Continuously variable transmission and shift control method

A continuously variable transmission mounted on a vehicle, and arranged to vary a rotational speed of an engine, the continuously variable transmission comprising:

• a variator arranged to continuously vary a transmission ratio;
• a stepwise auxiliary transmission mechanism disposed in series with the variator, and arranged to switch between a first shift stage on a lower speed side and a second shift stage on a higher speed side by engagements and disengagements of a plurality of frictional elements;
• and
• a shift controller configured to calculate a desired target rotational speed of the engine based on a driving state of the vehicle, to set a desired through transmission ratio which is a target transmission ratio, based on the calculated desired target rotational speed, to vary at least one of the transmission ratio of the variator and the shift stage of the auxiliary transmission mechanism, and to control so that a through transmission ratio which is an entire transmission ratio of the variator and the auxiliary transmission mechanism follows the desired through transmission ratio by a predetermined response, the shift control section including;
• a slope road upshift prohibiting section configured to prohibit an upshift of the auxiliary transmission mechanism when the vehicle runs on a slope road, and
• a slope road upshift section configured to upshift the auxiliary transmission mechanism when the vehicle runs in a predetermined running state when the slope road upshift prohibiting section prohibits the upshift of the auxiliary transmission mechanism, and to perform the shift of the auxiliary transmission mechanism while the transmission ratio of the variator is varied in accordance with the variation of the transmission ratio of the auxiliary transmission mechanism so as not to vary the through transmission ratio even when the vehicle runs on the slope road.