Patent Application
20110158842
1. Technical Field
The present invention relates to processes for manufacturing machine components such as carriers for a planetary gear system that is included in an automatic transmission of an automobile (hereinafter called a “planetary carrier”) by a powdered metallurgical method. Specifically, the present invention relates to a process for manufacturing composite sintered machine components in which a compact (an inner member) having plural pillars and another compact (an outer member) having holes corresponding to the pillars are tightly fitted and are sintered so as to bond each other.
2. Background Art
Although planetary carriers differ in design according to the type of transmission, they usually comprise a cylindrical drum, flanges formed at both ends or at the middle of the drum, and a center shaft hole into which a shaft of a transmission is inserted. Generally, the drum is formed with plural openings for holding planetary gears (not shown in the figure).
Thus, since a planetary carrier has such a complicated structure, if it is mass-produced by machining process such as cutting, great number of processing steps are required, whereby there are disadvantages in cost and accuracy of shape and size. Therefore, planetary carriers are usually manufactured by a powdered metallurgical method that is suitable for manufacturing products uniformly in large quantities; however, in the case of planetary carriers having openings forming undercuts, which are provided on a drum, it is difficult to form them unitarily in a die.
As a method developed to solve these problems, a required shape is divided into several portions, and after the portions are individually formed and sintered, they are combined to form the required shape. For convenience of explanation, a planetary carrier will be described based on a schematic shape shown in
Specifically, as shown in
When the disk-shaped member 30 and the body member 40 are brazed, since a liquid phase is generated at the bonding surface, the centers thereof may not be aligned (the axes thereof may not be aligned), and the phases thereof may be misaligned (they may be misaligned in circumferential direction), whereby the accuracy of the products tends to be decreased. Moreover, the bonding strength of the disk-shaped member 30 and the body member 40 mainly depends on the strength of the brazing metal, whereby it is difficult to obtain the required level of strength.
Methods of improvement have been suggested to deal with the above problems and are disclosed in Japanese Patents Nos. 1427539 corresponding to U.S. Pat. No. 4,503,009 (patent document 1), 1781330 (patent document 2), and 3495264 corresponding to U.S. Pat. No. 6,120,727, GB. Patent No. 2343682, and DE. Patent No. 19944522 (patent document 3). The methods of improvement employ a technique in which a hole provided in one compact is tightly fitted with a pillar portion provided at another compact, and these are sintered so as to bond together. That is, as shown in
In order to produce the above-described condition in which the amount of thermal expansion of the inner member (body member 40) is greater than the amount of thermal expansion of the outer member (disk-shaped member 30) in the high temperature range during sintering, in the patent document 1, carbon is included in an inner member as an essential ingredient at an amount greater than that of an outer member by at least 0.2 mass %. In the patent document 2, an iron powder forms an outer member, and 5 to 10% of the iron powder is made from a carbonyl iron powder. In the patent document 3, a zinc stearate is used as a powdered lubricant only in an inner member, and it is sintered in a carburizing atmosphere so that the amount of the thermal expansion of the inner member is increased.
According to the methods, the above-mentioned misalignments of the centers and the phases do not occur, but the bonding surfaces of the inner member and the outer member tend to be insufficiently bonded each other, and the required level of the bonding strength may not be obtained. The reason for this is described hereinafter. That is, in the case of the above method in which the pillar (which approaches the inner side by tightly fitting) is tightly fitted to the hole (which approaches the outer side by tightly fitting) of a compact, if the contacting surface thereof is a tightly fitted cylindrical surface, and the amount of thermal expansion of the pillar side (inner side) is grater than that of the hole side (outer side), the entire surface of the contacting surface is tightly contacted, whereby the pillar and the hole are bonded by diffusion. On the other hand, in the case of the planetary carrier shown in
Furthermore, a method is disclosed in Japanese Patent No. 3833502 (patent document 4). As shown in
The technique disclosed in the patent document 4 is an elaboration of the technique disclosed in the patent documents 1 to 3, and it is based on a condition in which the amount of thermal expansion of the body member 40 is greater than that of the disk-shaped member 30. In this case, not only the pillars 42, but also the entire body member 40 can expand, and even when the expansion of the pillars 42 is restricted by the holes 32 of the disk-shaped member 30, a deflection may occur because the remaining portion expands, and the degree of parallelization of the disk-shaped member 30 and the body member 40 is thereby lost.
Since the planetary carrier is formed by arranging flanges at both ends of the pillars, if the degree of parallelization is lost in this way, the shape is difficult to correct by applying pressure again. Therefore, deflection that occurred during sintering and bonding will be a disadvantage in manufacturing. Moreover, the disk-shaped member 30 has a thin portion 38 between an outer periphery 37 and the hole 32 of the disk-shaped member 30 shown in
An object of the present invention is to provide a process for manufacturing composite sintered machine components such as planetary carriers. In the composite sintered machine components, when a compact of an outer member having plural pillars and a compact of an inner member having hole portions corresponding to the pillars of the compact of the outer member are tightly fitted and sintered so as to bond each other, the outer member and the inner member can be bonded with a sufficient bonding strength without utilizing a difference in thermal expansion thereof in a high temperature range during sintering, and deflections of the outer member and the inner member, and deformations and fractures of thin portion of the outer member can be avoided.
The present invention provides a process for manufacturing composite sintered machine components. The composite sintered machine component has an approximately cylindrical inner member having pillars arranged in a circumferential direction at equal intervals and a center shaft hole surrounded by the pillars, and it also has an approximately disk-shaped outer member having holes corresponding to the pillars of the inner member and a center shaft hole which corresponds to the center shaft hole of the inner member and is connected to the holes. The process comprises compacting the inner member and the outer member individually with an iron-based alloy powder or an iron-based mixed powder so as to obtain compacts of the inner member and the outer member, tightly fitting the pillars of the inner member into the holes of the outer member, and sintering the inner member and the outer member and maintaining the above condition so as to bond them together. A circumferential side surface facing the circumferential direction of the pillars of the inner member and a circumferential side surface facing the circumferential direction of the hole of the outer member are interference fitted at 0 to 0.03 mm of interference. A radial side surface facing the radial direction of the pillars of the inner member and a radial side surface facing the radial direction of the hole of the outer member are interference fitted at not more than 0.01 mm of the interference or are through fitted (interference is minus).
In the present invention, specifically, the following may be mentioned as preferred embodiments.
The radial side surface of the pillar of the inner member and the radial side surface of the convex portion of the outer member are tightly fitted at 0 mm of the interference or are through fitted (interference is minus). The circumferential side surface of the pillars of the inner member is formed in a range −30 to 30° with respect to a radial line extending in a radial direction. Moreover, at least one concave portion is formed on the radial side surface of the pillars of the inner member, a convex portion corresponding to the concave portion is formed on the hole of the outer member, and each circumferential side surface of the concave portion and the convex portion facing each other is interference fitted at 0 to 0.03 mm of interference. Furthermore, the inner compact and the outer compact have the same compositions.
According to the present invention, the circumferential side surface of the pillars of the inner member and the circumferential side surface of the hole of the outer member are interference fitted at 0 to 0.03 mm of the interference, and a sufficient bonding strength is thereby obtained. The radial side surface of the pillars and the radial side surface of the hole are interference fitted at not more than 0.01 mm of the interference or are through fitted (interference is minus), whereby a deformation and a fracture of thin portion of the outer member can be avoided. Moreover, the inner member and the outer member can be made from raw powders having the same composition, whereby a step for preparing different raw powders for the inner member and the outer member can be omitted, and an error such as an inappropriate composing of raw powders can be avoided.
An embodiment of the present invention will be described with reference to the drawings hereinafter.
The embodiment shows a process in which a structure shown in
In the present invention, the compositions of the disk-shaped member 30 and the body member 40 may be selected to differ from each other in amount of thermal expansion in a high temperature range (diffusion temperature range of additive ingredients) during sintering, as disclosed in the patent document 1 to 3. In the present invention, the compositions of the disk-shaped member 30 and the body member 40 are preferable to have compositions in which amounts of thermal expansion are equal. That is, instead of preparing a zinc stearate as a powdered lubricant and another powdered lubricant, and arranging raw powders for the disk-shaped member 30 and the body member 40 respectively as disclosed in the patent document 3, raw powders having the same compositions, which include a powder lubricant, can be used.
Sintering the disk-shaped member 30 and the body member 40 by using raw powders having the same composition produces thermal expansions of the disk-shaped member 30 and the body member 40 respectively. In the embodiment, the holes 32 are press fitted with the pillars 42, whereby the fitting clearance between the disk-shaped member 30 and the body member 40 is not changed in high temperature range during sintering, and diffusion bonding is performed while maintaining a condition in which the boundary of the disk-shaped member 30 and the body member 40 are tightly contacted. When the fitting clearance of the disk-shaped member 30 and the body member 40 may be through fitting (the interference is less than 0 mm), they are insufficiently contacted, and sufficient bonding strength cannot be obtained. On the other hand, when the interference is more than 0.03 mm, the compacts may be broken during press fitting. Therefore, the interference is preferably set to be 0 to 0.03 mm.
When the circumferential side surface 45 of the pillars 42 and the corresponding circumferential side surface 35 of the holes 32 are coincided with the radial line extending in the radial direction, that is, when a center point of plural pillars 42 that are radially arrayed is formed on the extended line of the circumferential side surfaces 45 and 35, a stress occurring during press fitting goes to the radial direction, and the disk-shaped member 30 and the body member 40 are press fitted in a condition in which stiffness of the disk-shaped member 30 is the largest. In this case, most of the stress occurring during press fitting is spend for tightly fitting the disk-shaped member 30 and the body member 40, whereby they are strongly tightly fitted even when the fitting clearance is small. Accordingly, the disk-shaped member 30 and the body member 40 are press fitted in a condition in which the circumferential side surface 45 of the pillars 42 and corresponding circumferential side surface 35 of the holes 32 are coincided with the radial line extending in the radial direction, and the fitting clearance can thereby be minimized.
On the other hand, even when the circumferential side surface 45 of the pillars 42 and the corresponding circumferential side surface 35 of the holes 32 are coincided with the radial line extending in the radial direction, if they are largely inclined with respect to the radial line, the stiffness of the disk-shaped member 30 is decreased at press fitting, whereby the disk-shaped member 30 and the body member 40 are difficult to be brought into sufficient contact. Moreover, in this case, deformation of the disk-shaped member 30 at press fitting is large, and it tends to break. Therefore, the circumferential side surface 45 of the pillars 42 and corresponding circumferential side surface 35 of the hole 32 are required to be in a range −30 to 30° with respect to the radial line (0°). Thus, the circumferential side surface 45 of the pillars 42 and the circumferential side surface 35 of the holes 32 are bonded in the above range with respect to the radial line, whereby a strength with respect to a torsion in rotational direction of a planetary carrier is highly secured.
As described above, the circumferential side surface 45 of the pillars 42 and the circumferential side surface 35 of the hole 32 are bonded with a sufficient bonding strength, whereby a radial side surface 44 of the outer periphery of the pillars 42 and a radial side surface 34 of the hole 32 are bonded with a sufficient strength that is not strong as in the case of the circumferential side surfaces. Accordingly, in the radial side surface 44 of the pillars 42 and the radial side surface 34 of the holes 32, sizes thereof can be selected primarily for prevention of deformation of a thin portion 38 between an outer periphery 37 and the hole 32 of the disk-shaped member 30. Specifically, the disk-shaped member 30 and the body member 40 are interference fitted at not more than 0.01 mm of the interference or are through fitted (interference is minus). In this case, when the interference is more than 0.01 mm, the thin portion 38 tends to break at press fitting. When the compositions of the disk-shaped member 30 and the body member 40 differ in amount of thermal expansion in a high temperature range during sintering as disclosed in the patent documents 1 to 3, it is preferable that the disk-shaped member 30 and the body member 40 be fitted at 0 mm of interference or be through fitted.
The radial side surface 44 of the pillars 42 and the radial side surface 34 of the hole 32 may not be bonded as strongly as in the case of the circumferential side surfaces, and the bonding strength thereof may be improved by bonding. From this point of view, when raw powders having exactly the same composition are used for the disk-shaped member 30 and the body member 40, as described above, the disk-shaped member 30 and the body member 40 are expanded respectively, whereby they can be bonded by preventing deformation of the thin portion 38 even when they are interference fitted at not more than 0.01 mm of interference.
In the manufacturing process of the embodiment, even when the same raw powders are used for the disk-shaped member 30 and the body member 40, the circumferential side surface 45 of the pillars 42 and the corresponding circumferential side surface 35 of the holes 32 can be bonded with sufficient bonding strength, and the radial side surface 44 of the pillars 42 and corresponding radial side surface 34 of the holes 32 can be bonded, preventing deformation of the thin portion 38 between the outer periphery 37 and the hole 32 of the disk-shaped member 30. Moreover, raw powders having the same composition are used for the disk-shaped member 30 and the body member 40, whereby a step for preparing different raw powders for the inner member and the outer member can be omitted, and an error such as an inappropriate composing of raw powders can be avoided.
In order to further improve the bonding strength, the length of the bonding surface, that is, the circumferential side surfaces of the holes 32 and the pillars 42, may be elongated. In this case, for example, as shown in
Compacts of a body member having the same structure as the body member 40 and a compact of a disk-shaped member having the same structure as the disk-shaped member 30 as shown in
When the disk-shaped member 30 and the body member 40 were formed as compacts, a mixed powder in which 0.7% of zinc stearate was added as a powdered lubricant to a powder comprising, by weight, 1.5% of copper powder, 0.7% of graphite, and the balance of iron powder, was compression molded so as to have a compact density of 6.7 g/cm3. In this case, an interference of the circumferential side surface 45 of the pillars 42 and the circumferential side surface 35 of the holes 32 was modified according to the interference shown in Table 1, and plural (sample numbers 01 to 09) compacts were formed. The space between the radial side surface 44 of the pillar 42 and the radial side surface 34 of the hole 32 was set to be 0 mm. Then, the compacts were fitted by press fitting the hole 32 of the disk-shaped member 30 with the pillars 42 of the body member 40, and this was sintered at 1130° C. for 40 minutes in a carburizing denatured butane gas atmosphere so as to bond each other. After the degree of parallelization of the sintered components was investigated, a breaking test was performed in such a way that the body member 40 was held on a mount by a material test machine, and the disk-shaped member 30 was loaded. The bonding strength measured by the test and the degree of parallelization are also shown in Table 1. It should be noted that value (mm) of the degree of parallelization was obtained in such a way that the disk-shaped member 30 of the sintered component was placed with its face down on a flat surface, the distribution of heights of the top surface, which was the bottom surface of the body member 40, was measured, and the lowest value was subtracted from highest value of the height. The lower the value, the greater the degree of parallelization.
According to the test results shown in Table 1, in the case of the sample number 01 in which the interference was not more than 0 mm (through fit at 0.05 mm of the space), since the interference is small, the bonding was insufficient, and the bonding strength was low. On the other hand, in the case of the sample number 02 in which the interference was 0 mm, the bonding was sufficient, and the bonding strength was improved. According to the increase of the interference, the bonding strength was improved, but the bonding strength exhibited an approximately constant level when the interference was 0.02 mm or higher. In the case of the sample number 09 in which the interference was more than 0.03 mm, fracturing occurred during press fitting. Since the disk-shaped member and the body member were made from the same raw powder and they were fitted at 0 mm of interference, the degree of parallelization of each sample was good.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-305070 | Nov 2006 | JP | national |
This is a Continuation of application Ser. No. 11/979,323 filed Nov. 1, 2007, which claims foreign priority to Japanese Patent Application No. 2006-305070, filed Nov. 10, 2006. The disclosure of the prior applications is hereby incorporated by reference herein in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11979323 | Nov 2007 | US |
| Child | 13045910 | US |
