GB2321504A - Friction slip clutch - Google Patents

Abstract

A friction slip clutch 20 comprises a first ring 24 and two inner rings 31a, 31b each having frusto-conical clutch surfaces 41a, 35, 41b, 36 engaging one another. The amount of friction force generated, normal to the clutch surfaces 41a, 35, 41b, 36, is varied by adjustment member 56 so that as the force is increased, by the inner rings 31a, 31b being pushed closer together, either the outer ring 24 and/or the inner rings 31a, 31b radially resiliently deflect, eg expand or contract depending upon which ring is selected. Rings 24, 31a, 31b, because of their ability to resiliently expand/contract, replaces a resilient member and effectively act as a spring member between adjustment member 56 and clutch surfaces 41a, 35, 41b, 36 which makes setting of clutch slip torque less critical. The radial expansion/contraction of the rings 24, 31a, 31b is accommodated by splines 27, 38, 59, 43a, 43b which constrains the rings 24, 31a, 31b to rotate with shafts 21, 22 while allowing the rings 24, 31a and 31b to move axially.

Description

2321504 FRICTION SLIP CLUTCH APPARATUS The present invention relates

generally to the field of slip clutches for limiting the amount of torque transmitted from one member to another, and, more particularly, to an improved friction slip clutch in which two facing frusto-conical surfaces are adapted to bear against one another in such a way that at least one of those surfaces may deflect in a radial direction in response to a change in the normal force acting between the frusto-conical sur faces.

A slip clutch is normally employed between two members that are capable of rotating relative to one another. These two members may be operatively coupled by a slip clutch so as to limit the amount of torque transmitted from one member to the other. Axial ly-loaded frusto-conical clutch faces are well known and are used for their inherent capabili ty of providing an effective multiplication of the axial loading force applied to establish the friction-producing normal force acting on the circumferential slip faces of the clutch ele ments. The devices shown in U.S. Patents No. 804,778, 1,373,810, 3,648, 483, 4,652,249, 5,163.541 and 2,763,141 illustrate various types of friction clutches having facing frusto conical surfaces acting between the members. All of these references show some sort of axial spring or resilient member acting in series with the load-adjusting mechanism in order to make the setting less critical and to minimize any change in the desired clutch slip torque as a result of thermal expansion induced by the heat generated from clutch slipping.

However, when it is desired to change the normal force acting between the two frusto-conical surfaces so as to vary the amount of friction between the surfaces, and hence the maximum torque that may be transmitted from one member to the other, it is believed that the prior art arrangements did not accommodate, or provide for, radial deflection of the surfaces in response to the change in normal force acting thereon.

According to the invention, there is provided a friction slip clutch apparatus adapted to transfer torque from a first member to a second member and for selectively allowing relative rotation between said members when said torque equals an adjustable predetermined value, said first member having a first portion provided with a first frusto-conical surface arranged to face said second member, said second member having a second portion provided with a second frusto-conical surface coaxial with and arranged to bear against said first frusto-conical surface, said apparatus also having an adjustment member mounted on one of said first and second members for controlled movement toward and away from the associated portion on said one member, and an element functioning as a spring such that movement of said adjustment member relative to said associated portion causes a proportional variation of the normal force acting between said first and second frusto-conical surfaces, wherein said one of said first and second members is so configured and arranged as to permit radial movement of at least one of said surfaces in response to a change in the normal force acting between said surfaces, such that said one member acts as said element functioning as a spring.

Preferably, the radial movement in response to the change in normal force over the full adjustment range is much larger than that attributable to thermal expansion occasioned by heat generated when the frusto-conical surfaces slip relative to one another.

The first member preferably includes a first shaft and a first ring, the first ring being provided with the first frusto-conical surface and being mounted on the first shaft for deflective radial movement relative thereto. The second member preferably includes a second shaft and a second ring, the second ring being provided with the second frusto conical surface and being mounted on the second shaft for deflective radial movement relative thereto.

The first ring is preferably configured such that the radius of a circular line in the first frusto-conical surface changes proportionally in response to change in the normal force acting between the frusto-conical surfaces, and wherein the force- to-radius response constitutes the spring rate of the element.

In a preferred embodiment, the one of the first and second members also has an axial abutment stop, and at least one of the portions is operatively arranged to be axially compressed between the abutment stop and the adjustment member so as to vary the normal force acting between the frusto-conical surfaces, and to cause such radial movement of at least one of the surfaces.

The invention thus provides an improved friction slip clutch having facing frusto conical surfaces that are operatively arranged to bear against one another, with means for varying the normal force acting between these frusto-conical surfaces so as to vary the maximum torque transmitted from one member to another member, said means axially displacing one of the members so as to cause a corresponding radial deflection of its frusto-conical surface, and such radial deflection being accommodated so that the member will function as a spring.

An embodiment of a friction slip clutch in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a fragmentary longitudinal vertical sectional view of an improved friction slip clutch according to the present invention, this view showing the first member as including a second shaft and two second rings, and further illustrating spline connections between the various rings and the shafts on which they are mounted; Fig. 2 is a fragmentary transverse vertical sectional view thereof, taken generally on line 22 of Fig. 1, and particularly showing the spline connections between the rings and the shafts on which they are mounted; Fig. 3 is an enlarged fragmentary vertical sectional view of the upper portion of the improved friction slip clutch shown in Fig. 1, this view illustrating the position of the first and second rings when the adjustment member is in one axial position relative to the abutment stop; and, Fig. 4 is an enlarged fragmentary vertical sectional view thereof, generally similar to Fig. 3, but showing the adjustment member as having been moved axially toward the abutment member, with the second rings having been moved closer to one another, and showing the first and second rings as having deflected radially outwardly and inwardly, respectively, relative to the shafts on which they are mounted.

At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions, or surfaces, consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion. degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms "horizontal", "vertical", "left", "right", "up", and "down", as well as adjectival and adverbial derivatives thereof (e.g., "horizontally", "rightwardly", "upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and.1 outwardly" generally refer to the orientation of a surface relative to its axis or elongation, or axis of rotation, as appropriate.

Turning now to the drawings, and. more particularly, to Fig. 1 thereof, the present invention broadly provides an improved friction slip clutch apparatus, of which the presently-preferred embodiment is generally indicated at 20. This apparatus is adapted to transfer torque from a leftward or first member, generally indicated at 2 1, to a rightward or second member, generally indicated at 22, and for selectively allowing relative rotation (i.e., slippage) between the members when the transmitted torque equals an adjustable predeter- mined value.

In the preferred embodiment. the first member 21 is shown as including a hori zontally-elongated first shaft 23 and a first or outer ring 24. The first shaft 23 is shown as having a tubular hollow cylindrical portion 25, which terminates in a radial ly-enlarged right marginal end portion 26. Portion 26 is shown as having a plurality of inwardly-facing circumferential] y-spaced spline grooves, severally indicated at 27, alternating with spline teeth 28. The right marginal end portion of first shaft 213 is journalled in a bearing 29.

The second member 22 is shown as having a horizontal ly-elongated tubular second shaft 30 with a pair of axially-spaced left and right second or inner rings 31a and 31b, respectively.

As best shown in Figs. 3 and 4, the first ring 24 is shown as being an annular or ring-like member having an annular vertical left end face 32, an annular vertical right end face 33. an outwardly-facing horizontal cylindrical surface 34, an inwardly- and leftwardly facing frusto-conical surface 35 extending rightwardly and inwardly from the inner margin of left end face 32, and an inwardly- and rightward ly- facing frustoconical surface 36 con tinuing outwardly and rightwardly therefrom to join the inner margin of right end face 33.

A plurality of circumferential ly-spaced teeth. severally indicated at 38. extend radially out wardly from first ring outer surface 34. to be respectively received in first shaft slots or grooves 27. Thus, by virtue of the spline connection formed between teeth 38 and grooves 27. the first ring is constrained to rotate with the first shaft about horizontal axis x-.r. but is free to move radially inwardly and outwardly relative thereto within grooves 27.

Inner ring 3 la is shown as being an annular element having an annular vertical left end face 39a, an annular vertical right end face 40a, an outwardly- and rightwardly facing frusto-conical surface 40a joining the outer margins of these end faces, and an in wardly-facing horizontal cylindrical surface 42a joining the inner margins of these end faces. A plurality of circumferentially-spaced spline teeth, severally indicated at 43a, extend inwardly from inner surface 42a.

Ring member 30b is a mirror image of ring member 30a. Hence, to avoid duplication, the same reference numeral has been used to identify the corresponding parts, portions or surfaces of the right ring, with the suffix "b" being used to distinguish them from those of part 30a.

Second shaft 22 is shown as being a horizontally-elongated hollow or tubular member having an annular vertical left end face 44, an outwardly-facing horizontal cylin drical surface 45 extending rightwardly therefrom, a leftwardly-facing annular vertical sur face 46, an outwardly-facing horizontal cylindrical surface 47, a rightwardly-facing annular vertical surface 48, an outwardly-facing horizontal cylindrical surface 49, an externally threaded portion 50, and an outwardly-facing horizontal cylindrical surface 51 continuing rightwardly therefrom. As noted above, the second shaft is hollow, and has a blind axial hole bounded by a rightwardly- facing inner end face 52, and an inwardlyfacing horizontal cylindrical surface 53 continuing rightwardly therefrom.

The second shaft is journalled in a rightward bearing 54, and has its distal marginal end portion suitably journalled in a leftward bearing 55 acting between the first and second shafts.

An annular locking member, generally indicated at 56, is threaded on to second shaft threaded portion 50, and has an annular vertical left end face 58 operatively arranged to bear against the second ring right marginal end 39b. Second shaft surfaces 46, 47, 48 form a outwardly-extending annular lug, with surface 48 forming an abutment surface.

Thus, as the adjustment member 56 is rotated on threaded portion 50 so that adjustment surface 58 moves toward abutment surface 48, the two second rings 30a, 30b will be move axially toward one another. In this regard, it should be noted that a plurality of circumfer entially-spaced teeth, generally indicated at 59, extend radially outwardly from second shaft surface 49, and interfit in the grooves between the teeth 43a, 43b of the second rings 30a, 30b, respectively. Thus, it should be noted that each of second rings 30a, 30b is con strained to rotate with the second shaft, but may move independently inwardly and outward ly in a radial direction by virtue of the spline connections therewith.

Fig. 3 illustrates the initial condition of the apparatus. In this regard, it should be noted that there is an axial gap between the two Inner rings 30a, 30b, and that the rings are compressively engaged by abutment surface 48 and by adjustment member surface 58.

It should also be noted that the respective frusto-conical surfaces bear against one another.

in other words, surface 41a engages surface 35, and surface 41b engages surface 36. These various frusto-conical surfaces engage one another in area contact. Hence, a frictional force is developed between these frusto-conical surfaces which is directly proportional to the normal force acting therebetween.

This normal force may be varied by simply adjusting the position of adjustment member 56 relative to the abutment member. In other words, as comparatively illustrated in Figs. 3 and 4, if the adjustment member is caused to move toward the abutment member, the two second rings will be driven toward one another. This action operates to increase the normal force acting between the various facing frusto-conical surfaces, and causes the rings to respectively expand and contract radially in response. In other words, the outer ring 24 moves radially outwardly, this movement being accommodated by spline connection 27, 38, while the two inner rings move radially inwardly, this being accommodated by splines 43a, 59 and 43b, 59, as shown in Fig. 4. In other words, if the axial spacing between the abut ment surface 48 and adjustment member end face 58 is decreased from distance x, in Fig.

3 to a smaller distance x. in Fig. 4, this axial movement (i.e., Ax =x,x2) will cause the first ring to expand outwardly by a certain radial distanced,, and will also cause the two inner rings to contract radially inwardly, by a radial distance d2, as indicated in Fig. 4. In the illustrated drawings, the amount of radially outward movement is shown as being substan tially equal to the amount of radially inward movement. However, this need not invariably obtain. Indeed, dimensions and frictional contact between the engaged teeth of the splines may cause one of the frusto-conical surfaces to move a greater radial distance than the other.

In the mechanism just described, the radial expansion and contraction of the frusto-conical rings, as the rings are driven axially together by movement of the adjustment member, effectively constitutes the deflection of a spring element acting between the adjust ment member and the clutch surfaces. Such a spring element acts to make the adjustment less critical. The stiffness of the effective spring should be such that the amount of ring radial movement in response to the change in the normal force acting between the frusto conical surfaces over the full adjustment range is normally much larger than that attributable to thermal expansion occasioned by heat generated when the two frusto- conical surfaces slip relative to one another.

The present invention contemplates that many changes and modifications may be made. For example, in an alternative form, only one second ring might be provided.

Moreover, each ring may be formed integrally with its associated members. Alternatively, one ring may be formed separately and be movable relative to its shaft, whereas the other ring or rings may be formed integrally with its shaft, provided in any case that the rings are not constrained from radial deflection by such a formation. Connections, such as flexures, other than the specific type of spline connection may also be used. Suffice it to say here that the spline connection functions generally to accommodate such radial movement, while constraining the associated ring member to rotate with its associated shaft.

Unless otherwise indicated, the dimensions and materials of construction are not deemed critical (other than being consistent with the basic function of the slip clutch; i.e.. not galling under slip conditions). Nor is the particular shape or configuration of the first and second shafts, or the locking member, deemed to be critical to the invention.

Therefore, while a preferred form of the present invention has been shown and described, and several modifications thereof discussed, persons skilled in this art will appre ciated that various additional changes and modifications may be made, without departing from the scope of the invention, as defined and differentiated in the following claims.

Claims (6)

-8Claims

1 A friction slip clutch apparatus adapted to transfer torque from a first member to a second member and for selectively allowing relative rotation between said members when said torque equals an adjustable predetermined value, said first member having a first portion provided with a first frusto-conical surface arranged to face said second 5 member, said second member having a second portion provided with a second frustoconical surface coaxial with and arranged to bear against said first frusto-conical surface, said apparatus also having an adjustment member mounted on one of said first and second members for controlled movement toward and away from the associated portion on said one member, and an element functioning as a spring such that movement of said adjustment member relative to said associated portion causes a proportional variation of the normal force acting between said first and second frusto- conical surfaces, wherein said one of said first and second members is so configured and arranged as to permit radial movement of at least one of said surfaces in response to a change in the normal force acting between said surfaces, such that said one member acts as said element functioning as a spring.

2. A friction slip clutch as set forth in claim 1 wherein said first member includes a first shaft and a first ring, and wherein said first ring is provided with said first frusto-conical surface and is mounted on said first shaft for radial movement relative thereto.

3. A friction slip clutch as set forth in claim 2 wherein said second member includes a second shaft and a second ring, and wherein said second ring is provided with said second frusto-conical surface and is mounted on said second shaft for radial movement relative thereto.

4. A friction slip clutch as set forth in claim 2 wherein said first ring is configured such that the radius of a circular line on said first frusto-conical surface changes proportionally in response to changes in said normal force, and wherein such radius-to force response constitutes the spring rate of said element.

5. A friction slip clutch as set forth in claim 1 wherein one of said first and second members also has an axial abutment stop, and wherein at least one of said portions is arranged to be axially compressed between said abutment stop and said adjustment member so as to cause said radial movement.

6. A friction slip clutch according to claim 1, substantially as described with reference to the accompanying drawings.