JP2007064129A - Piston for internal combustion engine and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To strengthen a ring groove 13 and make finer the finish required. <P>SOLUTION: A friction stir area 18 subjected to friction stir processing is formed over whole circumference of a piston by relatively moving the piston 10 and a rotary tool 11 in a circumference direction while rotating the same around an axis under a condition where a pin 13 of the rotary tool 11 is inserted in an outer circumference part of the aluminum alloy piston 10 for an internal combustion engine. The ring groove 15 is formed in the friction stir area 18. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston for an internal combustion engine, and more particularly to a technique for forming a ring groove using a friction stirring process.

  As is well known, a ring groove in which a piston ring is mounted is formed on the outer periphery of a piston that reciprocates in a cylinder of an internal combustion engine. In order to improve the wear resistance, the surface of the ring groove has been subjected to alumite treatment as disclosed in Patent Document 1, for example.

By the way, in recent years, a technique for applying a friction stir processing to the surface of a member to be processed by applying a friction stir welding technique has attracted attention (see Patent Document 2). In this friction stir processing, the structure of the surface is refined by relatively moving the rotary tool while rotating it around the axis in a state where the rotary tool is inserted into the member to be processed.
Japanese Utility Model Publication No. 6-14620 JP 2004-225591 A

  However, if the ring groove is anodized on a light alloy piston such as a cast aluminum alloy with coarse crystal grains as in the former, the ring groove surface has a large roughness and a sufficient seal. It was difficult to ensure the property. Moreover, it is difficult to ensure sufficient wear resistance simply by subjecting a piston made of cast aluminum alloy having a relatively low hardness to an alumite treatment, and further improvement has been desired.

  In the latter friction agitation processing, when the rotary tool is pulled out from the member to be processed, there is a specific problem that a hole from which the pin is pulled out remains.

  The present invention provides a novel piston for an internal combustion engine in which a ring groove is formed using friction stirring and a method for manufacturing the same. That is, the present invention allows the piston and the rotary tool to move relative to each other in the circumferential direction while rotating around the axis with the pin of the rotary tool inserted into the outer peripheral portion of the light alloy piston for the internal combustion engine. The friction stir zone subjected to friction stir is formed over the entire circumference of the piston, and a ring groove is formed in this friction stir zone.

  In this way, by subjecting the part where the ring groove is formed in the outer periphery of the piston in advance to friction stir processing, the friction stir zone is strengthened by dynamic recrystallization refinement and surface oxide film dispersion. The wear resistance of the ring groove formed in the region can be improved. Thereby, the land width of the piston can be reduced, and the piston can be reduced in size, weight, and exhaust can be improved.

  In particular, when the piston is made of an aluminum alloy, coarse silicon particles, intermetallic compounds, and an aluminum phase are mechanically refined by the friction stir processing. Therefore, when the alumite treatment is applied to the ring groove after the friction stirring treatment, the surface roughness of the alumite coating is smaller than when the ring groove is not subjected to the friction stirring treatment. Smaller and better sealing performance between ring groove and piston ring. Alternatively, for example, an alumite treatment can be omitted for a relatively small piston for an engine, and accordingly, the number of work steps and the work time can be shortened.

  According to the present invention, since the friction stir processing is performed in advance on the portion where the ring groove is formed, the strength and wear resistance of the ring groove can be remarkably improved. Therefore, for example, the land width can be reduced to reduce the size and weight of the piston, and the sealing performance with the piston ring can be improved to improve the exhaust performance. Moreover, the pin hole, which is a problem specific to the surface treatment by friction stirring, can be eliminated at the same time when the ring groove is formed.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. A piston (base material) 10 as a member to be processed is fitted to a cylinder of an internal combustion engine so as to be movable up and down, and is cast by an aluminum alloy as a light alloy. As is well known, a ring groove 15 having a channel shape, that is, a substantially U-shaped cross section is formed on the outer periphery of the piston 10, and a piston for securing an oil film while closing a gap between the ring groove 15 and the cylinder. A ring is attached. 1 and 2, the piston 10 is shown in a base material state before the ring groove 15 (see FIG. 3) is processed.

  As shown also in FIG. 2, in the rotary tool 11 as a friction stir tool, a pin 13 with a small diameter protrudes from one end of a cylindrical (column) -shaped base portion 12 with a large diameter. A shoulder 14 that is a surface perpendicular or acute to the pin 13 is formed on one end side of the base 12 from which the pin 13 protrudes. An external thread 13A is preferably formed on the outer periphery of the pin 13 so that the pin 13 can enter the piston base material 10 satisfactorily.

  As shown in FIGS. 1A and 1B, the drive device 16 drives the base 12 and the pin 13 of the rotary tool 11 toward the piston base material 10 while rotating the shaft 12 around the axis. Push into the ring groove machining position on the outer periphery. Accordingly, the pins 13 are pushed into the piston base material 10 in such a manner that the shoulder 14 presses the surface of the piston base material 10. At this time, as shown in FIG. 3, in the friction stirrer region 18 having a substantially conical and bowl-shaped cross section around the pin 13, frictional heat generated between the pin 13 and the shoulder 14 and the material of the piston base material 10 causes The temperature of the material rises, the yield point drops, and the material is mechanically agitated by the rotating pin 13 inserted in the material, and a strong strain is applied to the material.

  Then, as shown in FIGS. 1B and 1C, while rotating the rotary tool 11 around the axis at a constant rotational speed, the piston base material 10 and the rotary tool 11 are connected to the ring groove center line (position) 15A. Along the circumferential direction Y1 at a constant speed and a constant load. At this time, the rotary tool 11 may be moved by the driving device 16 or the piston base material 10 may be driven. By this stirring movement, in the friction stirring region 18 in the vicinity of the pin 13 after the rotary tool 11 has passed, the structure of the material is controlled to fine recrystallized grains, and the strength can be increased. The friction stir zone 18 is also strengthened by breaking and dispersing the hard oxide film that has been generated on the casting surface by stirring. Further, in the friction stir zone 18, a cavity called “su” generated at the time of casting by friction stirring can be eliminated, and such casting defects can be eliminated.

  When the rotary tool 11 makes one round of the outer periphery of the piston base material 10 in the circumferential direction Y1 along the ring groove center line 15A in this way, the rotary tool 11 is pulled out from the piston base material 10. At this time, as shown in FIG. 3, a pin hole 17 corresponding to the size of the pin 13 remains in the piston base material 10 at a portion where the pin 13 is removed.

  Next, the ring groove 15 is cut into the piston base material 10 after the friction stirring process. Here, as shown in FIG. 3, the diameter D1 of the pin 13 is set to be equal to or smaller than the groove width D2 of the ring groove 15, and the height dimension H1 of the pin 13 is equal to or smaller than the depth dimension H2 of the ring groove 15. Is set. In this way, the pin hole 17 is formed in the portion cut by the ring groove 15, and the pin hole 17 disappears by cutting the ring groove 15. do not have to.

  As described above, according to the present embodiment, since the friction stir processing is performed in advance on the portion where the ring groove 15 is formed, the strength and wear resistance of the ring groove 15 are remarkably improved. For this reason, for example, the land width can be reduced to reduce the size and weight of the piston, and the exhaust HC can be reduced. Moreover, since the pin hole 17 which is a problem specific to the surface treatment by friction stirring is eliminated at the same time as the ring groove 15 is cut, an operation such as filling the pin hole 17 later is not necessary.

  Preferably, a well-known alumite treatment is performed on the ring groove 15. The aluminum alloy, which is a piston material, is composed of coarse silicon particles, an intermetallic compound, and an aluminum phase as cast, and a hard anodized film is formed only on this aluminum phase, while other large silicon particles and intermetallics are formed. It is not produced in compounds. Therefore, if alumite treatment is applied to the ring groove of the piston material that has not been subjected to frictional stirring treatment, it becomes a large anodized anodized film with one pitch as the distribution interval of silicon particles and intermetallic compounds, and the ring groove The surface roughness increases, the sealing performance with the piston ring decreases, and the oil consumption increases and the blowby gas flow rate increases.

  In the present embodiment, since the frictional stirring process is applied to the portion where the ring groove 15 is cut, the aluminum particles of the aluminum alloy, the intermetallic compound, and the aluminum phase are refined and stirred, and the anodized coating formed there The pitch of the unevenness becomes smaller. Accordingly, the surface roughness of the ring groove 15 is sufficiently reduced, the sealing performance between the piston ring and the ring groove 15 is improved, and the oil consumption and the blow-by gas flow rate can be sufficiently reduced.

Explanatory drawing which shows the procedure of the friction stirring which concerns on one Example of this invention. The cross-sectional view which shows the principal part of the rotary tool of the said Example. The cross-section corresponding view which shows the vicinity of the ring groove of the said Example.

Explanation of symbols

10 ... Piston (base material)
11 ... Rotary tool 13 ... Pin 14 ... Shoulder 15 ... Ring groove 17 ... Pin hole 18 ... Friction stir zone

Claims (4)

Friction is agitated by moving the piston and the rotary tool relative to each other in the circumferential direction while rotating around the axis with the pin of the rotary tool inserted into the outer periphery of a light alloy piston for an internal combustion engine. A stirring area is formed over the entire circumference of the piston,
A method of manufacturing a piston for an internal combustion engine, wherein a ring groove is formed in the friction stir zone.   2. A piston for an internal combustion engine according to claim 1, wherein a diameter of the pin is set shorter than a groove width of the ring groove, and a length of the pin is set shorter than a depth of the ring groove. Manufacturing method.   The method for manufacturing a piston of an internal combustion engine according to claim 1 or 2, wherein the surface of the ring groove is alumite-treated. A light alloy piston used in an internal combustion engine,
A friction stir zone is formed over the entire circumference of the piston by a friction stir process that rotates while rotating around the axis with the pin of the rotary tool inserted in the outer periphery of the piston, and a ring groove is formed in this friction stir zone A piston for an internal combustion engine characterized by the above.

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