DE102008002618B4 - Piston with load concentration hydro channel - Google Patents

Abstract

Piston for an internal combustion engine, the piston having bolt holes (2) for receiving a piston pin, wherein at least one pin bore (2) has an inner surface (2 ') with a groove (10) extending substantially in a longitudinal direction of the pin bore (2 ), characterized in that the groove has a cross-section perpendicular to the extension direction, wherein a bottom of the groove is wider than the entrance of the groove.

Description

Technical area

The The invention relates to a piston for an internal combustion engine, having a pin bore for receiving a piston pin, wherein the pin bore has an inner surface with a groove, which extends substantially in a longitudinal direction of the bore.

Background of the invention

Piston, which are used in internal combustion engines are high pressures and Exposed to stress. Structural defects, such as Cracking or cracking due to material fatigue, have their cause in the above demanding working conditions.

The explanation is in 1A a photograph of a pin bore of a piston used shown. 1B is an enlarged photograph showing part of a cross section of the pin bore. The cross section is taken along the top dead center of the pin bore and shows a typical piston pin bore crack.

Therefore it is desirable the stress and stress distribution and durability of the piston to control. Currently applied design features for modifying the pin bore contact surface of the Piston, for Durability of the components, include profiling the entire bore surface with a number of different conical, parabolic and oval shapes. Recessed bows, Partial sheets and Cones, collectively known as side-by-side features, which the whole or a part length along the horizontal bore surface surrounded, will also change the Durability of the piston components used.

profiles which are introduced into the bore area, are in the circumferential direction pronounced while side recesses partial cuts or recesses that are normally in the radial depth is not greater than 1 mm from the primary bore radius are. In general, the page cut features are outside cut the fundamental bore area of the piston and pin, approximately +/- 30 Degrees from the top dead center position of the pin hole.

The Reducing stress and improving durability the piston is an important field of research. Piston designs and Materials, for example, in terms of load distribution and Crack formation tested and analyzed. To understand the problems associated with material fatigue, the to structural defects, such as a tear propagation (almost fracture) leads, related, it is desirable to control the local stress concentration and distribution. accelerated fatigue tests For validation of technology can be additional, costly model forms and tools are needed.

The US 2006/0144351 A1 discloses a piston for an internal combustion engine having a pin bore for receiving a piston pin having an inner surface with an oil circulation groove and a transverse groove.

The DE 31 20 842 A1 describes a piston pin bearing for light metal piston, in which in the region of the zenith of the hub bore substantially parallel to the bolt axis extending and open to the piston interior recesses are provided.

Summary of the invention

It It is an object of the invention to provide control of a load or to improve the stress distribution of a piston.

The Task is solved with a piston according to claim 1. The dependent claims relate to preferred embodiments.

Of the Piston has a pin bore with an inner surface, which as a warehouse for a piston pin is used. The piston of the invention is characterized that the inner surface the bolt hole a groove with a cross section perpendicular to the extension direction wherein a bottom of the groove is wider than the entrance the groove is. Generating the desired durability of the piston By incorporating the above groove is an advantage of the invention, there are no special and additional Molds needed become. Problems associated with a tensile fracture propagation (fast fracture) are, can in fatigue tests be better controlled using the innovative groove. As a further advantage, the groove acting as a cooling oil transport channel acts, improved lubrication of the piston pin due to Channel designs (deposed from the contact surface) ready. The Groove can vary in size and shape to the desired Stress concentration for an accelerated fatigue test to create. Such control of local stress concentration allows the application of a better, more consistent "designed by analysis" philosophy.

Preferably, the groove is a so-called "tear drop" groove. The "tear drop" groove comprises an open, substantially circular cross-section, wherein the open arc of the circular cross-section is smaller than the closed arc. The above cross section is taken along the plane perpendicular to the longitudinal direction, ie the axial direction, of the pin bore. The closed arc refers to a segment of the circular contour defined by the interface between the circular groove and the fixed structure of the piston. Assuming that a remaining segment closes the above segment so as to form a closed circular contour, the remaining segment is referred to as an open arc.

Preferably is the cross section of the groove from the above circular cross section, which is on a rectangular Cross-section is located, so formed that the rectangular cross-section the inner surface the bore wall opens. The inlet channel, which is intended as the rectangular groove avoids the occurrence of splinter sections between the inner surface of the Bolt hole and stress concentration circular groove. The splinter avoiding rectangular section does not necessarily match the above circular Section can be combined and can just as well an entrance area for any another groove according to the invention form. The "tear drop "nut will simply introduced. Dependent on the piston size is the rectangular one Cross section preferably in the order of 2 to 5 mm. Of the Diameter of the circular Section is preferably 3 to 10 mm.

Preferably the piston has two opposite ones Bolt holes, both of which are provided with a "tear drop" groove, to avoid the generation of an asymmetric load distribution. The two pin bores are preferably flattened cylindrical piston stem formed at one end in one longitudinal direction of the shaft integrally connected to a cylindrical piston head is.

Preferably the groove extends along the entire longitudinal length of the Bolt hole to produce an asymmetric load distribution to avoid and / or to improve the reproducibility of the groove.

Preferably extends the groove through the area of the primary defect of the pin bore, to problems associated with train fracture propagation (fast fracture) in Areas of intense tension of the piston during accelerated fatigue tests related, to control. For this purpose, the groove is preferably through the upper Dead center of the bolt hole arranged.

Preferably the piston is made of aluminum or an aluminum alloy. The intention of improving the durability of a piston stands with the intention of weight reduction, in terms of energy efficiency desirable is, in contradiction. For a compromise between the two is the invention in particular for vehicle aluminum pistons important and suitable.

Out From the point of view of manufacture, the "tear drop" groove may preferably coincide with a third annular groove of the piston or, in some designs, fourth Soil / Schaftfurche be cut.

The "tear drop" cut is preferably a direct deep cut through the primary defect area made of, for example, vehicle aluminum piston pin bores is.

Brief description of the drawings

1A and 1B are photographs of a piston used, showing a crack in a region of top dead center of the pin bore.

2A and 2 B These are two different views showing bolt holes with "tear-trough" grooves.

3 shows the cross section of a "tear drop" groove.

Detailed description the preferred embodiment

2A and 2 B are three-dimensional views of a piston 1 , The piston 1 has a cylindrical head 3 with circular grooves for piston rings and a flattened cylindrical piston stem 4 on. Two bolt holes 2 for receiving a piston pin connecting the piston to a connecting rod are in the hollow piston shaft 4 intended. The piston shaft 4 is integral with the piston head at one end in its longitudinal direction 3 connected.

Every bolt hole 2 has an inner surface 2 ' with a "tear drop" groove 10 on, extending in the axial direction of the pin hole 2 extends and in the inner surface 2 ' the bolt hole 2 is arranged. The "tear drop" groove is a direct deep cut in the inner surface 2 ' the bolt hole 2 is arranged. One of the primary defect areas is around top dead center (TDC) of the pin bore. The TDC of the bolt hole is the line 0 ° in 1A is designated, ie the line of the inner surface 2 ' which extends in the longitudinal direction and a minimum distance to the piston head 3 having. The "tear trough" cut 10 of the piston in the 2A and 2 B is shown extends along the TDC and along the entire length of the corresponding pin hole 2 ,

3 shows a cross section of a "tear drop" groove 10 , The cross section is along a plane perpendicular to the axis of the pin bore 2 taken. The groove 10 includes a circular cross-section 11 which is above with respect to a rectangular cross-section 12 is positioned. The rectangular cross-section 12 the groove 10 reduces the likelihood of chipping.

Even though the embodiment described a so-called "tear drop 'groove used are changes of the groove design possible. The cross section of the groove perpendicular to the extension direction could, for example from a perfectly circular Deviate cross section. The groove could an ellipsoidal or oval cross section or a different type, flattened circular Have cross-section. The alignment can be either be vertical or horizontal to the piston bottom direction.

Claims (8)

Piston for an internal combustion engine, the piston having bolt holes ( 2 ) for receiving a piston pin, wherein at least one pin bore ( 2 ) an inner surface ( 2 ' ) with a groove ( 10 ) substantially in a longitudinal direction of the pin bore ( 2 ), characterized in that the groove has a cross-section perpendicular to the extension direction, wherein a bottom of the groove is wider than the entrance of the groove. Piston according to claim 1, characterized in that the groove ( 10 ) has an open, substantially circular cross-section ( 11 ), wherein the open arc of the circular cross section is smaller than the closed arc. Piston according to claim 2, characterized in that the cross section of the groove ( 10 ) of a circular cross-section ( 11 ), which extends above a rectangular cross-section ( 12 ) is formed so that the rectangular cross-section ( 12 ) the inner surface ( 2 ' ) of the bolt bore ( 2 ) opens. Piston according to one of the preceding claims, characterized in that the groove ( 10 ) along the entire longitudinal length of the pin bore ( 2 ). Piston according to one of the preceding claims, characterized in that the groove ( 10 ) through the primary defect area of the pin bore ( 2 ) is arranged. Piston according to one of the preceding claims, characterized in that the groove ( 10 ) through the top dead center of the pin bore ( 2 ) runs. Piston according to one of the preceding claims, characterized characterized in that the piston is made of aluminum or an aluminum alloy is made. Piston according to one of the preceding claims, characterized in that the piston has a piston head ( 3 ) with three annular grooves and the groove ( 10 ) is coincidentally cut with the third annular groove of the piston.