Automatic Transmission Rotational Inertia Effect on Shift Quality 2011-01-0393

The achievable shift quality of a modern automatic transmission may be greatly affected by the equivalent rotational inertia of the gearbox and driveline components. New, more mass- and packaging-efficient higher number of gear powerflows are being developed. These new architectures often result in more components being attached to a given rotational node. The rotational speed multiplication of the components must be considered when determining their inertial torque contribution to a given speed change event. An example of this multiplication effect is presented, with a discussion of the resulting impact to shift quality disturbance.

Opportunities to address the negative aspects of the higher inertial torque contribution to transmission output shaft disturbance are discussed. Coordination of engine torque control and clutch torque control is presented as a viable strategy to improve shift quality. Higher magnitudes of clutch torque and engine torque management are required to achieve fast shift times with desirable shift feel. The concerns with this approach may include customer perception of the torque interrupt, the ability to ramp in and out the engine torque in the allowable shift time, and the potential to affect emissions diagnostic compliance. Another concern may be the ability to ramp up and down the clutch torque in the allowable shift time. A discussion on the trade-off between faster inertia phase shift times and rate of change of transmission output torque is presented.

Analysis is performed using system simulation via math models of the physical system.