EP1038128A1

EP1038128A1 - An improved piston ring

Info

Publication number: EP1038128A1
Application number: EP98951900A
Authority: EP
Inventors: Hans Sundèn
Original assignee: DAROS HOLDING AB
Current assignee: Koncentra Verkstads AB
Priority date: 1997-12-09
Filing date: 1998-10-30
Publication date: 2000-09-27
Also published as: JP2001527197A; NO20002862L; WO1999032812A1; SE9704581D0; SE510108C2; SE9704581L; NO20002862D0

Abstract

The invention concerns an arrangement in piston rings (1, 1a) of the kind, which are formed with a gap (6, 6a) and which are arranged in their respective one of annual ring-receiving grooves (4) formed in combustion-engine pistons. The end portions (2, 3; 2a, 3a) of the piston ring (1, 1a) are formed with width dimensions that are smaller than the width dimensions (b) of the piston ring (1, 1a), and are arranged in overlapping relationship in such a manner that the first end portion (2, 2a) extends between the inner face of the second end protion (3, 3a) and the bottom of the piston-ring groove (4). The second end protion (3, 3a) extends externally of the first end portion (2, 2a), forming said gap (6, 6a) in the ring between its end-edge face (5, 5a) and the transitional area where said first-mentioned end portion (2, 2a) widens to its full width.

Description

AN IMPROVED PISTON RING

The invention concerns an arrangement in piston rings of the kind that are formed with a gap in the ring and are arranged in individual annual ring-receiving grooves formed in combustion-engine pistons. Each piston ring is configured as an open ring and it is provided with a slit joint of some kind formed between the ends of the ring in order to impart resili^¬ ency to the latter. If the slit is of the open kind and forms a gap, small amounts of combustion gases may pass through the slit during piston work in the engine. The passage of such small amounts of combustion gases through the gap in above all the uppermost piston ring may be acceptable for the reason that in consequence thereof pressure on this ring becomes smaller, with consequential reduction of the wear on the ring.

A considerable disadvantage in this connection is, however, that hot combustion gases penetrate also into the annular groove itself, pass along the inner face of the piston ring and are drained through the gap in the ring. This flow of hot gases contributes to heating the ring to a disadvantageous level and in addition gradually causes carburisation of the annular groove, making more frequent engine renovations and piston-ring replacements necessary. In order to .reduce and possibly even completely eliminate gas passage through piston rings of this kind, it has been suggested to form the ring with a gas-tight joint. A piston ring of this kind is shown and described in e.g. EP 742875, according to which publication the ring is configured with overlapping end portions, one end portion extending above the other, in order to bridge the joint between the piston ring ends. A disadvantage found in this construction is, however, that when a ring thus configured is located closest to the combustion chamber on a piston ring fitted with several piston rings, this ring will have to absorb the entire pressure drop, as indicated in the aforegoing, and consequently the entire load at each explosion stroke. As a result, the wear on this ring as well as on the engine cylinder lining will increase .

In order to relieve to some extent the pressure on the most exposed one of the piston rings, it has been suggested in said EP Publication to provide the ring with some channels for passage-through of combustion gases. These channels are equidistantly spaced around the ring in the wear face thereof. This solution brings about operational advantages, owing to the somewhat reduced load on the most exposed ring. However, at the same time the solution has caused the appearance of other drawbacks. The channels act as serious crack-initiation means in the entire ring. In addition, in the case of surface- coated rings having a hard and brittle plasma-sprayed wear layer damages in the form of scaling of the wear layer easily occur, both during the very formation of the channels and subsequently, during operation. The risks that fractures should occur are most imminent when the channels are straight, i.e. in the case of channels that extend perpendicularly from the top face to the bottom face of the ring. When the channels have an oblique extension, as is the case in the EP Publication mentioned above, the maximum risk of scaling exists at the top and bottom ends of the channel. In addition to being a serious disadvantage in the ring, scaling obviously also constitutes a serious cause of potential damages to the cylinder lining.

The present invention provides a device by means of which the above-mentioned problems have been solved. The characterising features of the invention appear from the appended claims. The invention will be described in more detail in the following with reference to the accompanying drawings, wherein:

Fig 1 is a plan view of a piston ring in accordance with the invention,

Fig 2 is a vertical sectional view through a part of a piston fitted with a couple of piston rings,

Fig 3 is a perspective view on an enlarged scale of a part of a piston ring from with a joint in accordance with the invention, and

Fig 4 is a view similar to that of Fig 3 but shows a modification of said joint.

The piston ring 1 in accordance with the present invention is configured with two end portions 2, 3 the width dimensions of which are smaller than the width dimensions b of the piston ring 1. These end portions 2, 3 are arranged in overlapping relationship in such a manner that one end portion 2 is sandwiched between the inner face of the second end portion 3 and the bottom of the piston-ring groove 4 in which the piston ring 1 is received. The second end portion 3 thus extends externally or in front of the first end portion 2. A gap 6 is allowed to form between the end-edge face 5 of the second end portion 3 and the transitional area where said first- mentioned end portion 2 widens to its full width.

This configuration of a piston ring 1 offers several advantages over rings configured according to prior-art technique. Only small amounts of hot combustion gases can penetrate into the annular groove 4 on top of and behind the piston ring 1 and remain there. Gas flows along the inner face of the piston ring 1 that may cause harmful heating of the ring 1 and carburisation of the annular groove 4 are prevented. At the same time, in contrast to the overlapping joint portions found in the prior art, the gap 6 in the ring allows passage-through of small amounts of combustion gases, which passage-through relieves the pressure on the piston ring 1. A further advantage is that a surface coating 7 may be applied on the piston ring 1 with which there is no need to interfere in accordance with the technique described above.

Fig. 4 shows a modification of the embodiment of Fig 3. In this case, the end edge faces 5a, 8a of the end portions 2a, 3a are bevelled obliquely as seen in the circumferential direction of the piston ring la. In this manner an oblique gap 6a is formed in the ring, as shown in Fig. 4. The invention is not limited to the features described herein and illustrated in the drawings but could be modified in a variety of ways within the scope of the appended claims .

Claims

1. An arrangement in piston rings (1, la) of the kind, which are formed with a gap (6, 6a) extending crosswise through the ring from the upper face thereof to the lower face thereof and each one of which is arranged in its respective one of annual ring-receiving grooves (4) formed in combustion-engine pistons, c h a r a c t e r i s e d in that the end portions (2, 3; 2a, 3a) of the piston ring (1, la) are formed with width dimensions that are smaller than the width dimensions (b) of the piston ring (1, la),- and in that these end portions (2, 3; 2a, 3a) are arranged in overlapping relationship in such a manner that the first end portion (2, 2a) extends between the inner face of the second end portion (3, 3a) and the bottom of the piston-ring groove (4) and the second end portion (3, 3a) extends externally of the first end portion (2, 2a), forming said gap (6, 6a) in the ring between its end-edge face (5, 5a) and the transitional area where said first-mentioned end portion (2, 2a) widens to its full width.

2. An arrangement as claimed in claim 1, c h a r - a c t e r i s e d in that the end edge faces (5a, 8a) of said end portions (2a, 3a) are bevelled obliquely as seen in the circumferential direction of said piston ring (la) .