Patent Description:
It is known to employ hydraulic dampers and/or absorbers to minimise the transmission of vibration from one component to another. The damping/absorbing response of hydraulic dampers/absorbers is non-linear, and is significantly affected by temperature, loading, and the frequency and amplitude of the vibration to be damped. The design of such dampers/absorbers to cope with the range of conditions, and multiple vibratory inputs (frequency and amplitude) experienced in practice is thus complex. Furthermore, in safety-critical applications, the loss of hydraulic fluid can have catastrophic results.

Document <CIT> discloses a vibration absorber comprising a linear friction damper.

According to the present invention there is provided a vibration damper and/or absorber including a first member having a bearing region and a friction contact region, and a second member including a body which is mounted on the bearing region for axial displacement with respect to the first member along an axis, the second member including a resilient member which projects from the body and which has a contact face which resiliently engages the friction contact region of the first member, whereby relative axial displacement between the first and second members is opposed by frictional contact between the contact face and the friction contact region.

The resilient member may project from the body in an axial direction with respect to the axis. The contact face may be provided at or near a free end of the resilient member.

The resilient member may be one of a pair of oppositely disposed resilient members extending axially from the body in the same direction and contacting the friction contact region on opposite sides of the axis. The forces applied by the oppositely disposed resilient members thus balance each other so as to eliminate any net transverse force applied by the members to the first member.

The oppositely disposed pair of resilient members may be one of two oppositely disposed pairs of resilient members which contact the contact region, the two pairs being offset from one another by <NUM>° about the axis. In such an embodiment, the frictional contact between the resilient members and the contact region can be increased. There may be more than two oppositely disposed pairs of members, distributed regularly around the axis. There may be an odd or even number of second members positioned around the axis.

The or each resilient member may constitute a first resilient member extending axially from the body in a first direction and in which the contact region constitutes a first contact region situated axially on one side of the bearing region, the body being provided with at least one second resilient member aligned with the or each respective first resilient member and extending axially from the body in a second direction opposite to the first direction and contacting a second contact region of the first member, situated axially on the other side of the bearing region.

The or each member may contact the respective contact region at a respective friction surface of the contact region. If the body is provided with two pairs of resilient members, on one or both sides of the bearing region, the contact region for each two pairs of members may have a square cross section (when viewed axially), the friction surfaces constituting the sides of the square. The cross-section may be non-square but still rectangular. The cross-section may be another polygonal shape.

The or each friction surface may extend parallel to the axis, which may be a generally central axis. The pressure applied to the friction surface by the resilient member acting on the respective friction surface will thus remain constant or substantially constant over the travel of the member. Consequently, the frictional resistance to travel will also remain constant, or substantially constant.

Alternatively, at least part of the friction surface or of at least one of the friction surfaces may be inclined to the axis. The pressure applied to the friction surface and hence the resistance to travel (linear rate) and the frictional resistance to travel, and consequently the damping/absorbing effect, will thus vary as the resilient member moves relative to the friction surface. The gradient of inclination may be constant or may increase as the friction surface extends towards the body.

It may be desirable for the friction surfaces and the contacting surfaces of the resilient members to be hardened and highly polished and hard coated, in order to achieve a long service life.

The bearing region of the first member may be one of a plurality of bearing regions and the friction contact region may be one of a plurality of friction contact regions, in which case the body may be one of a plurality of similar bodies supported on the first member at the respective bearing regions, the resilient members of the bodies contacting respective ones of the friction contact regions. Such an embodiment enables the damping/absorbing effect to be increased without increasing the radial width of the damper and/or absorber, with respect to the axis.

The second member may include a housing which accommodates the or each body, the or each body being secured to the housing.

The housing may contain a lubricant, the housing being sealed with respect to the first member.

The first member and the second member may each be provided with a respective coupling element for connecting the damper and/or absorber between two components.

The present invention also provides an installation including a support structure and a mechanism mounted on the support structure, a damper and/or absorber as defined above being connected between the support structure and the mechanism.

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:.

<FIG> show a linear damper and/or absorber which has a variety of uses but may, for example, be employed to minimise the transmission of vibration between a mechanism which generates, or is subjected to, vibration and a support structure (not shown). It is undesirable for these vibrations to be transmitted to the support structure as they can create potentially damaging stresses.

The damper and/or absorber shown in <FIG> includes a housing <NUM> including a tubular casing <NUM> having at one end an end cap <NUM> from which extends a rod <NUM> terminating at an adjustable ball joint coupling <NUM>.

A centre shaft <NUM> having a central axis X is situated within the housing <NUM> and is supported at one end in the end cap <NUM> and at the other end in a nose piece <NUM> which is secured to the casing <NUM>. The centre shaft <NUM> projects through the nose piece <NUM> and is provided with a second adjustable ball joint coupling <NUM>. Seals (not shown) are provided between the nose piece <NUM> and the centre shaft <NUM>, and between the casing <NUM> and the end cap <NUM>, so that the interior of the housing <NUM> constitutes a sealed enclosure which can retain lubricating oil.

The centre shaft <NUM> includes three cylindrical bearing regions <NUM> centred on the central axis X and situated in each case between friction contact regions <NUM> provided with friction surfaces <NUM> (see <FIG>). The friction surfaces <NUM> are substantially flat.

Finger assemblies <NUM> are secured by tapered screws <NUM> to the inside surface of the casing <NUM>. In order to enhance rigidity of the casing <NUM>, reinforcing ribs <NUM> are provided on the casing <NUM> in the region of the tapered screws <NUM>.

One of the finger assemblies <NUM> is shown in more detail in <FIG>. Each finger assembly <NUM> includes four quadrant elements <NUM>, as shown in <FIG>. The quadrant elements <NUM> are assembled together to form the finger assemblies <NUM>, the elements <NUM> being located with respect to one another by dowels placed in holes <NUM>, and secured together by bolts <NUM> fitted into screw holes <NUM>. The quadrant elements <NUM> are also provided with tapped bores <NUM> for receiving the tapered screws <NUM>.

As shown in <FIG>, each quadrant element <NUM> includes a body section <NUM> from which projects, in opposite directions, resilient members or fingers <NUM>. Each finger <NUM> tapers outwardly from the body section <NUM> and terminates at a contact face <NUM> which is directed inwardly with respect to the central axis X. In other words, the contact face <NUM> is provided at or near a free end of the resilient finger <NUM>. Each finger <NUM> has a rectangular cross-section with a constant width w measured tangentially with respect to the central axis X, and a depth d, measured radially with respect to the central axis X, which decreases in the direction away from the body section <NUM>. The contact face <NUM> is of a thin, rectangular shape with the larger dimension extending tangentially of the central axis <NUM> and the shorter dimension extending axially.

The body section <NUM> of each quadrant element <NUM> includes a pair of abutment faces <NUM> which are at <NUM>° to each other. The abutment faces <NUM> are interconnected at their radially inner ends by an inner arcuate surface <NUM>, which is complementary to the profile of the bearing regions <NUM>. At their radially outer ends, the abutment faces are interconnected by an outer arcuate surface <NUM> which is complementary to the inner surface of the casing <NUM>. Each quadrant element <NUM> has axial end faces <NUM> from which the fingers <NUM> project.

The quadrant elements <NUM> are assembled together around the respective bearing regions <NUM> of the centre shaft <NUM> to form the respective finger assemblies <NUM>. This is done by placing dowel pins in the holes <NUM>, and then fitting the quadrant elements <NUM> together, located by the dowel pins, by bringing the abutment faces <NUM> of adjacent quadrant elements <NUM> into contact with one another. The quadrant elements <NUM> are then secured together by means of the bolts <NUM> inserted into the tapped bores <NUM>. The bolts <NUM> extend at right-angles to the central axis X, i.e. in a tangential plane, and are situated generally centrally of the respective abutment faces <NUM>. The resulting assembly is shown in <FIG>, with the centre shaft <NUM> omitted, and it will be appreciated that the inner arcuate surfaces <NUM> together form a cylindrical bore in which the respective bearing region <NUM> of the centre shaft <NUM> is situated. The fingers <NUM> projecting from the axial faces <NUM> of the assembled body sections <NUM> are arranged to form a square opening defined by the contact faces <NUM> of the fingers <NUM>.

As shown in <FIG> and <FIG>, the fingers <NUM> project beyond the bearing region <NUM> to extend over the friction surfaces <NUM>. The fingers <NUM> are configured so that they are stressed when the finger assemblies <NUM> are fitted to the centre shaft <NUM>. As a result, there is a residual resilient radial load exerted by the fingers <NUM> at the contact faces <NUM>, on the friction surfaces <NUM>. The total force resisting extension or retraction of the damper and/or absorber as a whole may, for example, be in excess of 5000N.

If necessary, after assembling the finger assemblies <NUM> on the centre shaft <NUM>, the outer surfaces of the finger assemblies, formed from the outer arcuate surfaces <NUM>, may be ground to an accurate diameter to fit properly in the casing <NUM>.

The friction contact regions <NUM> of the centre shaft <NUM> have a square cross-section, with the result that the friction surfaces <NUM> are arranged as a square. With reference to <FIG>, the fingers <NUM> projecting to the left of the body section <NUM> can be considered to be first fingers, and the contact region <NUM> situated to the left of the bearing region <NUM> can be considered to be a first contact region, while the fingers <NUM> projecting to the right of the body section <NUM> can be considered to be second fingers, and the contact region <NUM> situated to the right of the bearing region <NUM> can be considered to be a second contact region. In <FIG>, only one pair of the first fingers <NUM> is shown, the fingers <NUM> of this pair being disposed opposite each other and engaging the friction surfaces <NUM> on opposite sides of the square profile of the first contact region <NUM>. Two further quadrants <NUM> (not shown in <FIG>) are present, providing a second pair of first fingers <NUM> which are offset by <NUM>° to the first fingers <NUM> shown in <FIG>. The finger assemblies <NUM> are generally symmetrical about a transverse plane passing through the body sections <NUM>, and so the second fingers, to the right of the body sections <NUM>, are aligned with the respective first fingers <NUM>, and extend from the respective body sections <NUM> in the opposite direction from the first fingers <NUM>. The second fingers <NUM> contact the friction surfaces <NUM> of the second friction contact region <NUM> in the same manner as described above for the first fingers <NUM>. A consequence of this arrangement is that the load applied by each finger <NUM> is opposed by the finger on the opposite side of the respective friction contact region <NUM> so that each friction contact region is gripped between two pairs of fingers <NUM>, oriented at <NUM>° to each other. As a result, there is no net radial force applied by the fingers <NUM> to the centre shaft <NUM>. Also, because each finger assembly <NUM> has first and second oppositely extending fingers <NUM> projecting from each body section <NUM>, there is a total of eight fingers <NUM> acting through their contact faces <NUM> on the first and second friction contact regions <NUM> situated to each side of the bearing region <NUM> on which the finger assembly <NUM> can slide.

Furthermore, because the centre shaft <NUM> has three bearing regions <NUM>, each carrying a finger assembly <NUM>, the total number of finger contact faces <NUM> engaging respective friction surfaces <NUM> is twenty-four. Of course, as will be appreciated, more or fewer than three finger assemblies <NUM> can be provided on a common centre shaft <NUM> in order to provide the required frictional force resisting axial displacement of the centre shaft with respect to the housing <NUM>.

Once all of the finger assemblies <NUM> have been fitted to the centre shaft <NUM> at the bearing regions <NUM>, the assembly including the centre shaft <NUM> and the finger assemblies <NUM> is inserted into the casing <NUM>. The end cap <NUM> and the nose piece <NUM> are then fitted to the casing <NUM> and the housing <NUM> is then filled, at least partly, with lubricating oil through a filler plug <NUM> so that in use the contact faces <NUM> of the fingers <NUM> and the friction surfaces <NUM> are continuously immersed in the lubricant. It is not necessary for the lubricant to be supplied under pressure between the friction surfaces <NUM> and the contact faces <NUM>.

The centre shaft <NUM> has a plain bearing diameter section <NUM> at one end that engages in a hardened bearing area <NUM> provided in the nose piece <NUM>. Axial drain holes <NUM> in the nose piece <NUM> and in the quadrant elements <NUM> allow flow of lubricant to all internal regions of the damper and/or absorber.

To enable accurate location, there is a small radial clearance between the surfaces of the bearing regions <NUM> and the cylindrical bores formed by the inner arcuate surfaces <NUM>. This clearance can accommodate any slight radial misalignment between the casing <NUM> and the centre shaft <NUM>, and also provides a path for lubricant to provide hydrodynamic lubrication between the bearing regions <NUM> and the finger assemblies <NUM>.

For use, the damper and/or absorber is fitted between two machinery components, for example a mechanism subject to vibration and a supporting structure, by means of the adjustable ball joints <NUM>, <NUM>. Any displacement between the two components, and in particular displacement resulting from vibration of one of the components, is damped/absorbed by the damper and/or absorber. This is achieved by virtue of the frictional contact between the centre shaft <NUM> at the friction surfaces <NUM> and the contact faces <NUM> of the fingers <NUM> on the finger assemblies <NUM>. The full surfaces of the contact faces <NUM> make contact with the friction surfaces <NUM>. Once the amplitudes and frequencies of the expected vibrations are known, the profile of the fingers <NUM> can be established so that the damping/absorbing characteristics of the damper and/or absorber as a whole are sufficient to isolate the two machinery components from each other, so as to minimise the transmission of vibration from one to the other.

It will be appreciated that, at relatively low axial forces between the ends <NUM>, <NUM> of the damper and/or absorber, the Coulomb friction between the contact faces <NUM> and the friction surfaces <NUM> will prevent any relative movement between the centre shaft <NUM> and the housing <NUM>, and the damper and/or absorber will then behave as a rigid strut. However, when the axial force exceeds a threshold, determined by the contact areas and the radial force exerted by the resilient fingers <NUM>, there will be axial sliding movement between the contact faces <NUM> and the friction surfaces <NUM>. This movement is opposed by the Coulomb friction between the surfaces. The opposing frictional force will be substantially constant regardless of the speed of relative axial movement. This will provide a nearly constant damping/absorbingH force axially at every point within an envelope of axial positions. This envelope, defining the maximum travel of the centre shaft <NUM> within the housing <NUM>, may be established by stops (not shown). The components of the damper and/or absorber, and in particular the profile of the fingers <NUM>, may be designed to ameliorate the vibration, with the ability to do so with multiple frequencies present, with suitable tunable damper and/or absorber characteristics (amplitude and frequency) of a vibratory input to be damped.

In a particular embodiment, the friction surfaces <NUM> of the centre shaft <NUM> and the contact faces <NUM> of the fingers <NUM> are hardened, polished and hard coated, for example using techniques known for the treatment of cam surfaces in internal combustion engines.

In the above description, the finger assemblies <NUM> are described as being assembled from individual quadrant elements <NUM>. It will be appreciated that this is one of a number of construction options for the finger assemblies <NUM>, and that other arrangements for fitting the finger assemblies <NUM> to the centre shaft <NUM> may be employed. Also, although the bearing regions <NUM> and the bores formed by the inner arcuate surfaces <NUM> are shown as cylindrical, this is not essential. The finger assemblies move only in the axial direction on the centre shaft <NUM>, but do not rotate. Consequently, the bearing surfaces <NUM> and <NUM> could be non-circular, and in particular the bearing regions <NUM> of the centre shaft <NUM> could be continuations of the friction surfaces <NUM>. The quadrant elements <NUM> would then have flat bearing surfaces in place of the inner arcuate surfaces <NUM>. Regardless of the profile of the bearing regions <NUM> and the arcuate surfaces <NUM>, they may be hardened, polished and hard coated in the same manner as the friction surfaces <NUM> and the contact faces <NUM>.

In some embodiments where the bearing regions have the same profile and dimensions as the friction contact regions <NUM>, the finger assemblies <NUM> may be assembled separately from the centre shaft <NUM> and subsequently pushed onto the centre shaft <NUM> from one end, for example the end supported in the end cap <NUM>. That end may have a tapered lead-in section to spread the fingers <NUM> onto the friction surfaces <NUM>/bearing regions <NUM>.

Referring to <FIG>, a helicopter structure is generally indicated at <NUM> including a rotating system including a main sustaining rotor <NUM>, a helicopter fuselage <NUM> having rearwardly extending tail part <NUM> carrying an anti-torque rotor <NUM>. The fuselage <NUM> carries an engine and gearbox <NUM> which transmits drive to the main sustaining rotor <NUM>, to drive the rotor <NUM> about an axis A. The gearbox <NUM> is attached to the fuselage <NUM> by means of a plurality of resilient strut assemblies <NUM>, each of which includes a damper and/or absorber according to the present invention, e.g. one as shown or in a form similar to that as shown in <FIG>. In the present embodiment there are four resilient strut assemblies <NUM>, one positioned generally at each corner of the gearbox <NUM>; two at the front and two at the rear.

The fuselage <NUM> and gearbox <NUM> include parts of the helicopter structure which are capable of relative motion at a frequency corresponding substantially with a vibration exciting frequency and the resilient strut assemblies are configured to dampen the vibrations which will necessarily occur as the rotating system rotates, so as to dampen the forces seen by the fuselage.

Whilst the present invention has been described above with reference to its use in a helicopter, is should be appreciated that the dampers and/or absorbers of the present invention could be applied to other vibrating systems, such as, for examples (by no means limiting):-.

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.

Claim 1:
A vibration damper and/or absorber including a first member (<NUM>) having a bearing region (<NUM>) and a friction contact region (<NUM>), and a second member (<NUM>) including a body (<NUM>) which is mounted on the bearing region (<NUM>) for axial displacement with respect to the first member (<NUM>) along an axis, the second member (<NUM>) including a resilient member (<NUM>) which extends axially from the body (<NUM>) and which has a friction surface (<NUM>) which resiliently engages the contact region (<NUM>) of the first member (<NUM>), whereby relative linear displacement between the first (<NUM>) and second (<NUM>) members is opposed by frictional contact between the friction surface (<NUM>) and the contact region (<NUM>), and characterised in that
the resilient member (<NUM>) constitutes a first resilient finger extending axially from the body (<NUM>) in a first direction and in which the contact region (<NUM>) constitutes a first contact region (<NUM>) situated axially on one side of the bearing region (<NUM>), the body (<NUM>) being provided with at least one second resilient member aligned with the or each respective first resilient member and extending axially from the body (<NUM>) in a second direction opposite to the first direction and contacting a second contact region (<NUM>) of the first member (<NUM>), situated axially on the other side of the bearing region (<NUM>).