JPH0143484Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a piston structure for an engine, and particularly to a piston structure in which a pin boss portion is connected to a skirt portion via a stay.

(Prior art) Conventionally, in order to prevent a decrease in rigidity due to the weight reduction of engine pistons, stays were extended on both sides of the piston pin boss in a direction orthogonal to the pin axis, and the pin boss was connected to the skirt part through the stays. A piston structure is known.

In particular, for diesel engine pistons, the temperature of the combustion chamber is high and the thermal conditions are severe, so cast iron pistons are generally used, and in order to reduce the weight of these cast iron pistons as much as possible, the above-mentioned In many cases, a piston structure is adopted.

For example, Japanese Utility Model Application Publication No. 57-47744 discloses that a notch is provided in the wall thickness of the skirt portion near the pin boss portion in a direction intersecting the pin hole, thereby connecting the pin boss portion to the skirt portion via a wall-shaped stay. The piston structure is described.

However, in the piston structure described in the above-mentioned publication, the explosion pressure acting on the upper surface of the piston causes the outer peripheral portion of the upper end of the piston to change downward, thereby changing the volume of the combustion chamber. Although the stay attempts to prevent this deformation, the skirt portion on the outer end side of the stay also deforms slightly downward due to its influence. At this time, the stay is also deformed diagonally so that its outer end side is lowered, so the part of the skirt part connected to the stay and the part near it are deformed so as to bulge outward, so that the skirt part of the piston is forced into the cylinder. Problems arise such as seizure and significant cylinder wear.

(Purpose of the invention) The present invention was made in order to solve the above-mentioned problems, and aims to provide a piston structure that can prevent the skirt portion from seizing on the cylinder with an extremely simple structure. purpose.

(Structure of the invention) The engine piston structure according to the invention is an engine piston structure in which a pin boss part and a skirt part are connected by a stay extending from a pin boss part of the piston in a direction orthogonal to the pin axis. A shallow recess for preventing seizure is provided on the outer circumferential surface of the connecting portion and the vicinity thereof.

(Effect of the invention) In the engine piston structure of the invention,
As described above, shallow recesses for preventing seizing are provided on the outer circumferential surface of the skirt part's connection part with the stay and its vicinity, so that the piston is deformed by the explosion pressure and the skirt part's stay connection part and its vicinity are deformed. Even if the neighboring parts deform to a state where they slightly bulge outward, this deformation is absorbed by the above-mentioned anti-seizure recess, thereby reliably preventing the skirt from seizing on the cylinder or causing significant wear on the cylinder. This can increase the durability of the engine.

Moreover, the recess for preventing seizure mentioned above is approximately 50~
Since only a very shallow recess of about 300 μm is required, there is no adverse effect on the strength and rigidity of the piston, and the structure is extremely simple, so it can be easily implemented.

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

The piston P of the engine according to this embodiment is a cast iron piston for a diesel engine, and
It has a structure as shown in FIGS. 1 to 3.

In order to reduce the weight of the piston P, the skirt portion near the pin boss portion 1 is removed, and each pin boss portion 1 is connected to the skirt portion 3 by a pair of horizontal stays 2 extending from both sides thereof in a direction perpendicular to the pin axis. At the same time, each pin boss part 1 is connected to the lower part of the ring belt 5 by a support 4 extending upward from its upper side.

Each of the skirt portions 3 forms an opening angle of approximately 90° with respect to the axis A of the piston P when viewed from above in FIG. It is integrally connected to the middle section of the.

By the way, when the explosion pressure acts on the upper end surface of the piston P, the vicinity of the outer periphery of the upper end surface of the piston P deforms downward as shown by the imaginary line in FIG. 4, and along with this, the skirt portion 3 also deforms. As the stay 2 deforms downward, the stay 2 also deforms diagonally.
With this deformation, the connecting portion of the skirt portion 3 with the stay 2 and its vicinity are deformed in such a manner that they bulge outward in the axial direction of the stay 2.

Although the amount of deformation of each of the above parts is minute, on the order of several tens of micrometers, the bulging deformation of the skirt part 3 may cause problems such as the skirt part 3 seizing on the cylinder or the cylinder being significantly worn. In order to prevent
For example, on the outer circumferential surface of the connecting part and its vicinity,
An extremely shallow recess 6 having a depth of about 50 to 300 μm is formed. Each of the recesses 6 has an opening angle of about 25° to 30° from the circumferential edge 3a of the skirt portion 3 with respect to the axis A of the piston P when viewed from above in FIG. It is desirable to form it in a range extending from the lower end of the portion 3 to a position slightly above the connecting portion with the stay 2.

As described above, by forming the shallow recess 6 on the outer circumferential surface of the connecting portion of the skirt portion 3 with the stay 2 and its vicinity, even if the skirt portion 3 is deformed to bulge outward as described above due to the explosion pressure. Since the deformation is absorbed by the recessed portion 5, problems such as the skirt portion 3 seizing on the cylinder and significant wear of the cylinder do not occur.

Incidentally, even if the piston P is provided with a skirt portion in the vicinity of the pin boss portion 1, the above-mentioned deformation will occur more or less in the piston P having the stay 2.
is valid.

Further, the recess 6 does not necessarily have to be formed to have a uniform depth, and may be such that the recess 6 gradually becomes shallower as it moves away from the connecting portion with the stay 2.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a side view of the piston viewed from the pin axis direction, FIG. 2 is a side view of the piston viewed from the direction perpendicular to the pin axis, and FIG. FIG. 1 is a sectional view taken along the line in FIG. 1, and FIG. 4 is a side view of the piston for explaining deformation of the piston due to explosion pressure. P... Piston, 1... Pin boss part, 2... Stay, 3... Skirt part, 6... Recessed part.

Claims (1)

[Scope of Claim for Utility Model Registration] In an engine piston structure in which a pin boss part and a skirt part are connected by a stay extending from the pin boss part of the piston in a direction orthogonal to the pin axis, the connecting part of the skirt part to the stay and its vicinity An engine piston structure characterized by having a shallow recess on the outer circumferential surface of the part to prevent seizure.