Control device for automatic transmission for vehicle

1. A control apparatus for a vehicular automatic transmission, the automatic transmission being a continuously variable transmission and equipped in a power transmission system between a driving source and driving wheels of a vehicle, comprising:

a vehicle speed detector configured to detect a vehicle speed of the vehicle;

an accelerator opening angle detector configured to detect an accelerator opening angle of the vehicle; and

an electronic control unit configured to control a gear ratio of the automatic transmission on a basis of the vehicle speed detected by the vehicle speed detector and the accelerator opening angle detected by the accelerator opening angle detector,

wherein the vehicle speed detector comprises an output shaft rotation numbers detector configured to detect rotation numbers of an output shaft of the automatic transmission and a road wheel rotation speed detector configured to detect rotation numbers of respective road wheels of the vehicle,

wherein the electronic control unit is configured to calculate the vehicle speed from information of the road wheel rotation numbers when a preset predetermined condition is established as a condition under which vertical variations of the rotation numbers of the output shaft, either up or down, are generate, and to calculate the vehicle speed from the information of a rotation speed of the output shaft when the preset predetermined condition is not established, and

wherein the predetermined condition includes three conditions, the three conditions being that an output torque request to the driving source is detected, a detected driving torque of the driving source is in a state equal to or below a torque determination threshold value, and a vehicular acceleration is in a state equal to or below an acceleration determination threshold value, all of the three conditions being established.

2. The control apparatus for the vehicular automatic transmission as claimed in claim 1 , wherein the road wheel rotation speed detector is installed for the respective road wheels, and the electronic control unit is configured to select at least one of the respective road wheel rotation speed detectors whose vertical variation width of a detected road wheel rotation speed from among the respective road wheel rotation speed detectors at a time point at which the predetermined condition is determined to be established is equal to or below a reference value, and to calculate the vehicle speed from information of the selected road wheel rotation speed detector.

3. The control apparatus for the vehicular automatic transmission as claimed in claim 1 , wherein the road wheel rotation speed detector is installed for the respective road wheels, and the electronic control unit is configured to select any one or more of the respective road wheel rotation speed detectors whose detected rotation speed is nearest to the rotation speed of the output shaft detected by the output shaft rotation numbers detector, from among the respective road wheel rotation speed detectors at a time point at which the predetermined condition is determined to be established, and to calculate the vehicle speed from the information of the selected road wheel rotation speed detector.

4. The control apparatus for the vehicular automatic transmission as claimed in claim 2 , wherein the electronic control unit is configured to, in a case where all of vertical variation widths of the plurality of road wheel rotation speeds are neither equal to nor below the reference value when the predetermined condition is established, determine whether the vertical variation width of the rotation speed of the output shaft is larger than each of the vertical variation widths of all of the rotation speeds of all road wheel rotation speed detectors, calculate the vehicle speed from an average value of the plurality of the road wheel rotation speeds when a positive determination that the vertical variation width of the rotation speed of the output shaft is larger than each of the vertical variation widths of the rotation speeds of all of the road wheel rotation speed detectors is made, and calculate the vehicle speed from the rotation speed of the output shaft when a negative determination is made.

5. The control apparatus for the vehicular automatic transmission as claimed in claim 4 , further comprising a notch filter configured to eliminate a particular frequency area from the information of the rotation speed inputted to the electronic control unit,

wherein the particular frequency area includes a frequency area of a frequency component related to the vertical variations of the rotation speed of the output shaft generated due to a periodic variation of the driving torque inputted to the driving wheels in a state in which the driving torque of the driving source inputted to the automatic transmission is equal to or below the torque determination threshold value, and the electronic control unit is configured to calculate the vehicle speed from the information detected by the output shaft rotation speed detector which is filter processed through the notch filter.

6. The control apparatus for the vehicular automatic transmission as claimed in claim 5 , wherein the particular frequency area includes a frequency area of vibrations of the output shaft in accordance with a gear ratio related to a natural frequency of the driving source.

7. The control apparatus for the vehicular automatic transmission as claimed in claim 1 , wherein the electronic control unit is configured to perform rate processing configured to smooth switching when the information of the rotation speed to calculate the vehicle speed is switched.