# Patent

## Title
Eight-speed transmissions

## Abstract

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets, six torque-transmitting devices, and two fixed interconnections. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting devices provide interconnections between various gear members and the transmission housing, and are operated in combinations of three to establish eight forward speed ratios and one reverse speed ratio.

## Background
TECHNICAL FIELD
The present invention relates to a power transmission having three planetary gear sets that are controlled by six torque-transmitting devices to provide eight forward speed ratios and one reverse speed ratio.
BACKGROUND OF THE INVENTION
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point during cruising, other than the most efficient point. Therefore, manually-shifted (countershaft transmissions) were the most popular.
With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
Six-speed transmissions offer several advantages over four- and five-speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions having six or more forward speed ratios, passenger cars are still manufactured with three- and four-speed automatic transmissions and relatively few five- or six-speed devices due to the size and complexity of these transmissions.
Seven-, eight-, nine- and ten-speed transmissions provide further improvements in acceleration and fuel economy over six-speed transmissions. However, like the six-speed transmissions discussed above, the development of seven-, eight-, nine- and ten-speed transmissions has been precluded because of complexity, size and cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved transmission having three planetary gear sets controlled to provide eight forward speed ratios and one reverse speed ratio.
The transmission family of the present invention has three planetary gear sets, each of which includes a first, second and third member, which members may comprise a sun gear, a ring gear, or a planet carrier assembly member, in any order.
In referring to the first, second and third gear sets in this description and in the claims, these sets may be counted “first” to “third” in any order in the drawing (i.e., left to right, right to left, etc.). Additionally, the first, second or third members of each gear set may be counted “first” to “third” in any order in the drawing (i.e., top to bottom, bottom to top, etc.) for each gear set.
Each carrier member can be either a single-pinion carrier member (simple) or a double-pinion carrier member (compound). Embodiments with long pinions are also possible.
The input member is continuously connected with the second or third member of the first planetary gear set. The output member is continuously connected with the second member of the third planetary gear set.
A first interconnecting member continuously connects the first or second member of the first planetary gear set with a member of said second planetary gear set.
A second interconnecting member continuously connects a member of the second planetary gear set with the first or third member of the third planetary gear set.
A first torque-transmitting device, such as a brake, selectively connects a member of the first planetary gear set with a stationary member (transmission housing/casing).
A second torque-transmitting device, such as a brake, selectively connects the second member of the first planetary gear set or the first or third member of the second planetary gear set with a stationary member (transmission housing/casing).
A third torque-transmitting device, such as a brake, selectively connects the second member of the second planetary gear set or the third member of the third planetary gear set with a stationary member (transmission housing/casing).
A fourth torque-transmitting device, such as a clutch, selectively connects a member of the first planetary gear set with the second member of the first planetary gear set or the second or third member of the second planetary gear set.
A fifth torque-transmitting device, such as a clutch, selectively connects the second or third member of the first planetary gear set with the second member of the second planetary gear set or the first or third member of the third planetary gear set.
A sixth torque-transmitting device, such as a clutch, selectively connects a member of the first or second planetary gear set with a member of the second or third planetary gear set.
The six torque-transmitting devices are selectively engageable in combinations of three to yield eight forward speed ratios and one reverse speed ratio.
A variety of speed ratios and ratio spreads can be realized by suitably selecting the tooth ratios of the planetary gear sets.
The above features and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWING
FIG. 1a is a schematic representation of a powertrain including a planetary transmission in accordance with the present invention;
FIG. 1b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 1a; 
FIG. 1c is a schematic representation of the powertrain of FIG. 1a depicted in lever diagram form;
FIG. 2a is a schematic representation of a powertrain including a planetary transmission incorporating another family member of the present invention;
FIG. 2b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 2a; 
FIG. 2c is a schematic representation of the powertrain of FIG. 2a depicted in lever diagram form;
FIG. 3a is a schematic representation of a powertrain including a planetary transmission incorporating another family member of the present invention;
FIG. 3b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 3a; 
FIG. 3c is a schematic representation of the powertrain of FIG. 3a depicted in lever diagram form;
FIG. 4a is a schematic representation of a powertrain including a planetary transmission incorporating another family member of the present invention;
FIG. 4b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 4a; and
FIG. 4c is a schematic representation of the powertrain of FIG. 4a depicted in lever diagram form.



DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, there is shown in FIG. 1a a powertrain 10 having a conventional engine and torque converter 12, a planetary transmission 14, and a conventional final drive mechanism 16. The engine 12 may be powered using various types of fuel to improve the efficiency and fuel economy of a particular application. Such fuels may include, for example, gasoline; diesel; ethanol; dimethyl ether; etc.
The planetary transmission 14 includes an input member 17 continuously connected with the engine 12, a planetary gear arrangement 18, and an output member 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 18 includes three planetary gear sets 20, 30 and 40.
The planetary gear set 20 includes a sun gear member 22, a ring gear member 24, and a planet carrier assembly member 26. The planet carrier assembly member 26 includes a plurality of pinion gears 27 rotatably mounted on a carrier member 29 and disposed in meshing relationship with both the sun gear member 22 and the ring gear member 24.
The planetary gear set 30 includes a sun gear member 32, a ring gear member 34, and a planet carrier assembly member 36. The planet carrier assembly member 36 includes a plurality of pinion gears 37 rotatably mounted on a carrier member 39 and disposed in meshing relationship with both the sun gear member 32 and the ring gear member 34.
The planetary gear set 40 includes a sun gear member 42, a ring gear member 44, and a planet carrier assembly member 46. The planet carrier assembly member 46 includes a plurality of pinion gears 47 mounted on a carrier member 49 and disposed in meshing relationship with both the ring gear member 44 and the sun gear member 42.
The planetary gear arrangement also includes six torque-transmitting devices 80, 82, 84, 85, 86 and 87. The torque-transmitting devices 80, 82 and 84 are stationary-type torque-transmitting devices, commonly termed brakes or reaction clutches. The torque-transmitting devices 85, 86 and 87 are rotating-type torque-transmitting devices, commonly termed clutches.
The input member 17 is continuously connected with the planet carrier assembly member 26 of the planetary gear set 20. The output member 19 is continuously connected with planet carrier assembly member 46 of the planetary gear set 40.
A first interconnecting member 70 continuously connects the sun gear member 22 of the planetary gear set 20 with the sun gear member 32 of the planetary gear set 30. A second interconnecting member 72 continuously connects the planet carrier assembly member 36 of the planetary gear set 30 with the ring gear member 44 of the planetary gear set 40.
A first torque-transmitting device, such as brake 80, selectively connects the ring gear member 24 of the planetary gear set 20 with the transmission housing 60. A second torque-transmitting device, such as brake 82, selectively connects the ring gear member 34 of the planetary gear set 30 with the transmission housing 60. A third torque-transmitting device, such as brake 84, selectively connects the planet carrier assembly member 36 of the planetary gear set 30 and ring gear member 44 of the planetary gear set 40 via interconnecting member 72 with the transmission housing 60. A fourth torque-transmitting device, such as clutch 85, selectively planet carrier assembly member 26 of the planetary gear set 20 with the ring gear member 34 of the planetary gear set 30. A fifth torque-transmitting device, such as clutch 86, selectively connects the ring gear member 24 of the planetary gear set 20 with the sun gear member 42 of the planetary gear set 40. A sixth torque-transmitting device, such as clutch 87, selectively connects the sun gear member 22 of the planetary gear set 20 and sun gear member 32 of the planetary gear set 30 via interconnecting member 70 with the sun gear member 42 of the planetary gear set 40.
As shown in FIG. 1b, and in particular the truth table disclosed therein, the torque-transmitting devices are selectively engaged in combinations of three to provide eight forward speed ratios and one reverse speed ratio, all with single transition sequential shifts and three overdrive ratios.
As set forth above, the engagement schedule for the torque-transmitting devices is shown in the truth table of FIG. 1b. The chart of FIG. 1b describes the ratio steps that are attained in the above described transmission. For example, the step ratio between the first and second forward speed ratios is 1.54, while the step ratio between the reverse speed ratio and first forward ratio is −0.59.
Referring to FIG. 1c, the embodiment of powertrain 10 depicted in FIG. 1a 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 gearset, wherein the three basic mechanical components of the planetary gear are each represented by a node. Therefore, a single lever contains three nodes: one for the sun gear member, one for the planet gear carrier member, and one for the ring gear member. The relative length between the nodes of each lever can be used to represent the ring-to-sun ratio of each respective gearset. 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, authored by Benford, Howard and Leising, Maurice, “The Lever Analogy: A New Tool in Transmission Analysis”, 1981, which is hereby fully incorporated by reference.
The powertrain 10 includes an input member 17 continuously connected with the engine 12, an output member 19 continuously connected with the final drive mechanism 16, a first planetary gear set 20A having three nodes: a first node 22A, a second node 26A and a third node 24A; a second planetary gear set 30A having three nodes: a first node 32A, a second node 36A and a third node 34A; and a third planetary gear set 40A having three nodes: a first node 42A, a second node 46A and a third node 44A.
The input member 17 is continuously connected with the node 26A. The output member 19 is continuously connected with the node 46A.
The node 22A is continuously connected with node 32A via interconnecting member 70. The node 36A is continuously connected with node 44A via interconnecting member 72.
A first torque-transmitting device, such as brake 80, selectively connects the node 24A with the transmission housing 60. A second torque-transmitting device, such as brake 82, selectively connects the node 34A with the transmission housing 60. A third torque-transmitting device, such as brake 84, selectively connects the nodes 36A and 44A via interconnecting member 72 with the transmission housing 60. A fourth torque-transmitting device, such as clutch 85, selectively connects the node 26A with the node 34A. A fifth torque-transmitting device, such as clutch 86, selectively connects the node 24A with the node 42A. A sixth torque-transmitting device, such as clutch 87, selectively connects the nodes 22A and 32A via interconnecting member 70 with the node 42A.
To establish ratios, three torque-transmitting devices are engaged for each gear state. The engaged torque-transmitting devices are represented by an “X” in each respective row of FIG. 1b. For example, to establish reverse gear, the brake 84 and clutches 85, 87 are engaged. The brake 84 engages the nodes 36A and 44A via interconnecting member 72 with the transmission housing 60. The clutch 85 engages the node 26A with the node 34A. The clutch 87 engages the nodes 22A and 32A via interconnecting member 70 with the node 42A. Likewise, the eight forward ratios are achieved through different combinations of clutch engagement as per FIG. 1b. 
The powertrain 10, and all other powertrains shown herein, may share components with a hybrid vehicle, and such a combination may be operable in a “charge-depleting mode”. For purposes of the present invention, a “charge-depleting mode” is a mode wherein the vehicle is powered primarily by an electric motor/generator such that a battery is depleted or nearly depleted when the vehicle reaches its destination. In other words, during the charge-depleting mode, the engine 12 is only operated to the extent necessary to ensure that the battery is not depleted before the destination is reached. A conventional hybrid vehicle operates in a “charge-sustaining mode”, wherein if the battery charge level drops below a predetermined level (e.g., 25%) the engine is automatically run to recharge the battery. Therefore, by operating in a charge-depleting mode, the hybrid vehicle can conserve some or all of the fuel that would otherwise be expended to maintain the 25% battery charge level in a conventional hybrid vehicle. It should be appreciated that a hybrid vehicle powertrain is preferably only operated in the charge-depleting mode if the battery can be recharged after the destination is reached by plugging it into an energy source.
Description of a Second Exemplary Embodiment
In FIG. 2a a powertrain 110 is shown having a conventional engine and torque converter 12, a planetary transmission 114, and a conventional final drive mechanism 16. The engine 12 may be powered using various types of fuel to improve the efficiency and fuel economy of a particular application. Such fuels may include, for example, gasoline; diesel; ethanol; dimethyl ether; etc.
The planetary transmission 114 includes an input member 17 continuously connected with the engine 12, a planetary gear arrangement 118, and an output member 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 118 includes three planetary gear sets 120, 130 and 140.
The planetary gear set 120 includes a sun gear member 122, a ring gear member 124, and a planet carrier assembly member 126. The planet carrier assembly member 126 includes a plurality of pinion gears 127 rotatably mounted on a carrier member 129 and disposed in meshing relationship with both the sun gear member 122 and the ring gear member 124.
The planetary gear set 130 includes a sun gear member 132, a ring gear member 134, and a planet carrier assembly member 136. The planet carrier assembly member 136 includes a plurality of pinion gears 137 rotatably mounted on a carrier member 139 and disposed in meshing relationship with both the sun gear members 132 and the ring gear member 134.
The planetary gear set 140 includes a sun gear member 142, a ring gear member 144, and a planet carrier assembly member 146. The planet carrier assembly member 146 includes a plurality of pinion gears 147 mounted on a carrier member 149 and disposed in meshing relationship with both the ring gear member 144 and the sun gear member 142.
The planetary gear arrangement also includes six torque-transmitting devices 180, 182, 184, 185, 186 and 187. The torque-transmitting devices 180, 182 and 184 are stationary-type torque-transmitting devices, commonly termed brakes or reaction clutches. The torque-transmitting devices 185, 186 and 187 are rotating-type torque-transmitting devices, commonly termed clutches.
The input member 17 is continuously connected with the ring gear member 124 of the planetary gear set 120. The output member 19 is continuously connected with the planet carrier assembly member 146 of the planetary gear set 140.
A first interconnecting member 170 continuously connects the planet carrier assembly member 126 of the planetary gear set 120 with the ring gear member 134 of the planetary gear set 130. A second interconnecting member 172 continuously connects the sun gear member 132 of the pgs 130 with the sun gear member 142 of the planetary gear set 140.
A first torque-transmitting device, such as brake 180, selectively connects the sun gear member 122 of the planetary gear set 120 with the transmission housing 160. A second torque-transmitting device, such as brake 182, selectively connects the planet carrier assembly member 126 of the planetary gear set 120 and the ring gear member 134 of the planetary gear set 130 via interconnecting member 170 with the transmission housing 160. A third torque-transmitting device, such as brake 184, selectively connects the ring gear member 144 of the planetary gear set 140 with the transmission housing 160. A fourth torque-transmitting device, such as clutch 185, selectively connects the ring gear member 124 of the planetary gear set 120 with the planet carrier assembly member 136 of the planetary gear set 130. A fifth torque-transmitting device, such as clutch 186, selectively connects the planet carrier assembly member 126 of the planetary gear set 120 and ring gear member 134 of the planetary gear set 130 via interconnecting member 170 with the planet carrier assembly member 136 of the planetary gear set 130. A sixth torque-transmitting device, such as clutch 187, selectively connects the planet carrier assembly member 136 of the planetary gear set 130 with the ring gear member 144 of the planetary gear set 40.
As shown in FIG. 2b, and in particular the truth table disclosed therein, the torque-transmitting devices are selectively engaged in combinations of three to provide eight forward speed ratios and one reverse speed ratio, all with single transition sequential shifts and two overdrive ratios.
As set forth above, the engagement schedule for the torque-transmitting devices is shown in the truth table of FIG. 2b. The chart of FIG. 2b describes the ratio steps that are attained in the above described transmission. For example, the step ratio between the first and second forward speed ratios is 1.56, while the step ratio between the reverse speed ratio and first forward ratio is −0.63.
Referring to FIG. 2c, the embodiment of powertrain 110 depicted in FIG. 2a is illustrated in a lever diagram format. The powertrain 110 includes an input member 17 continuously connected with the engine 12, an output member 19 continuously connected with the final drive mechanism 16, a first planetary gear set 120A having three nodes: a first node 122A, a second node 126A and a third node 124A; a second planetary gear set 130A having three nodes: a first node 132A, a second node 136A and a third node 134A; and a third planetary gear set 140A having three nodes: a first node 142A, a second node 146A and a third node 144A.
The input member 17 is continuously connected with the node 124A. The output member 19 is continuously connected with the node 146A.
The node 126A is continuously connected with node 134A via interconnecting member 170. The node 132A is continuously connected with the node 142A via interconnecting member 172.
A first torque-transmitting device, such as brake 180, selectively connects the node 122A with the transmission housing 160. A second torque-transmitting device, such as brake 182, selectively connects the nodes 126A and 134A via interconnecting member 170 with the transmission housing 160. A third torque-transmitting device, such as brake 184, selectively connects the node 144A with the transmission housing 160. A fourth torque-transmitting device, such as clutch 185, selectively connects the node 124A with the node 136A. A fifth torque-transmitting device, such as clutch 186, selectively connects the nodes 126A and 134A via interconnecting member 170 with the node 136A. A sixth torque-transmitting device, such as clutch 187, selectively connects the node 136A with the node 144A.
To establish ratios, three torque-transmitting devices are engaged for each gear state. The engaged torque-transmitting devices are represented by an “X” in each respective row of FIG. 2b. For example, to establish reverse gear, the brakes 180, 184 and clutch 187 are engaged. The brake 180 engages the node 122A with the transmission housing 160. The brake 184 engages the node 144A with the transmission housing 160. The clutch 187 engages the node 136A with the node 144A. Likewise, the eight forward ratios are achieved through different combinations of clutch engagement as per FIG. 2b. 
Description of a Third Exemplary Embodiment
In FIG. 3a a powertrain 210 is shown having a conventional engine and torque converter 12, a planetary transmission 214, and a conventional final drive mechanism 16. The engine 12 may be powered using various types of fuel to improve the efficiency and fuel economy of a particular application. Such fuels may include, for example, gasoline; diesel; ethanol; dimethyl ether; etc.
The planetary transmission 214 includes an input member 17 continuously connected with the engine 12, a planetary gear arrangement 218, and an output member 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 218 includes three planetary gear sets 220, 230 and, 240.
The planetary gear set 220 includes a sun gear member 222, a ring gear member 224, and a planet carrier assembly member 226. The planet carrier assembly member 226 includes a plurality of pinion gears 227 rotatably mounted on a carrier member 229 and disposed in meshing relationship with both the sun gear member 222 and the ring gear member 224.
The planetary gear set 230 includes a sun gear member 232, a ring gear member 234, and a planet carrier assembly member 236. The planet carrier assembly member 236 includes a plurality of pinion gears 237 rotatably mounted on a carrier member 239 and disposed in meshing relationship with both the sun gear members 232 and the ring gear member 234.
The planetary gear set 240 includes a sun gear member 242, a ring gear member 244, and a planet carrier assembly member 246. The planet carrier assembly member 246 includes a plurality of pinion gears 247 mounted on a carrier member 249 and disposed in meshing relationship with both the ring gear member 244 and the sun gear member 242.
The planetary gear arrangement also includes six torque-transmitting devices 280, 282, 284, 285, 286 and 287. The torque-transmitting devices 280, 282 and 284 are stationary-type torque-transmitting devices, commonly termed brakes or reaction clutches. The torque-transmitting devices 285, 286 and 287 are rotating-type torque-transmitting devices, commonly termed clutches.
The input member 17 is continuously connected with the ring gear member 224 of the planetary gear set 220. The output member 19 is continuously connected with the planet carrier assembly member 246 of the planetary gear set 240.
A first interconnecting member 270 continuously connects the planet carrier assembly member 226 of the planetary gear set 220 with the planet carrier assembly member 236 of the planetary gear set 230. A second interconnecting member 272 continuously connects the ring gear member 234 of the planetary gear set 230 with the sun gear member 242 of the planetary gear set 240.
A first torque-transmitting device, such as brake 280, selectively connects the sun gear member 222 of the planetary gear set 220 with the transmission housing 260. A second torque-transmitting device, such as brake 282, selectively connects the sun gear member 232 of the planetary gear set 230 with the transmission housing 260. A third torque-transmitting device, such as brake 284, selectively connects the ring gear member 244 of the planetary gear set 240 with the transmission housing 260. A fourth torque-transmitting device, such as clutch 285, selectively connects the sun gear member 222 of the planetary gear set 220 with the ring gear member 234 of the planetary gear set 230 and the sun gear member 242 of the planetary gear set 240 via interconnecting member 272. A fifth torque-transmitting device, such as clutch 286, selectively connects the planet carrier assembly member 226 of the planetary gear set 220 and the planet carrier assembly member 236 of the planetary gear set 230 via interconnecting member 270 with the ring gear member 244 of the planetary gear set 240. A sixth torque-transmitting device, such as clutch 287 selectively connects the ring gear member 234 of the planetary gear set 230 and the sun gear member 242 of the planetary gear set 240 via interconnecting member 272 with the ring gear member 244 of the planetary gear set 240.
As shown in FIG. 3b, and in particular the truth table disclosed therein, the torque-transmitting devices are selectively engaged in combinations of three to provide eight forward speed ratios and one reverse speed ratio, all with single transition sequential shifts and having two overdrive ratios.
As set forth above, the engagement schedule for the torque-transmitting devices is shown in the truth table of FIG. 3b. The chart of FIG. 3b describes the ratio steps that are attained in the above described transmission. For example, the step ratio between the first and second forward speed ratios is 1.73, while the step ratio between the reverse speed ratio and first forward ratio is −0.42.
Referring to FIG. 3c, the embodiment of powertrain 210 depicted in FIG. 3a is illustrated in a lever diagram format. The powertrain 210 includes an input member 17 continuously connected with the engine 12, an output member 19 continuously connected with the final drive mechanism 16, a first planetary gear set 220A having three nodes: a first node 222A, a second node 226A and a third node 224A; a second planetary gear set 230A having three nodes: a first node 232A, a second node 236A and a third node 234A; and a third planetary gear set 240A having three nodes: a first node 242A, a second node 246A and a third node 244A.
The input member 17 is continuously connected with the node 224A. The output member 19 is continuously connected with the node 246A.
The node 226A is continuously connected with node 236A via interconnecting member 270. The node 234A is continuously connected with the node 242A via interconnecting member 272.
A first torque-transmitting device, such as brake 280, selectively connects the node 222A with the transmission housing 260. A second torque-transmitting device, such as brake 282, selectively connects the node 232A with the transmission housing 260. A third torque-transmitting device, such as brake 284, selectively connects the node 244A with the transmission housing 260. A fourth torque-transmitting device, such as clutch 285, selectively connects the node 222A with the nodes 234A and 242A via interconnecting member 272. A fifth torque-transmitting device, such as clutch 286, selectively connects the nodes 226A and 236A via interconnecting member 270 with the node 244A. A sixth torque-transmitting device, such as clutch 287, selectively connects the nodes 234A and 242A via interconnecting member 272 with the node 244A.
To establish ratios, three torque-transmitting devices are engaged for each gear state. The engaged torque-transmitting devices are represented by an “X” in each respective row of FIG. 3b. For example, to establish reverse gear, the brake 284 and clutches 285, 286 are engaged. The brake 284 engages the node 244A with the transmission housing 260. The clutch 285 engages the node 222A with the nodes 234A and 242A via interconnecting member 272. The clutch 286 engages the nodes 226A and 236A via interconnecting member 270 with the node 244A. Likewise, the eight forward ratios are achieved through different combinations of clutch engagement as per FIG. 3b. 
Description of a Fourth Exemplary Embodiment
In FIG. 4a a powertrain 310 is shown having a conventional engine and torque converter 12, a planetary transmission 314, and a conventional final drive mechanism 16. The engine 12 may be powered using various types of fuel to improve the efficiency and fuel economy of a particular application. Such fuels may include, for example, gasoline; diesel; ethanol; dimethyl ether; etc.
The planetary transmission 314 includes an input member 17 continuously connected with the engine 12, a planetary gear arrangement 318, and an output member 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 318 includes three planetary gear sets 320, 330 and 340.
The planetary gear set 320 includes a sun gear member 322, a ring gear member 324 and a planet carrier assembly member 326. The planet carrier assembly member 326 includes a plurality of pinion gears 327 rotatably mounted on a carrier member 329 and disposed in meshing relationship with both the sun gear member 322 and the ring gear member 324.
The planetary gear set 330 includes a sun gear member 332, a ring gear member 334, and a planet carrier assembly member 336. The planet carrier assembly member 336 includes a plurality of pinion gears 337 mounted on a carrier member 339 and disposed in meshing relationship with both the sun gear member 332 and the ring gear member 334.
The planetary gear set 340 includes a sun gear member 342, a ring gear member 344, and a planet carrier assembly member 346. The planet carrier assembly member 346 includes a plurality of pinion gears 347 mounted on a carrier member 349 and disposed in meshing relationship with both the sun gear member 342 and the ring gear member 344.
The planetary gear arrangement also includes six torque-transmitting devices 380, 382, 384, 385, 386 and 387. The torque-transmitting devices 380, 382 and 384 are stationary-type torque-transmitting devices, commonly termed brakes or reaction clutches. The torque-transmitting devices 385, 386 and 387 are rotating-type torque-transmitting devices, commonly termed clutches.
The input member 17 is continuously connected with the ring gear member 324 of the planetary gear set 320. The output member 19 is continuously connected with the planet carrier assembly member 346 of the planetary gear set 340.
A first interconnecting member 370 continuously connects the planet carrier assembly member 326 of the planetary gear set 320 with the ring gear member 334 of the planetary gear set 340. A second interconnecting member 372 continuously connects the planet carrier assembly member 336 of the planetary gear set 330 with the sun gear member 342 of the planetary gear set 340.
A first torque-transmitting device, such as brake 380, selectively connects the planet carrier assembly member 326 of the planetary gear set 320 and the ring gear member 334 of the planetary gear set 330 via interconnecting member 370 with the transmission housing 360. A second torque-transmitting device, such as brake 382, selectively connects the sun gear member 332 of the planetary gear set 330 with the transmission housing 360. A third torque-transmitting device, such as brake 384, selectively connects the ring gear member 344 of the planetary gear set 340 with the transmission housing 360. A fourth torque-transmitting device, such as clutch 385, selectively connects the ring gear member 324 of the planetary gear set 320 with the planet carrier assembly member 326 of the planetary gear set 320 and the ring gear member 334 of the planetary gear set 330 via interconnecting member 370. A fifth torque-transmitting device, such as clutch 386, selectively connects the ring gear member 324 of the planetary gear set 320 with the ring gear member 344 of the planetary gear set 340. A sixth torque-transmitting device, such as clutch 387, selectively connects the sun gear member 322 of the planetary gear set 320 with the sun gear member 332 of the planetary gear set 330.
As shown in FIG. 4b, and in particular the truth table disclosed therein, the torque-transmitting devices are selectively engaged in combinations of three to provide eight forward speed ratios and one reverse speed ratio, all with single transition sequential.
As set forth above, the engagement schedule for the torque-transmitting devices is shown in the truth table of FIG. 4b. The chart of FIG. 4b describes the ratio steps that are attained in the above described transmission. For example, the step ratio between the first and second forward speed ratios is 1.59, while the step ratio between the reverse speed ratio and first forward ratio is −0.80.
Referring to FIG. 4c, the embodiment of powertrain 310 depicted in FIG. 4a is illustrated in a lever diagram format. The powertrain 310 includes an input member 17 continuously connected with the engine 12, an output member 19 continuously connected with the final drive mechanism 16, a first planetary gear set 320A having three nodes: a first node 322A, a second node 326A and a third node 324A; a second planetary gear set 330A having three nodes: a first node 332A, a second node 336A and a third node 334A; and a third planetary gear set 340A having three nodes: a first node 342A, a second node 346A and a third node 344A.
The input member 17 is continuously connected with the node 324A. The output member 19 is continuously connected with the node 346A.
The node 326A is continuously connected with node 334A via interconnecting member 370. The node 336A is continuously connected with the node 342A via interconnecting member 372.
A first torque-transmitting device, such as brake 380, selectively connects the nodes 326A and 334A via interconnecting member 370 with the transmission housing 360. A second torque-transmitting device, such as brake 382, selectively connects the node 332A with the transmission housing 360. A third torque-transmitting device, such as brake 384, selectively connects the node 344A with the transmission housing 360. A fourth torque-transmitting device, such as clutch 385, selectively connects the node 324A with the nodes 326A and 334A via interconnecting member 370. A fifth torque-transmitting device, such as clutch 386, selectively connects the node 324A with the node 344A. A sixth torque-transmitting device, such as clutch 387, selectively connects the node 322A with the node 332A.
To establish ratios, three torque-transmitting devices are engaged for each gear state. The engaged torque-transmitting devices are represented by an “X” in each respective row of FIG. 4b. For example, to establish reverse gear, the brakes 380, 384 and clutch 387 are engaged. The brake 380 engages the nodes 326A and 334A via interconnecting member 370 with the transmission housing 360. The brake 384 engages the node 344A with the transmission housing 360. The clutch 387 engages the node 322A with the node 332A. Likewise, the eight forward ratios are achieved through different combinations of clutch engagement as per FIG. 4b. 
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

## Claims

1. A multi-speed transmission comprising:
an input member;
an output member;
first, second and third planetary gear sets each having first, second and third members;
a first interconnecting member continuously connecting said first or said second member of said first planetary gear set with a member of said second planetary gear set;
a second interconnecting member continuously connecting a member of said second planetary gear set with said first or said third member of said third planetary gear set; and
six torque-transmitting devices being engaged in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio between said input member and said output member; wherein only one of said six torque-transmitting devices selectively connects one of said members of said first planetary gear set with said second or said third member of said second planetary gear set or with said second member of said first planetary gear set.

2. The transmission of claim 1, wherein a first of said six torque-transmitting devices selectively connects another of said members of said first planetary gear set with a stationary member.

3. The transmission of claim 2, wherein a second of said six torque-transmitting devices selectively connects said second member of said first planetary gear set or said first or said third member of said second planetary gear set with said stationary member.

4. The transmission of claim 3, wherein a third of said six torque-transmitting devices selectively connects said second member of said second planetary gear set or said third member of said third planetary gear set with said stationary member.

5. The transmission of claim 4, wherein said only one of said six torque-transmitting devices is a fourth of said six torque-transmitting devices.

6. The transmission of claim 5, wherein a fifth of said six torque-transmitting devices selectively connects said second or third member of said first planetary gear set with said second member of said second planetary gear set or with said first or said third member of said third planetary gear set.

7. The transmission of claim 6, wherein a sixth of said six torque-transmitting devices selectively connects said first member of said first planetary gear set or said second or said third member of said second planetary gear set with said first member of said second planetary gear set or said first or third member of said third planetary gear set.

8. The transmission of claim 7, wherein said input member is continuously connected with said second or said third member of said first planetary gear set; and said output member is continuously connected with said second member of said third planetary gear set.

9. The transmission of claim 8, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.

10. A multi-speed transmission comprising:
an input member;
an output member;
first, second and third planetary gear sets each having first, second and third members;
a first interconnecting member continuously connecting said first or said second member of said first planetary gear set with a member of said second planetary gear set;
a second interconnecting member continuously connecting a member of said second planetary gear set with said first or said third member of said third planetary gear set;
six torque-transmitting devices being engaged in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio between said input member and said output member; wherein one of said six torque-transmitting devices selectively connects one of said members of said first planetary gear set with said second or said third member of said second planetary gear set or with said second member of said first planetary gear set;
wherein said input member is continuously connected with said second member of said first planetary gear set;
wherein said output member is continuously connected with said second member of said third planetary gear set;
wherein said first interconnecting member continuously connects said first member of said first planetary gear set with said first member of said second planetary gear set;
wherein said second interconnecting member continuously connects said second member of said second planetary gear set with said third member of said third planetary gear set;
wherein a first of said six torque-transmitting devices selectively connects said third member of said first planetary gear set with a stationary member;
wherein a second of said six torque-transmitting devices selectively connects said third member of said second planetary gear set with said stationary member;
wherein a third of said six torque-transmitting devices selectively connects said second member of said second planetary gear set with said stationary member;
wherein said one of said six torque-transmitting devices is a fourth of said six torque-transmitting devices that selectively connects said second member of said first planetary gear set with said third member of said second planetary gear set;
wherein a fifth of said six torque-transmitting devices selectively connects said third member of said first planetary gear set with said first member of said third planetary gear set; and
wherein a sixth of said six torque-transmitting devices selectively connects said first member of said first planetary gear set with said first member of said third planetary gear set.

11. The transmission of claim 1, wherein
said input member is continuously connected with said third member of said first planetary gear set;
said output member is continuously connected with said second member of said third planetary gear set;
said first interconnecting member continuously connects said second member of said first planetary gear set with said third member of said second planetary gear set;
said second interconnecting member continuously connects said first member of said second planetary gear set with said first member of said third planetary gear set;
a first of said six torque-transmitting devices selectively connects said first member of said first planetary gear set with said stationary member;
a second of said six torque-transmitting devices selectively connects said second member of said first planetary gear set with said stationary member;
a third of said six torque-transmitting devices selectively connects said third member of said third planetary gear set with said stationary member;
said one of said six torque-transmitting devices is a fourth of said six torque-transmitting devices that selectively connects said third member of said first planetary gear set with said second member of said second planetary gear set;
a fifth of said six torque-transmitting devices selectively connects said second member of said first planetary gear set with said second member of said second planetary gear set; and
a sixth of said six torque-transmitting devices selectively connects said second member of said second planetary gear set with said third member of said third planetary gear set.

12. The transmission of claim 1, wherein
said input member is continuously connected with said third member of said first planetary gear set;
said output member is continuously connected with said second member of said third planetary gear set;
said first interconnecting member continuously connects said second member of said first planetary gear set with said second member of said second planetary gear set;
said second interconnecting member continuously connects said third member of said second planetary gear set with said first member of said third planetary gear set;
a first of said six torque-transmitting devices selectively connects said first member of said first planetary gear set with said stationary member;
a second of said six torque-transmitting devices selectively connects said first member of said second planetary gear set with said stationary member;
a third of said six torque-transmitting devices selectively connects said third member of said third planetary gear set with said stationary member;
said one of said six torque-transmitting devices is a fourth of said six torque-transmitting devices that selectively connects said first member of said first planetary gear set with said third member of said second planetary gear set;
a fifth of said six torque-transmitting devices selectively connects said second member of said first planetary gear set with said third member of said third planetary gear set; and
a sixth of said six torque-transmitting devices selectively connects said third member of said second planetary gear set with said third member of said third planetary gear set.

13. The transmission of claim 1, wherein
said input member is continuously connected with said third member of said first planetary gear set;
said output member is continuously connected with said second member of said third planetary gear set;
said first interconnecting member continuously connects said second member of said first planetary gear set with said third member of said second planetary gear set;
said second interconnecting member continuously connects said second member of said second planetary gear set with said first member of said third planetary gear set;
a first of said six torque-transmitting devices selectively connects said second member of said first planetary gear set with a stationary member;
a second of said six torque-transmitting devices selectively connects said first member of said second planetary gear set with said stationary member;
a third of said six torque-transmitting devices selectively connects said third member of said third planetary gear set with said stationary member;
said one of said six torque-transmitting devices is a fourth torque-transmitting device that selectively connects said third member of said first planetary gear set with said second member of said first planetary gear set;
a fifth of said six torque-transmitting devices selectively connects said third member of said first planetary gear set with said third member of said third planetary gear set; and
a sixth of said six torque-transmitting devices selectively connects said first member of said first planetary gear set with said first member of said second planetary gear set.

14. The transmission of claim 10, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.

15. The transmission of claim 11, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.

16. The transmission of claim 12, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.

17. The transmission of claim 13, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.

18. A multi-speed transmission comprising:
an input member;
an output member;
first, second and third planetary gear sets each having first, second and third members;
a first interconnecting member continuously connecting said first or said second member of said first planetary gear set with a member of said second planetary gear set;
a second interconnecting member continuously connecting a member of said second planetary gear set with said first or said third member of said third planetary gear set;
a first torque-transmitting device selectively connecting a member of said first planetary gear set with a stationary member;
a second torque-transmitting device selectively connecting said second member of said first planetary gear set or said first or said third member of said second planetary gear set with said stationary member;
a third torque-transmitting device selectively connecting said second member of said second planetary gear set or said third member of said third planetary gear set with said stationary member;
a fourth torque-transmitting device selectively connecting a member of said first planetary gear set with said second or said third member of said second planetary gear set or with said second member of said first planetary gear set;
a fifth torque-transmitting device selectively connecting said second or third member of said first planetary gear set with said second member of said second planetary gear set or with said first or said third member of said third planetary gear set;
a sixth torque-transmitting device selectively connecting said first member of said first planetary gear set or said second or said third member of said second planetary gear set with said first member of said second planetary gear set or said first or third member of said third planetary gear set; and
said six torque-transmitting devices being engaged in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio between said input member and said output member.

19. The transmission of claim 18, wherein said first, second and third members of said first, second and third planetary gear sets comprise a sun gear member, a planet carrier assembly member and a ring gear member, respectively.