GB2156479A

GB2156479A - Expansion-controlled light alloy piston

Info

Publication number: GB2156479A
Application number: GB08507376A
Authority: GB
Inventors: Bernd Waldhauer; Manfred Bordt
Original assignee: Kolbenschmidt AG
Current assignee: Kolbenschmidt AG
Priority date: 1984-03-23
Filing date: 1985-03-21
Publication date: 1985-10-09
Also published as: GB8507376D0; GB2156479B; DE3410655A1; FR2561711B1; FR2561711A1

Abstract

A light alloy piston, comprising segment-like expansion control elements 4,5, which are fusion- bonded to the load-carrying skirt portions 2,3, on the inside surface thereof and are anchored in the gudgeon pin bosses 8,9, the expansion control elements being exposed throughout their peripheral length in the machined oil ring groove and that portion of said expansion control elements which is adjacent to the piston head being covered on the inside for 10 to 50% of the height of the element by and fusion-bonded to a bead-like casting portion 13, which constitutes an extension of the piston head, is characterised in that, in order to ensure a reliable anchoring of the expansion control elements in the piston, each expansion control element is provided in that portion thereof, which is adjacent to the piston head with recesses 14, 15, which extend from the axial edges of the expansion control element over 20 to 30% of the total peripheral length of the element and have a height of up to 25% of the total height of the element and are filled with light alloy. <IMAGE>

Description

SPECIFICATION Expansion-controlled light alloy piston This invention relates to an expansion controlled light alloy piston for an internal combustion engines.

DE-AS 1078387 describes a so-called segment strip piston comprising segment-like, strip-shaped expansion control elements, which consist preferably of steel and are bonded to the inside peripheral surface of the piston along the load-carrying skirt portions and are anchored in the gudgeon pin bosses, the control elements being exposed almost throughout their peripheral extent in the machined oil ring groove above the gudgeon pin and that portion of each of said expansion control elements which is adjacent to the piston head is covered on the inside for 10 to 50% of the height of the element by and fusion-bonded to a bead-like casting portion, which extends between the gudgeon pin bosses as an extension of the piston head.

Such as segment strip piston combines the thermal and mechanical load-carrying capacity of a single-metal full skirt piston with the advantage of silent running afforded by a socalled ring belt piston in which a sheet steel ring is embedded in the upper end portion of the skirt between the gudgeon pin bosses and the oil ring groove above the gudgeon pin.

The two segment-like strip-shaped expansion control elements of the segment strip piston are in contact with the surface of the loadcarrying skirt throughout the peripheral extent of its inside surface and are anchored in the piston bosses. They have, as a rule, a radial thickness of about 1.5 mm and during the machining of the oil ring groove above the gudgeon pin have been intentionally exposed almost throughout their peripheral extent. A bead-like inner casting portion extends from the piston head approximately to the middle of the expansion control elements and is fusion-bonded to them. Because the light alloy shrinks on the expansion control elements, the operating temperature will result in an intermediate coefficient of expansion in that portion in which the expansion control elements are embedded.That coefficient of expansion depends upon the ratio of the wall thickness and lies between the coefficients of expansion of light alloy and steel. A specific feature of the segment strip piston is that the machining of the oil ring groove above the piston pin has not only the resuit that the embedded expansion control elements are exposed at their top edge but results also in the formation of a hardly noticeable small gap of about 50 ym between the expansion control element and the inwardly protruding casting portion covering said elements. This is due to the outward expansion of the expansion control elements and the light alloy shrunk on them from the outside. In response to a temperature rise, the expansion-controlled piston expands mainly in the plane of the pins and tends to return to its original round shape.The larger expansion of the piston head decreases the gap provided adjacent to the top edge of the skirt. Under a higher thermal loading, the internal casting portion covering the expansion control elements snugly contacts the latter so that the good backing required in that case is provided. There is also a bridge for the transfer of heat from the piston head to the skirt and that bridge is maintained as long as this is enforced by the high temperature of the piston head. The expansion control properties can be varied and adapted to the shape of a given piston by a variation of the height of the expansion control elements. Whereas the dissipation of heat in the manner described is not quite as effective as the dissipation of heat through a solid section of light alloy, it represents an optimum in cases in which an adequate expansion control of the piston is also required.But in many cases the height of the expansion control elements should be minimized, particularly in consideration of the weight. The manufacture of the piston requires a satisfactory casting operation involving a minimum tool expenditure and the embedded expansion control elements must be anchored in such a manner that they will not be loosened during the operation of the engine, even in modern internal combustion engines operating at high speeds.

It is an object of the invention to preclude a loosening of the expansion control elements during an operation of the engine. According to the invention there is provided an expansion-controlled light alloy piston for an internal combustion engine, wherein segment-like, strip-shaped expansion control elements are bonded to the inside peripheral surface of the piston along the load-carrying skirt portions and are anchored in the gudgeon pin bosses, the control elements being exposed almost throughout their peripheral extent in the machined oil ring groove above the piston pin and that portion of each of said expansion control elements which is adjacent to the piston head being covered on the inside for 10 to 50% of the height of the element by and fusion-bonded to a bead-like casting portion, which extends between the piston bosses as an extension of the piston head, and wherein each expansion control element is formed in that portion which is adjacent to the piston head with recesses, which extend from the axial edges of the expansion control element for 20 to 30% of the total peripheral length of the expansion control element, which have a height of up to 25% of the total height of the expansion control element and which are filled with light alloy.

The expansion control elements preferably consist of steel and are preferably pierced to assist their retention in the light alloy.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Figure 1 is a frong elevation of an expansion control element.

Figure 2 is a sectional view of the expansion control element taken on the line I-I in Fig. 1, Figure 3 is a longitudinal section through an expansion controlled piston showing on the left a longitudinal sectional view on the plane defined by the piston axis and the gudgeon pin axis and on the right a longitudinal sectional view on a plane which is at right angles to the first-mentioned plane, Figure 4 is a cross-sectional view taken on the line ll-ll in Fig. 3.

Referring now to the drawings, there is shown an expansion-controlled piston 1 comprising a light alloy casting, in which segment-like strip-shaped expansion control elements 4 and 5 of steel are fusion-bonded to the inside peripheral surface of the load-carrying skirt portions 2 and 3 of the piston. The expansion control elements have edge portions 6 and 7, which are laterally bent toward the interior of the piston and anchored in the gudgeon pin bosses 8 and 9, which define bores 10 and 11 for the gudgeon pin. The expansion control elements are pierced and exposed in the machined oil ring groove 1 2 above the piston pin.The upper portion of each expansion control element 4 and 5 is covered and fusion-bonded by a beadlike inner portion 1 3 of the casting, which extends between the bosses 8 and 9 from the inside contour over about 15% of the height of the expansion control element and constitutes an extension of the piston head. Each of the expansion control elements 4 and 5 is formed in that portion which is adjacent to the piston head with recesses 14 and 15, which extend from the axial edges of the expansion control element for 25% of the total peripheral length of the expansion control element and have a height of 20% of the total height of the expansion control element and are filled with light alloy.

Owing to the design of the expansion control elements of the present segment strip piston, the control elements will be firmly anchored in the light alloy even when the piston is subjected to particularly high loads in the operation of the engine, such as in cases of very high speed, valve contact, slight contact of the piston head with the cylinder wall, etc., because the anchoring of the expansion control elements is increased by a factor of about 4; this corresponds to an anchoring of 40 to 60% in the axial direction.

Claims

1. An expansion-controlled light alloy piston for an internal combustion engine, wherein segment-like, strip-shaped expansion control elements are bonded to the inside peripheral surface of the piston along the load-carrying skirt portions and are anchored in the gudgeon pin bosses, the control elements being exposed almost throughout their peripheral extent in the machined oil ring groove above the piston pin and that portion of each of said expansion control elements which is adjacent to the piston head being covered on the inside for 10 to 50% of the height of the element by and fusion-bonded to a bead-like casting portion, which extends between the piston bosses as an extension of the piston head, and wherein each expansion control element is formed in that portion which is adjacent to the piston head with recesses, which extend from the axial edges of the expansion control element for 20 to 30% of the total peripheral length of the expansion control element, which have a height of up to 25% of the total height of the expansion control element and which are filled with light alloy.

2. A piston as claimed in Claim 1, wherein the expansion control elements consist of steel.

3. A piston as claimed in Claim 1 or 2, wherein the expansion control elements are pierced.

4. An expansion-controlled light alloy piston for an internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.