US 5,079,970 AGranted

Acceleration-based control of power-on downshifting in an automatic transmission

AssigneeGeneral Motors Corporation

InventorsKenneth R. Butts, Kumaraswamy V. Hebbale

Life of this patent

Estimating the term…

Loading patent…

Abstract

A power-on clutch-to-clutch downshift control is initiated by partially releasing an off-going torque trasmitting device to permit an increase in the transmission input speed. At the same time, an on-coming torque transmitting device is filled in preparation for engagement. When the slip across the on-coming device is near zero, the on-coming device pressure is progressively increased while the off-going clutch pressure is controlled to maintain the near-zero on-coming slip speed condition. When the on-coming device develops significant capacity, a tie-up develops between the on-coming and off-going devices, causing a drop in output shaft acceleration. The drop is detected and used to release the off-going device, the shift being complete when the on-coming device is fully engaged. Engine torque controls are employed to ensure a smooth output torque transition at the end of the shift.

Claims5

Dependent claims

A method of downshifting a motor vehicle automatic shift power transmission having an input driven by a vehicle engine, and an output connected to drive a vehicle wheel, where downshifting involves releasing an off-going pressure to disengage an off-going torque transmitting device while increasing an on-coming pressure to engage an on-coming torque transmitting device, the method comprising the steps of:

controlling the release of the off-going pressure so as to allow the engine to increase the input to a synchronous speed at which a slip speed across the on-coming torque transmitting device is near zero, and thereafter controlling the off-going pressure at a level to maintain the input at such synchronous speed;
initiating a progressive increase of the on-coming pressure when the input approaches said synchronous speed, thereby to progressively engage the on-coming torque transmitting device;
monitoring the acceleration of the transmission output to detect a drop indicative of a tie-up condition characterized by concurrent engagement of the off-going and on-coming torque transmitting devices;
and
fully releasing the off-going pressure when the tie-up condition is detected, the downshift being complete when the on-coming pressure fully engages the on-coming torque transmitting device.

2 more elements

Dependencies are inferred from the claim text.