Four speed ratio automatic transmission with compact gearing

A multiple ratio power transmission mechanism comprising a compact planetary gear system and a hydrokinetic torque converter which define a torque delivery path from a torque input member to a torque output member;

• said gear system comprising planetary gear elements arranged in radially stacked relationship, one with respect to the other, and including also a first sun gear, a first ring gear, first planet pinions engageable with said first sun gear and said first ring gear and journalled rotatably on a first carrier, a second sun gear joined integrally to said first ring gear as part of a common assembly and surrounding said first sun gear, a second ring gear, second planet pinions engageable with second sun gear and said second ring gear and journalled on a second carrier;
• the hydrokinetic unit including an impeller and a turbine arranged in toroidal flow relationship, said impeller being connected to said torque input member;
• first clutch means for connecting said turbine to said first sun gear, second clutch means adapted to distribute driving torque to said first carrier, third clutch means for connecting said carriers together for rotation in unison during low speed ratio operation and during reverse drive operation, fourth clutch means for connecting together said first sun gear and said second ring gear during operation in second, third and fourth forward driving ratio;
• first brake means for selectively anchoring said first ring gear and said second sun gear and second brake means for selectively anchoring said second ring gear, said first brake means being applied during first and second underdrive ratio operation and during fourth ratio operation and said second brake means being applied during reverse drive operation.