GB2370091A

GB2370091A - Piston ring for a reciprocating piston machine

Info

Publication number: GB2370091A
Application number: GB0204494A
Authority: GB
Inventors: Lech Moczulski
Original assignee: MAN B&W Diesel AS
Current assignee: MAN B&W Diesel AS
Priority date: 1999-09-04
Filing date: 2000-08-19
Publication date: 2002-06-19
Anticipated expiration: 2020-08-19
Also published as: KR20020037045A; JP2003532823A; SE0200329D0; DE19942241A1; JP3931964B2; GB0204494D0; AU6571900A; DE19942241C2; KR100467380B1; GB2370091B; SE518994C2; SE0200329L; WO2001018434A1

Abstract

The invention relates to a reciprocating piston machine with at least one piston (5). Said piston is provided with at least one piston ring (6) that is located in a corresponding piston ring groove (7) of the piston (5), said piston ring groove having a supporting surface (8) that pertains to the piston ring (6). The aim of the invention is to facilitate a wear-free operation and high durability of such a piston despite high pressure in the area of the supporting surface (8). To this end, the piston ring (6), at least in the radial outer area of the lower surface facing the supporting surface (8), is provided with recesses (14, 15) which form oil pockets (13) and adjacent supporting areas (18). A filling (16, 17) is allocated to said oil pockets that consists at least partially of aluminum bronze with a wear resistance that differs from the wear resistance of the base material of the piston ring.

Description

237009 1

PISTON RING FOR RECIPROCATING-PISTON ENGINE

The invention relates to a reciprocating-piston engine, in particular to a two-stroke industrial diesel engine, 5 having at least one piston, which is provided with at least one piston ring disposed in an associated piston ring groove of the piston, which groove has a supporting surface, which is associated with the piston ring and is preferably reinforced at least in the radially outer 10 region by means of a chromium coating.

The forces acting upon the piston ring undergo a change of direction as a result of the up-and-down motion of the piston. The piston ring is therefore stimulated 15 into tilting movements. This leads in the region of the radially outer edge of the supporting surface of the piston ring groove to very high compressions, which may impair the lubricant film. The result is therefore poor lubrication and extreme abrasion. Attempts have already 20 been made to combat this by providing the supporting surface, particularly in the radially outer region, with a reinforcement coating. For the latter, as a rule, chromium is used. However, even in said case the previously mentioned abrasion occurs and then has a 25 particularly highly disadvantageous effect. In said connection it is namely to be assumed that at the surface of the chromium layer a thin CrO layer forms, which in a desired manner has a much greater hardness than chromium. However, as soon as said CrO layer has 30 been destroyed, the much softer chromium is exposed, with the result that very fast wear may occur.

Against said background, the object of the present

invention is therefore with simple and inexpensive means 35 to improve an arrangement of the type mentioned initially in such a way that, despite high compressions in the region of the supporting surface of the piston ring groove, low-wear operation and a long service life are achieved.

Said object is achieved according to the invention in that the piston ring at least in the radially outer region of its underside facing the supporting surface is, for the formation of oil pockets and bearing regions 45 adjacent thereto, provided with recesses, with which is associated a filling, which at least partially comprises an aluminium bronze having a wear resistance, which differs from the wear resistance of the piston ring basic material.

In the new state the recesses may be completely closed by the associated filling. The result is therefore a smooth, non-profiled surface which is easy to machine.

However, as early as during the running-in phase because 55 of the more rapid wear of the softer material the desired oil pockets develop, of which the depth in said case is in a desired manner very low but which with increasing wear of the piston ring progress at a rate

dependent on said wear, so that throughout the service life the desired oil pockets are present. In said oil pockets lubricating oil may be stored, which in the event of periodically arising compressions are pressed 5 into the gap between the supporting surface of the piston ring groove and the bearing surfaces of the piston ring, which surround the oil pockets. As the oil pockets have a comparatively low depth and hence a comparatively low capacity, the result is practically a 10 thin oil film which spreads over the entire piston ring surface, with the result that no localized rise of the surface pressure is to be expected. The above statements demonstrate that with the measures according

to the invention the initially stated object is achieved 15 in an extremely simple and inexpensive manner.

Advantageous refinements and practical developments of the above measures are indicated in the sub-claims.

Thus, the material forming the filling of the recesses 20 may have a lower or a higher wear resistance than the piston ring basic material. In the first case, the oil pockets develop in the region of the recesses, which are provided with a filling. In the second case, the oil pockets arise in the region between the recesses, which 25 are provided with a filling. In the first case, material breaking off from the supporting surface may be pressed into the comparatively soft filling material and hence fixed. In said manner it is possible to stop free movement of said material particles, thereby preventing 30 the destruction which they cause. In the second case, a material which is much harder than the piston ring basic material may be selected, resulting in wear which progresses only at a very slow rate.

35 As a filling material which is softer than the piston ring basic material, an aluminium bronze which contains aluminium, iron and copper may advantageously be used.

To form the filling material which is harder than the piston ring basic material, an aluminium bronze which 40 contains aluminium, iron, manganese, silicon, carbon and copper may be used.

In a further development of the above measures, the recesses may at least partially take the form of spaced 45 apart grooves and/or blind holes distributed uniformly over the associated surface. In the first case, manufacture is consequently comparatively easy. In the second case, a particularly good distribution over the respective associated surface is achieved.

A further advantageous measure may be such that the radially inner region of the piston ring underside is recess-free. By said means unwanted gas penetration may be avoided in a particularly reliable manner, even 55 though the filling of the recesses, which wears more slowly in the radially inner region of the piston ring

underside than in the outer region, also combats gas penetration. Further advantageous refinements and practical 5 developments of the above measures are indicated in the remaining sub-claims and inferable in detail from the following description of examples with reference to the

drawings. 10 The drawings described below show: Figure 1 a cylinder of a two-stroke industrial diesel engine partially in section, 15 Figure 2 a radial section through a piston ring with associated piston ring groove, Figure 3 an enlarged detail of the mutual contact regions of piston ring and piston ring groove 20 in the case of an embodiment with a soft filling of the recesses, Figure 4 a view as in Figure 3 in the case of an embodiment with a hard filling of the 25 recesses, Figure 5 a plan view of the underside of a piston ring with groove-shaped recesses and 30 Figure 6 a plan view of the underside of a piston ring with hole-shaped recesses.

The present invention is used in reciprocating-piston engines, in particular reciprocating-piston internal 35 combustion engines, preferably low-speed two-stroke industrial diesel engines of a crosshead style of construction. The construction and mode of operation of such arrangements are known as such and therefore in the present context require no further explanation.

The cylinder, shown in Figure 1, of a two-stroke industrial diesel engine comprises a cylinder liner 2, which is provided with inlet slots 1 and onto which an only partially illustrated cylinder head 3 containing a 45 non-illustrated outlet arrangement is mounted. Said cylinder head forms the upper boundary of a combustion chamber 4, the bottom boundary of which is formed by a piston 5, which is disposed in the cylinder, is capable of moving up and down and in a non-illustrated manner is 50 connected by a piston rod to a crosshead, which; cooperates via a connecting rod with a crankshaft.

The piston 5 is provided with a piston ring set, which in the present case comprises four piston rings 6. The 55 piston rings 6, as may best be seen from Figure 2, are disposed in each case in an associated piston ring

groove 7 of the piston skirt. The underside of the piston rings 6 rests in said case on an associated, bottom supporting surface 8 of the associated piston ring groove 7. The outer peripheral surface of the 5 piston rings 6 is designed as a running surface and lies against the inside, which is likewise designed as a running surface, of the cylinder liner 2.

For supplying lubricating oil to the running surfaces of 10 the piston rings 6 and the cylinder liner 2 as well as to the mutual contact surfaces of the piston rings 6 and the respectively associated piston ring groove 7, the cylinder liner 2 may, as indicated in Figure 1, be provided with radial lubricating oil bores 9, which by 15 means of a non- illustrated device may be loaded with lubricating oil during the stroke of the engine.

The piston ring grooves 7 are each overdimensioned relative to the associated piston ring 6, so that above 20 and radially at the inside of the piston rings 7 a gap 10 visible in Figure 2 arises, which is connected by the gap 11 between piston 5 and cylinder liner 2 to the combustion chamber 4 and hence in the course of operation is loaded with combustion gas. As a result, i 25 radially outwardly directed radial forces and downwardly I directed axial forces act upon the piston rings. The radial forces press the piston rings 6 against the cylinder liner 2. By means of the axial forces the piston rings 6 are pressed by their underside in each 30 case against the associated supporting surface 8.

Superimposed on the axial forces resulting from the pressure in the combustion chamber 4 are the frictional forces, which are directed downwards during the upward movement of the piston 5 and upwards during the downward 35 movement of the piston.

The downwardly directed forces lead to a very high compression between the underside of the piston rings 6 and the respective associated groove- side supporting 40 surface 8. The supporting surface 8 is therefore reinforced by a coating 12 preferably of chromium.

Chromium admittedly only has a hardness of around 300 HV. However, at the surface of the chromium layer a thin CrO layer develops, which reaches a much higher 45 hardness of around 800 HV, thereby resulting in good bearing properties.

Because of the change in the direction of force during the up-and-down movement of the piston 5, the piston 50 rings 6 execute a slight tilting movement, with the result that the compression in the radially outer region of the supporting surface 8 becomes particularly high.

Said region comprises approximately a third of the width of the supporting surface 8. Said high compression may 55 lead, without additional measures, to destruction of the oil film, with the result that the hard CrO layer is

worn away very quickly, leaving the comparatively soft chromium exposed, which then leads to wear progressing at an even faster rate.

5 To combat the above, the piston rings 6 at least in the region of their underside associated with the radially outer region of the supporting surface 8 are provided with oil pockets 13, which are merely indicated in Figure 2 and adjacent to which are bearing regions 18, 10 which are not visible in Figure 2 but are shown in Figures 3 and 4. The oil pockets 13 function as an oil reservoir. To form the said oil pockets 13, the piston rings 6, as 15 may best be seen from Figures 3 and 4, are provided in the region of their underside with recesses 14 and/or 15, with which is associated a filling 16 and/or 17 of a material having a wear resistance, which differs from the wear resistance of the basic material of the piston 20 rings 6.

In the example forming the basis of Figure 3, the filling 16 of the recesses 14 is based on a material having a wear resistance, which is lower than the wear 25 resistance of the piston ring basic material. To form said filling 16, an aluminium bronze containing aluminium, iron and copper may be used. Advantageously, in said case 2 - 20%, preferably 9\ 11\ Al, 0.5% - i 8%, preferably 0.5% - 2% Fe and the remainder Cu may be 30 provided.

In the new state, the recesses may be completely closed by the associated filling. The result is therefore a smooth, non-profiled surface which is easy to machine.

35 As early as during the running-in phase, however, as a result of the more rapid wear of the filling material compared to the basic material the desired oil pockets 13 develop, which have a comparatively low depth and hence function as a comparatively shallow oil reservoir.

The regions of the piston ring underside, which are situated outside of the recesses 14, form the bearing regions 18 already mentioned above. As a result of periodically occurring compression the oil stored in the 45 oil pockets 13 is pressed away sideways and in said case inevitably passes into the gap 19 between the supporting surface 8 of the piston ring groove and the bearing surfaces 18 of the piston ring. Because of the comparatively low oil volume and the comparatively low 50 depth of the oil pockets 13 this gives rise, over the entire supporting surface 8, to a continuous thin oil film, which spreads uniformly over the entire supporting surface 8, so that despite the provided oil pockets 13 there is no localized increase of the surface pressure 55 in the region of the bearing surface 18.

In the example forming the basis of Figure 4, the material forming the filling 17 of the recesses 15 has a wear resistance, which is higher than the wear resistance of the piston ring basic material. In the 5 new state, said recesses 15 may likewise be completely full, resulting in a smooth, non-profiled surface which is easy to machine. Here, as early as during the running-in phase because of the more rapid wear of the piston ring basic material compared to the filling 10 material the desired oil pockets 13 develop in the region between the fillings 17 of the recesses 15. The fillings 17 in said case remain in place or wear only very slowly and delimit the oil pockets 13.

15 Here, as a suitable material, an aluminium bronze containing at least aluminium, iron, manganese, silicon, carbon and copper may be used. Preferably said material may contain 2% - 20\ Al, 0.5% - 10% Fe, 0.1\ - 8\ Mn, =.1% - 2 Si, 0.1% - 10% Hi, =.1% - 2t C and in each 20 case at most 5% - 20% of at least one of the components Sb, Co, Be, Cr. Sn, Cd, En, Pb and the remainder Cu. In a particularly advantageous manner 14% - 17% Al, 3% 5% Fe, 1% - 3t Mn, 0.1% - 2% Si, at most 0.3% C and the remainder Cu may be provided.

The underside of the fillings 17, which remain in place, here forms the bearing surfaces 18 of the piston ring.

The effect is the same as already indicated above in connection with Figure 3. Each case leads to a 30 comparatively low depth of the oil pockets 13, which with increasing piston ring wear progress at a rate dependent thereon. During periodically occurring compressions the oil stored in the oil pockets 13 is pressed in the form of a film into the gap 19 between 35 the supporting surface 8 and the bearing surfaces 18.

Because of the low depth of the oil pockets 13 a thin oil film arises, which spreads uniformly over the entire supporting surface 8.

40 The above-mentioned recesses 14 and/or 15 may have any desired configuration, e.g. they may take the form of grooves 20, as illustrated in Figure 5, or blind holes 21, as illustrated in Figure 6. The spacedapart grooves 20 may have a radial shape or, as illustrated, a 45 curved shape. The grooves 20 may extend over the entire width of the piston rings 6, as indicated in Figure 5 on! the right, or be confined to the outer region, as indicated in Figure 5 on the left. Said last-mentioned variant makes it easier to prevent unwanted gas 50 penetration under the piston rings 6.

The blind holes 21 are advantageously distributed uniformly over the associated surface, wherein a distribution over the entire piston ring width may be 55 provided, as indicated in Figure 6 on the left, or only over the radially outer region, as indicated in Fiqure 6

on the right. The oil pockets 13 in said example form islands practically surrounded by the bearing surfaces 18, which always leads to good protection against unwanted gas penetration.

In order to guarantee good oil distribution in the region of the peripheral running surfaces of the piston rings 6, the piston rings 6, as Figure 2 further reveals, may be provided in the region of their lO peripheral running surface with at least one channel 22, which extends in peripheral direction and for forming an oil pocket 23 along the entire periphery of the associated piston ring 6 is set off from the piston ring top surface facing the cylinder head 3 by means of a 15 continuous circumferential web 24.

Claims

1. Reciprocating-piston engine, in particular a two stroke industrial diesel engine, having at least 5 one piston (5), which is provided with at least one piston ring (6) disposed in an associated piston ring groove (7) of the piston (5), which groove has a supporting surface (8), which is associated with the piston ring (6) and is preferably reinforced at 10 least in the radially outer region by means of a chromium coating (12), characterized in that the piston ring (6) at least in the radially outer region of its underside facing the supporting surface (8) is, for the formation of oil pockets 15 (13) and bearing regions (18) adjacent thereto, provided with recesses (14, 15), with which is associated a filling (16, 17), which at least partially comprises an aluminium bronze having a wear resistance, which differs from the wear 20 resistance of the piston ring basic material.

2. Reciprocating-piston engine according to claim 1, characterized in that the material forming the filling (16) entirely comprises the aluminium 25 bronze having a wear resistance, which differs from the wear resistance of the piston ring basic material.

3. Reciprocating-piston engine according to claim 1 or 30 2, characterized in that the material forming the filling (16) has a lower wear resistance than the piston ring basic material.

4. Reciprocating-piston engine according to claim 3, 35 characterized in that the aluminium bronze forming the filling (16) contains at least aluminium, iron and copper.

5. Reciprocating-piston engine according to claim 1 or 40 2, characterized in that the material forming the filling (17) has a higher wear resistance than the piston ring basic material.

6. Reciprocating-piston engine according to claim 5, 45 characterized in that the aluminium bronze forming the filling (17) contains at least aluminium, iron, manganese, silicon, carbon and copper.

7. Reciprocating-piston engine according to one of the 50 preceding claims, characterized in that the recesses provided for forming the oil pockets (13) at least partially take the form of spaced-apart grooves (20) .

55

8. Reciprocating-piston engine according to one of the preceding claims, characterized in that the

recesses provided for forming the oil pockets (13) at least partially take the form of blind holes (21), which are distributed uniformly over the associated surface.

9. Reciprocating-piston engine according to one of the preceding claims, characterized in that the radially inner region of the underside of the piston rings (6) is recess-free.

10. Reciprocating-piston engine according to one of the preceding claims, characterized in that the piston ring or piston rings (6) is or are provided in the region of its peripheral running surface with at IS least one channel (22), which extends in peripheral direction and for the formation of an oil pocket (23) along the entire periphery of the associated piston ring (6) is set off from the piston ring top surface facing the cylinder head (3) by means of a 20 continuous circumferential web (24).