JPS61106951A - Internal-combustion engine piston - Google Patents

Abstract

PURPOSE:To facilitate connection of a crown unit and restrein thermal stress by fitting a ceramic piston crown unit to a hole on an upper end of a metal skirt unit through an adiabatic material and pressing to fit a metal ring between the adiabatic material and an inner periphery of the skirt unit. CONSTITUTION:A peripheral edge of a crown unit 12 of a piston made of ceramic is superposed on an upper end wall 11b of a metal skirt unit 11 through an adiabatic material 21, and an axial unit 24 is fit to a hole 11a through an adiabatic cylinder 22. And a metal ring 23 is fit between an outer periphery of the adiabatic cylinder 22 and an inner periphery of the skirt unit 11, and the upper end wall 11b of the skirt unit 11 is pinched between the metal ring 23 and the piston crown unit 12. The metal ring 23 is made of nickel-cobalt group metal whose thermal expansion ratio is also the same as that of the ceramics of the crown unit. Then, ceramic piston crown unit 12 can be connected to the skirt unit 11 by simple mechanical processing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piston for an internal combustion engine that uses ceramics.

[Prior Art] When an internal combustion engine is running at low speed and low load, the temperature of the piston does not rise, combustion becomes unstable, exhaust gas components such as HC and Co increase, and odorous white smoke is emitted. On the other hand, at high speeds and high loads, the temperature of the piston becomes too high, leading to a reduction in suction efficiency and a reduction in engine output. This tendency is particularly strong in small-displacement diesel engines, and various measures have been taken to improve combustion at low temperatures, such as increasing the compression ratio, making the injection holes smaller and increasing the number of fuel injection nozzles. It is being taught. However, even if such measures are taken, they are not very effective in improving combustion at low temperatures, which is a major problem for small displacement direct injection diesel engines.

[Problems to be solved by the invention] One way to solve these problems is to insulate the combustion chamber by using ceramics for the piston crown, which accounts for about 30% of the engine's heat dissipation. By raising the temperature of the air, it is possible to significantly improve combustion conditions during low-speed, low-load operation at low temperatures.

A piston crown using ceramics has already been disclosed in Japanese Unexamined Patent Publication No. 57-2445. However, this conventional technology requires numerous processes such as chemical treatment and casting, making the management of these processes complicated and time-consuming to assemble.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piston for an internal combustion engine in which a piston crown made of ceramics can be mechanically joined to a skirt made of a general metal, and damage caused by thermal stress can be avoided. Our goal is to provide the following.

[Means for Solving the Problems] In order to achieve the above object, the present invention has a structure in which a hole is provided in the upper end wall of the skirt portion made of metal, and a hole is formed in the upper end wall of the skirt portion through a heat insulating material. At the same time, the shaft portion protruding from the center of the lower surface of the piston crown is fitted into the hole of the skirt portion through a heat insulating cylinder, and the heat insulating cylinder and the inner circumferential surface of the skirt portion are connected to each other. A metal ring with approximately the same coefficient of thermal expansion as the ceramic is press-fitted between them.

'□1 [Function] The piston crown part 12 made of ceramics is superimposed on the upper end wall of the skirt part 11 with the heat insulating material 21 in between, and the piston crown part 12 made of ceramics is placed on the upper end wall of the skirt part 11 through the heat insulating cylinder 22. The shaft part 24 of the piston crown part 12 is fitted, and a metal ring 5 having a coefficient of thermal expansion equivalent to that of ceramics is fitted on the outer peripheral side at the lower end part of the heat insulating cylinder 22, and the upper end wall part or the skirt part 11 is Attach the flange to the piston crown 1
It is sandwiched and fixed between 2.

The metal ring 23 is made of a nickel-cobalt metal and has a coefficient of thermal expansion that is almost the same as that of the silicon nitride that makes up the piston crown 12, so it is heated and softened to provide heat insulation f.
l! 22 and the inner circumferential surface of the skirt portion 11, a tight fit is maintained between the two even in high humidity.

[Examples of the Invention] The present invention will be described based on Examples. FIG. 1 is a front sectional view of a diesel engine equipped with a piston according to the present invention. The piston 4 is fitted into the cylinder 7a of the cylinder block 7, and the cylinder head 5 at the upper end of the cylinder block 7 is coupled. The cylinder head 5 is provided with an exhaust port 17, and a valve seat 1 is fitted and fixed to the end of the exhaust port 17.
An exhaust valve 6 a that is adjacent to and separate from the cylinder head 6 is supported by the cylinder head 5 via a guide 8 . Although not shown, the cylinder head 5 is provided with an intake boat that is similarly opened and closed by an intake valve. A combustion chamber is defined between the lower surface of the cylinder head 5 and the piston 4, and the reciprocating motion of the piston 4 is converted into rotational motion of a crankshaft (not shown) via a connecting rod 36 connected by a piston pin 37. .

The piston 4 according to the present invention is composed of a piston crown part 12 made of ceramics and a skirt part 11 made of ordinary metal joined to the lower side of the piston crown part 12 in order to insulate the combustion chamber. A piston ring 19 is attached to the outer peripheral surface of the skirt portion 11, and a hole 11a is provided in the center of the upper end wall.
is provided.

As shown in FIG. 2, the piston crown portion 12 is provided with a notch 13 on its upper end surface to promote swirling of intake air, and is integrally formed with a shaft portion 24 projecting downward from the center of the lower surface.
Cooling fins 12b are integrally formed on the lower surface of this shaft portion 24.

In order to cool the cooling fins 12b in a timely manner, a control valve 35 consisting of a housing 32 and a valve body 32a is provided adjacent to the oil gear rally 31 provided in the cylinder block 7. A nozzle 34 is attached to the valve housing 32 and extends toward the lower surface of the piston crown 12 . A valve body 32a is provided in the middle of the passage of the housing 32 that connects the oil gear rally 31 and the nozzle 34, and is opened at appropriate times by an actuator 33 such as a solenoid.

As shown in FIG. 2, the peripheral edge of the piston crown 12 is superimposed on the upper end wall 11b of the skirt portion 11 via a suitable heat insulating material 21, and at the same time, the shaft portion 24 is inserted into the hole 11a and the heat insulating tube 22 is overlapped. It is fitted through.

Then, a metal ring 23 is fitted between the outer peripheral surface of the heat insulating tube 22 and the inner peripheral surface of the skirt portion 11.
The upper end wall 11b of the skirt portion 11 is sandwiched between the piston crown portion 12 and the piston crown portion 12.

The metal ring 23 is made of nickel, which has approximately the same coefficient of thermal expansion as silicon nitride that constitutes the piston crown 12.
A cobalt-based metal is used, softened by heating, and press-fitted between the heat-insulating tube 22 and the skirt portion 11, and then pressed with a press to firmly form the outer circumferential surface of the heat-insulating tube 22 and the inner circumferential surface of the skirt portion 11. Closely attached.

[Effects of the Invention] By having the present invention configured as described above, the skirt portion 11, the piston crown portion 12, the heat insulating material 21, the heat insulating cylinder 22, and the metal ring 23 are each preformed, and the shaft portion of the piston crown portion 12 is formed in advance. 24 connects to the skirt portion 11 via the heat insulating tube 22
Since the tightening metal ring 23 is heated and softened while it is fitted into the hole 11a and brought into close contact between the heat insulating cylinder 22 and the skirt portion 11, the skirt portion 11 can be attached to the skirt portion 11 by simple mechanical processing. A piston crown 12 made of ceramics can be joined.

Since the tightening metal ring 23 is isolated from the piston crown 12 by the heat insulating material 21 and the heat insulating cylinder 22, heat transfer from the piston crown 12 exposed to combustion gas is suppressed, and the metal ring 23 is made of nickel/cobalt. Since the coefficient of thermal expansion is almost the same as silicon nitride, which is the ceramic that makes up the piston crown 12, the generation of thermal stress between the two is suppressed, and a tight fit is maintained even at high temperatures. be done.

Then, a heat insulating material of 2"l and a heat insulating tube 22 are attached to the skirt portion 11.
Since the piston crown part 12 made of ceramic is connected through the piston, the heat insulation effect of the combustion chamber can greatly suppress the radiation of heat from the combustion chamber to the crank chamber via the piston, increasing the temperature of the combustion chamber. As a result, stable combustion can be obtained even during low-speed, low-load operation at low temperatures.

On the other hand, in high-speed, high-load operation, the temperature of the combustion chamber may become too high. At this time, the actuator 33 opens the valve body 32a, and the lubricating oil in the oil gear rally 31 is supplied to the piston crown from the nozzle 34 via the control valve 35. When injected to the cooling fins 12b on the lower surface of the piston crown 12, the piston crown 12 is cooled and abnormal temperature rise in the combustion chamber is suppressed, and a decrease in engine output due to a decrease in intake efficiency can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of an internal combustion engine equipped with an internal combustion engine piston according to the present invention, and FIG. 2 is a front sectional view showing an enlarged main part of the piston. 11 Varnish force part 11a: Hole 12: Piston crown 21: Heat insulating material 22: Heat insulating tube 23: Tightening metal ring

Claims (1)

[Claims] A hole is provided in the upper end wall of the skirt portion made of metal, and a piston crown portion made of ceramics is superimposed on the upper end wall of the skirt portion via a heat insulating material. It is characterized by fitting into the hole of the skirt part via a heat insulating cylinder, and press-fitting a metal ring having approximately the same coefficient of thermal expansion as ceramics between the heat insulating cylinder and the inner peripheral surface of the skirt part. Pistons for internal combustion engines.