JPH0452453Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ceramic piston having a ceramic cap attached to the top of the piston.

[Prior Art] Ceramic pistons are used to reduce cooling loss and increase exhaust temperature. However, if the entire piston is made of ceramics, problems such as increased weight and cost will occur, as well as problems such as difficulty in machining and decreased impact resistance. Therefore, it is common to use ceramics only around the combustion chamber, which gets hot, and to attach a ceramic cap to the top of the piston. Figure 4 shows an example of this, where the piston 2
A ceramic cap 1A forming a combustion chamber 3 is attached to the top of the combustion chamber 3. A buffer material 4 is interposed between the abutting surfaces of the ceramic cap 1A and the piston 2, and bolts 5 are used to fix the two. Furthermore, the device disclosed in Japanese Patent Application Laid-Open No. 59-213938 is almost the same as that shown in FIG. 4, in which the piston body and the piston head (corresponding to the ceramic cap 1) are tightened with bolts. FIG. 5 shows a conventional technique in which a ceramic cap 1B is fitted onto the top of the piston 2 instead of fixing it with bolts 5.

[Problems to be solved by the invention] The device shown in Japanese Patent Application Laid-Open No. 59-213938 and FIG. In addition to problems such as the protruding head of the bolt and disturbing the combustion flow, stress concentration occurs around the bolt hole, and the bolt itself has poor heat resistance, resulting in strength problems. Further, the bolts 5 are stretched, making the ceramic cap 1A insufficiently fixed. Also the fifth
In the case shown in the figure, a large thermal stress is generated due to the difference in thermal expansion coefficients between the ceramic 2 and aluminum when the temperature rises due to cold fitting.

The present invention aims to solve the above-mentioned problems and provides a ceramic piston that has strong joint strength with the piston during use, generates little thermal stress, and does not inhibit combustion flow.

[Means for Solving the Problems] To this end, the present invention forms a concave part that widens toward the end on the abutting surface of the ceramic cap that is fitted into the top of the piston to form the combustion chamber, and the abutting surface. A bolt whose one end side is inserted into the recess is installed between the ceramic cap and the piston in order to press the ceramic cap, and a shape memory alloy whose shape changes at a predetermined temperature so as to fit tightly into the recess is inserted into the recess. This constitutes a ceramic piston made of.

[Function] The portion of the bolt inserted into the recess is deformed by the predetermined temperature and comes into close contact with the recess. Since the recess is formed to widen toward the end, the ceramic cap is pressed toward the piston and tightened. Since an irreversible shape memory alloy is used, the tightened state is maintained.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

As shown in FIG. 1, a ceramic cap 1 forming a combustion chamber 3 is attached to the top of the piston 2, and a cushioning material 4 is attached to the top of the piston 2.
It is attached via.

On the contact surface 6 of the ceramic cap 1 with the piston 2, there is a conical recess 7 that widens toward the combustion chamber 3 side.
are formed in appropriate numbers. In other words, the recess 7 is the contact surface 6
It is formed from a conical hole that is formed to have approximately the same diameter as the bolt 8 at the top and widens in a tapered shape toward the back. The bolt 8 is for tightening the ceramic cap 1 to the piston 2 side, and is installed between the two. One end of the bolt 8 is inserted into the recess 7, and the other end has a threaded part that is screwed into the nut 9. is formed.
The bolt 8 is formed from a shape memory alloy,
An example of its shape is shown in FIG.

The insertion portion 8a of the bolt 8 into the recess 7 is formed of a material having the same diameter as the threaded portion in a low temperature state, as shown by the two-dot chain line in FIG. Therefore, it can be inserted into the recess 7. Specifically, in a cold state, the bolt 8 is inserted so as to abut the deep bottom 10 of the recess 7, and is fixed to the piston 2 by a nut 9. The insertion portion 8a is made of a memory alloy and has an irreversible shape, and is processed so that it deforms into a conical shape as shown in the figure when it reaches a predetermined temperature (for example, the piston temperature during engine operation) and comes into close contact with the recess 7.
Because it is irreversible, once it has been deformed as described above, it remains in that state even if the temperature drops. As described above, since the recess 7 is formed into a conical shape that widens toward the end, when the insertion portion 8A of the bolt 8 is deformed as described above, the ceramic cap 1 is inserted into the piston 2.
Pressed to the side, the ceramic cap 1 is fixed. As described above, in this embodiment, the bolt head does not protrude into the combustion chamber 3, and the insertion hole for the bolt 8 is also provided at a relatively low temperature position of the piston 2, so stress concentration is small and the bolt 8 is There is almost no decrease in strength. Furthermore, the ceramic cap 1 is not inserted into the piston 2, and no thermal stress is generated. FIG. 3 shows another embodiment of the invention. The bolt 8 is made of a shape memory alloy as in the previous embodiment, but the difference is that the insertion portion 8b deforms when the temperature rises. The insertion portion 8b is in close contact with the recess 7, but is processed so that the center portion is recessed. This embodiment also provides the same effects as those of the previous embodiment.

The shape memory alloy can be processed into shapes other than the above embodiments, and the recess 7 is not limited to the above conical shape. In this invention, when the temperature changes, the ceramic cap 1 changes the shape of the bolt 8, causing the piston 2 to
It also includes other shapes that can be pressed to the side.

[Effects of the Invention] As is clear from the above explanation, the present invention has the effect that the joint strength with the piston is strong during use, the generation of thermal stress is small, and the combustion flow is not inhibited.

[Brief explanation of the drawing]

FIG. 1 is an axial sectional view of an embodiment of the present invention, and FIG. 2 is a partially enlarged sectional view for explaining the operation of the embodiment.
FIG. 3 is a partially enlarged sectional view for explaining the operation of another embodiment of the present invention, and FIGS. 4 and 5 are axial sectional views of a conventional ceramic piston. 1, 1A, 1B...ceramic cap, 2...
...Piston, 3...Combustion chamber, 4...Buffer material, 5,
8... Bolt, 6... Contact surface, 7... Recess, 8
a, 8b...insertion part, 9...Natsuto, 10...deep inside.

Claims (1)

[Scope of utility model registration request] Attach a ceramic cap to the top of the piston,
In a ceramic piston forming a combustion chamber, a concave part that widens toward the end is formed on the surface of the ceramic cap that contacts the piston, and a recess is formed between the ceramic cap and the piston to press the contact surface toward the piston. A ceramic piston, characterized in that a bolt is installed, one end of which is inserted into the recess, and the insertion portion of the bolt is made of an irreversible shape memory alloy that changes its shape to fit tightly into the recess at a predetermined temperature.