Abstract:
A paving machine which is configured to move in a paving 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 frame, including a center module, bolsters laterally movably connected to respective lateral sides of the center module for changing a spacing between the bolsters, and a crawler track associated with respective aft and forward ends of the bolsters. A bolster swing leg for each crawler track supports an upright jacking column secured to the swing leg proximate a free end thereof. A worm gear drive between the jacking column and the crawler track permits rotational movements of the crawler track and the jacking column about an upright axis. A hinge bracket is interposed between each swing leg and an associated surface of the bolsters and includes a fixed, upright pivot shaft that pivotally engages the swing leg to enable pivotal movements of the swing leg about an upright axis in a substantially horizontal plane. The hinge bracket further includes a pivot pin that is laterally spaced from and fixed in relation to the pivot shaft. A length-adjustable holder capable of being held at a fixed length has a first end pivotally engaging the pivot pin on the hinge bracket and a second end that pivotally engages the swing leg. The holder permits pivotal motions of the swing leg about the hinge pin when it is in its length-adjustable configuration and prevents substantially any motion of the swing leg when the holder is in its fixed-length configuration. A feedback loop cooperates with angular position transducers and automatically keeps the crawler tracks oriented in the paving direction of the machine when the swing legs move in a horizontal plane relative to a remainder of the paving machine. The paving machine can be reconfigured between its paving orientation and a road transport orientation by activating the crawlers to move the swing legs and the crawlers into a narrowed transport configuration.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of U.S. Provisional Application No. 61/318,223, filed on Mar. 26, 2010, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention concerns concrete slipform paving machines that have a propelling unit or tractor from which a paving kit is suspended with which a layer of concrete is shaped and finished over the underlying ground as the tractor 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. 
         [0003]    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. Other kits can be attached to these tractors such as kits for conveying and spreading concrete and trimming and spreading base materials. 
         [0004]    The tractor normally has four crawler tracks, but can also have only three, each mounted to a jacking column, supporting and propelling the frame during use of the paver in the paving direction. The jacking columns are carried on the bolsters, or on bolster swing legs connected to the fore and aft ends of the side bolsters, that are pivotable about vertical axes to change the relative position of the crawlers for a variety of reasons and/or for changing the movement correction of the crawlers and therewith of the paving machine during use. The bolster swing legs with jacking columns and crawlers can also be relocated and mounted directly to the front and rear of the tractor center module, to the outside of the side bolsters or directly to the outside of the tractor center module in some less conventional paving applications. For the purposes of this description, the focus is on the manner in which bolster swing arms and the orientation of the crawlers can be changed and controlled in the more conventional paving configuration of the machine. 
         [0005]    As is well known, tractor frames for slipform paving machines, which typically are extendable/retractable in the lateral direction to change the widths of the tractor frame and the remainder of the paving machine, 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. A side bolster is laterally movable and secured to each lateral side of the tractor frame (by means of male support tubes that telescopic in and out of the tractor center module), and bolster swing legs pivotally connect the fore and aft ends of the bolster to the respective jacking columns and crawlers of the paver. The swing legs are pivotally mounted to front and aft ends of the bolsters on vertically oriented hinge pins so that pivotal movement of the swing legs moves their end portions, which mount the jacking column and the crawlers, sideways relative to the paving direction of the paving machine and in a generally horizontal plane for increasing or decreasing the distance between the crawlers, and the distance and orientation of the crawlers relative to the tractor frame of the paving machine. Once the bolster swing legs supporting the jacking column with crawler track have the desired spacing between them and the desired orientation relative to the tractor frame, they are locked in place to prevent the crawler tracks from deviating from the desired direction/position and to absorb any existing tolerances between the bolster ends and the bolster swing legs which, if permitted to exist, allow undesired orientational deviations of the crawlers. In the past, turnbuckles and/or hydraulic cylinders were employed to prevent such tolerance-based play. To eliminate all play, two counteracting turnbuckle and/or hydraulic actuators arrangements were sometimes employed to establish a positive, immovably locked position and orientation for each crawler track. 
         [0006]    The position fixing turnbuckles and/or hydraulic actuators were secured to mounting brackets that were bolted to a hole pattern in the front (or aft) facing surfaces of the tractor frame and the bolster swing legs and/or between the side bolster ends and the bolster swing legs. To be effective, the turnbuckles/hydraulic actuators must have a substantial angular inclination relative to the bolster swing leg. If this angular inclination becomes too small, the turnbuckles/hydraulic actuators lose effectiveness and rigidity, which, if permitted to occur, can lead to undesired deviations in the desired orientation of the crawler tracks, and if the inclination becomes too large, the distance between the point of connection of the turnbuckles/hydraulic actuators to the tractor frame and to the bolster swing leg can exceed the effective length of the turnbuckle or hydraulic actuator. 
         [0007]    Thus, in the past, when the machine width had to be changed by a significant amount it became necessary to reposition the turnbuckle/hydraulic actuator mounting bracket along the length (in a lateral direction that is perpendicular to the travel direction) of the tractor frame to maintain the angular inclination of the turnbuckle/hydraulic actuator within an acceptable range. This was a time-consuming task that required skilled workers and, therefore, was costly. In addition, the time it takes to change the position of the mounting bracket for the turnbuckle/hydraulic actuator is a downtime for the machine during which it is out of use and cannot generate revenues. 
         [0008]    Bolster swing legs are used so that the crawler tracks can be relatively quickly relocated in relationship to the edge of the concrete pavement that is being laid down from the normal straight-ahead position, for example to avoid obstacles in the path of the crawler tracks or to make room that may be required to allow tie bars to pass the inside of the rear crawlers and the like. One of the conventional ways of relocating the crawler track was to support the side bolster of the tractor, using the jacking column to hydraulically lift the crawler off the ground, then to use one or more turnbuckles (or one or more hydraulic actuators) to mechanically pivot the bolster swing leg with the jacking column and crawler track and, once the desired position is reached, to hold it there with a turnbuckle or steamboat ratchet (or actuator). If only one turnbuckle is used in the normal position, which is the inboard side of the bolster swing leg, the swing leg is free to move due to the inevitable manufacturing and assembly clearances and tolerances in the turnbuckle connections. These clearances are undesirable because if the swing leg is allowed to pivot or tilt under varying loads, it can adversely affect steering and elevation control. Because of this connection play, opposing turnbuckle sets were at times employed, one being located in the inboard side and one or more turnbuckles being located on the outboard side of the swing leg. In such an arrangement, after the crawler track is in the desired position, the opposing turnbuckles are tensioned (pulled) against each other to keep the swing leg from moving. This transfers all the clearance in the pin connections to one side of the hole, eliminating any possible movement in the connection. The drawback of this approach is that the outboard turnbuckles increase the overall machine profile outside the edge of concrete and therefore require more room for the machine when paving past obstacles in tight confines. If the outboard turnbuckle angle is decreased to decrease the machine profile, the effectiveness of the turnbuckles at this flat angle in holding the swing leg can decrease to almost nil. Further, every time the crawler track is relocated, all the turnbuckles must be readjusted. 
         [0009]    Attempts have been made to eliminate the need for the outboard opposing turnbuckles by adding a hydraulic cylinder/actuator between the tractor frame and the swing leg behind the turnbuckle on the inboard of the leg. The cylinder effectively pushes the pin connection clearances to the inside of the turnbuckle connection holes and eliminates the risk of swing leg movement by keeping the hydraulic actuator pressurized. 
         [0010]    The relocation of the bolster swing leg and crawler track in relationship to the tractor frame is further adversely affected by the need to relocate the turnbuckle connection on the tractor frame where it connects to the bolsters to which the swing leg is attached. The turnbuckle connection on the bolster swing leg side typically stays at the same connection point. In the past, the turnbuckle connection to the tractor frame posed several problems. One such problem was when the tractor frame was telescoped narrower. At wider tractor widths, the turnbuckle connects to the outboard end of the support beam of the tractor frame with a turnbuckle bracket that is bolted to the male support beam (that telescopes in and out of the tractor center module) with two or more bolts; however, if the tractor frame is telescoped narrower, the bracket will eventually interfere with the tractor center module, which prevents the further narrowing of the tractor frame. Once this point is reached, the turnbuckle mounting bracket therefore had to be unbolted from the male support beam and rebolted to the tractor center module. To maintain the optimum turnbuckle angle to the swing leg so the turnbuckle is effective in holding the leg in the desired position, the turnbuckle bracket had to be relocated along the tractor center module repeatedly, which slowed down the machine width change process during each change. The inboard turnbuckles can also interfere with other attachments required on the front and rear of the machine, such as a spreader plow that is mounted off the front of the tractor frame, which had to be disconnected and reconnected, which increases costs further. Another problem was when the swing leg complete with jacking column and crawler track is relocated to the outside of the side bolster or mounted directly to the tractor center module, in some paving applications there was no place to connect the bolster swing leg or turnbuckles (hydraulic actuators). 
         [0011]    The relocation of the bolster swing legs and crawler track in relationship to the tractor frame is further adversely affected by the steering cylinders that typically were used on the jacking columns. The steering cylinders allow the crawler track angle to be changed in relationship to the jacking column for manual or automatic steering purposes. In the past, the steering cylinders at times protruded to the outside of the associated steering column. This is undesirable because it increases the outside width of the paving machine, which dictates and will limit how close the machine can pave next to a building or obstruction, and the stroke of the steering cylinder dictates how far the swing leg can be swung inboard or outboard. Amongst others, such a jacking column steering cylinder configuration does not allow the crawler tracks to be rotated 90° from their normal operating orientation without the time-consuming repinning or repositioning of the steering, which is a drawback. 
         [0012]    It is however highly advantageous to rotate the crawlers to such a 90° steering position (and being able to steer the crawler track in that position) from their normal position when readjusting the machine for paving different widths, maneuvering the machine around the jobsite, or for readying the machine for transport to a different paving site. In such an event, the swing legs with jacking columns and crawlers are pivoted relative to the tractor frame until the crawlers extend in the lateral direction (which is perpendicular to the normal paving direction) of the paving machine, which minimizes the width of the paving machine so the gauge between the crawler tracks in the transport position is narrow enough to walk the machine onto a trailer and for its transportation over normal roads to a new site. This outboard 90° bolster swing leg orientation is not to be confused with rotating just the crawler tracks in the 90° position using 90° steering. 
         [0013]    Thus, when repositioning the crawler tracks of a paving machine in accordance with conventional methods, the machine is initially appropriately supported so that a first one of the bolster swing leg-mounted crawler tracks can be lifted off the ground. The turnbuckle is then used to pivot the bolster swing leg until the jacking column and the associated crawler are at the desired (lateral) position and have the required crawler orientation. If the needed lateral movement of the crawler is too great, the turnbuckle mounting bracket must be repositioned by unbolting it from the frame and rebolting it thereto at a hole pattern located at the appropriate (lateral) point on the tractor frame or the center module. Thereafter, the turnbuckle is tightened in the new position of the crawler so that the bolster swing leg can no longer move and the orientation of the crawler is maintained. Thereafter, the crawler is lowered to the ground, it is rotated about the vertical axis of the jacking column to place it in the desired orientation, and an orientation measuring transducer is reset for the new crawler orientation to keep the crawler in the straight-ahead position. This has to be repeated for each of the typically four crawlers of the paving machine, a process that is time-consuming, costly and results in a prolonged, unproductive downtime for the machine. This cost is encountered each time the lateral position of the crawler and/or turnbuckle mounting bracket is changed and the crawlers must then be reoriented relative to the frame so that they face in the required transport direction. This procedure is also used to ready the paving machine for transportation to a new work site. In such an event, the swing legs are pivoted relative to the frame until the crawlers extend in the lateral direction (which is perpendicular to the normal paving direction) of the paving machine, which minimizes the width of the paving machine for transportation to a new site. 
         [0014]    In an alternative approach used in the past, the crawlers and the associated jacking columns were connected to the fore and aft ends of the side bolsters and fixed mounted to the end of the parallel linkages and oriented so that the crawlers extend in the paving direction of the paving machine. The parallel linkages typically include a hydraulic actuator to assist in the crawler track relocation and to hold the crawler track in the desired position. This approach simplified the lateral adjustment of the positions/orientations of the crawlers in relationship to the tractor as compared to crawlers mounted on pivoted swing legs because no matter where the crawler track was repositioned, the crawler track always remained oriented straight ahead and the turnbuckle relocation issue went away. However, in such arrangements, the limited range of movement of the parallel linkages with hydraulic actuator limits how narrowly the machine can be collapsed for transporting it over highways (with standard highway width restrictions) to new construction sites. The ability to quickly and efficiently move the paving machine from one site to the next, which is highly desirable for the efficient use of the machine, is lost with this approach. Instead, paving machines employing such parallel linkages for the crawlers required that the tractor frame itself had to be collapsed in order to narrow the width of the machine sufficiently so that it could be transported over highways. This requires that either the paving kit itself be telescopic or that the paving kit is removed from the tractor. In either case, this could significantly increase the overall cost of the machine or the cost or time required for moving the machine and is therefore an undesirable alternative. The only way to overcome this limitation is to add a pivot hinge (with a means to lock/pin the pivot hinge in either the working or transport position) between the side bolster and the parallel linkage to allow the parallel linkage with jacking columns and crawlers to pivot outboard relative to the tractor frame until the crawlers extend in the lateral direction (which is perpendicular to the normal paving direction) of the paving machine required for loading on a trailer and transport. Of course, adding the pivot hinge with a pinning mechanism to each corner of the machine is costly, and pinning and unpinning of the hinge is time-consuming. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    According to a first aspect of the present invention, each bolster swing leg is pivotally mounted on a hinge bracket that is secured to the front (or aft) ends of the side bolsters of the paving machine. This bracket also supports the turnbuckle or, preferably, a hydraulic actuator which eliminates the need to tie the swing leg into the tractor frame for holding the swing leg, and the crawler track secured to it, in a fixed position during paving. One end of the turnbuckle or actuator is tied into the swing leg conventionally, while the other end is mounted to the hinge bracket. This eliminates the need encountered in the past to relocate the turnbuckle mounts on the tractor frame when the width of the tractor frame is changed. Instead, in accordance with the present invention, every time the width of the paving machine is changed, the attachment point for the turnbuckle or hydraulic actuator automatically follows the positional change of the swing leg because the attachment point is mounted on the hinge bracket, that is, in a fixed position relative to the bolster and the swing leg. 
         [0016]    To facilitate the required realignment of the crawler tracks, another important aspect of the present invention preferably replaces the turnbuckles with hydraulic actuators and provides angular position transducers at the pivot connection for the swing leg at the hinge bracket and another such transducer between the jacking column and the crawler track. An onboard computer or other processor receives the outputs from the transducers and generates a signal to pivot the crawler track relative to the associated jacking column to keep the crawler tracks oriented in the paving direction when the angular orientation of the swing leg changes, and also keeps all the crawler tracks&#39; orientations synchronized. Thus, no matter what the swing leg angle is, the crawler track stays straight ahead in the paving direction and position. Of course it is also possible to override this computerized feature so the crawler track orientation can be changed relative to the bolster swing leg, which may be required from time to time for width change, maneuvering on site, etc. 
         [0017]    The bolster swing leg hydraulic actuator and the hydraulic rotary power drive or steering cylinder for pivoting the crawler track relative to the jacking column working in cooperation with the position transducers allow the swing leg with crawler track to be held in a fixed location in relationship to the edge of the concrete. A closed loop feedback system that connects the hydraulic actuator for the swing leg, the rotary power drive for the crawler, and the onboard computer always maintains the swing leg angle at a fixed, preset angle. If the swing leg migrates away from a preset angle, the swing leg hydraulic cylinder is actuated to maintain the preset angle and at the same time the necessary adjustments to the crawler track orientation are made with the hydraulic rotary power drive or steering cylinder. Alternatively, a hydraulic system using a locking valve can be provided instead of the position transducer and feedback loop for holding the swing leg in the desired position. 
         [0018]    Thus, the crawler track positions can be relocated when the machine is walked forward or backward while the crawler tracks at all times stay in their straight-ahead normal operating orientation and position without requiring any manual mechanical or electronic adjustments. The crawler tracks can also be relocated when the machine is stationary by supporting the weight of the machine off the ground, then hydraulically lifting each crawler track (one at a time) off the ground, and thereafter using the swing leg hydraulic cylinder and position transducer working in conjunction with the power drive or steering cylinder between the jacking column and the crawler track for moving the crawler track to another position. 
         [0019]    A still further aspect of the present invention eliminates the need to reposition the steering cylinder on the jacking columns when the crawler track is repositioned within the range of the swing leg cylinder and to allow 90° steering without having to reposition the steering cylinder by employing a hydraulic motor driven rotary actuator (slew gear) with an angular position transducer as the power drive between the crawler track and the jacking column. The rotary actuator also allows a wide range of steering angles while in the 90° steering mode to make the machine highly maneuverable on site. Working in conjunction with the swing leg position transducer, and after unpinning the swing leg hydraulic cylinder from the swing leg, the rotary actuators allow the machine to be preprogrammed to first turn the crawler tracks relative to the jacking columns normal to the paving direction, and then walk the crawler tracks on the ground in an arc around the pivot shaft of the swing legs into their outboard transport position (in which the crawlers are oriented 90°, i.e. substantially transverse to the paving direction) so that the paving machine can be sufficiently narrowed for moving it over ordinary highways to a new paving site with a legal or otherwise approved transport width dimension, or, for maneuvering the paving machine around a paving site which is tightly confined. The heretofore common need to manually move the swing legs with jacking columns and crawler tracks into the outboard position as previously described is thereby eliminated, which significantly reduces the time required to ready the machine for transport and/or for maneuvering the machine at the work site. 
         [0020]    Thus, a paving machine constructed in accordance with the present invention has a main frame that includes a center module, a side bolster that is laterally movably connected to respective lateral sides of the center module for changing a spacing between the bolsters, a crawler track associated with respective aft and forward ends of the bolsters, and a bolster swing leg for each crawler track. An upright jacking column is secured to the free end of the swing leg, and a connection between the jacking column and the crawler track permits rotational movements of the crawler track and the jacking column about an upright axis. A hinge bracket is interposed between each swing leg and an associated surface of the bolsters and includes a fixed, upright pivot shaft that pivotally engages the swing leg for pivotal movements in a substantially horizontal plane. The hinge plate includes a pivot pin that is laterally spaced from and fixed in relation to the pivot shaft. A length-adjustable, preferably hydraulically actuated, holder is capable of being held at a fixed length and has a first end that pivotally engages the pivot pin and a second end that pivotally engages the swing leg. The holder permits pivotal motions of the swing leg about the hinge pin when in its length-adjustable configuration and prevents substantially any motion of the swing leg when the holder is in its fixed-length configuration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a front elevational, perspective view of a complete paving machine having pivotable swing legs with a jacking column and a crawler, each constructed in accordance with the present invention; 
           [0022]      FIG. 2  is a partial, simplified plan view of portions of a paving machine illustrating the pivotal swing leg of the present invention; 
           [0023]      FIG. 3  is a perspective, front elevational view of a hinge bracket for securing the swing leg to the paving machine; 
           [0024]      FIG. 4  is a front elevational view, in section, taken through the vertical center line of the jacking column and crawler, which are only schematically shown in  FIG. 1 ; 
           [0025]      FIG. 4A  is an enlargement of the portion of  FIG. 4  within the circle A-A of  FIG. 4 ; 
           [0026]      FIG. 5  is a front elevational view, in section, through the pivot connection between the hinge bracket shown in  FIG. 3  and the bolster swing leg attached thereto with a pivot pin; 
           [0027]      FIG. 6  is a schematic plan view similar to  FIG. 2  and illustrates the attachment of the bolster swing legs to the aft portion of the paving machine, with the paving machine having an additional cross beam between the tractor frame and the swing legs for additional kits that may be mounted on the paving machine; 
           [0028]      FIG. 6A  shows in plan view a paving machine with a DBI Module incorporating special bolt-in short bolster extensions with built-in mounts for DBI longitudinal support beams; 
           [0029]      FIG. 6B  is an illustration similar to  FIG. 6A  with the paving machine and the DBI shown in various relative positions as they are being readied for transportation while in their respective transport orientations; 
           [0030]      FIG. 6C  is a side elevation of the paving machine shown in  FIG. 6B , in its transport orientation; 
           [0031]      FIG. 7  is a perspective, side-elevational view showing the bolster swing leg that is pivotally secured to the hinge bracket; and 
           [0032]      FIGS. 8A-E  are schematic plan views of the paving machine which illustrate reconfiguring the machine into its transportation mode (or vice versa). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    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 male support beams  10  extend outwardly in a lateral direction. Side bolsters  12  are secured to the respective outboard ends of the support beams. Upright jacking columns  14  are mounted in the vicinity of respective 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 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. 
         [0034]    The respective bolsters can be moved in the lateral direction relative to the center module so that the machine frame, including the crawlers, straddles a paving kit (not separately shown) 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. 
         [0035]    In use, the paving machine is aligned with the paving 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  63  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 ) are 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. 
         [0036]    Referring to  FIGS. 1-5 , each crawler  16  and the associated jacking column  14  are mounted to a free end  19  (shown in  FIG. 7 ) of a bolster swing leg  20 . The swing leg is typically formed as a box beam  22  and has another end  21  (shown in  FIG. 7 ) that is pivotal about a vertically oriented pivot shaft  24  which extends through a bearing bushing  26  that is supported in its vertical orientation on a hinge bracket  28  with spaced-apart support webs  30 . 
         [0037]    The hinge bracket has appropriately positioned fastening holes  32  for securing it to respective end surfaces  34  of side bolsters  12  with conventional bolt and nut fasteners  23  as shown, for example, in  FIG. 7 . A female keyway is provided on the jacking column bolting flange  57  (shown in  FIG. 4 ) with male keyways provided on the mating bolting flanges to take the shear of the bolts and to eliminate possible misalignment. 
         [0038]    The ends of box beams  22  adjacent bolster end surface  34  have connector plates  36 , secured to the top and bottom surfaces of the box beam by welding, for example. The connector plates project towards the tractor frame past the end of the box beam and have holes that pivotally engage pivot shaft  24  in bearing bushing  26  of the hinge bracket so that the swing legs are free to pivot relative to bolsters  12  in a horizontal plane (as indicated in  FIG. 2 ) about an upright axis defined by the pivot shaft. 
         [0039]    The closed end of the cylinder of a hydraulic actuator  38  is pivotally pinned to two spaced-apart support plates which are secured, e.g. welded, to the inside of the hinge bracket  28  and a mid-portion of bearing bushing  26 , as is best seen in  FIG. 3 . The support plates include aligned bores  42  that are laterally spaced some distance away from the bearing bushing  26 . The closed end of the hydraulic cylinder is pivotally movably secured to the support plates with a pin that extends through the bores. The piston  44  of the hydraulic actuator is pivotally pinned to a pair of spaced-apart brackets  46  which are located between the ends of the swing leg and typically relatively closer to its free end  19 . When the hydraulic actuator is pinned to the hinge bracket  28  and the brackets on bolster swing leg  20 , it is angularly inclined relative to the paving direction  18 , as best seen in  FIGS. 1 and 2 . It is foreseen that on a larger machine more than one, e.g. two, vertically spaced-apart hydraulic cylinders placed above each other may be required to generate the force required to hold the bolster swing leg in a fixed position relative to the male pivot hinge. Further, if desired, for example for cost reasons, hydraulic actuators can be replaced by turnbuckles. 
         [0040]    When assembled installed between hinge bracket  28  and swing leg  20 , hydraulic actuator  38  can be energized to pivot bolster swing leg  20  in a horizontal plane as schematically illustrated in  FIG. 2 . Since hinge bracket  28  is secured to end face  34  of bolster  12 , the angular inclination of the actuator relative to the bolster swing leg does not change when the length of the tractor frame  4  (in the lateral direction perpendicular to the normal paving direction  18 ) is changed. There is therefore no need to reposition the hinge bracket that secures one end of the hydraulic actuator to the machine frame, as was necessary in the past. The extendable length of the hydraulic actuator and its attachment points to hinge bracket  28  and swing leg  20  are chosen so that the angular inclination of the hydraulic actuator relative to the bolster swing leg is maintained over a reasonably large arc (as schematically illustrated in  FIG. 2 ) that is sufficient to permit repositioning of the swing leg during normal use encountering normal operating conditions of the paving machine without having to disconnect the actuator from the swing leg and/or the hinge bracket. 
         [0041]    However, when the swing legs are to be rotated 90° from the paving direction  18  towards a position that is laterally outward of bolsters  12 , principally for readying the paving machine so that it can be transported by truck and trailer to a new location, hydraulic actuator  38  is disengaged from at least one of the swing leg or the hinge bracket  28 , for example by pulling pin  41  that connects the end of piston  44  to brackets  46  on the swing leg, to prevent interference between the hydraulic actuator and support plates  40  and/or bearing bushing  26  of the hinge bracket. 
         [0042]    When bolster swing legs  20  are longitudinally aligned with tractor frame  4  and its laterally extending support beams  10 , a position in which the legs are oriented approximately perpendicular to paving direction  18 , it is preferred to pin the swing legs in that position during shipment of the paving machine with a turnbuckle or other fastener (not shown) to webs  45 ,  47  on the laterally facing surfaces of the bolster and the swing leg as seen in  FIG. 2 . The turnbuckle or the like is released at the new location so that the swing legs can be returned to their normal operating position in which they are parallel, or only slightly angularly inclined relative to the paving direction  18 . 
         [0043]    Each time the bolster swing legs  20  are pivoted inwardly or outwardly relative to tractor frame  4  of the paving machine, the relative angular inclination between the bolster swing legs and the tractor frame changes. This change is replicated by crawler tracks  16  mounted below jacking columns  14  at the free end of the swing legs. This change in crawler track orientation has to be compensated for so that, following the pivotal movement of the swing leg, and preferably simultaneously therewith in real time, the crawler tracks extend in the paving direction. This is done by adjusting the angular orientation of the crawler track by an amount that depends on or is a function of the angular displacement of the swing legs relative to the hinge bracket  28  so that the crawler tracks always remain in alignment with paving direction  18  of the paving machine, as is schematically illustrated in  FIG. 2  by the parallel orientation of the crawler tracks (in part shown in phantom lines in  FIG. 2 ) irrespective of the angular orientation of the swing legs. This relocation process can be accomplished while the machine is supported so the crawler track can be lifted off the ground and relocated to the desired location inwardly or outwardly. With this relocation process, typically each swing leg/crawler track is relocated one at a time. Alternatively, this relocation process can also be accomplished while the machine is walking forward or backward. For example, for moving outwards, the angle of the crawler can be hydraulically “jogged” slightly outward while walking the swing leg/crawler track to the desired location with or without the assistance of the swing leg hydraulic cylinder. Once the desired position is reached and the job switch disengaged, the crawler track will automatically go back to the straight-ahead position. In the alternate case, the crawler track relocation process is done while walking in the forward or reverse direction moving one swing leg/crawler track at a time or moving more or all four at a time. 
         [0044]    Referring to the drawings, and particularly to  FIGS. 4 and 7  thereof, jacking column  14  has telescoping outer and inner tubes  48 ,  50  of a generally rectangular cross-section, as is typical for jacking columns on paving machines, and a vertically oriented hydraulic actuator  52  having its cylinder and piston appropriately secured, e.g. by pinning, to the outer and inner tubes. Activation of the hydraulic actuator telescopingly moves the outer and inner tubes relative to each other for lengthening or shortening the distance between the crawler track and the bolster swing leg  20  for raising or lowering the paving machine relative to the ground or, while the paving machine is otherwise supported, raising or lowering the crawler track off the ground. Spaced-apart axial bearings  54  keep the tubes aligned and permit them to slide relative to each other in their axial direction while maintaining tight clearances to minimize backlash. A support structure  57  is further provided for securing the jacking columns to free ends  19  of the bolster legs. This construction of jacking column  14  is conventional and is therefore not further described herein. 
         [0045]    A slew or worm gear drive or other rotary actuator  60  is bolted to a mounting plate  56  at the lower end of inner tube  50  of the jacking column. The worm gear drive has a ring gear  58  that is driven by a pair of diametrically opposite, hydraulically activated helical worm drives  61  carried on a ring-shaped member  63  disposed between an inner bearing race  65  of the worm gear drives and a transverse portion  66  of yoke  62 , to which the ring-shaped member is secured. An outer bearing race  67  is secured, e.g. bolted, to the lower end of mounting plate  56  at the end of inner tube  50 . On its periphery, the outer bearing race  67  defines ring gear  58 . Such slew gear drives are commercially available from Kinematics Manufacturing, Inc., of 2221 W. Melinda Lane, Phoenix, Ariz. 85027, as “Slewing Drive s17b-102m-200ra”. Providing the slew gear drive with two oppositely arranged worm drives increases the power available to rotate the crawler track while a portion of the total machine load is carried by it. The slew drive design also effectively minimizes undesirable play or “backlash” during steering of the crawler track and effectively minimizes undesirable play or backlash between the yoke  62  and the jacking column  14  whether the slew gear drive is activated or deactivated. 
         [0046]    An angular position transducer or sensor  70  is arranged inside an upwardly open can  72  (provided to protect the sensor) that is disposed within an opening  69  in the transverse portion  66  of yoke  62 . Supports  74  extend across opening  69  and secure the can with transducer  70  at the rotational center between the jacking column and the yoke. The transducer cooperates with a trigger pin  68  extending downwardly from the under side of plate  56  and a suitable actuator arm that turns the transducer. Alternatively, the trigger pin can cooperate with the transducer via a belt drive  64  as schematically indicated in  FIG. 4A . 
         [0047]    Transducer  70 , in cooperation with trigger pin  68 , generates a signal that indicates the angular position of yoke  62  relative to jacking column  14  and any changes in the angular position due to rotational movements of the yoke. Corresponding output signals are generated by the transducer and fed to a lead  84  not shown in  FIG. 4  but shown in  FIG. 5 . 
         [0048]    Referring to the drawings, and in particular to  FIGS. 5 and 7  thereof, another angular position transducer  78  is placed on top of swing leg pivot shaft  24  ( FIG. 5 ). As is best seen in  FIG. 7 , the top of the pivot shaft defines a generally drop-shaped head  86  that is engaged by blocks  88  fixed to the upper side of connector plate  36  so that pivot shaft  24  is rotationally fixed to the connector plate and duplicates the angular movements of swing leg  20  about the pivot shaft. Replaceable bearings are provided at the top and bottom of the male hinge bearing (shown in  FIG. 3 ) as well as a means to get grease to them (not shown in the drawings) so the pivot shaft  24  does not seize in the bearing, which would prevent the swing leg from freely rotating. 
         [0049]    Angular position transducer  78  is mounted inside a downwardly open protective can  90 , as seen in  FIG. 5 , which is bolted to hinge bracket  28  via an upright holding arm  92 . 
         [0050]    A trigger pin  94  projects upwardly from the top surface of pivot shaft  24  and cooperates with angular position transducer  78  to generate an angular position signal which reflects the angular inclination between the pivot shaft and the hinge bracket, and which changes when the bolster swing leg  20  changes its angular position relative to the hinge bracket  28 , and therewith also relative to bolster  12  and tractor frame  4 . The output of transducer  78  is fed to a lead  80 . 
         [0051]    The output signal of the position transducer  78  is fed via lead  80  to an onboard computer  82  of the paving machine, or another suitable processor, which receives as its second input the output signal of position transducer  70  between jacking column  14  and crawler tracks  16  via a lead  84 , as is schematically illustrated in  FIG. 5 . 
         [0052]    Onboard computer or processor  82  and the associated transducers  70 ,  78  form a feedback loop in which the computer receives the angular position signal from swing leg transducer  78 . When the angular position of the swing leg changes, the output signal from transducer  78  changes correspondingly. As a result of this orientational change of the swing leg, the angular orientation of the crawler tracks becomes angularly inclined relative to paving direction  18 . Computer  82  calculates by how much the angle of the crawler track has to be changed relative to the jacking column (which has also been angularly offset relative to the transport direction by the swivel motion of the swing leg) to reset the crawler track suspended from yoke  62  to the angular orientation of the desired paving direction. The onboard computer then signals by how much worm gear drive  60  must rotationally adjust the orientation of yoke  62  and crawler tracks  16  to again align the crawler tracks with the paving direction. This process is repeated each time the angular position of the swing leg is changed, or when for other reasons the angular orientation of the crawler tracks becomes misaligned from the desired paving direction of the machine. 
         [0053]    Thus, the above-described feedback loop automatically adjusts the angular orientation of the crawler tracks so that the tracks remain oriented in the travel direction without any need to stop operation of the machine or manually adjust the orientation of the tracks and/or the swing legs. 
         [0054]      FIGS. 8A-E  illustrate with more particularity how the paving machine of the present invention is readily, quickly and inexpensively reconfigured between its paving orientation shown in  FIG. 8A  or configuration for laying down the layer of concrete, and its transportation orientation shown in  FIG. 8E  or configuration in which the width of the machine is reduced to a roadway accepted width with minimal efforts. 
         [0055]    As already mentioned, from time to time the paving machine must be reoriented, either at the work site for maneuvering or repositioning it around, or to ready the machine for transport to a different site, which requires loading the machine on a suitable trailer (not shown) and then hauling it to the new site over available roads. 
         [0056]    Maneuvering the paving machine around the work site is accomplished by rotating the crawlers  16  relative to the jacking column  14  and then, or simultaneously therewith, activating the crawlers to move the machine into the desired position or to a given location at the site. 
         [0057]    For loading the paving machine for transport to a different site on a trailer over standard highways, it is necessary to reduce the transport width of the paving machine to the maximum allowable width for highway vehicles. With the crawlers resting on the ground and initially facing in the paving direction  18 , they are rotated 90° about the vertical jacking column axis with worm gear drive  60  into a position in which they are substantially transverse to the paving direction. The respective hydraulic actuators  38  keep the associated swing legs  20  in their paving orientation as seen in  FIG. 8B . The ends of the hydraulic actuators  38  are then disconnected from the associated swing legs  20  by removing a pin, then with the crawler track on the ground, walking in an arc around the pivot shaft of the swing leg as shown in  FIG. 8C . Once in this position, the crawlers are again rotated 90° about the vertical jacking column axis with worm gear drive  60  to place the swing legs in their transport orientation (shown in  FIG. 8D ) which is perpendicular to the paving direction. Finally, a turnbuckle  95  or like holding device is applied to the main frame side bolster of the paving machine and the swing legs to fix the latter in their transport orientation. This process is repeated at each corner of the machine until each swing leg and crawler track is in the transport orientation and the swing legs are in their transport orientation ( FIG. 8E ) and perpendicular to the paving direction ( FIG. 8D ). 
         [0058]    With the earlier described, cooperating position transducers  70 , angular transducer  78  (not shown in  FIGS. 8A-E ) and worm gear drive  60 , or if desired manually, the crawlers  16  are thereby brought into alignment with the bolster swing legs, which, in the transport direction, are oriented perpendicular to the paving direction  18  and do not materially extend laterally past the remainder of the paving machine, so that the entire machine width is within permissible width limits for highway transportation. Once the crawler and the associated swing leg  20  are in their transport orientation, which preferably is slightly more than 90°, e.g. 95°, the tightened transportation turnbuckle  95  having its ends attached to the paving machine frame side bolster and the swing arm prevents movements of the swing leg and the crawler out of their transport orientation while the paving machine is moved to another site. 
         [0059]    Thus, in the transport position the swing legs and crawlers are parallel to and extend past the respective lateral ends of the paving machine while the overall width is kept within width limits allowed for highway vehicles. 
         [0060]    Placing the paving machine in the transport direction requires little time since the operation can be quickly performed and the crawlers can then be used to move the paving machine onto a trailer for transport to a different site without requiring heavy lifting equipment such as a crane to place the paving machine from the paving to the transport directions, and vice versa. 
         [0061]      FIG. 6  shows a paving machine  2  including a center module  6 , laterally extending support beams  10 , side bolsters  12 , jacking columns  14  and crawlers  16  as described above. The paving machine can be used, for example, with a dowel bar inserter  116  for intermittently inserting 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. 
         [0062]    To movably support the dowel bar inserter  116 , for example, or another kit of the paving machine from the tractor frame, the lateral ends  112  of a cross beam  110  are tied into, that is, they are typically bolted to, rearwardly extending bolster extensions  114 . The longitudinal support beams  43  for the dowel bar inserter shown (the rest of the dowel bar inserter is not shown) attach to the rear of the tractor frame by means of a mounting bracket attached to the support beam in the front and to the rear cross beam  110  in the rear. The forward ends of the bolster extensions  114  are secured to the rearwardly facing end surfaces of the main tractor frame bolsters  12  that can be provided with or without an additional bolt-in hinge  102 . When no hinge in the bolster is provided, the bolster extension  114  must be removed prior to transporting the machine. Prior to removing the bolster extensions for loading and transporting the paver, the rear hinge  36  and swing leg  20  along with the jacking column  14  and crawler track  16  (the entire assembly) must be removed and then lifted and bolted to the rear of the main frame side bolster  12  and the paver put into the transport orientation. The weight of this entire swing leg, jacking column and crawler track assembly can be handled with a relatively small crane. When the bolster extension is provided with a bolt-in hinge  102 , the bolster extension  114 , swing leg, jacking column and crawler track can be left on the paving machine so that by hinging the bolsters into the outboard transport position, the paving machine is capable of self-loading onto a trailer, with the bolster, swing leg and jacking column with crawler track folded up for transport. The advantage of this is that no crane is required to remove the bolster extension in order to transport. 
         [0063]    A variation to the DBI mounting arrangement shown in  FIG. 6  with a bolt-in hinge is the mounting arrangement shown in  FIGS. 6A and 6B . Instead of a bolt-in hinge  102 , a special bolt-in short bolster extension  104  with built-in mount  106  for the DBI longitudinal support beam  43  is supplied. Instead of the longitudinal support beams  43  attaching to the rear of the tractor frame by means of a mounting bracket described above, the longitudinal support beams mount to the bolster extension  104 . When the bolster extension is provided with a special bolt-in short bolster extension  104  with built-in mount  106  for the DBI longitudinal support beam, a practical and fast loading/transport solution is possible for both the paver and the DBI, providing a medium-size crane is readily available. Because the bolster extensions are tied to the DBI supporting longitudinal support beam  43  in this configuration and also to the rear cross beam  110 , a rectilinear frame is formed where the DBI, complete with bolster extensions  114  and  104 , becomes a kit (module)  108  of a legally transportable width. If this DBI Module is supported complete with bolter extensions  114  and  104 , while it is still attached to the paver, the rear hinge  36  and swing leg  20  along with the jacking column and crawler track (the entire assembly), it can be lifted with a relatively light small crane (without disconnecting any of the hydraulic or electrical connections) and bolted to the side of the main frame side bolster  12 , using the universal bolting pattern found on the side bolster  12  as shown in  FIGS. 6B and 6C  (that matches the hole pattern of the swing leg) covered and described in copending, commonly owned U.S. patent application Ser. No. 12/703,101, filed Feb. 9, 2010, for a Slipform Paving Machine With Adjustable Length Tractor Frame. This swing leg, jacking column and crawler track assembly is mounted in the transport orientation as shown in  FIG. 6B  and  FIG. 6C . Once this procedure is completed on the opposite side of the machine, the complete DBI with bolster extensions  114  and  104  and the DBI Module  108  can be lifted as a module  108  on a truck transporting trailer. With the DBI Module  108  removed from the rear of the paver tractor frame, then the other front swing leg and jacking column with crawler track can be walked into the transport orientation as described herein. With all the swing legs and jacking columns with crawler tracks now in the transport orientation, the paver can self-load by walking onto a transporting trailer. The advantage of this arrangement is that if a medium-size crane is available, adding or removing the DBI Module  108  and unloading or loading the DBI Module and paver can be done very rapidly. 
         [0064]      FIG. 6B  schematically illustrates the paving machine and the DBI Module arranged for transport in two loads, as a crawler track paver module and as a DBI Module  108 . The right and left rear jacking columns  14 /crawler  16 /swing leg  20 /rear hinge  36  subassembly has been moved into its transport orientation as previously described. The left front jacking column/crawler/swing leg/rear hinge subassembly has been rotated towards its transport orientation, while the right front jacking column, crawler/swing leg/front hinge subassembly is shown in its paving orientation and must still be rotated into its transport orientation before the modules are ready for loading onto a trailer (not shown). 
         [0065]    Cross beam  110  may comprise a non-telescoping or a telescoping cross beam, laterally extendable and retractable support system that has a female center housing  6 ′ which movably receives male support beams  10 ′ that extend in opposite directions from the center housing towards the rearward bolster extensions  76 . The construction and operation of telescoping cross beam  110  and the kits, such as a dowel bar inserter kit suspended therefrom, are described in copending, commonly owned U.S. patent application Ser. No. 12/703,101, filed Feb. 9, 2010, for a Slipform Paving Machine With Adjustable Length Tractor Frame, the disclosure of which is incorporated herein by reference.