FR2962169A1 - Metal alloy piston for diesel type internal combustion engine to displace alternatively in direction and parallel direction to central axis of piston, has non-return valve allowing prevention of passage of liquid phase along direction - Google Patents

Abstract

The piston has a heat pipe (20) whose hermetic enclosure (21) forms a closed fluid circulation loop with a condenser part (23), a supply pipe (24) and a return pipe (24'). The supply pipe supplies a liquid phase toward an evaporator part (22). The return pipe returns a vapor phase toward the condenser part. The heat pipe comprises a non-return valve (25) i.e. ball type valve, that is arranged in the supply pipe and allows passage of the liquid phase along direction and prevention of the passage of the liquid phase along another direction. The valve is formed with a passage section restriction.

Description

Piston comprising a heat pipe and engine comprising such a piston

TECHNICAL FIELD OF THE INVENTION The present invention relates to the cooling of pistons and more particularly to a piston comprising a heat pipe.

Technological background It is known to meet the need to reduce greenhouse gas emissions without reducing the power of the engines to make these engines more compact to reduce fuel consumption. This increases their specific power. However, the increase in the specific power of the engines is accompanied for the pistons of a sharp increase in the constraints in terms of pressure and heat flow.

It is known from the document FR2912188, for cooling the piston to develop a cooling cavity inside the upper part of the piston, said cavity having at least two openings opening on the surface of the piston side connecting rod in order to allow the lubricating fluid, which acts as heat transfer fluid, to enter the cavity and exit. However, such a solution is insufficient to correctly evacuate the thermal flows seen by the piston in the case of high specific power motors.

It is also known from US7603977 a piston for an internal combustion engine comprising a cooling cavity arranged at the circumference of the piston, at the grooves provided to receive the segmentation, as well as heat pipes.

Of known design, a heat pipe is in the form of a hermetic enclosure which encloses a fluid in equilibrium with its gaseous phase and its liquid phase. At one end of the heat pipe, the one near a hot source to cool, the liquid heats and vaporizes by storing energy from the heat emitted by this element. This gas is then diffused in the heat pipe to a cold source located at the other end of the heat pipe where the gas will be cooled, until it condenses to become again a liquid, and to give up energy. at the cold source. The liquid then returns to the evaporator by gravity or capillarity.

In the document US7603977, each of the heat pipes is arranged so that their evaporator side is oriented towards the surface of the piston exposed in the combustion chamber and placed in a hole made in the cooling cavity, while the condenser side is placed in the cooling cavity. However the operation of the heat pipes is disturbed by the reciprocating movements of the piston, which impart shaking to the liquid phase and the gas phase and disturb the correct evacuation of the heat flow received by the surface of the piston exposed in the combustion chamber to the cavity cooling.

The invention aims to solve one or more of these disadvantages.

The invention thus relates to a metal alloy piston intended to move alternately in a first direction and then a second direction parallel to a central axis of the piston, said piston comprising at least one heat pipe comprising a hermetic enclosure containing a fluid in equilibrium with its gas phase and its liquid phase, characterized in that the hermetic enclosure forms a closed fluid circulation loop having a condenser part, a supply duct for the liquid phase to an evaporator part, a return duct for the vapor phase. to the condenser part and in that the heat pipe comprises a non-return valve disposed in the feed duct and adapted to let the liquid phase pass in the first direction and to prohibit the passage of the liquid phase in the second direction. Thus the circulation of the vapor and liquid phases in the loop-shaped enclosure is not disturbed by the reciprocating movements of the piston, which improves the heat transfer between the evaporator and condenser parts of the heat pipe.

Preferably, the non-return valve is adapted to first open by inertia during movement of the piston in the first direction to allow the passage through the valve of a fraction of the liquid phase to the evaporator part and for the other hand prohibit the passage of the liquid phase to the condenser part during the movement of the piston in the second direction. Indeed, the clever use of the game of inertia put into play during the reciprocating movements of the piston, allows the automatic actuation of the nonreturn valve.

In a variant, the return duct comprises a passage section restriction, in order to allow the passage of the vapor phase towards the condenser part and to prevent the liquid phase from returning to the return duct. For reasons of simplicity of embodiment, preferably, the restriction is obtained by a constriction of the return duct. For reasons of reliability and cost, preferably, the non-return valve is of the ball type with return spring. . The ball is here the element which by its inertia moves and ensures the opening and closing of the valve according to the movement of the piston. The return spring also contributes to sealing the valve in closed mode. Preferably, the piston comprising a front surface, the evaporator portion extends close to said front surface, when the hot source is on the side of the front surface.

Preferably, the piston comprising a skirt, the condenser portion extends close to said skirt, in order to allow better evacuation of heat.

Preferably, the piston comprising a passage of a connecting pin, the at least one heat pipe is disposed in the piston on one side or the other of said passage.

Preferably, the evaporator portion extends in an arc around the central axis.

In a variant, the supply duct and the return duct are arranged side by side, in contact, in order to obtain a compact heat pipe.

In another variant, the supply duct and the return duct are connected to at least one of their end by a closure cap, which allows easier manufacture.

Preferably, the piston comprises at least one heat pipe inserted in the casting of the metal alloy during molding of said piston.

The invention also relates to an internal combustion engine, characterized in that it comprises at least one piston of the invention. 30

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages will appear on reading the following description of a particular embodiment, not limiting of the invention, with reference to the figures in which: FIG. 1 is a schematic representation of a piston comprising a heat pipe according to a first embodiment. - Figure 2 is a schematic representation of a heat pipe according to a second embodiment. - Figure 3 is a schematic representation of a heat pipe according to another embodiment - Figure 4 is present in top view a piston comprising a plurality of heat pipes arranged in a circle. - Figure 5 shows a top view of a piston 3 comprising two heat pipes disposed in said piston each on one side of the passage of the connecting axis of the piston. - Figure 6 shows a side view of the piston shown in a top view in Figure 5.

DETAILED DESCRIPTION FIG. 1 shows a partial section of an internal combustion engine 1 with direct injection, in particular of diesel type. The engine 1 comprises at least one combustion chamber 2 delimited by a piston 3, a cylinder head 4, and a cylinder 5. The piston 3 and the cylinder 5 have a central axis Z. Furthermore, the engine 1 comprises an injector 16 implanted in the cylinder head 4.

The piston 3 further comprises a front surface S brought to be in contact with the combustion gases and an outer cylindrical edge 6. The front surface S comprises an upper ring 7 which may be flat, an internal cavity or bowl 8. The bowl 8 may be centered with respect to the central axis Z. The bowl 8 may also comprise a central boss 9 forming an elevation in the bowl 8.

In addition, the piston 3 comprises a cylindrical passageway 10 for receiving a connecting pin of a connecting rod, not shown, with the piston 3.

The piston 3 is also provided with at least one annular groove 11 for receiving a segment. FIG. 1 shows a conventional segmentation of an internal combustion engine whose function is to seal the piston 3 in the cylinder 5. The segmentation is composed of a fire segment 12, the closest to the combustion chamber , then a sealing segment 13 and a scraper ring 14.35 The piston 3 also comprises a skirt 15 for guiding the piston 3 in the cylinder 5. The piston 3 is preferably made of metal alloy to ensure good conduction of heat. Thus the piston 3 can be for example aluminum alloy or steel.

When the combustion engine 1 is operating, the piston 3 is driven by a reciprocating rectilinear motion in the cylinder 5, as indicated by the arrows F1 and F2, parallel to the axis Z.

According to the invention, the piston comprises at least one heat pipe 20. The heat pipe 20 has in known manner a hermetic enclosure which encloses a fluid in equilibrium with its gas phase and its liquid phase. Preferably, the enclosure forms a conduit 21 for circulating the fluid in a closed loop.

The circulation duct 21 comprises a so-called evaporator part 22, a so-called condenser part 23. The duct 21 also comprises a portion serving as a feed duct 24 for the fluid towards the evaporator 22 and a part serving as a return duct 24 from the fluid to the condenser 23. The return feed pipes 24 '24' can be thermally insulated.

The evaporator portion 22 of the heat pipe 20 is disposed on the side of a hot source, in this case in the direction of the combustion chamber 2 of the engine 1, near the upper ring 7. The condenser part 23 is disposed on the side from a cold source. Preferably, the condenser portion 23 extends near the skirt 15 of the piston 3 because it exchanges heat with the cylinder 5 which is constantly cooled by a cooling circuit, not shown.

Preferably, the heat pipe 20 comprises a non-return valve 25 disposed in the conduit 21 for circulating the fluid and capable of allowing the liquid phase to pass in a first direction of movement of the piston 3 and to prohibit the passage of the liquid phase according to a second direction of movement of the piston 3. More specifically, the nonreturn valve 25 is placed in the supply duct 24 intended to allow the passage of the liquid phase of the condenser part 23 to the evaporator part 22. The anti-return valve 25 is mounted so as to allow only the circulation of the liquid phase of the condenser side 23 towards the evaporator side 22. The nonreturn valve 25 illustrated in FIG. 1 is of the ball type, which has the advantage of being simple, robust and very low cost.

As illustrated schematically in FIG. 1, the nonreturn valve 25 therefore comprises a ball 26 and a return spring 27. The spring 27 comes to one of its ends bearing against a stop 28 while the other end bears against on the ball 26. Under the action of the spring 27, the ball 26 is applied to a seat 29 to obstruct the passage of the liquid phase.

It should be noted that in the invention, the liquid phase and the vapor phase circulate in the heat pipe 20 in the opposite direction but are not mutually in contact with each other as in a conventional rectilinear and closed tubular heat pipe. In addition, unlike heat pipes operating by capillarity, the heat pipe 20 does not include a capillary network in the conduit 21, which simplifies the design and implementation.

The operation is as follows: When the engine 1 is in operation, the combustion made in the combustion chamber 2 give off heat and allow the animation of the piston 3 of a rectilinear motion alternately according to the arrows F1 and F2. The piston 3 receives a portion of this heat at its front surface S, which by conduction in the body of the piston 3 reaches the evaporator portion 22 of the heat pipe 20.

During a downward movement of the piston 3, according to the arrow F2, the ball 26, under the effect of its inertia takes off from its seat 29. Moreover, the spring 27 is expected to be tared sufficiently weakly not to to thwart this action. The nonreturn valve 25 is then open. During this same movement, a fraction of the liquid phase, also under the effect of its inertia, finds its way through the non-return valve 25 open, thus going up to the evaporator part 22.

During an upward movement of the piston 3, according to the arrow F1, the inertia of the ball 26 and the action of the spring 27 applies the ball 26 against the seat 29. The non-return valve 25 is then closed and prevents the liquid phase has to return to the condenser side 23 by gravity and by inertia.

The combination of the check valve 25, the reciprocating movements of the piston 3 and the play of the inertias of the liquid phase and of the ball 26 thus make it possible to "pump" the liquid phase on the condenser side 23 to make it rise towards the evaporator side 22 by the supply conduit 24 of the conduit 21 in a closed loop, and thus obtain a heat pipe 20 operating against gravity without using the conventional means of the capillary network, which simplifies the design and production of said heat pipe 20.

The evaporator part 22 is therefore regularly supplied with liquid phase fluid which, under the effect of the heat coming from the combustion chamber 2, evaporates. The vapor phase thus generated then returns via the return duct 24 'to the condenser part 23 where the heat is discharged through the skirt 15 to the cylinder 5.

This embodiment also has the advantage of allowing the simplification of the design of the piston. Indeed, it is not necessary to provide in the piston 3 the conventional oil circulation passages near the front surface S to ensure the evacuation of heat and the cooling of the piston.

Figure 2 now shows a second embodiment. This second embodiment differs from the first embodiment shown in FIG. 1 in that the return duct 24 'comprises a passage section restriction. This restriction 30 permits the passage of the vapor phase, but has an opening of insufficient size for the liquid phase to pass through the return duct 24 'by inertia during the downward movements of the piston 3. Advantageously, the restriction can be achieved by a throttling of the return duct 24 '.

FIG. 3 shows another embodiment of heat pipe 20 ', which differs from the previous embodiment shown in FIG. 2 in that it is formed of a supply duct 24 and a return duct 24' arranged side-by-side, in contact, and closure caps 32, 33 disposed at the end of the ducts, respectively side of the evaporator portion 22 and the condenser portion 23. The closure caps 32, 33 may be welded to the supply ducts 24 and 24 'back or crimped. In another variant, not shown the heat pipe may be formed of a U-shaped bent tube and closed by a cap at the free ends.

FIG. 4 shows, in plan view, a piston 3 comprising several heat pipes 20 as shown in FIG. 2. As FIG. 4 further illustrates, the heat pipes 20 are arranged in the piston 3 substantially in a circle around the axis Z, on one side or the other of the passage 10. Indeed, the presence of this passage 10 does not easily place a heat pipe in this area.

In this configuration, the evaporator portion 22 is arranged to extend near the front surface S of the piston 3 in contact with the combustion, while the condenser portion 23 is disposed near the edge of the skirt 15. The The distribution of the heat pipes 20 around the Z axis can be substantially regular, for a homogeneous heat dissipation, or chosen as a function, for example, of the presence of hot spots created by combustion zones at the point of impact of the sprayed jets. fuel, on the front surface S.

FIG. 5 and FIG. 6 show, respectively in top view and in side view, in the plane of the passage 10 of the connecting axis of the piston, a piston 3 comprising two heat pipes 40, each disposed on one side of the passage 10 of the connecting axis of the piston 3. In this variant, the condenser 23 and evaporator 22 portions of the heat pipes 40 extend in a circular arc, the supply ducts 24 and return 24 'connecting the condenser sides 23 and evaporator 22 being located near the passage 10 of the connecting axis of the piston, to best cover the cooling of the front surface S.

The manufacture of the piston 3 can advantageously be carried out according to the following main steps: a step of supplying the heat pipes, a step of installing the heat pipes in a piston mold, a step of casting the metal alloy of the piston in the mold,

The heat pipes are thus perfectly maintained inserted in the piston and in good thermal contact.

The invention is not limited to diesel engines and is suitable for any type of internal combustion engine or reciprocating piston machine whose piston or pistons must be cooled.

Claims (13)

REVENDICATIONS1. Metal alloy piston intended to move alternately in a first direction and then a second direction parallel to a central axis (Z) of the piston, said piston comprising at least one heat pipe (20, 20 ', 40) comprising a hermetic enclosure (21) comprising a fluid in equilibrium with its gaseous phase and its liquid phase, characterized in that the hermetic enclosure (21) forms a closed fluid circulation loop having a condenser part (23), a supply duct (24) of the liquid phase to an evaporator part (22), a return pipe (24 ') from the vapor phase to the condenser part (23) and the heat pipe (20, 20', 40) comprises a nonreturn valve (25) arranged in the feed duct (24) and adapted to let the liquid phase pass in the first direction and to prohibit the passage of the liquid phase in the second direction. 2. Piston according to claim 1, characterized in that the non-return valve is adapted to firstly open by inertia during the movement of the piston in the first direction to allow passage through the valve of a fraction of the liquid phase to the evaporator portion (22) and further prohibit the passage of the liquid phase to the condenser portion (23) during the displacement of the piston in the second direction. 3. Piston according to claim 1 or claim 2, characterized in that the return duct (24 ') comprises a passage section restriction (30). 4. Piston according to claim 3, characterized in that the restriction is obtained by a constriction of the return duct (24 '). Piston according to one of the preceding claims, characterized in that the non-return valve (25) is of the ball type with return spring. 6. Piston according to one of the preceding claims, characterized in that the piston comprising a front surface (S), the evaporator portion (22) extends close to said front surface (S). 7. Piston according to one of the preceding claims, characterized in that the piston comprising a skirt (15), the condenser portion (22) extends close to said skirt (15). 8. Piston according to any one of the preceding claims, characterized in that, the piston comprising a passage (10) of a connecting pin, the at least one heat pipe (20, 40) is disposed in the piston of a side of the said passage (10). 9. Piston according to any one of the preceding claims, characterized in that the evaporator portion (22) extends in an arc around the central axis (Z). 10. Piston one of claims 1 to 8, characterized in that the supply duct (24) and the return duct (24 ') are arranged side by side in contact. 11. Piston according to claim 9, characterized in that the supply duct (24) and the return duct (24 ') are connected to at least one of their end by a closure cap (32, 33). 12. Piston according to any one of the preceding claims, characterized in that it comprises at least one heat pipe (20, 20 ', 40) inserted in the casting of the metal alloy during molding of said piston. 13. Internal combustion engine, characterized in that it comprises at least one piston according to any one of the preceding claims.