The present disclosure relates generally to a cylinder liner for an internal combustion engine, and more particularly, to a cylinder liner with a case on at least a portion of a cuff-ring groove.
An internal combustion engine, such as a diesel or gasoline engine, includes a cylinder block defining a plurality of cylinder bores. Pistons reciprocate within the cylinder bores to generate mechanical power. Typically, each cylinder bore includes a replaceable cylinder liner. The cylinder liner includes a cylindrical sleeve that fits within the cylinder bore. The cylinder liner may also include a radial flange, at its top end, that supports the liner on the engine block. The inner surface of the cylinder liner (called, a running surface) serves as a sliding surface for the piston rings. Because the piston rings slide on the running surface during the operation of the engine, the cylinder liner may wear over time. When the liner wear detrimentally affects the performance of the engine, the liners may be replaced with a new or a refurbished liner.
In general, cylinder liners may be made of steel or cast iron. Steels and cast irons are both primarily iron, with carbon as the main alloying element. Steels contain less than 2% (usually less than 1%) carbon, while cast irons contain more than 2% carbon. Since 2% is about the maximum carbon content at which iron can solidify as a single-phase alloy, cast irons solidify as heterogeneous alloys with carbon (as graphite) in their microstructure. The graphite in cast iron acts as a lubricant and provides wear resistance in a cylinder liner application. Based on the morphology of graphite in the microstructure, cast irons may be classified as gray iron, vermicular iron, or ductile iron. In gray (or flake) iron, the graphite exists in the form of flakes. In ductile iron (or nodular iron), graphite exists in the form of small spheres. Having graphite in the form of spheres improve the stiffness, strength, and shock resistance of ductile iron over gray iron. Therefore, in applications requiring higher strength, cylinder liners may be fabricated from ductile iron. To increase the wear resistance of the liner, the running surface of the liner may be hardened by induction hardening.
During installation of the liner in the engine block, and during operation of the engine, high stresses may be induced in the liner. These stresses may be especially high near the base, or the root, of the flange that supports the cylinder liner on the engine block. Because of these high induced stresses, regions proximate the flange root are prone to fatigue failure. Therefore, various strengthening operations may be performed on the liner to increase the strength of the liner in this critical region. U.S. Pat. No. 6,732,699 (the '699 patent) discloses a cast iron cylinder liner with a radial upper flange having an arcuate fillet formed at the junction between the flange and the exterior surface of the liner. In the liner of the '699 patent, a portion of the material adjacent to the arcuate fillet (that is, flange root) is laser hardened to increase the fatigue resistance of the material in this region. While laser hardening the flange root may increase the fatigue life of the cylinder liner, this approach may not be suitable in some applications. For instance, implementation of a post manufacturing operation, such as laser hardening, may increase the cost of the cylinder liner. Additionally, in some applications, a potential failure initiation site of the cylinder liner may not be easily accessible for laser hardening.
The present disclosure is directed to overcoming these or other limitations in existing technology.
In one aspect, a cylinder liner for an engine is disclosed. The cylinder liner may include a hollow cylindrical sleeve, with an inner surface and an outer surface, that extends from a first end to a second end along a longitudinal axis. The cylinder liner may also include an annular cuff-ring groove, with a radiused fillet region, on the inner surface proximate the first end. The cylinder liner may further include a hardened case formed on the inner surface of the sleeve. The case may extend under a base of the fillet region of the cuff-ring groove.
In another aspect, a method of making a cylinder liner is disclosed. The method may include fabricating a hollow cylindrical sleeve, with an inner surface and an outer surface, that extends from a first end to a second end along a longitudinal axis. The method may also include forming a hardened case on the inner surface of the sleeve, such that a thickness of the case proximate the first end is greater than a thickness of the case on other regions of the inner surface. The method may further include machining a cuff-ring groove on the inner surface of the sleeve proximate the first end such that at least a portion of the case on a base of the cuff-ring groove is retained after the machining.
In yet another aspect, an engine is disclosed. The engine may include an engine block including one or more cylinder bores, and a cylinder liner positioned in at least one of the cylinder bores. The cylinder liner may include a hollow cylindrical sleeve with an inner running surface extending from a first end to a second end along a longitudinal axis, and an annular cuff-ring groove that extends from the first end towards the second end. The engine may also include a hardened case formed on the running surface by surface hardening. The case may extend under at least a portion of the cuff-ring groove. The engine may further include an anti polish ring, or a cuff-ring, positioned in the cuff-ring groove.
Liner 12 may be made of any type of steel or cast iron. In some embodiments, liner 12 may be made of ductile, or nodular, iron. It is also contemplated, that in some embodiments, liner 12 may be made of steel or another type of cast iron, such as gray iron or vermicular iron. In some embodiments with steel liners, as described in co-pending U.S. application Ser. No. 13/036,249, a lamellar annealing step of the steel may be replaced by a normalizing heat treat step. The specification of U.S. application Ser. No. 13/036,249 is incorporated herein by reference, in its entirety.
As is known in the art, a piston 26 may reciprocate in the piston bore 16 between a top dead center (TDC) position proximate the top of the liner and a bottom dead center (BDC) position proximate a bottom of the liner 12. As the piston 26 reciprocates, piston rings 36 (of a piston 26) slide on the running surface 22 of the liner 12. Due to repeated sliding of the piston rings 36 on the running surface 22, the running surface 22 may be subjected to abrasive wear. To improve the wear resistance of the running surface 22, running surface 22 may include a hardened shell or a case 40. Case 40 is a surface region of the running surface 22 in which the crystalline structure of the liner material is transformed to be substantially martensite by the application of heat. Case 40 may be formed by any surface hardening process, such as, for example, flame hardening, induction hardening, laser hardening, or any other known surface hardening process.
To form case 40, the running surface 22 of the liner 12 is heated to a high temperature and then cooled rapidly to create a “case” containing substantially martensite on the surface. As is known in the art, when an iron alloy (steel, cast iron, etc.) is heated to a temperature in the austenitic range of the alloy and held at this temperature for a sufficient time, the crystal structure of the iron alloy changes to an austenite structure. When the alloy is then is quenched (or rapidly cooled), the carbon atoms do not have time to diffuse out of the crystal structure and forms martensite. This transformation to martensite begins during cooling when the austenite reaches the martensite start temperature and ends at the martensite finish temperature. Martensite is a crystal structure that is hard and wear resistant. Therefore, case 40 provides wear resistance to the running surface 22.
In some embodiments, an induction hardening process is used to transform a layer of material on the surface of the running surface 22 into case 40. Induction hardening uses the principle of electromagnetic induction to heat the running surface 22 of liner 12. As known in the art, in induction hardening, an induction coil scans the inside surface of the liner 12 to apply an alternating magnetic field on the running surface 22, to heat the running surface 22 and form the case 40 thereon. By varying parameters of the scanning (such as, frequency, power level, scan speed, etc.), case 40 of a desired depth may be formed on the running surface 22. The depth of the case 40 may be varied by changing the frequency, the power level, or the scan rate of the coil. While a thick case 40 may seem desirable from a wear life point of view, it may have undesirable side effects. For instance, increasing the thickness of the case 40 may require increasing the thickness of the liner 12. Increasing the thickness of the liner 12 may undesirably increase the weight of the liner 12. Further, a thicker case 40 may have an undesirable impact on stresses in the liner. Therefore, the thickness of the case 40 is selected to achieve the beneficial increase in wear life while minimizing undesirable side effects. Although
Liner 12 may include an anti-polish or a cuff-ring 38 located in a cuff-ring groove 48 proximate the TDC. Although the cuff-ring groove 48 may be of any shape, in some embodiments, the cuff-ring groove 48 may be a step-like groove that extends from a top end of the sleeve. The cuff-ring 38 may assist in reducing the wear of the liner 12 by scraping off some of the combustion products that deposit on a top rim of the piston 26 during operation of the engine 10. Typically, a machining operation forms the cuff-ring groove 48 after the case 40 is formed. During formation of the cuff-ring groove 48, a radiused fillet region 48a (see
Although five different regions A, B, C, D, and E are illustrated in
The disclosed cylinder liner may be applied in any application where it is desired to increase the fatigue life of the cylinder liner. A case is formed on the running surface of the cylinder liner by surface hardening. In an exemplary embodiment of a cylinder liner with a cuff-ring groove, the case extends under a base of the fillet region of the cuff-ring groove. To form the case under the base of the fillet region, in some embodiments, a thicker case (as compared to other regions) is formed in the region of the cylinder liner where the cuff-ring will subsequently be formed. A machining operation is then used to form the cuff-ring groove while retaining at least a portion of the case at the base of the fillet region of the cuff-ring groove. However, other embodiments in which the case under the base of the fillet region is formed after the cuff-ring groove is machined, are also contemplated. An exemplary method of producing a disclosed cylinder liner will now be described.
An exemplary method of using a disclosed cylinder liner 12 may include installing a liner 12, with a case 40 on the running surface 22, on an engine 10. The liner 12 may include a newly fabricated or a refurbished liner 12 having the case 40 at least at the base of the fillet region 48a of the cuff-ring groove 48 of the liner 12. A cuff-ring 38 is then positioned on the cuff-ring groove 48, and the engine 10 assembled. The engine 10 is then operated. Since the residual stress state at the base of the fillet region 48a is compressive, initiation (if any) of a fatigue crack in this region will be delayed. Furthermore, if a fatigue crack is initiated in the fillet region 48a, the residual compressive stresses in this region will slow the progression of the crack. Fatigue life of the liner 12 is thus improved.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed cylinder liner. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed cylinder liner. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.