JPH03244875A - Piston ring - Google Patents

Abstract

PURPOSE:To improve a sliding characteristic inherent in a piston ring and to make the ring lighter in weight by applying hard surface treatment to a sliding surface, with at least a cylinder, of an aluminum alloy not lower than HRB40 in hardness at room temperature after heating as long as 100 hours at 250 deg.C. CONSTITUTION:A piston ring 10 is formed by an aluminum alloy as being more than HRB40 in hardness at room temperature after heating as long as 100 hours at 250 deg.C. Hard surface treatment is applied on a sliding surface, with at least a cylinder, of this piston ring 10. With this constitution, as for abrasion resistance, seizure resistance or the like, it has a characteristic equivalent to an iron piston ring, and as for blow-by gas and fluttering, it has such a characteristic as far surpassing the iron piston ring, thus the suchlike excellent piston ring 10 is securable.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a lightweight piston ring used in an internal combustion engine.

(Prior Art) Piston rings are generally made of cast iron, and some are also made of steel such as high carbon stainless steel. Further, the piston ring is subjected to surface treatments such as Cr plating, MO spraying, ferrochrome spraying, etc. to improve wear resistance and seizure resistance.

On the other hand, aluminum, which is a typical industrial material along with steel, is not used for piston rings because it inherently has lower strength and wear resistance than steel. However, in recent years, a rapid solidification powder metallurgy method for aluminum has been put into practical use as a technology that deserves attention, and the use of powder metallurgy products manufactured by this method as various automobile parts is being considered. Specific examples include cylinder liner connecting rods,
Piston, synchronizer ring (Japan Institute of Metals silver, 1
988 Vo1.27. No, 6. page 491),
Piston, connecting rod, cylinder sleeve, spring retainer, synchronizer ring (cited above, p. 494), cylinder liner valve guide (Japanese Patent Publication No. 61-45694), connecting rod, piston,
A cylinder (Japanese Patent Publication No. 20215) is being considered.

In addition, the use of aluminum matrix composite materials with ceramics such as SiC and A1□03 for connecting rods, pistons, cylinder liners, etc. is also being considered (
Nikkei New Material, December 11, 1989 issue No. 7
page 3).

However, no study materials have been found regarding what conditions the aluminum-based material must satisfy in order to be used for piston rings. This is because piston rings are thin-walled and slide at high speeds as described below, so materials that meet the required characteristics for thick-walled parts such as pistons and cylinders are suitable for piston rings. Because I can't say it.

Since it is essential to reduce the weight of moving parts in order to increase the speed of engine rotation, there is a demand for reducing the thickness of piston rings. This is because the piston ring is thinner, which allows the piston to be made smaller and thinner, and it is expected that both the piston ring and the piston will be lighter.

Furthermore, when the engine rotates at high speed, if the weight of the piston ring is large, the piston ring will cause fluffing due to inertia force, increasing blow pie, so there is a need to reduce the weight of the piston ring from this point of view as well.

Also, the piston ring is pressed against the cylinder by the combustion gas pressure, and this force seals the gas. However, it is necessary to constantly maintain a force that follows the deformation of the cylinder. For this reason,
The piston ring is machined into a shape that is slightly more open than a perfect circle in its free state, and is fitted by elastically closing the ring into a perfect circle along the inner diameter of the cylinder.

When it comes to the top ring of steel piston rings, the thickness was 1.5 10 years ago.
What used to be ~2.0mm is now 1.5~1.0m
m is increasingly being used. Furthermore, near ■, a top ring with a thickness of 0.8 mm or 0.6 mm is required.

However, if the piston ring is made thinner, the width of the piston ring groove will naturally become smaller, and a thinner cutting tool will need to be used. As a result, chatter and the like are likely to occur, the machining accuracy of the piston is insufficient, and the sealing performance is impaired. For this reason, 0.6 mm is currently said to be the limit for the thickness of a steel ring, and it is impossible to make the steel ring thinner or lighter than this.

(Problems to be Solved by the Invention) It is believed that if an aluminum alloy with a low specific gravity is used for the piston ring instead of the conventional iron-based material, weight reduction can be achieved without reducing the thickness. Considering that a surface treatment film such as Cr plating is usually formed on the sliding surface of steel piston rings, anodizing, Cr plating, Ni-based plating, Fe plating, etc. is applied to the sliding surface of aluminum piston rings. Since it will be necessary to carry out hard surface treatment applicable to A° C., such as base plating, it is not necessary to require good sliding properties from the base aluminum alloy itself. However, if the hardness or strength of the base is low, when abrasive particles are present on the sliding surface, the hard surface treatment film on the surface will peel off or wear out in the form of depressions. The base aluminum alloy is required to have the ability to support the surface treatment film.

As mentioned above, the piston ring seals the combustion gas inside the engine, so its temperature rises to nearly 300℃ during operation.For this reason, when using aluminum alloys made by conventional casting methods, even if they are made of T6 or similar material before use, Even if hardening heat treatment is performed, it will soften and plastically deform at the temperature during use.
Furthermore, the degree of softening and plastic deformation increases due to coarsening of crystal grains.

The predetermined number of piston rings is determined in accordance with the elastic modulus of the material when assembled to the cylinder so that the piston rings are pressed against the cylinder by their own elastic force. However, when ordinary aluminum alloys are exposed to the operating conditions of piston rings for a long time, they lose their elasticity due to plastic deformation such as creep deformation.

Furthermore, due to the decrease in hardness, the sliding characteristics of the piston ring sliding surface due to surface hardening treatment cannot be maintained.

As described above, it has not been possible to use ordinary aluminum alloys for piston rings even if the piston rings are intended to be subjected to surface hardening treatment.

The present invention was carried out in view of these circumstances, and it is an object of the present invention to provide a piston ring that achieves sliding characteristics better than that achieved with steel rings and is significantly lighter in weight.

(Means for Solving the Problems) The present invention is made of an aluminum alloy whose hardness at room temperature after heating at 250°C for 100 hours is H□40 or more,
It relates to piston rings that have hard surface treatment applied to at least the sliding surface with the cylinder.

The temperature of the piston ring, which is attached to the piston and moves up and down at high speed inside the cylinder while sealing high-pressure combustion gas, rises to nearly 300°C, and combustion products exist as abrasive particles on the sliding surface. , the sliding conditions of piston rings are severe. In order to withstand such severe sliding conditions, piston rings require measures from both the base material and surface treatment. As a countermeasure for the latter,
It is essential that at least the sliding surface with the cylinder be subjected to hard surface treatment for the purpose of improving wear resistance and seizure resistance. Furthermore, in recent high-output engines, the temperature inside the combustion chamber is high, and adhesion and wear between the piston groove and piston ring can become a problem. It may also be necessary to apply a hard surface treatment.

Note that the portion of the piston ring that slides on the piston groove may be treated with a self-lubricating film instead of the hard surface treatment.

Depending on the conditions under which this hard surface treatment film is used,
Wet plating films by electrolytic or electroless methods such as Cr plating, Fe-based plating, Ni-based plating, etc., metals, their carbides, nitrides, oxides, composite compounds, etc. by sputtering or ion blating methods, etc. Dry surface treatment films can be selected from.

However, even if such hard surface treatment is performed, if the hardness and strength of the underlying piston ring base material are low, the hard surface treatment film will break and fall off due to deformation of the base, making it difficult to maintain excellent sliding properties. Can not do it. In order to maintain the effects of hard surface treatment on improving wear resistance and seizure resistance, the base aluminum alloy must be used in a small amount (hardness at room temperature is H1lfi).
It needs to be 40 or more. Here, hardness refers to the value measured at room temperature after being heated at 250° C. for 100 hours, since we are considering application to piston rings that are used at high temperatures for long periods of time. Furthermore, if heating is performed at 250° C. for 100 hours, and then heating is performed again at 250° C., the hardness decreases. Therefore, the hardness (H, 1, ≧40) measured after the initial heating at 250° C. x 100 hours is a requirement of the present invention.

In aluminum alloys manufactured by ordinary casting methods, the strength and hardness at room temperature can be significantly improved by adding alloying elements such as copper and magnesium and performing age hardening heat treatment. However, when heated to a temperature exceeding 200° C., the precipitates rapidly become coarser and the strength and hardness decrease. If heated for a further long time, the structure will become coarser and the strength and hardness will further decrease. Therefore, when heated to 250°C for 100 hours, an alloy that can maintain hardness at room temperature exceeding HRB40 cannot be obtained;
It could not be used for piston rings whose temperature rises to close to ℃.

On the other hand, the rapidly solidified aluminum powder alloy contains Fe.

When a large amount of transition metals such as Ni and Mn are added, a structure in which intermetallic compounds are finely dispersed and is stable even at high temperatures can be obtained.

Transition metals include Fe, CrMn, Ti, Mo, Zr
, Ni, Co, Ta, W, etc. can be used.

However, although Cu and Ag are transition metals, they are easily alloyed with Aj2 and have a high diffusion coefficient in β, so they are not essential components (optional components) in the present invention.Also, transition elements other than the above, Rb , Sr., Y.

Since Cs-Hf is a relatively rare element, it is unsuitable for use in terms of cost.

In addition to the above-mentioned Cu, SL, Mg, etc. can be added as optional components to the aluminum alloy of the present invention. Si
forms eutectic or primary Si to improve wear resistance, and its content is 8 to 30%. Cu and Mg are aging components, and their content is 0.2 to 8.0%.

The diffusion coefficient of transition metals in aluminum is very small compared to copper 5, magnesium, etc., which are age-hardening components, and intermetallic compounds do not tend to coarsen even when heated to high temperatures for long periods of time. The dispersion-strengthening effect of steel remains almost unchanged even when heated to high temperatures for long periods of time. Therefore, the sliding properties of the hard surface treatment film are maintained during use of the piston ring. If a rapidly solidified aluminum powder alloy has a composition in which a large amount of transition metal is added, an aluminum alloy having a strength H of 11140 or more at room temperature can be obtained even if heated to 250° C. for 100 hours or more.

By using such an aluminum alloy, it is possible for the first time to obtain a piston ring that is significantly lighter in weight without impairing the effects of improving the wear resistance and seizure resistance of the hard surface treatment film.

Although several methods have been proposed for producing rapidly solidified aluminum powder metallurgy alloys, a method that combines air atomization and hot extrusion is currently practiced industrially. The cooling rate during powder production has a large effect on the properties, so if cost permits, the splat method, which has a faster cooling rate than the atomization method, can also be used.

The piston ring is pressed against the cylinder by the combustion gas pressure, and this force seals the gas. However, in order to perform stable sealing while following the deformation of the cylinder, it is necessary to constantly maintain the force pressing against the cylinder using the elastic force of the piston ring itself. For this reason, the piston ring is machined into a shape slightly more open than a perfect circle in its free state, and is fitted into the cylinder by elastically closing it into a perfect circle along the inner diameter of the cylinder. Even in rapidly solidified aluminum powder alloys whose hardness does not change even when heated to high temperatures for long periods of time, the yield strength at high temperatures is lower than at room temperature, so long-term operation causes plastic deformation and decreases in tension. .

Therefore, a suitable recess 1 as shown in Fig. 2 is made on the opposite side of the cylinder sliding surface so that the spring can be seated better.
The piston ring is machined into a "U" shape with 0a, and the piston ring is appropriately selected from iron-based alloys, nickel-based alloys, cobalt-based alloys, and titanium-based alloys. By incorporating a spring made of a unique material into the recess, the tension of the piston ring can be kept constant and the sealing performance can be maintained stably for a long time.

As the spring shape for maintaining tension, a torsion bar type shown in FIG. 3, a coil type shown in FIG. 4, etc. can be used.

The cross-sectional shape of the spring 11 (Fig. 3) does not need to be round;
A square cross section or an irregular cross section shape can be selected as appropriate.

The piston ring according to the present invention can be used as any one of a top ring, a second ring, and an oil ring, or can be used as all of them. That is, a combination of the piston ring of the present invention and a conventional piston ring is also possible, and all the piston rings can be the piston ring of the present invention.

Furthermore, when the piston ring of the present invention is used in an oil ring, it is necessary to apply tension and a spring must be incorporated in the same way as in the case of a steel ring. On the other hand, when the piston ring of the present invention is used as a top ring, it is not necessarily necessary to incorporate a spring, but it is preferable to use a tension applying mechanism using a spring. The oil ring can be a combination ring as well as a conventional steel ring.

Further, the dimensions of the piston ring are calculated using a known calculation formula. Among the various constants used here, those specific to rapidly solidified aluminum alloys are the elastic modulus E = 7000 to 120.
00kg/mm”.

Other constants are determined by the design of the internal combustion engine.

Note that even though the thickness (one dimension) is the same as that of a steel piston ring, it is possible to achieve a lighter weight than the latter. By setting the T dimension to 0.6 to 1.2 mm, that is, equal to or less than one dimension of a currently used piston ring, a piston ring with an extremely small amount of blow pie can be provided.

Hereinafter, the present invention will be explained in detail with reference to Examples.

(Example) Rapidly solidified powders (particle size average 45 μm) having compositions shown as A to J in Table 1 were produced by air atomization, and billets for extrusion were formed by cold isostatic deformation. Thereafter, preheating that also served as degassing was carried out in an argon atmosphere, and a molded article having substantially true density was obtained by hot indirect extrusion (extrusion temperature: 400° C., extrusion ratio: 20).

Table 1 shows the hardness of various alloys at room temperature when they were subjected to T6 or O treatment and then heated to 250° C. for 100 hours. Alloys A to G are rapidly solidified aluminum powder alloy compacts according to the present invention. H to J are comparative materials in which an alloy with excellent heat resistance was selected from commonly available casting alloys, and a round bar obtained by hot top casting was processed by hot indirect extrusion. K is the steel currently used for piston rings (steel type 5WO3C-V (silicon chrome steel for valve springs, oil tempered wire, hardness Hmv'r 500).

(Left below) From this, it can be seen that normal cast aluminum alloys are
Compared to the fact that the hardness decreases significantly after heating for 00 hours,
It can be seen that rapidly solidified aluminum powder alloys containing a large amount of transition metals and having a large amount of fine intermetallic compounds dispersed have little decrease in hardness.

Further, since high hardness can be obtained even in the O-treated state, by using the O-treated material, it is possible to obtain a product with almost no change in hardness due to heating.

For some of the materials in Table 1, the destruction of the surface hardened film due to sliding was compared using the method described below.

When surface hardening is performed on a base with low hardness, in order to reproduce the destruction of the film due to deformation of the base and the wear caused by falling off, a thick coating is applied to various materials, similar to that applied to ordinary piston rings. The load at which a crack would form in hard Cr plating with a thickness of 50 μm was investigated. The friction tester used is shown in Figure 5.

In the figure, 1 is the stator holder, 2 is the disk, 3 is the oiling hole, 4
is a rotor, 5 is a test piece holder, and 6 is a test piece. The piston ring material was processed into a bottle-shaped specimen 6 with a square cross section of 5 mm x 5 mm, and the bottle was Cr-plated and heat-treated as described above.
It was made to slide with disk 2 of. Engine oil is used for lubrication.
The sliding speed was kept constant at 5 m/sec, and the presence or absence of cracks was confirmed while gradually increasing the load. In this way, the maximum load at which cracks do not occur in Cr plating was determined, and the results are shown in FIG. 1 in comparison with the values when Cr plating is applied to current steel materials.

In the figure, the horizontal axis is the hardness (H,
, ), and the vertical axis shows the crack generation load (1 ton) when the steel material is 1.

The hardness of the cast materials (H, J) decreased significantly due to heating, and cracks occurred under low loads in the cast materials (H, J) with low deformation resistance.

On the other hand, rapidly solidified aluminum powder metallurgical alloy (A) maintains high hardness even after heating.

It can be seen that cracks do not occur in specimens C, E, and G) even under high loads.

Looking at the relationship between hardness and crack generation load, HR,
If it is 40 or more, it can be used as a piston ring because it shows almost the same load resistance as the current steel material.

Actual machine test The piston ring according to the present invention was installed in an actual engine, and the blow pie amount was compared with that of a conventional piston ring made of iron-based material.

The steel piston ring used in the actual machine test had a thickness (8
The dimensions) were 1.2.1.5.2.0 mm.

In this actual machine test, in order to clearly demonstrate the effect of reducing the weight of the top ring, only the top ring of the piston ring with a thickness of 1.2 mm was replaced with the inventive material and the conventional material, and the second and oil rings were made of the same material. used. As an aluminum alloy piston ring, A (0 treatment) in Table 1 was used here, and after processing it into a piston ring shape with a thickness of 1.2 mm, Cr plating (thickness of 50 μm) was applied to the outer peripheral surface that slides on the cylinder. The other parts were used in the test without surface treatment. FIG. 6 shows the amount of blow pie at full load, and FIG. 4 shows the amount of blow pie at no load.

From Figure 6, by reducing the thickness of the iron piston ring (8 dimensions) and reducing the weight of the top ring,
It can be seen that the amount of blow pie is decreasing. It can also be seen that by using an aluminum alloy to make the piston ring even lighter, the amount of blow pie can be further reduced.

As shown in FIG. 7, under no-load conditions, the amount of blow pie increases rapidly in the high rotation range where fluttering occurs. However, as the weight of the piston ring is reduced, the amount of blow pie is maintained even in the high rotation range, which shows the effect of reducing the weight of the piston ring. The aluminum alloy piston ring had no abnormalities in appearance after the test (and almost no wear was observed).

Change in Tension Due to High Temperature Heating The tension in the piston ring is generated by the elastic deformation stress when the piston ring closes in a perfect circle, so the tension depends on the size of the abutment gap in the free state. Therefore, to examine changes in tension, it is sufficient to examine changes in the abutment gap.

Here, as an example of the piston ring according to the present invention, a piston ring body 10 shown in FIG. 8 using an aluminum alloy of A (O treatment) in Table 1, and a spring using Inconel 750 shown in FIG. 11 were combined as shown in FIG. The piston ring has a gap of 9 mm in its free state, an outer diameter of 75 mm in a perfectly circular state, and a thickness of 1.
2 mm and 3.1 mm high, this piston ring weighed 45% compared to a steel piston ring.

Surface hardening treatment is applied not only to the outer peripheral surface that slides on the cylinder (
The upper and lower surfaces that slide on the piston groove and the inner circumferential surface that contacts the spring were also plated with hard Cr.

This piston ring is assembled into a disk with a top ring groove modeled after the shape of the piston, and this disk is assembled with an inner diameter of φ75m.
It was fitted into a cylinder corresponding to the m cylinder. This is 3
The sample was placed in an oven heated at 00°C, heated for 10 hours, then taken out and cooled to room temperature.

The piston ring was removed from the cylinder and disk, and changes in the abutment gap in the free state before and after heating were measured. Similar tests were conducted on steel and cast iron piston rings. These results are shown together in FIG. 10.

In the figure, the materials of steel and cast iron are as follows.

Steel A: 5US440 equivalent material, Steel B (
SWO3C-V equivalent material), cast iron A (FCD60 equivalent material)
, Cast iron B (FCD20 equivalent material). From Figure 10, by combining an aluminum alloy piston ring spring on the inner circumferential side, a piston ring with a gap reduction rate comparable to that of steel and cast iron piston rings can be obtained, and stable tension can be maintained for a long time. It is clear that this can be done.

(Operations and Effects of the Invention) According to the present invention, by applying hard surface treatment to an aluminum alloy base material having a predetermined hardness, it has properties equivalent to iron-based piston rings in terms of wear resistance, seizure resistance, etc. With regard to blow-by gas and fluttering, a piston ring can be obtained that has characteristics far superior to iron-based piston rings. Aluminum is inherently inferior to iron-based materials in wear resistance and seizure resistance, but hard surface treatment and the hardness of a given base material improve these properties.

On the other hand, aluminum is suitable for weight reduction and is more suitable for blow-by gas and fluttering than iron-based materials. Even if the hardness is specified as described above, aluminum tends to lose tension at high temperatures, which is not preferable in terms of piston ring characteristics. Although this problem can be avoided by designing the shape of the piston ring in consideration of the decrease in tension, it can be fundamentally solved by using a spring to compensate for the decrease in tension.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between piston ring hardness (H, I) and crack generation load, Figure 2 is a diagram showing the cross-sectional shape of a piston ring having a recess into which a spring is fitted, Figures 3 and 4 The figure shows the spring, Figure 5 is a partial cross-sectional view showing the outline of the friction tester, and Figure 6 is a graph showing the relationship between the 8 dimensions (thickness) of the piston ring subjected to the full load test and the amount of blow pie. , Figure 7 is a graph similar to Figure 6 for the no-load test, Figure 8 is a diagram of the piston ring in the example, Figure 9 is a diagram of the piston ring assembled in the disk in the example, and Figure 10 is a free graph. It is a graph which shows the abutment gap reduction rate in the state.

Claims (1)

[Claims] 1. Hardness at room temperature after heating at 250°C for 100 hours is H_
A piston ring made of an aluminum alloy having an R_B of 40 or more and having hard surface treatment applied to at least the sliding surface with the cylinder. 2. The piston ring according to claim 1, characterized in that a spring for supplementing tension is incorporated in a portion on the opposite side of the sliding surface with respect to the cylinder. 3. At least Fe, Cr, Mn, Ti as alloying elements
3. The piston ring according to claim 1, wherein the piston ring contains 2.5 to 20.0 wt% of transition metals such as , Mo, Zr, and Ni, singly or in combination of two or more.