Interrelated power delivery controls – including engine control – Transmission control – Engine controlled by transmission
Reexamination Certificate
2000-10-23
2002-11-12
Bonck, Rodney H. (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Engine controlled by transmission
C477S109000, C477S113000
Reexamination Certificate
active
06478713
ABSTRACT:
TECHNICAL FIELD
This invention relates to closed-throttle shifting of an automatic transmission, and more particularly to an engine speed and torque rate limit control for ensuring high shift quality in spite of increases in the driver torque request.
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 selectively establish reverse or forward speed ratios between the transmission input and output shafts. The input shaft is coupled to the vehicle engine through a torque converter which is selectively locked or un-locked, 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 transmission shifting during conditions of zero or near-zero driver torque demand, such shifts being referred to herein as closed-throttle shifts. In general, closed-throttle shifts include garage shifts (that is, shifts involving a transmission range change) and downshifts during coasting or braking conditions. Most control strategies for closed-throttle shifting involve determining an input synchronization (SYNC) speed based on the product of the transmission output speed and the target speed ratio, and controlling the engagement of the on-coming clutch to bring the transmission input speed into correspondence with the determined SYNC speed. For example, in the U.S. Patents to Lentz et al. U.S. Pat. No. 5,046,174 and Runde et al. U.S. Pat. No. 5,211,079, the SYNC speed is used to compute the on-coming clutch slip, and the on-coming clutch is engaged by a closed-loop control based on a deviation of the on-coming clutch slip from a desired slip profile. In another type of control, disclosed in the U.S. Patent to Downs et al. U.S. Pat. No. 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 SYNC speed, whereupon the on-coming clutch is engaged.
Regardless of the shift control strategy, there is a possibility that the driver will suddenly depress the accelerator pedal (correspondingly increasing the driver torque request) between dis-engagement of the off-going clutch and engagement of the on-coming clutch. When this occurs, the engine speed typically flares well above the SYNC speed, causing excessive on-coming clutch slippage during shift completion. In open (un-locked) converter shifts, the problem can be even worse due to the torque multiplication provided by the torque converter. Ultimately, the on-coming clutch has to be engaged to complete the shift, and inevitably, poor shift quality and/or excessive heating of the on-coming clutch friction elements occur. One approach for mitigating the severity of the problem, at least in the case of a power-on upshift, is disclosed in the U.S. Patent to Nitz et al. U.S. Pat. No. 5,129,286, where the shift control algorithm commands an immediate retard of the engine spark timing when a flare condition is detected for substantially eliminating the transmission input torque, and then returns the timing to a normal setting when the flare condition has been eliminated. While this approach can also be used in closed-throttle shift controls, the abrupt spark retard can introduce a torque disturbance of its own, and a significant calibration effort is required in order to produce just the right amount of spark retard for a given shift condition. Accordingly, what is needed is an improved closed-throttle shift control that utilizes engine controls to limit the transmission input torque during the shift while preserving shift quality and preventing clutch heating.
SUMMARY OF THE INVENTION
The present invention is directed to an improved engine and transmission control method for coordinated control of closed-throttle transmission shifting, wherein the transmission control provides engine speed and torque rate limits to the engine control based on the shift parameters. The speed and/or torque rate limits come into play if the driver suddenly increases the engine throttle setting. Additionally, in driver requested garage shifts, initiation of the shift is prevented until the engine speed is within the speed limit.
Preferably, the engine speed limit is set a calibrated amount above the computed input synchronization speed (SYNC). This serves to limit the slip speed of the on-coming clutch to the predetermined amount, and also limits the torque multiplication of the torque converter during open (un-locked) converter shifts. Alternately, the engine speed limit may be set to a value that limits the energy dissipated in the on-coming clutch to a predetermined value. With either approach, the engine speed and torque limits modify the engine control only to the extent necessary to preserve high shift quality while limiting the on-coming clutch energy dissipation to a safe level.
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Hubbard Gregory A
Robinson Timothy Alan
Runde Jeffrey Kurt
Bonck Rodney H.
General Motors Corporation
Hodges Leslie C.
Le David D.
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