DE102011006498A1 - Defined oil holding holes in bolt holes - Google Patents

Abstract

Piston for internal combustion engines, which has a piston shaft (11) with pin bores formed therein, the inner surface of at least one pin bore (20), which comes into contact with a piston pin when the piston is used as intended, has a plurality of pocket-shaped depressions.

Description

Technical area

The bolt holes provided in the piston skirt ensure the connection between the piston pin and the piston. The piston pin is in contact via friction surfaces in the pin bores, wherein, in addition to thermal stresses, mechanical gas and mass forces in particular act on the pin bores. The piston pin is floating for power transmission, d. H. stored with an oil film in the pin bore of the piston.

Again and again, it comes due to the thermal and mechanical stresses to mixed friction, caused by insufficient lubrication between the bolt and pin bore. This leads to increased friction and at worst to a seizure between piston pin and piston, which ultimately can lead to failure of the engine.

State of the art

Various measures have been taken so far to reduce the loads on the bolt holes. For example, is from the EP 0 740 750 B1 known to equip a light metal piston for internal combustion engines with bolt holes, which have in the region of the zenith of the bolt holes in the direction of the pin bore axis extending recesses. The recesses are produced without cutting by casting, roughening or the like, as well as by machining. The recesses extend from the piston pin retention groove to the interior of the piston, over a length of 10 to 80% of the bearing length of the piston pin.

An evolution of the EP 0 740 750 B1 is the EP 1 232 349 B1 , which proposes roughening the bolt holes in the area of the zenith by means of laser beams.

Although the above documents seek to improve the lubrication ratio in the pin holes, the specific distribution of thermal and mechanical stresses along the friction surface of the pin holes is not considered.

Description of the invention

An object of the invention is to reduce the probability of failure of a piston due to cracking or the like in the area of the bolt holes under optimized lubrication conditions.

The object is achieved with a piston according to claim 1 and a method according to claim 9.

According to the invention, the inner surfaces of one or both of the bolt bores, that is to say the surfaces which come into contact with a piston pin introduced therein when the piston is used as intended, are provided with a plurality of blind-hole-shaped depressions. By introducing, preferably by means of a laser, such depressions, oil depots are created which reduce the probability of the above-mentioned mixed friction by a defined and steady release of oil. At the same time, the recesses or blind holes damage the friction surface of the pin holes only locally, so that starting points for crack formation are reduced compared to a surface roughening or in comparison to extended, groove-shaped depressions. For this reason, the failure probability of the piston is reduced with excellent lubricating oil supply. Preferably, the blind holes are provided as micro-wells with about 50 microns in diameter and / or depth.

It should be noted that the recesses may be formed both in the piston material itself and in a separately inserted bushing. In both embodiments, the piston according to the invention can be advantageously combined with both a "floating" piston pin and a so-called. Klemmpleuelbolzen. By a "floating" bolt is meant that the bolt in the piston and / or connecting rod can rotate freely. In the starting d. H. When cold, there is a so-called cold play between the bolt and the connecting rod as well as between the bolt and the piston, which increases as a result of the heating during operation. Through the game, a rotational movement of the bolt is possible at any time. The resulting hydraulic state in the region of the bearing of the bolt is neither purely hydrostatic nor purely hydrodynamic, but is to be described as an intermediate state. In such a floating mounting the axial securing of the bolt usually takes place by introduced into the piston retaining rings. A Klemmpleuelbolzen be understood that the bolt is thermally joined in the connecting rod and so far can not rotate freely. However, there is a game between the bolt and the piston, only on the retaining rings for axial fixation can be dispensed with. Also in this embodiment, the bolt rotates with respect to the piston, so that the lubrication achieved with the present invention can be used advantageously as well as in a floating storage.

For a further reduction of the crack formation, several or all blind holes are preferably provided with a circular cylindrical cross section perpendicular to the axial direction of the blind hole.

In the area of the zenith of the bolt opening, the thermal and mechanical loads are greatest when the piston is used as intended. Thus, the depths of the blind holes in the zenith of the pin bore preferably smaller, in order to affect the structural integrity of the piston material in the region of high loads only slightly. More preferably, no blind holes are present directly in the area of the zenith. In order to cope with the stress distribution that occurs, the depths of the pin bores may gradually decrease from the bottom to the zenith of the bore. The term "gradual" also includes a gradual decrease, with the percentage or absolute decrease in depth from the bottom to the zenith not being linear.

In addition to an adaptation of the depth of the blind holes in the load distribution of the bolt holes may alternatively or additionally be provided a decrease in the opening cross-sections from the lower portion of the bore to the zenith, so that the opening cross-sections (perpendicular to the direction of insertion of the blind holes) in the zenith of the pin hole smaller, preferably the same Are zero, or gradually decrease from the bottom of the bolt hole to the zenith.

The blind hole density can additionally or alternatively be controlled in this way to the blind hole depths and / or opening cross sections. Blind hole density is the number of blind holes per unit area.

In addition to an increased load in the area of the zenith of the bolt holes, an unequal distribution along the bolt axis can be determined. The preferably cylindrical piston skirt has an outer side and an inner side forming a cavity. The thermal and mechanical loads on the pin bore are larger on the inside, in the axial direction of the pin bore, than on the outside. Thus, not only an adaptation of the blind hole depths, opening cross sections and / or densities in the circumferential direction of the pin bore is preferred, but also along the axial direction.

Thus, the depths of the blind holes in the axial direction of the pin bore inside preferably fall smaller than outside, or they fall away completely in an inner region, the depths preferably decreasing gradually from outside to inside.

Additionally or alternatively, the opening cross-sections may be smaller from the outside in, the decrease preferably taking place gradually.

Additionally or alternatively, the above-defined blind hole density can be smaller in the piston pin in the inner region of the piston shaft, the blind hole density preferably decreases gradually from outside to inside in the axial direction of the pin bore.

The six control parameters, blind hole depth, blind hole cross-section and blind hole density along the circumferential direction of the pin bore, and blind hole depth, blind hole cross-section and blind hole density along the axial direction of the bolt can be adjusted individually or in any combination to adapt to the given load conditions. By introducing the blind holes punctually, an adaptation or readjustment to the given load conditions, possibly incorporating new knowledge, in the context of the manufacturing process quickly, without a fundamental redesign of the oil retention and distribution structures possible.

For introducing the blind holes, a laser is preferably used with which damage to the material surrounding the blind holes areas is minimized. Alternatively, pits of the above type can be created by electron beam drilling. Due to the perforation with the electron beam, the holes have a typical shape. In the case of passage openings, which are not encompassed by the invention, the jet exit side is sharp-edged and gradfrei. On the entrance side there is a slightly conical inlet.

The drilling or lasering of the blind holes is preferably carried out with a high surface quality, as is ensured for example by helical drilling. When helical drilling, the laser radiation is set in a rotational movement relative to the workpiece. Here are the material removal due to the low Abtragsvolumens per pass multiple passes over the workpiece required. On the other hand, the formation of a melt base is kept low due to the small Abtragsvolumens in the opening reason, whereby a high surface quality of the opening wall is achieved.

Brief description of the drawings

1 shows in a cross section of a pin bore their thermal and mechanical stress distribution.

2 schematically shows a piston for illustrating the opening parameters to be controlled.

3a to 3g show distribution geometries and size changes of the blind holes.

Ways to carry out the invention

1 is a cross-section through a piston along the axial direction of a pin bore 20 and axially along a piston stem 11 taken.

The piston has a piston head 10 with combustion bowl 12 and grooves 13 . 14 . 15 for piston rings. Furthermore, a cooling channel 16 provided by which the piston can be cooled in its highly loaded areas.

The bolt hole 20 of the piston shaft 11 has a friction surface 21 on. Blind holes according to the invention are in the 1 Not shown. Rather, the 1 the distribution of thermal and mechanical loads in the intended use of the piston graphically dar. This shows the eingekringelte area 30 a section of particularly high thermal and mechanical stress. this section 30 forms around the zenith 22 around. In the area below 23 the bolt hole 20 , on the other hand, the piston material is exposed to lower loads.

Furthermore, the section is particularly high load 30 in the 1 shifted to the left, ie the piston material in the area of the pin bore 20 is exposed to higher loads inside than outside. Here, "outside" refers to the peripheral area of the shaft 11 and "inside" the cavity-side region of the stem 11 ,

The pistons point in the pin bore 20 at Zünddruckbelastung a high mechanical load. To prevent cracks at the lubrication pockets or blind holes due to an unauthorized high voltage increase, the lubrication pockets should be in the area of increased tension 30 less large and / or less deep and / or less frequently executed. If necessary for the strength and the lubrication still sufficient, these can be omitted in the highest loaded area. The lubrication pockets can be used on bushes and busheless pistons. The size and / or depth of the blind holes should be at zenith 22 are made smaller and / or less deep. This is also to be considered in the longitudinal direction of the piston bore. To the in 1 Thus, it has proven to be useful to make the blind holes according to the invention in the zenith 22 less pronounced than at the bottom 23 , This is in the side view of 2 shown schematically with an arrow. In the 2 are details from the 1 omitted.

In the 3a to 3g are shown geometries of the distribution of the blind holes and cross-sectional changes of the same, as in the friction surface 21 the bolt hole 20 can be introduced. The focus here is on the blind hole diameter and arrangement of the blind holes. The depth of the blind holes is not shown but may alternatively or additionally be varied as described above. It should be noted, however, that the 3a to 3g are schematic in nature and show only exemplary possible distribution geometries of the blind holes and changes in their diameters. The position and orientation of the friction surface cutouts shown in the overall structure of the piston are only partially apparent.

In 3a There are no blind holes in the area of the zenith and in the cavity-side area of the friction surface. In the 3a and 3b Blind holes are executed on both sides of the zenith, with their diameter in the 3b in the circumferential direction of the pin hole 20 from the zenith 22 increases away. The the 3b similar 3c shows a one-sided arrangement. In the 3d is the increase in the blind hole diameter shown in the longitudinal direction along the bolt axis. In 3e the blind holes extend in the circumferential direction, wherein no blind hole is provided in the zenith. In the circumferential direction from the zenith, the blind holes are larger. In 3f a line is shown along the bolt axis. A linear geometry, in which two lines of blind holes intersect, is in 3g shown.

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

• EP 0740750 B1 [0003, 0004]
• EP 1232349 B1 [0004]

Claims (11)

Piston for internal combustion engines having a piston skirt ( 11 ) with bolt holes formed therein ( 20 ), wherein the inner surface ( 21 ) at least one pin bore ( 20 ), which comes into contact with a piston pin in the intended use of the piston, having a plurality of blind-hole-shaped recesses. Piston according to claim 1, characterized in that several or all blind holes have a circular cylindrical cross section perpendicular to the axial direction of the corresponding blind hole. Piston according to claim 1 or 2, characterized in that the depths of the blind holes in the zenith ( 22 ) of the bolt bore ( 20 ) are smaller, preferably equal to zero, the depths from the lower region ( 23 ) of the bolt bore ( 20 ) to the zenith ( 22 ) preferably gradually decrease. Piston according to one of the preceding claims, characterized in that the opening cross-sections perpendicular to the direction of insertion of the blind holes in the zenith ( 22 ) of the bolt bore ( 20 ) are smaller, preferably equal to zero, wherein the opening cross sections of the lower area ( 23 ) of the bolt bore ( 20 ) to the zenith ( 22 ) preferably gradually decrease. Piston according to one of the preceding claims, characterized in that the blind hole density in zenith ( 22 ) of the bolt bore ( 20 ) is smaller, preferably equal to zero, wherein the blind hole density from the lower region ( 23 ) of the bolt bore ( 20 ) to the zenith ( 22 ) preferably decreases gradually. Piston according to one of the preceding claims, characterized in that the depths of the blind holes in the piston pin in the inner region of the piston skirt ( 11 ) are smaller, the depths from outside to inside with respect to the piston skirt ( 11 ) preferably gradually decrease along the piston pin direction. Piston according to one of the preceding claims, characterized in that the opening cross-sections perpendicular to the direction of insertion of the blind holes in the piston pin in the inner region of the piston skirt ( 11 ) smaller, wherein the opening cross-sections from outside to inside with respect to the piston shaft ( 11 ) preferably gradually decrease along the piston pin direction. Piston according to one of the preceding claims, characterized in that the blind hole density in the piston pin in the inner region of the piston skirt ( 11 ), wherein the blind hole density from outside to inside with respect to the piston skirt ( 11 ) preferably decreases gradually along the piston pin direction. Piston according to one of the preceding claims, characterized in that the blind holes have a depth and / or a cross-sectional diameter perpendicular to their insertion direction of a few tens of micrometers, preferably in the range of 50 micrometers. Method for producing a piston according to one of the preceding claims, wherein the blind holes are introduced by means of a laser or by means of electron beams. A method according to claim 10, characterized in that the blind holes are introduced by means of laser helical drilling.

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