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BACKGROUND OF THE INVENTION 
     The invention relates to a device for inserting dowels in the area of transverse expansion joints of newly laid road surfaces. 
     Such devices are required for producing concrete-paved road surfaces and are frequently integrated in a slip-form paver. With the aid of slip-form pavers concrete surfaces, in particular traffic roads, are produced with continuous advance. Trucks pour fresh concrete from or with the aid of special charging devices in front of the slip-form paver. By means of distributing screws or a distributing knife the concrete is spread evenly transverse to the traveling direction. Thereafter, the concrete is compacted using shaker means and shaped with a finishing board to take the desired monolithic profile. 
     With the aid of a dowel placing device a plurality of dowels arranged side by side and parallel to the traveling direction at predetermined distances are placed into the still unset concrete. When the concrete has set to a certain degree, an expansion joint is produced in the concrete in the dowel area such that the road surface breaks at these places when the concrete further hardens. In this way individual separate concrete plates are produced which are connected with each other by the pressed-in dowels. This allows longitudinal expansion and fixes the level of the concrete plates. 
     For automated insertion of the dowels it is necessary to transport a sufficient quantity of dowels to a storage container. The dowels have to be individually transported to retainers located immediately above the road surface of fresh concrete, and the dowels from said retainers can be pressed by means of dowel placing means into the concrete down to a predetermined depth. 
     A known device of the generic type is described in EP 0 196 698 A1. The device for inserting dowels described therein is integrated in a slip-form paver. The dowels are located in a floorless car loader movable transversely to the traveling direction, wherein the dowels can fall from the car loader, which is open towards the bottom, into recesses of a base plate serving as smoothing board. The car loader is moved over the overall working width of the machine, until dowels are inserted into all recesses. Thereafter, the car loader returns to its initial position. When all recesses are provided with dowels, the recesses are displaced such that the dowels can fall via slots in the base plate onto the fresh concrete and can then be shaken into the concrete using two forks each. 
     It is a disadvantage of the known device that the car loader has only a small acceptance capacity for dowels, in particular for reasons of weight, such that a person refilling the car loader must be permanently available. Another disadvantage is that the car loader must be moved beyond the working width of the machine such that an additional free space must be kept clear beside the roadway. 
     From U.S. Pat. No. 5,318,377 a device for inserting dowels is known where a larger quantity of dowels are stored in two magazines from which the dowels are individually fed to a chain conveyor. The chain conveyor transports the dowels to recesses in the base plate with several dowels being temporarily stored in each recess. Then the dowels are separated again and thrown by the separation device onto the fresh concrete. It is a disadvantage of the known device that the dowels have to be alignedly placed into the magazine, which results in excessive setting-up times. Further, the configuration requiring the dowels to be separated twice is too time-consuming and thus susceptible to failure. 
     From EP 0 518 535 A1 a device for inserting dowels is described wherein the dowels are first laid onto a place of deposit from where they are fed to a slot comprising retaining elements. A dowel placing means then presses the dowels from the retainer into the slots and into the fresh concrete. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to further improve a device of the aforementioned type such that a large quantity of dowels can be automatically deposited without interruption of work by means of a simple construction. 
     The invention advantageously provides that a line conveyor device accepts separated dowels from a section of a bottom or lateral area of the storage container and feeds the dowels to the slots in the smoothing board. 
     The invention allows use of a large-volume storage container which can be quickly loaded in a simple manner. The large storage container allows for operation without interruption of work. The simple loading of the container reduces the setting-up times and the requirement of personnel. The device according to the invention operates fully automatically, wherein only a single transporting means consisting of the line conveyor device is needed between the storage container and the smooting board. This helps to keep the construction very simple which results in a reduced susceptibilty to failure. 
     Preferably, the line conveyor device comprises at least two conveyor chains extending in parallel and at a distance to each other. In this way the dowels are transported at at least two places. 
     The line conveyor device comprises endless elements. 
     A chain conveyor device comprising at least one endless chain runs synchronously and in parallel to the line conveyor device in the same traveling direction and promotes the acceptance of separated dowels by the line conveyor device. 
     The chain of the chain conveyor device preferably runs between the conveyor chains of the line conveyor device. 
     On both sides of the machine frame one dowels storage container each may be arranged, wherein the traveling direction of the line conveyor device is reversible. Since the chains can run in both directions, reversing operation is also possible during which dowels are optionally taken from either of the two storage containers. This is advantageous in particular in the case of multi-lane road surfaces since in such cases the machine can be loaded from one side only. 
     The bottom area and/or lateral area of the at least one storage container extend at an inclination to the raod surface. In this way the dowels can descend to the lowermost point of the storage container by gravity alone when the dowels are continuously taken from the storage container. 
     The chain links of the conveyor chain of the line conveyor device and the chain conveyor device consist of undercut link elements between which pockets for accepting one dowel each are formed. Said pockets are dimensioned such that they can accept dowels of different diameters. Due to the fact that undercut link elements are provided the conveyor chains can reliably retain the dowels even in vertical positions without any additional guides being necessary. 
     The line conveyor device can be provided with a counting device counting the number of dowels accepted by the line conveyor device and transmits a counting signal to a control device for the line conveyor device. As soon as the control device detects that a sufficient quantity of dowels for the slots in the smoothing board have been accepted, the control device can stop further acceptance of dowels. For this purpose a release device is provided at the line conveyor device, which presses the dowels from the conveyor chains back into the storage container in reaction to a signal from the control device thus disengaging the dowels from the line conveyor device and the chain conveyor device. In this way it is ensured that the line conveyor device always accepts the required quantity of dowels such that the line conveyor device can continuously circulate. 
     The release device preferably comprises two release plates displaceable in parallel, which press the dowels out of the acceptance area in the bottom and lateral areas. 
     Alternatively, the release device can comprise release plates hinged to the storage container. This offers the advantage that the actuation mechanism for the release plates can be of simple configuration. 
     Further, the line conveyor device may comprise a means for removing excessive dowels and replacing missing dowels. Said means ensures that the line conveyor device can run continuously. 
     The bottom wall of the at least one storage container can be supported on elastic buffer elements and comprise a vibration device which is designed to facilitate descending of the dowels inside the storage container and sorting them into the separation means. 
     The retaining device for the dowels is preferably arranged in the slots, wherein the dowels are released from the retaining device when pressure is exerted by the dowel placing device. 
     The width of the slots in the smoothing board can be adapted to different dowel diameters, wherein the vertical position of the retaining devices is also adjustable when the slot width is varied. This ensures that the dowels cannot protrude towards the top from the slots and cannot collide with the line conveyor device. 
     The retaining devices in the slots can comprise pivotable spring elements. Said spring elements release the dowels at a force exerted by the dowel placing device, which considerably exceeds the force exerted by the weight of the dowels such that the dowels can fall onto the road surface and can be immediately pressed by the dowel placing device into the road surface. 
     With the aid of a control cam provided at the slot and a control face provided at the retaining device the retaining devices are preferably automatically adjustable in their vertical position in dependence on the slot width. This offers the advantage that together with adjustment of the slot width the height of the retaining device is adjusted, too. 
     The working width of the line conveyor device and the length of the slots in the smoothing board are adjustable such that they are adaptable to dowels of different lengths. In this way the machine is not only capable of processing dowels of different diameters but also dowels of different lengths. 
     On the slots guiding elements adjustable in the traveling direction are arranged for horizontal and vertical guidance of the line conveyor device. Said guiding elements are adjustably arranged at the smoothing board for the purpose of adaptation to the dowel length. 
     The smoothing board is designed such that the mutual distance between the slots transversely to the traveling direction can also be adjusted. 
     The conveyor chains of the line conveyor device preferably consist of twin chains so that both ends of the dowels are guided by two conveyor chains, respectively. 
     It is provided that the twin chains guide the dowels at the side by the inner surface of the outer part of the twin chains, the outer part of the twin chains traveling on the guides and the inner part of the twin chains transporting the dowels. 
     The line conveyor device operates linearly from bottom to top along the bottom or side portions of the storage container. 
    
    
     The following is a detailed description of an embodiment of the present invention with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary front view of the device according to the present invention, 
     FIG. 2 is an enlarged view of the storage container area in FIG. 1, 
     FIG. 3 is an enlarged view of the slot area in FIG. 1, 
     FIG. 4 is a lateral view of the dowel placing means; 
     FIG. 5 is a lateral view of a portion of the smoothing board, 
     FIG. 6 is a schematic illustration of the release means for dowels in a passive state, and 
     FIG. 7 is a schematic illustration of the release means for dowels in an activated state, 
     FIGS. 8 and 9 is an illustration corresponding to FIG. 3, showing an alternative embodiment of the slots, 
     FIG. 10 is a top plan view on the embodiment of FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a device for placing dowels  2  that may be integrated in a slip-form paver or may be designed as a self-contained machine with traveling devices  6  of its own. 
     The device extends over the entire width of a machine frame  8  supported by traveling devices  6 . 
     A smoothing board  20  contacts the freshly laid road surface  4  and comprises slots  24  extending in the traveling direction and parallel to each other, the slots being adapted to each receive a dowel  2  using a retaining means  28 . Two forks  34 , arranged successively in the traveling direction, of the dowel placing device  32  push the dowels  2  from the slots  34  into the road surface  4  for the desired depth. A vibratory means  36  transmits vibrations onto the forks  34  to facilitate pressing the dowels  2  into the road surface  4 . 
     For the sakes of simplicity of the drawing, FIG. 1 only illustrates two adjacent forks  34  of the dowel placing means  32 . 
     In the lateral portion of the machine frame  8 , a storage container  10 ,  12  is provided, respectively, which can both be filled with a plurality of dowels from the side of the machine. Optionally, dowels  2  may be taken from the one or the other storage container  10 ,  12 . To do so, one merely has to reverse the running direction of a line conveyor device  40 . The storage container has a bottom wall  48  inclined in the direction of the line conveyor device  40  and a side portion  52  extending at right angles to the bottom wall  48  and parallel to a section of the line conveyor means  40 , thus forming a transfer area for dowels  2 . It is understood that the line conveyor device  40  may also be guided along a portion of the bottom to receive dowels. 
     As illustrated in FIG. 1, the line conveyor device  40  runs continuously in the direction of the arrows, with dowels  2  being received in the side portion  52  of the storage container  10  and transported to the smoothing board  20 . The line conveyor device  40  passes the dowels transversely across the slots  24  in the smoothing board  20 , which extend longitudinal with respect to the traveling direction, the dowels  2  first falling on the retaining means  28  in the slots  24 , where they are retained until all slots  24  have been filled with one dowel  2  each. 
     In a preferred embodiment, it is provided that the line conveyor device  40  consists of at least two twin chains  56 ,  58 ;  60 ,  62 , guided in parallel spaced from each other. 
     The distance between the conveyor chains is adapted to the length of the dowels  2 , as is best seen in FIG.  5 . The distance between the chain wheels  65   a ,  65   b  and all other chain wheels of the line conveyor device  40  is adjustable along the associated axes or the shaft  41  so as to easily adapt the line conveyor device  40  to different lengths of dowels  2 . 
     As is best seen in FIG. 5, the free ends of the dowels  2  are received in pockets  70  by the inner twin chains  58 ,  60  that serve as conveyor chains, whereas the outer twin chains  5 ,  62  provide for the guiding of the dowels  2  in the longitudinal direction. Guide rails  35  for the twin chains  56 ,  58 ,  60 ,  62  are provided at the axial ends of the dowels  2 . The guide rails with their substantially U-shaped cross section comprise inner side plates  29 ,  30  projecting orthogonally upward from a plate  37  parallel to the bottom, as well as an outer side plate  33 ,  38 . The side plates  29 ,  30  support the dowels  2  on a sliding surface  108 , whereas the outer side plates  33 ,  38  support the outer twin chains  56 ,  62 . 
     The inner side plates  29 ,  30  are spaced from each other in the transporting direction of the twin chains  56 ,  58 ,  60 ,  62 , so as to leave a gap  39  through which the dowel  2  can fall into the slot  24 . The gap  39  is delimited by plate portions of the side plates  29 ,  30  that extend downward beyond the plate  37 . As is shown in FIG. 10, guide rails  35 , adjacent in the transporting direction of the twin chains, can overlap each other. To this effect, the side plates  29 ,  30  extend on mutually offset planes. The outer side plate  23 , which may be integral with the outer side plate  38  or which is fastened thereto, extends in two mutually offset planes, so as to allow for a nesting of adjacent guide rails  35 . 
     To support the conveyor chains  56 ,  58 ,  60 ,  62  of the line conveyor device  40 , an additional chain conveyor device  18  with a continuous twin chain  19  is provided in the vicinity of the storage containers  10 ,  12 , the chain running synchronously with the twin chains  56 ,  58 ,  60 ,  62  and in the same direction. The twin chain  19  runs around the chain wheels  21 ,  22 ,  23  that are arranged in the middle between the chain wheels  63   a ,  63   b ,  64   a ,  64   b  so that the twin chain  19  extends centrally and in parallel between the twin chains  58 ,  60  and  60 ,  62 . 
     The twin chains  56 ,  58 ,  60 ,  62  of the line conveyor device  40  may be tensioned using three idler chain wheels  67 ,  68 ,  69 , wherein the axis of the idler chain wheel  68  can be locked vertically at different positions to adjust different widths of the machine without having to change the length of the twin chains. This is the case, for example, when the smoothing board  20  is extended or shortened by one or several board elements  27 . FIG. 1 illustrates two alternative positions of the idler chain wheels  68 . 
     The shape of the chain links is best illustrated in FIG.  3 . Every second chain link  66  has a guide metal sheet  72  on both sides of the chain, which extends outward from the chain link  66  substantially flaring in a trapezoid-like manner. The guide metal sheets  72  thus have an undercut tooth-shape and form a pocket  70  between every second chain link  66  for receiving the dowels  2 , in which the dowels  2  are held securely even under vertical orientation of the conveyor chains. 
     The twin chains are disposed such that the guide metal sheets  72  of the outer conveyor chains  56 ,  62  cover the pockets  70  of the inner conveyor chains  58 ,  60  so that the dowels  2  are held in their longitudinal direction by the guide metal sheets  72  of the outer conveyor chains  56 ,  62 . Preferably, the twin chains  56 ,  58  and  60 ,  62  are coupled through a common bolt. 
     FIG. 3 explains how the line conveyor device  40  transfers the dowels  2  into the slots  24  of the smoothing board. In FIG. 3, the conveyor chains of the line conveyor device  40  run to the right. When a vertically downward open pocket is located above a free slot  24 , the dowel can fall into the slot  24  and is retained in the slot  24  by a retaining means  28  consisting of a spring element  94  pivotally movable about a receiving pin  104  such that the upper edge of the dowel  2  does not project beyond the sliding surface  108  on which the conveyor chains slide. 
     The width of the slots is adjustable to accommodate different dowel diameters by changing the position of the side plates  29 ,  30  on the board element  27  of the smoothing board  20 . When changing the width of the slot  24 , the retaining means  28  is also displaced since widening the slots causes the spring element  94  to be pivoted through a control cam  95  of a control surface  102  fastened to the side plate  29 . The spring element  94  is supported for pivotal movement about a receiving pin  104  on the side plate  30 . The free end of the spring element  94  is fastened on the side plate  30 . When the slot width is changed, the spring element  94  is displaced downward so that a dowel of a larger diameter will not protrude beyond the sliding surface  108  even when the slot width is increased. Besides increasing the slot width, the distance between the slots  24  can be increased by displacing adjacent board elements  27 . 
     FIGS. 8 to  10  show an alternative embodiment of the retaining means  28  for the dowels  2 . The retaining means  28  comprises at least two cam discs  98  arranged opposite and orthogonally relative to the dowel  2 , which discs are pivotable about receiving pins  104  and receive and hold the dowel  2  between them inn a spring-loaded start position. As is best seen in FIG. 10, the cam discs  98  may be provided on both sides of the side plates  29 ,  30 . The receiving pins  104  are supported both in the side plates  29 ,  30  of the sectionally U-shaped guide rail  35  and in the outer side plate  38  parallel to the inner side plates  29 ,  30 . A spring element  96  is wound around the receiving pins  104  and biases the cam discs  98  towards the start position so that the opposite cam discs  98  hold the dowel  2  by its axial ends in the start position illustrated in FIG.  8 . When pressure is exerted on the dowel  2 , the cam discs  98  pivot against the force of the spring element  96  and release the dowel into the slot  96 . 
     The forks  34  of the dowel placing means  32  grip the dowels  2  near their ends and press them out from the slot  24  into the road surface  4  against the force of the spring elements  94  or  96 .The distance between the board portions  31  of the board elements  27  is selected such that the forks  34  can be passed between the board portions  31 . 
     FIG. 9 illustrates a position in which the dowel  2  is pressed downward by the fork  34  into the slot  24 , whereby the cam discs  98  are pivoted outward and downward relative to the dowel  2 . In FIG. 9, the forks  34  are not illustrated for simplicity. 
     The cam discs have a control face  110  that supports itself on the dowel  2  when the dowel passes through and which prevents the cam discs  98  to suddenly return to their start position after having released the dowel  2 . The return movement of the cam discs  98  is thus slowed down so that the impact load on the spring elements  96  is reduced. 
     FIG. 2 illustrates the storage container  10  on an enlarged scale. The line conveyor device  40  with the conveyor chains  56 ,  58 ,  60 ,  62 , as well as the chain conveyor means  18  with the conveyor chain  19  are guided from bottom to top in the side portion  52  of the storage container in a linear section  44 , with dowels  2  falling into the pockets  70  between the guide metal sheets  72  of the inner conveyor chains  58 ,  60  and the conveyor chain  19 . The guide sheets  72  hold back the other dowels  2  in the storage container  10 ,  12 . The outer conveyor chains  56 ,  62  guide the dowels  2  laterally, with guide plates possibly being provided within the storage container  10 ,  12  that guide the dowels  2  in their lateral orientation such that they can be received between the guide sheets  72  of the outer conveyor chains. At the upper end of the storage container, preferably in area of the chain wheels  64 , a counting means  74  may be provided that counts the dowels  2  transported by the line conveyor means  40  and transmits a corresponding count signal to a control. When a sufficient number of dowels  2  has been received, a release device  76  is actuated that comprises two parallelogram-guided release plates  78   a ,  78   b , two parallel links  79   a ,  79   b  and a respective piston cylinder unit  80   a ,  80   b . The release plates or bars  78   a ,  78   b  extend, as is best seen in FIG. 4, between the conveyor chain  19  of the chain conveyor device  18  and the conveyor chains  56 ,  58 ,  60 ,  62  of the line conveyor device  40 . 
     FIG. 6 illustrates the release device  76  in the inactive state, wherein the line conveyor device  40  and the chain conveyor device  18  takes individual dowels  2  in the pockets  70  between the guide sheets  72  from the storage container  10 ,  12 , while FIG. 7 illustrates how the release plates  78   a ,  78   b  disengage the dowels  2  from the line conveyor device  40  and the chain conveyor device  18  by pushing the dowels  2  back into the storage container  10 ,  12 . 
     As an alternative, the release plates or rods  78   a ,  78   b  may also disengage the dowels  2  by a pivotal movement. 
     The bottom wall  48  of the storage container  10 ,  12  may be supported at the storage container  10 ,  12  by elastic buffer elements  86 . Further, a vibratory means  90  may be disposed on the bottom wall  48  so as to assist the advancing of the dowels  2  within the storage container  10 ,  12 . 
     For clarity, FIG. 4 does not illustrate the conveyor chains. The chain wheels  64   a ,  21  and  64   b  are mounted for rotation with a shaft  41  and are driven by a hydraulic motor  42 . Through the shaft  41 , the conveyor chains of the line conveyor device  40  and the conveyor chain  19  of the chain conveyor device  18  are driven. The chain wheels  64   a ,  64   b  are displaceable in the axial direction of the shaft  41  and may be locked in different positions. The same is true for all other chain wheels and idler chain wheels of the line conveyor device  40 , whereby an adaptation to different dowel lengths is possible. 
     Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined by the appended claims.

Summary:
In a device for inserting dowels ( 2 ) in the vicinity of transverse expansion joints of freshly laid concrete road surfaces ( 4 ), comprising a machine frame ( 8 ) supported by traveling mechanisms ( 6 ), at least one storage container ( 10,12 ) for the dowels ( 2 ), a smoothing board ( 20 ) resting on the road surface ( 4 ) and including slits ( 24 ) running in a direction of travel and provided for accommodating the dowels ( 2 ), a retaining device ( 28 ) for the dowels on the slots ( 24 ), and a dowel placing device ( 32 ), it is provided that a line conveyor device ( 40 ) accepts separated dowels ( 2 ) in a section ( 44 ) of a bottom or lateral area ( 48,52 ) of the storage container ( 10,12 ) and delivers the dowels ( 2 ) to the slots in the smoothing board ( 20 ).