JP2886266B2 - Method for manufacturing camshaft of valve train for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a camshaft which is a valve train part of an internal combustion engine.

2. Description of the Related Art Conventionally, a camshaft used as a valve mechanism of a vehicle engine has characteristics such as abrasion resistance and toughness because a cam portion makes sliding contact with a tappet or the like. The camshaft surface layer made of cast iron cast by a mold is chilled and formed.

At this time, as shown in FIG. 4, the surface layer of the molten metal filled in the cavity of the mold is rapidly cooled to form a shell-like solidified layer, and 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. 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. For this purpose, it is necessary to further improve the sliding characteristics of the camshaft. There is.

In other words, in spite of being lubricated with lubricating oil, as in the case of contact between the camshaft, especially the cam portion and the tappet,
For sliding parts such as bearings where good fluid lubrication cannot be expected, pitching (small holes in the shaft) and scuffing (scratching) by adjusting the properties of the material itself, such as hardness, self-lubricating properties, and surface treatment. It is necessary to suppress defects such as abnormal wear as much as possible.

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 manufacturing a camshaft for a valve train for an internal combustion engine, the present invention employs JIS.
FC20-FC30 equivalent cast iron component or Ni 0.4-0.6wt%, Cr
Casting that melts alloy cast iron containing 0.5-1.0 wt% and Mo 0.5-1.0 wt% as a constituent material, pours it into a mold, and then rapidly solidifies to obtain a reed-bright structure on the surface of the cam. Process and after release the cam part is below the A1 transformation point 600
Heating by high-frequency induction heating to austenite the pearlite in the chill layer while in the red heat state of the temperature range of ℃ or more, or high-frequency induction heating while in the temperature range of A1 transformation point or more and 900 ° C or less after mold release A quenching step of heating to maintain the retained austenite of the chill layer in an austenite state and then cooling by air cooling, and then a tempering step of tempering the entire camshaft at a predetermined temperature is performed. And a mixed structure of a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering, and a surface hardness of HRC 55 or more.

(Action) The cam portion has a mixed structure of a reed brite structure by chilling and a tempered martensite or a tempered sorbite structure by quenching and tempering to improve the toughness and fatigue strength of the same by setting a specific surface hardness. I can do it. Further, the scuffing resistance, pitching resistance, and wear resistance of the camshaft are also improved, and the durability is increased.

At this time, in the quenching step, the cast member after release is A1
By heating by high-frequency induction heating while the temperature is below the transformation point of 600 ° C or higher, more efficient heating is possible than once lowering to normal temperature and raising the humidity again,
Quenching time can be shortened.

Also, if quenching and heating are performed while the temperature is in the temperature range from the A1 transformation point to 900 ° C. or less, there is no volume change due to the passage of the transformation point when the temperature rises, and problems such as distortion, deformation, cracks, etc. accompanying quenching heating will occur. Is suppressed.

(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 sectional view of a camshaft according to the present invention, 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 raising and lowering the intake and exhaust valves 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 this cam lifter portion. Become.

Such a camshaft 1 is obtained by die casting.

In the case of the present embodiment, a cast iron component equivalent to JIS FC20 to FC30 or Ni 0.4 to 0.6 wt%, Cr 0.5 to 1.0 wt%, Mo 0.5
A chill layer is formed on the surface layer portion 1a by injecting a molten alloy of cast iron containing the remaining Fe component into a mold and rapidly cooling the surface. For this reason, the mold used for casting is made of a material having a high thermal conductivity, such as a Cu-Cr alloy containing 0.8 to 4.0 wt% of Cr, and the surface inside is rapidly cooled. A cooling path is formed in the section.

And the cast product obtained by such mold casting,
After being released from the mold, it is allowed to cool.
As shown in the figure, while the cast product is in the red heat state below the A1 transformation point and above 600 ° C., the cam portion 2 of the camshaft 1 as the cast product is heated to 900 ° C. to 1050 ° C. by the high frequency heating coil 4, Quench. Accordingly, the pearlite structure becomes austenite only from the redebrite structure and the pearlite structure formed in the chill layer at the A1 transformation point or lower, and is then rapidly quenched, thereby transforming the pearlite structure into martensite. By setting the holding time at 900 DC to 1050 ° C. to 0 during this time, decomposition of the redebrite structure, that is, graphitization of cementite is not performed.

Therefore, the chill layer of the cam portion 2 after the quenching treatment has a mixed structure of a redebrite structure and a martensite structure.

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

Therefore, according to the tempering at 600 ° C., the chill layer of the cam portion 2 is
It is a mixed structure of a reed brite structure obtained by die casting and a tempered sorbite structure obtained by quenching and tempering. On the other hand, according to the tempering at 180 ° C., a mixed structure of a redebrite structure obtained by die casting and a tempered martensite structure obtained by quenching and tempering is obtained. In each case, a surface hardness of HRC 55 or more can be secured.

Next, FIG. 3 shows a second method of the present invention, in which the induction heating start timing is started from the temperature range of the austenite region from the A1 transformation point to 900 ° C. or less. In this case, although the reedible structure other than the retained austenite is formed in the chill layer at the start of heating, the retained austenite maintains the austenite state as it is. Also in this case, the quenching temperature is 900 ° C ~ 1050
C. and forced air cooling is performed with a holding time of 0.

A chill layer composed of a mixed structure of a reedbrite structure and a martensite structure is formed on the cam portion 2 after the quenching treatment thus obtained, and the same tempering step as described above is performed.

In other words, by heating the electric furnace to 600 ° C. 1H (solid line) or 180 ° C. It can be a mixed tissue with the tissue. The mixed structure thus formed is excellent in tenacity against impacts and the like, and hardly causes fatigue fracture, and is tough. Note that the quenching and tempering may be performed only on a necessary portion of the cam lifter of the cam 2.

(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 present invention, a cast iron component equivalent to JIS FC20 to FC30 or Ni 0.4 to 0.6 wt%, Cr 0.5 to 1.0 wt% ,
Mo is cast into a mold with molten alloy cast iron containing 0.5 to 1.0 wt% as a constituent material.
During the casting process in which the surface layer of the cam part obtains a reed brite structure, and after the mold release, the cam part is heated by high frequency induction heating while the red part is in the temperature range of A1 transformation point or lower and 600 ° C or higher to reduce the pearlite of the chill layer. During the austenitization, or during the temperature range of 900 ° C or less after the A1 transformation point after mold release, a quenching step of heating by high frequency induction heating to keep the residual austenite of the chill layer in the austenitic state, and then cooling by air cooling, and thereafter A tempering step of tempering the entire camshaft at a predetermined temperature is performed, and a surface structure of the cam portion is 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. The camshaft is released from the mold because the surface hardness is set to HRC55 or more. , Subsequently without cooling to room temperature will be performed quenching heating, enables efficient heating, quenching treatment becomes faster, Hakare to shorten the hardening time, the cycle time is shortened.

In addition, there is no change in volume due to the passage of the transformation point at the time of heating, and therefore, it is possible to suppress distortion, deformation, cracks, and the like due to heating.

Furthermore, the cam portion of the obtained camshaft has excellent tenacity against impacts and the like, is hard to cause fatigue destruction, and is tough, and can obtain a camshaft that meets the demands of high rotation and high output of the engine. Performance can be improved.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of a camshaft according to the present invention, FIGS. 2 and 3 are process diagrams showing a manufacturing method, and FIG. 4 is a process diagram of a conventional manufacturing method. In the drawings, 1 is a camshaft, 1a is a surface layer, 2 is a cam, and 3 is a high-frequency heating coil.

──────────────────────────────────────────────────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 Minamiana Konanmae, Hadano-shi, Kanagawa Prefecture Hadano Mansion A-312 (72 ) Inventor Seiji Ehara 5532 Tamagaki 201, Minamitamagaki-machi, Suzuka-shi, Mie (56) References JP-A-62-256914 (JP, A) JP-A 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. In the casting step where the part obtains a reed-bright structure, and after the mold release, the cam part is in the glowing state in the temperature range below the A1 transformation point and 600 ° C or more, heated by high frequency induction heating to austenite the pearlite of the chill layer, or During the temperature range from the A1 transformation point to 900 ° C after the mold release, heating is performed by high-frequency induction heating to maintain the retained austenite of the chill layer in an austenite state, and then quenching by air cooling. A tempering step of performing a tempering treatment at a predetermined temperature is performed, and a surface layer portion of the cam portion is formed by a die rebright structure obtained by die casting and a tempered martensite obtained by quenching and tempering. A method for producing a camshaft for a valve train for an internal combustion engine, wherein the camshaft has a mixed structure of a tempered structure or a tempered sorbite structure and a surface hardness of HRC 55 or more.