Arrangement for controlling gear changes in a motor vehicle gear box

In a gear box comprising a main gear box with a number of gear ratios, and a two-geared range gear box coupled to a driven shaft of the main gear box, said range gear box having such gear ratios that the total gear ratio of the gear box with the higher ratio in the range box and the lowest ratio in the main box is higher than that with the lower ratio in the range gear box and the highest ratio in the main gear box, and an arrangement for controlling the shifting between two gear ratio ranges, said arrangement comprising a servo-aggregate which is connected to the gear-driving mechanism of the range gear box and which is coordinated with means which start operation of the servo-aggregate only upon shifting in the main gear box, as well as a sensor device which coacts with the driven shaft of the range gear box for reading the rpm of the shaft;

• the improvement in which said sensor device is connected to a control unit having at least two outputs over which the control unit provides a signal for maneuvering the servo-aggregate during shifting in the main gear box for shifting in the range gear box, said control unit providing a signal over the first output when the rpm of the driven shaft passes a first low rpm while increasing or decreasing, and over the second output when the rpm passes a second, greater rpm while increasing or decreasing, at least one of a plurality of two-position changeover switches adjusted by the lateral movement of a gear lever in the neutral position being connected between the two outputs for shifting an operating output of the gear box.