JPH0519559Y2 - - Google Patents

Description

[Detailed explanation of the idea]

INDUSTRIAL APPLICATION FIELD The present invention relates to a light alloy piston used in an internal combustion engine having a light alloy cylinder wall having a high coefficient of thermal expansion and compositely reinforced with reinforcing fibers such as alumina fibers and carbon fibers. Prior Art The top portion 02 of a piston 01 for an internal combustion engine (see Figure 1) forms part of the combustion chamber and is exposed to high temperatures like the cylinder, but is not directly cooled by cooling water or outside air. Its expansion rate is much larger than that of a cylinder. Therefore, the outer diameter of the piston head portion 02 is made slightly smaller than the outer diameter of the piston skirt portion 03 in consideration of expansion due to temperature differences. A ring groove 04 is formed around the upper part of the piston, and three or four piston rings are installed in the ring groove 04 to maintain airtightness and prevent lubricating oil from entering the combustion chamber. is fitted. The collar defining each ring groove is called a land, and the piston 01 has a first land 05, a second land 06, and a third land 07 in order from the top.
have. Piston ring 0 fitted into ring groove 04
9 (see Figure 2) is made of cast iron or steel;
A gap 010 is provided to obtain appropriate elasticity. If this abutment gap 010 is too large, gas leaks to the crank chamber side, and if it is too small, the abutment end will abut upon thermal expansion, resulting in an excessive contact pressure against the cylinder wall. By the way, commonly used aluminum alloy pistons are lightweight, suitable for high-speed rotation, and have good thermal conductivity, but they have the disadvantage of a large coefficient of thermal expansion, so various improvements have been made to the shape and structure. has been done. That is, for example, the piston boss portion 08 into which the piston pin is fitted is thicker than other parts, and when it receives high heat during engine operation, it expands more than other parts. The outer diameter of the piston pin in the axial direction is smaller than the outer diameter in the direction perpendicular to this (elliptical shape). Additionally, aluminum alloy pistons ensure a large piston clearance (the difference between the cylinder inner diameter and the piston's maximum outer diameter) at room temperature. Problems to be Solved However, in a piston whose cross section is elliptical, where the outer diameter in the direction of the piston pin axis is smaller than the outer diameter in the direction perpendicular to this, the skirt part has a smaller temperature rise than the top part. Since the distance (clearance) between the cylinder wall and the cylinder wall is large in the direction of the small diameter, oil tends to rise when the engine is started or when the accelerator is suddenly released, resulting in an increase in oil consumption. Furthermore, when using an aluminum alloy cylinder block whose cylinder wall is compositely reinforced with reinforcing fibers, the amount of thermal expansion and contraction of the cylinder wall is large, and the inner diameter of the cylinder is small at low temperatures (starting the engine). When the piston rings receive heat during a period of・Both ends of the ring may come into contact. In order to prevent this contact, especially when an aluminum alloy cylinder block is used, it is normal to make the gap sufficiently large. In this case, oil tends to rise through the large joint gap. Means and Effects for Solving the Problems The present invention relates to the improvement of a light alloy piston for internal combustion engines that overcomes the above-mentioned difficulties. In a light alloy piston used in an internal combustion engine having a cylinder wall, the light alloy piston has a plurality of ring grooves extending vertically at the top above the piston pin and an oil reservoir groove below the ring grooves and at the top of the piston skirt. The side surface of the oil sump groove near the piston top is formed perpendicular to the piston center line, and the side surface of the oil sump groove near the piston skirt is formed from the bottom of the oil sump groove to the end of the piston skirt. The piston ring is fitted into each of the ring grooves, and the land diameter above the lowermost ring groove is placed directly below the lowest ring groove of the plurality of ring grooves. The invention is characterized in that an oil spill prevention flange having a diameter larger than that of the oil sump groove is provided above the oil reservoir groove. In the present invention, a plurality of ring grooves are formed in the vertical direction at the top of the light alloy piston above the piston pin, and an oil reservoir groove is formed below the ring grooves and at the top of the piston skirt, and the piston is placed in each of the ring grooves. A ring is fitted therein, and an oil drainage prevention flange having a diameter larger than the land diameter above the lowest ring groove is provided above the oil sump groove immediately below the lowest ring groove of the plurality of ring grooves. When the piston moves from the cylinder head toward the crank chamber in a descending state, the oil adhering to the cylinder wall is scraped downward by the oil-flow prevention collar and the lowest piston ring directly above the prevention collar, and the oil is removed from the oil reservoir. It can be stored in the groove. In addition, in the present invention, the side surface of the oil sump groove near the piston top is formed perpendicular to the piston center line, and the side surface of the oil sump groove near the piston skirt is formed from the bottom of the oil sump groove to the end of the piston skirt. Because the piston is tilted toward the cylinder wall as it moves forward, when the piston descends, the oil is scraped downward from the cylinder wall by the oil-flow prevention flange and the lowest piston ring directly above the prevention flange, and the oil is collected in the oil reservoir. However, the center line of the piston in the oil sump is set at right angles to prevent the oil from being dragged upward by the oil adhering to the cylinder wall before being scraped off by the oil sump prevention collar. The grooved side surface near the top of the piston makes it possible to retain as much oil as possible in the oil reservoir, sufficiently suppressing oil leakage, and as a result, oil consumption can be significantly reduced. Furthermore, in the present invention, since there is no need to perform any processing on the vertically long piston skirt portion, processing is easy, productivity is high, and cost is low. Embodiment Hereinafter, an embodiment of the present invention shown in FIGS. 3 to 5 will be described. Figure 3 shows a cross-sectional view of the main parts of an internal combustion engine in which both the cylinder block 1 and the piston 3 are made of aluminum alloy. Fibers (e.g. Al ₁ O ₂ fibers)
Compositely strengthened by The piston 3 is sequentially moved from the top portion 4 toward the skirt portion 5 side.
It has a land 6, a second land 8, and a third land 10, and a second piston ring 13 is located in a second land groove 7 between the first land 6 and second land 8, and a second land 8 and a third land 10. The second piston ring 14 is placed in the second land groove 9 between them, and the third piston ring 1 is placed in the third ring groove 11 located below the third land 10.
5 are fitted respectively. Further, the piston 3 has a perfectly circular flange 12 located below the third ring groove 11 and used to prevent oil from rising. The diameter of this collar 12 is equal to that of the second land 8 and larger than that of the first land 6 and third land 10. The skirt portion 5 has an elliptical outer peripheral surface shape with its minor axis oriented in the direction of the piston pin axis _L0 , and the collar 12 has a perfect circular shape.
If you compare them, you will get something like Figure 5. In addition, Tsuba 1
2 and cylinder wall 2 (clearance) δ
is preferably 50 to 400 μm. Further, an oil reservoir groove 16 is formed below the collar 12 for preventing oil from rising. The structure of this embodiment is made as described above, and the distance (clearance) between the short diameter part of the skirt part 5 and the cylinder wall 2 is large, and it is compatible with the cylinder wall 2 formed of fiber-reinforced aluminum alloy. Since the gap between each piston ring is large, oil tends to rise, but oil rise can be suppressed by the action of the collar 12 that compensates for the large gap and the oil reservoir groove 16 below it. Therefore, the amount of oil consumed during sudden deceleration when the net average effective pressure in the combustion chamber becomes negative is reduced. Furthermore, the presence of the flange 12 makes it possible to increase the ratio of the major axis to the minor axis of the skirt portion 5, thereby suppressing oil leakage and preventing oil leakage around the skirt portion 5 (piston 3), especially during high-speed operation. This phenomenon in which oil escapes from between the cylinder wall 2 and the cylinder wall 2 to the crank chamber side can be facilitated, and a reduction in oil consumption can be attempted. In the embodiment described above, the flange 12 has a perfect circular shape, but it is also possible to adopt an elliptical flange whose major axis is oriented in the direction of the axis of the piston pin. Test Example An internal combustion engine having the structure shown in Figs. 3 and 4 (example of the present invention), except that it does not have a perfectly circular collar 12, and the other configurations are the same as those shown in Figs. 3 and 4. The same internal combustion engine (comparative example) was prepared. The cylinder block 1 is a cast product made of JIS ADC12 material, and the cylinder wall 2 is compositely reinforced with alumina fiber and carbon fiber. The fiber deposition rate (V ₁₀ ) of alumina fiber is 12%, the fiber deposition rate (V ₁₀ ) of carbon fiber is 9%, and the gelatinization rate of Al ₁ O ₂ in alumina fiber is 33%. The weight of silica (S O ₁ ) is less than 25% by weight. The piston 3 is a cast product made of JIS A351 material, and the diameter of the second land 8 = 80.3 mm, the diameter of the collar 12 = 80.3 mm, the protrusion amount of the collar 12 = 0.5 mm, and the wall thickness of the collar 12. = 0.8 mm, the distance between the second land 8, the collar 12 and the cylinder wall 2 (clearance δ) = 400 μm (however, the collar 12 does not exist for internal combustion engines). The oil consumption of the internal combustion engine was investigated under three operating conditions A, B, and C shown in FIG. The results are shown in the table below.

[Table] <Evaluation of test results> Under all operating conditions, the distance that can be traveled with the consumption of 1 oil increases significantly, and the oil consumption per hour is significantly reduced. In particular, it has been found that the improvement in oil consumption becomes more pronounced as the vehicle accelerates and decelerates at lower speeds.

[Brief explanation of the drawing]

Fig. 1 is a vertical side view of a conventional piston for an internal combustion engine, Fig. 2 is a plan view of a piston ring fitted to the piston, and Fig. 3 is a light alloy piston for an internal combustion engine according to the present invention. FIG. 4 is an enlarged view of the main parts, FIG. 5 is a plan view showing the cross-sectional outline of the skirt and collar in the embodiment, and FIG. 6 is a comparison with this embodiment. It is an explanatory diagram showing mode operation conditions with an example. 1... Cylinder block, 2... Cylinder wall, 3... Piston, 4... Top of head, 5... Skirt, 6... First land, 7... First ring groove, 8... Second Land, 9...Second ring groove, 1
0...Third land, 11...Third ring groove, 12
...Tsuba, 13...First piston ring, 14...
...Second piston ring, 15...Third piston ring, 16...Oil sump groove.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A light alloy piston used in an internal combustion engine having a light alloy cylinder wall compositely reinforced with reinforcing fibers such as alumina fiber and carbon fiber;・A plurality of ring grooves are formed in the vertical direction at the top above the pin, and an oil reservoir groove is formed below the ring grooves at the top of the piston skirt, and the side surface of the oil reservoir groove near the piston top is perpendicular to the piston center line. At the same time, the groove side surface of the oil sump groove near the piston skirt is inclined in a direction approaching the cylinder wall as it progresses from the bottom of the oil sump groove to the end of the piston skirt, and a piston ring is installed in each of the ring grooves. It is characterized in that an oil drainage prevention flange having a diameter larger than the diameter of the land above the lowest ring groove is provided above the oil sump groove directly under the lowest ring groove of the plurality of ring grooves. A light alloy piston for internal combustion engines. (2) The light alloy piston for an internal combustion engine according to claim 1, wherein the oil drainage prevention collar has a right circular shape. (3) The light alloy piston for an internal combustion engine according to claim 1, wherein the oil drainage prevention collar has an elliptical shape with its major axis oriented in the axial direction of the piston pin. .