Shift control method of automatic transmission for vehicles

1. A shift control method for an automatic transmission, comprising:

calculating a clutch engaging pressure for each shift speed corresponding to an engine load, while a line pressure variable control is being performed, and performing a hydraulic pressure control using the calculated clutch engaging pressure; and

calculating an optimal engaging pressure for an operating clutch in each shift ratio, if a shift command according to a change in vehicle operating conditions during the performing of the hydraulic pressure control is generated, generating a corresponding shift signal and performing a shift control using the calculated optimal engaging pressure.

2. The shift control method of claim 1 , wherein the optimal engaging pressure in each shift ratio is calculated as follows:

(optimal engaging pressure)={required torque ratio*×input torque×torque ratio safety factor/(clutch capacity)}, where the required torque ratio is a ratio of a torque for each clutch to a total input torque.

3. The shift control method of claim 1 , wherein the optimal engaging pressure is determined from a map data having optimal engaging pressures with respect to engine loads.

4. A shift control system for an automatic transmission, comprising:

a transmission control unit programmed to execute instructions for

calculating a clutch engaging pressure for each shift speed corresponding to an engine load, while a line pressure variable control is being performed, and performing a hydraulic pressure control using the calculated clutch engaging pressure; and

calculating an optimal engaging pressure for an operating clutch in each shift ratio, if a shift command according to a change in vehicle operating conditions during the performing of the hydraulic pressure control is generated, generating a corresponding shift signal and performing a shift control using the calculated optimal engaging pressure; and

a shift control condition means communicating with said transmission control unit to provide information regarding transmission operating parameters.

5. The system of claim 4 , further comprising engine control condition detection means communicating with an engine control unit to provide information regarding engine operating parameters to said transmission control unit through communication with said engine control unit.

6. The system of claim 5 , further comprising at least one damper clutch control member and at least one shift control driving member, each said member communicating with the transmission control unit and receiving signals for transmission control therefrom.

7. The system of claim 6 , wherein said transmission control unit further includes instructions for calculating the optimal engaging pressure in each shift ratio according to the formula:

(optimal engaging pressure)={required torque ratio*×input torque×torque ratio safety factor/(clutch capacity)}, where the required torque ratio is a ratio of a torque for each clutch to a total input torque.

8. The system of claim 4 , wherein the optimal engaging pressure is determined from a map data having optimal engaging pressures with respect to engine loads.