Interrelated power delivery controls – including engine control – Transmission control – Engine controlled by transmission
Reexamination Certificate
2000-05-19
2001-11-20
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Engine controlled by transmission
C477S116000, C477S117000
Reexamination Certificate
active
06319170
ABSTRACT:
TECHNICAL FIELD
This invention relates to the control of power-on downshifting in an automatic transmission, and more particularly to a model-based control of engine torque during the downshift.
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.
Various techniques have been used for electronically controlling the oncoming and off-going clutches during a power-on downshift. For example, the U.S. Pat. Nos. 5,029,494 and 5,070,747 to Lentz et al. disclose power-on downshift controls in which the off-going clutch is controllably released in an established sequence to allow the engine to accelerate the transmission input shaft to a post-shift or synchronization speed, whereafter the shift is completed by engaging the on-coming clutch and dis-engaging the off-going clutch. Similar control techniques are also described in the U.S. Pat. No. 4,653,351 to Downs et al., and the U.S. Pat. Nos. 4,796,490 and 5,079,970 to Butts et al. Additionally, it is known that the shift quality can be enhanced by momentarily reducing the engine torque as the input speed approaches the synchronization speed. For example, in Butts et al. U.S. Pat. No. 5,079,970, the engine spark timing is retarded when the slip of the on-coming clutch drops to a predefined value; the spark retard reduces the engine output torque by a predefined amount, and is immediately ramped out at an open-loop ramp rate to achieve a smooth torque transient upon completion of the shift.
While the known engine torque controls have the capability of enhancing downshift quality, control parameters such as the timing and quantity of torque reduction have been only generally defined, so that the potential enhancements are fully achieved only occasionally. Also, it has been found that torque controls not uniquely suited to a given set of shift conditions can actually degrade the shift quality. Accordingly, what is needed is an engine torque control that is uniquely suited to the particular shift conditions, and that can respond to and correct aberrant conditions occasioned by errors in the engine torque and clutch controls.
SUMMARY OF THE INVENTION
The present invention is directed to an improved engine torque control for an automatic transmission power-on downshift, wherein a dynamic model of the transmission is used to schedule both shift progression and engine torque reduction based on a desired trajectory of the transmission input shaft during the shift and the driver torque demand. The shift is initiated with the off-going clutch by using the dynamic model to conform the input speed to the desired trajectory, and the torque reduction is initiated based on an estimate of the time to synchronization relative to an expected control delay so that the torque reduction occurs when the input speed reaches synchronization. An appropriate torque reduction amount is calibrated for a specified driver torque demand, and in operation, the amount of torque reduction for a given shift is determined based on the current driver torque demand and a detected deviation of the desired trajectory from a nominal trajectory corresponding to the specified driver torque demand. Aberrant conditions, including under-achievement and over-achievement of input speed synchronization are detected and used to modify the engine torque control so that the shift is completed in a timely manner. Using the dynamic model to schedule the torque control achieves more consistent shift feel and improved adaptability to different powertrain and vehicle-type configurations, and reduces the number of calibrated parameters requiring adaptive correction.
REFERENCES:
patent: 4070927 (1978-01-01), Polak
patent: 4653351 (1987-03-01), Downs et al.
patent: 4796490 (1989-01-01), Butts et al.
patent: 5029494 (1991-07-01), Lentz et al.
patent: 5036729 (1991-08-01), Nitz et al.
patent: 5070747 (1991-12-01), Lentz et al.
patent: 5079970 (1992-01-01), Butts et al.
patent: 5445576 (1995-08-01), Motamedi et al.
patent: 5601506 (1997-02-01), Long et al.
patent: 5795262 (1998-08-01), Robinson
Hubbard Gregory A
Robinson Timothy Alan
Estremsky Sherry
General Motors Corporation
Hargitt Laura C.
Hodges Leslie C.
Lewis Tisha D.
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