The speed of an internal combustion engine is never completely uniform, even during steady state operation. The engine output to the driving shaft continuously accelerates and decelerates about an average speed, due mainly to power pulses delivered by the engine cylinders. Further irregularities in torque and speed of the driving shaft may be produced by non-uniform fuel/air mixture being delivered to the engine. These irregularities produce torsional"shocks"in driving shaft torque having variable amplitude and frequency. Such power pulses and shocks become evident as torsional vibrations in drive line components, which are then transmitted to the vehicle and its occupants.

Shock or vibrations are also introduced into drive line systems by stick-slip conditions at the tyre/ground interface, by the design of the suspension geometry or drive line layout and by the differential itself.

Various"flexible"couplings have been developed in an attempt to isolate and dampen torsional vibrations. These couplings generally include a yielding intermediate element between two halves of the coupling. The intermediate element may consist of rubber, leather, steel springs or some other flexible material, which serves to absorb the impact energy present in the pulses or shocks. Another method is the use of torsional mass dampers which are tuned to absorb the vibration over a narrow frequency range.

Pulse/shock absorption may be achieved by storage of energy or by conversion of energy or both. A coil-spring coupling, similar to the arrangement found in many clutches, stores the impact energy in its springs when the driving element of the coupling undergoes rotation relative to the driven element in consequence of a sudden variation in driving shaft speed or torque. When the springs subsequently return to their original length, they transmit the temporarily

stored impact energy to the driven element.

Every resilient mechanism forms an oscillating system whose natural frequency of oscillating will depend on the spring characteristic and oscillating masses. A torsional spring drive line will have a particular natural frequency and any torsional impact will cause torsional excitation at the natural resonant frequency of the drive line, causing objectional large amplitude oscillations.

Similarly, torsional vibration of the drive line system will cause excitation, and increased amplitude of the torsional vibration of the drive line system, depending on the excitation frequency. If the excitation frequency is sufficiently high relative to the resonant frequency, then excitation may not occur. Drive line excitation is manifested as noise or vibration of the main structure of a vehicle.

A number of damping devices have been proposed to dissipate the impact energy stored within the coupling's springs. Some of these devices rely on friction plates acting in parallel with the springs whilst others utilise viscous damping mechanisms, also acting in parallel with the springs. For example, US Patents 4,790,792,4,963,119 and 5,386,896 each disclose a torsional vibration damping device incorporating a viscous damping mechanism operating in parallel with, but functionally separate from, a coil-spring coupling device. Such devices are complicated and hence expensive to manufacture.

An object of the present invention is therefore to provide a torsional vibration damping coupling which is relative simple in construction and may be cheaper to manufacture than existing couplings.

The present invention accordingly provides a torsional vibration damping coupling including: a first coupling element rotatable about an axis; a second coupling element connectable to the first element; each of the first and second elements including a plurality of projections disposed about the axis and being arranged such that any one projection of either the first or second element is circumferentially interposed between two projections of the other element, whereby a torque is transmissible between the elements; a plurality of resilient members interposed between successive ones of the projections for allowing limited angular rotation between the elements against the

action of the resilient members; and viscous damping means including an annular cavity formed between the first and second elements for containing damping fluid, the cavity being divided by the projections into a plurality of chambers, wherein each chamber contains a said resilient member, the viscous damping means further including a fluid passage between selected ones of the chambers to facilitate viscous damping of torsional vibrations.

It can be seen that the resilient members are disposed within the chambers of the viscous damping means. This arrangement significantly simplifies the overall configuration of the coupling, simultaneously providing isolation of torsional vibrations, by means of the resilient members, and damping of those vibrations, by means of the viscous damping means. Further, specific parameters of the resilient members and viscous damping means may be"tuned"so as to optimise the characteristics of the coupling for particular applications.

The coupling of the present invention will operate over a relative large frequency range with high levels of damping compared to existing drive line dampers which operate over narrow frequency ranges, or with relatively low levels of damping.

In one embodiment each resilient member includes a block of resilient material such as a rubber-like compound. The block may be solid or it may be hollow. In the event that the block is hollow, it may be filled with a fluid, such as a liquid, gel or gas. A silicon-based fluid is one possibility.

Advantageously the block is shaped or otherwise modified so as to vary its force/compression characteristics (ie. its elasticity). In this way the torque/relative-rotation characteristics of the coupling may be optimised for particular applications. In one embodiment the block may be substantially cylindrical whilst in another it may be ellipsoid. Alternatively, the block may be tapered and may include one or more fusto-conical sections connected end-to- end. Various other possibilities will become apparent to those skilled in the art.

In another embodiment the block may be of uniform cross-section but may include several materials of different elasticity. Graduated blending of elastomeric compounds may also be used to tune the properties of the coupling so as to

achieve any desired torque/rotation characteristics.

In one embodiment the ends of each block abut the respective projections of the first and second coupling elements. Preferably the ends of the blocks are shaped to maintain a desired position in relation to the projections. More preferably the blocks are shaped so as to be approximately centered on the faces of the projections. Alternatively, or in addition, the face of each projection may be shaped to facilitate centering of the block. In one preferred embodiment the ends of the blocks may be convex and the faces of the projections may be concave.

However, the reverse configuration may alternatively be used.

In one embodiment each resilient member includes a spring, such as a helical coil spring. Other forms of resilient member may alternatively be employed or combinations of rubber blocks, springs and other resilient members may be used.

In one embodiment a fluid passage is provided between adjacent pairs of chambers. Alternatively, fluid passages may be provided between all chambers.

The or each fluid passage may include a clearance around one or more of the projections, such as between the projection and a wall of the annular cavity.

Alternatively, or in addition, a groove may be provided in a face of the projection or a duct may pass through the projection. In any of these arrangements the magnitude of viscous damping may be varied by modifying the size of the clearance, groove or duct, respectively. In this way, the amount of damping may be tuned for particular applications.

In one embodiment the fluid passage may include valving to control the flow of fluid between the chambers. In this way, the nature of the viscous damping effect may be further modified as required.

The fluid used in the coupling may be any suitable known fluid.

Advantageously the fluid is a viscous liquid and may be a silicon fluid such as dimethyl polysiloxane. It will be appreciated that fluids of greater or lesser viscosity may be used to further control the amount of damping provided.

In one embodiment the first coupling element includes a hub disposed about the axis and a cylindrical housing concentric with the hub. A space between the hub and housing may define the radial extents of the annular cavity.

The cylindrical housing may further include an end wall extending radially inward to an end of the hub, thereby closing one end of the annular cavity.

In one embodiment the second coupling element includes a disk which may be receivable within the cylindrical housing of the first coupling element. The disk may be disposed normally to the axis and is preferably configured to close a second end of the annular cavity. Extending laterally from the disk, along the axis of rotation, may be a spindle on which the hub of the first coupling element may be received.

In one embodiment the first coupling element includes a plurality of first projections extending into the annular cavity. Preferably the first projections extend between the hub and the cylindrical housing. The second coupling element may include a plurality of second projections extending into the annular cavity. Preferably the second projections extend from the disk and, more preferably, extend parallel to the axis. The first and second projections may thus partition the annular cavity into a plurality of chambers, as described above.

There may be any number of first and second projections and any number of chambers. Preferably there are two first projections and two second projections, together defining four chambers between those projections. As described above, the resilient members are received within these chambers.

The projections may have any suitable cross-sectional shape, and in one embodiment they are substantially trapezoidal. In this way, roughly rectangular chambers may be created.

It will be convenient to hereinafter describe the invention by reference to the accompanying drawings which illustrate a preferred embodiment thereof.

Other embodiments of the invention are possible, and consequently the particularity of the following description and accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

In the drawings: Figure 1 shows an exploded perspective view of a torsional vibration damping coupling in accordance with a preferred embodiment of the invention; Figure 2 shows a cross-sectional view of the coupling of Figure 1 taken

along the line 11-ll; Figure 3 shows a partial cross-sectional view of the coupling of Figure 1, taken along the line III-III in Figure 2.

Referring now to the drawings, Figure 1 shows a torsional vibration damping coupling suitable for transmitting a torque from a driving shaft to a driven shaft whilst damping torsional vibrations. The coupling includes a first coupling element 1 and a second coupling element 2. The first coupling element 1 may be rigidly secured to an end of a driving shaft (not shown) within a vehicle drive line and the second coupling element 2 may be rigidly secured to an end of a driven shaft (not shown). However, the reverse arrangement may equally be employed.

The first and second coupling elements 1 and 2 are interconnectable and both elements are rotatable about a common axis 3.

The first coupling element 1 includes a central hub 10, a cylindrical housing 11 concentric with the hub 10 and an end wall 12 extending between the hub 10 and cylindrical housing 11. The second coupling element 2 includes a disk 13, receivable within the cylindrical housing 11, and a spindle 14, receivable within the hub 10. Together, the hub 10, cylindrical housing 11, end wall 12 and disk 13 define a closed annular cavity 15 for containing a damping fluid.

The first coupling element 1 is provided with first projections 16 and 17 and the second coupling element 2 is provided with second projections 18 and 19, each projection 16-19 being disposed about the axis 3 and extending into the annular cavity 15. When the coupling is assemble, the projections 16-19 are arranged such that any one projection of either the first or second element 1 or 2 is circumferentially interposed between two projections of the other element 2 or 1. In this way, a torque is transmissible between the coupling elements 1 and 2.

In the embodiment shown, each coupling element includes two projections, however any alternative number of projections may be employed.

Figure 2 shows a cross-sectional view of the coupling taken along the line 11-11 in Figure 1 (ie. viewed from just above the level of the hub 10 as depicted in Figure 1). The interposed arrangement of the projections 16-19 can be best seen in Figure 2.

Referring again to Figure 1 it can be seen that, in the embodiment shown,

the first projections 16,17 extend between the hub 10 and the cylindrical housing 11. The second projections 18,19 extend from the disk 13 parallel to the axis 3.

This is merely one embodiment and alternative configurations would be apparent to those skilled in the art.

The four projections 16-19 divide the annular cavity 15 into four chambers 20-23 (best seen in Figure 2). Between chambers 20 and 21 are provided fluid passages, in the form of a clearance 24 between projection 19 and an inner wall of the cylindrical housing 11, and a groove 25 in a face of projection 19 (see also Figure 3). Similarly, fluid passages are provided between chambers 22 and 23, in the form of a clearance 26 between projection 18 and an inner wall of the cylindrical housing 11, and a groove 27 in a face of projection 28.

Relative rotational movement between the coupling elements 1 and 2, and hence between the first projections 16 and 17 and the second projections 18 and 19 will cause damping fluid to flow between chambers 20 and 21 and between chambers 22 and 23 via the fluid passages 24-27. It will be appreciated that either the clearances 24 and 26 or grooves 25 and 27 may be omitted whilst still maintaining the damping function of the coupling.

In order to properly contain damping fluid within the annular cavity 15 and to prevent entry of contaminants the first and second coupling elements 1 and 2 are each provided with sealing means in the form of 0-rings 28 and 29 respectively (see Figure 3). O-ring 28 is located within a groove at an end of the hub 10 and seals against the disk 13 whilst O-ring 29 is located within a groove at the outer edge of the disk 13 and seals against the inner wall of the cylindrical housing 11. It will be appreciated however that other suitable configurations or alternative sealing means may be employed.

Within each chamber 20-23 is a resilient member in the form of a rubber block 30-33 respectively. Each end of each block 30-33 abuts a face of a projection 16-19 and resiliently deforms upon relative movement between the respective projections of the coupling elements 1 and 2. In the embodiment shown, each block 30-33 is substantially cylindrical in shape and has convexly rounded ends. The faces of the projections 16-19 are made concave so as to facilitate self-centering of the blocks 30-33 on the respective faces of the

projections 16-19. The relative dimensions of the blocks 30-33 and projections 16-19 may be chosen such that the blocks are pre-loaded (ie. partially compressed) during manufacture of the coupling.

Figure 3 shows a cross-sectional view of the coupling taken along the line III-III in Figure 2. Positioned between the hub 10 and spindle 14 is a bearing 40.

The bearing 40 is held in place at one end by a shoulder 41 and at the other end a circlip 42. The circlip 42 is held within a circlip groove 43 in the spindle 14 and serves to prevent separation of the coupling elements 1 and 2. The bearing 40 may be a ball, roller, needle or other suitable type of bearing. Alternatively, a separate bearing may be omitted and a bushing used instead. In that event, the shoulder 41 may be omitted and the circlip 42 positioned against the outer surface (rightmost in Figure 3) of end wall 12, assuming the spindle 14 is suitably extended.

Those skilled in the art will appreciate that various adaptations and modifications of the just described preferred embodiment may be configured without departing from the scope and spirit of the invention. Therefore, it s to be understood that the invention may be practised other than as specifically described herein.