Compact four speed automatic transmission

A planetary, multiple-ratio power transmission mechanism having compound gearing and a hydrokinetic unit, the hydrokinetic unit having an impeller and a turbine arranged in a toroidal fluid flow circuit;

• said planetary gearing comprising two sun gears, two ring gears, two sets of planet pinions and a carrier that is common to each set of planet pinions, a driven member connected to said carrier, a driving member connected to said impeller;
• a first of said sun gears, a first of said ring gears, a second of said sun gears and a second of said ring gears being arranged in radial disposition one with respect to the other;
• said first ring gear and said second sun gear being common and formed on a ring, the external teeth of said second sun gear being formed on the periphery of said ring and the internal teeth of said first ring gear being formed on the internal periphery of said ring, a first of said sets of planet pinions engaging drivably the first sun gear and said first ring gear, a second of said sets of planet pinions engaging drivably said second sun gear and said second ring gear, said planet pinions being rotatably supported by said common carrier;
• first selectively engageable clutch means for distributing driving torque to said second ring gear, second selectively engageable clutch means for delivering driving torque from said turbine to said ring, third selectively engageable clutch means for distributing driving torque from said turbine to said first sun gear, and brake means selectively engageable for anchoring said first sun gear during operation in the first and fourth speed ratios, said first and second clutches being engaged during third speed ratio operation and said first clutch means being engaged during overdrive operation, said third clutch means being engaged during reverse drive operation as said second ring gear acts as a reaction point during reverse drive.