A five-forward speed automatic transmission, includes: a torque convertor connected to an output shaft of an engine for changing and transmitting engine torque; an input shaft connected to an output member of the torque convertor; first, second and third planetary gearsets disposed between the input and output shafts so as to shift power transmitted to the input shaft in five-forward speeds and one reverse speed; a first clutch selectively connecting a sun gear of the second planetary gearset to the input shaft; a second clutch selectively connecting a sun gear of the first planetary gearset to the input shaft; a third clutch selectively connecting a planet pinion gear carrier of the first planetary gearset to the input shaft; a fourth clutch selectively connecting a sun gear and a planet pinion gear carrier of the third planetary gearset with each other; a first one-way clutch for ensuring that the sun gear of the first planetary gearset and a ring gear of the second planetary gearset rotate in a single direction; a second one-way clutch for ensuring that the sun gear of the third planetary gearset rotates in a single direction; a first brake for fixing the sun gear of the first planetary gearset relative to a housing; a second brake for fixing both the ring gear of the second planetary gearset and the sun gear of the first planetary gearset relative to a housing; and a third brake for fixing the sun gear of the third planetary gearset relative to a housing.
A multiple ratio transmission having a planetary primary gear unit producing forward ratios and a reverse ratio, and a planetary auxiliary gear unit in series with the primary gear unit producing a direct drive ratio and either an underdrive ratio or an overdrive ratio. The transmission produces six or seven forward ratios and two reverse ratios by combining the ratios of the primary and auxiliary gear units. Five friction clutches and brakes plus one one-way clutch control operation of the primary unit, and operation of the auxiliary unit is controlled by a clutch and a brake plus one one-way clutch. The same six or seven ratios can be achieved with a total of seven friction clutches and brakes in the primary and auxiliary unit by deleting the one-way clutches.
