Abstract:
In an axial-piston machine of the swashplate or oblique-axis type of construction, a contact face of the cylinder head ( 1 ) is pressed against a stationary sealing face. The contact face has located in it transition orifices ( 15   a ) for the exchange of hydraulic fluid between the cylinder head ( 1 ) and the stationary part. The transition orifices ( 15   a ) are located on a raised annular collar ( 13 ) of the end face ( 11 ) of the cylinder head ( 1 ). Microgrooves ( 21 ) are recessed in the annular collar ( 13 ) between the individual transition orifices ( 15   a ), so that, of the supporting face, only two edge webs ( 13   a,    13   b ) remain. The depth of the microgrooves ( 21 ) is only a few hundredths of a millimeter. This design prevents a hydrodynamic carrying effect between the cylinder head and the stationary part.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to an axial-piston machine of the swashplate or oblique-axis type of construction, with a rotating cylinder block, with displacer spaces which are arranged in the form of a ring in the cylinder block and run parallel to the axis of rotation of the cylinder block and in which pistons are received slideably, with transition orifices of the displacer spaces, the said transition orifices issuing into an end contact face of the cylinder block, and with a stationary supporting face for the end contact face of the cylinder block, the supporting face having provided in it orifices which are connected alternately to the transition orifices of the cylinder block during the rotation of the latter, and the contact faces of the cylinder block and the supporting face being pressed against one another in a sealed-off manner.  
         [0002]     Axial-piston machines of this type are generally known. As a rule, kidney-shaped orifices of the stationary supporting face are located opposite the transition orifices of the cylinder block which are arranged regularly and at close intervals in the contact face. The object of these kidney-shaped orifices is to connect the displacer spaces of the cylinder block alternately, in each case for half a revolution, to a high-pressure and a low-pressure connection. Sealing webs in the stationary supporting face in this case separate the kidney-shaped orifice of the high-pressure region from those of the low-pressure region.  
         [0003]     Periodic and very rapid pressure-change processes occur in the sealing face between the contact face of the cylinder block and the stationary supporting face, so that the pressure conditions in the sealing face are not constant. To be precise, when the sealing webs, that is to say the sheet-like interspaces between the transition orifices of the cylinder block and the kidney-shaped orifices of the stationary supporting face, lie on one another, a considerable hydrodynamic carrying pressure may build up in the gap which has a height of only a few μm. However, this carrying pressure collapses again when, after a rotary travel of the cylinder block of only a few degrees of angle, a transition orifice of the cylinder block is again located opposite the sealing web of the stationary supporting face. These constantly changing pressure conditions in the sealing gap contribute to an uneven running of the axial-piston machine which is manifested in an unpleasant way in vibrations and troublesome noises.  
         [0004]     In order to keep the force pressing the cylinder block away from the supporting face low, it has already been proposed to design the transition from the displacer spaces of the cylinder block to the transition orifices in the form of block kidneys, the individual transition orifices then being in the form of annular segments in the shape of an arc of a circle. Efforts were made, furthermore, to slow the pressure build-up in the displacer space and consequently to reduce vibration and troublesome noise. This resulted in the orifices in the stationary supporting face having a kidney-shaped design and being separated from one another by sealing webs, reversal notches issuing from the kidney-shaped orifices into the sealing webs. When the contact face of the cylinder block sweeps over the stationary supporting face, a transition orifice of the cylinder block then briefly connects two adjacent kidney-shaped orifices. This, however, entails internal leakage losses. Moreover, the said measures involve structural constraints which can often be combined poorly with other structural requirements in the detailed design of axial-piston machines.  
         [0005]     The object on which the invention is based, in an axial-piston machine of the type mentioned in the introduction, is to improve further the smooth running and low noise in a structurally simple way.  
         [0006]     These and other objects will be apparent to those skilled in the art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     In an axial-piston machine of the type mentioned in the introduction, this object is achieved, according to the invention, to be precise by the formation of microgrooves in the end contact face of the cylinder block between adjacent transition orifices.  
         [0008]     The term “microgroove” means a depression which emanates from the end contact face of the cylinder block and the depth of which is very small in relation to its width. The absolute value of the depth is governed by the size of the machine; however, it will generally be of the order of magnitude of 10 to 100 μm.  
         [0009]     The design according to the invention seems at first sight to be absurd, since, of course, because of this there is no longer the full extent of sealing action between the adjacent displacer spaces. It has been shown, however, that the advantage achieved thereby, to be precise the substantial reduction in a hydrodynamic carrying pressure in the sealing face between the cylinder block and the stationary supporting face, carries far more weight. The disadvantage is naturally some leakage flow through the microgroove, although this flow remains very low. To be precise, a leakage gap of this order of magnitude constitutes considerable flow resistance, so that internal leakage will remain very low.  
         [0010]     In an advantageous design of the axial-piston machine according to the invention, in which the end contact face is located on an annular collar projecting from the remaining end face of the cylinder block, the microgrooves form segments of an annular groove running within the annular collar and extending over all the transition orifices. The peripheral annular collar is in any case recessed in the region of the transition orifices, so that only narrow annular webs remain on both sides in the radial direction. In the design according to the invention, a depression in the form of the said segment is also present in the region of connection between two transition orifices, so that the two annular webs which remain in the collar have a closed circular face and with their end faces alone form the contact face of the cylinder block. This design is advantageous in manufacturing terms and especially ensures a smooth running of the axial-piston machine.  
         [0011]     By virtue of the configuration according to the invention, the already known measures for the reduction of pressure pulsations and noises may readily be combined. Thus, for example, the individual displacer spaces of the cylinder block may merge in the form of a block kidney into their transition orifice, the individual transition orifices being in the form of annular segments in the shape of an arc of a circle. The annular segments of the transition orifices and of the microgrooves then alternate with one another in the contact face of the cylinder block.  
         [0012]     Furthermore, even in the case of axial-piston machines in which the orifices in the stationary supporting face have a kidney-shaped design and are separated from one another by sealing webs, it is possible to preserve the arrangement of reversal notches which issue from the kidney-shaped orifices into the sealing webs in such a way that, when the contact face of the cylinder block sweeps over the stationary supporting face, a transition orifice can briefly connect two adjacent kidney-shaped orifices.  
         [0013]     The advantage of the last-mentioned combination is, above all, that the reversal notches can then be made smaller, thus making further structural free spaces available. The leakage streams possibly occurring due to the microgrooves can as it were be partly avoided again by using the reversal notches.  
         [0014]     The end face of a valve plate advantageously serves as the stationary supporting face.  
         [0015]     Although the depth of the microgrooves in the axial-piston machine according to the invention depends largely on the size of the latter, the diameter of the cylinder block being decisive, an advantageous standard value which can be specified there for the depth of the microgroove, starting from the contact face of the cylinder block, is a range of between 5 and 200 μm, preferably of between 10 and 100 μm. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The invention is subsequently explained in more detail by means of an exemplary embodiment illustrated in the figures. The figures illustrate the following:  
         [0017]      FIG. 1  is a longitudinal section through an axial-piston machine according to the prior art in a greatly simplified illustration.  
         [0018]      FIG. 2  illustrates a view of the end face of the cylinder block in the viewing direction X according to  FIG. 1 .  
         [0019]      FIG. 3  reproduces the view of the end face of the valve plate in the viewing direction Y according to  FIG. 1 .  
         [0020]      FIG. 4  shows the view corresponding to  FIG. 2  in the case of an axial-piston machine designed according to the invention.  
         [0021]      FIG. 5  relates to a greatly enlarged sectional view of a radial section through the end face of the cylinder head in the region of the supporting face. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     FIGS.  1  to  3  show the design of an axial-piston machine according to the prior art. About a central journal  4  rotates a cylinder block  1  which is provided with displacer spaces  8  running axially. In the example illustrated, there are nine displacer spaces  8 , cf.  FIG. 2 . In the displacer spaces  8  slide the pistons  2  which are acted upon axially by the rotating drive flange  3 . The axis of rotation  9  of the drive flange  3  runs obliquely to the axis of rotation  10  of the cylinder block  1 . The pistons  2  thereby execute a lifting movement with the action of sucking in and expelling hydraulic fluid.  
         [0023]     5 designates a valve plate, through which the hydraulic fluid is supplied to the displacer spaces  8  of the cylinder block  1  and discharged. The cylinder block  1  is prestressed axially against the valve plate  5  by means of a pressure spring  7  arranged on the axial bearing  6  of the said cylinder block. In this case, the end face  11  of the cylinder block  1  bears at least with a contact face against the end face  12  of the valve plate  5 , the said end face forming a stationary supporting face  12 . A sealing face is thereby formed between two parts rotating relative to one another, to be precise the cylinder block  1  and the valve plate  5 . The emergence of hydraulic fluid from the sealing face outwards should as far as possible be avoided.  
         [0024]     According to the illustration in  FIG. 1 , the cylinder block  1  bears with its entire end face  11  against the end face of the valve plate  5 . However, this is not necessary and even not expedient. A technically detailed design is shown in  FIG. 2 . According to this, the actual contact face  14  with which the cylinder block touches the valve plate consists of the end face or a relatively narrow annular collar  13 . This becomes clearly apparent in  FIG. 2 , particularly from the accompanying part-section A-A. The block kidneys  15  are led through the annular collar  13 . They connect the displacer spaces  8  to the valve plate  5 . In comparison with the inside diameter d of the displacer spaces  8 , the block kidneys  15  have an extent a in the circumferential direction which is greater than d and a radial extent b which is smaller than d. Owing to the configuration of the annular collar  13  and of the block kidneys  15 , the width c of the sealing webs  16  between the block kidneys  15  for the cylinder block  1  is reduced, without the outlet cross sections of the displacer spaces  8  in the contact face becoming too large.  FIG. 2  shows, further, that only very narrow edge webs  13   a,b  remain in the annular collar  13  in the region of the block kidneys  15  radially on the two sides of these.  
         [0025]     Kidney-shaped orifices  17  are provided in the valve plate  5 . Their task is to connect the displacer spaces  8  of the cylinder block  1  alternately, in each case for half a revolution, to a high-pressure and a low-pressure connection. Sealing webs  18  of the valve plate  5  in this case separate the kidney-shaped orifice  17  of the high-pressure region from those of the low-pressure region. Moreover, a reinforcing web  19  is provided in the middle of the arcuate extent of each kidney-shaped orifice  17 , so that the valve plate  5  can generally withstand the very high pressure stress in the region of the kidney-shaped orifices  17 . A plurality of reinforcing webs may also be present at each kidney-shaped orifice.  
         [0026]     When the axial-piston machine is in operation, the contact face  14  is exposed to complex stress. On the one hand, it acts as an axial plain bearing for the cylinder block  1  loaded with the axial force of the pressure spring  7  and for a part of the pressure force of the hydraulic fluid; on the other hand, it must seal off the pressurized displacer spaces  8  by means of the annular collar  13  in relation to the pressureless surroundings. In the reversal region, that is to say whenever a sealing web  16  of the cylinder block  1  sweeps over a sealing web  18  of the valve plate  5 , the annular collar  13  must also bring about sealing-off between two adjacent displacer spaces  8  or their associated block kidneys  15 .  
         [0027]     A pressure field which largely compensates the said axial forces builds up in the sealing face between the cylinder block  1  and the valve plate  5 . However, since periodic and very rapid pressure changes occur in the displacer spaces  8 , the pressure conditions in the sealing face are not constant. The force and moment balance at the cylinder block  1  is subject to rapid fluctuations, and uneven running occurs. This may be further intensified by disturbances introduced from outside, for example by pressure fluctuations in the connecting lines and by vibrations. To be precise, when a sealing web  16  between two block kidneys  15  runs over a sealing web  18  of the valve plate  5 , a considerable hydrodynamic carrying pressure may build up in the gap which has a height of only a few micrometers. However, this carrying pressure collapses again when, after a rotary travel of only a few degrees of angle, the sealing web  18  of the valve plate no longer has located opposite it a sealing web  16  of the cylinder block  1 , but, instead, a block kidney  15  which is connected to its associated displacer space  8 . The same effect may arise at the reinforcing webs  19 .  
         [0028]     The outlined design of the block kidneys  15  can only partially compensate the disadvantage shown. If the sealing webs  18  between the block kidneys  15  are to be made very narrow, the block kidneys  15  must be made long in the circumferential direction, that is to say the dimension a must be enlarged. This, however, increases the pressure-loaded area and consequently the force acting on the cylinder block  1  with a pressing-away effect. Since the latter must always remain lower than the force having a pressing-on effect, compensation is required elsewhere and can take place only by a reduction in the radial width of the annular collar  13 . Then, however, the edge webs  13   a,b  become very narrow, and the external leakage increases as a result.  
         [0029]     Moreover,  FIG. 3  also shows reversal notches  20  in the entrance and exit of the kidney-shaped orifices  17 . The reversal notches are arranged in such a way that a short circuit in the flow of the hydraulic fluid occurs for a few degrees of angle in the rotation of the cylinder block  1 . A transition orifice  15   a , depicted by broken lines at the top in  FIG. 3 , is then for a short time connected simultaneously to both kidney-shaped orifices, albeit only over relatively small throttle cross sections. With this measure, some internal leakage is deliberately brought about, that is to say some impairment of the volumetric efficiency is deliberately taken into account. Instead, however, noise reduction and an improvement in the internal adjustment forces are achieved.  
         [0030]     In  FIGS. 4 and 5 , according to the invention, the end contact face  14  which is located on the annular collar  13  is provided in the region of the sealing webs  16  with depressions which are designed as microgrooves  21 . Only the edge webs  13   a,b  remain on both sides of the microgrooves  21  and in a similar way delimit the transition orifices  15   a  in the radial direction. This gives rise, within the annular collar  31 , to a peripheral annular groove in which the transition orifices  15   a  alternate with the microgrooves  21 . The microgrooves  21  are segments of this annular groove and are separated from one another by the transition orifices  15   a . In the design according to the invention, the contact face  14  is formed only by the edge webs  13   a,b.    
         [0031]     The depth of the microgrooves, starting from the contact face  14 , is about 50 to 100 μm and depends on the size of the axial-piston machine, in particular on the outside diameter of the cylinder block  1 . Where large units are concerned, a depth range of 130 to 200 μm will come into consideration.  
         [0032]     By the contact face  14  being drawn in or shouldered in the region of the sealing webs  16 , this largely prevents the possibility of a hydrodynamic carrying pressure being formed in the sealing face between the cylinder block and the valve plate  5 . The leakage gap formed by the microgrooves constitutes considerable flow resistance, so that internal leakage between the displacer spaces in the reversal region, that is to say when they sweep over the sealing webs  18  of the valve plate S, will remain relatively low. As compared with this, the advantage of having largely prevented the generation of the hydrodynamic carrying pressure carries much more weight.  
         [0033]     The microgrooves provided according to the invention may advantageously be associated with the already known measures for improving the sealing action and the running behavior. Thus, as before, the transition orifices  15   a  may be formed by block kidneys  15  which vary the outlet cross section of the displacer spaces  8 .  
         [0034]     Furthermore, the reversal notches  20  at the edges of the kidney-shaped orifices  17  in the valve plate  5  may also be preserved. If the microgrooves  21  result in additional internal leakage, this can be partially or even completely compensated with the reversal notches  20 ; these are then compensated in such a way that the short-circuit angle range and/or the throttle cross sections in this region are reduced.  
         [0035]     The geometry of the reversal notches  20  serves for influencing a large number of different properties of the axial-piston machine. Due to the limited possibilities of the configuration, a compromise is only ever achieved where these properties are concerned. However, since, by virtue of the invention, the subfunction of the “limited short circuit” is transferred to another component, to be precise the microgrooves, the freedom of configuration in the case of the reversal notches is increased. These consequently become genuine fine-control notches, by means of the geometry of which the remaining functions of the axial-piston machine can be set more independently than hitherto.  
         [0036]     Advantages also arise with regard to sensitivity to soiling: small particles can pass via the grooves from the high-pressure to the low-pressure side, without damaging the sealing faces. At least some of the particles can be filtered out, without having caused damage beforehand.  
         [0037]     Whereas the invention has been shown and described in connection with the embodiments thereof, it will be understood that many modifications, substitutions, and additions may be made which are within the intended broad scope of the following claims. From the foregoing, it can be seen that the present invention accomplishes at least all of the stated objectives.