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TECHNICAL FIELD 
   The present invention relates to equipment for asphalt paving; more particularly, to paving equipment having rubber tires for compacting a layer of hot asphalt, and to paving equipment having steel rollers for smoothing a layer of hot asphalt; and most particularly, to a combination compacting and smoothing asphalt finishing machine wherein rubber tires and steel rollers may be used alternatively for compaction and smoothing, respectively, of the hot asphalt layer. 
   BACKGROUND OF THE INVENTION 
   Paving of roads and parking lots with asphalt is a mature prior art. Typically, asphalt paving medium (referred to herein as “asphalt”) is prepared in a batch plant wherein a crushed stone aggregate is mixed with a hot tar preparation, yielding a highly viscous slurry of aggregate in tar that can be poured or laid in a layer onto a designated paving surface and then worked by specialized equipment to provide a durable surface for vehicular traffic when cool. 
   Hot asphalt, as it comes from the plant and is laid in a layer, contains significant amounts of entrained air and is in a non-compressed state. Thus paving comprises at least three distinct steps: a) laying the asphalt slurry in a layer of approximately the final thickness and lateral distribution; and finishing the layer by b) compacting the layer to remove air and ensure compaction into any depressions in the underlying substrate surface, and c) final smoothing of the compacted layer. 
   Once the designated surface is prepared to receive the asphalt, the first step of laying the asphalt is typically carried out by a laying machine that receives sequential batches of hot asphalt from delivery trucks and dispenses a continuous ribbon of the material while moving along the surface to be paved. In irregular areas such as parking lots, the distribution may be augmented manually by workers with shovels and/or screeds. 
   The second step of compacting the asphalt typically is carried out by a compacting machine that travels on one or more sets of smooth-surface, ganged rubber tires and that propels itself along the freshly-laid layer of hot asphalt. The tires are independently suspended in pairs such that the gangs of tires may follow the contours of the underlying surface to compact the asphalt in surface depressions as well as in the higher surface areas. This is an important step in assuring a long-wearing finished surface; failure to compact the material properly in depressions can result in development of potholes and premature failure of the finished layer. 
   The third step of smoothing the asphalt typically is carried out by a smoothing machine that travels on one or more smooth-surface steel rollers and that propels itself along the freshly-compacted layer of hot asphalt. The steel rollers work the compacted asphalt both forwardly and laterally to eliminate depressions and thus provide an overall even layer. In addition, the steel rollers intensely compact the upper part of the layer to impart a very fine-grained surface finish to the layer. 
   After the smoothing operation, the finished asphalt layer is allowed to cool and solidify, preferably before vehicular traffic is allowed onto the surface. 
   A shortcoming of the prior art is that two separate finishing machines are required for compacting and smoothing, respectively. These prior art machines, while very similar in overall construction and operation, are equipped with rubber tires and steel rollers, respectively. Each machine, even modest versions thereof, may cost in excess of $100,000, making ownership of both such machines prohibitive for many smaller paving companies; instead, one or both machines typically is/are rented for specific paving jobs, which entails rental fees, and coordinating rental and construction schedules, and machine transportation to and from the paving site. Further, as a paving business grows and the purchase of paving machines becomes feasible, each additional increment of production capacity requires the purchase of two finishing machines, one of each type. 
   What is needed in the art is an improvement whereby only one compacting and smoothing finishing machine is required for a paving operation. 
   It is a principal object of the present invention to reduce the cost of buying or renting finishing machines for an asphalt paving contractor. 
   It is a further object of the invention to simplify the logistics and reduce the cost of a paving operation. 
   SUMMARY OF THE INVENTION 
   Briefly described, a combination compacting and smoothing finishing machine in accordance with the invention comprises one or more primary finishing elements which may be either compacting tires or smoothing rollers. The primary finishing elements are driven and steered by engine and hydraulic mechanisms as in the prior art. The machine further comprises one or more secondary finishing elements which are complementary to the primary elements, being either smoothing rollers or ganged rubber tires. The secondary finishing elements are pivotably attached to the frame of the machine. In a first position, the secondary elements are not in contact with the asphalt layer or with the primary elements and the weight of the machine is borne only by the primary elements. The secondary elements are hydraulically actuable and may be pivoted into a second position wherein only the secondary elements are in contact with the asphalt layer and are in driving contact with the primary elements which are thus raised from contact with the asphalt layer. 
   Such a machine may be fabricated as an entirely new assembly or may be a retrofit of a prior art single-function compacting or smoothing machine. 
   Thus, a combination finishing machine in accordance with the invention may function, interchangeably and with equal facility, as either a compacting machine or a smoothing machine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is an elevational side view of a prior art finishing machine, which may be either a compacting machine or a smoothing machine; and 
       FIG. 2  is an elevational side view of a combination compacting and smoothing finishing machine in accordance with the invention. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The advantages and benefits of a combination asphalt compacting and smoothing finishing machine in accordance with the invention may be better appreciated by first considering a prior art compacting or finishing machine. 
   Referring to  FIG. 1 , a prior art asphalt compacting or finishing machine  10  comprises a chassis  12  supporting a motive engine  14  and a hydraulic system  16  driven by engine  14 . Chassis  12  is borne upon at least one front rollable element (“front element”)  18  and at least one rear rollable element (“rear element”)  20  for rolling along a surface  22  of a layer  24  of hot asphalt composition. Typically, front element  18  is steerable by being supported in a suspension fork  26  pivotably connected to chassis  12  about a turning axis  28  and connected to a steering wheel  30  via a steering mechanism (not shown) which may be hydromechanical. Typically, only rear element  20  is motively driven by engine  14  although in some types of prior art machine  10  both the front and rear elements are driven. 
   A prior art machine  10  typically includes a hydraulic lifting mechanism  30  mounted on a forward portion of chassis  12  which may comprise a lifting arm  32  that is conveniently formed as a bellcrank, a pivot  34  for lifting arm  32 , and a hydraulic cylinder  36  pivotably mounted at a first end  38  on chassis  12  and pivotably connected to lifting arm  32  at a second end  40 . The outer end  42  of lifting arm  32  is thus radially pivotable about pivot  34  by hydraulic cylinder  36  between a raised position  44  and a lowered position  46 . 
   When prior art machine  10  is a compacting machine, front element  18  and rear element  20  each comprise a plurality of smooth-surfaced rubber tires that are ganged together across at least the width of machine  10 . Typically, the tires are independently suspended in pairs such that each gang of tires may follow the contours of the underlying surface to compact the aerated asphalt in layer  24 . Typically, the front and rear elements contain differing numbers of tires, for example, five and six tires, and are laterally staggered by half a tire width such that all of surface  22  is covered in a single pass of machine  10 . Typically, machine  10  is also provided with substantial dead weight (not shown) distributed appropriately on chassis  12  to assure proper weighting of the front and rear elements. To enhance the dead weight of the overall machine, it is known to fill the tires with water or saline solution. 
   When prior art machine  10  is a smoothing machine, front element  18  and rear element  20  each comprise one or more smooth-surfaced steel rollers extending across at least the width of machine  10 . The steel rollers work the previously-compacted asphalt layer  24  both forth and back and laterally to eliminate depressions and thus provide an overall even layer. In addition, the steel rollers intensely compact the upper part of the layer to impart a very fine-grained finish to the surface  22  of layer  24 . 
   Referring now to  FIG. 2 , a combination asphalt compacting and smoothing machine  110  in accordance with the present invention has elements in common with prior art machine  10  which are commonly numbered. In addition, front and rear rollable elements  18 , 20  are to be considered as primary elements. The primary elements and features are shown in solid lines, and secondary elements and features are shown in dashed lines. Thus, machine  110  is shown in  FIG. 2  in primary-element mode wherein the primary front and rear elements  18 , 20  are in contact with asphalt surface  22 . 
   At the front of machine  110 , a secondary front rollable element  118  is mounted on a secondary fork  126  attached via a yoke  150  to an angle arm  152  that is pivotably connected to lever arm  32  (defining thereby a front pivotable arm) via a generally vertical hinge pin  154 . Primary front element  18  may be either of a gang of compacting rubber tires or a smoothing steel roller; and secondary front element  118  is the counterpart thereof, being either of a smoothing steel roller or a gang of compacting rubber tires, respectively. 
   In first position  44 , the axis  156  of secondary front element  118  is higher than the axis  56  of primary front element  18  such that the front portion of machine  110  is supported on surface  22  by primary front element  18 , and secondary front element  118  is separated from surface  22  by a front gap  158   a.    
   Similarly, at the rear of machine  110 , a secondary rear rollable element  120  is mounted on a rear pivotable arm  160  at a pivot axis  162 , the rear pivotable arm being pivotably connected to chassis  12  at pivot  164 . A hydraulic cylinder  166  operationally connected to hydraulic pump  16  is pivotably connected to secondary element  120  at pivot axis  162  and is pivotably connected to chassis  12  at pivot axis  168 . Primary rear element  20  may be either of a gang of compacting rubber tires or a smoothing steel roller; and secondary rear element  120  is the counterpart thereof, being either of a smoothing steel roller or a gang of compacting rubber tires, respectively. Preferably, a second set of components comprising a second rear pivotable arm  160  and a second hydraulic cylinder  166  is similarly disposed on the opposite side of machine  110  (not visible in  FIG. 2 ) and are connected by yoke  170  extending horizontally therebetween. 
   In a first position  144 , the axis  162  of secondary rear element  120  is higher than the axis  58  of primary rear element  20  such that the rear portion of machine  110  is supported on surface  22  by primary rear element  20 , and secondary rear element  120  is separated from surface  22  by a rear gap  158   b , which may be the same size as front gap  158   a.    
   In the configuration as described thus far, machine  110  functions substantially identically with prior art machine  10 , being borne on the primary front and rear rollable elements  18 , 20 , whether the front and rear primary elements  18 , 20  are compacting rubber tires or smoothing steel rollers. 
   A principal advantage of improved machine  110  over prior art machine  10  is that improved machine  110  may function as either a compacting machine or a smoothing machine by switching alternatively between a primary-element mode and a secondary-element mode. 
   As is seen in  FIG. 1 , extending of hydraulic cylinder  36  drives the outer end  42  of lever arm  32  from the “up” position  44  to the “down” position  46 . Such movement is seen in  FIG. 2  to drive secondary element axis  156  along arc  157  to a new position  156   a  that is lower than axis  56  of primary front element  26 . In so doing, secondary front element  118  engages primary front element  18  at a nip point  172  below the horizontal equatorial level  174  of axis  56 . In this way, secondary front element  126  raises primary front element  18  from contact with surface  22  and becomes instead the load-bearing element for the front portion of machine  110  and is driven by friction with surface  22 , shown herein as surface  22   a . (Note: it will be recognized that the elevation of surface  22  does not change, but rather the machine is raised by a height  176 ; however, for purposes of illustration herein, the surface is lowered rather that the machine being raised. Note further that in a machine wherein both the front and rear elements are positively driven by the engine, the front primary and secondary elements must counter-rotate, and thus in the secondary-element mode, “forward” and “reverse” of the machine are reversed.) 
   Considering now the rear portion of machine  110 , contraction of hydraulic cylinder  166  drives secondary rear element axis  162  along arc  178  to a new position  162   a  that is lower than axis  58  of primary rear element  20 . In so doing, secondary rear element  120  engages primary rear element  20  at a nip point  180  below the horizontal equatorial level  174  of axis  58 . In this way, secondary rear element  120  raises primary rear element  20  from contact with surface  22  by height  176  and becomes instead the load-bearing element for the rear portion of machine  110  and is driven by frictional contact with primary rear element  20  which remains driven by engine  14 . (Note as with the front elements that the rear primary and secondary elements also must counter-rotate.) 
   In secondary-element mode, the distance between the secondary front and rear element axes  156   a , 162   a  is less than the distance between the primary front and rear element axes  56 , 162 , thus causing machine  110  to be borne solely on the secondary front and rear elements  118 , 120 , through weight-bearing contact with the primary front and rear elements  18 , 20 , respectively. Return to primary-element mode is the reverse. 
   The invention as described thus far is applied to a paving machine having a gang of compacting rubber tires or a smoothing steel roller means at both the front and the rear portions of the machine. However, it is well known in the prior art that paving machines alternatively may be constructed having either of a gang of compacting rubber tires or a smoothing steel roller disposed only at either a front portion or a rear portion of the machine. It should be understood that the combination of a gang of compacting rubber tires and a smoothing steel roller in alternative employment on a single machine as described herein is fully envisioned by the invention and is applicable to design and construction of single-roller machines. 
   While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.

Summary:
A combination compacting and smoothing asphalt finishing machine comprising primary finishing elements which may be either compacting tires or smoothing rollers. The primary elements are driven and steered by engine and hydraulic mechanisms conventionally. The machine further comprises secondary asphalt finishing elements which complement the primary elements, being either smoothing rollers or ganged rubber tires. The secondary elements are pivotably attached to the frame of the machine. In a first position, the secondary elements are not in contact with the asphalt layer or with the primary elements and the weight of the machine is borne only by the primary elements. The secondary elements are hydraulically actuable and may be pivoted into a second position wherein only the secondary elements are in contact with the asphalt layer and are in driving contact with the primary elements which are thus raised from contact with the asphalt layer.