Torque ramp down control

Details Torque ramp down control Torque ramp down control

2000-12-21

2002-06-18

Wright, Dirk (Department: 3681)

Interrelated power delivery controls, including engine control

Transmission control

Engine controlled by transmission

Reexamination Certificate

active

06406403

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control method/system for ramping down engine torque to a value calculated to provide a substantially zero driveline torque at a rate determined by comparing sensed rate of change of throttle pedal position (drive torque demand) to a predetermined maximum rate of decrease and a predetermined minimum rate of decrease.
2. Description of the Prior Art
Fully or partially automated mechanical transmission systems that, upon determining that a shift from a currently engaged ratio into neutral and then into a target ratio is desirable, will, preferably but not necessarily while maintaining the vehicle master friction clutch engaged, initiate automatic fuel control to cause reduced torque across the jaw clutches to be disengaged, are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,850,236; 5,582,558; 5,735,771; 5,775,639; 6,015,366; and 6,126,570, the disclosures of which are incorporated herein by reference.
These systems include systems that attempt to fuel the engine to achieve a sustained zero driveline torque, see U.S. Pat. No. 4,593,580, the disclosure of which is incorporated herein by reference, and systems that fuel the engine to force one or more torque reversals, see U.S. Pat. No. 4,850,236.
Systems utilizing the engine fueling technique of forced torque reversals, especially repeated forced torque reversals, provide a highly reliable routine for allowing a shift to neutral, but may provide a somewhat less than desirable shift feel. Systems utilizing the engine fueling technique of aiming and attempting to remain at zero driveline torque provide a relatively high quality shift fuel, but did not provide desirable reliability of allowing an engaged jaw clutch to be acceptably disengaged.
In accordance with the above-mentioned copending U.S. Ser. No. 09/704,288, an adaptive engine fueling control is provided which, based upon a sensed movement, preferably a rate of movement of a shift member, such as a shift lever in the Y—Y direction or the like, will utilize engine fueling to achieve the most appropriate (a) of aiming at a zero driveline torque, (b) or causing torque bumps to force torque reversals across the jaw clutch to be disengaged, or (c) a combination of thereof. This is accomplished by, upon determining that a shift into transmission neutral is required, causing the engine to be fueled to cause an output (flywheel) torque determined to cause a substantially zero driveline torque while monitoring shift member position. After a period of time, if the rate of change of the shift member position is greater than a reference value, than the desired substantially zero torque condition has been achieved (as expressed by the operator's ability to move the shift lever toward the Y—Y neutral position) and a torque bump routine to forced torque reversals is not required. If however, the shift member rate of movement is not at least equal to the reference value, than the torque bump routine may be necessary and will be initiated.
Automated transmission systems attempt to gently ramp down engine torque (i.e., fueling) to provide a smooth disengagement which is perceived as a “high quality shift”. A problem with this technique is that the time required to perform the step of ramping down fuel/torque may result in a shift that takes too long to complete.
If the shift takes too long to complete, the vehicle will slow down more than desired. Also, engine speed at shift completion will be lower than at shift initiation (see U.S. Pat. Nos. 5,272,939; 5,335,566; and 4,937,749, the disclosures of which are incorporated herein by reference).
If fuel is ramped down very rapidly, the shift quality will suffer.
SUMMARY OF INVENTION
In accordance with the present invention, a method/system for controlling engine torque ramp down rate is provided which will vary the rate depending on driver demand and minimum and maximum allowable rates. A maximum rate of engine torque decrease (MAX) is selected which will provide the quickest shift to neutral at acceptable shift quality. A minimum rate of engine torque decrease (MIN) is selected which will provide a high shift quality but slowest acceptable shift. The drivers rate of change of throttle pedal position (rate of change of torque demand), d/dt (THL), is compared to the minimum (MIN) and maximum (MAX) reference rates. If the rate of change of throttle position exceeds the maximum reference value ((d/dt(THL))>MAX), then the engine will be commanded to decrease torque at said maximum reference rate (MAX). If the rate of change of throttle position is less than the minimum reference value ((d/dt(THL))<MIN), then the engine will be commanded to decrease torque at said minimum reference rate (MIN). If the rate of change of throttle position is less than the maximum reference value and exceeds the minimum reference value, ((MAX)>(d/dt)(THL))>(MIN)), then the engine will be commanded to decrease torque at a rate generally equal to said rate of change of throttle position (d/dt)(THL)).
Accordingly, it is an object of the present invention to provide an improved method/system for adaptively controlling engine fueling control the rate at which engine torque is ramped down to a value corresponding to zero driveline torque. The rate is determined by the rate of change of throttle pedal position and is subject to upper (MAX) and lower (MIN) limits.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.


REFERENCES:
patent: 4593580 (1986-06-01), Schulze
patent: 4850236 (1989-07-01), Braun
patent: 5582558 (1996-12-01), Palmeri
patent: 5735771 (1998-04-01), Genise
patent: 5743143 (1998-04-01), Carpenter et al.
patent: 5830104 (1998-11-01), Desautels et al.
patent: 5911787 (1999-06-01), Walker
patent: 5950491 (1999-09-01), Wadas
patent: 6015366 (2000-01-01), Markyvech et al.
patent: 6126570 (2000-10-01), Bohm et al.
patent: 6352492 (2002-03-01), Steeby et al.

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