Shift control system for a multiple ratio automatic transmission

An automatic control system for a multiple ratio transmission having gearing defining a low speed ratio, an intermediate speed ratio, a high speed ratio and an overdrive ratio;

• a high speed ratio clutch connecting two torque delivery elements of said gearing to establish high speed ratio;
• a coast clutch means for connecting together elements of said gearing for bidirectional torque delivery;
• an intermediate speed ratio brake means for braking an intermediate reaction element of said gearing to establish an intermediate speed ratio;
• said brake means including a fluid pressure operated intermediate brake servo having a double acting piston defining an intermediate brake apply pressure chamber and an intermediate brake release pressure chamber;
• a fluid pressure pump, a main regulator valve means for regulating pressure from said pump to establish a line pressure;
• a clutch pressure modulator valve means communicating with said main regulator valve means for establishing a modulated pressure;
• a control valve circuit having shift valve means for selectively distributing said line pressure to said brake release pressure chamber and to said high clutch and for selectively distributing said modulated pressure to said brake apply pressure chamber;
• said shift valve means including solenoid actuators having an intermediate speed ratio shift solenoid state, a high speed ratio shift solenoid state and a shift solenoid state between said intermediate speed ratio and high speed ratio shift solenoid states;
• said high speed ratio clutch and said brake release chamber being connected together at the initiation of a speed ratio change from said intermediate speed ratio to said high speed ratio;
• a ratio change from said intermediate speed ratio to said high speed ratio being characterized by a transient change in said shift solenoid states resulting in said shift solenoid state between said intermediate speed ratio solenoid state and said high speed ratio solenoid state following initiation of an upshift from said intermediate speed ratio to said high speed ratio;
• shift solenoid valve means for triggering movement of said shift valve means between upshift and downshift positions;
• microprocessor means for developing control signals for activating and deactivating said solenoid valve means in response to operating variables;
• said brake apply pressure chamber being pressurized with said modulated pressure and said brake release pressure chamber and high speed ratio clutch being pressurized with said line pressure independently of said modulated pressure following completion of a speed ratio change from said intermediate ratio to said high speed ratio, said brake release pressure chamber and said high speed ratio clutch being exhausted during execution of said transient change in shift solenoid states.