JPS60237145A - Combination of cylinder liner and piston ring - Google Patents

Abstract

PURPOSE:To reduce abrasion by combining a cylinder liner applied with porous chrome plating and a spherical cast graphite piston ring aplied with gas nitriding. CONSTITUTION:A cylinder liner is made by applying porous chrome plating 2 onto the cylinder liner base material 1 such as cast iron, aluminum alloy, steel, etc. The porous plating layer 2 has the hardness Hv of 850-950 and a recess 3 is formed in the surface of said layer 2 through electrolysis, special honing, plasting, etc. The plateau face 4 has the coarseness of 0.5-2mum. Such cylinder liner and piston ring 5 are combined. The piston ring 5 is made by applying gas nitriding on the base material of piston ring such as chrome, molybdenum or spherical graphite cast iron.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an effective combination of a piston ring incorporated into a piston of an engine and a cylinder lychee for sliding the piston ring.

(Background technology) Cylinder lychees and piston rings slide at high speed under the pressure of high-temperature explosive gas, so they are required to have good corrosion resistance and wear resistance. Properties such as oil retention and high hardness are required.

In order to improve these properties, hard chrome plating,
Processes such as nitriding have been developed. The hard chrome plating used in the cylinder litchi.

Although it has excellent properties as a friction material, such as high hardness, good corrosion resistance, and a low coefficient of friction, chromium plating itself has extremely poor self-lubricating properties and poor oil retention, and furthermore, due to its high hardness, it It has the disadvantage of poor familiarity. Therefore, various methods have been used to make the sliding surface of these porous to improve oil retention and initial stain resistance, but this narrows the range of selection of an appropriate piston ring, which is the sliding mating material. There is a drawback. That is, there is a limit to the compatibility of piston rings.

As a way to improve the wear resistance of piston rings,
Piston rings have been put into practical use by using special cast iron containing special ingredients, and for some high-load engines, with a hardened layer formed by thermal spraying. However, with thermal spraying, the hardened layer inevitably becomes porous, and if both the inner sliding surfaces of the cylinder liner and piston ring become porous, seizure may occur during the initial break-in operation. This has the drawback of causing the porous layer to fall off and accelerating mutual wear of the inner sliding surfaces.

For example, the top ring, which has the highest load among piston rings, is designed to have a tapered or barrel-shaped sliding surface to increase the initial surface pressure in order to reduce oil consumption. If the sliding surface is rough, it will increase scratches and initial wear.

(Objective of the present invention) An object of the present invention is to obtain a combination of a cylinder liner and a piston ring with good corrosion resistance and durability.

(Structure of the present invention) The inner peripheral surface has a hardness of Hv 750 to 950 and a porosity of 5 to 40.
% porous chrome plated cylinder liner,
The cylinder liner and piston ring are basically combined with a gas-nitrided spheroidal graphite cast iron piston ring, thereby providing a cylinder liner and piston ring combination with good corrosion resistance and durability.

The present invention will be described in detail below.

(a) Cylinder liner FIG. 1 is an enlarged cross-sectional view showing the state of porous chromium plating applied to the cylinder liner in the present invention.
2 is a cylinder liner base material such as cast iron, aluminum alloy, or steel, and 2 is a porous chromium plating layer having a hardness of Hv850 to 950. Since the hardness of this plating layer decreases to about Hv750 due to thermal strain imposed by engine operation, the required lower limit hardness was set to Hv750. 3 is a recess formed on the surface of the chrome plating M2 by means such as electrolysis, special honing, or blasting, and 4 is a roughness. , 5~
This is the plateau surface of 2pII+.

The recesses 3 are formed to give the chrome plating layer 2 oil retention and initial conformability.If the area ratio (porosity) of the recesses to the whole is less than 5%, the oil retention will be insufficient and seizure will occur. If it exceeds 40%, oil consumption becomes excessive, so set it to 5 to 40%.For engines that consume a lot of oil within this range, select a value depending on the engine characteristics so as to reduce porosity. Note that there are three types of porous types: a channel type, a pinpoint type, and an intermittent type, and an appropriate one can be selected from these three types in relation to the porosity and engine characteristics.

(b) Piston ring Piston rings are designed to have high surface pressure to reduce oil consumption, and when combined with a porous chromium-plated cylinder liner, the surface pressure becomes even higher. It is necessary to reduce the size and provide toughness that can withstand high surface pressure through surface hardening treatment that allows finishing.

FIG. 2 shows a cross-section of a piston ring that is combined with a porous chrome-plated cylinder liner in the present invention. 5 is a piston ring base material of spheroidal graphite cast iron with a chromium content of 0.1-0.8% (in this specification, it is expressed as weight %) and a molybdenum content of 0.5-1.0%, and 6 is a hardness Hv550-750. 7 is a barrel-shaped sliding surface.

Since the porous chromium plating layer 2 of the cylinder liner on which the piston ring base material 5 slides has poor self-lubricating properties, it is necessary to make the piston ring base material 5 a cast iron material with graphite precipitated thereon to compensate for this.

However, with flaky graphite cast iron, the toughness deteriorates due to hardening during nitriding, causing problems such as the inability to withstand the expansion stress during assembly to the piston and breakage, so the tensile strength is 80 kg/
It is desirable that the material be a spheroidal graphite cast iron material with a martensite base of crn' or higher.

(c) Limits on elements added to the base material Molybdenum added to the piston ring base material 5 has no effect on hardening due to nitriding treatment, but if added in an amount of 2% or less, it only slightly increases hardness, but when high temperature nitriding This is necessary to improve high-temperature properties such as reducing the decrease in hardness caused by processing. If the amount added is less than 0.5%, there is no effect, and if it exceeds 1.0%, the hardness will become Hv 750 or more due to the amount of chromium added, which will be described later, which is inappropriate.

Although it is possible to increase the hardness by increasing the amount of molybdenum, it is necessary to add a larger amount than chromium, which will be described later, and it is an element more expensive than chromium.
In the present invention, the upper limit is set to 1.0%, which is necessary for improving high-temperature characteristics.

Chromium is cheaper than molybdenum.

Moreover, a small amount of addition is effective, and a nitrided layer hardness of Hv 550 to 750 was obtained with an addition amount of 0.1 to 0.8%.

This is a synergistic effect with the effect of adding 0.5 to 1.0% molybdenum, and the addition of chromium alone has a hardness of Hv40.
The results were low, ranging from 0 to 600. Chromium addition amount is 0.1
%, the hardness will be Hv550 or less, and if it exceeds 0.8%, the hardness will exceed Hv750 due to the relationship with the amount of molybdenum added, so the upper limit for the amount of chromium added is set at 0.8%.

(d) Hardness limit cylinder hardness of lychee hard chrome plating) (v850
~950, the hardness decreases due to the heat load during engine operation and the hardness decreases to about 1 (V750), so the hardness of the piston ring is reduced to Hv750 or less, and there is a problem in sliding compatibility with members of the same hardness. In order to eliminate this and provide wear resistance, the lower limit of nitriding hardness was set to Hv550.

Chromium has been described above as an important element because it changes to chromium nitride in the nitriding treatment and increases hardness, but other hardening elements such as vanadium (V) and aluminum (AM) can also be used.

(e) Curing depth In order to guarantee sufficient durability, the curing depth should be 10 g.
It is necessary that the number is greater than or equal to m. Even if the hardness is sufficient, if the hardness and thickness are insufficient, it will not be able to withstand surface pressure and will wear out quickly.

(f) Limitations of the nitriding method Nitriding by the commonly used salt bath method (tuftride) yields a hardened layer with a hardness of Hv550 or more and a thickness of 30 jLm, but produces a porous layer with a depth of approximately -. This porous layer has a characteristic that it becomes deeper in proportion to the processing time. Although the porous layer has high hardness, it lacks toughness, so if it slides against the porous chromium plating under high surface pressure, it will fall off, accelerating mutual wear of the Schilling Lichee and piston ring, and also inducing scuffing, which is undesirable.

The gas nitriding method rarely generates such a harmful porous layer, and the process for removing this porous layer is also easy. Therefore, in the present invention, a gas nitriding method was used.

(Example of the present invention) The results of bench-operation of the cylinder liner and piston ring manufactured according to the present invention using an actual machine are shown below.

(a) Test engine and operating conditions Engine: Cylinder diameter 85IIIllφ, stroke 105mm, 4 cylinders, 2370cc, 74PS decel engine Speed: 30QOrpm Water temperature, 110°C Oil temperature: 100°C Lubricating oil: 5c-cc class Operating time: 100 Hr (b) Specifications of test cylinder litchi After hard chromium plating was applied to the steel base material, the following properties were imparted by electrolytic etching and honing.

Porosity = 25-30% Porous depth: 4-6 m Plateau surface roughness: Approximately 1.5 pm Plateau surface ratio: 75-85% at 2 gm head Hardness:
Hv850-900 (C) Specifications of sample piston rings The following four types A to D were tested.

Piston ring C: Made of spheroidal graphite cast iron, without surface treatment.

Total carbon: 3.8%, St: 2.7%, M
n: 0, 4%, Cr: 0.3%, M.

20.8%, Cu: 0.8% Hardness: Rockwell C scale 30-40 Surface roughness: 1.0mm Piston ring B: Plasma sprayed on sliding surface.

The composition of the sprayed surface is Mo: 50%, Fe-Cr alloy = 50
% Hardened layer depth: 150 wells ■ Piston ring C: Made of spheroidal graphite cast iron and gas nitrided Base material composition: Same as piston ring A Gas used for nitriding: Ammonia Nitriding conditions: IHr at 560°C Depth with hardness Hv550 or more Hardness distribution: As shown by the broken line C in Fig. 3, Piston ring D is made of spheroidal graphite cast iron and nitrided in a salt bath.Base material composition: Same as piston ring A. Nitriding method: Tuftride Nitriding conditions: 580℃ TelHr Depth of hardness Hv550 or more: 30uLIll Hardness distribution:
As per the solid line in Figure 3.

Each piston ring was finished with a barrel length on the outer circumferential surface by a ramping process to a drum-shaped protrusion of about 20 gm with respect to a ring thickness of about 2.5 m+e, and this was tested as a top ring. For the second ring, a material equivalent to FC-25 was used in all tests without treatment.

FIG. 4 shows the amount of wear of each sample piston ring and cylinder liner after 100 hours of bench testing.

The upper row shows the amount of wear on the outer periphery of the piston rings A to D used as the top ring, and the lower row shows the amount of wear on the cylinder liner at the top ring top dead center position.

When using the piston ring C according to the invention, there is a tendency for cylinder liner wear to increase compared to the case of the untreated piston ring A, but the piston ring wear is significantly reduced, and the wear of the piston ring is significantly reduced. It is in a state. Therefore, it is effective in extending the life of the engine.

(Effects of the present invention) By combining a cylinder liner whose sliding surface is plated with porous chrome and a piston ring made of spheroidal graphite cast iron whose sliding surface is gas-nitrided, the compatibility between the two is matched and wear is reduced. We were able to obtain a less expensive and more durable engine.

[Brief explanation of the drawing]

Figure 1 is an enlarged sectional view showing the state of porous chrome plating, Figure 2 is a partial sectional view of the piston ring, Figure 3 is a diagram showing the hardness distribution of sample piston rings C and D, and Figure 4 is a diagram showing the hardness distribution of sample piston rings C and D. FIG. 3 is a diagram showing the amount of wear between sample piston rings A to D and a cylinder liner. 1 Nijiring liner base material, 2 Nichrome plating layer, 3: recess, 4 Nibrado surface, 5: piston ring, 6: gas nitrided layer, 7: sliding surface.

Claims (1)

[Claims] l) The inner peripheral surface has a hardness of Hv750 to 950 and a porosity of 5 to
A combination of cylinder lychee and piston ring made of 40% porous chrome plated cylinder lychee and gas nitrided spheroidal graphite cast iron piston ring. 2) Piston ring contains 0.1-0.8% chromium by weight
The combination of cylinder lychee and piston ring according to claim 1, which is spheroidal graphite cast iron containing 0.5 to 1.0% by weight of molybdenum. 3) Gas nitriding of the piston ring is carried out in a gas atmosphere of ammonia or ammonia and nitrogen at a temperature of 500 to 600°C, and the depth of the hardened layer with a hardness of 550 to 750 Hv is 10 p, m or more, and the final machined surface is Roughness 2,
The combination of a cylinder lychee and a piston ring according to claim 1, which has Op, va or less.