JP2886268B2 - Camshaft of valve train for internal combustion engine and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a camshaft constituting a valve train of an internal combustion engine, and a method for manufacturing the same.

(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. The surface layer of the cast iron camshaft cast by the method described above is chilled.

At this time, as shown in FIG. 6, 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 is:
It has a mixed structure of perlite structure and redebrite structure.

(Problems to be Solved by the Invention) However, according to the formation of the chill layer using such a mold, the surface layer of the cast member is chilled over the entire area, unlike the case where the cooling metal is set in the sand mold, and after the casting, When performing cutting or the like of a spline groove or the like, the hardness of the machined portion becomes too hard and shortens the life of the cutting tool. Therefore, it is necessary to locally soften necessary parts to improve the life of the cutting tool.

On the other hand, the cam portion is required to further improve the sliding characteristics in order to follow the trend of high-speed rotation and high output of the engine. That is, in the contact between the cam portion and the tappet, good fluid lubrication such as a bearing cannot be expected in spite of lubrication with lubricating oil, so the hardness of the cam portion itself, self-lubricating property, It is necessary to optimize characteristics such as surface treatment and to suppress as much as possible defects such as pitting (small hole damage in the shaft), scuffing (scorching), and abnormal wear.

For this reason, in the cam part, the mixed structure of perlite and redebrite of the chill layer obtained by the conventional metal casting,
A reedbrite structure with excellent toughness and abrasion resistance and a mixed structure of a tempered sorbite structure, or a mixed structure of a reedbrite structure and a tempered martensite structure, and
It is desirable to improve the pitting resistance and the scuffing resistance by increasing the direction hardness, and to reduce the surface hardness of the portion to be softened as a structure similar to the structure of the core that is not chilled.

(Means for Solving the Problems) In order to solve such problems, the present invention relates to a camshaft of a valve train for an internal combustion engine, which is defined by JIS FC20-F.
Cast iron component equivalent to C30 or Ni 0.4-0.6wt%, Cr 0.5-1.
A molten alloy cast iron containing 0 wt% and 0.5-1.0 wt% Mo was poured into a mold and melted.
Quenching, having a mixed structure with a tempered martensite structure or a tempered sorbite structure obtained by tempering,
The cam portion having a surface hardness of HRC55 or more, and other predetermined portions of the surface layer portion have graphite, redebrite and tempered sorbite structures by local softening treatment, and have a surface hardness of HR.
And a journal section that is C35 or less.

Claim 2 is a method for manufacturing a camshaft of a valve train for an internal combustion engine, comprising: a cast iron component corresponding to JIS FC20 to FC30 or Ni 0.4 to 0.6 wt%, Cr 0.5 to 1.0 wt%, Mo 0.5 to 1.0 wt%.
A casting process in which an alloy cast iron containing a wt% composition is melted as a constituent material and poured into a mold and then rapidly solidified to obtain a reed-bright composition on the surface of the cam portion. 95% A1 transformation point or more in red heat immediately after release
An intermediate step of performing a quenching process of cooling the cam portion of 0 ° C. or lower by forced air cooling and a local softening process of other portions of the surface layer portion to be softened including the journal portion, and a tempering process of tempering the cam shaft at a predetermined temperature. Sequentially,
The surface layer part of the cam part has a reed brite structure obtained by die casting, a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering, and the surface hardness is HRC 55 or more, and the journal part to be softened is The surface layer of the portion including the graphite, the reed brite and the tempered sorbite structure has a surface hardness of HRC 35 or less.

According to a third aspect of the present invention, in the method for manufacturing a camshaft of the valve train for an internal combustion engine according to the second aspect, the local softening process in the intermediate step of the portion including the journal portion is performed in parallel with the quenching process, and the portion to be softened is formed. While the temperature is in the glowing state in the temperature range between 600 ° C and the A1 transformation point, the part
The temperature of the part to be graphitized and austenite in the pearlite part of the chill layer, or the temperature of the part to be softened, is a temperature not lower than the A1 transformation point and not higher than 950 ° C. While it is in the range, the same part is heated and held at 1000 ° C. to 1100 ° C. to graphitize a part of cementite constituting the redebrite eutectic and to keep the retained austenite in an austenite state, and subsequently allowed to cool or forcibly air-cool. It is characterized by turning austenite into martensite.

According to a fourth aspect of the present invention, in the method for manufacturing a camshaft of the valve train for an internal combustion engine according to the second aspect, in the tempering step, simultaneously with the tempering process of the quenched sliding portion, the tempering process of the martensitized portion of the softening portion is performed. It is characterized by performing.

(Action) The cam portion of the camshaft 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 toughness and fatigue strength by having a specific surface hardness. I can do it. In addition, the scuffing resistance, pitching resistance, and wear resistance of the cam portion of the camshaft are also improved, and the durability is increased.

On the other hand, by decomposing a part of the redebrite structure of the portion to be softened and graphitizing, the hardness of the surface layer is reduced and the cutting process is facilitated. Further, by performing these processes almost simultaneously in parallel, the work efficiency can be improved.

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

1 and 2 are partial cross-sectional views of an example of a camshaft. FIG. 1 is a chill layer structure after casting, FIG. 2 is a surface layer structure after quenching and softening, and FIG. FIG. 5 is a process chart showing a manufacturing method.

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

Such a camshaft 1 is obtained by die casting,
Cast iron component equivalent to JIS FC20-FC30, or Ni 0.4-0.6wt
%, Cr 0.5-1.0 wtt%, and Mo 0.5-1.0 wt%, a chill layer is formed on the surface layer 1a by injecting a melted alloy cast iron into a mold and rapidly cooling the surface.

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 Cu-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. After the mold member is released from the casting, the cam 2 is subjected to the intermediate step shown in FIG. 3 and the journals 3 at both ends of the shaft are subjected to the intermediate step shown in FIG. Each is processed concurrently.

That is, as shown in FIG. 3, after the cam portion 2 is released from the mold, it is forcibly air-cooled from the red heat state in the temperature range of 930 ° C. to 980 ° C. and quenching is performed. A mixed structure of a reed brite structure and a martensite structure is formed in the layer.

On the other hand, while the temperature range of the journal portion 3 between the cam portions is within the range from the A1 transformation point to 950 ° C. as shown in FIG.
After heating locally to 1100 ° C and holding for 20 to 30 seconds, it is left to cool or forced air cooled to soften. For this reason, during the heating and holding, a part of cementite constituting the redebrite eutectic of the chill layer in the same part undergoes a change of Fe ₃ C-3Fe + C to become graphite (carbon C), and the residual austenite of the chill layer becomes , Keep the state of austenite as it is.

Then, by allowing to cool or forced air cooling, the austenite turns into martensite, and the chill layer in the same part,
A structure of graphite, redebrite and martensite is formed.

As described above, when the intermediate process of quenching the cam portion 2 and the softening process of the journal portion 3 is completed, a tempering process of the entire camshaft 1 is performed.

That is, this tempering step is performed by electric furnace heating as shown in FIGS. 3 and 4, and in this embodiment, at 600 ° C.
Treated by heating and holding for 2H. For this reason, the cam portion 2
Changes to a tempered sorbite structure, and the surface layer structure after the treatment becomes a mixed structure of a redebrite structure and a tempered sorbite structure.

Incidentally, for example, when the tempering temperature is tempered at a grinding temperature of about 180 ° C., the martensite structure changes to tempered martensite (β martensite), and the surface layer of the same portion becomes a redebrite structure and a tempered martensite structure. In any case, the surface hardness can be HRC 55 or more.

On the other hand, in the journal part 3, the marcinite is similarly changed to a tempered sorbite structure by tempering at 600 ° C. and 2H, and as shown in FIG. 2, the surface layer structure is similar to the structure of the core part 1b, such as graphite, redebrite, and tempered. It becomes sorbite structure and surface hardness becomes HRC35 or less.

Next, FIG. 5 is a process chart showing a second method of the softening treatment in the intermediate step of the journal portion 3. In this case, the temperature range of the cast member after the casting step is 600 High-frequency induction heating is performed from a temperature of not less than ° C and not more than the A1 transformation point.

In this case, by being below the A1 transformation point, the pearlite component formed on the surface layer is austenitized by high-frequency induction heating, and a part of cementite constituting the redebrite eutectic is graphitized, and the same structure as in the previous example. You can wait.

Therefore, the final surface layer structure and surface hardness obtained by the following tempering process substantially match the structure and hardness of the core 1b as in the previous example.

The structure of the cam portion 2 after the quenching and tempering treatment is excellent in tenacity such as impact value, abrasion resistance, hard to cause fatigue fracture, and tough, while the workability of the softened journal portion 3 is improved. Improves.

(Effect of the Invention) As described above, according to the present invention, in claim 1, the camshaft of the valve train for an internal combustion engine has a cast iron component equivalent to JIS FC20 to FC30 or Ni 0.4 to
The surface layer of the sliding part obtained by pouring into a mold a molten alloy cast iron containing 0.6wt%, 0.5-1.0wt% of Cr and 0.5-1.0wt% of Mo The portion has a mixed structure of a rendezvous structure, a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering, and a cam portion having a surface hardness of HRC 55 or more, and other predetermined portions of a surface layer portion. By having a journal part having graphite, redebrite and tempered sorbite structure by a local softening treatment and having a surface hardness of HRC 35 or less, the surface layer structure of the cam part has abrasion resistance,
A camshaft excellent in workability can be obtained by making the structure of the journal part to be softened the same as the structure of the core part, as well as the structure having excellent toughness and the like. Therefore, it is possible to meet the demand for higher performance of the engine as a camshaft of the valve train for an internal combustion engine.

According to a second aspect of the present invention, there is provided a method for manufacturing a camshaft of a valve train for an internal combustion engine, comprising: a cast iron component equivalent to JIS FC20 to FC30, Ni 0.4 to 0.6 wt%, Cr 0.5 to 1.0 wt%, Mo 0.5 to 1.0
A casting process in which an alloy cast iron containing a wt% composition is melted as a constituent material and poured into a mold and then cooled and solidified to obtain a reed-bright composition on the surface layer of the cam portion. In red heat immediately after mold release, above the A1 transformation point 950
An intermediate step of performing a quenching process of cooling a cam portion having a temperature of not more than 0 ° C. by forced air cooling and a local softening process of a portion to be softened of other surface layer portions including a journal portion, and a tempering process of tempering a cam shaft at a predetermined temperature. Sequentially, the surface layer portion of the cam portion should be softened while the surface hardness is HRC 55 or more, with the reed brite structure obtained by die casting and the tempered martensite structure or tempered sorbite structure obtained by quenching and tempering. The surface layer of the part including the journal part is made of graphite, leedrite, and tempered sorbite so that the surface hardness is HRC 35 or less, so the quenching treatment of the cam part and the local softening treatment of the journal part to be softened are performed simultaneously, and By performing the tempering process, the processing operation is smooth and the productivity is good.

Especially as a quenching treatment, immediately after demolding, 950 below the A1 transformation point
The method of quenching and quenching the cam portion in a temperature range of not more than ℃ or less, and the method of heating from a red-hot state without cooling to a normal temperature once in the local softening treatment enables efficient processing. .

[Brief description of the drawings]

1 and 2 are partial cross-sectional views of one example of the camshaft of the present invention. FIG. 1 is a chill layer structure after die casting, and FIG. 2 is a surface layer structure after quenching and softening. 3 to 5
FIG. 1 is a process chart showing a manufacturing method of the present invention, and FIG. 6 is a process chart showing a conventional manufacturing method. In the drawings, 1 is a cam shaft, 1a is a surface layer, 1b is a core, 2 is a cam, 3 is a journal, and 4 is a high frequency induction 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 Minami Yana Konanmae, Hadano City, Kanagawa Prefecture Hadano Mansion A312 (72) Invention Person Seiji Ehara 5532 Tamagaki, Minamitamagaki-cho, Suzuka-shi, Mie 201 (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 (4)

(57) [Claims] [1] A cast iron component or Ni equivalent to JIS FC20 to FC30.
A sliding part obtained by casting a molten alloy cast iron containing a composition of 0.4 to 0.6 wt%, Cr 0.5 to 1.0 wt%, and Mo 0.5 to 1.0 wt% into a mold and rapidly solidifying it. Has a mixed structure of a redebrite structure, a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering, and a cam portion having a surface hardness of HRC 55 or more, and a predetermined other surface layer portion. Part is graphite by local softening treatment,
A camshaft for a valve train for an internal combustion engine, comprising: a journal portion having a redebrite and a tempered sorbite structure and having a surface hardness of HRC35 or less. 2. A cast iron component corresponding to JIS FC20 to FC30 or Ni.
0.4-0.6wt%, Cr 0.5-1.0wt%, Mo 0.5-1.0wt%
A casting process in which a molten alloy cast iron containing the following components is poured into a mold and then rapidly solidified to obtain a reed-bright composition at the surface of the cam portion. An intermediate step of performing a quenching process of cooling the cam portion having a temperature of not less than the A1 transformation point and not more than 950 ° C. in a red hot state by forced air cooling and a local softening process of other portions of the surface layer including the journal portion to be softened, A tempering process of sequentially tempering the shaft at a predetermined temperature is sequentially performed, and a surface layer portion of the cam portion is made to have a redebrite structure obtained by die casting and a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering. Hardness is HRC55 or more, and the surface layer of the part including the journal part to be softened is made of graphite, redebrite and tempered sorbite. A method for producing a camshaft of a valve train for an internal combustion engine, characterized in that the surface hardness is HRC 35 or less. 3. The local softening process in the intermediate step of the portion including the journal portion is performed in parallel with the quenching process, and the temperature of the portion to be softened is set to a red heat state in a temperature range of 600 ° C. or more and A1 transformation point or less. Meanwhile, the temperature of the portion to be softened by heating and maintaining the same portion at 1000 ° C. to 1100 ° C. to graphitize a part of cementite constituting the redebrite eutectic of the chill layer and austenite the pearlite portion of the chill layer, or While the temperature is within the temperature range from the A1 transformation point to 950 ° C, 1000 parts
C. to 1100.degree. C. to graphitize a part of the cementite constituting the redebrite eutectic and to keep the retained austenite in the austenitic state, followed by cooling or forced air cooling to transform the austenite into martensite. 3. A method for manufacturing a camshaft for a valve train for an internal combustion engine according to claim 2. 4. The valve train for an internal combustion engine according to claim 2, wherein in the tempering step, tempering processing is performed on the martensitized portion of the softening processing part simultaneously with tempering processing on the quenched sliding part. Method of manufacturing a camshaft.