Automatic transmission system for automobiles having hydraulic and electronic control systems

An automatic transmission system in an automobile having an engine, a brake, a throttle valve, a shift lever, a clutch, and transmission gears associated with synchromesh systems, said automatic transmission system comprising;

• (a) a throttle actuator means for actuating the throttle value;
• (b) a clutch actuator means for actuating the clutch;
• (c) a gear selection actuator means for selectively actuating the synchromesh systems to shift the transmission gears;
• (d) a fluid pressure control unit means for applying working fluid pressures to said gear selection actuator;
• and
• (e) an electronic control unit means for transmitting control signals to said control actuator means, said clutch actuator means and said fluid-pressure control unit means in response to detected signals indicative of a rotational speed of the engine, and operation of the brake, and operative position of the throttle valve, a selected position of said shift lever, a releasing position of the clutch, and a speed of travel of the automobile;
• wherein said gear selection actuator means comprises double-acting hydraulic cylinders each comprising a cylinder tube, a piston slidably disposed therein and composed of a pair of relatively movable piston members defining a circumferential groove therebetween, said piston members being slidably movable in said cylinder tube independently of each other in response to fluid pressures supplied into said cylinder tube, a pair of seats disposed in said circumferential groove between said piston members, respectively, and a spring disposed in said circumferential groove between said seats and normally urging said seats apart from each other against said piston members, respectively, said seats having outer peripheral portions larger in diameter than said piston, said cylinder tube having steps engagable respectively with said outer peripheral portions of said seats for limiting axial movement of said seats.