Gear shift control apparatus and method for automatic transmission

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

gear shift control means for releasing a first frictional engagement element which has been engaged at a gear stage prior to a gear shift and to engage a second frictional engagement element which has been released at the gear stage prior to the gear shift to perform the gear shift to another gear stage; and

inertia phase control means for temporarily reducing a command hydraulic pressure to the second frictional engagement element when a parameter indicating a degree of progress of the gear shift detected during the gear shift to the another gear stage has reached a predetermined value representing an inertia phase finish immediate prior region at a time of an inertia phase developed during a replacement gear shift, wherein the inertia phase control means includes finish pressure control means for setting a reduction quantity of the command hydraulic pressure whenever a predetermined time has elapsed on a basis of the parameter detected whenever the predetermined time has elapsed in the inertia phase finish immediate prior region to progressively reduce the command hydraulic pressure.

2. The gear shift control apparatus for the automatic transmission as claimed in claim 1 , wherein the finish pressure control means is further for holding the reduction quantity of the command hydraulic pressure at a previous value when the parameter detected, whenever the predetermined time has elapsed in the inertia phase finish immediate prior region, is varied in a direction opposite to a direction toward which the parameter is to be varied.

3. The gear shift control apparatus for the automatic transmission as claimed in claim 2 , wherein the gear shift control means includes a degree of progress calculating means for calculating a degree of progress of the gear shift to the another gear stage on a basis of a gear ratio calculated whenever the predetermined time has elapsed, the finish pressure control means included in the inertia phase control means and for further setting the reduction quantity of the command hydraulic pressure whenever the predetermined time has elapsed on a basis of the degree of progress of the gear shift in the inertia phase finish immediate prior region calculated whenever the predetermined time has elapsed and configured to hold the reduction quantity of the command hydraulic pressure at the previous value when the degree of progress of the gear shift is a state in which the degree of progress of the gear shift is smaller than the degree of progress previously calculated.

4. The gear shift control apparatus for the automatic transmission as claimed in claim 3 , wherein the finish pressure control means is further for setting the reduction quantity of the command hydraulic pressure to be negatively larger as the degree of progress of the gear shift to the another stage becomes smaller.

5. The gear shift control apparatus for the automatic transmission as claimed in claim 4 , wherein, when the degree of progress of the gear shift becomes equal to or smaller than zero, a maximum reduction quantity of the command hydraulic pressure is set to the reduction quantity of the command hydraulic pressure which becomes negatively larger as an input torque to the automatic transmission becomes larger.

6. The gear shift control apparatus for the automatic transmission as claimed in claim 5 , wherein the degree of progress calculating means for calculating the degree of progress uses an actual gear ratio as follows:

degree of progress=(GR_End−GR)×1000/(GR—End−GR1),

wherein GR_End denotes an inertia phase finish determination gear ratio, GR denotes a present actual gear ratio, and GR 1 denotes an inertia phase finish immediate prior gear ratio.

7. The gear shift control apparatus for the automatic transmission as claimed in claim 6 , wherein the inertia phase control means is further for calculating the command hydraulic pressure to be supplied to the second frictional engagement element by adding a base gradient set on a basis of a turbine torque and a vehicle speed obtained from an output shaft revolution speed sensor, a feedback correction quantity calculated on a basis of a turbine revolution speed obtained from a first turbine speed sensor and a second turbine speed sensor and the output shaft revolution speed obtained from the output shaft revolution speed sensor, and the reduction quantity obtained through an interpolation thereof on a basis of the degree of progress.

8. The gear shift control apparatus for the automatic transmission as claimed in claim 7 , wherein the reduction quantity of the command hydraulic pressure is set to 0 when the actual gear ratio indicates a value from the inertia phase finish determination gear ratio to the inertia phase immediate prior gear ratio, the reduction quantity thereof is set to a value which is progressively reduced in accordance with the degree of progress thereof to the another gear stage when the actual gear ratio indicates a value from the inertia phase finish immediately prior gear ratio to the inertia phase finish determination gear ratio, and the reduction quantity thereof is set to the maximum reduction quantity when the actual gear ratio is equal to or larger than inertia phase finish determination gear ratio.

9. The gear shift control apparatus for the automatic transmission as claimed in claim 8 , wherein the actual gear ratio is detected from an input shaft revolution speed obtained from the first turbine speed sensor and the second turbine speed sensor and obtained from the output shaft revolution speed sensor whenever the predetermined time has elapsed.

10. The gear shift control apparatus for the automatic transmission as claimed in claim 1 , wherein the finish pressure control means is further for setting the reduction quantity of the command hydraulic pressure in order for the reduction quantity of the command hydraulic pressure to become larger, as an input torque to the automatic transmission detected during the gear shift to the another gear stage becomes larger.

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

while releasing a first frictional engagement element which has been engaged at a gear stage prior to a gear shift, engaging a second frictional engagement element which has been released at the gear stage prior to the gear shift to perform the gear shift to another gear stage; and

temporarily reducing a command hydraulic pressure to the second frictional engagement element when a parameter indicating a degree of progress of the gear shift detected during the gear shift to the other gear stage has reached to a predetermined value representing an inertia phase finish immediate prior region at a time of an inertia phase developed during a replacement gear shift, wherein a reduction quantity of the command hydraulic pressure is set whenever a predetermined time has elapsed on a basis of the parameter detected whenever the predetermined time has elapsed in the inertia phase finish immediate prior region to progressively reduce the command hydraulic pressure.