JPH0526252Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oil-cooled piston used in an internal combustion engine.

[Conventional technology]

Piston crowns for large-diameter, high-output internal combustion engines are exposed to high-temperature gas, and therefore require active cooling to prevent seizure of the pistons.
Cooling means for the piston crown are broadly classified into water-cooled types and oil-cooled types, and both types are in practical use. Among these, oil-cooled piston crowns are increasingly being used for internal combustion engines because they can reduce cooling loss and simplify the structure.

[The problem that the idea attempts to solve]

However, in oil-cooled piston crowns, the specific gravity of oil is light and the specific heat is small, so the heat transfer coefficient is about 1/10 that of water under the same speed conditions, so we devised ways to increase the cooling effect. It has become necessary to do so. Examples of this include a speed type in which the oil flow rate is partially increased, or a type in which a jet of oil is ejected near the cooling area. However, these devices are often subject to structural limitations, and it is currently difficult to obtain a sufficient cooling effect over all parts. That is, when cooling is performed using the piston crown cooling oil jet nozzles a and b, as shown in the right half of Fig. 3, when cooling oil is jetted into the oil in the cooling chamber 1a, the oil resistance is large and the cooling oil is This has the drawback that the jet stream 14 is diffused and its speed decreases when it reaches the cooling surface, making it impossible to obtain a sufficient heat transfer coefficient.

The purpose of the present invention is to eliminate the drawbacks of the conventional device,
To provide an oil-cooled piston capable of obtaining a sufficiently large heat transfer coefficient when cooling a piston crown with oil.

[Means for Solving the Problems] The oil-cooled piston according to the present invention is configured to cool the piston crown by jetting cooling oil into the cooling chamber in the piston crown, and one end of the piston is connected to the piston underside chamber. an air introducing member formed with an air passage whose other end is open to the cooling chamber; and a non-return member provided in the air passage that allows air to flow only from the piston underside chamber side to the cooling chamber side. It is characterized by having a valve.

[Effect]

Air in the piston underside chamber is introduced into the piston crown cooling chamber through the air passage in the air introduction member and the check valve, and an air layer is retained on the target cooling surface. Thereby, the cooling oil ejected from the nozzle of the piston crown is ejected into the air without being ejected into oil. Thereby, the initial velocity of the cooling oil is not lost on the way and the cooling oil can go straight to the target cooling surface, so a sufficiently large heat transfer coefficient can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. 1 is a piston crown, 2 is a piston skirt, and 3 is a piston rod which is connected to the piston crown 1 and the piston skirt by bolts. . 1a is a cooling chamber formed inside the piston crown 1, 1b is a cooling hole formed in a large number in the piston crown 1, 4 is a cooling oil inlet fitting, 7 is a cooling oil inlet pipe, 1
8 is a cooling oil inlet passage, 19 is a cooling oil outlet pipe, 20
is the cooling oil sump. A is a nozzle for spouting cooling oil into the cooling hole 1b, and b is a nozzle for spouting cooling oil toward the cooling surface of the piston crown 1.

Reference numeral 12 denotes an air introduction member which also serves as a tightening bolt between the piston crown 1 and the piston rod 3. 13 is a check valve built into the air introduction member 12 and the valve seat 2
1, a valve body 22, and a spring 23. 25 is an air passage. The outlet of the check valve 13 is communicated with the cooling chamber 1a of the piston crown via a passage 26 and a jet hole 17. In this way, in the present invention, scavenging air (cleaning air) pumped from a supercharger (not shown) is used.
An air passage leading from the piston underside chamber A, which communicates with a scavenging chamber (not shown) in which is stored, to the cooling chamber 1a via the air passage 25 in the air introduction member 12, the check valve 13, the passage 26, and the jet hole 17. will be formed. In the piston configured in this way, the cooling surface of the piston crown 1 is
Nozzle a and oil sump casing 8 provided inside
It is cooled by cooling oil jetted from a nozzle b provided in the. Furthermore, due to the inertial force caused by the reciprocating motion of the piston, the oil in the cooling chamber 1a also collides with the cooling surface of the piston crown at a certain time, thereby cooling the cooling surface.
At this time, if the cooling chamber 1a is filled with cooling oil, the jets from the nozzles a and b and the upward flow of oil due to the inertia of the piston are blocked and difficult to reach the cooling surface of the piston crown. In this way, in order to prevent cooling oil from accumulating in the cooling chamber 1a, the air in the piston underside chamber A, that is, the scavenging air, is transferred to the cooling chamber of the piston crown 1 through the air introduction member 12 having a built-in check valve 13. 1a. Spring 2 of the check valve 13
3 is set to open at low pressure.
Therefore, the pressure in the piston underside chamber A
When P ₁ is higher than the pressure P ₂ in the cooling chamber 1a,
The scavenging air pushes open the valve body 22 of the check valve 13 and opens the cooling chamber 1.
a and forms an air layer near the cooling surface.
Conversely, when P ₂ >P ₁ , the check valve 13 closes to prevent the cooling oil from flowing back from the cooling chamber 1a to the piston underside chamber A. As a result, the cooling oil ejected from the nozzles a and b is jetted into the air, and the initial velocity of the cooling oil does not disappear midway. To explain the above operation in more detail, during the reciprocation of the piston, the cooling oil in the cooling chamber 1a does not flow out continuously from the outlet pipe 19 due to its own inertia, but flows out intermittently. That is, during the downward stroke of the piston, the cooling oil in the cooling chamber 1a is less likely to flow out, and conversely, during the upward stroke, the cooling oil is more likely to flow out. As a result, even if a constant flow rate of cooling oil is supplied into the piston crown 1, the pressure within the cooling chamber 1a varies greatly. In the case of large diesel engines, the supply pressure is 3 kg/cm ² at high engine speeds.
It has been confirmed that it reaches a maximum of about ±1Kg/cm ² .

On the other hand, the pressure of the scavenging air supplied to the piston underside chamber is approximately 2 kg/cm ² in the case of large marine diesel engines, and the pressure fluctuation due to the vertical movement of the piston is compared to the fluctuation of the pressure in the cooling chamber of the piston crown. Very small.

Therefore, piston crown cooling chamber 1 for piston cooling oil
Considering the pressure loss up to a, the pressure in the piston underside chamber communicating with the scavenging chamber becomes higher than the pressure in the piston crown cooling chamber 1a during the piston upward stroke. As a result, the air in the piston underside chamber A flows into the check valve 1 of the air introduction member 12.
3 is pushed open and introduced into the cooling chamber 1a. After cooling the piston crown 1, the cooling oil flows through the cooling oil outlet pipe 1.
9 and is discharged into the crankcase B.

[Effect of idea]

The larger the diameter of the piston crown of an internal combustion engine, the greater the heat load, so effective cooling means are required. The oil-cooled piston of the present invention jets the cooling oil spouted from the cooling oil jet nozzle into the air instead of into the oil, making it possible for the cooling oil to travel straight to the target cooling surface without losing its initial velocity on the way. I can do it,
Sufficient heat transfer coefficient can be obtained on the cooling surface. This improves the cooling efficiency of the piston crown, and is extremely effective in preventing accidents such as burnout of the piston crown top surface and scuffing of the piston and liner.

[Brief explanation of drawings]

FIG. 1 is a structural explanatory diagram of an oil-cooled piston according to the present invention, FIG. 2 is an enlarged sectional view of section X in FIG. 1, and FIG. 3 is an explanatory diagram of the operation of the oil-cooled piston according to the present invention. 1... Piston crown, 12... Air introduction member, 1
3...Check valve, 17...Blowout hole, 1a...Cooling chamber, a, b...Oil spout nozzle, A...Piston underside chamber.

Claims (1)

[Scope of utility model registration request] In a piston configured to cool the piston crown by jetting cooling oil into a cooling chamber within the piston crown, air having one end opened to a piston underside chamber communicating with a scavenging chamber and the other end opened to the cooling chamber. An oil-cooled piston comprising: an air introducing member having a passage formed therein; and a check valve provided in the air passage and allowing only air to flow from the piston underside chamber toward the cooling chamber side. .