Patent Description:
Rotating machinery, for example gas turbines, can produce vibrations in use which may not be desirable, and which can lead to wear and subsequent damage to internal machine components.

Known solutions to the problem of unwanted vibrations include oil squeeze films, which can provide damping and reduce vibrations. A squeeze film may, for example, be a layer of oil between a bearing and a housing which increases the damping effect. This solution requires the presence of a radial clearance to accommodate the oil film. However, such a radial clearance provides a space which can lead to component misalignment problems.

Sealing rings have also been used to provide centralising, damping and sealing effects. However, the sealing rings can be subjected to high loads causing the sealing rings to wear out relatively quickly. Furthermore, when the gap between the shaft and the housing is filled with hot fluid, such as oil, the chemical structure of the material forming the sealing rings (e.g. rubber) can break down and cause the ring to deform. Over time, the sealing rings become less effective at sealing and providing the necessary damping/centralisation effects. <CIT> discloses a handle assembly for a rotating shaft which reduces shaft wobble. The handle assembly has a bearing in the form of a split ring which is arcuate in cross section to provide a reduced friction when the bearing is placed between the shaft and a housing axial bore. The handle assembly is employed to engage and rotate the stem of a valve. In a preferred manner, the bearing affords a cavity for a shaft lubricant. <CIT> discloses a mounting assembly comprising a static cylinder liner mounted in a housing by means of a spring ring.

It is therefore an object of embodiments of the present invention to address at least one of the above disadvantages.

The invention provides a shaft mounting assembly comprising:.

The spring can be a stiff, high-rate spring to provide radial anti-vibration action, and also to provide a centralising effect between the shaft and the cylinder. The spring of the present invention can provide radial centralising of the shaft within the cylinder, thus allowing any sealing rings to act only as seals. This can help to increase the longevity of the sealing rings.

Furthermore, the axially arcuate, or crescent, shape of the inner and outer surfaces of the band, combined with the material the band is made of, means that the spring is both axially and radially resilient and compliant (flexible). In turn, this can allow the spring to withstand higher axial and radial loads in use compared to sealing rings alone.

The outer surface of the shaft may comprise the groove, such that the groove extends around the circumference of the outer surface of the shaft. Alternatively, the inner surface of the cylinder may comprise the groove, such that the groove extends around the circumference of the inner surface of the cylinder.

The groove can comprise a recessed base, and two substantially parallel side faces arranged perpendicular to the base. The groove can comprise an opening, such as opposite the recessed base, such that the spring can protrude from the groove through the opening. The opening can be flush with the inner surface of the cylinder, or the outer surface of the shaft.

In the energised state, the spring can be compressed within the bore between the outer surface of the shaft and the inner surface of the cylinder. The portion of the band between the axial edges can protrude out of the groove in the de-energised and the energised states. In the energised state, the portion of the band can extend across the gap to make a single point of contact with the inner surface of the cylinder or the outer surface of the shaft, depending on whether the groove is located around the outer surface of the shaft or the inner surface of the cylinder respectively. The single point of contact can be located at the mid-point between the two axial edges of the band.

The maximum, or outer, diameter of the outer surface of the band may be greater than the inner diameter of the cylinder, when the groove extends around the outer surface of the shaft. Alternatively, the minimum, or inner, diameter of the inner surface of the band may be less than the outer diameter of the shaft, when the groove extends around the inner surface of the cylinder.

In the de-energised state, the axially arcuate surfaces of the band can have an arc measure (the arc angle) of from <NUM> degrees to <NUM> degrees relative to the radius of the arc. The arc angle may be around <NUM> degrees relative to the radius of the arc.

The band can have correspondingly shaped arcuate inner and outer surfaces along the longitudinal axis of the band. The outer surface of the band may be axially convex in shape and the inner surface of the band may be correspondingly axially concave in shape. Alternatively, the outer surface of the band may be axially concave in shape and the inner surface of the band may be correspondingly axially convex in shape.

The portion of the band which protrudes out of the groove may be the peak, or apex, of the outer surface of the band, when the groove is located around the outer surface of the shaft. The apex can be located at the mid-point between the two axial edges of the band. Alternatively, the portion of the band which protrudes out of the groove may be the trough of the inner surface of the band, when the groove is located around the inner surface of the cylinder. The trough can be located at the mid-point between the two axial edges of the band.

The inner and outer surfaces may have a circular arc shape. As the spring is energised by radial compression (due to compression between the outer surface of the shaft and the inner surface of the cylinder), the width of the band increases as the axial edges of the band move away from each other in an axial direction.

In the de-energised state, the narrower width of the band compared to the width of the groove means that there is sufficient space to allow the band to axially spread (i.e. the axial width of the band increases) as the spring is energised. As explained further below, in addition to a centralising effect, this can help to provide a radial restorative effect.

The band can have a substantially regular or uniform profile. In both the de-energised and energised states, the band can have a substantially constant thickness.

The thickness of the band may be at least <NUM>. The ratio of the width of the band (chord of the axially arcuate surfaces) to the thickness of the band may be approximately <NUM>:<NUM> in the de-energised state.

The aspect ratio of the axial width of the band (the chord of the axially arcuate surfaces) to the height of the arcuate surfaces (the sagitta) can be <NUM>:<NUM> in the de-energised state. The sagitta in the de-energised state is greater than the sagitta in the energised state (when the spring is compressed within the bore).

The aspect ratio of the width of the groove to the depth of the groove can be <NUM>:<NUM>. In both the energised and de-energised states, the height of the band can be greater than the depth of the groove, such that at least a portion of the band can protrude out of the opening of the groove.

The width of the band can be less than the width of the groove in the energised state.

The discontinuous band can comprise a gap in its circumference, such that the ends of the band are spaced apart. As the spring is compressed within the bore, the ends of the band can be brought closer together to allow the band to contract around the shaft, or the ends of the band are spaced further apart to allow the band to expand within the bore. The gap can become smaller when compared to the de-energised state as the band contracts around the shaft. The gap can become bigger when compared to the de-energised state as the band expands within the bore. In use, when the spring is in the energised state, the gap can allow the spring to expand or contract due to thermal fluctuations within the assembly.

In some embodiments, the discontinuous band may be comprised of spring steel. However, it will be appreciated that any other suitable material can be used. The material preferably has a stiff, high spring rate. For example, the spring rate can be in the range of <NUM> N/mm to <NUM> N/mm.

The assembly can additionally comprise a further spring comprising a substantially circular and discontinuous band having correspondingly shaped axially arcuate inner and outer surfaces. The further spring can be positioned in the groove such that both axial edges of the band of the further spring are located within the groove. The spring and the further spring can be double banked, such that they are stacked on top of the other within the groove. The depth of the groove may be increased by one spring thickness to accommodate the stacked spring arrangement. The combined spring rate of the stacked springs can be in the range of <NUM> N/mm to <NUM> N/mm, for example <NUM> N/mm.

The further spring can also comprise a gap in its circumference. The gap of the spring and the gap of the further spring can be aligned. Alternatively, the gap of the spring and the gap of the further spring can be circumferentially offset.

Using a single spring arrangement, a greater spring rate can typically be achieved by increasing in the spring thickness. However, a thicker spring will have a reduced range of radial movement because the stress in the spring can become too high. Using a stacked spring arrangement instead, the spring rate can be increased without having to make the individual springs thicker. This means that the range of radial travel is very similar to a single spring arrangement. Therefore, a stacked spring arrangement can provide a greater spring rate compared to a single spring arrangement, whilst maintaining the same range of radial travel as the single spring arrangement.

The shaft can have a further groove extending around the circumference of the outer surface of the shaft. Alternatively, the inner surface of the cylinder can have a further groove extending around the circumference of the inner surface of the cylinder. A sealing ring can be positioned within the further groove.

The cylinder can have a side wall port communicating with the bore. The groove can be located between the further groove and the side wall port. The outer surface of the shaft can comprise a groove and a further groove on both sides of the side wall port. Alternatively, the inner surface of the cylinder can comprise a groove and a further groove on both sides of the side wall port. Each groove can be located between the respective further groove and the side wall port. Each groove can contain a spring, as described herein. Each groove can also contain a further spring, as described herein. Each further groove can contain a sealing ring.

The side wall port can provide a supply of a bearing fluid to the gap. The assembly can be a static piston assembly. A static piston assembly can be defined as non-rotational and non-reciprocating.

The invention also provides a method of assembling the assembly according to the invention, the method comprising the steps of:.

In embodiments where the band is positioned around the shaft, the step of inserting the shaft into the bore and compressing and energising the spring causes the ends of the band to be brought closer together. In embodiments where the band is positioned within the bore, the step of inserting the shaft into the bore and compressing and energising the spring causes the ends of the band to be moved further apart.

Due to the shape of the spring, the net radial force acting on the shaft will be zero, which helps to keep the shaft concentric with the bore, and also provide a radial restorative effect. If the shaft is moved off-centre in a given direction, the spring will act to re-centre the shaft within the bore, by increasing the reaction force in the given direction whilst reducing the force in the opposite direction. As such, the load on the spring may not be even around the circumference of the spring, but the net force will remain zero. When the groove is located around the outer surface of the shaft, the action of the spring may be referred to as outspringing. When the groove is located around the inner surface of the cylinder, the action of the spring may be referred to as inspringing.

The method may further comprise installing the further spring within the groove, by either:.

In embodiments comprising a spring and a further spring stacked on top of the other within the groove, this may minimise the force that is required to re-centre the shaft within the cylinder, and provide a stronger restorative effect.

Whilst the invention has been described above, it extends to any inventive combination falling within the scope of the claims, either as set out above, or in the following description or drawings.

The invention may be performed in various ways, and an embodiment thereof will now be described by way of example only, reference being made to the accompanying drawings, in which:.

The term "axial" as used herein is defined as in a direction parallel to the longitudinal axis of the spring, which extends through the centre of the band. For example, "axial width of the spring" is defined as the width of the spring extending along the longitudinal axis of the spring.

The term "radial" as used herein is defined as in a direction perpendicular to the longitudinal axis of the spring, and extends from the longitudinal axis to a point on the circumference of the band.

<FIG> show a side view of a spring and a cross section through line A-A. The figures are labelled with various terminology used to describe the geometry of the spring herein.

<FIG> shows a de-energised spring <NUM> comprising a discontinuous band <NUM> having a substantially circular cross-section with diameter d<NUM> (seen in <FIG> and <FIG>). In this example, the diameter d<NUM> may be around <NUM>. As also shown in <FIG>, the discontinuity is formed by creating a gap <NUM> in the band, such as by axially cutting the band. The gap <NUM> causes the ends of the band to be spaced apart. This allows the spring to be easily fitted around a shaft, such as a piston, by separating the two ends of the band, and releasing them around the shaft (see <FIG>). In this example, the band <NUM> is made of spring steel which is stiff, with a high spring-rate, and ensures that the band is sufficiently resilient to not be permanently deformed by such manipulation. It will be appreciated that other suitable materials can also be used.

The band <NUM> comprises an outer surface <NUM> and an inner surface <NUM>, as seen in <FIG>. The outer and inner surfaces <NUM>, <NUM> of the band are correspondingly arcuately shaped. The outer surface <NUM> has an axially convex shape, and the inner surface has a corresponding axially concave shape (see <FIG> and <FIG>). In this example, the arc length is around <NUM>. The width (or chord) of the axially arcuate surfaces, w, can be seen in <FIG>. The width in this example is around <NUM>. The height, or sagitta, of the arc is demonstrated in <FIG>, and is around <NUM> when in a de-energised state. When in use, in an energised state, the height of the arcuate shape is around <NUM>. Thus, the axially arcuate shape of the band has an aspect ratio (the ratio of the chord to the sagitta) of around <NUM>:<NUM>.

As can be seen in <FIG>, the band <NUM> also comprises a regular or uniform profile and a constant thickness. In this example, the thickness of the band <NUM> is around <NUM>.

As shown in <FIG>, the outer surface <NUM> at boundaries 18a, 18b has a first radial distance r<NUM>, that is the radial distance from the axis of the band to the boundaries of the band. The outer surface <NUM> at apex <NUM> has a second radial distance r<NUM>, that is the radial distance from the axis of the band to the apex of the band.

The second radial distance r<NUM> is greater than the first radial distance r<NUM>. This defines the arcuate shape, with the apex <NUM> positioned at the mid-point between the boundaries 18a, 18b of the band. The difference between r<NUM> and r<NUM> defines the sagitta. The arcuate shape may also be referred to as a crescent shape. The outer surface <NUM> and the inner surface <NUM> have corresponding arcuate shapes. The (outer) diameter d<NUM> is defined by the apex <NUM> of the outer surface <NUM>.

In embodiments, a stacked spring arrangement <NUM> may be provided (see <FIG>). The stacked spring arrangement <NUM> comprises spring <NUM> and a further spring <NUM>. Spring <NUM> is identical to spring <NUM>, both structurally and functionally. As shown in <FIG>, spring <NUM> and further spring <NUM> are stacked on top of each other. Spring <NUM> may be referred to as the inner spring, and further spring <NUM> may be referred to as the outer spring. Alternatively, the springs may be switched, such that spring <NUM> is the outer spring, and further spring <NUM> is the inner spring.

One use for spring <NUM>, or stacked arrangement <NUM>, is within a shaft mounting assembly <NUM>, part of which can be seen in <FIG>. Specifically, <FIG> shows a cross-section through one half of an elongate shaft <NUM> located within the bore of a cylinder or housing <NUM>. The shaft mounting assembly <NUM> is non-reciprocating and non-rotational. That is, the shaft <NUM> and cylinder <NUM> are not intended to move relative to each other.

The cylinder <NUM> comprises a side wall port <NUM>. The inner diameter of the cylinder <NUM> is larger than the outer diameter of the shaft <NUM>, thus creating a gap <NUM> between the outer surface of the shaft <NUM> and the inner surface of the cylinder <NUM>. The gap <NUM> is filled with a fluid <NUM>, such as oil. In use, the layer of fluid <NUM> between the cylinder <NUM> and the shaft <NUM> is supplied via the port <NUM>, and provides an anti-vibration damping effect, which in turn can help to minimise the vibrations and noise transmitted through the assembly when in use.

The shaft <NUM> has a substantially circular cross-section, and comprises two longitudinally spaced apart grooves <NUM>, and two further longitudinally spaced apart grooves <NUM>, around the circumference of the outer surface of the shaft <NUM>. The grooves <NUM> each contain a spring <NUM>, as described above. The spring <NUM> is entirely located within groove <NUM>, such that both axial edges of the spring <NUM> (boundaries 18a, 18b) are located within the groove <NUM>. Alternatively, the grooves <NUM> can comprise a stacked spring arrangement <NUM>, comprising the spring <NUM> and a further spring <NUM>. Both the spring <NUM> and the further spring <NUM> are entirely located within groove <NUM>, such that both axial edges of the spring <NUM> and the further spring <NUM> are located within the groove <NUM>.

The grooves <NUM> comprise a recessed base, two substantially parallel side faces arranged perpendicular to the base, and an opening located opposite the recessed base through which the spring <NUM> can protrude from the groove <NUM>. The opening is flush with the outer surface of the shaft <NUM>.

The grooves <NUM> each contain a seal in the form of an O-ring <NUM>. As can be seen in <FIG>, the springs <NUM> (and grooves <NUM>) are located between the O-rings <NUM> (and grooves <NUM>) and the port <NUM>.

Conventionally, the O-rings alone would provide the damping and centralising effects, as well as providing the required sealing effect. The springs of the present invention carry the radial load so that the O-rings can act predominantly as seals, whilst the springs act as centralisers. This can help to prolong the lifespan of the O-rings.

The width (or chord), w, of the band <NUM> is less than the width g<NUM> of groove <NUM>. Whilst in the de-energised state, the height of the arc is greater than the depth of the groove, such that the apex <NUM> of the band protrudes out of the opening of groove <NUM>. There is also a gap between one or both side edges of the groove <NUM>, and one or both axial edges (boundaries 18a, 18b) of the band. The gap allows the band to axially expand when compressed and energised in use. In embodiments, the width of the groove may be <NUM>, and the width of the band (namely, the chord of the axially arcuate surfaces) may be less than <NUM> (in both the energised and de-energised states). When energised, the width of the band <NUM> remains less than the width of the groove <NUM>.

In the de-energised state, diameter d<NUM> defined by the apex <NUM> of the outer surface <NUM> is greater than the inner diameter of the cylinder. When energised, the sagitta/height of the arc remains greater than the height of the groove, such that the apex <NUM> of the band protrudes out of the opening of groove <NUM> and into and across the gap <NUM>. The outer surface <NUM> of the band then makes a single point of contact with the inner surface of the cylinder <NUM> (defining the bore), which helps the springs <NUM> to provide the required centralising effects. Furthermore, the springs <NUM> can provide an element of sealing, although in this embodiment, this is not their primary purpose.

The above description also applies to stacked arrangement <NUM>. The width of the band of further spring <NUM> may also be less than <NUM> (in both the energised and de-energised states). In embodiments utilising the stacked spring arrangement <NUM>, the apex of the band of the outer spring (further spring <NUM> in <FIG>) protrudes out of the opening of groove <NUM> and into the gap <NUM>. The outer surface of the band then contacts the inner surface of the cylinder <NUM>, which helps the stacked spring arrangement <NUM> to provide the required centralising effect. Furthermore, the depth of the groove <NUM> is increased by around one spring thickness compared to the groove depth for spring <NUM> alone in order to accommodate the further spring <NUM>.

<FIG> shows some test results obtained by the Applicant which show the relationship between the radial deflection of the spring <NUM> and O-rings <NUM> and the radial load applied. Both O-rings tested were manufactured by Rhondama, and comprise different spring rates (<NUM> Nmm-<NUM> and <NUM> Nmm-<NUM>). The spring <NUM> was manufactured by the Applicant. The graph clearly shows that springs <NUM> are able to withstand higher radial loads compared to O-rings alone. Therefore, the springs <NUM> are much better suited to providing the required centralising effects for the shaft compared to O-rings alone. By allowing the springs <NUM> to take most of the radial load, the O-rings are much more effective at providing the required sealing.

In use, the cylinder <NUM> and shaft <NUM> are assembled by firstly installing a spring <NUM> within each groove <NUM>, by spacing apart the ends of the band and releasing them around the respective groove <NUM>. At this point, a further spring <NUM> may also be installed within one or both of the grooves <NUM>, by spacing apart the ends of the band and releasing them around the respective groove <NUM>, such that spring <NUM> sits on top of spring <NUM> within the groove <NUM>.

The following process will be described with regard to the single spring arrangement comprising spring <NUM> within each groove <NUM>, but the process will also apply to the stacked spring arrangement <NUM> comprising spring <NUM> and further spring <NUM> within each groove <NUM>.

At this point springs <NUM> are de-energised, and there is a gap between the axial edges of the band (boundaries 18a, 18b) and the edges of the respective groove <NUM>.

The shaft <NUM> is then inserted into the cylinder <NUM> (from left to right in <FIG>). As the first spring <NUM> (the rightmost spring in <FIG>) enters the bore, it is deformed and compressed, and becomes energised. In the energised state, the ends of the band <NUM> are brought together around the shaft <NUM>. As the band is compressed between the outer surface of the shaft and the inner surface of the cylinder, the height of the band is reduced, and the edges of the band (boundaries 18a, 18b) move away from each other in the axial direction and towards the edges of the groove, and the spaced apart ends of the band are brought closer together around the shaft. However, at no point does the chord distance between 18a and 18b become equal to the groove width g<NUM>, that is the band arcuate shape is not controlled axially by the groove <NUM>, and the chord distance between 18a and 18b is always less than g<NUM>. The rightmost spring <NUM> is held in the energised position between the shaft <NUM> and the cylinder <NUM>. The apex <NUM> of the spring <NUM> makes a single point of contact with the inner surface of the cylinder <NUM>.

As the shaft <NUM> moves further into the bore, the rightmost spring <NUM> has to move past radial port <NUM>, which provides a side opening to the cylinder <NUM>. There may be up to four radial ports, set <NUM> degrees apart around the circumference of the cylinder <NUM>. As the rightmost spring <NUM> moves past port <NUM>, it can relax and at least partially de-energise. However, when the rightmost spring <NUM> reaches the other side of the port, it is again deformed and compressed, and becomes fully re-energised.

Conventionally shaped rings are more likely to catch on the corner where the port <NUM> meets the remainder of the cylinder <NUM>, thus making assembly more difficult. The axially arcuate shape of spring <NUM>, along with its resilience and compliance, makes assembly easier and more efficient.

As the shaft <NUM> moves even further into the cylinder <NUM>, the second or leftmost spring <NUM> of <FIG> will eventually enter the bore, and will deform and compress, and become energised. The leftmost spring <NUM> does not move past radial port <NUM>.

When the shaft <NUM> is fully inserted into the bore of the cylinder <NUM>, a spring <NUM> is located on either side of radial port <NUM>. Both springs <NUM> are held in the energised position between the shaft <NUM> and the cylinder <NUM>.

Once the shaft <NUM> is fully inserted into the bore of the cylinder <NUM>, the gap <NUM> is then filled with oil <NUM> via port <NUM>. In use the fluid acts as a bearing.

In the energised position, the spring <NUM> exerts a net zero radial force against the inner surface of the cylinder <NUM>, which in use centres the shaft <NUM> within the cylinder <NUM>. The energised spring <NUM> also provides a radial anti-vibration effect, along with the oil <NUM> (which also acts as a bearing).

The net force acting on the shaft is zero, which helps to keep the shaft <NUM> centralised within the cylinder <NUM> (that is, the shaft and cylinder are concentric), and also provide a radial restorative effect. If the shaft is moved off-centre in a given direction, the spring <NUM> provides the required force to re-centre the shaft <NUM> within the cylinder <NUM>, by increasing the reaction force in the given direction whilst reducing the force in the opposite direction. As such, the load on the spring <NUM> may not be even around the circumference of the spring <NUM>, but the net force will remain zero. The spring <NUM> can react to approximately <NUM> N/mm of force in the radial direction, with a maximum displacement of around <NUM> (as determined by the radial clearance provided by the gap <NUM>).

It is therefore no longer the responsibility of the O-rings to provide a damping and centralising effect, and as such they can focus on sealing the shaft <NUM> in the cylinder <NUM>. In this embodiment, the spring <NUM> does provide an element of sealing, which can help to further increase the longevity of the O-rings by reducing the amount of hot oil <NUM> reaching the O-rings.

<FIG>, <FIG> and <FIG> show a further embodiment of the spring <NUM>. The structural and functional features described above with respect to spring <NUM> also apply to spring <NUM>, with any differences being highlighted below.

The spring <NUM> is essentially an inverted version of spring <NUM>, that is the outer surface <NUM> has an axially concave shape, and the inner surface <NUM> has a corresponding axially convex shape. The inner surface <NUM> at boundaries 218a and 218b has a larger radial distance than the inner surface <NUM> at trough <NUM>, which defines the arcuate shape. The trough <NUM> is positioned at the mid-point between boundaries 218a and 218b of the band <NUM>.

<FIG> show a side view of the spring <NUM> and a cross-section through line A-A. The figures are labelled with various terminology used to describe the geometry of the spring <NUM>. <FIG> show a de-energised spring <NUM> comprising a discontinuous band <NUM> having a substantially circular cross-section with (inner) diameter d<NUM> defined by the trough <NUM> of the inner surface <NUM>. The discontinuity is formed by creating a gap <NUM> in the band, which causes the ends of the band <NUM> to be spaced apart. This allows the spring to be easily fitted within a bore, by compressing the two ends of the band together, inserting the band <NUM> into the bore of a cylinder and releasing the band <NUM> so it seats in a groove <NUM> extending around the inner surface of the cylinder (see <FIG>).

Spring <NUM> can be used in a shaft mounting assembly as shown in <FIG>. Specifically, <FIG> shows a cross-section through one half of an elongate shaft <NUM> located within the bore of a cylinder or housing <NUM>. The bore defined by the inner surface of the cylinder <NUM> has a substantially circular cross-section. The inner surface of the cylinder <NUM> comprises a groove <NUM> extending around the circumference of the inner surface of the cylinder <NUM>. The groove <NUM> is the same as groove <NUM>, except it is located around the inner surface of the cylinder <NUM> instead of around the outer surface of the shaft <NUM>. The groove <NUM> contains a spring <NUM>, which is entirely located within groove <NUM>, such that both axial edges of the spring <NUM> (boundaries 218a, 218b) are located within the groove <NUM>.

Similar to <FIG>, the inner diameter of cylinder <NUM> is larger than the outer diameter of the shaft <NUM>, thus creating a gap <NUM> between the outer surface of the shaft <NUM> and the inner surface of the cylinder <NUM>. Diameter d<NUM> defined by the trough <NUM> of the inner surface <NUM> of the band <NUM> is less than the outer diameter of the shaft <NUM>. In use, the shaft <NUM> is inserted into the cylinder <NUM>, and as the shaft <NUM> passes across spring <NUM>, the spring <NUM> is deformed and compressed, and becomes energised. As the band is compressed between the outer surface of the shaft <NUM> and the inner surface of the cylinder <NUM>, the height of the band <NUM> is reduced, and the edges of the band (boundaries 218a, 218b) move away from each other in the axial direction and towards the edges of the groove, and the spaced apart ends of the band are moved further apart within the bore. The trough <NUM> of the spring <NUM> protrudes out of the opening of the groove <NUM> and extends across the gap <NUM> to make a single point of contact with the outer surface of the shaft <NUM>.

For comparison, <FIG> additionally shows a groove <NUM> located around the shaft <NUM> and comprising a spring <NUM>, as described above. Although spring <NUM> is an inverted version of spring <NUM>, it functions in exactly the same way as spring <NUM> in both the de-energised and energised states. In embodiments, a stacked spring arrangement may be provided, as described above, which comprises spring <NUM> and a further spring stacked on top of each other.

Claim 1:
A shaft mounting assembly (<NUM>) comprising:
an elongate shaft (<NUM>) comprising an outer surface having a substantially circular cross-section;
a cylinder (<NUM>) having an inner surface defining a bore, the bore housing the shaft (<NUM>), wherein the inner diameter of the cylinder (<NUM>) is larger than the outer diameter of the shaft (<NUM>) such that a gap is defined between the outer surface of the shaft (<NUM>) and the inner surface of the cylinder (<NUM>); and,
a spring (<NUM>) comprising a substantially circular discontinuous band;
wherein one of the outer surface of the shaft (<NUM>) and the inner surface of the cylinder (<NUM>) comprises a groove (<NUM>); and wherein the groove (<NUM>) extends around the circumference of the outer surface of the shaft (<NUM>) or the circumference of the inner surface of the cylinder (<NUM>) respectively;
wherein the spring (<NUM>) is positioned in the groove (<NUM>) such that both axial edges of the band are located within the groove (<NUM>); and,
wherein the spring (<NUM>) has a de-energised state in which the height of the band is greater than the depth (g2) of the groove (<NUM>), so that a portion of the band between the axial edges protrudes out of the groove, and the axial width of the band is less than the width (g1) of the groove (<NUM>); and,
an energised state in which the spring (<NUM>) is compressed within the bore such that the height of the band is reduced, and the axial width of the band is increased compared to the de-energised state; and
wherein the substantially circular discontinuous band of the spring (<NUM>) has correspondingly shaped axially arcuate inner and outer surfaces; and the axial width of the band is less than the width (g1) of the groove (<NUM>) in the energised state;
wherein
the shaft (<NUM>) is a static piston which is housed in the cylinder (<NUM>) so as to be non-reciprocatable and non-rotatable relative to the cylinder (<NUM>).