Abstract:
A piston machine, in particular a fluid piston machine, is described as having a plurality of piston units, which have differently sized output volumes for reasons of geometry, and are able to be deactivated individually for the discrete adjustment of a total output volume of the piston machine. In this context, the larger output volume of one of the piston units is twice as high as the next smaller output volume of one of the other piston units.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a piston machine, especially a fluid piston machine, having a plurality of piston units which, for reasons of geometry, have output volumes of different size, and which are able to be deactivated individually for the discrete adjustment of an overall output volume of the piston machine. 
       BACKGROUND INFORMATION 
       [0002]    Piston machines of the type described at the outset are known from the related art. In many technological fields piston machines are used as pumps and/or motors. Different principles are known for generating a variable volumetric flow or volume flow, possibly also a variable pressure (pump) or rotational speed and torque (motor). Conventional types for the continuous variation/setting of the output volume of the piston units are, for example, piston machines having a swash plate, an oblique axis or a wobble plate. By changing the angle, the upper and lower dead centers of the piston strokes are varied and the output volume continually modified in this manner. However, such constructions have low efficiency, especially in the partial-load range. This low efficiency essentially is due to the leakage at the corresponding control, oblique or swash plate, the friction at the control/oblique or swash plate as well as a constantly required control current for supporting the control/oblique or swash plate. In addition to a continual variation of the output volume or the delivery time of the piston units, it is also known to implement discrete variations of the output volume by deactivating individual piston units or switching them off. 
         [0003]    European patent document EP 1 306 553 A2 discusses a piston machine in the form of a fuel pump, in which individual piston units are switched off, thereby allowing for a discrete adjustment of the total output volume; to provide greater adjustment options, the output volumes of the individual piston units are of different size. 
       SUMMARY OF THE INVENTION 
       [0004]    The piston machine according to the exemplary embodiments and/or exemplary methods of the present invention has the features described herein. Accordingly, the piston machine is developed in such a way that the larger output volume of one of the piston units is twice as large as the next smaller output volume of one of the other piston units. That is to say, the piston units have output volumes of different sizes, and the piston unit having a greater output volume is designed such that its output volume is twice as large as that of the other piston unit having the next smaller output volume. For example, when three piston units are provided, the output volume of the second piston unit is twice as high as that of the first, and the output volume of the third piston unit is twice as high as that of the second piston unit. This applies analogously to any other number of piston units of the piston machine. This makes it possible to vary or adjust the total output volume of the piston machine in discrete manner in equidistant stages. 
         [0005]    In the aforementioned exemplary embodiment featuring three piston units, it is possible to adjust eight different total output volumes, from zero to seven times the output volume of the piston unit having the smallest output volume. For practical purposes, the piston units are configured in such a way that the stage in the increase or reduction of the total output volume in each case corresponds to the output volume of the piston unit having the smallest output volume. This creates a piston machine whose total output volume is variably adjustable in equidistant stages and which provides high efficiency even in partial-load range. 
         [0006]    Furthermore, each piston unit is assigned a switchable drain valve for deactivating the piston unit. The drain valve is designed such that opening of the drain valve prevents pressure from being generated in the piston unit, thereby preventing the supply of fluid. The drain valve thus allows the volume contained in the piston unit to “run dry”. 
         [0007]    Advantageously, the drain valve furthermore is developed in such a way that during opening of the drain valve, the exit cross-section of the piston unit through which the volume to be output is to be pumped is sealed simultaneously. As an alternative, the drain valve may also be developed in such a way that it prevents an inflow of fluid into the piston unit, so that the piston unit is drained. Of course, quite different deactivation mechanisms for the particular piston unit are conceivable as well. For example, each piston unit may be driven by a separate drive shaft, so that the drive shafts are able to be controlled or switched off individually. 
         [0008]    According to one further development of the exemplary embodiments and/or exemplary methods of the present invention, the piston units have a bypass channel assigned to the corresponding drain valve. The bypass channel returns the undesired volume, which was output by the piston unit nevertheless, past a consumer, so that the volume is resupplied to the piston machine “in unused condition”. 
         [0009]    Furthermore, the piston machine is to have at least three piston units. This already makes it possible, as stated before, to adjust eight different total output volumes of the piston machine in equidistant steps/stages. 
         [0010]    For practical purposes, the piston machine is developed as a radial and/or in-line piston machine. This reduces both friction losses and losses caused by leakages, and it ensures high efficiency of the piston machine, especially in partial-load range. 
         [0011]    Each piston unit advantageously has at least one piston which is axially displaceable inside a cylinder. It is also conceivable to provide two cylinders for each piston unit, each having a piston which is axially displaceable therein. In this case, they form a piston set. Accordingly, the total output volume is adjustable by varying the output volume of the piston set. Additionally it is conceivable, for example, that only the output volume of one of the piston-cylinder units of a piston set is deactivated. This allows further gradations in the adjustment of the total output volume of the piston machine. 
         [0012]    For practical purposes, the differently sized output volumes of the piston units are defined by differently sized cross-sectional areas of the cylinders and pistons. This geometric construction easily makes it possible to provide and ensure the different output volumes, as described earlier. 
         [0013]    As an alternative or in addition, the output volumes of different sizes are definable by piston strokes of different magnitude of the piston units. 
         [0014]    Notwithstanding the fact that previously the function of the piston machine was essentially described as that of a piston pump, one skilled in the art naturally understands that the afore-described specific developments are also applicable to piston machines developed as piston motor. 
         [0015]    In the following text, the exemplary embodiments and/or exemplary methods of the present invention are elucidated in greater detail with the aid of an exemplary embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows an exemplary embodiment of an advantageous piston pump in a schematic representation. 
           [0017]      FIG. 2  shows an adjustable total output volume of the piston pump. 
           [0018]      FIG. 3  shows another adjustable total output volume of the piston pump. 
           [0019]      FIG. 4  shows another adjustable total output volume of the piston pump. 
           [0020]      FIG. 5  shows another adjustable total output volume of the piston pump. 
           [0021]      FIG. 6  shows another adjustable total output volume of the piston pump. 
           [0022]      FIG. 7  shows another adjustable total output volume of the piston pump. 
           [0023]      FIG. 8  shows another adjustable total output volume of the piston pump. 
           [0024]      FIG. 9  shows another adjustable total output volume of the piston pump. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  constitutes a schematic representation of a piston machine  1  for fluids, which is developed as in-line piston pump  2 . For this purpose, piston machine  1  has three cylinders  3 ,  4  and  5  formed inside a housing, in which a piston  6 ,  7  and  8  is supported in axially displaceable manner. Pistons  6 ,  7 ,  8  in cylinders  3 ,  4 ,  5  are displaced by a drivable crankshaft  9 . Cylinder  3  and piston  6 , cylinder  4  and piston  7 , as well as cylinder  5  and piston  8  form a piston unit  10 ,  11  or  12  of piston machine  1  in each case. Piston units  10 ,  11  and  12  have different output volumes, which are defined by the size of the individual cross-sectional surfaces of cylinders  3 ,  4 ,  5  and pistons  6 ,  7 ,  8 . In an advantageous manner, volume v 11  of piston unit  11  is twice as large as volume v 10  of piston unit  10 , and volume v 12  of piston unit  12  is twice as large as output volume v 11  of piston unit  11 . Thus, the greater output volume of one of the piston units in each case is twice as large as the next smaller output volume of another piston unit. 
         [0026]    In general, the output volume of piston units  10 ,  11 ,  12  may thus be expressed as 
         [0000]        V   i =2 ·V   i-1   , i  corresponding to the number of piston units. 
         [0027]    Each piston unit  10 ,  11 ,  12  or each cylinder  3 ,  4 ,  5  is assigned a drain valve  13 ,  14  and  15 , respectively. From each drain valve  13 ,  14 , and  15 , the volume supplied by corresponding piston unit  10 ,  11  or  12  is guided out of piston machine  1  by a bypass channel  16 ,  17  and  18  in “unused condition”, provided the individual drain valve  13 ,  14 ,  15  is switched appropriately, i.e., is open. For practical purposes, bypass channels  16 ,  17  and  18  are combined to form a common (return) channel, which is not shown here. By opening drain valves  13 ,  14  and/or  15 , individual piston unit  10 ,  11  or  12  is thus able to be switched off, so that the output volume it has supplied is not pumped but forwarded unused, or returned, and therefore not supplied to the total output volume of piston machine  1 . 
         [0028]    By deactivating piston units  10 ,  11 ,  12 , or setting drain valves  13 ,  14 ,  15 , it is therefore easily possible to vary the total output volume V G  of piston machine  1  in equidistant stages in discrete manner. This is best represented by the following formula 
         [0000]    
       
         
           
             
               V 
               G 
             
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         [0029]    Due to the afore-described advantageous development of piston machine  1 , the particular abrupt change between the different total output volumes corresponds to the output volume of the piston unit having the smallest output volume, in this case, v 10 . Maximum total output volume V G,max  corresponds to: 
         [0000]    
       
         
           
             
               
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         [0000]    in this case, 
         [0000]    
       
         
           
             
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         [0030]      FIGS. 2 through 9  illustrate the output volume of piston units  10 ,  11 ,  12  and the total output volume of piston machine  1  or in-line piston pump  2  derived from the corresponding adjustment of drain valves  13 ,  14  and  15 . The delivered (dashed line) output volume supplied by individual piston units  10 ,  11  and  12 , and the possible (blank) output volume of piston units  10 ,  11 , and  12  are shown on the left side. Accordingly, the resulting total output volume V G  is shown on the left side. 
         [0031]      FIG. 2  shows the corresponding output volumes in the event that all bypass channels  16 ,  17  and  18  are enabled by corresponding drain valve  13 ,  14  and  15  or in case all piston units  10 ,  11 ,  12  are deactivated, so that none of the potential output volumes is utilized and the total output volume V G  is equal to zero. 
         [0032]    If drain valve  13  is closed, i.e., piston unit  10  is activated, as shown in  FIG. 3 , then total output volume V G  corresponds to the output volume of piston unit  10 . 
         [0033]    According to  FIG. 4 , piston unit  10  is deactivated and piston unit  11  is activated, so that the resulting total output volume corresponds to the output volume of piston unit  11  and thus to twice the output volume of piston unit  10 . 
         [0034]    If piston unit  10  is switched on as well according to  FIG. 5 , then resulting total output volume V G  is supplemented by output volume V 10  of piston unit  10 , i.e., increased by an additional stage. 
         [0035]    By deactivating piston units  10  and  11  and activating piston unit  12 , a total output volume V G =V 12  results, which once again is one stage greater than the previous output volume. 
         [0036]    To increase the total output volume by another stage, piston unit  10  is switched on as well according to  FIG. 7 . 
         [0037]    To increase the output volume by yet another stage, piston unit  10  is deactivated and piston unit  11  is activated, according to  FIG. 8 . 
         [0038]      FIG. 9  shows the setting of piston machine  1  or in-line piston pump  2  in the event that maximum total output volume V G,max  is set. All three piston units  10 ,  11 ,  12  are activated for this purpose, i.e., none of piston units  10 ,  11 ,  12  is deactivated. In this case, V G =V G,max =7·V 10 . 
         [0039]    With the aid of advantageously developed piston machine  1 , it is therefore easy to adjust a total output volume V G  discretely, in equidistant stages (V 10 ), it already being possible to adjust eight different total output volumes in case of three differently developed piston units  10 ,  11 ,  12 , at unchanged high efficiency.