DE102009060352A1 - Method for manufacturing cam shaft to control valve of internal combustion engine, involves connecting empty shaft and cams to cam shaft, and forming coarse pattern in sections of cam openings inner surfaces and empty shaft outer surface - Google Patents

Abstract

The method involves undercooling an empty shaft of a rounded outer profile relative to multiple disk-like cams (10), and inserting the undercooled empty shaft into aligned cam openings (14). Temperature equalization is managed among the empty shaft and the cams such that the empty shaft and the cams are firmly connected to a cam shaft. A coarse pattern is formed in sections of inner surfaces (16) of the cam openings and/or an outer surface of the empty shaft, where the coarse pattern is produced by laser ablation and the sections are enclosed by the cam openings in an insertion condition.

Description

Field of the invention

• – Ausrichten einer Mehrzahl scheibenartiger Nocken mit je einem zentralen, runden, senkrecht zu einer Nockenhauptebene erstreckten Durchbruch derart, dass die Durchbrüche der axial beabstandet angeordneten Nocken miteinander fluchten,
• – Unterkühlen einer Leerwelle runden Außenprofils relativ zu den Nocken, wobei der Außendurchmesser der unterkühlten Leerwelle kleiner und der Außendurchmesser der nicht unterkühlten Leerwelle größer als der Innendurchmesser der Nockendurchbrüche ist,
• – Einschieben der unterkühlten Leerwelle in die fluchtenden Nockendurchbrüche, Herbeiführen eines Temperaturausgleichs zwischen der Leerwelle und den Nocken, sodass die Leerwelle und die Nocken fest zu einer Nockenwelle verbunden werden.

The invention relates to a method for producing a camshaft for valve control of an internal combustion engine, comprising the steps:

• Aligning a plurality of disc-like cams, each with a central, circular, perpendicular to a cam main plane extending breakthrough such that the openings of the axially spaced cams are aligned,
• Subcooling an empty shaft round outer profile relative to the cams, wherein the outer diameter of the supercooled idler shaft is smaller and the outer diameter of the non-subcooled idler shaft is greater than the inner diameter of the cam openings,
• - Inserting the supercooled idler shaft in the aligned cam openings, causing a temperature compensation between the idler shaft and the cam, so that the idler shaft and the cam are firmly connected to a camshaft.

State of the art

Such a method is known from the WO 2009/065970 A1 , The method disclosed therein is used in particular for the production of camshaft cylinder head cover modules for internal combustion engines. For this purpose, a series of axially spaced positioning discs is fixed on a machine platform. Each positioning disc has a receptacle for a cam. The cams are provided as disk-shaped elements with ground contour. The outer contour corresponds to a calculated shape which is optimized in each case for the specific application case, ie the specific internal combustion engine in which the module is to be used. The discs also have a round through hole perpendicular to their disc plane. In the positioning discs, the cams are aligned with each other so that their relative angular and axial position corresponds to the desired position on the camshaft. The holes are aligned by the disk body to each other in alignment. Further, a hood member is slipped over the aligned cam so that holes in the walls of the hood element are aligned with the cam holes. A highly supercooled relative to the cam and the hood element empty shaft is then inserted into the holes. The outer diameter of the empty shaft and the inner diameter of the holes are dimensioned so that the idler shaft can be inserted in the supercooled state without force or at least low-force into the holes, whereas their diameter in the non-supercooled state slightly larger than the inner diameter of the cam holes and very slightly smaller than that Inner diameter of the hood bores is. With such dimensioning of the diameter, a subsequently introduced temperature compensation leads to a fixed press connection of the empty shaft with the cams and to a backlash-free, rotatably movable mounting of the empty shaft in the hood bores.

Those skilled in the art will recognize that the exact sizing of diameters is critical to the function of the resulting shaft hood module. Correspondingly high demands are placed on the manufacturing precision of the corresponding elements. The higher the precision requirements, the higher the manufacturing costs. For cost reasons, therefore, higher tolerances would be desirable.

task

It is the object of the present invention to develop a generic method such that larger manufacturing tolerances are possible.

Presentation of the invention

This object is achieved in conjunction with the features of the preamble of claim 1, characterized in that the inner surfaces of the cam openings and / or the outer surface of the empty wave in their embraced state of the cam openings embraced sections have a generated by laser ablation spatial pattern.

The basic idea of the invention is to produce an increased friction between the cams and the idler shaft, so that a greater undersize of the idler shaft or a larger excess of the cam penetrations becomes tolerable without adversely affecting the strength of the camshaft, in particular the torsional safety of the cams. For this purpose, it is concretely proposed to roughen at least one of the surfaces which interact with one another during the resulting press connection, laser ablation being used as the roughening agent. In contrast to purely mechanical processes, laser ablation has the advantage that it is not subject to wear and is highly reproducible, but on the other hand is also very flexible with regard to the details of the generated spatial pattern.

The space pattern preferably has a maximum amplitude, ie a maximum radial distance between its lowest and its highest points of 2 to 20 microns, in particular of 4 to 6 microns. In this case, the maximum difference to the level of the unprocessed surfaces is preferably ± 1 to 10 micrometers, in particular ± 2 to 4 Micrometers. These values have proven to be particularly favorable in experiments.

The generation of the space pattern by means of laser ablation is particularly suitable for producing a space pattern which, as is preferred, deviates in both directions from the level of the unprocessed area. In laser ablation, the surface is irradiated with a laser beam whose energy density is above the damage threshold of the processed material. The concrete location of the damage threshold depends, among other things, on the absorption capacity of the material for the selected laser wavelength. The person skilled in the absorption properties of the different materials are known, so that he can determine the choice of the appropriate laser wavelength and the choice of energy density used without extensive experiments in each case. During the irradiation of the material whose surface absorbs laser energy and is partially melted. This leads to a partial evaporation of the material, for. But also for raising walls and crater edges in the micrometer range. The machined surface thus has surface points that are below the surface level of the unprocessed surface, as well as points that are above this level. This is considered to be particularly favorable, since the empty wave can be produced with its calculated nominal dimension, regardless of whether the method according to the invention is to be used or not. The same applies to the cam openings. The application of the method according to the invention only leads to an improvement in the frictional engagement of the press connections, thus increasing the manufacturing tolerances. Nevertheless, the use of the method according to the invention requires no conversion of an already established and rehearsed production process.

In an advantageous embodiment of the invention, the spatial pattern is modulated in the axial direction. This means that the microscopic space pattern is overlaid with a "stripe structure" of varying mean height level. The strips preferably extend in the axial direction. As a result, a tooth-like structure is established in addition to improving the frictional engagement by the roughening, which counteracts a torque acting on the cam and thus its rotation relative to the shaft.

The method according to the invention is not only suitable for improving the production of separate camshafts; In particular, it can also be used to improve it basically known, already explained above method for the production of shaft hood modules.

In other words, it is preferably provided that prior to insertion of the empty shaft, a hood element, relative to which the supercooled idler shaft is also undercooled and whose walls have round openings, is aligned relative to the cams so that the cam openings and the hood openings are aligned with each other the hood openings larger than the cam openings are that the idle shaft in the inserted state, both the cam openings and the hood breakthroughs interspersed and that after insertion of the empty shaft temperature compensation also takes place relative to the hood. It is particularly provided that the inner diameter of the hood openings are dimensioned so that after the induction of the temperature compensation, the camshaft is mounted without play and rotatably in the hood openings. Here, the inventive method even has special advantages: to ensure the best possible synchronization and low wear of the camshaft in the cylinder head cover, it is necessary that in particular the bearing points of the shaft in the hood walls are of the highest precision. In the preferred embodiment, no separate bearing elements are provided; Rather, the shaft is mounted directly in the precision holes of the hood walls. This means that particular importance must be attached to this interface during production. In the event of deviations from the nominal values, such shafts and hood elements must be combined with one another whose production deviations compensate each other. However, the cams and their holes are produced in a separate, separate manufacturing process. It would therefore mean a decidedly high cost and possibly high rejection, if even the cams would have to be individually selected so that their manufacturing deviations also "match" the manufacturing deviations of the shaft and the hood elements. The advantage achieved by the invention of a higher manufacturing tolerance, especially in the case of the cams, is therefore of very particular importance in the manufacture of shaft-hood modules.

Further features and advantages of the invention will become apparent from the following specific description and the drawings.

Brief description of the drawings

Show it:

1 a perspective view of a cam for use in the inventive method,

2 a schematic representation of a portion of an empty shaft for use in the inventive method,

3 a pseudo-perspective view of a room model on a microscopic scale.

Detailed description of preferred embodiments

1 shows a cam 10 for use in the method of the invention. The cam 10 has disc-shaped shape with a polished outer contour 12 and a central hole 14 , On the inner surface 16 the bore 14 is applied by laser ablation a spatial pattern, however, that in 1 can not be seen.

2 shows an empty wave 20 for use in the method according to the invention, in which, alternatively or in addition to the in 1 roughening of the cam bore shown 14 at different axially adjacent positions 22 Spatial pattern by laser ablation on the surface of the empty wave 20 are applied. The axial positions 22 correspond to those positions where on the finished shaft, the cams 10 are positioned.

Details of the room pattern in a preferred embodiment are in 3 recognizable. 3 shows a computer-generated, pseudo-perspective view of the room model at the axial positions 22 the empty wave 20 and / or on the inner surface 16 the cam bore 14 , The with the reference number 32 marked, comparatively flat pattern areas correspond substantially to the unprocessed surface. A stripe-like exposure of the surface with laser light of suitable wavelength and energy density leads to a strip-like cratering ( 34 ), with the longitudinal crater 34 of ramparts 36 flanked by molten and thrown up material. This stripe structure represents a modulation superimposed on the microscopic space pattern, where the width of the in 3 each strip shown is about 0.1 mm. Microscopic material roughening, especially in the area of crater strips, has characteristic dimensions of one to a few micrometers. The height difference between the bottom of the craters 34 and the tops of the ramparts 36 are about 5.5 microns. Differences to the level of unprocessed strips 32 is about ± 2 to 3 microns.

Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative embodiments of the present invention. A broad range of possible variations will be apparent to those skilled in the art in light of the disclosure herein. In particular, the actual selected room pattern may differ from the embodiment shown here. For example, crossed structures or non-modulated uniform space pattern structures are also conceivable. Although the use of a Nd: YaG laser is preferred, other types of lasers may be used.

LIST OF REFERENCE NUMBERS

10

cam

12

Outer contour of 10

14

Bore of 10

16

Inside surface of 14

20

empty shaft

22

Axial position on 20

30

Space Uster Profile

32

unprocessed strip

34

crater

36

rampart

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2009/065970 A1 [0002]

Claims (6)

Method for producing a camshaft for valve control of an internal combustion engine, comprising the steps of: - aligning a plurality of disk-like cams ( 10 ) each having a central, circular, perpendicular to a cam main plane extending breakthrough ( 14 ) such that the breakthroughs ( 14 ) of the axially spaced cam ( 10 ), - subcooling an idle shaft ( 20 ) round outer profile relative to the cam ( 10 ), wherein the outer diameter of the supercooled hollow shaft ( 20 ) smaller and the outer diameter of the not supercooled idle shaft ( 20 ) greater than the inner diameter of the cam openings ( 14 ), - inserting the supercooled idle shaft ( 20 ) in the aligned cam openings ( 14 ), - causing a temperature compensation between the idle wave ( 20 ) and the cam ( 10 ), so that the empty wave ( 20 ) and the cams ( 10 ) are fixedly connected to a camshaft, characterized in that the inner surfaces ( 16 ) of the cam openings ( 14 ) and / or the outer surface of the empty wave ( 20 ) in their inserted state of the cam openings ( 14 ) sections ( 22 ) a space pattern produced by laser ablation ( 30 ) exhibit. Method according to claim 1, characterized in that the spatial pattern ( 30 ) has a maximum amplitude of 2 to 20 microns, especially 4 to 6 microns. Method according to one of the preceding claims, characterized in that the spatial pattern ( 30 ) has a maximum difference from the unprocessed surface level of ± 1 to 10 microns, more preferably ± 2 to 4 microns. Method according to one of the preceding claims, characterized in that the spatial pattern ( 30 ) is modulated in the axial direction. Method according to one of the preceding claims, characterized in that - before the insertion of the idle shaft ( 20 ) a hood element relative to which the supercooled idle shaft ( 20 ) is also undercooled and whose walls have round openings, relative to the cam ( 16 ) is aligned so that the cam openings ( 14 ) and the hood openings aligned with each other, wherein the hood openings larger than the cam openings ( 14 ), - the empty wave ( 20 ) in the inserted state both the cam openings ( 14 ) and the hood breakthroughs interspersed and - after insertion of the empty wave ( 20 ) Temperature compensation also takes place relative to the hood. A method according to claim 5, characterized in that the inner diameter of the hood openings are dimensioned so that after the induction of the temperature compensation, the camshaft is mounted without play and rotationally movable in the hood openings.

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