Patent ID: 7476177

Claim:
A method of estimating a transmission ratio of a power transmission path defined between an input shaft and an output shaft, the method comprising: detecting a rotational speed of the input shaft; detecting a rotational speed of the output shaft; calculating a rotational-speed ratio between the detected rotational speed of the input shaft and the detected rotational speed of the output shaft; determining whether or not a difference between the rotational-speed ratio calculated at a certain time and a rotational-speed ratio calculated earlier is within a first predetermined threshold value; and estimating a value relating to the later rotational-speed ratio to be the transmission ratio of the power transmission path and storing the value in a memory if the difference between the rotational-speed ratios is determined to be within the first predetermined threshold value, while estimating a value relating to the earlier rotational-speed ratio stored in the memory to be the transmission ratio of the power transmission path if the difference between the rotational-speed ratios is determined not to be within the first predetermined threshold value.