JP2003014085A - Assembled camshaft - Google Patents

Abstract

(57) [Problem] To provide an assembling camshaft that can prevent cracking of a cam piece at the time of shaft diameter expansion processing. SOLUTION: In an assembling camshaft in which a hollow shaft 2 is inserted into a cam piece 1 and then the shaft 2 is fixed in a non-separable manner by expanding the diameter of the shaft 2, the cam piece 1 has a density of 7%. .1 to 7.4 g / c
It is formed by subjecting an iron-based sintered compact warm-formed to a range of m ³ to a heat treatment of quenching and tempering. The composition of the iron-based sintered compact was Cu:
1.5 to 4% by weight and C: 0.7 to 1.0% by weight, respectively, with the balance being Fe and unavoidable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camshaft that functions as a main element of a valve train of an internal combustion engine, and particularly to a hollow shaft and a sintered metal campiece that are separately formed. The present invention relates to an improvement of a prefabricated camshaft which is integrated with each other by a diameter expansion (expansion) process.

[0002]

2. Description of the Related Art As an assembly type camshaft of this type, for example, JP-A-8-333659 and JP-A-9-316.
In addition to those described in Japanese Patent Application Laid-Open No. 12-52110 and Japanese Patent Application Laid-Open No. 11-50210, those described in Japanese Patent Application Laid-Open No. 10-339110 are proposed.

JP-A-8-333659, JP-A-9-31612 and JP-A-11-50210.
The technique described in Japanese Patent Laid-Open No. Hei 10-101868 is based on the inclusion of molybdenum for the purpose of improving wear resistance of a cam alloy (cam lobe) made of a sintered alloy containing iron (Fe) as a main component. In the technique described in Japanese Patent No. 339110, as a countermeasure against the cracking of the cam piece when the diameter of the shaft is expanded, the heat treatment condition is adjusted so that the inner peripheral side has a lower hardness than the outer peripheral side.

[0004]

[Patent Document 1] Japanese Patent Application Laid-Open No. 8-33365
No. 9, JP-A-9-31612, and JP-A-1
As described in Japanese Patent Publication No. 1-50210, attention is paid to the compositional improvement of the sintered alloy, and that alone does not provide a countermeasure against cracking on the cam piece side at the time of shaft diameter expansion processing, and there is still room for improvement.

In Japanese Patent Laid-Open No. 10-339110, the crack of the cam piece when the diameter of the shaft is expanded is taken into consideration, but the cam piece should be forged by a hot multi-stage former. Since it is based on the above, it is not necessarily a countermeasure against cracking of the sintered metal cam piece, and there is still room for improvement as in the above case.

The present invention has been made in view of the above problems, and presumes the use of a sintered metal cam piece, and in particular, prevents the cam piece from cracking during shaft diameter expansion processing. (EN) Provided is a prefabricated camshaft capable of

[0007]

According to a first aspect of the present invention, an assembling cam is formed by inserting a hollow shaft into a cam piece and expanding the diameter of the shaft so that the both shafts are fixed in a separated manner. In the shaft, the cam piece is characterized by being formed of an iron-based sintered compact that has been warm-formed so that its density is in the range of 7.1 to 7.4 g / cm ³ .

In this case, as in the invention described in claim 2, the cam piece has a density of 7.1 to 7.4 g /
It is desirable that the iron-based sintered compact (compacted powder compact) warm-molded to have a range of cm ³ is formed by subjecting it to heat treatment such as quenching and tempering.

More preferably, as in the invention according to claim 3, the iron-based sintered compact for forming the cam piece has a composition of Cu: 1.5 to 4% by weight,
C: 0.7 to 1.0% by weight, respectively, with the balance being F
e and unavoidable impurities.

Therefore, in the inventions according to claims 1 and 2, mechanical density such as tensile strength after heat treatment is improved by setting the density of the iron-based sintered compact to 7.1 g / cm ³ or more, For example, it becomes possible to sufficiently withstand the stress generated on the cam piece side when the diameter of the shaft is expanded by using a predetermined mandrel, and it works effectively in preventing cracking. Moreover, as a means for improving the density, since the warm molding method in which the material powder and the mold are heated to about 130 ° C. to perform compression molding is adopted, the iron-based sintered material is produced without economical disadvantage. The density of the features can be increased to within the range of 7.1-7.4 g / cm ³ .

In particular, according to the invention of claim 3, the composition of the iron-based sintered compact is Cu: 1.5 to 4% by weight,
C: 0.7 to 1.0% by weight, respectively, with the balance being F
With e and unavoidable impurities, the wear resistance required for the cam piece can be sufficiently satisfied.

Since the cam piece manufactured by the sintering method is excellent in dimensional accuracy, it has been proposed that the cam piece is positively adopted for the assembly type cam shaft. On the other hand, when a pipe-shaped shaft is expanded with a mandrel and the cam piece is fixed to the shaft, the internal stress generated in the cam piece is large and cracks occur in ordinary sintered materials, making practical application difficult. Has become. There is also a method of increasing the density of the cam piece itself by a method of repeating molding and sintering in order of molding, pre-sintering, re-molding, and main sintering so as to be able to withstand the internal stress during the diameter expansion process, or by sintering forging. However, both methods inevitably increase costs due to a large number of steps.

On the other hand, in recent years, a method called warm forming has been attempted, in which powder as a sintering material and a molding die are heated to about 130 ° C. and compression-molded. It is said that a higher density molded body can be obtained without increasing the number. That is, as shown in FIG. 2, in the conventional cold forming method which has been widely used, the limit of the density of the green body after sintering is about 7.1 g / cm ³ , whereas the above The warm compaction method can increase the density of the green compact before sintering to about 7.4 g / cm ³ , and the present invention is premised on the use of this warm compaction method. In addition, since it is difficult to increase the density to a value much higher than 7.4 g / cm ³ under industrial production conditions, the density range of the sintered compact is set to 7.1 to 7.4 g / cm ^3.
Stipulated.

The mechanical properties of the sintered compact, particularly the tensile strength, have a high correlation with the density, and the tensile strength is improved almost in proportion to the increase in the density. For example, the density of the sintered compact is 7.1 g / c.
In the case of m ³ , the tensile strength reaches 1000 MPa or more. As a result, when fixing the cam piece formed of the iron-based sintered compact to the opposite shaft, for example, the stress generated on the cam piece side when the shaft is expanded by a mandrel is the tensile strength described above. It was confirmed that the both can be securely fixed by expanding the diameter of the shaft without causing cracking of the cam piece.

The above-mentioned cam piece is obtained by sintering a green compact warm-formed into a predetermined shape at a sintering temperature of 1080 ° C. or higher,
Further, it is manufactured by performing heat treatment such as carburizing and tempering treatment or induction hardening and tempering treatment. The improvement of strength by densification is a property common to other materials, but in order to obtain the required mechanical strength and at the same time to manufacture by a more economical manufacturing method, it is necessary to select the components contained in the material. is there.

For example, although an iron-based sintered material containing Cr is widely used for a cam piece, the atmosphere for sintering and heat treatment is limited in order to prevent grain boundary oxidation, and continuous production with high productivity. It is preferable not to contain it, because treatment in a furnace becomes impossible. For Ni, 2
%, The amount of retained austenite is largely precipitated, so that the content thereof is not preferable from the viewpoint of improving wear resistance.

The Fe-Cu-C type sintered material is the most general material without containing expensive alloying elements. Cu is effective in strengthening the base material and improving the strength,
If it is less than 1.5%, the desired effect cannot be obtained. On the other hand, if its content exceeds 4%, embrittlement occurs and dimensional expansion during sintering becomes large, so excessive content is not preferable. Therefore, the content of Cu is set to 1.5 to 4% by weight as described in claim 3, and more preferably 2 to 3% by weight.

C has the function of forming a solid solution in the matrix to improve the strength, and is an indispensable element on the assumption that the sintered compact is subjected to quenching treatment. The material structure after quenching is composed of martensite and fine pearlite, but in order to obtain a sufficient martensite structure for parts requiring wear resistance such as cam pieces, 0.7%
The above contents are required. On the other hand, the content of C is 1.
When the content exceeds 0%, embrittlement occurs and the compressibility during compression molding is impaired, and it becomes difficult to improve the density. Therefore, the C content is 0.7 to 1.0% as described in claim 3. And

The invention according to claim 4 is based on the invention according to claim 2 or 3, and is characterized in that the thickness of the cam piece in the axial direction is 5 mm or more.

Further, the invention according to claim 5 is based on the invention according to any one of claims 2 to 4, and the annular shape is raised to a position corresponding to the inside of the base circle on at least one side surface of the cam piece. It is characterized in that the convex portion is formed by warm forming.

Therefore, in the invention described in claim 4,
This means that a minimum thickness of 5 mm is sufficient for the cam piece, and as a result, it has an advantageous effect in reducing the weight of the engine, reducing friction, and improving the degree of freedom in designing the engine, as well as the manufacturing cost of the cam piece itself. Can also contribute to the reduction of That is, a cam piece used for an automobile engine is required to have its thickness dimension (thickness in the axial direction of the cam piece itself) as small as possible in order to reduce the weight of the engine itself and reduce friction. Has been. On the other hand, as the thickness of the cam piece is made smaller, the internal stress generated when the shaft is expanded is increased, which is disadvantageous in terms of strength, but due to the effect of improving the tensile strength as described above,
It has been confirmed that if the thickness of the cam piece can be at least 5 mm, the tensile strength of the material itself exceeds the internal stress when the shaft is expanded and cracks can be prevented when the shaft is expanded.

According to the fifth aspect of the present invention, the increase in the weight of the cam piece and the increase in the sliding area with the mating valve lifter are suppressed, and the inner peripheral area of the cam piece is increased, whereby the diameter of the cam piece is relatively increased. It becomes effective in reducing the stress generated during processing. That is, by forming the local annular convex portion, it is possible to suppress the increase in weight of the cam piece as compared with the case where the thickness dimension of the entire cam piece is increased, and of course, friction between the sliding surface of the valve lifter on the other side is suppressed. Also does not increase. Further, since the annular convex portion is formed at the same time during warm forming, it is not necessary to cut out by mechanical processing,
For example, when the thickness of the cam piece is 12.5 mm, it was confirmed that the stress generated during the diameter expansion can be reduced by about 5% simply by forming the annular protrusion having a height of about 0.5 mm.

[0023]

According to the invention as set forth in claim 1, the mechanical strength such as tensile strength is improved by subjecting the warm-formed cam piece to the heat treatment, and the crack of the cam piece during the shaft diameter expansion processing is surely performed. It is possible to prevent the occurrence of cracks. Particularly, when the quenching and the tempering are performed as the heat treatment as in the second aspect of the invention, there is an advantage that the effect of preventing the cam piece from cracking becomes more remarkable.

According to the invention described in claim 3, F
Since the content of Cu and C in the sintered material containing e as a main component is defined to be a specific value, in addition to the effect similar to that of the invention described in claim 2, wear resistance required for the cam piece It is also effective in satisfying sexual performance.

According to the invention described in claim 4, since the minimum thickness dimension of the cam piece is specified to a specific value, in addition to the same effect as the invention described in claim 2 or 3, There are advantages that it can contribute to weight reduction, reduction of friction, and expansion of design freedom when designing an engine.

Further, according to the invention of claim 5, since the annular convex portion is formed on the side surface of the cam piece during the warm forming, the weight increase of the cam piece and the sliding area of the mating valve lifter are reduced. There is an advantage that the stress generated on the cam piece side at the time of the diameter expansion processing can be reduced while suppressing the increase.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows details of a cam piece made of a sintered compact as a preferred embodiment of a cam shaft according to the present invention.

The cam piece 1 is compression-molded into a shape including a predetermined cam profile by a warm molding method using a Fe-Cu-C-based metal powder for sintering, and after sintering the green compact, Further, it is formed by performing heat treatment such as carburizing and quenching and tempering. At the time of compression molding, a shaft hole 3 with a concave groove 3a is formed at the same time for inserting the hollow shaft 2 on the opposite side, and both sides of the cam piece 1 correspond to the inside of the base circle. The ring-shaped convex portion 4 having a minute height is simultaneously formed at the position.

The warm compaction method is a method of compacting a green compact by compressing and compacting both the metal powder for sintering and the mold at about 130 ° C., as shown in FIG. It is characterized in that the density of the green compact can be further increased compared to the conventional compression molding method at room temperature. Here, the compact is compacted to have a density of 7.1 to 7.4 g / cm ³ .

Further, Fe--C used in the warm forming method described above.
The composition of the u-C-based metal powder for sintering contains Cu of 1.5 to 4% by weight and C of 0.7 to 1.0% by weight, and the balance is Fe and inevitable impurities. To use. As described above, the Cu content is not preferably too low or too high, and is more preferably 2.0 to 3.0% by weight.

The sintering treatment subsequent to the above compression molding is carried out under a temperature condition of 1120 ° C. in a butane metamorphic gas atmosphere, and the heat treatment after sintering is carried out after carburizing treatment at a carburizing temperature of 900 ° C. Oil quenching treatment is performed at 60 ° C., and further tempering treatment is performed at 180 ° C.

The tensile strength of the cam piece 1 after heat treatment is increased in proportion to its density, and as is clear from FIG. 3, it reaches 1030 MPa or more when the density is 7.1 g / cm ³ .

The cam piece 1 completed by the above heat treatment is externally inserted into a hollow shaft (for example, made of steel pipe) 2 on the opposite side to be positioned relative to the other, and then a predetermined amount is provided inside the shaft 2. By press-fitting the mandrel and expanding or expanding the diameter of the mandrel at a diameter expansion ratio of about 3.3%, the both are fixed in a separated manner. The term "diameter expansion ratio" here means that the diameter of the shaft 2 after the diameter expansion is A,
When the diameter of the shaft 2 before the diameter expansion is B, (A-
B) / B.

As Example 1, 3.0 wt% Cu and C
Of Fe-Cu-C based metal powder containing 0.8% by weight of Fe and the balance being Fe and unavoidable impurities, and warm compacted to a density of 7.1 g / cm ^3. The temperature of the powder is 1120 ° C in a butane metamorphic gas atmosphere.
At a carburizing temperature of 9 as a heat treatment after sintering.
After performing a carburizing treatment at 00 ° C., an oil quenching treatment was performed at 60 ° C., and a tempering treatment was further performed at 180 ° C. to manufacture a cam piece.

In Example 2, the composition of the Fe—Cu—C based metal powder for sintering was set to Cu: 3.0% by weight, C: 0.8% by weight, Fe and inevitable impurities: balance. Then, a cam piece was manufactured under the same conditions as in Example 1 except that warm molding was performed so that the density was 7.2 g / cm ³ .

As Comparative Example 1, the density during warm forming was 6.
The green compact was compression-molded to 7 g / cm ^3, and a cam piece was manufactured under the same conditions as in Example 1 except for the above.

In Comparative Example 2, the composition of the Fe-Cu-C based metal powder for sintering was Cu: 3.0% by weight, C: 0.5% by weight, Fe and unavoidable impurities: balance. A cam piece was manufactured under the same conditions as in Example 1 except for the above.

Table 1 summarizes the conditions and the like of Examples 1 and 2 and Comparative Examples 1 and 2. The size of the manufactured cam piece 1 is, as shown in FIG. 1, the thickness dimension of the cam piece 1 (thickness dimension in the axial direction) W = 12.5 m
m, diameter D of shaft hole 3 = 18.2 mm, annular protrusion 4
Maximum diameter M = 34 mm, height of the annular convex portion C = 0.5
mm, and the wall thickness t of the base circle portion was t = 5.65 mm. Further, the specific wear amount is evaluated by a pin-on-disk tester and is expressed as a ratio when the wear amount in Example 1 is 1.

[0039]

[Table 1]

[0040]

[Table 2]

As is clear from Table 1, both Examples 1 and 2 are small in specific wear amount and excellent in tensile strength, and it is understood that the required performance is satisfied. On the other hand, in Comparative Example 1, since the density during compression molding is low, sufficient tensile strength cannot be obtained after sintering and heat treatment. Further, in Comparative Example 2, since the content of C is small, the specific wear amount is as large as 1.7, and there is a problem in wear resistance.

Table 2 shows the internal stress generated in the cam piece 1 when the cam piece 1 corresponding to the first embodiment is joined by expanding the diameter of the shaft 2 with the mandrel. In the third to fifth embodiments, the cam piece 2 is shown. 7 shows the internal stress when only the thickness dimension W of is changed. As is clear from Example 1, if the internally generated stress is smaller than the tensile strength, the cam piece 1 will not crack when the shaft diameter is expanded. Further, even when the thickness dimension W of the cam piece 1 is smaller than that of the first embodiment as in Examples 3 to 5, the tensile strength of the material itself exceeds the internally generated stress, even if the thickness dimension W of the cam piece 1 is 5 mm. Even when the shaft diameter is expanded, it can be seen that no crack occurs.

Further, as shown in FIG. 1, the thickness dimension W = 1
0.5mm height on both sides of 2.5mm cam piece 1
Since the annular convex portion 4 is formed, the internally generated stress at the time of diameter expansion is reduced by enlarging the pressure receiving area, and as described above, the annular convex portion 4 having a height of 0.5 mm has a size of about 5 mm. % Stress reduction effect was confirmed. However, if the height dimension C of the annular convex portion 4 is unnecessarily increased, the step difference of the annular convex portion 4 becomes large, so that non-uniformity in density with other parts does not occur during warm molding (compression molding). Like
Since there is a risk of complicating the apparatus and lowering productivity, such as dividing the punch of the die and controlling the pressure applied to each punch equally, it is preferable to limit the thickness to about 20% of the thickness W at the maximum. desirable.

[Brief description of drawings]

1A and 1B are views showing an embodiment of an assembled camshaft according to the present invention, in which FIG. 1A is a front view thereof, and FIG.

FIG. 2 is an explanatory diagram showing a relationship between a molding load and a density during compression molding of a sintered compact.

FIG. 3 is an explanatory view showing the relationship between the density and the tensile strength of a sintered compact after sintering.

[Explanation of symbols]

1 ... Cam piece 2 ... Shaft 4 ... annular protrusion

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01L 1/04 F01L 1/04 H (72) Inventor Makoto Iwakiri 520 Minorita, Matsudo City, Chiba Hitachi Powdered Metals Stock Company (72) Inventor Takao Mitsuno 520 Minoridai, Matsudo City, Chiba Prefecture Hitachi Powdered Metals Co., Ltd. (72) Inventor Takayuki Hirao 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Kimio Nishimura Nissan Motor Co., Ltd. 2 Takaramachi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Koji Itakura Koji Itakura 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa F-Term, Nissan Motor Co., Ltd. (reference) 3G016 AA19 BA34 CA04 EA03 EA09 EA10 EA24 FA08 GA05 3J030 EA01 EB01

Claims (5)

[Claims] 1. A prefabricated camshaft in which a hollow shaft is inserted into a cam piece and then the shaft is expanded so as to be fixedly fixed to each other, wherein the cam piece has a density of 7.1. ~ 7.4g / cm
^A prefabricated camshaft, characterized in that it is formed of an iron-based sintered compact that is warm-formed within the range of ³ . 2. The cam piece has a density of 7.1 to 1.
The prefabricated cam according to claim 1, which is formed of an iron-based sintered compact that has been warm-formed to a range of 7.4 g / cm ³ and that has been subjected to heat treatments such as quenching and tempering. shaft. 3. The iron-based sintered compact for forming the cam piece contains Cu: 1.5-4 wt% and C: 0.7-1.0 wt%, respectively, as the composition, and the balance. Is an Fe and unavoidable impurities, The prefabricated camshaft according to claim 2, wherein 4. The thickness dimension of the cam piece in the axial direction is 5 mm or more.
Assembled camshaft according to. 5. A raised annular protrusion is formed at a position corresponding to the inside of the base circle on at least one side surface of the cam piece by warm forming. Assembled camshaft described.