JP2008144654A - Sliding component for valve gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sliding component for a valve gear having hard coating improving seizure resistance and wear resistance as compared with sliding components for valve gears having hard coating formed thereon by conventional methods for forming hard coating. <P>SOLUTION: In the sliding components for the valve gear having hard coating formed on a cam surface of a camshaft constructing the valve gear of an internal combustion engine, or on a slide surface of a slipper which is to be a mating material, namely in the camshaft, the slipper and the like, chromium nitride coating formed by dipping iron nitride formed by nitriding treatment into a salt bath containing chromium to substitute chromium atom for iron atom in iron nitride is used for the hard coating. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of a sliding component of a valve gear.

  Along with higher output and higher rotation of the internal combustion engine, the cam surface of the camshaft that drives the intake and exhaust valves that constitute the valve operating device, and the driven parts that are the counterpart material of the camshaft (for example, the direct acting type) Since the sliding contact surfaces of tappets and rocker arm slippers slide at higher sliding speeds and driven surface pressures, technologies for forming various hard coatings that improve seizure resistance and wear resistance have been proposed. ing.

As a technique for forming such a hard coating on a sliding part of a conventional valve operating device, a PVD method (see Patent Document 1), an ion plating method (see Patent Document 2), a CVD method (see Patent Document 3). .)It has been known.
JP-A-9-112219 JP-A-9-125916 JP 2001-280494 A

  In Patent Document 1, PVD (Physical Vapor Deposition) is provided on an alloy tool steel base material having a hardness of HRC55 or more and a structure in which carbide is precipitated and dispersed on a cam slip surface where a high-speed rocker arm is in sliding contact with a high-speed cam. The hard film by is formed.

  In Patent Document 2, a surface layer of a metal nitride such as chromium nitride having a thickness of 1 to 200 μm is formed on at least one of a sliding surface of a cam and a sliding surface of a rocker arm that is in sliding contact with the cam by a reactive ion plating method. Is formed by.

  In Patent Document 3, a sliding surface of a shift fork as an engine sliding component is formed on a base material surface having a undulation and a microdimple shape, and a PVD method or CVD (chemical vapor deposition: A hard thin film such as chromium nitride is formed by a Chemical Vapor Deposition method.

  The PVD method, the ion plating method, and the CVD method shown in Patent Document 1 to Patent Document 3 described above all form a hard film by adhering and depositing the material in the gas phase state on the sliding component surface. Adhesion between the hard coating and the base material of the sliding part is insufficient, and the hard coating tends to peel off. Under severe conditions due to high rotation and high surface pressure of the camshaft, seizure resistance and wear resistance There is a limit.

  An object of the present invention is to slide a valve operating device having a hard coating with improved seizure resistance and wear resistance against sliding parts of a valve operating device having a hard coating formed by a conventional hard coating forming method. It is to provide moving parts.

  According to a first aspect of the present invention, there is provided a sliding member for a valve operating device in which a hard coating is formed on a cam surface of a camshaft constituting a valve operating device of an internal combustion engine or a sliding contact surface as a counterpart material thereof. Is a chromium nitride film formed by immersing iron nitride formed by nitriding in a salt bath containing chromium to replace iron atoms in the iron nitride with chromium atoms.

  As an action, an iron nitride layer is formed on the cam layer of the camshaft or the surface layer portion of the slidable contact surface as the counterpart material by nitriding. Next, the chromium nitride is replaced by diffusing and penetrating chromium atoms into the iron nitride by immersing the camshaft on which the iron nitride layer is formed or its counterpart in a salt bath containing chromium to replace the iron atoms. Form a film.

  The above chromium nitride film is formed by diffusion penetration treatment, and has a stronger bond strength with the base material than conventional hard films formed by PVD, CVD, and ion plating methods. And no peeling occurs.

The invention according to claim 2 is characterized in that at least the surface of the hard coating is composed only of chromium nitride.
Since iron nitride has a lower hardness than chromium nitride, if iron nitride is present on the surface of the hard coating, seizure occurs or the amount of wear increases. If at least the surface of the hard coating is composed only of chromium nitride, the hardness of the surface of the hard coating is increased, and seizure resistance and wear resistance are improved as compared with the case where iron nitride is present.

The invention according to claim 3 is characterized in that the content of chromium nitride is continuously reduced from the surface of the hard coating toward the inside of the base material.
As an effect, in conventional hard film forming methods such as PVD, CVD, and ion plating, the content of the composition constituting the hard film changes discontinuously from the surface of the hard film toward the inside of the base material. However, in the present invention, the chromium nitride content is continuous from the surface of the hard coating toward the inside of the base material. Therefore, the adhesion between the hard coating and the base material increases.

  In the invention according to claim 1, the hard film is formed by immersing the iron nitride formed by nitriding treatment in a salt bath containing chromium and replacing the iron atoms in the iron nitride with chromium atoms. Since the chromium nitride film is used, the bonding force between the hard chromium nitride film and the base material is stronger and the chromium nitride film does not peel off compared to conventional hard film forming methods. The seizure resistance and wear resistance of the sliding parts can be improved.

  In the invention according to claim 2, since at least the surface of the hard coating is composed only of chromium nitride, the sliding of the valve operating device is made of chromium nitride having a high hardness as compared with the case where iron nitride is present on the surface of the hard coating. The seizure resistance and wear resistance of the moving parts can be further improved.

  In the invention according to claim 3, since the content of chromium nitride is continuously reduced from the surface of the hard coating toward the inside of the base material, compared with the conventional hard coating forming method, Since the adhesion with the base material can be increased and the hard coating does not peel off, the seizure resistance and the wear resistance of the sliding parts of the valve gear can be improved.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is an explanatory view of a valve operating apparatus having sliding parts according to the present invention. An internal combustion engine 10 includes a cylinder head 11, and the cylinder head 11 includes an intake valve 12 and an exhaust valve (not shown). In addition, a valve forcible opening / closing type valve operating device 15 that forcibly drives and opens and closes the intake valve 12 and the exhaust valve is provided.

  The valve operating device 15 is rotatably attached to the camshaft 17 rotatably attached to the cylinder head body 11a, the rocker shafts 21 and 22 attached to the cylinder head body 11a, and the rocker shafts 21 and 22. The valve opening rocker arm 23 and the valve closing rocker arm 24 driven by the camshaft 17, and the intake valve 12 driven by the valve opening rocker arm 23 and the valve closing rocker arm 24 to open and close the intake port 26 are provided. . A combustion chamber 28 communicates with the intake port 26 when the intake valve 12 is opened.

  The camshaft 17 includes a valve opening cam 31 that drives the valve opening rocker arm 23 and a valve closing cam 32 that drives the valve closing rocker arm 24. Reference numeral 31 a denotes a cam surface that slides with the valve-opening rocker arm 23, and reference numeral 32 a denotes a cam surface that slides with the valve-closing rocker arm 24.

  The valve-opening rocker arm 23 is provided with a slipper 34 (34a is a sliding surface of the slipper 34) that slides with the valve-opening cam 31, and a valve-side sliding surface 23a that slides with the end 12A of the intake valve 12. Is formed.

  The valve closing rocker arm 24 is provided with a slipper 36 (36a is a sliding surface of the slipper 36) that slides with the valve closing cam 32, and a valve side sliding surface 24a that slides with the end 12A of the intake valve 12. Is formed.

  The end 12A of the intake valve 12 slides with the valve-side sliding surface 12a that slides with the valve-side sliding surface 23a of the valve-opening rocker arm 23 and with the valve-side sliding surface 24a of the valve-closing rocker arm 24. And a valve closing side sliding surface 12b.

  At least one of the cam surface 31a of the valve opening cam 31 and the cam surface 32a of the valve closing cam 32, the sliding surface 34a of the slipper 34, and the sliding surface 36a of the slipper 36 is a hard surface described later on the surface. A chromium nitride film, which is a film, is formed to improve seizure resistance and wear resistance.

FIG. 2 is an operation diagram showing a procedure for forming a hard film on the sliding component according to the present invention.
As step 1, nitriding treatment is applied to the iron-based material that is the sliding component (camshaft and slipper as a counterpart of the camshaft) shown in FIG. 1, and the surface layer portion of the iron-based material is iron nitride. An iron nitride (FeN) layer is formed.
As the nitriding method, a gas nitriding method, a gas soft nitriding method, a salt bath nitriding method, and a salt bath soft nitriding method are suitable.

As step 2, the iron-based material on which the iron nitride layer is formed in step 1 is immersed in a salt bath to perform a salt bath treatment, and chromium atoms in the salt bath are diffused and permeated to replace the iron atoms. A chromium nitride (CrN) film, which is a hard film, is formed from iron. The salt bath treatment is performed until all of the surface iron nitride is replaced with chromium nitride. That is, finally, only the chromium nitride film exists on the surface of the iron-based material.
Further, the content of chromium nitride decreases from the surface of the hard coating toward the inside of the base material, that is, continuously decreases.
The film thickness of the above chromium nitride film is 1 to 5 μm only for CrN (surface), 2 to 20 μm at the part where CrN and FeN are mixed (Cr diffusion part), the surface hardness is HV1800 or more, SACM645 [JIS G 4202] is preferred.

  As conditions for the salt bath treatment, the composition of the salt bath treatment agent is composed of alkali metal chloride, alkaline earth metal chloride, chromium and other trace components, and the immersion time of the iron-based material is 1 to 3 Hour, Immersion temperature is 500-700 degreeC.

FIG. 3 is an explanatory view for explaining a test apparatus and a test method for evaluating the durability of the sliding component according to the present invention.
The test device 40 is for evaluating the durability of the sliding component of the valve operating device, particularly the seizure resistance, and is used as an evaluation sample of the sliding component in which the chromium nitride film is formed on the cam surface 41a. The seismic resistance of the camshaft 41 is evaluated, and a measurement arm 44 that is vertically fixed to the base portion 43 and a strain gauge that is attached to an intermediate portion of the measurement arm 44 and detects distortion of the measurement arm 44. A strain sensor 46, a rigid arm 48 attached to the upper portion of the measurement arm 44 via a support shaft 47 so as to be swingable up and down, and a cam surface of the camshaft 41 detachably attached to the lower surface of the rigid arm 48. A sliding plate 51 that slides on 41a, and a sliding plate 5 that is provided on the back surface 51b of the sliding surface 51a of the sliding plate 51 and is equivalent to the temperature of the cam surface 41a that is a sliding portion. A temperature sensor 52 consisting of a thermocouple for detecting the temperature of, consisting air cylinder 53 for pushing down the rigid arm 48 to press the slide plate 51 the cam surface 41a.

  As a test method, the camshaft 41 is rotatably supported by a receiving portion (not shown), the camshaft 41 is rotated at a predetermined rotational speed, the air cylinder 52 is operated, and the sliding plate is placed on the cam surface 41a of the camshaft 41. 51 is pressed with a predetermined load, the friction load generated in the direction of the white arrow A on the rigid arm 48 at that time is measured by the strain sensor 46, the temperature of the cam surface 41a is measured by the temperature sensor 52, and the cam The presence or absence of seizure of the surface 41a is also observed. At this time, as indicated by the white arrow B, engine oil at a constant flow rate is continuously supplied to the sliding portion between the cam surface 41a and the sliding plate 51.

Next, the load that presses the sliding plate 51 against the cam surface 41a is increased to a predetermined load, and the friction load and cam surface temperature are measured and seizure is observed. The results obtained by repeating this will be described with reference to FIG.
The test conditions in this test are as follows.

[Seizing test conditions]
Camshaft rotation speed: 6000 rpm
Engine oil supply: 450cc / min
Engine oil specifications: API SM / CF grade 15W-50
Engine oil temperature: 60-80 ° C
Sliding plate material: SNCM420 [JIS G 4103] (carburization treatment)
Sliding plate hardness: Base material HV300-375, surface HV700 or more

    The samples are Examples, Comparative Example 1 and Comparative Example 2 shown in Table 1.

Example:
The material is SACM645 [JIS G 4202], the heat treatment is gas nitriding, the surface treatment is the diffusion substitution chromium nitride film of the present invention (formed by the nitriding treatment and salt bath treatment shown in FIG. 2), the base material hardness is HV320 to 350, the surface Hardness is HV1800 or more.

Comparative Example 1:
The material is SACM645 [JIS G 4202], the heat treatment is gas nitriding, the surface treatment is not performed, the base material hardness is HV320 to 350, and the surface hardness is HV900 or more.
Thus, if the surface treatment is not performed only by gas nitriding, the surface hardness is lower than that of the above embodiment.

Comparative Example 2:
The material is SACM645 [JIS G 4202], the heat treatment is gas nitriding, the surface treatment is a chromium nitride film formed by CVD, the base material hardness is HV320 to 350, and the surface hardness is HV1800 or more.

  FIG. 4 is a graph showing the results of the seizure resistance evaluation of the sliding parts according to the present invention, and shows the test results by the test apparatus 40 shown in FIG. The horizontal axis represents the friction load (unit is N), and the vertical axis represents the temperature of the cam surface 41a of the camshaft 41 shown in FIG. 3, that is, the specimen temperature (unit is ° C.). The temperature of the cam surface 41a here is equivalent to the temperature of the sliding plate 51 (see FIG. 3), and is the temperature detected by the temperature sensor 52 (see FIG. 3).

  In Comparative Example 1 shown in Table 1, the specimen temperature rises with a large slope until the friction load is close to 10N, and when the friction load is exceeded, the slope of the rise is slightly reduced. Appearance occurred. The specimen temperature at this time is 108.7 ° C.

  In Comparative Example 2 shown in Table 1, the specimen temperature increased in the same manner as in Comparative Example 1 until the friction load was close to 10 N, and when the friction load exceeded 19 N, seizure occurred on the cam surface. did. The specimen temperature at this time is 96.3 ° C.

  In this example shown in Table 1, the slope of the specimen temperature rise is smaller than that of Comparative Example 1 and Comparative Example 2 until the friction load is 10 N, and after that, the slope of the rise is gentler. Thus, in the vicinity of 19N where seizure occurred in Comparative Example 1 and Comparative Example 2, the specimen temperature was as low as about 80 ° C., and seizure did not occur. Even when the load was further increased and the friction load became 32.1N (about 1.7 times that of 19N), the specimen temperature rose only to 93.7 ° C., and seizure did not occur.

  As described above, in this example, the diffusion substitution chromium nitride film is applied to the cam surface, so that the comparative example 1 (surface treatment is not performed) and the comparative example 2 (surface treatment is chromium nitride film by CVD) are significantly increased. It was confirmed that the seizure resistance was improved.

FIG. 5 is a graph showing the results of the wear resistance evaluation of the sliding parts according to the present invention. The vertical axis represents the surface roughness of the cam surface of the camshaft as a sample, that is, the average roughness Ra (unit: μm). The horizontal axis represents the sample before and after the test.
The test here is a wear test performed using the test apparatus 40 shown in FIG. 3, and the conditions of the wear test are as follows.

[Wear test conditions]
Camshaft rotation speed: 6000 rpm
Sliding plate pressing load: 100 to 1250N (data in graph is 1250N)
Test time: 0.5 Hour (Comparative Example 1 and Comparative Example 2 burn-in occurs within 2 minutes)
Engine oil supply: 450cc / min
Engine oil specifications: API SM / CF grade 15W-50
Engine oil temperature: 60-80 ° C (data in graph is 60 ° C)
Sliding plate material: SNCM420 [JIS G 4103] (carburization treatment)
Sliding plate hardness: base material HV300-375, surface HV700-

  The average roughness of the example before the test, the comparative example 1 and the comparative example 2 was 0.09 μm, and after the test, the average roughness slightly increased to 0.13 μm in the example than before the test. However, in Comparative Example 1 and Comparative Example 2, the average roughness was greatly deteriorated compared to the Examples, both exceeding 0.7 μm.

  In Comparative Example 1, since the surface treatment was not performed, Fe was present on the surface, the temperature was increased due to sliding heat generation, the hardness was lowered, and the counterpart material was compared. In Comparative Example 2, a CrN film having a high temperature hardness reduction resistance was applied as a countermeasure to Comparative Example 1, but since it was a treatment by the CVD method, chromium nitride was applied to the base material. It is considered that the adhesion of the film was insufficient and peeling of the chromium nitride film occurred.

  On the other hand, in this example, the formation of the chromium nitride film by diffusion substitution strengthened the adhesion between the base material and the chromium nitride film, and the amount of wear was small because the peeling of the chromium nitride film did not occur. Conceivable.

  As shown in FIGS. 1 and 2, the present invention firstly includes the cam surfaces 31 a and 32 a of the camshaft 17 constituting the valve gear 15 of the internal combustion engine 10, or a slipper 34 as a counterpart material thereof. The sliding parts of the valve operating device 15 in which a hard film is formed on the sliding contact surfaces 34a, 36a of the 36 (that is, the camshaft 17 (the camshaft 17, the valve opening cam 31, and the valve closing cam 32 are separated). In this case, in the camshaft 17, the valve opening cam 31 and the valve closing cam 32) and the slippers 34, 36), the hard film is nitrided by immersing iron nitride formed by nitriding in a salt bath containing chromium. A chromium nitride film is formed by replacing iron atoms in iron with chromium atoms.

  Thereby, compared with the conventional hard film formation method, the bonding force between the chromium nitride film, which is a hard film, and the base material becomes stronger, and the chromium nitride film does not peel off. The seizure resistance and wear resistance of the parts can be improved.

Secondly, the present invention is characterized in that at least the surface of the hard coating is composed only of chromium nitride.
Thereby, the seizure resistance and the wear resistance of the sliding component of the valve operating device 15 can be further improved by chromium nitride having a high hardness as compared with the case where iron nitride is present on the surface of the hard coating.

Third, the present invention is characterized in that the content of chromium nitride is continuously reduced from the surface of the hard coating toward the inside of the base material.
As a result, the adhesion between the hard coating and the base material can be increased compared to the conventional hard coating forming method, and the hard coating does not peel off, so that the sliding parts of the valve gear 15 are not seized. And wear resistance can be improved.

  In addition to the materials shown in the present embodiment, iron-based materials may be nitriding materials such as SKD61 [JIS G 4404].

  The sliding component of the present invention is suitable for a valve operating device.

It is explanatory drawing of the valve operating apparatus provided with the sliding component which concerns on this invention. It is an effect | action figure which shows the hard film formation point to the sliding components which concern on this invention. It is explanatory drawing explaining the test apparatus and test method which evaluate the durability of the sliding component which concerns on this invention. It is a graph which shows the result of the seizure resistance evaluation of the sliding component which concerns on this invention. It is a graph which shows the result of abrasion resistance evaluation of the sliding component which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 15 ... Valve operating device, 17, 41 ... Cam shaft, 31, 32, 34, 36 ... Sliding parts (valve opening cam, valve closing cam, slipper, slipper), 31a, 32a, 41a ... cam surfaces, 34a, 36a ... sliding surfaces (sliding surfaces).

Claims (3)

In a sliding part of a valve operating device in which a hard film is formed on a cam surface of a camshaft constituting a valve operating device of an internal combustion engine or a sliding contact surface which is a counterpart material thereof,
The hard film is a chromium nitride film formed by immersing iron nitride formed by nitriding treatment in a salt bath containing chromium and replacing iron atoms in the iron nitride with chromium atoms. A sliding part of a valve gear characterized by   The sliding component of the valve gear according to claim 1, wherein at least a surface of the hard coating is composed only of the chromium nitride.   The sliding component of the valve operating device according to claim 1 or 2, wherein the chromium nitride is continuously reduced in content from the surface of the hard coating toward the inside of the base material.

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