Patent Publication Number: US-2018029425-A1

Title: Noise-reducing device for a vehicle

Description:
TECHNICAL FIELD 
     The present disclosure relates to a noise-reducing device for a vehicle. Particularly, but not exclusively, the disclosure relates to a device for reducing tyre cavity noise. Aspects of the invention relate to a device, to a wheel rim and to a vehicle. 
     BACKGROUND 
     An important marketing and design concern for modern vehicles is to reduce the level of noise and vibration that is experienced by the occupants. There are many sources of noise in a vehicle, but as engines become more refined and produce less noise, the contribution of road/tyre interactions becomes more noticeable. In modern vehicles, as the vehicle speed exceeds 40 km/h, these road/tyre interactions become the dominant source of interior noise and vibration. 
     There are two significant contributors to the interior noise related to road/tyre interactions: external noise generated by vibration of the tyre on the road surface; and tyre cavity noise (TCN). TCN originates from resonance of the air column inside the tyre cavity as the tyre wall vibrates due to contact with the road surface. TCN is tonal in nature; that is to say it has one prominent frequency. 
     It is known for tyres to contain foam to reduce TCN. However, this is an expensive solution, particularly as the noise-reducing foam must necessarily be replaced when the tyre is changed. 
     Noise-reducing devices that instead fit into a well portion of the rim of the vehicle wheel are also known. Such devices typically rely on Helmholtz resonators as vibration dampers. It is also known to use Helmholtz resonators to reduce noise in exhaust and air intake systems. In its simplest form, a Helmholtz resonator includes a hollow main body defining an internal chamber, the chamber having a single outlet that is formed in a protruding neck extending from the main body. A well-known example of Helmholtz resonance is the sound generated when air is blown across the top of an empty bottle. A Helmholtz resonator has a natural resonant frequency, known as the Helmholtz frequency, which is dependent on a number of parameters, for example the length of the neck or the volume of the cavity. 
     Known noise-reducing devices require the shape of the wheel rim to be modified such that it complements the shape of the noise-reducing device, allowing the device to be attached to the wheel. Such modifications are both costly and time-consuming. Furthermore, this arrangement precludes retrofitting of noise-reducing devices to existing wheels, thereby limiting implementation of the devices. 
     It is against this background that the present invention has been devised. 
     SUMMARY OF THE INVENTION 
     Aspects and embodiments of the invention provide a noise-reducing device, a wheel rim and a vehicle as claimed in the appended claims. 
     According to an aspect of the invention, there is provided a noise-reducing device for a vehicle wheel rim. The device may comprise at least two elements arranged to be coupled to secure the device around a region of the wheel rim that is configured to form part of a tyre cavity. The device may further comprise at least one cavity formed in one of the elements, the or each cavity having an opening providing communication between the or each cavity and the tyre cavity. The elements may be arranged to form a closed loop when coupled that is a close fit with the wheel rim, so that the device is self-retaining on the wheel rim. The or each cavity may be arranged to define at least in part a chamber that acts as a Helmholtz resonator when the device is installed onto the wheel rim. 
     This aspect of the invention provides the advantage that, by virtue of the coupling of the elements around the wheel rim and the close fit of the resulting closed loop with the wheel rim, the device is self-retaining on the wheel rim. The wheel rim therefore does not need to be modified to accommodate the noise-reducing device, for example to provide features on the wheel rim to retain the device. Therefore, devices in accordance with this aspect of the invention can be retro-fitted to substantially any wheel rim. 
     The or each cavity may be defined by a concavity in one of the elements, in which case a perimeter of the or each concavity is arranged to seal against a surface of the wheel rim when the device is fitted to the wheel rim so that the surface of the wheel rim and the or each concavity together define the or each chamber. In this open-backed arrangement, the cavities of the device cooperate with the wheel rim to create the required chambers for noise-reducing Helmholtz resonance. The fact that the cavities are open-backed means that the elements can be more lightweight, and also easier to manufacture. In this embodiment, the device may comprise a channel around the perimeter of the or each concavity, the channel being arranged to receive a sealing member. 
     Alternatively, the or each cavity may be closed-backed to define a self-contained chamber. This provides a more robust device that is easier and quicker to install onto the wheel rim compared with the open-backed embodiment, since there is no need to provide a seal around each cavity. 
     The or each opening may be formed on a respective protrusion that extends into the or each cavity, in which case the or each protrusion is provided with a passage which communicates with the respective opening. 
     In an embodiment, the or each opening breaks out flush with an outer surface of the device. This provides a degree of protection from ingress of fluids such as puncture sealant or water, which could otherwise alter the sonic characteristics of the resonator. 
     Each element may comprise at least one cavity. This improves the effectiveness of the device at reducing tyre cavity noise. The cavities can be tuned to the same frequency to maximise the effectiveness of the noise-reducing device at that frequency. Advantageously, this frequency can be the same as the tonal frequency of the tyre cavity noise. In other embodiments, the resonators may be tuned to different frequencies, allowing the device to reduce noise across a range of frequencies in order to handle variations in the tyre cavity noise frequency caused by changes in temperature, for example. 
     Each element may comprise the same number of cavities. In such embodiments, each element may be substantially identical. This means that the two elements can be manufactured less expensively. 
     The device may comprise a fastening member arranged to encircle the elements and to apply inward radial force to press the elements onto the wheel rim, in use. In this case, the elements may comprise a circumferential groove arranged to receive the fastening member. This ensures that the device is tightly retained against the wheel rim. 
     Each element may comprise an axially extending flange arranged to abut a lip of the wheel rim so as to ensure correct positioning of the device on the wheel rim, to ease installation of the device. 
     In some embodiments, at least one of the elements includes a recess that is arranged to accommodate a tyre pressure monitoring system and the recess may be defined by a taper at an end of the element. This aids fitment of the device to wheel rims that include a tyre pressure monitoring system. 
     In another aspect of the invention, there is provided a wheel having a wheel rim comprising a noise-reducing device. The device may comprise at least two elements that are coupled to secure the device around a region of the wheel rim that is configured to form part of a tyre cavity. The device may further comprise at least one cavity formed in one of the elements, the or each cavity having an opening providing communication between the or each cavity and the tyre cavity. The coupled elements may form a closed loop that is a close fit with the wheel rim, so that the device is self-retaining on the wheel rim. The or each cavity may define at least in part a chamber that acts as a Helmholtz resonator. 
     The wheel rim may comprise a damping layer and/or an adhesive layer between the device and the wheel rim. This ensures that the device is decoupled from vibrations of the wheel. 
     According to another aspect of the invention, there is provided a vehicle comprising a noise-reducing device according to the above described aspect, or a wheel rim comprising such a noise-reducing device. The wheel rim may further comprise a damping layer and/or an adhesive layer between the device and the wheel rim to prevent movement of the device on the wheel rim. 
     According to a further aspect of the invention, there is provided a method of reducing tyre cavity noise. The method may comprise coupling at least two elements around a region of a wheel rim that is configured to form part of a tyre cavity such that the elements form a closed loop that is a close fit with and self-retaining on the wheel rim, and using at least one of the elements to define at least in part a chamber that acts as a Helmholtz resonator when the elements are attached to the wheel rim. 
     The method may comprise sealing a perimeter of a cavity formed in one of the elements against a surface of the wheel rim to define the chamber. 
     The method may comprise attaching a fastening member arranged to encircle the elements and to apply inward radial force to press the elements onto the wheel rim. 
     Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a noise-reducing device in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of the noise-reducing device of  FIG. 1  installed on a wheel rim of a vehicle; 
         FIG. 3  is a perspective view of a portion of the noise-reducing device of  FIG. 1 ; 
         FIG. 4  is a cross-section view of the noise-reducing device of  FIG. 1 ; 
         FIG. 5  corresponds to  FIG. 2  but shows the noise-reducing device and the wheel rim in axial cross-section; 
         FIG. 6  is a perspective view of the noise-reducing device of  FIG. 1 , showing an opening to the neck shown in  FIG. 3 ; 
         FIG. 7  is another perspective view, from a different angle, of the noise-reducing device of  FIG. 1 , showing another opening to the neck shown in  FIG. 3 ; 
         FIG. 8  is a perspective view of the noise-reducing device of  FIG. 1 , showing an attachment mechanism; and 
         FIG. 9  is a perspective view of a vehicle incorporating the noise-reducing device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a noise-reducing device  10  in accordance with an embodiment of the present invention is shown. The noise-reducing device  10  is generally annular in form and attaches around a vehicle wheel and specifically a wheel rim (shown in  FIG. 2 ). The noise-reducing device  10  is open-backed and cooperates with the wheel rim to create chambers that act as Helmholtz resonators to damp vibration of an air column defined within a tyre cavity, the tyre cavity being defined as the volume enclosed by the surface of the wheel rim and the interior surface of a fitted tyre. 
     In this embodiment, the noise-reducing device  10  is formed from two elements or halves  12  that connect at diametrically opposed points on the device  10 . It will be appreciated that although the elements of the device are referred to as “halves” of the device, the two parts need not be identical nor form exact halves in shape, size nor mass of the whole device. 
     As will be explained later, the connection between the two sections may be realised in many different ways. Each half  12  is a band of plastics material formed as a half-ring, such that the two halves  12  together create a continuous ring. The width of the device  10  is relatively small compared with its radius, and is less than the width of the wheel rim. 
     Protrusions  14  extend radially from an outer surface  16  of the noise-reducing device  10 , the protrusions  14  being hollow to define concavities  18  on an inner surface  20  of the device  10 . 
     In this embodiment, each half  12  of the device  10  includes two protrusions  14  separated by a gap  22 , such that there are two concavities  18 , each of which occupies almost a quarter of the overall circumference of the device  10 . An upper surface of each protrusion  14  includes a central circumferential groove  24  along its entire length. 
     In this embodiment, the cross-section of each protrusion  14  is uniform circumferentially. However, in alternative embodiments, the protrusions  14  may take many different shapes and their cross-sections may vary around the circumference of the device  10  so as to tailor the vibration damping response of the device  10  as required. 
     Each concavity  18  includes a single opening (shown in  FIGS. 5 to 7 ) that provides communication between the concavity  18  and the outer surface  16  of the device  10 . As is explained in more detail below with reference to  FIGS. 6 and 7 , the opening breaks out onto the outer surface  16  of the device  10  flush with that surface  16 , while on the inner surface  20  a protrusion into the concavity  18  defines a neck  28  on which the opening is located. 
     Each half  12  of the noise-reducing device  10  also includes a flange  30  that projects axially away from the protrusions  14 . The flanges  30  have tapered end portions  32  such that a v-shaped gap  31  is defined between neighbouring flanges  30  when the two halves  12  of the device  10  are coupled together. 
     Referring to  FIG. 2 , the device  10  of  FIG. 1  is shown attached to and encircling a wheel rim  40  of a vehicle wheel. As will be familiar to the skilled reader, the wheel rim  40  includes a roughly cylindrical central portion  42  with radially enlarged lips  44   a ,  44   b  at either side, those lips  44   a ,  44   b  being arranged to engage in use a bead of a tyre (not shown). The profile of the central portion  42  of the wheel rim  40  is slightly tapered and as such, the circumference of the wheel rim  40  on the outboard side  46  is smaller than the circumference on the inboard side  48 . The wheel rim  40  also includes a tyre pressure monitoring system (TPMS)  50 , which protrudes from the curved surface  52  of the wheel rim  40  at a point close to the outboard lip  44   a.    
     The interior circumference and profile of the noise-reducing device  10  are arranged to correspond to the circumference and taper of the central portion  42  of the wheel rim  40 . Therefore, when the device  10  is installed around the wheel rim  40 , the inner surface  20  of the device  10  seals against the surface  52  of the central portion  42  of the wheel rim  40 , enclosing a volume of air within each concavity  18 . This creates four separate resonance chambers when the device  10  is retained against the wheel rim  40 . 
     As the device  10  forms a continuous ring, it cannot fall off the wheel rim  40  once assembled. Moreover, as the device  10  is sized for a close fit with the wheel rim  40 , it will generally maintain its position on the wheel rim  40  once installed. In this way, the device  10  is self-retaining on the wheel rim  40 . This sits in contrast with known noise-reducing devices, for which bespoke modifications must be made to each wheel rim to enable installation of the device. 
     It is noted that, as the noise-reducing device  10  is open-backed, the concavities  18  are not closed to form resonance chambers until the device is attached to the wheel rim  40 . The noise-reducing device  10  therefore cooperates with the wheel rim  40  to create the partially closed volumes that are required for Helmholtz resonance. In this way, the noise-reducing device  10  of this embodiment of the invention can be more lightweight and less costly to manufacture than the closed cell resonator arrangements known from the prior art. 
     In alternative embodiments the device may be closed-backed, in which case the resonance chambers are formed integrally as part of the device rather than in conjunction with the wheel rim  40 . In comparison with the open-backed arrangement described above, a closed-backed arrangement provides benefits such as increased strength and robustness, along with easier installation by virtue of the fact that there is no need to ensure a seal around the concavities as with the open-backed design. Furthermore, as with the open-backed arrangements, a closed-back embodiment also has the advantage that the noise-reducing device  10  is self-retaining on the wheel rim  40 , in that the wheel rim  40  does not require modification in order to support the device. 
     Open-backed arrangements can be manufactured using injection moulding or extrusion moulding, for example, whereas blow moulding may be required for a closed-backed arrangement. 
     A fastening member in the form of a retaining band  54  fits into the groove  24  on the exterior surface  16  of the device  10  to ensure that the device  10  is held firmly against the surface  52  of the wheel rim  40 . The retaining band  54  is arranged to encircle the device  10  and to apply inward radial force to press the two halves  12  of the device  10  onto the wheel rim  40 . The ends of the retaining band  54  may have a buckle or cable tie strap mechanism, or they may be fused or bonded together. 
     The interior surfaces of the flanges  30  of the noise-reducing device  10  are also arranged to correspond to the circumference and taper of the central portion  42  of the wheel rim  40 . Therefore, when the device  10  is installed around the wheel rim  40 , the inner surface of the flange is in close contact with the surface  52  of the central portion  42  of the wheel rim  40 . The edge of the flange  30  abuts the wheel lip  44   a  so that the device  10  is installed and maintained such that the concavities  18  are correctly distanced from the wheel lip  44   a . One of the v-shaped gaps  31  between neighbouring flanges  30  accommodates the TPMS protrusion  50 , allowing the flange  30  to fit around the TPMS  50 . In alternative embodiments, a gap or cut-out portion may be defined at another point on the device  10  in order to accommodate the TPMS protrusion  50 . 
     The openings into each concavity  18  connect the chambers to the tyre cavity (when a tyre is installed), and the necks  28  defined by the box-like protrusions allow the resonance chambers to act as Helmholtz resonators. The vibration of the air column inside the tyre cavity is damped by the Helmholtz resonance in the chambers, reducing the TCN close to its source. As noted above, the TCN is tonal, and so, elegantly, the resonators are identical and tuned to the frequency of the TCN by appropriate configuration of the concavities  18 . For example, the resonator can be tuned to a desired frequency by altering the volume of air contained in the resonance chambers. The volume of air in the chambers affects the Helmholtz frequency of the resonator: the greater the volume, the lower the Helmholtz frequency. 
     In the following description, reference will be made to a single resonator; it should, however, be appreciated that this description equally applies to any other resonator of the noise-reducing device  10 . 
       FIG. 3  shows the inner surface  20  of the noise-reducing device  10  in more detail, and a part of a concavity  18  can be seen;  FIG. 4  shows a corresponding portion of the noise-reducing device  10  in cross-section. As can be seen most clearly in  FIG. 4 , around the edge of the concavity  18  a channel  60  is formed on the inner surface  20  of the noise-reducing device  10 . Referring to  FIG. 3 , a rubber O-ring  62  (not shown) is received in the channel  60  and is used to ensure an airtight seal between the noise-reducing device  10  and the wheel rim  40 . This seal maintains the resonance characteristics of each of the chambers so that each Helmholtz resonator remains tuned to the TCN frequency. Ensuring firm contact between the noise-reducing device  10  and the wheel rim  40  also prevents rattle and resists rotation of the device  10  relative to the wheel in use. In other embodiments, alternative sealing material may be provided, for example in the form of a layer of foam or adhesive covering the surface area in contact with the wheel rim  40 . In closed-backed embodiments, no seal is required as the chambers are self-contained. However, foam or adhesive material may still be used between the device  10  and the wheel rim  40  to minimise transmission of vibration. 
     It can also be observed from  FIG. 3  that a central protrusion  64  is present in the concavity  18 , the central protrusion  64  corresponding to the central groove  24  formed on the outer surface  16  of the noise-reducing device  10 . A secondary protrusion  66  extends radially from the central protrusion  64  around part of its circumference. The secondary protrusion  66  reinforces the structure of the concavity  18 , making it stiffer and preventing the concavity  18  from deforming, for example due to air vibration. This ensures that the volume of the chamber does not vary significantly during use. Additionally, reinforcement of the concavity  18  protects the device  10  from damage if the central retaining band  54  is over-tightened. 
     Features of the neck  28  of the resonator will now be described with reference to  FIGS. 5 to 7 .  FIG. 5  shows the assembly of  FIG. 2 , namely the noise-reducing device  10  installed on the wheel rim  40 , in axial cross-section. As can be seen, the device  10  is held against the central portion  42  of the wheel rim  40 , with the edge of the flange  30  abutting the outboard lip  44   a . The cross-section is taken through the portion of the device  10  that includes the neck  28 .  FIGS. 6 and 7  are perspective views of the noise-reducing device  10 ,  FIG. 6  showing a portion of the inner surface  20  including the neck  28 , and  FIG. 7  showing a corresponding portion of the outer surface  16  including the opening  72 . 
     As noted above, the wall of the noise-reducing device  10  has an opening  72  to allow air to pass between the tyre cavity and the chamber via the neck  28 . As best seen in  FIG. 6 , the neck  28  is defined by a box-like protrusion that extends axially into the chamber along the inner surface  20  of the noise-reducing device  10 . The edges of the protrusion are rounded for ease of manufacturing.  FIG. 5  shows that a central bore  70  formed in the neck  28  provides communication between the chamber and the tyre cavity. 
     As can be seen in  FIG. 7 , and as noted previously, the opening  72  to the neck  28  on the outer surface  16  is flush with that surface  16 . This provides a degree of protection from ingress of fluids such as puncture sealant or water, which could otherwise alter the sonic characteristics of the resonator. 
     The length and cross-sectional area of the bore  70  of the neck  28  are both relevant parameters for determining the Helmholtz frequency. Therefore, the resonator can be tuned to a desired frequency, typically the TCN frequency, by varying the length or cross-sectional area of the bore  70 . In other embodiments, the form of the neck  28  may be adapted to improve the sound absorption capacity of the resonator. For example, in this embodiment opposing walls of the bore  70  are parallel, but in other embodiments the walls may be angled to form a tapered neck. 
     Noise-reducing devices  10  in accordance with embodiments of the present invention allow reduction of the TCN close to its source, preventing transfer of noise to the vehicle cabin (not shown). As noted above, the air column inside the tyre cavity vibrates due to the vibration of the tyre wall caused by contact with the road surface. This establishes a standing wave inside the tyre cavity with the characteristic frequency of the TCN. Since the Helmholtz resonators of the noise-reducing device  10  are tuned to the same frequency as the TCN, they exhibit Helmholtz resonance in response to this excitation. Each Helmholtz resonator acts to damp the vibration of the air column by acting as a simple harmonic oscillator. By analogy with a mass on a spring, the air within the chamber behaves like the spring and the air within the neck  28  behaves like the mass. The oscillations of the air column are therefore damped and the TCN is reduced. 
     To maximise the effectiveness of the noise-reducing device  10  at a particular frequency, in this embodiment all of the resonators are identical. Alternatively, dissimilar resonators may be tuned to the same frequency if desired through control of the relevant parameters. In other embodiments, the resonators may be tuned to different frequencies, allowing the device to reduce noise across a range of frequencies in order to handle variations in the TCN frequency caused by changes in temperature, for example. This may be achieved by varying any one or more of the relevant parameters of the resonators; such as the resonator chamber volume or resonator neck  28  length. 
     It will be appreciated by a person skilled in the art that connection of the two halves  12  of the device  10  could be realised in many different ways. One example is described below, with reference to  FIG. 8 , which shows the two halves  12  of the noise-reducing device  10  being attached together, in an arrangement not unlike a jigsaw. In the following description one of the connections will be described; it should, however, be noted that the diametrically opposed connection point on the noise-reducing device  10  will typically connect in the same manner. Alternatively, one of the connections may be semi-permanent, for example a hinged connection, to simplify assembly. 
     The outer surface  16  of each half  12  of the noise-reducing device  10  includes a depression  80  extending from its connecting edge  82 . When the connecting edges  82  of the two halves  12  of the device  10  are abutted against one another the depressions  80  align, forming a single continuous recess  81  spanning the joint  84  on the outer surface  16  of the device  10 . 
     This recess  81  has a generally hourglass shape and an attachment piece or clip  86  of complementary shape is provided to fit inside the recess  81 . By virtue of the interlocking engagement between the recess  81  and the hourglass shape of the clip  86 , the two halves  12  of the device  10  cannot be pulled apart when the clip  86  is inserted. The retaining band  54  fits over the clip  86  to hold it in place in the recess  81 . Additionally or alternatively, one half  12  of the device  10  may be provided with pins (not shown) extending from the connecting edge  82  and the other half  12  with holes (not shown) to receive said pins, to enhance the integrity of the joint  84 . 
     Providing the noise-reducing device  10  in two halves  12  allows easy installation to a wheel rim  40 , with the flange  30  and v-shaped gap  31  for the TPMS  50  together facilitating reliable locating of the device  10  on the wheel rim  40 . Additionally, since the noise-reducing device  10  is self-retaining and open-backed, the wheel rim  40  need not be modified to complement the form of the noise-reducing device  10 , as is necessary with prior art arrangements. Therefore, with appropriate sizing the noise-reducing device  10  can be retrofitted to most existing wheel rims  40 , provided the interior circumference and profile of the noise-reducing device  10  are tailored to match the dimensions of the wheel rim  40 . 
     As can be seen from  FIG. 9 , the invention also extends to a vehicle  90  incorporating a noise-reducing device  10  as described above. 
     It will be appreciated by a person skilled in the art that the embodiments of the present invention described above could be modified to take many other alternative forms without departing from the inventive concept defined by the claims. For example, an adhesive band or foam could be provided underneath the device to decouple it from the wheel vibrations.