GB2347194A

GB2347194A - I.c. engine piston of light construction

Info

Publication number: GB2347194A
Application number: GB0003887A
Authority: GB
Inventors: Hubert Buehr
Original assignee: Federal Mogul Burscheid GmbH
Current assignee: Federal Mogul Burscheid GmbH
Priority date: 1999-02-27
Filing date: 2000-02-18
Publication date: 2000-08-30
Anticipated expiration: 2020-02-18
Also published as: ITMI20000358A0; FR2790286B1; DE19908670A1; ITMI20000358A1; IT1316789B1; DE19908670C2; GB2347194B; FR2790286A1; GB0003887D0

Abstract

The piston 1, which may be cast from light metal, has pin boss eyes 6, 6' the external spacing of which is less than the piston diameter, and skirt parts 4, 4' of different sizes. The skirt part 4 on the thrust side is of greater circumferential extent than the skirt part 4' on the counter-thrust side. The skirt parts 4, 4' are connected to the pin boss by respective pairs of stiffening walls 7, 7' and 8, 8' which are parallel and offset in the direction of the pin boss axis 9. The connecting walls 4' of the counter-thrust side are connected to the inner end regions of the pin boss eyes 6, 6'. The stiffening walls 7, 7', 8, 8' may have different axial heights to affect the mass distribution.

Description

PISTON FOR INTERNAL COMBUSTION ENGINE This invention relates to a piston for internal combustion engines, especially of light metal, with a piston crown and a pin boss extending centrally from the piston crown and having boss eyes whose external spacing corresponds to 60 to 80% of the piston diameter, a skirt part arranged on each of the thrust and counterthrust sides, wherein the skirt part arranged on the thrust side is larger at least in the circumferential direction than that on the counter-thrust side and the skirt parts are buttressed relative to the pin boss by stiffening walls and the stiffening walls of one skirt part are offset in the direction of the pin boss axis relative to the stiffening walls of the opposite skirt part.

A prime objective with modern internal combustion engines is the reduction of weight of individual components, since this not only reduces the fuel consumption but noise and vibration properties can also be affected advantageously. The requirement for the smallest possible oscillating masses runs counter to that for ruggedness of the piston, on account of the high stresses.

Pistons of light construction formed as so-called box or H pistons have two individual skirt parts which extend only over the thrust and counter-thrust sides. The pin boss is shorter than the piston diameter in the direction of the pin axis. A light metal piston for internal combustion engines of the kind described is known from EP 0 171 825 A.

This piston of the kind specified has asymmetrically formed skirt parts. The skirt parts are made larger in the circumferential direction in the thrust region than on the counter-thrust side. The buttressing of the individual skirt parts is effected through stiffening walls connected to the pin boss, the points of connection to the pin boss being at the outer end regions of the boss eyes. The stiffening walls on the thrust side run at an angle into the pin boss. The result of this is that both longitudinal and transverse forces have to be absorbed at the bearing, with the consequence that the points of connection of the stiffening walls both to the pin boss and to the skirt part have to be made relatively thick walled in cross-section. The weight of the piston on the thrust side of the piston is increased by this strengthening, so that the piston tends to tilt at the upper and lower dead centre points during engine operation.

The invention is based on the object of so improving a piston of the type defined that the weight of the piston is further reduced and a symmetrical distribution of weight is provided at the same time.

This object is met according to the invention by the characterizing features of claim 1.

Advantageous arrangements of the invention are set forth in the dependent claims.

The piston according to the invention is preferably made from an aluminium alloy and is distinguished by a favourable weight, through reduction of the piston skirt to two skirt parts. Through the parallel offset of the stiffening walls the connections between the pin boss and the skirt part are effected by the shortest path. The right-angled connection of the stiffening walls makes possible the smallest of wall thicknesses at the points of connection, since no longitudinal forces are transmitted into the bearing. By varying the height and/or width of the stiffening walls on the thrust side and the opposing side, equalisation of mass is possible, so that for example pistons with an asymmetrical piston crown can be so compensated by wide and/or higher stiffening walls on the thrust side or the counter-thrust side that a symmetrical distribution weight relative to the pin boss axis is established.

The invention is shown in the drawings in relation to one embodiment and is explained in more detail as follows. In the drawings: Fig. 1 is an elevation of a piston according to the invention, Fig. 2 is a view from below of the piston according to Fig. 1, Fig. 3 is a view according to the section line III-III in Fig.

1.

Figure 1 shows a piston produced in light metal by a casting method. The piston head 2 has annular grooves 2 for reception of piston rings (not shown). The skirt of the piston 1 consists of two diametrically opposed skirt parts 4,4'. The piston 1 is of open form in the direction of the axis of the pin boss 5, which comprises two boss eyes 6,6'spaced from one another (Fig. 2). The outer spacing of the boss eyes 6,6'corresponds to about 60 to 80% of the piston diameter, i. e. the piston 1 is connected to a piston rod by a short pin (not shown).

Fig. 2 shows a view from below. The skirt parts 4, 4'have different sizes in the circumferential direction. The skirt parts 4, 4'are connected to the pin boss by stiffening walls 7,7', 8,8'.

The stiffening walls 7,7'of the skirt part 4'extend perpendicular to the pin boss 9 and are connected at the inner end regions 10,10' of the boss eyes 6,6'. The stiffening walls 8,8'run offset in the direction of the pin boss axis 9 parallel to the stiffening walls 7, 7'. Through the perpendicular connection of the stiffening walls 7, 7', 8,8'no lateral forces occur on the stiffening walls, so that the connection relative to both the boss eyes 6,6'and the skirt parts 4,4'takes place with minimum radii R, R2. Very narrow stiffening walls 7,7', 8,8'are possible in this way. By varying the wall thicknesses tl, t2, t3, t4 it is possible to balance the weight of the asymmetrical piston 1, so that a piston symmetrical in relation to weight distribution can be made.

As appears from Fig. 3, the stiffening walls 7,7', 8,8'can be made with different axial heights, in order also to affect the mass distribution.

An especially light piston 1 is created through the special construction of the stiffening walls 7,7', 8,8'and their particular connection to the pin boss 5 while at the same time being designed for high thermal mechanical loading.

Claims

CLAIMS 1. A piston for internal combustion engines, especially of light metal, with a piston crown and a pin boss extending centrally from the piston crown and having boss eyes whose external spacing corresponds to 60 to 80% of the piston diameter, a skirt part arranged on each of the thrust and counter-thrust sides, wherein the skirt part arranged on the thrust side is larger at least in the circumferential direction than that on the counter-thrust side and the skirt parts are buttressed relative to the pin boss by stiffening walls and the stiffening walls of one skirt part are offset in the direction of the pin boss axis relative to the stiffening walls of the opposite skirt part, characterized in that the stiffening walls (7,7', 8,8') extend parallel to one another and perpendicular to the pin boss axis (9), wherein the stiffening walls of the skirt part (4') arranged on the counter-thrust side are connected to the inner end regions (10,10') of the boss eyes (6,6').
2. A piston according to claim 1, characterized in that the axial height and/or width of the stiffening walls (7,7', 8, 8') on the thrust and counter-thrust sides are made different.
3. A piston according to claims 1 and 2, characterized in that the wall thickness (tl) of the skirt part (4') arranged on the counterthrust side is smaller than the wall thickness (t2) of the other skirt part (4).