EP4735749A1

EP4735749A1 - A piston for a reciprocating internal combustion piston engine, a reciprocating internal combustion engine and use of such piston

Info

Publication number: EP4735749A1
Application number: EP23738817.8A
Authority: EP
Inventors: Sami OJALA; Jorma KUITUNEN; Kim BERG; Hannu Nurmi
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2023-06-27
Filing date: 2023-06-27
Publication date: 2026-05-06
Also published as: WO2025003549A1; CN121358941A; KR20260015226A

Abstract

The disclosure relates a piston (1) for a reciprocating internal combustion piston engine. The piston has a scraper ring groove (2), for receiving an oil scraper ring, the groove (2) extending annularly around a circumference of the piston (1). A receptacle volume (3) is arranged below the scraper ring groove (2), and a receiver conduit (4) extends between the scraper ring groove (2) and the receptacle volume (3), so as to provide fluid communication therebetween. A drainage conduit is provided (5) extending from the receptacle volume (3) towards a bottom (1b) of the piston. Notably, a bottom (3b) of the receptacle volume (3) has an annular inclination towards the drainage conduit (5). During an upstroke of the piston, the inclined bottom of the receptacle volume thrusts lubrication oil residing within the receptacle volume towards the drainage conduit.

Description

A PISTON FOR A RECIPROCATING INTERNAL COMBUSTION PISTON ENGINE, A RECIPROCATING INTERNAL COMBUSTION ENGINE AND USE OF SUCH PISTON

FIELD OF THE DISCLOSURE

The present disclosure relates to reciprocating internal combustion piston engine, and more particularly to pistons used in such engines. The present disclosure further concerns efficient drainage of lubrication oil recovered from walls of the cylinder.

BACKGROUND OF THE DISCLOSURE

In conventional reciprocating internal combustion piston engines, excessive lubrication oil is recovered from combustion cylinder walls by scraper rings provided on the piston, so as to prevent lubrication oil from entering the combustion chamber.

Lubrication oil contamination in the combustion chamber may lead to premature or irregular combustion and increased emissions. To this end, conventional arrangements include the provision of an receptacle volume on piston below the scraper ring, into which volume excess lubrication oil enters during a downstroke of the piston. Certain arrangements even include a drainage duct for draining the lubrication oil from the receptacle volume back to the crank case.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide for reducing the risk of lubrication oil contamination in the combustion chamber. The object of the disclosure is achieved by a piston for a reciprocating internal combustion piston engine, a reciprocating internal combustion engine, and the use of such piston, which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the discovery that insufficient drainage from a receptacle volume results in the lubrication oil splashing within the receptacle volume, or even out therefrom back onto the cylinder wall. The present disclosure aims at improving drainage from the receptacle volume by providing an inclination at the bottom thereof, such that said inclination leads towards a drainage conduit. As a result, during an upstroke of the piston, the inclined bottom of the receptacle volume thrusts the lubrication oil residing within the receptacle volume towards the drainage conduit. The present disclosure is considered particularly advantageous in connection with gaseous fuels, e.g., hydrogen fuel, where issues related to lubrication oil contamination within the combustion chamber are more prominent as compared to more traditional fuels According to a first aspect of the present disclosure, a piston for a reciprocating internal combustion piston engine is provided. The piston is configured to be arrangeable in a combustion cylinder of the engine, such that a top of the piston faces a combustion chamber, and preferably, the a bottom of the piston faces a crank case.

The piston comprises a scraper ring groove for receiving an oil scraper ring. Moreover, the scraper ring groove extends annularly around a circumference of the piston. That is, the scraper ring groove extends around the whole skirt of the piston.

In the context of this disclosure, a scraper ring is used to describe a non-compression ring, also known as an oil control ring. That is, the primary function of a scraper ring is to control the amount of lubrication oils passing up and down the cylinder walls and to prevent lubrication oil from entering the combustion chamber, as opposed to that of a compression ring, which is sealing the combustion chamber

The piston further comprises a receptacle volume arranged below the scraper ring groove. Such a receptacle volume is suitably delimited by the piston, preferably the body thereof. Preferably, the receptacle volume is of an annular shape, i.e., it extends for a full revolution about an central axis of the piston. Alternatively, the receptacle volume may be provided as one or more discrete, intermittent volumes, suitably also extending about the central axis of the piston. Moreover, such a receptacle volume may be provided internal to the piston, or alternatively, open to an outer surface of the piston.

The piston further comprises a receiver conduit extending between the scraper ring groove and the receptacle volume, so as to provide fluid communication therebetween. Suitably, the receiver conduit defines such fluid communication internal to the piston, i.e., within the piston.

The piston further comprises a drainage conduit extending from the receptacle volume towards a bottom of the piston. Suitably, the drainage conduit provides fluid communication with the receptacle volume, such fluid communication being preferably internal to the piston.

Particularly, a bottom of the receptacle volume has an annular inclination towards the drainage conduit. That is, the bottom of the receptacle volume has different elevations at different circumferential positions of the receptacle volume, such that the drainage conduit is arranged on the bottom of the receptacle volume at an elevation thereof lower than portions of the receptacle volume bottom surrounding said drainage conduit. According to one aspect of the invention, Most suitably, the drainage conduit is arranged at an bottommost portion of the receptacle volume.

Such a configuration allows for any lubrication oil residing in the receptacle volume to be thrusted towards the drainage conduit during an upstroke of the piston, thereby improving disposal of lubrication oil from the cylinder walls. This, in turn, reduces the risk of premature or irregular combustion resulting from lubrication oil entering the combustion chamber.

Preferably, a plurality of receiver conduits may be provided extending between the scraper ring groove and the receptacle volume, so as to provide fluid communication therebetween, as discussed above.

Preferably, a plurality of drainage conduits may be provided extending from the receptacle volume towards a bottom of the piston, as discussed above.

In an embodiment according to the first aspect of the disclosure, the inclination of the bottom of the receptable volume is shaped so as to ensure an even distribution of the collected oil along the receptable volume in the annular direction. In other words, the oil is arranged to flow in the inclined volume evenly towards the one or more drainage conduits without any significant spatial build-up of oil. For example, this may be achieved by varying the inclination of the bottom of the receptable volume at different locations along the annular direction. Alternatively, or in addition, the width of the receptable volume (particularly the bottom thereof), defined in radial direction of the piston, may be varied. It should be noted, that the receptacle volume may advantageously be provided as a single continuous annular volume, or multiple discrete volumes. Such an arrangement ensures even lubrication of the cylinder liner and/or piston rings without creating uneven distribution of friction along the circumference of the piston. This further helps to avoid uneven thermal load to piston rings, which together with repeated heat cycles, could lead to an unwanted tendency of the piston rings rotating slowly from their original positions causing increased wear and/or misalignment of the piston ring end caps with respect to their original positions.

Preferably, the receptable maintains at least some inclination towards the drainage conduit along its whole length, i.e., extend along the circumferential direction.

In an embodiment according to the first aspect of the disclosure, the drainage conduit extends between the receptacle volume and an internal space of the piston. Suitably, such an internal space is open towards a bottom of the piston, thereby allowing lubrication oil to drain from the drainage conduit to the crankcase. Alternatively, or in addition, the drainage conduit may extend between the receptacle and an external surface of the of piston. Suitably, such external surface is located at a boxed portion of the piston, and preferably below an additional scraper ring groove, as discussed in more detail below.

Such a configuration provides for draining lubrication oil to a suitable position, where it is not immediately susceptible of being re-introduced on the cylinder wall and/or the combustion chamber.

In an embodiment according to the first aspect of the disclosure, the piston is of a boxed - type. That is, at least a bottom portion of the piston skirt is being provided with opposing radial indentations. The portion of such radial indentation if often referred to as the boxed portion of the piston. Moreover, such box-type pistons are more susceptible to oilsplashing related issues due to the partial lack of piston skirt. Consequently, the advantages associated to the present disclosure are more prominent with pistons of the boxed type.

In an embodiment according to the first aspect of the disclosure, the piston comprises an internal cooling oil gallery coupled in fluid communication with a cooling oil inlet for capturing a cooling oil stream directed towards the cooling inlet from below the piston. Suitably, the fluid communication is arranged internal to the piston. Typically, such a cooling oil inlet is open at external surface of the piston, suitably an external surface facing the crankcase. In such configurations a jet of lubrication oil from below the piston is directed upwardly to the cooling oil inlet, from where it is conducted to the cooling oil gallery to dissipate excess heat off the piston. Nevertheless, such configurations and pistons are more susceptible to oil-splashing related issues due to the jet spray of cooling oil. Consequently, the advantages associated to the present disclosure are more prominent with pistons of the boxed type.

In an embodiment according to the first aspect of the disclosure, the piston comprises a top portion and a bottom portion detachably fixed to each other. Suitably, at least a top surface intended to face the combustion chamber is located on the top portion. Suitably, at least, an aperture for receiving a gudgeon f is located on the bottom portion.

Preferably, but not necessarily, the receptacle volume is located at an interface between the top portion and the bottom portion. That is, the interface between top portion and the bottom portion intersects or coincides with the receptacle volume. For example, a top surface of the receptacle volume may be formed by the top portion of the piston, while a bottom surface of the receptacle volume may be formed by the bottom portion of the piston

Such a configuration facilitates the provision of the receptacle volume. In an embodiment according to the first aspect of the disclosure, the piston comprises an additional scraper ring groove extending around the circumference of the piston. Notably, such an additional scraper ring groove is arranged below the receptacle volume. For example, the additional scraper ring may be similar to the scraper ring described above.

Such an additional scraper ring mitigates splashing lubrication oil from entering the receptacle volume and consuming its capacity from draining lubrication oil removed from the cylinder walls by the (upper) scraper ring.

Notably, should the piston be of the box-type, the additional scraper ring is suitably located above the boxed portion of the piston.

Preferably, but not necessarily, the additional scraper ring groove is not in internal fluid communication receptacle volume associated to the (upper) scraper ring groove.

For example, the additional scraper ring may be provided with one or more of the following: a respective additional drainage conduit leading towards the bottom of the piston, e.g. an internal space of the piston open towards the bottom and draining to the crankcase, or external surface of the piston; an respective additional receptacle volume provided in connection with the additional scraper ring groove in a similar manner as the (upper) scraper ring groove and the (upper) receptacle volume, including a respective additional receiver conduit and a respective additional drainage conduit, and an respective additional receiver conduit connected to the (upper) drainage conduit of the (upper) receptacle volume.

In an embodiment according to the first aspect of the disclosure, a receiver opening extends through the skirt of the piston to the receptacle volume. Such a receiver opening is arranged below the oil scraper ring groove, so as to provide a flow route into receptacle volume.

Suitably, the receiver opening extending annularly around the circumference of the piston, although it may alternatively be provided as one or more discrete openings.

Suitably, the receiver opening is provided at an axial level of the receptacle volume.

Preferably, the receptacle volume extends above the receiver opening. This provides room for oil residing in receptacle volume to splash into during a downstroke of the piston. Consequently, the lubrication oils is less prone to out of the receiver opening back to the cylinder wall. In an embodiment according to the first aspect of the disclosure, the piston comprises one or more compression ring grooves above the scraper ring groove. Most suitably, the compression ring grooves are not in internal fluid communication with the receptacle volume

In an embodiment according to the first aspect of the disclosure, the piston may comprise a scraper ring fitted in the scraper ring groove. Moreover, the piston may comprise an additional scraper ring fitted in the additional scraper ring groove. Particularly, such scraper rings may be provided as discussed above.

The piston may further comprise one or more compression rings fitted in the one or more compression ring grooves, respectively.

It should be noted that the first aspect of the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

According to a second aspect of the present disclosure, a reciprocating internal combustion engine is provided. Particularly, the engine comprises a piston according to the first aspect of the disclosure received in a combustion cylinder and mechanically coupled to a crankshaft.

Preferably, the engine is configured for use with gaseous fuel. For example, the engine may be provided with a gas admission valve for introducing said gaseous fuel into an intake manifold. Gaseous fuels have been found to be more susceptible to problems related to premature or irregular combustion caused by lubrication oil contamination within the combustion chamber. Suitably, the engine is configured for use with hydrogen fuel. Issues related to lubrication oil contamination within the combustion chamber have been discovered to be particularly prominent with gaseous fuel. Further, use of hydrogen fuel having small molecular size requires improvements in piston ring sealing where the invention also provides improvements. For example, better controlled oil film quality on the cylinder liner surface and improved collection of the excess oil maintain the performance of the piston rings at optimum level without being degraded through carbon built-up.

It should be noted that the second aspect of the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

According to a third aspect of the present disclosure, a piston according to the first aspect of the disclosure is used in operating a reciprocating internal combustion engine with gaseous fuel. Suitably, the gaseous fuel used is hydrogen fuel. That is, a reciprocating internal combustion engine is operated, such that gaseous fuel (e.g. , hydrogen) is fed to a combustion chamber for combusting with air. Moreover, a piston according to the first aspect being fitted in a combustion cylinder to form said combustion chamber.

The invention is particularly advantageous for use in an engine operating within the range from 250 rev/min to about 1200 rev/min, having its bore diameter at least 200 mm and/or nominal power at least 150 kW/cylinder. Further the invention is particularly advantageous in running the engine in lean burn combustion mode having lambda value over 1 , for example between 1 ,5 - 2,2. When running an high power large engine in lean burn combustion mode and especially when using gaseous fuels, for example hydrogen or hydrogen as part of the fuel, the combustion process becomes even more sensitive for interference caused by any unwanted ignition sources inside the combustion chamber. Aiming for high combustion efficiency and minimal emissions in such engines requires improved control of lubrication oil within the combustion chamber, i.e. cylinder liner. Piston and piston rings therein are the key components in achieving this.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Fig .1 illustrates a cross-sectional side view of a piston according to an embodiment of the present disclosure, as seen along a direction of an aperture for receiving a gudgeon pin;

Fig. 1 a is detailed view of the piston shown in Fig. 1 , and

Fig. 2 illustrates a cross-sectional side view of the piston shown in Fig. 1 , as seen along a direction transverse to the aperture for receiving the gudgeon pin.

DETAILED DESCRIPTION OF THE DISCLOSURE

Fig.1 illustrates a cross-sectional side view of a piston 1 according to an embodiment of the present disclosure. Particularly, the illustration is seen from a direction of an aperture 9 for receiving a gudgeon pin. That is, Fig. 1 is seen along a direction in which the gudgeon pin is intended to extend.

The piston comprises a scraper ring groove 2 extending around the piston 1 on the outer circumference thereof. A respective scraper ring 2a, depicted by a dashed-line rectangle may be inserted into the scraper ring groove, when the piston 1 is fitted in a respective engine. Notably, a receptacle volume 3 is arranged on the piston 1 , below the scraper ring groove 2. Suitably, also the receptacle volume 3 extends around the piston 1 . A receiver conduit 4, more clearly illustrated in the detail of Fig 1 a, extends between the scraper ring groove 2 and the receptacle volume 3, thereby establishing a flow route therebetween. Furthermore, a drainage conduit 5 extends from the receptacle volume 3 towards the bottom 1 b of the piston. In the embodiment of Fig. 1 , the drainage conduit 5 extends into an inner space of the piston 1 .

As illustrated by the dashed line in Fig.1 , a bottom 3a of the receptacle volume 3 is annularly inclined towards the drainage conduit 5. As the piston of Fig. 1 comprises multiple drainage conduits 5, the inclination of the bottom 3a of the receptacle volume 3 is achieved by varying the elevation thereof at different circumferential positions. In other words, the elevation of the bottom 3a of the receptacle volume 3 is higher at positions between the drainage conduits 5, and respectively, said elevation is lower at positions corresponding to the drainage conduits 5. A lower elevation of the bottom 3a corresponding to a position of the drainage outlet 5, is denoted as EL, whereas a higher elevation of the bottom 3a corresponding to a position between drainage outlet(s) 5 is denoted as EH.

In the embodiment of Fig. 1 , the piston 1 comprises a top portion 1c located at a top 1 a of the piston, and bottom portion 1d located at the bottom 1 b of the piston. That is, the top portion 1c and bottom portion 1d are separate entities, which are detachably fixed to each other.

The embodiment of Fig. 1 also has an additional scraper ring groove 6, in which an additional scraper ring 6a may be fitted. Notably, the additional scraper ring is situated below the receptacle volume 3 and the receiver opening 7.

Moreover, the embodiment of Fig. 1 shows the receptacle volume 3 extending above the receiver opening 7, constituted by the extension of the receptacle volume 3 into the receiver conduit 4. It should be noted that the receptacle volume 3 may alternatively, or in addition, extend above the receiver opening 7 separately from the receiver conduit 4.

The embodiment of Fig. 1 also illustrates two compression ring grooves 8, one above the other, extending around the outer circumferent of the piston 1 . Both of the compression ring grooves 8 are positioned above the scraper ring groove 2. The compression ring grooves 2 illustrated in Fig. 1 are blank i.e., no internal passages extend therefrom. As illustrated in Fig. 1 the compression ring grooves 8, may be fitted with respective compression rings. 8a. Although the scraper ring 2a, additional scraper ring 6a and compression rings 8 are depicted on only one side of the piston 1 for the purpose clarity, they suitably extend substantially around the circumference of the piston 1 .

More clearly seen in Fig. 1 a, the receptacle volume 3 is located at an interface between the top portion 1c and the bottom portion 1d of the piston 1 . That is, the receptacle volume 3 is delimited by both the top portion 1c and the bottom portion 1d.

Furthermore, a receiver opening 7, situated below the scraper ring groove 2, extends through the outer circumference of the piston 1 into the receptacle volume 3, thereby providing an additional flow route to the receptacle volume 3 for oil scraped from the cylinder wall.

Fig. 2, in turn, illustrates the piston of Fig.1 as seen along a direction transverse to the aperture for receiving the gudgeon pin. Notably, the elevation of the bottom 3a of the receptacle volume 3 is higher at the position illustrated in Fig. 2, than at the position illustrated in Fig. 1 .

Furthermore, Fig. 2 illustrates the boxed portion 1 e, depicted as the portion delimited by the dot-dashed rectangle, being formed as an indentation of the piston 1 . Notably, the additional scraper ring groove 6 is positioned above the boxed portion 1 e. Fig. 2 also clearly shows the drainage conduit 5 being located at the boxed portion 1 e.

LIST OF REFERENCE NUMERALS

1 piston

1 a top of piston

1 b bottom of piston

1c top portion

1 d bottom portion

1 e boxed portion

2 scraper ring groove

2a scraper ring

3 receptacle volume

3a bottom of receptacle volume

4 receiver conduit

5 drainage conduit 6 additional scraper ring groove

6a additional scraper ring

7 receiver opening

8 compression ring groove 8a compression ring 89

9 aperture

EH higher elevation of receptacle volume bottom

EL lower elevation of receptacle volume bottom

Claims

1. A piston (1 ) for a reciprocating internal combustion piston engine, said piston being configured to be arrangeable in a combustion cylinder of the engine, such that a top

(l a) of the piston faces a combustion chamber, the piston (1 ) comprising: a scraper ring groove (2) for receiving an oil scraper ring, the scraper ring groove (2) extending annularly around a circumference of the piston (1 ); a receptacle volume (3) arranged below the scraper ring groove (2), a receiver conduit (4) extending between the scraper ring groove (2) and the receptacle volume (3), so as to provide fluid communication therebetween, and a drainage conduit (5) extending from the receptacle volume (3) towards a bottom

(l b) of the piston, characterized in that a bottom (3b) of the receptacle volume (3) has an annular inclination towards the drainage conduit (5).

2. The piston (1 ) according to claim 1 , characterized by comprising one or more of the following: a plurality receiver conduits (4) extending between the scraper ring groove (2) and the receptacle volume (3), so as to provide fluid communication therebetween, and a plurality of drainage conduits (5) extending from the receptacle volume (3) towards a bottom of the piston (1b).

3. The piston (1 ) according to claim 1 or 2, characterized in that the drainage conduit (5) extends between the receptacle volume and either or both of an internal space of the piston, and an external surface of the of piston.

4. The piston (1 ) according to any of the preceding claims 1 -3, characterized in that the piston being of a boxed -type.

5. The piston according to any of the preceding claims 1-4, characterized in that the piston comprises an internal cooling oil gallery coupled in fluid communication with a cooling oil inlet for capturing a cooling oil stream directed towards the cooling oil inlet from below the piston.

6. The piston (1 ) according to any of the preceding claims 1 -5, characterized in that the piston (1 ) comprises a top portion (1c) and a bottom portion (1d) detachably fixed to each other.

7. The piston (1 ) according to claim 6, characterized in that the receptacle volume (3) is located at interface between the top portion (1c) and the bottom portion (1d).

8. The piston according to any of the preceding claims 1 -7, characterized in that the piston comprises an additional scraper ring groove (6) extending around the circumference of the piston (1 ), wherein the additional scraper ring groove (6) is arranged below the receptacle volume (3).

9. The piston (1 ) according to any of the preceding claims 1-8, characterized by a receiver opening (7) extending through a skirt of the piston (1 ) to the receptacle volume (3), said receiver opening (7) being provided below the oil scraper ring groove (2).

10. The piston (1 ) according to claim 9, characterized in that the receptacle volume (3) extends above the receiver opening (7).

11. The piston (1) according to any of the preceding claims 1 -10, characterized by comprising one or more compression ring grooves (8) above the scraper ring groove (2).

12. The piston (1) according to claim 11 , characterized by comprising one or more of the following: a scraper ring (2a) fitted in the scraper ring groove (2); an additional scraper ring (6a) fitted in the additional scraper ring groove (6), and one or more compression rings (8a) fitted in the one or more compression ring grooves (8), respectively.

13. A reciprocating internal combustion engine, comprising a piston (1 ) according to any of the preceding claims 1 -12 received in a combustion cylinder and mechanically coupled to a crankshaft.

14. The reciprocating internal combustion engine according to claim 13, characterized in that the engine is configured for used with gaseous fuel, such as hydrogen fuel.

15. Use of the piston (1 ) according to any of the preceding claims 1 -14 in operating a reciprocating internal combustion engine with gaseous fuel, such as hydrogen fuel.