JPH0330608Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an adiabatic piston for a reciprocating engine.

[Conventional technology]

FIGS. 3 and 4 are block diagrams of conventional heat insulating pistons. The piston crown 1 has a combustion chamber formed in its upper part and is made of heat-resistant alloy, heat-resistant steel, or heat-resistant ceramic material. A piston body 2 is made of aluminum alloy material and has a piston ring groove 3 and a piston pin boss 4 formed therein. A fixing nut 5 mechanically fastens the piston crown 1 and the piston body 2. Reference numeral 6 denotes a heat insulating disc, which is a disc-shaped member having a plurality of ring-shaped protrusions 7, and is fastened by a fixing nut 5 with one or more discs sandwiched between the piston crown 1 and the piston body 2. An air layer 8 is formed between these ring-shaped projections.

Next, the operation of the above embodiment will be explained.

During operation of the engine, heat from the combustion hot gas formed in the piston crown 1 is transferred to the piston crown 1 and becomes high temperature. The piston body 2 made of aluminum alloy, which is cooled by a cooling means (not shown), is at a low temperature, and the piston groove 3 is also maintained at a low temperature to the extent that its function is not inhibited. The heat flow path to the body 2 is blocked by an air layer 8 formed in the heat insulating disc 6, and is reduced to only a fastening section formed by a plurality of narrow ring-shaped protrusions 7 and a fixing nut 5. Because of this, a highly insulated structure is formed.

As a result, the amount of heat loss transferred from the working gas in the combustion chamber to the outside through the piston is significantly reduced compared to a normal piston, resulting in improved engine performance. On the other hand, in this insulated piston, the gas pressure acting on the piston crown 1 is supported by the piston body 2 made of aluminum alloy through the ring-shaped protrusion 7 of the insulating disk 6 that is in contact with the crown 1, and the reciprocating movement of the piston is supported by the piston body 2 made of aluminum alloy. The upward inertia force acting on the crown 1 due to the piston body 2 is supported by the fixing nut 5.

The force acting on the ring-shaped protrusion 7 of the heat insulating disc 6 is the sum of the tightening force due to the tightening of the fixing nut 5, the downward force due to thermal deformation of the piston crown 1, and the press force due to gas pressure, and is transmitted to the member. As shown in FIG. 3, the generated surface pressure P is uniformly transmitted from above as P ₁ determined by the width t of the ring-shaped projection 7. In addition, although the lowermost insulating disk is supported on its entire surface by the piston body 2, the surface pressure P ₂ increases as the stress flow spreads as shown by the broken line in the figure.
It has become somewhat smaller.

[Problem that the invention attempts to solve]

However, in order to improve the heat insulation performance of the piston, it is necessary to increase the thermal resistance by reducing the protrusion width t as much as possible, but as the width t is reduced, the surface pressures P ₁ and P ₂ increase, and this value becomes If the strength limit of the material is exceeded, the abutment surface will sag, and if the backlash increases and the tightening force of the fixing nut 5 becomes loose, it will be damaged. In particular, even if a heat-resistant alloy, heat-resistant steel, or heat-resistant ceramic material with strong high-temperature strength is used as the material for the piston crown 1 and the heat insulating disc 6, due to the strength limitations of the aluminum alloy piston body, P ₂
Therefore, in conventional products, it was not possible to reduce t below a certain limit, and it was not possible to obtain sufficient heat insulation performance.

The purpose of the present invention is to eliminate the drawbacks of the conventional device, to connect a piston crown made of a heat-resistant material forming a combustion chamber and an aluminum alloy piston body having a piston ring with bolts, and further to connect the piston crown and the piston body. One or more heat insulating discs having multiple ring-shaped protrusions are inserted between the piston crown and the piston body, and the heat insulating properties of the air layer formed between these protrusions prevent the flow of heat from the piston crown to the piston body. In this structure, the heat resistance of the heat insulating disc is increased without increasing the risk of damage to the piston due to fatigue of the contact surfaces between the piston crown, the heat insulating disc, and the aluminum alloy piston body. The aim is to provide a piston with improved thermal insulation.

[Means for solving problems]

In the heat-insulating discs used in the heat-insulating piston of the present invention, the width of the ring-shaped protrusions provided on the plurality of discs is lower than the width of the protrusion on the top layer that contacts the piston crown. As the temperature of the member gradually decreases due to thermal resistance, the width of the protrusion is gradually reduced within a range below the high-temperature permissible surface pressure of the member at that temperature, and the width of the protrusion of the lowest layer in contact with the aluminum body is Compared to the protrusion width, the protrusion width located in the upper layer gradually becomes smaller, and the protrusion width located in the middle layer takes a minimum value, thereby reducing the surface pressure on the aluminum alloy piston body. It is characterized in that the reduction angle and expansion angle of the protrusion width in the vertical direction are kept below the allowable value of the alloy material and are 45° or less on one side.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

1 is the piston crown, on which the combustion chamber is formed, and is made of heat-resistant alloy, heat-resistant steel, or heat-resistant ceramic material. A piston body 2 is made of aluminum alloy material, and has a piston ring groove 3 and a piston pin boss 4 formed therein.
A fixing nut 5 mechanically fastens the piston crown 1 and the piston body 2. A plurality of heat insulating discs 16 are sandwiched between the piston crown 1 and the piston body 2 and fastened with a fixing nut 5. In FIG. 1, (n-1) heat insulating disks are sandwiched. A plurality of ring-shaped protrusions 17 are provided on the heat insulating disc 16, and the protrusions 17 on the plurality of discs 16 are located on the same radius, and in the assembled state, each protrusion is vertically aligned. They are arranged in a continuous ivy shape. Protrusion 17
The width t is the width of the top layer in contact with the piston crown 1
Compared to t ₁ , the protrusion width t ₂ located in the lower layer,
t ₃ gradually decreases, and the protrusion width t(n
−1) The protrusion width t located in the upper layer compared to this
(n-2) and t(n-3) gradually decrease, and the protrusion width located in the middle layer portion takes a minimum value. Further, the vertical reduction angle and expansion angle of the protrusion width t are 45° or less at one corner.
An air layer 18 is formed between the protrusions 17 on the heat insulating disc 16.

Next, the operation of the above embodiment will be explained.

The surface pressure P generated by the tightening force of the fixing nut 5 acting on the ring-shaped protrusion 17 of the heat insulating disk 16, the pressing force due to thermal deformation of the piston crown 1, and the pressing force due to gas pressure is applied to each cross-sectional disk. P ₁ : P ₂ : P 3 : P 1 : P 2 : P ₃ :
...: P _o-1 : P _o = (1/t ₁ ): (1/t ₂ ): (1/t ₃ ):
...: (1/t _o-1 ): (1/tn) and is inversely proportional to t.

Since the member temperature of the protrusion 17 rapidly decreases from the upper layer due to the thermal resistance using the air layer of the heat insulating disk 16, as shown in FIG. (q ₁ <
q ₂ < q ₃ ...) P never exceeds q.

In the layer below the minimum point of the protrusion width t, the protrusion width t increases as it goes lower, so the surface pressure P gradually decreases again. The surface pressure P _o of the surface can be made smaller than the allowable surface pressure 〓n of the aluminum alloy.

Since the angle of vertical reduction and expansion of each protrusion width t is 45 degrees or less at one corner, the flow of stress in the thick part of the disk 16 is also reduced by the protrusion, as shown by the two-dot chain line in FIG. It is continuous with respect to changes in the width t, and no excessive stress is generated locally.

In this embodiment, compared to the conventional one shown in FIG. 4, the surface pressures P ₁ , P ₂ , ... P _o generated in each part are kept below the allowable surface pressure q according to each temperature level of the member, and Since the heat flow path width t is significantly reduced in the middle layer, the thermal resistance of the heat insulating disk 16 can be significantly increased.

[Effect of idea]

As mentioned above, by using the heat insulating piston for the heat insulating piston according to the present invention, it is possible to prevent backlash due to the settling of the contact surfaces between the piston crown, heat insulating disc, and aluminum alloy piston body, and to prevent tightening of the fixing nut. It is possible to significantly increase the thermal resistance of the heat insulating disc without reducing the applied force or increasing the risk of piston breakage, improving the heat insulation performance of the heat insulating piston, and removing the piston from the working gas in the combustion chamber. It is possible to significantly reduce the amount of heat loss transferred to the outside through the engine, thereby improving engine performance.

[Brief explanation of drawings]

Figures 1 and 2 relate to the embodiment of the present invention. Figure 1 is a cross-sectional view of a heat insulating disc ring-shaped projection, and Figure 2 shows that the temperature of the members of the projection gradually decreases from the upper layer due to thermal resistance using an air layer. Therefore, the allowable surface pressure q of the material gradually increases from the upper layer, and the diagram shows a situation in which the pressure P never exceeds q. Figure 3 is a cross-sectional view of an insulated piston using an insulated disk FIG. 4 is an explanatory diagram regarding the surface pressure P in a conventional heat insulating disc. 1...Piston crown, 2...Piston body, 16...Insulating disc, 17...Protrusion, 18...
Air layer, t... width of protrusion.

Claims (1)

[Scope of utility model registration request] An aluminum alloy piston body that has a piston crown that is made of heat-resistant materials such as heat-resistant alloys, heat-resistant steel, and heat-resistant ceramic materials and forms a combustion chamber, and a piston ring that is mechanically connected to the piston crown at the center of the piston diameter. and a heat insulating disc having a plurality of ring-shaped protrusions between the piston crown and the piston body.
In a piston crown having one or more protrusions, the flow of heat from the piston crown to the piston body is suppressed by the heat insulating properties of the air layer formed between these protrusions,
The plurality of ring-shaped protrusions provided on the plurality of heat insulating discs are located on the same radius in the radial direction of the piston, and the ring-shaped protrusions provided on the plurality of heat insulating discs The width of the protrusions is gradually smaller than the protrusion width of the uppermost layer that contacts the piston crown, and the protrusion width of the protrusions located on the lower layer is gradually smaller than the protrusion width of the protrusion that is located on the lowermost layer that contacts the piston body. The width of the protrusion gradually decreases, and the width of the protrusion located in the middle layer takes a minimum value compared to that of other protrusions, and the angle of reduction and expansion of the width of the protrusion in the vertical direction is one-sided. A heat insulating piston having a heat insulating disc characterized by an angle of 45° or less.