# Patent

## Title
Transmission having at least eight speeds

## Abstract

A transmission of the present invention has 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. The torque transmitting devices are selectively engageable in combinations of at least two to establish at least eight forward speed ratios and at least one reverse speed ratio.

## Background
FIELD
The present invention relates generally to a multiple speed transmission having a plurality of planetary gear sets and a plurality of torque transmitting devices, and more particularly to a transmission having eight or more speeds, four planetary gear sets and a plurality of torque transmitting devices.
BACKGROUND
The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical multiple speed transmission uses a combination of friction clutches and brakes, 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 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 transmission.
SUMMARY
A 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 are for example clutches and brakes.
In an aspect of the present invention a transmission is provided having an input member, an output member, a first, second, third and fourth planetary gear sets each having sun gears, carrier members and ring gears. The input member is continuously interconnected with sun gear member of the first planetary gear set. The output member is continuously interconnected with the carrier member of the fourth planetary gear set.
Additionally, a first interconnecting member continuously interconnects the ring gear member of the first planetary gear set with carrier member of the second planetary gear set, a second interconnecting member continuously interconnects the carrier member of the first planetary gear set with the ring gear member of the second planetary gear set and the ring gear member of the third planetary gear set, a third interconnecting member continuously interconnects the carrier member of the third planetary gear set with the ring gear member of the fourth planetary gear set and a fourth interconnecting member continuously interconnects the sun gear member of the third planetary gear set with the sun gear member of the fourth planetary gear set.
Further, a first torque transmitting device is selectively engageable to interconnect the input member and the sun gear member of the first planetary gear set with the carrier member of the third planetary gear set, a second torque transmitting device is selectively engageable to interconnect the input member and the sun gear member of the first planetary gear set with the sun gear member of the third planetary gear set, a third torque transmitting device is selectively engageable to interconnect the ring gear member of the fourth planetary gear set with the stationary member, a fourth torque transmitting device is selectively engageable to interconnect the carrier member of the first planetary gear set, the ring gear member of the third planetary gear set and the ring gear member of the second planetary gear set with the stationary member, a fifth torque transmitting device is selectively engageable to interconnect the carrier member of the second planetary gear set and the ring gear member of the first planetary gear set with the stationary member and a sixth torque transmitting device selectively engageable to interconnect the sun gear member of the second planetary gear set with the stationary member. The torque transmitting devices are selectively engageable in combinations of at least two to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member. In operation, the torque transmitting devices are selectively engageable in combinations of at least two to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member.
It is thus an object, aspect and advantage of the present invention to provide a transmission having four planetary gear sets.
It is a further object, aspect and advantage of the present invention to provide a transmission having at least eight forward speeds and at least one reverse.
It is a still further object, aspect and advantage of the present invention to provide a transmission having four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices.
Further objects, aspects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature.



DRAWINGS
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
FIG. 1 is a lever diagram of an embodiment of a eight speed transmission according to the present invention;
FIG. 2 is a diagrammatic view of an embodiment of a eight speed transmission according to the present invention; and
FIG. 3 is a truth table presenting the state of engagement of the various torque transmitting elements in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in FIGS. 1 and 2.



DETAILED DESCRIPTION
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
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 components or elements of the four planetary gear sets. A second component or element of a first planetary gear set is permanently coupled to a first component or element of a second planetary gear set and a first component or element of a third planetary gear set. A third component or element of the first planetary gear set is permanently coupled to a second component or element of a second planetary gear set. A second component or element of the third planetary gear set is permanently coupled to a first component or element of a fourth planetary gear set. A third component or element of the third planetary gear set is permanently coupled to a third component or element of a fourth planetary gear set.
Referring now to FIG. 1, an embodiment of an eight speed transmission 10 is 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 of the planetary gear set 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. In some cases, two levers may be combined into a single lever having more than three nodes (typically four nodes). For example, if two nodes on two different levers are interconnected through a fixed connection they may be represented as a single node on a single lever. 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 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 transmission 10 includes an input shaft or member 12, a first planetary gear set 14, a second planetary gear set 16, a third planetary gear set 18, a fourth planetary gear set 20 and an output shaft or member 22. In the lever diagram of FIG. 1, the first planetary gear set 14 has three nodes each: a first node 14A, a second node 14B and a third node 14C. The second planetary gear set 16 has three nodes each: a first node 16A, a second node 16B and a third node 16C. The third planetary gear set 18 has three nodes each: a first node 18A, a second node 18B and a third node 18C. The fourth planetary gear set 20 has three nodes each: a first node 20A, a second node 20B and a third node 20C.
The input member 12 is coupled to the first node 14A of the first planetary gear set 14. The second node 14B of the first planetary gear set 14 is coupled to the first node 16A of the second planetary gear set 16 and to the first node 18A of the third planetary gear set 18. The third node 14C of the first planetary gear set 14 is coupled to the second node 16B of the second planetary gear set 16. The second node 18B of the third planetary gear set 18 is coupled to the first node 20A of the fourth planetary gear set 20. The third node 18C of the third planetary gear set 18 is coupled to the third node 20C of the fourth planetary gear set 20. The output member 22 is coupled to the second node 20B of the fourth planetary gear set 20.
A first clutch 24 selectively connects the first node 14A of the first planetary gear set 14 and the input member 12 with the second node 18B of the third planetary gear set 18 and the first node 20A of the fourth planetary gear set 20. A second clutch 26 selectively connects the first node 14A of the first planetary gear set 14 with the third node 18C of the third planetary gear set 18 and the third node 20C of the fourth planetary gear set 20. A first brake 28 selectively connects the third node 18B of the third planetary gear set 18 with a stationary element or a transmission housing 50. A second brake 30 selectively connects the second node 14B of the first planetary gear set 14 with the stationary element or a transmission housing 50. A third brake 32 selectively connects the third node 14C of the first planetary gear set 14 with a stationary element or a transmission housing 50. A fourth brake 34 selectively connects the third node 16C of the third planetary gear set 16 with a stationary element or a transmission housing 50.
Referring now to FIG. 2, a stick diagram presents a schematic layout of the embodiment of the eight speed transmission 10 according to the present invention. In FIG. 2, the numbering from the lever diagram of FIG. 1 is carried over. The clutches, brakes, 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, the planetary gear set 14 includes a sun gear member 14A, a ring gear member 14C and a planet gear carrier member 14B that rotatably supports a set of planet gears 14D (only one of which is shown). The planet gears 14D are each configured to intermesh with both the sun gear member 14A and the ring gear member 14C. The sun gear member 14A is connected for common rotation with a first shaft or interconnecting member 42 and with input shaft or member 12. The ring gear member 14C is connected for common rotation with a second shaft or interconnecting member 44. The planet carrier member 14B is connected for common rotation with a third shaft or interconnecting member 46.
The planetary gear set 16 includes a sun gear member 16C, a ring gear member 16A and a planet gear carrier member 16B that rotatably supports a set of planet gears 16D (only one of which is shown). The planet gears 16D are each configured to intermesh with both the sun gear member 16C and the ring gear member 16A. The sun gear member 16C is connected for common rotation with a fourth shaft or interconnecting member 48. The ring gear member 16A is connected for common rotation with the third shaft or interconnecting member 46. The planet carrier member 16B is connected for common rotation with the second shaft or interconnecting member 44 and a fifth shaft or interconnecting member 52.
The planetary gear set 18 includes a sun gear member 18C, a ring gear member 18A and a planet gear carrier member 18B that rotatably supports a set of planet gears 18D (only one of which is shown). The set of planet gears 18D are each configured to intermesh with both the sun gear member 18C and the ring gear member 18A. The sun gear member 18C is connected for common rotation with a sixth shaft or interconnecting member 54 and with a seventh shaft or interconnecting member 56. The ring gear member 18A is connected for common rotation with the third shaft or interconnecting member 46. The planet carrier member 18B is connected for common rotation with an eighth shaft or interconnecting member 58 and with a ninth shaft or interconnecting member 60.
The planetary gear set 20 includes a sun gear member 20C, a ring gear member 20A and a planet gear carrier member 20B that rotatably supports a first set of planet gears 20D (only one of which is shown). The set of planet gears 20D are each configured to intermesh with both the sun gear member 20C and the ring gear member 20A. The sun gear member 20C is connected for common rotation with the seventh shaft or interconnecting member 56. The ring gear member 20A is connected for common rotation with the eighth shaft or interconnecting member 58 and with the tenth shaft or interconnecting member 62. The planet carrier member 20B is connected for common rotation with the output shaft or member 22.
The input shaft or member 12 is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft or member 22 is continuously connected with the final drive unit or transfer case (not shown).
The torque-transmitting mechanisms or first clutch 24, second clutch 26 and brakes 28, 30, 32 and 34 allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and the housing. For example, the first clutch 24 is selectively engageable to connect the first shaft or interconnecting member 42 with the ninth shaft or interconnecting member 60. The second clutch 26 is selectively engageable to connect the first shaft or interconnecting member 42 with the sixth shaft or interconnecting member 54. The first brake 28 is selectively engageable to connect the tenth shaft or interconnecting member 62 with a stationary element or the transmission housing 50 in order to prevent the tenth shaft or interconnecting member 62 from rotating relative to the transmission housing 50. The second brake 30 is selectively engageable to connect the third shaft or interconnecting member 46 with a stationary element or the transmission housing 50 in order to prevent the third shaft or interconnecting member 46 from rotating relative to the transmission housing 50. The third brake 32 is selectively engageable to connect the fifth shaft or interconnecting member 52 with a stationary element or the transmission housing 50 in order to prevent the fifth shaft or interconnecting member 52 from rotating relative to the transmission housing 50. The fourth brake 34 is selectively engageable to connect the fourth shaft or interconnecting member 48 with a stationary element or the transmission housing 50 in order to prevent the fourth shaft or interconnecting member 48 from rotating relative to the transmission housing 50.
Referring now to FIGS. 2 and 3, the operation of the embodiment of the eight speed transmission 10 will be described. It will be appreciated that the transmission 10 is capable of transmitting torque from the input shaft or member 12 to the output shaft or member 22 in at least eight forward speed or torque ratios and at least one reverse speed or torque ratio with triple overdrive. Each forward and reverse speed or torque ratio is attained by engagement of one or more of the torque-transmitting mechanisms (i.e. first clutch 24, second clutch 26, first brake 28, second brake 30, third brake 32 and fourth brake 34), as will be explained below. FIG. 3 is a truth table presenting the various combinations of torque-transmitting elements 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 transmission 10. An example of the gear ratios that may be obtained using the embodiments of the present invention are also shown in FIG. 3. Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected.
To establish reverse gear, the first brake 28 and the third brake 32 are engaged or activated. The first brake 28 connects the tenth shaft or interconnecting member 62 with a stationary element or the transmission housing 50 in order to prevent the tenth shaft or interconnecting member 62 from rotating relative to the transmission housing 50. The third brake 32 connects the fifth shaft or interconnecting member 52 with a stationary element or the transmission housing 50 in order to prevent the fifth shaft or interconnecting member 52 from rotating relative to the transmission housing 50. Likewise, the eight forward ratios are achieved through different combinations of clutch and brake engagement, as shown in FIG. 3.
It will be appreciated that the foregoing explanation of operation and gear states of the eight speed transmission 10 assumes, first of all, that all the clutches and brakes 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.
The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

## Claims

1. A transmission comprising:
an input member;
an output member;
first, second, third and fourth planetary gear sets each having first, second and third members;
a first interconnecting member continuously interconnecting the third member of the first planetary gear set with second member of the second planetary gear set;
a second interconnecting member continuously interconnecting the second member of the first planetary gear set with the first member of the second planetary gear set and the first member of the third planetary gear set;
a third interconnecting member continuously interconnecting the second member of the third planetary gear set with the first member of the fourth planetary gear set;
a fourth interconnecting member continuously interconnecting the third member of the third planetary gear set with the third member of the fourth planetary gear set; and
six torque transmitting devices selectively engageable to interconnect one of the first, second, and third members with at least one other of the first members, second members, third members, and a stationary member, and
wherein the torque transmitting devices are selectively engageable in combinations of at least two to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member.

2. The transmission of claim 1 wherein a first of the six torque transmitting devices is selectively engageable to interconnect the input member and the first member of the first planetary gear set with the second member of the third planetary gear set.

3. The transmission of claim 2 wherein a second of the six torque transmitting devices is selectively engageable to interconnect the input member and the first member of the first planetary gear set with the third member of the third planetary gear set.

4. The transmission of claim 3 wherein a third of the six torque transmitting devices is selectively engageable to interconnect the first member of the fourth planetary gear set with the stationary member.

5. The transmission of claim 4 wherein a fourth of the six torque transmitting devices is selectively engageable to interconnect the second member of the first planetary gear set, the first member of the third planetary gear set and the first member of the second planetary gear set with the stationary member.

6. The transmission of claim 5 wherein a fifth of the six torque transmitting devices is selectively engageable to interconnect the second member of the second planetary gear set and the third member of the first planetary gear set with the stationary member.

7. The transmission of claim 6 wherein a sixth of the six torque transmitting devices is selectively engageable to interconnect the third member of the second planetary gear set with the stationary member.

8. The transmission of claim 1 wherein the first member of the first planetary gear set, the third member of the second planetary gear set, the third member of the third planetary gear set and the third member of the fourth planetary gear set are sun gears, the second member of the first planetary gear set, the second member of the second planetary gear set, the second member of the third planetary gear set and the second member of the fourth planetary gear set are carrier members and the third member of the first planetary gear set, first member of the second planetary gear set, the first member of the third planetary gear set and the first member of the fourth planetary gear set are ring gears.

9. The transmission of claim 1 wherein the input member is continuously interconnected with the first member of the first planetary gear set and output member is continuously interconnected with the second member of the fourth planetary gear set.

10. The transmission of claim 1 wherein four of the six torque transmitting devices are brakes and two of the six torque transmitting devices are clutches.

11. The transmission of claim 1 wherein the stationary member is a transmission housing.

12. A transmission comprising:
an input member;
an output member;
first, second, third and fourth planetary gear sets each having first, second and third members, wherein the input member is continuously interconnected with the first member of the first planetary gear set and output member is continuously interconnected with the second member of the fourth planetary gear set;
a first interconnecting member continuously interconnecting the third member of the first planetary gear set with second member of the second planetary gear set;
a second interconnecting member continuously interconnecting the second member of the first planetary gear set with the first member of the second planetary gear set and the first member of the third planetary gear set;
a third interconnecting member continuously interconnecting the second member of the third planetary gear set with the first member of the fourth planetary gear set;
a fourth interconnecting member continuously interconnecting the third member of the third planetary gear set with the third member of the fourth planetary gear set;
a first torque transmitting device selectively engageable to interconnect the input member and the first member of the first planetary gear set with the second member of the third planetary gear set;
a second torque transmitting device selectively engageable to interconnect the input member and the first member of the first planetary gear set with the third member of the third planetary gear set;
a third torque transmitting device selectively engageable to interconnect the first member of the fourth planetary gear set with the stationary member;
a fourth torque transmitting device selectively engageable to interconnect the second member of the first planetary gear set, the first member of the third planetary gear set and the first member of the second planetary gear set with the stationary member;
a fifth torque transmitting device selectively engageable to interconnect the second member of the second planetary gear set and the third member of the first planetary gear set with the stationary member; and
a sixth torque transmitting device selectively engageable to interconnect the third member of the second planetary gear set with the stationary member, and
wherein the torque transmitting devices are selectively engageable in combinations of at least two to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member.

13. The transmission of claim 12 wherein the first member of the first planetary gear set, the third member of the second planetary gear set, the third member of the third planetary gear set and the third member of the fourth planetary gear set are sun gears, the second member of the first planetary gear set, the second member of the second planetary gear set, the second member of the third planetary gear set and the second member of the fourth planetary gear set are carrier members and the third member of the first planetary gear set, first member of the second planetary gear set, the first member of the third planetary gear set and the first member of the fourth planetary gear set are ring gears.

14. The transmission of claim 12 wherein the stationary member is a transmission housing.

15. A transmission comprising:
an input member;
an output member;
first, second, third and fourth planetary gear sets each having a sun gear member, a carrier member and a ring gear member, wherein the input member is continuously interconnected with the sun gear member of the first planetary gear set and output member is continuously interconnected with the carrier member of the fourth planetary gear set;
a first interconnecting member continuously interconnecting the ring gear member of the first planetary gear set with carrier member of the second planetary gear set;
a second interconnecting member continuously interconnecting the carrier member of the first planetary gear set with the ring gear member of the second planetary gear set and the ring gear member of the third planetary gear set;
a third interconnecting member continuously interconnecting the carrier member of the third planetary gear set with the ring gear member of the fourth planetary gear set;
a fourth interconnecting member continuously interconnecting the sun gear member of the third planetary gear set with the sun gear member of the fourth planetary gear set;
a first torque transmitting device selectively engageable to interconnect the input member and the sun gear member of the first planetary gear set with the carrier member of the third planetary gear set;
a second torque transmitting device selectively engageable to interconnect the input member and the sun gear member of the first planetary gear set with the sun gear member of the third planetary gear set;
a third torque transmitting device selectively engageable to interconnect the ring gear member of the fourth planetary gear set with the stationary member;
a fourth torque transmitting device selectively engageable to interconnect the carrier member of the first planetary gear set, the ring gear member of the third planetary gear set and the ring gear member of the second planetary gear set with the stationary member;
a fifth torque transmitting device selectively engageable to interconnect the carrier member of the second planetary gear set and the ring gear member of the first planetary gear set with the stationary member; and
a sixth torque transmitting device selectively engageable to interconnect the sun gear member of the second planetary gear set with the stationary member, and
wherein the torque transmitting devices are selectively engageable in combinations of at least two to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member.

16. The transmission of claim 15 wherein the stationary member is a transmission housing.