Eight speed automatic transmission

An automatic transmission is provided having an input member, an output member, four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices. Each of the planetary gear sets includes first, second and third members. The torque transmitting devices may include clutches and brakes.

FIELD

The invention relates generally to a multiple speed automatic transmission having a plurality of planetary gear sets and a plurality of torque transmitting devices and more particularly to an eight speed automatic transmission having four planetary gear sets and a plurality of torque transmitting devices.

BACKGROUND

A typical multiple speed automatic transmission uses a combination of friction clutches, planetary gear arrangements and fixed interconnections to achieve a plurality of gear ratios. The number and physical arrangement of the planetary gear sets, generally, are dictated by packaging, cost and desired speed ratios.

While current automatic transmissions achieve their intended purpose, the need for new and improved transmission configurations which exhibit improved performance, especially from the standpoints of efficiency, responsiveness and smoothness and improved packaging, primarily reduced size and weight, is essentially constant. Accordingly, there is a need for an improved, cost-effective, compact multiple speed automatic transmission.

SUMMARY

An automatic transmission is provided having an input member, an output member, four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices. Each of the planetary gear sets includes first, second and third members. The torque transmitting devices may be either clutches or brakes.

One embodiment of the transmission includes an input member, an output member, and first, second, third and fourth planetary gear sets each having first, second and third members. A first interconnecting member continuously interconnects the first member of the first planetary gear set with the first member of the third planetary gear set and the third member of the fourth planetary gear set. A second interconnecting member continuously interconnects the second member of the first planetary gear set with a stationary member. A third interconnecting member continuously interconnects the third member of the first planetary gear set with the third member of the second planetary gear set. Five torque transmitting devices are selectively engageable to interconnect one of the first members, second members, and third members with at least one of the first members, second members, third members, and the stationary member. The torque transmitting devices are selectively engageable in combinations of at least three to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member.

In one aspect of the present invention, a first of the five torque transmitting devices is selectively engageable to interconnect at least one of the second member of the third planetary gear set and the input member with the second member of the fourth planetary gear set.

In another aspect of the present invention, a second of the five torque transmitting devices is selectively engageable to interconnect the third member of the third planetary gear set with the second member of the fourth planetary gear set.

In yet another aspect of the present invention, a third of the five torque transmitting devices is selectively engageable to interconnect the first member of the fourth planetary gear set with at least one of the second member of the first planetary gear set and the stationary member.

In yet another aspect of the present invention, a fourth of the five torque transmitting devices is selectively engageable to interconnect the third member of the third planetary gear with at least one of the second member of the second planetary gear set and the output member.

In yet another aspect of the present invention, a fifth of the five torque transmitting devices is selectively engageable to interconnect the first member of the fourth planetary gear set with the first member of the second planetary gear set.

In yet another aspect of the present invention, the first members are sun gears, the second members are carrier members, and the third members are ring gears.

In yet another aspect of the present invention, the input member is continuously interconnected with the second member of the third planetary gear set and the output member is continuously interconnected with the second member of the second planetary gear set.

In yet another aspect of the present invention, four of the torque transmitting devices are clutches and one of the torque transmitting devices is a brake.

In yet another aspect of the present invention, the stationary member is a transmission housing.

Another embodiment of the transmission of the present invention includes an input member, an output member, first, second, third and fourth planetary gear sets each having a sun gear, a carrier member, and a ring gear, wherein the input member is continuously interconnected with the carrier member of the third planetary gear set and the output member is continuously interconnected with the carrier member of the second planetary gear set. A first interconnecting member continuously interconnects the sun gear of the first planetary gear set with the sun gear of the third planetary gear set and the ring gear of the fourth planetary gear set. A second interconnecting member continuously interconnects the carrier member of the first planetary gear set with a stationary member. A third interconnecting member continuously interconnects the ring gear of the first planetary gear set with the ring gear of the second planetary gear set. A first torque transmitting device is selectively engageable to interconnect at least one of the carrier member of the third planetary gear set and the input member with the carrier member of the fourth planetary gear set. A second torque transmitting device is selectively engageable to interconnect the ring gear of the third planetary gear set with the carrier member of the fourth planetary gear set. A third torque transmitting device is selectively engageable to interconnect the sun gear of the fourth planetary gear set with at least one of the carrier member of the first planetary gear set and the stationary member. A fourth torque transmitting device is selectively engageable to interconnect the ring gear of the third planetary gear with at least one of the carrier member of the second planetary gear set and the output member. A fifth torque transmitting device is selectively engageable to interconnect the sun gear of the fourth planetary gear set with the sun gear of the second planetary gear set. The torque transmitting devices are selectively engageable in combinations of at least three to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member.

DETAILED DESCRIPTION

At the outset, it should be appreciated that in the particular example provided, the eight speed automatic transmission of the present invention has an arrangement of permanent mechanical connections between the elements of the four planetary gear sets. These permanent mechanical connections relate the transmission embodiments. More specifically, a first component or element of a first planetary gear set is permanently coupled to a first component or element of a second planetary gear set. A second component or element of the first planetary gear set is permanently coupled to a ground or stationary member. A third component or element of the first planetary gear set is permanently coupled to a first component or element of a third planetary gear set and to a first component or element of a fourth planetary gear set.

Referring now toFIG. 1, an embodiment of an eight speed automatic transmission10is illustrated in a lever diagram format. A lever diagram is a schematic representation of the components of a mechanical device such as an automatic transmission. Each individual lever represents a planetary gear set wherein the three basic mechanical components or members of said planetary gear are each represented by a node. Therefore, a single lever contains three nodes: one for the sun gear, one for the planet gear carrier, and one for the ring gear. The relative length between the nodes of each lever can be used to represent the ring-to-sun ratio of each respective gear set. These lever ratios, in turn, are used to vary the gear ratios of the transmission in order to achieve an appropriate ratios and ratio progression. Mechanical couplings or interconnections between the nodes of the various planetary gear sets are illustrated by thin, horizontal lines and torque transmitting devices such as clutches and brakes are presented as interleaved fingers. If the device is a brake, one set of the fingers is grounded. Further explanation of the format, purpose and use of lever diagrams can be found in SAE Paper 810102, “The Lever Analogy: A New Tool in Transmission Analysis” by Benford and Leising, which is hereby fully incorporated by reference.

The automatic transmission10includes an input shaft or member12, a first planetary gear set14having three nodes: a first node14A, a second node14B and a third node14C, a second planetary gear set16having three nodes: a first node16A, a second node16B and a third node16C, a third planetary gear set18having three nodes: a first node18A, a second node18B and a third node18C, a fourth planetary gear set20having three nodes: a first node20A, a second node20B and a third node20C and an output shaft or member22.

The first node14A of the first planetary gear set14is coupled to the first node16A of the second planetary gear set16. The second node14B of the first planetary gear set14is coupled to a ground, stationary member, or housing50. The third node14C of the first planetary gear set14is coupled to the first node18A of the third planetary gear set18. The first node18A of the third planetary gear set18is coupled to the first node20A of the fourth planetary gear set20. The second node18B of the third planetary gear set18is coupled to the input shaft12. The second node16B of the second planetary gear set16is coupled to the output shaft22.

A first clutch26selectively connects the second node18B of the third planetary gear set18to the second node20B of the fourth planetary gear set20. A second clutch28selectively connects the third node18C of the third planetary gear set18to the second node20B of the fourth planetary gear set20. A first brake30selectively connects the third node20C of the fourth planetary gear set20to the ground, stationary member, or transmission housing50. A third clutch32selectively connects the third node18C of the third planetary gear set18to the second node16B of the second planetary gear set16and to output shaft22. A fourth clutch34selectively connects the third node20C of the fourth planetary gear set20to the third node16C of the second planetary gear set16and to output shaft22.

Referring now toFIG. 2, a stick diagram presents a schematic layout of the embodiment of the eight speed transmission10according to the present invention. InFIG. 2, the numbering from the lever diagram ofFIG. 1is carried over. The clutches, brake and couplings are correspondingly presented whereas the nodes of the planetary gear sets now appear as components of planetary gear sets such as sun gears, ring gears, planet gears and planet gear carriers.

For example, planetary gear set14includes a ring gear member14A, a planet gear carrier member14B and a sun gear member14C. Ring gear member14A is connected for common rotation with a first interconnecting shaft or member42. The planet gear carrier member14B rotatably supports a first set of planet gears14D (only one shown) and a second set of planet gears14E (only one shown) and is connected to a second interconnecting shaft or member44and to ground, stationary member, or transmission housing50. Sun gear member14C is connected for common rotation with a third interconnecting shaft or member46. First set of planet gears14D are each configured to intermesh with both ring gear member14A and second set of planet gears14E. Second set of planet gears14E are each configured to intermesh with both first set of planet gears14D and with sun gear member14C.

The input shaft12is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft22is continuously connected with the final drive unit or transfer case (not shown).

Planetary gear set16includes a sun gear member16C, a planet carrier member16B that rotatably supports a set of planet gears16D and a ring gear member16A. Sun gear member16C is connected for common rotation with a fourth interconnecting shaft or member48. Planet carrier member16B is connected for common rotation with output shaft22. Ring gear member16A is connected for common rotation with the first interconnecting shaft42. Planet gears16D are each configured to intermesh with both sun gear member16C and ring gear member16A.

Planetary gear set18includes a sun gear member18A, a planet carrier member18B and a ring gear member18C. Sun gear member18A is connected for common rotation with third interconnecting shaft46. The planet gear carrier member18B rotatably supports a first set of planet gears18D (only one shown) and a second set of planet gears18E (only one shown) and is connected for common rotation with a fifth interconnecting shaft or member52and to input shaft12. Ring gear member18C is connected for common rotation with a sixth interconnecting shaft or member54and a seventh interconnecting shaft or member56. First set of planet gears18D are each configured to intermesh with ring gear member18C and second set of planet gears18E. Second set of planet gears18E are each configured to intermesh first set of planet gears18D and with sun gear member18A.

Planetary gear set20includes a sun gear member20C, a ring gear member20A and a planet carrier member20B that rotatably supports a set of planet gears20D. Sun gear member20C is connected for common rotation with an eighth interconnecting shaft or member58. Ring gear member20A is connected for common rotation with third interconnecting shaft46. Planet carrier member20B is connected for common rotation with a ninth interconnecting shaft or member60. Planet gears20D are each configured to intermesh with both sun gear member20C and ring gear member20A.

The torque-transmitting devices or clutches26,28,32,34and brake30allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and the housing. For example, first clutch26is selectively engageable to connect fifth interconnecting shaft52to ninth interconnecting shaft60. Second clutch28is selectively engageable to connect sixth interconnecting shaft54to ninth interconnecting shaft60. Third clutch32is selectively engageable to connect seventh interconnecting shaft56to output shaft22. Fourth clutch34is selectively engageable to connect fourth interconnecting shaft48to eighth interconnecting shaft58. Brake30is selectively engageable to connect eighth interconnecting shaft58to transmission housing50to restrict rotation of shaft58relative to housing50.

Referring now toFIGS. 2 and 3, the operation of the embodiment of the eight speed automatic transmission10will be described. It will be appreciated that the automatic transmission10is capable of transmitting torque from the input shaft12to the output shaft22in at least eight forward speed or torque ratios and at least one reverse speed or torque ratio. Each forward and reverse speed or torque ratio is attained by engagement of one or more of the torque-transmitting devices (i.e. first clutch26, second clutch28, third clutch32, fourth clutch34and brake30), as will be explained below.FIG. 3is a truth table presenting the various combinations of torque-transmitting devices that are activated or engaged to achieve the various gear states. Actual numerical gear ratios of the various gear states are also presented although it should be appreciated that these numerical values are exemplary only and that they may be adjusted over significant ranges to accommodate various applications and operational criteria of the automatic transmission10. An example of the gear ratios that may be obtained using the embodiments of the present invention are also shown inFIG. 3. Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected.

To establish gear ratios, three torque transmitting devices are engaged for each gear state. The engaged elements are represented by an “X” in each respective row. For example, to establish reverse gear, brake30, third clutch32, and fourth clutch34are engaged or activated. Brake30connects eighth interconnecting shaft58to transmission housing50to restrict rotation of shaft58relative to housing50. Third clutch32connects seventh interconnecting shaft56to output shaft22. Fourth clutch34connects fourth interconnecting shaft48to eighth interconnecting shaft58. Likewise, the eight forward ratios are achieved through different combinations of torque transmitting device engagement, as shown inFIG. 3.

It will be appreciated that the foregoing explanation of operation and gear states of the eight speed automatic transmission10assumes, first of all, that all clutches and brake not specifically referenced in a given gear state are inactive or disengaged and, second of all, that during gear shifts, i.e., changes of gear state, between at least adjacent gear states, a clutch or brake engaged or activated in both gear states will remain engaged or activated.