Abstract:
A track-supporting roller assembly, according to the disclosure, for supporting a crawler track of a crawler chassis includes a bearing unit and a track-supporting roller rotatably coupled to the bearing unit. The track-supporting roller includes at least one supporting body made of plastic. The supporting body serves as a damper and prevents a metal-on-metal contact between track chain links of the crawler track and the track-supporting roller. The track-supporting roller assembly according to the disclosure ensures a reduced noise development in the crawler chassis. At the same time, it is possible to also reduce the wear of the track-supporting rollers to a considerable extent.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to European patent application number EP 13001923.5, filed Apr. 12, 2013, which is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a track-supporting roller assembly for supporting a crawler track of a crawler chassis. 
     BACKGROUND 
     Conventionally, track-supporting rollers made of steel are used to support the upper crawler section of a crawler track in a crawler chassis. The crawler track chain links roll directly on the steel rollers, which may lead to an undesired noise development at the workplace. In addition, it has shown that the metal-on-metal contact between the chain links and the steel rollers results in a greater wear not only of the steel rollers, but also of the chain links of the crawler track. Remedying such signs of wear is very expensive, and cannot be done right at the construction site, but has to be carried out in a workshop. Also, rust deposits may be formed between the steel rollers and the chain links if the construction machine with the crawler chassis remains outdoors on the construction site for a longer period. Above all, this may lead to split-offs on the steel roller surface when the construction machine starts moving, resulting in an unsteady and noisy run of the crawler track. 
     EP 1 666 345 B1 discloses a crawler chassis having a track-supporting roller assembly which is positioned next to a drive wheel. The track-supporting roller assembly comprises a supporting roller which is mounted on both sides and on which the crawler track rolls along. The supporting roller has an increased diameter at its outer ends, on which position the chain links are supported. 
     US 2010/0096196 A1 discloses another crawler chassis. The crawler chassis comprises several track-supporting rollers which are arranged on a carrier, respectively mounted on both sides, between a drive wheel and a return wheel. The supporting surface for the chain links is formed by outer portions of the respective track-supporting rollers that have an increased diameter. The respective track-supporting rollers are mounted in a lubricating bushing on both sides. It is difficult, however, to seal the lubricating bushing bearing in such a way that an escape of lubricant from the bearing during the operation is prevented, which could result in an unsteady run of the respective track-supporting rollers. 
     EP 1 798 138 B1 discloses a mounting structure for a track-supporting roller for a crawler track which is mounted on a lower frame of the crawler chassis. The mounting structure comprises a mounting part and a support part for the carrier roller. The support part comprises a clamping closure which can be screwed such that a shaft of the carrier roller can be mounted in the clamping closure, on which shaft the carrier roller is rotatably fixed. The drawback of this arrangement is that the screw closure can become loose when vibrations occur during the operation, so that the carrier roller may slip out of the support part. 
     SUMMARY 
     It is an object of the present disclosure to provide a track-supporting roller assembly by means of which a smooth and reliable guidance of the crawler track can be obtained, and which ensures at the same time that the extent of wear signs on the track-supporting roller and on the track chain links of the crawler track guided on the track-supporting roller is reduced. 
     This object is achieved by providing the track-supporting roller with at least one supporting body made of plastic. The supporting body made of plastic is provided on the track-supporting roller such that the track chain links of the crawler track roll along on the supporting body. The supporting body acts like a damper and, therefore, is able to buffer movements of the upper crawler section of the crawler track such that the noise development is reduced. The supporting body made of plastic is not only characterized by its excellent damping properties during the operation, but also provides for a certain protective function during a standstill of the crawler chassis. This protective function is noticeable, above all, because construction machines remaining outdoors on the construction site for a longer period are no longer subject to rust deposits between the track-supporting rollers and the track chain links. Thus, a gentle start of the crawler chassis is possible without creating split-offs on the track-supporting roller, respectively on the track chain links. 
     In a preferred embodiment of the disclosure the supporting body is made of polyurethane. Polyurethane is particularly characterized by a high resistance against climatic influences and, therefore, is extremely well suited for use on the construction site. In addition, polyurethane is pertinacious to abrasion and offers excellent adhesive properties, which is an advantage in particular for the guidance of the crawler track. A supporting body of polyurethane furthermore offers excellent damping properties, so that movements of the crawler track can be buffered well without stressing the bearing unit of the track-supporting roller assembly. Thus, a prolonged service life of the bearing unit can be expected. In order to realize a particularly abrasion-resistant support for a crawler track the supporting body is, in another embodiment of the disclosure, made of rubber, above all with a hardness grade of more than 90 shore. 
     In addition to the excellent abrasion resistance, a supporting body made of rubber also allows the excellent dampening of impact forces of the crawler track so as to prevent these forces from being transferred to the bearing unit of the track-supporting roller assembly. 
     Preferably, the supporting body has an outer diameter between 40 mm and 100 mm, specifically 50 mm. Thus, the track-supporting roller assembly is very compact. Such a track-supporting roller assembly allows guiding a crawler track at a small height relative to the ground. Guiding the crawler track at a small height is above all advantageous for road finishers as the installation space of the crawler chassis in an upward direction is limited by the material bunker. 
     According to another embodiment of the disclosure the supporting body is hollow-cylindrical and has an inner diameter between 20 mm and 60 mm. A supporting body with such dimensions is easy to manufacture and easy to couple to the track-supporting roller. 
     Preferably, the track-supporting roller comprises a shaft on which the supporting body is fixed. The shaft provides for a stable basis on which the supporting body can be mounted in a rotation-fixed manner. The shaft is advantageously made of a metal that has a high bending stiffness. As compared to the supporting body the shaft does not yield to the movement of the crawler track so that the bearing unit can be relieved. 
     It is particularly favorable if the supporting body is shrunk or cast onto the shaft. Thus, it is possible to fix the supporting body on the shaft in a rotation-fixed and anti-slip manner. This is an advantage because great forces act on the supporting body owing to the guiding, respectively carrying of the crawler track. Rotatability of the supporting body relative to the shaft is not desirable as the supporting body is thus heated up to a particularly great extent and could be damaged. 
     In another embodiment of the disclosure it is provided that the shaft comprises a stop against which the supporting body bears. Even in the case of great axial lateral forces the supporting body is thus secured against the stop and cannot slip out of place on the shaft. 
     Preferably, the stop has a smaller outer diameter than the supporting body. Thus, it can be prevented that the stop collides with chain links of the crawler track. This diameter difference relative to the supporting body also helps to achieve a form-fit contact of the crawler track chain links on the track-supporting roller, so that the crawler track can be guided positionally accurate and smoothly. 
     It is also an advantage if the stop has a greater outer diameter than the shaft on which the supporting body is arranged. Thus, the stop defines a particularly robust counter-bearing for the supporting body. 
     According to another embodiment of the disclosure the stop has a hollow-cylindrical shape, wherein its inner diameter substantially corresponds to the outer diameter of the shaft. Thus, the stop may be arranged concentrically on the shaft, resulting in a smooth guidance of the crawler track. 
     An excellent resistance against climatic influences is exhibited by the stop if it is made of plastic, especially of polyurethane. In case the stop, like the supporting body, is permanently in contact with chain links of the crawler track it can thus be prevented that rust deposits occur in the contact area to the chain links. Moreover, the stop, if made of plastic, acts as a protective envelope for the shaft of the track-supporting roller. 
     The stop may be fixed on the shaft in a particularly stable manner if it is shrunk or cast onto the shaft. This may be accomplished simultaneously with shrinking on, respectively casting on, the supporting body, or in a subsequent or preceding process. 
     Alternatively, the stop may also be formed integrally with the shaft, however, e.g., formed as a cast body or body of rotation of metal. In the appropriate case this would result in a greater stability of the track-supporting roller. 
     It is also conceivable that the supporting body encases, at least section-wise, the shaft and also the stop. Thus, the supporting body protects both the stop and the shaft. At the same time, the stop holds the supporting body on the shaft in a stable manner. 
     Preferably, the bearing unit comprises at least one bearing body which rotatably supports one end of the shaft. The bearing body can be easily fixed to the crawler chassis and ensures a regular rotation of the shaft. 
     The track-supporting roller assembly is particularly smooth in operation if the track-supporting roller is coupled to the bearing unit by a roller bearing. The roller bearing allows the support of great radial forces, which may take effect in particular in supporting and guiding a crawler track. 
     According to a particularly preferred embodiment of the disclosure the roller bearing is a self-aligning roller bearing. The self-aligning roller bearing has, above all, the advantage that it can be loaded to a great extent both axially and radially in both directions. In addition, the self-aligning roller bearing is capable of compensating misalignments or deflections of the track-supporting roller, respectively shaft. 
     Another improvement of the disclosure provides that the self-aligning roller bearing comprises an inner ring which bears against the supporting body. The inner ring thus provides a roller track for the self-aligning roller bearing and, at the same time, an attachment, respectively support, for the supporting body. This has the result that the supporting body is secured against the inner ring and can thus be fixed on the shaft in a stable manner. 
     Preferably, the self-aligning roller bearing comprises an outer ring which is arranged in the bearing unit. The bearing unit offers enough protection for the outer ring and forms a stable receptacle for same. 
     The self-aligning roller bearing may be coupled to the bearing unit in a particularly reliable manner by means of a clamping plate. Also, the clamping plate is able to prevent dirt and moisture from penetrating into the self-aligning roller bearing. 
     The subject matter of the present disclosure also is directed to a crawler chassis having at least one track-supporting roller assembly of the above-described type. The crawler chassis furthermore comprises a crawler track having an upper crawler section and a lower crawler section, wherein the upper crawler section rests on the track-supporting roller of the track-supporting roller assembly in a sagging manner. The sagging of the upper crawler section entails a reduced installation volume of the crawler chassis, which is an advantage in particular for road finishers. This will be described below by means of the figures. 
     The crawler chassis is suited particularly well for use in a road finisher if it is configured such that the crawler track can be guided by the track-supporting roller assembly such that an upper edge of the upper crawler section of the crawler track is positioned maximally 700 mm, in particular 650 mm, above a lower edge of the lower crawler section. As compared to other crawler chassis heights the height of the herein described crawler chassis is clearly smaller, so that it can be easily installed in a road finisher underneath a material bunker. 
     The subject matter of the present disclosure also is directed to a road finisher having a crawler chassis with at least one track-supporting roller assembly according to the disclosure of the above-described type. In this road finisher the upper edge of the upper crawler section is at least 50 mm away from a material bunker bottom. This distances is a dimension sufficient for the crawler track not to strike against the material bunker bottom. At the same time, it is possible to maintain a low filling height of the material bunker for the loading of the truck. 
     The subject matter of the disclosure is explained in more detail by means of the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a track-supporting roller assembly according to the disclosure; 
         FIG. 2  shows a top view of the track-supporting roller assembly of  FIG. 1 , including a partial sectional view; and 
         FIG. 3  shows a road finisher comprising a crawler chassis and track-supporting roller assemblies according to the disclosure installed therein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a track-supporting roller assembly  1  according to the disclosure. The track-supporting roller assembly  1  is characterized by a compact design and is excellently suited for supporting a crawler track of a road finisher, as will be described below in connection with  FIG. 3 . 
     The track-supporting roller assembly  1  comprises a bearing unit  2  which includes a first bearing body  3  and a second bearing body  4 . The first and the second bearing bodies  3 ,  4  are identical in design. Two bore holes  34  are respectively provided on the bearing bodies  3 ,  4  and serve to fix the bearing bodies  3 ,  4 . 
     A track-supporting roller  6  is arranged between the two bearing bodies  3 ,  4 . The ends of the track-supporting roller  6  are rotatably received in the bearing bodies  3 ,  4 . 
     According to  FIG. 1 , the track-supporting roller  6  comprises two supporting bodies  7  which are arranged coaxially side by side and spaced apart by a stop  8 . The two supporting bodies  7  have the same outer diameter A7, which is greater than the outer diameter A8 of the stop  8  arranged there between. Furthermore, as explained above, the supporting bodies  7  may be made of plastic. 
       FIG. 1  furthermore shows an impact shoulder  9  respectively formed on the bottom of the bearing bodies  3 ,  4 , which acts as an abutment for fixing the bearing bodies  3 ,  4 . The impact shoulder  9  of the bearing bodies  3 ,  4  has the purpose to rest against the carrier  29  of the crawler chassis  22  as shown in  FIGS. 1 and 3  in a form-fit manner so as to ensure a form-fit construction of the track-supporting roller assembly  1  relative to the carrier  29 . This particularly has the advantage that the track-supporting roller assembly  1  can be held safely on the carrier  29 , without slipping out of place, despite impact forces acting on the crawler track  26  (see  FIG. 3 ). Thus, in particular the impact shoulders  9  of the bearing bodies  3 ,  4  achieve a particularly stable support of the track-supporting roller assembly  1  on the carrier  29 .  FIG. 1  furthermore shows that two vertical bore holes  34  are respectively provided in the bearing bodies  3 ,  4 . The vertical bore holes  34  may be oriented on the carrier to be aligned with threaded holes  35  provided in the carrier  29 . Thus, it is possible to screw the track-supporting roller assembly  1  to the carrier  29  by non-illustrated fixing screws. 
       FIG. 2  shows a top view of the track-supporting roller assembly  1  according to the disclosure, including a sectional view of the portion on the right. 
     It can be easily seen in  FIG. 2  that the track-supporting roller  6  furthermore comprises a shaft  10  on which the supporting bodies  7  are arranged. The portion of the track-supporting roller assembly  1  shown in the sectional view will now be described in detail. This description equally applies to the other half of the track-supporting roller assembly  1  which is not shown in a sectional view in  FIG. 2 . 
     In  FIG. 2 , the bearing body  7  is hollow-cylindrical and abuts against the stop  8  on the side pointing away from the bearing body  3 . The stop  8  has a greater outer diameter A8 than the shaft  10  and a smaller outer diameter A8 than the hollow-cylindrical supporting body  7 . The supporting body  7  preferably has an outer diameter A7 of 50 mm. 
     The shaft  10  is coupled to the bearing body  3  by means of a roller bearing R, which is configured as a self-aligning roller bearing  11  in  FIG. 2 . The self-aligning roller bearing  11  comprises an inner ring  12  and an outer ring  13  and defines there between a roller bearing track for rollers  14 . A receptacle  15  is formed in the bearing body  3 , in which the outer ring  13  of the self-aligning roller bearing  11  in completely received. 
     The inner ring  12  is axially broader than the outer ring  13 . The inner ring  12  protrudes into the receptacle  15  of the bearing body  3  and extends substantially up to one end of the shaft  10 . The roller bearing track with rollers  14  is completely received in the receptacle  15 . The inner ring  12  protrudes out of the receptacle  15  and extends up to the supporting body  7 . Thus, the inner ring  12  can prevent the supporting body  7  on shaft  10  from slipping outwardly. The supporting body  7  is thus enclosed between the stop  8  and the inner ring  12  of the self-aligning roller bearing  11 , so that the supporting body  7  cannot be displaced in the axial direction along the shaft  10 . In the area where the supporting body  7  bears against the inner ring  12  the inner ring  12  may have a greater outer diameter A12 which substantially corresponds to the outer diameter A8 of the stop  8 . The inner ring  12  is preferably shrunk onto the shaft  10 , but may also be fixed to same by other fixing means. 
     The self-aligning roller bearing  11  is held in the receptacle  15  by means of a clamping plate  16 . The clamping plate  16  is annular and screwed against an end face  17  of the bearing body  3 . The clamping plate  16  presses the outer ring  13  of the self-aligning roller bearing  11  positionally fixed into the receptacle  15  so that the outer ring  13  is unable to move in the receptacle. Also, sealing means, e.g., a sealing lip  18 , may be provided on the clamping plate  16 , which allow a rotation of the inner ring  12  relative to the clamping plate  16 , but prevent, at the same time, that dirt, respectively moisture, penetrates into the receptacle  15 . 
     The receptacle  15  comprises a storage or storage area  19 . The storage  19  may receive a lubricating grease or lubricating oil. The lubricating grease or lubricating oil may be supplied to the storage  19  through an inlet screw  20 . The inlet screw  20  is shown in  FIG. 2 , on the other bearing body  4 . 
       FIG. 3  shows a road finisher  21  having a crawler chassis  22  and a material bunker  23 . The material bunker  23  is arranged above a front portion of the crawler chassis  22 . The crawler chassis  22  comprises a drive wheel  24  and a return wheel  25 . A crawler track  26  is tightened around the drive wheel  24  and the return wheel  25 . The crawler track  26  comprises a profile  27  as well as numerous track chain links  28  arranged one behind the other. The crawler chassis  22  further includes a carrier  29  by means of which the crawler chassis  22  is fixed to the road finisher  21 . 
       FIG. 3  shows in a schematic view that three track-supporting roller assemblies  1  are arranged on the carrier  29  side by side. The crawler track  22  comprises an upper crawler section  30  which sags downwardly and is supported by means of the track chain links  28  on the three track-supporting roller assemblies  1  which are arranged side by side. The crawler track  26  also comprises a lower crawler section  31  which runs on the ground. 
     The material bunker  23  has a material bunker bottom  32  which is arranged above a front portion of the upper crawler section  30 . The material bunker bottom  32  is arranged above the upper crawler section  30  by a distance X. An upper edge  33  of the upper crawler section  30  is positioned, at least along the material bunker bottom  32 , at a medium height H, which preferably is 650 mm. Guiding the upper crawler section  30  underneath the material bunker bottom  32  at such a height can be achieved by the compact design of the track-supporting roller assembly. The height H added to distance X results in maximum of 1000 mm. Thus, it is possible to position the material bunker  23  at a preferred loading height above the crawler chassis  22 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.