This invention relates to multi-speed power transmissions and more particularly to power transmissions having a compound planetary gear set controllable to provide six forward ratios and one reverse ratio.
Multi-speed power transmissions are incorporated into powertrains to provide an extended operating range for the internal combustion engine that supplies the power for the powertrain. The number of ratios that are incorporated into automatic transmissions, especially for passenger car and small truck usage, has increased from two forward speed ratios to five forward speed ratios. Currently some manufacturers are considering transmissions incorporating six forward speed ratios. Examples of such proposals can be seen in the United States Patents issued to Liu and Malloy (U.S. Pat. No. 5,046,999) on Sep. 10, 1991 and Haka (U.S. Pat. No. 5,577,976) on Nov. 26, 1996.
These transmissions generally employ a Ravigneaux gear arrangement comprised of a long pinion and two or more short pinions that are intermeshing. The pinions interconnect two sun gears and two ring gears. By combining at least six selectively operable torque transmitting mechanisms (clutches and brakes), six forward speed ratios and one reverse ratio is available. The gears of these planetary arrangements are aligned in two axial planes. However the overdrive ratios achieved with these arrangements have a large step and the sixth ratio has a low numerical value.
Other six speed transmissions, having three axial planes of gears, have been proposed. One such mechanism is shown in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 1, 1978. This arrangement uses three simple interconnected planetary gear sets and five torque transmitting mechanisms. The transmission described in the Polak patent has been used extensively in large trucks.
It is an object of the present invention to provide an improved multi-speed power transmission.
In one aspect of the present invention, a compound planetary gear set has three sun gear members, one ring gear member and a planet carrier assembly member. In another aspect of the present invention, the planet carrier assembly member has a pair of intermeshing long pinion gear members that interconnect two of the sun gear members and the ring gear member, and a short pinion gear member that interconnects the other sun gear member with one of the long pinion gear members. In yet another aspect of the present invention, the ring gear member is continuously connected with a transmission output shaft.
In still another aspect of the present invention, six selectively operable torque transmitting mechanisms are provided and engageable in combinations of two to establish six forward ratios and one reverse ratio. In yet still another aspect of the invention, the three sun gear members define the axial location of three gear planes with one of the gear planes containing one sun gear member, two long pinion members and the ring gear member. In a further aspect of the present invention, a second of the gear planes contains a second sun gear member, the short pinion gear member and the two long pinion gear members. In a yet further aspect of the present invention, a third of the gear planes contains the third sun gear member, and one of the long pinion gear members. In still a further aspect of the present invention, one of the long pinion gear members is engaged with other members in at least the first and third of the gear planes.