WO2001018433A1 - Piston ring for a reciprocating internal combustion engine - Google Patents

Abstract

The invention relates to a reciprocating internal combustion engine with at least one piston (5). Said piston is provided with at least one piston ring (6) that is provided with at least one channel (11) that extends in the area of the circumference thereof. The aim of the invention is to facilitate a wear-free operation and a high durability of such a piston. To this end, at least the upper circumferential channel (11), across the entire circumference of the pertaining piston ring (6), is set off from the upper face of the piston ring that faces the cylinder head (3) by a continuous web (12) to form an oil pocket (10).

Description

 PISTON RING FOR PISTON PISTON ENGINE

The invention relates to a reciprocating piston internal combustion engine, in particular a two-stroke large diesel engine, with at least one piston which is provided with at least one piston ring which is provided in the region of its circumferential running surface with at least one channel running in the circumferential direction.

An arrangement of this type is known from GB 2 124 332 A. The circumferential channels provided in the area of the running surface of the piston rings are intended to ensure good lubricating oil distribution. In the known arrangement, however, the channels mentioned communicate via side arms arranged transversely thereto with the region of the gap between the piston and the cylinder liner that extends from the combustion chamber and is located above the respective associated piston ring. This area is therefore exposed to hot combustion gases with each work cycle, which in the manner of a flame enter the side arms at high speed and temperature and, via these, enter the associated, circumferential channel and burn and expel the lubricating oil present there. As a result, it can become inadequate Lubricating oil supply and thus lead to thermal corrosion and a rapid spreading of beginning piston seizures. Another, very particular disadvantage of the known arrangement is that the gas entering the side arms and via them into the circumferential channel pushes the piston ring in question radially inward away from the cylinder liner. The consequence of this is poor efficiency and great lateral mobility of the piston, which has a wear-promoting effect. In the known arrangement, therefore, the desired effect of good lubricating oil distribution practically does not come into play.

Proceeding from this, it is therefore the object of the present invention to improve an arrangement of the type mentioned at the outset with simple and inexpensive means in such a way that low-wear operation and thus a long service life are ensured.

This object is achieved in that, in the generic arrangement, at least the uppermost, circumferential channel for forming an oil pocket on the entire circumference of the associated piston ring is offset from the top of the piston ring facing the cylinder head by an uninterrupted web.

The continuous web separating the circumferential channel from the top of the piston ring advantageously ensures that the combustion gases have no access to the find circumferential channel. The lubricating oil collected in the channel is therefore not burned and expelled, but is distributed over the entire running surface of the associated piston ring when the piston moves up and down. In the arrangement according to the invention, the circumferential channel functions as a real oil pocket that can hold a desired oil supply. Since the combustion gases cannot find access to the circumferential channel, it is also ensured that the combustion gases reliably reach the back of the affected piston ring opposite the piston ring tread and press the tread onto the tread of the cylinder liner, which provides reliable gap sealing and reliable stabilization of the piston and thus a low-wear run and a high degree of efficiency. With the measures according to the invention, the disadvantages of the known arrangement are evidently completely eliminated and the above-mentioned object is achieved in a highly simple and inexpensive manner.

Advantageous refinements and appropriate further training of the higher-level measures are specified in the subclaims. Thus, the upper piston rings of a piston ring package can expediently have more circumferential oil pockets than the lower piston rings. This results in a larger number of oil pockets in the area of the upper piston rings corresponding to the higher load on the upper piston rings. In the area of the lower piston rings, a circumferential oil pocket is usually sufficient, which reduces the manufacturing effort. A further advantageous measure can consist in the fact that the oil pocket on the circumference has a screw-shaped course. This results in a particularly good oil distribution, in particular in the case of arrangements with only one oil pocket.

In a further development of the superordinate measures, the circumferential oil pocket in the region of the ends can be closed in the case of an open piston ring with ends delimiting a gap. The closed ends counteract oil loss. Rather, the oil is kept in the oil pocket thus formed. In addition, this measure also counteracts access of the combustion gases from the gap. The measure mentioned is therefore a particularly preferred training.

The oil pocket can advantageously have a cross section rounded by radii in the region of the corners. This ensures good heat removal from the endangered corner areas, which also has an advantageous effect on achieving a long service life.

A further expedient measure can consist in the circumferential channel having radially outwardly diverging side flanks. This advantageously facilitates the application of a coating. In the case of coated piston rings, the above-mentioned closure provided in the region of the piston ring ends of the circumferential one Channel can be easily achieved by appropriate thickening of the coating.

Further advantageous refinements and expedient further developments of the superordinate measures are specified in the remaining subclaims and can be found in more detail in the following description of the examples with reference to the drawing.

In the drawing described below:

1 shows a cylinder of a two-stroke large diesel engine, partly in section,

FIG. 2 shows detail A from FIG. 1 in an enlarged view,

FIG. 3 shows a view of the end region of a standard piston ring provided with a gap,

4 shows a partial cross section through an upper piston ring and

Figure 5 shows a partial cross section through a lower piston ring.

The present invention finds application in reciprocating piston Jα-aftjr machines, preferably slow-running two-stroke large diesel engines in crosshead design. The construction and the The mode of operation of such arrangements is known per se and therefore does not require any further explanation in the present context.

The cylinder of a large two-stroke diesel engine shown in FIG. 1 contains a cylinder liner 2 provided with inlet slots 1, on which a cylinder head 3, which is only partially shown and contains an exhaust arrangement (not shown), is placed. This forms the upper boundary of a combustion chamber 4, the lower boundary of which is formed by a piston 5 which is arranged in the cylinder and can be moved up and down and which is connected in a manner not shown via a piston rod to a crosshead which interacts with a crankshaft via a connecting rod.

The piston 5 is provided with a piston ring package consisting of four piston rings 6 here. The piston rings 6, as can best be seen from FIG. 2, are arranged in a respectively assigned groove 7 of the piston jacket and rest with their outer peripheral surface on the inside of the cylinder liner 2. The grooves 7 have an oversize compared to the respectively assigned piston ring 6, so that there is a gap 8 above and within the piston rings 6, which is acted upon by fuel gas during operation.

The outer circumferential surface of the piston rings 6 and the inner circumferential surface of the cylinder liner 2 are designed as running surfaces which are supplied with lubricating oil. For this, the Cylinder liner 2, as indicated in Figure 1, be provided with radial lubricating oil bores 9, which can be supplied with lubricating oil in time with the engine via a device, not shown.

In order to achieve a good distribution of the lubricating oil over the mentioned running surfaces, the piston rings 6, as can also be seen in FIG. 2, are provided with at least one circumferential oil pocket 10 on their outer peripheral surface facing the cylinder liner 2. This acts as an oil reservoir that distributes the absorbed lubricating oil over a larger area during the up and down movement of the piston 5 and thus counteracts the formation of piston seizures or stops a beginning piston seizure and thus the previously feared, rapid spread of what was damaged at the start of a piston seizure Area prevented.

To form each such oil pocket 10, the piston rings 6 are each provided in the area of their circumferential running surface facing the cylinder liner 2 with a channel 11 running in the circumferential direction, at least the uppermost channel 11 over the entire circumference by an uninterrupted web 12 from the cylinder head 3 facing top of the associated piston ring 6 is offset, as can be seen from Figure 2. The continuously continuous web 12 prevents a connection of each channel 11 located underneath it to the area of the gap which extends from the combustion chamber 4 and is located above the associated piston ring 6 between piston 5 and cylinder liner 2. The combustion gases entering this gap therefore do not enter a circumferential channel 11 and therefore cannot push the piston ring 6 away from the cylinder liner 2. The circumferential web 12 also ensures a reliable loading of the gap 8 with combustion gases, so that there is an effective formation of the radial forces indicated at K in FIG. 2, by means of which the piston rings 6 are pressed against the cylinder liner 2.

In order to ensure complete isolation of the oil pocket or pockets 10 from the fuel gases penetrating into the gap between the piston 5 and cylinder liner 2, in the case of a standard piston ring which has a gap 13 and ends, each channel 11 containing an oil pocket 10 is in the region of each The end of the piston ring is closed, as indicated in FIG. 3 by filler pieces 14 attached in the channels 11. This also prevents access to the channels 11 from the gap 13. To form channels 11 that are closed at the ends, end pieces can also be left standing when machining the channels.

The first and the second piston ring 6 of the piston ring package have more than one circumferential oil pocket 10. In the example shown, the first and the second piston ring 6, as can be seen in FIGS. 2 and 3, are each provided with two oil pockets 10 one above the other. These can be formed by parallel channels 11 running in planes normal to the axis and are arranged symmetrically to the center plane of the associated piston ring 6. In such cases, the center distance indicated at a in FIG. 4 is about 40% of the height H of the associated piston ring 6. The third and fourth piston rings of the piston ring package each have only one oil pocket 10. The channel 11 forming this can, as shown in FIG. 5 , each be arranged at the middle height of the associated piston ring 6. In the examples shown, the channels 11 each forming an oil pocket 10, as has already been indicated above, run in planes normal to the axis. However, a helical course of the oil pockets 10 would also be conceivable.

The depth of the oil pockets 10 indicated at t in FIG. 4 is expediently in the range from 0.25% to 0.4%, preferably approximately 0.33% of the diameter of the respectively associated piston ring 6. This also results in the event of circumferential wear of the Piston ring 6 still a reliable capacity of the oil pockets 10 and thus a long period of action.

The piston rings 6 according to FIGS. 4 and 5 are each provided with a peripheral coating 15 to form their running surface. This consists of a good sliding properties, corrosion and seizure-resistant material, such as aluminum-bronze, nickel-graphite and the like. Oxides and carbides could also be used. The coating 15 is also provided in the region of the oil pockets 10 on the circumference. With piston rings 6 coated in this way, before coating grooves 17 corresponding to the desired oil pockets 10 are cut into the base material 16. These expediently have a cross section with outwardly diverging side flanks, which facilitates the subsequent application of the coating 15, for example as a welding or spray application. The subsequently applied coating 15 follows the contour of the grooved base material, so that after the application of the coating 15, taking into account the thickness d of the coating 15, the channels 11 each containing an oil pocket 10 result. The thickness d is expediently 0.5 mm.

The channels 11 have a cross section with rounded corners, as indicated by the radii r in FIG. The inner, bottom-side radius can be 1.5 mm, and the radius provided in the area of the outer edges can be about 0.5 mm. The rounded edges ensure that the heat is quickly removed. The larger the radius, the better the heat dissipation. To generate the radii r, the grooves 17 also have a cross section with rounded edges, as indicated by the radii R. These are matched to the radii r, taking into account the thickness of the coating 15, which can be approximately 0.5 mm.

The bearing surfaces of the piston-side grooves 7 assigned to the piston rings 6 are often provided with a chrome coating, on the surface of which CrO is formed, which has a desired high hardness. In the radially outer edge area, the CrO layer is stressed due to the high pressure. As soon as the CrO layer is worn out, the chrome layer is exposed, the hardness of which is significantly lower than the hardness of CrO. In order to prevent this, or in any case to counteract it, only indicated oil pockets 18 are provided on the underside of the piston rings 6 in FIG. 2.

For this purpose, at least in the radially outer region of the underside of the piston rings 6, recesses are provided, to which a filling is assigned, which consists of a material that is less wear-resistant than the base material. In the new state, the above-mentioned recesses can be completely closed by the associated filling, so that a smooth, non-profiled surface results that can be easily machined. The desired oil pockets are already formed during the running-in phase due to the faster wear of the softer material. These have a comparatively shallow depth. During operation, these oil pockets 18 fill with oil which is pressed out laterally in the event of sudden pressure and thus passes under the support surfaces of the piston ring 6 in question, which are adjacent to the oil pockets 18. This results in reliable lubrication of these support surfaces, which protects the CrO layer.

Radial grooves, bores, etc. can be provided to form the recesses on which the oil pockets are based.

Claims

Expectations Reciprocating piston internal combustion engine, in particular a large two-stroke diesel engine, with at least one piston (5) which is provided with at least one piston ring (6) which is provided in the area of its peripheral running surface with at least one channel (11) running in the circumferential direction, characterized in that at least the uppermost channel (11) running in the circumferential direction to form an oil pocket (10) on the entire circumference of the associated piston ring (6) from the cylinder head (3) facing the top of the piston ring is offset by an uninterrupted web (12). Reciprocating piston combustion engine according to claim 1, characterized in that the upper piston rings (6) of a piston ring package have more peripheral oil pockets (10) than the lower piston rings (6 Reciprocating piston engine according to one of the preceding claims, characterized in that at least the uppermost piston ring, preferably the first and the second piston ring, of a piston ring package has or have more than one oil pocket (10), preferably two oil pockets (10) and that each The piston ring (6) underneath contains an oil pocket (10). 4. Reciprocating combustion engine according to one of the preceding claims, characterized in that the Oil pocket or pockets (10) at least partially have a helical course. 5. Reciprocating piston internal combustion engine according to one of the preceding claims, characterized in that the depth of the oil pocket or pockets (10) is in the range between 0.25% - 0.40%, preferably at approximately 0.33% of the diameter of the associated piston ring (6 ) lies. 6. Reciprocating piston combustion engine according to one of the preceding claims, characterized in that with an open piston ring (6) with ends delimiting a gap (13), each oil pocket (10) is closed in the area of the piston ring ends. 7. Reciprocating internal combustion engine according to claim 6, characterized in that the groove-side closure of the oil pocket or pockets (10) is each designed as a filler piece (14). 8. Reciprocating internal combustion engine according to one of the preceding claims, characterized in that the oil pocket or pockets (10) has or have a cross section rounded off by radii in the area of the corners. 9. Reciprocating piston brake engine according to one of the preceding claims, characterized in that at least the uppermost, circumferentially extending channel (11) to form an oil pocket (10) on the entire circumference of the associated piston ring (6) from the cylinder head (3) facing piston ring top is offset by an uninterrupted web (12), a circumferential coating (15) being provided which is applied to the piston ring base material (16) and at least one groove (17) being machined into the base material (16). and the coating (15) follows the contour of the groove (17). 10. Reciprocating piston combustion engine according to claim 9, characterized in that the groove has a cross section with outwardly diverging side flanks. 11. Reciprocating internal combustion engine according to claim 9 or 10, characterized in that in the case of an open piston ring with ends delimiting a gap (13), the coating (15) in the area of the piston ring ends is designed as a closure for the oil pocket or pockets (10). 12. Reciprocating piston engine according to one of the preceding claims, characterized in that the coating (15) is made of a corrosion- and seizure-resistant Material, preferably aluminum-bronze and/or nickel-graphite. 13. Reciprocating piston combustion engine according to one of the preceding claims, characterized in that the piston rings (6) are provided in the area of their underside with recesses to which a filling is assigned, the wear resistance of which deviates from the wear resistance of the base material to form oil pockets (18). .