Slippage detection system and method for continuously variable transmissions

Abstract

A slippage detection system for a continuously variable transmission capable of continuously changing a gear ratio between an input rotation speed of an input member and an output rotation speed of an output member is provided. The slippage detection system compares a difference between an actual gear ratio calculated from measurement values of the input rotation speed and the output rotation speed and a target gear ratio with a predetermined reference value, and determines slippage in the continuously variable transmission when the difference exceeds the reference value at least a predetermined number of times in a predetermined period of time.

1 . A slippage detection system for a continuously variable transmission capable of continuously changing a gear ratio between an input rotation speed of an input member and an output rotation speed of an output member, comprising:
 a comparator configured to compare a difference between an actual gear ratio calculated from measurement values of the input rotation speed and the output rotation speed and a target gear ratio with a predetermined reference value; and   a slippage determining portion configured to determine slippage in the continuously variable transmission when the difference exceeds the reference value at least a predetermined number of times in a predetermined period of time.   
   
   
       2 . The slippage detection system according to  claim 1 , wherein:
 the continuously variable transmission includes the input member, the output member, and a torque transmitting member for transmitting torque between the input member and the output member; and   the slippage determining portion determines slippage of the torque transmitting member in the continuously variable transmission.   
   
   
       3 . The slippage detection system according to  claim 1 , wherein the target gear ratio is determined based on a value obtained as a result of a smoothing operation performed on a target input rotation speed that is determined based on an output requirement of a vehicle in which the continuously variable transmission is installed. 
   
   
       4 . The slippage detection system according to  claim 1 , further comprising a slippage determination canceling portion configured to inhibit determination of slippage when the continuously variable transmission is determined to be in the process of a shifting action based on a change in a running state of a vehicle in which the continuously variable transmission is installed. 
   
   
       5 . A method of detecting slippage in a continuously variable transmission capable of continuously changing a gear ratio between an input rotation speed of an input member and an output rotation speed of an output member, comprising the steps of:
 comparing a difference between an actual gear ratio calculated from measurement values of the input rotation speed and the output rotation speed and a target gear ratio with a predetermined reference value; and   determining slippage in the continuously variable transmission when the difference exceeds the reference value at least a predetermined number of times in a predetermined period of time.   
   
   
       6 . The method according to  claim 5 , wherein:
 the continuously variable transmission includes the input member, the output member, and a torque transmitting member for transmitting torque between the input member and the output member; and   the determining step determines slippage of the torque transmitting member in the continuously variable transmission.   
   
   
       7 . The method according to  claim 5 , wherein the target gear ratio is determined based on a value obtained as a result of a smoothing operation performed on a target input rotation speed that is determined based on an output requirement of a vehicle in which the continuously variable transmission is installed. 
   
   
       8 . The method according to  claim 5 , further comprising the step of inhibiting determination of slippage when the continuously variable transmission is determined to be in the process of a shifting action based on a change in a running state of a vehicle in which the continuously variable transmission is installed.