Eight speed transmission with planetary and layshaft gearing
View Patent ↗A transmission is provided that utilizes three planetary gear sets and three layshaft gear sets, as well as four rotating-type clutches and one brake that are engagable in different combinations to provide eight forward speed ratios between an input member and an output member of the transmission. By combining features of a layshaft transmission with those of a planetary transmission, the low spin losses and packaging convenience typical of a layshaft transmission are available while still achieving the high torque capacity typical of a planetary transmission.
1. A multi-speed transmission comprising:
an input member and an output member spaced parallel to one another to establish first and second axes of rotation;
a first, a second and a third layshaft gear set, each having a first gear concentric about the first axis of rotation and a second gear intermeshing with the first gear and concentric about the second axis of rotation;
a stationary member;
a first, a second, and a third planetary gear set, each having a ring gear member, a sun gear member, and a carrier member and a set of pinion gears that intermesh with both the sun gear member and the ring gear member, with the carrier member rotatably supporting the set of pinion gears; wherein each of the planetary gear sets is concentric about either the first or the second axis of rotation, with at least one of the planetary gear sets concentric about the first axis of rotation and at least one other of the planetary gear sets concentric about the second axis of rotation; wherein the ring gear member of the first planetary gear set is continuously connected for common rotation with the first gear of the first layshaft gear set; wherein the second gear of the first layshaft gear set is continuously connected for common rotation with the sun gear member of the second planetary gear set; wherein the sun gear member of the first planetary gear set is continuously connected for common rotation with the first gear of the third layshaft gear set;
an interconnecting member continuously connecting the carrier member of the third planetary gear set for common rotation with the carrier member of the second planetary gear set;
a first torque-transmitting mechanism selectively engagable to ground the sun gear member of the first planetary gear set to the stationary member;
a second torque-transmitting mechanism selectively engagable to connect the ring gear member of the first planetary gear set and the first gear of the first layshaft gear set for common rotation with the first gear of the second layshaft gear set;
a third torque-transmitting mechanism selectively engagable to connect the carrier member of the first planetary gear set for common rotation with the first gear of the second layshaft gear set;
a fourth torque-transmitting mechanism selectively engagable to connect the ring gear member of the second planetary gear set for common rotation with the second gear of the second layshaft gear set and the sun gear member of the third planetary gear set;
a fifth torque-transmitting mechanism selectively engagable to connect the ring gear member of the third planetary gear set for common rotation with the second gear of the third layshaft gear set; and
wherein engagement of different combinations of the torque-transmitting mechanisms establishes eight forward speed ratios between the input member and the output member.
2. The transmission of claim 1 , wherein the input member is continuously connected for common rotation with the carrier member of the first planetary gear set; and wherein the output member is continuously connected for common rotation with the carrier member of the third planetary gear set.
3. The transmission of claim 1 , wherein the planetary gear sets are single pinion planetary gear sets.
4. The transmission of claim 1 , wherein the torque-transmitting mechanisms are engaged in combinations of three to establish the eight forward speed ratios.
5. The transmission of claim 1 , wherein shifts between the forward speed ratios are single transition shifts.
6. The transmission of claim 1 , wherein each layshaft gear set is axially spaced from another of the layshaft gear sets with a respective one of the planetary gear sets therebetween.