variable transmission, self-adaption to load, and absorption of vibration from the engine [1]. It is widely used in the transmission systems of passenger cars, off-road vehicles, construction machinery, cruise ships, liners, tankers, large marine vehicles, etc. [[77,8,8]] ssttuuddiieedd tthhee ccaavviittaattiioonn cchhaarraacctteerriissttiiccss ooff aa ttoorrqquuee ccoonnvveerrtteerr uunnddeerr ddiiffffeerreenntt cchhaarrggiinngg pprreessssuurreess aanndd ooppeerraattiinngg ccoonnddiittiioonnss. These findings can serve as good guidance on how to choose the operating conditions of the hydraulic torque converter and how to improve its hydrodynamic performance and stability
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