Patent Description:
Typically a bush for resisting vibration comprises two anchor parts that are connected by resilient material, such as rubber. One anchor part is attached to one component of the vibrating machinery, and the other anchor part attached to another component. As the two components vibrate relative to each other, the resilient material to provide isolation between vibrating component and anchor. Such bushes thus permit some relative movement, but act to prevent excessive movement between components.

<CIT> discloses an example of a bush, in which the anchor part for one component of the vibrating machinery is in the form of a hollow sleeve and the other anchor part in the form of a rod or tube extending approximately centrally and coaxially of the sleeve. A resilient body, e.g. of rubber or other suitable elastomeric material, is disposed within an annular volume between the sleeve and the rod. The resilient body can be secured in place, e.g. by radial crimping of the sleeve towards the rod.

The resilient body between the sleeve and the rod represents a spring element for isolating vibration. The dynamic stiffness of this spring element varies with vibration frequency depending on a number of factors, including the resilient material used, and the shape and configuration of the connection between the sleeve and rod. However, in any given arrangement, the resilient body will exhibit one or more eigenmodes where the dynamic stiffness increases and the vibrational isolation between the interconnected components is reduced.

It is desirable for dynamic stiffness increases due to eigenmodes of the resilient body to be reduced within a frequency range associated with normal operation of the two components to be interconnected (e.g. engine and chassis in a vehicle). <CIT> proposes a shaft bearing. <CIT> proposes a cylindrical vibration isolating device. <CIT> proposes an elastic support for a vibrating mass.

At its most general, the disclosure describes a tuning element that can be integrally formed with a resilient body of a bush and configured to reduce dynamic stiffness increases associated with eigenmodes of the resilient body within a predetermined operational vibration frequency range. The tuning element may resemble an upstanding wall or wing on an outer surface of the resilient body. A bush configured in this way may be particular suitable for use in scenario where the operational vibration frequency range comprises high frequency, such as an engine mount for an electric vehicle. The predetermined operational frequency range may be a sensitive vibration frequency range, e.g. associated with vibration frequency that may be expected to occur regularly or for extended periods during operation. For example, where the bush is connected in a vehicle, the predetermined operation vibration frequency range may be associated with motor vibrations associated with cruising across a range of conventional speeds.

According to the present invention, there is provided a bush for isolating vibrations as set out in claim <NUM>. The tuning element preferably comprises an annular wall or wing that encircles the longitudinal axis and protrudes from the outer surface of the resilient body.

The term "resilient" is used herein to indicate generally the ability to recoil or spring back, e.g. in an elastic manner, after application of a deforming force.

The tuning element may be integrally formed with the resilient body. In other words both the resilient body and the tuning element may be made from the same resilient deformable material, e.g. natural rubber or the like. However, in other examples, the tuning element may be a separate entity that is bonded or otherwise secured to the resilient body.

The tuning element may comprise a plurality of annular walls. Each annular wall may be coaxial with the longitudinal axis.

The outer surface of the resilient body may be any exposed surface of the resilient body from which the tuning element can extend without interfering with operation of the bush. For example, the tuning elements may comprise protrusions on axially-facing surfaces or radially-facing surfaces of the resilient body. As mentioned above, the tuning element may comprise annular elements, e.g. in the form or a wall or wing that projects from a surface of the resilient body. The annular wall or wing may project in any direction relative to the longitudinal axis. For example, it may extend in a direction parallel or normal to the longitudinal axis. Or it may be angled relative to the longitudinal axis.

In one embodiment, the second anchor part may be disposed coaxially with respect to the first anchor part. The resilient body may thus extend radially between the first anchor part and the second anchor part. In this example, the upstanding wall may be on an axial end surface of the resilient body. The upstanding wall may be an annular wall having a height extending in the axial direction. For example, the tuning element may comprise an upper annular wall protruding from an upper axial end surface of the resilient body, and a lower annular wall protruding from a lower axial end surface of the resilient body. In some examples there may be multiple annular walls on one or both axial end surfaces.

Each annular wall may have a maximum radial thickness that is less than half, preferably less than a third or a quarter, of the radial length of the axial end surface. Each annular wall may have a substantially uniform radial thickness along its axial length.

The resilient body comprises a plurality of radial arms spaced apart around the longitudinal axis, and wherein each pair of adjacent arms are separated by a longitudinally extending passageway. The upstanding wall bridges across each longitudinally extending passageway so that it encircles the longitudinal axis in a continuous manner.

In one example, the first anchor part may be a rod extending along the longitudinal axis. The second anchor part may comprise a sleeve surrounding the rod and defining an annular space therebetween. The resilient body may extend radially between an outer surface of the rod and an inner surface of the sleeve. The resilient body may be a solid resilient member that fills the annular volume between the rod and the sleeve, or may be a moulded resilient member having passages or cavities therein to facilitate relative movement between the first anchor part and the second anchor part during vibration.

The resilient body may comprise an upper lobe that extends radially between the first anchor part and second anchor part and a lower lobe that extends radially between the first anchor part and second anchor part. The upper lobe and lower lobe may be separated by an annular space. The upper axial end surface may be on the upper lobe and the lower axial end surface may be on the lower lobe.

The resilient body may comprise a snub portion in the annular space. The snub portion may be configured to limit radial travel of the first anchor part relative to the second anchor part.

Preferably the resilient body is formed by injection moulding.

Preferably the first anchor part is connectable to a first machine component and the second anchor part is connectable to a second machine component, whereby the bush is operable to isolate vibrations between the first machine component and second machine component. For example, the first machine component may be an electric motor. Alternatively, the first machine component and the second machine component are the engine and chassis of a vehicle.

Embodiments of the invention and constructions useful for understanding the invention are described in detail below with reference to the accompanying drawings, in which:.

<FIG> is a cross-sectional view of a known type of bush <NUM> that is described here to facilitate understanding of the invention. The bush <NUM> has a generally cylindrical configuration that exhibits rotation symmetry about a longitudinal axis. The cross-sectional side view shown in <FIG> is taken parallel to the longitudinal axis <NUM>.

The bush <NUM> comprises a first anchor part <NUM> and a second anchor part <NUM>. The second anchor part <NUM> is spaced from the first anchor part <NUM> by a resilient body <NUM> which extends between them.

The first anchor part <NUM> comprises a rigid rod, which may be a hollow tube, made from any suitable material, e.g. a metal such as aluminium or steel. In some embodiments, the first anchor part <NUM> may be formed of two or more components. For example, the first anchor part <NUM> may have a core component, such as a hollow metal tube, surround by an annular plastic component (e.g. formed by injection moulding) which connects the core to the resilient body <NUM>.

The first anchor part <NUM> is configured to be attached to a first component of vibrating machinery (not shown) in any conventional manner.

The second anchor part <NUM> comprises a rigid sleeve, e.g. formed from plastic or metal, disposed coaxially with the first anchor part <NUM> to define an annular space therebetween. The second anchor part <NUM> may configured to be attached to a second component of vibrating machinery (not shown). The second anchor part <NUM> may comprise a metal (e.g. extruded aluminium) housing or canister that contains the resilient body <NUM>. The metal housing may have a protective coating (not shown) on its outer surface, e.g. made from vulcanised rubber or the like.

For example, the first component may be an engine or motor and the second component may be the chassis of a vehicle. The bush <NUM> may be particularly suitable for use between the drive unit, such as the motor, and chassis in an electric vehicle.

In the annular space between the first anchor part <NUM> and the second anchor part <NUM>, a resilient body <NUM> is provided. The resilient body <NUM> may be formed from a resiliently deformable material such as rubber. For example, the resilient material may be rubber having a hardness of between <NUM> and <NUM> as measured with a Shore A durometer. The resilient body <NUM> could either have voids/passageways or be solid rubber, as required by the desired stiffness characteristic.

In some examples, the resilient body <NUM> may be bonded to one or both of the first anchor part <NUM> and the second anchor part <NUM>. For example, the resilient body <NUM> may be bonded to the first anchor part <NUM> and this arrangement may be push-fitted into the second anchor part <NUM> to increase durability. The increase in durability comes from pre-compressing the rubber to remove residual stresses caused by the rubber shrinking during moulding.

The resilient body <NUM> extends radially between an outer surface of the first anchor part <NUM> and an inner surface of the second anchor part <NUM>. The second anchor part <NUM> may comprise an upper ring element <NUM> and a lower ring element <NUM> which are affixed to respective upper and lower lobes <NUM>, <NUM> of the resilient body <NUM>. The upper ring element <NUM> and the lower ring element <NUM> may be formed from a suitably rigid plastic material, e.g. by injection moulding. The material may be selected to provide a robust connection to the material of the resilient deformable material.

The second anchor part <NUM> may include a radially inwardly protruding portion <NUM> disposed between the upper ring element <NUM> and the lower ring element <NUM>. The radially inwardly protruding portion <NUM> may be arranged to limit the radial travel of a snub portion <NUM> on the resilient body. In this example, the snub portion <NUM> is a circumferential rib that protrudes outwardly from an outer surface of the first anchor part <NUM>. The radially inwardly protruding portion <NUM> may be integrally formed with the second anchor part <NUM> or may be a separate moulded component, e.g. injection moulded, that is retained by the second anchor part <NUM>. The upper ring element <NUM> and lower ring element may be secured to the radially inwardly protruding portion <NUM>, e.g. around axial ends thereof.

<FIG> is a cross-sectional view of a bush <NUM> that is a construction useful for understanding the invention. Features in common with the bush <NUM> of <FIG> are given the same reference number and are not described again.

The bush <NUM> differs from the bush <NUM> of <FIG> in the provision of tuning elements <NUM>, <NUM> operably connected to the resilient body <NUM>. In this example, the tuning elements <NUM>, <NUM> are coupled respectively to an upper surface <NUM> of the upper lobe <NUM> of the resilient body and a lower surface <NUM> of the lower lobe <NUM> of the resilient body. In principle the tuning elements <NUM>, <NUM> can be coupled to other regions of the resilient body <NUM>, but these locations may be advantageous because they do not interfere with operation of the movement limiter formed by the snub portion <NUM> and radially inwardly projecting surface <NUM>.

It may be desirable to provide a tuning elements <NUM>, <NUM> on both the upper surface <NUM> and the lower surface <NUM> as shown in <FIG>. Where the bush is symmetrical (i.e. the upper and lower lobes <NUM>, <NUM> are the same), the tuning elements <NUM>, <NUM> may have the same configuration. More generally, any number of tuning elements may be provided on the upper and lower surfaces <NUM>, <NUM> in order to provide a smooth dynamic stiffness response across the operational vibration frequency range.

In this example, the tuning elements <NUM>, <NUM> each comprise an extension of the resilient body <NUM> in the form of an axially extending annular wall or wing that encircles (e.g. is coaxial with) the longitudinal axis <NUM>. The tuning elements <NUM>, <NUM> may be integrally formed with the resilient body <NUM>, i.e. may be formed of the same resilient deformable material. However, in other embodiments, the tuning elements may be formed separately and bonded or otherwise secured to the resilient body <NUM>.

In the construction of <FIG>, each tuning element <NUM>, <NUM> comprises a single upstanding annular wing that extends in the axial direction. In other example, each tuning element may comprise a plurality of spaced annular wings, and/or each wing may extend at an angle relative to the longitudinal axis. Each wing may have a radial thickness that is much less than the radial extent (e.g. width) of the resilient body. This has the effect of controlling the position on the resilient body where the additional mass of the tuning element is effective.

The tuning elements <NUM>, <NUM> operate as mass dampers for the purpose of damping resonances of the bush, so that the bush exhibits a low dynamic stiffness across a desired vibration frequency range. In this case, it has been found that the tuning elements <NUM>, <NUM> are particular useful in damping resonance across a vibration frequency range associated with the normal operation of an electric motor, e.g. in an electric or hybrid motor vehicle. This vibration frequency range may be higher than that associated with conventional internal combustion engines. The desired vibration frequency range in which the tuning elements <NUM>, <NUM> cause damping may be <NUM>-<NUM>, for example.

In use, the resilient body <NUM> and the tuning elements <NUM>, <NUM> operate together to isolate vibrations between the first anchor part <NUM> and the second anchor part <NUM>. In this way, a first component may be isolated from vibrations of a second component, and vice versa, by interconnecting the two components using the bush <NUM>. As the two components affixed to the bush <NUM> vibrate relative to each other, the resilient body <NUM> and the tuning elements <NUM>, <NUM> deform to isolate the vibration. The resilient body <NUM> may have one or more eigenmodes at which the dynamic stiffness of the resilient material increases, tending to reduce vibrational isolation between the two interconnected components. As explained above, the provision of the tuning elements <NUM>, <NUM> serves to reduce these stiffness increases at the eigenmodes, ensuring that two components are isolated from relative vibration at all operating frequencies.

Properties of the resilient body <NUM> and tuning elements <NUM>, <NUM> may be selected to isolate vibrations across the operating frequency range of the two components. In particular, the properties and dimensions of the tuning elements <NUM>, <NUM> may be selected so as to isolate the first anchor part <NUM> and second anchor part <NUM> from dynamic stiffness increases associated with eigenmodes of the resilient body <NUM>. The shape, material and configuration of the tuning elements <NUM>, <NUM> may be selected so that the bush exhibits a desirable dynamic stiffness characteristic, as discussed below. For example, the tuning elements <NUM>, <NUM>116b may be manufactured from a resilient material having a desired stiffness and/or hardness, or any other material property. The tuning elements <NUM>, <NUM> may also be tuned to ensure that they isolate dynamic stiffness increases at the eigenmodes of the resilient body <NUM>.

<FIG> is a cut-away perspective view of the bush <NUM> provided to show the three-dimensional nature of the features in more detail. Features discussed above are given the same reference number and are not discussed again.

<FIG> shows a graph of dynamic stiffness against frequency for a known bush such as the bush <NUM> shown in <FIG> and a bush such as the bush <NUM> shown in <FIG>.

As can be seen in <FIG>, a dynamic stiffness characteristic <NUM> for a known bush exhibits stiffness peaks <NUM>, <NUM> corresponding to eigenmodes at approximately <NUM> and <NUM>. These peaks represent reduced vibrational isolation between two components interconnected by the bush. For example, where the bush is used to mount an engine or motor to the chassis of a vehicle, this may result in unwanted noise. It is therefore desirable to reduce or eliminate the stiffness increases in the bush at these frequencies.

A bush such as that shown in <FIG> may have a dynamic stiffness characteristic <NUM> in which dynamic stiffness peaks at approximately <NUM> and <NUM> are reduced or eliminated. Eigenmodes of the bush are dependent on the size or material of the resilient body <NUM>. Therefore, by suitable configuration of the tuning element <NUM>, <NUM>, the damping effect at these frequencies may be adjusted, and the frequencies of the damping effect may be 'tuned' to more closely match the eigenmodes of the resilient body <NUM>. By providing the tuning element <NUM>, 204in this way, it can be seen in <FIG> that the dynamic stiffness peaks are much reduced, meaning that two components which are connected by bush are isolated from relative vibration across the desired range of operating frequencies.

<FIG> show various views of a bush <NUM> that is another construction useful for understanding the invention. Features in common with the bushes <NUM>, <NUM> shown in <FIG> and <FIG> are given the same reference number and are not described again.

<FIG> shows a top view of the bush <NUM>. Similarly to the bush <NUM> shown in <FIG>, the bush <NUM> includes a tuning element <NUM> coupled to an upper surface of resilient body <NUM>. In this example, the resilient body <NUM> is formed with a plurality of axial passageways <NUM> therethrough, such that it comprises a plurality of radial arms that extend between the anchor parts <NUM>, <NUM>. The passageways <NUM> are disposed regularly around the axis <NUM> of the bush. In this example there are four passageways <NUM>, but the bush <NUM> need not be limited to this number of configuration.

Each passageway <NUM> is defined by an aperture <NUM> through in the upper surface of the resilient body <NUM>. The passageway <NUM> preferably extends completely through the resilient body in the axial direction. In <FIG> the snub portion <NUM> and radially inwardly projecting surface <NUM> within the bush are visible when looking down through the aperture <NUM>. However, in other examples the passageway <NUM> may be closed, e.g. at the lower surface of the upper lobe <NUM> and/or the upper surface of the lower lobe <NUM>. In such an example, the passageway <NUM> may resemble a pocket or blind channel formed in the respective lobe of the resilient body <NUM>. The passageway <NUM> may be closed by a web or skin of resilient material that spans across the passageway <NUM> within the resilient body <NUM>. The web may be integrally formed with the resilient body <NUM>.

The passageways <NUM> provide gaps in the circumferential extent of the resilient body <NUM>. Such gaps may improve the performance of the bush for dampening high frequency vibrations between the anchor parts <NUM>, <NUM> compared with a configuration having an unbroken circumferential resilient body.

As shown in <FIG>, the resilient body <NUM> in the bush <NUM> has both an upper lobe <NUM> and a lower lobe <NUM>. Passageways <NUM> are provided in both the upper lobe <NUM> and the lower lobe <NUM> in an aligned manner, i.e. in which each passageway in the upper lobe has a corresponding passageways in the lower lobe aligned therewith in an axial direction.

In the bush <NUM> shown in <FIG>, a tuning element <NUM> is coupled to each portion of the resilient body <NUM> that extends between adjacent passageways <NUM>. Similarly to the bush <NUM> shown in <FIG>, each tuning element <NUM> is an upstanding wing that extends in the axial direction. Corresponding tuning elements <NUM> are provided on the lower surface of the lower lobe <NUM>, such that the bush is symmetrical about a lateral mid plane.

<FIG> shows a top view of the bush <NUM>. Similarly to the bush <NUM> shown in <FIG>, the bush <NUM> has a resilient body <NUM> that is formed with a plurality of axial passageways <NUM> therethrough. The passageways <NUM> are disposed regularly around the axis <NUM> of the bush. In this example there are four passageways <NUM>, but the bush <NUM> need not be limited to this number of configuration.

Each passageway <NUM> is defined by an aperture <NUM> through in the upper surface of the resilient body <NUM>. The passageway <NUM> preferably extends completely through the resilient body in the axial direction. In <FIG> the snub portion <NUM> and radially inwardly projecting surface <NUM> within the bush are visible when looking down through the aperture <NUM>. However, in other examples the passageway <NUM> may be closed, e.g. at the lower surface of the upper lobe <NUM> and/or the upper surface of the lower lobe <NUM>, as discussed above.

Unlike the bush <NUM>, however, where the tuning element <NUM>, <NUM> are confined to the surface of the resilient body <NUM>, in the bush <NUM>, each tuning element <NUM> has a portion <NUM> that extends over the boundary of the aperture <NUM> to protrude into the passageway <NUM>. The extent and direction in which the portion <NUM> protrudes into the passageway <NUM> may be selected to assisting tuning of the bush's performance. <FIG> shows that the portion <NUM> protrudes along the whole length of the respective lobe of the resilient body, but this need not be essential.

<FIG> show various views of a bush <NUM> that is an embodiment of the invention. Features in common with the bushes <NUM>, <NUM> shown in <FIG> and <FIG> are given the same reference number and are not described again.

<FIG> shows a top view of the bush <NUM>. Similarly to the bush <NUM> shown in <FIG>, the bush <NUM> has a resilient body <NUM> that is formed with a plurality of axial passageways <NUM> therethrough. The passageways <NUM> are disposed regularly around the axis <NUM> of the bush. In this example there are four passageways <NUM>, but the invention need not be limited to this number of configuration.

In the bush <NUM> shown in <FIG>, a tuning element <NUM> is coupled to a top surface of the upper lobe <NUM> of the resilient body <NUM>. However, unlike the arrangement discussed above in which a separate tuning element was provided on each portion of the resilient body between the passageways, in this embodiment the tuning element <NUM> is a continuous entity that encircles the axis <NUM>. The tuning element <NUM> is coupled to each portion of the resilient body <NUM> that extends between adjacent passageways <NUM>. But rather than terminating at or in the passageways <NUM>, the tuning element <NUM> bridges between opposite sides of passageway <NUM>. <FIG> shows that the bridging portion (i.e. the part of the tuning element within the passageways) extends down the whole axial length of the respective lobe of the resilient body. However, this arrangement need not be essential. For example, the bridging portion may pass only over the top of the passageway <NUM>.

As shown in <FIG>, the tuning element <NUM> is in the form of a circle centred on the axis <NUM>. However, other geometries (e.g. elliptical or irregular) may be used. Similarly to the bush <NUM> shown in <FIG>, the tuning element <NUM> is an upstanding annular wing that extends in the axial direction. A corresponding tuning elements <NUM> is provided on the lower surface of the lower lobe <NUM>, such that the bush is symmetrical about a lateral mid plane.

Claim 1:
A bush (<NUM>) for isolating vibrations, the bush comprising:
a first anchor part (<NUM>) that defines a longitudinal axis;
a second anchor part (<NUM>) spaced from the first anchor part;
a resilient body (<NUM>) extending between the first anchor part and the second anchor part and operably engaged with the first anchor part and the second anchor part to isolate vibrations therebetween, the resilient body comprising a plurality of radial arms spaced apart around the longitudinal axis, wherein each pair of adjacent arms is separated by a longitudinally extending passageway (<NUM>); and
a tuning element (<NUM>, <NUM>) operably coupled to an outer surface of the resilient body,
wherein the tuning element is configured to reduce dynamic stiffness increases associated with eigenmodes of the resilient body within a predetermined operational vibration frequency range, and
characterised in that the tuning element comprises an upstanding wall on the outer surface of the resilient body, the upstanding wall bridging across each longitudinally extending passageway.