Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Clutch control
Reexamination Certificate
2000-05-11
2001-10-23
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Clutch control
C701S068000, C701S053000, C701S054000
Reexamination Certificate
active
06308125
ABSTRACT:
TECHNICAL FIELD
This invention relates to closed-throttle downshifting of an automatic transmission, and more particularly to an adaptive clutch control for synchronizing the transmission input speed with a target speed corresponding to the downshifted speed ratio.
BACKGROUND OF THE INVENTION
In general, a motor vehicle automatic transmission includes a number of gear elements and selectively engageable friction elements (referred to herein as clutches) that are controlled to establish one of several forward speed ratios between the transmission input and output shafts. The input shaft is coupled to the vehicle engine through a fluid coupling such as a torque converter, and the output shaft is coupled to the vehicle drive wheels through a differential gearset. Shifting from a currently established speed ratio to new speed ratio involves, in most cases, disengaging a clutch (off-going clutch) associated with the current speed ratio and engaging a clutch (on-coming clutch) associated with the new speed ratio.
The present invention is directed to downshifts, and in particular, to downshifts performed during coast or braking conditions with the engine throttle essentially closed, such shifts being referred to herein as closed-throttle downshifts. Various clutch controls have been proposed for controlling closed-throttle downshifting. For example, the U.S. Pat. No. to Lentz et al. 5,046,174 and U.S. Pat. No. Runde et al. 5,211,079 are directed to a control in which the off-going clutch is released, and the transmission input speed is raised to the synchronous speed of the target speed ratio by a closed-loop control of the on-coming clutch based on the deviation of the on-coming clutch slip from a desired slip profile. In another type of control, disclosed in the U.S. Pat. No. to Downs et al. 4,671,139, the off-going clutch is released after the transmission input speed falls below the engine idle speed, and the closed-throttle engine torque raises the input speed to the synchronous speed of the target speed ratio, whereupon the on-coming clutch is engaged.
While the control disclosed by Downs et al. has the potential of achieving high quality closed-throttle downshifts with no negative output torque disturbance, clutch and pressure control variability make it difficult to consistently achieve the desired timing for off-going clutch dis-engagement and on-coming clutch engagement. This is particularly the case for shifts occurring at very low vehicle speeds, such as the shift to the first or lowest speed ratio. Accordingly, what is needed is a control that produces consistent high quality closed-throttle downshifts in spite of such variability, and that has the ability to adaptively adjust the control parameters for achieving optimum shift quality.
SUMMARY OF THE INVENTION
The present invention is directed to an improved adaptive control for an automatic transmission closed-throttle downshift in which closed-throttle engine torque is used to raise the transmission input speed to the synchronous speed of the target speed ratio, wherein clutch control parameters are adaptively adjusted to coordinate the off-going clutch release and the on-coming clutch apply, and to tune the on-coming clutch controls for optimum shift quality.
A primary on-coming clutch control fills the on-coming clutch and maintains it in readiness for engagement while reducing the off-going clutch pressure to a hold value and then progressively reducing it to releasing the off-going clutch. When the input speed reaches the synchronous speed, the primary control raises the on-coming pressure by an amount designed to maintain the input speed synchronization. If the primary control is unable to maintain input speed synchronization, a contingent control schedules the on-coming clutch pressure for gradually re-establishing the input speed synchronization, and thereupon engages the on-coming clutch to complete the shift.
According to an aspect of this invention, the fill time or the maintenance pressure of the on-coming clutch is adaptively decreased for reduced driveline disturbance in subsequent shifts of the same type if the transmission shaft jark during the primary control exceeds a threshold. According to another aspect of this invention, the fill time or the maintenance pressure of the on-coming clutch is adaptively increased based on a measure of the effort required by the contingent control for reduced dependence on the contingent control in subsequent shifts of the same type if the measured effort exceeds a threshold level. According to a further aspect of this invention, the off-going clutch release control is adaptively adjusted for improved on-coming and off-going clutch coordination in subsequent shifts of the same type based on when off-going clutch slippage is observed relative to the fill period of the on-coming clutch. The reduced driveline disturbance, reduced over-shoot of the synchronous speed and the improved clutch coordination tune the control to provide optimum shift quality despite clutch and pressure control variability.
REFERENCES:
patent: 4070927 (1978-01-01), Polak
patent: 4665772 (1987-05-01), Greene
patent: 4671139 (1987-06-01), Downs et al.
patent: 4913004 (1990-04-01), Panoushek et al.
patent: 5046174 (1991-09-01), Lentz et al.
patent: 5046383 (1991-09-01), Butts et al.
patent: 5072390 (1991-12-01), Lentz et al.
patent: 5079970 (1992-01-01), Butts et al.
patent: 5211079 (1993-05-01), Runde et al.
patent: 5601506 (1997-02-01), Long et al.
Gleason Sean E
Runde Jeffrey Kurt
Cuchlinski Jr. William A.
General Motors Corporation
Hodges Leslie C.
Marc-Coleman Marthe Y.
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