Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1999-05-10
2001-04-03
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S064000, C477S015000, C477S068000
Reexamination Certificate
active
06212458
ABSTRACT:
TECHNICAL FIELD
This invention relates to vehicle braking and more particularly to powertrain ratio interchanges during vehicle braking.
BACKGROUND OF THE INVENTION
Grade braking in passenger vehicles has been left to the purview of the operator of the vehicle. If the operator wishes the vehicle to decelerate or have a constant speed on a down grade, the brake pedal is depressed in an effort to slow the vehicle. Many drivers recognize that, with automatic transmissions, it is possible to control the down grade speed somewhat by shifting the transmission to a lower drive ratio (fourth to third, or fourth to third to second) and employing the brakes simultaneously. As with manual or countershaft type transmissions, this requires a manual input or shift effort from the operator.
In some instances, the operator may be slow to recognize the increasing speed rate of the vehicle. Under these conditions, the brake application pressure must be increased. While this maintains the vehicle speed in a range that the operator finds comfortable, the brake wear, lining and rotor temperature and the amount of brake fade increase. This can have a shortening effect on the life of the brakes which will require the vehicle owner to replace or service the brakes more often.
With the advent of electro-hydraulic controls, many additional automatic functions can be made available to the operator and transmission control becomes more precise. Ratio interchanges are considerably improve with the use of lookup tables to determine the shift sequence and timing. The widespread introduction of anti-lock braking systems has also improved the vehicle braking function.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide and improved relationship between the ratio interchange function of the transmission and the vehicle braking operation.
In one aspect of the present invention, brake actuation is a measure of the deceleration rate desired by the operator. In another aspect of the present invention, compensation for brake fade conditions are provided.
In yet another aspect of the present invention, the transmission gear ratio is considered during braking maneuvers. In still another aspect to the present invention, a ratio interchange is commanded during vehicle braking depending on the brake pressure and sensed grade condition.
In a further aspect of the present invention, the downshift range is a function of the current transmission ratio, the speed of the vehicle and the brake pressure. In a yet further aspect of the present invention when a downshifting range is perceived, the speed threshold for a shift decision is determined by brake pressure. In a still further aspect of the present invention, brake pad temperature is maintained below a predetermined level by issuing a transmission downshift command if necessary to assist the braking function even if the vehicle is not on a grade.
The present invention is particularly useful with electronically controlled multi-speed power transmissions, but can be easily adapted to other types of power transmissions such as continuously variable type systems. The electronic control incorporates a central processing unit which includes a preprogrammed digital computer. During control of the transmission a grade braking algorithm is processed to determine if the vehicle speed is compatible with the perceived desired deceleration of the driver.
To maintain the desired deceleration, the transmission control is instructed to downshift the transmission to a lower gear ratio if the vehicle braking is not sufficient to attain the desired result. To accomplish this the algorithm responds to driver input signals from the throttle and the vehicle brake control. The control has grade downshift requirements or grade percentage thresholds and vehicle speed targets for each of the gear ratios below the top ratio which, in most current passenger vehicles, is fourth gear. If the driver is perceived as wishing to slow the vehicle, brake applied and or throttle released, the algorithm will command a downshift when the grade downshift requirements and the speed targets are met for the next lower gear available. The downshift requirement and the speed threshold vary with the brake input which is usually determined by brake pressure.
REFERENCES:
patent: 5056637 (1991-10-01), Miyawaki et al.
patent: 5217086 (1993-06-01), Morimoto
patent: 5319998 (1994-06-01), Iwatsuki et al.
patent: 5389046 (1995-02-01), Timte et al.
patent: 5707318 (1998-01-01), Shimei et al.
Kloess Scott R.
Leppek Kevin Gerard
Walenty Allen John
Arthur Gertrude
Cuchlinski Jr. William A.
General Motors Corporation
Sedlar Jeffrey A.
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