Four-speed ratio automatic power transmission mechanism

Claim 1

A multiple ratio power transmission mechanism comprising three sets of planetary gear elements each having a ring gear, a sun gear, a carrier and planet pinions mounted on said carrier in meshing engagement with the sun and ring gears, a transmission housing having two housing portions, a first of said gear units being situated in one housing portion and the second and third of said gear units being situated in the other housing portion, said gear units being axially aligned, a power input shaft journalled with one end thereof within said one housing portion, a power output shaft journalled with one end thereof in said other housing portion, an intermediate shaft situated between said input shaft and said output shaft in coaxial alignment, first brake means in said one housing portion for anchoring the reaction element of said first gear unit, first clutch means in said one housing portion for locking together elements of said first gear unit, a torque output element of said first gear unit being connected directly to one end of said intermediate shaft, the sun gears of said second and third gear units being connected together, the carrier of said second gear unit and the ring gear of said third gear unit being connected to said output shaft, second clutch means in said other housing portion for connecting selectively said intermediate shaft to the sun gears for said second and third gear units, second brake means for anchoring the sun gears of said second gear units during second speed ratio operation, third clutch means for connecting selectively said intermediate shaft to the ring gear of said second gear unit during operation of said mechanism in each forward driving speed ratio, brake means for anchoring the carrier of said third gear unit during operation in a first forward driving speed ratio, said first brake means being applied to provide torque multiplication in said first gear unit during operation of said mechanism in each forward driving underdrive ratio, said first brake means comprising a brake drum connected mechanically to the sun gear of said first gear unit, said brake drum being journalled on said one housing portion, friction means for selectively anchoring said brake drum, a fluid pressure operated brake servo for actuating and releasing said friction means comprising a piston and a cooperating cylinder defining two fluid pressure chambers on either side of said piston, said piston frictionally engaging said friction means when it is stroked in one direction and to release said friction means when it is stroked in the opposite direction, fluid pressure operated servos for engaging and releasing each of said other clutches and each of said other brakes, a control circuit pressure source, conduits connecting said pressure source with said fluid pressure operated servos including separate conduits extending to each pressure chamber of the servo for said first gear unit, a pressure distributor valve means situated in and partly defining said conduit structure for controlling selectively the distribution of pressure to the release side of said last named servo as ratio changes are accomplished between a third speed ratio and the direct drive ratio, manual valve means situated between said pressure source and said pressure distributor valve means for controlling distribution of pressure to the latter, a source of a governor pressure signal that is proportional in magnitude to the driven speed of said power output shaft, flow coNtrol orifice means communicating with the release side of saId servo for said first gear unit through which fluid displaced from said release side is passed during the ratio changes from the direct drive ratio to the third speed ratio, first timing valve means communicating with the release side of said servo for said first gear unit for bypassing at least a portion of the displaced fluid around said flow control orifice means when the governor pressure is less than a first limiting value, and second timing valve means communicating with said release side for bypassing at least a portion of the displaced fluid around said orifice means when governor pressure is greater than a second limiting value, each timing valve means communicating with said governor pressure source.