JP2006299979A - Piston cooling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston cooling device adaptable to a higher output engine by increasing the amount of cooling liquid to be supplied into a cooling chamber to improve the cooling effect of the whole piston and cooling the piston to be at a uniform temperature in the peripheral direction with no cooling irregularity to reduce the thermal stress of the piston, while preventing a lack of the amount of lubricating oil in an engine lubricating part of the engine in a low rotation region. <P>SOLUTION: The piston cooling device comprises the piston having the annular cooling chamber formed in the back of a ring groove and a cooling liquid inlet for introducing the cooling liquid into the cooling chamber, and a cooling liquid jet nozzle for jetting the cooling liquid toward the cooling liquid inlet. There are two cooling liquid inlets in the piston and two cooling liquid jet nozzles corresponding to the cooling liquid inlets. Valve opening pressure control mechanisms for the two cooling liquid jet nozzles are set to be different in valve opening pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is applied to an oil-cooled piston cooling device for an engine, and includes a piston having an annular cooling chamber formed at the back of a ring groove and a coolant inlet hole for supplying a coolant to the cooling chamber, and the cooling The present invention relates to a piston cooling device having a coolant jet nozzle for jetting coolant toward a liquid inlet hole.

7 to 9 show an example of a conventional cooling device for a cooling piston for a diesel engine, FIG. 7 is a longitudinal sectional view of a piston including a coolant jet nozzle, FIG. 8 is a bottom view of the piston, and FIG. ) Is a partial cross-sectional view along the coolant inlet hole of the piston, and (B) is a partial cross-sectional view along the drain hole of the piston.
7 to 9, 1 is a piston of the diesel engine, 1a is a ring groove into which a piston ring is fitted, 2 is a cooling chamber formed in an annular shape at the back of the ring groove 1a inside the piston, A cooling liquid inlet hole 4 that opens into the cooling chamber 2 and introduces the cooling liquid into the cooling chamber 2 is a drain hole that opens into the cooling chamber 2 and discharges the cooling liquid in the cooling chamber 2.
One cooling liquid inlet hole 3 is provided, and as shown in FIG. 8, it is provided in a lower part of the exhaust port 20 where the temperature becomes high. 21 is an intake port, 5 is a back surface of the piston 1, 6 is a piston pin hole, and 7 is a piston pin boss.

Reference numeral 10 denotes a coolant jet nozzle, which is provided corresponding to the coolant inlet hole 3 and jets the coolant from the jet hole 11 toward the coolant inlet hole 3.
FIG. 5 shows the details of the coolant jet nozzle 10, 12 is a nozzle body, 13 is a spherical valve, 17 is a valve seat, 14 is a pressure adjusting spring, and the spherical valve 13 is an attachment load of the pressure adjusting spring 14. The valve seat 17 is pressed with a set valve opening pressure. A coolant inlet passage 16 is supplied with coolant (lubricant oil) branched from the engine lubricant passage.

When the coolant branched from the lubricating oil passage (not shown) and introduced into the coolant inlet passage 16 of the coolant jet nozzle 10 exceeds the valve opening pressure set by the pressure adjusting spring 14, the spherical valve 13 is pushed open. Into the outlet passage 15, and is ejected from the ejection hole 11 toward the cooling liquid inlet hole 3 through the outlet passage 15, and enters the cooling liquid inlet hole 3 facing one cooling liquid ejection nozzle 10. Each flows in.
The coolant flows into the cooling chamber 2 from the coolant inlet hole 3, cools the piston 1 by flowing in the cooling chamber 2 in the circumferential direction, and flows out from the drain hole 4 to the back surface 5 of the piston 1. Then it is dropped down.

  Further, as a piston cooling device in which the piston is cooled by the cooling liquid (lubricating oil) ejected from the cooling liquid ejection nozzle, Patent Document 1 (Japanese Patent Laid-Open No. 9-96248) and Patent Document 2 (Japanese Patent Laid-Open No. Hei 10). -54236) and the like.

JP-A-9-96248 Japanese Patent Laid-Open No. 10-54236

  In the conventional piston cooling device shown in FIGS. 7 to 9, one cooling liquid inlet hole 3 for supplying the cooling liquid is provided in the annular cooling chamber 2 and directed toward the cooling liquid inlet hole 3. Since the cooling liquid ejection nozzle 10 for ejecting the cooling liquid is provided corresponding to the cooling liquid inlet hole 3, the amount of the cooling liquid supplied into the cooling chamber 2 is reduced particularly in the low rotation range. The cooling effect is reduced, and the cooling liquid flows into the cooling chamber 2 from one cooling liquid inlet hole 3 provided in the lower portion of the exhaust port 20, so that it is difficult for the cooling liquid to be uniformly supplied to the entire cooling chamber. Further, uneven cooling occurs in the circumferential direction of the piston 1, which contributes to an increase in the thermal stress of the piston, and hinders the engine output from being increased.

FIG. 6 shows the relationship between the engine speed and the lubricating oil pressure. In the prior art, as shown in FIG. 6A, the valve opening pressure Ps of the coolant jet nozzle 10 is shown. _{Since 0} is lower than the lubricating oil pressure P ₁ , the lubricating oil flows to the coolant jet nozzle 10 side where the spherical valve 13 is open at the start of rotation in the low engine speed range, and serves as the coolant for the piston 1. break out because, not easily increased lubricating oil pressure P _1, a problem occurs that tends to occur a shortage of lubricating oil.

  In view of the problems of the prior art, the present invention increases the amount of cooling liquid supplied to the cooling chamber to improve the cooling effect of the entire piston, and supplies the cooling liquid uniformly to the entire cooling chamber to In order to reduce the thermal stress of the piston by cooling to a uniform temperature without causing uneven cooling in the direction, a piston corresponding to high engine output can be obtained. To provide a piston cooling device capable of preventing the occurrence of an insufficient amount of lubricating oil in an engine lubricating portion in a low engine speed range by avoiding a decrease in lubricating oil pressure on the engine side while maintaining a supply of cooling fluid. Objective.

  The present invention achieves such an object. An annular cooling chamber formed at the back of a ring groove, a piston having a cooling liquid inlet hole for introducing the cooling liquid into the cooling chamber, and the cooling liquid inlet hole. In the piston cooling device having a coolant jet nozzle for jetting coolant, two coolant coolant inlet holes are provided in the piston, and two coolant jet nozzles are provided corresponding to the coolant inlet holes. It is characterized by that.

  According to this invention, two cooling liquid inlet holes for supplying the cooling liquid are provided in the annular cooling chamber, and the cooling liquid jet nozzle for jetting the cooling liquid toward the cooling liquid inlet hole is provided in the cooling liquid inlet hole. Since the two correspondingly provided, the amount of the coolant supplied to the cooling chamber is doubled as compared with the prior art having one coolant inlet hole and one coolant jet nozzle, and 2 in the cooling chamber. Since the coolant is supplied from the coolant inlet hole that opens at the location, the coolant can be supplied uniformly throughout the cooling chamber, improving the cooling effect of the entire piston and causing uneven cooling of the piston in the circumferential direction. The piston can be cooled to a uniform temperature without any problems, and the thermal stress of the piston can be reduced, so that the piston corresponding to the high output of the engine can be provided.

In this invention, preferably, the engine is provided with an engine having two intake ports and two exhaust ports, and the two coolant inlet holes are respectively provided in the exhaust port lower portion and the intake port lower portion. Provide.
With this configuration, the cooling liquid is normally supplied to the cooling chamber from only one part below the exhaust port of the piston, and the cooling liquid is also cooled from the lower part of the intake port in addition to the lower part of the exhaust port. Since it is configured so as to be supplied to the chamber, the cooling effect of the entire piston can be improved by adjusting the amount of cooling liquid to the lower part of the exhaust port and the amount of cooling liquid to the lower part of the intake port.

In the invention, it is preferable that the engine is provided with an engine having two intake ports and two exhaust ports, and the two coolant inlet holes are respectively provided at the lower portions of the two exhaust ports. Provide.
With this configuration, the coolant is normally supplied to the cooling chamber from only one location below the exhaust port of the piston, whereas the coolant is supplied to the cooling chamber from each of the two locations below the exhaust port. With this configuration, it is possible to improve the cooling effect in the vicinity of the lower portion of the exhaust port that is at a high temperature, to prevent overheating of the piston at the time of high heat load, and to obtain a piston that can cope with high engine output.

In the invention, it is preferable that the two coolant inlet holes have different inner diameters.
If comprised in this way, while setting the arrangement of the two coolant inlet holes according to the circumferential temperature distribution of the piston, and setting the inner diameter of the two coolant inlet holes, the circumferential direction of the piston The temperature distribution can be made uniform, thereby reducing the thermal stress due to the temperature difference in the circumferential direction of the piston.

In this invention, it is preferable that a drain hole for discharging the cooling liquid in the cooling chamber to the lower space of the piston is a position between the two cooling liquid inlet holes in the circumferential direction of the cooling chamber, or the piston. Two or more are provided at either one of the positions opposite to the two coolant inlet holes with respect to the center.
If comprised in this way, since the two coolant inlet holes and the drain hole are arrange | positioned in the position away in the circumferential direction of the cooling chamber, the coolant introduced into the cooling chamber from the coolant inlet hole immediately It is possible to avoid getting out of the drain hole, and a sufficient amount of coolant can flow along the circumferential direction of the cooling chamber.

Further, according to the present invention, each of the two cooling liquid ejection nozzles includes a valve opening pressure adjusting mechanism for adjusting a pressure at which the cooling liquid starts to be ejected, and the two valve opening pressure adjusting mechanisms have different valve opening pressures. The valve pressure is set.
According to this invention, by setting the valve-opening pressure of the coolant jet nozzle to the low valve-opening pressure (Ps ₀ ) and the high valve-opening pressure (Ps ₁ ), sufficient engine low speed can be achieved even with a small amount of coolant. In the region, the coolant is supplied to the piston only from the coolant opening nozzle on the low valve opening pressure (Ps ₀ ) side to sufficiently cool the piston, and the coolant jet nozzle on the high valve opening pressure (Ps ₁ ) side is Since it is closed, a decrease in the lubricating oil pressure on the engine side that is in communication with the inlet side of the coolant jet nozzle 10 on the high valve opening pressure (Ps ₁ ) side is avoided, and sufficient in a low engine speed range. A quantity of lubricating oil can be supplied to the engine lubrication part.
Thereby, by setting the valve opening pressure of the coolant jet nozzle 10 to a two-stage valve opening pressure of a low valve opening pressure (Ps ₀ ) and a high valve opening pressure (Ps ₁ ), in the low engine speed range. This makes it possible to avoid a decrease in the lubricating oil pressure on the engine side while maintaining the supply of the required amount of cooling liquid to the piston 1, thereby causing an insufficient amount of lubricating oil in the engine lubricating portion in the low engine speed range. Can be prevented.

In this invention, preferably, the valve opening pressure adjusting mechanism is configured such that the spherical valve opens when the pressure of the coolant exceeds the set pressure of the pressure adjusting spring, and the two coolant discharges The nozzle is composed of different members only in the pressure adjusting spring.
With this configuration, the valve opening pressures of the two coolant jet nozzles can be set to different valve opening pressures only by changing the mounting load of the pressure adjusting spring, and the same coolant jetting can be achieved simply by changing the pressure adjusting spring. A nozzle can be used.

  According to the present invention, two cooling liquid inlet holes for supplying the cooling liquid into the cooling chamber are provided and two cooling liquid ejection nozzles are provided corresponding to the cooling liquid inlet holes. Since the amount of coolant supplied into the cooling chamber is doubled and the coolant is supplied from the coolant inlet holes that are opened at two locations in the cooling chamber, the coolant can be supplied uniformly throughout the cooling chamber, The cooling effect of the whole piston is improved, and the piston can be cooled to a uniform temperature without causing uneven cooling in the circumferential direction. Thereby, the thermal stress of a piston can be reduced and the piston corresponding to the high output of an engine can be provided.

Further, according to the present invention, by setting the valve opening pressure of the coolant jet nozzle to the low valve open pressure and the high valve open pressure, only the coolant jet nozzle on the low valve open pressure side is used in the low engine speed range. The coolant is supplied to the piston to sufficiently cool the piston, and the coolant opening nozzle on the high valve opening pressure side is closed, so that a decrease in the lubricating oil pressure on the engine side is avoided and a sufficient amount of lubricating oil is supplied. Can be supplied to the engine lubrication section.
As a result, by setting the valve opening pressure of the coolant jet nozzle to a two-stage valve opening pressure of a low valve opening pressure and a high valve opening pressure, the required amount of coolant is applied to the piston in the low engine speed range. It is possible to avoid a decrease in the lubricating oil pressure on the engine side while maintaining the supply, and it is possible to prevent an insufficient amount of lubricating oil in the engine lubricating portion in the low engine speed range.

  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

FIG. 1 is a longitudinal sectional view of a piston including a coolant jet nozzle in a cooling device for a cooling piston for a diesel engine according to an embodiment of the present invention, and FIG. 2 shows a first example of an arrangement of coolant inlet holes in the embodiment. 3 is a bottom view of the piston, FIG. 3A is a partial cross-sectional view along the coolant inlet hole of the piston in the embodiment, and FIG. 3B is a partial cross-sectional view along the drain hole of the piston.
Such a diesel engine includes two intake ports 21 and 21 and two exhaust ports 20 and 20, as shown in FIG.

1 to 3, 1 is a piston of a diesel engine, 1a is a ring groove into which a piston ring (not shown) is fitted, and 2 is a cooling chamber formed in an annular shape at the back of the ring groove 1a inside the piston. It is.
3 is a coolant inlet hole that opens into the cooling chamber 2 and introduces the coolant into the cooling chamber 2, and 4 is a drain hole that opens into the cooling chamber 2 and discharges the coolant in the cooling chamber 2. .
Further, 5 is the back surface of the piston 1, 6 is a piston pin hole, and 7 is a piston pin boss.

Two coolant inlet holes 3 are provided. In this first example, as shown in FIG. 2, positions substantially symmetrical with respect to the cylinder center (piston center) 1 a at the lower part of the exhaust port 20 and the lower part of the intake port 21. Are provided respectively.
With this configuration, the coolant is normally supplied to the cooling chamber 2 from only one part below the exhaust port 20 of the piston 1 from the part below the intake port 21 in addition to the part below the exhaust port 20. Since the coolant is supplied to the cooling chamber 2, the entire amount of the piston 1 is adjusted by adjusting the amount of the coolant below the exhaust port 20 and the amount of the coolant below the intake port 21 to the optimum amount. The cooling effect can be improved.

In the first example, the drain hole 4 is provided with the coolant inlet hole 3 among the two intake ports 21 and 21 and the two exhaust ports 20 and 20, as shown in FIG. It is the lower part of the intake port 21 and the exhaust port 20 on the non-side, and is provided at substantially symmetrical positions with respect to the cylinder center (piston center) 1a.
Note that three or more drain holes 4 may be provided as long as the drain holes 4 are located away from the coolant inlet hole 3 in the circumferential direction of the cooling chamber 2.

On the other hand, in the second example of the arrangement of the coolant inlet holes 3 shown in FIG. 4, the two coolant inlet holes 3, 3 are provided in the lower portions of the two exhaust ports 20, 20, respectively. Yes.
With this configuration, the cooling liquid is normally supplied to the cooling chamber from only one part below the exhaust port 20 of the piston 1, and the cooling liquid is supplied from each of the two lower parts of the exhaust port 20 to the cooling chamber. By being configured to supply to 2, the cooling effect in the vicinity of the lower portion of the exhaust port 20 that becomes high temperature can be improved, and overheating of the piston at the time of high heat load can be prevented.

Further, in the second example, the two drain holes 4 are respectively provided below the two intake ports 21 and 21 as shown in FIG.
In this second example as well, the drain hole 4 is located away from the coolant inlet hole 3 provided in the lower part of the exhaust ports 20, 20 in the circumferential direction of the cooling chamber 2. Three or more may be provided.

  As in the first and second examples, the drain hole 4 is located at a position (first example) between the two coolant inlet holes 3 in the circumferential direction of the cooling chamber 2 or in the piston center 1a. On the other hand, the two coolant inlet holes 3 and the drain holes 4 are separated from each other in the circumferential direction of the cooling chamber 2 by being provided at a position opposite to the two coolant inlet holes 3 (second example). Therefore, it is possible to avoid that the coolant introduced into the cooling chamber 2 from the coolant inlet hole 3 immediately escapes to the drain hole 4, and a sufficient amount of coolant is supplied along the circumferential direction of the cooling chamber 2. It can be made to flow.

In FIG. 1, reference numeral 10 denotes a coolant jet nozzle, which will be described in detail later. Two coolant jet nozzles are provided corresponding to the coolant inlet hole 3, and jet the coolant from the jet hole 11 toward the coolant inlet hole 3. It is like that.
In FIG. 5 showing the details of the coolant jet nozzle 10, 12 is a nozzle body, 13 is a spherical valve, 17 is a valve seat, 14 is a pressure regulating spring, and the spherical valve 13 is an attachment load of the pressure regulating spring 14. The valve seat 17 is pressed with a set valve opening pressure.
A coolant inlet passage 16 is supplied with coolant (lubricant oil) branched from the engine lubricant passage.

In the coolant jet nozzle 10, when the coolant introduced into the coolant inlet passage 16 exceeds the valve opening pressure set by the pressure adjusting spring 14, the spherical valve 13 is pushed open and flows into the outlet passage 15. Through the outlet passage 15, the liquid is ejected from the ejection hole 11 toward the coolant inlet hole 3 and flows into the coolant inlet holes 3 facing the two coolant ejection nozzles 10.
Then, the cooling liquid flows into the cooling chamber 2 from each of the cooling liquid inlet holes 3, and cools the piston 1 by flowing in the cooling chamber 2 in the circumferential direction, so that the two drain holes 4, 4 Then, it flows out to the back surface 5 of the piston 1 and drops downward.

  According to this embodiment, two cooling liquid inlet holes 3 for supplying the cooling liquid are provided in the annular cooling chamber 2, and the cooling liquid ejection nozzle 10 that ejects the cooling liquid toward the cooling liquid inlet hole 3 is provided. Since two cooling liquid inlet holes 3 are provided corresponding to the cooling liquid inlet holes 3, the cooling liquid supplied into the cooling chamber 2 is provided as compared with the prior art having one cooling liquid inlet hole 3 and one cooling liquid jet nozzle 10. Since the amount of the coolant is doubled and the coolant is supplied from the coolant inlet holes 3 opened at two locations in the cooling chamber 2, the coolant can be uniformly supplied to the entire interior of the cooling chamber 2. As a result, the piston 1 can be cooled to a uniform temperature without causing uneven cooling in the circumferential direction, and the thermal stress of the piston 1 can be reduced, corresponding to higher engine output. A piston can be provided.

In this embodiment, the two coolant inlet holes 3 may be configured with different inner diameters.
If comprised in this way, while setting arrangement | positioning of the said 2 coolant inlet hole 3 with the circumferential direction temperature distribution of piston 1, and setting the internal diameter of these 2 coolant inlet holes 3, piston 1 can be made uniform in the circumferential temperature distribution, thereby reducing the thermal stress due to the circumferential temperature difference of the piston 1.

Further, in this embodiment, the two cooling liquid jet nozzles 10 are configured to reduce the valve opening pressure by the spherical valve 13 and the pressure adjusting spring 14 as the valve opening pressure adjusting mechanism for adjusting the pressure at which the cooling liquid starts to be jetted. Different valve opening pressures are set for the individual coolant jet nozzles 10.
FIG. 6 shows the relationship between the engine speed and the lubricating oil pressure. FIG. 6A is the case of the prior art shown in FIG. 7 and, as described above, the valve opening pressure Ps ₀ is lower than the lubricating oil pressure P _1. Since the lubricating oil flows to the coolant jet nozzle 10 side where the spherical valve 13 is open and escapes as the coolant of the piston 1, the lubricating oil pressure P ₁ is difficult to increase, and the lubricating oil shortage tends to occur.

On the other hand, in this embodiment, as shown in FIG. 6B, the valve opening pressure of the coolant jet nozzle 10 is set to the low valve opening pressure Ps ₀ and the high valve opening pressure Ps _1. In a low engine speed range where a small amount of coolant is sufficient, the coolant enters the coolant inlet of the piston 1 corresponding to the coolant jet nozzle 10 only from the coolant jet nozzle 10 on the low valve opening pressure Ps ₀ side. is supplied into the hole 3, with the piston 1 can be sufficiently cooled, the cooling-liquid ejecting nozzle 10 of the high opening pressure Ps ₁ side is closed, the coolant ejection nozzle 10 of the high opening pressure Ps ₁ side A decrease in the pressure of the lubricating oil on the engine side communicated with the inlet side is avoided, and a sufficient amount of lubricating oil can be supplied to the engine lubricating portion even in a low engine speed range.
As a result, by setting the valve opening pressure of the coolant jet nozzle 10 to a two-stage valve opening pressure of the low valve opening pressure Ps ₀ and the high valve opening pressure Ps ₁ , the piston 1 is applied to the piston 1 in the low engine speed range. While maintaining the supply of the required amount of coolant, it is possible to avoid a decrease in the lubricating oil pressure on the engine side and to prevent the occurrence of an insufficient amount of lubricating oil in the engine lubrication part in the low engine speed range. .

  Further, since the two cooling liquid ejection nozzles 10 are composed of different members, only the pressure regulating spring 14, the valve opening pressure of the two cooling liquid ejection nozzles 10, 10 is set to the mounting load of the pressure regulating spring 14. It is possible to set different valve opening pressures only by changing them, and the same coolant jet nozzle 10 can be used only by changing the pressure adjusting spring 14.

  According to the present invention, the amount of cooling liquid supplied into the cooling chamber is increased to improve the cooling effect of the entire piston, and the cooling liquid is uniformly supplied to the entire cooling chamber so that cooling unevenness is prevented in the circumferential direction of the piston. By cooling to a uniform temperature without being generated, it is possible to reduce the thermal stress of the piston and obtain a piston corresponding to the high output of the engine. Providing a piston cooling system that can prevent a decrease in the lubricating oil pressure on the engine side while maintaining the supply of the liquid amount, and can prevent the occurrence of insufficient lubricating oil amount in the engine lubrication part in the low engine speed range it can.

It is a longitudinal cross-sectional view of a piston including a coolant jet nozzle in a cooling device for a cooling piston for a diesel engine according to an embodiment of the present invention. It is a bottom view of the piston which shows the 1st example of the cooling fluid inlet hole arrangement | positioning in the said Example. (A) is a fragmentary sectional view in alignment with the coolant inlet hole of the piston in the said Example, (B) is a fragmentary sectional view in alignment with the drain hole of a piston. It is a bottom view of the piston which shows the 2nd example of the cooling fluid inlet hole arrangement | positioning in the said Example. It is a longitudinal cross-sectional view of the cooling fluid ejection nozzle in the said Example. It is a valve opening pressure diagram of a coolant jet nozzle, (A) shows the case of a prior art, (B) shows the case of the said Example. It is a longitudinal cross-sectional view of a piston including a coolant jet nozzle, showing an example of a conventional cooling device for a cooling piston for a diesel engine. It is a bottom view of the piston in the said prior art. (A) is a fragmentary sectional view in alignment with the coolant inlet hole of the piston in the said prior art, (B) is a fragmentary sectional view in alignment with the drain hole of a piston.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston 1a Ring groove 2 Cooling chamber 3 Coolant inlet hole 4 Drain hole 10 Coolant jet nozzle 11 Jet hole 13 Spherical valve 14 Pressure regulating spring 16 Coolant inlet passage 20 Exhaust port 21 Intake port

Claims (7)

  An annular cooling chamber formed at the back of the ring groove, a piston having a coolant inlet hole for introducing the coolant into the cooling chamber, and a coolant jet nozzle for jetting the coolant toward the coolant inlet hole In the piston cooling apparatus provided, two cooling liquid inlet holes of the piston are provided, and two cooling liquid ejection nozzles are provided corresponding to the cooling liquid inlet holes.   Equipped in an engine having two intake ports and two exhaust ports, the two coolant inlet holes are provided in the exhaust port lower part and the intake port lower part, respectively. The piston cooling device according to claim 1.   The engine is provided with an engine having two intake ports and two exhaust ports, and the two coolant inlet holes are respectively provided in the lower portions of the two exhaust ports. The piston cooling device according to claim 1.   2. The piston cooling device according to claim 1, wherein the two coolant inlet holes have different inner diameters.   A drain hole for discharging the cooling liquid in the cooling chamber to the lower space of the piston is provided at a position between the two cooling liquid inlet holes in the circumferential direction of the cooling chamber or the two cooling liquids with respect to the piston center. 2. The piston cooling device according to claim 1, wherein two or more are provided at any one of positions opposite to the inlet hole.   Each of the two coolant jet nozzles is provided with a valve opening pressure adjusting mechanism for adjusting the pressure at which the coolant starts to be jetted, and the valve opening pressures of the two valve opening pressure adjusting mechanisms are set to different valve opening pressures. The piston cooling device according to claim 1. The valve opening pressure adjusting mechanism is configured such that the spherical valve opens when the pressure of the coolant exceeds the set pressure of the pressure adjusting spring, and the two coolant jet nozzles are only the pressure adjusting spring. 7. The piston cooling device according to claim 6, wherein the piston cooling device is composed of different members.

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