JPH04104148U - internal combustion engine piston - Google Patents

Abstract

(57) [Summary] [Purpose] After preventing the ceramic piston head portion 9 from falling off from the aluminum piston body 7, the boundary surfaces 19a and 3 between the piston head portion 9 and the piston body 7 are
[Structure] The piston body 7 is formed by casting an aluminum alloy, and the piston head portion 9 is made of ceramic. The inside of the pin boss portion 23 of the piston body 7 into which the piston pin for connecting the connecting rod is inserted is formed of ceramic integral with the piston head portion 9.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This idea was designed to replace the piston body, which is formed by casting a light alloy, with a piston head. The present invention relates to a piston for an internal combustion engine whose lead portion is made of ceramic.

0002

[Conventional technology]

The piston body is made of aluminum alloy to reduce the weight of the piston, and The piston head located on the combustion chamber side of this piston body is made of ceramic. By doing so, it is possible to improve the heat resistance and thermal conductivity of the piston.

0003 Such a piston for an internal combustion engine is described, for example, in Japanese Utility Model Application Publication No. 58-148244. There is something written. The piston described in this publication is cast as shown in Figure 4. Therefore, for the piston body 1 made of aluminum alloy, the piston The pad portion 3 is made of ceramic. The ceramic piston head part 3 is , has a small diameter portion 3a on the lower side, and the small diameter portion 3a is formed at the top of the piston body 1. A low expansion layer enters the recess 1a and is formed between the outer periphery of the small diameter portion 3a and the inner periphery of the recess 1a. A cylindrical cushioning material 5 made of expanded metal is interposed. An annular groove 3 is provided in the small diameter portion 3a. b is formed, and the buffer material 5 has a plurality of holes 5a formed therein.

0004 The piston body 1 is cast from aluminum alloy, and the piston head portion 3 is cast around it. At this time, the molten aluminum alloy flows from the hole 5a of the buffer material 5 to the groove 3b of the small diameter portion 3a. The piston body of the piston head portion 3 is Falling off from the body 1 is prevented.

[0005]

[Problem that the idea aims to solve]

However, in the piston of such a conventional internal combustion engine, the piston main body The protrusion 1b of the body 1 enters the groove 3b of the piston head 3, so that the piston head Although the door portion 3 is prevented from falling off from the piston body 1, the vicinity of this fixed portion is not combustible. Aluminum alloys have a higher coefficient of thermal expansion than ceramics because they are close to the room and are at high temperatures. Due to the thermal expansion of the gold, the piston head part 3 rises and a gap is created at the mutual boundary part 6. combustion gases enter through these gaps, deteriorating exhaust performance and thermal efficiency, and There is a risk that the piston itself will be damaged. To prevent the inflow of combustion gas from the boundary part 6 , a method of joining the boundary part 6 is also considered, but this is because the difference in thermal expansion between the two is large. , the piston head portion 3 is damaged during casting.

[0006] Therefore, this idea was developed to prevent the ceramic piston head from falling off the piston body. In addition to preventing the mutual tightness at the boundary between the piston head and the piston body, The purpose is to improve accessibility.

[0007]

[Means to solve the problem]

In order to solve the above-mentioned problems, this idea was developed to create a piston formed by casting a light alloy. The piston head that forms the top of the piston body is made of ceramic. In order to connect the connecting rod in the piston of an internal combustion engine formed by At least half of the piston pin inside the pin boss part into which the second piston pin is inserted. A portion extending beyond the circumference is formed of ceramic integral with the piston head portion. It is.

[0008]

[Effect]

In the piston of an internal combustion engine configured in this way, the piston main body is made of light alloy. The body and the ceramic piston head are fixed with a pin boss, and the piston head is made of ceramic. When the piston becomes hot, the piston body moves to the high temperature side centering on the pin boss part which is the low temperature side. Extends toward the piston head side. On the other hand, ceramics with a small coefficient of thermal expansion The piston head part is designed to hold the piston body that is about to extend, It is pressed at the boundary with the ton head, which improves the tightness of this boundary. Ru.

[0009]

【Example】 Hereinafter, embodiments of this invention will be described based on the drawings.

0010 Figure 1 shows an oblique cutout of a part of the piston of an internal combustion engine showing one embodiment of this invention. This is a perspective view. This piston is made of aluminum alloy, which is a light alloy. Silicon nitride comprising a body 7 and a piston head 9 forming the top of the piston body 7 The ceramic sintered body 11 is composed of a ceramic sintered body 11 such as a raw material. The piston head portion 9 is A small diameter portion 13 protruding from the bottom is formed, and a portion inside the upper surface 15 corresponds to the small diameter portion 13. A combustion chamber 17 is formed in the center. By forming the small diameter portion 13, the upper surface 15 The outer peripheral side becomes the flange portion 19.

[0011] As shown in a perspective view in FIG. 2, the ceramic sintered body 11 has a Provided inside the pin boss portion 23 of the piston body 7 having the piston pin hole 21. A pair of substantially annular fixing portions 25 are formed. In the above piston pin hole 21 , a piston pin for connecting a connecting rod (not shown) is inserted. . The aluminum alloy constituting the piston body 7 is It includes a piston land portion 31 in which a piston ring groove 29 and a piston ring groove 29 are formed. Ru.

0012 The ceramic sintered body 11 is fixed to a mold (not shown), and this ceramic sintered body In contrast to No. 11, when an aluminum alloy is integrally formed by casting, a ceramic sintered body is produced. The parts exposed to the outside of 11 are the upper surface 15 of the piston head part 9, the combustion chamber 17, and Only the side surface of the flange 19 is used; all other parts are made of aluminum, which constitutes the piston body 7. It is covered with aluminum alloy and is not exposed to the outside.

[0013] When operating an internal combustion engine using a piston with this structure, the temperature of the piston increases. As a result, the vicinity of the piston head portion 9 having the combustion chamber 17 becomes high temperature, but the pin boss portion The temperature around 23 is lower than that of the piston head 9. Therefore, the coefficient of thermal expansion is large. As the temperature rises, the piston body 7 made of hard aluminum alloy loses its pin boss on the low temperature side. The piston land portion 31 is mainly connected to the flange of the piston head portion 9 on the high temperature side, centering on the portion 23. Extending upwardly in FIG. 1 toward section 19. At this time, the pin of the ceramic sintered body 11 The periphery of the fixed part 25 integrated with the stone head part 9 is covered with aluminum alloy. Therefore, the ceramic sintered body 11 and the piston body 7 are firmly fixed, The ceramic sintered body 11 is prevented from falling off the piston body 7.

[0014] In contrast, the coefficient of thermal expansion of ceramic materials is approximately 1/7 that of aluminum alloys. Therefore, the boundary surface 31a between the upper end of the piston land portion 31 and the collar portion 19, which is about to expand. , the interface 19a of the flange 19 of the ceramic sintered body 11 with the piston body 7 is pressed. Attach. At this time, since the mutual contact pressure at the boundary surfaces 31a and 19a increases, Combustion gas is prevented from entering through the boundary surfaces 31a and 19a. In addition, the above boundary surface 3 The ceramic sintered body 11 and the piston body 7 in 1a and 19a are not joined. Therefore, damage to the ceramic sintered body 11 during casting due to the difference in thermal expansion between the two is prevented. This also prevents stress from occurring due to differences in thermal expansion in the circumferential direction during operation.

[0015] Note that by forming the boundary surfaces 31a and 19a parallel to the upper surface 15, the boundary surfaces 31a and 19a are It is possible to secure the desired surface pressure at 31a and 19a, and when the surface pressure increases, the ceramic This prevents slippage between the aluminum alloy and the aluminum alloy, and prevents bending stress from occurring due to slippage. Ru.

[0016] Fig. 3 shows a partially cut-out oblique view of a piston of an internal combustion engine showing another embodiment of this invention. This is a perspective view. In this embodiment, the boundary surface 19a of the ceramic sintered body 11 and the piston main body are A copper ring 41 having a small Young's modulus is provided between the body 7 and the boundary surface 31a. The rest of the configuration is the same as the embodiment shown in FIG. 1, and the same components as in FIG. The same reference numerals are given. This embodiment has the same effects as the embodiment of FIG. In addition, if this piston is used in a high-output engine, the piston will have a significant temperature, and the boundary surface 19a of the ceramic sintered body 11 and the boundary surface 31 of the piston body 7 There will be a large amount of contact pressure with a, but the copper ring 41 deforms and absorbs this contact pressure, and the piston It has the effect of preventing damage to tons.

[0017] Note that the piston body 7 may be made of a material with a larger coefficient of thermal expansion than ceramic. For example, it is not limited to aluminum alloy. Further, the upper end of the fixed part 25 is connected to the small diameter part 13. It is formed integrally with the lower surface and has an annular shape as a whole, but the piston pin is small. If the shape is such that it covers at least half the circumference, the upper end will meet the lower surface of the small diameter part 13 even if it is not annular. It is enough if they are united.

[0018]

[Effect of the idea]

As explained above, according to this invention, a ceramic body with a piston head The cylinder body and the piston body made of light alloy are connected to the piston on the low temperature side away from the combustion chamber. Since it is fixed at the pin boss, the piston body will not move when the temperature rises. It extends from the pin boss toward the piston head, which is at high temperature. The surface pressure increases at the boundary between the stone head and the piston body, and from this boundary It is possible to prevent the inflow of combustion gas, prevent deterioration of exhaust performance and thermal efficiency, and , damage to the piston itself can also be prevented.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of a piston of an internal combustion engine showing an embodiment of this invention.

FIG. 2 is a partially cutaway perspective view of the ceramic sintered body used in FIG. 1;

FIG. 3 is a partially cutaway perspective view of a piston of an internal combustion engine showing another embodiment of the invention.

FIG. 4 is a sectional view of a piston of an internal combustion engine showing a conventional example.

[Explanation of symbols]

7 Piston body 9 Piston head part 11 Ceramic sintered body 23 Pin boss part

Claims (1)

[Scope of utility model registration request] 1. A piston pin for connecting a connecting rod in an internal combustion engine piston in which a piston head forming the top of the piston body is formed of ceramic to a piston body formed by casting a light alloy. A piston for an internal combustion engine, characterized in that a portion inside the pin boss portion into which the piston pin is inserted, extending at least half the circumference of the piston pin, is made of ceramic integral with the piston head portion.