JPH0143485Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) The present invention relates to an assembly-type piston for an engine, and more specifically, to an assembly-type piston in which a piston skirt portion and a piston head portion are constructed separately. It is.

(Prior Art) Assembly-type pistons for engines have a long history, and a screw fastening method is known as one of the assembly methods.
Conventionally, prefabricated pistons have generally been made of iron-based homogeneous materials, but recently, prefabricated pistons made of dissimilar materials have become mainstream. In particular, there is a strong desire to make automobiles smaller and lighter in order to improve combustion and fuel efficiency, and diesel engines are increasingly constructed with a piston head made of fine ceramics and a piston skirt made of metal. It is becoming widely adopted.

(Problem to be solved by the invention) In this way, when a prefabricated piston is constructed from different materials in the piston head and piston skirt, the thermal expansion coefficients of these different materials become large, so it is difficult to fasten them together. Technology has become extremely difficult. For example, U.S. Pat.
No. 4419925 discloses that a male thread is formed on the periphery of a ceramic piston head portion, a female thread formed on the periphery of a metal piston skirt portion is screwed into this, and the two are screwed together. Although a prefabricated piston equipped with a stopping means is disclosed, in this type of prefabricated piston, the screw tightening may occur due to overheating of the piston during high-speed operation, vibration, drastic changes in operating environment conditions, etc. There is a problem in that it is not possible to instantly respond to the loosening of the belt.

(Means for Solving the Problems) The present invention solves the above problems, and its technical means is to provide a piston in which the piston skirt part and the piston head part are integrally assembled by screw fastening. The piston head is characterized in that means is provided between the piston head and the piston head for constantly urging the two to rotate in the direction in which they are screwed into each other.

In the prefabricated piston of the present invention, even if the screw connection between the piston skirt and the piston head loosens during operation, the piston skirt and the piston head will be screwed together by the rotational biasing means. Since rotational force acts in the direction,
Loosening of the screw connection between the two can be instantly prevented.

(Embodiment) An embodiment of the present invention will be explained below with reference to the drawings. In Figs. 1 and 2, 1 is a piston skirt portion, and the piston skirt portion 1 is made of aluminum alloy material that is lightweight and has good heat dissipation. It is manufactured.
A recess is provided on the upper surface side of the piston skirt portion 1, and a female thread (regardless of whether it is a right-hand thread or a left-hand thread) 2 is formed inside the recess. A fitting groove 3 having a rectangular cross section is provided in the upper bottom surface of the piston skirt portion 1.
A base end portion 4a having a rectangular cross section of a rod spring (rotation biasing means) 4 extending in the radial direction is press-fitted. Although spring steel is used here as the material for the bar spring 4, heat-resistant Inconel, NiCr, or Mo-based materials can also be used as long as they have appropriate elasticity. As a means for preventing detachment of the base end portion of the rod spring 4, an appropriate portion 5 corresponding to the fitting groove 3 of the piston skirt portion 1 is used.
It is sufficient to plastically deform the two locations.

The center portion and tip portion 4b of the bar spring 4 excluding the base end portion 4a have a circular cross section. Bar spring 4
The tip portion 4b is bent upward into an L-shape in FIG. 1, and projects upward through a clearance hole 6 formed in the upper part of the piston skirt portion 1. The diameter of the clearance hole 6 is set to be larger than the diameter of the rod spring 4 by a required dimension, taking into account the elastic movable region with the base end portion 4a of the rod spring 4 as a fulcrum.

Reference numeral 7 designates a piston head portion for a diesel engine, and a cavity portion 8 is formed on the upper surface of the piston head portion 7 in order to generate a desired swirl. The piston head portion 7 is made of fine ceramics with excellent heat resistance, such as SiCSi ₃ N ₄ ,
Manufactured from Al ₂ O, ZrO ₂ , etc. A convex portion 10 formed with a male thread 9 is provided on the lower surface side of the piston head portion 7 . Piston head part 7
and the piston skirt portion 1 are integrally screwed together by screwing the male thread 9 of the convex portion 10 and the female thread 2 of the piston skirt portion 1. The screw fastening portion is normally locked so that it cannot move in the rotational direction so that a fastening preload due to minute deformation acts between the two screws 9 and 2 in the final locked state. In such a state, even if vibrations due to high-speed reciprocating motion of the piston are transmitted, the screw fastening is configured so as not to loosen.

Fitting hole 1 drilled in the lower part of the piston head part 7
1 is press-fitted with the tip portion 4b of the rod spring 4 described above. Due to the force of this rod spring 4, the piston head portion 7 moves against the piston skirt portion 1.
The male thread 9 and the female thread 2 are constantly biased to rotate in the tightening direction. Base end portion 4a of bar spring 4
The amount of elastic deformation e around the fulcrum is set to an appropriate amount so that the screw fastening does not bite excessively. δ indicates the elastic deformation angle of the bar spring 4.

The spring constant of the bar spring 4 can be set to any size by changing the diameter d and effective span l of the bar spring 4. Since the rod spring 4 is provided at the upper part of the piston skirt portion 1 which is susceptible to thermal effects, the spring constant of the rod spring 4 is likely to change due to temperature changes during operation. Lubricating oil scattering from the pool 15
As a result, the rod spring 4 is cooled and a substantially constant spring constant is ensured.

Between the piston skirt part 1 and the piston head part 7, there is an extremely thin metal shim 12 on the outer peripheral edge thereof.
A metal shim 13, which is softer than the shim 12, is interposed at the inner center portion. By interposing the shims 12 and 13, the tightening load increases geometrically as the tightening amount increases. Even without intervening these seams 12 and 13, the split contact surface 14 at the outer peripheral edge of the piston skirt portion 1 and the piston head portion 7 alone is sufficient for practical use. Note that the material of the shims 12 and 13 is not limited to metal.

In the assembled piston having the above configuration,
During engine operation, the piston skirt 1 and the piston head 7 deform by different amounts due to the difference in their coefficients of thermal expansion due to the high temperature in the combustion chamber. If the difference in the amount of deformation between the two 1 and 7 exceeds an amount commensurate with the preload, loosening (play) will occur in the screw fastened portion. In this way, when the threaded engagement between the female thread 2 of the piston skirt part 1 and the male thread 9 of the piston head part 7 begins to loosen, the piston skirt part 1 and the piston head part 7 are connected to each other by the rod spring 4. An appropriate rotational force acts elastically in the direction in which the parts 7 are tightened together. As a result, it not only instantly prevents the screw connection between the piston skirt portion 1 and the piston head portion 7 from loosening, but also actively acts to strengthen the tightening force of the screw connection, thereby improving the engine performance. Failures are reliably prevented and safety is significantly improved.

Although the embodiments have been described above, the present invention also includes the following.

The screw fastening means includes a ring-shaped recess that fits into the piston skirt and the piston head;
A ring-shaped convex portion may be formed, and a female thread may be provided on the outside or inside of the concave portion, and a male screw may be provided on the inside or outside of the convex portion for fastening. Alternatively, a male thread may be provided on the piston skirt portion, and a female thread that engages with the male thread may be provided on the piston head portion for screw fastening.

In the embodiment, the piston skirt part was made of an aluminum alloy material and the piston head part was made of a fine ceramic material, but the selection of materials for the piston skirt part and the piston head part according to the present invention is not particularly limited. do not have. For example, if the piston skirt part is made of iron-based material and the piston head part is made of _ZrO2 , there is almost no difference in the coefficient of thermal expansion, so the range of possible operating conditions is further expanded, and the engine performance is significantly improved. It will improve.

Although a rod spring is used as the rotational biasing means in the embodiment, the shape of the rotational biasing means is not limited to a rod shape.
It may be arch-shaped or plate-shaped.

Of course, the assembled piston of the present invention is applicable not only to diesel engines but also to all internal combustion engines.

(Effects of the invention) As described above, according to the invention, the screw connection between the piston skirt and the piston head is prevented due to differences in thermal expansion due to temperature changes or mechanical vibrations during engine operation. Even if I try to relax,
Since the rotational force in the tightening direction is automatically applied to the screw fastening section by the rotational biasing means, it not only prevents the screw fastening section from loosening, but also maintains the tightening force of the screw fastening section to the normal state. It has the effect of instantaneously returning and maintaining the condition.

Furthermore, the assembly type piston of the present invention has a greater degree of freedom in selecting materials for the piston skirt and piston head, contributes to overall improvement in engine performance, is easy to disassemble and assemble, and can be mass-produced at low cost.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 2 is a view taken along arrow A in FIG. 1...Piston skirt part, 2...Female thread, 4
. . . Bar spring (rotation biasing means), 7 . . . Piston head portion, 9 . . . External thread, e .

Claims (1)

[Scope of utility model registration request] The piston skirt part and piston head part, which are provided separately from each other, are assembled together by screw fastening.
A prefabricated piston for an engine, characterized in that a rotational biasing means is provided between the piston skirt portion and the piston head portion for constantly biasing the piston skirt portion and the piston head portion to rotate in a screw tightening direction.