Automatic transmission control system incorporating an exhaust brake

Claim 1

An automatic transmission for an automotive vehicle having a torque converter, a planetary gear mechanism receiving an output from the torque converter and including a brake actuated by servo hydraulic pressure to achieve low gear, and a hydraulic pressure circuit for supplying the hydraulic pressure that actuates the brake, said automatic transmission comprising: a regulator valve for providing line hydraulic pressure; a manual pump receiving the line hydraulic pressure from said regulator valve; a low-coast valve provided with the line hydraulic pressure by said manual pump for producing regulated low-coast hydraulic pressure; a 1-2 shift valve which receives the hydraulic pressure from said low-coast valve and which is shifted for supplying the hydraulic pressure to a chamber in the brake to actuate said brake; and a governor valve arranged between said regulator valve and said low-coast valve for receiving the line hydraulic pressure from said regulator valve and for supplying a valve chamber of said low-coast valve with governor hydraulic pressure, the hydraulic pressure supplied to said 1-2 shift valve taking on a value regulated by said governor valve, whereby the hydraulic pressure supplied to the chamber of said brake varies depending upon vehicle velocity.