JP2013167254A - Piston for internal combustion engine with double layer film composition and piston surface treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston having superior adhesion to a piston base material made of aluminum alloy or the like, as well as superior initial fitness, configured to wear promptly to obtain a smooth sliding surface, especially in an early stage of sliding.SOLUTION: On the outer peripheral surface of both skirts 8, 9 of a piston 1 base material 1a made of aluminum alloy, a double layer film composition formed of a lower layer film composition 22 and an upper layer film composition 21 above it is formed. The lower layer film composition and the upper layer film composition include at least one of polyamideimide resin or polyimide resin, or epoxy resin, which are binding resins. In the lower layer film composition, content of solid lubricant made of molybdenum disulfide is 50wt% or less. In the upper layer film composition, content of molybdenum disulfide is 50 to 95 wt%, respectively.

Description

  The present invention relates to a technology of a piston of an internal combustion engine to which an inner / outer double multilayer coating composition is applied and a surface treatment method of the piston.

  As well known, for example, as a method for improving the wear resistance or seizure resistance on the surface of a sliding part such as a piston of an internal combustion engine for automobiles, a composition containing a solid lubricant in a resin serving as a binder is used. Various techniques applied to the surface have been proposed.

  As one of the techniques described in Patent Document 1 below, in order to achieve a low coefficient of friction and high wear, at least one of a polyamide-imide resin and a polyimide resin as a binding resin material is 50 to 73 wt%, a solid A sliding resin composition comprising 3 to 15 wt% of polytetrafluoroethylene, 20 to 30 wt% of molybdenum disulfide and 2 to 8 wt% of graphite as a lubricant, wherein the total of the solid lubricant is 27 to 50 wt% is provided. ing.

  However, if the blending amount of molybdenum disulfide or graphite is more than necessary in order to improve the seizure resistance, the strength of the resin coating layer itself is extremely lowered and the wear amount of the resin coating layer is increased. There was a fear.

  Therefore, as described in Patent Document 2, there is provided a technique for forming a double coating composition on the surface of a piston base material made of an aluminum alloy material of an internal combustion engine.

  That is, on the surface of the piston base material, at least one of an epoxy resin and a polyamideimide resin as a binding resin is 50 to 79 wt%, polytetrafluoroethylene as a solid lubricant is 15 to 30 wt%, and molybdenum disulfide is 5 to 20 wt%. % Of the lower layer coating composition, and on this surface, at least one of an epoxy resin and a polyamide-imide resin as a binding resin is 50 to 70 wt%, boron nitride as a solid lubricant is 5 to 20 wt%, and hard particles A double coating composition is formed by applying an upper coating composition comprising 15 to 30 wt% of at least one of silicon nitride and alumina.

  As a result, the wear resistance is excellent, and the initial familiarity and seizure resistance are improved.

Japanese Patent Application Laid-Open No. 07-097517 JP 2008-56750 A

  However, in the technique described in Patent Document 2, the upper layer coating composition is particularly set to 5 to 20 wt% boron nitride which is a solid lubricant, and further includes at least one of silicon nitride and alumina which are hard particles. Since the surface is set to 15 to 30 wt%, the surface is more easily worn than metals such as aluminum alloys, but the surface is relatively hard, so it takes a long time to become smooth. However, quick wear cannot be obtained. As a result, there is a technical problem that initial familiarity cannot be obtained quickly and sufficiently.

  An object of the present invention is to provide a piston for an internal combustion engine having excellent adhesion to a base material such as an aluminum alloy piston, and excellent initial adaptability.

According to the first aspect of the present invention, there is provided a lower layer coating composition formed on the surface of the piston base material on the outer peripheral surface of the piston skirt that slides on the cylinder wall surface, and a coating formed on the upper surface of the lower layer coating composition A piston for an internal combustion engine in which a multilayer lubricating film is formed by the upper layer coating composition,
Having a streak on the outer peripheral surface of the skirt,
The lower layer coating composition and the upper layer coating composition each include one or two types of polyamideimide resin, polyimide resin, or epoxy resin, which are binding resins, and the lower layer coating composition is made of graphite or molybdenum disulfide. The content of the solid lubricant containing any one is 50 wt% or less, and the upper layer coating composition is that the content of the solid lubricant containing either graphite or molybdenum disulfide is 50 to 95 wt%. It is a feature.

  According to the present invention, the lower layer coating composition contains 50 wt% or less of a solid lubricant containing either graphite or molybdenum disulfide, and the upper layer coating composition is made of either graphite or molybdenum disulfide. By making the content of the solid lubricant containing either of them 50 to 95 wt%, the adhesion of the lower layer coating composition to the piston base material is excellent, and the initial familiarity when the outer peripheral surface of the piston slides on the cylinder wall surface That is, when the surface of the upper layer coating composition is worn in a short time, a smooth sliding surface is quickly formed, and excellent initial conformability is obtained.

It is a principal part longitudinal cross-sectional view which shows the state by which the piston of this invention was applied to the internal combustion engine. FIG. 3 is a front view showing a part of the piston in cross section. A is a characteristic diagram showing the relationship between the content of the solid lubricant and the friction coefficient, and B is a characteristic diagram showing the relationship between the streak height and the friction coefficient. A schematically shows the state before and after abrasion of the multilayer coating composition by sliding in this example, and B shows the state before and after abrasion due to non-surface-treated sliding where no coating is formed. It is an expanded sectional view showing typically. It is a characteristic view which shows the relationship between content of a solid lubricant, and adhesive force.

  Hereinafter, embodiments of a piston of an internal combustion engine according to the present invention will be described in detail with reference to the drawings. The piston used in this example is applied to a 4-cycle gasoline engine.

[Example 1]
As shown in FIG. 2, the piston 1 is slidably provided on a substantially cylindrical cylinder wall surface 3 formed in the cylinder block 2, and a combustion chamber 4 is interposed between the cylinder wall surface 3 and a cylinder head outside the figure. And is connected to a crankshaft (not shown) via a connecting rod 6 connected to the piston pin 5.

  The piston 1 is integrally cast as a whole by an AC8A Al—Si-based aluminum alloy, and is formed in a substantially cylindrical shape as shown in FIGS. 1 and 2, and defines the combustion chamber 4 on the crown surface 7a. A crown portion 7 formed, a pair of arc-shaped thrust side skirt portion 8 and anti-thrust side skirt portion 9 provided integrally on the outer peripheral edge of the lower end of the crown portion 7, and the circumferential direction of the skirt portions 8, 9 A pair of apron portions 11 and 12 connected to each side end of each via a connecting portion 10.

  The crown portion 7 has a disk shape formed with a relatively large thickness, and a valve recess (not shown) that prevents interference with the intake / exhaust valve is formed on the crown surface 7a. Ring grooves 7b, 7c and 7d for holding three piston rings such as an oil ring are formed.

  Both the skirt portions 8 and 9 are disposed at symmetrical positions about the axis of the piston 1 and are formed in a substantially arcuate cross section. Is formed. The thrust side skirt portion 8 is adapted to be in pressure contact with the cylinder wall surface 3 while being inclined in relation to the angle of the connecting rod 6 when the piston 1 is stroked toward the bottom dead center during an expansion stroke or the like. The skirt portion 9 on the anti-thrust side comes into pressure contact with the cylinder wall surface 3 while inclining in the opposite direction when the piston 1 moves up during the compression stroke or the like. The thrust load on the cylinder wall surface 3 of each of the skirt portions 8 and 9 is larger in the thrust side skirt portion 8 that receives the combustion pressure and presses against the cylinder wall surface 3.

  And the multilayer coating composition 20 is given to the thrust side skirt part 8 and the anti-thrust side skirt part 9 of the said piston 1 as shown in FIG.1 and FIG.4A.

  This multi-layer coating composition 20 comprises an upper layer coating composition 21 and a lower layer coating composition 22, and as a binding resin, an epoxy resin, a polyimide resin, or a polyamide-imide resin excellent in heat resistance, wear resistance, and adhesion. Use one or two of them.

More specifically, the upper layer coating composition 21 is set to 5 to 50 wt% of any one of an epoxy resin, a polyimide resin, and a polyamideimide resin as a binding resin, and molybdenum disulfide as a solid lubricant. (MoS ₂ ) was set to 50 to 95 wt%.

  When the binding resin is less than 5 wt%, the adhesiveness with the lower layer coating composition 22 is reduced due to a decrease in bonding strength, and conversely, when it exceeds 50 wt%, the amount of solid lubricant is relatively reduced, so that the initial adaptability is reduced. descend.

In the lower layer coating composition 22, the binding resin was set to 50 wt% or more of one of an epoxy resin, a polyimide resin, and a polyamideid resin, like the upper layer coating composition 21. On the other hand, as the solid lubricant, at least one of polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS ₂ ), and graphite (GF) is basically set to 50 wt% or less.

  In the lower layer coating composition 22, when the binding resin is less than 50 wt%, the adhesion with the piston substrate 1a is lowered. As shown in FIG. 5, the change in adhesion when each solid lubricant is added to the binder resin PAI decreases rapidly when the solid lubricant exceeds 50 wt%, that is, when the binder resin is less than 50 wt%. I understand that

  That is, the lower layer coating composition 22 has a role of ensuring adhesion with the piston substrate 1 and ensuring adhesion with the upper layer coating composition 21.

  Therefore, it is not necessary to contain the solid lubricant in the lower layer coating composition 22, but the improvement of the coating properties is permitted by adding the solid lubricant within a range in which adhesion is ensured, and the polytetrafluoroethylene is 15 wt%. If it is less than 30%, the lubricity is lowered.

  Further, if the molybdenum disulfide as the solid lubricant is less than 5 wt%, the seizure resistance is lowered, and if it exceeds 20 wt%, the wear amount is increased due to a decrease in coating strength.

  In addition, with regard to molybdenum disulfide, which is a solid lubricant, the seizure resistance can be improved by a synergistic effect with graphite.

  That is, for the lower layer coating composition 22, molybdenum disulfide and graphite can be used in combination as the solid lubricant in addition to the polytetrafluoroethylene. In this case, it is desirable that the total of molybdenum disulfide and graphite is 5 to 20 wt%, and molybdenum disulfide is 1 to 10 wt%.

  This is because if the molybdenum disulfide content is less than 1 wt%, the effect of improving the seizure resistance by the combined use cannot be obtained, and if it exceeds 10 wt%, the wear resistance decreases.

  In addition, the content of the upper layer coating composition 21 such as molybdenum disulfide, which is a solid lubricant, is set to 50 to 95 wt%. From the experimental results shown in FIG. If it exceeds 95 wt%, the binding resin becomes less than 5 wt%, and as described above, the adhesiveness with the lower layer coating composition 22 is reduced due to a reduction in the binding force.

  In order to adjust the upper layer coating composition 21 and the lower layer coating composition 22 constituting the multilayer coating composition 20, for example, an epoxy resin, a polyimide resin, and a polyamideimide resin which are binding resins are mixed with an organic solvent, and the resin A solid lubricant may be added to the solution, and hard particles may be further added as necessary, and mixed and dispersed using a bead mill or the like.

The combined amount of the binder resin, the solid lubricant of PTFE, MoS ₂ , and GF, and the hard particles is adjusted so as to be 100 wt% in total.

  Moreover, the multilayer coating composition 20 of this invention is diluted with an organic solvent as needed, and is apply | coated to the piston base material 1a as a coating material.

  That is, the lower layer coating composition 22 and the upper layer coating composition 21 are sequentially applied to the outer peripheral surface of the piston base material 1a (thrust side skirt portion and anti-thrust side skirt portion), fired and cured, thereby forming a multilayer. A coating composition 20 is obtained.

  The organic solvent used for the dilution is not particularly limited as long as the binder resin can be dissolved even in a solvent system.

  Firing conditions such as the firing temperature and firing time may be set as appropriate, and firing at 200 ° C. or lower is also possible, so that it can also be applied to the base material of the aluminum alloy piston 1.

  In addition, although the film thickness of the multilayer coating composition 20 can be selected suitably, when the workability | operativity of application | coating, a cost surface, etc. are considered, about 5-40 micrometers is desirable.

  Hereinafter, a specific method for surface-treating the multilayer coating composition 20 on the piston substrate 1a will be described.

[First surface treatment method]
First, oil and dirt are removed from the surface of the piston substrate 1a by a pretreatment such as solvent degreasing or alkali degreasing.

  Next, the lower layer coating composition 22 is applied to the surface of the piston substrate 1a by a known method such as air spraying or screen printing, and then the upper layer coating composition 21 is applied to the upper surface of the lower layer coating composition 22. To do.

  Thereafter, the organic solvent is removed by drying, and, for example, a multilayer composed of the lower layer coating composition 22 and the upper layer coating composition 21 is baked under known conditions such as 180 ° C. × 30 minutes or 200 ° C. × 20 minutes. The coating composition 10 can be formed.

[Second surface treatment method]
As another surface treatment method, oil and dirt are removed from the surface of the piston substrate 1a on which the multilayer coating composition 20 is to be formed by pretreatment such as solvent degreasing and alkali degreasing.

  First, the lower layer coating composition 22 is applied to the surface of the piston substrate 1a by a known method such as air spraying or screen printing. Then, for example, baking is performed under known conditions such as 180 ° C. × 30 minutes or 200 ° C. × 20 minutes.

  Subsequently, the piston base material 1a is taken out from the firing furnace, and the upper layer coating composition 21 is applied to the upper surface of the lower layer coating composition 22 when the temperature of the piston base material 1a is 50 to 120 ° C. Then, the multilayer coating composition 10 which consists of the lower layer coating composition 22 and the upper layer coating composition 21 can be formed by making it dry without baking.

  The multilayer coating composition of the present invention can be widely applied to sliding members for various uses in an oil lubrication environment and a dry lubrication environment. The epoxy resin, polyimide resin, and polyamide-imide resin, which are the binding resins of the multilayer coating composition, are excellent in adhesion, so any substrate can be selected. For example, in addition to various aluminum alloy materials, cast iron, steel, copper alloy, etc. It is possible to apply to the substrate. Among them, the application to the piston 1 of the internal combustion engine as in the above-described embodiment, particularly the thrust side skirt portion 8 and the anti-thrust side skirt portion 9 is preferable.

[Experimental example]
That is, in the piston 1 having a streak shape on the outer peripheral surface, when the film thicknesses of the lower layer coating composition 22 and the upper layer coating composition 21 are t1 and t2, and the streak height is a, the following formula Satisfied.

t2 ≧ a-5 (μm) t1 ≧ 2 (μm)
The content of polyamideimide resin (PAI) as the binder resin, graphite (GF), molybdenum disulfide (MoS ₂ ), and polytetrafluoroethylene (PTFE) as the solid lubricant was varied from 0 to 95 wt%.

  The upper layer coating composition and the lower layer coating composition shown in Table 1 below were blended.

  An organic solvent was added to and mixed with each of the coating compositions of Samples 1 to 59 excluding Sample 21, and then dispersed in a bead mill for 30 minutes to obtain an upper layer coating material and a lower layer coating material, respectively.

  Each of the upper layer coating material and the lower layer coating material is applied to the test piece 20 made of an aluminum alloy AC8A having the surface shape shown in FIG. 4 so that all the lower layer coatings have a coating thickness of 3 to 6 μm. Then, baking was performed at 190 ° C. for 30 minutes.

  Subsequently, all the upper layer coatings were applied so as to have a coating thickness of 5 to 11 μm, and then naturally dried without firing.

  For the obtained samples 1 to 20 of the two-layer surface-treated and untreated (sample 21) without a surface treatment, a tip-on-ring friction and wear tester was used to determine the sliding speed: 2 m / sec. Material: FC250, sliding distance: 600 m, surface pressure: 1.3 MPa, engine oil drop amount was tested in a lubricating environment of 5 mg / min, and the coefficient of friction at the sliding distance was measured.

  3A and 3B show the relationship between the resulting streak height and the coefficient of friction. As is apparent from this figure, the friction coefficient is uniquely determined by the height of the streak. When the streak height is 5 μm or less, the friction coefficient is the lowest and becomes a constant value.

That is, in order to obtain a low coefficient of friction, it is understood that the upper layer film should be worn quickly. Therefore, as is apparent from FIG. 3A, the upper layer coating composition 21 that easily wears only needs to contain a solid lubricant of 50 wt% or more. Molybdenum disulfide (MoS ₂ ) is the most effective as the solid lubricant. The effect is small with (GF) and polytetrafluoroethylene (PTFE).

  In FIG. 4, A shows the present embodiment. As a result of making the upper layer coating composition 21 easy to wear, the original streak height c0 becomes c1 by sliding. On the other hand, in the case of no treatment of C, the original streak height a0 becomes a1 by sliding, but the aluminum alloy is harder to wear than the coating composed of the solid lubricant and the binding resin. It is clear that a1> c1.

  That is, low friction is obtained by this embodiment. In the case of B, which is a conventional material, the original streak height is b0 is b1. Since this conventional single layer coating is more easily worn than the aluminum alloy but less wearable than the upper layer coating of A, it is apparent that a1> b1> c1. In this embodiment, lower friction than that of the conventional material is obtained. For example, in FIG. 3A, when a0 = 10 μm and sliding, it is worn by 1 μm and becomes a height of the streaks a1 = 9 μm, and the friction coefficient is extremely high at 162% with respect to the solid lubricant of 0 wt% of the upper film. It became large (sample No. 21).

On the other hand, in the case of the coating containing 75 wt% of MoS ₂ as the upper coating, 7 μm was worn and b1 = 3 μm, and the friction coefficient was extremely small as 60% (Sample No. 6).

  Further, as shown in FIG. 3A, the upper layer coating is shown in the conventional patent publication, when the binding resin exceeds 50 wt%, that is, when the solid lubricant is less than 50 wt%, the wear is not promoted, and the non-treatment. Can achieve low friction, but does not reach the present embodiment (see Sample Nos. 2, 3, 8, 9, 20).

  Then, when the solid lubricant of the lower layer coating is 50 wt% or more, as shown in FIG. 5, the adhesion with the piston base material 1 is lowered and is not suitable for practical use (Sample Nos. 22 to 22). 40).

  Therefore, the lower layer film ensures adhesion with the piston base material 1 and at the same time ensures adhesion with the upper layer film containing 50 wt% or more of the solid lubricant.

A coating of 5 wt% binding resin and 95 wt% molybdenum disulfide having no adhesion to the aluminum alloy substrate is used as the upper coating, and the lower coating is made of PAI, MoS ₂ , and PTFE using the binding resin PAI as a solid lubricant. , 50, 60, 75, and 95 wt% of the coating composition containing the adhesive force measured (Samples 41 to 59), all the lower layer coating and the upper layer coating composition having no adhesion due to peeling from the lower layer coating and the aluminum alloy substrate It can be seen that the adhesive strength can be secured by setting the solid lubricant to 50 wt%.

As described above, according to this example, the adhesion of the lower layer coating composition 22 to the piston substrate 1a is excellent, and in particular, the solid lubricant of the upper layer coating composition 21 is at least molybdenum disulfide (MoS ₂ ). Is set to 50 wt% to 95 wt%, so that the initial familiarity when the outer peripheral surfaces of the thrust side and anti-thrust side skirt portions 8, 9 of the piston 1 slide on the cylinder wall surface 3, that is, the upper layer coating When the surface of the composition 21 is worn in a short time, a smooth sliding surface is quickly formed, and excellent initial conformability is obtained immediately.

DESCRIPTION OF SYMBOLS 1 ... Piston 1a ... Piston base material 3 ... Cylinder wall surface 8 ... Thrust side skirt part 9 ... Anti-thrust side skirt part 20 ... Multi-layer coating composition 21 ... Upper layer coating composition 22 ... Lower layer coating composition

Claims (3)

A lower layer coating composition formed on the surface of the piston base material on the outer peripheral surface of the piston skirt that slides on the cylinder wall surface, and an upper layer coating composition formed on the upper surface of the lower layer coating composition A piston of an internal combustion engine having a multilayer lubricant film formed thereon,
Having a streak on the outer peripheral surface of the skirt,
The lower layer coating composition and the upper layer coating composition include either one or two of a polyamide-imide resin, a polyimide resin, or an epoxy resin, which are binding resins,
The lower layer coating composition has a solid lubricant content containing either graphite or molybdenum disulfide of 50 wt% or less,
The piston for an internal combustion engine, wherein the upper layer coating composition has a solid lubricant content containing either graphite or molybdenum disulfide of 50 to 95 wt%. A piston for an internal combustion engine according to claim 1,
A piston for an internal combustion engine, wherein the solid lubricant content of the upper layer coating composition is 60 to 95 wt%. On the outer peripheral surface of the piston skirt that slides on the cylinder wall surface, the surface of the piston base material having streaks contains one or two types of polyamideimide resin, polyimide resin, or epoxy resin as a binding resin. After forming a lower layer coating composition in which the content of the solid lubricant containing either graphite or molybdenum disulfide is 50 wt% or less,
Inclusion of a solid lubricant containing either one or two of polyamideimide resin, polyimide resin or epoxy resin, which is a binding resin, and graphite or molybdenum disulfide on the upper surface of the lower layer coating composition A surface treatment method for a piston, characterized in that an upper layer coating composition having an amount of 50 to 95 wt% is formed.

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