GB2426311A

GB2426311A - A rotational drive assembly

Info

Publication number: GB2426311A
Application number: GB0510214A
Authority: GB
Inventors: Christopher Paulet Mel Walters
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-05-18
Filing date: 2005-05-18
Publication date: 2006-11-22
Also published as: GB0510214D0

Abstract

A rotational drive assembly comprise a rotational drive component 2 supported on a hub 6, the component comprising a ring 2 and a plurality (preferably more than eight) of resilient projections 12 extending radially inwardly of the ring 2, the inner ends of the projections 12 being located with respect to the hub 6 so that rotation of the ring relative 2 to the hub 6 causes resilient deflection of the projections 12, said assembly also having friction damping means 20, 22, 28, 30 provided between the hub 6 and the ring 2 which serve to damp rotational oscillations of the ring 2 relative to the hub 6. The assembly may be a gear wheel 2, while friction damping means may be provided by friction rings 22, 30 pressed against the gear wheel 2 by Belleville springs 20, 28. The hub may have lubricant supply passages. Bolts may hold the assembly together.

Description

A ROTATIONAL DRIVE ASSEMBLY

This invention relates to a rotational drive assembly and is particularly, although not exclusively, concerned with a rotational drive assembly in the form of a gear wheel assembly, for example for transmitting drive between components of an internal combustion engine. The present invention may also be applied to other forms of drive assembly, for example chain and sprocket drives and pulley drives.

In many mechanisms such as internal combustion engines, drive is transmitted to or from a part of the mechanism which is subject to fluctuating torque. An example is the camshaft drive in an internal combustion engine. The input from the crankshaft is subject to torque fluctuations as a result of the firing of the individual cylinders and the output to the camshaft is subject to torque fluctuations as a result of the varying reaction forces generated during valve operation. It is desirable to prevent the transmission of these torque fluctuations between the input and the output.

According to the present invention there is provided a rotational drive assembly comprising a rotational drive component supported on a hub, the component comprising a ring and a plurality of resilient projections extending radially inwardly of the ring, the inner ends of the projections being located with respect to the hub so that rotation of the ring relatively to the hub causes resilient deflection of the projections, friction damping means being provided which acts between the hub and the ring to damp rotational oscillations of the ring relative to the hub.

Tuning of the damping characteristics of the assembly to suit the conditions under which the assembly operates can be achieved by varying the friction applied by the friction damping means, and by appropriate design of the flexural characteristics of the projections. In a preferred embodiment, the projections may taper in the radially inwards direction. The projections may be located with respect to the hub by engagement of the ends of the projections in respective recesses in the hub. The radially inwards ends of the projections may have enlarged heads which engage the respective recesses.

The hub may be provided with lubricant supply passages which open into the recesses.

The supply of lubricant to radially outer parts of the assembly may be achieved by permitting the flow of lubricant from the lubricant supply passages past the inner ends of the projections. The resilient deflection of the projections may cause movement of the region of contact between the inner ends of the projections and the recesses to vary the flow area for lubricant past the inner ends of the projections. For example, flexure of the projections may increase the flow area for lubricant.

In a preferred embodiment in accordance with the present invention, a relatively large number of projections is provided. For example, there may be at least eight, and more preferably at least twenty, of the projections.

The friction damping means may comprise a friction ring which is mounted for rotation with the hub and frictionally engages the ring of the rotational drive component. The frictional contact between the friction ring and the ring of the rotational drive component preferably occurs at a position radially outwards of the projections. A resilient element may be rotationally secured to the hub at an inner region of the resilient element, and may engage the friction ring at an outer region in order to bias the friction ring into frictional engagement with the ring of the rotational drive component.

The inner region of the resilient element may be clamped to a radial face of the hub.

The friction ring and the resilient element may be rotationally interlocked with each other, for example by dogs provided on the friction ring and complementary recesses formed in the resilient element. The dogs and recesses may have rectangular profiles so that both radial and circumferential forces can be transmitted between them.

The friction ring is preferably disposed between opposed circumferential surfaces on the ring of the component and the resilient element. This enables the friction ring to transmit radial forces to the resilient element and thence to the hub, thus avoiding the need for the resilient projections to withstand radial forces.

The resilient element is preferably in the form of a disc, such as a Belleville spring.

In a preferred embodiment, similar friction rings are provided on both axial sides of the rotational drive component. Also, similar resilient elements may be provided to bias the friction rings into contact with the rotational drive component.

The hub may be provided with a further rotational drive component to enable rotational drive to be input to or taken off the hub. The further rotational drive component may be secured to the hub, for example with its inner periphery supported on an outer face of an axial projection of the hub. The securing of the further rotational drive component to the hub may be achieved by bolts which extend through openings at the interface between the further rotational drive component and the hub. The bolts may be tapered bolts. The inner region of the resilient element may be clamped between radial faces of the hub and the further rotational drive component, in which case the inner periphery of the resilient element may be notched to receive the bolts. In a preferred embodiment, the rotational drive components are gear wheels having gear teeth at their outer peripheries.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is an exploded isometric view of a gear assembly; Figure 2 shows one axial end view of the assembled gear assembly; Figure 3 is a sectional view taken on the line A-A in Figure 2; Figure 4 is an enlarged view of the region G in Figure 3; Figure 5 corresponds to Figure 4, but shows a region on the line H-H; Figure 6 is a view in the direction of the arrow C in Figure 3; Figure 7 is a sectional view taken on the line E- E in Figure 3; Figure 8 is a sectional view taken on the line B-B in Figure 3; Figure 9 is an enlarged view of the region D in Figure 8; Figure 10 is a further enlarged view of the region shown in Figure 9, illustrating the assembly under torsion; Figure 11 corresponds to Figure 7 but shows an alternative embodiment; Figure 12 is an enlarged view of the region F in Figure 11; and Figure 13 is a sectional view on the line J-J in Figure 12.

The assembly shown in Figure 1 comprises first and second externally toothed gear wheels 2, 4 supported on a hub 6. The hub has an outer periphery 8 provided with recesses 10, which receive respective projections 12 extending inwardly from an outer ring 14 of the first gear 2. The projections 12 are formed integrally with the rest of the gearwheel 2. The hub 6 has an axial projection 16 which supports the second gear wheel 4. There is a radial shoulder 18 between the projection 16 and the outer periphery 8, and a Belleville spring 20 is clamped against this radial shoulder 18 by the second gear wheel 4. A friction ring 22 is retained between the Belleville spring 20 and the first gear wheel 2, in a recess 24 formed in the ring 14.

The hub 6 has a boss 26 extending in the direction away from the second gear wheel 4. A further Belleville spring 28 is located on the boss 26, and retains a further friction ring 30.

The assembly is held together by tapered bolts 32. As will be appreciated from Figure 1, the inner peripheries of the second gear wheel 4 and the Belleville spring 20 have part-circular recesses or notches 34, 36 which are complementary to corresponding part-circular recesses 38 formed on the projection 16. The part-circular recesses 38 lead into holes 40 through the hub 6, and these holes 40 correspond to screw threaded holes 32 in the second Belleville spring 28. When the second gear wheel 4 and the Belleville spring 20 are fitted over the projection 16, the recesses 34 and 36 coincide with the recesses 38 which receive the bolts 32. The bolts 32 also pass through the holes 40 and are screwed into the holes 42 in the Belleville spring 28.

Each of the Belleville springs 20, 28 has a castellated shape at its outer periphery, comprising generally rectangular notches 44. Situated just radially inwards of the bottom edges of the notches 44, there is a circumferential rib 46. Inwardly of the rib 46, the web of the Belleville spring 20, 28 has a gradually increasing thickness in the direction towards the inner periphery, in order to provide the Belleville spring 20, 28 with the desired resilient characteristic.

The notches 44 receive, as a relatively close fit, axially directed dogs 48 on the friction rings 22, 30. On the sides of the rings 22, 30 opposite the dogs 48, the friction rings have shallow recesses 50.

As best seen in Figures 8 and 9, the radiaDy inwards projections 12 of the first gear wheel 2 engage in the respective recesses or cups 10 formed in the outer periphery of the hub 6. The cups 10 extend across the full width of the outer periphery 8 of the hub 6 and have a curved profile which, at least at the bottom of each cup 10, may be part- circular.

Each projection 12 is tapered in the radially inwards direction from the ring 14 to an enlarged head 52 at the radially inner end of each projection 12. The radially inner surface of each head 52 has a profile which substantially conforms to that of the cup 10. The length of each projection 12 is such that the heads 52 seat within the cups 10 with minimal clearance.

The first gear wheel 2 is supported on the hub 6 through the friction rings 22, 30 and the Belleville springs 20, 28. Thus, any radial forces applied to the gear wheel 2 are transferred by the radially outer wall of the recess 24 to the friction rings 22, 30 and thence to the Belleville springs 20, 28 either by contact between the dogs 48 and the bottoms of the notches 44, or by the contact of the remainder of the friction rings 22, 30 with the ribs 46, as best seen in Figures 4 and 5. The forces are then transferred to the hub 6 by the contact of the inner peripheries of the Belleville springs 20, 28 with the projections 16 and the boss 26.

As a result of this arrangement, the projections 12 are relieved of any radial loading, i.e loading in their lengthwise directions. Their length is determined so that they are a close fit within the cups 10.

The axial support of the first ring 2 on the hub 6 is achieved by the Belleville springs 20, 28 which close the ends of the recesses or cups 10, so retaining the heads 52 of the projections 12 within the cups 10.

Rotation of the first gear wheel 2 on the hub 6 is resisted both by frictional engagement between the friction rings 22, 30 and the inner surfaces of the recesses 24, and by the projections 12 engaging the cups 10. As shown in Figure 10, relative rotation between the outer ring 14 of the gear wheel 2 causes the projections 12 undergo resilient bending deflection and the restoring force thus applied by the projections 12 resists further relative rotation and biases the ring 14 towards a neutral rotational position relative to the hub 6. Furthermore the hub 6 has lubrication passages 54 which extend from the internal bore of the hub 6 to the cups 10. Where the bolts 32 intersect the lubricant passages 54, adequate clearance 57 is provided, as shown in Figure 9, to allow lubricant to migrate to the cups 10. In the unstressed condition of the projections 12, the surfaces at the radially inner extremities of the head 52 substantially close the lubricant passages 54. However, as can be seen in Figure 10, upon deflection of the projections 12, the contact point between the head 52 and the surface of the cup 10 moves up the surface of the cup 10 so causing the head 52 to lift away from the opening of the lubricant passage 54, allowing lubricant to emerge and travel up the projection 12 to the recesses 24, so providing lubrication between the friction rings 22, and the gear wheel 2. The recess 50 in the friction rings 22, 30 provide reservoirs for the lubricant to assist distribution of the lubricant over the contact faces. In operation, therefore, the resilient projections 12, the friction rings 22, 30 and the Belleville springs 20, 28 provide a torsional spring and damper unit which, if appropriately tuned, can damp any torsional vibration which might otherwise be transmitted between the gear wheels 2 and 4. Such tuning may be achieved by varying the flexural characteristics of the Belleville springs 20, 28, for example by varying their thickness profile or their initial, unstressed configuration. Also, the flexural characteristics of the projections 12 can be adjusted by changing their profile and the number of projections that are provided.

It will be appreciated that the Belleville springs 20, 28 differ from each other at their inner regions. Correct functioning of a Belleville spring requires its inner periphery to be held substantially rigidly. For this reason, the Belleville spring 20 is clamped firmly between the second gear wheel 4 and the shoulder 18 on the hub 6, by means of the bolts 32. This holds the web of the Belleville spring 20 substantially rigidly. By contrast, the Belleville spring 28 is unclamped, but instead is supported against the boss 26 by the bolts 32. The Belleville spring 28 thus has a thickened central region 56 (Figure 3) to provide the required rigidity.

In many circumstances, the engagement between the projections 12 and the cups 10 will be sufficient to prevent continued rotation of the gear wheel 2 about the hub 6.

However, in some circumstances, it may be desirable to provide additional means to prevent such relative rotation. By way of example, Figures 11 to 3 show a modification for this purpose.

Figure 11 corresponds to Figure 7, but in the embodiment of Figure lithe Belleville spring 28 is provided with three equally spaced lugs 58 which project radially outwardly beyond the remainder of the periphery of the Belleville spring 28, by a short extension 60, seen more clearly in Figures 12 and 13. These extensions 60 are situated in a stop recess 62 formed in the circumferential wall of the recess 24 in the ring 14 of the gear wheel 2. The circumferential extent of each stop recess 62 is greater than that of the lug 58. Consequently, limited relative rotation between the Belleville spring 28, and consequently of the hub 6 and the gear wheel 4, is possible about a neutral position, as shown in Figure 12, before the lug 58 engages one or other of the ends of the stop recess 62.

Consequently, relatively small amplitude oscillations, such as occur as a result of harmonic vibration in the mechanism are possible, but larger amplitude displacement is prevented by cooperation between the lugs 58 and the stop recesses 62.

A gear assembly as described above may be used in any mechanism in which the transmission of torsional vibration is to be avoided. The assembly is particularly suited for use in internal combustion engines, for example as part of a camshaft drive system.

Although the assembly has been described as incorporating gear wheels 2 and 4, it will be appreciated that different drive components could be used. For example, the gear wheels 2 and 4 could be replaced by sprocket wheels, for use in a chain drive system, or by pulley wheels, for use in a belt drive system.

Claims

1. A rotational drive assembly comprising a rotational drive component supported on a hub, the component comprising a ring and a plurality of resilient projections extending radially inwardly of the ring, the inner ends of the projections being located with respect to the hub so that rotation of the ring relatively to the hub causes resilient deflection of the projections, friction damping means being provided which acts between the hub and the ring to damp rotational oscillations of the ring relative to the hub.

2. A rotational drive assembly as claimed in claim 1, in which the resilient projections are tapered in the radially inwards direction.

3. A rotational drive assembly as claimed in claim I or 2, in which the inner ends of the resilient projections engage recesses in the hub.

4. A rotational drive assembly as claimed in claim 3, in which the inner ends of the resilient projections comprise enlarged heads which engage the respective recesses.

5. A rotational drive assembly as claimed in claim 3 or 4, in which the hub is provided with lubricant supply passages which open into the recesses.

6. A rotational drive assembly as claimed in claim 4 or 5, in which deflection of each projection, as a result of relative rotation between the ring and hub, causes displacement of the point of contact between the head of the projection and the respective recess.

7. A rotational drive assembly as claimed in claim 6, in which the deflection of the projection causes an increase in the flow crosssectional area between the lubricant supply passage and the head of the projection.

8. A rotational drive assembly as claimed in any one of the preceding claims, in which the projection is an array of not less than eight projections.

9. A rotational drive assembly as claimed in claim 8, in which the projection is one of an array of not less than 20 projections.

10. A rotational drive assembly as claimed in any one of the preceding claims, in which the friction damping means comprises a friction ring which is mounted for rotation with the hub and frictionally engages the ring of the rotational drive component.

11. A rotational drive assembly as claimed in claim 10, in which a resilient element is rotationally secured to the hub at an inner region of the resilient element and engages the friction ring at an outer region of the resilient element, thereby to bias the friction ring into engagement with the rotational drive component.

12. A rotational drive assembly as claimed in claim 11, in which the resilient element is clamped against a radial face of the hub.

13. A rotational drive assembly as claimed in claim 11 or 12, in which the friction ring and the resilient element are rotationally interlocked with each other.

14. A rotational drive assembly as claimed in claim 13, in which the friction ring and the resilient element are rotationally interlocked by means of dogs provided on the friction ring which engage in complementary recesses in the resilient element.

15. A rotational drive assembly as claimed in claim 14, in which the dogs and the recesses have rectangular profiles.

16. A rotational drive assembly as claimed in any one of claims 11 to 15, in which the friction ring is disposed between opposed circumferential surfaces provided respectively on the ring of the rotational drive component and on the resilient element.

17. A rotational drive assembly as claimed in any one of claims 11 to 16, in which the resilient element is a Belleville spring.

18. A rotational drive assembly as claimed in any one of claims 10 to 17, in which the friction ring is one of a pair of friction rings disposed on opposite sides of the rotational drive component.

19. A rotational drive assembly as claimed in claim 18 when appendant to claim 11, in which the resilient element is one of a pair of resilient elements engaging the respective friction rings.

20. A rotational drive assembly as claimed in any one of the preceding claims, in which a further rotational drive component is secured to the hub.

21. A rotational drive assembly as claimed in claim 20, in which the further rotational drive component has an inner periphery which is supported on an axial projection of the hub.

22. A rotational drive assembly as claimed in claim 20 or 21, in which the further rotational drive component is secured to the hub by means of bolts which extend through openings provided at the interface between the further rotational drive component and the hub.

23. A rotational drive assembly as claimed in claim 22, in which the bolts are tapered.

24. A rotational drive assembly as claimed in any one of claims 20 to 23, in which the inner region of the resilient element is clamped between the further rotational drive component and a radial face of the hub.

25. A rotational drive assembly as claimed in claim 24, in which the inner periphery of the resilient element is notched to receive the bolts.

26. A rotational drive assembly as claimed in any one of the preceding claims, in which the rotational drive component, or at least one of the rotational drive components, is a gear wheel.

27. A rotational drive assembly substantially as described herein with reference to, and as shown in, the accompanying drawings.

28. A drive mechanism including a rotational drive assembly as claimed in any one of the preceding claims.