Multi-speed transmission

This application is a continuation-in-part of U.S. application Ser. No. 13/569,462 filed Aug. 8, 2012, the disclosure of which is incorporated in its entirety by reference herein. This application is also a continuation-in-part of U.S. application Ser. No. 13/771,660 filed Feb. 20, 2013, the disclosure of which is incorporated in its entirety by reference herein.

This disclosure relates to the field of automatic transmissions for motor vehicles. More particularly, the disclosure pertains to an arrangement of gears, clutches, and the interconnections among them in a power transmission.

Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising. Typically, a transmission has a housing mounted to the vehicle structure, an input shaft driven by an engine crankshaft, and an output shaft driving the vehicle wheels, often via a differential assembly which permits the left and right wheel to rotate at slightly different speeds as the vehicle turns.

FIG. 1 is a schematic diagram of a first transmission gearing arrangement.

FIG. 2 is a schematic diagram of a second transmission gearing arrangement.

FIG. 3 is a schematic diagram of a third transmission gearing arrangement.

FIG. 4 is a schematic diagram of a fourth transmission gearing arrangement.

Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.

A gearing arrangement is a collection of rotating elements and shift elements configured to impose specified speed relationships among the rotating elements. Some speed relationships, called fixed speed relationships, are imposed regardless of the state of any shift elements. Other speed relationships, called selective speed relationships, are imposed only when particular shift elements are fully engaged. A linear speed relationship exists among an ordered list of rotating elements when i) the first and last rotating element in the group are constrained to have the most extreme speeds, ii) the speeds of the remaining rotating elements are each constrained to be a weighted average of the first and last rotating element, and iii) when the speeds of the rotating elements differ, they are constrained to be in the listed order, either increasing or decreasing. The speed of an element is positive when the element rotates in one direction and negative when the element rotates in the opposite direction. A discrete ratio transmission has a gearing arrangement that selectively imposes a variety of speed ratios between an input and an output.

A group of rotating elements are fixedly coupled to one another if they are constrained to rotate as a unit in all operating conditions. Rotating elements can be fixedly coupled by spline connections, welding, press fitting, machining from a common solid, or other means. Slight variations in rotational displacement between fixedly coupled elements can occur such as displacement due to lash or shaft compliance. One or more rotating elements that are all fixedly coupled to one another may be called a shaft. In contrast, two rotating elements are selectively coupled by a shift element when the shift element constrains them to rotate as a unit whenever it is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. A shift element that holds a rotating element against rotation by selectively connecting it to the housing is called a brake. A shift element that selectively couples two or more rotating elements to one another is called a clutch. Shift elements may be actively controlled devices such as hydraulically or electrically actuated clutches or brakes or may be passive devices such as one way clutches or brakes. Two rotating elements are coupled if they are either fixedly coupled or selectively coupled.

FIGS. 1 and 2 depict a transaxle that provides a variety of speed ratios between input 50 and output 52 . Input 50 may be driven by an internal combustion engine or other prime mover. A launch device such as torque converter or launch clutch may be employed between the prime mover and transaxle input 50 permitting the engine to idle while the vehicle is stationary and a transaxle ratio is selected. Output 52 may be a sprocket driving a chain that transmits power to a differential axis. Alternatively, output 52 may be a gear that transmits power to a differential axis through a series of meshes. In a longitudal arrangement, input 50 would enter from the left and output 52 would be a shaft extending to the right.

The transaxle of FIGS. 1 and 2 utilizes four simple planetary gear sets 10 , 20 , 30 , and 40 . A planet carrier 12 rotates about a central axis and supports a set of planet gears 14 such that the planet gears rotate with respect to the planet carrier. External gear teeth on the planet gears mesh with external gear teeth on a sun gear 16 and with internal gear teeth on a ring gear 18 . The sun gear and ring gear are supported to rotate about the same axis as the carrier. Gear sets 20 , 30 , and 40 are similarly structured. Gear set 30 may be positioned beside the other gear sets. However, to reduce axial length, gear set 30 may be positioned radially outside gear sets 10 and 20 as shown in FIG. 1 or radially outside gear set 40 as shown in FIG. 2 .

A simple planetary gear set is a type of gearing arrangement that imposes a fixed linear speed relationship among the sun gear, the planet carrier, and the ring gear. Other known types of gearing arrangements also impose a fixed linear speed relationship among three rotating elements. For example, a double pinion planetary gear set imposes a fixed linear speed relationship between the sun gear, the ring gear, and the planet carrier.

A suggested ratio of gear teeth for each planetary gear set is listed in Table 1.

Sun gear 36 is fixedly held against rotation; carrier 42 is fixedly coupled to input 50 ; carrier 12 is fixedly coupled to ring gear 28 ; and ring gear 18 , carrier 22 , ring gear 38 , and sun gear 46 are mutually fixedly coupled. Output 52 is selectively coupled to carrier 32 by clutch 60 and selectively coupled to ring gear 48 by clutch 62 . Input 50 is selectively coupled to sun gear 26 by clutch 64 . Sun gear 16 is selectively coupled to input 50 by clutch 66 and selectively held against rotation by brake 68 . The combination of carrier 12 and ring gear 28 is selectively held against rotation by brake 70 . Optional one-way-brake 72 passively precludes the combination of carrier 12 and ring gear 28 from rotating in a negative direction while permitting rotation in the positive direction.

Various combinations of gear sets, clutches, and brakes selectively impose particular speed relationships. The combination of gear sets 10 and 20 impose a linear speed relationship among sun gear 16 , the combination of carrier 12 and ring gear 28 , the combination of ring 18 and carrier 22 , and sun gear 26 . The combination of gear set 30 and clutch 60 selectively imposes an underdrive relationship between carrier 22 and output 52 . In other words, when clutch 60 is engaged, output 52 is constrained to rotate slower than carrier 22 and in the same direction.

As shown in Table 2, engaging the shift elements in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input 50 and output 52 . An X indicates that the shift element is required to establish the speed ratio. An (X) indicates the clutch can be applied but is not required. In 4th gear, clutches 60 and 62 establish the power flow path between input 50 and output 52 . Any one of the remaining shift elements can also be applied. Applying clutch 64 ensures that all single and two step shifts from 4th gear can be accomplished by engaging only one shift element and releasing only one shift element. When the gear sets have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in Table 2.

A second example transaxle is illustrated in FIGS. 3 and 4 . This transaxle utilizes three simple planetary gear sets 10 , 20 , and 40 , each having a sun gear, a ring gear, and a planet carrier supported for rotation about a first axis. Additionally, axis transfer gears 82 and 86 are supported for rotation about this first axis. Gear 86 is radially larger than gear 82 . Output gear 52 and axis transfer gears 84 and 88 are supported for rotation about a second axis substantially parallel to the first axis. Output 52 transmits power to a differential axis through an additional gear mesh. Gear 84 meshes with gear 82 and gear 88 meshes with gear 86 . Carrier 42 is fixedly coupled to input 50 ; axis transfer gear 84 is fixedly coupled to output gear 52 ; carrier 12 is fixedly coupled to ring gear 28 ; and ring gear 18 , carrier 22 , and sun gear 46 are mutually fixedly coupled. Axis transfer gear 82 is selectively coupled to carrier 22 by clutch 60 ′. Output gear 52 is selectively coupled to axis transfer gear 88 by clutch 62 ′. Input 50 is selectively coupled to sun gear 26 by clutch 64 . Sun gear 16 is selectively coupled to input 50 by clutch 66 and selectively held against rotation by brake 68 . The combination of carrier 12 and ring gear 28 is selectively held against rotation by brake 70 . Optional one-way-brake 72 passively precludes the combination of carrier 12 and ring gear 28 from rotating in a negative direction while permitting rotation in the positive direction.

To save axial space, gear 86 may be located radially outside of ring gear 48 as shown in FIG. 3 . Alternatively, planetary gear set 40 may be located radially outside of planetary gear sets 10 and 20 as shown in FIG. 4 .

Various combinations of gear sets, clutches, and brakes selectively impose particular speed relationships. The combination of gear sets 10 and 20 impose a linear speed relationship among sun gear 16 , the combination of carrier 12 and ring gear 28 , the combination of ring 18 and carrier 22 , and sun gear 26 . The combination of axis transfer gear 82 , axis transfer gear 84 , and clutch 60 ′ selectively imposes a first speed ratio between carrier 22 and output 52 . In other words, when clutch 60 ′ is engaged, the speed of output 52 divided by the speed of carrier 22 is a first fixed value, which is a negative value. Similarly, the combination of axis transfer gear 86 , axis transfer gear 88 , and clutch 62 ′ selectively imposes a second speed ratio between ring gear 48 and output 52 . When clutch 62 ′ is engaged, the speed of output 52 divided by the speed of ring gear 48 is a second fixed value. The second fixed value is also negative value but is greater in absolute value than the first fixed value.

A suggested ratio of gear teeth for each planetary gear set and each pair of axis transfer gears is listed in Table 3.

As shown in Table 4, engaging the shift elements in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input 50 and output 52 . When the gear sets have tooth numbers as indicated in Table 3, the speed ratios have the values indicated in Table 4.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.