Traditionally driveline ratios are selected based on trial and error method of proto vehicle testing. This consumes lot of time and increases overall vehicle development effort. Over last few decades, simulation-based design approach has been extensively used to alleviate this problem.
This paper describes torque converter and final drive ratio (FDR) selection at concept phase for new Automatic Transmission (AT) vehicle development. Most of the critical data required for simulating vehicle performance and fuel economy (FE) targets were not available (e.g. shift map, clutch slip map, pedal map, dynamic torque, coast down, etc.) at an initial stage of the project. Hence, the risk for assuming right inputs and properly selecting FDR/Torque converter was particularly high.
Therefore, a validated AVL Cruise simulation model based on an existing AT vehicle was used as a base for new AT vehicle development to mitigate the risk due to non-availability of inputs. The simulation model shows 97% correlation with the test results by using base shift map. The shift map was further optimized by using Gear Shifting Program (GSP) and FE improved by ~ 1.5% over base shift map without deterioration in performance.
Finally, Torque converter and FDR were selected based on Performance and FE trade-off through simulation. The new AT proto vehicle was built with suggested configuration and Jury feedback on drivability on proto vehicle was found to be excellent. The FDR and Torque converter were subsequently confirmed to supplier for mass production. Hence, the FDR and torque converter selected by simulation met the requirements of “First Time Right” Quality Crusade while conforming to strict project deadlines.
