JPH0248658Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an improvement in a cooling structure for cooling an engine piston from inside with cooling oil.

(Prior Art) Conventionally, as a cooling structure for this type of piston, as disclosed in, for example, Japanese Utility Model Application Publication No. 57-200650, an oil passage formed of an annular cavity in the top of the piston when viewed from the direction of the piston center line has been used. The oil inlet and outlet openings on the back surface of the piston in the annular oil passage are arranged diametrically opposite to each other, and the engine oil is ejected as an oil jet from a jet pipe provided on the crank chamber wall through the oil inlet. It is known that the top of the piston facing the combustion chamber of the engine is cooled by forcibly introducing the oil into the engine, circulating it, and then discharging it from the oil outlet.

(Problem to be solved by the invention) However, in the above-mentioned conventional device, since the oil inlet and outlet are arranged diametrically opposite to each other with respect to the annular oil passage, the area around the oil inlet and the area around the oil outlet of the piston are There was a problem in that the temperature difference became large and a thermal gradient was generated on the top surface of the piston, causing a partial increase in thermal load.

Further, since the oil passage is essentially one system, there is a limit to the flow rate of oil flowing through the oil passage, and there is also the problem that a good cooling effect cannot be obtained. In order to secure this oil flow rate, the passage diameter of the oil passage may be increased, but on the other hand,
It is inevitable that the strength of the piston will decrease. Further, in the case of a piston for a direct injection diesel engine in which a cavity constituting a combustion chamber is formed at the top of the piston, an oil passage with a large diameter cannot actually be formed because the space of the cavity is limited.

Furthermore, the length of one system of oil passages increases, and the cooling performance on the oil outlet side decreases.

In particular, in a piston for a direct injection diesel engine having the cavity described above, the temperature around the cavity rises to a high temperature, so that both of the above problems become even more pronounced.

This invention was made in view of these points,
The purpose of this is to increase the diameter of the oil passage by creating two oil passages in the top of the piston, and by appropriately specifying the positional relationship between the oil inlets and outlets of both oil passages. Instead, the objective is to enhance the cooling effect on the top of the piston due to the oil flow and to maintain a uniform temperature distribution at the top of the piston.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention provides a pair of approximately arc-shaped oil passages in the top of the piston, each having an oil inlet/outlet opening on the back surface of the piston. The oil passages are formed approximately symmetrically with respect to the center line and approximately along the inner side of the piston ring, and the oil inlets and outlets of each oil passage are arranged such that the oil inlet of one oil passage is adjacent to the oil outlet of the other oil passage. It is set to .

(Function) With the above configuration, in the present invention, two oil passages are formed in the top of the piston symmetrically with respect to the piston center line, approximately along the inner side of the piston ring, and one of the oil passages is connected to the oil inlet of the piston. Because the oil outlet and the other oil outlet are located adjacent to each other, the temperature rises near the oil outlet where hot oil flows after receiving heat from the piston in one oil passage, and immediately after being supplied from the jet pipe in the other oil passage. The temperature decrease near the oil inlet through which low-temperature oil flows cancels each other out, suppressing uneven temperature distribution at the top of the piston.

In addition, since two oil passages each having an oil inlet and outlet are formed in the top of the piston,
The overall flow rate of oil flowing inside the piston increases, and the cooling effect on the piston increases without increasing the diameter of the oil passage.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

1 and 2, 1 is a cylinder block of a direct injection diesel engine, 2 is a cylinder formed inside the cylinder block 1, and inside the cylinder 2 is a piston according to an embodiment of the present invention. 3 is fitted so that it can freely reciprocate. At the top of the piston 3, a ski-lip type circular cavity 4 is formed at a position offset by a predetermined amount e from the piston center line O, and the diameter increases from the opening toward the back. A combustion chamber is configured within the cavity 4.

Further, within the top of the piston 3, a pair of substantially arc-shaped oil passages 7, 7 having an oil outlet 5 and an oil inlet 6 at each end, which are open on the back surface of the piston 3, surround the cavity 4. approximately symmetrically with respect to the piston center line O, and the piston 3
It is formed approximately along the inner side of the piston ring on the outer periphery of the top. The oil inlets and outlets 5 and 6 of each of the oil passages 7 are set such that the oil inlet 6 of one oil passage 7 is adjacent to the oil outlet 5 of the other oil passage 7, as shown in FIG. .

Furthermore, as shown in FIG.
On the wall of the crank chamber 8 that is continuous to the lower part, there are oil inlets 6 for each oil passage 7 in the top of the piston 3.
Jet pipes 9, 9 for jetting cooling oil upward as an oil jet are attached to corresponding positions. Each jet pipe 9 is connected to an oil gear gallery 10 in the cylinder block 1, and the oil in each oil gear gallery 10 is jetted from the jet pipe 9 toward the oil inlet 6 on the back surface of the piston 3 that moves up and down, and is supplied to the oil passage 7. It is configured as follows.

Therefore, in the above embodiment, the oil in the oil gears 10, 10 of the cylinder block 1 is jetted upward from the jet pipes 9, 9, respectively, and flows through the oil inlets 6, 6 on the back surface of the piston 3, which moves up and down, into the oil passage. Introduced within 7,7,
After flowing through the oil passages 7, 7, the oil outlet 5,
5 and falls into the crank chamber 8. and,
The top of the piston 3 is cooled by heat exchange with the oil flowing through the oil passages 7, 7.

In that case, since the pair of oil passages 7, 7 formed in the top of the piston 3 are separate and independent from each other, the oil flow rate in each oil passage 7 is higher than in the case where there is only one oil passage. can be ensured, and the cooling effect on the piston 3 can be increased accordingly without increasing the passage diameter of the oil passage 7.

In addition, since the oil inlet 6 of one oil passage 7 is arranged adjacent to the oil outlet 5 of the other oil passage 7, the high temperature oil used for cooling the piston 3 is kept at the top of the piston 3. The vicinity of the flowing oil outlet 5 is cooled by the vicinity of the oil inlet 6 of the other oil passage 7, whose temperature has been lowered by the relatively low temperature oil supplied from the jet pipe 9, and the temperature rise is suppressed. The overall thermal gradient becomes gentler, and therefore the temperature distribution at the top of the piston 3 can be kept substantially uniform, thereby preventing a local increase in thermal load.

In the above embodiment, the present invention is applied to a piston for a direct injection type diesel engine, but it goes without saying that the present invention can also be applied to pistons for various other types of engines.

(Effect of the invention) As explained above, according to the invention, two oil passages are formed in the top of the piston approximately symmetrically with respect to the piston center line and approximately along the inner side of the piston ring. The oil inlet of one oil passage is placed adjacent to the oil outlet of the other oil passage, which increases the oil flow inside the piston and enhances its cooling effect, and suppresses thermal gradients caused by oil temperature differences. This makes it possible to equalize the temperature distribution of the piston and prevent a local increase in heat load.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a plan view of a cylinder portion of an engine, and FIG. 2 is a sectional view taken along the line -- in FIG. 1. 3... Piston, 4... Cavity, 5... Oil outlet, 6... Oil inlet, 7... Oil passage, 9... Jet pipe.

Claims (1)

[Scope of utility model registration request] A pair of generally arcuate oil passages each having an oil inlet/outlet opening on the back surface of the piston are formed in the top of the piston so as to be approximately symmetrical with respect to the piston center line and approximately along the inner side of the piston ring;
A piston cooling structure characterized in that the oil inlets and outlets of each oil passage are set such that the oil inlet of one oil passage is adjacent to the oil outlet of the other oil passage.