This application is based upon and claims the benefit of priority from Japanese patent application No. 2014-219541, filed on Oct. 28, 2014, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention The present invention relates to a method for manufacturing a cylinder block, and in particular to a method for manufacturing a cylinder block of an engine for a vehicle.
2. Description of Related Art
Japanese Unexamined Patent Application Publication No. 2012-179629 discloses a technique used in a method for manufacturing a die-cast article (i.e., a cylinder block) including a semicircular support surface on which a crankshaft is rotatably supported, in which a pressure is locally applied to molten metal located at or near the summit of the semicircular support surface by using a pressure pin. A pressure is applied to molten metal located in an area directly ahead of the pressure pin in its longitudinal direction by that pressure pin. As a result, the formation of blowholes in that area can be reduced.
However, the technique disclosed in Japanese Unexamined Patent Application Publication No. 2012-179629 cannot sufficiently reduce the occurrences of blowholes in areas outside the area directly ahead of the pressure pin in its longitudinal direction. It should be noted that an oil flow channel extends from a main gallery toward the semicircular support surface so that a lubricant can be supplied to the crankshaft. For example, if this oil flow channel is connected to a bolt hole for attaching a crank cap due to the formation of a blowhole, an oil leak occurs, thus making the die-cast article defective. That is, there has been a problem that the yield of products deteriorates due to the formation of blowholes.
The present invention has been made in view of the above-described problem and an object thereof is to reduce the formation of blowholes in a cylinder block better than the related art does and thereby to improve the yield of products.
A first exemplary aspect of the present invention is a method for manufacturing a cylinder block including a semicircular bearing section that rotatably supports a crankshaft, the method including:
pressure-injecting molten metal into a cavity formed inside a metal mold; and
sliding a pressure pin disposed in the metal mold after the pressure-injecting of the molten metal and thereby applying a pressure to the molten metal injected in the cavity, in which
in the applying of the pressure to the molten metal, the pressure pin is slid toward an area where the bearing section is formed, a tip of the pressure pin protruding in an arc shape so as to conform to a shape of the bearing section.
In the method for manufacturing a cylinder block according to the above-described aspect of the present invention, the pressure pin, whose tip protrudes in an arc shape so as to conform to the shape of the bearing section, is slid toward the area where the bearing section is formed in the step for applying a pressure to the molten metal. Therefore, the pressure applied to the molten metal is not only applied to the area located directly ahead of the pressure pin in its longitudinal direction but also applied radially from the center of the tip of the pressure pin. As a result, the formation of blowholes can be reduced in the entire area inside the cylinder block, thus leading to an improvement in the yield of products.
The tip of the pressure pin is preferably formed in a semicircular shape. This structure can reduce the machining margin of the bearing section.
Further, the tip of the pressure pin is preferably formed in an arc shape shorter than a semicircle, and hence, in the pressure-injecting of the molten metal, no recess is formed in the boundary between the metal mold and the pressure pin. This structure can reduce deformations and cracking on the surface of the bearing section caused by microscopic solidification pieces.
Further, notches are formed on both edges of the tip of the pressure pin, which are in contact with the metal mold, so that the boundary between the metal mold and the pressure pin becomes flat without any difference in level formed therein in the pressure-injecting of the molten metal. This structure can reduce deformations and cracking on the surface of the bearing section caused by pulled-in solidification shells.
According to the present invention, it is possible to reduce the formation of blowholes in a cylinder block better than the related art does and thereby improve the yield of products.
The above and other objects, features and advantages of the present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Specific exemplary embodiments to which the present invention is applied are explained hereinafter in detail with reference to the drawings. However, the present invention is not limited to exemplary embodiments shown below. Further, the following descriptions and the drawings are simplified as appropriate for clarifying the explanation.
Firstly, a cylinder block manufactured by a manufacturing method according to a first exemplary embodiment is explained with reference to
Note that, needless to say, the right-handed xyz-coordinate systems shown in
The cylinder block 1 is a die-cast article made of, for example, an aluminum alloy. As shown in
As shown in
A cylinder head (not shown) is mounted on the top end (end on the positive side on the z-axis) of the cylinder wall 12, i.e., on the so-called “upper deck”. Further, the cylinder bore 11, the piston, and the cylinder head form a combustion chamber. A passage (water jacket) 13 through which a coolant is circulated is formed inside the cylinder wall 12, so that the cylinder section 10 can be cooled to an appropriate temperature.
The skirt section 20 includes skirt walls 21 that form an outer shell of the crank case, and bulkheads 22 that partition the crank case into each cylinder bore 11. As shown in
A semicircular bearing section 23 for rotatably supporting a journal (not shown) of the crankshaft is formed at the center of the bottom end (end on the negative side on the z-axis) of each bulkhead 22. Bolt holes 24 for attaching a crank cap (not shown) are formed on both sides of the bearing section 23.
Further, to enable the journal to be supplied with a lubricant, an oil flow channel 26 extends from a main gallery 25 toward the bearing section 23 inside each bulkhead 22. Note that as shown in
Further, a through hole 27 is formed near the center of each bulkhead 22. The through hole 27 is formed to connect the spaces partitioned by the bulkhead 22 with each other. In this exemplary embodiment, the through hole 27 is formed by using a core pin when the die-cast article is cast. However, needless to say, the through hole 27 may be formed by machining after the casting process.
It should be noted that if the oil flow channel 26 is connected to the bolt hole 24 or the through hole 27 in
Next, a method for manufacturing a cylinder block according to the first exemplary embodiment is explained with reference to
As shown in
Further, as shown in
When molten metal is injected, the pressure pin 33 is positioned in a retreated position as indicated by a chain double-dashed line in
It should be noted that in the related art, a pressure pin whose tip is flat is slid toward an area where a bearing section is formed. In contrast to this, in this exemplary embodiment, the pressure pin 33, whose tip protrudes in an arc shape to conform to the shape of the bearing section 23, is slid toward the area where the bearing section 23 is formed. Therefore, the pressure applied to the molten metal is not only applied to the area located directly ahead of the pressure pin 33 in its longitudinal direction (i.e., the area located on the positive side on the z-axis) but also applied radially from the center of the tip of the pressure pin 33. As a result, the formation of blowholes can be reduced in the entire area inside the bulkhead 22, thus leading to an improvement in the yield of products.
Further, since the tip of the pressure pin 33 protrudes in an arc shape to conform to the shape of the bearing section 23, the withdrawal resistance of the pressure pin 33. Further, the bearing section 23 can be formed in a near net shape. That is, the maching margin (excess metal) of the bearing section 23 can be reduced, meaning that the productivity of this exemplary embodiment is superior to the relate art.
In particular, in the first exemplary embodiment, the width of the pressure pin 33 is roughly equal to the diameter of the semicircular bearing section 23. That is, the tip of the pressure pin 33 is formed in a semicircular shape to conform to the shape of the bearing section 23. Therefore, the maching margin is significantly reduced. In the related art, the pressure pin is moved forward with a sufficient maching margin. Thus, compared to this exemplary embodiment, the related art requires more time in a subsequent machining process. Therefore, the productivity of the related art is inferior to that of this exemplary embodiment.
Further, the width w of the pressure pin 33 according to this exemplary embodiment is larger than that of a pressure pin in the related art. Provided that the amount of the volume change in the pressurization process in this exemplary embodiment is equal to that in the related art, the traveling distance of the pressure pin 33 can be reduced compared to that in the related art. As a result, the withdrawal resistance of the pressure pin 33 can be reduced.
Next, a method for manufacturing a cylinder block according to a second exemplary embodiment is explained with reference to
As shown in
To cope with this problem, in the method for manufacturing a cylinder block according to the second exemplary embodiment, as shown in
This structure can reduce deformations and cracking on the surface of the bearing section 23 caused by microscopic solidification pieces because no recess is formed in the boundary between the movable mold 30 and the pressure pin 33a before the pressurization process. However, since the width w of the pressure pin 33a is reduced, the maching margin could increase. Other configurations are similar to those in the first exemplary embodiment, and therefore their explanations are omitted. Similarly to the first exemplary embodiment, the method for manufacturing a cylinder block according to the second exemplary embodiment can reduce the formation of blowholes in the entire area inside the bulkhead 22, thus leading to an improvement in the yield of products.
Next, a method for manufacturing a cylinder block according to a third exemplary embodiment is explained with reference to
By this structure, the boundary between the movable mold 30 and the pressure pin 33b is flat without any difference in level formed therein before the pressurization process. Therefore, solidification shells that are continuously formed over the movable mold 30 and the pressure pin 33b can be easily sheared (i.e., cut) by moving the pressure pin 33b forward. As a result, deformations and cracking on the surface of the bearing section 23 caused by pulled-in solidification shells can be reduced even better than it is in the second exemplary embodiment. However, since the notches 35 are formed, the maching margin could increase.
Other configurations are similar to those in the first and second exemplary embodiments, and therefore their explanations are omitted. Similarly to the first exemplary embodiment, the method for manufacturing a cylinder block according to the third exemplary embodiment can reduce the formation of blowholes in the entire area inside the bulkhead 22, thus leading to an improvement in the yield of products. Further, similarly to the second exemplary embodiment, since no recess is formed between the movable mold 30 and the pressure pin 33b before the pressurizing process, deformations and cracking on the surface of the bearing section 23 caused by microscopic solidification pieces can be reduced (or prevented).
Next, a method for manufacturing a cylinder block according to a fourth exemplary embodiment is explained with reference to
Next, advantageous effects of the method for manufacturing a cylinder block according to the first exemplary embodiment are explained with reference to
In both experiment examples, a test piece was produced by die casting as an imitation of a bulkhead 22 of a cylinder block as shown in
Casting was performed in the following manner: two seconds after molten metal was pressure-injected in a state where the pressure pin 33 was in a retreated position, the pressure pin 33 was moved forward by 4 mm and a pressure of 160 MPa was thereby applied to the molten metal.
Casting was performed by pressure-injecting molten metal in a state where the pressure pin 33 was in a retreated position without moving the pressure pin 33.
As seen from the observations of the macro-structures shown in
Note that the present invention is not limited to the above-described exemplary embodiments, and various modifications can be made without departing from the spirit and scope of the present invention.
From the invention thus described, it will be obvious that the embodiments of the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.
Number | Date | Country | Kind |
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2014-219541 | Oct 2014 | JP | national |