JP2552523B2 - Combination of cylinder sleeve and piston for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combination of a cylinder sleeve and a piston of an internal combustion engine, and particularly to a sintered Al alloy cylinder sleeve having good heat resistance and wear resistance, and a skirt outer peripheral surface. The present invention relates to a combination with an Al alloy piston covered with heat resistant resin.

2. Description of the Related Art The sill block of an internal combustion engine is a basic part of the engine body, and its life affects the life of the entire internal combustion engine.
Cylinder blocks are often made of cast iron because they have good wear and corrosion resistance, are easy to machine, and are inexpensive, but in recent years the body weight has been reduced and Al alloys are also used to improve conductivity.

As an Al alloy cylinder block, a cast iron sleeve is fitted on the inner wall of the cylinder (eg, Japanese Patent Laid-Open No.
No. 61-142352), and the entire cylinder including the inner wall of the cylinder is formed of an Al alloy (eg, JP-A-61-61).
-14451).

However, when using the cast iron sleeve which is the first type, since the sleeve facing the combustion chamber is made of cast iron with poor thermal conductivity, the heat dissipation performance as an Al alloy cylinder block with good thermal conductivity. Is not sufficiently exhibited, and the coefficient of thermal expansion of Al alloy is about twice that of cast iron,
Cast iron sleeve and Al surrounding it when the temperature rises
A gap tends to be formed between the alloy cylinder block body and the body.

The second type of Al alloy cylinder block uses a high Si content Al alloy casting sleeve called Aldil to secure the heat resistance and wear resistance of the cylinder inner wall. have. The grain size of primary crystal Si is large (30 to 100 μm) and the machinability after casting is poor.
It is necessary to perform an etching process in order to expose the Si particles, which are hard particles, to the inner wall surface of the cylinder where abrasion resistance is required because the distance between the Si particles is large. The hardness of Si particles is not so large (about Hv1200), and the wear resistance under a large load is insufficient. Particularly, in an air-cooled engine, when the temperature of the inner wall of the cylinder reaches 200 ° C to 300 ° C, the hardness of the base material sharply decreases and the wear resistance at the time of temperature rise deteriorates. In addition, in the case of general Al alloy sleeves, in connection with the above items, it is necessary to give wear resistance by subjecting the inner wall surface of the cylinder to surface treatment such as hard Cr plating, SiC dispersed Ni plating, etc. Grows.

From the above, it is desired to develop an Al alloy material having excellent heat resistance and wear resistance that can be used as a sleeve material for a cylinder.

On the other hand, since the piston of the internal combustion engine thermally expands during operation of the engine, a certain gap is provided between the piston and the inner wall of the cylinder at room temperature by allowing for this expansion in advance. This clearance is called a piston clearance and is represented by the difference between the cylinder inner diameter and the piston maximum outer diameter. If the piston clearance is too small, seizure with the inner wall of the cylinder will occur. Conversely, if the piston clearance is too large, the compression pressure will drop, blow-by (blown-out), oil will rise, and dilution (engine oil from gasoline will (Dilution) etc. and also causes the piston slap sound.

The piston skirt that contacts the inner wall of the cylinder receives the side thrust (side pressure) generated by the inclination of the connecting rod and keeps the linear motion of the piston correct. Impact the cylinder wall when changing the direction of movement. This is the piston slap. If the piston slap is intense, wear of the piston ring and ring groove will be accelerated.
Since problems such as increased consumption of engine oil occur, the minimum piston clearance must be set within the range where such phenomena do not occur.

However, since the Al alloy piston, which is lightweight and suitable for high-speed rotation, has a large coefficient of thermal expansion, there is no choice but to increase the piston clearance especially at the crown when using it in combination with the inner wall of the cast iron cylinder. Various modifications have been made to the shape of the skirt to keep the piston clearance small in the skirt where the temperature rises little.

On the other hand, while adopting an Al alloy piston, the entire cylinder block including the cylinder inner wall is made of Al.
In an engine formed of an alloy, the piston clearance can be set smaller than that of the combination of the Al alloy and cast iron.

Thus, when using Al alloy pistons, special measures are taken to minimize the piston clearance, in which case wear of the piston skirt must be noted. In particular, in a cylinder using a cast sleeve made of a high Si content Al alloy such as Aldil, defects such as "galling" and seizure are likely to occur in the skirt portion.
Therefore, conventionally, the outer peripheral surface of the skirt has been treated by iron plating, heat-resistant resin coating, or the like. However, when the iron plating treatment is applied, there is a problem that wear of the Al alloy sleeve becomes a problem, and the piston manufacturing cost becomes high.

The present invention has been devised under such a technical background, and its main purpose is to reduce wear of an Al alloy sleeve and an Al alloy piston that is in sliding contact with the sleeve as much as possible.

Another object of the present invention is to improve the wear characteristics of a heat-resistant resin coating that can be coated at a cost lower than that of plating, and to improve the heat-resistant resin coating of an Al alloy piston. By applying it to the outer circumference, it is possible to further reduce the wear of the piston and reduce the manufacturing cost of the piston.

Means and Actions for Solving the Problem The purpose is to reduce the grain size of primary Si contained in the structure to 20 μm.
Below, Si11-30%, Cu0.8-5%, Mg0.3-3.5%,
Fe2 to 10% (all numbers are weight%), balance ... Al and Al alloy powder with inevitable impurities
1 to 5% by weight of Al ₂ O ₃ powder consisting of spherical particles of m was uniformly mixed, and after compacting, a cylinder sleeve was formed with a sintered Al alloy obtained by sintering at a predetermined temperature or hot working. It is achieved by forming and covering the outer circumference of the Al alloy piston with a heat-resistant resin in which at least one of M ₀ S ₂ powder, thermosetting fluororesin powder, boron nitride powder, and graphite powder is added and dispersed. .

In cast products made of Al alloys containing a large amount of Si such as Aldil, coarse primary Si crystallizes out and the required strength cannot be obtained, so improved treatment (eg, adding Na to the melt)
Is performed to measure the refinement of primary crystal Si. However, since the refinement effect is limited, the grain size of primary Si is suppressed to 20 μm or less by producing a high Si-containing Al alloy powder containing Fe that exceeds the solid solution limit by an atomizing method. A method for obtaining a high-strength sintered Al alloy member by hot-extruding a powder compact has been proposed.

The Al alloy cylinder sleeve of the present invention was obtained in accordance with this method, but in order to further improve the wear resistance at normal temperature and high temperature, an Al ₂ O ₃ powder composed of spherical particles having an average particle diameter of 1 to 10 μm. Is added. It is appropriate to add the Al ₂ O ₃ powder in an amount of 1 to 5% by weight based on the raw Al alloy powder. If it is less than 1% by weight, the effect of improving wear resistance cannot be obtained, and if it exceeds 5% by weight. The effect on the mating sliding member is large, and the hot workability of the powder compact decreases as the amount added increases. Further, the reason why the spheroidized Al ₂ O ₃ particles are used is to alleviate the opponent attack of Al ₂ O ₃ whose hardness reaches H _V 2500, and the particle size is set to 1 to 10 μm. If it is less than 1 μm, the raw material Al ₂ O ₃ powder has poor handleability and it is difficult to obtain the necessary wear resistance, and if it exceeds 10 μm, the machinability of the sintered product deteriorates, and This is because falling off is likely to occur, resulting in accelerated wear of the piston, which is the sliding member itself and the mating sliding member.

In addition to Al ₂ O ₃ powder, other ceramic powders harder than Si particles (eg, SiC, Si ₃ N ₄ ) can be used, but their wear resistance (wear resistance of sintered products) is It is slightly inferior to the case of using Al ₂ O ₃ powder. It is also effective to use a powder of a lubricating material such as graphite, boride, or sulfide together with a ceramic powder such as Al ₂ O ₃ to disperse hard ceramic particles in the sintered material and to mix the lubricating material with particles. Can be dispersed to provide self-lubricating properties to improve wear resistance. In some cases, even if only the powder of the lubricating material is used without using the ceramic powder, the wear resistance can be improved due to the self-lubricating property of the sintered material.

The reasons for limiting the composition of the Al alloy powder and the grain size of the primary crystal Si are as follows.

(1) Si (11 to 30% by weight) ... Si contributes to improvement of wear resistance and Young's modulus of a sintered product, and can suppress thermal expansion coefficient to be low and improve thermal conductivity. However, if the Si content is less than 11% by weight, the wear resistance and strength are poor, and if it exceeds 30% by weight, the formability during hot extrusion or hot forging is poor and the product is likely to crack.

Also, if the particle size of primary crystal Si particles is 20 μm or less, if the particle size exceeds 20 μm, the machinability of the sintered product deteriorates, and a large concentrated load is caused due to the sliding contact relationship with the mating sliding member piston. This is because the Si particles are apt to be broken due to the damage, and the Si particles dropped by the breakage promote the wear of themselves and the piston. Atomization method in which the particle diameter of 20 μm or less causes the molten Al alloy to flow out from the pores and inject an inert gas into it,
Alternatively, the cooling rate from the molten state can be adjusted by the centrifugal atomization method.
It can be obtained at 10 ² to 10 ⁶ ° C / sec. Such a high cooling rate cannot be obtained when the sliding member (cylinder sleeve) is formed by the melting method.

(2) Cu (0.8 to 5% by weight) ... Cu is effective for strengthening the matrix by heat treatment. However, if it is less than 0.8% by weight, there is no effect of addition, and if it exceeds 5% by weight, hot workability is deteriorated and the corresponding corrosion corrosion cracking property is deteriorated.

(3) Mg (0.3 to 3.5% by weight) ... Mg is effective for strengthening the matrix by heat treatment, like Cu. However, if it is less than 0.3% by weight, there is no effect of addition, and if it exceeds 3.5% by weight, hot workability is deteriorated and corresponding corrosion corrosion cracking property is deteriorated.

(4) Fe (2 to 10% by weight) ... The Al alloy hardness in the case where Fe is not added sharply decreases with heating at a temperature of 200 ° C. to 300 ° C. as shown in FIG. On the other hand, such an abrupt decrease in hardness is not observed in the Al alloy containing 2 to 10% by weight of Fe. Fe
It is preferable to add 2 to 10% by weight of 2% by weight
If it is less than 10% by weight, improvement in high temperature strength of the sintered product cannot be expected, and if it exceeds 10% by weight, high speed hot working becomes impossible.

On the other hand, as the heat resistant resin applied to the Al alloy piston, a polyimide resin, a polyamide resin, and a polyimideamide resin (or a polyamideimide resin) are particularly suitable. The wear resistance of the resin coating is improved by adding powders having good lubricity such as M ₀ S ₂ powder, polytetrafluoroethene resin powder, boron nitride powder, and graphite powder to the heat-resistant resin. .

The upper limit of the addition amount of M ₀ S ₂ powder, polytetrafluoroethylene resin powder, boron nitride powder, and graphite powder is as follows due to the difference in specific gravity.

The preferable film thickness of the resin coating is 2 to 50 μm. Film thickness is 2
If it is less than μm, the adhesion to the piston / skirt surface is poor and the skirt base may be exposed. If it exceeds 50 μm, no improvement in sliding characteristics (seizure resistance, wear resistance) is observed.

When a chemical conversion film is formed on the surface of the piston as a base layer for coating the resin film, the adhesion of the resin film is improved.
As a method for chemical conversion coating of Al alloy, a mixed solution of chromate and alkali such as sodium carbonate is used at a temperature of 70-
The MBV method of treating at 100 ° C and the allodine method (Alodine method) using a mixture of phosphoric acid, chromic acid and fluoride are known, and in particular, the film obtained by the MBV method is
Since the surface is roughened to some extent, the adhesiveness of the resin coating is good.

Practical Example FIG. 2 shows a water-cooled engine 1 for a motorcycle as a side view with a main part cut away. The engine 1 uses a double overhead camshaft type valve operating mechanism, and the crankshaft 8
A piston 4 (for example, made of JIS AC8A material) connected to is inserted into the cylinder 2. The inner wall of the cylinder 2 is made of Al
It is formed of a cylinder sleeve 3 which is integrated with a cylinder block body made of an alloy (eg, JIS ADC12 material) by casting. The outer peripheral surface of the skirt 5 of the piston 4 fitted into the cylinder sleeve 3 is covered with a polyimideamide resin coating 6 (Fig. 3). M ₀ S ₂ particles 7 were added and dispersed in the polyimide amide resin coating 6, and the polyimide amide resin coating 6 was prepared by mixing the polyimide amide resin and the M ₀ S ₂ powder in hexadimethylpyrrolidone as a solvent. It is formed by spray-coating the liquid on the outer peripheral surface of the skirt 5 and subjecting it to a heating and baking treatment at a temperature of 190 ° C. for 30 minutes.

The cylinder sleeve 3 which is a sintered product is manufactured as follows.

Manufacture of raw material Al alloy powder: An Al alloy having a specified composition is melted, and the particle size is controlled by an atomizing method using an inert gas, a centrifugal atomizing method, a roll quenching method, etc. under a cooling rate of 10 ² to 10 ⁶ ℃
A powder of less than 105 μm is produced.

Mixing of powders: 1 to 5% by weight of Al ₂ O ₃ powder composed of spherical particles having an average particle size of 1 to 10 μm is added to Al alloy powder and mixed uniformly.

Powder compaction: The obtained powder is compacted by a cold isostatic pressing method (CIP method) at a pressure of 4,000 kgf / cm ² to obtain a cylindrical compact compact as an extrusion material.

Hot extrusion (sintering) ... A cylinder sleeve 3 is obtained by hot extruding a material for extrusion, which is a green compact, at a temperature of 450 ° C. Note that, when considering the oxidation prevention of the molded product, it is preferable to perform hot extrusion in a non-oxidizing atmosphere.

Wear resistance of the cylinder sleeve 3 thus obtained,
Heat resistance is good, and in combination with the fact that the outer surface of the piston skirt 5, which is the mating sliding member, is coated with the polyimide amide resin 6, the sliding surface of the cylinder sleeve 3 is plated with hard Cr. Exhibits excellent durability without surface treatment such as. Further, since the cylinder sleeve 3 has an initial room temperature hardness even after being heated to a temperature of 200 ° C. to 300 ° C. (when returning to a normal temperature), it can be used also for an air-cooled engine. Further, the cylinder sleeve 3 in which Al ₂ O ₃ particles are dispersed has a characteristic that the hardness does not decrease even if it receives heat at the time of integration with the cylinder block main body by casting and has a great practical effect.

On the other hand, a polyimide amide resin coating 6 in which M ₀ S ₂ particles 7 having lubricity are dispersed is attached to the outer peripheral surface of the skirt of the piston 4 that is in sliding contact with the cylinder sleeve 3, so that seizure of the piston 4 does not easily occur. It has good durability.

In manufacturing the cylinder sleeve 3, Al ₂ O
Powder of lubricating material (graphite, boride, sulfide, etc.) of 0.5 to 5% by weight together with ₃ powders may be mixed with Al alloy powder,
In that case, since the cylinder sleeve 3 can be provided with self-lubricating property, the seizure resistance is excellent in the sliding contact relationship with the piston 4 whose skirt 5 is covered with the polyimide amide resin coating 6 in which the M ₀ S ₂ particles 7 are dispersed. Exert.

EFFECTS OF THE INVENTION As is clear from the above description, in the combination of the cylinder sleeve and the piston of the internal combustion engine according to the present invention, the Al alloy, which is the base material of the cylinder sleeve, has excellent wear resistance and heat resistance. In addition, the base material has a high hardness of Al ₂ O ₃
Since the particles are dispersed, the cylinder sleeve exerts excellent wear resistance in the temperature range from normal temperature to high temperature even if the sliding surface is not subjected to surface treatment such as hard Cr plating, and M ₀ S ₂ powder etc. The outer periphery is covered with a heat-resistant resin in which lubricating powder is dispersed
The Al alloy piston has good durability because the high hardness Al ₂ O ₃ particles contained in the cylinder sleeve are spheroidized and the opponent attack is low, so that seizure and wear hardly occur. Further, the cost of applying the heat-resistant resin coating to the piston is lower than that of applying the plating treatment, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a graph showing the hardness change with temperature of an Alzir-based Al alloy, and FIG. 2 is a side view of the essential parts showing a water-cooled engine for a motorcycle adopting a combination of a cylinder sleeve and a piston according to the present invention. FIG. 3 is an enlarged view of the skirt portion of the piston. 1 ... Engine, 2 ... Cylinder, 3 ... Cylinder sleeve, 4 ... Piston, 5 ... Skirt, 6 ... Polyimideamide resin coating, 7 ... M ₀ S ₂ particles, 8 ... Crankshaft.

Claims (3)

(57) [Claims] 1. The grain size of primary crystal Si contained in the structure is 20 μm or less, Si 11 to 30%, Cu 0.8 to 5%, Mg 0.3 to 3.5%, Fe
2 to 10% (all numbers are weight%), balance ... Al and Al alloy powder with unavoidable impurities, average particle size 1 to 10 μm
A cylinder made of a sintered Al alloy obtained by compacting a mixed powder obtained by uniformly mixing 1 to 5% by weight of Al ₂ O ₃ powder consisting of spherical particles of, and sintering or hot working at a predetermined temperature. Piston made of Al alloy with sleeve and heat-resistant resin containing at least one powder selected from M ₀ S ₂ powder, thermosetting fluororesin powder, boron nitride powder, and graphite powder. A combination of a cylinder sleeve and a piston of an internal combustion engine composed of. 2. A combination of a cylinder sleeve and a piston for an internal combustion engine according to claim 1, wherein 0.5 to 5% by weight of graphite powder is mixed with the mixed powder. 3. The combination of a cylinder sleeve and a piston for an internal combustion engine according to claim 1, wherein the heat resistant resin is a polyimide resin, a polyamide resin or a polyimideamide resin.