GB2239927A

GB2239927A - Piston for internal combustion engines

Info

Publication number: GB2239927A
Application number: GB9100541A
Authority: GB
Inventors: Hans Spaeth; Stefan Lipp
Original assignee: Mahle GmbH
Current assignee: Mahle GmbH
Priority date: 1990-01-13
Filing date: 1991-01-10
Publication date: 1991-07-17
Anticipated expiration: 2011-01-10
Also published as: FR2657120B1; DE4000846C2; GB2239927B; DE4000846A1; JPH04292558A; FR2657120A1; JP3065361B2; GB9100541D0

Abstract

In a piston for internal combustion engines, comprising a lower part 1 forming the skirt and an upper part forming the 1 ring region and connected to the former by tension bolts, wherein each tension bolt in the piston lower part bears against a compression sleeve 2 fitted into a bore in the piston lower part. The compression sleeve 2 sealing surface of the piston leads tangentially into the cylindrical wall surface of the bore housing the compression sleeve (2) via a radius R1, the magnitude of which is greater than the difference in the radii of the bore and that of the inner periphery of the compression sleeve (2). <IMAGE>

Description

- 1 PISTON FOR INTERNAL COMBUSTION ENGINES This invention relates to a

piston for internal combustion engines of a kind including a lower part forming the skirt region, an upper part having a crown, and tension bolts connecting the two parts together, wherein the tension bolts in the piston lower part each bear against compression sleeves engagiong into associated bores in the piston lower part, the material of the sleeves having a higher E-modulus than that of the piston lower part, and wherein each bearing between compression sleeve and piston lower part, in the unstressed condition, is provided by surfaces inclined relative to each other, a radially, outwardly diverging annular gap existing in this condition between the surfaces opposite one another, the size of this gap being so designed that the bearing surfaces, in the tightened condition, bear against each other without any gap with uniform prestress.

In pistons of this kind, the bearing surfaces of the compression sleeve and piston, at which the compression sleeve and piston touch each other, are inclined only very slightly to the plane perpendicular to the piston longitudinal axis. The inclination of the seating surface at the p i ston s i de on 1 y has advantages f rom the mach i n i ng aspect and is therefore only as large as is necessary for achieving good machining. The slope in each case is obtained by an annular spherical surface portion, this portion leading via a different transition radius, into the wall of the bore provided for the particular compression sleeve. The bearing surface on the associated compression sleeve is, in these cases in which the seating surface at the piston side is concave, correspondingly convex. The curvatures of the two bearing surfaces differ to the extent that, in the cold state, an outwardly diverging annular gap exists between the bearing surfaces. The size of the annular gap is so designed that this gap, in the tightened state, no longer exists and the bearing forces in the radial direction are approximately of uniform magnitude.

Such forms of construction of the mutual bearing surfaces at the compression sleeve and piston sides are themselves known, one specific form of embodiment, for example, being described in DE-C 26 47 250. The special feature in the embodiment of the bearing surfaces according to that specification is that the radii of curvature for the bearing surfaces on the compression sleeve and inside the piston do not have their centre-point in common located on the axis of the tension bolt. This special feature is, in practice, not usually realized. Here, the centre-points of both radii of curvature as a rule lie on the axis of the tension bolt, being spaced only axially from each other.

In forms of construction of this type of the bearing surfaces between compression sleeve and piston, a problem consists in that only a very small space is available radially inside the bore for receiving the compression sleeve. Consequently, the bearing surface inside the piston must be utilized radially as far out as possible. As a result, frequently a sufficiently large transition radius from the concave seating surface into the cylindrical wall surface of the bore housing the compression sleeve cannot be real i zed. This leads, in certain cases of especially high loading, to cracks occurring within the piston material in the region of the aforementioned radius of curvature.

Bearing surfaces of small diameter of the compression sleeves that support tension bolts in a piston of this category are known from DE Patent Application M 12787 Ia/46c. In the construction in that document, the relevant bearing surfaces are relatively steeply inclined with respect to a plane perpendicular to the bolt axis. In pistons, in which the compression sleeves do not bear against intermediate components fitted into the piston, but directly against the piston material, accurate manufacture of bearing surfaces inclined in this manner and adjoining transition radii is difficult, because these surfaces are each at the end of a blind hole.

An object of the present invention is to provide an improvement in a piston of this category according to DE-C 26 47 250, with the simplest possible means.

According to the invention there is provided a piston for internal combustion engines, comprising a lower part forming the skirt region, an upper part having a crown, and tension bolts connecting the two parts together, wherein the tension bolts in the piston lower part each bear against compression sleeves engaging into associated bores in the 1 piston lower part, the material of the sleeves having a higher E-modulus than that of the piston lower part, and wherein each bearing between compression sleeve and piston lower part, in the unstressed condition, is provided by surfaces inclined relative to each other, a radially, outwardly diverging annular gap existing in this condition between the surfaces opposite one another, the size of this gap being so designed that the bearing surfaces, in the tightened condition, bear against each other without any gap with uniform prestress, characterised in that the bearing surface of the piston for the compression sleeve leads via a rad i us tangen ti al 1 y i nto the wal 1 f ace of the bore contai ni ng the compression sleeve, the value of which radius is greater than the difference between the radii of the bore present there and that at the internal periphery of the compression sleeve seating at the piston side.

Further according to the invention the bearing surface at the piston side has, at its inner periphery, an inclination of more than 10 with respect to a plane perpendicular to the piston longitudinal axis.

The fundamental advantage of the solution according to this invention lies in the fact that, as a result of an overall greater slope of the bearing surface between compression sleeve and counter-bearing on the piston, a larger force transmission surface between compression sleeve and piston-side counter-bearing can be achieved for a given diameter of the bore which houses the compression sleeve.

0 Consequently, the radial extent of the bearing region can be reduced compared with less inclined bearing surfaces, with the result that space for a larger transition radius from the piston-side bearing surface into the cylindrical wall face of the piston bore housing the compression sleeve can be created.

Since the curved seating surface simultaneously constitutes a transition radius running tangentially into the cylindrical wall of the bore, the transition radius can be constructed ideally large.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a section through a part of a compression sleeve seated in a seating bore of a piston, and FIGURE 2 is a part section of a portion of the section shown in Figure 1 on a larger scale.

Reference 1 denotes the piston and reference 2 the compression sleeve. Between the points A and B, a bearing exists in the tightened state. The different radii R, and R2 of the radii of curvature of the seating at the piston side and surface of the compression sleeve respectively are to be so dimensioned that the bearing forces, in the tightened condition, within the entire bearing region between A and B are approximately uniform, the different materials of the compression sleeve 2 and piston 1 to be taken into account accordingly. With a radially outwardly diverging gap in the region between A and B, the material of the compression 1 6 sleeve 2 has a larger E-modulus than the material of the piston 1. The piston 1 may be, for example, of light metal and the compression sleeve 2 of steel.

The centres of the radii of curvature R, for the curved piston bearing surface and R2 for the curved compression sleeve bearing surface each lie adjacent to the axis of the bore, the length and position of the centre of radius of curvature being such that a tangential transition from the piston bearing surface into the cylindrical region of the compression sleeve seating bore is obtained.

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Claims

CLAIMS:

1. A piston for internal combustion engines, comprising a lower part forming the skirt region, an upper part having a crown, and tension bolts connecting the two parts together, wherein the tension bolts in the piston lower part each bear against compression sleeves engaging into associated bores in the piston lower part, the material of the sleeves having a higher E-modulus than that of the piston lower part, and wherein each bearing between compression sleeve and piston lower part, in the unstressed condition, is provided by surfaces inclined relative to each other, a radially, outwardly diverging annular gap existing in this condition between the surfaces opposite one another, the size of this gap being so designed that the bearing surfaces, in the tightened condition, bear against each other without any gap with uniform prestress, characterised in that the bearing surface of the piston (1) for the compression sleeve (2) leads via a radius (R,) tangentially into the wall face of the bore containing the compression sleeve (2), the value of which radius is greater than the difference between the radii of the bore present there and that at the internal periphery of the compression sleeve seating at the piston side.

2. A piston according to claim 1, characterised in that the bearing surface at the piston side has, at its inner periphery, an inclination v more than 10 with respect to a plane perpendicular to the Diston longitudinal axis.

3. A piston for internal combustion engines substantially as described with reference to the accompanying drawings.

Published 1991 at Tbe Patent OMce. State House. 66/71 High Holborn, London WCIR 47?. Further copies rnay be obtained from Sales Branch. Jnit 6. Nine Mile Point. Cwmfelinfach, Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.

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