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Computer simulations of vehicle dynamics can be a useful investigative tool in drive-ability and NVH studies. As the present work demonstrates, oscillations of the drive-train under steady-state and transient conditions are amenable to mathematical analysis, especially in the torsional mode. Simulations of such a system with a lock-up torque converter are shown with emphasis on tip-in response, transmissibility of engine firing pulsations and self-excited oscillations. In particular, the method of interactive simulation is shown to be an effective design-aid tool in the investigation of drivetrain vibrations.

Performance, driveability and NVH characteristics of a vehicle are altered when the hydraulic torque converter is bypassed with a mechanical clutch device in an effort to increase the overall efficiency of the transmission. To better illustrate and explain some of the behavior of such systems, a theoretical investigation of a torque converter with a centrifugal bypass (lock-up) clutch is presented. Computer-based simulations demonstrate how the lock-up characteristics of the clutch affect the torsional vibrations and the tip-in response of the drivetrain. In particular, the bypass clutch slip capacity is shown to be responsible for self-excited oscillations if “negative damping” is present. In addition, the dynamic responses of open, locked and slipping drivertrains are investigated with regard to firing torque transmissibility and sudden changes in throttle. Comparisons with instrumented vehicle results are also presented.