Automatic Transmission Shift Control for Canceling Inertia Torque

A step-ratio automatic transmission is a system of planetary gear sets, wet clutches, hydraulic control system and torque converter to provide the flexibility in gear ratio selection. Gearshifting is realized by the engagement and disengagement of clutches which are commanded by control strategy through the hydraulic actuators. A complex interaction between components results in transient drive shaft torque, affecting shift quality. In particular, it is difficult to achieve fast upshift without inducing a large inertia torque spike due to changing speed ratios. A deep understanding of the system kinematics and dynamics becomes critical to control clutches for fast and smooth gearshifting. This article performs detailed analytical study to explain the upshift behaviors of a 10-speed automatic transmission by deriving the system’s governing equations. These equations show insights of working principles of the transmission and provide a new method to improve shift quality. Specifically, a managed tie-up between the on-coming and off-going clutches is introduced during the inertia phase. Shift simulations are conducted to systematically evaluate the effectiveness of the managed tie-up for suppressing the effects of inertia torque while shortening the inertia phase. The simulations also illustrate that the managed tie-up does not necessarily result in deeper torque hole during torque transfer phase of shifting. The managed tie-up is implemented in a test vehicle through open loop control to demonstrate its feasibility.