PROCESS FOR OBTAINING A PISTON RING AND INTERNAL COMBUSTION ENGINE

Abstract

A process for obtaining a piston ring may include providing a piston ring of an internal combustion engine and submitting a surface of the piston ring to a laser surface heat treatment. The surface may be a sliding surface of the piston ring. The piston ring may be a one piece piston ring and/or a scrapper ring.

Claims

1. A process for obtaining a piston ring comprising: providing a preformed ring for an internal combustion engine; and submitting a sliding surface of said ring to a laser surface heat treatment.

2. The process as claimed in claim 1, wherein said sliding surface is a contact surface of the ring with a cylinder liner.

3. The process as claimed in claim 1, wherein providing said ring includes providing a one piece scraper ring having a U-shaped profile with respect to a cross-section thereof.

4. The process as claimed in claim 3, wherein said sliding surface is at least one surface defined by the U-shaped profile and is configured to maintain contact with a cylinder liner of the internal combustion engine.

5. The process as claimed in claim 3, wherein said sliding surface includes two surfaces provided by the U-shaped profile and configured to contact a cylinder liner of the internal combustion engine.

6. The process as claimed in claim 1, wherein said ring is composed of a carbon steel.

7. The process as claimed in claim 1, wherein said ring is composed of alloyed steel including Cr, Mo, and Nb.

8. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes quenching via a laser beam.

9. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes case hardening said sliding surface via a laser beam.

10. The process as claimed in claim 1, further comprising tempering said ring after submitting said sliding surface to said laser surface heat treatment.

11. The process as claimed in claim 1, further comprising, prior to said laser surface heat treatment, subjecting said ring to at least one of shaping, machining and heat treatment.

12. A piston ring, of an internal combustion engine, comprising: a steel U-shaped ring having a laser radiated case hardened sliding surface.

13. An internal combustion engine, comprising: at least one piston; at least one piston ring arranged in a groove of the at least one piston, said at least one piston ring composed of a steel material and having a laser radiated hardened sliding surface.

14. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes subjecting said sliding surface to an incident laser beam having a power density of 20 to 180 W/mm.sup.2.

15. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes rotating said sliding surface relative to an incident laser beam at a speed of 25 mm/second to 105 mm/second.

16. The process as claimed in claim 1, further comprising applying an external chemical material onto said sliding surface, wherein submitting said sliding surface to said laser surface heat treatment includes diffusing said external chemical material upon said sliding surface by an incident laser beam.

17. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes applying a carbon material onto said sliding surface and carburizing said sliding surface by an incident laser beam at a relative rotational speed of less than 70 mm/second.

18. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes subjecting said sliding surface to an incident laser beam having a rectangular geometry, a circular geometry or an elliptical geometry.

19. The process as claimed in claim 1, wherein submitting said sliding surface to said laser surface heat treatment includes subjecting said sliding surface to an incident laser beam having a power density of 20 to 180 W/mm.sup.2 while rotating said sliding surface relative to said incident laser beam at a speed of 25 mm/second to 105 mm/second.

20. The process as claimed in claim 6, wherein said carbon steel includes from 0.4 to 0.95% by weight of carbon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention shall now be described in relation to the particular embodiments thereof, making reference to the attached figures. Such figures are schematic and the dimensions and proportions thereof may not correspond to the reality by virtue of the fact that the sole intention thereof is to describe the invention in a didactic manner, they not imposing any limitation whatsoever other than those defined in the claims below. Certain technical characteristics may have been omitted from the figures for purposes of greater clarity and comprehension, wherein:

[0031] FIG. 1 is a partial perspective view of a piston ring, in particular a one piece scraper ring of a piston;

[0032] FIG. 2 is a flow diagram of the flow of the process of manufacture of the present invention;

[0033] FIG. 3A is a spatial schematic view of the laser beam treating the one piece scraper ring on one sliding surface;

[0034] FIG. 3B is a schematic cross-section view of the one piece scraper ring having been treated by the laser on one side and undergoing laser treatment on the second side of the same ring, according to FIG. 3A;

[0035] FIG. 4 is an image obtained by an optical microscope showing the depth of the material modified as a function of the laser hardening treatment;

[0036] FIG. 5A is an image obtained by an optical microscope showing the depth of the material modified as a function of the laser case hardening;

[0037] FIG. 5B is an image of the analysis of the measurement of the carbon content for laser carburized carbon steel; and

[0038] FIG. 6 is a graphic showing comparative wear performance for two versions of rings, laser treated and non-laser treated.

DETAILED DESCRIPTION

[0039] The invention shall now be described in relation to the particular embodiments thereof. Specific embodiments are described in detail, it being understood that they shall be considered as an exemplification of the principles thereof and are not destined to restrict the invention to solely that described in the present memorandum. It shall be recognized that the different teachings of the embodiments discussed below may be employed separately or in any appropriate combination to yield the same technical effects. The reference numerals are repeated for the same technical characteristics throughout the figures.

[0040] FIG. 1 shows a partial perspective view of a ring (10) of an internal combustion engine and, in particular, a one piece scraper ring of a piston of an internal combustion engine. As aforementioned, the oil ring has the purpose of removing the oil film formed between the cylinder liner and the piston with the objective of preventing the burning of oil during combustion and, in this manner, likewise preventing the consumption of oil and the emission of polluting gases. A scraper ring as shown in FIG. 1 is already known in the state of the art, for example in the patent publication WO 2014/066965, incorporated herein as reference.

[0041] FIG. 2 shows the process of manufacture for one piece oil control rings. The principal stages comprise piercing and forming (2) the U shape by the die process, obtained from a flat wire (1). Subsequently, the wire in a U shape is spirally wound in the form of a ring (stage 3). The final dimensions of the ring are adjusted by a grinding operation (4). Properties of the material of the sliding surface (33) are modified by laser treatment, the matter of a specific embodiment of this invention, in order that the finishing of the sliding surface may be executed by machining the same, utilizing a process of polishing or of grinding or of burnishing (6). These stages of a process for the obtainment of a piston ring, except for stage 5, the object of the present invention, are already known in the state of the art.

[0042] The invention proposes that the contact surface (33, 33′) with the cylinder liner be submitted to a hardening process utilizing laser radiation.

[0043] In the first embodiment of the invention, the use is proposed of laser radiation for quenched carbon or alloyed steel. In order to obtain such a hardening effect at least 0.3% of the equivalent C content is required. For the purposes of industrial production the rings are mounted on a mandrel rotating at a constant angular velocity (ω) about an axis (3-3′) (FIGS. 3a and 3b). For the purposes of the present invention an ω was utilized in the band capable of providing a relative velocity between the laser beam and the peripheral surface of the ring under treatment (33 and 34) from 25 mm/sec. to 105 mm/sec. A further key parameter utilized for the hardening of the sliding surface is the power density of the incident laser beam. The laser beam was adjusted for operation in the band from 20 to 180 W/mm.sup.2. It must be noted that different types of laser, that is to say solid diode or CO.sub.2 laser, may be used for obtaining similar results. However the power density and the relative velocity between the laser beam and the surface under treatment must be adjusted as a function of the absorption of the laser radiation. In order to achieve the aforedescribed power density band, different geometries of laser points may be used, that is to say incident projection of the laser beam onto the surface under treatment. The point of the laser beam may be adjusted by laser optic (32), for example rectangular, circular, elliptic and other formats may be produced by an appropriate laser optic (32).

[0044] FIG. 4 shows a partial cross-section of the region treated on the sliding surface obtained by the process of the invention. It has been chemically etched in order to reveal the treated region. The sample shown was generated in a single pass of the laser beam over the surface to be modified with the power density adjusted to 100 W/mm.sup.2 and relative speed of 70 mm/sec. The hardness of the material in the P region attained 1000 HV.sub.0.05 whilst the material of the nucleus (region C) is of 550 HV.sub.0.05. The depth of the modified coating attained 60 μm. The depth of the hardened coating may be increased through raising the power density or diminishing the relative speed furnished by the rotational movement of the rings under treatment.

[0045] In a second embodiment of the invention, the raised temperature generated by the laser beam is used to produce the diffusion of an external chemical material upon the surface. The cross-section shown in FIG. 5a is an example of carburized surface caused by the laser. In this case adjustment to a relative speed of less than 70 mm/sec. is required. Such lower speed permits a higher temperature and a longer time for diffusion of the carbon applied upon the surface to be carburized. Typically, lampblack is applied upon the surface to be laser treated. The example shown in FIG. 5a was generated by applying a power density of 200 W/mm.sup.2 and a relative speed of 40 mm/sec. Differing from the laser hardening executed in a single pass, the case hardening was carried out repeating the interaction of the laser beam on the surface to be carburized. Experiments have shown that solely 5 passes may provide 5 μm of carbon diffusion. The carbon diffusion diminishes as a function of the depth of the carburized coating and the 10 microns of carburized coating shown in FIG. 5b was obtained utilizing 15 passes of the laser beam upon the same region. Considerably extending the duration of the time for treatment, thicker carburized coatings may be obtained. A very long treatment time (or many passes) may generate localized melting on the surface under treatment, consequently an additional reduction in the power density may be used to control such undesirable effects in order to obtain a carburized depth exceeding 50 μm.

[0046] According to the invention, the development of wear of the one piece scraper ring obtained by the process of manufacture described in the first and second embodiments was high. The wear performance was characterized by the fact of maintaining a set of one piece oil control rings (those three different versions, uncoated, hardened and carburized) in the same disposition and testing reciprocating sliding movement under lubricated conditions. Abrasive particles were intentionally added into the oil to accelerate the wear of the sliding surface of the one piece control rings. Careful selection of the rings under test was realized to provide a good comparative evaluation, considering that modification of the surface to be the sole characteristic influencing the wear performance. In other words, the geometry, the contact pressure of the sliding surface and the test conditions were exactly the same for those three different versions of the rings under test.

[0047] Carburized sliding surfaces, together with hardened surfaces, present improved wear resistance when compared with untreated surfaces. FIG. 6 shows radial wear measured by superimposing the profiles, prior to and subsequent to the test, for the sliding surfaces (upper and lower contacts of the one piece scraper ring). The modification of the surface by carburization or hardening had the objective of reducing the wear on the sliding surfaces. The verification shows a reduction in wear of 40%, considering the untreated surface.

[0048] In spite of the invention having been described in relation to the particular embodiments thereof, those versed in the art will be capable of realizing alterations or combinations not contemplated above without, however, deviating from the teachings described herein, in addition to extending to other applications not considered in the present descriptive memorandum. For example, in spite of the embodiment herein described making reference to an oil ring of an internal combustion engine, it is obvious that the process of the invention may be applied to other parts, the improved surface hardness characteristic whereof may be desirable, such as the compression ring. Consequently, the claims appended shall be interpreted as covering each and every equivalent falling within the principles of the invention.