Abstract:
A hydraulic axle includes a reversible hydraulic pump. The hydraulic axle has a multi-surface cylinder with two retraction surfaces and two deployment surfaces. A first deployment surface and a first retraction surface are configured to interconnect with each other and separate from other surface during a rapid-traverse stroke. A pressure medium is configured to act on the second deployment surface to enable deployment.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2013 227 053.4, filed on Dec. 23, 2013 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The disclosure relates to a hydraulic axle. 
         [0003]    In the context of this application, a hydraulic axle is to be understood to mean a hydraulic actuator, for example a hydraulic cylinder, and the hydraulic or electro-hydraulic control arrangement or circuit that charges the actuator with fluid. Such hydraulic axles are compact and powerful high-performance drives. They can be used for numerous industrial automation applications, for example in presses, plastics machines, bending machines and so forth. In particular, such drives are designed for realizing at least two movement profiles, specifically a fast transfer movement—hereinafter referred to as rapid-traverse stroke or rapid-traverse movement—and a force-imparting working movement—hereinafter referred to as power stroke, working movement or pressing stroke. 
         [0004]    A known hydraulic axle is presented in the applicant&#39;s application DE 10 2009 043 034. A main cylinder, a rapid-traverse stroke cylinder and a hydraulic machine which can be reversed in terms of its direction of rotation are interconnected in a preloaded hydraulic system. By means of valves, the interconnection of the components can be varied such that one of several hydromechanical transmission ratios predefined for example by means of piston surfaces is selected. In this way, the said rapid-traverse movements or working movements can be performed in an efficient manner. 
         [0005]    Furthermore, the applicant&#39;s DE 10 2012 020 581 discloses a hydraulic axle with a multi-surface cylinder. The latter has one deployment surface and two retraction surfaces. In the rapid-traverse stroke, the deployment surface and the first retraction surface are fluidically connected to one another by means of a regeneration valve and, together, have a pressure medium connection to the second retraction surface via a hydraulic pump. During the rapid-traverse deployment stroke of a piston of the multi-surface cylinder, for example, it is thus possible for the deployment surface and the first retraction surface to be connected to a high-pressure side of the hydraulic pump. The hydraulic pump then delivers pressure medium from the second retraction surface to the deployment surface and to the first retraction surface. A resulting exertion of pressure on the deployment surface and on the first retraction surface has the effect that numerous seals are subjected to a high pressure. In particular at seals of a chamber that is delimited by the outer, second retraction surface, the exertion of pressure leads to high friction resistances, such that in particular in the rapid-traverse stroke, high pressures are required to move the piston. 
       SUMMARY 
       [0006]    By contrast, it is the object of the disclosure to provide a hydraulic axle in which a piston of a cylinder can be moved with less friction. 
         [0007]    Said object is achieved by means of a hydraulic axle having the feature described below. 
         [0008]    Further advantageous refinements of the disclosure are described in the claims and the FIGURE. 
         [0009]    According to the disclosure, a hydraulic axle, in particular a compact axle, having a reversible hydraulic machine is provided. The hydraulic machine is preferably a hydraulic pump which is variable in terms of its rotational speed. Furthermore, the axle has a hydraulic circuit. The circuit has control valves for controlling a piston of a multi-surface cylinder, in particular of a five-surface cylinder. By means of the control valves, the piston can be moved in a rapid-traverse stroke and in a power stroke in two axial directions. According to the disclosure, the piston has two retraction surfaces (A 2 , A 3 ) which can be acted on with pressure medium in a retraction direction. Furthermore, the piston has two deployment surfaces (A 1 , A 5 ) which can be acted on with pressure medium in a deployment direction. It is preferably the case that, in the rapid-traverse stroke, the first deployment surface (A 1 ) and the first retraction surface (A 3 ) are interconnected in particular in substantially unpressurized fashion by means of the circuit and are in particular fluidically separated from the other surfaces. Furthermore, during a rapid-traverse deployment movement, the second deployment surface (A 5 ) can be acted on with pressure medium by being connected to a high-pressure side of the hydraulic pump. The second retraction surface (A 2 ) can be connected to the low-pressure side of the hydraulic pump. 
         [0010]    This solution has the advantage that an additional deployment surface is provided in relation to the prior art in DE 10 2012 020 581 discussed in the introduction. In this way, a deployment surface and a retraction surface can be interconnected in unpressurized fashion, and the other surfaces can be correspondingly acted on for the purpose of displacing the piston. Thus, during the deployment movement, only one of the deployment surfaces is acted on with an elevated pressure or connected to the high-pressure side of the hydraulic pump. It is furthermore advantageous that, in the multi-surface cylinder, fewer seals are subjected to pressure in particular during the rapid-traverse deployment stroke than in the prior art. In this way, the piston can be moved with considerably lower friction, and is more free-moving. 
         [0011]    It is advantageously the case that, during a rapid-traverse retraction movement, the second retraction surface (A 2 ) is acted on with pressure medium and thus connected to the high-pressure side of the hydraulic pump. The first deployment surface (A 1 ) and the first retraction surface (A 3 ) can in this case again be interconnected in substantially unpressurized fashion by means of the circuit. The second deployment surface (A 5 ) can be connected to a low-pressure side of the hydraulic pump. In this way, it is also the case during the rapid-traverse retraction stroke that a relatively small number of seals are subjected to a high pressure. In this way, the piston is extremely free-moving even during retraction movements. 
         [0012]    In a further refinement of the disclosure, in the power deployment stroke, the deployment surfaces (A 1 , A 5 ) are interconnected. In this way, large surfaces are advantageously provided for the power stroke. 
         [0013]    It may additionally be provided that, in the power deployment stroke, the retraction surfaces (A 2 , A 3 ) are interconnected. 
         [0014]    In an extremely simple manner in terms of control, it may be provided that, in the power deployment stroke, the interconnected retraction surfaces (A 2 , A 3 ) are connected via the hydraulic machine to the interconnected deployment surfaces (A 1 , A 5 ). It is thus possible for pressure medium to be delivered by the hydraulic machine from the retraction surfaces (A 2 , A 3 ) to the deployment surfaces (A 1 , A 5 ). 
         [0015]    It is preferably the case that, in the power retraction stroke of the piston, the retraction surfaces (A 2 , A 3 ) are interconnected in parallel, whereby large surfaces are also available for the power retraction stroke. 
         [0016]    In the power retraction stroke of the piston, it is also possible for the deployment surfaces (A 1 , A 5 ) to be interconnected in parallel. 
         [0017]    In an extremely simple manner in terms of control, it may be provided that, also in the power retraction stroke of the piston, the interconnected retraction surfaces (A 2 , A 3 ) are connected via the hydraulic machine to the interconnected deployment surfaces (A 1 , A 5 ). Pressure medium is thus delivered in a simple manner from the deployment surfaces (A 1 , A 5 ) to the retraction surfaces (A 2 , A 3 ) for the purposes of a power retraction stroke. 
         [0018]    In a further refinement of the disclosure, the first deployment surface (A 1 ) and the first retraction surface (A 3 ) are of substantially equal size. Then, if they are interconnected in the rapid-traverse stroke, one pressure surface merely delivers the pressure medium to the other pressure surface, without excess pressure medium having to be supplied or discharged, as would be necessary in the case of pressure surfaces of different size. 
         [0019]    It is advantageously also the case that the second deployment surface (A 5 ) and the second retraction surface (A 2 ) are of substantially equal size. In this way it is for example possible here, too, for pressure medium to simply be delivered from one surface to the other surface in the rapid-traverse stroke. 
         [0020]    In terms of apparatus, it is possible in a simple manner for a connecting valve to be provided for the interconnection of the first retraction surface (A 3 ) and the first deployment surface (A 1 ). The surfaces (A 3 , A 1 ) can then be directly connected by means of said connecting valve. 
         [0021]    In the deployment direction, the piston may have an additional, pressure-relieved surface (A 4 ). The multi-surface cylinder is thus a five-surface cylinder, by contrast to the prior art in DE 10 2012 020 581 discussed in the introduction, in which a four-surface cylinder is provided. 
         [0022]    The second deployment surface (A 5 ) is preferably smaller than the first deployment surface (A 1 ). In this way, in particular in the rapid-traverse deployment stroke of the piston, it is necessary only for the small or relatively small deployment surface (A 5 ) to be acted on with pressure medium or with a pressure. 
         [0023]    The second retraction surface (A 2 ) is advantageously smaller than the first retraction surface (A 3 ). In this way, in particular in the rapid-traverse retraction stroke of the piston, it is necessary only for the small retraction surface (A 2 ) to be acted on with pressure medium or with a pressure. 
         [0024]    It is possible, in a simple manner, for a first control valve to be provided for connecting the second deployment surface (A 5 ) to a first pressure side of the hydraulic machine. For the second retraction surface (A 2 ), a second control valve may be provided for connecting said surface to a second pressure side of the hydraulic machine. Furthermore, it may be provided that the first retraction surface (A 3 ) can be connected by means of a third control valve to the second pressure side of the hydraulic machine. It is preferably also the case that the first deployment surface (A 1 ) can be connected by means of a fourth control valve, and by means of the first control valve arranged fluidically with respect thereto, to the first pressure side of the hydraulic machine. Such an arrangement of control valves is particularly easy to implement in terms of apparatus and is thus inexpensive. 
         [0025]    The control valves are for example designed, in a simple manner, as switchable 2/2 directional valves. A valve slide of the first, second and third control valve is in this case preferably acted on in the direction of a closed position by a spring force of a valve spring, and can be acted on in the direction of an open position by an actuation force of an actuator. By contrast, it may be provided that a valve slide of the fourth control valve is acted on in the direction of its open position by a spring force of a valve spring and can be acted on in the direction of its closed position by an actuation force of an actuator. The connecting valve may be designed correspondingly to the first, second or third control valve. 
         [0026]    A hydraulic accumulator can preferably be fluidically connected directly to the first and/or second pressure side of the hydraulic machine. This is advantageous for a decompression of the cylinder after the power deployment or retraction stroke and/or for a pressure build-up phase for preloading the piston. 
         [0027]    It may be provided that the hydraulic accumulator can be connected directly to the first pressure side of the hydraulic machine via a first accumulator valve and can be connected directly to the second pressure side of the hydraulic machine via a second accumulator valve. Furthermore, it may be provided that the hydraulic accumulator can be connected via a first check valve, which opens in the flow direction away from said hydraulic accumulator, to the first pressure side of the hydraulic machine, and via a second check valve, which opens in the flow direction away from said hydraulic accumulator, to the second pressure side of the hydraulic machine. 
         [0028]    It is advantageously the case that the multi-surface cylinder and the hydraulic machine form a unit and are assembled together. Furthermore, the hydraulic circuit may be provided for the unit. It is conceivable for the hydraulic circuit to be arranged together with the hydraulic machine in a valve block. A drive unit that drives the hydraulic machine can be connected to said valve block. In this way, a compact axle is realized in a simple manner. 
         [0029]    The piston of the multi-surface cylinder may have an annular space which is formed by an inner axial piston rod which is fixed to the piston. Said piston rod may protrude into an approximately hollow cylindrical guide rod which is fixed to a housing. The guide rod in turn may protrude, together with an outer radial collar, into the annular space. Conversely, the piston may protrude by way of an outer and an inner radial collar of its outer shell into an annular space which is delimited by the guide rod and by an outer housing. A structurally simple five-surface cylinder is realized in this way. 
         [0030]    An annular base surface of the piston may then form the first deployment surface (A 1 ). A face surface of the piston rod may constitute the second deployment surface (A 5 ). An annular surface, pointing toward the base surface, of the inner radial collar of the piston may be provided as a second retraction surface (A 2 ). An annular surface, pointing toward the base surface, of the outer radial collar of the piston is then preferably the first retraction surface (A 3 ). An annular face surface, pointing away from the base surface, of the piston may in turn be connected to the atmosphere and constitute the pressure-relieved surface (A 4 ). 
         [0031]    The outer radial collar of the guide rod and the inner radial collar of the piston may engage behind one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    A preferred embodiment of the disclosure will be explained in more detail below on the basis of a drawing. 
           [0033]    The FIGURE shows the hydraulic axle according to the disclosure in a hydraulic circuit diagram. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The single FIGURE illustrates a hydraulic axle  1 . This has a multi-surface cylinder  2  (five-surface cylinder) which can be controlled by means of a hydraulic circuit  4 . For the supply of pressure medium, a reversible hydraulic pump  6  is provided which can be driven, with variable rotational speed, in two directions of rotation by a drive unit  8 . The circuit  4  with the hydraulic pump  6  is arranged in a valve block  10  to which the drive unit  8  and the multi-surface cylinder  2  are connected. From the multi-surface cylinder  2 , four pressure ports A, B, C and E are provided on the valve block  10 . A first deployment surface A 1  of a piston  12  of the multi-surface cylinder  2  is connected to the pressure port A. A second retraction surface A 2  of the piston  12  is fluidically connected to the pressure port B. A first retraction surface A 3  of the piston  12  is in turn connected to the pressure port C. A further, second deployment surface A 5  of the piston  12  is connected to the pressure port E. Furthermore, a surface A 4  which acts in the deployment direction is connected to a pressure port D, which in turn is connected to the atmosphere, whereby the surface A 4  is relieved of pressure. The first, outer annular retraction surface A 3  is of equal size to the first annular deployment surface A 1 . The circular second deployment surface A 5  and the annular second, inner retraction surface A 2  are likewise of equal size. The small second deployment surface A 5  is connected by means of a first switching valve  14  (control valve) to a first pressure side P 1  of the hydraulic pump  6 . The second retraction surface A 2  is connected by means of a second switching valve  16  (control valve) to a second pressure side P 2  of the hydraulic pump  6 . Fluidically in parallel with respect to the second switching valve  16 , a third switching valve  18  (control valve) is connected to the second pressure side P 2  of the hydraulic pump  6 , which third switching valve can connect the first retraction surface A 3  to the second pressure side P 2 . A fourth switching valve  20  (control valve) is arranged fluidically in series with respect to the first switching valve  14 , wherein the first switching valve  14  is arranged between the fourth switching valve  20  and the hydraulic pump  6 . Said fourth switching valve can connect the first deployment surface A 1  to the second deployment surface A 5  and, when the first switching valve  14  is open, can connect the first deployment surface A 1  to the first pressure side P 1 . The connection to the second deployment surface A 5  is provided fluidically between the first switching valve  14  and the fourth switching valve  20 . 
         [0035]    The first deployment surface A 1  and the first retraction surface A 3  can be interconnected by means of a connecting valve  22  (switching valve). The connecting valve  22  is connected to the pressure medium flow path between the first deployment surface A 1  and the fourth switching valve  20 . The connection to the third switching valve  18  branches off from the pressure medium flow path between the first retraction surface A 3  and the connecting valve  22 . 
         [0036]    The circuit  4  furthermore has a hydraulic accumulator  24 . Said hydraulic accumulator can be connected by means of a first accumulator valve  26  (switching valve) to the first pressure side P 1  and by means of a second accumulator valve  28  (switching valve) to the second pressure side P 2  of the hydraulic pump  6 . In this case, the first accumulator valve  26  is connected to the pressure medium flow path between the hydraulic pump  6  and the first switching valve  14 , and the second accumulator valve  28  is connected to the pressure medium flow path between the hydraulic pump  6  and the second switching valve  16 . Furthermore, said accumulator valves are jointly connected to the hydraulic accumulator  24 . A respective check valve  30  and  32  is provided fluidically in parallel with respect to the respective accumulator valve  26  and  28 . Said check valves open in each case in a pressure medium flow direction away from the hydraulic accumulator  24  toward the first pressure side P 1  or second pressure side P 2  respectively. 
         [0037]    The piston  12  of the multi-surface cylinder  2  is guided slidingly in a cylinder housing  34 . Said piston is of hollow cylindrical form, wherein an inner piston rod  38  extends axially in the interior of said piston proceeding from its base  36 . A hollow cylindrical guide rod  42 , which is fixed with respect to the housing, protrudes by way of its shell into the annular chamber  38  thus formed. The piston rod  38  in turn protrudes into a cylinder chamber  44 , which is delimited by the shell, of the guide rod  42 . The guide rod  42  has an outer radial collar on its end and the piston  36  has an inner radial collar, wherein these engage behind one another and delimit an annular space  46 . Furthermore, the piston  12  has an outer radial collar by means of which it, together with the cylinder housing  34 , delimits a further, outer annular space  48 . The first deployment surface A 1  is thus acted on with pressure medium via the annular chamber  40 . The second deployment surface A 5  is acted on with pressure medium via the cylinder chamber  44 . The second and first retraction surfaces A 2 , A 3  are acted on with pressure medium via the annular chambers  46  and  48  respectively. The pressure-relieved surface A 4 , together with an inner shell surface of the cylinder housing  34  and an outer shell surface of the guide rod  42 , delimits a pressure-relieved annular space  50 . In this case, the surface A 4  points away from the surfaces A 2  and A 3 . 
         [0038]    The mode of operation of the hydraulic axle will be described below. 
         [0039]    Rapid-traverse deployment stroke: 
         [0040]    In the rapid-traverse deployment stroke, the hydraulic pump  6  delivers pressure medium from its second pressure side P 2  to its first pressure side P 1 . Actuators of the switching valves  14  and  16  are energized and the switching valves  14 ,  16  are thus open. The actuator of the fourth switching valve  20  is likewise energized, as a result of which said fourth switching valve is closed. Furthermore, the actuator of the connecting valve  22  is energized, and said connecting valve is thus open. The other switching valves  18 ,  26  and  28  are deenergized, and closed. Owing to the connecting valve  22  being open, the second deployment surface A 1  and the first retraction surface A 3 , which is of equal size, are interconnected and separated from the other piston surfaces. The hydraulic pump  6  now delivers pressure medium from the second retraction surface A 2  via the switching valve  16  to the switching valve  14  and onward to the second deployment surface A 5 , as a result of which the piston  12  is deployed. During said deployment movement, therefore, only the second deployment surface A 5  is subjected to pressure, as a result of which only a small number of seals of the multi-surface cylinder  2  are subjected to a high pressure. The piston  2  can thus be deployed in a freely moving manner. 
       Power Deployment Stroke: 
       [0041]    In this case, the hydraulic pump  6  again delivers pressure medium from the second pressure side P 2  to the first pressure side P 1 . Now, both deployment surfaces A 1  and A 5  are connected to the high-pressure side of the hydraulic pump  6 , that is to say to the first pressure side P 1 . For this purpose, the switching valves  14  and  20  are open and the connecting valve  22  is closed. Furthermore, the first and second retraction surfaces A 3 , A 2  have a pressure medium connection to the low-pressure side of the hydraulic pump  6 , that is to say to its second pressure side P 2 . For this purpose, the switching valves  16  and  18 , which are fluidically in parallel, are open. The accumulator valves  26  and  28  are closed. The hydraulic pump  6  now delivers pressure medium from the retraction surfaces A 2 , A 3  via the switching valves  16 ,  18  to the deployment surfaces A 1  and A 5  via the switching valves  14  and  20 . 
         [0000]    Decompression after the Power Deployment Stroke: 
         [0042]    In the decompression after the power deployment stroke, the deployment surfaces A 1  and A 5  are connected to the hydraulic accumulator  24 , and the retraction surfaces A 2  and A 3  are shut off. For the connection of the deployment surfaces A 1  and A 5  to the hydraulic accumulator  24 , the first switching valve  14  and the fourth switching valve  20  are opened. Furthermore, the second accumulator valve  28  is opened. The second switching valve  16 , the third switching valve  18  and the connecting valve  22  are closed. The hydraulic pump  6  delivers pressure medium from its first pressure side P 1  to its second pressure side P 2 . Thus, pressure medium is delivered from the first deployment surface A 1  and the second deployment surface A 5  via the fourth switching valve  20  and the first switching valve  14  to the hydraulic accumulator  24  via the second switching valve  28 . 
       Rapid-Traverse Retraction Stroke: 
       [0043]    In the rapid-traverse retraction stroke, the hydraulic pump  6  delivers pressure medium from its first pressure side P 1  to its second pressure side P 2 . The first deployment surface A 1  and the first retraction surface A 3  are interconnected by means of the connecting valve  22  and are fluidically separated from the other piston surfaces. The first and second switching valves  14  and  16  are open. The third and fourth switching valves  18  and  20  are closed. Furthermore, the accumulator valves  26  and  28  are closed. The hydraulic pump  6  now delivers pressure medium from the second deployment surface A 5  via the first switching valve  14  to the second retraction surface A 2  via the second switching valve  16 . 
       Power Retraction Stroke: 
       [0044]    In this case, the hydraulic pump  6  delivers pressure medium from its first pressure side P 1  to its second pressure side P 2 . In the power retraction stroke, pressure medium is delivered from the deployment surfaces A 1  and A 5  to the retraction surfaces A 2  and A 3 . For this purpose, all of the switching valves  14  to  20  are open. The accumulator valves  26 ,  28  and the connecting valve  22  are closed. The hydraulic pump  6  then delivers pressure medium from the deployment surfaces A 1  and A 5  via the switching valves  14 ,  20  to the retraction surfaces A 2  and A 3  via the switching valves  16 ,  18 . 
         [0000]    Decompression after the Power Retraction Stroke: 
         [0045]    The hydraulic pump  6  delivers pressure medium from its second pressure side P 2  to its first pressure side P 1 . In the decompression, the retraction surfaces A 2  and A 3  are connected to the hydraulic accumulator  24 , whereas the deployment surfaces A 1  and A 5  are shut off. The second and third switching valves  16  and  18  and the first accumulator valve  26  are open. The first switching valve  14  and the connecting valve  22  are closed. If required, the fourth switching valve  20  may also be closed. The hydraulic pump  6  now delivers pressure medium from the retraction surfaces A 2  and A 3  via the switching valves  16  and  18  to the hydraulic accumulator  24  via the accumulator valve  26 . 
       Pressure-Holding Phase: 
       [0046]    In the pressure-holding phase, all of the switching valves  14  to  20  and the connecting valve  22  are closed in order that pressure medium at the deployment surfaces A 1 , A 5  and at the retraction surfaces A 2 , A 3  cannot escape, and the piston  12  is braced in its position. 
       Pressure Build-Up Phase for Preloading: 
       [0047]    In the pressure build-up phase for preloading, the deployment surfaces A 1  and A 5  and the retraction surfaces A 2  and A 3  are connected to the hydraulic accumulator  24 . The hydraulic pump  6  delivers pressure medium from the first pressure side P 1  to the second pressure side P 2 . The first switching valve  14  and the accumulator valves  26  and  28  are closed. The switching valves  16 ,  18  and  20  and the connecting valve  22  are open. The hydraulic pump  6  can now deliver pressure medium from the hydraulic accumulator  24  via the first check valve  30  to the deployment surfaces A 1  and A 5  and to the retraction surfaces A 2  and A 3 . 
         [0048]    The disclosure discloses a hydraulic axle with a reversible hydraulic pump. The axle has a multi-surface cylinder with two retraction surfaces and two deployment surfaces. In a rapid-traverse stroke, a first deployment surface and a first retraction surface can be interconnected and separated from the other surfaces. For deployment, the second deployment surface is acted on with pressure medium. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  Hydraulic axle 
           2  Multi-surface cylinder 
           4  Circuit 
           6  Hydraulic pump 
           8  Drive unit 
           10  Valve block 
           12  Piston 
           14  First switching valve 
           16  Second switching valve 
           18  Third switching valve 
           20  Fourth switching valve 
           22  Connecting valve 
           24  Hydraulic accumulator 
           26  First accumulator valve 
           28  Second accumulator valve 
           30  First check valve 
           32  Second check valve 
           34  Cylinder housing 
           36  Base 
           38  Piston rod 
           40  Annular chamber 
           42  Guide rod 
           44  Cylinder chamber 
           46  Annular space 
           48  Annular space 
           50  Annular space 
         A 1  First deployment surface 
         A 2  Second retraction surface 
         A 3  First retraction surface 
         A 4  Pressure-relieved surface 
         A 5  Second deployment surface 
         P 1  First pressure side 
         P 2  Second pressure side