Patent Application
20240167165
The present invention relates to the field of crankshaft technologies, and in particular to a method for increasing wear resistance of a surface of a crankshaft using a ceramic coating.
A crankshaft is one of the most important parts of an engine, and the reliability of the crankshaft is directly related to the stability of the entire engine. In recent years, with the implementation of Euro 6 and China 6 emission standards, engines have developed toward light weight, energy saving, and high speed, and the explosion pressure of engines keeps increasing. The maximum explosion pressure has increased from 160 bar to 180 bar during China 5 emission standards to 200 bar to 260 bar during China 6 emission standards, resulting in an increasing risk of a scoring failure in a crankshaft. Since the implementation of China 6 standards, the proportion of scoring in crankshafts in four- and six-cylinder engines has increased significantly, and scoring failures account for more than 30% of all failures, becoming the main factor affecting the reliability of engines. The main failure mechanism of scoring is that as the explosion pressure of an engine increases, an actual pressure on a journal of a crankshaft increases, and a fluid lubricating oil film tends to break. As a result, a friction pair of a crankshaft and a shell is in a boundary lubrication state. In the friction pair, local metal micro-convex bodies are in direct contact, causing severe wear and a lubrication failure. Therefore, how to reduce a friction coefficient of a surface of a crankshaft and reduce scoring and burning of the crankshaft becomes an urgent problem to be resolved to improve the reliability of the crankshaft.
At present, conventional treatments of a surface of a crankshaft mainly includes surface induction quenching and surface nitriding. However, in both treatments, a hardness difference in a friction pair of a journal and a shell is increased by improving surface hardness without changing a friction coefficient of a material, and friction resistance of the surface of the crankshaft is not fundamentally changed. Therefore, conventional crankshaft surface treatment technologies cannot adapt to requirements of engines with higher emission standards, and it is urgent to study new technologies and new methods to reduce a friction coefficient of a surface of a crankshaft, extend the service life of the crankshaft, reduce scoring and burning, and improve the overall reliability of engines.
For this, a technical problem to be resolved by the present invention is to overcome disadvantages in the prior art, and provide a method for increasing wear resistance of a surface of a crankshaft using a ceramic coating, which can reduce a friction coefficient of a surface of a crankshaft, increase the wear resistance of the surface of the crankshaft, reduce scoring and burning failures, and extend the service life of the crankshaft.
To resolve the foregoing technical problems, the present invention provides a method for increasing wear resistance of a surface of a crankshaft using a ceramic coating, including:
Preferably, the surface of the rounded corner of the crankshaft before spraying is higher than the surface of the rounded corner of the finished crankshaft by 0.1 mm to 0.15 mm, and the size of the journal coating portion is smaller than the size of the journal of the finished crankshaft by 0.1 mm to 0.15 mm in the radical direction of the journal.
Preferably, a width of the journal grinding portion in a direction perpendicular to the radical direction of the journal ranges from 1 mm to 2 mm.
Preferably, the surface of the rounded corner of the crankshaft before spraying and the surface of the journal grinding portion are seamlessly joined, and a connection between the journal grinding portion and the journal coating portion is arc-shaped.
Preferably, before the ceramic coating is sprayed on the surface of the journal coating portion, a pretreatment is performed on the crankshaft before spraying, and the pretreatment includes quenching of the journal, protection of an oil hole in the journal, and a roughening treatment of the surface of the journal.
Preferably, the thickness of the ceramic coating in the radical direction of the journal ranges from 0.05 mm to 0.2 mm.
Preferably, the spraying a ceramic coating on the surface of the journal coating portion is specifically:
Preferably, during spraying of the ceramic coating, the distance of spraying ranges from 50 mm to 380 mm.
Preferably, a size of the journal after the grinding is greater than the size of the journal of the finished crankshaft by 0.004 mm to 0.006 mm in the radical direction of the journal.
Preferably, a roughness of the surface of the journal of the finished crankshaft ranges from 0.1 μm to 0.4 μm.
Compared with the prior art, the foregoing technical solution of the present invention has the following advantages:
In the present invention, a journal coating portion and journal grinding portions are provided on the surface of a journal, a ceramic coating of a specific thickness is sprayed on a surface of the journal coating portion, and then the surface of the journal is ground and polished to reach a design size of a finished crankshaft. The wear resistance of the crankshaft is significantly increased by spraying the ceramic coating, thereby reducing a friction coefficient of a surface of the crankshaft, extending the service life of the crankshaft, and significantly reducing probabilities of scoring and burning failures.
To make the content of the present invention clearer and more comprehensible, the present invention is further described in detail below according to specific embodiments of the present invention and the accompanying draws. Where:
Reference numerals in the accompanying drawings of the specification: 1. journal, 2. rounded corner, 3. contact between the journal and the rounded corner, 4. crank arm, 5. surface of journal before spraying, 6. surface of the journal of the finished crankshaft, 7. surface of the rounded corner before grinding, 8. surface of a rounded corner of the finished crankshaft, 9. ceramic coating, 10. journal grinding portion, 11. journal coating portion, 12. connection between the journal grinding portion and the journal coating portion, and 13. surface of the finished crankshaft.
The present invention is further described below with reference to the accompanying drawings and specific embodiments, to enable a person skilled in the art to better understand and implement the present invention. However, the embodiments are not used to limit the present invention.
In the description of the present invention, it needs to be understood that orientation or location relationships indicated by terms “center”, “up”, “down”, “front”, “rear”, “left”, “right”, “top”, “bottom”, “inside”, “outside” are based on orientation or location relationships shown in the accompanying drawings, and are only used to facilitate description of the present invention and simplify description, but are not used to indicate or imply that the apparatuses or elements must have specific orientations or are constructed and operated by using specific orientations, and therefore, cannot be understood as a limit to the present invention. In addition, the terms “first” and “second” are used only for description, but are not intended to indicate or imply relative importance or implicitly specify a quantity of indicated technical features. Therefore, the features defined with “second” and “first” may explicitly or implicitly comprise one or more features. In the description of the present invention, the term “plurality of” means two or more, unless specifically and specifically limited otherwise.
In the present invention, unless otherwise expressly specified and defined, terms such as “mounted”, “connected”, “connection”, and “fixed” should be understood in a broad sense, for example, fixedly connected, detachably connected or integrally connected; or mechanically connected or electrically connected; or communicatively connected; or connected directly or indirectly through an intermediate, or two elements communicated internally or two elements having mutual effects. A person of ordinary skill in the art may understand specific meanings of the foregoing terms in the present invention according to specific cases.
Unless expressly stated or limited otherwise, the expression of the first feature being “above” or “below” the second feature may include the case that the first feature is in direct contact with the second feature or include the case that the first feature and the second feature are in indirect contact through an intermediate. In addition, the term “include” is intended to cover a non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units not only includes those specified steps or units, but optionally further includes steps or units that are not specified, or optionally further includes other steps or units that are inherent to these processes, methods, products or devices.
With reference to the flowchart in
Step 1: as shown in
A gap between the journal 1 of the finished crankshaft and the shell is usually approximately 0.06 mm. According to different crankshafts, in this embodiment, the surface of the rounded corner 2 of the crankshaft before spraying is higher than the surface 8 of the rounded corner of the finished crankshaft by 0.1 mm to 0.15 mm. That is, in
Step 2: Perform a pretreatment on the crankshaft before spraying, where the pretreatment includes quenching of the journal 1, protection of the oil hole in the journal 1, and a roughening treatment of a surface of a journal 1.
Step 2-1: Perform quenching of the crankshaft and previous processing procedures, which are conventional production processes. Details are not described herein.
Step 2-2: Perform protection of the oil holes in the journal 1 of the crankshaft before spraying. All oil holes on main shafts and rod journal 1, and oil hole chamfers are a protection area for spraying. A boundary of the protection area is a joint between an external contour of an oil hole chamfer and the surface of the journal 1.
Step 2-3: Perform a roughening treatment on the surface of the journal 1. Before spraying is performed, a sandblasting treatment is performed on the surface of the journal coating portion 11 by using sand grains, to roughen the surface, thereby increasing the binding force between a coating layer and the journal 1, and a roughness of the roughened surface reaches Ra5 μm to Ra10 μm.
Step 3: Spray the ceramic coating 9. After the pretreatment, the ceramic coating 9 is sprayed on the surface of the journal coating portion 11. The coating is sprayed only on the surface of the journal coating portion 11 of the journal 1, and the coating is not sprayed on the rounded corner 2 and other positions.
Step 3-1: Spray one metal bonding bottom layer on the surface of the journal coating portion 11, to increase the binding force between the ceramic and a matrix material of the crankshaft, where the thickness of the metal bonding bottom layer in the radical direction of the journal 1 ranges from 0.05 to 0.10 mm. The metal bonding bottom layer is made of Co, Ni, or an alloy material added with Cr, Al, and Y.
Step 3-2: Spray one uniform and dense ceramic coating 9 on the surface of the journal coating portion 11, where the temperature of the heat source for spraying ranges from 2000° C. to 3500° C., and the temperature of the surface of the journal coating portion 11 ranges from 80° C. to 150° C. The thickness of the ceramic coating 9 in the radical direction of the journal 1 ranges from 0.05 mm to 0.2 mm.
During spraying of the ceramic coating 9, according to different spraying materials and spraying processes, the distance of spraying is adjusted between 50 mm and 380 mm. In this embodiment, a photo of the journal 1 of the crankshaft before spraying is shown in
Step 4: Perform grinding and polishing to obtain the finished crankshaft.
Step 4-1: Grind, with a grinding machine, the surface of the journal 1 of the crankshaft, the surface of the crank arm 4, and the surface of the rounded corner 2 after the ceramic coating 9 is sprayed, until the surface of the ceramic coating 9 and the surface of the rounded corner 2 are seamlessly joined, where the size of the journal 1 after grinding is greater than the size of the journal 1 of the finished crankshaft by 0.004 mm to 0.006 mm in the radical direction of the journal 1, and is 0.005 mm in this embodiment. A grinder is a CBN grinding wheel. The journal of the crankshaft and the surface of the rounded corner after spraying are ground simultaneously. The ceramic coating of the journal and an unsprayed metal surface are seamlessly joined, to ensure a smooth surface transition between the journal of the crankshaft and the rounded corner.
Step 4-2: Perform polishing on the surface to obtain the finished crankshaft. The journal 1 of the crankshaft and the rounded corner 2 are polished with a diamond abrasive band on an automatic abrasive polishing machine tool. The sizes of the journal 1 of the crankshaft and the rounded corner 2 after polishing reach finished sizes. The roughness of the surface of the journal 1 of the finished crankshaft ranges from Ra 0.1 μm to Ra 0.4 μm.
In the present invention, it is ensured that the journal of the finished crankshaft after spraying has a ceramic coating of a specific thickness, and the rounded corner is still a metal matrix, so that the friction wear resistance performance of the journal of the crankshaft is increased and the strength of the crankshaft is not lost.
In the present invention, a journal coating portion and a journal grinding portion are provided on a surface of a journal, a ceramic coating of a specific thickness is sprayed on a surface of the journal coating portion, and then the surface of the journal is ground and polished to reach a design size of a finished crankshaft. The wear resistance of the surface of the crankshaft is significantly increased by spraying the ceramic coating, thereby reducing a friction coefficient of the surface of the crankshaft. The ceramic layer on the surface of the crankshaft significantly reduces the friction coefficient between the crankshaft and a shell. A high porosity of the ceramic layer enhances the lubrication performance of the surface of the journal, so that probabilities of scoring and burning of the crankshaft are significantly reduced, and the service life is significantly extended. The main principle of improving tribological performance between the crankshaft and the shell by means of the ceramic coating includes several aspects as follows:
(1) The types of contact materials are changed. The friction pair of the journal of the crankshaft and the shell is changed from the original metal-metal pair into a ceramic-metal pair, so that an adhesive force in a friction pair caused by metal compatibility can be significantly reduced, thereby reducing a friction coefficient, and reducing the risk of adhesive wear.
(2) The ceramic material has high porosity, and has an oil storage function in terms of the microscopic structure. When the friction pair is in a boundary lubrication state, the lubricant that remains in material pores is pressed to flow out, so that the lubrication performance of the surface can be significantly enhanced.
(3) The surface of the ceramic material is in a mirror state after polishing. The roughness is significantly reduced compared with a conventional metal surface, thereby reducing the risk that local metal micro-convex bodies of the friction pair are in direct contact with each other.
(4) The ceramic material is less harmful. In a wear process, once falling off the surface of the matrix of the crankshaft, the ceramic material is very likely to be crushed into powder, to avoid three-body abrasive wear caused by falling off of the surface material, so that little contamination is caused to a friction surface.
To further describe the beneficial effects of the present invention, in this embodiment, a crankshaft of a six-cylinder engine shown in
The holes on the journal in
As can be comprehensively seen from Table 2, after a ceramic coating is sprayed, when an overpressure is loaded, wear in the journal of the crankshaft with a ceramic coating is clearly less than that in the crankshaft without a ceramic coating. When contact friction occurs between the journal and the shell, heat generated from friction in the crankshaft with a ceramic coating is clearly less than in the crankshaft without a ceramic coating, and no occlusion occurs between the journal and the shell in the crankshaft with a ceramic coating. In addition, the processing technologies of the present invention are advanced, and the process is feasible. Therefore, as can be seen from the experiments, the probabilities of scoring and burning of the crankshaft with a ceramic coating are significantly reduced. The crankshaft with a ceramic coating obtained in the present invention has reliable functions, so that the beneficial effects of the present invention are proved.
The foregoing embodiments are merely preferred embodiments used to fully describe the present invention, and the protection scope of the present invention is not limited thereto. Equivalent replacements or variations made by a person skilled in the art to the present invention all fall within the protection scope of the present invention. The protection scope of the present invention is as defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202211461667.2 | Nov 2022 | CN | national |
