This application claims benefit of the 06 April 201 1 filing date of United States provisional patent application number 61 /472,337.

FIELD OF THE INVENTION

This disclosure relates generally to the field of clutches, and more particularly to mechanical clutches that allow an input to drive an output without the application of electrical power, and that will freewheel when back-driven from output to input.

BACKGROUND OF THE INVENTION

Many types and sizes of clutches are known for selectively coupling a mechanical input to a mechanical output, particularly for the bi-directional transfer of rotational mechanical energy along a shaft. In certain applications, when the clutch is engaged to connect the input to the output, it is desired to allow for an occasional overrun condition where the output is forced, by some force other than the input, to move faster in the driven direction than the input. When such an overrun condition exists, it may be preferred for the input and output to become disengaged so that the output can freewheel, thereby avoiding the acceleration of the entire driveline by the back driven load.

One application of such a bidirectional clutch with freewheeling back drive capability is in an automotive closure, such as a power door or trunk lid. The drive line of such devices must be capable of freewheeling during a "slam event" when the operator of the vehicle accelerates the closure to a speed greater than that generated by the power actuation mechanism. One such device is described in United States Patent No. 5,755,059 titled "Solenoid Operated Clutch for Powered Sliding Door" and another is described in United States Patent No. 6,799,669 titled "Dynamic Clutch Control."

The present inventor has recognized that known solenoid operated and dynamically controlled clutches are relatively complicated and require electrical power input to the clutch, and thus they are relatively expensive to manufacture and difficult to incorporate into a vehicle design. Recognizing a need for a simpler, lower cost, yet highly reliable clutch mechanism, the present inventor has considered known roller ramp clutch designs, as illustrated in the partial cross-sectional view of FIG. 1 . A roller ramp clutch 10 generally incorporates an outer race 12 with a cylindrical inside surface, an inner race 14 having an outside surface with wedge shaped friction faces, and locking rollers 16 interspaced within the wedge shaped regions 18 between the two. The locking rollers 16 are individually spring 20 loaded to provide constant contact between the rollers 1 6 and the races 1 2,14 in order to ensure proper and rapid engagement and disengagement of the clutch. FIG. 1 illustrates the clutch 10 in its engaged condition where the inner race 14 is being rotated counter-clockwise in this view and the roller 16 is forced into the smaller end of the wedge shaped region 18, becoming wedged therein and causing the outer race 12 to rotate in the counterclockwise direction along with the inner race 14. When the outer race 12 is accelerated beyond the speed of the inner race 14 in the counter-clockwise direction (not illustrated), the roller 16 will move into the wider end of the wedge shaped region 18 and allowing the outer race 12 and inner race 14 to rotate independently. While such clutches provide the desired functionality, they are relatively expensive due to their complicated design and large number of small, precisely dimensioned parts.

Another known type of bi-directional clutch 22 with freewheeling back drive capability is used in the driveline of all-terrain vehicles, as illustrated in FIG. 2. An input cam 24 is surrounded by a precision-machined roller cage 26. The roll cage 26 includes a plurality of fingers extending from a back plate to define a plurality of openings for the respective rollers 28. A circumferential groove 30 is formed in the outer surface of the cage, and a corresponding groove 32 is formed in each of the rollers 28. As with other roller ramp clutches, the clutch 22 is engaged when the input cam 24 is rotated relative to the cage 26 to urge the rollers 28 radially outward to engage a surrounding wheel hub (not shown). A spring member 34 is disposed within the cage and roller grooves 30, 32 to urge the rollers 28 inward to disengage the clutch 22 when the input cam 24 is unloaded. BRIEF DESCRIPTION OF THE DRAWINGS

The following description may be appreciated in view of the drawings that show:

FIG1 . 1 is a partial cross-sectional view of a prior art roller ramp clutch in the engaged condition.

FIG. 2 is a perspective view of another prior art roller ramp clutch.

FIG. 3 is a sectional view of a first embodiment of a clutch.

FIG. 4 is an axial cross-sectional view of the clutch of FIG. 3.

FIGs. 5A, 5B and 5C are perspective, end and side sectional views respectively of the right cage member of the clutch of FIG 3.

FIG. 6A, 6B and 6C are perspective, end and side views respectively of the input member of the clutch of FIG 3.

FIG. 7A, 7B and 7C are perspective, end and side sectional views respectively of the output member of the clutch of FIG 3.

FIG. 8 is a perspective view of a clutch in accordance with a further embodiment of a clutch.

FIGs. 9A, 9B and 9C are perspective, end and side sectional views respectively of the right cage member of the clutch of FIG 8.

DETAILED DESCRIPTION OF THE INVENTION

The present inventor has recognized that, while the prior art design of FIG. 2 requires fewer parts than the design of FIG. 1 , it is disadvantaged by requiring the spring member 34 to be in direct contact with the rollers 28, and furthermore, it requires that both the cage 26 and the rollers 28 be machined with aligned grooves 30, 32 to receive and to retain the spring member 34. The present inventor has developed a clutch which provides the desired drive and freewheeling functions while overcoming the disadvantages of the prior art designs. The present clutch can be embodied with a low number of parts and with parts that can operate effectively with less dimensional precision than is necessary with prior art devices. Consequently, the present clutch is expected to be of less complex construction and less costly, yet more reliable than prior art devices. A clutch 40 in accordance with one embodiment is illustrated in FIGs. 3, 4, 5A- 5C, 6A-6C and 7A-7C. FIG. 3 shows the clutch 40 as viewed looking along an axis of rotation R of the device and FIG. 4 is a sectional view along that axis. The clutch 40 includes an input member 42 that is rotated by a drive mechanism such as an electric motor (not shown), and an output member 44. The output member 44 has a cylindrical inner surface 46, while input member 42 has an outer surface 48 that is formed as a cam having a plurality of radially extending bulges 50 disposed between relatively flat areas 52. A cage 54 having a plurality of fingers 56 is disposed between the input member 42 and output member 44. Further details of the cage member 54 are shown in FIGs. 5A, 5B, 5C, further details of the input member 42 are shown in 6A, 6B, 6C, and further details of the output member 44 are shown in 7A, 7B, and 7C as may be appreciated in view of the description that follows.

The cage 54 includes a plurality of relatively sloped surfaces defining a plurality of wedge shaped regions 58. A roller 60 is disposed within each of the wedge shaped regions 58. When the input member 42 is positioned such that the rollers 60 rest on the flat areas 52 of the cam shape, the rollers 60 do not protrude beyond the outer circumference of the cage 54 and the input member 42 is disengaged from the output member 44. However, when the input member 42 is rotated relative to the output member 44 such that the rollers 60 move relative to the input member 42 to a position in which the rollers 60 engage (i.e., are supported by) the cam bulges 50 on the input member 42, the rollers 60 are urged radially outwardly within the tapered confines of the wedge shaped regions 58 and protrude beyond the outer circumference of the cage 54 to come into contact with the inner surface 46 of the output member 44. As the input member 42 continues to turn and the rollers 60 become wedged into hard contact against the output member 44 and the cage 54, the clutch 40 engages causing the output member 44 to rotate together with the input member 42. One will appreciate that the clutch 40 is thereby completely self-actuating to engage the input with the output without the application of any electrical power to the clutch.

When the input member 42 is not being driven against the output member 44, or when the output member 44 is being driven at a faster rotational speed than the input member 42, the force of the cam bulges 50 against the rollers 60 is removed and the rollers 60 can then be urged inward by a structure that is best appreciated with reference to the axial cross-sectional view of the clutch 40 shown in FIG. 4. In this view, it can be seen that the cage 54 is actually formed of two cooperating cage members 54, called a left cage member 54L and a right cage 54R member for discussion herein when viewing FIG. 4. In this embodiment, the two cage members 54L, 54R are identical 54 and are installed in mirror-image positions. Each of the cage members 54 has a plurality of sloped surfaces 62 which are angled with respect to a radius of the device. Cooperating pairs of the surfaces 62L, 62R, one surface 62 from each cage member 54 in each pair, are sloped relative to each other and to a radial direction, such that each surface 62L, 62R makes contact with a respective end of each respective roller 60. When the input force is removed or when the output member 44 is rotated at a speed greater than the rotational speed of the input member 42, the relatively sloped surfaces 62L, 62R of each respective pair are urged together by an elastic member, which in this embodiment is in the form of a wave spring 64. As a result, the rollers 60 are urged radially inwardly by the slope of the surfaces 62. In this manner, a single wave spring 64 is operable to disengage or to freewheel the clutch 40 by drawing together the two cage members 54L, 54R and their respective cooperating sloped surfaces 62L, 62R, which in turn results in the simultaneous inward movement of all of the rollers 60 (four rollers in the illustrated embodiment). The wave spring 64 is disposed between a flanged end 66 of the output member 44 and a shoulder 68 formed on the right cage member 54R. A compressive force opposing the wave spring compression force is applied as a pre-load against the end surface of the left cage member by a structural member (not shown) into which the clutch 40 is installed.

Radial reaction forces are applied against the clutch 40 by the surrounding structural members around the outside circumference of the exposed ends of the two cage members. Since the cage members 54 act as bearings in relation to the surrounding structural members, the input member 42, and the output member 44, they may be formed of an oil-impregnated powdered metal material, or a plastic bearing material, or a bronze bushing material in various embodiments, for example. Low friction surfaces, such as Teflon ^® coatings or washers, may be used as desired to reduce friction and to extend wear between relatively moving portions of the clutch 40 and surrounding structures.

It will be appreciated that the input member 42 and output member 44 may be formed of any suitable material such as a metal alloy, plastic or powdered metal, and they may be formed to include a spline, notch, hex shape or other means for engaging the drive source and driven load. The rollers 60 may be formed to have a small taper or radius around the outer circumference at both ends where the rollers 60 contact the cage side tapering surfaces 62. All parts can be formed to near net shape (i.e. cast directly to a final shape which needs little or no finish machining), thereby reducing the cost of the clutch 40. An optional retaining ring 70 may be provided to maintain the clutch 40 as an assembled unit prior to it being installed into a surrounding structure, although the retaining ring would not be intended to make contact with the left cage member 54L or to carry any load once the clutch 40 is pre-loaded into its intended use position against the surrounding structures.

Another embodiment of a clutch 80 is illustrated in perspective view in FIG. 8.

The input member 82 of this embodiment is shown in part in FIG. 8 and it is can be generally the same structure as that illustrated by input member 42 in FIGs. 6A-6C. The output member of this embodiment is not illustrated, but may be generally the same structure as that illustrated in FIGs. 7A-7C. The embodiment of FIG. 8 also includes a cage 84 formed of two cooperating cage members, described herein as the left and right cage members 84L, 84R when viewing FIG. 8.

Details of the right cage member 84R are provided in FIGs. 9A, 9B and 9C, and in this embodiment, the two cage members are identical and are installed in mirror image positions. For the illustrated embodiment of a clutch 80 incorporating four rollers 86, each cage member 84 is formed to have two fingers 88 extending axially from a hub portion 90. At the end of each finger 88 is an axially extending tab 92 having a radially extending pillar 94. The radially inner surface of the finger 88 is formed to fit over an outer circumferential surface of the hub 90 of the opposed cage member when the clutch 80 is assembled as shown in FIG. 8. The hub member 90 also includes a radially extending pillar 96 which is disposed proximate the pillar 94 extending from the finger 88 of the opposed cage member, to create four pairs of closely positioned pillars 94, 96 for the four roller embodiment of FIG. 8. The two cage members 84L, 84R cooperate to define wedge shaped openings having relatively sloped surfaces for receiving respective rollers 86, and those surfaces are urged toward each other when an elastic member 98 is connected between respective ones of the closely positioned pillars 94, 96.

In the presence of driving force from the input member 82, the cam bulges force the rollers 86 outward to make contact with the output member (not shown), and in the process, the sloped surfaces of the wedge shaped openings are forced farther apart causing relative rotation of the two cage members 84L, 84R about the central drive axis. This rotation causes respective ones of the closely positioned pillars 94, 96 to move away from each other, thereby stretching the elastic member 98 connected there between. Once the input driving force is removed, or when the output is accelerated beyond the speed of the input, the elastic members 98 draw the closely positioned pillar pairs 94, 96 together, thereby moving the relatively sloped surfaces together against the rollers 86, which in turn moves the rollers 86 radially inward to allow the clutch 80 to freewheel. It will be appreciated that the relative movement of the cooperating cage members 54L, 54R in the embodiment of FIGs 3-4 is in an axial direction wherein sloped surfaces of the cage members act on ends of the roller 60, whereas in the embodiment of FIG. 8, the relative movement of the cooperating cage members 84L, 84R is in a rotational direction about the drive axis wherein sloped surfaces of the cage members 84L, 84R act on the longitudinal surface of the rollers 86.

The elastic members in various embodiments may be elastic bands 98 or springs 64, for example. In one embodiment of rotationally moving cage members 84, the elastic members are springs having at least one turn wound around the circumference of the hub 90 with tangs on the opposed ends, wherein the tang on one end is engaged with the hub 90 of a first of the cage members and the tang on the other end is engaged with the finger 88 of a second of the cage members.

While various embodiments have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the inventive concepts disclosed herein. For example, the cage may be formed of more than two members, any number of rollers and fingers may be used, and any number of spring members may be placed in various positions to act upon the cage members. Clutches may be embodied in mono-directional or bi-directional drive and freewheeling applications. The relative positions of the input and output members may be reversed and the cam may be formed on either of these. The roller may be bar shaped or ball shaped. Spring members of various types may be used. Accordingly, it is intended that the concepts disclosed be limited only by the spirit and scope of the appended claims.