Multi-speed transmission

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.

In a transmission, four gearing arrangements impose specified speed relationships among an input, an output, and first through fourth shafts. A first gearing arrangement fixedly imposes a linear speed relationship among the input, the first shaft, and the second shaft. The first gearing arrangement may be, for example, a simple planetary gear set having a sun gear fixedly coupled to the input, a ring gear fixedly coupled to the second shaft, and a carrier fixedly coupled to the first shaft. A second gearing arrangement fixedly imposes a proportional speed relationship between the second shaft and the third shaft. The second gearing arrangement may be, for example, a simple planetary gear set having a sun gear fixedly coupled to the second shaft, a ring gear fixedly held against rotation, and a carrier fixedly coupled to the third shaft. A third gearing arrangement fixedly imposes a linear speed relationship among the third shaft, the output, and the fourth shaft. The third gearing arrangement may be, for example, a simple planetary gear set having a sun gear fixedly coupled to the fourth, a ring gear fixedly coupled to the third shaft, and a carrier fixedly coupled to the output. Finally, a fourth gearing arrangement selectively imposes a linear speed relationship among the first shaft, the input, and the output. The fourth gearing arrangement may be, for example, a simple planetary gear set having a sun gear fixedly coupled to the first shaft, a ring gear selectively coupled to the output by a clutch, and a carrier fixedly coupled to the input. As another example, the fourth gearing arrangement may be a simple planetary gear set having a sun gear selectively coupled to the first shaft by a clutch, a ring gear fixedly coupled to the output, and a carrier fixedly coupled to the input. The transmission may further include brakes selectively holding the first shaft and the second shaft, respectively, against rotation. Clutches may selectively couple the fourth shaft to the first shaft and the input, respectively.

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 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. Shift elements may be positive engagement devices such as dog clutches or friction devices capable of transmitting torque between elements in the presence of relative rotation. Two rotating elements are coupled if they are either fixedly coupled or selectively coupled.

A gearing arrangement is a collection of gearing elements and shift elements configured to impose specified speed relationships among a set of shafts. 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. The speed of a shaft is positive when the shaft rotates in one direction and negative when the shaft rotates in the opposite direction. A proportional speed relationship exists between a first shaft and a second shaft when the ratio of their speeds is constrained to be a predetermined value. A proportional speed relationship between a first shaft and a second shaft is an underdrive relationship if the ratio of the second shaft speed to the first shaft speed is between zero and one. Similarly, a proportional speed relationship between a first shaft and a second shaft is an overdrive relationship if the ratio of the second shaft speed to the first shaft speed is greater than one. A linear speed relationship exists among an ordered list of shafts when i) the first and last shaft in the ordered list are constrained to have the most extreme speeds, ii) the speeds of the remaining shafts are each constrained to be a weighted average of the speeds of the first and last shafts, and iii) when the speeds of the shafts differ, they are constrained to be in the listed order, either increasing or decreasing.

FIG. 1 depicts a transmission that provides seven forward and one reverse speed ratios between input 10 and output 12 . Input 10 may be driven by an internal combustion engine or other prime mover. A launch device such as a torque converter or launch clutch may be employed between the prime mover and input 10 permitting the engine to idle while the vehicle is stationary and a transmission ratio is selected. Output 12 drives the vehicle wheels, preferably via a differential that allows a slight speed difference between left and right wheels while the vehicle goes around a corner.

The transmission of FIG. 1 utilizes four simple planetary gear sets 20 , 30 , 40 , and 50 . A planet carrier 22 rotates about a central axis and supports a set of planet gears 24 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 26 and with internal gear teeth on a ring gear 28 . The sun gear and ring gear are supported to rotate about the same axis as the carrier. Gear sets 30 , 40 , and 50 are similarly structured. A suggested ratio of gear teeth for each planetary gear set is listed in Table 1.

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 among the sun gear, the ring gear, and the planet carrier.

Sun gear 26 and carrier 52 are fixedly coupled to input 10 . Carrier 42 is fixedly coupled to output 12 . Ring gear 38 is fixedly held against rotation. Carrier 22 is fixedly coupled to sun gear 56 forming a first shaft. Ring gear 28 and sun gear 36 are fixedly coupled forming a second shaft. Carrier 32 is fixedly coupled to ring 48 forming a third shaft. Sun gear 46 forms a fourth shaft. Brake 60 selectively couples the first shaft to housing 14 to selectively hold the first shaft against rotation. The fourth shaft is selectively coupled to the second shaft by clutch 62 and selectively coupled to input 10 by clutch 64 . The second shaft is selectively held against rotation by brake 66 . Ring gear 58 is selectively coupled to output 12 by clutch 68 . Optional one-way-brake 70 passively holds the first shaft against rotation in a reverse direction, opposite the normal rotation of input shaft 10 , while permitting rotation in a positive direction.

Various subsets of the gearing arrangement of FIG. 1 impose particular speed relationships. Gear set 30 fixedly imposes an underdrive relationship between carrier 32 and sun gear 36 . Gear set 30 and brake 66 collectively selectively hold both the second and the third shafts against rotation. The same effect could be accomplished if brake 66 selectively directly held the third shaft against rotation or if it selectively coupled the second shaft to the third shaft. Gear set 50 and clutch 68 selectively impose a linear speed relationship among the first shaft, input 10 , and output 12 .

As shown in Table 2, engaging the shift elements in combinations of two establishes seven forward speed ratios and one reverse speed ratio between input 10 and output 12 . An X indicates that the shift element is required to establish the power transfer path. If optional one-way-brake 70 is present, it will engage in 1st gear, making engagement of brake 60 unnecessary to transfer power from the input to the output. However, brake 60 must be engaged to transfer power from the output to the input in 1st gear. When the gear sets have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in Table 2.

In operation, brakes 60 may be engaged while the vehicle is in park. If the driver then selects reverse, clutch 62 is engaged. If the driver shifts from park to drive, clutch 64 is engaged. If optional one-way-brake 70 is present, clutch 60 may be released in drive. All single and two step shifts are accomplished by gradually releasing one shift element while gradually engaging another shift element. If one-way-brake 70 is present, then it will release passively during any upshift from 1st gear.

FIG. 2 depicts a transmission that provides nine forward and one reverse speed ratios between input 10 and output 12 . The transmission of FIG. 2 utilizes four simple planetary gear sets 20 , 30 , 40 , and 50 . A suggested ratio of gear teeth for each planetary gear set is listed in Table 3.

Sun gear 26 and carrier 52 are fixedly coupled to input 10 . Carrier 42 and ring gear 58 are fixedly coupled to output 12 . Ring gear 38 is fixedly held against rotation. Carrier 22 forms a first shaft. Ring gear 28 and sun gear 36 are fixedly coupled forming a second shaft. Carrier 32 is fixedly coupled to ring 48 forming a third shaft. Sun gear 46 forms a fourth shaft. The first shaft is selectively held against rotation by brake 60 and selectively coupled to the sun gear 56 by clutch 72 . The fourth shaft is selectively coupled to the second shaft by clutch 62 and selectively coupled to input 10 by clutch 64 . The second shaft is selectively held against rotation by brake 66 and selectively coupled to output 12 by clutch 74 . Optional one-way-brake 70 passively holds the first shaft against rotation in a reverse direction while permitting rotation in a positive direction.

Various subsets of the gearing arrangement of FIG. 2 impose particular speed relationships. Gear set 30 fixedly imposes an underdrive relationship between carrier 32 and sun gear 36 . Gear set 30 and brake 66 collectively selectively hold both the second and the third shafts against rotation. Gear set 50 and clutch 72 selectively impose a linear speed relationship among the first shaft, input 10 , and output 12 .

As shown in Table 4, engaging the shift elements in combinations of two establishes nine forward speed ratios and one reverse speed ratio between input 10 and output 12 . When the gear sets have tooth numbers as indicated in Table 3, the speed ratios have the values indicated in Table 4. Operation of the transmission of FIG. 2 is analogous to the transmission of FIG. 1 as described above.

FIG. 3 depicts a transmission that provides nine forward and one reverse speed ratios between input 10 and output 12 . The transmission of FIG. 3 utilizes four simple planetary gear sets 20 , 30 , 40 , and 50 . A suggested ratio of gear teeth for each planetary gear set is listed in Table 5.

Sun gear 26 and carrier 52 are fixedly coupled to input 10 . Carrier 42 and ring gear 58 are fixedly coupled to output 12 . Ring gear 38 is fixedly held against rotation. Carrier 22 forms a first shaft. Ring gear 28 and sun gear 36 are fixedly coupled forming a second shaft. Carrier 32 is fixedly coupled to ring 48 forming a third shaft. Sun gear 46 forms a fourth shaft. The first shaft is selectively held against rotation by brake 60 and selectively coupled to the sun gear 56 by clutch 72 . The fourth shaft is selectively coupled to the second shaft by clutch 62 and selectively coupled to input 10 by clutch 64 . The second shaft is selectively held against rotation by brake 66 and selectively coupled to sun gear 56 by clutch 76 . Optional one-way-brake 70 passively holds the first shaft against rotation in a reverse direction while permitting rotation in a positive direction.

As shown in Table 6, engaging the shift elements in combinations of two establishes nine forward speed ratios and one reverse speed ratio between input 10 and output 12 . When the gear sets have tooth numbers as indicated in Table 5, the speed ratios have the values indicated in Table 6. Operation of the transmission of FIG. 3 is analogous to the transmission of FIG. 1 as described above.

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.