Patent US 4,285,252

A speed-change control system for an automatic transmission includes a vehicle speed sensor, an engine load sensor, speed change program memory circuits, a comparator for comparing signals from the sensors with signals from the memory circuit, and a speed change control circuit for producing a signal for changing the transmission into a determined speed position in response to an output from the comparator. According to the invention the control system comprises a differentiation unit for differentiating the signal from the vehicle speed sensor to produce a signal corresponding to an actual acceleration, a programmed acceleration memory circuit for storing programmed accelerations obtained corresponding to the signals from the engine load sensor at every speed positions to produce signals corresponding to the programmed accelerations, and means for changing the speed change programs in response to differences between the signals corresponding to the actual acceleration and to the programmed acceleration, thereby automatically selecting a speed change program suitable for a grade of a road and a loaded condition without a troublesome hand operation of a switch for selecting a speed change program by a driver.