EP1321229B1 - Method for forming a bore - Google Patents

Description

The invention relates to a method of the type specified in the preamble of claim 1.

Particularly in cylinder bores of reciprocating engines such as internal combustion engines or compressors is trying to obtain good tribological conditions by a uniform and low clearance between the piston and cylinder. Since the cylinder bore deforms due to the stresses such as stresses and temperature in the operating state, the shape of a cylindrical bore in the unloaded state deviates in operation from the cylindrical shape.

In order to obtain a cylindrical bore in the operating state, is in the document JP 11267960 proposed to clamp the bore during machining with original expansion screws and original torques as in the operating state. In order to additionally simulate the deformation due to the effect of temperature, it is known to heat the workpiece by means of hot honing oil. However, these methods cause a great deal of effort in the production of the hole through the required devices. This processing causes high costs. Because of the relatively long heating time to temperatures of about 80 ° C to 140 ° C, the required safety devices, the seal wear and the required temperature, this method is used only for the individual production of high-quality engines. The actual state of deformation in operation is also insufficiently simulated by the said devices.

The DE-A-40 07 121 describes the honing of oval holes, as they are provided for example in cylinder blocks, in view of the thin webs ("fire bars") between adjacent holes also in the direction perpendicular to thinner walls and thus achieve a more uniform heat distribution. Instructions for solving the above problem do not arise from this.

The invention has for its object to provide a method of the generic type, which allows the production of holes with an ideal operating condition under deformation form with little effort. Furthermore, the object of the invention is to provide a honing machine for carrying out the method.

This object is achieved by a method having the features of claim 1.

The method provides to determine the deformation in the operating state for a particular hole and to determine from the deformation the initial shape, ie the shape to be produced during machining, which corresponds to the shape before installation. The determination of the deformation and the initial shape must be carried out only once per bore geometry and operating state. In particular, for the production of series components thereby reduces the cost compared to the distortion and heating of each hole during processing considerably. Because the deformation state does not have to be present on the machine itself, this can be determined much more accurate, so that the production of holes, which actually have a predetermined geometry in the operating state, is possible.

In an embodiment of the invention it is provided that the desired shape, i. the mold is cylindrical under operating conditions. Another embodiment variant provides that the initial shape is cylindrical. In particular, in the case of a cylindrical nominal shape, it is provided that the initial shape is determined theoretically.

The deformation is expediently determined experimentally. In particular, the deformation is determined by static compression and measuring the geometry obtained. In order to obtain particularly accurate deformation data, however, it may be advantageous for the deformation to be determined by dynamic measurement during operation. The deformation can also be determined theoretically, in particular by computer simulation.

It is envisaged that the initial shape is produced by temporally and spatially varied machining parameters. In principle, the initial shape can be produced by methods with a defined cutting edge, grinding, spark erosion or honing. However, the machining process is in particular a honing process, the tool being a honing tool which is arranged on a spindle and which comprises at least one honing stone which is pressed against the wall of the bore with a feed pressure. It is envisaged that the delivery pressure of at least one honing stone during the processing time is varied. The delivery pressure is varied in particular as a function of the rotational position of the spindle. As a result, different bore inner radii can be achieved in the circumferential direction of the bore. Appropriately, the delivery pressure is varied depending on the stroke position of the spindle, resulting in different bore inner radii seen in the axial direction of the bore.

Fig. 1

einen Schnitt durch eine Bohrung mit Ausgangsform,

Fig. 2

einen Schnitt entlang der Linie II-II in Fig. 1,

Fig. 3

eine schematische Darstellung eines Schnitts entlang der Linie III-III oder III'-III' in Fig. 1,

Fig. 4

eine schematische Darstellung eines Schnitts entlang der Linie IV-IV oder IV'-IV' in Fig. 1,

Fig. 5

einen Schnitt durch eine Bohrung in Sollform (Betriebsform).

An embodiment of the invention will be explained below with reference to the drawing. Show it:

Fig. 1

a section through a hole with initial shape,

Fig. 2

a section along the line II-II in Fig. 1 .

Fig. 3

a schematic representation of a section along the line III-III or III'-III 'in Fig. 1 .

Fig. 4

a schematic representation of a section along the line IV-IV or IV'-IV 'in Fig. 1 .

Fig. 5

a section through a hole in nominal form (operating form).

To make a hole 1 with the in Fig. 5 shown cylindrical nominal shape 3, which results from deformations in the operating state, the first in the Fig. 1 and 2 illustrated output form 2 of the bore 1 determined. The initial shape 2 is the shape of the hole 1 before installation. The initial shape 2 is largely cylindrical in an upper region 5 and elliptical in a lower region 7. The representation of the deviation of the elliptical from the cylindrical shape is in the Fig. 1 and 2 not to scale, but shown greatly enlarged. In fact, the deviation is in the range of about 8 to 60 microns. The central region 6 represents a transition region from the cylindrical cross-sectional shape 8 to the elliptical cross-sectional shape 9. The cylindrical cross-sectional shape 8 is in Fig. 3 illustrated and the elliptical cross-sectional shape 9 in Fig. 4 ,

To determine the initial shape 2, the deformation of the desired shape 3 is determined in the operating state. The deformation can be determined experimentally by static distortion. For this purpose, a bore, in particular the cylinder bore of an engine block, in nominal form 3, in particular in a cylindrical shape, produced. Appropriately, the hole is machined by honing. The hole is then exposed to the stresses that occur during operation. For this purpose, for example the cylinder bore to be braced by the cylinder head, wherein the expansion screws used for fixing are tightened with the intended operating torques using the original seals. Depending on the operating state and required accuracy, in addition or as an alternative to this, the component can be heated to operating temperature and / or pressure can be applied with pressures prevailing in the operating state. The resulting form softening is determined by form test measurements.

However, the deformation can also be determined by the dynamic measurement of the change in shape during operation. Dynamic measurement is performed on cylinder bores, in particular during firing. The deformation can also be determined theoretically, in particular by a computer simulation. The computer simulation simulates the deformation during the fired operation with all detectable influencing variables. Suitably, the method by which the deformation is determined is selected depending on the required accuracy and the effort required for the determination.

From the determined deformation and the desired shape 3, the initial shape 2 is determined theoretically. The initial shape 2 is then produced by means of a machining process, in particular by means of a honing process. The honing machine for machining the hole comprises one to four honing stones. The delivery pressure with which each honing stone is pressed against the wall of the bore 1 is separate for each honing stone controllable. The honing tool performs an oscillating movement in the direction of the axis 4 of the bore 1 and a rotational movement about the axis 4. To edit the upper portion 5 of the hole 1 all honing stones are pressed with the same feed pressure against the wall of the hole 1. The delivery pressure is not varied over the processing time. This creates the in Fig. 3 shown cylindrical cross-sectional shape 8. For the preparation of the elliptical cross-sectional shape 9, the Fig. 4 is shown, the feed pressure is increased to the honing stones in the direction of the X-axis and reduced in the direction of the Y-axis. In the central region 6, the feed pressure is additionally controlled in dependence on the stroke position of the spindle on which the honing tool is fixed. Since the bore geometry changes continuously in the middle region 6, honing stones with very little axial extension are used. To achieve greater accuracy, the tool has a lower and / or an upper guide.

If holes are needed which have a different from the cylindrical shape inner contour, the in Fig. 5 represented contour represent the initial shape and resulting from the load bore shape in the Fig. 1 and 2 have shown contour, which then represents the desired shape.

In principle, other production methods which permit the production of an inner contour deviating from the cylindrical shape can also be used in the production of a bore using the method according to the invention.

Claims (13)

1. Method for creating a bore, in particular the cylinder bore of a reciprocating piston engine, wherein, in the unloaded condition, the bore (1) has a starting form (2) and, in the operating condition, a target form (3) which differs from the starting form (2), characterised in that the deformation of a bore (1) to the target form (3) in the operating condition is determined, the starting form (2) is determined by means of the target form (3) and the deformation, and the bore (1) is brought into the starting form (2) with a processing method.
2. Method according to claim 1, characterised in that the target form (3) or the starting form (2) is cylindrical.
3. Method according to claim 1 or 2, characterised in that the starting form (2) is determined theoretically.
4. Method according to one of the claims 1 to 3, characterised in that the deformation is determined experimentally.
5. Method according to claim 4, characterised in that the deformation is determined by means of static pressing and measurement of the geometry obtained.
6. Method according to claim 4, characterised in that the deformation takes place by means of heating to the operating temperature.
7. Method according to claim 4, characterised in that the deformation is determined by dynamic measurement in operation.
8. Method according to one of the claims 1 to 3, characterised in that the deformation is determined theoretically, in particular by computer simulation.
9. Method according to one of the claims 1 to 8, characterised in that the starting form (2) is created by processing parameters which are varied temporally and spatially.
10. Method according to one of the claims 1 to 9, characterised in that the processing method is a honing process wherein the tool is a honing tool which is arranged on a spindle and which comprises at least one honing stone which is pressed with a feed pressure against the wall of the bore (1).
11. Method according to claim 10, characterised in that the feed pressure of at least one honing stone is varied during the processing time.
12. Method according to claim 11, characterised in that the feed pressure is varied depending on the rotary position of the spindle.
13. Method according to claim 11 or 12, characterised in that the feed pressure is varied depending on the stroke position of the spindle.

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