JPS59215942A - Piston of 2-cycle internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent effectively a knock pin from dropping out of a piston in high temperature by making the knock pin of austenite system stainless steel which prevents a piston righ fitted in the aluminum alloy piston from turning. CONSTITUTION:An aluminum alloy piston 1 is formed on the outer peripheral surface with an annular groove 3 in which a knock pin hole 5 is radially formed in the form of a blind hole. A knock pin 2 of austenite system stainless steel is fitted into this pin hole 5 with an interference delta. The piston ring 4 is formed on the back corners of a slit 4b with arcuate notches 4a. And the piston ring 4 is fitted in the annular groove 3 with the notches 4a being aligned with the knock pin 2. Thus, since the difference of expansion coefficient between the knock pin 2 and the piston 1 can be maintained small, the interference delta remains even in high temperature of the piston 1 to prevent the pin 2 form dropping out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston for a two-stroke internal combustion engine in which a knock pin for preventing rotation of a piston ring is prevented from coming off when the temperature of the piston increases.

Generally, in a two-stroke engine, the piston ring is prevented from rotating using a knock pin so that the abutment of the piston ring is exposed above the cylinder boat. Conventionally, this dowel pin for rotation prevention has been made of tool steel 1, for example 8
It was made in K4. By the way, as the output of engines has increased in recent years, the temperature of the piston has also increased, so if the piston is made of aluminum alloy,
The knock pin falling out due to the difference in thermal expansion coefficient between the piston and the knock pin has been considered a drawback. Various measures have been taken to prevent this omission.

For example, Fig. 1 (A) and (B) (This Fig. 1 is a diagram of one embodiment of the present invention, but since it is common to the conventional example except for the material, the conventional example will also be explained using this figure.) There is a structure in which a knock pin 2 driven in the radial direction of the piston 1 is stopped by a piston ring 4 fitted in an annular groove 3, as shown in FIG. In this structure, when the dowel pin 2 comes out due to an increase in the temperature of the piston, it interferes with the arcuate notch 4a on the back side of the piston ring 4, so both the piston ring 4 and the knock pin 2 require sufficient strength. Therefore, there is a disadvantage that the weight of the piston ring increases. Also, the dowel pin hole 5 is sealed to prevent the dowel pin 2 from coming out inside the piston 1, but when the temperature rises and the gas pressure inside the dowel pin hole 5 increases, the dowel pin 2 is pushed. - To avoid this, in conventional dowel pins made of tool steel, a longitudinal V-notch 2& is provided on the outer periphery of the dowel pin 2 in the length direction, as shown in FIG. 7(a), ←). Since this V-notch 2a is required, the cost increases accordingly.

In addition, as shown in FIGS. 3(a) and 3(b) (this is an embodiment of the present invention, but the drawings are similar to the conventional example), the piston ring 4 does not hit the knock pin 2. For structural types, make the tightening margin of the dowel pin sufficiently large,
One idea is to make sure that a tightness allowance remains even when the temperature rises, but with conventional dowel pins made of tool steel, if you take a large tightening allowance at room temperature so that the tightness remains even when the temperature rises, the yield strength of the aluminum alloy will increase. If it is insufficient, plastic deformation will occur on the inner wall of the knock bottle hole 5 of the piston, which is undesirable.

The interference within the limit of the yield strength of aluminum alloy is fi
When FAffLF rises, the tightening margin is lost and it comes out.

In addition, as shown in Fig. 8, a knock pin 2 is driven into the top surface of the piston 1 in the sliding direction of the piston 1, and its tip is exposed in a hole 6 made on the side surface of the piston 1, and is caulked to prevent it from coming out. There is something like that. This structure has the disadvantage that the cost increases due to the number of man-hours required for caulking.Also, when two piston rings are provided, it is necessary to use space for the caulking hole 6, so the upper piston ring and the lower piston ring are Since the abutment cannot be shifted, it is possible to prevent the dowel pin from coming off, but even with two rings, there is a drawback that compressed gas escapes to a large extent.

The above-mentioned drawbacks occur because the conventional dowel pin is made of tool steel, and there is a large difference in thermal expansion coefficient between the piston and the piston, which is made of aluminum alloy, and the tightening margin of the dowel pin is lost when the temperature rises. The dowel pin is made of JLti.
It was natural to use i, and it was natural that the interference would disappear when the temperature rose.

The invention was made against the above-mentioned background, and its purpose is to obtain a piston that can prevent the dowel pin from being pulled out by remaining a tightening margin even when the temperature of the piston rises, and its characteristics are as follows. The piston is made of aluminum alloy and has at least one annular groove on its outer circumferential surface, and has a dowel hole that opens into the annular groove in the sliding direction of the piston or in the radial direction. An austenitic stainless steel knock pin is fitted into the annular groove to prevent the piston ring from turning.

Examples of the present invention are shown below at Figures 1-m! This will be explained with reference to Figure 6. In each embodiment, the material of the piston 1 is cast aluminum alloy, such as AC8A or AC9A (hypereutectic aluminum silicon alloy), and the material of the knock pin 2 is austenitic stainless steel, such as 8U8302.

FIGS. 1(A) and 1(B) show the first embodiment. To explain this structure in detail again, the piston 1 has one annular groove 3 on the outer circumferential surface, and a knock bottle hole 5 is bored in the radial direction at the position of the annular groove #13. That is, the knock bottle hole 5 opens into the annular groove 3. Austenitic stainless steel 5US302R for dowel hole 5 with
No. 11 knock pins 2 are fitted with a certain tightening margin δ. The piston ring 4 has an arcuate notch 4a at the rear corner of the abutment 4b, and the piston ring 4 is fitted into the annular groove 3 with the abutment 4b aligned with the knock pin 2.

In the above configuration, the dowel pin 2 is made of SUS 302 and has a small difference in coefficient of thermal expansion with respect to the AC3A or AC9A of the piston l. There is no exception. Therefore, the knock pin 2 does not interfere with the arcuate notch 4a of the piston ring 4, and there is no need to increase the strength of the interference as in the conventional case.
The ring 4 does not require an extra increase in size and does not result in an increase in weight. In addition, even if the gas pressure inside the dowel pin hole 5 becomes high when the temperature rises, the tension of the dowel pin 2 is maintained sufficiently, so it will not come out. There is no need to attach a , which reduces manufacturing man-hours and costs.

FIG. 2 shows a second embodiment. In this embodiment, the knock pin hole 5 is passed through the inside of the piston l, and other points are the same as those in FIG. 1. Conventionally, it was necessary to cover the dowel hole with a bag to prevent it from coming out inside the piston when the loosening became significant due to hidden rise, but with the present invention, the tightness remains even when the temperature rises, so the piston l
There is no leakage to the inside, and there is no need to use the knock bottle hole as a bag. Therefore, there is no need to provide the bulging portion 1a as shown in FIG. 81, and the piston shape is simple. In addition, the gas pressure in the bag-shaped dowel pin hole does not cause any force in the direction of removal to occur, making removal even more reliable.

3() and (b) show a third embodiment. Although the outline of this structure has been described above, the piston ring 4 has a dowel pin 2 at the corner of the upper surface of the abutment 4b. It has an arcuate notch 4C that matches the diameter of the dowel pin 2, and is prevented from rotating by the dowel pin 2 in this arcuate notch 4c.
The dowel pin 2 does not come off even without adopting a special structure for preventing the dowel pin 2 from coming off. In this case as well, use dowel pin 2.
Notuchi is unnecessary.

FIGS. 4(a) and 4(b) show a fourth embodiment. This structure was also briefly explained earlier, but a knock pin hole 5 is drilled from the upper surface of the piston 1 across the annular groove 3 in the sliding direction of the piston 1, and the knock pin 2 is driven into this knock pin hole 5. , has an arcuate notch 4d matching the outer diameter of the dowel pin 2 at the rear corner of the abutment 4b, and the dowel pin 2 is prevented from rotating at this arcuate notch 4d. In this example, the air bleed hole 7 is made from the side of the piston 1 without making the lower end of the knock bottle hole 5 into a bag. It's okay. Even if the gas pressure inside the bag due to the temperature rise acts as a releasing force, the dowel pin 2 has sufficient tension and will not come off. In that case, it is better to make the 50 dowel pin holes a little thicker.

Figure g5 ((a), (b), and H show the fifth embodiment. This Ij! embodiment has two piston rings,
It has an annular groove 3.3', and a dowel hole 5.5' separates each annular groove 3, 3' from the upper surface of the piston l in the circumferential direction in the sliding direction of the piston. The hole was opened and a dowel pin 4.4' was driven in. The annular groove 3 in Fig. 5 (a) is for the upper piston ring;
The annular groove 3' in FIG. 5(b) is for the lower piston 1). A degassing prevention plug 8 is fitted into the upper end of the lower knock bottle hole 5' to prevent gas from escaping from the upper annular groove 3.

As in this embodiment, when two piston rings are provided in the present invention, their abutments can be shifted from each other, so that leakage of compressed gas can be suppressed to a small level.

In the structures shown in each of the above embodiments, since the dowel pin 2 is made of austenitic stainless steel, the tightening margin of the dowel pin 2 remains even when the temperature rises, and the tension is maintained.
Although the dowel pin 2 does not come off, this is made clear by calculating thermal expansion. .

Target piston, dowel pin material, thermal expansion mooring,
Young's modulus and yield strength are shown in Table 1 below.

In the above table, the proof stress of the knock bottle is omitted because it is sufficiently larger than that of the piston.

Since the proof stress of the piston is smaller than that of the knock bottle, if the interference of the knock bottle is increased, plastic deformation occurs on the inner wall of the knock bottle hole of the piston.

Unfortunately, the tightening allowance is limited by the piston's proof strength. If the tightening allowance (upper limit) at room temperature is 620% calculated from the proof stress of the piston, and the upper limit of the tightening allowance at room temperature is δ2o, the calculated tightening allowance δT when the temperature rises at ToOf is It is as shown in Table 2 below.

Note that the calculation formula is omitted because it is a general one.

The graph of Table 2 is shown in FIG. 6.

2nd i above! , or as clearly shown in Figure 6, if the material of the knock bottle is conventional (psK4), the tightness becomes negative when the temperature rises (dotted line (A), ←
). In other words, the tension is gone and the knock bottle falls out. However, in the case of the stainless steel material of the present invention, the interference remains positive even when the temperature rises (solid line (/tsu, ni)).
), the knock bottle will maintain its tension and will not be missed.

The present invention has found that austenitic stainless steel is the most suitable material for the knock bottle in terms of coefficient of thermal expansion, strength, and heat resistance; however, for example, when the requirement for heat resistance is low, beryllium steel etc. Copper alloys such as
Nickel-based alloys such as nichrome are also considered.

As explained above, in the present invention, since the knock pin is made of austenitic stainless steel, the difference in coefficient of thermal expansion is small compared to the aluminum branch piston, and the tightness remains even when the temperature rises, so it is difficult to remove the knock pin. It's hard to see what's going on. Therefore, there is no need to provide a V-notch or swage the knock pin as in the past in order to prevent the knock pin from coming off, and the additional cost is reduced accordingly. In addition, since it does not interfere with the piston ring, there is no need to increase the strength extra.
It does not cause an increase in C1M1'. Furthermore, when driving a knock pin in the sliding direction of the piston, even if two or more piston rings are provided, their abutments can be shifted, and leakage of compressed gas can be suppressed to a small level.

[Brief explanation of the drawing]

FIGS. 1 to 5 show Iji! of the present invention. Fig. 1(a) is a sectional view of the piston of the embodiment of series 1, and Fig.
2 is a sectional view taken along the line A-A in the same figure (A), FIG. 2 is a sectional view showing the second embodiment, FIG. =) is the main part B in the same figure (a)
4(A) is a sectional view showing the fourth embodiment, FIG. 4(B) is a sectional view taken along the line C-C in FIG. -D line sectional view, Figure 6 is a piston temperature-tightness characteristic diagram explaining the present invention in detail, Figures 7 (A) and (B) are front views of the knock pin in the conventional example, and fjlI drawing, Figure 8 The figure is a sectional view of a piston showing a conventional example. 1... Piston, 2... Dowel pin,
3.3'...Annular groove, 4...Group/Piston ring, 5.5'...Group/Dowel hole. Figure 4: Figure 6: Figure 4: Figure 6

Claims (1)

[Claims] At least 1 on the outer peripheral surface of the aluminum alloy piston
It has a round annular groove, and has a knock pin hole that opens in the annular ring in the sliding direction of the piston or in the radial direction, and a rotation stopper of the piston ring fitted in the annular groove is provided in the knock pin hole. A piston for a two-stroke internal combustion engine characterized by having a dowel pin made of austenitic stainless steel inserted therein.