Severyn, P., Hemphill, J., George, P., and Sturgin, T., "Launch Devices for Turbo-Charged Engines," SAE Int. J. Passeng. Cars - Mech. Syst. 5(1):647-655, 2012, doi:10.4271/2012-01-0811.
The demand for both reduced fuel consumption and increased performance has resulted in the current trend of downsizing and turbo-charging the combustion engine. This started in diesel engines and is being carried over to gasoline direct inject engines. The fuel economy benefit using this strategy is clear, however, the requirements of the launch device are not. One drawback of downsizing and turbo-charging is the effect of lag in boost pressure resulting in a decrease of vehicle performance. This is intensified at increased altitude. One way to reduce turbo lag is by operating the engine at a higher speed. In order to diminish lag, the launch device must allow for faster acceleration of the engine. At the same time, enough engine torque must be transmitted to the wheels to maintain acceptable launch feel. Using a traditional torque converter, the hydrodynamic characteristics can be made looser to allow for faster acceleration of engine speed. This however has a negative impact on fuel consumption. This paper will examine the effects of turbo-charging on launch performance and document the results of different options for launch devices including variable characteristic devices that abate turbo lag while maintaining fuel economy. These options include optimized torque converter characteristics, the Multi-Function Torque Converter, and a new launch device called the Fluid Launch Clutch. These options have been studied both through simulation and hardware testing.