JP2009216416A - Internal flaw inspection method of piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and easily inspect the internal flaw of a piston by a non-destructive method. <P>SOLUTION: The physical quantity related to the temperature rising speed of a crown surface 10 is measured while injecting a liquid heating medium of a predetermined temperature in an oil flow channel 40 and compared with a predetermined reference value. A heat conducting route becomes long because a region where the internal flaw is present has high heat insulating properties and the temperature rising speeds of the crown surface 10 are different between a defective article and a reference article. Accordingly, by comparing the difference of the temperature rising speed with the reference article, the presence of the internal flaw can be discriminated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for inspecting internal defects such as a hollow of a piston used in an internal combustion engine by a nondestructive method.

  In recent automobiles, it is desired to further improve the combustion efficiency of the engine as part of the suppression of global warming, and further improvement in fuel efficiency has been an issue.

  In an automobile engine, in order to improve fuel efficiency, it is effective to cool the piston crown to prevent knocking and improve the compression ratio. Therefore, for example, Japanese Utility Model Publication No. 59-130020 discloses a piston in which a hollow portion is formed in a piston crown portion, and an oil inlet and an oil outlet are formed to communicate the hollow portion and the outside of the piston. . According to this piston, oil is supplied into the hollow portion from the oil inlet, and the oil in the hollow portion is discharged from the oil discharge port, so that the piston crown can be cooled by the oil flowing through the hollow portion.

  Japanese Patent Application Laid-Open No. 05-288049 discloses a piston cooling device in which a spiral oil passage is formed inside a piston crown and the piston crown is cooled by oil flowing through the oil passage. ing.

  In a system that directly injects fuel into the cylinder, the distribution of sprayed fuel on the crown, which is the surface of the piston crown, is an important factor for the combustion efficiency. For the purpose of increasing the surface area and improving fuel consumption, The shape of the crown surface is also made uneven.

  Such a piston is generally manufactured by casting from an aluminum alloy or the like. However, the more complicated the shape of the piston is, the more likely it is that a void is generated during casting. In particular, when a void is generated inside the piston crown, air is present in the void, so that the cooling efficiency is lowered by the heat insulation action of the air, and as a result, the degree of improvement in fuel consumption is reduced. .

  In order to form an oil flow path, another member made of steel or the like is cast. Furthermore, in order to suppress wear caused by the piston ring, cast iron wear-resistant rings having ring grooves are also cast. However, when these separate members are cast, there is a case where a poor connection between the separate member and the piston body occurs, and peeling occurs at the interface between the separate member and the piston body. Air exists in such a peeled portion, and the cooling efficiency is lowered by the heat insulating action like the cast hole.

  Therefore, it is necessary to inspect the produced piston to detect defective products having cast holes and peeling. This inspection is preferably performed by nondestructive inspection, and various inspection methods have been proposed.

  For example, Japanese Utility Model Laid-Open No. 06-078808 describes a method for detecting an internal defect of a piston using ultrasonic waves. However, in this inspection method, there is a problem that the incident wave of ultrasonic waves is reflected in a complex manner at the unevenness of the piston crown and the interface with another member, and the inspection accuracy is low. In addition, there is a problem that the inspection man-hour is large because the subject needs to be rotated or the operation of a plurality of probes must be switched between inactive and inactive.

Japanese Laid-Open Patent Publication No. 01-156662 describes a method for inspecting internal defects of a piston having a fiber reinforced portion by using an acoustic emission method. However, the acoustic emission method can detect dynamically generated defects such as cracks that develop during cooling, but it is difficult to detect statically generated defects such as cast holes.
Japanese Utility Model Publication No.59-130020 Japanese Patent Laid-Open No. 05-288049 Japanese Utility Model Publication No. 06-078808 Japanese Patent Laid-Open No. 01-156662

  This invention is made | formed in view of the said situation, and makes it the problem which should be solved to enable it to test | inspect easily and easily the internal defect of a piston by a nondestructive method.

The feature of the piston internal defect inspection method of the present invention that solves the above problems is that it has a bottomed cylindrical shape with the piston crown as the upper base, and an oil flow path having an oil inlet and an oil outlet at the piston crown. A non-destructive method for inspecting internal defects of a piston crown using a provided piston,
Measuring a physical quantity related to the temperature rise rate of the crown surface, which is the surface of the piston crown, while injecting a liquid heat medium at a predetermined temperature into the oil flow path, and comparing the physical quantity with a predetermined reference value And

  In the piston internal defect inspection method of the present invention, a physical quantity related to the temperature rise rate of the crown surface is measured while injecting a liquid heat medium having a predetermined temperature into the oil passage. Parts with internal defects such as cast holes and peeled parts have higher heat insulation than other normal parts, so the heat from the liquid heat medium in the oil flow path is transferred to avoid internal defects and heat transfer. The distance gets longer. Therefore, by measuring in advance as a reference value a physical quantity related to the temperature rise rate at a predetermined position of a reference product without an internal defect, if there is a difference from the reference value in the same physical quantity at the same position of the specimen, It is determined that the sample has an internal defect.

  That is, according to the internal defect inspection method for a piston of the present invention, the presence or absence of internal defects can be inspected with high accuracy in a nondestructive manner, and the number of inspection steps is small. Therefore, 100% inspection is possible and the reliability of the product is improved.

  The piston internal defect inspection method according to the present invention is applied to a piston having an oil flow path in a piston crown. There are no particular limitations on the shape of the piston crown and the shape of the oil passage. The piston crown is formed with an oil inlet and an oil outlet that communicate the oil flow path with the outside.

  If the oil flow path is formed locally at the crown portion of the piston, the detection accuracy of the presence of an internal defect at a site far from the oil flow path is lowered. Therefore, it is desirable that the oil flow path is uniformly distributed as viewed from the surface of the piston crown. However, it does not have to be uniformly distributed over the entire surface as viewed from the surface of the piston crown, and it is sufficient that at least the oil flow path is formed so as to substantially make a round of the piston crown.

  In the piston internal defect inspection method of the present invention, first, a liquid heat medium having a predetermined temperature is injected into the oil passage. As this liquid heat medium, water, a high boiling point organic solvent, various oils, glycols, and the like can be used. A liquid that is liquid at room temperature, has a boiling point of 50 ° C. or higher, and has a high heat capacity is desirable, and engine oil that does not have any harmful effects even if it remains in the oil passage is particularly desirable. The temperature of the liquid heat medium injected into the oil flow path is not particularly limited, but a temperature difference of about 50 to 100 ° C. with respect to the temperature of the piston as the specimen is recommended. If the temperature difference is too small or too large, the detection accuracy of internal defects may decrease.

  The liquid heat medium can be injected into the oil flow path by ejecting the liquid heat medium from the nozzle toward the oil inlet or the oil outlet, similarly to the supply of oil during use. In order to prevent cooling of the liquid heat medium being ejected, it is desirable that the nozzle tip be inserted into the oil inlet or the oil outlet or ejected while being in close contact with the oil inlet or the oil outlet.

  After the liquid heat medium having a predetermined temperature is injected into the oil flow path, a physical quantity related to the temperature rise rate of the crown surface, which is the surface of the piston crown, is measured. The liquid heat medium may stay in the oil flow path. However, if it stays in the oil flow path, the temperature of the liquid heat medium will gradually decrease due to heat transfer, so the difference from the physical quantity reference product related to the heating rate will be small, and the inspection accuracy will be low There is. Therefore, it is desirable that the liquid heat medium having a predetermined temperature always flows in the oil flow path at a constant flow rate. If the flow rate of the liquid heat medium varies, the detection accuracy may decrease.

  The physical quantity related to the rate of temperature increase can be selected from the temperature of a predetermined part after a predetermined time has elapsed, the time until the temperature of the predetermined part reaches a predetermined temperature, the maximum temperature reached at the predetermined part, and the like. One of these may be used, and it is also preferable to measure a plurality of physical quantities. Moreover, although the predetermined part may be only one place, it is desirable to set it as multiple places.

  By measuring the temperature of the predetermined part after the lapse of the predetermined time or the time until the temperature of the predetermined part reaches the predetermined temperature, the presence of a cast hole or the like can be detected. Further, by measuring the maximum temperature reached at a predetermined site, it is possible to detect abnormalities such as blockage of the oil flow path.

  To measure the physical quantity related to the rate of temperature rise, measure the time from the injection of the liquid heat medium, measure the surface temperature at a given point on the crown surface by contacting a thermocouple, It can be measured by using a known means such as a method of detecting an infrared intensity and analyzing an image.

  The physical quantity related to the measured heating rate is compared with a predetermined reference value. The predetermined reference value is a value measured by injecting a liquid heat medium in the same manner as described above using a reference product that is known in advance to have no internal defects. The reference product has the same shape as the specimen and is manufactured from the same material.

  In the internal defect inspection method of the present invention, the initial temperature of the reference product and the specimen must be the same temperature, and the temperature of the liquid heat medium injected when measuring the reference product and the specimen must also be the same. The initial temperature of the reference product and the specimen is not particularly limited, but when the temperature difference between the temperature of the liquid heat medium and the specimen is about 50 to 100 ° C., the initial temperature is preferably about room temperature. If the initial temperature is about room temperature, the time until the manufactured piston is set to the initial temperature is short, so that the number of inspection steps can be further reduced.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
FIG. 1 shows a sectional view of a piston for a diesel engine of an automobile used in this example. The piston is integrally formed of an aluminum alloy by casting, and includes a bottomed cylindrical piston crown portion 1 constituting an upper base, and a thin skirt portion 2 formed at a lower portion of the piston crown portion 1. . The skirt portion 2 is formed with a pair of pin holes 20 for holding pins that pivotally support the connecting rod.

  The piston crown 1 includes a crown surface 10 having an uneven shape on the upper surface, and a plurality of ring grooves 11 are formed on the outer periphery of the piston crown 1. The uppermost ring groove 11 is formed of a wear-resistant ring 3 made of cast iron having a U-shaped cross section. A steel ring 4 having a C-shaped cross section is disposed on the back surface of the wear-resistant ring 3, and a ring-shaped space surrounded by the inner peripheral surface of the wear-resistant ring 3 and the steel ring 4 constitutes an oil flow path 40 for cooling. ing. The oil flow path 40 goes around the piston crown 1. The wear ring 3 and the steel ring 4 are cast and integrated when the piston is cast.

  An oil inlet 12 and an oil outlet 13 are opened on the inner peripheral surface of the piston crown 1, and both the oil inlet 12 and the oil outlet 13 communicate with the oil passage 40 through the communication passage 14. ing.

  First, a reference product for a piston that was found to be free from internal defects by ultrasonic flaw detection was prepared. This reference product has the same shape and the same material as the piston as the specimen.

  As shown in FIG. 2, the reference product was set in the inspection apparatus. This inspection device is composed of a surface thermometer 5 that measures the surface temperature of the crown surface 10 of the piston crown 1 and an oil supply device 6 that supplies engine oil to the oil passage 40. A plurality of thermocouples 50 are connected to the surface thermometer 5. The plurality of thermocouples 50 are in contact with predetermined portions of the crown surface 10, respectively. The surface thermometer 5 simultaneously processes signals from a plurality of thermocouples 50 and simultaneously detects surface temperatures at a plurality of predetermined portions of the crown surface 10.

  The oil supply device 6 includes a container 61 that stores engine oil 60, a pump 62, a heater 63, and a nozzle 64. The pump 62 sends the engine oil 60 in the container 61 to the heater 63 at a predetermined pressure, and the engine oil 60 heated to a predetermined temperature by the heater 63 is ejected from the nozzle 64 at a predetermined pressure. The tip of the nozzle 64 is in close contact with the oil inlet 12, and engine oil 60 is injected from the oil inlet 12 into the oil passage 40 through the communication path 14. The engine oil 60 that has flowed through the oil flow path 40 is discharged from the oil discharge port 13 and returns to the container 61.

  During the inspection, the pump 62 and the heater 63 are always driven, and the engine oil 60 at a constant temperature (100 ° C.) always flows through the oil passage 40 at a constant flow rate (0.5 m / sec).

  The reference product is set in the inspection device at room temperature (25 ° C). When engine oil 60 at 100 ° C is injected into the oil passage 40, the engine oil 60 flows through the oil passage 40 at a constant flow rate (0.5m / second). ). The surface thermometer 5 detects the temperature of a plurality of portions of the crown surface 10 immediately after oil injection and continuously measures it with time. A measurement result at a portion where a certain thermocouple 50 is in contact is shown by a solid line in FIG. The surface temperature of the part increases linearly immediately after the injection of the engine oil 60 and becomes a constant temperature after a predetermined time has elapsed.

  Next, the specimen piston (25 ° C.) was set in the inspection apparatus instead of the reference product, and the change in the surface temperature of the same portion of the crown surface 10 was measured in the same manner as described above. The results are shown in FIG. The surface temperature of the part rises linearly immediately after the injection of the engine oil 60, and becomes the same constant temperature as that of the reference product after a predetermined time. However, if there is an internal defect in the piston crown 1, the rate of temperature rise is lower than that of the reference product.

  That is, as shown in FIG. 4, when the casting hole 100 exists in the piston crown 1, the heat from the engine oil 60 is transferred so as to avoid the casting hole 100, and compared to the case where the casting hole 100 does not exist. The route becomes longer. Therefore, the rate of temperature rise at the crown surface portion on the extension of the heat transfer path decreases. Moreover, when the peeling part 101 exists in the back surface of the steel ring 4, the same phenomenon will arise, and the temperature increase rate in the site | part of the crown surface near the peeling part 101 will fall.

The degree of decrease in the heating rate increases as the number of casting holes 100 and peeling parts 101 increases or as the volume increases. Therefore, from FIG. 3, the temperature after a predetermined time (t) has elapsed from the start of injection of the engine oil 60 (for example, after 10 seconds) is read. The surface temperature of the reference product at that time is T _s , whereas the surface temperature of the specimen is T ₁ which is lower than T _s by ΔT. Therefore, the pass / fail of the quality of the specimen can be determined by comparing the value of ΔT with the standard value.

(Example 2)
In this example, measurement was performed in the same manner as in Example 1 except that the method for determining whether the quality of the specimen was acceptable or not was different.

That is, as shown in FIG. 5, the time required for the temperature of the predetermined part of the crown surface 10 to reach a predetermined temperature (T: for example, 60 ° C.) for both the reference product and the sample (reference product: t _s , sample: t ₁ ) Was measured. As a result, since the sample is delayed by Δt = t ₁ −t _s , the quality of the sample can be determined to pass or fail by comparing the value of Δt with the standard value.

(Example 3)
In this example, the measurement was performed in the same manner as in Example 1 except that the determination method of the quality of the specimen was different.

That is, as shown in FIG. 6, the maximum temperature reached at a predetermined portion of the crown surface 10 (reference product: T _s , sample: T ₁ ) was measured for both the reference product and the sample. Thus, when there is a difference in the maximum temperature reached and the difference (ΔT) is larger than a predetermined value, it is assumed that some abnormality exists in the oil flow path 40.

  The piston internal defect inspection method of the present invention is not limited to pistons for automobile engines, but can be used to inspect pistons used in various internal combustion engines.

It is sectional drawing of the piston used for one Example of this invention. It is sectional drawing which shows schematic structure of the test | inspection apparatus in one Example of this invention. It is a graph which shows the measurement result in one Example of this invention, and shows the relationship between measurement time and surface temperature. It is sectional drawing of the piston with a cast hole used for one Example of this invention. It is a graph which shows the measurement result in 2nd Example of this invention, and shows the relationship between measurement time and surface temperature. It is a graph which shows the measurement result in the 3rd Example of this invention, and shows the relationship between measurement time and surface temperature.

Explanation of symbols

1: Piston crown 2: Skirt 5: Surface thermometer
10: Crown 40: Oil flow path 50: Thermocouple
60: Engine oil 62: Pump 63: Heater

Claims (4)

Uses a piston with an oil flow path with an oil inlet and an oil outlet in the piston crown, with a bottomed cylindrical shape with the piston crown as the upper base, and nondestructive internal defects in the piston crown An internal defect inspection method for a piston to be inspected,
Measuring a physical quantity related to the temperature rise rate of the crown surface, which is the surface of the piston crown, while injecting a liquid heat medium at a predetermined temperature into the oil flow path, and comparing the physical quantity with a predetermined reference value An internal defect inspection method for a piston characterized by   The piston internal defect inspection method according to claim 1, wherein the measurement is performed while the liquid heat medium is circulated through the oil passage at a constant flow rate.   3. The piston according to claim 1, wherein the piston crown portion is provided with a ring groove having a wear-resistant ring, and the oil flow path is formed on a back surface of the wear-resistant ring so as to substantially go around the piston crown portion. Internal defect inspection method.   The physical quantity is at least one selected from the temperature of a predetermined part after a predetermined time has elapsed, the time until the temperature of the predetermined part reaches the predetermined temperature, and the maximum temperature reached at the predetermined part. The internal defect inspection method of the piston as described in 1.

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