Patent Application
20180180111
The present disclosure relates to a wedge clutch for selectively coupling two or more powertrain components to each other.
In a motor vehicle, a four-wheel drive system or an all-wheel drive system can be selectively activated by a clutch. The clutch can be part of a power transfer unit for connecting a power source to a secondary drive shaft when it is desired to deliver power to the secondary drive shaft. It is known that such a clutch can be a dog clutch. Dog clutches are prone to teeth clash or blocking. It is also known that such a clutch can be a wet clutch in a differential. Pressurized fluid must be continuously supplied to keep the clutches in a closed mode, adding to the power usage associated with usage of the clutch. Wedge clutches are known, such as those described in U.S. Patent Publication Numbers 2015/0083539, 2015/0014113, and 2015/0152921.
According to one embodiment, a wedge clutch includes a hub configured to rotate about an axis. The hub has a tapered surface facing the axis. A rotatable member is configured to rotate about the axis and has a groove facing away from the axis. A disk is configured to radially expand and contract about the axis. The disk has an outer surface facing the tapered surface of the hub, and an inner surface facing the groove of the rotatable member. Axial movement of the hub along the axis toward the rotatable member slides the tapered surface of the hub along the outer surface of the disk to move the inner surface of the disk toward the groove of the rotatable member to frictionally engage the hub and the rotatable member.
The disk may include a plurality of disk segments arranged annularly about the axis. A retainer ring may be coupled to the disk segments to provide a biasing force to force the disk segments radially outward from the axis. The disk segments may collectively define an annular shoulder with an annular groove defined therein, and the retainer ring may be disposed in the annular groove.
The tapered hub surface may be tapered away from the axis toward the rotatable member. The disk outer surface may be correspondingly tapered away from the axis toward the rotatable member.
The hub may have an inner surface with spline surface features for spline-connecting the hub to a shaft extending along the axis while enabling axial movement of the hub along the shaft.
The rotatable member may be a ring gear having teeth disposed radially outward from the hub.
According to another embodiment, a clutch includes a first rotatable member rotatable about an axis and having an inner surface facing the axis. A second rotatable member is rotatable about the axis and has an outer surface facing the inner surface of the first rotatable member. The outer surface has a groove defined therein. A wedge plate is compressible and expandable toward and away from the axis. The wedge plate has an outer surface disposed on the inner surface of the first rotatable member. The wedge plate also has an inner surface selectively engagable with the groove to selectively engage the first rotatable member with the second rotatable member.
According to another embodiment, a wedge clutch includes a first race having an outer circumferential surface with a groove. A second race has a tapered inner circumferential surface located radially outward from the groove. The second race is translatable along an axis relative to the first race. A wedge plate is disposed radially between the inner and outer races. The wedge plate has an inner circumferential surface configured to engage with the groove and a tapered outer circumferential surface configured to engage with the tapered inner circumferential surface of the second race.
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 embodiments. 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.
Referring to
In one embodiment, a shaft 12 acts as an input member to input torque into the wedge clutch 10 from an engine of the vehicle. To activate all-wheel drive or four-wheel drive, the wedge clutch 10 is controlled to close in order to transfer torque from the shaft 12 to an output member 14 (which may be referred to as an inner race or a first race), which is coupled to the all-wheel drive or four-wheel drive system. In one example, the output member 14 is a ring gear with external teeth that engage a corresponding gear of the all-wheel or four-wheel drive system.
Both the shaft 12 and the output member 14 may be supported by a housing for rotation about an axis 16. The output member 14 may be supported for rotation about the axis via bearing 18. When no torque is transmitted to the output member 14, the output member 14 may freely rotate about the shaft via the bearing 18 irrespective of the rotation of the shaft 12. Alternatively, when the wedge clutch 10 is closed to transmit torque to the output member 14, the output member 14 is fixed to rotate with the shaft 12, as will be described below. The output member 14 may be driveably connected to a transmission output shaft. Two components are driveably connected if they are connected by a power flow path that constrains their rotational speeds to be proportional.
The wedge clutch 10 includes a hub 20 (which may be referred to as an outer race or a second race) that is coupled to the shaft 12 via a spline connection, generally shown at 22. For example, the hub 20 may include an inner surface facing the shaft 12 that includes spline surface features that engage with corresponding spline surface features on an outer surface of the shaft 12. While fixing the hub 20 and the shaft 12 radially with respect to one another, the spline connection also enables relative axial movement of the hub 20 relative to the outer surface of the shaft 12.
The hub 20 includes an inner surface 26 that circumferentially extends about the axis 16 and faces the axis 16. Likewise, the output member 14 includes an outer surface 28 that circumferentially extends about the axis 16 and faces the inner surface 26. A wedge plate 30 is disposed between the inner surface 26 and the outer surface 28. The wedge plate 30 may be an annular disk or a group of separable disks segments connected together. As will be described below in greater detail, the wedge plate 30 includes an outer surface 32 facing away from the axis 16 that is slideably disposed on the inner surface 26, and an inner surface 34 facing toward the axis 16 that is configured to move into an out of engagement with the outer surface 28 of the output member 14. When the inner surface 34 of the wedge plate 30 engages the inner, angled surface of the groove 50 of the output member 14, the clutch may be closed and torque may be transmitted through the wedge clutch 10; when the inner surface 34 of the wedge plate 30 is spaced from or disengaged from the groove 50 of the output member 14, the clutch may be open and the torque may not be transmitted through the wedge clutch 10. It should be noted that in one embodiment, the wedge plate 30 and the groove 50 are shaped such that the inner surface 34 of the wedge plate is only able to contact the angled surfaces of the groove 50 but not other portions of the outer surface 28 of the output member 14.
The outer surface 32 of the wedge plate 30, or the outer surface of each wedge plate segment 40, is tapered. As shown in
Locking and unlocking of the wedge clutch 10 will now be described with reference to
In the unlocked position illustrated in
In the locked position illustrated in
When the hub 20 has moved a sufficient distance along the shaft 12, the inner surface 34 of the wedge plate segments 40 is pressed radially inward into and against the groove 50 of the output member 14. This allows torque or power to be transferred from the wedge plate segments 40 to the output member 14 at the interface of the inner surface 34 and the groove 50. The transfer of torque to the output member 14 causes the output member 14 to increase in speed to match that of the hub 20. Once the speeds of the output member 14 and the hub 20 are matched, the clutch is considered to be locked.
The outer surface 32 of each wedge segment 40 may also be provided with a cam surface 58 with an apex. In other words, the outer surface 32 may be tapered circumferentially such that an apex of the cam surface (indicated at 58) is located radially outward from the remainder of the outer surface 32. This cam surface 58 engages with a corresponding cam receptacle formed in the inner surface 26 of the hub 20. In other words, the inner surface 26 may be tapered circumferentially similar to the circumferential taper of the outer surface 32 of the wedge segments. As explained above, when the hub 20 slides axially to lock the wedge clutch, the wedge segments 40 are compressed into the groove 50 of the rotatable member 14. When pressed into the groove 50, the wedge segments 40 are biased to or may attempt to move with the rotatable member 14, but the hub 20 does not. The circumferential tapers and cam surface 58 force the wedge segments 58 to rotate about the axis with respect to the hub 20 as the hub 20 moves axially. As the wedge segments 40 rotate relative to the hub 20, the circumferential tapers compress the wedge plate further into the groove 50 to hold a higher amount of torque than the axial displacement alone. When in the locked position, each cam surface 58 is wedged within a respective cam receptacle. This inhibits rotation of the wedge plates with respect to the hub 20 when the wedge plate is locked. The inner surface 26 of the hub 20 removes lash from the wedge clutch system and the cam surface 58 creates a wedge effect to lock or couple the powertrain components to transfer power.
It should also be understood that the relative radial locations of the hub and the output member may be swapped, such that the hub includes a groove on its outer surface for engagement with the wedge plate, and the output member includes a tapered inner surface for sliding engagement with the wedge plate. In such an embodiment, the output member can be translatable along the axis and the hub can be fixed to the shaft.
The wedge clutch described in the various embodiments above is designed to combat centrifugal force. More specifically, implementing a taper on the outer surface of the wedge plate and the groove on the outer surface of the hub (as opposed to having a taper on the inner surface of the wedge plate and the groove on an inner surface of the hub) can inhibit unintentional lock-up which could otherwise be caused by centrifugal force of the spinning components forcing the wedge plate outward into engagement with the groove. The retainer ring is biased to press the wedge plate segments radially outward even without the presence of a centrifugal force.
The wedge clutch described in the various embodiments also improves torque capabilities. Having the taper on the inner surface (as opposed to the outer surface) of the wedge plate has a potential to limit torque capabilities due to the inner surface of the wedge plate segments being an area of high stress. Moving the taper to the outer surface of the wedge plate segments creates a larger circumference and surface area of engagement between the wedge plate segments and the groove, making it possible to carry higher torque under the same contact force at the same stress level.
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, to the extent any embodiments are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and can be desirable for particular applications.
