4547-1.doc Noise Suppression Bands for Tracked Vehicles Field of Invention [0001] This invention relates to wheels for tracked vehicles, in particular to noise suppression bands fitted to idler wheels, which reduce the noise produced by the track impacting the wheel. Background [0002] Tracked vehicles are commonly used in earthmoving, mining, construction and military applications. The vehicle's tracks have a large surface area which distributes a vehicle's weight relatively uniformly over that part of the track surface which is in contact with the ground. This allows the tracked vehicle to travel more easily over soft ground than would be the case for a wheeled vehicle of similar weight. [0003] The tracks, known as continuous tracks, form a continuous loop driven by one or more drive wheels. The continuous track is formed of metal. The tracks pass under a number of non-driven road wheels or bogeys, and under one or more non-driven idler wheels. Idler wheels are used to maintain tension in the track. [0004] The construction of idler wheels and bogey wheels is typically of steel, comprising a steel hub with a retainer portion around the circumference which slots into the track to prevent substantial lateral movement of the track with respect to the wheels. The wheel has a number of circumferential bands of contact area which contact the track, and act to distribute the load across the track. The circumferential bands are a source of noise emission.
4547-1.doc -2 [0005] The circumferential bands are not continuous, but are typically constructed from a number of segments with a central retaining band located in circumferential grooves formed into the wheel. Each band usually comprises eight to ten segments spaced around the circumference of the wheel rim, with the ends of adjacent segments being separated by a small gap. Two opposing keys in each band prevent the movement of two segments thus limiting bunching of the segments. [0006] These segments are presently constructed of two or more materials, typically with a steel core coated with an external layer of rubber of approximately 3-6mm thickness. The rubber coating is intended to reduce noise produced by the movement of the metal tracks over the wheels, and therefore the bands constructed from these segments are known as noise suppression bands. As the rubber coating wears, there is a greater space between segments allowing additional movement of the segments, and allowing ingress of dirt and grit, further accelerating wear of the segments. [0007] Furthermore, as the rubber wears, the additional movement has the effect of increasing the noise levels due to the the segments rattling, and of damaging the outer edge of the wheel through the resulting peening action of each segment. Noise may be produced by the segments rattling, and also by the metal on metal contact of the track on the segments. Noise suppression is an important occupational health and safety issue, for the operator of the tracked vehicle, for other workers in the vicinity of the tracked vehicle, and for the local community at large. [0008] The noise suppression bands therefore need to be replaced relatively often to maintain their noise suppression properties. Since the noise suppression band segments are made predominantly of steel, they are relatively heavy and therefore relatively difficult to fit.
4547-1.doc -3 Summary of the Invention [0009] The present invention provides improved noise suppression bands for the wheels of tracked vehicles. These wheels may include idler wheels or bogey wheels. The noise suppression bands comprise multiple noise suppression band segments. [0010] In one broad form, the present invention provides a noise suppression band segment for a non-driven wheel of a tracked vehicle, wherein in use multiple band segments extend around the circumference of the wheel, the noise suppression band segment comprising; a first segment portion which in use extends over at least part of the periphery of the rim of the wheel, and a contact surface which in use contacts a track of the tracked vehicle; and wherein the noise suppression band segment is constructed of substantially a single body of at least one noise-reducing material. [0011] The noise suppression band segment may in use retain the ability to reduce noise when it is worn. [0012] The noise suppression band segment may in use extend laterally beyond the periphery of the rim of the wheel. [0013] The noise suppression band segment may comprise a second segment portion which in use extends over at least part of the outer portion of a side of the rim of the wheel. [0014] The noise suppression band segment may comprise a third segment portion such that in use at least part of the periphery of the rim of the wheel is located between the third segment portion and the first segment portion. [0015] The noise suppression band segment may comprise a retaining portion 4547-1.doc -4 whereby in use at least part of the retaining portion is clamped between a retainer and the wheel. [0016] The noise suppression band segment, for use with a wheel having at least one circumferential groove or ridge, may have a retaining portion adapted to engage the at least one circumferential groove or ridge. [0017] The noise suppression band may in use comprise either two or three or four band segments together which extend substantially around the full circumference of the wheel. [0018] The noise suppression band segments may be equally sized. [0019] The noise suppression band segments may in use substantially limit rotation of the band segments relative to the wheel due to friction between the band segments and the rim of the wheel. [0020] The noise suppression band segment may have the single body of noise reducing material reinforced with a minor amount of strengthening material. [0021] The noise suppression band segment may have the strengthening material configured such that, if exposed by wear, the contact surface remains substantially formed of the single body of noise reducing material. [0022] The noise suppression band segment may have the strengthening material comprising less than ten percent of the cross-sectional area of the noise suppression band segment. [0023] The noise suppression band segment may have at least one noise reducing material being a relatively lightweight material. [0024] The noise suppression band segment may have at least one noise- 4547-1.doc -5 reducing material being an engineering plastic. [0025] The noise suppression band segment may have at least one noise reducing material being a cast nylon. [0026] The noise suppression band segment may have the single body of noise reducing material formed of a single noise-reducing material. [0027] The noise suppression band segment may have at least one noise reducing material which has coefficient of linear expansion less than about 95 x 10-6 m/m/K and more preferably less than about 80 x 10-6 m/m/K. [0028] The noise suppression band segment may have at least one noise reducing material which has tensile strength greater than about 65 N/mm 2 and more preferably greater than about 70 N/mm 2 . [0029] The noise suppression band segment may have at least one noise reducing material which has modulus of elasticity greater than about 2300 N/mm2. [0030] The noise suppression band segment may have at least one noise reducing material which has density less than about 1.15 g/cm3. [0031] The present invention further provides a noise suppression band for the non-driven wheel of a tracked vehicle, comprising two or more noise suppression band segments as described above. [0032] The present invention further provides a wheel assembly for the non driven wheel of a tracked vehicle, comprising a wheel, and two or more noise suppression band segments as described above.
4547-1.doc -6 Brief Description of the Drawings [0033] Figure 1 shows a perspective view of a wheel fitted with prior art noise suppression bands. [0034] Figure 2 shows a view of a wheel partially fitted with the noise suppression bands of the present invention. [0035] Figure 3 shows a cross-section view of the noise suppression band of the present invention. [0036] Figure 4 shows a cross-section view of an alternative embodiment of the noise suppression band of the present invention. [0037] Figure 5 shows a cross-section view of another alternative embodiment of the noise suppression band of the present invention. Detailed Description of Preferred and other Embodiments [0038] Figure 1 shows a prior art wheel fitted with noise suppression bands from a Caterpillar model D11 bulldozer. The wheel comprises hub 10 and noise suppression bands 12 disposed around the circumference of the wheel rims 14. The hub has a retainer which is bolted into place around the periphery of the central portion of the hub. The retainer consists of a number of retainer segments 16. The retainer holds the noise suppression bands in place around the periphery of the wheel rim 14. [0039] The noise suppression bands 12 are typically constructed of steel coated with soft rubber. Typically a noise suppression band comprises eight to ten noise suppression band segments. Figure 1 shows a wheel two noise suppression bands comprising in total twenty segments 12, with ten segments 4547-1.doc -7 on each side of the wheel, with the band segments held in place by retainer segments 16. . [0040] Slippage between the band segments and the wheel rim of Figure 1 may occur. This slippage becomes greater as the band segments become worn. This slippage is prevented by the use of two locking keys (not shown) which are opposingly mounted in the wheel groove and insert into a slot machined into two separate segments, to prevent substantial relative circumferential movement between the segments and the rim. [0041] Retainer segments 16 further act as a guide for the tracks of the tracked vehicle, preventing substantial lateral movement between the wheel and the tracks. [0042] The present invention provides improved noise suppression bands for the wheels of tracked vehicles. These wheels may include idler wheels or bogey wheels. The noise suppression bands are constructed in segments, each segment being constructed of substantially a single body of noise-reducing material(s). [0043] Figure 2 shows a wheel partially fitted with the noise suppression band 20 of the present invention. The cast wheel has rims 14 comprising a landing 15, a groove 17and a machined central section 18. Retainer segments 16 are bolted onto central section 18, and act to retain the noise suppression band segments 20 assembled into groove 17 and landing 15. [0044] Figures 3, 4 and 5 show cross-section views of embodiments of the noise suppression band segment 20. The noise suppression band segment comprises a first segment portion 34 which acts to separate a vehicle track which contacts surface 36 and the wheel hub which contacts surface 38. The 4547-1.doc -8 noise suppression band segment further comprises a retaining portion 30, adapted to the shape of the hub to which it is to be fitted, and a retaining surface 32 whereby a retainer contacts the retaining surface 32, and thereby retains the retaining portion 30 against the hub. [0045] The noise suppression bands may have a cross-section shape which may extend laterally beyond the edge of the rim. The bands may extend radially inwards to partially or fully cover the edge of the rim, which assists noise suppression and which reduces ingress of dirt between the bands and the wheel. These features alone or in combination reduce wear and therefore reduce long-term maintenance costs. [0046] Figures 4 and 5 show a noise suppression band segment which further comprises second segment portion 40 which extends laterally and radially over the edge of the wheel rim thereby protecting the edge of the rim against mechanical damage, and reducing ingress of dirt between the noise suppression bands and the wheel rim. [0047] The noise suppression band segment may optionally include both second segment portion 40 and a third segment portion 42 which secures the noise suppression band to the rim, and minimises the ingress of dirt and grit. [0048] The noise suppression bands are constructed of substantially a single body of noise-reducing materialss. It will be understood that the body of noise-reducing material may be formed of a single noise-reducing material or of multiple noise-reducing materials. Multiple noise reducing materials may be layered within the noise suppression band, or may be incorporated into the band in some other configuration. [0049] It will be further understood that the noise-reducing material may be 4547-1.doc -9 reinforced with wire or some other strengthening material to reduce the flexibility and/or increase the strength of the installed noise suppression band, particularly once the band becomes partially worn. Preferably any reinforcing is configured so that if exposed through wear the contact surface of the band is still substantially formed of the noise-reducing material(s). Any such reinforcing typically comprises less than 10% of the cross-sectional area of the noise suppression band. [0050] In operation of the wheel, noise is produced by the relative movement of the track in contact with the surface 36. As such, the choice of material for the main portion 34 of the noise suppression band is important so as to minimise the noise produced. Furthermore, as the material wears, the radial thickness of the main portion 34 will be reduced. By constructing the noise suppression bands of a substantially single body of material with suitable noise suppression properties, the noise suppression bands will retain the ability to reduce noise as the bands wear down. [0051] The noise suppression bands are preferably constructed of a relatively lightweight material. A suitable lightweight material must offer good wear and abrasion resistance, and high compressive strength compared with rubber and with other industrial plastics, with high impact resistance, excellent noise reduction, vibration dampening properties, and low friction. [0052] Such a material may be an engineering plastic, including cast nylon. For example the product commercially available in Australia as "AustLon C90 Black" manufactured by McNeall Plastics of Melrose Park NSW is a suitable cast nylon material. Cast nylon has high machinability and excellent noise reduction properties. [0053] A preferred noise reducing material has the following properties: 4547-1.doc - 10 coefficient of linear expansion less than about 95 x 10-6 m/m/K and more preferably less than about 75-80 x 10-6 m/m/K. tensile strength greater than about 65 N/mm 2 and more preferably greater than about 70 N/mm 2 . modulus of elasticity greater than about 2300 N/mm 2 [0054] A preferred relatively lightweight noise reducing material will additionally have the following property: density less than about 1.15 g/cm 3 [0055] By using a relatively lightweight material to construct noise suppression bands, each segment can be proportionally larger for a matching comparative weight compared to prior steel/rubber noise suppression segments. [0056] Typically, two segments per band may be provided having less weight than prior smaller steel segments. The use of two segments offers the advantage of each segment having a natural wrapping property with the hub holding the segment in place unassisted, reducing the required skill level for assembly, and reducing the time taken for assembly. [0057] Having only two segments eliminates the need for a segment key which prevents rotation of the segments in the wheel groove, as there are only two segment gaps which does not give rise to any bunching issue. Furthermore, with two segments there are fewer segment gaps, which in turn means fewer places for dirt and grit to enter under the assembled noise suppression band, which reduces abrasive wear between the segments and between the segments and the hub. This leads to extended lifetime of the bands and of the wheels, and therefore to reduced long-term maintenance expenses.
4547-1.doc - 11 [0058] Furthermore, use of materials such as engineering plastics and cast nylon allow the noise suppression bands to be more firmly attached to the rim, and the use of a locking wedge or key to prevent slippage between the bands and the wheel rim may be no longer necessary. [0059] The present invention further provides a wheel assembly for a tracked vehicle, comprising one or more noise suppression bands or band segments as described above. [0060] Unless the context clearly requires otherwise, throughout the description and any claims the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". [0061] The features of the invention described or mentioned in this document may be combined in any combination of features where features are not mutually exclusive. [0062] It will be apparent to those skilled in the art that many obvious modifications and variations may be made to the embodiments described herein without departing from the spirit or scope of the invention.