Method for driver-dependent shift control of a vehicle sub-transmission which maximizes fuel economy

A shift control method for a sub-transmission of a vehicle which is also equipped with a manual transmission operated by a driver, said method comprising the steps, in order, of:

• detecting said driver's shifting of said manual transmission at a certain gearing ratio;
• measuring a value of a parameter related to vehicle speed and a value for throttle opening at said driver's shift point of the manual transmission set to said certain gearing ratio;
• determining, on the basis of said certain gear ratio and of said measured parameter values, a driver-determined sub-transmission shift line for said gearing ratio of the manual transmission, said shift line indicating the relationship between said parameter related to the vehicle speed and said throttle opening when said sub-transmission is to be shifted;
• performing, for a first time period, shift control of the sub-transmission in accordance with said driver-determined sub-transmission shift line, while the manual transmission is set to said gearing ratio;
• and performing, for a second time period which directly follows the first time period, shift control of the sub-transmission in accordance with a standard prdetermined shift line, said standard predetermined shift line providing a relationship between vehicle speed and throttle opening along which said sub-transmission is shifted to provide substantially optimum fuel economy, said shift control for a second period being performed while the manual transmission is set to said gearing ratio.