Patent Publication Number: US-8118518-B2

Title: Slipform paving machine with adjustable length tractor frame

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns concrete slipform paving machines that have a propelling unit or tractor from which a paying kit is suspended with which a layer of concrete is shaped and finished over the underlying ground as the propelling unit travels along a road or airfield alignment. The tractor of a concrete slipform paver has a rectilinear frame which straddles the concrete roadway or airfield pavement section that is being paved. The frame is propelled and supported on either end by crawler tracks mounted on side bolsters. These side bolsters each typically have two hydraulic supporting jacking columns, each of which connects to a crawler track, that allow the tractor frame elevation to be manually or automatically varied relative to the ground. The frame, and in particular a center module thereof, supports a diesel engine-driven hydraulic power unit which supplies power to the tractor and the paving kit. 
     The paving kit is conventionally suspended below the tractor frame by mechanical means, such as with hooks and a locking mechanism. The paving kit takes its hydraulic power from the power unit on the tractor. The tractor and the paving kit pass over fresh concrete placed in and distributed over its path as a relatively even and level mass that can be conveniently slipform-paved. During this process, the tractor-attached paving kit spreads the semi-solid concrete dumped in the path of the paver, levels and vibrates it into a semi-liquid state, then confines and finishes the concrete back into a semi-solid slab with an upwardly exposed and finished surface. The sideforms mounted on each side of the slipform paving kit shape and confine the sides of the slab during the slipform paving process. 
     The tractor normally has three or four crawler tracks, each mounted to a jacking column, supporting and propelling the frame during use of the paver in the paving direction. Other kits can be attached to these tractors such as kits for conveying and spreading concrete and trimming and spreading base materials. For the purposes of this description, the focus is on the tractor frame which carries the paving kit. 
     The length of the tractor frame is adjustable in a transverse direction that is normal to the direction of the paving movement to span different widths of pavements. It is known to use telescopic extensions for changing the length of the frame. Once the telescopic extension limits are reached, a bolt-in, fixed support beam extension can be added to one or both sides of the telescopic frame for further extension. 
     As is well known, tractor frames for slipform paving machines have a generally rectangularly shaped center module or platform which supports, for example, the power unit including the engine for the paver, an operator platform, and the like. The bolsters that connect the jacking column with the crawlers of the paver are connected to the platform with telescopic extension arms or support beams which can be retracted into the center module, to reduce the length of the paver (in a direction perpendicular to the normal paving direction), or extend it outwardly from the center module, to increase the width for paving. However, the length of the center module limits the distance over which the support beams can be extended away from the center module because a substantial portion of the support beams, typically about three to four feet, must remain secured inside the center module so that the support beams are firmly supported by the center module. It is highly desirable that the paving widths can be adjusted by as much as possible without having to disassemble the tractor frame, and to this end it is known to employ two-stage or double telescopic support beams which, in their collapsed position, nest within each other, as is well known in the art. Thus, there are now slipform pavers on the market which employ a two-stage tractor that can vary the length of the tractor (in a direction normal to the paving direction) over a range between a minimum of about eight feet, three inches (2.5 m) to about twenty feet (6.10 m). If the paver is to lay down a strip of concrete that is wider, it is necessary to partially disassemble the frame to install one or more fixed frame extensions between the ends of the support beams (that are telescoping or not) and the bolsters of the paver to which the jacking columns with the crawlers are mounted. While it is relatively simple and not very time-consuming to change the length of the tractor frame by moving the telescoping support beams in or out, installing bolt-in, fixed support beam extensions to increase the length of the frame past its maximum width attainable with the telescopic support beams significantly increases the time, complexity and difficulty of changing the width of the tractor frame. 
     Thus, it is highly desirable to construct the tractor frame so that its width can be increased as much as possible with the telescoping support beams to thereby reduce the frequency with which bolt-in, fixed support beam extensions must be installed, which in turn enhances the efficiency and profitability of the paver. 
     Pavers which employ two-stage, hydraulic, double telescopic extenders with which the maximum length of the tractor frame can be increased without the need for installing fixed frame extensions simplify extending the length of the support beams for a greater paving width. The drawback of such arrangements is that two-stage, hydraulic, double telescopic extenders are complicated, costly to build and maintain, and are difficult to keep from deflecting under vertical loads, thereby reducing the effective paving capability of the paver. 
     BRIEF SUMMARY OF THE INVENTION 
     It is a principal object of the present invention to streamline and speed up changing the width of the tractor frame of a slipform paving machine by increasing the range over which the bolsters of the machine can be extended by means of moving the telescoping support beams in or out in a simple, effective and inexpensive manner to thereby reduce the frequency with which bolt-in, fixed support beam extensions must be installed. 
     This is attained with an adjustable width paving machine that moves in a travel direction for spreading, leveling and finishing concrete into a form having a generally upwardly exposed, finished concrete surface and terminating in lateral concrete sides. The paving machine has a main tractor frame including a center module, a bolster next to each lateral end of the center module, and first and second crawlers connected to jacking columns which are secured to each bolster. The crawlers are pivotable about substantially vertical axes of the jacking columns between the travel direction and a lateral direction that is transverse to the travel direction. 
     First and second telescopic support beams are firmly attached to an inner side of each bolster that faces the center module. Each beam has a length greater than a minimum distance between the inner sides of the bolsters so that free ends of the support beams extend past the respective inner sides of the bolsters and, preferably, past the outer side of the bolsters. Each bolster has openings formed to receive and permit passage of the free ends of the support beams attached to the other, opposite bolster past the inner side of the bolster to which the support beams are not attached. 
     When the width of a concrete strip laid down by the paving machine must be changed, the length of the main frame, which can be changed between a minimum length at which inner sides of the bolsters facing the center module are closest to the center module and a maximum length at which the inner sides of the bolsters are farthest apart from the center module, at least one, and typically both, of the bolsters and the support beams attached to them are moved in the lateral direction relative to the other bolster and relative to the center module as needed. Depending on the selected length of the main frame in the lateral direction, the support beams attached to the bolsters will extend through associated openings in and past outer sides of the other bolster when the main frame has its shortest length. When the main frame is fully extended in the lateral direction, the free ends of the support beams are retracted inside the passages in the center module. 
     As is described in detail below, this change in the length of the tractor frame is preferably performed in accordance with the present invention by moving one or both of the bolsters relative to the center module with the crawlers of the respective bolsters. This change is fast and effective, saves machine down-times during the change, and thereby enhances the efficiency of the paver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational, perspective view of a complete paving machine having a paving kit with tractor frame constructed in accordance with the present invention; 
         FIG. 2  is a perspective, simplified view of a paving machine constructed in accordance with the present invention and only shows the tractor frame of the paving machine as supported by crawlers and from which the paving kit and other details of the paving machine have been omitted for clarity; 
         FIG. 3  shows the tractor frame with bolsters only as used on the paving machine shown in  FIG. 2  in its fully retracted position at which it has a minimal length in the transverse direction; 
         FIG. 4  is a perspective view similar to  FIG. 2  and shows the tractor frame of the paving machine at its maximum length for paving relatively wide strips of concrete; 
         FIG. 5  is a view similar to  FIG. 3  and shows the tractor frame with bolsters only when it is at its maximum length; 
         FIG. 6  is a view similar to  FIG. 5  but shows an arrangement of the tractor frame with bolsters in which only one side of the tractor frame is lengthened while the other side is fully retracted; 
         FIG. 7  is a view similar to  FIG. 5  but shows an additional, bolt-in, fixed support beam extension at one side of the tractor frame to further increase the width of the concrete strip that can be laid down with the paving machine; 
         FIG. 8  is a perspective view similar to  FIG. 4  but shows one set of crawlers of the tractor rotated perpendicular to the direction of paving so that the crawlers extend laterally to the paving direction for moving and propelling the bolster attached to the crawlers into or out of a center module of the tractor frame for shortening or lengthening, respectively, the paving width of the machine; 
         FIG. 9  is a plan view of the center module of the present invention fitted with rollers that support and mechanical or hydraulic clamping locks that secure the support beams relative to the center module for locking the support beams at their set locations to the center module and prevent changes in the spacing between the bolsters during use of the paving machine for laying down a strip of concrete; 
         FIG. 10  is a side elevational view, in section, and is taken on line  10 - 10  of  FIG. 9 ; 
         FIG. 11  is an enlarged detail of the portion of the center module within circle  11 - 11  of  FIG. 10 ; and 
         FIG. 12  is a plan view, with portions broken away, schematically illustrating a paving machine with a dowel bar inserter kit cross beam constructed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , a concrete slipform paving machine  2  has a main tractor frame  4  defined by a center module or platform  6  that carries the diesel engine powered power unit  8  of the paving machine and from which extendable or telescoping support beams  10  extend outwardly in a lateral direction. Bolsters  12  are secured to the respective outboard ends of the support beams. Upright jacking columns  14  are mounted at front and aft ends of the bolsters, and crawlers  16  are conventionally secured to the lower ends of the jacking columns. The jacking columns are preferably hydraulically powered for raising and lowering of the paving machine relative to the crawlers on the ground. The crawlers are mounted to the lower ends of the jacking columns, and they are rotatable relative to the jacking columns about vertical axes, an arrangement that is known in the art. The crawlers support the entire machine and move it over the ground. 
     The respective bolsters can be moved in the lateral direction so that the machine frame, including the crawlers, straddles a paving kit  17  that extends over, clears and forms a strip of concrete (not shown) being laid down by the machine. When finished, the strip of concrete defines an upwardly exposed, appropriately leveled and finished concrete surface (not shown) that extends across the strip between the upright sides of the concrete strip. 
     In use, the paving machine is aligned with the travel direction  18  so that the concrete strip can be laid between the crawlers  16  of the machine over a width determined by a paving kit suspended from the main tractor frame. Fresh concrete is deposited in front of the machine, a spreader plow or a spreading auger (not shown) approximately levels the concrete over a major portion of the width of the concrete strip, and, as the machine advances forwardly, a metering gate substantially evenly spreads the top of the fresh concrete. Following the “liquification” of the concrete by vibrators supported by a vibrator rack at a fixed elevation on the front side of the paving kit, finishing pans (not shown in  FIG. 1 ) can be provided on the aft end of the paving kit to finish the top surface of the concrete as the paving kit passes over it, while sideform(s) form the sides of the concrete strip or slab. A finished concrete strip emerges from the aft end of the paving machine and is permitted to conventionally set and harden. 
     Following the completion of the concrete strip, the paving machine is typically diverted to a new site for laying another strip of concrete. When the width of the next concrete strip differs from the width of the strip that had just been laid down by the machine, it is necessary to change, e.g. lengthen, the span of the machine and the paving kit (in a lateral direction perpendicular to the travel direction  18 ) by correspondingly extending (or shortening) the length of the tractor frame  4  (and of the paving kit suspended from the frame), as is described in the following. 
     Referring to  FIGS. 4 and 5 , tractor frame  4  includes a center module  6  that has a generally rectangular plan configuration and is preferably of a relatively lightweight, high strength box-like construction with end plates  20  that face in the lateral direction and extend generally parallel to the travel direction  18 . Box beams  22  internal of the center module are at the forward and aft ends (in the travel direction  18 ) of the center module and extend from one end plate  20  to the other. Each box beam defines a tunnel-like passage  24  that extends from one end plate opening  26  over the length (in the lateral direction) of the box beams to a corresponding, aligned opening  26  in the other end plate  20 . Each passage  24  through the center module is dimensioned to receive, side-by-side, two elongated preferably tubular support beams  10 , one being attached to one bolster  12 , and the other to the opposite bolster, as is further described below. In the presently preferred embodiment, each passage is divided into two passage halves by placing vertical divider plates  28  centrally inside the passageway to keep two box beams  10  that are slidably disposed in the passage halves separate. The divider plates can be continuous or a plurality of shorter plate sections can be intermittently placed along the vertical center plane of passage  24  between its openings  26  as is schematically shown in  FIG. 5 . 
     In the preferred embodiment of the invention, two elongated, spaced-apart support beams  10  are secured to an inner side  30  of each bolster (which faces center module  6 ) with bolting flanges  32 . The support beams are positioned on the bolsters so that they are aligned with the respective passage halves in the center module assigned to them, and they have a length so that, when the bolster side  30  to which they are attached is as close as possible to the end plate  20  of the center module, their free ends  36  extend past the center module  6  towards and past the other bolster when it too is as close to the center module as possible (as shown in  FIG. 6 ). To enable this, each bolster defines a through opening  34  which is dimensioned to permit free ends  36  of support beams  10  (shown in  FIG. 6 ) to pass through it past an outer side  38  of the bolster which faces away from the center module  6  (as shown in  FIG. 2 ). 
     Thus, support beams  10  have a length so that when the inner sides  30  of the bolsters have a minimal spacing between them, that is, when each bolster is as close to center module end plate  20  as possible (substantially as shown in  FIG. 3 ), the free ends  36  of the support beams  10  extend past the outer sides  38  of the other bolster, that is, the bolster to which the beam is not attached, as can be seen in  FIG. 3 . It is also possible due to the common bolting pattern of center module plate  20 , the inner side  30  of bolster  12  and bolting flanges  32  of support beam  10  to eliminate or remove support beams  10  on one or both sides of the center module and then connect bolster  12  directly to end plates  20  of center module  6 . 
     In an alternative embodiment (not shown), if the bolsters  12  were lengthened, an additional single box beam  22  with divider plates  28  complete with support beams  10  which can slide past each other (not shown) having the required rigidity can be attached between each longer bolster to provide additional structure for the longer bolsters. 
     The effective length of tractor frame  4  (in the lateral direction) can be changed by moving the bolsters  12  towards or away from center module  6  until the distance between inner sides  30  of the bolsters has the required length for supporting the paving kit used for forming a concrete strip of the desired width. Tractor frame length adjustments are made by slidably moving either one or both of the bolsters relative to the center module with the support beams. 
     In this context, it is to be noted that the inward or outward movement of the bolsters relative to the center module need not be the same and, if desired, the bolsters can be moved so that the center module is, for example, not at the center (as shown in  FIGS. 4 and 5 ), but adjacent one and spaced from the other one of the bolsters, as shown in  FIG. 6 . A locking mechanism  46 , further described below, is provided on the center module for locking the support beams at their set locations to the center module to prevent changes in the spacing between the bolsters during use of the paving machine for laying down a strip of concrete. To facilitate slidable movement of the support beams  10  into and out of passage  22  through the center module, low-friction supports, such as rollers with bearings  56  (further described below), can be provided. 
     Each support beam  10  has a length sufficient to extend from inner side  30  of the bolster through passage  24  in the center module, through and beyond openings  34  in the bolster that is opposite from the bolster to which the beam is attached so that the free end  36  of the beam protrudes past outer bolster side  38  as is illustrated in  FIGS. 2 and 3 . The further the free ends of the support beams extend past outer side  38  of the opposing bolster, the greater the width adjustability of the main frame becomes. Preferably, however, when the bolsters are in their fully retracted state (with a minimal distance between the inner sides  30  of the opposing bolsters), the length of support beam  10  projects past outer side  38  of the bolster no further than the laterally outermost point of the paver, typically defined by crawlers  16  of the paver, in order to prevent excessive support beam lengths which could project past the outer sides of the bolsters from interfering with the concrete laying operation in tight spaces, at obstacles and the like that may be close to the paving path of the machine as it operates. 
     Referring now to  FIGS. 2-7 ,  FIG. 2  shows an arrangement of tractor frame  4  in which both bolsters  12  are retracted as far as possible towards end plates  20  of center module  6  to place the paving machine into a position for laying the narrowest possible strip of concrete. When in this position, the free ends  36  of the beams attached to one of the bolsters extend past openings  34  in the opposite bolster and are located beyond outer sides  38  of the opposing bolster as shown in  FIGS. 2 and 3 . 
     When it is necessary to increase the span of the paving machine in order to lay down a wider concrete strip, bolsters  12  and the crawlers  16  carried by them are moved laterally outwardly to the positions shown in  FIGS. 4 and 5 . In accordance with the present invention, this is done by initially pivotally turning the set of crawlers  16 ′ (shown in  FIG. 8 ) on the lower end of jacking columns  14  on the bolster that is to be moved so that the crawlers are perpendicular to the travel direction  18  and face in the lateral direction, while the crawlers on the opposing bolster can remain in their paving direction. In one embodiment of the invention, center module  6  is lowered onto four (two front and two rear) schematically shown support blocks or columns  40  on the ground by appropriately activating the respective jacking columns  14  so that the weight of the center module  6 , and the equipment carried by it, is carried by blocks  40  and not by support beams  10 . Next, crawlers  16 ′ are activated to move/propel bolster  12 ′ carried by them in a lateral direction  42 . This pulls (or pushes) support beams  10  attached to bolster  12 ′ away from (or towards) the center module, thereby increasing (or shortening) the length of the tractor frame and the concrete strip width that can be laid down with the machine. While support beams  10  are moved away (or towards) the center module with crawlers  16 ′, the weight and resulting friction of the center module resting on support blocks  40 , as well as the perpendicular orientation of crawlers  16  on the other bolster  12 , maintain the entire tractor frame stationary, thus making it easier to telescope the support beams  10 . 
     To maintain structural stability, an inboard end section  48  of extended support beams  10  in  FIGS. 5  (and  10 ′ in  FIG. 5 ), shown by hidden lines, must remain inside box beams  22  of the center module. In a presently preferred embodiment, in which the box beams have dimensions of about thirteen inches in height and six inches in width, a section of between about three to four feet should remain inside the passages  24  in the center module. Of course this same design can be applied to tractor frames that span wider widths and have deeper support beams. Thus, the maximum distance by which a given bolster can be moved laterally away from center module end plate  20  is the distance between inner surface  30  of the bolster to which support beam  10  is attached and its free end  36  (that protrudes past outer side  38  of the bolster as seen in  FIG. 2 ), less the length of the support beam section  48  that must remain inside center module passage  22  to maintain the structural stability of the tractor frame. 
     In the past, the maximum distance by which the bolsters could be moved laterally away from the center module equaled the lateral length of the center module less the support beam section  48  that must remain inside the center module passage  22 . This maximum extension distance could be further increased only by using the earlier mentioned bolt-in, fixed support beam extensions, which is a time-consuming process to add and remove. With the present invention, the maximum effective length of the tractor frame that can be reached telescopically is substantially increased as compared to prior art pavers. Typically the effective maximum width of the main tractor frame  4  constructed in accordance with the present invention can be increased by up to about two feet per bolster on each side for a total of approximately four feet for the whole paving machine. 
       FIG. 6  schematically illustrates the state of tractor frame  4  after bolster  12 ′ has been moved laterally away from center module  6  to the maximum extent.  FIG. 6  also schematically illustrates the state of tractor frame  4  after opposite bolster  12 ′ has been moved laterally toward the center module  6  to the closest extent possible. Tractor frame  4  shown in  FIG. 6  can be used as shown, in which event the center module will be off-center relative to the paving direction. Alternatively, following the lateral extension of bolster  12 ′, the opposite bolster  12  shown in  FIG. 6  can be laterally extended in the opposite direction by repeating the above-described steps for extending bolster  12 ′ up to the maximum extent. 
     Referring briefly to  FIG. 7 , in instances in which a full extension of support beams  10  is insufficient to attain the required paving width, a bolt-in fixed support beam extension  44  with bolting connection flanges  32 ′ on each end can be inserted between bolting flange  32  (at the end of the telescopic support beam  10 ) and corresponding bolting connection holes on the inner side  30  of the bolster. 
     Referring to  FIG. 5  and  FIGS. 9-11 , following the setting of the desired distance between the opposing, inner sides  30  of the bolsters, the support beam sections  48  (the ends of which are shown by hidden lines in the drawings) which remain inside passages  24  through the center module are fixed in place relative to center module  6  with locks  46 , as described below, and the jacking columns  14  are hydraulically energized to raise center module  6  above support blocks  40 . Upon removal of the support blocks from beneath the center module, the tractor frame is lowered into its operative position and the crawlers  16  are rotated about the axes of jacking columns  14  to orient the crawlers in the paving direction. Thereafter a fresh strip of concrete having the prescribed width can be laid down. 
     As mentioned, to facilitate sliding support beams  10  in and out of support beam passages  24  in center module  6 , rollers  56  can be installed on the top and lower surfaces  52 ,  54  of the center module, and the center module is provided with a hole (not separately shown) through which rollers extend so that their respective peripheries engage the upper and lower surfaces, respectively, of the support beams  10  arranged side-by-side in each passageway  24 . In the embodiment of the invention illustrated in  FIGS. 9-11 , each support beam passageway is provided with two such rollers. The height of the passageway halves is slightly greater than the height of the support beams  10  so that the support beams can freely slide through them so that support beams  10  can be freely moved in and out of the passageways. 
     Providing the friction-reducing rollers  56  is a presently preferred embodiment of the invention. The rollers significantly reduce friction between support beams  10  and passageway  24  when moving the support beam into or out of the passageway so that the center module  6  can be carried by crawlers  16  and the bolsters  12  and support beams  10 , which eliminates the need to place separate supports  40  beneath the center module as schematically shown in  FIG. 8 . 
     Still referring to  FIGS. 9-11 , after the relative position of support beams  10  inside passageways  24  has been set to allow room to mount the paving kit underneath to lay a strip of concrete of a desired width, as was described above, locking mechanism  46  is activated to firmly clamp each support beam to the center module  6 . In a presently preferred embodiment, the locking mechanism is formed by a hydraulically activated piston  58  mounted in a schematically illustrated housing  60  that defines a cylinder for the piston and that is secured, e.g. by screws  62 , to the respective upper and lower surfaces  52 ,  54  of the center module. In the preferred embodiment a press-block  64  is engaged by the piston and forced against the upper and lower surfaces of the support beams  10 . 
     In an alternative embodiment of the present invention, locking mechanism  46  is defined by an appropriately shaped plate, schematically identified in  FIG. 11  by reference numeral  60 ′, that engages a clamping plate, schematically illustrated by reference numeral  58 ′, that is configured (not separately shown in  FIG. 11 ) so that the clamping plate  58 ′ forces press-block  64  against the support beam when screws  62  are firmly tightened to press block  64  against the respective upper and lower surfaces  52 ,  54  of the support beams  10  to thereby lock the support beams to the center module  6 . 
     As previously mentioned and referring to  FIG. 10 , the height of support beams  10  is slightly less than the height (not separately shown) of the passageways  24  in center module  6 . After the support beams have been extended or retracted relative to the center module, as needed for the desired paving width, the locking mechanism  46 , whether a hydraulically activated piston  58  or a bolted-down press block  64 , is tightened to force the inboard end of each support beam upwardly against the top surface of the respective passageway  24 , and the laterally outer locking mechanism is tightened to force the lower side of the support beams against the lower end or edge formed by the bottom surface of the passageway. As a result, each laterally outwardly extending support beam is slightly downwardly inclined relative to the other and relative to the associated passageways, which together form a camber defined by the downwardly inclined support beams alone when their inboard ends overlap (as schematically indicated by the spaced-apart inboard ends  48  of the beams in  FIG. 5 ), or together with the platform  4  when the support beams do not overlap. This has the advantage that under load conditions the weight carried by the center module causes a slight deflection of the inclined support beams, which has the tendency to straighten and align them with each other. As a result, a potential interference, or lack of clearance, between the paving kit (not shown in  FIG. 10 ) mounted below the tractor frame is prevented. If the support beams are not pretensioned as just described, the tractor frame can deflect downwardly, thereby reducing and potentially eliminating the required and desired spacing between the underside of the tractor frame and the paving kit suspended therefrom. 
       FIG. 12  shows a paving machine  2  including a center module  6 , support beams  10 , bolsters  12  and crawlers  16  as described above. The paving machine can be used with a dowel bar inserter for intermittently placing dowel bars (not shown) into the freshly laid down concrete strip immediately behind the paving kit. Such a dowel bar inserter, its construction and attachment to the paving machine are described, for example, in commonly owned, copending U.S. patent application Ser. No. 12/556,486, filed Sep. 9, 2009, for a Paver Having Dowel Bar Inserter With Automated Dowel Bar Feeder, the disclosure of which is incorporated herein by reference as if it were fully set forth herein. 
     A dowel bar inserter  70  is positioned rearwardly of main tractor frame  4  and center module  6 . To movably support the dowel bar inserter from the paving machine, which is required for properly inserting the dowel bars into the freshly placed concrete, the lateral ends  74  of a cross beam  72  are tied into, that is, they are typically bolted to, rearwardly extending bolster extensions  76 . The forward ends of the bolster extensions are secured to main tractor frame bolster  12 , and its aft ends are suitably connected to the aft jacking columns  14  which mount aft crawlers  16 . 
     Cross beam  72  for supporting dowel bar inserter  70  comprises a telescoping, laterally extendable and retractable support system that has a center housing  6 ′ which, on its interior, defines a pair of open-ended, parallel passageways (not separately shown in  FIG. 12 ) which movably receive support beams  10 ′ that extend in opposite directions from the center housing towards the rearward bolster extensions  76 . The passageways on the inside of center housing  6 ′ are separated, for example with plates like those discussed above in connection with center module  6 , and have rollers and locking mechanisms (not shown in  FIG. 12 ) which engage support beams  10 ′ and lock them in place in the same manner as this is done for moving and securing support beams  10  to center module  6  discussed above. 
     The dowel bar inserter  70  is movable (with wheels, not separately shown in  FIG. 12 ) along a pair of spaced-apart rails  84 , the forward end of which is secured to the aft support beams  10  of the tractor frame  4 , and its aft ends are secured to support beams  10 ′ at the opposite location between the center housing  6 ′ and the rearward bolster extension  76 . As a result, the dowel bar inserter kit can stay stationary relative to the concrete being laid down during the insertion of the dowels in the plastic concrete while the paver continues to travel forward. Once the dowels are inserted and the insertion forks have cleared the top of the plastic concrete, the dowel bar inserter is retracted back behind the tractor frame to await the next joint/insertion cycle. 
     When dowel bars are to be inserted into the fresh concrete, cross beam  72  (which is part of the dowel bar inserter) is necessary to provide structural stability to the bolster extensions  76  which provide space for the dowel bar inserter to operate as well as room for the cross beam. The support beams  10 ′ of cross beam  72  are extended inwardly or outwardly, as needed, so that the aft jacking columns  14  are at the desired positions and the cross beam has the required length (transverse to the travel direction  18 ) for attaching the dowel bar inserter thereto in a conventional manner. 
     In the preferred embodiment of the invention, cross beam  72  is constructed analogously to center module  6  as far as the lateral expandability of the cross beam is concerned. Thus, an elongated, spaced-apart support beam  10 ′ is secured to the inner side of each rearward bolster extension  76  with bolting flanges (not shown in  FIG. 12 ). The support beams are positioned on the bolsters so that they are aligned with the respective passages  48 ′ in the center housing  6 ′ assigned to them, and they have a length so that, when the bolster side to which they are attached is as close as possible to the center housing, their free ends (not separately shown in  FIG. 12 ) extend past the center housing towards and past the other rearward bolster extension  76  when it is as close to the center housing as possible (as shown in  FIG. 6 ). To enable this, each rearward bolster extension  76  defines a through opening  34 ′ which is dimensioned to permit the free ends of support beams  10 ′ to pass through it past an outer side  38 ′ of the bolster which faces away from the center housing. 
     Thus, support beams  10 ′ also have a length so that when the inner sides of the rearward bolster extensions  76  have a minimal spacing between them, which occurs when each bolster  12  is as close to center module end plate  20  as possible (substantially as shown in  FIG. 3 ), the free ends of the support beams  10 ′ extend through openings  34 ′ past the outer sides  38 ′ of the other rearward bolster extensions  76 , that is, the rearward bolster extension  76  to which the beam is not attached. It is also possible due to the common bolting pattern of center module plate  20 , the inner side  30  of bolster  12  and bolting flanges  32  of support beam  10  to eliminate or remove support beams  10  on one or both sides of the center module and then connect bolster  12  directly to end plates  20  of center module  6 . 
     When it is necessary to change the paving width of the machine, support beams  10  and  10 ′ are moved relative to center module  6  and center housing  6 ′ until the desired width has been reached. Thereafter all beams are secured to the center module and housing, preferably in the above-described manner. Simultaneous therewith, the length (in the transverse direction) of dowel bar inserter  17  is correspondingly adjusted by lengthening or shortening it as needed so that its wheels (not shown in  FIG. 12 ) engage rails  84  for moving the dowel bar inserter in forward and aft directions relative to the main tractor frame  4 .