JP2886267B2 - Method for manufacturing camshaft of valve train for internal combustion engine - Google Patents

Description

The present invention relates to a method for manufacturing a camshaft, which is a component of a valve train for an internal combustion engine.

(Prior Art) Conventionally, a camshaft used as a valve mechanism of a vehicle engine is required to have characteristics such as wear resistance and toughness because a cam portion makes sliding contact with a tappet or the like. It is formed by chilling the surface layer of a camshaft made of cast iron cast by a mold.

At this time, as shown in FIG. 3, the surface layer of the molten metal filled in the cavity of the mold is rapidly cooled to a shell-like solidified layer, then released from the mold and allowed to cool, so that the rapidly cooled surface layer portion is raised. A method of forming a chill structure of hardness is known. And the steel structure of the chill layer thus formed was a mixed structure of a pearlite structure and a redebrite structure.

(Problems to be Solved by the Invention) However, the current trend of engines of vehicles and the like is to further increase the speed and output of the engine, and for this purpose, it is necessary to further improve the sliding characteristics of the camshaft. is there. That is, especially in the case of a cam portion where good fluid lubrication such as a bearing cannot be expected even though it is lubricated with lubricating oil, such as the contact between the cam portion and a tappet, the hardness of the member itself, the self-lubricating property In addition, it is necessary to minimize defects such as pitching (small hole damage in the shaft), scuffing (scratching), and abnormal wear by optimizing the characteristics such as surface treatment.

For this reason, the mixed structure of pearlite and redebrite of the chill layer obtained by the conventional mold casting, the mixed structure of the redebrite structure and sorbite structure excellent in toughness and wear resistance,
Alternatively, it was desired to improve the pitting resistance and the scuffing resistance as a mixed structure of a reed brite structure and a tempered martensite structure.

(Means for Solving the Problems) In order to solve such problems, the present invention relates to a method for manufacturing a camshaft of a valve train for an internal combustion engine, which is based on JIS FC20.
~ Cast iron equivalent of FC30 or Ni 0.4-0.6wt%, Cr 0.
Casting that melts the alloy cast iron containing 5 to 1.0 wt% and Mo 0.5 to 1.0 wt% as a constituent material, then pours it into a mold and then rapidly solidifies to obtain a reed-bright structure in the cam surface. Process, a quenching step of continuously forcibly cooling the cam portion in a temperature range of 980 ° C. or lower, which is in the red heat state immediately after mold release of the die casting, and then cooling the entire camshaft to a predetermined temperature A tempering step of performing a tempering treatment at a temperature is performed, and the surface layer portion of the cam portion is formed as a mixed structure of a redebrite structure obtained by die casting and a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering. It is characterized in that the height is set to HRC 55 or more.

(Operation) In manufacturing the camshaft, the cam portion is made into a mixed structure of a reed brite structure by chilling, a tempered martensite by quenching and tempering or a tempered sorbite structure, and has a surface hardness of HRC 55 or more.
The toughness and fatigue strength of the cam can be improved. In addition, scuffing resistance, pitting resistance, and abrasion resistance are also improved, and durability can be increased. Also, as a quenching step, immediately after releasing the mold casting, the cam portion in the temperature range from the A1 transformation point to 980 ° C. or less is forcibly air-cooled as it is, and then the entire camshaft is tempered at a predetermined temperature. The process of lowering the temperature to room temperature and raising the temperature again can be omitted,
A device for quenching and heating is not required, and the cycle time can be reduced. In addition, it is possible to suppress the occurrence of problems such as distortion, deformation, and cracks due to quenching heating.

(Embodiment) An embodiment of a method for manufacturing a camshaft of a valve train for an internal combustion engine according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a partial cross-sectional view of the camshaft, and FIG. 2 is a process diagram showing a manufacturing method.

As is well known, the camshaft 1 shown in FIG. 1 is formed with a plurality of cam portions 2.
A journal portion 3 is provided integrally between 2, 2 and the shaft end. The cam portion 2 is provided with a cam lifter portion for performing a valve lift of an intake / exhaust valve of the engine. The contact pressure applied from a tappet or the like that comes into sliding contact with the cam portion is particularly high in the cam lifter portion. Become.

Such a camshaft 1 is obtained by die casting,
In the present invention, JIS FC20 ~ FC30 equivalent cast iron component, or Ni
0.4-0.6wt%, Cr 0.5-1.0wt%, Mo 0.5-1.0wt
%, The molten cast iron composed of the remaining Fe component is poured into a mold, and the surface is rapidly cooled to form a chill layer on the surface layer portion 1a.

For this reason, the mold used for casting is, for example, 0.8 to 4.0 wt%
It is made of a material having high thermal conductivity, such as a Cr-Cr alloy containing Cr, and a cooling passage is formed in a predetermined portion inside the mold in order to rapidly cool the surface portion. Then, the cast product obtained by such die casting is allowed to cool after release, but in the present invention, as shown in FIG.
While in the temperature range of ° C., quenching is performed by forced air cooling.

For this reason, a mixed structure of a redebrite structure and a martensite structure is formed in the chill layer of the cam portion after quenching,
After the mold release, the same surface structure as that obtained by temporarily cooling to room temperature and then quenching is obtained. The quenching by forced air cooling immediately after the release is particularly effective in high-temperature release (QC).

The tempering step after quenching is performed by heating in an electric furnace.
In the present embodiment, tempering at 600 ° C. for 1H (solid line in FIG. 2) and 180 ° C.
An example of 1H tempering (broken line in Fig. 2) is shown. When tempered at 600 ° C, the martensite structure by quenching changes to tempered sorbite structure, and when tempered at 180 ° C, the martensite structure by quenching changes. Changes to tempered martensite (β martensite) structure.

Therefore, according to the tempering at 600 ° C., the chill layer of the cam portion 2 has a mixed structure of a reed brite structure obtained by die casting and a tempered sorbite structure obtained by quenching and tempering. And a mixed structure of a redebrite structure obtained by die casting and a tempered martensite structure obtained by quenching and tempering. In each case, a surface hardness of HRC 55 or more can be secured. The mixed structure thus formed is excellent in tenacity against impact and the like, hardly causes fatigue fracture, and is tough.

The quenching and tempering process may be performed only on a necessary portion of the cam portion, that is, only on the cam lifter portion of the cam portion.

(Effects of the Invention) As described above, in the method for manufacturing a camshaft of a valve train for an internal combustion engine according to the large invention, a considerable cast iron component of JIS FC20 to FC30 or Ni 0.4 to 0.6 wt%, Cr 0.5 to 1.0 wt% , Mo
A casting process in which an alloy cast iron containing 0.5 to 1.0 wt% is melted as a constituent material and poured into a mold and then rapidly solidified to obtain a reed-bright structure at the surface of the cam portion. A1 in red heat immediately after mold release from mold casting
A quenching step of forcibly cooling and cooling the cam part in the temperature range of the transformation point or more and 980 ° C or less, and then a tempering step of tempering the entire camshaft at a predetermined temperature is performed, and the surface part of the cam part is molded by die casting. The mixed structure of the obtained redebrite structure and a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering,
In addition, since the surface hardness is set to HRC 55 or more, there is no need for a reheating step of once lowering the temperature to room temperature and raising the temperature again, and also requires a high-frequency heating device or the like required for reheating, and Since no time is required for once lowering the temperature to normal temperature and raising the temperature again, the cycle time can be reduced.

In addition, the camshaft obtained by the production method of the present invention can suppress the occurrence of distortion, deformation, cracks, and the like associated with reheating for raising the temperature from normal temperature, particularly in the cam portion, and A good camshaft can be obtained.

Further, according to the camshaft obtained by the manufacturing method of the present invention, it is possible to meet the demand for high rotation and high output of the engine, and to achieve high performance of the engine.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a camshaft showing an example of a camshaft obtained by the present invention, FIG. 2 is a process diagram showing a manufacturing method, and FIG. 3 is a process diagram of a conventional manufacturing method. In the drawings, reference numeral 1 denotes a cam shaft, 1a denotes a surface portion, and 2 denotes a cam portion.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI F01L 1/04 F01L 1/04 B J (72) Inventor Isao Matsumoto 2044 Minami-Yana Konanmae, Hadano-shi, Kanagawa Prefecture Hadano Mansion A312 (72) Invention Person Seiji Ehara 5532 Tamagaki, Minamitamagaki-machi, Suzuka-shi, Mie 201 Satellite Tamagaki 201 (56) References JP-A-62-256914 (JP, A) JP-B-64-5087 (JP, B2) JP-B-57-38651 ( JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21D 1/00-5/00 C22C 37/00 F01L 1/04

Claims (1)

(57) [Claims] [1] A cast iron component or Ni equivalent to JIS FC20 to FC30.
A cast iron containing a composition of 0.4-0.6wt%, Cr 0.5-1.0wt%, Mo 0.5-1.0wt% is melted as a constituent material, poured into a mold, and then rapidly solidified to form the surface layer of the cam part. A quenching step of forcibly air-cooling and cooling a cam portion having a temperature range of not less than A1 transformation point and not more than 980 ° C. which is continuously in a red hot state immediately after the mold release of the mold casting, After that, a tempering step of tempering the entire camshaft at a predetermined temperature is performed, and a surface layer portion of the cam portion is made up of a redebrite structure obtained by die casting and a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering. A method of manufacturing a camshaft for a valve train for an internal combustion engine, wherein the camshaft has a mixed structure and a surface hardness of HRC 55 or more.