Caterpillar is a world leader in the manufacture of heavy equipment such as track-type tractors, wheel loaders and off-highway trucks, all requiring highly sophisticated torque converters in their power transmission devices. In its Transmission Business Unit (TBU), which designs and manufactures these torque converters, engineers use CFD to evaluate a wide range of possible designs to reach the best possible efficiency, quality and durability at the lowest possible cost.

The most crucial components of a torque converter are the impeller, turbine and stator wheels, which are arranged in a closed loop. Finding the correct blade shapes is a major iterative effort involving: 3-D blade geometry specification, 1-D converter performance and thrust prediction, and 3-D CFD analysis of the oil flow in the converter.

We use CFX-TurboGrid and CFX-TASCflow for our CFD analysis. CFX-TurboGrid’s ‘templates’ greatly reduce our grid generation effort and allow us to create high-quality 3-D grids for the three bladed passages with minimum effort.

The powerful CFX-TASCflow post-processing tools make it easy to examine the results, providing an excellent insight into the nature of the complex converter flow - insight that cannot be gained any other way due to the difficulty of direct measurement within the device. In addition, CFX-TASCflow command macros can be easily set up to estimate torque on the three wheels from the calculated pressure and velocity fields making it easy to predict the performance of the converter at any desired turbine-to-impeller speed ratio.

The bottom line is that Caterpillar engineers find it relatively easy to understand the impact of the critical blade design variables on the performance of the torque converter and are able to optimize the design to a higher level than was previously possible.

Streamlines near the stator blade suction side at stall.

Velocity vectors in the turbine blade passage halfway between shell and core.