WO1999046517A1

WO1999046517A1 - Drive shafts

Info

Publication number: WO1999046517A1
Application number: PCT/EP1999/001606
Authority: WO
Inventors: Kaare Groenbaek; David Fleischer
Original assignee: Dansk Uni-Cardan A/S
Priority date: 1998-03-12
Filing date: 1999-03-11
Publication date: 1999-09-16
Also published as: GB2335252A; GB2335252B; GB9805149D0

Abstract

A drive shaft (10) has means for damping axial movement of the shaft relative to a rotary element to which it is connected, the daping means comprising a fluid contained in an internal cavity (18, 19, 20) of the shaft, a displacement member (14, 15) at an end of the shaft, the displacement member engaging a part relative to which the shaft is able to undergo the axial movement and being arranged to displace the fluid within the shaft when the shaft mobes axially, thereby damping such axial movement.

Description

Title: DRIVE SHAFTS

Description of Invention

This invention relates to drive shafts, and more specifically it relates to the provision in a drive shaft of damping means, for damping axial vibration or oscillation in the shaft.

Drive shafts are omnipresent in machineiy and equipment. At the ends of a drive shaft, connections have to be made to provide for the transmission of torque thereby, and very frequently such connections are made by couplings which allow for some angular misalignment (articulation) between the rotational axis of the shaft and the rotational axis of the component to which it is connected. There are various types of coupling by which such connection can be made and one type of such a coupling utilises a flexible element which typically is in the form of a disc or annulus of flexible material. Coupling members respectively provided on the drive shaft and the rotary element to which it is to be connected are fastened to the flexible coupling element, one such coupling member lying to one side of the coupling element and being connected thereto at a number of positions spaced circumferentially around the flexible coupling element, and the other coupling member being disposed at the other side of the flexible coupling element and being connected to it at a further number of circumferentially spaced positions therearound, between the first such positions.

The flexibility of the flexible coupling element provides for articulation up to a small angle between the drive shaft and the rotaiy element to which it is connected. It also allows for a small amount of relative axial movement therebetween, and it will be appreciated that if a drive shaft is connected to other rotary elements by such a coupling at each end, the shaft is able to move a small distance axially therebetween (unless it is constrained by some other means, e.g. a bearing or bearings resisting such movement). Sometimes the lexible coupling element is made of a material which has high internal damping characteristics and thus tends to damp vibrations of the drive shaft, but if the flexible coupling element is of a metal or of a composite, fibre-reinforced plastics, material, it does not have such high internal damping as a material such as a fabric-elastomer composite material.

Accordingly there is a requirement for a means for damping movement such as vibrations or oscillations of the shaft in the direction axially thereof, and it is broadly the object of the present invention to approach or meet this requirement.

According to the present invention, we provide a drive shaft having means for damping axial movement of the shaft relative to a rotary element to which the shaft is connected, said damping means comprising a quantity of fluid contained in an internal cavity of the shaft; and a displacement member at an end of the shaft, adapted to engage a part relative to which the shaft is able to undergo said axial movement and to effect a displacement of said fluid upon said shaft movement; whereby said displacement of fluid effects damping of axial movement of the shaft.

Preferably the displacement member is or is connected to a diaphragm element closing the internal cavity of the shaft at said end thereof.

Preferably the fluid is gaseous. It may be air, which may simply be trapped in the internal cavity of the shaft in manufacture thereof, or it may be a gas which is intentionally introduced into the shaft, e.g. nitrogen.

The internal cavity of the shaft may be divided into two or more portions, with the displacement member aπanged to displace said fluid between said portions by way of throttling means to provide the required damping.

Such division of the internal cavity of the shaft into portions may be effected by a partition or partitions in the shaft interior, having orifice means to provide said throttling. A shaft in accordance with the invention may have a displacement member at one end only, or it may preferably have same at each end, where the shaft is, in use, to be connected to other rotary elements at both ends by flexible couplings.

With such a coupling at the end of the shaft, the displacement member is able to extend through an aperture provided in the centre of the flexible coupling element, to engage the coupling member which is connected to the flexible coupling element at the opposite side from that at which the shaft is situated.

There may be provided means providing for communication with the internal cavity of the shaft for permitting fluid to be introduced or removed therefrom. The pressure of a gaseous fluid in the shaft may be increased to increase its density and thereby the damping effect, or may be reduced possibly to a sub-atmospheric pressure, in which case partial retraction of the or each displacement member towards the interior of the shaft may ensue. This may be used to facilitate installation of the shaft.

The invention will now be described by way of example with reference to the accompanying drawings, of which:-

Figure 1 is a diagrammatic illustration of the principle of the invention as applied to a shaft;

Figure 2A is a partial section through an embodiment of shaft in accordance with the invention having a flexible coupling at each end, with Figure 2B showing an enlargement of part thereof;

Figure 3 is an axial view of the shaft.

Referring firstly to Figure 1 of the drawings, this shows a hollow, tubular, shaft 10. The axis of the shaft is indicated at 11, and the shaft extends axially between two abutment surfaces 12, 13. At each of its ends the shaft is closed by a respective diaphragm element 14, 15 which respectively extend axially outwardly from the shaft end to engage the abutment surfaces 12, 13. Two transverse partitions 16, 17 extend across the interior of the shaft to divide its internal space into three portions 18, 19, 20 and the partitions have respective orifices 21, 22 to provide for communication between the spaces 18, 19 and 19, 20.

The entire internal cavity of the shaft, delimited by the diaphragms 14, 15, contains a fluid which conveniently is gaseous, e.g. air. It will be apparent that if the shaft moves axially towards the abutment surface 12 then such fluid will be displaced from the space 18 to the space 19, and from the space 19 to the space 20, by way of the orifices 21, 22. Displacement of the shaft in the opposite direction, towards the abutment surface 13, will cause displacement of the fluid in the opposite direction. The orifices 21, 22 throttle the fluid in the course of such displacement, thereby providing a damping effect in respect of such axial displacement of the shaft. The magnitude of such damping effect depends on the size of the orifices and on the nature of the fluid in the shaft. The pressure of gaseous fluid in the shaft may be adjusted by using a valve 23 provided in the shaft wall and it will be appreciated that if the pressure within the shaft is reduced to a sub-atmospheric value the effect will be to cause the diaphragms 14, 15 to be withdrawn axially towards the interior of the shaft. This effect can be used to facilitate installation of the shaft.

Referring now to Figures 2 and 3 of the drawings, these show a shaft 110 of tubular form. At both its right hand and left hand ends it is identically provided, being connected to further shafts or other rotary elements 90, 91 by respective flexible couplings indicated generally at 92, 93. The flexible - couplings 92, 93 are of the same type as other another and as illustrated are identical to one another: it will be appreciated, however, that one of the flexible couplings might be of different configuration, e.g. to connect to a different type of further shaft or other rotary element. The coupling 93, shown in Figures 2A and 3 and part of which is shown enlarged in Figure 2B, comprises a coupling member indicated generally at 109 which has an inner annular part 108 welded to the exterior of the tubular shaft 110. From the part 108 three limbs 107, equally angularly spaced from one another, extend radially outwardly. Adjacent their outermost ends these limbs have apertures 106 for bolted connection to a flexible coupling element 94 at equally circumferentially spaced positions thereabout on a pitch circle 105. A further three-limbed coupling member 95 is disposed at the opposite side of the flexible coupling element 94, and is likewise connected to the latter at three positions spaced circumferentially therearound, mid-way between the positions at which the coupling member 109 is connected thereto.

As shown in outline in Figure 3, the flexible coupling element is of annular configuration and somewhat hexagonal in overall shape, having a central opening 96. The coupling members 109, 95 are connected to the coupling element 94 at the apices of hexagon. The flexible coupling element may be of composite, fibre-reinforced plastics, material and an example of such a coupling element is disclosed in published UK Patent Application 2322428 for example. The further coupling member 95 has an abutment surface 97.

Referring now more particularly to Figure 2B of the drawings, it will be seen that just within the shaft 1 10 it is fitted with a transverse partition 1 17 in which there is a small orifice 117a. A flexible diaphragm, e.g. of a flexible plastics or rubber material, is secured in airtight manner to the end of the shaft 110, the outer peripheiy of the diaphragm 115 being held by a clamping flange 104 secured by a plurality of circumferentially spaced axially extending screws. The diaphragm carries an abutment plate 103 which contacts the abutment ^■ surface 97 of the coupling member 95. The diaphragm 1 15 extends axially outwardly beyond the end of the shaft, sufficiently far for the abutment plate 103 to extend through the central aperture of the flexible coupling element, to abut the surface 97.

A valve 123 communicating with the interior space of the shaft 110 is shown in Figure 2A. By virtue of having a flexible coupling at each end, utilising a flexible coupling element of disc-like form and preferably of a composite, fibre- reinforced plastics, material, the nature of the flexible coupling element does not exert a high damping effect against axial vibrations of the shaft. However, in most installations one or both of the other shafts or rotary elements to which the shaft is connected will be constrained against axial movement. Therefore, in accordance with the invention, displacement of fluid within the shaft on axial movement thereof is used to provide the required damping effect.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A drive shaft having means for damping axial movement of the shaft relative to a rotary element to which the shaft is connected, said damping means comprising a fluid contained in an internal cavity of the shaft; and a displacement member at an end of the shaft, said displacement member being adapted to engage a part relative to which the shaft is able to undergo said axial movement and to effect a displacement of said fluid upon said shaft movement, whereby said displacement of fluid effects damping of axial movement of the shaft.

2. A drive shaft according to Claim 1 wherein said displacement member is or is connected to a diaphragm element closing the internal cavity of the shaft at said end thereof.

3. A drive shaft according to Claim 1 or Claim 2 wherein the internal cavity of the shaft comprises two or more poitions, and the displacement member is arranged to displace said fluid between said poitions by way of throttling means.

4. A drive shaft according to Claim 3 wherein the internal cavity of the shaft is divided into said portions by at least one partition in the shaft interior and having orifice means to provide throttling of fluid passing therethrough.

5. A drive shaft according to any one of the preceding claims wherein the fluid ' is gaseous.

6. A drive shaft according to Claim 5 wherein the fluid is air.

7. A drive shaft according to any one of the preceding claims having a displacement member at one end only.

8. A drive shaft according to any one of Claims 1 to 6 having a respective displacement member at each end.

9. A drive shaft according to any one of the preceding claims having at each end a coupling member comprising parts spaced angularly about the shaft and adapted for fastening to a flexible coupling element of disc-like form, at positions circumferentially spaced therearound.

10. A drive shaft according to any one of the preceding claims having a respective flexible coupling at each end.

11. A drive shaft according to Claim 10 wherein at least one of said couplings comprises a coupling member secured to the shaft, a flexible coupling element to which the coupling member is fastened at a number of positions spaced circumferentially around the flexible coupling element, and a further coupling member disposed at the other side of the flexible coupling element and connected thereto at a fuither number of circumferentially spaced positions therearound between the first said positions.

12. A drive shaft according to Claim 11 wherein said displacement member of the damping means at said flexible coupling extends through an aperture in the centre of the flexible coupling element to engage the other said coupling member.

13. A drive shaft according to any one of the preceding claims comprising means affording communication with the internal cavity of the shaft, for pe╧Çr╬«tting fluid to be introduced or removed therefrom.

14. A drive shaft substantially as hereinbefore described with reference to the accompanying drawings.

15. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.