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.

A transmission is disclosed having four gearing arrangements which can be, for example, simple planetary gear sets. The gearing arrangements constrain the speeds of various rotating members. A first gearing arrangement fixedly constrains an input shaft to rotate at a speed between the speeds of a first element and a second element. A second gearing arrangement fixedly constrains an output shaft to rotate at a speed between the speeds of a third element and a fourth element. A third gearing arrangement selectively constrains an intermediate shaft to rotate at a speed between the speeds of the second element and the third element. Finally, a fourth gearing arrangement selectively constrains the fourth element to rotate at a speed less than the speed of the first element. Six clutches selectively couple gear elements to each other, to the input shaft, to the intermediate shaft, or to a transmission case. Engaging the clutches in various combinations establishes ten forward speed ratios and one reverse speed ratio.

In one embodiment, three of the clutches form a clutch module in which each of the three clutches selectively couple the intermediate shaft to a different gear element. Engaging the clutches in the module in combinations of two couples various pairs of gear elements. In another embodiment, three of the clutches form a clutch module in which each of the three clutches selectively couple two gear elements directly to each other.

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.

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 clutches configured to impose specified speed relationships among elements. Some speed relationships, called fixed speed relationships, are imposed regardless of the state of any clutches. A gearing arrangement imposing only fixed relationships is called a fixed gearing arrangement. Other speed relationships are imposed only when particular clutches are fully engaged. A gearing arrangement that selectively imposes speed relationships is called a shiftable gearing arrangement. A discrete ratio transmission has a shiftable gearing arrangement that selectively imposes a variety of speed ratios between an input shaft and an output shaft.

A group of elements are fixedly coupled to one another if they are constrained to rotate as a unit in all operating conditions. 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. In contrast, two elements are selectively coupled by a clutch when the clutch constrains them to rotate as a unit whenever the clutch is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. Clutches include actively controlled devices such as hydraulically or electrically actuated clutches and passive devices such as one way clutches. A clutch that holds an element against rotation by selectively connecting the element to the housing may be called a brake.

An example transmission is schematically illustrated in FIG. 1 . The transmission utilizes four simple planetary gear sets 20 , 30 , 40 , and 50 . A simple planetary gear set is a type of fixed gearing arrangement. 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. A simple planetary gear set imposes a fixed speed relationship. The speed of the carrier is constrained to be between the speed of the sun gear and the speed of the ring gear. (This relationship is defined to include the condition in which all three rotate at the same speed.) More specifically, the speed of the carrier is a weighted average of the speed of the sun gear and the speed of the ring gear with weighting factors determined by the number of teeth on each gear. Similar speed relationships are imposed by other known types of fixed gearing arrangements. For example, a double pinion planetary gear set constrains the speed of the ring gear to be a weighted average between the speed of the sun gear and the speed of 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.

In the transmission of FIG. 1 , sun gear 26 is fixedly coupled to sun gear 36 , carrier 22 is fixedly couple to ring gear 58 , ring gear 38 is fixedly coupled to sun gear 46 , ring gear 48 is fixedly coupled to sun gear 56 , input shaft 60 is fixedly coupled to carrier 32 , and output shaft 62 is fixedly coupled to carrier 52 . Ring gear 28 is selectively held against rotation by brake 66 and sun gears 26 and 36 are selectively held against rotation by brake 68 . Input shaft 60 is selectively coupled to ring gear 48 and sun gear 56 by clutch 70 . Intermediate shaft 64 is selectively coupled to carrier 42 by clutch 72 , selectively coupled to carrier 22 and ring gear 58 by clutch 74 , and selectively coupled to ring gear 38 and sun gear 46 by clutch 76 .

As shown in Table 2, engaging the clutches and brakes in combinations of four establishes ten forward speed ratios and one reverse speed ratio between input shaft 60 and output shaft 62 . An X indicates that the clutch is required to establish the speed ratio. An (X) indicates the clutch can be applied but is not required. In 1 St gear, either clutch 74 or clutch 76 can be applied instead of applying clutch 72 without changing the speed ratio. When the gear sets have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in Table 2.

Another example transmission is illustrated in FIG. 2 . In this transmission, intermediate shaft 64 is fixedly coupled to carrier 42 and ring gear 48 is selectively coupled to sun gear 56 by clutch 72 ′. The remaining features are as described with regard to the transmission of FIG. 1 . Clutch 72 ′ is applied in the same ratios as clutch 72 of FIG. 1 .

A third example transmission is illustrated in FIG. 3 . In this transmission, clutch 78 selectively couples carrier 22 and ring gear 58 to carrier 42 , clutch 80 selectively couples carrier 22 and ring gear 58 to ring gear 38 and sun gear 46 , and clutch 82 selectively couples ring gear 38 and sun gear 46 to carrier 42 . This module of three clutches, like the module of clutches 72 , 74 , and 76 in FIG. 1 , permits the selective coupling any two of the three rotating elements. In the transmission of FIG. 1 , selectively coupling two elements is accomplished by engaging two clutches, thereby coupling each element to intermediate shaft 64 . In the transmission of FIG. 3 , a single clutch is engaged to selectively couple two elements. As shown in Table 3, engaging the clutches and brakes of FIG. 3 in combinations of three establishes ten forward speed ratios and one reverse speed ratio between input shaft 60 and output shaft 62 . When the gears have the same number of teeth as the corresponding gears in FIGS. 1 and 2 , the resulting speed ratios are identical.

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.