JPH0674770B2 - Structure of adiabatic piston - Google Patents

Description

TECHNICAL FIELD The present invention relates to the structure of a heat insulating piston in a heat insulating engine or the like.

[Conventional technology]

Conventionally, engine members such as adiabatic pistons that use a ceramic material as a heat insulating material or a heat resistant material are disclosed in
It is disclosed in Japanese Patent No. 13557, Japanese Patent Laid-Open No. 60-93161, and the like.

First, the structure of the piston disclosed in Japanese Utility Model Laid-Open No. 59-113557 will be outlined with reference to FIG. In FIG. 2, a closed space is formed by the lower surface side of the ceramic crown portion 21 having the combustion chamber 29 on the upper surface and the piston ring groove 27 on the peripheral wall and the upper surface side of the metal skirt portion 22 having another piston ring groove 28 on the peripheral wall. The ceramic crown portion 21 and the metal skirt portion 22 are joined by the fastening bolts 26 so as to form the portion 23, and further at the end of the piston pin fitting hole 24 opened on the peripheral surface of the metal skirt portion 22. A piston 20 in which a seal member 25 is freely fitted is shown.

Next, the structure of the heat insulating piston disclosed in JP-A-60-93161 will be outlined with reference to FIG. In FIG. 3, the structure of the adiabatic piston is indicated generally by the numeral 30.

Regarding the structure 30 of the heat insulating piston, a fitting hole 33 is provided in the upper end portion of the piston body 32 including the piston skirt portion, and the projection 34 formed on the crown 31 is fitted into the fitting hole 33, so that the piston body 32 The periphery of the fitting hole 33 is heated and pressed to join the piston body 32 and the crown 31.

The piston body 32 is made of aluminum, malleable cast iron or the like, and the crown 31 is made of ceramics such as silicon nitride. A combustion chamber 37 is formed on the protrusion 34 of the crown 31, and a protrusion 35 is formed on the outer peripheral portion of the crown 31. Further, the heat insulating material 36 made of ceramics fiber or stainless steel mesh, which is arranged in the void 38 formed between the protrusion 34 and the protrusion 35, is fixed in a sandwiched state by the crown 31 and the piston body 32. .

[Problems to be solved by the invention]

However, in a heat insulating engine member such as a piston that uses the ceramic material as a heat insulating material or a heat resistant material, it is extremely difficult to obtain sufficient heat insulating properties. The ceramic material is in a state of being exposed to the high temperature on the combustion chamber side, which causes a heat shock, which causes a problem in strength of the ceramic material.

In addition, if the thickness of the ceramic material on the wall surface is increased for heat insulation, the heat capacity increases, and the intake air receives much heat from the wall surface of the combustion chamber during the intake stroke, becomes hot and expands, and a predetermined amount of intake air enters the combustion chamber. However, there is a problem in that the suction efficiency is lowered and air is not sucked in. However, there is a problem that the adiabaticity must be improved in the expansion stroke.

Further, if the ceramic material forming the piston head portion that forms one surface of the combustion chamber is made thin, it cannot withstand the pressure applied by the press when the piston head portion is attached to the piston skirt portion and may be destroyed. Further, in the case where a heat insulating air layer is formed between the piston head portion and the piston skirt portion in order to improve the heat insulating property, there is a problem in that the strength is not sufficient when receiving a compressive force due to an explosion.

By the way, regarding the structure of the piston disclosed in Japanese Utility Model Laid-Open No. 59-113557, the crown portion 21 is made of ceramic, but its thickness is extremely large, and therefore the heat capacity of the crown portion 21 is extremely large. As a result, the above problem occurs. Further, since the combustion chamber 29 is formed in the crown portion 21 itself, there is a problem that the thickness of the crown portion 21 must be made thick in view of its structure and strength.

Further, regarding the structure of the heat insulating piston disclosed in the above-mentioned JP-A-60-93161, the sealing function of the connecting portion of the crown 31 and the piston body 32, in other words, the connecting portion of the heat insulating material 36 interposed between them Is not sufficient, and the function of the heat insulation on the combustion chamber side is not sufficient. Moreover, the thickness of the crown 31 made of ceramics is extremely thick like the above, and it is directly exposed to the combustion chamber 37 side. Since it is configured to be heated, it has a large heat capacity and suffers from a heat shock, which causes a problem in strength.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems and to obtain an extremely high degree of heat insulating property, and to construct a piston head which is exposed to combustion gas and becomes high temperature by a ceramic thin plate and a ceramic ring. However, the heat capacity of the surface exposed to the combustion gas is configured to be as small as possible to improve the suction efficiency and the cycle efficiency. Improves deformability, corrosion resistance, etc., and is able to obtain a stable mounting state. Furthermore, the structure is such that the pressure acting on the piston head during an explosion can be received in a favorable state. It can receive the press load in good condition when connecting with the skirt and improves the sealing function between the piston head and the piston skirt. It is to provide a structure of a heat-insulating piston in adiabatic engine or the like capable of and.

[Means for solving problems]

The present invention is configured as follows to achieve the above object. That is, according to the present invention, since the piston head portion is attached to the piston skirt portion in a pressed state, the step portion formed on the ceramic ring that presses the piston head portion to the outer periphery of the piston skirt portion through the heat insulating gasket is used. Attaching to the piston skirt portion while supporting the outer peripheral portion of the piston head portion,
The structure of a heat insulating piston is characterized in that an elastic and heat insulating metal support material is enclosed in a space between the piston head portion and the piston skirt portion.

Further, in the structure of this heat insulating piston, the support member is made of a metal honeycomb.

Further, in the structure of this heat insulating piston, a heat insulating material is arranged between the piston head portion and a ceramic thin plate constituting a surface portion exposed to combustion gas.

Further, in this structure of the heat insulating piston, the thin plate and the ring are formed as thin as possible to reduce the heat capacity of the thin plate and the ring.

Further, in this structure of the heat insulating piston, the piston head portion is made of a material having a thermal expansion coefficient substantially equal to that of the ceramics forming the ring.

Further, in the structure of this heat insulating piston, the thin plate and the ring are made of silicon nitride.

Further, in the structure of this heat insulating piston, a gasket of a carbon seal is interposed on the contact surface between the ring and the piston skirt portion.

[Action]

The structure of the adiabatic piston according to the present invention is configured as described above, and operates as follows. That is, according to the present invention, since the piston head portion is attached to the piston skirt portion in a pressed state, the step portion formed on the ceramic ring that presses the piston head portion to the outer periphery of the piston skirt portion through the heat insulating gasket is used. Since the outer peripheral portion of the piston head portion is supported and attached to the piston skirt portion, and a metallic support material having elasticity and heat insulation is enclosed in a space portion between the piston head portion and the piston skirt portion, Even if it receives a shock, there will be no problem in strength, heat resistance, deformation resistance,
Corrosion resistance and the like can be improved, and a stable mounting state can be obtained.

Furthermore, since a metallic honeycomb is arranged as a support material in the heat insulating air layer formed between the piston head portion and the piston skirt portion, structural rigidity can be increased and the compressive force due to explosion can be increased. Not only the heat insulating gasket interposed between the piston head portion and the piston skirt portion and the step portion of the ring are received, but also the structure is received by the metal honeycomb, so that the strength is improved and the inertia force due to the light weight is obtained. It does not work so much and is preferable in that respect.

Further, it is formed by a flat thin ceramic thin plate which is joined to the ring and constitutes a surface exposed to combustion gas, and the piston head upper surface, the thin plate lower surface and the ring inner peripheral surface. Since it has a heat-insulating material enclosed in the space, the thickness of the thin plate and the ring located on the surface of the piston head exposed to the combustion gas and having a high temperature can be made thin, and the heat capacity thereof is made as small as possible. It is possible to improve the suction efficiency and the cycle efficiency, and to obtain high heat insulation, deformation resistance and corrosion resistance.

The thinner the thin plate is configured, the better the followability to the gas temperature is, that is, the wall temperature amplitude between the high temperature and the low temperature in the combustion chamber becomes large as compared with the case where the thickness is large, and the result As a result, the temperature difference between the combustion gas and the thin plate is reduced, and the amount of heat transfer is reduced, so that the heat received by the intake air is reduced.

Further, the pressure acting on the ceramic thin plate at the time of explosion can be received in a preferable state, and the sealing function between the piston head portion and the piston skirt portion can be improved.

〔Example〕

Hereinafter, embodiments of the structure of the heat insulating piston according to the present invention will be described in detail with reference to the drawings.

In FIG. 1, the structure of an adiabatic piston according to an embodiment of the present invention is generally indicated by reference numeral 10. The heat insulating piston structure 10 mainly includes a piston head portion 1 and a metal piston skirt portion 2.

The piston head portion 1 has a mounting boss portion 4 in the center, and also has a ceramic material or a material having a thermal expansion coefficient approximately equal to that of the ceramic, high strength, and a relatively high Young's modulus, such as ceramic, cermet, or metal. It is composed of materials such as. No combustion chamber is formed in the piston head portion 1 itself, and the combustion chamber 15 side of the piston head portion 1 is formed in a flat shape. A central mounting hole 12 into which the mounting boss portion 4 of the piston head portion 1 is fitted is formed at the center of the piston skirt portion 2.

The mounting boss portion 4 of the piston head portion 1 is fitted in the central mounting hole 12 of the piston skirt portion 2, and is formed in the fitting groove 14 formed in the mounting boss portion 4 and the central mounting hole 12 of the piston skirt portion 2. By deforming and housing the metal ring 11 over the fitting groove 13, the piston head portion 1 is locked to the piston skirt portion 2 in a pressed state.

Further, a cushioning material 8 which is a heat insulating gasket is provided at a contact portion between the piston head portion 1 and the piston skirt portion 2 at a central portion thereof.
Are interposed in a pressed state, and the cushioning material 8 also has a heat insulating function. A heat insulating air layer 9 is formed between the piston head portion 1 and the piston skirt portion 2.

The structure 10 of the heat insulating piston according to the present invention is characterized by the following structure in the above structure. That is, in order to reduce the heat capacity, the thin ceramic plate 5 that is as thin as possible is arranged on the piston head portion 1 via the heat insulating material 3 so as to face the combustion chamber 15, and the compressive force due to the explosion is insulated. By receiving at least the metal honeycomb 18 arranged in the air layer 9, and further receiving the deformation load of the metal ring by the pawl portion 19 provided on the ceramic thin plate 5 when the piston head portion 1 and the piston skirt portion 2 are joined together. is there.

First, the thin thin plate 5 is made of ceramics such as silicon nitride and is manufactured to have a thickness of about 1 mm or less than 1 mm. A ceramic ring 6 made of a similar material is fitted to the outer peripheral portion of the thin plate 5, and the ceramic thin plate 5 and the ceramic ring 6 are joined by, for example, CVD (chemical vapor deposition). There is. A step portion 16 is formed on the inner peripheral surface of the ceramic ring 6, and is fitted to the ceramic ring 6 so that the outer peripheral portion 17 of the piston head portion 1 contacts the step portion 16 of the ceramic ring 6. There is.

In the space formed by the ceramic thin plate 5, the ceramic ring 6 and the piston head portion 1, the heat insulating material 3 is provided.
Is enclosed. The heat insulating material 3 is made of a material such as titanium-made potassium whiskers, zirconia fiber, etc., and functions as a structural material that improves the heat insulating function and receives the pressure acting on the ceramic thin plate 5 at the time of explosion.

By mounting the piston head portion 1 on the piston skirt portion 2 in a pressed state, the outer peripheral portion 17 of the piston head portion 1 is pressed against the step portion 16 of the ceramic ring 6, and the ceramic ring 6 surrounds the piston skirt portion 2. Is pressed by the part. In this case, the ceramic ring 6
A carbon seal 7, which is a gasket, is interposed to seal the piston skirt portion 2 and the piston skirt portion 2. The seal axial force on the carbon seal 7 acts by the piston head portion 1 being attached to the piston skirt portion 2 in a pressed state.

With respect to the structure of this heat insulating piston, it is necessary to uniformly receive the compressive force due to the explosion by the heat insulating material 3 such as potassium titanate. For this reason, the surface of the piston head 1 on the combustion chamber side and the ceramic thin plate 5 are flat. It has a flat shape.

The next characteristic of the structure of this heat insulating piston is that the heat insulating air layer 9 formed between the piston head portion 1 and the piston skirt portion 2 is filled with the metal honeycomb 18 which is a supporting material. The metal honeycomb 18 is made of a metal material such as stainless steel or aluminum, and has elasticity and heat insulation. By interposing the metallic honeycomb 18 in the adiabatic air layer 9, the compressive force due to the explosion is
Not only the heat insulating gasket which is the cushioning material 8 interposed between the piston head portion 1 and the piston skirt portion 2 and the step portion 16 formed on the inner peripheral surface of the ceramic ring 6, but also the metal honeycomb 18 Since it can be received, it is in a very preferable state in terms of strength.

Another feature of the structure of this adiabatic piston is that the thin ceramic plate 5 is provided with a pawl portion 10 that abuts on the upper surface of the piston head portion 1. By forming the claw portion 19 on the ceramic thin plate 5, it is possible to prevent excessive stress from acting on the ceramic thin plate 5. That is, the mounting boss portion 4 of the piston head portion 1 is fitted into the central mounting hole 12 of the piston skirt portion 2, and then the fitting groove 14 of the piston head portion 1 and the fitting groove 13 of the piston skirt portion 2 are straddled. In order to accommodate the metal ring 11 in a deformed manner, as shown by the arrow P in the figure, the metal ring 11 is pressed by a press and deformed and press-fitted. An excessive stress is applied to the head portion 1. By supporting this excessive stress by the claw portion 19, the ceramic thin plate 5 is prevented from being broken.

〔The invention's effect〕

The structure of the heat insulating piston according to the present invention is configured as described above, and thus has the following effects. That is, according to the present invention, the outer peripheral portion of the piston head portion is supported by the step portion formed on the ceramic ring that presses the piston head portion on the outer periphery of the piston skirt portion through the heat insulating gasket, and the piston skirt portion is supported by the step portion. Since a metallic support material having elasticity and heat insulation is enclosed in the space between the piston head portion and the piston skirt portion and the piston head portion is attached to the piston skirt portion in a pressed state, Even if a shock is received, no problem in strength occurs, heat resistance, deformation resistance, corrosion resistance, etc. are improved, and a stable mounting state can be obtained. Furthermore, the piston head portion and the piston skirt can be obtained. Since a metallic honeycomb is placed in the adiabatic air layer formed between the piston and the Not only is received by the heat insulating gasket and the stepped portion of the ring interposed between the sleeve portion and the piston skirt portion, but is also received by the metal honeycomb, and structural rigidity can be increased and strength is improved. In addition, since it is lightweight, inertial force does not work so much, which is preferable.

Further, it is sealed in a flat thin-walled ceramic thin plate which is joined to the ring and constitutes a surface exposed to combustion gas, and a space formed by the piston head part, the thin plate and the ring. Since it has a heat insulating material, the thickness of the thin plate located on the surface of the piston head which is exposed to combustion gas and becomes high in temperature can be made thin, and its heat capacity can be made as small as possible, and the suction efficiency and It is possible to improve cycle efficiency and obtain a high degree of heat insulation. The thinner the thin plate is configured, the better the followability to the gas temperature is, that is, the wall temperature amplitude between the high temperature and the low temperature in the combustion chamber becomes large as compared with the case where the thickness is large. As a result, the temperature difference between the combustion gas and the ceramic thin plate is reduced, and the amount of heat transfer is reduced, so that the heat received by the intake air is reduced.

Furthermore, the pressure acting on the thin plate at the time of explosion can be received in a preferable state, and the sealing function between the piston head portion and the piston skirt portion can be improved.

Moreover, since the thin plate and the piston head portion such as the cermet have substantially the same thermal expansion coefficient, there is no problem in the joint state of the two, and the piston head portion has high rigidity and high pressure was applied. It is difficult to deform,
The coupling state between the piston head portion and the piston skirt portion is stable, and moreover, the gas seal at the boundary portion can be stably achieved.

Further, the heat insulating material is, for example, potassium titanate whiskers, zirconia fibers, or the like, or a mixture of these and glass fibers, and performs a high-performance heat insulating function with respect to the combustion chamber of the engine. There is no outflow of thermal energy from the chamber through the piston and the thermal energy can be trapped in the combustion chamber. Therefore, the thermal energy can be effectively recovered by the energy recovery device installed downstream in the exhaust gas flow direction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of the structure of a heat insulating piston according to the present invention, FIG. 2 is a sectional view showing an example of a conventional piston, and FIG. 3 is a conventional heat insulating piston. 3 is a cross-sectional view showing an example of the structure of FIG. 1 ... Piston head part, 2 ... Piston skirt part,
3 ... Insulation material, 5 ... Ceramic thin plate, 6 ... Ceramic ring, 7 ... Carbon seal, 8 ... Cushioning material (insulation gasket), 9 ... Insulation air layer, 10 ... Insulation piston structure , 11 …… Metal ring, 15 …… Combustion chamber, 16…
… Steps, 17 …… Piston head outer circumference, 18 …… Metal honeycomb.

Claims (7)

[Claims] 1. A piston ring formed on a ceramic ring for pressing the piston head onto the piston skirt so that the piston head is pressed against the outer circumference of the piston skirt by a step formed on a ceramic ring. The piston head portion is supported on an outer peripheral portion thereof and attached to the piston skirt portion, and a metallic support material having elasticity and heat insulation is enclosed in a space portion between the piston head portion and the piston skirt portion. The structure of the heat insulating piston. 2. The structure of the heat insulating piston according to claim 1, wherein the support member is made of a honeycomb made of metal. 3. The structure of the heat insulating piston according to claim 1, wherein a heat insulating material is arranged between the piston head portion and a thin ceramic plate forming a surface portion exposed to combustion gas. 4. The heat insulating piston according to claim 3, wherein the thin plate and the ring are formed as thin as possible to reduce the heat capacity of the thin plate and the ring. Construction. 5. The structure of the heat insulating piston according to claim 1, wherein the piston head portion is made of a material having a thermal expansion coefficient substantially equal to that of the ceramics forming the ring. 6. The structure of the heat insulating piston according to claim 1, wherein the thin plate and the ring are made of silicon nitride. 7. The structure of the heat insulating piston according to claim 1, wherein a gasket of a carbon seal is provided on a contact surface between the ring and the piston skirt portion.