Method and apparatus for controlling an automatic transmission of a vehicle in response to a gradient of a road

A method and apparatus to estimate slopes accurately, as well as to eliminate slope estimation errors, taking error generating conditions into account. The slope on which the vehicle is running is estimated from the vehicle speed and the engine rpm value. The result is entered to the slope estimation unit through a low pass filter, then to the navigation unit. A noise eliminator is provided to the output of the slope estimation unit so that noises can be eliminated, for example, during gear-shifting or for a certain time after the gear shifting is completed by obtaining the "gear shifting" information from the automatic transmission control. The preceding estimated slope value is held during the noise elimination period.