Continuously variable transmission and control method thereof

Abstract

When a through speed ratio, which is an overall speed ratio of a variator and a subtransmission mechanism, varies from a larger speed ratio than a mode switch speed ratio to a smaller speed ratio than the mode switch speed ratio, a gear position of the subtransmission mechanism is changed from a first gear position to a second gear position. The mode switch speed ratio is set at a through speed ratio obtained when the speed ratio of the variator is a Highest speed ratio and the gear position of the subtransmission mechanism is the first gear position.

1 . A continuously variable transmission installed in a vehicle, comprising:
 a continuously variable transmission mechanism (to be referred to hereafter as a “variator”) which modifies a speed ratio continuously;   a subtransmission mechanism provided to the rear of and in series with the variator and including, as forward gear positions, a first gear position and a second gear position having a smaller speed ratio than the first gear position; and   a shift control unit which modifies a through speed ratio, which is an overall speed ratio of the variator and the subtransmission mechanism, by modifying the speed ratio of the variator and changing the gear position of the subtransmission mechanism on a basis of an operating condition of the vehicle,   wherein the through speed ratio when the speed ratio of the variator is a Highest speed ratio and the gear position of the subtransmission mechanism is the first gear position is set as a mode switch speed ratio, and   when the through speed ratio varies from a larger speed ratio than the mode switch speed ratio to a smaller speed ratio than the mode switch speed ratio, the shift control unit changes the gear position of the subtransmission mechanism from the first gear position to the second gear position.   
     
     
         2 . The continuously variable transmission as defined in  claim 1 , wherein, when changing the gear position of the subtransmission mechanism from the first gear position to the second gear position, the shift control unit modify the speed ratio of the variator to a large speed ratio side. 
     
     
         3 . A continuously variable transmission installed in a vehicle, comprising:
 a continuously variable transmission mechanism (to be referred to hereafter as a “variator”) which modifies a speed ratio continuously;   a subtransmission mechanism provided to the rear of and in series with the variator and including, as forward gear positions, a first gear position and a second gear position having a smaller speed ratio than the first gear position; and   shift control means for modifying a through speed ratio, which is an overall speed ratio of the variator and the subtransmission mechanism, by modifying the speed ratio of the variator and changing the gear position of the subtransmission mechanism on a basis of an operating condition of the vehicle,   wherein the through speed ratio when the speed ratio of the variator is a Highest speed ratio and the gear position of the subtransmission mechanism is the first gear position is set as a mode switch speed ratio, and   when the through speed ratio varies from a larger speed ratio than the mode switch speed ratio to a smaller speed ratio than the mode switch speed ratio, the shift control means changes the gear position of the subtransmission mechanism from the first gear position to the second gear position.   
     
     
         4 . The continuously variable transmission as defined in  claim 3 , wherein, when changing the gear position of the subtransmission mechanism from the first gear position to the second gear position, the shift control means modify the speed ratio of the variator to a large speed ratio side. 
     
     
         5 . A control method for a continuously variable transmission installed in a vehicle and including a continuously variable transmission mechanism (to be referred to hereafter as a “variator”) which modifies a speed ratio continuously and a subtransmission mechanism provided to the rear of and in series with the variator and including, as forward gear positions, a first gear position and a second gear position having a smaller speed ratio than the first gear position; the control method comprising:
 a shift control step for modifying a through speed ratio, which is an overall speed ratio of the variator and the subtransmission mechanism, by modifying the speed ratio of the variator and changing the gear position of the subtransmission mechanism on a basis of an operating condition of the vehicle,   wherein the through speed ratio when the speed ratio of the variator is a Highest speed ratio and the gear position of the subtransmission mechanism is the first gear position is set as a mode switch speed ratio, and   when the through speed ratio varies from a larger speed ratio than the mode switch speed ratio to a smaller speed ratio than the mode switch speed ratio, the shift control step changes the gear position of the subtransmission mechanism from the first gear position to the second gear position.   
     
     
         6 . The control method as defined in  claim 5 , wherein, when changing the gear position of the subtransmission mechanism from the first gear position to the second gear position, the shift control step modify the speed ratio of the variator to a large speed ratio side.