US 5,113,343 AGranted

Sequenced control of double transition powered downshifting in an automatic transmission

AssigneeGeneral Motors Corporation

InventorsJoseph H. Hunter, Peter E. Swingler

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Abstract

In an automatic transmission having an electronic control, a double transition powered downshift to a target range requires the release of two off-going clutches and the engagement of two on-coming clutches. The shift begins by releasing one clutch and applying another to begin (but not complete) an upshift to a third range having a speed ratio lower than both the initial range and the target range so that first an input speed increase occurs followed by an input speed decrease (pull-down). The speed decrease triggers respective application and release of the other clutches to arrest the upshift and complete the downshift. Each clutch application and release occurs gradually under an open loop control. Slip of the first off-going clutch, pull-down, speed sync at the low gear ratio and a near sync condition are determined from turbine speed and output speed and are used to time pressure command changes to smoothly coordinate clutch releases and applications.

Claims9

Dependent claims

In a vehicular automatic transmission having input and output shafts, a turbine connected to the input shaft to couple driving torque thereto, in which a downshift from a first speed ratio to a second speed ratio lower than said first speed ratio is carried out through concurrent disengagement of first and second off-going fluid pressure operated torque transmitting devices and engagement of first and second on-coming fluid pressure operated torque transmitting devices, wherein the engagement of said second off-going torque transmitting device and said first on-coming torque transmitting device establishes a third speed ratio lower than said second speed ratio, and further having turbine and output speed sensing means, a method of controlling said torque transmitting devices to carry out a downshift from said first speed ratio to said second speed ratio comprising the steps of:

gradually releasing said first off-going torque transmitting device,
gradually engaging said first on-coming torque transmitting device in response to a detected slip of said first off-going torque transmitting device while said second off-going torque transmitting device is still engaged, thereby to begin a shift to said third speed ratio, and
releasing said second off-going torque transmitting device and gradually engaging said second on-coming torque transmitting device in response to a detected pulldown of said turbine, thereby to complete a shift to said second speed ratio.

In a vehicular automatic transmission having input and output shafts, a turbine connected to the input shaft to couple driving torque thereto, in which a downshift from a first speed ratio to a second speed ratio lower than said first speed ratio is carried out through concurrent disengagement of first and second off-going fluid pressure operated torque transmitting devices and engagement of first and second on-coming fluid pressure operated torque transmitting devices, wherein the engagement of said second off-going torque transmitting device and said first on-coming torque transmitting device establishes a third speed ratio lower than said second speed ratio, and means for supplying fluid pressure to said torque transmitting devices in accordance with pressure commands for controlling their engagement and disengagement, a method of controlling said torque transmitting devices to carry out a downshift from said first speed ratio to said second speed ratio comprising the steps of:

initiating pressure commands for disengagement of said first off-going torque transmitting device and for engagement of said first on-coming torque transmitting device upon shift initiation,
controlling said pressure commands to said first on-coming torque transmitting device and said first of-going torque transmitting device in response to a detection of slip of said first off-going torque transmitting device, to permit a controlled turbine speed increase followed by a pulldown of said turbine speed, and
controlling said pressure commands to said second on-coming torque transmitting device and said second off-going torque transmitting device in response to said pulldown to synchronize said first and second on-coming torque transmitting devices.

Dependencies are inferred from the claim text.