GB2282431A

GB2282431A - Piston ring system

Info

Publication number: GB2282431A
Application number: GB9418167A
Authority: GB
Inventors: Jordan Gentscheff; Georg Wachtmeister
Original assignee: MAN B&W Diesel GmbH
Current assignee: MAN B&W Diesel GmbH
Priority date: 1993-09-15
Filing date: 1994-09-09
Publication date: 1995-04-05
Anticipated expiration: 2014-09-09
Also published as: GB9418167D0; ITRM940473A1; DE4331324C2; IT1272333B; DE4331324A1; ITRM940473A0; GB2282431B

Description

2282431 Piston Ring System The invention relates to a piston ring system

for a piston in a lifting piston internal combustion engine according to the preamble of claim 1.

Such piston ring systems formed from several sealing rings, which in addition normally also include at least one oil scraper ring on the side of the crankcase, have been known for a long time. The sealing rings should first and foremost seal the cylinder area but they also affect the amount of oil remaining on the cylinder wall and hence the friction conditions for the piston and the rings themselves. The piston has a number of recessed annular grooves, which are limited by an upper and a lower groove flank respectively. Because of the cross-movement of the piston the rings have to be movable in the grooves. Therefore the structural height of the piston rings is less than that of the grooves. In order to obtain satisfactory lubrication conditions on the flank bearing surfaces an axial movement of the piston rings is necessary within the annular groove clearances so that oil can penetrate between the annular flanks and the groove flanks. An axial movement is triggered in accordance with the forces acting on the piston rings in the axial direction, it being possible for the rings to abut either the upper or the lower groove flank. In order to take the high load from the uppermost sealing ring it is important to divide the pressure difference existing between the working area and the crankcase in a uniform gradation between the annular spaces present between the sealing rings.

Forces which have an effect are: the gas force (in the axial direction) resulting from the product of the pressure difference at the upper side and the lower side of the ring and the surfaces acted on by these pressures, the mass force (in the axial direction) resulting from the mass of the rings and the piston acceleration, and the frictional forces (in the axial direction) exerted by the cylinder wall as a result of ring prestress and the gas force acting additionally on the rear of the rings (in the radial direction) in connection with the friction coefficient.

Of these movement possibilities of the piston rings the undisturbed axial movement, i.e. the alternation of support from one groove flank to the other, has the greatest influence on the functional efficiency of the piston ring system.

Since the specific power, the maximum ignition pressure and the intake pressure of modern internal combustion engines are becoming ever higher, the gas forces represent the significant influencing factor on the axial movement behaviour of the piston rings. With the level of pressure in the working area of the internal combustion engine becoming higher, it becomes more and more difficult to discharge the ring chambers between the individual sealing rings in time so that the pressure difference reverses its sign in order to make possible, in the compression cycle of the piston, a prescribed change of support of the piston rings from the lower to the upper groove flank. The timely change of flank of the piston rings is prevented more and more and the danger of "floating" of the piston rings increases.

The aim of the invention is, therefore, on the one hand to produce a good sealing piston ring system of the above type which, on the other hand, also ensures a timely flank change of the piston rings with an ever increasing level of pressure in the working area, so that the stress on the first sealing ring does not become too great.

The aim is achieved according to the invention by the features in the characterising part of claim 1.

c 1.

Because for at least some of the sealing rings a support surface of the lower ring flank on the lower groove flank reduced with respect to the entire crankcase-side lower ring flank is provided in such a way that a step is formed which, on the one hand, is used as a support surface and on the other hand for the spatial limiting of an intermediate chamber for receiving gas below the lower ring flank when the ring lies on the lower groove flank, the medium causing the gas pressure on the upper ring surface can now reach partially below the lower ring flank with the relevant sealing rings, so that the pressure difference between two annular areas separated by such a ring is reduced to such an extent, or changes its sign, that the annular chamber pressure caused by the leakage loss due to the ring gap can make possible a change of flank of the piston rings.

It is particularly preferred, in order to ensure a good sealing effect of the system of the sealing rings and in order to reduce the pressure drop in the direction of the crankcase in a controlled way, that the sealing rings are additionally constructed with ring gaps which become narrower in the direction of the crankcase from ring to ring, and thus with a metered "leakage".

Advantageous developments of the invention can be seen in the sub-claims.

Several exemplary embodiments of the invention are explained below by means of the drawings. These show schematically: Fig. 1 a partial longitudinal section of a piston cylinder arrangement at the level of a first piston ring system of the invention in the expansion cycle with three sealing rings, a view of the piston ring system of the invention corresponding to Fig. 1 with four Fig. 2 Fig. 4 sealing_rings, Fig. 3 a view of a piston ring system of the invention corresponding to Fig. 1 with steps of different radial width, a view of a piston ring system corresponding to Fig. 1 in which all the sealing rings have a step, Fig. 5 a view of a second piston ring system of the invention in the expansion cycle with three sealing rings, in which all the lower groove flanks of the annular grooves of the sealing rings have a step.

In Figures 1 to 5 a piston is referenced 1 and a cylinder of a lifting piston internal combustion engine (not shown in detail) is referenced 2. In Fig. 1 an annular gap 4 located between the side wall of the piston 1 and the cylinder 2 is sealed by three sealing rings 5, 6, 7, and in Fig. 2 by four sealing rings 5, 6, 7, 8. This should make it clear that the more sealing rings used, the better the piston ring system functions since the leakage losses in the direction of the crankcase become smaller from ring to ring.

The piston 1 has a number of recessed annular grooves 9, 10, 11, 12; 25, 26, 27 which are axially limited by an upper and a lower groove flank respectively.

The sealing rings 5, 6, 7, 8 (Fig. 1 and 2), 13, 14, 15 (Fig. 3) and 17, 18, 19 (Fig. 4) and 30, 31, 32 (Fig. 5) are inserted with axial clearance into the annular grooves 9, 10, 11 and, if present, 12, and 25, 26, 27 and limited respectively by an upper and a lower ring flank.

In Figs. 1 and 2, with the exception of the first sealing ring 5 all the other sealing rings 6, 7 and 8, on the lower annular surface of radial width S, each have a step 20 with the same radial width s, which of i, 1 9 -5 course is smaller than the entire radial width S of the lower ring flank. The support surfaces of the relevant sealing rings 6, 7 and 8 are thus reduced towards the lower groove flank in each case and their radial widths are reduced by the amount S - sl.

Furthermore, in all the exemplary embodiments the sealing rings 5, 6, 7, 8; 13, 14, 15; 17, 18, 19; 25, 26, 27 are slit, i.e. provided with ring gaps which become narrower in the direction of the crankcase from ring to ring. The flow of exhaust gases from the working chamber into the crankcase is therefore prevented to a great extent in spite of metered leakage losses, and the pressure drop in the direction of the crankcase from annular chamber to annular chamber can be controlled.

In the exemplary embodiment according to Fig. 3 the size of the steps 21, 22 of the second and third sealing ring 14, 15, hence the amount of the radial width si with i = 2, 3, varies.

The amount of effective gas and mass forces can in this way be influenced in a thoroughly controlled way.

For instance, the effective gas force, and hence mass force, for each sealing ring 14, 15 can be adapted to the acceleration or rotational speed of the piston 1.

Fig. 4 shows a piston ring system in which all the sealing rings 17, 18, 19, including the first sealing ring 17, have a step 23 on their lower ring flanks as an advantageous measure. This consequently has a further wear-reducing effect on the first piston ring 17. This is because the maximum force of the uppermost piston ring 17 pressing on the cylinder wall in the socalled wedge region is substantially proportional to the radial piston friction force on the lower flank of this uppermost piston ring 17. Since the support surface is reduced the friction force and wear are therefore also reduced.

Furthermore, experiments have shown that the radial widths si, with i = 1, 2, 3..., of a step 20, 21, 22 or 23 should preferably amount to at least half the radial width S of a lower ring flank.

-her piston ring system in which Fig. 5 shows a furt all the annular grooves 25, 26, 27 for the sealing rings 30, 31, 32 have a step 33 on their lower groove flanks which on the one hand provides the support surface for the rings 30, 31, 32 and on the other hand is used for the spatial limitation of an intermediate chamber 34 for receiving gas below the lower ring flank when the ring 30, 31, 32 is laid on the lower groove flank.

Also applying to this exemplary embodiment according to Fig. 5 is the fact that the more sealing rings used the better the piston ring system functions.

The size of the steps from annular groove to annular groove according to the exemplary embodiments of Fig. 1 to 4 may remain the same or vary. Here also the radial widths of the steps 33 with the annular gap 4 should amount to at least half the radial width of the lower ring flank.

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Claims

Claims:

1. Piston ring system for a piston of a lifting cylinder internal combustion engine having several annular grooves recessed into this piston which are axially limited respectively by an upper and a lower groove flank, wherein the sealing rings inserted with axial clearance into the annular grooves, are limited by an upper and a lower ring flank and each have a ring gap, and at least some of the sealing rings comprise a support surface of the lower ring flank on the lower groove flank, the support surface is reduced with respect to the entire lower ring flank on the crankcase side in such a way that a step is formed which is used on the one hand as a support surface and on the other hand for the spatial bounding of an intermediate chamber for receiving gas below the lower ring flank when it lies on the lower groove flank.

2. Piston ring system according to claim 1, wherein the ring gaps of the sealing rings become narrower from ring to ring in the direction of the crankcase.

3. Piston ring system according to claim 1 or 2, wherein at least some of the sealing rings each have a step with a radial width si (i = 1, 2, 3.... ) on the lower ring flank with the radial width S so that the respective support surface for the lower groove flank is reduced with respect to the entire crankcase-side surface width S.

4. Piston ring system according to claim 1 or 2, wherein at least some of the annular grooves for the sealing rings have on their lower groove flanks a step which is used on the one hand as a support surface for the rings and on the other hand for the spatial bounding of an intermediate chamber for receiving gas below the lower ring flank when the ring lies on the lower groove flank.

5. Piston ring system according to any of claims 1, 2 or 3 wherein all the sealing rings have a step on their lower ring flank.

6. Piston ring system according to any of claims 1, 2 or 4 wherein all the annular grooves have a step on their lower groove flank.

7. Piston ring system according to one of the preceding claims, wherein all the steps are the same size.

8. Piston ring system according to claim 3 or 5, wherein the steps on the lower flanks of the various sealing rings have different radial widths Si and so are adapted to the respective pressure ratios in the individual annular chambers.

9. Piston ring system according to claim 4 or 6, wherein the steps on the lower groove flanks of the various annular grooves have different radial widths.

10. Piston ring system according to one of the preceding claims, wherein the radial width si of one step is at least half the radial width S of a lower ring flank.

11. Piston ring system substantially as hereinbefore described with reference to Figures 1 to 3, Figure 4 or Figure 5.

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