Design of an Automobile Torque Converter

TURBOdesign1 has been applied to the design of a three-component automobile torque converter. Due to the strong curvature of the flow passages and high loading, the flow behavior is extremely complex and difficult to optimize using a conventional design approach. Using TURBOdesign1, it is possible to achieve the best matching between the components, control secondary flows, and suppress flow separation.

Each component such as a pump or turbine is designed separately, but the effects of upstream components are included in the design by specifying the appropriate inlet boundary conditions. The design and analysis of the full machine using CFD have to be repeated a few times because of the coupling between the inlet and outlet boundary conditions. However, the use of logical flow related input parameters for TURBOdesign1 greatly accelerates the optimization process.

Fig.1: Example of the three components of a torque converter: pump, stator and turbine.

Fig.2: Typical blade loading distribution for a torque converter pump.

 

 

The blade loading parameters and stacking condition are key to the optimization of the three-dimensional flow field, as well as maintaining ease of manufacture. Figure 2 shows a typical blade loading distribution for a pump designed with zero incidence. Figures 3 and 4 show the static pressure contours in 3-D and 2-D respectively, and Figure 5 the blade surface static pressure distribution showing a very smooth pressure rise across the blade.

Fig.3: Static pressure contours in 3-D.

Fig.4: Static pressure contours in 2-D.

Fig.5: Blade surfaces from TURBOdesign1.

A conventionally designed torque converter was evaluated using CFD. Although experiments confirmed that this conventional torque converter already had reasonably high efficiency, large areas of flow separation were still observed on both pump and turbine blade suction surfaces (Figure 6). The CFD prediction revealed the three-dimensional flow-field to be of an extremely complex nature, having interactions of secondary flows, which are beyond the control of a conventional design.

The torque converter was redesigned using TURBOdesign1. The CFD prediction confirmed that the areas of flow separation on both the pump and turbine blade suction surfaces had been suppressed, as shown in Fig.7. CFD predicts 1.7 points improvement in overall torque converter efficiency. Such an improvement will have a very big impact on the fuel consumption of automobiles. Through the careful control of the blade loading and vortex pattern specified, a good compromise between performance improvements and the manufacturability of the three dimensional blades is possible.

Fig.6: CFD results of the conventionally designed torque converter with areas of flow separation in the pump and the turbine.

Fig.7: CFD results of the torque converter redesigned with TURBOdesign1, the areas of flow separation have been removed.

TURBOdesign1 gives the user more freedom to control the three dimensional flows, and it should be possible to improve the performance of more compact torque converters with high flatness ratio using this method.

Reference: Zangeneh, et al., 1997, On 3D Inverse Design of an Automotive Torque Converter Pump Impeller in Shear Flows, Proceedings of JSME Centennial Grand Congress, ICFE97-702.