Abstract:
A crawler-dozer has a track assembly that includes an idler wheel with an elastomeric ring extending around its outer surface. The ring is continuous, having no breaks in its periphery that permit it to fall off. The ring is not held onto the idler wheel by fasteners but by being force fit on or molded around the periphery of the idler wheel. The ring may be inhomogeneous, having different hardnesses or having reinforcing materials embedded in an elastomeric matrix.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to track type implements and, more particularly, to an apparatus for reducing noise levels generated by the tracks during operation.  
       BACKGROUND OF THE INVENTION  
       [0002]     Crawler tractors and other types of off-highway implements are typically provided with endless tracks on opposite sides thereof. During operation of the implement, noise is generated by the metal tracks as they bang against a drive wheel, front idler, and carrier rollers.  
         [0003]     A typical track is comprised of a series of metal links. Adjacent ends of the links are pivotally interconnected by pin and bushing assemblies to form an endless chain. The noise generated by the track arises from the bushing and links banging against the periphery of the wheel, idler, and rollers as the track circulates during movement of the implement. Noise production is transmitted through the implement structure, radiated to the interior and amplified by resonant conditions.  
         [0004]     Attempts at reducing the noise level by reducing the mass of the track or by increasing the diameter of the idler wheels for the tracks have been made in the past. Tensioning the track has also been used to reduce the noise level of the track during implement operation by mounting the drive wheel and idler wheel with their axes resiliently positioned with respect to each other in order to hold the chain or track taut.  
         [0005]     One partial solution to the noise problem has been to clamp a length of elastomeric material around the periphery of an idler wheel. The elastomeric material contacts the individual links of the crawler track before it contacts the periphery of the idler wheel. The elastomeric material decelerates the links as they approach the idler wheel and reduces their speed of impact. In addition, the contact of the elastomeric material absorbs the high frequencies that are generated by the link-on-idler impact, significantly muffling the sound.  
         [0006]     The above efforts notwithstanding, relatively high noise levels continue to be an inherent problem and pose a public nuisance problem during operation of crawler tractors and the like. Furthermore, the elastomeric material requires a separate fastening means that extends around the middle of the length of material. The fastening means requires a fastener-receiving groove in the middle of the length of material that cannot be used to support the bushing and dampen noise. Further, the reduced width due to the fastening means causes accelerated wear.  
         [0007]     Thus, there is a need and a desire for an apparatus capable of further reducing the noise level inherent with circulation of an endless track during operation of a crawler tractor and the like.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with a first aspect of the invention, there is provided a noise attenuator that includes an annular elastomeric ring affixed about an idler wheel about which a track is entrained. It is fixed to the idler without separate mechanical fastening means. The idler wheel is supported by the track frame. A recoil assembly is mounted between the idler wheel and drive sprocket to act as a tensioning device and cushion against shock loads. The elastomeric ring is positioned such that pin and bushing assemblies of the track directly and resiliently engage with the periphery of the ring thus reducing noise as the track assembly rotates about the wheel. The elastomeric ring is formed as a single unit, having a solid cross section.  
         [0009]     The idler wheel is preferably configured with a central annular rim sized with a diameter greater than other axially spaced rims provided on the idler wheel. The elastomeric ring is formed as a continuous ring, having no beginning or end. In a most preferred form of the invention, the central rim of the idler wheel is provided with an annular channel which defines crown rims on opposite sides thereof. A widthwise portion of the dual crown rims acts as a support for the elastomeric ring. A central portion of the elastomeric ring is received within the channel to prevent lateral shifting of the ring relative to the idler wheel.  
         [0010]     The elastomeric ring provides a cushion about the periphery of the idler wheel. The elastomeric cushion absorbs a substantial portion of the energy present in the movement of the chain about the periphery of the idler wheel thereby reducing noise and impact force transmitted to the wheel mount. The ring can be formed separately and later attached to the wheel, or alternatively it can be formed integrally with the wheel, such as by casting the ring directly to the wheel. If formed separately as an endless ring, it has a smaller diameter than the wheel, thereby providing a tight interference fit when it is later forced around the idler wheel.  
         [0011]     Numerous other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a fragmentary side elevational view of a track assembly incorporating principles of the present invention.  
         [0013]      FIG. 2  is an enlarged side elevational view of the track assembly with parts broken away to illustrate certain features of the present invention.  
         [0014]      FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2 .  
         [0015]      FIG. 4  is a plan view of a separately formed elastomeric ring having no beginning or end as it would appear before being forced onto the idler wheel.  
         [0016]      FIG. 5  is a cross-sectional view of an alternative and inhomogeneous elastomeric ring  52  having a harder portion and a softer portion.  
         [0017]      FIG. 6  is a cross-sectional view of yet another alternative and inhomogeneous elastomeric ring  52  having a fiber reinforcing layer.  
         [0018]      FIG. 7  is a cross-sectional view of yet another alternative and inhomogeneous elastomeric ring  52  in which a fibrous reinforcing material is distributed throughout an elastomeric matrix.  
         [0019]      FIG. 8  is a cross sectional view through a carrier roller employing an elastomeric ring  52 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     While the present invention is susceptible of being made in any of several different forms, the drawings show a particularly preferred form of the invention. One should understand, however, that this is just one of many ways the invention can be made. Nor should any particular feature of the illustrated embodiment be considered a part of the invention, unless that feature is explicitly mentioned in the claims. In the drawings, like reference numerals refer to like parts throughout the several views.  
         [0021]     Referring now to the FIGURES, there is illustrated a portion of a track assembly for a crawler tractor or other form of off-highway implement. As shown, the track assembly includes an endless track  10  trained about an idler wheel  12  mounted to a track frame  14 . The track assembly further includes a recoil assembly  16 .  
         [0022]     Track  10  comprises a plurality of track shoes  20  secured to an articulated chain  22  in a conventional manner. Laterally spaced pairs of links  24  of the chain  22  are pivotally interconnected by pin and bushing assemblies  26 . Each pin and bushing assembly is adapted to engage with a notch or root defined between circumferentially adjacent teeth on a drive wheel (not shown) for driving the track in a conventional manner. The above described elements are all well known in the art.  
         [0023]     Track frame  14  is mounted to the crawler tractor in a conventional manner. The track frame  14  has a bifurcated end section including a pair of spaced general horizontal beams  28  and  30  which sandwich the idler wheel  12  therebetween.  
         [0024]     The recoil assembly  16  is mounted to the frame  14  to maintain the track  10  in tension. Recoil assembly  16  further allows the idler wheel  12  to recoil and relieves tension on the track to a limited degree in the event that a rock or other hard object is entrapped on the inside of the track. In the illustrated embodiment, recoil assembly  16  includes a resiliently biased yoke  32  including a pair of spaced legs  34  and  36 . Legs  34 ,  36  extend generally parallel to the frame  14  and have the idler wheel  12  mounted therebetween. A pair of idler wheel mounts  38  are secured to the distal end of each leg  34 ,  36 . Each idler wheel mount  38  is preferably formed from a unitary block structure and journals an idler wheel spindle  40  about which wheel  12  rotates.  
         [0025]     As shown in  FIGS. 2 and 3 , the idler wheel  12  is configured with a plurality of axially spaced annular rims  44 ,  46  and  48 . Rims  44  and  48  are arranged on opposite sides of the idler wheel  12  for supporting and guiding the links  24  of chain  22  thereabout. As shown, the annular rims  44  and  48  are substantially equal in diameter and are smaller in diameter than the central rim  46 .  
         [0026]     According to the present invention, a noise reducing or attenuating elastomeric ring  52  is carried by the idler wheel  12 . Ring  52  circumferentially surrounds the central rim  46  and is adapted to directly and resiliently engage the pin and bushing assemblies  26  thereby reducing contact noise between track  10  and the wheel  12  as the track rotates about the wheel  12 .  
         [0027]     As shown in  FIG. 3 , the central annular rim  46  has a predetermined diameter schematically represented by D 1 . The pin and bushing assemblies  26  are disposed such that an underside of each bushing is disposed at a predetermined diameter D 2  as the chain  22  rotates about the wheel  12 . D 2  is greater than D 1 . Ring  52  is disposed within the space between rim  46  and the underside of the pin and bushing assemblies  26 . The outer free surface of ring  52  has a diameter D 3  that is greater than the diameter D 2  of underside of pin and bushing assemblies  26  as they are positioned when wrapped around idler wheel  12 . The center of each of diameters D 1 , D 2 , D 3 , and D 4  is the rotational axis of idler wheel  12 . Thus, the undersides of each bushing of pin and bushing assemblies  26  compresses the top surface of ring  52  when the chain is wrapped around idler wheel  12 . A portion of ring  52  is thereby placed in compression between the pin and bushing assemblies  26  and the outer rim  46  as the track  10  moves about the wheel  12 . It is this compression of ring  52  that provides a cushioning and noise attenuating effect.  
         [0028]     As shown in  FIG. 3 , the central rim  46  of idler wheel  12  has an annular channel or groove  54  which opens to the periphery of rim  46  and defines dual crown rims  56  and  58  on opposite lateral sides of channel  54 . At least a widthwise portion of each crown rim  56 ,  58  acts as a support for corresponding and overlying lateral portions  60 ,  62  of the elastomeric ring  52 . Channel  54  on rim  46  receives and accommodates a central portion  50  of the ring  52  circumferentially arranged about the rim  46  such that the cushion  52  has a generally T-shaped cross-section (as shown in  FIG. 3 ) when assembled to the idler wheel  12 . With central portion  50  of ring  52  receivably accommodated within channel  54 , ring  52  is inhibited against lateral shifting on the annular rim  46  during operation of the tractor.  
         [0029]     During operation, compression of the elastomeric ring  52  between the pin and bushing assemblies  26  and the outer rim  46  of wheel  12  attenuates metallic sounds and vibrations normally resulting from the impact between chain  10  and wheel  12 . Moreover, recess  54  in the wheel rim  46  interacts with central portion  50  of ring  52  to inhibit inadvertent lateral shifting of the ring or cushion  52  during operation of the implement. Providing the ring  52  between the chain  22  and wheel  12  furthermore reduces impact forces of the idler  12  against the spindle  40 .  
         [0030]     Substantially the entire width of the outer surface of ring  52  abuts and is compressed by pin and bushing assemblies  26 . Lateral portions  60  and  62  and central portion  50  of ring  52  all have the same outer diameter D 3  when stretched to cover rim  46 , and all engage the inner surface of pin and bushing assemblies  26 .  
         [0031]     In the preferred form of the invention, ring  52  is cast or molded separately from a liquid elastomeric material that is placed into a mold cavity. This process provides a freestanding elastomeric ring  52  (as shown in  FIG. 4 ) that can be later attached to wheel  12 .  
         [0032]     A urethane compound which is suitable for the environmental conditions and has a durometer hardness sufficient to allow compression thereof by the pin and bushing assemblies  26  passing about the wheel  12  is one elastomeric material which would suffice to provide the desired cushion and dampening affect of the present invention. Recommended urethanes include “RenCast 6494”, Ren RP-6401-1”, “Ren RP-6400-1”, and “Ren RP-6442” polyurethane systems, which are provided by Freeman Manufacturing and Supply Co., 1101 Moore Road, Avon, Ohio 44011. These materials are identified as having good strength, tear resistance, wear resistance, and hardness in the preferred ranges.  
         [0033]     The mold that produces ring  52  of  FIG. 4  is sized such that when the ring is initially formed, the inner diameter D A  ( FIG. 4 ) of ring portions  60 , 62 , (which will abut crown rims  56 , 58 , respectively, when installed) is less than the outer diameter D 1  ( FIGS. 2, 3 ) of crown rims  56 , 58  of the wheel  12  on which it is to be installed. When the ring is later elastically stretched, placed around rim  46  and released, however, it contracts such that ring  52  has the same diameters as rim  46 . Since D A  (as molded) is less than D 1 , crown rims  56 ,  58  and lateral ring portions  60 , 62  interengage with an interference fit once the ring and idler are assembled.  
         [0034]     When the ring is made, inner diameter D A  is smaller than diameter D 1  by 0.5 to 4.0 centimeters, preferably by 1.0 to 3.0 centimeters, and even more preferably by 1.5 to 2.5 centimeters.  
         [0035]     Similarly, the mold that produces ring  52  of  FIG. 4  is sized such that when the ring is initially formed, the inner diameter D B  ( FIG. 4 ) of central portion  50  (which will abut the bottom of recess  54  when installed) is less than the outer diameter D 4  ( FIGS. 2, 3 ) of recess  54  of the wheel  12  on which it is to be installed. When the ring is later elastically stretched, placed around rim  46  and released, however, it contracts such that ring  52  has the same diameters as rim  46 . Since D B  (as molded) is less than D 4 , recess  54  and central ring portion  50  interengage with an interference fit once the ring and the idler wheel are assembled.  
         [0036]     When the ring is made, inner diameter D B  is smaller than diameter D 4  by 0.5 to 4.0 centimeters, preferably by 1.0 to 3.0 centimeters, and even more preferably by 1.5 to 2.5 centimeters.  
         [0037]     Once the ring is manufactured, it can be lubricated by a water, soap, detergent or surfactant containing mixture, stretched, and forced over rim  46  and released. It then contracts such that the central portion of ring  52  rests in and is supported by channel  54 , and the two lateral portions  60 , 62  rest on and are supported by crown portions  56 , 58 .  
         [0038]     Alternatively, ring  52  can be cast directly on wheel  12 . In this process, wheel  12  is placed in a mold that surrounds rim  46 . A liquid elastomer, such as any of the liquid urethanes referred to herein, is then poured into the mold and cured. The mold is then removed and wheel  12 , together with its integrally formed ring  52 , may be used. This method advantageously produces an intimate bond between the outer surfaces of wheel  12  and the ring. This bond reduces or prevents dirt and other materials from working their way between the urethane and the wheel. Dirt between the ring and wheel may abrade the urethane from the inside out, reducing its grip on wheel  12  and eventually causing the ring to fail prematurely. Further, a break or cut in integrally molded ring  52  will not cause the entire ring to detach from wheel  12  and fail.  
         [0039]     The ring, whether formed separately from wheel  12  or formed integrally with wheel  12 , may have a homogeneous structure. Alternatively, it may be formed to have an inhomogeneous structure. Several of these inhomogeneous structures are shown in  FIGS. 5-7 .  
         [0040]      FIG. 5  shows a cross-section of a ring  52  having a first preferred inhomogeneous structure. In  FIG. 5 , ring  52  includes a first high hardness region  64  and a second low hardness region  66 . This two-region construction is indicated by the two different cross-hatched regions shown in  FIG. 5 .  
         [0041]     High hardness region  64  defines an outer wall and surface  68  of ring  52 , and is positioned to abut pin and bushing assemblies  26 . The high hardness provides a durable wearing surface. It has a hardness of 65-85 on the Shore A scale.  
         [0042]     Low hardness region  66  defines an inner wall and surface  70  of ring  52  that faces, is bonded to, or is formed integral with rim  46 . It has a hardness of 45-65 on the Shore A scale.  
         [0043]     The two layers may be formed by casting or injecting the urethane liquid of which they are made in two separate filling steps, with two separate compositions, either in simultaneous filling steps or in sequential filling steps.  
         [0044]     Ring  52  may also be made by casting the ring in a single pour with a single composition, followed by post treatment of the cast material. This post treatment is calculated to cure the outer layer to the proper hardness. This post-treated region then becomes high hardness region  64  when the cure is complete.  
         [0045]     While the two regions  64 , 66  are shown as well-defined adjacent portions of ring  52  in  FIG. 5 , their hardnesses may change on a gradient as a function of distance, providing a smoother transition from one region to the other with no sudden hardness discontinuities.  
         [0046]      FIG. 6  shows a second alternative inhomogeneous structure for ring  52 . In  FIG. 6 , the outer wall  72  of the ring is reinforced with a flexible reinforcement  74  made of elongated fibers. These fibers may be made in a variety of forms including mat, fabric, cords or threads. They are preferably embedded in ring  52  just below the outer surface  72  of the ring and preferably closer to the outer surface of ring  52  facing pin and roller assemblies  26 , than they are to the inner surface of ring  52  abutting wheel  52 .  
         [0047]      FIG. 7  shows a third alternative inhomogeneous structure for ring  52 . In the arrangement of  FIG. 7 , fibers  76  are embedded in the matrix of elastomeric material of ring  52  distributes throughout the matrix material. In all other respects the elastomeric ring  52  of this FIGURE is the same as any of the other elastomeric rings  52  described above.  
         [0048]      FIG. 8  illustrates an alternative wheel, here shown as a track carrier roller  78  that incorporates the elastomeric ring  52 . Track carrier roller  78  includes a hollow cylindrical roller body  80  is supported for free rotation on roller shaft  82 . Bearings  84  and  86  support roller body  80  for rotation on shaft  82 . An end cap  88  is inserted into aperture  90  in the free end  92  of roller body  80  to enclose the end of the roller body and to provide a sealed chamber  94  that can be filled with grease or other lubricants (not shown). A seal  96  is disposed between shaft  82  and roller body  80  to prevent contaminants such as water and dirt from entering sealed chamber  94  and bearings  84 ,  86 .  
         [0049]     Shaft  82  is fixed to the chassis of the crawler such that body  80  rotates about a substantially horizontal axis. Roller  78  is located inside the endless loop of track  10  and supports the slack portion of track  10  that extends from the top of wheel  12 . Elastomeric ring  52  is disposed in a recess or groove  98  that extends circumferentially around the outer cylindrical surface of roller  78 . Ring  52  is constructed identically to any of the aforementioned rings  52 .  
         [0050]     From the foregoing, it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It will be appreciated that the present disclosure is intended as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.