BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to devices for attenuating noise
generated by rolling tire and wheel assemblies of the type defining a closed interior
cavity, for example, pneumatic tire and wheel assemblies. More particularly, the
invention relates to a device mounted in a tire cavity for attenuating noise relating
to cavity vibration modes.
Cavity noise in tires is generated by the excitation of
the air contained inside the closed tire cavity. Generally, the air is excited by
the deflection of the tire tread and sidewalls when the tire is rolling. The air
in the cavity, although confined in a toroidal cavity, acts as an air column under
the effect of the excitation. Various solutions have been proposed to reduce or
eliminate cavity noise, including Helmholtz resonators incorporated in the wheel
and sound absorbing materials arranged in various configurations in the cavity.
These solutions themselves have difficulties including high cost, manufacturability,
The present invention proposes a solution for reducing
cavity noise that is simple, inexpensive, easy to manufacture, and effective.
The invention starts from the point that a closed cavity
defined by a tire mounted on a wheel defines a toroidal space which is substantially
uniform in the circumferential direction. During rotation of the tire, the substantially
uniform space acts as an infinitely long tube of air and allows standing acoustic
waves to form in the cavity. The energy of the waves is transmitted through the
wheel to the vehicle as noise. The inventor realized that while the acoustic wave
can be thought of as a standing wave in the cavity, the rotating tire and wheel
could be thought of as moving relative to the wave. Thus, by placing a device on
the tire or wheel to interfere with the maximum and minimum peaks of a wave, the
wave could be attenuated.
According to the invention, acoustic waves can be disturbed
and the transmission of energy to the wheel attenuated by a device that provides
nonuniformities in the cavity circumferential direction. Such a device, according
to the invention, comprises at least one circumferential ring providing a non-continuous
profile of alternating ridges and gaps. The at least one ring is located in the
tire cavity on a surface of the tire or the wheel.
According to one embodiment, the ring is formed from a
plurality of strips in circumferential alignment and mutually spaced to have one
or more gaps. According to another embodiment, the ring is formed of a single strip
having a plurality of ridges separated by gaps formed in the strip. It is believed
that the profile of raised and lower surfaces (strips/ridges and gaps) moves through
the acoustic wave so that ridge momentarily coincides with the wave peak, causing
an interruption, and thus diminishing the noise generated by the tire cavity.
The number of the ridges and gaps is related to the order
of the acoustic wave to be attenuated by the device. As will be understood by those
skilled in the art, the first-order mode is a complete wave occurring once per revolution,
meaning the wave will have two peaks, at a maximum and a minimum about the circumference
of the tire. A ring in accordance with the invention for attenuating a first order
mode vibration provides at least two equally spaced ridges and gaps. Preferably,
the ring comprises four ridges and gaps, which is believed to facilitate the interrupting
capability of the ring.
According to the invention, the alternating position of
the ridges and gaps provides the improved waved interrupting function as compared
to a continuous ring of absorbent material, as known in the art. The ridges and
gaps can be of equal circumferential length. Alternatively, the ridges can be longer
than the gaps, or the gaps longer than the ridges, the ridges being substantially
of equal length, and the gaps being substantially of equal length.
According to a preferred embodiment of the invention, the
ring is formed of sound absorbing material to assist noise reduction by absorbing
some of the sound energy and not providing sound reflective surfaces.
According to an aspect of the invention, wave interruption
can be improved by placing two rings in the tire cavity in parallel and mutually
oriented so that the gaps in each ring are positioned relatively staggered about
the circumference so as not to be aligned in the lateral or axial direction.
The rings may be positioned on the cavity-defining surfaces
of the tire or the wheel or both. Preferably, the rings are located on the crown
of the tire or the well region of the wheel between the bead seats so that mounting
or dismounting the tire does not damage the strips.
The strips forming the rings are formed of a material capable
of being mounted in the tire and withstanding the tire environment and stresses
from rolling and other deflections. Rubber or plastic strips, metallic, textile,
or composite materials can be placed in the tire cavity, understanding that non-flexible
or rigid materials are more suitable for placement on the wheel rather than the
The sound absorbing strips may be formed of any material
capable of absorbing acoustic or vibration energy, for example, rubber, foamed rubber
and plastic, cork, textiles, or felts.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood by reference to
the following detailed description in conjunction with the appended figures, in
Figure 1 is a radial sectional view of a tire and wheel
showing the placement of rings in accordance with the invention;
Figure 2 is a side view of a ring according to a first
embodiment formed of a single strip having longer ridges and shorter gaps;
Figure 3 is a side view of a ring according to a second
embodiment formed of a single strip having shorter ridges and longer gaps;
Figure 4 is a projection of a wheel in a single plane showing
a circumferential arrangement of two rings of long ridges, each formed of a plurality
of strips; and
Figure 5 is a projection of a wheel in a single plane showing
a circumferential arrangement of two rings of short ridges, each formed of a plurality
Figure 1 is a radial sectional view of a tire 20 and wheel
30. The interior surface 22 of the tire 20 and the interior surface 32 of the wheel
30 define the boundaries of a tire cavity 24. In a pneumatic tire, the tire cavity
24 contains air under pressure that tensions the tire body to support the load on
the tire and wheel assembly. The deflection of the tire 20 as it rolls in contact
with the ground or encounters obstacles (not shown) transmits energy to the air
in the tire cavity 24 which generates acoustic energy in the cavity air. Acoustic
energy from the air is transmitted from the tire cavity as noise, which is undesirable.
Because the tire cavity is substantially uniform in the
circumferential direction, the direction into the plane of Figure 1, the acoustic
energy can form so-called standing waves in the ring of air contained in the cavity.
As will be understood by those skilled in the art, a standing wave has maximum and
minimum peaks and zero pressure nodes. A first order wave completes one cycle of
maximum and minimum peaks.
According to the invention, cavity noise can be attenuated
by one or more profiled rings mounted in the tire cavity to make the interior space
non-uniform in the circumferential direction. The ring may be a single strip of
profiled material or a plurality of individual strips of material positioned in
circumferential alignment, that is, forming a ring, as will be described.
According to the invention, the ring has a non-uniform
profile along its length, the length corresponding to the circumferential direction
in the tire cavity. The ring geometry, as will be further described below, comprises
ridges separated by gaps defining a stepped radially outer surface. The ridges and
gaps are formed with radially outer surfaces that extend circumferentially between
step-like transitions, thus providing abrupt changes in profile between the ridge
and the adjacent gap. The change in tire cavity circumferential profile as the ring
rotates about the standing wave, which disturbs the wave, and accordingly attenuates
the cavity noise. It is believed that positioning alternately the ridges and gaps
with the peaks of the wave achieves the improved attenuation as compared to a continuous
In Figure 1, for purposes of illustration, a single ring
40 is shown on the inner surface 22 of the tire crown 24 and two rings 40 are shown
mounted to the surface 32 of the wheel 30. The ring 40 may be positioned anywhere
on the interior surface of the tire 20 or the wheel 30, preferably, but not exclusively,
on the crown or wheel well, as described below. Two or more rings may be provided
and mounted on either or both of the tire or wheel, as further described below.
In addition, the ring 40 may be relatively narrow, as shown, or have the full width
of the mounting surface, the crown or wheel.
According to one embodiment of the invention, the circumferential
ring comprises a single strip having at least two ridges separated by two gaps as
seen along the length or circumference. A preferred embodiment, illustrated in Figures
2, 3, and 4, has rings of four ridges and four gaps separating the ridges. For attenuating
first order acoustic modes, the ring 40 preferably comprises two, three, or four
ridges and gaps, which facilitates positioning a ridge with a wave peak during tire
and wheel rotation. For other order acoustic modes, multiples of four ridges and
gaps will be suitable.
The ridges and gaps each have a substantially constant
height, as measured in the radial direction. Preferably, a height of the gaps 46
occupies at least half the height of the ridges 42. That is, the base 48 of the
strip 42 at the gap 46 is less than half the height of the ridge 44.
Figure 2 shows ridges 44 that are relatively much longer
than the gaps 46. This is believed to facilitate the wave interrupting capability
by having a relatively long dwell time of the ridge at the wave peak maximum and
minimum. The ridges 44 have substantially equal length, and the gaps 46 are of a
different, substantially equal length. Alternatively, the ridges and gaps may be
of a single substantially equal length.
Figure 3 shows another alternative, a ring 41 formed of
a single strip 43 having alternating ridges 45 and gaps 47, in which the ridges
45 are relatively much shorter than the gaps 47. Again, in this embodiment, the
ridges 45 are of substantially an equal length and the gaps are of a different,
substantially equal length.
The strips 42, 43 may easily be formed by a tape or ribbon
having blocks bonded thereto and mutually spaced. The strips 42, 43 alternatively
could be molded or machined, depending on the material used.
According to another embodiment, illustrated in Figure
3, the ring 40 comprises individual strips 50 mounted directly to the tire or the
wheel surface in circumferential alignment and mutually spaced. The spacing between
strips 50 forms the gaps 52 that interrupt the profile of the strips.
According to a preferred embodiment of the invention illustrated
in Figures 2 and 4, the ridges 44, 50 are longer than the gaps 46, 52, and the gaps
each have a length being a minimum of about 0.01 % of the circumference of the surface
on which the rings 40 are mounted. For the interior crown surface of passenger tires,
the gaps will typically be about 2 mm. A maximum gap is about 15% of the circumferential
distance of the mounting surface. Again, for mounting on the interior crown surface
of passenger tires, this will be about 200 mm between ridge 44, 50 ends.
According to another aspect of the invention, two or more
rings 40 may be mounted in parallel in the cavity 24, which, as shown in Figure
1, could be on the tire inner surface 22 or the wheel inner surface 32, or both.
In an unloaded tire, a single first-order wave will set
up having its maximum and minimum at 180 degrees separation. A tire under load,
however, will have two first-order waves because the loaded tire has a different
diameter in the vertical direction (which includes the contact patch) than the diameter
in the fore-aft direction. On a graph of sound pressure vs. frequency, these waves
will appear as two sharp peaks of similar sound pressure value in close frequency
proximity. The maxima and minima of the two first-order waves in the loaded tire
are equally spaced and are relatively out of phase by 90 degrees.
Referring now to Figure 4 and Figure 5, which represent
projections of the wheel inner surface 32 onto the plane of the drawing sheet, an
advantageous arrangement includes two rings 40 mounted in parallel. Figures 4 and
5 illustrate the rings 40 as being formed of individual strips 50, 60 forming the
ridges, however, the rings may also take the single strip form 42, 43 described
above. The ridges 50, 60 are arranged so that the gaps 52, 62 defined between circumferentially
adjacent ridges 50, 60 are in staggered relationship, that is, non-aligned in the
lateral or axial direction. Preferably, the gaps and ridges are staggered 90 degrees
out of phase. This arrangement improves the wave interrupting function of the rings
40 by its capability of interfering with both of the first-order waves. As will
be appreciated by those skilled in the art, this principle could be easily extended
to other sound at other frequency modes by mounting rings having ridges in the appropriate
multiple of 4.
According to another aspect of the invention, the number
of strips 50 in each ring 40 can be the same, as shown in Figure 3, or, alternatively,
can be different, that is, two strips in one ring and four strips in a second ring.
The rings 40 may be placed in the wheel well 34, as shown
in Figure 1, to avoid subjecting the strips or ridges to stress during rolling of
the tire. However, the rings 40 may be placed on the interior surface 22 under the
crown 24, which is advantageous in avoiding damage to the rings when mounting the
tire on the wheel.
The strips 42, 50 may be formed of rubber or plastic, metallic,
or composite materials that are suitable for placing in a tire cavity. As will be
understood, non-flexible materials are more suitable for placement on wheel and
the flexible materials more suitable for the tire. The strips may be solid or hollow,
a hollow strip having the advantage of saving weight.
According to a preferred embodiment, the strip 42 or strips
50 forming the ring 40 are made of sound absorbing material. Such strips may be
formed of any material capable of absorbing acoustic or vibration energy, for example
foamed rubber and plastic, cork, or felts. Sound absorbing strips are believed to
assist the attenuation by absorbing energy which might otherwise be reflected.
The invention has been described in terms of preferred
principles, structure and embodiments, however, those skilled in the art will understand
that equivalents may be substituted for what is described without departing from
the scope of the invention as defined in the claims.