JPH03179154A - Piston for internal combustion engine - Google Patents

Abstract

PURPOSE:To keep off any increase of friction with an increment of combustion pressure by forming a local thick wall part in the backside of a skirt part in a piston so as to cause a step-form rigid change in a gap with a thin wall part adjoining to the circumferential direction. CONSTITUTION:In this piston, there is provided with a ring land part 3 equipped with plural ring grooves 2 around a crown part 1 receiving combustion pressure, and a thin cylindrical skirt part 4 is solidly formed in this lower part, while each pin boss part 5 is formed in two spots parted as far as 180 degrees as being projected to the inner circumferential side. In this case, each local thick wall part 7 of almost rectangular form is formed in two spots in both thrust and antithrust directions as one body with a reinforced rib 6 formed in the backside of the skirt part 4. With this constitution, the skirt part 4 is deformed so as to reduce a contact area with a cylinder wall when it is pressed by this cylinder wall, thus any increase of friction is kept back.

Description

[Detailed description of the invention] Industrial applications This invention relates to improvements in pistons for internal combustion engines.

PRIOR ART A piston for an internal combustion engine is generally made of an integrally cast product such as an aluminum alloy, and as shown in FIG. 1 and FIG. At the same time, a thin cylindrical skirt portion 13 is integrally formed at the bottom thereof. Furthermore, a pair of thick pin boss portions 14 that support both ends of the piston pin are formed at two locations 180° apart.

In such a piston, the upper part near the crown part 11 becomes high temperature and thermal expansion becomes large, so the part itself at room temperature has a tapered shape with the maximum diameter at the lower part of the skirt part 13. There is. In the illustrated example, a skirt reinforcing lip 15 along the circumferential direction is placed at the height position where the maximum diameter is reached.
is provided. Incidentally, the wall thickness of the skirt portion 13 and the cross-sectional shape of the skirt reinforcing lip 15 are generally -shaped in the circumferential direction.

Therefore, the rigidity distribution in the circumferential direction of the skirt portion 13 is the first with respect to the angle θ with respect to the piston pin axis.
The characteristics are as shown by the solid line in Figure 3. In other words, the stiffness is highest at the pin boss portion 14 and lowest in the thrust direction or anti-thrust direction, which is θ-90°, and changes smoothly in the intermediate portion between the two.

Furthermore, as shown in FIG. 14, a piston has been proposed in which the thickness of the skirt portion 13 is gradually changed so that the wall thickness in the thrust direction and anti-thrust direction is thicker than in the middle portion (Utility Model Application No. 56-157350). Public notices, etc.). In this case, the rigidity distribution in the circumferential direction of the skirt portion 13 is
The characteristics are as shown by the imaginary line in FIG. 3, which are basically the same as those described above, and the rigidity changes in the portions other than the bottle boss portion 14 are smooth.

Problems to be Solved by the Invention As is well known, in the piston of an internal combustion engine, a so-called lateral pressure is generated which tries to press the skirt part 13 against the cylinder wall surface as a component of the combustion pressure, and the reaction force causes the skirt part 13 to press against the cylinder wall surface. The portion 13 is pressed inward.

In this case, in the conventional piston, as can be seen from the above-mentioned rigidity distribution of the skirt portion 13, the skirt portion 13 as a whole tends to deform along the cylinder wall surface due to the reaction force F, as shown in FIG. . Therefore, as the combustion pressure increases, that is, as the side pressure increases, the substantial contact area between the cylinder wall surface and the skirt portion 13 increases.

Figure 16 shows this situation. When the combustion pressure is relatively low, only the three parts near the same height as the piston pin are in strong pressure contact with the cylinder wall, but when the combustion pressure is higher than this, the lower part The area including the 6th part is strongly pressed,
When the combustion pressure is further increased, a very wide range including the 0 part is strongly pressed.

Therefore, when the combustion pressure is high, there is a drawback that the frixillane generated in the skirt portion 13 becomes extremely large.

Means for Solving the Problems Accordingly, the present invention uses deformation caused by combustion pressure to conversely reduce the contact area with the cylinder wall. That is, in a piston for an internal combustion engine, which has a thin cylindrical skirt part at the lower part of the crown part and a pair of thick bottle boss parts that support both ends of the piston pin,
On the back surface of the skirt in the thrust and anti-thrust directions perpendicular to the piston pin, there is a step-like stiffness change between the circumferentially adjacent thin-walled portion in the axial range that includes at least the height position where the piston diameter is maximum. This feature is characterized by the provision of locally thickened portions so that this occurs.

Effect: In the above configuration, the rigidity of the thick portions provided in the thrust direction and the anti-thrust direction is locally increased, and the rigidity of the bottle boss portion is also extremely high. Further, the rigidity of the thin wall portion between the bottle boss portion and the thick wall portion is low. In other words, a step-like change in rigidity occurs in the circumferential direction.

Therefore, when a strong reaction force is applied from the cylinder wall, the thick wall part is pushed inward as it is, and as a result, some of the thin wall wall
Specifically, the portion adjacent to the thick portion attempts to deform so as to bulge outward.

Therefore, the contact area in pressure contact with the cylinder wall is reduced, and friction is reduced.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIGS. 1 and 2 show an embodiment of a piston according to the present invention.

This piston is made of, for example, an aluminum alloy that is integrally cast, and has a ring land portion 3 having a plurality of rings FII2 formed around a crown portion that receives combustion pressure, and a thin cylindrical ring below the ring land portion 3. A shaped skirt portion 4 is integrally formed, and bottle boss portions 5 are formed at two locations 1800 degrees apart in a shape that protrudes toward the inner circumferential side.

The skirt portion 4 is formed to extend downward at two locations, one in the thrust direction and the other in the anti-thrust direction perpendicular to the piston pin. Also, the part slightly below the bottle boss part 5 has the maximum diameter, and the skirt part 4N at that height
A continuous annular skirt reinforcing rib 6 is formed on the surface with a constant width.

Integrating with the skirt reinforcing ribs 6, substantially rectangular locally thickened portions 7 are provided at two locations in the thrust direction and in the anti-thrust direction. This thick part 7
The thickness tl is equal to or larger than the thickness t of the skirt reinforcing rib 6, as shown in FIG. For example, if the bore diameter is about φ8011, tl” (1,0 to 2
．． 0)tt. Further, the thickness t of the skirt reinforcing rib 6 is usually less than twice the thickness t of the skirt portion 4.

The thick portion 7 is laterally symmetrical about a central point A orthogonal to the piston pin, and is formed in an angular range of about 20 to 60 degrees in the circumferential direction. In addition, in this illustrated example, the skirt reinforcing ribs 6 are vertically symmetrical as well.

Incidentally, the thick portion 7 has a substantially -like thickness 1 at each portion of the circumference. Further, the cross-sectional shape of the thin wall portion 8 adjacent to the thin wall portion 8 also has a substantially −-shaped shape at each portion of the circumference.

In the piston configured as described above, the circumferential rigidity distribution of the skirt portion 4 has characteristics as shown in FIG. 3 with respect to the angle θ with respect to the piston pin axis. In other words, it goes without saying that the pin boss portion 5 has the highest rigidity, but the rigidity of the thick wall portion 7 is also extremely high.
In addition, the rigidity of the intermediate thin portion 8 is extremely low, resulting in an extreme step-like change in rigidity in the circumferential direction.

Therefore, when the reaction force F of the lateral pressure received from the cylinder wall becomes larger than a certain value, the highly rigid thick part 7 itself is pushed inward without deforming much, and the thin part Since only 8 tries to bend and deform greatly,
A part of the thin part 8, specifically a part 8a adjacent to the thick part 7
On the contrary, it tries to expand outward and comes into pressure contact with the cylinder wall. In other words, only a portion 8a of the thin wall portion 8 is intensively pressed against the cylinder wall, and a clearance can be maintained between the other portions and the cylinder wall, so that the friction of the piston as a whole is reduced.

Note that the portion 8a that mainly contacts the cylinder wall as described above is shown cross-hatched in FIG.

Further, the relationship between the reaction force F and the contact area is shown in FIG.

The broken line in the figure shows the change in contact area in the conventional piston.

Furthermore, in the above embodiment, as can be understood from FIG.
Since the periphery of the piston is in contact with the cylinder wall around the height position where the piston diameter is maximum, the inclination of the piston with respect to the cylinder bore center line is reduced, and the piston reciprocates in a stable posture, suppressing the occurrence of slap noise.

Next, the embodiment shown in FIG. 7 is formed by extending the thick part 7 in the axial direction of the piston, and the upper end is connected to the thick part on the back surface of the ring land part 3, and the lower end is connected to the thick part on the back surface of the ring land part 3. It also extends to the lower end of the skirt portion 4.

According to this embodiment, the rigidity of the skirt portion 4 as a whole is further increased, making it suitable for an internal combustion engine with even greater lateral pressure. In this case, the portion 8a which mainly contacts the cylinder wall is shown by cross hatching in FIG.

Further, both the embodiment shown in FIG. 9 and the embodiment shown in FIG. 1O are examples in which the skirt reinforcing rib 6 is not provided.
Only a thick portion 7 is locally provided on the back surface of the skirt portion 4 having a thickness of approximately -.

Effects of the Invention As is clear from the above explanation, according to the piston of the internal combustion engine according to the present invention, when the skirt portion is strongly pressed by the cylinder wall as a reaction force of side pressure due to combustion pressure, the skirt portion is prevented from coming into contact with the cylinder wall. Since the skirt portion is deformed to reduce its area, it is possible to prevent an increase in friction due to an increase in combustion pressure.

[Brief explanation of drawings]

FIG. 1 is a front view of a piston showing an embodiment of the present invention;
Fig. 2 is a sectional view taken along the line ■-■, Fig. 3 is a characteristic diagram showing the rigidity distribution in the circumferential direction of this embodiment, Fig. 4 is an explanatory diagram showing its deformed state, and Fig. 5 is An explanatory diagram showing the distribution of the contact surface, FIG. 6 is a characteristic diagram showing the relationship between the reaction force from the cylinder wall and the contact area, FIG. 7 is a front view of a piston showing a different embodiment of the present invention, and FIG. 8 9 is an explanatory diagram showing the distribution of the contact surface in this embodiment, FIGS. 9 and 10 are front views of a piston showing further different embodiments of the present invention, FIG. The figure is a half-sectional view taken along the line ■-■, Figure 13 is a characteristic diagram showing the rigidity distribution in the circumferential direction of this conventional example, Figure 14 is a cross-sectional view showing another conventional example, and Figure 15 is a FIG. 16 is an explanatory diagram showing the deformed state of a conventional piston, and FIG. 16 is an explanatory diagram showing the distribution of the contact surface in the conventional piston. DESCRIPTION OF SYMBOLS 1... Crown part, 4... Skirt part, 5... Pin boss part, 6... Skirt reinforcement rib, 7... Thick wall part,
8... Thin wall part. Fig. 1 Notes---Kufuuso static 4---1---Skirt official p 5---1-Sen boss sound p 6------Skirt λ Extinguisher bow arrow 7---Thick part 8---・Induction interior Figure 2 Figure 3 Circle e (deg) Figure 4 Figure 6 Figure 9 Figure 10 Figure 1 Figure it Figure 12 Figure 13 (wide) Figure 14 Figure 3 Figure 15 4

Claims (1)

[Claims] (1) In an internal combustion engine piston that has a thin cylindrical skirt at the lower part of the crown and a pair of thick pin bosses that support both ends of the piston pin, the thrust direction perpendicular to the piston pin and the The back surface of the skirt part in the thrust direction is locally thickened so that a step-like change in rigidity occurs between the circumferentially adjacent thin-walled part at least in the axial range including the height position where the piston diameter is maximum. A piston for an internal combustion engine characterized by having a thick walled portion.