Shift quality in automatic transmissions is greatly affected by deterioration and variation of engine torque, hydraulic pressure control valves, friction elements and other factors. This paper presents a new control system that improves shift quality by using a turbine speed sensor to monitor the shift duration, particularly the duration of the inertia phase.
The use of feedback control to vary the line pressure according to the shift duration makes it possible to eliminate the effects of aging and component variability. Other factors affecting shift quality, such as atmospheric pressure, road gradient and additional engine load from the air conditioner and alternator, were also examined, and it was found that their effects can be virtually eliminated through feedback control. The inertia phase usually becomes shorter as the engaging clutch capacity increases. However, an extremely small torque capacity can cause a short inertia phase, resulting in a large torque disturbance. This problem is avoided by measuring the interval from the initiation of the shift command to the completion of the inertia phase, this making it possible to distinguish between small and large torque capacity conditions.
Power-off upshifts, resulting from abrupt throttle closing, can cause shock and chatter. These disturbances are eliminated through synchronized clutch engagement, achieved by sensing the speed ratio between the turbine and output shaft.
Power-on downshifts when going downhill pose a critical condition for clutch slip. Friction elements are protected from damage in this system by controlling the timing and capacity of the engaging and releasing elements.