EP2855952A2

EP2855952A2 - Partial structuring of sliding surfaces

Info

Publication number: EP2855952A2
Application number: EP13726787.8A
Authority: EP
Inventors: Leo Schreiber; Wolfgang Hafner; Matthias Weber; Jürgen REINGEN; Hans Kuhn; Emanuel GROß; Maarten Brussee
Original assignee: MAG IAS GmbH Eislingen
Current assignee: MAG IAS GmbH Eislingen
Priority date: 2012-06-04
Filing date: 2013-06-04
Publication date: 2015-04-08
Also published as: WO2013182539A2; US9879726B2; JP2015525323A; US20150167737A1; CN104813042A; KR20150018785A; MX2014012354A; RU2014149142A; WO2013182539A3

Abstract

When structuring the sliding bearing surfaces (1) of a crankshaft by selectively introduced, microscopically small depressions (27), to achieve a great reduction in friction during use of the crankshaft with little effort, it is proposed in the case of centre bearings and pin bearings to structure specifically only the regions of the bearing surface that are subjected to high levels of loading, both in the circumferential direction and in the axial direction, since even these are difficult to reach in view of the working gap from the tool of only a few microns.

Description

Area-wise structuring of sliding surfaces

I. Field of application The invention relates to a sliding surface of a sliding pair, in particular the plain bearing surface of a radial bearing, in particular the bearing points of a crankshaft in an internal combustion engine, on the one hand with respect to the engine block and on the other hand with respect to the connecting rods.

II. Technical background

In the case of the sliding surfaces of a lubricated sliding mating, it is essential for both the magnitude of the sliding friction and for the life of the sliding mating, in particular of the slide bearing, that in all operating conditions as much lubricant as possible and in as even a distribution as possible between the contact surfaces of the sliding mating is available. Above all, the beginning of the relative movement between the two sliding surfaces is critical.

With the increasing use of start-stop systems in motor vehicles, this significance is increasing dramatically, in particular with regard to the bearing points of a crankshaft, because this increases the number of starting operations of the plain bearings by a factor of 100 or more.

For this reason, the contact surfaces of sliding surfaces, in particular of plain bearings, are processed so that they have small recesses, which serve as a reservoir for lubricants. These depressions are due to the normal roughness of the material of the sliding surface present, or are deliberately introduced. Because of this, the carrying portion of a plain bearing, ie the area proportion, with which the contact surfaces actually concern each other, always well below 100%, sometimes even less than 60%.

The corresponding structuring of the sliding surfaces is achieved by special processing steps such as grinding, finishing or honing, whereby, however, the specific arrangement of the depressions can not be specified, and also the scattering with respect to the size, in particular the depth, of these depressions is relatively large. Above all, the result of the structuring also depends heavily on the experience of the executing person.

In order to achieve a structuring of the contact surface of a slide bearing defined with regard to number, size, depth and distribution of the depressions, it is likewise already known to bombard this surface by means of a laser and thereby achieve the desired depressions.

However, this approach has the disadvantage that it is very time-consuming with a large number of depressions, and moreover, the incident laser beam on the surface not only produces a depression, but also a formation which surrounds the depression in an annular manner Cases is not desirable, and requires a re-processing to eliminate this posing. In general, the flanks shape of the recess made by laser is hardly controllable.

Another disadvantage is that the laser processing is a spatially limited strong heating and subsequent rapid cooling, resulting in undesirable new hardness zones. Further known is the electrochemical erosion (ECM) processing method, which is also used in pulsed mode (PECM). Hereby, three-dimensional surfaces are generated, for example, the three-dimensional surface of coins produced or introduced the recesses described in surfaces, usually only a removal of a maximum of 30 μιτι with this method is economically reasonable.

As a result of the approach of a correspondingly negatively designed electrode to the surface to be processed, serving as another electrode, material is removed from this surface in the form of ions, which results in a much finer structure in this process than, for example, by means of spark erosion is.

For the power line and the removal of the dissolved substances, an electrically conductive liquid is forced through the gap between the tool and the workpiece during the entire process.

In the case of crankshafts as workpieces, in particular in the case of crankshafts for passenger car engines with high numbers of cylinders, it is added that during machining they are unstable and thus difficult to position and also difficult to machine during structuring workpieces.

The assessment of the dimensional accuracy of a finished crankshaft is primarily - in addition to the axial bearing width - by assessing the following parameters:

Diameter deviation = maximum deviation from the specified nominal diameter of the trunnion,

Roundness = macroscopic deviation from the circular nominal contour of the bearing journal, indicated by the distance of the outer and inner enveloping circle,

Concentricity = radial dimensional deviation with rotating workpiece, caused by an eccentricity of the rotating bearing point and / or a deviation in shape of the bearing of the ideal circular shape, Roughness in the form of the average single roughness Rz = calculated microscopic roughness of the surface of the bearing, calculated value,

Supporting component = the bearing surface portion of the microscopically considered surface structure, which is in contact with an adjacent mating surface,

and additionally at the stroke bearings:

Stroke deviation = dimensional deviation of the actual stroke (distance of the actual center of the crankpin from the actual center of the center bearing), the desired stroke and

Angular deviation = in degrees or as a stroke-related measure of length in the circumferential direction specified deviation of the actual angular position of the pin bearing pin from its desired angular position relative to the center bearing axis and with respect to the angular position to the other lifting bearing pin.

In this case, compliance with the desired tolerances in these parameters is limited both by the available processing methods as well as the instability of the workpiece and the processing forces.

The efficiency and cost-effectiveness of a machining process also plays a major role in practice, especially for series production, in which cycle time and hence production costs play a decisive role, whereas in the case of single-work or prototype machining, these are not restricted.

This applies in particular to the last process steps in the production of, for example, a crankshaft, fine machining and surface structuring. III. DESCRIPTION OF THE INVENTION a) Technical Problem It is therefore the object of the invention to propose a structured sliding surface as well as a method and a tool for its manufacture, which enables an efficient production despite a significant reduction of the friction, in particular in a hydrodynamic sliding bearing.

b) Solution of the task

This object is solved by the features of claims 1, 10, 12 and 14. Advantageous embodiments will be apparent from the dependent claims.

Regarding the sliding surface - what a sliding bearing surface or the sliding surface z. B. a camshaft - this problem is solved by not the entire sliding surface is structured, but only partial areas, which drastically reduces the structuring effort, but almost to the same result in terms of friction reduction leads as a complete structuring of the sliding surface, especially by structuring or subdividing those subareas only the ones that are the most burdened. In this case, a distinction has to be made between the subregions to be structured or to be structured in the direction of movement of the sliding surface relative to the mating surface of the sliding mating, the longitudinal direction, or transversely thereto.

The less heavily loaded subregions are either not structured at all or are less structured, which may mean that the number, size, depth or other parameters of the depressions by means of which the structuring takes place are selected to be lower, thereby reducing the structuring effort in these areas or completely eliminated, when these less stressed subregions are not structured at all.

In the following, we will always speak only of structured subareas, which means that these subareas are either structured as one, ie the remaining subareas are not structured at all, or that these subareas are more structured than the rest of the sliding surface.

Transverse to the direction of movement, the middle region is preferably structured relative to the edge regions, especially if one of the two sliding surfaces of a sliding surface pairing is convexly convex in the direction of movement. Because then results in the central region of the smallest thickness of the lubrication gap forms and there the risk of dry running is greatest.

In the case of rotationally symmetrical sliding surfaces, in particular plain bearing surfaces, only a certain circumferential region, in particular of less than 90 °, better still less than 70 °, better still less than 60 °, of the circumference is structured in the direction of movement.

If the sliding surface is the plain bearing surfaces of a crankshaft for a reciprocating internal combustion engine, the structure is structured as follows: In the circumferential direction, only the segment of the lateral surface of the crankpin is structured, which upon ignition of the corresponding piston and the resulting explosion pressure on the piston strongest is loaded by the connecting rod. This is preferably a range of 30 ° in the direction of rotation to 60 ° against the direction of rotation of the roller bearing, in particular 20 ° in the direction of rotation to 55 ° against the direction of rotation from the radially outermost point of the crank pin viewed from the central bearing axis of the crankshaft.

There are two options for the center-pivot spigots: Either only that circumferential segment of the central bearing is structured, which lies opposite the two adjacent crankpole journal in the radial direction and points away from the structured surfaces of these crankpins, wherein there is only one adjacent crankpipe journal in the first and last center-bearing journal.

The other possibility consists of structuring the same circumferential regions on each center-pivot journal, specifically those peripheral regions which lie opposite the structured regions of all crankcage trunnions-again in the axial direction-and point away from them. In the case of a crankshaft for a six-cylinder engine, these would then generally be three circumferential regions per center-bearing journal, in the case of a four-cylinder engine generally only two peripheral regions per central journal journal. This reduces the sliding friction, especially in the heavily loaded peripheral areas, where due to the heavy load, the sliding friction during operation can be several times higher than in the other peripheral areas. Therefore, despite structuring only a portion of the sliding surface, usually well below 50%, a total reduction in friction causes, which is 80 or 90% of the friction reduction, as would occur at the same level in the complete structuring of the sliding surface.

The structuring is preferably carried out with electrochemical erosion (ECM), in particular pulsed electrochemical erosion (PECM). The latter consists in that the current application of the two electrodes, on the one hand tool and on the other hand workpiece, is pulsed. Preferably, a periodic approach and again removal of the tool relative to the workpiece is provided synchronously, usually by vibrating movement of the tool, the current being applied at the point of the greatest approximation between the tool and the workpiece. In the currentless intermediate times, in which the distance is even greater, the ablated metal ions are flushed out through the electrolyte pumped in between. In the case of a sliding pairing of two sliding surfaces moving relative to one another, preferably only one of the sliding surfaces is partially structured in the above-described sense, since the structuring of the counter-surface usually also brings only a minor increase in friction reduction.

In this case, the depressions should have a depth of at most 10 μm, in particular a maximum of 5 μm, in particular a maximum of 1 μm, since too great a depth can prevent sufficient pressure build-up of the lubricant in the region of the recess. It has also been found that the depth in relation to the largest superficial extent of the depression should be in a certain ratio, namely between 0.005 and 0.002, in particular between 0.008 and 0.012. In the area between the recesses, the surface should have a roughness, the roughness Rz is preferably less than the depth of the recesses, in particular less than 5 μιτι, better between 1 and 4 μιτι amounts. The area between the recesses should be at least 50% and at most 85% to achieve optimal low friction.

It has also been shown that viewed in the plan, the small extent of each well should be a maximum of 150 μιτι, better only a maximum of 100 μιτι or even a maximum of 50 μιτι. Furthermore, the ratio of the largest to the smallest extent of the depression should be at most a factor of 10, better only a factor of 5 or even only a factor of 3. With regard to the area occupied by depressions surface portion of the structured surface of this should be between 1% and 30%, in particular between 10% and 20%. Furthermore, it has proven to be useful, the edge of the wells, ie the transition between the edges of the wells to the other surface of the sliding surface, with a rounding with a radius of at least 2 μιτι and / or a helix angle of less than 60 ° to the top - form surface, as a result, the accumulated in the recess lubricating oil can get out of the well better.

For the same reason - cut in the direction of the relative direction of movement of the sliding surface to the counter surface - directed against the direction of movement of the sliding surface edge of the recess should be less steep than the opposite edge, in particular at an angle of not more than 45 °, better 30 ° , better a maximum of 25 °, better a maximum of 20 ° to the surface between the wells.

With regard to the machine for machining rotationally symmetrical sliding surfaces, in particular at the bearing points of a crankshaft, by means of electrochemical ablation, the object is achieved by the machine is a machine tool with a workpiece-spindle arrangement as in a lathe, which has a controlled C-axis and in which the removal tool is arranged in particular in a tool unit, which is actively movable in the X and Z directions, but in the Y direction limited mobility, in particular floating, is, in particular by +/- 100 μιτι.

Preferably, the tool unit is limited to the B-axis rotatable and thus stored floating.

With regard to the tool for machining rotationally symmetrical sliding surfaces, in particular the bearing points on a crankshaft, by means of electrochemical ablation (ECM), this object is achieved in that the active surface of the tool in the direction of movement, in the circumferential direction of the rotationally symmetrical bearing surface, a range of less than 90 °, in particular particular of less than 70 °, in particular less than 60 °, in particular less than 45 °. Preferably, the effective surface of the tool

either flat and arranged tangentially to the convexly curved sliding surface of the bearing - or concave curved, but with a particular by the factor

1, 1 to 2.0 larger radius of curvature designed as the convex curved to be machined sliding surface.

This ensures that the distance between the tool and the workpiece is the lowest in the center of the sliding surface area machined by the active surface and thus the depth of the introduced recesses is greatest there and is reflected most strongly on the sliding surface, while away from the location of the shortest distance the wells are increasingly less deep and thereby decreases the structuring.

In addition, at the area of the shortest distance, the smoothing effect between the recesses, which enters through the working surface of the tool, is greatest. Both together cause the greatest reduction in friction at the point of the smallest distance, if this point of the smallest distance coincides with the point of the highest load in the circumferential direction.

For the same reason, the elevations on the effective surface of the tool should be at least a factor of 2, better by a factor of 3 higher than the maximum depth of the wells to be produced with it.

With regard to the method for machining sliding surfaces by means of electrochemical ablation (ECM), the object is achieved in that during machining, the distance between the tool and the workpiece is alternately larger and smaller, in particular by means of appropriate vibration of the tool. On the other hand, the application of current to the tool may be pulsating (PECM) to keep the workpiece heating low, in particular in synchronism with the vibration, ie the change in distance, so that the current surge in particular at the time of the greatest approximation between tool and workpiece takes place, and thereby the extraction of the metal ions is particularly well possible. In the subsequent larger spacing, the dissolved out metal ions are better dissipated by the electrolyte flowing in between. In the circumferential direction, the tool stands still relative to the workpiece.

In order to be able to position the tool relative to the workpiece sufficiently accurately despite the small working gap and the crankshaft which is difficult to handle, spacers are preferably fastened to the tool with which the tool rests on the surface to be machined, the bearing surface, of the crankshaft. For this purpose, the spacers must be made of electrically non-conductive material.

Preferably, the spacers are formed as spacer strips, which are located at the ends of the tool in the circumferential direction.

Since the circumferential direction in this case is the largest extension direction of the tool, a flushing groove is preferably incorporated in the circumferential direction in the active surface of the tool, in which the outlet for the electrically conductive liquid, the purging electrolyte, opens, and in particular at least 1/10 mm is deep. As a result, the electrolyte flows in the circumferential direction to the ends of the tool, where the spacer strips cause an at least partial seal, and from there the electrolyte flows through the working gap in the axial direction to the two axial ends of the active surface of the tool.

For the control of the process, in particular for the time of termination of the processing, the continuous application of power is the Temperature of the electrolyte and / or the changing current used as a reference variable.

In the case of pulsed current application, on the other hand, the number of pulses and / or the duration of the pulses are used as the reference variable for this purpose.

If, on the other hand, the distance between the tool and the workpiece is changed in an oscillating manner during machining, then the pressure change in the supply for the electrically conductive liquid is used as the reference variable for the control of the processing, in particular for the time of the termination of the processing, because with increasing approach the tool to the surface of the workpiece, the flow of the electrolyte through the working gap is difficult and it builds up in the supply line of the electrolyte increasing pressure.

Another possibility is to make the spacers, in particular the spacer strips, oscillating in their thickness variable, for example, as a piezoelectric element, and to cause an oscillating change in its thickness by appropriate current application of this element.

Another possibility is to leave the spacers, in particular spacer strips, to be placed continuously on the surface to be machined during machining, but to fix the tool relatively movably to and guided against the spacers and to oscillate the tool in an appropriate manner Moving workpiece to and from this path, which he must do very quickly given a total processing time of a few seconds. In order to change the imaging accuracy of the surface structure of the tool on the workpiece, can either the distance between the tool and the workpiece can be changed, ie the minimum distance during the vibration, or the current can be changed.

In this way, two independent influenceable variables for the variation of the imaging accuracy, and thus in particular the depth of the wells with the same tool available. As economical it has been proven by means of the electro-chemical removal, especially when processing the entire surface, so not only the introduction of individual wells, a material removal of max. 30 μιτι, better only 20 μιτι, better only 10 μιτι provide, but in particular of at least 0.5 μιτι, better of at least 2 μιτι. In this size range, it is ensured that a microscopic smoothing effect already occurs without the existing microstructure being removed down to the lowest valleys.

For such economic processing, the tool is best kept at a distance of 5 to 400 μm, more preferably from 10 to 100 μm, to the sliding surface to be machined.

In order to produce recesses, the tool can have on its active surface either corresponding elevations, which represent the corresponding negative structure of the surface to be achieved of the workpiece, or the tool has a smooth active surface, and the active surface is covered with a mask of electrically non-conductive material, the breakthroughs through which a current flow can take place. In this case, the required liquid electrolyte in particular between this mask and the surface of the workpiece to be machined along the surface and discharged. Preferably, in the same operation with the structuring of the sliding surface and in the interior of the workpiece deburring be carried out by electrochemical removal, especially at the intersections of holes, and also at the entrance of the holes in the workpiece. For this purpose, an appropriate design of the tool may be necessary, but it requires no additional processing time.

The machining parameters such as machining time, number of pulses, applied current, distance between tool and workpiece at the time of closest approach are preferably determined so that in the area between the recesses, the surface of the workpiece thereafter has a roughness, which is smaller than the depth the recesses to be produced and / or the roughness Rz is between 1 and 4 μιτι.

The supporting portion in the area between the recesses should be at the surface of the workpiece after structuring between 50% and 85%, in order to ensure despite the introduced wells still a sufficient buoyancy of the sliding surface.

c) Embodiments:

Embodiments according to the invention are exemplified below with reference to the figures. Show it:

1 shows a crankshaft for a 4-cylinder internal combustion engine in the side view, Figure 2a: the crankshaft of Figure 1 in the axial direction, cut through one of the center bearings, a crankshaft for a 6-cylinder internal combustion engine viewed in the axial direction and cut through a center bearing, a plan view of a structured region of a sliding surface, the enlarged view of a bearing point of a crankshaft,

Sections through recesses in the sliding surface, a first procedure in the manufacture of the structuring, a second and third procedure in the manufacture of structuring, a plan view of the effective surface of the tool and an axial view in producing the structuring,

Figure 6: an enlarged view of the tool in use on the

Sliding surface.

Figure 1 shows a typical workpiece on which sliding surfaces 1 are to be structured for reducing friction by means of depressions, a crankshaft 2 for a 4-cylinder reciprocating engine in the side view, in which on the later axis of rotation 10 of the crankshaft five central bearings 1 b with their about cylindrical lateral surfaces are provided as sliding surfaces 1. Between each of these center bearing points 1 b, each offset radially outwards, there is one each of a total of four stroke bearing points 1 a, which likewise each have an approximately cylindrical bearing surface as sliding surface 1 for one each. have ordered connecting rods, and are connected to the central bearings 1 b cheeks 5.

Already from this illustration it is obvious that such a crankshaft 2, which only at their axial ends during machining in a z. B. lathe is due to their structure and thus easily possible deflection in the central region is a relatively unstable workpiece, especially when it comes to machining accuracies and approximations of a tool in the order of a few μιτι.

The friction in a hydrodynamic sliding bearing, in which a lubricant, usually oil, is located between the two sliding surfaces of the sliding pair, which is distributed over the sliding surface relative to one another by the relative movement of the sliding surfaces and forms a sliding film in the bearing gap, friction can be reduced. when distributed in the sliding surface 1 recesses 27 are introduced, as shown in Figure 3a in plan view of a sliding surface 1.

In order to be able to produce reproducibly and economically in large numbers such recesses 27 lying in the μ range with a defined shape, size, depth and distance from one another, electro-chemical manufacturing (ECM) is used:

In this case, an electrode, which usually represents the negative shape of the sliding surface 1 to be produced, that has elevations 26 on its active surface, as shown in Figures 5a, b, placed at a very close distance of a few μιτι to be machined sliding surface. By the tool 25 to the workpiece 2 via an electrically conductive liquid 4, the electrolyte in the working gap 3 between them flowing electric current metal ions are dissolved out of the surface of the workpiece and the contour of the tool 25 is formed on the surface of the workpiece 2 from. Already with a flat workpiece surface to be machined, the approximation of the tool 25 to 10-20 μηη is difficult to realize in practice and only possible with special machines. For curved, also rotationally symmetric, surfaces to be machined, such as the bearing surfaces of a crankshaft, which can not only be curved in the circumferential direction but also in the axial direction 10, this is particularly difficult, especially if the entire bearing surface is to be structured. Because hitherto, only methods exist in which no relative movement along the working surface 24 of the tool 25 may take place during machining between the workpiece 2 and the tool 25, and since in the circumferential direction the active surface 24 of the tool 25 is theoretically a maximum of 180 °, in practice even only can cover significantly less, must be used for the structuring of the entire peripheral area either with several tools simultaneously or successively in segments, which multiplies the difficulties in terms of the exact low approximation.

According to the invention, only one subregion of a bearing point of the crankshaft is therefore structured in each case, in the circumferential direction of the bearing points as shown in FIGS. 2 a and b:

For in the illustrated crankshafts for a four-cylinder (Fig. 2a) or a six-cylinder reciprocating engine (Fig. 2b) takes place during operation, the largest load on the crankpins 1a at the time of ignition of the gas mixture and in the short time thereafter, in which builds up the explosion pressure in the cylinder and accelerates the piston down. The connecting rod (not shown) then presses on the peripheral region 11a1 of the currently located overhead bearing 1a, the center of which is located in the direction of rotation 28 of the crankshaft 2 behind the point 13 of this crankcaster journal 1a that is farthest radially away from the axis of rotation 10 of the crankshaft. Since the bearing shell of the connecting rod is not supported selectively but over a certain circumferential area on the bearing journal, the most heavily loaded peripheral region 11a1 - depending on how generous it is interpreted - an area that may even begin just before the radially outermost point 13 and extending over an angular segment opposite to the direction of rotation 28 of eg 60 °.

For the other crankpin 1a, this is the analogous area when it is in the highest position.

The pressure exerted by the connecting rod transmits primarily to the corresponding crankpins, from there, however, on the cheeks 5 and at least on the two axially adjacent center pivot 1 b and less strongly on the axially farther center pivot 1 b, through the Pressure of the connecting rod on the circumferential area 11a1 opposite side with the peripheral portion 111 'are pressed into their bearing shell.

For this reason, the circumferential regions 11a1 ', 11a2' of the center-bearing journal 1b which are diametrically opposite the two circumferential regions 11a1 and 11a2 are likewise heavily loaded regions.

The heavily loaded peripheral areas are exclusively structured or structured more strongly than the rest of the peripheral area, but preferably only these areas are structured so as to be able to save processing of the remaining peripheral areas.

It is shown by the example of a six-cylinder crankshaft in FIG. 2b that the entire heavily loaded regions 11a1, 11a2, 11a3 of all crankshaft journals opposite circumferential regions 11a1 ', 11a2', 11a3 'are in each case structured, even though only in all of the center journal 1b which could be structured to the two axially adjacent Hublagerzapfen opposite circumferential regions. This is based on the consideration that the load on further distant pivot bearing journals can place more stress on the respective center pivot in the corresponding peripheral area.

FIG. 3 b further shows that only the middle width region of the bearing 1 is structured transversely to the direction of movement of the circumferential direction, that is to say in the axial direction 10. This is sufficient in many cases, especially if the bearing surface 1 - as shown in Figure 5d - is not cylindrical but slightly convex, because in sliding mating with a cylindrical bearing shell then results in the central region of the axial extent of the smallest bearing gap in Operation and thus the greatest danger of eating the camp.

As FIG. 3 a shows, in the axial direction either the entire width of the bearing 1 or only the axially middle region of the bearing 1 is structured in accordance with the invention, possibly also in addition to the structuring, which may also be zone-wise in the circumferential direction. Here, the sliding surface is provided in the structured area with a plurality of very small recesses 27, as shown in the enlarged plan view of Figure 3a, since it has been found that even a regional structuring significantly reduces the friction, the non-structured area, however, contributes to Bearing load of the bearing to drop only slightly:

These recesses 27 are viewed in plan view, for example, round or elongated, for example in the form of a short groove with semicircular ends, designed, wherein the distance 21 between the recesses 27 about ten times that of round recesses 27 diameter d or elongated recesses 27 of smallest extension e corresponds.

The area fraction of the depressions within the structured area should be in the range of 1% to 30%. Preferably, the recesses 27 are arranged in a uniform grid, for example a diamond-shaped grid, one diagonal of which lies in the circumferential direction 28.

In elongated recesses 27, the main direction of extension 20 should primarily in the circumferential direction 28 of the bearing 1, ie the later direction of rotation, and for this purpose occupy an angle of 30 ° maximum. Furthermore, it has been found that the shape and size of the depressions 27 are of great importance in achieving this goal, as illustrated in the sectional representations of FIGS. 4a, b:

Because the wells should have a maximum depth of a few μιτι, sometimes deep even under a μιτι, as this minimizes the carrying capacity, but still a sufficient depot effect and thus a reduction in friction by itself.

Compared to the depth t of the recesses 27, the recesses 27 may have a smallest extension e, for example in the case of round recesses 27 having a diameter d of 50 or even 150 μιτι, so that the recesses 27 are very large and flat in relation to their depth t , which is not shown realistically in FIGS. 4a, b for reasons of clarity, because the shape of the flanks 18 of the depressions 27 is to be represented there:

In the vertical section can - as shown in Figure 4 a - the depressions symmetrically, in particular rotationally symmetrical, be designed so the flanks 18 have the same skew angle 9 to the surface of the bearing 1, which should be less than 60 °.

Additionally and / or instead, the flank 18 should extend into the surface of the bearing 1 with a rounding 20 of at least a radius of two Turn over μηη. Both measures contribute to the fact that the lubricant received in the depressions 27 during operation of the crankshaft can be well transported away in the peripheral direction 28 by means of adhesion to the contact surface of the bearing block and thus can be transported into the bearing gap away from the recesses 27.

It is also not harmless to form the steep edge in the later rotational direction 35 of the crankshaft 2 18 steeper, since the entrainment of the lubricant takes place only in the opposite direction. As a result, the volume of the individual depressions 27 is increased without negative influence and thus the depot effect is improved.

Due to the said small depth t of the depressions 27 -which, by the way, also unfold their full effect even without deliberately induced connections with each other, it is obvious that in the areas between the depressions 27, the roughness of the surface of the bearing 1 must be in a range which less than the depth t of the recesses 27. Apart from the fact that these areas between the wells should also have a sufficient support portion of, for example 60% to 70%, it is therefore useful - depending on the last processing step before the PECM processing - To smooth the areas between the recesses 27 electro-chemically, so in particular remove the tips of the microscopic surface structure in these areas.

FIG. 6 shows how this may also be possible in one operation together with the introduction of the depressions 27: As explained with reference to FIG. 2, a material removal takes place over the entire active surface 24 of the electrode 25, but the size of the material removal also depends on the material Distance 3 between the active surface 24 and the workpiece 2 from: Therefore, it is possible to execute the elevations 26 on the electrode 25 with a substantially greater height h than the desired depth t of the recesses 27 to be produced therewith, which results in the distance 3 between the electrode 25 and the workpiece 2 between the elevations 26 remains much larger and the material removal occurring there correspondingly lower.

By determining the height h in comparison to the desired depth t, thus controlling the minimum achievable distance 3 in the region between the elevations 26 toward the workpiece 2 during processing, the material removal and thus the smoothing effect during the introduction of the recesses 27 in the Areas are controlled in between, of course, depending on other parameters such as current flow, material of the workpiece 2, etc.

As shown in FIG. 6 in an enlarged partial area, the tips of the microscopic surface structure present there are partially removed in the region between the depressions 27, so that the remaining valleys between them are less deep and the carrying proportion between the depressions 27 increases.

FIGS. 5a to d show possible procedures for introducing the depressions into the surface of the bearing 1:

The difficulty lies in the fact that at a working gap 3 between the tool 25, the electrode, and the sliding surface 1 to be machined, for example, the curvature of the active surface 24 of the tool 25 in the circumferential direction 28 coincides very precisely with the curvature of the sliding surface 1 must, in order to ensure at all points in the range of 10 to 20 μιτι equal working gap. In view of the machining inaccuracies of the lateral surface of the bearing, which are always present in the μ-range, 1, this is a great challenge, even when the tool 25 is stationary during machining relative to the bearing 1.

As Figure 5a shows, the tool 25, the active surface 24 extends in the circumferential direction 28 over a circumferential angle 6, for example, 100 °, before and behind this peripheral region via spacers 16 which extend in the axial direction 10, the Z-direction, and the contact are placed on the peripheral surface of the bearing 1, thereby creating a defined working gap 3.

For this purpose, preferably, the bearing point 1 on the opposite side stable by means of a support 23, for example, a Lü- nice 23, radially supported. For this purpose, however, it is necessary that either the tool 25 or the entire tool unit 14, in which the tool 25 is located, either floating in the Y direction over a limited path of, for example, 50 μιτι, because an active setting in Y-. Direction around such small amounts and in adaptation to the individually slightly different shaped bearing 1 is hardly possible.

The other possibility is that the tool 25 or the tool unit 14 is limitedly pivotable about an axis parallel to the C-axis, so that both spacers 16 can bear against the bearing point 1 nen. In the same way, in addition or instead, a pivotability about the B-axis makes sense, in order to ensure the contact of the active surface with the two axial ends at the bearing via spacers 16. The spacers 16 are preferably designed as spacer strips. These can, as can be seen in FIG. 5a, extend in the axial direction or extend in the circumferential direction, as can be seen in FIG. 5d, or they can individual, more punctual, spacers each at the corners of the rectangular active surface 24 of the tool 25 may be present.

Preferably, however, the active surface 24 should not be in an always the same distance, the working gap, to be machined surface of the bearing 1 during processing, but this distance should intermittently, so pulsating, change during processing, so in the state of a slightly larger Spacing the metal ions dissolved out of the surface of the workpiece 2 can be flushed out more easily by means of the electrolyte 4 pressed into the working gap 3 by the tool 25.

Such a pulsating movement of the tool 25 and thus alteration of the working gap 3, the change of which is likewise intended to carry only a few μιτι, is in practice even more difficult to represent:

On the tool 25 fixedly arranged spacers 16 would strike in this case at each renewed approach again on the workpiece 2, which either leads to a strong wear of the spacers 16, which still have to be electrically non-conductive material, such as plastic or ceramic , and / or leave unwanted marks on the bearing 1.

One possibility - as shown in FIG. 5a in the left-hand half of the figure - is therefore that the spacers 16 are arranged movably on the tool 25 in the radial direction. As a result, it is possible for the spacers 16 to remain permanently attached to the sliding surface 1 to be processed, and for the tool 25 to oscillate in a pulsating manner relative to the spacers 16 in the direction of the sliding surface 1 and back away therefrom.

In the right half of Figure 5a is shown as a second solution that a variable in thickness element, such as a piezoelectric element 15, is arranged either in the spacer 16 or in the tool 25 or in between, and on the control of the thick-variable element, a relative movement between the consistently fixed to the sliding surface 1 abutting spacers 16 and the tool 25 is achieved.

Both in these solutions and in solutions that do not require any spacers 26, the back pressure created in the supply line for the electrolyte 4 could be determined by means of a pressure sensor 17 in the supply line between the pump and outlet opening in the active surface 24 for the electrolyte 4 and be used as a parameter for the control of the distance between the tool 25 and to be machined sliding surface 1, because the worse by the narrowing work gap drainage of the electrolyte will lead to an immediately higher pressure in the supply line.

FIG. 5 d shows that, in the axial direction 10, a straight active surface 24 with the elevations 26 on the tool 25 can be selected, despite the convex contour of the bearing 1 in this direction. It can rest in the tool 25 at the axial ends via spacers 16 on the sliding surface 1. Due to the lower working gap 3 in the middle region in the axial direction, the recesses formed there will be deeper in the surface of the workpiece than in the axial end regions, which however corresponds to the load and the lowest bearing gap in later operation. In addition, it is avoided in this way to have to produce an also in this direction spherical active surface 24 on the tool 25.

FIG. 5b shows in the lower half of the figure that with large circumferential areas to be structured it is also possible to work with a plane active surface 24, which can roll on the rotationally symmetrical bearing point 1 through circumferentially extending, lateral stop bars 16 via a desired circumferential segment. In the upper half of the figure, it is shown that the workpiece 25 can also have an effective surface 24 concavely curved in the axial direction, but whose radius of curvature 7 is slightly larger than the convex curvature of the bearing point 1.

Regardless of whether the tool is stationary to the workpiece during work or these roll on each other, can be adjusted in this way, the existing during processing gap 3 either in the circumferential direction 28 in the middle region, ie in the highest load, the lowest and there produced wells 27 have the greatest depth or 28 everywhere equal deep recesses 27 are generated in the circumferential direction. The surface to be structured and also the active surface 24 of the tool 25 is not square as a rule, but larger in one direction of extent than in the other. In the example shown in FIGS. 5 a and c-with FIG. 5 c showing a plan view of the active surface 24-the larger direction of extent is the circumferential direction 28.

In order nevertheless to ensure a uniform outflow of the electrolyte 4 in all directions at the same speed from the feed opening for the electrolyte 4, a flushing groove 22 running in the direction of the greatest extension direction of the active surface 24 is preferably inserted into the active surface 24 End surfaces of the active surface 24 can end freely, but can also end before. As a result, the electrolyte 4 can distribute itself in the direction of the greatest extent with low flow resistance and from there flow away in the direction of the lesser extent, in this case the axial extent of the active surface 24, through the working gap 3. LIST OF REFERENCE NUMBERS

1 bearing point, sliding surface

1a stroke bearing surface, stroke bearing

1 b center bearing surface, center bearing

2 crankshaft, workpiece

3 distance, working gap

4 fluid, electrolyte

5 cheek

6 circumference angle

7 radius of curvature

8 rounding

9 skew angle

10 axial direction, axis of rotation

11 subarea

11a peripheral area

11 b width range

12 total width

13 radially outermost point

14 tool unit

15 piezo element

16 spacers

17 pressure sensor

18 flank

20 main direction

21 distance

22 groove

23 support, bezel

24 effective area

25 tool, electrode

26 survey

27 deepening 28 direction of movement, Drehnchtung

29 transverse direction

B B axis

d diameter

e smallest extent

E largest extent

t depth

h height

Claims

1. sliding surface (1), in particular sliding bearing surface, in particular rotationally symmetrical sliding bearing surface, for sliding movement along a

Counter surface whose surface is structured by depressions,

characterized in that

- The sliding surface in the direction of movement (28) in those portions (11) in which the main load occurs,

and or

- In the transverse direction (29) to this direction of movement (28) in the sub-areas (11) in which the bearing gap during operation is the lowest, differently structured, in particular only in these sub-areas (11) structured, than in the other areas.

2. sliding surface according to claim 1,

characterized in that

transverse to the direction of movement, the middle width region (11b), in particular of 50% of the total width, is more structured than the edge regions, or only the central region is structured.

3. sliding surface according to claim 1 or 2,

characterized in that

in circumferential sliding surfaces, in particular in rotationally symmetrical sliding bearing surfaces, in the direction of movement (28), the circumferential direction, only a range of less than 90 °, in particular less than 70 °, in particular less than 60 °, in particular less than 45 ° deviating from the rest or even only structured, and / or

in the rotationally symmetrical sliding bearing surfaces of a crankshaft (2) for a reciprocating internal combustion engine

on the slide bearing surface of the stroke bearing (1a) of the peripheral region (11a1, 11a2) of 30 ° in the direction of rotation to 60 ° against the direction of rotation (28) of the stroke bearing, in particular of 20 ° in the direction of rotation is up to 55 ° against the Drehhchtung of the lifting bearing from the radially outermost point (13) of the pin bearing pin from stronger or even only structured.

4. sliding surface according to one of the preceding claims,

characterized in that

in the rotationally symmetrical sliding bearings of a crankshaft for a reciprocating internal combustion engine on the plain bearing surface of the center bearing (1b)

either those one or two peripheral regions (11a1 \ 11a2 ') which correspond to the more or less structured peripheral regions (11a1,

11a2) of the one end or the two adjacent crankpins (1a) are opposite and facing away from it

or the peripheral regions (11a1, 11a2 ') which are opposite to all stronger or even structured circumferential regions (11a1, 11a2) of all the journal bearing journals are stronger or even structured.

5. sliding surface according to one of the preceding claims,

characterized in that

only one of the sliding surfaces of a sliding pair is structured.

6. sliding surface according to one of the preceding claims,

characterized in that

the depressions (27) have a depth (f) of at most 10 μιτι, in particular a maximum of 5 μιτι, in particular a maximum of 1 μιτι own, and / or

- In the area between the wells, the surface has a roughness of Rz, which is less than the depth of the wells, in particular of less than 5 μιτι, in particular between 1 and 4 μιτι and / or a carrying amount of at least 50%, but not more than 85%.

7. sliding surface according to one of the preceding claims,

characterized in that

the area occupied by depressions (27) - in the case of area-wise structuring, only calculated on the more or less structured range - 1% to 30%, in particular 10% to 20%, and / or

the ratio of the depth (t) to the largest superficial extent (E) of the recesses is between 0.005 and 0.02, in particular between 0.008 and 0.012.

8. sliding surface according to one of the preceding claims,

characterized in that

- In the supervision considered a smallest extension (s) of a maximum of 150 μιτι, better at most 100 μιτι, better at most 50 μιτι, and / or

- viewed in the top view, the maximum extent (E) of the recess (27) is at most a factor of 10, better only by a factor of 5, better only by a factor of 3 as the smallest extent (e).

9. sliding surface according to one of the preceding claims,

characterized in that

the recesses (27) at the transition between the flanks (18) to the surface of the bearing (1) has a rounding (20) with a radius of at least 2 μιτι and / or a skew angle (9) of less than 60 ° to the surface, and /or

at a relative to the direction of movement of the sliding surface, in particular the circumferential direction (28), the recesses (27) lying section directed against the direction of flank (18) of the recess (27) is less steep than the opposite edge (18), in particular with a Angle of maximum 45 °, better of maximum 30 °, better of maximum 25 °, better of maximum 20 ° to the surface between the recesses (27).

10. Machine (30) for machining rotationally symmetrical bearing points (1), in particular on a crankshaft (2), by means of electrochemical removal,

characterized in that the machine (30) is a machine tool with a workpiece spindle arrangement as in a lathe, has a controlled C axis and the tool (25) is arranged in a tool unit (14) which is actively movable in the X and Z directions and In the Y-direction limited movable, in particular floating, is, in particular by a maximum of 100 μιτι, or is floating around the C-axis.

11. Machine according to claim 10,

characterized in that

the tool unit (34) is rotatably rotatable about the B-axis, in particular is limited to float floating.

12. Tool (25), with an active surface (24), the elevations (26), for processing convexly curved sliding surfaces, in particular rotationally symmetrical bearing points, in particular on a crankshaft (2), by means of electro-chemical erosion (ECM),

characterized in that

the active surface (24) of the tool (25) extends only over a range of less than 90 °, in particular less than 70 °, in particular less than 60 °, in particular less than 45 °.

13. Tool according to claim 12,

characterized in that

in the circumferential direction, the active surface (24) of the tool (25) either flat and tangential to the convexly curved surface of the workpiece (2) or concave curved, but with a particular by a factor of 1.1 - 2.0 larger radius of curvature (7) than is the convexly curved sliding surface, and / or

the elevations (26) on the active surface (24) of the tool (25) at least a factor of two, better by a factor of three, larger

Have height (h) as the depth (t) of the recesses (27) to be produced therewith.

14. Method for machining sliding surfaces by means of electrochemical erosion (ECM),

characterized in that

During machining, the distance between tool (25) and workpiece (2) alternately increases and decreases by means of vibration, in particular by means of vibration of the tool (25), and / or the application of current to the tool (25) pulses (PECM), in particular synchronous to the vibration.

15. The method according to any one of the preceding method claims, characterized in that

the tool (25) during removal by means of spacers (16) is held at a defined distance from the sliding surface and the spacers, in particular spacer strips, are arranged at the opposite ends of the tool in the largest direction of extent

and in particular in the direction of movement of the sliding surface running in the tool, a flushing groove for the conductive fluid is incorporated, which is in particular at least 1/10 mm deep, and / or with pulsating current application, the down payment of the pulses and / or the duration of the pulses as a reference variable for the Control of the

Method, in particular for the termination of processing, is used.

16. The method according to any one of the preceding method claims, characterized in that

in continuous current application, the temperature of the electrically conductive liquid and / or the current is used as a reference variable for the control of the process, in particular for the termination of processing.

17. The method according to any one of the preceding method claims, characterized in that

with an oscillating change in the distance between the tool and sliding surface during machining

either the pressure change in the electrically conductive liquid is used for the control of the distance

or the spacers, in particular spacer strips, of the tool can be changed in their thickness, in particular in the form of a piezoelectric element,

- The tool is movably disposed on the sliding surface on the sliding spacer in the direction of the sliding surface and away from the sliding surface and is driven.

18. The method according to any one of the preceding method claims, characterized in that

for changing the imaging sharpness of the surface structure of the tool (25) on the workpiece (2)

- either the distance (3) between the tool (25) and the workpiece (2) is changed, in particular at a vibrating distance (3) the smallest distance is changed during the vibration

- or the current is changed.

19. The method according to any one of the preceding method claims, characterized in that

- By means of the electro-chemical ablation, especially in the surface treatment, a material removal of a maximum of 30 μιτι, better only 20 μιτι, better only 10 μιτι, but in particular at least 0.5 μιτι, better of at least 2 μιτι, and / / or

when machining the tool (25) at a distance (3) to the sliding surface of 5 μιτι to 400 μιτι, better at a distance (3) of 10 μιτι to

100 μιτι, is held.

20. The method according to any one of the preceding method claims, characterized in that

for producing recesses (27) in the sliding surface

- Either a tool (25) with elevations (26) is used, and the fluid required for the current flow (4) in particular over the center of the active surface (24) of the tool (25) during machining in the gap (23) between the tool (25) and workpiece (2) is supplied

- Or a tool (25) with a smooth active surface (24) is used and a mask (22) of non-electrically conductive material with openings between the workpiece (2) and tool (25) is held, and the required fluid (4) in particular between the mask (22) and the sliding surface along the surface is supplied and removed.

21. The method according to any one of the preceding method claims, characterized in that

simultaneously with the machining of the sliding surface in the interior of the workpiece (2) a deburring is carried out by electro-chemical removal, in particular at the intersections of holes.

22. The method according to any one of the preceding method claims, characterized in that

the structuring is introduced by means of ECM or PECM.