Abstract:
The invention relates to vibration generator for a soil compacting device referred to as a towed vibrating device. The vibration generator has two parallels arranged unbalanced shafts that each support a fixed and a freely rotating unbalanced mass. An unbalance adjusting device enables the position of both freely rotating unbalanced masses to be adjusted in such a manner that, during a maximum unbalance action of one of the unbalanced shafts, the unbalance action on the other unbalanced shaft is minimized. The unbalance adjusting device can alter the position of the unbalanced masses whereby rendering possible a to-and-fro movement of the soil compacting device or a compaction when stationary.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a vibration generator for a soil compacting device. 
   2. Description of the Related Art 
   For compacting soil, among others vibration plates known as “plate compactors” are known. In plate compactors, a vibration generator is seated in off-center fashion on a soil contact plate. The vibration generator is standardly a rotating imbalance shaft. The imbalance force, or centrifugal force, produced by the imbalance shaft pulls the soil contact plate (because of the off-center placement) upwards on one side and towards the front before the contact plate is pressed downward again, communicating the compacting energy to the soil. The vibration generator, which has a very simple construction, is thus able not only to produce the vibration required for the soil compacting, but also to move the soil contact plate forward. 
   Plate compactor plates of this type have outstanding movement behavior, in particular on difficult soil surfaces containing a high proportion of clay and high water content. Precisely on such cohesive soils, vibration plates having other designs can experience difficulty in moving forward. The advantageous characteristic of plate compactor plates is due to a comparatively large amplitude of the vibration generator, and to the presence of a constant reaction moment that, given a suitable direction of rotation of the imbalance shaft, permanently effects a determinate friction on the end of the soil contact plate situated opposite the vibration generator. 
   However, this design has turned out to have the disadvantage that it is not possible, using reasonably economical means, to execute a continuous reversing, i.e. a traveling back and forth, of the vibration plate, with the possibility of compacting at a point, i.e., purposive compacting at one location without forward movement of the vibration plate. 
   It is true that it is possible to situate imbalance shafts at the two opposite ends of the soil contact plate, and to drive only one of the two for forward or backward movement. However, in this case the imbalance shafts must be operated synchronously at double power consumption and with precise rotational speed, both for the stationary point compacting and for the transition from forward travel to backward travel, so that a considerable energy and control expense is required. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   The underlying object of the present invention is to indicate a vibration generator for soil compacting which retains on the one hand the advantageous design of what is known as the plate compactor, while on the other hand enabling forward and backward movement of the soil compacting device, as well as stationary compacting. 
   According to the present invention, this object is achieved by a vibration generator having the features of patent claim  1 . Advantageous developments of the present invention can be found in the dependent claims. 
   A vibration generator according to the present invention for a soil compacting device has two imbalance shafts that are coupled with one another in positively locking fashion so as to be capable of rotation, each bearing a fixedly attached first imbalance mass and a second imbalance mass that can be rotated on the imbalance shaft between at least two extreme positions. Thus, for each imbalance shaft it is possible to adjust the second imbalance mass carried thereon in such a way that its imbalance action either coincides with the action of the fixedly attached first imbalance mass, thus reinforcing this action, or counteracts the action of the first imbalance mass, thus compensating it largely or entirely. 
   According to the present invention, an imbalance adjustment device is provided that couples the second imbalance masses on the first and second imbalance shaft in positively locking fashion, and so as to be capable of rotation in opposite directions. Using the imbalance adjustment device, it is possible to set the imbalance effects of the first and second imbalance shafts in such a way that, in the extreme case, only one of the imbalance shafts produces, with the imbalance masses carried thereon, an imbalance effect, while the imbalance effects of the imbalance masses on the other imbalance shaft compensate one another, so that no imbalance arises there. Thus, it is possible to modify what is known as the “MR value”—the product of the imbalance mass and the imbalance radius—of the imbalance masses installed on the two imbalance shafts situated parallel to one another, in such a way that at the respective maximum of the one imbalance shaft, the other imbalance shaft has a minimum MR value, which can even be zero in the ideal case. 
   In these respective extreme positions, the pure plate compacting effect is achieved, as occurs also in known plate compactor plates having only one vibration generator having a single imbalance shaft. This effect can be achieved even though both imbalance shafts are in rotation, which is very significant for the life of the bearing, because the bearing is not statically loaded on one side by impacts. 
   Between the two extreme positions, it is also possible to set arbitrary additional intermediate positions for the two second imbalance masses. In this way, the soil compacting device that carries the vibration generator according to the present invention can move back and forth comfortably. 
   If the imbalance action of the two imbalance shafts is equal, stationary operation, at one location, of the soil compacting device is possible, and here a tilting vibration effect that is especially advantageous for the compacting occurs to its maximum extent. In this situation, the soil contact plate alternates between striking at the front and at the rear, enabling a particularly effective soil compacting. 
   In an advantageous further development of the present invention, the above-described vibration generator system is provided twice, the two systems being axially adjacent to one another. For this purpose, each imbalance shaft has two axially displaced first imbalance masses and two associated second imbalance masses that can be rotated. The two additional second imbalance masses on the first and second imbalance shaft are coupled with one another in positively locking fashion by a second imbalance adjustment device, in the same way as the two original second imbalance masses. 
   If the two imbalance adjustment devices can be controlled separately from one another, it is possible to produce a yawing moment about the vertical axis of the vibration generator, and thus the vertical axle of the soil compacting device, thus enabling steerability of the soil compacting device. 
   Advantageously, a steering device is provided with which the two imbalance adjustment devices can be controlled. 
   In another particularly advantageous further development of the present invention, it is attempted to keep the axial distance between the two imbalance shafts as large as possible. 
   For this purpose, two intermediate shafts that can be coupled in positively locking fashion so as to be capable of rotation are situated between the two imbalance shafts; these intermediate shafts transmit the rotational movement of the driven first imbalance shaft to the second imbalance shaft. Through the large distance between the two imbalance shafts, the drag action and the compacting action can be amplified. 
   Of course, the axial distance between the two imbalance shafts can be further increased through the placement of additional pairs of intermediate shafts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further advantages and features of the present invention are explained in more detail below on the basis of a plurality of examples, with the aid of the accompanying figures. 
       FIG. 1  shows a schematic sectional top view of a vibration generator according to the present invention; 
       FIG. 2  shows, in a schematic side view, the force vectors produced by the individual imbalance masses, and the directions of motion resulting therefrom; 
       FIG. 3  shows a second specific embodiment of the present invention, having a vibration generator, for the steerability of a soil compacting device; and 
       FIG. 4  shows a third specific embodiment of the present invention having a vibration generator, having an enlarged axial distance between the two imbalance shafts. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a first specific embodiment of a vibration generator according to the present invention, having a first imbalance shaft  1  and a second imbalance shaft  2 . 
   First imbalance shaft  1  is driven rotationally in a known manner by a drive  3  (not shown in more detail), for example a hydraulic motor or a coupling with an internal-combustion engine (not shown). 
   Via two toothed wheels  4  and  5 , first imbalance shaft  1  is coupled with second imbalance shaft  2  in positively locking fashion, so as to be capable of rotation in the opposite direction. That is, first and second imbalance shafts  1 ,  2  rotate in a manner counter to one another. 
   A first imbalance mass  6  is situated on first imbalance shaft  1 , and second imbalance shaft  2  bears a first imbalance mass  7 . First imbalance masses  6 ,  7  can be connected in one piece with imbalance shafts  1 ,  2  bearing them. It is also possible to fasten first imbalance masses  6 ,  7  to imbalance shafts  1 ,  2 , for example using screws. 
   In addition, first and second imbalance shafts  1 ,  2  each bear a second imbalance mass  8 ,  9 , which however is not connected fixedly with the imbalance shaft that bears it but rather is held by this shaft so as to be capable of being rotated. Second imbalance masses  8 ,  9  can each be rotated freely on first or second imbalance shaft  1 ,  2 . It is also possible to realize only a limited capacity for rotation, which however should extend over a range of at least 180°. 
   The two second imbalance masses  8 ,  9  are coupled with one another by an imbalance adjustment device  10  in positively locking fashion, so as to be capable of rotation in opposite directions. 
   Imbalance adjustment device  10  has two toothed wheels  11  and  12 , toothed wheel  11  being connected fixedly with second imbalance mass  8  of first imbalance shaft  1 , while toothed wheel  12 , which meshes with toothed wheel  11 , is fixedly connected with second imbalance mass  9  on second imbalance shaft  2 . 
   Toothed wheel  11  can be rotated freely, together with second imbalance mass  8 , on first imbalance shaft  1 . In contrast, as a component of imbalance adjustment device  10  a rotation device  13  is provided on second imbalance shaft  2 , with which the relative position between second imbalance mass  9 , or toothed wheel  12 , on the one hand and second imbalance shaft  2  on the other hand can be adjusted precisely. 
   Rotation device  13  is known in its design and its manner of operation. It has a piston-cylinder unit  14  that can be actuated hydraulically or pneumatically, with which a positioning element  15 , situated inside second imbalance shaft  2 , can be moved back and forth axially. 
   Control element  15  has a pin  16  that extends through grooves  17  in second imbalance shaft  2  and engages in spiral grooves  18  that are formed on the inside of a hub that bears second imbalance mass  9 . 
   As a result of this design, given an axial displacement of control element  15  by piston-cylinder unit  14 , a rotation of second imbalance mass  9  relative to second imbalance shaft  2  is effected by means of pin  16 . 
   This rotation is transmitted by toothed wheels  12  and  11 , in the opposite direction, to second imbalance mass  8  on first imbalance shaft  1 . 
   In this way, with the aid of imbalance adjustment device  10  it is possible to adjust the two second imbalance masses  8 ,  9  in such a way that they either counteract first imbalance masses  6 ,  7  (shown in  FIG. 1  in the lower half of the picture by the position of imbalance masses  6 ,  8 ) or reinforce the action of the first imbalance mass (shown in  FIG. 1  in the upper half of the picture by imbalance masses  7 ,  9 ). 
   However, as is also shown in  FIG. 1 , the adjustment takes place in such a way that it is always the case that only one imbalance mass pair on an imbalance shaft reaches a maximum imbalance action, while at the same time the imbalance masses on the other imbalance shaft compensate their action. In this way, the plate compactor principle is maintained. The imbalance shaft that does not achieve an imbalance effect is simply carried along without adversely affecting the action of the imbalance shaft that is producing the actual vibration. Due to the fact that the “deactivated” (so to speak) imbalance shaft also rotates, a one-sided loading of the shaft bearing is avoided. 
   A modification of the state by imbalance adjustment device  10  has the effect that the imbalance shaft, which still has no effect at the beginning, produces an imbalance, while the imbalance of the other imbalance shaft is reduced, and finally goes to zero. In this way, a change of direction of the plate compactor can be achieved. 
     FIG. 2  shows different positions for imbalance shafts  1 ,  2 , or imbalance masses  6  to  9 . 
   In part a) of  FIG. 2 , the state is shown that was already illustrated in the top view of  FIG. 1 . While imbalance masses  7 ,  9  in on second imbalance shaft  2  supplement one another in their action, the actions of imbalance masses  6 ,  8  on first imbalance shaft  1  compensate one another. This results in forward motion, to the left, of a soil contact plate  19  bearing the vibration generator. Due to their off-center situation, imbalance masses  7 ,  9  effect a one-sided lifting of soil contact plate  19 , so that the soil compacting device shown in  FIG. 2   a  moves to the left. 
     FIG. 2   b  shows an intermediate position. While imbalance shafts  1 ,  2 , and first imbalance masses  6 ,  7  held fixedly thereby, remain unmodified in comparison with  FIG. 2   a ), second imbalance masses  8 ,  9  are rotated relative to imbalance shafts  1 ,  2 , with the aid of imbalance adjustment device  10 . Both imbalance shafts  1 ,  2  now achieve an approximately equally large imbalance action, which is however directed upward and downward in alternating fashion. In this way, there results the tilting vibration effect, which is very effective for stationary compacting. No forward travel of soil contact plate  19  or of the overall soil compacting device takes place. 
     FIG. 2   c  corresponds to a reversal of the state shown in  FIG. 2   a . Here, imbalance masses  6  and  8  of first imbalance shaft  1  are adjusted in such a way that their action is superposed, while the effects of imbalance masses  7 ,  9  on second imbalance shaft  2  compensate one another. This results in travel in the opposite direction (to the right in  FIG. 2   c ). 
     FIG. 3  shows a top view of a second specific embodiment of the present invention, in a schematic sectional representation. 
   In principle, the second specific embodiment corresponds to a doubling, i.e., a situation alongside one another of the first specific embodiment according to  FIG. 1 . Therefore, for simplification identical reference characters are used for the components already known from  FIG. 1 . 
   First imbalance shaft  1  now carries, besides first imbalance mass  6 , an additional first imbalance mass  20 , while second imbalance shaft  2  carries, alongside first imbalance mass  7 , an additional first imbalance mass  21 . Likewise, first imbalance shaft  1  carries, besides second imbalance mass  8 , an additional second imbalance mass  22 , and second imbalance shaft  2  carries, besides second imbalance mass  9 , an additional second imbalance mass  23 . 
   As second imbalance masses  8 ,  9  are coupled with one another in positively locking fashion so as to be capable of rotation in opposite directions by imbalance adjustment device  10 , additional second imbalance masses  22  and  23  are also coupled with one another in positively locking fashion so as to be capable of rotation by a second imbalance adjustment device  24 . The manner of functioning of second imbalance adjustment device  24  corresponds to that of first imbalance adjustment device  10 , so that a detailed specification is not required here. 
   The rotational coupling of the two imbalance shafts  1  and  2  takes place, as in  FIG. 1 , by means of toothed wheels  4 ,  5 . 
   Through a separate controllability of the two imbalance adjustment devices  10  and  24 , it is possible to produce different resulting forces for the respective interacting imbalances. In this way, it is possible to produce a yawing moment about the vertical axle of the vibration generator (which stands perpendicular to the drawing plane of  FIG. 3 ), and thus also about the vertical axle of the soil compacting device; with the aid of this yawing moment, it is possible to steer the soil compacting device. 
   Advantageously, the interaction of the two imbalance adjustment devices  10  and  24  is coordinated using a steering device (not shown) that can easily be handled by the operator. 
     FIG. 4  shows a third specific embodiment of the present invention, in which the axial distance of the two imbalance shafts  1  and  2  has been enlarged. Because the two imbalance shafts  1  and  2 , as well as the imbalance masses  6  to  9  carried thereby, correspond in their design to the first embodiment according to  FIG. 1 , a repetition of the description is omitted. 
   Between toothed wheels  4  and  5  of imbalance shafts  1  and  2 , two intermediate shafts  25  and  26  are placed, which have toothed wheels  27 ,  28  and thus transmit the rotational movement of first imbalance shaft  1  to second imbalance shaft  2 . In the same way, toothed wheels  29  and  30  are placed between toothed wheels  11  and  12  of imbalance adjustment device  10 , and are carried by intermediate shafts  25 ,  26 , but can be rotated freely on these shafts. 
   Through this arrangement, it is possible to significantly increase the axial distance between the two imbalance shafts  1  and  2 , making it possible likewise to increase the spacing of imbalance shafts  1 ,  2  from the center. In this way, the drag effect can be improved. 
   Of course, for a large plate compactor, the second and third specific embodiments of the present invention, according to  FIGS. 3 and 4 , can be combined with one another.