F2010A015
A Study on AT Damper Clutch for Improving Fuel Efficiency and Driveline Vibration
This paper presents an approach to widen torque converter clutch lock-up zone to improve fuel efficiency of a vehicle equiped with automatic transmission. Former studies on this theme have mainly focused on how to tune stiffness of damper clutch spring of the first stage, K1, to reduce the level of boom noise generated by AT output shaft torsional vibration due to engine torque pulsation. But, if damper clutch spring rate is not tuned along with engine torque characteristics and transmission control strategy as well as drive line vibration characteristics, sub-harmonic vibration can happen in specific lock-up driving conditions. In this paper, we investigated how the sub-harmonic vibration happens, and how to predict it and avoid it, so that vehicle can have wider lock-up zone which contributes toward better fuel efficiency. These are conclusions. 1. Lock-up damper clutches which consist of two states of spring rate can introduce sub-harmonic vibration (half frequency of engine combustion), if engine torque meets the first stage limit torque of the damper clutch during specific lock-up driving condition. 2. The sub-harmonic vibration (c1 component for I4 engine) can be developed enough to be a serious problem by resonance, if sub-harmonic vibration frequency is close to 2nd mode frequency of driveline. And for almost all vehicles with I4 engines, the resonance happen in the vicinity of 1500~2000rpm 3. TCU lock-up zone and torque capacity of the first stage of damper clutch should be set according to engine type and torque characteristics, such as number of cylinders, turbo charger and fuel. 4. We carried out simulation with lumped mass drive line model, and predicted where sub-harmonic vibration can occur. 5. We designed torque converter damper clutch according to the simulation results, and tested in the vehicle. The test result showed that there was no sub-harmonic vibration for all lock-up diving conditions as predicted. And boom noise level of the vehicle reduced by more than 4dBC by optimizing first stage torque capacity of damper clutch as low as sub-harmonic vibration can be just prevented. 6. To prevent this sub-harmonic vibration ultimately, we suggested innovative clutch design. We removed root cause of sub-harmonic vibration by smoothening stiffness change in damper clutch.
This abstract is supplemented by a PDF, which can be viewed here.
Session: Consumption and Emission Reduction