JP2022146454A - Piston for diesel engine, manufacturing method thereof, and diesel engine - Google Patents

Abstract

To provide a piston for a diesel engine which can be reduced in weight while suppressing the lowering of wear resistance.SOLUTION: A piston for a diesel engine has a top ring groove and a second ring groove at a piston head. The inside of the top ring groove is applied with remelting treatment, and formed with an anodic oxide coating, and the inside of the second ring groove is applied with remelting treatment, and formed with an anodic oxide coating. The diesel engine is manufactured by a process for preparing a piston raw material having two or more grooves at a piston head part, a process for applying the remelting treatment on the inside of one groove out of the two or more grooves, also applying the anodic oxide treatment, and forming the top ring groove, and a process for applying the remelting treatment on the inside of the other groove out of the two or more grooves, also applying the anodic oxide treatment, and forming the second ring groove.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to pistons for diesel engines and methods of manufacturing the same, and diesel engines.

Diesel engine pistons operate in a higher pressure and higher temperature environment than gasoline engine pistons, so the piston head portion is required to have high strength and heat resistance. For this reason, in pistons for diesel engines, a cast iron wear-resistant ring is usually cast inside the piston head groove to increase the durability of the piston ring groove, which is easily worn out due to friction with the piston ring (for example, Patent Document 1, etc.).

As a piston for a gasoline engine, a piston is known in which the inside of the top ring groove is subjected to remelting treatment and anodizing treatment. Patent Literature 2 describes that the remelting treatment and the anodizing treatment suppress the deterioration of the sealing performance due to the settling of the upper and lower surfaces of the piston ring groove. Further, in Patent Document 3, the layer formed by the remelting treatment is cut to form a ring groove, and the ring groove is anodized to smooth the surface of the ring groove and improve the sealing performance. It says it can be improved.

WO2015/136818 JP-A-05-017899 JP-A-08-151953

A cast iron wear-resistant ring is cast into a diesel engine piston as described in Patent Document 1. Since iron, which is the material of the cast-iron wear-resistant ring, is heavier than aluminum, which is the material of the piston, the piston for a diesel engine is inevitably heavy. On the other hand, from the viewpoint of improving the fuel efficiency of the engine, there is a demand for further weight reduction of the piston while maintaining sufficient wear resistance to withstand use in diesel engines.

An object of the present disclosure is to provide a diesel engine piston, a method for manufacturing the diesel engine piston, and a diesel engine having the diesel engine piston, which can be reduced in weight while suppressing a decrease in wear resistance. to provide.

A diesel engine piston according to one aspect has a top ring groove and a second ring groove in a piston head. The inside of the top ring groove is remelted and an anodized film is formed, and the inside of the second ring groove is remelted and an anodized film is formed.

In addition, a method for manufacturing a piston for a diesel engine according to one aspect includes the steps of preparing a piston base material having two or more grooves in a piston head portion; forming a top ring groove by remelting and anodizing; and forming a second ring groove by remelting and anodizing the inside of another groove among the two or more grooves. and have

Further, a diesel engine according to one aspect has the piston for a diesel engine.

According to the present disclosure, a diesel engine piston, a method for manufacturing the diesel engine piston, and a vehicle wear resistance having the diesel engine piston, which can be reduced in weight while suppressing a decrease in wear resistance Provided are a diesel engine piston, a method for manufacturing the diesel engine piston, and a diesel engine having the diesel engine piston, which are capable of reducing the weight while suppressing the deterioration of the strength.

1 is an exemplary cross-sectional view of a diesel engine piston according to one embodiment of the present disclosure; FIG. FIG. 2 is a flowchart illustrating a method of manufacturing a diesel engine piston according to another embodiment of the present disclosure;

Embodiments of the present disclosure are described in more detail below. In addition, the embodiment described below is an example, and the present disclosure is not limited to this embodiment.

[Piston for diesel engine]
1 is an exemplary cross-sectional view of a diesel engine piston according to one embodiment of the present disclosure; FIG.

The diesel engine piston is made of an aluminum alloy. The aluminum alloy may contain aluminum as a main component and further contain silicon.

The content of silicon is preferably 10 mass to 13.5 mass %, more preferably 11.5 mass % or more. As another optional component, the content of Cu is preferably 1 mass% to 5.5 mass%, more preferably 2.5 mass% or more. The Ni content is preferably 1 mass% to 3.5 mass%, more preferably 2 mass% or more. The content of Mg is preferably 0.1 to 1 mass%. In addition, Mn, Fe, Zn, V, Zr, Ti, P and B may be included. Examples of the aluminum alloys also include AC8A and AC8B.

The composition of the aluminum alloy can be identified by emission spectroscopy.

The piston 100, as shown in FIG. 1, has a piston head 110 having a top portion 102 and an outer peripheral surface 104, and a skirt portion 120 which is a cylindrical wall member. The piston head 110 and the skirt portion 120 are integrally cast from aluminum. The skirt portion 120 has a hollow shape with one end 122 of the cylindrical shape connected to the piston head 110 and closed, while the other end 124 is open. In addition, a pair of piston pin holes 130 are opened on the side surface of the skirt portion 120 at positions facing each other. Each of the piston pin holes 130 is connected to a hollow portion 140 formed by the piston head 110 and the skirt portion 120, and each has an inner diameter through which the piston pin can be inserted. Further, the piston 100 has a thick piston boss portion 150 for supporting the piston pin inserted through the piston pin hole 130 on the inner surface of the skirt portion 120 in contact with the piston pin hole 130 .

In addition, the piston head 110 is provided with a combustion chamber 160, which is a concave groove-shaped recess, in a region including the central portion of the top portion 102, and circulates oil for cooling the piston (especially the combustion chamber 160). A cooling channel (cooling cavity) 170 , which is an annular cavity, is provided around the combustion chamber 160 . A mouth portion 162 protruding inward is provided at the edge of the combustion chamber 160, and the fuel injected into the combustion chamber 160 moves in the circumferential direction along the mouth portion 162. ing.

Piston head 110 also includes a plurality of piston ring grooves 106 . In this embodiment, the piston ring groove 106 has three grooves, a top ring groove 106a, a second ring groove 106b and an oil ring groove 106c, in order from the top portion 102 side. When the piston 100 is used, compression rings (neither shown) are fitted in the top ring groove 106a and the second ring groove 106b, respectively, and an oil ring (not shown) is fitted in the oil ring groove 106c.

The inside of the top ring groove 106a is a processed layer 180 that is remelted and anodized. More specifically, a remelt treatment layer formed by remelt treatment is arranged inside the top ring groove 106a, and an anodized film covering the remelt treatment layer is arranged outside the remelt treatment layer.

The inside of the second ring groove 106b is remelted and anodized. More specifically, a remelt treatment layer formed by remelt treatment is arranged inside the second ring groove 106b, and an anodized film covering the remelt treatment layer is arranged outside the remelt treatment layer.

The remelt treatment increases the strength and heat resistance inside these grooves. In addition, the remelt treatment reduces the grains of crystals formed inside these grooves. The anodizing treatment enhances wear resistance and thermal insulation inside these grooves. At this time, since the crystal grains are made finer by the remelt treatment, the hardness of the anodized film formed by the anodizing treatment increases, and the adhesive wear caused by the friction between the piston ring and the inside of the top ring groove 106a increases. unlikely to occur. Therefore, it is expected that the inside of the top ring groove 106a will be remelted and then anodized to provide wear resistance and heat resistance to the extent that the piston can withstand use without a cast iron wear-resistant ring.

However, according to the new findings of the present inventors, in a piston for a diesel engine, in which the mixed air has a high compression concentration and a higher load is applied to the piston, the inside of the top ring groove 106a is remelted and then anodized. However, wear resistance and heat resistance are insufficient, and adhesive wear occurs due to use of the piston.

On the other hand, in addition to the inside of the top ring groove 106a, the inside of the second ring groove 106b is also remelted and then anodized, so that sufficient wear resistance and heat resistance are obtained, and adhesive wear due to use of the piston is achieved. is reduced to the extent that it does not become a problem.

In addition, in a piston for a gasoline engine, which is required to have a lower degree of wear resistance than a piston for a diesel engine, it is not necessary to remelt and anodize the inside of the second ring groove 106b. It is believed that in Patent Document 2 and the like, only the top ring groove 106a is subjected to remelt treatment and anodization treatment.

In this embodiment, the top ring groove 106a and the second ring groove 106b are remelted and anodized to enhance the wear resistance and heat resistance of the diesel engine piston 100. As shown in FIG. As such, the diesel engine piston 100 may not have a cast iron wear ring like other diesel engine pistons. As a result, the weight of the diesel engine piston 100 can be reduced.

In addition, since the cast iron wear-resistant ring has a predetermined height (the height in the direction from the boundary between the piston head 110 and the skirt portion 120 toward the top portion 102), the piston head 110 of the conventional diesel engine piston is , had a height corresponding to the cast iron wear-resistant ring. In contrast, in the present embodiment, by eliminating the cast iron wear-resistant ring, the top ring groove 106a and the top portion 102 can be arranged closer to each other, thereby reducing the height of the piston head 110. can do. At this time, since the cooling channel 170 can be moved to a position closer to the top portion 102 by not using the cast iron wear-resistant ring, the cooling efficiency of the piston head 110 can be further enhanced. Therefore, even if the height of the piston head 110 is lowered, the problem of overheating of the piston and the connecting rod is less likely to occur. In addition, by reducing the height of the piston head 110, the waste volume of the piston head 110 is reduced, the friction is reduced, the air utilization rate is improved, and the fuel consumption of the piston 100 for diesel engines is improved. There is also the effect of doing

For example, in the present embodiment, the top ring groove 106a can be made to have the same height as the mouth portion 162 provided in the combustion chamber 160 . The top ring groove 106a has a predetermined width in the vertical direction (height direction), and the mouth portion 162 also has a predetermined width in the vertical direction (height direction). When the top ring groove 106a and the mouth portion 162 are at the same height, at least part of the predetermined width of the top ring groove 106a in the vertical direction is equal to that of the mouth portion 162 in the vertical direction. It means included.

More specifically, for example, in the diesel engine piston 100 of the present embodiment, the top land height (the distance from the end of the top ring groove 106a on the side of the top portion 102 to the top portion 102) is set to It can be from 4% to 9%.

At this time, since the cooling channel 170 is also arranged in the vicinity of the mouth portion 162, the thickness of the mouth portion 162 in the inward direction (the distance between the mouth portion 162 and the cooling channel 170) becomes small. To compensate for this loss of strength, mouth portion 162 is also preferably remelted and anodized. More specifically, it is preferable that a remelt-treated layer formed by remelt treatment be arranged in the mouth portion 162, and an anodized film covering the remelt-treated layer be arranged outside the remelt-treated layer. At this time, the total thickness of the remelt treatment layer and the anodized film in the mouth portion 162 where higher strength is required is greater than the total thickness of the remelt treatment layer and the anodized film in the top ring groove 106a and the second ring groove 106b. can be thicker.

The thickness of the anodized coating in the top ring groove 106a, the second ring groove 106b, and the mouth portion 162 imparts sufficient strength and heat resistance to the diesel engine piston 100, and sufficiently ensures durability during use of the piston. From the viewpoint of increasing the thickness, the thickness is preferably 5 μm or more, more preferably 20 μm or more. From the viewpoint of ensuring sufficient wear resistance, the thickness of the anodized film is preferably 100 μm or less.

The thickness of the anodized film may be any value that represents the thickness of the anodized film, and may be, for example, the average value of the thicknesses at a plurality of arbitrary locations. The thickness of the anodized film can be obtained with an overcurrent film thickness meter.

[Manufacturing method of piston for diesel engine]
FIG. 2 is a flowchart illustrating a method of manufacturing a diesel engine piston according to another embodiment of the present disclosure; As shown in FIG. 2, the method for manufacturing a diesel engine piston according to the present embodiment includes a step of casting a diesel engine piston base material (step S110), a step of forming grooves (step S120), and forming the grooves. It has a step of remelting the inside (step S130), an anodizing the inside of the remelted groove (step S140), and a step of removing the salt core (step S150).

[Step S110: Casting of Piston Base Material]
In this step, a piston base material for a diesel engine is cast.

Specifically, in this step, molten metal, which is the material of the piston, may be poured into a mold having the shape of the piston to be manufactured, and then cooled, solidified under pressure, or gravity forged. At this time, a salt core for forming the cooling channel is cast into the position where the cooling channel 170 is to be formed. On the other hand, at this time, the cast iron wear-resistant ring is not cast.

The molten metal is a molten metal made of the aluminum alloy described above. The ratio of each element in the molten metal to be poured may be, for example, the same as the composition of each element described above. The molten alloy may be prepared by heating and melting each element individually prepared, or by melting standard products such as AC8A, AC8B, AC9A and AC9B specified in JIS H 5202 (2010). It may be produced by

Through this process, a piston base material having substantially the same shape as the manufactured diesel engine piston 100 is cast, except that it does not have the top ring groove 106a, the second ring groove 106b, and the oil ring groove 106c.

[Step S120: Groove Formation]
In this step, two or more grooves are formed in the piston head portion of the piston base material. Specifically, of the surface exposed to the outside of the cast piston base material, the positions where the top ring groove 106a, the second ring groove 106b and the oil ring groove 106c are formed are cut, and these positions are cut. , forming a groove that circumnavigates the circumference of the piston base.

At this time, a groove shallower than the top ring groove 106a and a groove shallower than the second ring groove 106b are formed at positions where the top ring groove 106a and the second ring groove 106b are formed. On the other hand, a groove having the depth of the oil ring groove 106c is formed at the position where the oil ring groove 106c is formed.

[Step S130: Remelt treatment]
In this step, the inside of one of the two or more grooves formed as described above is remelted.

The method of remelt treatment is not particularly limited, and known remelt treatment methods such as laser irradiation and arc discharge can be used. At this time, grooves are formed in the previous process, and the inside of the grooves is subjected to remelt treatment, so that the remelt treatment layer is formed to a deeper position inside the top ring groove 106a and the second ring groove 106b that are formed. can be done.

In this step, the remelt treatment is performed over the entire circumference of the groove while rotating the piston base material or rotating a nozzle for laser or arc discharge.

Through this process, a remelt layer is formed inside the top ring groove 106a and the second ring groove 106b.

At this time, a portion of the piston base material corresponding to the mouth portion 162 of the combustion chamber 160 may be similarly remelted.

Finishing may be performed after the remelt treatment.

[Step S140: Anodizing treatment]
In this step, the insides of the remelted top ring groove 106a and second ring groove 106b are anodized.

For example, the top ring groove 106a and the second ring groove 106b formed by immersing the piston base material in the electrolytic solution are brought into contact with the electrolytic solution, and the top ring groove 106a and the second ring groove 106b are used as anodes. The electrolytic solution may be energized. At this time, the electrolytic solution preferably contains 0.5 mol/L or more and 4.0 mol/L or less of sulfuric acid and 0.05 mol/L or more and 0.2 mol/L or less of organic acid. Moreover, it is preferable that the energization is performed for 0.5 hours or more.

The organic acid may be an organic acid that is commonly used in anodizing treatment, such as an organic acid having two or more carboxyl groups. Examples of such organic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, itaconic acid, malic acid, tartaric acid and citric acid, among which oxalic acid and citric acid. preferable.

The concentration of sulfuric acid may be 0.5 mol/L or more and 4.0 mol/L or less, preferably 1.0 mol/L or more and 2.0 mol/L or less.

The concentration of the organic acid may be 0.05 mol/L or more and 0.2 mol/L or less, preferably 0.08 mol/L or more and 0.15 mol/L or less.

The concentration ratio of the sulfuric acid and the organic acid is preferably (concentration of sulfuric acid)/(concentration of organic acid) = 1/20 or more and 1/5 or less, and (concentration of sulfuric acid)/(concentration of organic acid). concentration)=1/15 or more and 1/8 or less.

The current density of the energization may also be equivalent to the current density when performing normal anodizing treatment, for example, 2.0 A/dm ² or more and 30 A/dm ² or less, preferably 6 A/dm ² or more and 15 A/dm ² . can be:

By this process, a remelt treatment layer and an anodized film covering the outside of the remelt treatment layer are formed inside the top ring groove 106a and the second ring groove 106b.

In addition, when the position corresponding to the mouth portion 162 is remelted in the previous step, the remelted mouth portion 162 may also be anodized in the present step.

[Step S150: Removal of salt core]
In this step, the salt core is removed.

The salt core may be removed by a known method such as dissolving in water. By removing the salt core, a cavity corresponding to the cooling channel is formed inside the piston head of the cast piston base material.

In this embodiment, as described above, the cast iron wear-resistant ring is not cast, so the thickness of the piston base material in the top ring groove 106a (or the second ring groove 106b), the cooling channel 170, and the mouth portion 162 becomes smaller. More specifically, the distance between the top ring groove 106a (or the second ring groove 106b) and the cooling channel 170 and the distance between the mouth portion 162 and the cooling channel 170 become smaller. Therefore, by performing the remelt treatment before removing the salt core, it is possible to suppress the destruction or deformation of the piston base material having the small thickness during the remelt treatment. When the remelt treatment is performed before removing the salt core, the removal of the salt core may be performed before the anodizing treatment (step S140) or after the anodizing treatment (step S140). good.

On the other hand, if destruction or deformation of the piston base material due to remelting does not appear to be a problem, the salt core should be removed first (e.g., the salt core should be removed before groove formation is performed). A remelt treatment may be performed after the removal.

[Use]
The diesel engine piston can be used in diesel engines for various applications. In addition, the diesel engine having the diesel engine piston can be used in various applications such as vehicles, ships, railways and airplanes.

[Other embodiments]
In addition, the above-described embodiments each show an example of the present disclosure, and the present disclosure is not limited to the above-described embodiments, and various other embodiments are also possible within the scope of the spirit of the present disclosure. It goes without saying that it is possible.

In addition, in the above-described method for manufacturing a piston for a diesel engine, the salt core is carried on the ring-shaped base material, but as long as it is easy to remove later, a core other than the salt core may be used. good.

A salt core having the shape of a cooling channel was placed in a mold for producing a piston with a diameter of 95 mm. AC8A was injected into the above mold and solidified under pressure to obtain a piston base material.

Three grooves were formed by cutting portions of the ring-shaped member corresponding to the top ring groove, the second ring groove and the oil ring groove. At this time, a groove shallower than the top ring groove and a groove shallower than the second ring groove were formed at the positions where the top ring groove and the second ring groove were formed, respectively. On the other hand, a groove having the depth of the oil ring groove was formed at the position where the oil ring groove was formed.

After that, the inside of the groove corresponding to the top ring groove and the second ring groove and the mouth portion of the combustion chamber were remelted and anodized to form the top ring groove and the second ring groove, respectively. After that, the salt core was removed by dissolving in water to obtain a diesel engine piston (Experiment 1).

Further, when forming the groove, a groove having the depth of the second ring groove is formed at the position where the second ring groove is formed, and the inside of the top ring groove and the mouth of the combustion chamber are remelted and anodized. A top ring groove was formed. After that, the salt core was removed by dissolving in water to obtain a diesel engine piston (Experiment 2).

A cast iron wear ring and a salt core having the shape of a cooling channel were placed in a mold for making pistons. A piston base material was obtained by pressurization and solidification in the above mold. Of the ring-shaped member, portions corresponding to the top ring groove, the second ring groove and the oil ring groove were cut to the depth of these grooves to form the top ring groove, the second ring groove and the oil ring groove. . After that, the salt core was removed by dissolving in water to obtain a diesel engine piston (Experiment 3).

In addition, the anodizing treatment in each of the above experiments was carried out with 1.5 mol/L sulfuric acid and 0.1 mol/ It was carried out by immersing in an electrolytic solution containing L of oxalic acid and applying a current with a current density of 10 A/dm ² for 50 minutes.

When the pistons of Experiments 1 and 2 were loaded into a diesel engine and a 200-hour actual machine test was conducted, the piston for the diesel engine of Experiment 1, in which the top ring groove and the second ring groove were remelted and anodized, showed significant No significant adhesive wear was observed.

When the pistons of Experiments 1 and 3 were loaded into a diesel engine and operated at the same engine speed and load under the same conditions, the diesel engine piston of Experiment 1, which did not use a cast iron wear-resistant ring, was The fuel efficiency calculated from the amount of fuel used during operation was improved by 1.5% compared to the diesel engine piston of Experiment 3 using the cast iron wear-resistant ring.

The pistons of Experiment 1 and Experiment 3 both had a diameter of 95 mm. On the other hand, the diesel engine piston in Experiment 3 using the cast iron wear-resistant ring had a top land height of 12.5 mm, but the diesel engine piston in Experiment 1 without the cast iron wear-resistant ring had a top land height of 12.5 mm. was shortened to 6.5 mm. As a result, the piston of Experiment 1 was able to form the top ring groove at the same height as the mouth of the combustion chamber. Also, in the piston of Experiment 1, the position of the cooling channel could be moved to a position closer to the top of the piston by about 6 mm than in the piston of Experiment 3.

The above-mentioned improvement in fuel efficiency is considered to be due to the weight reduction of the piston, the reduction in friction due to the reduction in the top land height, and the improvement in the air utilization factor in Experiment 1.

The diesel engine piston of the present disclosure is lighter than conventional pistons, and is less prone to adhesive wear. INDUSTRIAL APPLICABILITY The piston for diesel engines of the present disclosure is expected to extend the life of pistons in various applications where diesel engines are used, such as vehicles and ships, and contribute to further development of this field.

REFERENCE SIGNS LIST 100 diesel engine piston 102 top portion 104 outer peripheral surface 106 piston ring groove 106a top ring groove 106b second ring groove 106c oil ring groove 110 piston head 120 skirt portion 122 one end portion 124 other end portion 130 piston pin hole 140 hollow portion 150 Piston boss portion 160 Combustion chamber 162 Mouth portion 170 Cooling channel 180 Working layer

Claims (8)

Having a top ring groove and a second ring groove in the piston head,
The inside of the top ring groove is remelted and an anodized film is formed,
The inside of the second ring groove is remelted and an anodized film is formed,
Piston for diesel engine. The piston head has a mouth portion protruding inward from the edge of the combustion chamber,
The mouth portion is remelted and an anodized film is formed,
A piston for a diesel engine according to claim 1. The piston head has a mouth portion protruding inward from the edge of the combustion chamber,
The top ring groove is formed at the same height as the mouth portion,
A piston for a diesel engine according to claim 1 or 2. providing a piston base having two or more grooves in the piston head;
remelting and anodizing the interior of one of the two or more grooves to form a top ring groove;
forming a second ring groove by remelting and anodizing the inside of the other of the two or more grooves;
A method for manufacturing a piston for a diesel engine, comprising: The piston base member has a mouth portion protruding inward from the edge portion of the combustion chamber,
a step of remelting and anodizing the mouth portion;
A method for manufacturing a piston for a diesel engine according to claim 4. The piston base material is formed by casting a core for forming a cooling channel,
The remelt treatment is performed before removing the core,
A method for manufacturing a piston for a diesel engine according to claim 4 or 5. The piston base material is formed by casting a core for forming a cooling channel,
The remelt treatment is performed after removing the core,
A method for manufacturing a piston for a diesel engine according to claim 4 or 5. A diesel engine comprising the diesel engine piston according to any one of claims 1 to 3.

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