JP6889692B2 - Alcohol fuel piston - Google Patents

Description

The present invention relates to a piston equipped with a piston ring, and particularly to a piston useful for an internal combustion engine using alcohol fuel.

The piston mounted on the cylinder of the internal combustion engine is provided with a ring groove for arranging the compression ring and the oil ring in order on the outer wall thereof, and the compression ring and the oil ring are mounted on the groove, respectively. The compression ring has a function of suppressing the outflow of high-pressure combustion gas from the combustion chamber side to the crank chamber side and the outflow of excess engine oil in the cylinder from the crank chamber side to the combustion chamber side. Further, the oil ring has a function of scraping off excess engine oil adhering to the inner wall of the cylinder of the internal combustion engine to form an appropriate oil film.

On the other hand, in recent years, an internal combustion engine capable of using a fuel consisting only of alcohol such as ethanol or a fuel obtained by mixing alcohol and another fuel (hereinafter, both are also collectively referred to as alcohol fuel) has been known. Pistons for use in such internal combustion engines have been proposed.

In Patent Document 1, in order to improve the seizure resistance of the sliding member and further improve the corrosion resistance and the wear resistance when using alcohol fuel, the sliding surface of one of the members is sprayed with Fe—Cr alloy powder. A technique has been proposed in which a surface is used and the sliding surface of the other member is a nitrided surface.
Further, in Patent Document 2, as an oil ring for an internal combustion engine having seizure resistance, wear resistance and corrosion resistance that can be used for alcohol fuel, a nitride layer is provided on a sliding surface, and a base material is specified. An oil ring having a composition, a specific quenching and tempering hardness, and a web portion having a specific thickness has been proposed.
Further, in Patent Document 3, a Cr-B-VN-based alloy coating is provided on the sliding surface as a piston ring having higher wear resistance, crack resistance and peeling resistance, which can be applied to alcohol fuel. A coated piston ring is disclosed.

On the other hand, since the outer circumference of the oil ring slides at high speed with the inner wall of the cylinder, wear resistance is required. Therefore, a technique has been proposed in which a diamond-like carbon (hereinafter, also referred to as DLC) coating having high wear resistance is provided on the outer peripheral surface of the oil ring (see Patent Document 4).

Japanese Unexamined Patent Publication No. 04-175577 Japanese Unexamined Patent Publication No. 06-137430 International Publication No. 2016/002810 Japanese Unexamined Patent Publication No. 11-315924

In recent years, from the viewpoint of fuel efficiency, which is more demanding, it is preferable that the outer peripheral surface of the piston ring sliding with the inner wall of the cylinder is covered with a DLC coating having low friction.
On the other hand, in an internal combustion engine that uses alcohol fuel, more fuel is injected into the cylinder than gasoline fuel, and unburned alcohol during combustion and water generated during combustion react with calcium components contained in the combustion chamber. This can result in alcohol fuel products such as calcium carbonate and calcium sulfate. The present inventors have found that the alcohol fuel product may be deposited on the inner wall of the cylinder and the roundness of the inner wall of the cylinder may be deteriorated.

In an internal combustion engine that uses alcohol fuel, when a low friction DLC coating is provided on the outer peripheral surface of the piston ring that slides with the cylinder inner wall from the viewpoint of fuel efficiency, the DLC coating has low friction, so that the cylinder inner wall has a low friction coating. Since the effect of scraping off the accumulated alcohol fuel product is very weak, the roundness of the inner wall of the cylinder may be deteriorated, which may lead to deterioration of LOC (Lubricating Oil Consumption). The present invention has been made under such circumstances, and an object of the present invention is to provide a piston ring-mounted piston that achieves both improvement of fuel efficiency and prevention of deterioration of LOC.

The present inventors have studied to solve the above problems, and the top ring and the combined oil ring mounted on the piston have their outer peripheral surfaces coated with a DLC coating, and the second ring has a friction coefficient higher than that of the DLC. Completed the invention by finding that it is possible to provide a piston for alcohol fuel that achieves both improvement in fuel efficiency and prevention of deterioration of LOC by coating with a coating selected from a PVD coating, a nitride coating, and a hard chrome plating coating. I let you.

The present invention relates to a piston for an internal combustion engine having a ring groove in which a piston ring is mounted, and a top ring, a second ring and a combination oil ring mounted in the ring groove of the piston.
A piston for alcohol fuel consisting of
The top ring and the oil ring have a DLC coating on the outer peripheral surface thereof.
The second ring has a coating selected from PVD coating, nitride coating, and hard chrome plating on its outer peripheral surface.
It is a piston for alcohol fuel.

The second ring preferably has a PVD coating on its outer peripheral surface.
Further, the alcohol fuel preferably has an alcohol content of 20% by volume or more.

Another aspect of the present invention is a method for manufacturing an internal combustion engine for alcohol fuel, which comprises a step of mounting a top ring, a second ring and a combined oil ring on a piston for an internal combustion engine having a ring groove.
The top ring and the oil ring have a coating having a friction coefficient μ of 0.1 or less on the outer peripheral surface thereof.
The second ring has a coating on its outer peripheral surface having a higher coefficient of friction than the coatings of the top ring and the oil ring.
This is a method for manufacturing an internal combustion engine for alcohol fuel.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a piston for alcohol fuel that achieves both improvement in fuel efficiency and prevention of deterioration of LOC when used in an internal combustion engine for alcohol fuel. Further, since the deposits on the inner wall of the cylinder can be scraped off, deterioration of the roundness of the inner wall of the cylinder can be prevented.

It is sectional drawing of the piston which attached the piston ring. It is a figure which shows the result of having measured the roundness of the inner wall of a cylinder after the continuous high-speed rotation operation test of an internal combustion engine using alcohol fuel. It is a schematic diagram of the measuring instrument which performed the reciprocating dynamic friction test. It is a chart which shows the IR spectrum which analyzed the deposit of the cylinder inner wall.

An embodiment of the present invention is a piston for alcohol fuel, which comprises a piston for an internal combustion engine having a ring groove in which a piston ring is mounted, and a top ring, a second ring and a combination oil ring mounted in the ring groove of the piston. is there. Hereinafter, the configuration will be described with reference to FIG.

FIG. 1 is a cross-sectional view of a piston equipped with a piston ring.
The piston 2 is formed with a first groove 24, a second groove 34, and a third groove 14 from the combustion chamber side. A top ring 20 which is a compression ring is attached to the first groove 24, a second ring 30 which is a compression ring is attached to the second groove 34, and a combination oil ring 10 is attached to the third groove 14. Is installed.

The right end of the top ring 20, the second ring 30, and the combined oil ring 10 in the drawing is a sliding surface that slides in contact with the inner wall of the cylinder 1, and is covered with a coating film.
In the present embodiment, the sliding surface of the top ring 20 and the combination oil ring 10 with the inner wall of the cylinder 1, that is, the outer peripheral surface of the top ring 20 and the combination oil ring 10 has a DLC coating.
The thickness of the DLC coating is not particularly limited, but is usually 0.5 μm or more, preferably 1 μm or more, and usually 30 μm or less, preferably 10 μm or less.
The hardness of the DLC film is not particularly limited, but is usually 800 Hv or more, preferably 1200 Hv or more, and usually 3500 Hv or less, preferably 2500 Hv or less.
The arithmetic surface roughness (Ra) of the DLC coating is usually 0.1 μm or less, and may be 0.05 μm or less. The arithmetic surface roughness (Ra) is a value measured according to JIS B0601 (2001).

The combination oil ring 10 includes a pair of upper and lower segments 11 and 12 whose outer peripheral surface slides on the inner wall of the cylinder, and an expander spacer 13 arranged between the segments. The sliding surfaces at the right ends of the pair of upper and lower segments 11 and 12 in the drawing each have a DLC coating. The upper and lower pairs of segments 11 and 12 may be the same DLC coating, or may be different types of DLC coatings.
Further, the combination oil ring 10 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.

On the other hand, since the sliding surfaces of the top ring 20 and the combined oil ring 10 with the inner wall of the cylinder 1 have a DLC coating, as shown in the experiment described later, the internal combustion engine is operated at high speed using alcohol fuel. It was found that deposits such as calcium sulfate were deposited on the inner wall of the cylinder. Then, they have found a new problem that arises when using alcohol fuel, that the roundness of the inner wall of the cylinder deteriorates due to the influence of sediments, which causes deterioration of LOC.

In the present embodiment, in order to solve such a new problem, a coating having a higher friction coefficient than DLC, that is, a coating selected from PVD coating, nitride coating, and hard chrome plating is applied to the outer peripheral surface of the second ring. Have. Of these, a PVD coating having excellent wear resistance is preferable.

In the present specification, the alcohol fuel refers to a fuel consisting only of alcohol such as ethanol, or a fuel in which alcohol and other fuel are mixed, but when the fuel is a mixture of alcohol and other fuel, it is usually alcohol. The content may be 20% by volume or more, 30% by volume or more, 40% by volume or more, and 50% by volume or more.

The thickness of the coating film covering the sliding surface of the second ring cylinder 1 with the inner wall is not particularly limited, but is usually 0.5 μm or more, preferably 1 μm or more, and usually 150 μm or less, preferably 50 μm or less. You can.
The hardness of the coating film covering the sliding surface of the second ring cylinder 1 with the inner wall is not particularly limited, but is usually 700 Hv or more, preferably 800 Hv or more, and usually 2000 Hv or less, preferably 1500 Hv or less.
Further, the arithmetic surface roughness (Ra) of the coating film covering the sliding surface of the second ring cylinder 1 with the inner wall is usually 0.3 or less.

The experimental results that led to the knowledge of the present invention are shown below.
<High-speed operation test using alcohol fuel>
A top ring, a second ring and a combination oil ring were installed in the ring groove of the piston for an internal combustion engine. The sliding surface of the top ring, the second ring and the combined oil ring with the inner wall of the cylinder has a DLC coating (hardness 1850 Hv, friction coefficient (μ) 0.086 by the reciprocating friction test shown below).
Using the above piston for internal combustion engine, using 85% by volume alcohol fuel (the remaining 15% by volume is gasoline), an internal combustion engine with a displacement of 2L was subjected to a continuous operation test (200 hours) at high rotation (6000 rpm), and LOC. As a result of evaluation, the LOC value deteriorated to 2.2 times.
As shown in FIG. 2, the cylinder bore of the internal combustion engine after the LOC evaluation had deteriorated in roundness.

<Reciprocating friction test>
This was performed using the reciprocating friction tester 100 whose outline is shown in FIG. The ring material 101 used in the reciprocating dynamic friction test was a cut-out piece of the piston ring, and the entire surface of the ring material 101 was covered with DLC or PVD in the same manner as the piston ring base material.
The sliding surface of the ring material 101 was mirror-finished so that the radius of curvature was 18 mm. The cylinder material 102 that slides with the ring material 101 is based on a cylinder bore cutting material (FC250 equivalent material: HRB100, A type graphite 75%, carbide precipitation 0.5% or less, Rz 2.0 μm (JIS B0601 (2001)). )) Was used.

In the reciprocating dynamic friction test, lubricating oil was supplied from the lubricating oil supply mechanism 103 to the sliding interface between the ring material 101 and the cylinder material 102. The test conditions at this time are shown below.
<Test conditions>
・ Stroke: 50 mm
・ Load: 5N
-Speed: 100 cycles / min
・ Evaluation temperature: Room temperature ・ Lubricating oil: Ethanol, 3 mL / h is dropped every 20 seconds ・ Test time: 5 min
The reciprocating dynamic friction test was performed on the DLC coating and the PVD coating (hardness 1100Hv) in which the high-speed operation test using alcohol fuel was performed. The coefficient of friction (μ) in the reciprocating friction test of the PVD coating was 0.170.

Next, when the IR spectrum of the deposit attached to the cylinder bore of the internal combustion engine was measured, it was in agreement with the IR spectrum of calcium sulfate. The measurement result of the IR spectrum is shown in FIG.

From the above, in an internal combustion engine that uses alcohol fuel, when a DLC coating with low friction is used as a coating on the sliding surface of the piston ring in order to improve fuel efficiency, deposits such as calcium sulfate are formed on the inner wall of the cylinder. It was found that the adhesion caused the roundness of the inner wall of the cylinder to deteriorate, and as a result, the LOC deteriorated.
Therefore, in order to scrape off the deposits accumulated on the inner wall of the cylinder, the sliding surface of the second ring with the inner wall of the cylinder should have a PVD coating having a higher friction coefficient, a nitride coating, and a coating selected from hard chrome plating. However, it is effective in achieving both improvement of fuel efficiency and prevention of deterioration of LOC. Further, since the deposits on the inner wall of the cylinder can be scraped off, deterioration of the roundness of the inner wall of the cylinder can be prevented.

1 Cylinder 2 Piston 10 Combination oil ring 11, 12 Segment 13 Expander spacer 14 Third groove 20 Top ring (compression ring)
24 1st groove 30 Second ring (compression ring)
34 Second groove 100 Reciprocating friction tester 101 Ring material 102 Cylinder material 103 Lubricating oil supply mechanism

Claims (3)

A piston for an internal combustion engine having three ring grooves to which a piston ring is mounted, and a top ring, a second ring and a combination oil ring mounted in the ring groove of the piston in order from the combustion chamber side of the piston.
A piston for alcohol fuel consisting of
The top ring and the oil ring have a DLC coating on the outer peripheral sliding surface thereof.
The second ring has a coating on its outer peripheral sliding surface selected from a PVD coating, a nitride coating, and a hard chrome plating, which is a coating having a higher coefficient of friction than the outer peripheral sliding surface of the top ring.
The alcohol fuel has an alcohol content of 20% by volume or more.
Piston for alcohol fuel. The alcohol fuel piston according to claim 1, wherein the second ring has a PVD coating on its outer peripheral sliding surface. A method for manufacturing an internal combustion engine for alcohol fuel, which comprises a step of mounting a top ring, a second ring and a combined oil ring on a piston for an internal combustion engine having three ring grooves.
The top ring, the second ring, and the combination oil ring are mounted in the ring groove of the piston in order from the combustion chamber side of the piston.
The top ring and the oil ring have a DLC coating on the outer peripheral sliding surface thereof.
The second ring has a coating selected from a PVD coating, a nitride coating, and a hard chrome plating on the outer peripheral sliding surface thereof, which has a higher friction coefficient than the outer peripheral sliding surface of the top ring.
The alcohol fuel has an alcohol content of 20% by volume or more.
A method for manufacturing an internal combustion engine for alcohol fuel.

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