EP3036448A2

EP3036448A2 - Sliding surface,tool and method for producing said sliding surface

Info

Publication number: EP3036448A2
Application number: EP14753259.2A
Authority: EP
Inventors: Andreas Grützmacher; Emanuel GROß; Wolfgang Hafner; Matthias Weber; Jürgen REINGEN; Leo Schreiber
Original assignee: MAG IAS GmbH Eislingen
Current assignee: MAG IAS GmbH Eislingen
Priority date: 2013-08-21
Filing date: 2014-08-21
Publication date: 2016-06-29
Also published as: US9926968B2; CN105451921A; KR20160046805A; WO2015025004A3; WO2015025004A2; US20160273576A1; DE102013109025A1; JP2016532835A; MX2016001496A

Abstract

According to known solutions, in order to reduce friction in a sliding bearing (1), the sliding surface (1) is structured using ECM, by introducing a plurality of microscopically small depressions (27). According to the invention, in particular in the same working step, the intermediate spaces (6) between the depressions (27) are also smoothed, removing the peaks of the surface profile.

Description

sliding surface

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 pair, it is essential both for the magnitude of the sliding friction and for the service life of the sliding pair, in particular of the sliding bearing, that in all operating conditions as much lubricant as possible and in the most uniform possible distribution between the contact surfaces of the sliding pair , 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 microscopic depressions, which serve as a reservoir for lubricants. These recesses are due to the normal roughness of the material of the sliding surface, 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.

This approach, however, is time consuming with a large number of cavities, and the laser beam creates an undesirable pose surrounding the cavity annularly, and the laser machining results 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 produced, for example, the recesses described in introduced into 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 shaped electrode to the surface of the workpiece to be processed, serving as another electrode, material is removed from this surface in the form of ions. 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 shape deviation of the bearing of the ideal circular shape, roughness in the form of the average single roughness Rz = the microscopic roughness of the surface of the bearing point representing value in the form of the sum the height of the highest profile peak and the depth of the deepest valley, averaged over five individual measuring distances,

Roughness in the form of the arithmetic mean roughness value Ra = arithmetic mean of the magnitudes of the coordinate value of the roughness profile within a single measurement path,

Roughness in the form of the reduced peak height Rpk = height of the triangle of the same area with the summit surfaces with a specific base length in the case of an S-shaped Abott curve; this value allows the assessment of the tip area of a surface profile 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 between the actual center of the journal bearing pin from the actual center of the center bearing), the target 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

Center bearing axis and with respect to the angular position to the other crankpins.

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

The efficiency and cost-effectiveness of a machining process also plays a major role in practice, especially for mass production, in which cycle time and thus manufacturing costs play a decisive role, while processing in individual tests or for prototypes are not subject to these restrictions.

This applies in particular to the last method steps in the case of a workpiece, for example a crankshaft, fine machining and surface structuring, in particular of the bearing points.

In this context, it is known in principle to use the ECM method to achieve a certain low roughness, as described, for example, in DE 10 2008 011 893 and DE 10 2004 027 89. 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 production, 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, 7 and 10. Advantageous embodiments will be apparent from the dependent claims.

With regard to the sliding surface, the object is achieved by the roughness Rz is reduced in the structured area in the entire spaces between the wells over the roughness Rz in the non-structured areas of the sliding surface.

As a result, the bearing behavior in the interstices between the recesses is improved and the friction is reduced to a greater extent than merely by the introduction of the recesses in the structured region.

The areas between the recesses in the structured area should have a roughness R _a of max. 0.2 μιτι and / or a roughness R _pk of max. 0.16 m. The roughness Rz in the area between the recesses of the structured area should be at least 10%, better at least 20%, better at least 30% lower, than in the unstructured area. It has proven to be favorable that given in absolute values, the roughness Rz in the region between the depressions of the structured region is less than the depth of the depressions there, in particular less than 5 μιτι, better less than 4 μιτι, better less than 2 μιτι.

The carrying proportion in the region between the depressions of the structured region should preferably be at least 50%, better at least 75%. The roughness Rz should either increase or decrease between the wells with increasing distance from the wells, depending on the distance between two adjacent wells:

If the distance between two adjacent depressions is more than twice the lateral extent of the stray electric field of one of the elevations of the tool beyond the edge of this elevation, or if this distance is greater than the greatest extension of the depressions considered in the plan view the roughness Rz between the recesses increases with increasing distance from the recesses. The low roughness in the surrounding area of the recesses is then sufficient to effect the desired reduction in friction.

If neither condition is present, the roughness Rz between the wells should decrease with increasing distance from the wells. Because of the small distance in this case in the entire space between the wells the required low roughness for minimizing the sliding friction is necessary.

Preferably, in the structured region between the depressions, the tips of the microscopic surface profile removed by the reduction of the roughness Rz should each yield a convexly curved surface, preferably giving a hemispherical curve, so that no level plateau of the worn tip is more present. As a result, the sliding friction is also kept low.

With regard to the tool used for the electrochemical removal during structuring, the object is achieved in that the elevations on the effective surface of the tool have an at least a factor of 2, better at least a factor of 3, better at least a factor of 5, greater height as the depth of the wells to be made with it. The surface of the tool should have a roughness Ra in the region between the elevations which amounts to a maximum of 200%, better only a maximum of 50%, better still only a maximum of 20% of the roughness Ra of the surface to be produced at the corresponding point. This takes into account the fact that in the area between the elevations, the distance between the tool and the workpiece is substantially greater than in the region of the elevations themselves, and decreases with increasing distance between the tool and workpiece, the imaging accuracy of the structure of the tool on the workpiece.

Due to a bulge on the tool exactly between the elevations, the possibly no longer effective stray field of the elevations of the tool can be compensated in this area, and an approximately uniform reduction of the roughness Rz over the entire space between the elevations can be achieved. With regard to the production method, the object according to the invention is achieved by carrying out a roughness-reducing material removal in the structured area in the surface areas between the depressions, namely by the same method and in particular in the same working step as the introduction of the depressions.

In this case, the structuring and introduction of the recesses is preferably carried out by means of electrochemical removal, in particular pulsating electrochemical removal. The aim of the method is that in the structured area in the entire intermediate area between the depressions a material removal of the surface takes place and in particular the roughness Rz is at least 10%, better at least 20%, better at least 30% less than in the non-structured area ,

For this purpose, the manufacturing parameters are chosen accordingly, ie - the height of the elevations of the tool relative to the depth of the wells to be produced

and or

the distance between the wells

and or

- The distance between tool and workpiece during machining.

In the case of a rotationally symmetrical slide bearing surface, the structuring is carried out by introducing depressions and material removal between the depressions immediately after the grinding, so that the step of finishing in the structured region can be completely eliminated.

Since structuring is only carried out where there is a significant load on the rotationally symmetric slide bearing surface anyway, virtually no stress is present in the non-structured regions anyway, so there is no need to finish it. This saves on finishing as a whole.

The structuring by introducing recesses and the material removal between the recesses should thus be, in particular, the last material-removing machining step before the use of the plain bearing surface. c) embodiments Embodiments according to the invention are described in more detail below by way of example. Show it:

FIG. 1a shows a plan view of a structured region of a sliding surface;

FIG. 1 b: the enlarged view of a bearing point of a crankshaft,

FIG. 2: a section through depressions in the sliding surface,

Figure 3: an enlarged view of the tool in use on the

Sliding surface.

The friction in a hydrodynamic plain bearing, in which between the two sliding surfaces of the sliding pair is a lubricant, usually oil, which is distributed by the relative movement of the sliding surfaces to each other over the sliding surface and forms a sliding film in the bearing gap, friction can be reduced when in The sliding surface 1 distributes many microscopically small, in this case viewed in plan view, recesses 27, as shown in FIG. 1 a in the plan view of a sliding surface 1. Depending on the lubricant used, the material and surface finish of the sliding surface and a variety of other parameters, this effect can be enhanced by an optimized shape, size, depth, spacing and other parameters of the recesses 27. FIG. 1b shows, as a typical application of such a structured sliding surface 1, a bearing point of a crankshaft 2, in which recesses 27 are usually introduced only in a structured area 11, namely borrowed a peripheral region 11a and usually only a certain width range 11b of the total width 12 of the bearing 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:

As shown in FIG. 3, an electrode, which usually represents the negative shape of the sliding surface 1 to be produced, ie has elevations 26 on its active surface, is brought into the sliding surface 1 to be machined at a very close distance of a few μm. As a result of the electric current flowing from the tool 25 to the workpiece 2 via an electrically conductive liquid 4, the electrolyte, in the working gap 3, metal ions are dissolved out of the surface of the workpiece and the elevations 26 of the tool 25 form as depressions 27 on the surface 1 of the workpiece 2 from.

The area fraction of the depressions within the structured area should be in the range of 15% to 40%.

The area fraction of the interspaces 5 between the depressions 27 in the structured region is therefore significantly larger than the area fraction of the depressions 27.

The friction-reducing effect of the recesses 27 stems from the depot effect for the lubricant, by virtue of the plurality of recesses 27, which have a small absolute distance from each other, especially at the beginning of the relative movement in the sliding bearing, the lubricant pulled out of the recess 27 and in the Interspaces 5 is distributed between the recesses 27 in the bearing gap. As shown in Figure 2, at least the edge 9 of the recess through which the lubricant is pulled out during operation of the sliding bearing, formed obliquely. In general - especially at round recesses 27 - but all flanks 9 designed the same and have a rounding 8 at the transition to the spaces 5 on.

However, since the interstices 5 between the recesses 27 still primarily mechanically bear the load of the plain bearing, it comes to the load capacity of the bearing and other properties on the microscopic design of the surface in the interstices 5, in particular their roughness and supporting component, such as shown in the enlarged section in FIG.

This has hitherto been effected by a corresponding mechanical processing by means of grinding and finishing, until the desired roughness and, above all, a sufficient carrying component were present, and then the depressions 27 are introduced into the surface.

According to the invention, the introduction of the depressions 27 by means of ECM is used to reduce, in particular simultaneously, the roughness Rz in the interstices 5 between the depressions 27. FIG. 3 shows a possibility, as can be achieved by appropriate design of the tool 25 for the electrochemical removal:

For this purpose, the projections 26 formed on the active surface 24 of the tool 25, which are intended to image as recesses 27 in the surface of the workpiece 2, have a substantially greater height h than the depth t of the recesses 27 to be produced therewith.

This causes even at maximum approximation of the elevations 26 to the surface of the workpiece 2 - and if the recesses 27 have already partially formed therein, also in the recesses 27 - as shown in the left half of Figure 3, between the surveys 26 a significantly larger distance 3 between the tool 25 and workpiece 2 remains as in the area of the elevations 26th Since the removal action of the electrochemical removal depends, inter alia, on the size of this distance 3, the removal effect by the flowing in the spaces 5 between the elevations 26 stream from the tool 25 to the workpiece 2 is lower than in the area of the elevations 26, but still present.

By selective choice of the distance 3 at the maximum approximation of tool 25 and workpiece 2 - often an oscillating approach of tool and workpiece is used in electrochemical abrading, coupled with a synchronous pulsating current application - the size of the material removal in the spaces 5 can be determined become.

The removal of material in this area can be adjusted so that only the tips of the microscopic surface profile of the surface of the workpiece 2 are removed, so in particular the abraded tips a convex, in particular semi-spherical, contour thus form according to the enlarged view in Figure 2 of Traganteil is increased and the roughness Rz and / or Ra is reduced.

In this context, other factors have to be considered:

On the one hand, the current flow between the tool 25 and workpiece 2 is not only exactly perpendicular to the macroscopic contact plane between the two parts, but from the corners of the elevations 26 of the current flows also directed perpendicular to the surface of the tool 25, for example, their elevations 26, in the form my so-called stray field 29, and thus reaches the surface of the workpiece 2 even in the edge regions 6 of the intermediate spaces 5, as shown in Figure 2 in the right half of the picture. Since the distances 21 between the recesses 27 - as shown in Figure 1a, but are usually a multiple of the diameter of the recesses 27, thereby not the entire surface of the interstices 5 is processed. At the same time, a flow of current from the planar regions of the active surface 24 of the tool, ie the region between the elevations 26, in the direction of the interspaces 5 on the surface of the workpiece 2, and is superimposed in the edge regions 6 of the interstices 5 with the stray field 29 the surveys 26.

If this results in excessive material removal in these edge regions 6, this can be ensured by the specific design of the active surface 24 of the tool 25 in the area between the elevations 26, for example by this active surface 24 being lowered around the elevations 26 in the edge region 6 and in the middle region between a bulge 7 again. Furthermore, it must be taken into account that the microscopic structure of the surface of the tool 25 also images on the surface of the workpiece 2 in the area between the elevations 26, albeit on account of the greater distance with somewhat reduced imaging accuracy.

For this reason, care must be taken that the microscopic structure of the surface of the tool 25, taking into account the given imaging accuracy, also corresponds to predetermined parameters with respect to roughness and bearing component, especially in the region between the elevations 26, as shown in FIG.

Because an excessive roughness in these areas of the active surface 24 of the tool 25 would be where a sufficient support ratio and a required maximum roughness, the load of the sliding bearing depends, namely in the gaps 5 of the surface of the workpiece 2, by means of electrochemical ablation just one Surface structure with too little support and generate too high roughness. LIST OF REFERENCE NUMBERS

Bearing point, sliding surface

Crankshaft, workpiece

Distance, working gap

Fluid, electrolyte

gap

border area

on vault

curve

flank

axial direction, axis of rotation structured area

peripheral region

wide area

overall width

effective area

Tool, electrode

survey

deepening

Direction of movement, direction of rotation stray field

depth

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, wherein the surface of the sliding surface (1) by microscopic

Wells (27) is structured,

characterized in that

in the structured region (11) in the entire interstices (5) between the depressions (27) the roughness Rz is reduced compared to the non-structured regions.

2. sliding surface according to claim 1,

characterized in that

in the structured region (11), the intermediate spaces (5) between the recesses (27) have a roughness R _a of at most 0.2 μm and / or a roughness R _pk of not more than 0.16 μm.

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

characterized in that

in the intermediate spaces (5) between the depressions (27) of the structured region (11) the roughness Rz is at least 10%, better at least 20%, better at least 30% lower than in the non-structured region.

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

characterized in that

in the region between the recesses (27) the surface has a roughness Rz which is less than the depth (t) of the recesses (27), in particular of less than 5 μιτι, better of less than 4 μιτι, better of less than 2 μιτι, and / or a minimum of 50%, preferably at least 75%.

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

the roughness Rz in the region between the recesses (27) increases with increasing distance from the recesses (27), if the distance (21) between see two adjacent recesses (27)

- Either more than twice as large as the lateral extent of the electrical stray field (29) of the elevations (26) over the edge of the elevation (26) addition

- or greater than the maximum extension (E) of the well (27) considered in the supervision,

otherwise, conversely, the roughness Rz decreases with increasing distance from the recesses (27).

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

characterized in that

the peaks of the microscopic surface profile removed in the structured area in the course of the reduction of the roughness Rz are in each case so strongly rounded that the abraded tips no longer represent a plateau, but a convexly curved surface, in particular hemispherical rounding.

7. Tool (25) for machining convexly curved sliding surfaces (1), in particular rotationally symmetrical bearing points, in particular on a crankshaft (2), by means of electro-chemical ablation (ECM), characterized in that

the elevations (26) on the active surface (24) of the tool (25) have a height (h) greater than the depth (t) of at least a factor of two, better at least a factor of three, better at least a factor of five Wells to be produced therewith (27).

8. Tool according to claim 7,

characterized in that

the tool (25) in the region between the elevations (26) has a roughness Ra which amounts to a maximum of 200%, better still only a maximum of 50%, better only a maximum of 20% of the roughness Ra of the surface to be produced at the corresponding point.

9. Tool according to claim 7 or 8,

characterized in that

the tool (25) in the region between the elevations (26) has a bulge (7).

10. A method for at least partially structuring a sliding surface (1) by introducing recesses (27) in the surface thereof, characterized in that

in the structured area (11), a material removal which reduces the roughness Rz is also carried out in the intermediate spaces (5) between the depressions (27) by the same method and in particular in the same working step as the introduction of the depressions (27).

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

the structuring is carried out by means of electrochemical ablation, in particular an electrochemical ablation takes place in which the distance between the tool (25) and the workpiece (2) and / or the application of electrical current pulsate.

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

the height (h) of the elevations (26) of the tool (25) relative to the depth (t) of the recesses (27) to be produced on the workpiece (25) and / or the distance (21) between the recesses (27) and / or the Distance (3) between tool (25) and workpiece (2) during machining, so be selected that in the structured area (11) in the entire space (5) between the recesses (27) of the surface material removal takes place and in particular the roughness Rz by at least 10%, better at least 20%, better at least 30% less than in unstructured area.

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

in a rotationally symmetrical slide bearing surface structuring by introducing recesses (27) and material removal in the structured region between the recesses (27) is performed immediately after grinding, and this is in particular the last material removal machining step before the use of the sliding bearing surface.