US2261405A - Piston - Google Patents

Description

Patented Nov. 4, 1941 Application February 24, 1939, Serial No. 258,324 In Great Britain September 21, 1938 (Cl. sos- 14) 2 claims.

' This invention relates to pistons primarily for internal combustion engines and has -for its bject to provide a piston which is made mainly of light alloy and which shall not only have an effective coeicient of expansion less than the light alloy itself, but shall also expand uniformly under working conditions. 'I'he two greatest problems met with in using pistons of light alloys are:

(I) That the coefficients of expansion of light alloys are greater than that of cast-iron and other materials of which cylinders are made, and

(II) That there is always a tendency for the top of a piston skirt to expand more than'the bottom thereof,

The invention, therefore, seeks to overcome these problems.

In a broad aspect the invention consists in a piston primarily for internal combustion engines wherein a sheath or sleeve encircling the skirt of the piston and having a coeflicient of expansion less than that of the skirt is adapted, when the piston expands, to oppose such expansion in a radial direction y Thus, according to the invention, a sheath or sleeve, of steel for example, may be shrunk or pressed upon the skirt and the latter may be formed with peripheral grooves into which the adjacent'edge of the sheath or sleeve is turned, by spinning for example, 'to prevent displacement of the sheath, or the sheath or sleeve may be lightly shrunk upon the piston skirt and be 1ocated thereon by being secured, -as by spot welding, to steel inserts within apertures inthe piston skirt.

The piston skirt may be formed from a siliconaluminium alloy of relatively low expansion coeiiicient and the sheath be of steel, a suitable alloy for the formation of the skirt having the following composition:

Per cent Si1icon 14 Nickel 2 Copper- I 0.9 Magnesium 1 Remainder aluminium. l

This alloy has a coeflicient vof expansion of, approximately, 0.000019 C.

'With a piston thus constructed comparatively little stress additional to the original stress due to the sheath shrinking operation is generated on account of heating of the piston under working conditions, while the employment of a steel sheath enables the advantage of an aluminium alloy piston, as to light weight, to be retained.

It is -recognised in connection with pistons for internal combustion engines that the top. portion of the skirt tends to expand more than the bottom portion thereof.. The sheath or sleeve provided in accordance with the invention is provided with the object of resisting this expansion, and by making the sheath, which is conveniently of steel, thicker in the region thereof where the lskirt tends to expand more, it is possible to provide that the pistonv shall have an overall equal expansion. The same object would be achieved n.

'only the skirt of a piston but also the head thereof, so that the sheath extends right up to the edge of the crown of the piston, in which case the portion of the sheath in the region of the piston head will be thick enough to permit of the turning of grooves therein for the reception of piston rings in the sheath. It is thus possible to provide the ring grooves in steel instead of in the aluminium of the piston, thereby affording a remedy against wear of the piston ring grooves which often gives rise to serious trouble in the case of aluminium or aluminium alloy pistons as employed in internal combustion engines.

The steel sheath may also be made to enclose only the head of the piston, in which case it is possible to provide ring grooves in steel and at the same time to restrict the expansion of the top part of the skirt, In this case, of course, the lower part of the skirt will expand at the rate normal to the light alloy employed. 'I'he top part of the skirt (which tends to expand more than the bottom), being adjacent to the steel sheath, will have its expansion to some extent checked by the sheath; and provided the sheath is properly proportioned the result will be a skirt expanding more or less uniformly at the rate normal to the light alloy. The object of such modification of the invention is to secure a piston of uniform expansion affording a remedy against wear of piston ring grooves, and lighter than the design mentioned in the immediately preceding paragraph.

In the accompanying drawing: i

Figures 1 and 2 show in half sectional elevation views of two forms which the invention may conveniently take.

Figure 1 shows a piston tted with a sheath c encircling the skirt a which is of reduced diameter in its upper portion so that the sheath is correspondingly increased in thickness in its upper portion and may be provided with grooves d for the piston rings.

Figure 2 shows an adaptation of the invention where the encircling sheath c may be lightly shrunk upon the piston skirt a and be properly located upon the latter by securing the sheath as by spot welding (a spot welded joint being indicated at d) the same to a series of plugs :a`

in and provided with at least one aperture com'- municating with the recess, a metallic sleeve having a coeiiclent of expansion less than that of the metal of the piston, a plug fitted tightly within said aperture, and means securing the plug to the sleeve so that rotary displacement of the ysleeve in the recess is prevented.

2. A piston of the type having a metal body j provided with ring receiving grooves and having a skirt provided with at least one radial aperture therein, a metallic sleeve having a coeiicient of expansion less than that of the metal of the piston, a plug tting within said aperture and capable of having a sliding movement therein radially of the piston body and means securing the plug to the sleeve so that-rotary and axial displacement of the sleeve is prevented while slight relative radial movement between the sleeve and the body of the piston is permitted.

ARTHUR VHLENEUVE MCOLLE.

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