Abstract:
An axial piston machine ( 1 ) which includes a cylinder block ( 2 ) having cylinder bores ( 3, 4 ) in which pistons ( 5, 6 ) are movably guided, with the pistons ( 5, 6 ) being supported on an inclined or wobble plate ( 25 ) in order to perform a lifting movement. The axial piston machine ( 1 ) further includes a pivot device ( 31 ) for varying the inclination of the inclined or wobble plate ( 25 ) by pivoting about a pivot axis ( 27 ). Provided is a damping element ( 41 ) which includes a damping piston ( 40 ) which acts on the inclined or wobble plate ( 25 ) and is movably disposed in a damping cylinder ( 42 ) which is connected to a pressure fluid reservoir ( 48 ) via a throttle element ( 47 ) and a non-return valve ( 44 ) is disposed parallel thereto. The non-return valve ( 44 ) enables pressure fluid to flow in an unthrottled manner from the pressure fluid reservoir ( 48 ) into the damping cylinder ( 42 ) and prevents the pressure fluid from flowing out of the damping cylinder ( 42 ) in an unthrottled manner by bypassing the throttle element ( 47 ). In this way, a damped pivoting movement of the inclined or wobble plate ( 25 ) is brought about.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an axial piston machine according to the preamble of claim  1  including a cylinder block having cylinder bores provided therein for the displaceable guidance of pistons so as to execute a lifting movement against an inclined or wobble plate. A pivoting device is adapted to change the inclination of the inclined or wobble plate by pivoting ht latter about a pivot axis. 
     2. Discussion of the Prior Art 
     An axial piston machine of this type is known for example, from DE 34 28 591 A1. In this axial piston machine, a plurality of cylinder bores, in which pistons are displaceably guided, are formed in known manner in a rotating cylinder block. The pistons are supported via slippers against a non-rotating inclined plate. The inclination of the inclined plate, which determines the displacement volume of the axial piston machine, is adjustable by means of a hydraulic adjusting piston, in that the inclined plate is pivotable through a given angle range about a pivot axis. When the inclined plate is pivoted back from the lift position in the direction of the zero lift position, the adjusting pressure acting upon the hydraulic adjusting piston is increased and the inclined plate pivots back until it reaches the zero lift position by abutting against an abutment surface. However, the movement of the inclined plate is relatively uncontrolled, so that the inclined plate strikes hard against the abutment surface upon reaching the zero lift position. This is undesirable, since it increases wear to the abutment and the inclined plate and also results in a mechanical impact loading of the entire axial piston machine. 
     Disclosed in DE 44 40 452 A1 is an axial piston machine with an inclined plate construction, in which two separate hydraulic cylinders are provided for the variation in the inclination of the inclined plate. In this respect, one of the hydraulic cylinders is used for pivoting the inclined plate outwards and the second hydraulic cylinder is used for pivoting the inclined plate back. Whilst the inclined plate is guided in a controlled manner during the entire movement sequence in this solution, the second hydraulic cylinder requires a comparatively large structural outlay, which results in relatively high manufacturing costs. Furthermore, a separate hydraulic control of both hydraulic cylinders is required. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to further develop an axial piston machine having an inclined or wobble plate construction in such a manner that the movement sequence during the pivoting of the inclined or wobble plate is not effected abruptly but continuously. 
     The invention is based upon the knowledge that the pivoting back of the inclined or wobble plate can be controlled by providing a damping element acting upon the inclined or wobble plate. The damping piston is displaceably arranged in a damping cylinder, which is connected via a throttle element and a non-return valve arranged parallel to the throttle element to a pressure fluid reservoir. In this respect, the non-return valve allows for an unthrottled supply of the pressure fluid from the pressure fluid reservoir into the damping cylinder and prevents an unthrottled outflow of the pressure fluid from the damping cylinder bypassing the throttle element. 
     According to the invention, a restoring spring can act upon the damping piston in such a manner that the damping piston draws further pressure fluid out of the pressure fluid reservoir via the non-return valve and optionally via the throttle valve as soon as the damping piston is freely movable in the direction of an increase in volume of the damping cylinder. In this manner, it is ensured that the damping cylinder is instantaneously refilled with pressure fluid and therefore that the pivoting movement of the inclined or wobble plate occurs directly. According to an inventive aspect, the pressure medium reservoir can be a leakage fluid collecting chamber surrounding the damping element, the leakage fluid collecting chamber usually being formed by the housing interior of the axial piston machine. 
     According to a further feature, the inclined or wobble plate can have a first pivot position with a larger angle of inclination and a second pivot position with a smaller angle of inclination and can be pivoted back and forth between these two pivot positions. According to invention, the axial piston machine can also be designed with an inclined plate construction, it being possible to arrange the damping element in the inclined plate or in a stationary counter element opposing the inclined plate according to FIG.  9 . In this respect, the restoring spring holds the damping piston in abutment against the inclined plate or against the stationary counter element. 
     According to the invention, the inclined plate can also comprise a first and a second abutment surface on its side facing away from the pistons, the abutment surfaces each forming an abutment for the first and second pivot position of the inclined plate. 
     According to another feature, it is particularly advantageous to offset the point of application, at which the damping piston acts upon the inclined plate, relative to the cylinder block axis in such a manner that the resulting force, which is composed of the force exerted by the damping piston upon the inclined plate, the force exerted by the pivoting device upon the inclined plate during the pivoting procedure and the force exerted by the pistons upon the inclined plate, acts at a center of gravity of the forces which is located on the cylinder block axis. In this manner, non-symmetrical bearing forces are prevented and a levering-out of the bearing is avoided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail in the following with the aid of preferred embodiments with reference to the drawings, in which: 
     FIG. 1 is a partial axial section through a first embodiment of the axial piston machine further developed according to the invention in a first pivot position of the inclined plate; 
     FIG. 2 shows the first embodiment illustrated in FIG. 1 of the axial piston machine further developed according to the invention in a second pivot position of the inclined plate; 
     FIG. 3 is a schematic illustration of the method of operation of the damping element; 
     FIG. 4A shows the force distribution in the embodiment illustrated in FIG. 1 of the axial piston machine further developed according to the invention; 
     FIG. 4B is a side view of the illustration according to FIG. 4A; 
     FIG. 4C is a plan view of the illustration according to FIG. 4A; 
     FIG. 5 is a partial axial section through a second embodiment of the axial piston machine further developed according to the invention in a second pivot position of the inclined plate; 
     FIG. 6 shows the second embodiment illustrated in FIG. 5 of the axial piston machine further developed according to the invention in a second pivot position of the inclined plate. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG.  1  and FIG. 2 are axial longitudinal sections through an only partially illustrated axial piston machine  1  further developed according to the invention. The axial piston machine  1  illustrated by way of example in FIG.  1  and FIG. 2 is designed with an inclined plate construction and comprises a cylinder block  2 , in which a plurality of cylinder bores  3 ,  4  are provided, which are arranged uniformly distributed over a graduated circle. Displaceably arranged in the cylinder bores  3 ,  4  are pistons  5 ,  6 . The cylinder bores  3 ,  4  are connected via connecting ducts  7 ,  8  to the kidney-shaped control apertures  9 ,  10  of a stationary control disc  11 . The cylinder block  2  rotates about the cylinder block axis  12 , so that the cylinder bores  3 ,  4  are cyclically connected to a low pressure line, not shown, which is connected to the control aperture  9 , and a high pressure line, not shown, which is connected to the control aperture  10 . The pistons  5 ,  6  are molded at their ends remote from the control disc  11  to form spherical heads  13 ,  14 , which are mounted in spherical bearings  15 ,  16  of slippers  17 ,  18  associated with the pistons  5 ,  6 . The pistons  5 ,  6  are constructed as hollow pistons and each comprise a piston recess  19 ,  20 . For hydrostatic relief, the piston recesses  19 ,  20  are connected via connecting ducts  21 ,  22  of the pistons  5 ,  6  and also via connecting ducts  23 ,  24  of the slippers  17 ,  18  to push-buttons provided on the slippers  17 ,  18 . 
     The pistons  5 ,  6  are supported via the slippers  17 ,  18  against a slide surface  26  of the inclined plate  25 . The inclined plate  25  is mounted so as to pivot about a pivot axis  27  and on its side facing away from the pistons  5 ,  6  comprises a first abutment surface  28  and a second abutment surface  29 . When the inclined plate rests with its first abutment surface  28  against a stationary counter element  30 , as shown in FIG. 1, the inclined plate or its slide surface  26  is inclined relative to the cylinder block axis  12  with a first, relatively large angle of inclination. In contrast, when the inclined plate rests with its second abutment surface  29  against the stationary counter element  30 , as shown in FIG. 2, the inclined plate or its slide surface  26  is inclined relative to the cylinder block axis  12  with a second angle of inclination, which is smaller than the first angle of inclination. In the embodiment, the inclination of the inclined plate  25  can therefore be pivoted back and forth between two distinct pivot positions by means of a pivoting device  31 , only schematically indicated. The pivoting device  31  can comprise a hydraulically actuated adjusting piston, for example, which acts upon the inclined plate  25  in a force-locking manner. 
     According to the invention, the damping piston  40  of a damping element generally designated by the reference  41  also acts upon the inclined plate  25 . In the embodiment illustrated in FIGS. 1 and 2, the damping element  41  is integrated in the inclined plate  25 . The damping piston  40  is displaceably arranged in a damping cylinder  42  provided in the inclined plate  25  in the embodiment of FIGS. 1 and 2. The damping cylinder  42  is constructed as a blind bore, which opens onto the second abutment surface  29  of the inclined plate  25 . The damping piston  40  is brought into abutment against the stationary counter element  30  by means of a restoring spring  43  also arranged in the damping cylinder  42 . The stationary counter element  30  can be a housing end plate, for example. The damping cylinder  42  is connected via a non-return valve  44  and a supply duct  45  to the housing interior  46 , which encloses the inclined plate  25  and the cylinder block  2 , acts as a leakage fluid collecting chamber and is accordingly filled with leakage fluid. The damping cylinder  42  is additionally connected via a throttle element  47  to the housing interior  46  of the axial piston machine  1 . In the illustrated embodiment, the throttle element  47  is constructed as a bore with a relatively small cross section. The supply duct  45  and the non-return valve  44  are thus arranged parallel to the throttle element  47 . 
     The damping element  41  according to the invention operates as follows: 
     When the inclined plate  25  is pivoted from the second pivot position illustrated in FIG. 2 in the direction of the first pivot position illustrated in FIG. 1 as a result of a relief of the pivoting device  31 , then the damping piston  40  is brought into abutment against the stationary counter element  30  by means of the restoring spring  43 . During this procedure, pressure fluid is drawn via the supply duct  45  and the opened non-return valve  44  and parallel via the throttle element  47  out of the housing interior  46  filled with leakage fluid. The filling of the damping cylinder  42  is effected via the supply duct  45  and the non-return valve  44  so speedily that the damping piston  40  is held in continuous abutment against the stationary counter element  30 . 
     Conversely, when the pivot plate  25  is pivoted from the first pivot position illustrated in FIG. 1 into the second pivot position illustrated in FIG. 2 as a result of actuation by means of the pivoting device  31 , the non-return valve  44  closes the supply duct  45  and the pressure fluid located in the damping cylinder  42  can only flow out of the damping cylinder  42  via the throttle element  47 . In this manner, the desired damping is attained and the pivoting movement of the inclined plate  25  is prevented from occurring abruptly so that the abutment surface  29  strikes sharply against the stationary counter element  30 . This would result in relatively rapid wear of the pivot plate  25  and the stationary counter element  30 . In addition, the entire axial piston machine  1  would be subjected to impact loading during this pivoting movement, which is undesirable. 
     As a result of the damping element  41  provided according to the invention, the pivoting procedure is therefore slightly delayed and a continuous, non-abrupt pivoting movement of the inclined plate  25  is attained. Furthermore, in the second pivot position illustrated in FIG.  2  and during pivoting from the first pivot position illustrated in FIG. 1 into the second pivot position illustrated in FIG. 2, the damping element  41  according to the invention ensures a certain degree of support of the section of the inclined plate  25  disposed above the pivot axis  27 , so that the loading to which the inclined plate  25  is subjected is advantageously reduced by the further development according to the invention. 
     FIG. 3 illustrates the method of operation of the damping element  41  according to the invention by way of a hydraulic equivalent circuit diagram. Elements which have already been described are provided with corresponding reference numerals in order to facilitate the allocation of numerals. As already described, the suction of pressure fluid from a pressure fluid reservoir  48 , which can be the housing interior  46 , for example, is effected via the supply duct  45  and the non-return valve  44  arranged between the supply duct  45  and the damping cylinder  42 . Arranged parallel to the non-return valve  44  and the supply duct  45  is the throttle element  47 , which ensures a throttled outflow of the pressure fluid from the pressure fluid cylinder  42  into the pressure fluid reservoir  48  with the non-return valve  44  closed. 
     FIGS. 4A to  4 C illustrate the distribution of forces in the axial piston machine  1  according to the invention according to the embodiment already explained with the aid of FIGS. 1 and  2 . In this respect, FIG. 4A is a drawing corresponding to FIG. 1, whilst FIG. 4B is a side view in the direction of the side of the inclined plate  25  facing away from the pistons  5 ,  6  and FIG. 4C is a plan view of the arrangement illustrated in FIG.  4 A. 
     As shown in FIGS. 4A to  4 C, the inclined plate  25 , as it is adjusted, is acted upon by the force component F V  exerted by the pivoting device  31 , the bearing force F L/R  exerted upon the bearing of the pivot axis  27 , the force F DR  exerted by the damping pistons  40   a  and  40   b,  of which there are two in the embodiment, and the force F KL  exerted in the opposite direction by the pistons  5 ,  6 . In this respect, it is particularly advantageous if the point of application, at which the respective damping piston  40   b  or  40   a  acting on the right or left acts upon the inclined plate  25 , is offset relative to the cylinder block axis in such a manner that the resulting force, composed of the force F DR  exerted by the corresponding damping piston  40   b  or  40   a  upon the inclined plate  25 , the force F V  exerted by the pivoting device  31  upon the inclined plate  25  during the pivoting procedure and the force F KL  exerted by the pistons  5 ,  6  upon the inclined plate  25 , acts at a centre of gravity of the forces (S) which is located on the cylinder block axis  12 . In this manner, a symmetrical distribution of the bearing forces acting upon the bearing of the cylinder block  2  is attained and products of inertia are prevented. In this manner, a levering-out of the bearing of the cylinder block  2  is counteracted. A force triangle according to FIG. 4B could also be drawn for the left-hand damping piston  40   a,  which is omitted for the sake of simplification. 
     FIGS. 5 and 6 are axial longitudinal sections through a second embodiment of an axial piston machine  1  further developed according to the invention. Already-described elements are provided with corresponding reference numerals, so that a repeat description of said elements is unnecessary. 
     The embodiment illustrated in FIGS. 5 and 6 differs from the embodiment illustrated in FIGS. 1 and 2 in that the damping element  41  according to the invention is not arranged in the inclined plate  25 , but on the stationary counter element  30  lying opposite the inclined plate  25 , i.e. in a housing end plate. The damping element  41  has essentially the structure already described with the aid of FIG.  1 . The damping piston  40  is displaceably arranged in the damping cylinder  42  and is acted upon by means of the restoring spring  43  in such a manner that the damping piston  40  rests against the inclined plate  25 , preferably against the second abutment surface  29 . The drawing of the pressure fluid from the housing interior  46  is effected via the supply duct  45  and the non-return valve  44 , which is open in the suction phase. When the inclined plate  25  is pivoted from the first pivot position illustrated in FIG. 5 into the second pivot position illustrated in FIG. 6, the pressure fluid is forced out of the damping cylinder  47  via the throttle element  47 , also constructed in this embodiment as a bore with reduced diameter, and via the outflow duct  48  connected thereto, so that the intended damping of the movement of the inclined plate  25  and the support of the inclined plate  25  during the pivoting is effected. 
     The invention is not limited to the illustrated embodiments. As already mentioned, the present invention can also be used in axial piston machines having a wobble plate construction. The damping arrangement can also be arranged at any other desired location, provided that it is ensured that the damping piston  40  acts in an appropriate manner upon the inclined plate  25  or wobble plate. Furthermore, additional damping elements can be provided in the region of the first abutment surface  28  in order to also ensure sufficient damping for the other pivoting device.