The invention relates to improved piston rings fitted on internal combustion engine pistons.

In accordance with well known approved prior art such piston rings are designed as open rings having a slit or gap between the ring ends in order to allow flexing of the ring. Often, the slit extends obliquely. Reduced passage of combustion gases occurs through the slit but such passage-through may reach unacceptable amounts when several piston rings on one and the same piston assume a position wherein all the slits of the rings are aligned.

In order to reduce and possibly to entirely eliminate gas passage through piston rings of this kind the rings may be formed with a gas-sealed joint. However, this arrangement has proved to be disadvantageous in other respects, as will be explained in closer detail below.

In order to remedy deficiencies as may occur in piston rings having a gas-sealed joint an obliquely extending groove has been formed in the ring in the peripheral edge face of the ring, i.e. in its wear face. While operational advantages have been gained the arrangement does, however, suffer from other drawbacks, as will likewise be discussed later on. The present invention provides a piston ring solving the problems outlined above. The characteristic features of the piston ring appear from the subsequent claims. Some prior-art designs and the invention will be explained in the following in more detail with reference to the accompanying drawings, wherein

Figs 1 and 2 illustrate parts of a piston ring in accordance with two prior-art designs,

Fig. 3 illustrates a part of a piston ring designed in accordance with the invention, and

Fig. 4 is a vertical sectional view through a part of a piston fitted with a piston ring in accordance with the invention.

Fig. 1 illustrates a piston ring 1 formed with a gas-sealed joint as mentioned above. In this case the piston ring 1 is formed in a prior-art manner with end portions 2,3 configured to be fitted together in overlapping relationship so as to bridge the joint between the ends of the piston ring 1. A disadvantage found in this design is, however, that when a thus configured ring is placed closest to the combustion chamber on a piston fitted with several rings this ring will have to absorb the entire pressure drop and thus the entire load at each explosion stroke, with consequential increase of wear on the ring as well as on the engine cylinder lining.

For the purpose of somewhat removing the load on the piston ring 1 one prior-art solution illustrated in Fig. 2 suggests the provision on the ring 1 of grooves spaced equidistantly around the wear face 5 of the ring 1. In this manner, operational advantages have been obtained, as a consequence of the somewhat reduced load on the ring 1. However, at the same time the solution has caused the appearance of other disadvantages. The grooves 4 act as serious crack initiation means through the entire ring 1. In addition, in the case of surface-coated rings having a hard and brittle spray-coated plasma wear layer 5 damages easily occur in the form of scaling of the wear layer 5 during the formation of the grooves 4 as well as during operation. The risks that fractures should occur are the largest one when the grooves 4 are straight, i.e. grooves 4 extending perpendicularly from the top face to the bottom face of the ring 1. When the grooves 4 have an oblique extension the maximum risk of scaling exists at the top and bottom ends of the groove 4. Scaling is a

serious disadvantage in the ring 1 but obviously it also is a serious cause of potential damages to the cylinder lining.

The present invention provides a device solving the above-outlined problems. Characteristic features of the invention are that holes 9 (only one shown) extend from the top face 7 of a piston ring 6 to the bottom face 8 thereof for passage-through of a smaller amount of combustion gases from the engine combustion chamber. As illustrated in Fig. 4 the bottom face 8 of the piston ring 6 is pressed during operation against the associated piston 10 while a smaller gap 11 exists between the piston 10 and the top face 7 of the ring 6. For outlet of said amount of combustion gases into the cylinder below the piston ring 6 a channel 12 therefore is provided between each hole opening on the bottom face 8 of the ring 6 and the peripheral edge face 13 thereof, which latter face forms the wear face sliding against the engine cylinder bore. As appears from Figs 3 and 4 a channel 14 extends also from each hole opening on the top face 7 of the ring 6 to the peripheral edge face 13 of the ring, with the exception of the gap 11, in order to facilitate inlet of combustion gases into the holes 9. Like the above slits 4, said holes preferably are equidistantly spaced around the ring 6.

Owing to the provision of these holes 9 the load on the uppermost one of a series of rings 6 fitted on a piston is reduced as a result of a calculated passage- through of a smaller amount of combustion gases, without significant deterioration of the strength and durability of the ring 6 and without any significant effect on the wear face 13 of the ring 6.

The invention is not limited to the features shown and described but could be varied in many ways within the scope of the appended claims. As illustrated in the drawing the holes 9 may extend between the upper face 7

and the bottom face 8 perpendicularly to the planes of the faces but they could equally well extend obliquely between said planes. It is equally possible to position the holes 9 further inwards, i.e. somewhat closer to the inner peripheral edge of the ring 6 than illustrated in the drawing.