JPH0131026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston for a reciprocating engine.

In a reciprocating engine, reducing the piston clearance between the piston outer surface and the cylinder inner wall surface is effective in reducing engine noise, particularly piston slap noise. However, this piston clearance has a limit of about 40μ even in an autothermal piston that suppresses thermal expansion of the skirt, and any reduction beyond that will increase the piston's sliding resistance and cause the piston to burn out. bring about attachment. Therefore, the reality is that the slap sound cannot be sufficiently reduced.

In order to solve this problem, attempts have been made to reduce the piston clearance without increasing the sliding resistance by coating the outer surface of the piston with a coating material having desired properties. For example, according to the applicant's prior patent application (Japanese Patent Application No. 54-3312), the outer surface of the piston contains 10-25% by weight of flaky aluminum and 15-30% by weight of molybdenum disulfide (MoS ₂ ). Disclosed is an invention characterized in that a covering material made by dispersing epoxy resin in an epoxy resin is baked to a predetermined layer thickness. According to this invention, the fit of the piston, especially the skirt portion, to the inner circumferential wall of the cylinder improves, and noise is reduced. However, since the coating material with the above-mentioned composition has the property of being easily worn out, it is advantageous in forming the optimum piston profile at an early stage by lap operation of the engine. It is difficult to hold for a long period of time, and the clearance gradually increases, resulting in increased noise.

In addition, other patent applications by the applicant (Patent Application
No. 53-71167) discloses an invention in which wear and noise of the piston are reduced by forming a fluororesin coating on the surfaces of both side skirt portions of the piston. The above-mentioned fluororesin coating has excellent wear resistance, and the piston clearance does not gradually increase as the engine is used. However, the boiling point of the solvent is high, and it is difficult to apply additional layers to the coating layer baked at normal temperatures.If the coating layer is baked at a temperature lower than the normal baking temperature and coated thickly, the solvent will not come through. However, the range of use is limited due to the thickness of the layer, such as the formation of bubbles when it is applied as a thick poultice and then baked at a normal temperature. In addition, since the wear resistance is too good, an optimum profile cannot be formed by short-time lap operation under normal conditions.

The present invention has been made in order to solve the above-mentioned problems regarding the pistons of reciprocating engines, and reduces the piston clearance by coating the outer surface of the skirt portion of the piston with a coating material. In the case,
It is constructed so that the optimum piston profile can be obtained in a short time by lap operation of the engine without increasing sliding resistance, and the profile or the optimum piston clearance can be maintained for a long period of time. be. The purpose of this is to realize a highly reliable piston that maintains the slapping sound reduction effect for a long period of time and consumes less lubricating oil.

That is, the piston of the present invention has 10 to 40% by weight of scale-like aluminum in 35 to 75% by weight of a heat-resistant resin made of any one of epoxy resin, phenolic resin, silicone resin, and polyimide resin on the outer surface of the skirt portion. Weight% and fluororesin powder 15-55% by weight
The present invention is characterized in that a coating material made of a dispersed material is baked to a layer thickness of 15 microns or more, and the surface roughness of the coating material is adjusted to 5 to 20 microns. According to such a configuration,
Due to the small friction coefficient of the coating material, the piston clearance can be reduced without increasing sliding resistance, and the abrasion resistance is improved due to the action of the fluororesin. The piston clearance after the formation of the optimum profile is maintained substantially constant, and this optimum profile can be formed quickly by adjusting the surface roughness of the coating material within the above range.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 shows a piston according to the invention,
The outer surface of the skirt portion 2 of the piston 1, that is, the portion below the oil ring groove 3, is coated with a coating material 4. As shown in FIG. 2, this coating material 4 includes a heat-resistant resin 5 containing scale-like aluminum 6 and fluororesin powder 7 dispersed therein.
This is heat-cured.

The above-mentioned heat-resistant resin can withstand temperatures of around 250°C, as the temperature of the piston skirt can exceed 200°C, especially in diesel engines, and it can withstand temperatures such as fuel, lubricating oil, blow-by gas, etc. It must be something that cannot be violated.
Suitable materials include epoxy resins, phenolic resins, silicone resins, and polyimide resins. In addition, the resin needs to function as an adhesive to the outer surface of the piston skirt.
For this purpose, the ratio of the covering material to the whole must be at least 35.
% by weight is required. In addition, the upper limit of the ratio of the resin is:
The minimum required amount of scaly aluminum and fluororesin powder is 75% by weight.

Aluminum flakes are added to improve the heat resistance of the coating material and the peeling resistance against shear loads.
It is necessary to add more than % by weight. However, if it exceeds 40% by weight, the effect will be saturated, and the strength of the coating material will decrease.
That is, the adhesion force to the outer surface of the piston is reduced.

Fluororesin powder is an abrasion resistance improver for coating materials, and the reason for using powder is that liquid fluororesin has the following drawbacks. In other words, the liquid fluororesin has extremely poor miscibility with the base resin;
In addition, the original characteristics cannot be obtained unless the material is thermally hardened at a high temperature of 300° C. or higher, and at this temperature, the strength of the piston is drastically reduced in the case of an aluminum alloy piston. Note that the particle size of the fluororesin powder is preferably 24 μm or less in relation to the surface roughness of the coating material.

The graph in FIG. 3 shows how this fluororesin powder is involved in improving the abrasion properties of the coating material. This graph shows the ratio of fluororesin powder to 10, 15,
19, 26, 32, and 40% by weight, and the heat-resistant resin is an epoxy resin coating material, and the amount of wear (reduction in piston diameter) is compared by test operation under certain conditions. As a conventional example, data is shown for a coating material disclosed in the above patent application (Japanese Patent Application No. 54-3312) consisting of 20% by weight of molybdenum disulfide, 25% by weight of scaly aluminum, and 55% by weight of epoxy resin. . In addition, the test conditions are:
The coating thickness of the coating material is 20μ, the surface roughness is 2 to 3μ, the piston clearance during coating is 0μ, and the heat curing conditions of the coating material are 225℃, 30 minutes (the conventional example is 180℃, 30 minutes).
For coating materials with a fluororesin powder ratio of 15% by weight, heat curing conditions were also conducted at 180°C for 30 minutes, which is shown in the broken line bar graph in Figure 3. It shows. The engine used is a 1.5 gasoline engine, and the operating conditions are
3000RPM, full load, 50 hours. According to this, when the fluororesin powder is 10% by weight, the significant difference from the conventional example is small, but when it is 15% by weight or more, the amount of wear decreases significantly, and the fluororesin powder improves the wear resistance of the coating material. I can see that it is improving.

Furthermore, the wear resistance of the coating material is also influenced by the thermosetting conditions, as shown in FIG. In other words, the wear resistance improves as the thermosetting temperature increases, but 225
It becomes saturated at around ℃, and its wear resistance is not sufficient at 160℃. Therefore, considering the influence on piston strength, the temperature is preferably 180°C to 225°C, and in that case, the baking time should be 30 minutes or more. Here, the fourth
The data in the figure shows that the composition of the coating material is fluororesin powder 26
The test conditions are the same as the test shown in FIG. 3 above.

In addition, as each component of the above-mentioned coating material, for example, heat-resistant resin and scaly aluminum, epoxy resin containing scaly aluminum can be used.
DHX-M1 (product name) and fluororesin powder are
Mitsui Fluorochemical TLP-10 (trade name) is used. Coating methods for the covering material include spraying, transfer, sheet adhesion, electrostatic coating, and the like.

As described above, by adding the fluororesin powder, a coating material with excellent wear resistance can be realized. but,
If the wear resistance is too good, it will be difficult to obtain an optimum piston profile or piston clearance during short lap operations after application of the cladding material. Therefore, by adjusting the surface roughness during coating of the coating material to a relatively rough fixed range, reducing the apparent wear resistance and accelerating initial wear, an optimal profile can be achieved by short-term lap operation. Aim to be formed. In order to form this optimal profile, the amount of wear of the coating material of 2.5μ or more (radius) is required.

By the way, the current piston clearance is the diameter, that is, the difference between the cylinder inner diameter and the piston outer diameter.
For gasoline engines, it is 30 to 60μ, and for diesel engines, it is 40 to 200μ, but in the case of pistons coated with coating materials, it is 10 to 30μ for gasoline engines, and 20 for diesel engines.
It can be reduced to ~40μ without increasing the sliding resistance. This is compared to a piston with a clearance of 40μ without coating and a piston with clearance of 20μ with coating.
Taking the piston as an example, it can be seen that there is almost no difference in resistance loss between the two as shown in FIG. 5, and that the piston clearance can be halved by coating the piston with a covering material. Note that even if the piston is coated with a coating material, the resistance loss will be large if the clearance is 0μ. Here, the coating material used in this test was 26% by weight of fluororesin powder, 30% by weight of scaly aluminum, and epoxy resin.
44% by weight was thermally cured at 225°C for 30 minutes, and the surface roughness was 2 to 3μ. The engine used is a 2.0 gasoline engine.

In other words, for a piston coated with a coating material, it is only necessary to obtain an optimum piston clearance of 10 to 30μ for a gasoline engine and 20 to 40μ for a diesel engine through initial wear due to lap operation. It is only necessary to obtain the optimum profile of the piston skirt portion. The surface roughness of the coating is adjusted to achieve this.

FIG. 6 shows the relationship between the surface roughness of the coating material and the initial wear due to lap operation, and there is a certain range depending on the displacement per cylinder for both gasoline engines and diesel engines. Now, assume that the current piston is coated with a coating material so that the piston clearance becomes 0μ, and that the above-mentioned optimum piston clearance is obtained through initial wear due to lap operation. First, in the case of a gasoline engine, the current piston clearance is 30 to 60μ (for the diameter), so the coating thickness is 15 to 30μ (for the radius).
In order to wear this until the optimum clear run is 10 to 30μ (for the diameter), the amount of wear is 5 to 15μ (for the radius).
Therefore, the remaining coat thickness is 10 to 15μ (radius).
To obtain this amount of wear, the surface roughness during coating must be approximately 7 to 20μ, as shown at points a and b in Figure 6.
Just adjust it. Also, in the case of diesel engines, the current piston clearance is 40 to 200μ.
(diameter), the coating thickness is 20 to 100μ
(half a length), and this is the optimum clearance of 20~
To wear down to 40μ (diameter), a wear amount of 10 to 40μ (radius) is required, and the remaining coat thickness is 10 to 40μ (radius).
80μ (radius). To obtain this amount of wear,
As shown by points c and d in FIG. 6, the surface roughness at the time of coating may be adjusted to about 10 to 12 microns. Taking all of this into consideration, when coating the covering material, it is only necessary to adjust the coating thickness to 15μ or more and the surface roughness to a range of 5 to 20μ, and within this surface roughness range. Since the coating material wears out by more than 2.5μ (radius), it is possible to form the optimum profile for the piston skirt.
In addition, the above test conditions are 26% by weight of fluororesin powder,
The coating material is made of 30% by weight of flaky aluminum and 44% by weight of epoxy resin and is heat-cured at 225℃ for 30 minutes.The lap operation of each engine can be varied from no load to full load depending on the engine. While changing
It lasted 20 hours. The coating material whose surface roughness has been adjusted as described above is as shown in Figures 7 and 8.
The initial wear was almost completed after 10 hours of lap operation.
There will be almost no wear after that. Here, the experimental data shown in Figures 7 and 8 are 26% by weight of fluororesin powder, 30% by weight of scaly aluminum, and epoxy resin.
44% by weight of the coating material was thermally cured at 225℃ for 30 minutes. Figure 7 shows the case of lap operation for 10 hours at 3500 RPM, 3/4 load, with a 1.5 gasoline engine. Figure 8 shows the case of a 3.0 diesel engine running at 2500 RPM, 3/4 load, and 10 hours of lap operation.

Next, based on the above study results, we will explain the results of a test to confirm the durability of the coating material (change in wear amount with respect to operating time) and change in noise over time, which was conducted on specific examples. . Here, the coating materials are 26% by weight of fluororesin powder, 30% by weight of flaky aluminum, and 44% by weight of epoxy resin, and the thermosetting conditions are 225°C for 30 minutes, and 15% of fluororesin powder. weight%, flaky aluminum 34% by weight,
A second example B with 51% by weight of epoxy resin and the same heat curing conditions as the first example A, and 20% by weight of molybdenum disulfide, 25% by weight of scaly aluminum, and 55% by weight of epoxy resin were heated. Curing conditions are 180℃, 30℃
A comparison was made of the conventional examples.

Figure 9 shows a 1.5 gasoline engine with a piston clearance of 0 μ at the start of the test, a coating thickness of 20 μ, and a surface roughness of 2 to 3 μ.
This shows the results when operating at 3000 RPM and full load. In both Examples A and B, the amount of wear was significantly smaller than in the conventional example, and moreover, the amount of wear was almost negligible in a short time after the start of operation. It stops changing. Figure 10 shows a 3.0 diesel engine with a piston clearance of 10μ at the start of the test, a coating thickness of 35μ, and a surface roughness of 2 to 3μ.
9th when operating at 3800 RPM and full load.
The results are similar to those shown in the figure. Furthermore, Figure 11 shows the change in noise level over time when operation is started with a piston clearance of 0μ (uncoated conventional example is 170μ) and a surface roughness of the coating material of 15μ. About diesel engine
This is when operating at 3000 RPM and full load.
As a result, in the conventional example, the noise level reaches the same level as in the uncoated case after a very short running distance, but in both Examples A and B, the noise level is maintained at a low level.

As described above, according to the present invention, in a piston of a reciprocating engine, the piston clearance can be reduced without increasing the sliding resistance, and the optimum piston clearance and the optimum profile of the piston skirt can be reduced in a short period of time. It can be obtained by lap operation and is retained for a long period of time. As a result, the effect of reducing slapping noise and the like is maintained for a long period of time, and a piston with low lubricant consumption and high reliability is realized.

[Brief explanation of drawings]

Figure 1 is a partial vertical cross-sectional view of a piston according to the present invention, Figure 2 is an enlarged vertical cross-sectional view of the coating material in Figure 1, and Figure 3 is the amount of fluororesin powder added to the coating material and wear resistance. Figure 4 is a graph showing the relationship between heat curing temperature and wear resistance of the coating material, Figure 5 is a graph showing the sliding resistance of a piston coated with the coating material, and Figure 6 is a graph showing the relationship between the heat curing temperature and wear resistance of the coating material. A graph showing the relationship between the surface roughness of the material and the amount of wear. Figures 7 and 8 are graphs showing the state of initial wear of the covering material. Figures 9 and 10 compare the durability of the embodiment of the present invention and the conventional example. The graph in FIG. 11 is also a graph comparing the noise levels. DESCRIPTION OF SYMBOLS 1... Piston, 2... Skirt portion, 4... Covering material, 5... Heat-resistant resin, 6... Scale-like aluminum, 7... Fluorine resin powder.

Claims (1)

[Claims] 1 10-40% by weight of flaky aluminum and 15-55% by weight of fluororesin powder in 35-75% by weight of a heat-resistant resin made of any one of epoxy resin, phenolic resin, silicone resin, and polyimide resin. A piston for an engine, characterized in that the outer surface of the skirt part is baked and coated with a coating material made by dispersing the above to a thickness of 15 microns or more, and the surface roughness of the coating material is adjusted to 5 to 20 microns.