JP6896040B2 - Combination of piston and piston ring for internal combustion engine - Google Patents

Description

The present invention relates to a combination of a piston for an internal combustion engine and a piston ring.

In recent years, as the output and rotation speed of an engine have increased, a high pressure is also applied to the piston, so that it has become necessary to select a piston material having high strength. Examples of the piston material having high strength include aluminum alloys.

When an aluminum alloy is used as a piston material, there is a problem that aluminum adhesion occurs on the upper and lower surfaces of the piston ring because the piston ring groove provided in the piston is hit by the upper and lower surfaces of the piston ring mounted on the piston. there were. In the present specification, the upper surface of the piston ring means the surface located on the combustion chamber side when the piston ring is mounted in the piston ring groove, and the lower surface of the piston ring means that the piston ring is mounted in the piston ring groove. The surface located on the crank chamber side. Further, when simply referred to as the side surface of the piston ring, it means the outer peripheral surface of the piston ring that slides on the cylinder bore.

As a technique for suppressing such aluminum adhesion, a piston ring having a coating film made of DLC (diamond-like carbon) containing a specific element on the upper and lower surfaces of the piston ring is disclosed (see Patent Document 1).

Patent No. 3355306

The problem of aluminum adhesion on the upper and lower surfaces of the piston ring that may occur when an aluminum alloy is used as the piston material can be solved by the piston ring having the upper and lower DLC coatings of Patent Document 1.
On the other hand, when the piston ring is attached to the piston to move the engine, the piston ring itself also rotates, so that not only the problem of aluminum adhesion on the upper and lower surfaces of the piston ring but also the upper and lower surfaces of the piston ring and the piston ring groove It was found that the problem of wear of the piston ring groove also occurs due to the sliding of the piston ring.
The present invention provides a technique for solving both the problem of aluminum adhesion on the upper and lower surfaces of the piston ring and the problem of wear of the piston ring groove, which may occur when an aluminum alloy is used as the piston material.

The present inventors have studied to solve the above problems, and by using a piston ring having a hydrogen-containing DLC coating on at least one of the upper and lower surfaces, in addition to the problem of aluminum adhesion on the upper and lower surfaces of the piston ring, the piston He found that the problem of ring groove wear could be solved, and completed the invention.

One embodiment of the present invention has a piston ring groove in which a piston ring is mounted, is mounted in a piston for an internal combustion engine made of an aluminum alloy, and a piston ring groove of the piston, and hydrogen is mounted on at least one of the upper and lower surfaces. A combination of a piston for an internal combustion engine and a piston ring, including a piston ring having a DLC coating.

The aluminum alloy is preferably an Al—Cu based alloy, and preferably an aluminum alloy having a Si content of 2% or less. Aluminum alloys with a low Si content tend to have inferior sliding characteristics and are suitable for such pistons.
Further, the piston ring may further have a hydrogen-containing DLC coating on the side surface.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a technique for solving both the problem of aluminum adhesion on the upper and lower surfaces of the piston ring and the problem of wear of the piston ring groove of the piston, which may occur when an aluminum alloy is used as the piston material.

It is sectional drawing which shows one Embodiment of the piston which attached the piston ring. It is sectional drawing of a part of the piston ring of this embodiment. It is a schematic diagram of the testing machine used for the tapping friction test performed in an Example. It is a schematic diagram of the testing machine used for the sliding friction test performed in the Example.

One embodiment of the present invention has a piston ring groove in which a piston ring is mounted, is mounted in a piston for an internal combustion engine made of an aluminum alloy, and a ring groove of the piston, and contains hydrogen in at least one of the upper and lower surfaces. A combination of a piston for an internal combustion engine and a piston ring, including a piston ring having a DLC coating. This embodiment will be described with reference to FIG.

FIG. 1 is a cross-sectional view of a piston equipped with a piston ring.
A piston ring groove is formed in the piston 2, and a first groove 3, a second groove 4, and a third groove 5 are formed from the combustion chamber side. A top ring 13 which is a compression ring is attached to the first groove 3, a second ring 14 which is a compression ring is attached to the second groove 4, and a combination oil ring 15 is attached to the third groove 5. Is installed.
The right end portion of the top ring 13, the second ring 14, and the combined oil ring 15 in the drawing is a sliding surface that slides in contact with the inner wall of the cylinder 1, and may be covered with a coating film.

In this embodiment, the piston 2 is made of an aluminum alloy. The aluminum alloys are, for example, A2000 series aluminum alloys (Al-Cu based alloys) specified by JIS, A4000 series aluminum alloys (Al-Si based alloys) specified by JIS, and A6000 series aluminum alloys (Al) specified by JIS. -Mg-Si based alloy) and the like. Of these, an A2000 series aluminum alloy (Al—Cu based alloy) specified by JIS is preferable from the viewpoint of piston strength.

Further, the aluminum alloy preferably has a Si content of 2 wt% or less, more preferably 1 wt% or less, and further preferably 0.5 wt% or less. When the Si content is low, the strength is high, but the sliding characteristics of the piston material tend to be poor, so that the amount of wear of the piston ring groove tends to be large due to sliding with the piston ring. This embodiment, which can suppress wear of the piston ring groove, is suitable for a piston made of an aluminum alloy having a low Si content.

As a means of reducing the amount of wear of the piston ring groove of the piston, there is a method of applying alumite treatment to the piston or a method of combining an abrasion resistant ring, but the alumite treatment causes an increase in the roughness of the piston ring groove and adversely affects blow-by. It also increases the manufacturing cost of the piston. The method of combining the wear-resistant rings generates vibration due to the increase in the weight of the piston, increases the noise caused by the vibration, and increases the manufacturing cost of the piston. By combining with the piston ring of the present embodiment, the amount of wear of the piston ring groove of the piston can be reduced without using the method of applying anodizing treatment to the piston or the method of combining the anti-wear ring.

The roughness Rz of at least one of the upper and lower surfaces of the piston ring groove of the piston may be 6.3 μm or less, 3.2 μm or less, or 1.6 μm or less. The upper surface of the piston ring groove is, for example, the upper surface (the surface on the combustion chamber side) of the piston ring groove 3 of FIG. 1, and the lower surface of the piston ring groove is, for example, the lower surface of the piston ring groove 3 of FIG. (Crank chamber side). Rz is the maximum height defined by JIS B 0601.

FIG. 2 is a cross-sectional view of a part of the piston ring of the present embodiment. The upper and lower surfaces of the piston ring 20 and the side surfaces (also referred to as a sliding surface with the cylinder bore and an outer peripheral surface) have a DLC coating 22. In the present embodiment, at least one of the upper and lower surfaces of the piston ring 20 has a DLC coating 22, but the outer peripheral surface may also have a DLC coating. The thickness of the DLC coating on the outer peripheral surface may be thinner than the thickness of the DLC coating on the upper and lower surfaces, and may be 1/2 or less of the thickness of the DLC coating on the upper and lower surfaces. Further, the thickness of the DLC coating on the outer peripheral surface may be thicker than that on the upper and lower surfaces. Further, the inner peripheral surface may also have a coating film.

The material of the piston ring base material 21 of the piston ring 20 is not particularly limited as long as it is a material conventionally used as a piston ring base material. For example, stainless steel, steel, and the like are preferably used, and specifically, martensitic stainless steel, silicon chrome steel, and the like are preferably used.

In the present embodiment, the DLC coating is a hydrogen-containing DLC coating, not a so-called hydrogen-free DLC. In one example, the hydrogen content may be 5.0 at% or more, 10.0 at% or more, 15.0 at% or more, 20.0 at% or more, and so on.
It may be 25.0 at% or more, and the upper limit value is not particularly limited, but may be 30.0 at% or less. Since the DLC film is a DLC containing hydrogen, the compatibility with the piston made of an aluminum alloy is improved, wear between the piston ring groove and the piston ring groove can be suppressed, and aluminum adhesion can also be suppressed.

Further, the DLC coating may contain other elements, and containing W (tungsten) as the other element improves the sliding characteristics, reduces the internal stress of the coating, and facilitates the thickening of the film. preferable. When W is contained, the content may be 1 at% or more, 3 at% or more, 5 at% or more, 40 at% or less, and 30 at% or less. ..

The thickness of the DLC coating is not particularly limited and may be usually 0.5 μm or more and 1 μm or more, and usually 10 μm or less and 5 μm or less.
The hardness of the DLC coating is not particularly limited, but may be HV500 or higher, HV700 or higher, HV1800 or lower, and HV1500 or lower.
A Cr plating film, a chromium nitride film, a titanium nitride film, or the like may be further provided between the DLC film and the piston ring base material, and any one of Cr, Ti, Si, and WC may be provided at the boundary with the DLC film. A coating film or a mixed coating film of two types may be used, or a DLC coating film may be formed directly on the piston ring substrate.

At least one of the upper and lower surfaces of the piston ring having the DLC coating may have a roughness Rz of 4.0 μm or less, 3.2 μm or less, or 2.0 μm or less.

Of the piston rings provided in the piston, at least one of the top ring 13 and the second ring 14 may have the hydrogen-containing DLC coating described above on at least one of the upper and lower surfaces, and the top ring 13 and the second ring may be provided. Both 14 may have the hydrogen-containing DLC coating described above on at least one of the upper and lower surfaces.
The combination oil ring 15 includes a pair of upper and lower segments 151 and 152 whose outer peripheral surface slides on the inner wall of the cylinder, and an expander spacer 153 arranged between the segments. The combination oil ring 15 is an oil ring having a three-piece structure, but is not limited to this, and may be an oil ring having a two-piece structure.

As a method for forming the hydrogen-containing DLC film on the piston ring, a known method can be used, and examples thereof include an ion plating method and a sputtering method. For example, while rotating the work in the vacuum chamber, an inert gas is introduced, the surface of the work is cleaned by ion bombardment with argon ions, and then a carbon-based gas (methane, acetylene, etc.) is introduced into the chamber. A film can be formed on the outer peripheral surface of the piston ring by a sputtering method that evaporates W at the same time as keeping the vicinity of the work in a plasma state.
Specifically, heating is performed for 1 hour, and then the Cr layer is treated as an intermediate layer with a sputtering output of 3000 W, a bias voltage of 300 V, and an argon gas introduction of 100 sccm, and then while introducing an acetylene gas of 200 sccm, a bias voltage of 300 V and an output of 3000 W. Then, sputtering can be formed by using a target containing W element.

Hereinafter, the present invention will be described in more detail with reference to Examples.
<Reference test 1: Hitting friction test (aluminum adhesion test)>
A tapping friction test was performed assuming the space between the upper and lower surfaces of the piston ring and the piston ring groove. Using the tapping friction tester 30 outlined in FIG. 3, the piston material is an Al—Cu alloy (A2618: Si content 0.1 to 0.25 wt%) and an Al—Si (A4032: Si content). In the case of 11 to 13.5 wt%), a tapping friction test was performed on the nitrided piston ring. The test conditions were as follows. As a result, the time required for aluminum adhesion was 30 minutes for the Al—Si alloy and 15 minutes for the Al—Cu alloy. It can be understood that the Al—Cu alloy is more likely to cause aluminum adhesion.
・ Striking load 100N
・ Striking speed 700 times / minute ・ Temperature 250 ℃ / 170 ℃ (piston / piston ring)
・ Lubricating oil 10W 0.1mL applied before the start of test ・ Piston material surface finish 2.0μmRz

<Examples 1 and 2 and Comparative Example 1: Striking friction test (aluminum adhesion test)>
The following test was performed using the tapping friction tester 30 shown in the outline in FIG. 3 in the same manner as in the reference test 1. The piston ring coating used in the test was manufactured as follows.
Hydrogen-containing DLC of Examples:
Heating was performed for 1 hour using a sputtering device, and then the Cr layer was treated as an intermediate layer with a sputtering output of 3000 W, a bias voltage of 300 V, and an argon gas introduction of 100 sccm, and then a bias voltage of 300 V and an output while introducing acetylene gas 200 sccm. The film thickness was set to 3000 W, and the target film thickness was processed by forming a film using a WC target for sputtering. In the hydrogen-containing DLC coatings of Examples 1 and 2, the hydrogen concentration in the coatings was changed by changing the pressure inside the apparatus furnace at the time of film formation.

Comparative example hydrogen-free DLC:
After vacuum exhaust using an arc ion plating device, heating is performed for 1 hour, and then a bias voltage is applied in the range of (-500 to -1000) V, and an arc current of 50 is used using a Cr target. The discharge was performed at ~ 100 A, and Cr ion bombarding was performed.
Next, in arc ion plating, with a bias voltage applied to the piston ring base material in the range of (-10 to -100) V, a Cr target was used to discharge the piston ring with an arc current of 50 to 100 A. A Cr coating was formed on the piston ring base material as an adhesive layer. Next, an amorphous carbon layer was formed on the Cr film. The amorphous carbon layer is formed by discharging and forming a film with an arc current of 50 to 100 A using a carbon target with a bias voltage applied to the base material in the range of (0 to -100) V. Got a layer.
The piston materials, piston rings, and results used in the test are summarized in Table 1.

<Reference test 2: Sliding friction test>
A friction test was conducted between a nitrided product and a piston material, which is a surface treatment for the upper and lower surfaces of a piston ring that has been generally used so far. The upper and lower surfaces of the ring groove in the piston generate friction due to a moment in which the piston ring rotates in the circumferential direction of the piston ring as the piston moves up and down. Therefore, the reciprocating friction tester 40 outlined in FIG. A friction test was performed using. The test conditions were as follows.
・ Load 30N
・ Striking speed 300 times / minute ・ Time 30 minutes ・ Temperature Room temperature (23 ℃)
・ Lubricating oil Bearing oil 2.0mL / h
In both Reference Example 1 and Reference Example 2, the pin material (ring material) was a SU-3 nitride product with a mirror finish at the tip SR18. The plate (piston material) had a surface finish of 1.3 μmRz. The results are shown in Table 2 below, and it can be understood that the Al—Cu based alloy is more easily worn.

<Example 3 and Comparative Example 2: Sliding friction test (DLC)>
The following tests were performed using the reciprocating dynamic friction tester 40 shown in the outline in FIG. 4 in the same manner as in the reference test 2. In both Example 3 and Comparative Example 2, an Al—Cu alloy was used as the plate (piston material).

1 Cylinder inner wall 2 Piston 3 First groove 4 Second groove 5 Third groove 13 Top ring 14 Second ring 15 Combination oil ring 151 Upper segment 152 Lower segment 153 Expander spacer 20 Piston ring 21 Piston ring base material 22 DLC coating 30 tapping friction tester
31 Piston ring 32 Piston material 34 Oil 35 Heater 36 Spring 40 Sliding friction tester 41 Pin (ring material)
42 plate (cylinder bore material)

Claims (4)

A piston for an internal combustion engine having a piston ring groove to which a piston ring is mounted and made of an aluminum alloy, and a piston ring mounted in the piston ring groove of the piston and having a hydrogen-containing DLC coating on at least one of the upper and lower surfaces. A combination of a piston and a piston ring for an internal combustion engine, including
The aluminum alloy, Si content is less 2 wt%, a combination of a piston and a piston ring for an internal combustion engine (where Except hydrogen-containing DLC film containing Si element less 1 at.% Or more 10at%, and, Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni: 0.3 to 0.8% by mass and Mg: 1. excluding a piston for an internal combustion engine made of an aluminum alloy containing at least from 5 to 2.0 wt%). A piston for an internal combustion engine having a piston ring groove to which a piston ring is mounted and made of an aluminum alloy, and a piston ring mounted in the piston ring groove of the piston and having a hydrogen-containing DLC coating on at least one of the upper and lower surfaces. A combination of a piston and a piston ring for an internal combustion engine, including
The aluminum alloy is an Al—Cu based alloy and has a Si content of 0.5 wt% or less, which is a combination of a piston for an internal combustion engine and a piston ring (provided that Si: 0.4 to 0.7 mass%, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni: 0.3 to 0.8% by mass and Mg: 1.5 to 2.0% by mass at least Except for pistons for internal combustion engines made of aluminum alloy) . The internal combustion engine piston includes a top ring, a second ring and an oil ring.
The combination of a piston for an internal combustion engine and a piston ring according to claim 1 or 2, wherein at least one of the top ring and the second ring has a hydrogen-containing DLC coating on at least one of the upper and lower surfaces. The combination of a piston for an internal combustion engine and a piston ring according to any one of claims 1 to 3, wherein the piston ring has a hydrogen-containing DLC coating on the side surface.

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