The invention relates to an inwardly biassed sealing ring for a piston-ring assembly.

Piston-ring assemblies operate with a piston ring, which through inherent elasticity presses itself against the cylinder bearing surface of the reciprocating engine. This for instance prevents transfer of fluid in combustion engines from the combustion chamber to the crankcase and passage of oil in the reverse direction. The continual upward and downward sliding movement of the piston ring over the cylinder bearing surface does not cause any consi¬ derable wear on the inner jacket however.

The outward bias of the piston ring, is supplemented by the pressure of the fluid which gains access to the space behind the piston ring, that is the space at the in- ner side of the piston ring.

If the pressure developed by the cylinder or the pressure setting the piston in motion is very high, the pressure acting on the piston ring radially outwards is very high as well, so that considerable wear on the cylinder bearing surface taken place through the outer surface of the pis¬ ton ring. The effect of this is an substantial pressure loss in the reciprocating engine, resulting in a power loss of about _/ £.

The application of such piston rings and therewith the piston-ring sealing causedπany problems and in many cases could not even be realizedj With a fluid pressure greater than 2000 atmospheres ( zzz=z* 2.10 Pa) it is still impossible to realize a durable sealing between the cy¬ linder and the piston ring using a piston ring assembly, which only comprises one or more outwardly biassed piston rings; with such a fluid pressure the piston ring is des¬ troyed in a short time. The cause thereof must be

in the large pressure exerted by the piston ring under t influence of the fluid pressure acting on the inner jack The result is that the oil film on the inner jacket is fully squeezed out, giving rise to a grinding action bet the piston ring and the cylinder, so that the service li of the piston ring is shortened considerably. A solution to this problem is known from the German utility model specification 7725199. The piston ring assembly of the above mentioned specifi— cation also comprises a sealing ring that is located at t pressure side of the piston ring and that, unlike the out wardly biassed piston ring, is biassed inwardly, i.e. it tends to clamp itself down against the inner side of the vertical wall of the piston-ring groove. Hence, fluid ca not reach the space behind the piston-ring, neither via t mating sidesof piston ring and sealing ring, nor via the mating sides of the sealing ring and the bottom of the pi ton groove. However, the problem remaining is, that the split of the sealing ring has to be made in such a way, that fluid can not easily flow via the split of the sealing ring to the space behind the χjiston ring.

It is therefore an object of the present invention to pro vide a solutio to the above-mentioned problem. According to the invention one end of the sealing ring is provided with a narrow protruding part, while the other ring end is provided with a gap correspondingly shaped to accommodate the narrow protruding part with a tight fi the mating surfaces of said protruding part and the gap extending from the ring surface mating with the inner wal of the piston groove to the ring surface mating with the piston ring.

There are two feasible embodiments of the sealing ring wi respect to the location of the protruding part and the ga In a first embodiment the gap is located in the inner wal of the sealing ring, while in the second embodiment the g forms a groove in the respective ring end.

The application of any type of sealing ring in a piston ring assembly for a piston groove of rectangular cross section requires that the mating surfaces of the protruding part and the respective gap are tapered off from the surface mating with the inner wall of the piston groove to the sur¬ face mating with the piston ring.

If an inner wall of the piston groove slopes inwardly from the pressure side, the above two embodiments are also appli¬ cable, provided the shape of the ring surface mating with the inner wall of the piston groove corresponds with that of the piston groove. The latter embodiment of a sealing ring is not merely applicable in some type of piston ring assembliesj for the piston ring can displace itself to excess, ^" so that it will vibrate in its groove, pressing the sealing ring upwardly and hence outwardly; through the fric¬ tion then acting between the sealing ring and the cylinder wall, the sealing ring will no longer follow the movement of the piston ring completely, thus permitting the fluid to escape between the piston ring and the sealing ring. The fluid can therefore penetrate the space behind the pis¬ ton ring. This problem can be solved by providing the sea¬ ling ring with a flat top at the pressure side and the pis¬ ton groove with a corresponding flat surface. The invention will now be described with reference to the accompanying figures, of which

Pig. 1 is a sectional view of an embodiment of a piston ring assembly comprising a first type of sealing ring. Pig. 2 is a three-dimensional view of the above-rmentioned embodiment; Pig. 3A-C are a plan view, a sectional view and a side view of a second embodiment of a sealing ring;

Fig. 4 is a sectional view of an embodiment of a piston ring assembly comprising a third type of sealing ring; Pig. 5 is a three-dimensional view of the last-mentioned embodiment of a piston ring assembly;

Fig. 6 are a plan view, a sectional view and a side view of a fourth type of sealing ring; and

Pig. 7-9 are sectional views of three other embodiments

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of a piston ring assembly.

Pig. 1 refers to a reciprocating engine, which is shown partly only, and which comprises at least a cylin 1 , in which a piston 2 is accommodated. To obtain a prop sealing between piston 2 and cylinder 1, piston 2 is pro vided with a piston-ring assembly 3 which is accommodate in a groove 4 in the bearing surface around the piston 2 A piston with a groove 4 accommodating only one or more outwardly biassed piston rings 5 has the disavantage tha with the continuous motion of piston 2 the inner wall of cylinder 1 is subjected to heavy wear. A wear-affected cylinder causes a pressure loss in the working chamber and hence a loss in engine power (about 5 ). This wear on the cylinder wall is not developed so much through the outwardly acting bias force of the appl piston ring 5 _> but rather through the fluid pressure exe ted on the inner side of piston ring 5 via groove 4. This causes piston ring 5 to be pressed against cylinder barrel 1 to an increasing extent, with the result that greater wear takes place, making it impossible to obtain a durable sealing between cylinder 1 and piston 2 with a

8 pressure greater than 2000 atmospheres ( ^* ^ 2.10 Pa).

Further, with a piston 2 having one or more piston rings 5 in groove 4 the situation arises that, through rotation of piston ring 5 during the reciprocating motio one of the ends of this ring 5 takes up a position befor the outlet port 7. Just with large types of reciprocatin engines with a large outlet port, the fluid pressure act behind piston ring 5 presses this ring at a point near a end outwardly and hence into outlet port, causing this e to break off through the continuing reciprocating motion of piston 2.

A possible solution to this problem is obtained by making the piston ring assembly 3 of the piston 2 in Pig to form a combination of a normal outwardly biassed pist ring 5 and an inwardly biassed sealing ring 6 which is pr sed against piston ring 5 through -the fluid pressure acting on the flat side of ring 6. The inwardly biasse

sealing ring 6 then clamps itself down around the bottom or inner wall 7 of groove 4 and seals off the space 8 at the inner side of the piston ring 5, thus preventing the fluid pressure from building up in this space. This de- creases the outwardly acting pressure of piston ring 5 on cylinder 1 and hence reduces the wear on the cylinder wall. In this way a durable sealing between piston 2 and cylinder 1 is obtaine Qd for a pressure greater than 2000 atmospheres ( p^> 2.10 Pa). However for reciprocating engines of the combustion type the application of piston 2 and piston ring assembly 3 has the disadvantage that the space 9 of piston-ring groove 4 above sealing ring 6 will get filled with carbon deposits, so that sealing ring 6 cannot be pressed suffi- ciently against piston ring 5 by the fluid pressure. This in turn provides again an easy path for the fluid to reach the space behind piston ring 5 _» causing the wear on the cylinder wall 1 to increase, the risk of fracture of piston ring 5 to become considerable higher, and the problem of obtaining a durable sealing between cylinder 1 and piston 2 to remain.

It is therefore recommendable to provide the outer top surface of the sealing ring 6 with annularly recessed surfaces 10 and 11. If the space 8 of the piston groove 4 above the sealing ring 6 has been filled with car¬ bon deposits,the fluid pressure in the recess 11 is then to press the sealing ring 6 back against the piston ring 5 if the former (6) happens to seperate from the piston ring 5 at the end of an upward stroke and bear against the top side of the piston groove 4.

Pig. 2 shows a three-dimensional view of the piston ring assembly for a piston machine of Pig. 1. This piston ring assembly 3 comprises an inwardly biassed sealing ring 6 and an outwardly biassed piston ring 5. The sealing ring 6 is of the split type, where ends 12 and 13 substantially overlap each other; this is achieved by providing the end 13 with a narrow protruding

and the other end 12 with a gap 15 correspondingly shape to accommodate the narrow protruding part 14'with a tigh fit.

In this embodiment the gap 15 and the protruding part 14 are located in the inner wall of the sealing ring 6 nea the piston ring 5.

The end 12 and the protruding part 14 of the sealing rin 6 comprise mating sides 16 and 17, which closely slide over each other and slope outwardly downwards from the pressure side. The cross sectional view of Pig. 1 shows that these mating sides 1β and 17 do not extend diagonal they start from the inner side 18 and end at side 19 mat with the piston ring 5. For this reason, the end 12 comprises a part, functionin as a damm wall 20 at the inner side 18 of the sealing ri 6, and also a part functioning as a bearing surface of side 19 (for a gastight sealing of the space behind the piston ring 5). This gas-tight sealing is further stimulated by. the tape ring sides 16 and 17, so that these sides 16 and 17 are well pressed to each other through the fluid pressure on the top side and the outer side of the sealing ring 6. With the sealing ring 6 in position, the ends 12 and 13 are slightly shifted apart, to accommodate for the expan- sion caused by the temperature increase; consequently, t chambers 22 and 23 are obtained. However, there will be no transfer of fluid from the chamber 22 at the pressure side 24 (see arrow) to chamber 23 via the mating surface 16 and 17 (due to the tight fitting between them) For reasons mentioned-above the outer top surface of the sealing ring 6 is provided with an annular recess 11. Any fluid in chamber 22 cannot penetrate the space 8 be¬ hind the piston ring 5 via the inner side of end 13, as sealing ring 6 seals off the bottom of the piston groove 4. Fluid at the upper side 24 of the sealing ring 6 can not penetrate the space 8 behind the piston ring 5 via chamber 23 on account of the sealing of the damm wall 20

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Such an inwardly biassed sealing ring 6, which does not permit a fluid transport to any significant extent to the spice 8 behind the piston ring 5, can appropriately be cal¬ led a ring 6 with a gas-tight split joint; all other known types of inwardly biassed sealing rings 6 permit a sub¬ stantial extent of fluid to penetrate the space 8 behind the piston ring 5, so that these rings 6 are inappropria¬ tely referred to as gas tight split rings. Admittedly, a sealing ring 6 of the type claimed cannot completely prevent the penetration of fluid, the amount of fluid, entering the space 8 behind the piston ring 5, must be carried off via the piston ring 5; this piston ring 5 specially constructed thereto, will now be described. For the above-mentioned reason the piston ring 5 is provi- ded v/ith two ends 25 and 26 with protruding parts and with adjoining gaps 27 and 28 respectively. The ends 25 and 26 comprise mating surfaces 29 and 30, which closely slide over each other and slope outwardly downwards from the pressure side. The cross sectionial view of the piston ring assembly in question shows that these mating surfaces 29 and 30 do not extend diagonally; as shown in Pig. 1, the contact surfaces 29 and 30 start from the top side 31 of the piston ring 5 and end in the outer wall 32 of this ring. In this way the end 25 of the piston ring 5 also compri¬ ses a part in the inner wall near the top side of the piε _r ton ring 5 and also a part in the outer wall of the piston ring j the part in the inner wall also functioning as a damm wall of end 25, is designated by 33. Fluid in the space 8 behind the piston ring 5 will be trans¬ ported downwards via gap 27 to e.g. the crankcase. Fluid in gap 28 cannot reach the space 8 behind the piston ring, neither via the mating surfaces 29 and 30 of the two ends 25 and 26, not via the inner wall of end 25 on account of the damm wall 33 and the further part of the top surface 31 of piston ring 5, on which the sealing ring 6 is pressed to prevent fluid transport to the space 8 behind the piston

ring 5 via a passage between the rings 5 and 6.

A combination of ^" a piston ring and a sealing ring 6 of t type mentioned substantially prevents fluid leakage to t space 8 behind the piston ring 5, and ensures that any fluid penetrated is carried off easily. In this way the fluid pressure in the space 8 behind the piston ring 5 i rather low in comparison with the fluid pressure above t piston 2.

Instead <$f flat mating surfaces 16, 17 of the inwardly biassed gas-tight sealing ring 6 and the mating surfaces

29 and 30 of the outwardly biassed piston ring 5 _» these surfaces cp-n also be curved (resulting in a concave or a convex surface).

It is to be emphasized, that the outwardly biassed gas- tight piston ring 5 has mating surfaces 29 and 30, which are tapered downwards from the flat top side 31 to the outer wall 32.

This, however, is unlike the mating surfaces 16 and 17 of the inwardly biassed sealing ring 6, which are tapere downwards from the inner wall 18 to the bottom side 19 o the sealing ring 6.

The inwardly biassed sealing ring 6 of the type claimed may only be used in combination with the mentioned pisto ring 5 in the given way. Y/hen using another type of piston ring 5 (e.g. with a ri slot) of the above-mentioned type of piston ring 5 mount in a reversed position, the result wanted will not be obtained; in the first case the piston ring 5 does provi a path for the fluid to the space 8 behind the piston ri 5 and in the second case gap 27 is in connection with the combustion chamber, so that fluid can be supplied to the space 8 behind the piston ring 5, resulting in excessive wear on the piston ring 5 and cylinder 1.

Pig. 3A shows a plan view of a second embodiment of a sea ling ring 6 for a piston ring assembly 3 in a piston groo

4 having a rectangular section. The ends 12 and 13 of thi sealing ring 6 also overlap each other.

In this embodiment this is ^" also achieved by providing the end 13 with a narrow protruding part 14 and the other end 12 a gap 15 correspondingly shaped to accommodate the narrow protruding part 14 with a tight fit. In this embodi- raent, however the gap 15 in the end 12 is shaped as a groove; this gap 15 slopes downwards from the inner wall 18 to the surface 19 of the sealing ring 5 _» which surface mates with the sealing ring 6. A cross sectional view of the sealing ring 6 through line

1 AA is shown in Pig. 3B where the protruding part 14 is accommodated in the groove-shaped gap 15, extending from the inner wall 18 to the bottom side 19. Further a side view of this sealing ring 6 is shown in Fig. 3C However for reciprocating engines of the combustion type the application of the above-mentioned embodiments keeps the disadvantage, that the space 8 of the piston groove 4 above the sealing ring 6 and the chamber 11 turned in the upper surface of the sealing ring 6, will get filled with carbon deposits, so that sealing 6 cannot be pressed sufficiently against piston ring 5 by the fluid pressure. This in turn provides again an easy path between the sea¬ ling ring 6 and the piston ring 5 for the fluid to reach the space 8 behind piston ring 5 with all its consequences. A feasible solution to the above problem of carbon deposits is obtained with the use of the type of piston 2 and pis¬ ton ring assembly as shown in Pig. 4. This figure also illustrates a part of a cylinder 1 and a part of piston 2 and piston ring assembly 3. Piston ring assembly 3, for which a piston ring groove 4 is provided in the circumfe¬ rential surface of the piston, comprises a flat outwardly biassed piston ring 5 and an inwardly biassed sealing ring 6. Side 34 of groove 4 situated on the side of the sealing ring 6 is tapered off the outside and the surface of sea- ling ring 6 mating with side 34 of groove 4 is tapered accordingly. The surface of sealing ring 6 mating with piston ring 5 is

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however flat, through the inwardly tapered sides 34 of groove 4 and sealing ring 6 this will result in a force of sealing ring 6 acting in the direction of piston rin Consequently, sealing ring 6 will bear tightly against piston ring 5, and the space 8 behind piston ring 5 wil sealed off from the fluid pressure produced in combusti chamber.

Unlike the sealing ring 6 described in the cited u lity model specification, the inner side of the sealing ring 6 does not bear against the bottom 7 of piston rin groove 4.

The slope of the taper of groove 4 depends, among others, upon dimensions of sealing ring 6, the coeffici of friction of the applied material, and the magnitude the fluid pressure. The vibrating action of the piston

5 in an active piston engine causes the sealing ring 6 be lifted upwards to excess and so to be pressed outwar against the cylinder wall 1 ; through the wear acting th between sealing ring 6, outer side 34 and cylinder wall the sealing ring 6 will no longer follow the movement o the piston ring 5 completely, thus permitting the fluid to escape between the sealing ring 6 and the piston rin The fluid can therefore penetrate the space 8 behind th piston ring 5. To prevent this, the piston groove 4 is provided with a wall part 35 being perpendicular to the direction of mo tion of the piston 5, where the sealing ring 6 is provi with a correspondingly shaped top surface 36. Therefore, the vibrating action of the piston ring 5 in groove 4 will hardly move the sealing ring 6 upwards so the sealing ring 6 will not be pressed against the cyli wall 1.

Such a shaped sealing ring 6 is shown in the three dime sional view of Fig. 5, differing from the sealing ring of Fig. 2 in such a way that surface 18 of the sealing

6 is tapered. In the embodiment of the piston ring asse bly 3 shown in Fig. 5 the sealing ring 6 then clamps it¬ self down around the surface 34, thus blocking

fluid transport via a path between the seeing ring 6 and the bottom 7 of groove 4 to the space 8 behind the piston - ring 5.

A second embodiment of a sealing ring 6 for a piston ring assembly 3 which is accomodated in the piston groove 4 with an .Inner wall 18 tapered off, is shown in Fig. 6A-C; just like the case was in Fig. 3A-C, the end 12 of the sealing ring 8 of this embodiment is also provided with a groove shaped gap 15 while the end 13 is provided with a protruding part 14 correspondingly shaped to accommodate in the gap 15 with a tight fit. Fig. 6B shows a cross sec- tionial view of this sealing ring 6 through line AA , where the side 18 of the sealing ring 6 mating with the tapered inner wall of piston groove 4 is tapered accordingly; further the sealing ring 6 has a flat top 36 which is perpendicular to the direction of motion of the piston 5 to prevent contact between the sealing ring 6 and the cylinder wall 1 through the vibrating action of the piston ring 5. The close fitting of the protruded part 14 in the groove shaped gap 15 of end 12 makes tapering of this part (14) and the gap 15 superfluous.

The troublesome vibrating action of piston ring 5 can be prevented in two ways to be explained with reference to some embodiments. An embodiment of a piston 2 and piston ring assembly 3 according to the invention is shown in Pig. 7, where only a part of side 34 is tapered; the part 37 between the bot¬ tom 7 and the side 34 and also that 35 at the outer side of groove 4 are however straight. Since groove 4 near the bottom 7 is rectangular, the flat piston ring 5 is suppor¬ ted in groove 4. The sealing ring 6, on the other hand, ma¬ tes with the sides 34 and 35, and is therefore of a corres¬ ponding shape. Besides the supporting effect of piston ring 5 in groove 4 near the bottom 7, it is impossible that, in the event of fracturing of piston ring 5, a fractured part gets under the piston ring 5, so that the sealing ring 6 cannot be pressed against the cylinder wall 1.

Still another embodiment of a piston 2 and piston r assembly 3 according to the invention is illustrated in Fig. 8, where only a part of side 34 situated near the o ter side of groove 4 is tapered; the remaining part 37 o side 34 is however straight. The groove part 7 with rec¬ tangular cross section is of such a with that the combi¬ nation of piston ring 5 and sealing ring 6 are supported at both sides in groove 4. The side of sealing ring 6 mating with the side 37 is of corresponding shape, causing the sealing ring 6 to be pressed inwards by the fluid pressure produced in the co bustion chamber, thereby sealing off the space 8 in groo 4 behind it. When the piston ring 5 has a restricted movement space a shown in Pig. 9 the special provisions as to the upper surface 36 are superfluous.

As shown in Pigs. 4, 7 and 9, some parts of the sealing ring 6 having sharp edges may be provided with rounded o flattered surfaces 38 to prevent splintering of the edge The inner part 39 of the sealing ring 6 shown in Fig. 8 can be considered as an annular protruding part of the m tioned flat wall 38 shown in Pig. 4.

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