JPH0122915Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a cast iron piston used in internal combustion engines, particularly diesel engines, in which a ceramic member having a heat insulating effect is incorporated.

2. Description of the Related Art Conventionally, in order to improve the thermal efficiency of a diesel engine and improve its fuel efficiency, it has been known to partially fit a ceramic member with excellent heat insulation effect to the head of a cast iron piston body. Shrink fitting is generally known as one of the methods for fitting ceramic and metal together, but when applied to pistons of internal combustion engines, the following problems arose. When the axial shrink-fit joint part of the outer periphery of the ceramic member that fits into the recess of the cast iron piston body is used in an internal combustion engine, the temperature of the joint part is such that the combustion chamber side exposed to combustion gas is on the inner side of the fitting part. As shown in FIG. 1, the circumferential end 28 of the recess 25 of the piston body 21 is pulled in the radial direction, so it gradually expands and the bonding force decreases, causing the ceramic member 26 to hold for a long time. It was difficult to maintain the temperature stably. Moreover, such non-uniform temperature distribution causes ceramic members to be easily damaged.

The present invention has been developed in view of the above-mentioned circumstances, and includes a ceramic member that fits into the recess of the cast iron piston body, and has an axially long An annular gap is formed in which the thickness t is in the range of 1/2 to 1/5 of the thickness t of the ceramic member, and the two are shrink-fitted so that the upper end surface of the ceramic member and the upper surface of the piston head are flush with each other. By forming the ceramic member into one piece, the ceramic member maintains a stable shrink-fit connection with the head of the piston body over a long period of time, and prevents damage to the ceramic member, resulting in a highly durable ceramic member. The purpose is to provide a built-in piston for internal combustion engines.

Hereinafter, the present invention will be explained based on the embodiments shown in the drawings.

FIG. 2 is a front vertical cross-sectional view of a piston showing an embodiment of the present invention, and 1 is a cast iron piston body used in diesel engines, etc., and the sliding surface between it and a cylinder liner (not shown). A plurality of piston ring grooves 2 are formed on the circumferential side, and a piston pin hole 3 for inserting and holding a connecting rod (not shown) is provided inside. Reference numeral 4 represents a piston head facing the combustion chamber, and reference numeral 5 represents a recess of a bottomed hole concentrically formed in the head. Reference numeral 6 denotes a disk-shaped ceramic member made of a sintered body such as silicon nitride, zirconia, sialon, etc., which has heat resistance and excellent heat insulation properties, and is shrink-fitted into the recess 5, and the upper end surface of the ceramic member 6. and the upper surface of the piston head 4 are formed flush with each other.
This ceramic member 6 has a small-diameter portion 6b having a stepped portion at the back of the outer peripheral portion 6a on the side opposite to the combustion chamber side, which fits into the inner wall 5a of the recess 5. This is a piston with a space 7 interposed therebetween.

The piston of the present invention has an annular configuration in which the dimensional relationship of the gap is set so that the axial gap length l is in the range of 1/2 to 1/5 with respect to the thickness t of the ceramic member, It is difficult for the heat of the ceramic member in the deep part of the fitting to be transmitted to the cast iron piston body through the gap.
Since the heat from the circumferential end 8 of the recess 5 on the combustion chamber side of the piston main body is radiated straight, the temperature of the circumferential end 8 decreases, making the temperature of the fitted part uniform, and thereby increasing the temperature of the ceramic member. The fit is maintained stably, and thermal stress is reduced by making the temperature uniform, so that damage to the ceramic member can be effectively prevented.

In order to provide durability to the ceramic member 6, the thickness t in the axial direction is preferably 8 mm or more. In addition, the shrinkage allowance and the temperature depend on the material of the ceramic member,
It is selected appropriately depending on the dimensions and the like.

Now, in the example shown in Fig. 2, the diameter of the small diameter part made of zirconia sintered body is 63 mmφ x thickness t12 mm.
Ceramic member 6 with 60mmφ x length l5mm is shrink-fitted (diameter difference) 0.05±0.02mm and the outer diameter is 200℃.
The piston A of the present invention is shrink-fitted into the recess 5 of the piston body 1 with a diameter of 73 mm, and the piston A with a diameter of 63 mm is made of the same material and has no small diameter part.
Comparative product B, which had mmφ x 12 mm thickness and was similarly shrink-fitted into the piston body, was installed in a diesel engine and a durability test was conducted. As a result, comparative product B is
At 2200 rpm x no load, the circumferential end surface of the cast iron piston body expands and the ceramic member falls off, whereas the piston A of the present invention, which has a gap formed by the small diameter part, operates at 2200 rpm x 4/4 x 100 hr. There were no abnormalities during operation.

Figure 3 shows another embodiment of the present invention.
Inner wall 15a of recess 15 of cast iron piston body 11
The piston is provided with a large-diameter portion 15b having a stepped portion in the inner part thereof, and a disc-shaped ceramic member 16 is shrink-fitted at the outer peripheral portion 16a into this recessed portion 15 to form a gap 7. Particularly, the piston having such a structure is applicable when the peripheral end 8 of the cast iron piston body 11 is relatively thick, and has an excellent effect of preventing the peripheral end from expanding. Note that the dotted line 9 shown inside the ceramic member
This is an example in which a crown combustion chamber is provided in the head.

As described above, the present invention is designed to provide a recess in the inner wall of the cast iron piston body or the outer periphery of the mating ceramic member, at the back of the side opposite to the combustion chamber side, so that the axial length l is relative to the thickness t of the ceramic member. By forming an annular gap in the range of 1/2 to 1/5 and shrink-fitting the two, the upper end surface of the ceramic member and the upper surface of the piston head are formed flush with each other. The temperature of the circumferential portion of the piston body into which the ceramic member is fitted is made uniform to prevent loosening due to expansion of the circumferential end face, and the shrink-fit bonding force of the ceramic member is stably maintained over a long period of time. It prevents damage to parts and has excellent durability.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of main parts showing the state of use of a conventional piston with a built-in ceramic member, Fig. 2 is a front vertical cross-sectional view of a piston showing an embodiment of the present invention, and Fig. 3
The figure is a front vertical sectional view of a piston showing another embodiment of the present invention. 1, 11... Piston body, 4, 14... Head, 5, 15... Recess, 5a, 15a... Inner wall,
6, 16... Ceramic member, 6a, 16a...
Outer periphery, 7... void.

Claims (1)

[Scope of utility model registration request] In a piston for an internal combustion engine in which a recess is provided in the head of a cast iron piston body and a ceramic member is fitted into the recess, the inner wall of the recess or the outer circumferential portion of the ceramic member that fits into the inner wall faces the combustion chamber. An annular gap having an axial length I in the range of 1/2 to 1/5 of the thickness t of the ceramic member is formed in the inner part on the opposite side, and the two are shrink-fitted. A structure in which the upper end surface of the member and the upper surface of the piston head are flush with each other.