A control system for an automatic transmission of an automotive vehicle comprising:
- a reverse frictional element of the automatic transmission, said reverse frictional element serving to selectively establish a reverse mode in the automatic transmission for allowing the vehicle to move backward when a selector lever is placed in a reverse position;
- first valve means having valve positions which are switched for modifying hydraulic pressure supplied to a preselected element of the automatic transmission to control given operation of the automatic transmission;
- second valve means for selectively establishing and blocking fluid communication between a first pressure line connected to a pressure source and a second pressure line connected to said first valve means;
- third valve means for modifying a level of hydraulic pressure supplied from the first pressure line to the second pressure line through said second valve means for switching the valve positions of said first valve means;
- manual selector valve means having an R-range port which provides hydraulic pressure of a preselected level to said reverse frictional element when the selector lever is placed in the reverse position and a drain port which drains the hydraulic pressure from said reverse frictional element;
- forward speed holding valve means having a first valve position communicating between a third pressure line connected to the reverse frictional element and a fourth pressure line connected to the R-range port of said manual selector valve means for supplying the hydraulic pressure to said reverse frictional element to establish the reverse mode of the automatic transmission and a second valve position communicating between the third pressure line and a fifth pressure line connected to the drain port of said manual selector valve means for draining the hydraulic pressure from said reverse frictional element to release the reverse mode;
- a sixth pressure line communicating between the first pressure line and said forward speed holding valve means through said second valve means when the selector lever is shifted to the reverse position;
- vehicle speed sensor means for monitoring vehicle speed to provide a signal indicative thereof;
- selector lever position sensor means for detecting a position of the selector lever of the automatic transmission and providing a signal indicative thereof;
- and
- control means responsive to the signals from said vehicle speed sensor means and said selector lever position sensor means to provide a first control signal to said third valve means for modifying the hydraulic pressure in said sixth pressure line to a first level so that said forward speed holding valve means assumes the first valve position when vehicle forward speed is lower than a preselected value and the selector lever is placed in the reverse position for establishing the reverse mode of the automatic transmission and a second control signal to said third valve means for modifying the hydraulic pressure in said sixth pressure line to a second level so that said forward speed holding valve means assumes the second valve position when vehicle forward speed is higher than the preselected value and the selector lever is shifted to the reverse position for preventing the automatic transmission from shifting to the reverse mode when the vehicle is traveling forward at a speed higher than the preselected value.