Continuously variable transmission and shift control method

A shift control method for a continuously variable transmission which includes a variator which changes a speed ratio continuously and a stepped sub-transmission mechanism provided in series with the variator and is installed to shift and transmit output rotation of a driving source in a vehicle having a transmission controller, the shift control method comprising:

• setting, by the transmission controller, a final through speed ratio as a target speed ratio based on a driving condition of the vehicle;
• causing, by the transmission controller, a through speed ratio, which is an overall speed ratio of the variator and the sub-transmission mechanism, to follow the final through speed ratio in a specified response by changing at least one of the speed ratio of the variator and a gear position of the sub-transmission mechanism;
• causing, by the transmission controller, the through speed ratio to follow the final through speed ratio by changing only the speed ratio of the variator if a speed ratio corresponding to a shift instruction from a driver is smaller than a first speed ratio at which the sub-transmission mechanism is in a second gear position at a high speed side and the speed ratio of the variator is lowest and larger than a second speed ratio at which the sub-transmission mechanism is in a first gear position at a low speed side and the speed ratio of the variator is highest when a manual mode is selected in which a plurality of gear positions are set beforehand and a speed ratio corresponding to any one of the plurality of gear positions is set as the final through speed ratio based on the shift instruction from the driver, and
• thereafter shifting, by the transmission controller, the sub-transmission mechanism while the speed ratio of the variator is changed in response to a change in a speed ratio of the sub-transmission mechanism such that the through speed ratio does not change.

A continuously variable transmission installed in a vehicle to shift and transmit output rotation of a driving source, comprising:

• variator which changes a speed ratio continuously;
• a sub-transmission mechanism provided in series with the variator and having a first gear position at a low speed side and a second gear position at a high speed side;
• means for setting a final through speed ratio as a target speed ratio based on a driving condition of the vehicle and for causing a through speed ratio, which is an overall speed ratio of the variator and the sub-transmission mechanism, to follow the final through speed ratio in a specified response by changing at least one of the speed ratio of the variator and a gear position of the sub-transmission mechanism,
• means for selecting a manual mode in which a plurality of gear positions are set beforehand and a speed ratio corresponding to any one of the plurality of gear positions is set as the final through speed ratio based on a shift instruction front a driver, and
• means for shifting the sub-transmission mechanism while changing the speed ratio of the variator in response to a change in a speed ratio of the sub-transmission mechanism such that the through speed ratio does not change after the through speed ratio is caused to reach the final through speed ratio by changing only the speed ratio of the variator if the speed ratio corresponding to the shift instruction from the driver is smaller than a first speed ratio at which the sub-transmission mechanism is in the second gear position at the high speed side and the speed ratio of the variator is lowest and larger than a second speed ratio at which the sub-transmission mechanism is in the first gear position at the low speed side and the speed ratio of the variator is highest when the manual mode is selected.