Eight speed automatic transmission with dual area clutch piston

A transmission includes four planetary gearsets and five torque transmitting devices operative to provide eight forward speed ratios. At least one of the torque transmitting devices is engaged during two different speed ratios. The torque transmitting device includes a piston partially defining two separate and independently pressurizable chambers. Accordingly, the transmission enables both chambers to be pressurized for speed ratios in which a high torque capacity is required of the torque transmitting device, and only one of the chambers to be pressurized for speed ratios in which a low torque capacity is required of the torque transmitting device.

TECHNICAL FIELD

This invention relates to transmissions having planetary gear arrangements, torque transmitting devices for selectively coupling members of the planetary gear arrangements to other members, and pistons partially defining separate pressure chambers for actuating the torque transmitting devices.

BACKGROUND OF THE INVENTION

Certain multi-speed transmissions are characterized by differences in the amount of torque a clutch is subjected to in various gear states. The torque capacity of a clutch is, at least in part, determined by the axial force exerted on the clutch plates and discs by a hydraulically actuated piston. The force of the piston is determined by the pressure of the hydraulic fluid and the surface area of the piston exposed to the hydraulic fluid. Thus, the surface area of a clutch piston exposed to hydraulic pressure must be sized to produce the amount of axial force necessary for the highest torque condition of the clutch.

A clutch with a large torque capacity has a large gain between hydraulic pressure exerted on the piston and clutch torque. Small errors in pressure control may result in large clutch torque errors. In speed ratios with lower mechanical gains, the resulting clutch torque errors can be a significant percentage of the total torque required to complete a shift.

SUMMARY OF THE INVENTION

A transmission includes an input member, an output member, a stationary member, and first, second, third, and fourth planetary gearsets. Each of the gearsets has respective first, second, and third members. The first member of the first planetary gearset is continuously operatively connected to the first component of the second planetary gearset for unitary rotation. The second member of the second planetary gearset is continuously operatively connected to the second member of the third planetary gearset for unitary rotation. The third member of the first planetary gearset is continuously operatively connected to the third member of the fourth planetary gearset for unitary rotation. The first member of the third planetary gearset is continuously operatively connected to the first member of the fourth planetary gearset for unitary rotation.

The second member of the first planetary gearset is continuously operatively connected to the input member for unitary rotation. The second member of the third planetary gearset is continuously operatively connected to the output member for unitary rotation.

The transmission also includes first, second, third, fourth, and fifth torque transmitting devices that are operative to selectively connect members of the planetary gearsets with the input member, the stationary member, or with other members of the planetary gearsets to provide at least eight forward speed ratios. At least one of the torque transmitting devices includes a piston that partially defines two separate pressure chambers and that is selectively moveable in response to hydraulic pressure in the pressure chambers.

The transmission provided herein improves upon the prior art because, where a relatively high amount of torque capacity is required by one of the torque transmitting devices, both chambers of the piston may be pressurized to provide the required torque capacity. Where a relatively low amount of torque capacity is required by the torque transmitting device, only one of the chambers may be pressurized, thereby reducing the amount of torque disturbance resulting from pressure errors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a lever diagram of a transmission10in accordance with the invention. The mechanisms will be described with specific reference to the stick diagram ofFIG. 2, wherein like reference numerals refer to like components fromFIG. 1. Referring toFIGS. 1 and 2, the transmission10includes a first planetary gearset14, a second planetary gearset18, a third planetary gearset22, and a fourth planetary gearset26. Each of the planetary gearsets14,18,22,26includes respective first, second, and third members.

More specifically, planetary gearset14includes a sun gear member30, a ring gear member34, and a planet carrier38. Planet gears40are rotatably mounted with respect to the planet carrier38and are meshingly engaged with the ring gear member34and the sun gear member30. Planetary gearset18includes a sun gear member42, a ring gear member46, and a planet carrier50. Planet gears52are rotatably mounted with respect to the planet carrier50and are meshingly engaged with the ring gear member46and the sun gear member42. Planetary gearset22includes a sun gear member54, a ring gear member58, and a planet carrier62. Planet gears64are rotatably mounted with respect to the planet carrier62and are meshingly engaged with the ring gear member58and the sun gear member54. Planetary gearset26includes a sun gear member66, a ring gear member70, and a planet carrier74. Planet gears76are rotatably mounted with respect to the planet carrier74and are meshingly engaged with the ring gear member70and the sun gear member66.

It should be noted that, where used in the claims, first, second, and third members of planetary gearsets do not necessarily refer to a member of a particular type; thus, for example, a first member may be any one of a ring gear member, sun gear member, or planet carrier assembly member. Similarly, as used in the claims, the respective first, second, or third members of two or more gearsets may or may not be the same type of member.

The transmission10also includes an input member80that is continuously operatively connected to the planet carrier38for unitary rotation therewith. An output member84is continuously operatively connected to the planet carrier62for unitary rotation therewith. Sun gear member30and sun gear member66are continuously operatively connected to one another for unitary rotation by interconnecting member88. Planet carrier50and planet carrier62are continuously operatively connected to one another for unitary rotation by interconnecting member92. Sun gear member42and ring gear member34are continuously operatively connected to one another for unitary rotation by interconnecting member96. Planet carrier74and ring gear member58are continuously operatively connected to one another for unitary rotation by interconnecting member100.

The transmission10also includes a plurality of torque transmitting devices that are selectively engageable to couple members of the planetary gearsets with the input member, the stationary member, or with other members of the planetary gearsets. Torque transmitting device104is a clutch that is configured to selectively couple the input member80and planet carrier38to ring gear member54for unitary rotation. Torque transmitting device108is a clutch that is configured to selectively couple interconnecting member96, sun gear member42, and ring gear member34to sun gear member54for unitary rotation. Torque transmitting device112is a clutch configured to selectively couple ring gear member46to sun gear member54for unitary rotation. Torque transmitting device116is a brake that is configured to selectively couple interconnecting member88, sun gear member30, and sun gear member66to a stationary member, such as transmission housing118. Torque transmitting device120is a brake configured to selectively couple ring gear member70to the housing118.

Referring toFIG. 3, a shift logic sequence for torque transmitting devices104,108,112,116,120is depicted that provides eight forward speed ratios and one reverse speed ratio between the input member80and the output member84. Referring toFIGS. 1-3, a reverse speed ratio is achieved when torque transmitting devices116,120, and112are engaged and torque transmitting devices108and104are disengaged.

A first forward speed ratio is achieved when torque transmitting devices116,120, and104are engaged and torque transmitting devices108and112are disengaged. A second forward speed ratio is achieved when torque transmitting devices116,120, and108are engaged and torque transmitting devices104and112are disengaged. A third forward speed ratio is achieved when torque transmitting devices120,108, and104are engaged and torque transmitting devices116and112are disengaged. A fourth forward speed ratio is achieved when torque transmitting devices120,108, and112are engaged and torque transmitting devices116and104are disengaged. A fifth forward speed ratio is achieved when torque transmitting devices120,104, and112are engaged and torque transmitting devices116and108are disengaged. A sixth forward speed ratio is achieved when torque transmitting devices108,104, and112are engaged and torque transmitting devices116and120are disengaged. A seventh forward speed ratio is achieved when torque transmitting devices116,104, and112are engaged and torque transmitting devices120and108are disengaged. An eighth forward speed ratio is achieved when torque transmitting devices116,108, and112are engaged and torque transmitting devices120and104are disengaged.

Referring toFIG. 4, wherein like reference numbers refer to like components fromFIGS. 1 and 2, torque transmitting device120is schematically depicted. Torque transmitting device120includes a plurality of evenly-spaced pressure plates124operatively connected to the housing118. Torque transmitting device120also includes a plurality of discs128that are spaced apart from one another and operatively connected to the ring gear member70. At least part of each plate124is disposed between two discs128, as understood by those skilled in the art.

The torque transmitting device120also includes a piston132that is biased by a return spring, i.e., belleville spring134, into a disengaged position as shown inFIG. 4. When the piston132is in the disengaged position, it does not act on the plates124and discs128; thus the discs128and the ring gear member70are free to rotate with respect to the plates124and the housing118. The piston132is selectively moveable axially into engagement with the plates124and discs128, thereby compressing the plates124and discs128together such that the plates124and discs128, and therefore the ring gear member70and the housing118, cannot rotate with respect to each other.

The surface of the piston132is characterized by a first area136and a second area140. The first area136cooperates with transmission structure144to define a first piston chamber150, and the second area140cooperates with the transmission structure144to define a second piston chamber154. The first and second chambers150,154are in selective fluid communication with a source of pressurized fluid, such as the pump (shown at160inFIG. 4a).

More specifically, and with reference toFIGS. 4 and 4a, valve164is selectively moveable between open and closed positions. When valve164is in its open position, the first chamber150is in fluid communication with the pump160via conduit168. When valve164is in its closed position, valve164prevents fluid communication between the pump160and the first chamber150. Valve172is selectively moveable between open and closed positions. When valve172is in its open position, the second chamber154is in fluid communication with the pump via conduit176. When valve172is in its closed position, valve172prevents fluid communication between the second chamber154and the pump160. Valves164,172include actuators, such as solenoids, to cause the valves164,172to move between their respective open and closed positions. The valves164,172are operatively connected to a controller180to be controlled thereby.

The transmission structure144defines three axially oriented surfaces184,188,192. The piston132includes three axially oriented surfaces196,200,204. Surfaces184and196are positioned to remain in contact with one another during axial translation of the piston132; surfaces188and200are positioned to remain in contact with one another during axial translation of the piston132; and surfaces192and204are positioned to remain in contact with one another during axial translation of the piston132.

Chamber150is sealed by the contact between surfaces184and196, and by contact between surfaces188and200. Chamber154is sealed by contact between surfaces188and200and by contact between surfaces192and204. Seals (not shown) may be employed between surfaces184,188,192,196,200,204to further seal the first and second chambers150,154. The first and second chambers150,154are not in fluid communication with one another; that is, fluid or fluid pressure from conduit168affects the first chamber150but not the second chamber154. Similarly, fluid or fluid pressure from conduit176affects the second chamber154but not the first chamber150. Accordingly, the first and second chambers150,154may be separately and independently pressurized by the controller180.

More specifically, by opening valve164and maintaining valve172in its closed position, the controller180causes the first chamber150to be pressurized while the second chamber154remains unpressurized. By opening valve172and maintaining valve164in its closed position, the controller180causes the first chamber150to remain unpressurized while the second chamber154is pressurized. The controller causes concurrent pressurization of both chambers150,154by causing both valves164,172to be concurrently open.

The first area136is arranged such that pressure in chamber150acts on the first area136to overcome the bias of the belleville spring134and move the piston132axially into engagement with the plates124and discs128. Similarly, the second area140is arranged such that pressure in chamber154acts on the second area140to overcome the bias of the belleville spring134and move the piston132axially into engagement with the plates124and discs128.

Pressurizing only one of the chambers150,154results in less piston force, and therefore less torque capacity of the torque transmitting device120, than pressurizing both of the chambers150,154. A given amount of pressure error with only one of the chambers150,154pressurized results in a smaller amount of torque disturbance than the same amount of pressure error subjected to both chambers150,154.

Torque transmitting devices116and112are similar to torque transmitting device120in having respective pistons with separate chambers that may be separately and independently pressurized by controller180. As shown inFIG. 3, relatively high torque capacity is required from torque transmitting device116for the reverse and first speed ratios, and relatively low torque capacity is required from torque transmitting device116for the second, seventh, and eighth speed ratios. Relatively high torque capacity is required from torque transmitting device120for the reverse, first, second and third speed ratios, and relatively low torque capacity is required from torque transmitting device120for the fourth and fifth speed ratios. Relatively high torque capacity is required from torque transmitting device112for the reverse speed ratio, and relatively low torque capacity is required from torque transmitting device112for the fourth, fifth, sixth, seventh, and eighth speed ratios.

Where a relatively high torque capacity is required from any of torque transmitting devices116,120,112, the controller180is programmed to pressurize both piston chambers of the torque transmitting device. Where a relatively low torque capacity is required from any of torque transmitting devices116,120,112, the controller80is programmed to pressurize only one of the piston chambers of the torque transmitting device.

More specifically, both of the chambers of the piston of torque transmitting device116are pressurized in the reverse and first speed ratios, and only one of the chambers of the piston of torque transmitting device116is pressurized while shifting into the second, seventh, and eighth speed ratios. Both of the chambers150,154of the piston132of torque transmitting device120are pressurized in the reverse, first, second, and third speed ratios, and only one of the chambers150,154of the piston132of torque transmitting device120is pressurized while shifting into the fourth and fifth speed ratios. Both of the chambers of the piston of torque transmitting device112are pressurized in the reverse speed ratio, and only one of the chambers of the piston of torque transmitting device112is pressurized while shifting into the fourth, fifth, sixth, seventh, and eighth speed ratios. It should be noted that, where only one chamber is pressurized during shifting, it may be desirable to pressurize both areas after the shift in order to reduce overall line pressure (pump pressure) for improved fuel economy.

Thus, for speed ratios where a large amount of clutch torque capacity is required to finish a shift, both piston chambers or areas will be pressurized. While shifting into speed ratios where smaller amounts of clutch torque capacity is required, only one of the chambers or areas will be pressurized. The result is that any pressure error induced torque disturbance is small compared to the torque required to complete the shift. In addition, using the smaller area to stroke the clutch reduces the oil volume needed to start the shift. The result is reduced shift delay.