Steuersystem für ein hydraulisch betätigtes Fahrzeuggetriebe

摘要

A hydraulic control system for a hydraulically operated vehicle transmission. The system is configured to have a first gearshift mode for determining a gear ratio to be shifted to in accordance with a predetermined gearshift schedule based on detected parameters and a second gearshift mode for changing a gear ratio in accordance with at least one of an upshift command and a downshift command given by the driver. The first mode or the second mode is selected. And when the engine coolant temperature is found to be less than a predetermined value, the selection is prohibited or invalidated. This is because when the temperature is low, the viscosity of the ATF may be high and the time taken for completion of the gearshift is long, causing the driver to sense a time lag between the point at which the command was output and the point at which the actual gearshift is conducted. In the first mode, the driver does not sense this kind of time lag because the gearshift command is output by an electronic control unit without the driver knowing when it was output.