JPH07269413A - Piston - Google Patents

Abstract

PURPOSE:To prevent trouble such as ring breakage in a structure having a top ring groove for reducing smoke. CONSTITUTION:A top ring 12 is formed of a shape memory alloy which expands a diameter in a low temperature region lower than a specified temperature while contracts the diameter in a high temperature region higher than a specified temperature. In a low and intermediate engine speed range wherein a temperature of piston 11 is relatively low, the top ring 11 is swelled from a top ring groove 14 at a high position and a dead volume VD1 is reduced in accordance with a top land 22 thereof. In a high engine speed region wherein the temperature of the piston 11 is high, the top ring 12 is received in the top ring groove 14 so as to prevent seizure between the top ring 12 and a cylinder liner 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine.

[0002]

2. Description of the Related Art As shown in FIG. 5 (a), a piston 1 is provided with a ring groove for mounting a piston ring (not shown).
A second ring groove 3 and an oil ring groove 4 are arranged. Further, recently, as shown in FIG. 5B, the top ring groove 5 is provided at a higher position (the height L ₁ > L _{2 of} the top lands 6 and 7), and the top land 7 and the cylinder (see FIG. Smoke is reduced by reducing the dead volume (waste volume) generated between (not shown).

[0003]

However, when the position of the top ring groove 5 is raised, the temperature of the top ring groove 5 and the top ring mounted in the top ring groove 5 tends to rise more than in the conventional position. Therefore, the top ring and the top ring groove 5 are fixed and worn. For this reason, the cooling cavity 8 is provided in the vicinity of the top ring groove 5 inside the piston, but there is a limit to the temperature drop of the top ring groove 5, and the wear of the top ring and the top ring groove 5 progresses and the ring There was a problem of leading to troubles such as breakage.

Therefore, the present invention was devised to provide a piston capable of preventing troubles such as ring breakage in a structure having a top ring groove for reducing smoke. The prior arts related to the present invention include "piston ring structure of internal combustion engine" (Japanese Utility Model Laid-Open No. 4-56263), "Piston having ceramic piston ring".
(Japanese Utility Model Publication No. 4-44455), "Inner ring"
(Japanese Patent Laid-Open No. 62-167975).

[0005]

According to the present invention, a top ring is formed of a shape memory alloy that expands in a low temperature region below a predetermined temperature and contracts in a high temperature region above a predetermined temperature.

[0006]

With the above construction, the top ring swells out from the top ring groove at a high position in the engine low / medium speed range where the piston is at a relatively low temperature, and the dead volume is reduced corresponding to the top land. In the high engine speed region where the temperature is high, the top ring fits in the top ring groove, and seizure between the top ring and the cylinder liner is prevented.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

1 and 2 show an embodiment of a piston according to the present invention. This piston 11
The top ring 12 is formed of a shape memory alloy that expands in the low temperature region and contracts in the high temperature region. In other words, the top ring 12 is formed so that the diameter D ₁ at low temperature is larger than the diameter D ₂ at high temperature (D ₁ > D ₂ ). The shape memory alloy may be any material as long as it has a function required for the compression ring, and is, for example, a known Ni—Ti alloy. Further, the temperature (Ms point) that becomes the boundary of the deformation is the temperature at the boundary between the piston temperature in the high speed region of the engine and the piston temperature in the low / medium speed region.

That is, as shown in FIG. 3, the tendency of smoke generation varies depending on the engine rotation range. The smoke volume increases as the dead volume V _D increases in the low speed range and the medium speed range, but increases in the high speed range. V _D
Has little effect on the value of. Therefore, if the dead volume V _D is made small especially in the low / medium speed range, the occurrence of smoke can be effectively reduced. Further, as shown in FIG. 4, the piston temperature is largely controlled by the engine speed.
For example, in the vicinity of the top of the piston (arrow A in the figure), at a rotational speed of 3,500 rpm and a 1/2 load, the piston temperature (approximately 180
(° C) is higher than the piston temperature (about 160 ° C) at 2,500 rpm and full load. Therefore, top ring 12
Is expanded at low temperatures and contracted at high temperatures,
In the medium speed range, the dead volume V _D is reduced to reduce the generation of smoke, and in the high speed range of the engine, contact between the top ring 12 and the cylinder liner 13 is avoided, and a large combustion pressure is applied to the top ring 12. And the occurrence of sticking and wear of the top ring 12 and the top ring groove 14 is suppressed. In the present embodiment, the Ms point is set to 170 ° C. in consideration of FIG. 4, and if the temperature is below this temperature, the top ring 12 expands in diameter and slides on the cylinder liner 13 to reduce the temperature. -The dead volume V _D1 in the medium speed range is _defined to be smaller than the dead volume V _D2 in the high speed range (V _D1 <
V _D2 ).

The high top ring groove 14 for mounting the top ring 12 is formed at a position extremely close to the top of the piston 11. That is, the height of the top land 22 is extremely small, and in the present embodiment, the row top ring groove 16 for mounting the second top ring 15 is formed below the top land 22. Contrary to the top ring 12, the second top ring 15 is made of a shape memory alloy that contracts in a low temperature range and expands in a high temperature range. The Ms
The point is 170 ° C., which is the same as that of the first top ring 15, or is set to an appropriate value of 170 ° C. or less in consideration of the temperature difference due to the difference in position. That is, over the entire rotation range,
Only one of the first top ring 12 and the second top ring 15 slides on the cylinder liner 13. The position of the row top ring groove 16 is
This corresponds to the position of the top ring groove of the conventional piston shown in FIG. 5 (a), and tends to have a lower temperature than the high top ring groove 14.

As shown in FIG. 2, the top ring 1
The two joints 23a and 23b are made extremely narrow at high temperatures in order to make the clearance as narrow as possible at low temperatures. Further, as shown in FIG. 1, the high top ring groove 14 and the low top ring groove 16 are partitioned into a ring body (ring tregger) 17 of nigerest cast iron or FRM that is cast as a measure against wear. In the piston body near the ring trigger 17, the top ring groove 14,
A cooling cavity 18 for cooling 16 is provided in an annular shape so as to surround the bottom of the cavity 19. In addition, the second ring groove 20 similar to the conventional one is provided on the body of the piston 11.
Also, an oil ring groove 21 is provided.

Next, the operation of this embodiment will be described.

In the low / medium speed rotation range of the engine, the vicinity of the top of the piston 11 is in a relatively low temperature of 170 ° C. or less, and as shown in FIG. 1 (a), the first top ring is used. 1
Reference numeral 2 swells from the high top ring groove 14 and makes sliding contact with the inner surface of the cylinder liner 13 to seal combustion gas.
Dead volume V _D is now high top ring groove 1
It becomes a small one corresponding to the height of the top land 22 of 4 (V _D1 ). The second top ring 15 is in a state of being reduced in diameter and contained in the row top ring groove 16, and does not slide on the cylinder liner 13.

In the high speed region, the temperature near the top of the piston 11 reaches a high temperature of 170 ° C. or higher, and as shown in FIG. 1 (b), the first top ring 12 is reduced in diameter into the high top ring groove 14. It fits in and does not slide on the cylinder liner 13. On the other hand, the second top ring 15 expands in diameter and swells from the row top ring groove 16 and slides on the cylinder liner 13 at a position appropriately separated from the top of the piston 11 to seal combustion gas.

As described above, the first top ring 12 to be mounted in the high top ring groove 14 is formed of a shape memory alloy, and the diameter is expanded in the low and medium speed regions of low temperature to slide on the cylinder liner 13. In the high temperature and high speed range, the diameter is reduced so that the high top ring groove 14 can be accommodated in the high top ring groove 14. Therefore, even if the first top ring 12 is provided at a high position, there is no excessive temperature rise and It is possible to prevent sticking to the top ring groove 14, abrasion and seizure with the cylinder liner 13. That is, the generation of smoke can be suppressed by reducing the dead volume V _D , and there is no risk of ring breakage or the like.

Further, in this embodiment, the top ring grooves 14 and 16 are provided in two steps, and any one of the top rings 1 is formed.
Since the cylinders 2 and 15 are slid on the cylinder liner 13, the sliding friction does not increase and the function of the gas seal can be properly maintained.

When the top rings 12 and 15 are made of a shape memory alloy, for example, the rings may be formed in an atmosphere having a deformation temperature or higher and then plastically deformed at room temperature (low temperature). Further, the deformation temperature is not limited to 170 ° C., and may be appropriately set before and after that.

In the present embodiment, the row top ring groove 16 is provided below the high top ring groove 14 and the top rings 12 and 15 made of shape memory alloy are attached to each row. The groove 16 may be provided with a normal metal top ring, or the like.
It is also conceivable to omit the row top ring groove 16 and perform gas sealing only by the second ring in the high speed range.

[0019]

In summary, according to the present invention, the dead volume can be reduced to reduce smoke and the troubles such as ring breakage can be prevented.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of a piston according to the present invention, (a) showing a state at low / medium speed,
(B) is a diagram showing a state at a high speed.

FIG. 2 is a plan view showing the top ring of FIG.
(A) is a diagram showing a state at a low temperature, and (b) is a diagram showing a state at a high temperature.

FIG. 3 is a relationship diagram between smoke and dead volume for explaining the operation of the present invention.

FIG. 4 is a piston temperature distribution chart for each piston position due to changes in engine speed and load for explaining the operation of the present invention.

FIG. 5 is a view showing a conventional piston, FIG. 5A is a side sectional view of the piston in which a top ring groove is at a normal position,
(B) is a side sectional view of the piston in a position where the top ring groove is high.

[Explanation of symbols]

11 Piston 12 First Top Ring (Top Ring) 13 Cylinder Liner 14 High Top Ring Groove (Top Ring Groove) 22 Top Land V _D1 Dead Volume (Low / Medium Speed Range)

Claims (1)

[Claims] 1. A piston, wherein the top ring is formed of a shape memory alloy that expands in a low temperature range below a predetermined temperature and contracts in a high temperature range above a predetermined temperature.