Abstract:
In a self-propelled construction machine, in particular cold milling machine, recycler or surface miner, for working ground surfaces, comprising a milling drum supported at a machine frame and a conveying device arranged at the machine frame which accepts the milled-off material from the milling drum during the working operation and, on a continuously revolving first transport belt, unloads it, in conveying direction, onto a point of discharge at a discharge end along a parabolic trajectory, it is provided for the following features to be achieved: as a minimum, the last section of the conveying device as seen in conveying direction comprises no less than one continuously revolving cover belt arranged above the transport belt, said cover belt extending essentially parallel to the transport belt and resting against the milled-off material on the transport belt at least in a partial section of the length of the transport belt.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a self-propelled construction machine, in particular cold milling machine, recycler, surface miner, and to a method for milling off and transporting away a milled-off stream of material. 
     2. Description of the Prior Art 
     When removing ground or road material using a road milling machine, milled material is produced that is loaded onto a transport vehicle by the road milling machine by means of a conveying device. In this arrangement, the conveying device may comprise one or multiple transport belts which accept the material from the milling drum and unload it at a discharge end along a parabolic discharge trajectory. Loading of the milled material is effected in operation, that is, while the road milling machine and the transport vehicle are in motion. In the process, it is of significance to transfer the milled material onto the transport vehicle in a controlled fashion as the milled-off material is otherwise not unloaded to a specified point of discharge and may impair the traffic flowing alongside or, if the milled material does not entirely come down on the loading surface of the transport vehicle, causes additional sweeping operations. 
     To guide the stream of material, at least the last section of the conveying device as seen in conveying direction may preferably be mounted to pivot laterally and/or in height, in which case the parabolic trajectory can additionally be influenced by means of the adjustment of the conveying speed. 
     The properties of the milled-off material differ depending on the task to be performed, for example, fine milling or the removal of complete road pavements, as well as on the operating parameters adjusted, for example, the advance speed of the road milling machine, the milling depth and the type of the milled-off material. 
     The quantity of the material milled off per unit of time, as well as the composition of the same and the size of the fragments of milled material, in particular, may differ. 
     It is generally known to load the milled-off material onto a transport vehicle by means of one or multiple successive transport belts. 
     With steep-incline conveyors, it is also known to use a double-belt belt conveyor (EP 0 249 084). 
     With the simple transport belts known from road milling machines, a discontinuous stream of material may form as a result of the inhomogeneity of the milled material and the changing quantity of the milled material. 
     This is due to the fact that, depending on the size of the fragments of the milled-off material, a relative movement of the fragments among themselves and to the transport belt may result, namely, in particular if there is very much or very little milled-off material on the transport belt, or in the case of slab-like fragments of the milled-off material. 
     A fluctuating amount of slip may form between the milled-off material and the transport belt, namely, in particular in the case of a high speed of the transport belt. As a consequence, different discharge speeds of individual components of the milled-off material may occur, in which case, in addition, flight paths of the different fragments of the milled-off material deviating from the specified parabolic trajectory may result. A further consequence is that, in the mean, the effective discharge speed is lower than the speed of the transport belt which results in a loss of energy. 
     In addition, a decelerated stream of material is more vulnerable to exterior influences, such as wind loads acting transverse to the transport belt, as the kinematic energy is reduced in conveying direction. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to specify a construction machine, as well as a method for milling off and transporting away a milled-off stream of material of a construction machine, in which the discharge of the milled-off material can be computed in an improved fashion and adjusted with a higher level of reproducibility. 
     One embodiment advantageously provides for, as a minimum, the last section of the conveying device as seen in conveying direction to comprise no less than one continuously revolving cover belt arranged above the transport belt, said cover belt extending essentially parallel to the transport belt and resting against the milled-off material on the transport belt at least in a partial section of the length of the transport belt. 
     The following advantages may be provided: 
     By arranging no less than one cover belt above the transport belt, the form and direction as well as bundling of the stream of material can be adjusted more precisely. Altogether, a higher and more homogeneous discharge speed of the milled-off material as well as a more precise adjustment of the discharge speed can be achieved, especially since an improved transmission of force from the transport belt to the milled-off material can be effected in the sense of a lower amount of slip occurring. 
     Lateral sealings, which were needed up to now and generated friction losses at the transport belt, are avoided as the sealing is now ensured by the overlying cover belt. Overall, an improved energy performance ensues, it being possible to reduce the fuel consumption and to better comply with legal requirements also in terms of pollutant emission. 
     In a preferred embodiment, it is intended for the conveying device or the last section of the conveying device to be arranged to pivot at the machine frame in terms of inclination and/or lateral alignment. 
     The cover belt is preferably pre-tensionable resiliently in the direction towards the transport belt. In this arrangement, the contact force may also be generated by the own weight of the cover belt. 
     In a preferred embodiment, it is intended for the cover belt to be adjustable in height and/or to be supported in a pre-tensionable fashion in the direction towards the transport belt. Being supported resiliently enables a part of the weight of the cover belt to be compensated for, or the initial tension vis-à-vis the weight load to even be increased, or also just the lower strand to be pressed against the milled-off material on the transport belt dynamically. 
     In a further development of the invention, it is intended for the transport belt to be of foldable design, with a front section of the transport belt, or a last section as seen in conveying direction, being pivotable downwards when in a transport position. For this purpose, the cover belt may preferably be of a divided design so that a total of two cover belts arranged behind one another are arranged above the transport belt. In this arrangement, the last cover belt as seen in the direction of transport is foldable preferably downwards together with the front section of the transport belt. The transport length of a road milling machine can thus be reduced significantly. 
     The cover belt may also be arranged in the area of the foldable front section of the transport belt only. 
     In a preferred embodiment, it is intended for the transport belt to comprise support rollers for the upper and lower strands, and for the support rollers for the upper strand of the transport belt, in a plane extending orthogonal to the conveying direction, to form a transport channel with a concave cross-section on the upper strand of the transport belt. 
     According to a further development, it is intended for the cover belt to comprise support rollers for the upper and lower strands of the cover belt, and for the support rollers for the lower strand of the cover belt, in a plane extending orthogonal to the conveying direction, to allow flexible adjustment of the cross-sectional shape of the lower strand of the cover belt to the quantity of milled material present on the transport belt. Flexible adjustment of the cross-sectional shape of the lower strand to the quantity of milled material present on the transport belt is effected dynamically at each position of arrangement of the support rollers. 
     It is preferably intended for articulated support rollers of the lower strand of the cover belt to be pre-tensionable resiliently in the direction towards the first transport belt. To this effect, as a minimum, the support rollers for the upper strand of the transport belt and the support rollers for the lower strand of the cover belt may comprise multiple roller segments coupled to one another in an articulated fashion. In this arrangement, the segments of the upper strand of the transport belt are preferably supported in a fixed position while the support rollers for the lower strand of the cover belt are supported in a movable fashion so that the individual roller segments can assume different angular positions relative to one another. 
     Alternatively, it is also possible for the support rollers for the lower strand of the cover belt to be provided in a V-shaped dual arrangement behind one another as seen in conveying direction. 
     The conveying speed of the belts, namely of the transport belt and no less than one cover belt, may be variable and/or adjustable individually. 
     The no less than one cover belt may, in the area of the discharge end in front of the end of the transport belt, diverge from the same. 
     The no less than one cover belt may, in the area of the discharge end, protrude beyond the end of the transport belt as seen in conveying direction. 
     In one embodiment, it may be intended for the cover belt, at the discharge end, to project vis-à-vis the transport belt as seen in the direction of transport and for the projecting part of the cover belt to be pivotable, relative to the transport belt, about an axis extending transverse and parallel to the transport belt or to be guided about the end of the transport belt in the shape of an arc. The pivotability of the projecting part of the cover belt makes it possible to influence the parabolic discharge trajectory of the milled-off stream of material. 
     In such an embodiment in which, for example, the lower strand of the cover belt is guided about the end of the transport belt in the shape of an arc, there is the possibility for the last deflection roller of the cover belt to be moved from a position in which the lower strand of the cover belt surrounds the end of the transport belt in the shape of an arc, for example, in an angular range of approx. 90°, into a position in which the last deflection roller as seen in the direction of transport is located in a rectilinear extension of the cover belt. 
     Depending on the position of said deflection roller, the parabolic trajectory can be changed so as to enable adjustment of the point of impingement of the milled-off material on a loading surface of a transport vehicle. 
     It may be intended for the belts to comprise an essentially rectilinear deflection roller each on the inlet side and outlet side, and for no less than one of the last deflection rollers as seen in conveying direction to be pivotable relative to the respective opposite deflection roller. The adjustability of the deflection rollers at the discharge end enables the stream of material to be bundled more strongly, should the need arise, and the parabolic trajectory to be shortened, where appropriate, despite a high conveying speed so that the point of discharge is moved closer to the conveying device. 
     In a method for milling off and transporting away a milled-off stream of material of a road milling machine, it is intended for the milled-off material to be transported, at least on a part of the length of the transport belt, between a transport belt and no less than one upper cover belt of the conveying device. 
     In the process, the cover belt may be pre-tensioned resiliently in the direction towards the lower transport belt carrying the milled-off material at least in that part which is in contact with the milled-off material. 
     The milled-off material may be transported in a transport channel of the lower transport belt, in which process the lower strand of the upper cover belt is guided in such a fashion that the strand, which has a convex to concave cross-sectional shape depending on the quantity of the milled-off material, is pressed against the milled-off material. 
     The belts accepting the milled-off material between themselves may be guided in a converging fashion on the inlet side and/or in a diverging fashion on the outlet side. 
     In the following, embodiments of the invention are explained in more detail with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is shown: 
         FIG. 1  a road milling machine, 
         FIG. 2  a section through the conveying device according to  FIG. 1  in a longitudinal median plane, 
         FIG. 3  a section along line III-III in  FIG. 2 , 
         FIG. 4  a section according to  FIG. 3  with loaded transport belt, 
         FIG. 5  a side view of the conveying device in folded state, 
         FIG. 6  an alternative design of the support rollers for the upper strand of the transport belt, and 
         FIG. 7  an embodiment with a projecting and pivotable cover belt. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a construction machine  1  for milling ground surfaces or traffic surfaces which is also referred to as a cold milling machine. 
     The cold milling machine features a chassis comprising, for example, four crawler track units, said chassis supporting the machine frame  2  of the road milling machine  1 . It is understood that the crawler track units may be substituted, wholly or in part, by wheels. 
     A milling drum  6  extending transversely to the direction of travel is mounted in the machine frame  2 . The milling depth is preferably set by means of the height adjustment of the crawler track units via lifting columns. The cold milling machine depicted in  FIG. 1  is also referred to as a front-loading road milling machine as it is capable of conveying the milled-off material  3  towards the front as seen in the direction of travel onto a point of discharge on a transport vehicle. A first transport belt  5  of a conveying device  18  is arranged in front of the milling drum  6  as seen in the direction of travel, said first transport belt  5  preferably transferring the milled-off material  3  to a second transport belt  10 . It is understood that the road milling machine  1  may also comprise a single transport belt only which may also be arranged at the rear of the road milling machine  1 . 
     The cold milling machine depicted in  FIG. 1  shows a typical embodiment of a construction machine which also allows the use of a folding conveying device  18 . A foldable transport belt is generally already known from EP 2 113 613 A1. (U.S. Pat. No. 8,424,666) 
       FIG. 2  shows a partial section through the longitudinal median plane of the conveying device  18  which comprises a lower transport belt  10  and two successive upper cover belts  12   a ,  12   b . No less than one cover belt  12   a ,  12   b  is arranged above the transport belt  10  of the conveying device  18  so that, notwithstanding the embodiments shown in the figures, a single cover belt  12  only may also be arranged above the transport belt  10 . 
     The transport and cover belts  10 ,  12   a ,  12   b  are continuously revolving belts which revolve about essentially rectilinear deflection rollers  20  to  25 , where the front deflection rollers  20 ,  22 ,  24  as seen in conveying direction  30  may preferably be driven deflection rollers, and where the rear deflection rollers  21 ,  23 ,  25  as seen in conveying direction  30  may also be of spherical design. 
     The belts  10 ,  12   a ,  12   b  each comprise an upper strand  13 ,  15  and a lower strand  14 ,  16 , in which arrangement the lower strand  14  of the single cover belt or the cover belts  12   a ,  12   b  may be pre-tensioned in the direction towards the upper strand  15  of the transport belt  10 . 
     Altogether, the no less than one cover belt  12   a ,  12   b  may be adjustable in height relative to the transport belt  10 . To this effect, the conveying device  18  comprises a frame  44  for the transport belt  10  and frames  42   a ,  42   b  for the cover belts  12   a ,  12   b , with guiding elements  40  being intended at the sides of said frames which enable the no less than one cover belt  12   a ,  12   b  to be adjusted in height relative to the transport belt  10 . 
     In this arrangement, the cover belts  12   a ,  12   b , with their lower strands  14  each, may rest, due to their own weight, on the transport belt  10  or on the milled-off material  3  transported on the transport belt  10 . 
     The lateral guiding devices  40  ( FIG. 1  and  FIG. 5 ), which are arranged on both sides of the cover and transport belts  10 ,  12   a ,  12   b , may be combined with spring devices so that the cover belts  12   a ,  12   b  do not rest on the upper strand  15  of the transport belt  10  with their full weight. 
     It goes without saying that the guiding devices  40  may also be adjusted so as to enable a specific permanent distance to be preset between the frames  42   a ,  42   b ,  44  of the transport and cover belts  10 ,  12   a    12   b.    
     The guiding elements  40  may alternatively also be combined with spring elements which pre-tension the frame  42   a ,  42   b  of the no less than one cover belt  12   a ,  12   b  downwards. As can best be inferred from  FIGS. 3 and 4 , which represent a section along line III-III in  FIG. 2 , support rollers  32  are preferably intended for the upper strand  15  of the transport belt  10 , with the roller segments  32   a ,  32   b ,  32   c  of said support rollers  32  being connected to one another in an articulated fashion and, together with the upper strand  15 , creating a bed of concave cross-section for the milled-off material  3 . In this design, the support rollers  32  are preferably arranged in a fixed position in the frame  44 . 
     The lower strand  14  of the no less than one cover belt  12   a ,  12   b  comprises movable support rollers  34  which may also be segmented and are connected to one another in an articulated fashion such that they can change from a lowest position with minimal loading of the transport belt  10 , as shown in  FIG. 3 , to a position in loaded state of the transport belt  10 , as shown in  FIG. 4 . A gear, for example, is intended to this effect which guides the support rollers  34  in an essentially orthogonal plane to the cover belt  12   a  and  12   b  respectively. In this arrangement, each support roller  34  is comprised of, for example, three roller segments  34   a ,  34   b ,  34   c , with all roller segments being guided in the orthogonal plane by, for example, a four-link mechanism  50  at the frame  42   a ,  42   b.    
     The support rollers  34  for the lower strand  14  of the cover belt  12   a  or  12   b  respectively may be pre-tensioned against the lower strand  14  by means of spring elements, for example, Rosta-Blocks. 
     The upper support rollers  35  of the no less than one cover belt  12   a ,  12   b  and the lower support rollers  33  of the transport belt  10  may be rectilinear rollers which are supported in a fixed position relative to the frames  42   a ,  42   b ,  44 . 
     Furthermore, the transport or cover belts  10 ,  12   a ,  12   b , respectively may comprise lateral guiding devices  46  which are arranged at the upper strand  13  of the no less than one cover belt and at the lower strand  16  of the transport belt respectively in a specific height position relative to the frames  42   a ,  42   b ,  44  in order to ensure a lateral guidance. The cover belts  12   a ,  12   b  are guided, on the inlet side, between the deflection rollers  23 ,  25  and the first support roller  34  in a converging fashion to the transport belt  10  while, on the outlet side, they are guided in a diverging fashion in the direction towards the front deflection rollers  22 ,  24  as seen in conveying direction  30 . 
     In this design, the front deflection roller  22  as seen in conveying direction  30  of the last cover belt  12   b  as seen in conveying direction  30  may be arranged to pivot relative to the deflection roller  20  of the transport belt  10  so that the direction of discharge of the milled-off material  3  between the transport belt  10  and the no less than one last cover belt  12   b  can be adjusted in different ways. Alternatively the deflection roller  20  of the transport belt or both deflection rollers  20 ,  22  can be pivotable. 
     The upper strand  15  of the transport belt  10  and the lower strand  14  of the no less than one cover belt  12   a ,  12   b , respectively move, in conveying direction  30 , with the same, preferably adjustable conveying speed or with an adjustable different conveying speed. The shape of the parabolic trajectory  9  at the discharge end  11  can be influenced by means of the conveying speed and the height adjustment of the conveying device  18 , as well as by means of the adjustment of the distance or the pivoting angle, respectively between the last cover belt  12   b  and the transport belt  10 . 
     As can be inferred from  FIG. 5 , the front section of the conveying device  18  can be folded downwards and locked, for transport purposes, in an end position inferable from  FIG. 5 . An example of a swivel gear  60  suitable for this purpose has, in principle, been described in EP 2 113 613 A (U.S. Pat. No. 8,424,666). It is preferably intended for the folded front section of the conveying device  18  to have its own cover belt  12   b . Such segmentation of the cover belt  12   a ,  12   b  arranged above the transport belt  10  enables the folding possibility of the transport belt  10  to be maintained. 
       FIG. 6  shows an alternative embodiment for the support rollers  32  of the upper strand  15  of the transport belt  10 . 
     In this embodiment, a dual arrangement of rectilinear support rollers  32  is used which are arranged immediately behind one another in conveying direction  30  and together enable a V-shaped support, in conveying direction  30 , of the upper strand  15  of the transport belt  10 . 
     The transport and cover belts  10 ,  12   a ,  12   b  feature a profile on the surfaces facing the milled-off material  3  which minimize the amount of slip on the transport surface. 
       FIG. 7  shows an embodiment in which a projecting section  12   c  of the cover belt  12   b  is pivotable in order to adjust the parabolic trajectory of the milled-off stream of material  3  to a specified point of discharge  27 . 
     The upper cover belt  12   b  is extended, at the discharge end  11 , beyond the deflection roller  22  and comprises, at a distance from the deflection roller  22 , an additional deflection roller  26  which, in the direction towards the transport belt  10 , is pivotable about a normally horizontal axis  36  preferably coaxially to the axis of the deflection roller  22 . 
     It is understood that, notwithstanding the illustration in  FIG. 7 , the section  12   c  projecting vis-à-vis the transport belt  10  may also be longer in such a fashion that the lower strand  14  of the cover belt  12   b ,  12   c  can wrap around the transport belt  10 , in the area of the deflection roller  20 , for example, in the shape of an arc of up to 90°. 
     As depicted in  FIG. 7  in dashed lines, the deflection roller  26  may also be brought into a position in which the pivotable section  12   c  of the cover belt  12   b  extends in a rectilinear elongation of the remaining cover belt  12   b . In this case, a different parabolic trajectory results for the milled-off material  3  that is depicted in dashed lines in  FIG. 7 . 
     It is thus possible, by means of the pivoting position of the projecting section  12   c , to determine the position of the point of discharge  27  on a loading surface  28  of a transport vehicle.