Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
1998-07-15
2001-12-04
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S117000, C477S156000
Reexamination Certificate
active
06325742
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shift control system and method for an automatic transmission in a vehicle; and more particularly, to a shift control system and method for reducing shift shock in an automatic transmission when shifting from reverse to drive.
2. Discussion of Related Art
Automatic transmissions make it possible for unskilled drivers to quickly and easily learn to operate a vehicle. The provision of a torque converter between the engine and the automatic transmission eliminates the need for a driver to learn how to use a clutch pedal for engaging and disengaging the transmission. Furthermore, the control system for the automatic transmission automatically decides when to shift up and down, thus eliminating the need for the driver to learn these skills.
FIG. 1
illustrates a conventional hydraulic control system for an automatic transmission which includes a front clutch
100
, rear clutch
110
, low reverse brake
120
, end clutch
130
and kickdown band brake
140
(i.e., the friction elements).
FIG. 1
also illustrates the torque converter TC that is coupled between the engine and the automatic transmission. The conventional hydraulic control system as shown in
FIG. 1
includes shift solenoids S
1
and S
2
which control the flow of hydraulic fluid to the front clutch
100
, rear clutch
110
, low reverse brake
120
, end clutch
130
and kickdown band brake
140
to effect gear change operations. A pressure control solenoid S
3
controls the pressure in the hydraulic system, and thus how quickly the various friction elements are engaged and disengaged. A transmission or shift control unit (TCU) controls the operation of the shift solenoids S
1
and S
2
and the pressure control solenoid S
3
.
As further shown in
FIG. 1
, in conjunction with the shift solenoids S
1
and S
2
, the flow of hydraulic fluid to the friction elements is also controlled in accordance with the position of a driving mode select lever
150
. An operator uses the driving mode select lever
150
to place the vehicle in park P, reverse R, neutral N and drive D. The driving mode select lever
150
can also be used to select the second speed stage of drive (as the maximum forward speed stage) D
2
or the low speed stage of drive.
When driving the vehicle in reverse and at low speeds, shifting the driving mode select lever
150
from reverse to drive does not cause great shift shock. The reason for this is that the rear clutch
110
is applied when moving from reverse to the first speed stage of drive, and that the application of the rear clutch
110
does not cause a significant instantaneous change in vehicle speed.
However, when driving in reverse at high speeds, and a shift is made into drive, instead of shifting into the first speed stage of drive, the control system attempts to shift into the second speed stage of drive due to the high speed at which the vehicle is travelling. Shifting into the second speed stage of drive requires application of the kickdown band brake
140
. Application of the kickdown band brake
140
causes a significant instantaneous change in vehicle speed, such that great shift shock occurs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a shift control system and method for an automatic transmission which overcomes the problems and disadvantages discussed above with respect to the prior art.
Another object of the present invention is to provide a shift control system and method for an automatic transmission which prevents shift shock when shifting from reverse to drive.
These and other objects are achieved by providing a shift control system for an automatic transmission in a vehicle, comprising a plurality of sensors each sensing a vehicle operating condition; a transmission control unit controlling shift control solenoids and a pressure control solenoid in a hydraulic control system for said automatic transmission based on said sensed vehicle operating conditions, said shift control solenoids controlling operation of friction elements in said automatic transmission, said pressure control solenoid controlling hydraulic pressure supplied to said friction elements; and said transmission control unit detecting a change in driving mode from a reverse mode to a drive mode based on said sensed vehicle operating conditions, and controlling said shift control solenoids such that said automatic transmission shifts into only a first speed stage in said drive mode when said transmission control unit detects said change in said driving mode from said reverse mode to said drive mode.
These and other objects are further achieved by providing a shift control method for an automatic transmission in a vehicle, comprising sensing a plurality of vehicle operating condition; first detecting a change in driving mode from a reverse mode to a drive mode based on said sensed vehicle operating conditions; and controlling shift solenoids and a pressure control solenoid in a hydraulic control system for said automatic transmission based on said sensed vehicle operating conditions, said shift control solenoids controlling operation of friction elements in said automatic transmission, said pressure control solenoid controlling hydraulic pressure supplied to said friction elements, said controlling step controlling said shift control solenoids such that said automatic transmission shifts into only a first speed stage in said drive mode when said first detecting step detects said change in said driving mode from said reverse mode to said drive mode.
REFERENCES:
patent: 4768636 (1988-09-01), Ito et al.
patent: 5121656 (1992-06-01), Baba
patent: 5224398 (1993-07-01), Sasaki
patent: 5733220 (1998-03-01), Iizuka
patent: 5807207 (1998-09-01), Hisano et al.
patent: 10-78117 (1998-03-01), None
Estremsky Sherry
Hyundai Motor Co. Ltd.
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