Abstract:
A testbench device for the analysis and/or optimization of tribological properties in a piston ring/cylinder runway system, includes a cylinder segment-holding device for holding a cylinder runway segment as a testpiece, and a piston ring-holding device holding at least one piston ring element and capable of bringing the at least one piston ring element into bearing contact with the cylinder runway segment. An actuation device actuates the cylinder runway segment and/or the piston ring element such that relative displacement with respect to one another takes place in at least one defined direction of space, in particular in the form of an oscillating movement. The piston ring-holding device has a piston having a ring-shaped outer contour and with at least one circumferentially continuous piston ring groove, in which a piston ring is held as a piston ring element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of DE 10 2013 016 004.9 filed Sep. 26, 2013, which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a testbench device, in particular a tribometer. 
     For a substantial and, in particular, effective analysis or optimisation of friction systems, tribometers, as they are known, are regularly used. Tribometers are testbenches developed especially for investigating tribological variables, such as, for example, friction, wear or lubrication. In vehicle development, above all, the optimisation of the most diverse possible friction systems constitutes an essential area of development in order to utilise the potential of optimisations relating to efficiency and to service life and in order to satisfy future requirements. In particular the piston group/cylinder runway friction system plays an important part in this context, since up to 50 percent of the overall friction losses of an internal combustion engine may occur here. 
     DE 10 2009 008 272 A1 discloses a tribometer testbench, by means of which friction and wear between a cylinder runway segment, produced, for example, from a cylinder crankcase or from a cylinder liner, and a piston ring or a piston ring segment can be measured. The piston ring is fastened here to a sturdy fixed holder. The cylinder runway segment, capable of being brought into bearing contact with the piston ring, is fastened to a travelling slide which can be moved back and forth in oscillation in a defined direction in relation to the holder and with a defined stroke. As a result of the movement of the cylinder runway segment in relation to the piston ring, the processes in an internal combustion engine are thus to be simulated. Furthermore, the travelling slide has a heating element that can heat the cylinder runway segment to a defined temperature. Moreover, the cylinder runway segment can be pressed against the piston ring with a defined pressure force by means of weights. Using the heating element and the weights, simulation is to be made increasingly close to reality. However, such a tribometer testbench nevertheless has the disadvantage that the reproducibility of the simulation results and, in particular, also the transferability of the simulation results to a real internal combustion engine system are greatly restricted. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to provide a testbench device, in particular a tribometer, in which the reproducibility of the simulation results and/or the transferability of the simulation results to the real internal combustion engine system are/is improved in a simple way. 
     The invention relates to a testbench device, in particular a tribometer, for the analysis and/or optimisation of the tribological properties in a piston ring/cylinder runway system. A cylinder runway segment is held on a cylinder segment-holding device as a testpiece. In addition, at least one piston ring element is held on a piston ring-holding device and capable of being brought into bearing contact with the cylinder runway segment. Further, an actuation device is provided, by means of which the cylinder runway segment and/or the piston ring element can be actuated in such a way that relative displacement with respect to one another takes place in at least one defined direction of space, in particular in the form of an oscillating movement. According to the an embodiment of invention, the piston ring-holding device has a piston having a ring-shaped outer contour and with at least one circumferentially continuous piston ring groove, in which a piston ring is arranged and/or inserted as a piston ring element. 
     By a complete piston ring being arranged and/or inserted in the circumferentially continuous piston ring groove of the piston, simulation results especially close to reality can be obtained by means of the testbench device according to the invention, since abstraction is markedly reduced, as compared with a real system. 
     Preferably, the piston ring element arranged and/or introduced in the piston ring groove is guided in the piston ring groove with a defined axial play, so that the piston ring can also execute what is known as a “twisting movement” in the piston ring groove, such as regularly occurs under real conditions. 
     In one embodiment, the piston ring-holding device has a cylinder element which at least partially surrounds the piston in the circumferential direction and which is in bearing contact by its cylinder running face with the piston ring element, the cylinder element and the piston being secured in such a way that relative movement between the cylinder element and the piston is prevented. Thus, the piston ring element can be supported on the cylinder running face and the simulations are made increasingly close to reality. Preferably, the cylinder element may surround the piston completely in a ring-shaped manner, so that the piston can be supported over its entire circumference on the cylinder running face and realistic piston ring tangential forces can be copied. 
     In another embodiment, the cylinder element and the piston may be secured to a parallelepipedal reception block of the piston ring-holding device, and the reception block may have a measuring device, by means of which a coefficient of friction between piston ring and to the cylinder runway segment can be determined. Such a set-up makes it possible to determine the coefficient of friction reliably and accurately. 
     In a further embodiment, the cylinder element may have a window-like cylinder element recess providing free access from outside to the piston ring element, the cylinder element recess being designed and/or arranged in such a way that the cylinder runway segment held on the cylinder segment-holding device can be brought through the cylinder element recess into bearing contact with the piston ring element and can be displaced in relation to the piston ring element in defined directions of space. By means of the window-like cylinder element recess, the cylinder runway segment can be brought into bearing contact with the piston ring element in a simple way. 
     In a preferred embodiment, a lubrication device is provided, by means of which a defined quantity of lubricant, in particular lubricating oil, can be delivered at least to the contact regions of the piston ring element, piston ring groove and cylinder runway segment. Lubrication of these contact regions which is close to reality can thereby be achieved. Preferably, the defined delivery quantity of lubricant may amount to about 2.5 microliters per minute, in order to copy a deficient lubrication state, such as occurs, for example, at the top dead centre of a piston. 
     The piston may have a lubricant duct which is fluidically connected to the piston ring groove through which the lubricant can be conveyed into the at least one piston ring groove. The lubricant temperature in the lubricant duct can thereby be adapted to the piston temperature. Preferably, the at least one piston ring groove may be formed by two ring lands spaced apart from one another and the lubricant duct may issue into at least one of these ring lands by means of an issue port towards the piston ring groove. The lubricant can be conveyed directly to the piston ring element by means of the issue port issuing towards the piston ring groove. 
     According to a further embodiment, a piston heating element, in particular a heating cartridge, is provided, by means of which the piston can be heated to a defined temperature, in particular to about 350 degrees Celsius. Moreover, a cylinder runway segment beating element, in particular a heating foil, may be provided, by means of which the cylinder runway segment can be heated to a defined temperature, in particular to about 130 degrees Celsius. The simulations can be made increasingly close to reality by the piston heating element and/or the cylinder runway heating element. 
     In a concrete embodiment, the reception block is arranged at least partially in an inner cavity of the piston designed as a hollow piston, the reception block being secured to the piston by an adapter element arranged between reception block and piston, and the piston heating element being secured to the reception block in such a way that the heating warmth of the piston heating element passes into the piston via the reception block and the adapter element. Especially effective heating of the piston is thereby made possible. 
     In a another embodiment, the cylinder segment-holding device has a testpiece holder and a testpiece stay which is secured to the testpiece holder and to which the cylinder runway segment is secured, the testpiece stay being secured to the testpiece holder pivotably and/or rotatably, in such a way that an angular offset between a cylinder segment axis running in the axial direction of the cylinder runway segment and a piston ring element axis running in the axial direction of the piston ring element can be compensated and/or set. By the angular offset being compensated and/or set, a contact region between piston ring element and cylinder runway segment can be optimised. 
     A blocking arrangement may be provided, by means of which the pivoting and/or the rotation of the testpiece stay in relation to the testpiece holder can be blocked and released. By means of the blocking arrangement, reliable blocking and release of the pivoting and/or rotation of the testpiece stay in relation to the testpiece holder become/becomes possible. Preferably, the blocking arrangement may have one or more screw elements, in particular spherical pressure screws, which can be screwed into the testpiece holder and/or into the testpiece stay in order to block pivoting and/or rotation. Pivoting and/or rotation can thereby be blocked in an especially simple way. 
     In a further preferred embodiment, the testpiece stay is of U-shaped form, the cylinder runway segment, manufactured particularly in the manner of a cylinder crankcase, being arranged between the U-legs of the testpiece stay and/or being secured to the U-legs of the testpiece stay. By virtue of this type of construction, in particular, thick-walled cylinder runway segments can be secured to the cylinder segment-holding device in a simple way. 
     In an alternative embodiment, the testpiece stay has a bearing region contour-adapted to a side, facing away from the piston ring element, of the cylinder runway segment, manufactured particularly in the manner of a cylinder liner, in which case, to secure the cylinder runway segment to the testpiece stay, the cylinder runway segment can be clamped against the bearing region by at least one clamping element, in particular a clamping jaw. As a result, in particular, thin-walled cylinder runway segments can be secured reliably to the testpiece stay. 
     A pressing device may be provided, by means of which the cylinder runway segment can be pressed against the piston ring element with a defined pressure force. By means of the pressing device, the simulations carried out by means of the testbench device according to the invention can be varied and optimised. 
     According to another embodiment, the cylinder segment-holding device is designed in such a way that the setting and/or compensation of the angular offset take place/takes place by the cylinder runway segment being pressed against the piston ring element with the defined pressure force. The angular offset can be set and/or compensated especially simply in this way. Preferably, the testpiece holder may have a cylindrical recess, in which a cylindrical pin of the testpiece stay is guided with a radial play enabling the angular offset to be set and/or compensated. This makes it possible to set and/or compensate the angular offset especially simply. 
     In a preferred embodiment, the cylinder runway segment is arranged above the piston ring element in a vertical axis direction. Thus, the cylinder runway segment is capable of being brought by a bearing region into bearing, contact with the piston ring element, the cylinder runway segment being secured to the cylinder segment-holding device in such a way that the bearing region is displaced in the axial direction of the cylinder runway segment as a result of the rotation of the cylinder runway segment through 180 degrees about a vertical axis running in the vertical axis direction. A single cylinder runway segment can thereby be used for two test runs. 
     A tilting device may be provided, by means of which the cylinder segment-holding device, together with the piston ring-holding device, can be tilted from a horizontal to a vertical position, and vice versa, in which case, in the horizontal position, a piston axis running in the piston axial direction runs horizontally and, in the vertical position, the piston axis runs vertically. Thus, the testbench device can be mounted and adjusted in the horizontal position and simulations close to reality can be carried out in the vertical position. 
     In a preferred embodiment, the piston ring-holding device may be held stationarily and, by means of the actuation device, the cylinder segment-holding device may be displaced in relation to the stationary piston ring-holding device in the defined directions of space, in particular in the piston axial direction. Relative movement between cylinder runway segment and piston ring element can thereby be implemented in an especially simple way. 
     The advantageous embodiments and/or developments of the invention which are explained above and/or are reproduced in the subclaims may be employed individually or else in any combination with one another, except, for example, in cases of unequivocal dependencies or incompatible alternatives. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its advantageous refinements and/or developments and also the advantages thereof are explained, merely by way of example, hereafter with reference to the drawings in which: 
         FIG. 1  is a perspective view of an exemplary embodiment of a testbench device according to the invention; 
         FIG. 2  shows the components of the testbench device according to  FIG. 1  in an exploded illustration; 
         FIG. 3  is a sectional view along the sectional plane A-A of  FIG. 1 ; 
         FIG. 4  is a perspective view of a cylinder segment-holding device of the testbench device of the testbench device of  FIG. 1 ; 
         FIG. 5  is a perspective view of a first degree of freedom of the cylinder segment-holding device of  FIG. 4 ; 
         FIG. 6  is a side view to illustrate a second degree of freedom of the cylinder segment-holding device of  FIG. 4 ; 
         FIG. 7  is a perspective view of a bottom and side of the cylinder segment-holding device according to a first exemplary embodiment; 
         FIG. 8  is a perspective view of a bottom and side of the cylinder segment-holding device according to a second exemplary embodiment; and 
         FIG. 9  is a bottom view of the cylinder segment-holding device according to  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a testbench device  1  simulating close to reality a piston ring/cylinder runway system. The testbench device  1  has a piston ring-holding device  5  secured to a fixing plate  3  and a cylinder segment-holding device  9  secured to a rocker  7 . The rocker  7 , arranged above the fixing plate  3  so as to be spaced apart in the vertical axis direction is displaceable in the longitudinal axis direction x in relation to the fixed fixing plate  3  by means of an actuation device, not shown in the figures. A complete piston ring  11  is held on the piston ring-holding device  5 , while a cylinder runway segment  12  ( FIG. 2 ) manufactured in the manner of a crankcase is held on the cylinder segment-holding device  9 . For simulations of the real processes in the piston ring/cylinder runway system, the cylinder runway segment  12  can be brought into bearing contact with the piston ring  11  by means of the actuation device and be displaced in relation to the piston ring  11 . The displacement of the cylinder runway segment  12  in relation to the piston ring  11  preferably takes place in the form of an oscillating movement over a defined distance, with the result that a friction track  14  with a track width Δx ( FIG. 9 ) is formed on the cylinder runway segment  12 . 
     The detailed set-up of the piston ring-holding device  5  and of the cylinder segment-holding device  9  may be gathered from  FIG. 2 . The piston ring-holding device  5  has a ring-shaped piston adaptation  13  manufactured from a piston and having a circumferentially completely continuous piston ring groove  15  into which the piston ring  11  can be inserted. The piston adaptation  13  can be secured to a parallelepipedal reception block  19  of the piston ring-holding device  5  by means of an adapter element  17  and by means of a plate-shaped abutment  18 . The adapter element  17  consists here, for example, of an adapter body  20  and a plate-shaped leg  22  arranged on the outside of the adapter body  20  in a transverse axis direction y and projecting downwards from the adapter body  20  in the vertical axis direction z. To secure the piston adaptation  13  to the adapter element  17 , the ring-shaped piston adaptation  13  is brought with its inner face  21  into sheet-like bearing contact with a bearing face  23 , contour-adapted to the inner face  21 , of the adapter body  20  and is clamped by means of a plurality of, here two, screws  25  against a land  27  of the adapter body  20 , the said land  27  projecting upwards from the bearing face  23  in the vertical axis direction z. Further, the plate-shaped abutment  18  is tied, opposite to the leg  22 , to the outside of the adapter body  20  in a transverse axis direction y and, together with the said adapter body and the leg  22 , forms a U-shaped set-up ( FIG. 3 ). The adapter body  20 , as seen in the vertical axis direction z, has at the bottom a planar bearing face which can be brought into sheet-like bearing contact with a topside  29  of the parallelepipedal reception block  19 . The securing of the adapter element  17 , bearing with the bearing face against the reception block  19 , to the reception block  19  takes place here, for example, by means of three screw connections ( FIG. 2 ) which are led through the leg  22 , through the abutment  18  tied to the adapter element  17  and through the reception block  19  and which run in the transverse axis direction y. 
       FIG. 2  shows, further, a cylinder adaptation  33  of the piston ring-holding device  5 , the said cylinder adaptation being likewise securable to the reception block  19  and surrounding the piston completely in a ring-shaped manner. As shown in  FIG. 3 , the cylinder adaptation  33  secured to the reception block  19  is in bearing contact by means of its cylinder running face  35  with the piston ring  11 . The cylinder adaptation  33  has at the top, as seen in the vertical axis direction z, a window-like recess  37  ( FIG. 2 ) providing free access from outside to the piston ring  11 . Via this window-like recess  37 , the cylinder runway segment  12  held on the cylinder segment-holding device  9  can be brought into bearing contact with the piston ring  11  and therefore be displaced in relation to the piston ring  11  in the longitudinal axis direction x. 
     It may be gathered, further, from  FIG. 1  that the reception block  19  lies on a here U-shaped intermediate plate  41  or is screwed to the intermediate plate  41 . According to  FIG. 2 , the intermediate plate  41  has, at its and regions projecting from the cylinder adaptation  33  in the longitudinal axis direction x, U-legs  45  which project downwards in the vertical axis direction z and which are in bearing contact with U-legs  47 , projecting upwards in the vertical axis direction z, of a U-shaped baseplate  49  arranged beneath the intermediate plate  41  in the vertical axis direction z. The intermediate plate  41  and the baseplate  49  are screwed to one another at their U-legs  45  and  47  and form a free space  51  ( FIG. 1 ), through which the piston adaptation  13 , the piston ring  11  and the cylinder adaptation  33  are led. According to  FIG. 3 , a U-base  53  of the intermediate plate  41  and a U-base  55  of the baseplate  49  are spaced apart from one another, in such a way that the cylinder adaptation  33  is out of bearing contact with the U-base  55  of the baseplate  49  with a height offset Δh ( FIG. 3 ). Since the cylinder adaptation  33  is out of bearing contact with the baseplate  49 , it is possible to determine accurately a coefficient of friction between the piston ring  11  and the cylinder runway segment  12  by a measuring device  54  provided on the reception block  19  and indicated in  FIG. 3  by dashed lines. Furthermore, the baseplate  49  is in bearing contact on the underside in a vertical axis direction z with the fixing plate  3  and is fastened to the fixing plate  3  by means of screw connections. 
     Further, the reception block  19  may have a heating cartridge  56 , indicated in  FIG. 3  by dashed lines, by means of which the piston adaptation  13  can be heated to a defined temperature, for example to about 350° C. In order to ensure as high an introduction of heat as possible into the piston adaptation  13 , as already mentioned, the parallelepipedal reception block  19  with the adaptation element  17  and the adaptation element  17  with the piston adaptation  13  bear one against the other in a sheet-like bearing connection. Moreover, the piston ring-holding device  5  may have a lubrication device, at which  FIG. 1  shows merely a conveying line  60  issuing into the piston ring groove  15  as indicated by dashed lines. By means of the lubrication device, a defined quantity of lubricating oil, for example 2.5 microliters per minute, can be conveyed into the piston ring groove  15 . 
     As illustrated in  FIGS. 2 and 3 , the cylinder segment-holding device  9  comprises, further, a testpiece holder and a testpiece stay  59  securable to a testpiece holder  57  by means of a fastening device  58  ( FIG. 4 ) and holding the cylinder runway segment  12 . 
     The fastening device  58  is designed in such a way that the testpiece stay  59  secured to the testpiece holder  57  is rotatable ( FIG. 5 ) in relation to the testpiece holder  57  about an axis A running in the vertical axis direction and is pivotable ( FIG. 6 ) about a pivoting point S. The rotation and the pivoting of the testpiece stay  59  in relation to the testpiece holder  57  make it possible to compensate an angular offset between a cylinder segment axis running in the axial direction of the cylinder runway segment and a piston ring axis running in the axial direction of the piston ring. 
     According to  FIG. 4 , the fastening device  58  has, further, a cylindrical recess  65  which is formed on the testpiece holder  57 , runs in the vertical axis direction z and issues on the underside at the testpiece holder  57  and into which a cylindrical pin  67  projecting upwards from the testpiece stay  59  in the vertical axis direction z can be introduced with a defined radial play. The pin  67  introduced into the recess  65  is in bearing contact with a ball  68  arranged in an upper end region of the recess  65 . The radial play and the ball  68  allow simple rotation and pivoting of the testpiece stay  59  in relation to the testpiece holder  57 . 
     The fastening device  58  has, further, two spherical pressure screws  69  which can be screwed into the testpiece holder  57  in which, in the screwed-in state, are in bearing contact by means of their spherical contact face with a circumferentially running wave profile of the cylindrical pin  67 , in such a way that the rotational movement of the testpiece stay  59  in relation to the testpiece holder  57  is blocked. 
     Moreover, the fastening device  58  comprises here further (here, for example, three) spherical pressure screws  73  which can be screwed into the testpiece holder  57  and by means of which the pivoting movement of the testpiece stay  59  can also be blocked. The here, for example, three spherical pressure screws  73  form, as seen from above in the vertical axis direction z, a triangle and, by being screwed into the testpiece holder  57  or by pivoting of the testpiece stay  59  in relation to the testpiece holder  57 , can be brought into bearing contact with a planar topside  75  of the testpiece stay  59 . The blocking of the pivoting movement of the testpiece stay  59  takes place when all three spherical pressure screws  73  are brought into bearing contact with the topside  75  of the testpiece stay. Depending on the depth to which the spherical pressure screws  73  are screwed in, a pivot angle of the testpiece stay  59  in relation to the testpiece holder  57  can be set. 
     Compensation of the angular offset between the cylinder segment axis and the piston ring axis takes place by means of a pressing device which presses the cylinder segment-holding device  9  against the piston ring-holding device  5  with a defined pressure force F ( FIG. 3 ). The pressure force F causes a compensating movement of the testpiece stay  59 , which is rotatable and pivotable in relation to the testpiece holder  57 , or of the cylinder runway segment  12  held on the said testpiece stay and thus makes it possible to produce optimal contact between cylinder runway segment  12  and piston ring  11 . After the angular offset has been compensated, the rotatability and pivotability of the testpiece stay  59  in relation to the testpiece holder  57  are blocked. 
       FIG. 7  shows the U-shaped testpiece stay  59  holding the cylinder runway segment  12 . The testpiece stay  59  of U-shaped form has U-legs  77  which are arranged at front and rear in a longitudinal axis direction x and project in the vertical axis direction z and between which the cylinder runway segment  12  can be chucked. The chucking of the cylinder runway segment  12  between the U-legs  77  takes place here, for example, by means of two cylindrical pins  79  inserted into one U-leg  77  and by means of a spherical pressure screw  81  screwed into the other U-leg  77  and pressing the cylinder runway segment  12  against the two cylindrical pins  79 . 
     Furthermore, the cylinder runway segment  12  capable of being chucked between the U-legs  77  can be chucked to the testpiece stay  59  both in a first chucking position and in a second chucking position rotated through 180 degrees about a vertical axis running in the vertical axis direction z. According to  FIG. 9 , the cylinder runway segment  12  is secured to the testpiece stay  59  in such a way that, as a result of this rotation of the cylinder runway segment  12  through 180 degrees, the friction track having the track width Δx is displaced in the longitudinal axis direction x. Two test runs can thereby be carried out by means of a single cylinder runway segment  12 . 
       FIG. 8  shows a second embodiment of the testpiece stay  59 . The testpiece stay  59  according to this second embodiment is designed in such a way that a cylinder runway segment  12  manufactured in the manner of a cylinder liner can be secured to it. The testpiece stay  59  has a bearing face  82  which is contour-adapted to the cylinder runway segment  12  and which can be brought into sheet-like bearing contact with that side of the cylinder runway segment  12  which faces away from the piston ring  11 . By means of clamping jaws  85 , likewise contour-adapted to the cylinder runway segment  12 , the cylinder runway segment  12  can be pressed against the bearing face  82 . 
     Furthermore, the cylinder segment-holding device  9  may have a heating foil  87  ( FIG. 6 ) which is chucked between the testpiece holder  57  and the testpiece stay  59  and by means of which the cylinder runway segment  12  can be heated to a defined temperature, for example to about 130° C. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Testbench device 
           3  Fixing plate 
           5  Piston ring-holding device 
           7  Rocker 
           9  Cylinder segment-holding device 
           11  Piston ring 
           12  Cylinder runway segment 
           13  Piston adaptation 
           14  Friction track 
           15  Piston ring groove 
           17  Adapter element 
           18  Abutment 
           19  Reception block 
           20  Adapter body 
           21  Inner face piston adaptation 
           22  Leg 
           23  Bearing face adapter body 
           25  Screws 
           27  Land 
           29  Topside reception block 
           33  Cylinder adaptation 
           37  Recess cylinder adaptation 
           41  Intermediate plate 
           45  U-leg intermediate plate 
           47  U-leg baseplate 
           49  Baseplate 
           51  Free space 
           53  U-base intermediate plate 
           54  Measuring device 
           55  U-base baseplate 
           56  Heating cartridge 
           57  Testpiece holder 
           58  Fastening device 
           59  Testpiece stay 
           60  Conveying line lubrication device 
           65  Cylindrical recess 
           67  Cylindrical pin 
           68  Ball 
           69  Spherical pressure screw 
           73  Spherical pressure screw 
           75  Topside testpiece stay 
           77  U-leg testpiece stay 
           79  Cylindrical pin 
           81  Spherical pressure screw 
           82  Bearing face testpiece stay 
           85  Clamping jaws 
           87  Heating foil 
         A Axis 
         F A  Pressure force 
         S Pivoting point 
         Δh Height offset 
         Δx Track width