WO2009097667A1

WO2009097667A1 - A piston ring, an expander element and an internal combustion engine

Info

Publication number: WO2009097667A1
Application number: PCT/BR2008/000037
Authority: WO
Inventors: André FERRARESE; Rafael Antonio Bruno
Original assignee: Mahle Metal Leve S/A
Priority date: 2008-02-08
Filing date: 2008-02-08
Publication date: 2009-08-13

Abstract

A two-piece oil control piston ring is described, having a ring core (2) and an expander element (3) positioned with a gap in an annular cavity (4) laterally provided in an engine piston (5), the cavity (4) having at least a first internal surface (4a), the ring core (2) surrounding the expander element (3) and the expand element (3) tending to expand, the expander element (3) having at least one end portion (3a) which press the first internal surface (4a) of the cavity (4) exerting sealing forces (Fs) which prevent the oil flow through the annular cavity (4).

Description

Title: "A PISTON RING, AN EXPANDER ELEMENT AND AN INTERNAL COMBUSTION ENGINE"

The present invention relates to a piston ring, mostly for regulating internal combustion engine oil consumption, being comprised of two pieces and designed to have improved performance relating to lateral sealing, which is normally a drawback of two pieces oil control ring designs.

The present invention also relates to an expander element itself (the innovative part of the present piston ring) and an internal combustion engine having at least one piston engine to which is associated the innovative two pieces oil control ring. Prior art

The internal combustion engines with pistons used in vehicles like cars, trucks and motorcycle, among several others, have at least one piston which moves in a reciprocate manner to generate torque. The reciprocating motion of the pistons is translated into crankshaft rotation via connecting rods. As a piston moves back and forth, a connecting rod changes its angle; its distal end has a rotating link to the crankshaft.

In order to achieve the desired operation, pistons have rings to seal the combustion chamber, support heat transfer from the piston to the cylin- der wall and regulate lube oil consumption. A piston ring is an open-ended ring that fits into a groove on the outer diameter of a piston in an internal combustion engine. The gap in the piston ring compresses to a few thousandths of an inch when inside the cylinder bore.

Normally, an spark ignited engine comprises one or more pistons, ea- ch one having in most cases three rings, the top two to seal the combustion chamber, maintaining a high compression inside it (compression rings) and the third ring to control the oil consumption (the oil supplied to the liner which lubricates the piston skirt and the compression rings). The oil consumption is to be avoiding since it causes a very high atmospheric pollution and the mo- dern engines have to comply with very restrictive smog regulations.

Typical compression ring designs will have an essentially rectangular cross section or a keystone cross section. The periphery will then have either a barrel profile (top compression rings) or a taper Napier form (second compression rings). There are some taper faced top rings and on some old engines simple plain faced rings were used.

Oil control rings (OCR) of spark ignited engines typically are of two ty- pes:

(i) 2-piece (helicoil spring backed cast iron or steel), or

(ii) 3-piece.

The 2-piece design has essentially peripheral forms which consist of two scraping lands of various detailed form. The 3-piece oil control rings u- sually consist of two rails or segments (these are thin steel rings) with a spacer expander spring which keeps the two rails apart and provides the radial load.

There are many differences between 2-piece and 3-piece OCR designs. In general, 3-piece OCR is cheaper than 2-piece OCR, however both OCR designs present some advantages and drawbacks and these differences will be summarized ahead.

With respect to the effects of the design, the main advantage of 3- piece OCR is the lateral sealing, obtained by the contact of the segments against the groove flanks. This characteristic avoids the oil flow through the clearance between the ring lateral and the groove flank. The 2-piece OCR does not present good lateral sealing, but presents higher conformability than 3-piece. It means that under high load and steady state condition, 2- piece usually presents better results in terms of lower lube oil consumption. However, for low load and transient regimes, 3-piece OCR usually presents better results

Regarding the thermal effect and radial wear, the OCR tangential load is one of the most important characteristic that affects oil ring performance. The tangential load loss during work can jeopardize the OCR performance. The tangential load loss is caused by two factors: Coil spring / expander stress relief when exposed to engine working temperatures; • Lower coil spring / expander deflection caused by wear. The 2-piece OCR presents lower Ft Loss due to thermal effects than the 3-piece architecture.

The characteristics of conformability / unitary pressure / ring dynamics together define the OCR performance. It is possible to improve the ring per- formance changing each one of these characteristics individually (increasing ring conformability or changing the unitary pressure) or in group, for example, changing the ring design (2-piece or 3-piece OCR).

Piston ring conformability is a parameter to indicate the ring ability to conform itself to deformed bores. So the higher is the deformation of bore, the higher is the ring conformability required. The conformability parameter ("k" factor) is expressed by the equation 1 presented by [1]:

The current values of k factor for 2-pieces OCR are from 0.5 up to 0.9. And, for 3-piece OCR are from 0.2 up to 0.5.

The unitary pressure is the design contact pressure between the faces of the OCR and the cylinder. The increase of the unitary pressure of the OCR usually improves the ring performance (reduces the LOC - lower lube oil consumption), but also increases the tangential force and radial wear [2]. The tangential force of a 3-piece and a 2-piece OCR can be calculated by the following formulas:

Ft = dλ hλ2 P_n

(2)

Ft = dλ h5 - P_n (3) Where:

• PO is unitary pressure (MPa)

• h12 and h5 are contact pressure width (mm) for 3-piece and 2- piece rings, respectively; and

• Ft is ring tangential load (N) The ring dynamics is the characteristic influenced by the ring design, and the way the OCR responds to the dynamics solicitations of the engine. For instance, the 3-piece OCR has a better performance than 2-piece in a low or partial load engine condition, probably because of the side sealing, however in full load the 2-piece presents a better performance due to its higher conformability (see equation 1 ).

An important challenge would be to have a ring with the conformability of a 2-piece OCR and the side sealing of a 3-piece OCR.

The proposal of this innovative OCR design is to add the benefit of the lateral sealing (characteristic of 3-piece OCR design) to the usual high conformability and thermal stability of the 2-piece OCR. Some similar patents were found, but none of them are able to achieve the aims of lateral sealing effect and high conformability.

Document JP8105543 revert to an improved OCR with reduced oil consumption.

The OCR comprises a lug section intermittently formed in the inner circumferential section of a ring main body while being inclined, and a sup- port projection intermittently formed in the outer circumferential section of the ring main body.

The inner circumferential section of the outer surface of one side rail is brought in contact with one wall surface in the radial direction of a ring groove by the elastic force of a coil expander energizing the ring main body to the outer side in the radial direction, and concurrently the outer surface of the other side rail is brought in contact with the other wall surface in the radial direction of the ring groove.

Since a cut-out section is formed between the lug section and an arm section projected to the outer side in the radial direction, the lug section and the arm section are bent toward the ring main body by different angles respectively. The inclined angle of the lug section to the arm section is 95° to 130°, preferably within a range of 100° to 115°.

Essentially, this document reverts to a 2-piece OCR with extra piece segment. Document US2003/0184023 reverts to a piston ring comprising a piston ring main body and an expander ring arranged on an inner peripheral surface thereof, the expander ring comprising two oil expander rings, one of which is housed in a space in a spiral of the other.

The expander ring is formed so that the pressing force in the diameter expanding direction is larger in a high temperature state than in a low temperature state, and comprises two different kinds of expander members. One of these expander members has the same functions as those of a conventional expander, and the other is a member in which there occurs a change in tension in the diametric direction with temperature. As a result, the pressing force of the master expander member having the same effects as those of the conventional expander is made variable. Essentially, it is described a double bimetallic expander element, without lateral sealing.

Document SU 920245 (from the former Soviet Union) reverts to a 3- piece OCR having a hard geometry expender element, giving a better performance with respect to the oil consumption. Document JP7293695 reverts to a way to reduce the oil consumption by restraining an opening between an oil control ring and the diametrical wall surface of a ring groove.

A bent portion, whose section is of a V shape and which projects on a side rail side, is formed into a web and a cutout portion to reduce the rigidity of the web partially is formed at the outer side annular projection of the V shaped section of the web.

When a coil expander is made to butt against the web, the bent portion of the V shaped section is expanded by the large deformation of the cutout portion, and the outer surface of the inner periphery portion of the side rail is made to butt against the diametrical wall surface of a ring groove.

As a result, at the time of internal combustion engine high speed operation, an opening is not generated between a ring main body and the diametrical wall surface of the ring groove, and therefore the oil leak into a combustion chamber at the time of internal combustion engine operation can be restrained.

Finally, document EP 0937923 refers to a piston ring which reduces the amount of oil consumption and is continuously formed of resin without being provided with an abutment. A stepped portion is formed on a third land, which is located below a second ring having a construction wherein an outer ring continuously formed of polyimide without being provided with an abutment is pressed against a cylinder wall by a coil expander via an inner ring continuously formed of PTFE without being provided with an abutment. Several oil spill ports are provided so as to allow communication between the stepped portion and an inner wall of the piston. Objectives of the invention

The proposal of the invention is an innovative OCR design is to add the benefit of the lateral sealing (characteristic of 3-piece OCR design) to the usual high conformability and thermal stability of the 2-piece OCR.

Also, the proposal of the invention is an innovative 2-piece OCR which has better performance when compared to regular 2-piece OCR and an e- quivalent cost of manufacture. Additionally, the proposal of the invention is an innovative expander element of an innovative 2-piece OCR which gives the ring a better performance in lateral sealing.

Finally, it is also proposed an internal combustion engine having at least one piston engine to which is associated the proposed 2-piece oil control ring.

Brief description of the invention

The proposals of the invention are achieved by means of a two-piece oil control piston ring, having a ring core and an expander element positioned with a gap inside an annular cavity laterally provided in an engine piston, the cavity having at least a first internal surface. The ring core surrounds the expander element and it tends to radially expand. Additionally, the expander element has at least one end portion which presses the first internal surface of the cavity exerting sealing forces, due to its tendency to expand, preventing the oil flow through the annular cavity. The proposals of the invention are also achieved by means of a two- piece oil control piston ring, having a ring core and an expander element positioned with a gap inside an annular cavity laterally provided in an engine piston, the ring core surrounding the expander element and the expander element tending to expand and therefore pressing the ring core in a manner that (i) the diameter of the ring core tends to increase and (ii) the outside portion of the ring core is forced against a wall of a cylinder of an engine block when the piston is inside the cylinder, generating a substantially radial sealing forces. The expander element exerts sealing forces against at least one wall of the annular cavity, substantially axially and orthogonal to the radial sealing forces.

The proposals of the invention are also achieved by means of a ex- pander element, specially designed for use on a two-piece oil control piston ring as defined above, comprising at least one end portion which press the first internal surface of a cavity provided in an engine piston, exerting sealing forces and preventing an oil flow through the annular cavity when the expander element is associated to said cavity. The proposals of the invention are also achieved by means of an internal combustion engine, having at least one piston with a two-piece oil control piston ring, the ring having a ring core and an expander element and being positioned with a gap inside a cavity, laterally provided in the piston and having at least a first internal surface, the ring core surrounding the expander element and the expander element tending to expand. The expander element of the ring has at least one end portion which presses the first internal surface of the cavity exerting sealing forces, due to its tendency to expand, preventing the oil flow through the annular cavity.

Finally, the proposals of the invention are achieved by means of an in- ternal combustion engine, having at least one piston with a two-piece oil control piston ring, the ring having a ring core and an expander element and being positioned with a gap inside a cavity, laterally provided in the piston and having at least a first internal surface, the ring core surrounding the expander element and the expander element tending to expand and therefore pressing the ring core in a manner that (i) the diameter of the ring core tends to increase and (ii) the outside portion of the ring core is forced against a wall of a cylinder when the piston is inside the cylinder, generating a substantially ra- dial sealing forces. The expander element of the ring exerts sealing forces against at least one wall of the annular cavity, substantially axially and orthogonal to the radial sealing forces. Brief description of the drawings This invention shall be thereafter described in more details based on an embodiment represented in the drawings. The figures show:

Figure 1 - is a cross-section view of a known 2-piece oil control ring, associated to a piston.

Figure 2 - is a cross-section view of a known 3-piece oil control ring, associated to a piston.

Figure 3 - is a cross-section view of the 2-piece oil control ring object of the present invention, associated to a piston (not shown) inside the cylinder (not shown).

Figure 4 - is an enlarged cross-section view of the 2-piece oil control ring object of the present invention.

Figure 5 - corresponds to four embodiments of expander elements part of the 2-piece oil control ring object of the present invention.

Figure 6 - corresponds to the preferred embodiment of the expander element part of the 2-piece oil control ring object of the present invention. Figure 7 - is a perspective view of the preferred embodiment of the expander element part of the 2-piece oil control ring object of the present invention. Detailed description of the drawings

The present inventions relates to a 2-piece oil control piston ring (O- CR) of an innovative design to add the benefit of the lateral sealing, which is a weak point is this kind of product, to its usual high conformability and thermal stability.

As already mentioned OCR of Otto cycle engines typically are of two types: (iii) 2-piece (helicoil spring backed cast iron or steel), or

(iv) 3-piece.

The 2-piece design has essentially peripheral forms which consist of two s- craping lands of various detailed form. The 3-piece oil control rings usually consist of two rails or segments (these are thin steel rings) with a spacer expander spring which keeps the two rails apart and provides the radial load.

There are many differences between 2-piece and 3-piece OCR de- signs. In general, 3-piece OCR is cheaper than 2-piece OCR, however both OCR designs present some advantages and drawbacks.

The main advantage of 3-piece OCR is the lateral sealing, obtained by the contact of the segments against the groove flanks. This characteristic avoids the oil flow through the clearance between the ring lateral and the groove flank.

The 2-piece OCR, on the other hand, does not present lateral sealing, but presents higher conformability than 3-piece. It means that under high load and steady state condition, 2-piece usually presents better results in terms of lower lube oil consumption. However, for low load and transient re- gimes, 3-piece OCR usually presents better results.

The present invention is a 2-piece OCR that has a conformability of a 2-piece OCR and the side sealing of a 3-piece OCR.

As already mentioned, the OCR tangential load is one of the most important characteristic that affects oil ring performance, since the tangential load loss during work can jeopardize the OCR performance. The tangential load loss is caused by two factors:

• Coil spring / expander stress relief when exposed to engine working temperatures;

• Lower coil spring / expander deflection caused by wear. The 2-piece OCR presents lower values of Ft Loss and radial wear due to thermal effects than the 3-piece architecture. The OCR of the present invention, despite being a 2-piece, has a Ft loss and radial wear values similar to those of a 3-piece OCR.

As an example, a conventional 2-piece OCR shows values of radial wear around 5.5 to 6 micrometers and Ft Loss around 1.5 to 2%, while a conventional 3-piece OCR show values of 12 to 12.5 micrometers and 10%, respectively. Essentially, the 2-piece OCR of the present invention has a ring core 2 and an expander element 3. The ring is to be positioned with a gap (of micrometers) inside an annular cavity 4 laterally provided in an engine piston 5 (not shown). The ring core 2 surrounds the expander element 3, as can be seen in figures 3-4, when the OCR is assembled.

To perform the seal as desired, every ring has to compress the cylinder wall, avoiding lubricant oil or compression gases to go through the lateral wall of the piston. In order to do so, the expander element 3 tends to expand and therefore presses the ring core 2 in a manner that two things occur:

(i) the diameter of the ring core 2 tends to increase and, therefore, (ii) the outside portion 2a of the ring core 2 is forced against a wall 6a of a cylinder 6 of an engine block (not shown) when the piston 5 is inside the cylinder 6.

The forces exerted by the expander element 3 which forces the ring core 2 against the cylinder wall 6a can be defined as substantially radial (with respect to the cylinder) sealing forces Fc, and can also be named as first sealing forces. These radial sealing forces are high and very efficient to a- void oil consumption.

As can be seen in figure 3, the cavity 4 is annular in shape, surrounding the whole piston. Its cross section is preferably substantially rectangular, but the shape can vary if desired or necessary. In some cases, the cavity 4 has a small protuberant section to help the assemblage of the OCR, but its constitution is not relevant for the present invention. Hence, the cavity 4 may vary enormously.

However, whatever is the constitution of the cavity 4, it has to have a first internal surface 4a, substantially parallel to the diameter D of the piston 5, and preferably a second internal surface 4b substantially parallel to the first internal surface 4a.

It is mentioned that the OCR 1 is positioned inside the cavity with a gap since it can move some micrometers in the vertical direction, from the first internal surface to the second (4a,4b) and vice-versa.

The main innovation of the present invention relates to the form and mostly to the operation of the expander element 3, allowing the 2-piece OCR to have the superior side sealing properties of the 3-piece OCRs. Apart from the known 2-piece OCR, in the present invention the expander element 3 is innovative and different from the coil spring mostly used, since it provides lateral sealing.

The expander element 3 is substantially annular in shape and has an aperture to be correctly positioned in the cavity 4, when it will be surrounded by the ring core 2, as already mentioned.

The cross section of the expander element 3 may vary, but it needs to have at least one end portion 3a to be associated with the respective first internal surface 4a of the cavity 4 as will be explained ahead. In a preferred embodiment, the expander element also has a second end portion 3b to be associated to the second internal surface 4b of the cavity. It is manufactured in any material desired, preferably a metallic material.

Preferably, the expander element has a cross section with a shape of "U", but evidently other geometries can be used, as, for example, with shapes of "V", "M", "J", "L", etc. Some examples are presented in Fig. 5. When the OCR 1 is assembled inside the cavity 4, the expander element 3, due to its tendency to expand, generates sealing forces Fs against the first internal surface 4a of the cavity 4. These sealing forces Fs are axial- Iy generated with respect to the piston 5 and cylinder 6, being therefore orthogonal to the sealing forces Fc above mentioned. These axial sealing for- ces Fs can also be named as second sealing forces.

Still more preferably, the two end portion 3a, 3b of the expander element generates axial sealing forces Fs against the first and second internal surfaces 4a,4b of the cavity 4, respectively, preventing the oil flow through the annular cavity 4. In other words, the expander element 3 has two end portions 3a, one of the end portions pressing first internal surface 4a and the other end portion pressing the second internal surface 4b of the cavity 4. As a result, there is no oil flow through the cavity 4.

The expander element 3 is responsible for the side sealing and the Ft. Scraping and conformability is given by the ring core 2. In assembling, there is an expander tip overlapping and the expander tips must be located at di- ametrically opposite position from ring gap.

Another advantage of the OCR object of the present invention is the possibility of keeping the same ring core (or with slight modifications) that is used in usual 2-piece OCR, replacing only the coil spring to the new expander element 3. That is because the ring core 2 is not detailed described here. The expander element 3 itself is also an invention, for use on a 2- piece oil control piston ring above defined, provided that it comprises at least one end portion 3a which press the first internal surface 4a of a cavity 4 provided in an engine piston 5, exerting sealing forces Fs and preventing an oil flow through the annular cavity 4 when the expander element 3 is associated to said cavity 4.

Figure 6 is a detailed view of one preferred embodiment of the expander element 3 with its main dimensions marked (thickness - E; bend radius - R; diameter - D"). These dimensions can vary enormously according to the engine to which the OCR will be installed (its size, capacity, power, piston geometry, cycle of operation, etc.).

Finally, it is important to note that an internal combustion engine using having at least one piston 5 with the 2-piece OCR 1 object of the present invention is also an invention itself.

It shall be understood that the scope of this invention encompasses other possible variations, being limited only by the contents of the appended claims, included therein the possible equivalents.

Claims

1. A two-piece oil control piston ring, having a ring core (2) and an expander element (3) positioned with a gap inside an annular cavity (4) laterally provided in an engine piston (5), the cavity (4) having at least a first internal surface (4a), the ring core (2) surrounding the expander element (3) and the expander element (3) tending to expand, the ring (1 ) being characterized in that the expander element (3) has at least one end portion (3a) which press the first internal surface (4a) of the cavity (4) exerting sealing forces (Fs), due to its tendency to expand, preventing the oil flow through the annular cavity (4).

2. A two-piece oil control piston ring according to claim 1 , characterized in that the cavity has a second internal surface (4b) substantially parallel to the first internal surface (4a).

3. A two-piece oil control piston ring according to claim 2, characteri- zed in that the expander element (3) has two end portions (3a), one of the end portions pressing first internal surface (4a) and the other end portion pressing the second internal surface (4b) of the cavity (4).

4. A two-piece oil control piston ring according to claim 1 , 2 or 3, characterized in that the expander element (3) has a "U" shape transversal cross section.

5. A two-piece oil control piston ring according to claim 1 , 2 or 3, characterized in that the expander element (3) has a "M" shape transversal cross section.

6. A two-piece oil control piston ring according to claim 1 , 2 or 3, cha- racterized in that the expander element (3) has a "V" shape transversal cross section.

7. A two-piece oil control piston ring, having a ring core (2) and an expander element (3) positioned with a gap inside an annular cavity (4) laterally provided in an engine piston (5), the ring core (2) surrounding the expander element (3) and the expander element (3) tending to expand and therefore pressing the ring core (2) in a manner that (i) the diameter of the ring core (2) tends to increase and (ii) the outside portion (2a) of the ring core (2) is forced against a wall (6a) of a cylinder (6) of an engine block when the piston (5) is inside the cylinder (6), generating a substantially radial sealing forces (Fc), the ring (1 ) being characterized in that the expander element (3) exerts sealing forces (Fs) against at least one wall of the annular cavity (4), substantial- Iy axially and orthogonal to the radial sealing forces (Fc).

8. A two-piece oil control piston ring according to claim 7, characterized in that the expander element (3) has a "U" shape transversal cross section.

9. A two-piece oil control piston ring according to claim 7, characteri- zed in that the expander element (3) has a "M" shape transversal cross section.

10. A two-piece oil control piston ring according to claim 7, characterized in that the expander element (3) has a "V" shape transversal cross section.

11. Expander element, specially designed for use on a two-piece oil control piston ring as defined on claims 1 to 10, characterized in that it comprises at least one end portion (3a) which press the first internal surface (4a) of a cavity (4) provided in an engine piston (5), exerting sealing forces (Fs) and preventing an oil flow through the annular cavity (4) when the expander element (3) is associated to said cavity (4).

12. Expander element according to claim 11 , characterized in that it has a "U" shape transversal cross section.

13. Expander element according to claim 11 , characterized in that it has a "M" shape transversal cross section.

14. Expander element according to claim 11 , characterized in that it has a "V" shape transversal cross section.

15. Internal combustion engine, having at least one piston (5) with a two-piece oil control piston ring (1 ), the ring (1 ) having a ring core (2) and an expander element (3) and being positioned with a gap inside a cavity (4), laterally provided in the piston (5) and having at least a first internal surface (4a), the ring core (2) surrounding the expander element (3) and the expander element (3) tending to expand, the engine being characterized in that the expander element (3) of the ring (1) has at least one end portion (3a) which press the first internal surface (4a) of the cavity (4) exerting sealing forces (F$), due to its tendency to expand, preventing the oil flow through the annular cavity

(4).

16. Internal combustion engine,_, having at least one piston (5) with a two- piece oil control piston ring (1), the ring (1) having a ring core (2) and an expander element (3) and being positioned with a gap inside a cavity (4), laterally provided in the piston (5) aηd having at least a first internal surface (4a), the ring core (2) surrounding the expander element (3) and the expander element (3) tending to expand and therefore pressing the ring core (2) in a manner that (i) the diameter of the ring core (2) tends to increase and (ii) the outside portion (2a) of the ring core (2) is forced against a wall (6a) of a cylinder (6) when the piston (5) is inside the cylinder (6), generating a substantially radial sealing forces (Fc), the engine being characterized in that the expander element (3) of the ring (1) exerts sealing forces (Fs) against at least one wall of the annular cavity (4), substantially axially and orthogonal to the radial sealing forces (Fc).