Electronic and hydraulic control system for automotive, automatic gear change transmissions

Hydraulic control system for an automotive automatic gear change transmission having three forward gear ranges (1, 2, 3) and a reverse (R) range, and a system of clutch (46, 53) and brake (39, 44, 49) means to control selective engagement of the gears of the transmission comprising

• a pressure pump (11) and a pressure regulator means (14) to supply pressurized hydraulic fluid under predetermined pressure to operate the clutch and brake means;
• a manual selector means (15') and a selector valve (15) controlled thereby to command a predetermined gear range position;
• a control unit (C) having input signals applied thereto representative of engine and vehicle operating parameters and providing output signals to select the proper gears for operation of the vehicle as determined by said engine vehicle operation parameters;
• a first gear control valve (31) having first and second inputs (29, 41) controlling engagement of the respective clutch and brake means of the second and third gear ranges and normally in a position to connect hydraulic pressure fluid to the respective clutch and brake means commanding the transmission to be in third gear;
• a second gear control valve (35) controlling engagement of the respective clutch and brake means of the first and second gear range;
• a pressure line (26, 26a) in fluid communication with said pump (11) and pressure regulator (14) and including a hydraulic choke (27);
• a first control valve (28) connected to and controlled by said control unit (C) and hydraulically connected in said pressure line (26) between the choke (27) and the first input (29) of the first gear control valve (31);
• the first control valve (28) being normally open to bleed pressure fluid from said line whereby the first gear control valve (31) will command engagement of the third gear and, upon energization from the control unit (C) upon sensing that the operation parameters require the second gear, said first control valve (28) being energized to thereby prevent bleeding of pressurized fluid and cause change-over of said first gear control valve (31);
• said system being characterized by
• a three-way check valve (18) having a first input (17) connected to an output (16) of the selector valve (15) and a second input (37) connected to an output (36) of the second gear control valve (35) and having its output connected to the second control input (41) of the first gear control valve (31), said check valve thereby providing pressure through its output to the first gear control valve (31) under control of the second gear control valve (37) for operation under normal operating conditions and additionally providing output to the first gear control valve (31) and manual selection of the selector means (15') operating said selector valve (15) even if said control unit (C) is disabled and does not provide operating signals to said control valve (28).