[0001] The present invention relates to an oil control ring which is designed for internal combustion engines and which, thanks to its structural configuration, allows a better distribution of the contact pressure and scraping of the oil and a better conformance of the ring with the cylinder wall.

Description of the Prior Art

[0002] Internal combustion engines are mechanisms for transforming energy which are used by the vast majority of motor vehicles. They basically are comprised of two main parts: one or more heads and the engine block. In the base of the head(s) are located the combustion chambers (in Diesel motors the combustion chambers are generally located in the piston heads) and in the engine block there are located the cylinders and the crank shaft assembly. The crank shaft assembly is composed of pistons, connecting rods, and the crank. [0003] The engine converts the energy produced by the burning of the mixture (fuel and air) in the combustion chambers into mechanical energy able to impart movement to the wheels.

[0004] Since the driving force needed for moving the automobile comes from the burning of the fuel and air mixture in the combustion chamber, and in order to assure a homogeneous combustion without burning oil and also to prevent excessive gas going from the cylinder to the crankcase, it is necessary to make use of rings to provide a good seal for the gap between the piston and the cylinder wall.

[0005] Normally, three rings are used, there being two compression rings and one oil ring. The compression rings have the function of preventing combustion gases from getting into the crankcase, and the oil ring has the function of scraping the excess oil from the cylinder wall and returning it to the crankcase. [0006] Moreover, the oil rings found in the prior art have slits or holes distributed along the length of the peripheral transverse section of the body.

[0007] These slits or holes have the function of draining the excess oil accumulated between the two external working faces of the ring and increasing its flexibility by means of reducing the rigidity of the transverse section containing the slits.

[0008] Another important function of the rings is to serve as a bridge for transmitting heat from the piston to the cylinder wall/jacket, where the heat is dissipated through the cooling system.

[0009] The oil rings may be composed of one, two, or three pieces, the last two types being used most commonly in internal combustion engines.

[00010] As its principal characteristics, the one-piece ring utilizes the intrinsic elastic properties of its base material in order to achieve the force of expansion required by the application, while the two-piece ring basically comprises a body and an elastic element, and the three-piece ring comprises basically a support body and two ring segments to accomplish the same purpose.

[00011] Motivated by the quest for greater energy efficiency, engine design trends aim at producing smaller engines, reducing the power losses caused by friction.

[00012] In pace with these developments, oil rings have come to have increasing smaller height, as well as smaller loads and/or expansion force.

[00013] Further following these trends of reducing the operating friction of the engine, it is possible to maintain a suitable contact pressure at the ring/cylinder interface by reducing the contact area of the ring, even when reduced expansion loads are operating.

[00014] However, difficulties in the fabrication and manipulation of the parts and even a possible breakage during use are obstacles which need to be overcome in designs whose purpose is to reduce the contact area of the oil control rings.

[00015] As such, the ring described in the Brazilian patent application PI 9202268 tries to solve the problem of reducing the contact area by using truncated conical profiles of the contact surface, yet the contact surface has an inclined face where such a configuration only allows a pointlike contact at the edge with the cylinder wall, possibly resulting in breakage of same and consequently causing damage to the cylinder wall, as well as being more susceptible to increasing the contact region on account of radial wear and tear.

[00016] The ring described in the Brazilian patent applications PI 1014611-3 and P11003187-1 attempts to solve the problem of reducing the contact area by using profiles having a contact surface parallel to the cylinder wall and associated with inclined faces.

[00017] Specifically, the ring described in these applications has contact surfaces oriented such that the inclined faces are turned toward each other, that is, being symmetrical, are alternatively such that the inclined faces are turned toward the same direction, that is, being asymmetrical, which primarily focuses the reduction in friction of the contact surfaces on the cylinder wall.

[00018] As already pointed out, the automotive industry is at present facing the challenge of meeting increasingly more strict environmental regulations, resulting in developments increasingly oriented toward the quest for less friction and smaller, more energy efficient engines. [00019] Therefore, the present application deals with an oil control ring which, thanks to the use of an improved profile, is able to enhance the adequate levels of contact pressure, provide a reduced contact between the ring and the interface with the cylinder, and offer a robustness in is design, handling, and operation. Objectives of the Invention

[00020] A first objective of the present invention is to provide an oil control ring which allows, thanks to the use of the peripheral working face with reduced contact surface, a better distribution of the pressure, thus guaranteeing an adequate thickness of the oil film between the ring and the cylinder wall and making possible a reduced load due to the design expansion force of the ring, and therefore a corresponding reduction in the power dissipated by friction.

[00021] A second objective of the present invention is to provide an oil control ring which allows, thanks to the use of the peripheral working face with reduced contact surface, the lubricating oil to not accumulate (or to accumulate less) on the upper portion of the ring, as well as to make possible a better scraping of oil by the ring, this oil being better redistributed along its area of operation.

[00022] A third objective of the present invention is to provide an oil control ring which allows, thanks to the use of the peripheral working face profile with reduced contact surface, as well as the use of a larger cone angle between the contact face and the internal wall of the cylinder, a minimizing of the effect of radial wear on the increasing of the axial width of the contact face, thus assuring a maintaining of the design pressure and consequently the control of the oil film between the ring and the cylinder wall during the service life of the engine.

Brief Description of the Invention

[00023] The objectives of the present application are achieved by means of an oil control ring for internal combustion engines, formed by a body, comprising two external contact surfaces, each of them having a first and a second terminal edge, two inclined faces, each of them having a third terminal edge, a peripheral transverse section facing toward the cylinder wall and an internal section facing toward the piston side, wherein each contact surface is planar and parallel to the cylinder wall and they are oriented such that the respective inclined faces are facing opposite each other and are symmetrical.

[00024] In one possible embodiment, the oil control ring has each inclined face making an angle between 10 and 60 degrees.

[00025] In one possible embodiment, the oil control ring has each contact surface with a height of up to 0.15 millimetres between the first and the second terminal edges.

[00026] In one possible embodiment, the oil control ring has a body with a height between 1.5 millimetres and 4 millimetres.

[00027] In one possible embodiment, the oil control ring has at least one of the contact surfaces (10) being conical.

[00028] In one possible embodiment, the oil control ring comprises a transverse section having at least one slit or hole.

[00029] In one possible embodiment, the oil control ring comprises a body made of cast iron or steel.

[00030] In one possible embodiment, the oil control ring has an external surface of the ring with a metallic coating applied to it.

[00031] In one possible embodiment, the oil control ring has an external surface of the ring with a ceramic coating applied to it.

[00032] In one possible embodiment, the oil control ring has the external surface of the ring with a surface heat treatment applied to it. [00033] In one possible embodiment, the oil control ring has the external surface of the ring with an amorphous carbon coating applied to it.

[00034] The aforementioned characteristics, as well as other aspects of the present invention, will be better comprehended through the following examples and the detailed description of the drawings. Brief Description of the Drawings

[00035] The present invention will be described in greater detail in the following, based on one exemplary embodiment represented in the drawings. The figures show:

[00036] Figure 1 is a transverse sectional view of an oil ring for an internal combustion engine of the prior art.

[00037] Figure 2 is a transverse sectional view of an oil ring for an internal combustion engine of the prior art.

[00038] Figure 3 is a transverse sectional view of the oil ring for an internal combustion engine which is the subject of the present invention.

[00039] Figure 4 is a schematic view of the transverse section of the oil ring for an internal combustion engine of the present invention. [00040] Figure 5 is a graph comparing the minimum oil film between the parallel contact face and the cylinder wall for the subject of the present invention and rings of the prior art.

[00041] Figure 6 is a graph comparing the oil film left behind on the cylinder wall after the passage of the ring which is the subject of the present invention and rings of the prior art.

Detailed Description of the Figures

[00042] Figures 1 and 2 represent the ring as described in the Brazilian patent applications PI 1014611-3 and P11003187-1, where contact surfaces are oriented such that the inclined faces are turned toward each other or such that the inclined faces are turned in the same direction.

[00043] On the contrary, as is observed in Figure 3, the subject of the present invention deals with an oil control ring in which each contact surface is planar and parallel to the cylinder wall and they are oriented such that the respective inclined faces are turned opposite each other.

[00044] Specifically, as is observed in Fig. 4, the oil control ring 1 which is the subject of the present invention is formed by a body 2, comprising two external contact surfaces 10, each having a first 11 and a second 12 terminal edge, two inclined faces 20, each having a third terminal edge 13, a peripheral transverse section 4 turned toward the cylinder wall 5 and an internal section 6 turned toward the piston side 7, wherein each contact surface 10 is planar and parallel to the cylinder wall 5 and they are oriented such that the respective inclined faces 20 are turned opposite to each other.

[00045] Thus, advantageously, the inclined faces 20 turned opposite to each other provide an improved control of the oil film between the ring and the cylinder wall during the service life of the engine.

[00046] This is because this solution, as compared to the prior art, eliminates the possibility or the probability of oil being stored up in the region above the contact of the ring, thus reducing the oil consumption in the motor assembly of the vehicle.

[00047] In a preferred, but not limiting fashion, the oil control ring 1 of the present invention is formed by a preferably ferrous body 2, such as cast iron or steel, and by a resilient/elastic element, such as a helical spring, a flat spring, or some other expanding means, o provide the expansion force needed for this type of application.

[00048] Alternatively, one may conceive of a ring in which the properties or characteristics of the base material of the body 2 itself are sufficient to generating the desired expansion force.

[00049] In a preferred, but not limiting fashion, the body 2 has a total height H between 1.5 and 4.0 millimetres (mm) taken in the axial direction, in order to impart slightly more rigidity, although it is quite possible to design a ring falling within the scope of protection of this invention whose body has a height less than 1.5 mm.

[00050] The body 2, regardless of its height H, has two external contact surfaces 10, each of them being bounded by an inclined face 20, an intermediate section 4 turned toward the cylinder wall 5, and a circular section 6 turned toward the piston side 7, where the external contact surfaces 10 are projected against the cylinder wall 5 when the assembly is installed.

[00051] Each external contact surface 10 of the oil control ring 1 has a first 11 and a second 12 terminal edge, and a height h situated between the edge 11 and the edge 12 where the inclined face 20 begins. This height corresponds to the contact surface with the oil film. [00052] In a preferred, but not limiting fashion, the height h of each of the external contact surfaces 10 is up to 0.15 millimetres.

[00053] In similar manner, the angle (a) of the inclined face 20 should be between 10° and 60°, preferably 26° and 34° (degrees), in relation to the axial length of the ring.

[00054] Thus, advantageously, the subject of the present invention makes possible less scraping of oil by the ring in the direction of the combustion chamber, thus producing an oil film which is better redistributed along its area of operation.

[00055] In the following, the subject of the present invention, by means of each contact surface 10 being planar and parallel to the cylinder wall 5 and being oriented such that the respective inclined faces 20 are turned opposite each other, focuses on solving the problem of the irregular contact between the upper and lower contact projection of the oil ring (that is, a different contact, since the contact of one projection is greater than that of the other) such as may occur (and which in practice does occur) due o the deformation of the piston channel and the displacement of the centre of gravity of the rings due to the singularity added to the contact portions of the ring.

[00056] The positioning of the contact surfaces 10 such that the respective inclined faces 20 are opposite each other significantly helps ensure that the characteristics of stability and geometrical balancing of the ring are such that the contact of both of the contact surfaces is substantially uniform, even in situations of increased dynamic stressing of the ring.

[00057] In addition, as shown in Fig. 5 and 6, the subject of the invention has significant advantages over the prior art in regard to decreasing the wear on the ring and the cylinder wall, and substantially less build-up of lubricating oil in the upper portion of the ring, so that it is better redistributed along its area of operation.

[00058] This is because, in the present invention, as opposed to the prior art, there is a better scraping of the oil thanks to a reduction in the oil excess between the cylinder wall and the ring in the direction of the combustion chamber.

[00059] Once this oil excess has been diminished, the assembly has greater efficiency, since the oil layer is better distributed. It should further be noted that the reduced scraping of oil in the direction of the combustion chamber, typically in the descending motion, is associated with an improved maintaining of the functioning of the piston, inasmuch as the oil flow collected by the cylinder wall is significantly less.

[00060] This can be seen in Fig. 5 and 6, by the formation of a larger oil film in the subject of the invention than that in the rings of the prior art. That is, a larger thickness of the oil film is maintained between the ring and the cylinder wall 5 during the movement of the piston in the direction of the combustion chamber, which is typically an ascending motion.

[00061] In order to further reduce the accumulation of lubricant, the ring may comprise one or more oil drainage areas, preferably in the form of a slit or hole 8 positioned on the intermediate section 4 in order to make possible the flow of lubricant.

[00062] Inasmuch as this relates to a solution familiar to those skilled in the art, there is no need for further detail in the description. The existence of these slits 8 is more interesting, and preferable, when the height of the ring is greater than 2.0 mm, which maintains a still acceptable value of rigidity, yet nothing prevents them from being provided in a ring whose height value is smaller, if such is necessary or desirable.

[00063] Thus, the present invention has the benefit of making possible the use of smaller contact surfaces in oil rings made of steel with metallic or ceramic coatings applied to them and the use of hardening surface treatments of the contact surface in order to make the product more wear-resistant and decrease the friction forces. [00064] In the specifications found in the prior art, the use of this technology on reduced contact surfaces may result in high levels of localized stress due to the fact that the ratio between the thickness of the contact portion and the hardened layer is approximately one.

[00065] Thus, it is clear that the ring of the present invention makes feasible a use with surface treatments and coatings to increase the wear resistance when the use of profiles with excessive reduction of the contact surface, such as the rings belonging to the prior art, becomes restricted, due to the build-up of stresses caused by the great surface hardness provided by the surface treatments and coatings, not to mention another major advantage of the invention, pointed out above, which is the superior maintaining of the contact pressure throughout the life of the engine thanks to having a larger angle of inclination of the supporting edge relative to the contact face.

[00066] Having described one preferred embodiment, it should be understood that the scope of the present invention encompasses other possible variations, being limited solely by the content of the claims, and including their possible equivalents.