JP2008014404A - Ringless piston and engine equipped with the same - Google Patents

Abstract

An object of the present invention is to provide a ringless piston having a simple structure capable of avoiding an increase in friction between a piston and a cylinder liner.
A ringless piston (1) is provided with an interference fitting portion (5) that is elastically pressed against a cylinder liner (3a) on a side peripheral portion of a piston main body (4). The interference fitting part (5) is provided in the skirt part (6) which is thin by making the peripheral side wall of the piston body (4) into a barrel shape. Such a ringless piston (1) is accommodated and mounted in the cylinder block by pressing and contracting the interference fitting portion (5). An oil film is formed between the interference fit portion (5) and the cylinder liner, and a gas seal function is exhibited by the hydraulic pressure generated in the oil film.
[Selection] Figure 1

Description

  The present invention relates to a ringless piston that does not require mounting of a piston ring and an engine including the same.

  A conventional general piston has a structure in which a piston ring is mounted in a piston ring groove. However, such a piston has a problem that the friction between the piston and the cylinder inner wall (cylinder liner) is high. When the friction between the piston and the cylinder liner is high, there is an influence such as deterioration of fuel consumption.

  In view of such circumstances, Patent Document 1 proposes the following piston. That is, a piston body that includes a top surface that forms a combustion chamber with a cylinder head, and a piston that reciprocates within the cylinder, with respect to the piston body so as to surround the reciprocating direction of the piston. A piston is proposed that has an annular portion that is integrally formed and contacts an inner wall of the cylinder.

  In such a piston proposed in Patent Document 1, the annular portion exhibits a gas seal function on the combustion chamber side and an oil seal function on the combustion chamber side. For this reason, this piston is mounted on the engine without mounting the piston ring. Moreover, since this annular part is integrally formed with respect to the piston body, Patent Document 1 describes that friction with the cylinder liner can be reduced.

  On the other hand, Patent Document 2 discloses a light oil lubricated diesel engine that uses light oil as a fuel as a lubricating oil. In such a light oil-lubricated diesel engine, light oil as a fuel is also used as a lubricating oil for each part of the engine and circulates through each part of the engine. For this reason, the oil only for lubrication is unnecessary, and the effort of oil replacement can be saved.

  In such a diesel engine, light oil is generally used as a fuel, and light oil is supplied to a lubrication system to be used for lubrication of each part. Also in such a diesel engine, the piston proposed in Patent Document 1 can be employed.

JP 2002-317695 A Japanese Utility Model Publication No. 60-194112

In a light oil lubricated diesel engine as described in Patent Document 2, light oil is also supplied to the sliding surfaces of the piston and the cylinder liner.
However, light oil has a viscosity lower than that of general engine oil and has a characteristic of being easily evaporated. In particular, when the combustion chamber is at a high temperature, such as when the engine is heavily loaded, the viscosity of the light oil is significantly reduced. For this reason, if the surface pressure between the piston and the cylinder liner is high, there is a concern about an increase in the friction at the relevant part. If the piston proposed in Patent Document 1 is employed in a light oil lubricated diesel engine having such characteristics, friction reduction between the piston and the cylinder liner is expected.

  By the way, in the sliding part of the cylinder liner and the piston in the light oil lubricated diesel engine as described in Patent Document 2, a high oil seal function is not required as long as a gas seal function that prevents the combustion gas from blowing through is secured. . This is because a slight increase in oil is not a problem because the lubricating oil is common with the fuel. In response to such a request, the piston proposed in Patent Document 1 has a gas seal function and an oil seal function, but has a complicated structure. The complicated structure also increased the weight of the moving part piston, and there was room for improvement in this respect.

  Accordingly, an object of the present invention is to provide a ringless piston having a simple structure capable of avoiding an increase in friction between the piston and the cylinder liner.

  In order to solve such a problem, the ringless piston of the present invention is characterized in that an interference fitting portion that is pressed against the cylinder liner by elasticity is provided on a side peripheral portion of the piston main body (claim 1). The interference fitting portion is pressed against the cylinder liner side by its elasticity to ensure a gas sealing function. Moreover, the space | interval between a piston and a cylinder liner is appropriately adjusted with the elasticity of an interference fitting part, and the friction increase of the said location can be avoided. The elasticity of the interference fitting portion is set so that an appropriate gas sealing function can be exhibited in any situation such as when the engine is cold, after warm-up is completed, or when the temperature is high.

  In such a ringless piston, it is desirable that the interference fitting portion is disposed in a skirt portion of the piston main body (claim 2). This is because it is easy to obtain desired elasticity in the skirt portion of the piston body. Further, by adopting a configuration in which a slit is provided in the skirt portion (Claim 3), elasticity can be obtained more easily. That is, by providing a slit in the skirt portion and dividing the skirt portion, the skirt portion can be easily elastically deformed.

  The ringless piston as described above has a diameter of the interference fit portion larger than the inner diameter of the cylinder of the engine, and is mounted in the cylinder so as to compress and retract the interference fit portion. When the lubricating oil is supplied between the interference fit portion and the cylinder liner, a hydraulic pressure due to the so-called wedge effect is generated at that portion. That is, since the interference fit portion is pressed against the cylinder liner by its elasticity, the lubricating oil existing between the interference fit portion and the cylinder liner generates hydraulic pressure. This oil pressure provides a gas sealing function.

  As described above, in the engine of the present invention, the gas seal function is realized by the oil pressure of the lubricating oil existing between the interference fitting portion of the ringless piston and the cylinder liner. The relationship with the inner diameter of the liner is important. Therefore, in the engine of the present invention, the material of the interference fitting portion can be the same as the material of the cylinder liner (claim 5). If the same material is used, both have the same linear expansion coefficient, so that the relationship between the interference fit portion and the cylinder liner can always be properly maintained regardless of the temperature change of the engine.

  Moreover, both materials are not limited to the completely same case. In other words, the interference fit portion may be made of a material having a linear expansion coefficient corresponding to the linear expansion coefficient of the material of the cylinder liner, and may be configured to maintain a distance between the interference fit portion and the cylinder liner ( Claim 6).

  Such an engine can be configured to use fuel as lubricating oil. The ringless piston of the present invention can also be used in a general engine in which fuel and lubricating oil are separately prepared. However, if a fuel that does not cause so-called oil rise or oil drop is used as a lubricating oil, it solves the problem of increased friction between the piston and cylinder liner of such a type of engine. Can be effective.

  According to the present invention, since it is a ringless piston having an interference fitting portion that is pressed against the cylinder liner by elasticity, an appropriate gas sealing function can be ensured while avoiding an increase in friction between the piston and the cylinder liner. Can do.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  1A and 1B show a ringless piston 1 according to the present invention, in which FIG. 1A is a perspective view and FIG. 1B is a sectional view taken along line AA in FIG. FIG. 2 is an explanatory view showing the relationship between the ringless piston 1 and the cylinder liner 3a when the ringless piston 1 is mounted in the cylinder block 3 of the engine 2. As shown in FIG. The engine 2 is a diesel engine of a type that uses light oil as a fuel as a lubricating oil.

  The ringless piston 1 is provided with an interference fitting portion 5 that is elastically pressed against the cylinder liner 3 a on the side peripheral portion of the piston body 4. More specifically, the interference fitting part 5 is provided in the thin skirt part 6 by making the peripheral side wall of the piston main body 4 into a barrel shape. However, the barrel shape of the piston body 4 in FIG. 1B is exaggerated for convenience of explanation. Here, the interference fitting portion 5 is provided in the skirt portion 6 because the skirt portion 6 is located on the lower end side of the piston body 4 as is apparent from FIG. It is easy.

  The skirt portion 6 of the piston body 4 is provided with slits 7 at equal intervals over the entire circumference. The reason why the slit 7 is provided is to impart further elasticity to the skirt portion 6 so that the skirt portion 6 in which the interference fit portion 5 is disposed can be easily deformed. Further, the reason why the slits 7 are provided at equal intervals over the entire circumference of the skirt portion 6 is to impart elasticity evenly over the entire circumference of the skirt portion 6 to cause deformation.

  Such a ringless piston 1 is formed of cast iron of the same quality as the cylinder liner 3a. Further, as exaggeratedly shown in FIG. 2, the diameter of the interference fit portion 5 is larger than the inner peripheral diameter of the cylinder liner 3a. Therefore, the ringless piston 1 is housed and mounted in the cylinder block 3 so that the interference fitting portion 5 in the state indicated by the broken line is compressed into the state indicated by the solid line, and the interference fitting is made at that location. Since the interference fit portion 5 has elasticity, the positional relationship with the cylinder liner 3a can be adjusted.

  As described above, light oil as lubricating oil is supplied between the interference fitting portion 5 of the ringless piston 1 mounted in the cylinder block 3 and the cylinder liner 3a. FIG. 3 is an explanatory diagram showing the pressure state around the interference fit portion 5 when the engine 2 is in operation. During operation of the engine 2, the pressure on the combustion chamber side of the ringless piston 1 is P1, and the pressure on the crankcase side is P2. Further, an oil film is formed by the lubricating oil 8 on the cylinder liner 3a. Here, the interference fit part 5 and the cylinder liner 3a are interference fits, and the oil film between them generates a hydraulic pressure Po by a so-called wedge effect. The hydraulic pressure Po is higher than the pressures P1 and P2. For this reason, the flow of gas between the combustion chamber side and the crankcase side is restricted. That is, the gas sealing function is exhibited.

  As described above, the compression of the engine 2 is ensured by exerting the gas sealing function. Further, by restricting the gas flow around the cylinder liner 3a, the lubricating oil adhering to the cylinder liner 3a is not scraped off, and the risk of increased friction due to lack of lubricating oil is reduced.

When the engine 2 becomes hot, both the ringless piston 1 and the cylinder liner 3a are thermally expanded. Here, the ringless piston 1 and the cylinder liner 3a are both formed of cast iron. Therefore, since the interference fit portion 5 is made of a material whose linear expansion coefficient corresponds to the linear expansion coefficient of the material of the cylinder liner 3a, the interval between the interference fit portion 5 and the cylinder liner 3a is determined in any temperature state. Even if it becomes, it is maintained in a substantially constant range. As a result, it is possible to avoid an excessive increase in the pressing force of the interference fit portion 5 against the cylinder liner 3a.
If the thermal expansion of the ringless piston 1 is greater than the thermal expansion of the cylinder liner 3a, the pressing force of the ringless piston 1 against the cylinder liner 3a will increase, leading to an increase in friction at that location. In the example, this situation can be avoided. Moreover, a desired gas sealing function can always be exhibited.

  As described above, according to the ringless piston 1 of the present invention, an appropriate gas sealing function can be exhibited despite the simple structure, and the friction between the piston and the cylinder liner is increased. Can be avoided and suppressed. Further, since the ringless piston 1 has a simple structure, the weight can be easily reduced.

  The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited thereto. Various modifications of these embodiments are within the scope of the present invention. It is apparent from the above description that various other embodiments are possible within the scope. In addition, various types of piping are conceivable for diesel engines that use fuel as a lubricating oil, and various components may be included. If there is any engine, the piston of the present invention can be adopted.

  Further, the ringless piston 1 of the present invention can also be employed in a general engine that prepares lubricating oil separate from fuel.

It is a figure which shows the ringless piston of this invention, (a) is a perspective view, (b) is the sectional view on the AA line in (a). It is explanatory drawing which showed the relationship between a ringless piston and a cylinder liner at the time of mounting a ringless piston in the cylinder block of an engine. It is explanatory drawing which showed the pressure state of an interference fitting part periphery when an engine is working.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ringless piston 2 Engine 3 Cylinder block 3a Cylinder liner 4 Piston main body 5 Close fitting part 6 Skirt part 7 Slit 8 Lubricating oil

Claims (7)

A ringless piston, characterized in that an interference fitting portion that is pressed against a cylinder liner by elasticity is provided on a side peripheral portion of the piston body. The ringless piston according to claim 1,
The ringless piston, wherein the interference fitting portion is disposed in a skirt portion of the piston body. The ringless piston according to claim 1,
A ringless piston, wherein the interference fitting portion is disposed in a skirt portion of the piston body, and a slit is provided in the skirt portion. An engine comprising the ringless piston according to any one of claims 1 to 3,
An engine characterized in that an oil film is formed between the interference fit portion and the cylinder liner. An engine comprising the ringless piston according to any one of claims 1 to 3,
2. The engine according to claim 1, wherein a material of the interference fitting portion is the same as a material of the cylinder liner. An engine comprising the ringless piston according to any one of claims 1 to 3,
The engine is characterized in that the interference fit portion is made of a material whose linear expansion coefficient corresponds to the linear expansion coefficient of the material of the cylinder liner, and maintains an interval between the interference fit portion and the cylinder liner. The engine according to any one of claims 4 to 6,
An engine characterized by using fuel as lubricating oil.

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