JPS62203967A - Piston made of ceramic - Google Patents

Abstract

PURPOSE:To make it possible to form a piston with ceramic and reduce weight of the piston by making a boss independent of a skirt portion and that arranged on the reverse side of a piston head and integral with the piston head, thereby reducing thermal stresses exerted on the boss. CONSTITUTION:A skirt portion 14 is formed on the side surface of a piston 11 below a ring portion 13 with a uniform wall thickness. And bosses 15 and 15' are arranged integrally with and extending from the reverse side of a piston head 12. With this configuration, heat during a combustion stroke is dissipated as shown with arrows from the piston head 12 via a ring portion 13 and the skirt position 14 to a cylinder liner. Here, since the bosses 15 and 15' are independent of the skirt portion 14, heat is prevented from dissipated via the bosses 15 and 15' to the cylinder liner. Accordingly, temperature gradient in the vertical direction of the bosses 15 and 15' is reduced to reduce thermal stresses.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention can be suitably used for ceramic pistons for internal combustion engines such as diesel engines and gasoline engines.

``Prior Art'' FIG. 2 (4) and FIG. 2) respectively show a sectional view of a conventional piston in the axial direction of the piston pin and a sectional view in the direction perpendicular to this. As shown in FIGS. 2 and 2, the piston 21 is generally cylindrical in shape. The combustion chamber (not shown) side of the cylinder is closed to form a piston head 22, and the upper side of the piston ring (not shown) is provided with a piston ring (not shown). (omitted) is provided to form a ring part 2B, and the side surface below the ring part 28 is provided with a skirt part 2 for preventing piston slap.
4, and has a structure in which a part of the skirt portion 24 is made thick, and holes are provided in the thick portion in the radial direction to form bosses 25 and 25'.

As is well known, the piston 21 is connected to the connecting rod by fitting a piston pin (not shown) into a hole in the boss 25, 25' and a hole in the small end of the connecting rod (not shown), and reciprocates up and down during use. . The material of the piston 21 is generally aluminum alloy, cast iron, or the like.

By the way, during explosive combustion, heat is transmitted from the piston head 22 to the cylinder liner via the ring part 23 and skirt part 24 and dissipated as shown by the arrow in FIG. A temperature gradient occurs, which causes thermal stress. In addition to such thermal stress, the piston is subjected to alternating loads from the piston pin due to pressure and inertia during the explosion.
．． Since the largest load acts on 25', it is more likely to deform than other parts.

On the other hand, ceramics has excellent heat resistance and wear resistance, and has a small coefficient of thermal expansion, so if it is applied to pistons, it is possible to reduce the thickness of the piston head, and the gap between the cylinder liner and the cylinder liner can be made extremely small. It is expected that the length of the piston will be significantly shorter than that of a metal piston, resulting in weight reduction.

``Problem to be solved by the invention'' However, in the case of a ceramic piston, more consideration is required in the design of the boss than in the case of a metal piston in order to withstand the load from the piston pin. First, as long as the boss is constructed by making part of the skirt thicker, as in the conventional case, by recessing the end face of the boss inward from the outer periphery of the piston head, it is possible to avoid heat being transferred directly from the boss to the cylinder liner. However, it is of little use in alleviating the temperature gradient in the vertical direction of the boss.
In order to maintain mechanical strength, the boss had to be made thicker than before, which was contrary to the goal of reducing weight.

The present invention aims to solve the above problems and provide a lightweight ceramic piston.

"Means for solving the problem" The means is to make the boss independent of the skirt in a ceramic piston in which the end face of the boss is recessed inward from the outer periphery of the piston head, and to attach the boss to the back surface of the piston head. It is located integrally with the piston head.

The ceramics used are preferably silicon nitride, sialon, and silicon carbide.

"action" The operation of the present invention will be explained based on FIG.

1B and 1B are a sectional view in the direction of the piston pin and a sectional view in the direction perpendicular thereto, respectively, showing a general example of the ceramic piston of the present invention.

The outer shape of the piston 11, the piston head 12, and the ring portion 13 are essentially the same as the parts labeled with corresponding numbers in FIG.

Reference numeral 14 denotes a skirt portion, which is provided on the side surface of the piston 11 and below the ring portion 13, and has a uniform wall thickness unlike the conventional structure.

Bosses 15 and 15' are provided on the back surface of the piston head 12, extending downward and integrally with the piston head 12, and are provided with holes into which piston pins (not shown) are fitted in the radial direction. Due to the bending structure, heat is transferred from the piston head 12 to the ring part 13 as shown by the arrow at the time of explosion.
It is different from the conventional technology in that heat is dissipated to the cylinder liner via the skirt portion 14, but since the bosses 15 and 15' are independent of the skirt portion 14, heat is dissipated to the cylinder liner via the skirt portion 14.
This is largely different from the conventional method in that the temperature gradient in the vertical direction of the bosses 15 and 15' is further alleviated without dissipating into the cylinder liner via the bosses 15'. Therefore, thermal stress is also reduced.

In addition, by adopting this structure, the bending force acting on the bottle boss due to thermal deformation of the piston head can be reduced, so the length between the bottle bosses can be shortened, and the strength against the force from the piston pin can be increased. It can also reduce weight.

Note that the skirt length of ceramic pistons can be significantly shorter than that of metal pistons, but in order to clarify the difference between the present invention and the prior art, in the general example of the present invention, the skirt length is The length of the skirt is intentionally made to be almost the same as the skirt length of a conventional metal piston.

"Example" Example 1 FIGS. 3(2) and ω) respectively show a sectional view of a ceramic piston according to a first embodiment of the present invention in the bislevin axial direction and a sectional view in a direction perpendicular thereto.

3(2) and (B), the piston 81 has the skirt portion 34 provided only on the thrust surface 34a, and the boss 35
, 85' end side, and the thickness of the piston head 31 is half that of the conventional piston head 31. There is no structural difference from the piston 11 in FIG.

The piston 31 is made by injection molding ceramic blended powder.
It is manufactured by firing, and its material is mainly Sialon, which is approximately 20% lighter than the conventional metal piston 21 shown in Figure 2 (CB). When this piston 31 was installed in a gasoline engine and operated at 6000 rpmX% for 200 hours, no abnormalities were found, and the engine noise during low-temperature operation was reduced by about 4 denbels.

Embodiment 2 Figures 4 and CB) show a sectional view in the direction of the piston pin and a sectional view in the direction perpendicular to this, respectively, of a ceramic piston according to a second embodiment of the present invention.

In FIG. 4 and (B), the piston 41 is connected to the boss 45.
．． The radial direction A-A' cross section of the connecting portion 46 between the piston head 45' and the piston head 42 is similar to that of the piston 31 in the 31st case and (B) except that it is an inertia circle as shown in FIG. 4 (0). There is almost no structural difference between the connecting part 46 and the connecting part 46. By making the connecting part 46 circular, thermal deformation of this part can be more effectively prevented than if it were a rectangular shape.A-A'
The same applies even if the cross section is circular.

Embodiment 8 FIGS. 5(2) and ω) respectively show a sectional view in the direction of the piston pin and a sectional view in the direction perpendicular thereto, of a ceramic piston according to the third embodiment of the present invention.

In FIG. 5 (4) and Q3), the piston 51 has a recess 57 in the connecting portion 56 in the direction of the piston pin, the connecting portion 56 is composed of two riffs 56a and 56b, and a skirt portion. The length of 54 is the skirt part 5
There is no structural difference from the piston 11 in Figure 1 and (I3), except that the vertical position of the lower end of 4 is shortened to the same extent as the upper end of the piston pin hole of the bosses 55 and 55'. As a result, the weight can be reduced by 30% compared to conventional aluminum alloy pistons.

Incorporate piston 51 into gasoline engine 6000r
When operated at pmXy4 for 200 hours, there were no abnormalities, fuel consumption improved by 10%, and engine noise decreased by about 3 denbels.

"Effects of the Invention" Since the thermal stress acting on the boss is reduced, the piston can be made of ceramics without making the boss thicker than before. As a result, the piston head can be made thinner and the skirt length can be shortened, resulting in lighter weight, lower fuel consumption, and improved acceleration performance. Additionally, the gap between the piston and cylinder liner can be reduced, resulting in lower engine noise.

[Brief explanation of drawings]

Figures 1 and CB), 31 and CB), Figure 4 (g) and CB), and Figure 5 and CB) are a general example, a first embodiment, and a second embodiment of the present invention, respectively. A piston pin axial cross-sectional view and a cross-sectional view perpendicular to this of a ceramic piston according to an example and a third example are shown, and a fourth
Figure C is a sectional view taken along line AA' in Figure 4B. Second
Figures 1 and 2) show a sectional view of a conventional metal piston in the axial direction of the piston pin and a sectional view in the direction perpendicular to this. 11.21, 81.41.51 ... Piston, 12
゜22.32, 42.52...Piston head, 13
゜28.83, 43.58...Ring part, 14, 2
4. 34.44.54...Skirt part, 15, 15',
25°25', 3.5, 85', 45.45', 55
．． 55'...Boss Patent Applicant NGK Spark Plug Co., Ltd.---Representative Tei Suzuki -No. 5 (A) 9F... Person

Claims (2)

[Claims] (1) A piston in which the end face of the boss is recessed inward from the outer periphery of the piston head, characterized in that the boss is independent of the skirt, and the boss is provided integrally with the piston head on the back surface of the piston head. Ceramic piston. (2) Claim 1, characterized in that the radial cross section of the connecting portion between the boss and the piston head is a circle or an inertia circle.
Ceramic piston as described in section.