EP0827567B1 - Intake manifold with ringed air tubes for internal combustion engines - Google Patents

Abstract

Between two half-shells (2, 3) molded and fixed to each other in order to form an envelope (1), there are mounted air tubes (12a) with a ringed external face (14) and a smooth internal face (13) which are fixed by means of end sleeves (17a, 18a) to the envelope (1). The outlet sleeve (18a) is held within a half-shell (3) by means of a fixing clamp (6) to the cylinder-head of the engine by being sealingly connected to an opening (7) of the clamp (6) for the supply of one cylinder by a tubular nozzle comprised of a cradle (29a) integrally cast with the clamp (6) and the half-shell (3), and a cover (31a) fixed to the cradle in order to hold a seal (28) to the extremity of the outlet sleeve (18a), the seal being compressed between the sleeve (18a) and the nozzle (29a, 31a). Application particularly to intake manifolds of internal combustion engines, preferably with controlled ignition.

Description

The invention relates to an intake manifold, for internal combustion engine fitted with an installation fuel supply preferably by injection, particular of the type called "multipoint", comprising, for each engine cylinder, at least one injector which injects fuel in a manifold suction line air intake to the engine, directly upstream of the engine cylinder head and intake valve (s) corresponding cylinder.

• une enveloppe, délimitant un plenum destiné à être alimenté en air d'alimentation du moteur, en général par une vanne à débit variable telle qu'un corps de papillon, et munie d'au moins une bride de fixation à au moins une culasse du moteur, la ou lesdites brides présentant au moins une ouverture d'alimentation de chaque cylindre du moteur, chaque ouverture d'alimentation débouchant, d'une part, dans l'enveloppe et, d'autre part, dans une face de fixation de la bride sur ladite culasse, et
• des tubes d'aspiration d'air recourbés, chacun d'une seule pièce, et en nombre au moins égal à celui des cylindres du moteur, et montés dans l'enveloppe, de sorte que chaque tube alimente un cylindre correspondant en air qu'il reçoit par son entrée dans le plenum et qu'il transmet à l'ouverture correspondante de la bride correspondante par sa sortie reliée par des moyens de raccordement étanches à ladite ouverture d'alimentation.

By GB-A-2 238 350, there is known such an intake manifold, which comprises:

• an envelope, delimiting a plenum intended to be supplied with air supplying the engine, in general by a variable flow valve such as a throttle body, and provided with at least one flange for fixing to at least one cylinder head of the engine, said flange (s) having at least one supply opening for each cylinder of the engine, each supply opening opening, on the one hand, into the casing and, on the other hand, into a fixing face of the flange on said cylinder head, and
• curved air suction tubes, each in one piece, and in a number at least equal to that of the engine cylinders, and mounted in the casing, so that each tube supplies a corresponding cylinder with air that it receives by its entry into the plenum and which it transmits to the corresponding opening of the corresponding flange by its outlet connected by sealed connection means to said supply opening.

We already know how to make collectors of this type in molding two half-shells of complementary shapes corresponding to the shape of the envelope and intended to be joined together by their peripheral rim, in a parting line, to form the envelope.

The outer part, relative to the center of curvature of the bent tubes, of all the air tubes is formed by the hollow molded impression bottoms in each of the two half-shells, and which extend when the half-shells are closed against each other the other. Similarly, the inner part of all the air tubes are formed by the impression bottoms molded into at least two molded inserts, generally in the same material as the half-shells, for example in moldable synthesis, preferably thermoplastic, such as polyamide, and which can be loaded with reinforcing fibers, and each reported in one half-shells respectively, so that the footprints inserts also extend during the joining half shells against each other. This process thus makes it possible to form the tubes by cooperation of surfaces presented by at least four molded parts (two half-shells and two inserts) which are associated.

A collector thus produced is suitable for the equipment of a diesel engine, due to the low pressure gradient between the atmosphere and the plenum of the collector, in operation of the motor.

On the other hand, in a spark ignition engine, where this pressure gradient can reach average values larger, around 70 kPa, when the engine, the presence of air leaks between the parts assembled to form contained air suction tubes inside the plenum has the effect of modifying the impedance collector acoustics, resulting in a drop in the efficiency of the engine.

It is therefore imperative that in a collector of this type a good seal, especially at the air tubes, be assured.

For this purpose, a seal must be made between the inserts and the half-shells by fitting cords of suitable polymerizable material, which is a long and delicate operation, adding to the difficulty of realization with low tolerances of the parts to assemble to precisely define the air tubes.

As a result, such a collector can become an expensive achievement.

The problem underlying the invention is to propose a collector of an economic achievement, essentially in thermomouldable and semi-modular synthesis, because acoustically adaptable to a whole family of engines of different displacements by dimensional adjustment, in particular of the diameter and the length of the air tubes.

For this purpose, the intake manifold according to the invention, of the type known from GB-A-2 238 350, is characterized in that each tube is an external face tube corrugated, preferably with parallel rings, and internal face smooth delimiting a central passage of cross section constant in shape and in surface, so that the tube has great flexibility or transverse flexibility, but low flexibility or axial flexibility.

Such monoblock air tubes being by nature waterproof, the need to make joint cords sealing along the generators disappears. Moreover, the rings of the corrugated external face of such tubes keep the shape and surface constant the cross section of the central passage, participating maintaining the acoustic impedance of the tubes, while providing good flexibility or suppleness in direction radial or transverse, allowing bending of the tubes as desired, while their smooth internal surface limits pressure losses and gives the tubes a low flexibility or axial flexibility, necessary to maintain their acoustic impedance.

Advantageously, each tube is made of synthesis, preferably moldable, such as thermoplastic, and cut, perpendicular to its longitudinal axis, at the desired length, to give the collector an impedance acoustic tuned to the engine, in an element tubular supplied in great length, and preferably of circular section, so that the tubular element is obtained at a very favorable cost, compared to others possible solutions for making waterproof tubes.

Although the annular conformation of the external face of the tube can be defined by one or more ribs helical wound in the outer face of the tube, its inlet to outlet, the corrugated outer face of each tube is advantageously a surface of cylindrical revolution at corrugated generator before the tube is bent at the desired shape, to simultaneously benefit from a large transverse flexibility but very low flexibility axial.

The collector envelope may consist of, known manner, of two half-shells of complementary shapes corresponding to the shape of the envelope and molded, preferably in moldable synthetic material, preferably thermoplastic, with fixing flanges on their peripheral edges in a joint plane, the half-shells being closed and fixed against each other at level of their fastening flanges, for example by welding, preferably by vibration, in which case it is advantageous that each tube is fixed only by its ends with half shells.

To this end, at least one of the ends of each tube is advantageously fixed to a half-shell using of a sleeve which is partly force-fitted into the corresponding end of the tube and retained on said half-shell by a part of sleeve external to the tube. To ensure excellent axial retention of the sleeve in the tube, it is advantageous that the sleeve has, on the external face of its part which is fitted at one end corresponding tube, at least one peripheral redent anchor, which is formed at the axial end, facing the said end of the tube, of a surface substantially frustoconical with small base facing the central part of the tube, several axially offset redents preferably being formed in this way on the sleeve. In addition, the latter advantageously comprises at least one projecting stop substantially radial towards the outside to limit its fitting into a corresponding end of the tube.

Advantageously, the sleeve or each of the two connecting sleeves of a tube, is molded from a material of synthesis, which is preferably a thermosetting material.

In a preferred embodiment, for each manifold tube, an air inlet sleeve, fitted into an inlet end of a tube, is shaped, in its external part at said inlet end of the tube, in a tulip converging towards the inside of the tube and provided with minus one fixing lug to that of the two half-shells which is not provided with the mounting flange having the feed opening at which said tube is connected by its output, the fixing being for example provided by heat sealing or by rolling at the fixing lug (s).

Likewise, each tube is advantageously connected by an air outlet sleeve, fitted into the end of outlet of the tube, to that of the half-shells which is provided with said fixing flange having said opening to which said tube is so connected waterproof by its outlet, said connection means watertight including a tubular manifold tip, in projection on said flange on the side opposite to the cylinder head, in the extension of said corresponding feed opening, and in which tip part of said sleeve outlet, which is external to the tube, is retained with interposition at least one flexible seal between said external part of the outlet sleeve and said end piece collector.

• un berceau, moulé d'une seule pièce avec ladite demi-coquille et ladite bride de fixation correspondante, et de forme sensiblement hémi-cylindrique, dont l'extrémité interne à ladite demi-coquille présente un fond en forme de U formant butée en saillie vers l'intérieur du berceau, et
• un couvercle rapporté de maintien du manchon de sortie et du ou des joints d'étanchéité montés sur ce dernier dans le berceau, ledit couvercle présentant une butée en saillie vers l'intérieur du berceau et en regard du fond en forme de U du berceau, et étant fixé sur des bords du berceau, de préférence par soudure aux ultrasons.

Advantageously, to facilitate the production of the constituent parts of the collector and their assembly, each collector endpiece comprises:

• a cradle, molded in one piece with said half-shell and said corresponding fixing flange, and of substantially semi-cylindrical shape, the internal end of said half-shell having a U-shaped bottom forming a projecting stop towards the inside of the cradle, and
• an attached cover for holding the outlet sleeve and the seal (s) mounted on the latter in the cradle, said cover having a stop projecting towards the inside of the cradle and facing the U-shaped bottom of the cradle, and being fixed on edges of the cradle, preferably by ultrasonic welding.

A good seal can be ensured using a single flexible gasket for each tube, if gasket, mounted around the part of the outlet sleeve corresponding which is external to the tube and retained in the nozzle corresponding collector, is molded in shape, preferably made of elastomer, with a cross section corresponding to that of the space available between, on the one hand, said outlet sleeve, and, on the other hand, said cradle and said cover, and so that the seal is compressed radially between these three elements.

For cases where the cross section of the tube is circular or oblong, while the cross section of the corresponding feed opening is respectively oblong or circular, the corresponding manifold tip advantageously has a substantially cross section of the same shape as that of said feed opening, and the corresponding outlet sleeve has a central passage having a cross section of form evolutionary, varying gradually from the section shape of the manifold tip, in the part of the outlet sleeve which is external to the tube, to the cross-sectional shape of the tube, in the part of the outlet sleeve which is fitted into the outlet end of this tube, so that the sleeve of outlet constitutes an adapter sleeve ensuring the transition between the shapes of the tip sections manifold and air tube.

In addition, in the envelope, the tubes can be grouped at least in pairs of tubes joined on at least part of their length, and, in order to limit the transverse displacements of tubes or groups of tubes attached to the envelope, housing can be delimited by recesses in the internal face of the envelope, and parts of tubes or joined parts of tubes can be accommodated in these recesses, possibly bordered by protruding ribs on the inner face of at least one of the half-shells constituting the envelope.

• la figure 1 est une vue en coupe transversale d'un collecteur pour moteur à quatre cylindres en ligne, la coupe étant sensiblement perpendiculaire à l'axe du moteur,
• la figure 2 est une demi-vue en partie en élévation en plan et en partie en coupe de la demi-coquille aval du collecteur de la figure 1, avec une des deux paires de tubes qui sont regroupés et retenus dans cette demi-coquille par leur extrémité de sortie,
• les figures 3 et 4 sont des coupes transversales respectivement selon III-III et IV-IV de la figure 1, et
• la figure 5 est une vue partielle en coupe axiale et à plus grande échelle d'un détail de la figure 2.

Other characteristics and advantages of the invention will emerge from the description given below, without implied limitation, of exemplary embodiments described with reference to the appended drawings in which:

• FIG. 1 is a cross-sectional view of a manifold for an in-line four-cylinder engine, the section being substantially perpendicular to the axis of the engine,
• Figure 2 is a half-view partly in plan elevation and partly in section of the downstream half-shell of the collector of Figure 1, with one of the two pairs of tubes which are grouped together and retained in this half-shell by their outlet end,
• FIGS. 3 and 4 are cross sections respectively on III-III and IV-IV of FIG. 1, and
• FIG. 5 is a partial view in axial section and on a larger scale of a detail in FIG. 2.

The manifold of Figures 1 and 2, for a motor with four cylinders in line, includes a rigid casing 1, in moldable and heat-sealable synthetic material such as a polyamide possibly reinforced with reinforcing fibers, and made up of two half-shells 2 and 3, each molded in this material, having complementary shapes which correspond to the shape of envelope 1. The two half-shells 2 and 3 close against each other, by their peripheral edges, to reconstitute the shape of envelope 1, and are secured to each other in a joint plane P, defined by fastening flanges 4 and 5, projecting outwards on their edges, by vibration welding at these flanges 4 and 5, after mounting in the half-shells 2 and 3 of four tubes air intake (one per engine cylinder), grouped in two pairs of joined tubes, as shown in the figure 2, and their sleeves as described below.

The flange 5 of the half-shell 3, coming opposite of the flange 4 of the half-shell 2 over the entire periphery half-shells, is supported, on one side of the envelope 1, through the upper part of a fixing flange 6 from the manifold to the engine cylinder head, this flange 6 being molded in one piece with the half-shell 3 and its flange peripheral 5. The flange 6 has, for each cylinder of the motor, a feed opening 7, coming from molding, circular or oblong cross section, which opens out on one side in the flat face 8 for fixing the flange 6 on the engine cylinder head and, on the other side, inside the half-shell 3, lower in FIG. 1 and called the half-shell downstream, because intended to accommodate the downstream parts of air tubes as opposed to the upper 2 half shell in FIG. 1, called the upstream half-shell, since it is intended to accommodate the upstream parts of the air tubes. The flange 6 has also, for each cylinder, a housing 9 for a fuel injector, this housing 9 opening in the face 10 of the flange 6 which is opposite to the face 8 for fixing to the cylinder head, and outside the half-shell 3, of a part, and, on the other hand, each housing 9 opens into a corresponding feed opening 7. The flange 6 finally has holes 11, also from molding like openings 7 and housings 9, for passage of collector fixing elements on the cylinder head.

The collector also includes a curved tube air intake for each cylinder, or, as already mentioned, four air tubes grouped into two pairs of tubes joined together over part of their length.

Each tube, such as 12a or 12b of the pair of tubes of FIG. 2, is a curved tube, obtained by cutting, perpendicular to its longitudinal axis, a length determined, to give the tube 12a or 12b an impedance acoustic tuned to the engine, in a large tube length in thermoplastic, having an internal face 13 smooth, delimiting a central passage of cross section of constant shape and surface, for example circular, and a corrugated external face 14, with peripheral rings in planes substantially parallel to each other and perpendicular to the axis of the tube, before the tube section cut is not bent to the desired shape by the closure half-shells 2 and 3, each of which each tube 12a or 12b is fixed only by one respectively of its inlet ends such as 15a and outlet ends 16a or 16b. A light tube 12a or 12b is thus produced, with a thin wall and waterproof, having great flexibility or transverse flexibility or radial, and low flexibility or flexibility axial, so that it can be bent to the desired shape without losing the constant shape and surface of the section transverse of its central passage with smooth wall, and without vary significantly in length, which ensures losses of practically constant load and acoustic impedance. Each tube such as 12a or 12b is bent in a loop almost complete in the plan of figure 1, on a large part of its length substantially from its entrance such as 15a, and its downstream part is further angled or bent in a direction perpendicular to the plane of Figure 1, as shown in Figure 2. Thanks to their curved shapes, two tubes such as 12a and 12b, grouped into a pair of tubes to supply each one respectively of two adjacent cylinders, can be joined on much of their length substantially from their inputs such as 15a, while their outputs 16a and 16b (see Figure 2) are spaced from each other to each be tightly connected to one respectively two adjacent supply openings 7 one of the other in the flange 8 to supply the two cylinders corresponding contiguous.

The inlet end such as 15a of each tube 12a or 12b is fixed to the upstream half-shell 2 by a air inlet sleeve such as 17a, while the end outlet 16a or 16b of the tube is connected to the half-shell downstream 3 by an air outlet sleeve 18a or 18b, each of sleeves 17a, 18a or 18b being preferably molded in a synthetic material, preferably thermosetting.

The inlet sleeve 17a comprises a tubular part 19a which is forced into the end inlet 15a of the tube 12a, and which extends towards the front, outside this entry 15a, by a shaped part in volute or inlet tulip 20a converging inwards from tube 12a and downstream. This entrance tulip 20a has a fixing lug 21a, by which the sleeve 17a is fixed to the half-shell 2 at at least one point, by example by heat sealing or by a dowel, as shown schematically in 22a. To reduce pressure drops, the internal face of the tubular part 19a is smooth, and substantially in line with the smooth internal face 13 of the tube 12a, while to ensure a good fit axial of the sleeve 17a in the inlet 15a of the tube 12a, the face outer of the tubular part 19a has redents peripherals, as described below for the output 18a with reference to Figure 5.

Each outlet sleeve 18a or 18b includes, as shown for the sleeve 18a in FIG. 5, a part tubular 23a which is force fitted into outlet 16a of tube 12a, and which extends backwards or towards downstream, outside this exit 16a, by a part tubular 24a external to tube 12a and retained on the half-shell 3 while being connected with sealing at the opening 7 corresponding as described below. The parts 23a and 24a, between which the sleeve 18a has an annular stop 25a projecting radially outwards to limit fitting in outlet 16a of the tube 12a, have a smooth internal face, substantially in the extension of the smooth internal face 13 of the tube 12a, while that the external face of the fitted part 23a has two peripheral and axially offset redents 26a, each formed at the axial end, facing the stop 25a, of a substantially frustoconical surface 27a with small turned base towards the end of the innermost part 23a of the tube 12a, so as to facilitate penetration at the fitting and to ensure good anchoring.

A flexible, annular seal 28, molded made of elastomer with the sectional shape shown on the Figure 4, is mounted around the outer part 24a of the sleeve 18a, and this external part 24a surrounded by the seal 28 is introduced into a cradle 29a, molded in one part with the half-shell 3 and the flange 6. This cradle 29a protrudes from the flange 6 on the side opposite the cylinder head of the engine and substantially in the shape of an open semi-cylinder towards the joint plane P, with a cross section of substantially constant surface U-shape, defining a central duct which extends a corresponding opening 7 towards the inside of the half-shell 3. At its end in the half-shell 3, the cradle 29a has a chamber annular delimited by a projecting U-shaped bottom 30a radially inward of the cradle 29a to form a stop opposing the axial outlet of the seal 28 on the external part 24a of the sleeve 18a. During this implementation place of the external part 24a in the cradle 29a, the seal seal 28 around the sleeve 18a is compressed radially between the sleeve 18a and the cradle 29a. The restraint of the part 24a of the sleeve 18a in the cradle 29a of the half-shell 3 and its tight connection to the opening 7 corresponding, thanks to the gasket 28, are completed by a flat cover 31a attached transversely to the part 24a of the sleeve 18a engaged in the cradle 29a, and leaning by its periphery against the edges of this cradle 29a, the cover 31a having a rim 32a in inwardly projecting arcuate abutment shape of cradle 29a, and opposite the U-shaped bottom 30a of this last, so that the rim 32a and the bottom in the shape of U 30a together form an annular stop. This cover 31a is molded in synthetic material, preferably thermoplastic, and preferably ultrasonically welded to its around the edges of the cradle 29a. Maintaining the sleeve 18a and the tightness of its connection to the opening 7 corresponding are thus ensured thanks to the seal 28 and to a tubular manifold end, formed by the cradle 29a and the corresponding cover 31a. As shown in the section of Figure 4, the seal 28 is molded with a sectional shape such that it occupies radially all the space available between the part 24a of the sleeve 18a, in the center, and the cradle 29a and the cover 31a, at the periphery, being compressed radially between these parts. Beyond the joint 28 and towards the opening 7, the part 24a of the sleeve 18a is extended by a half-cylinder-shaped end open towards the bottom of the cradle 29a which receives it, and having, as shown in the section of FIG. 3, a recess complementary to that of the cradle 29a for define a duct of progressively variable section connecting the outlet, for example circular, 16a of the tube 12a to the section, for example oblong, of the opening 7 corresponding, as shown in the drawings. The sleeve outlet 18a is molded so that its central passage presents this corresponding section evolution, the section of the end of the sleeve 18a fitted into the tube 12a always having the same shape as the section of the tube 12a, and the section of the end of the sleeve 18a facing opening 7 having, alone or with the section complementary to the bottom of the cradle 29a which receives it, the same forms as the section of the opening 7.

The outlet sleeve 18b of the tube 12b is mounted from the same way with a seal such as 28 in one manifold tip consisting of a similar cradle 29b closed by a corresponding analog cover.

To limit their transverse movements, the two tubes 12a and 12b are also arranged, by their adjoining parts, in a housing delimited in the half-shell downstream 3 by a recess between ribs 33 in projection on the internal face of this half-shell 3.

Tubes 12a and 12b can be joined so that the rings of the external face of one are engaged between each other’s rings, and possibly ribs 33 bordering the housings may have protrusions engaging between the outer rings of the tubes 12a, 12b to better position them in the envelope 1.

As tubes 12a and 12b flexible transversely are fixed to the casing 1 by their only ends, the mounting of the sleeves 17a and 18a is carried out to give the tubes a general radius of curvature which is slightly less at the radius of curvature of the rounded parts of the half-shells 2 and 3 of envelope 1.

The transverse flexibility of the tubes allows, during assembling the half-shells 2 and 3, small displacements alternating relative of these in the perpendicular direction to the radius of curvature of the tubes, thus providing the possibility of assembling the half-shells 2 and 3 for example by vibration welding.

A collector is thus obtained, the envelope 1 of which delimits an internal chamber 34, called plenum, which is supplied with engine feed air through an opening (not shown) for example formed in an end face of the envelope 1 parallel to the plane of FIG. 1, this opening being connected to a butterfly body. Each tube such as 12a or 12b mounted in the casing 1 sucks from the air in plenum 34 by its entry such as 15a and transmits this air through its outlet 16a or 16b to an opening supply 7 of the flange 6 to supply a cylinder corresponding. We understand that the envelope 1 contains, in its half not shown in Figure 2, two other tubes symmetrical air suction tubes 12a and 12b and mounted in the same way.

Claims (14)

1. Inlet manifold for an internal combustion engine and comprising:

   an envelope (1), delimiting a plenum chamber (34) intended to be supplied with air for supplying the engine, and equipped with at least one flange (6) for attaching it to at least one cylinder head of the engine, the said flange or flanges having at least one opening (7) for supplying each cylinder of the engine, each supply opening (7) opening, on the one hand, into the envelope (1) and, on the other hand, into a face (8) for attaching the flange (6) to the said cylinder head, and

   curved air-induction tubes (12a, 12b) each made as a single piece, and of which there are at least as many as there are cylinders in the engine, and which are mounted in the envelope (1) so that each tube supplies a corresponding cylinder with air which it receives via its inlet (15a) in the plenum chamber (34) and which it transmits to the corresponding opening (7) in the corresponding flange (6) via its outlet (16a, 16b) connected by leaktight connecting means to the said supply opening (7), characterized in that each tube (12a, 12b) is a tube with a ringed external face (14) and a smooth internal face (13) delimiting a central passage with a cross section which is constant in terms of shape and in terms of surface-area, so that the tube (12a, 12b) has great transverse suppleness or flexibility but low axial suppleness or flexibility.
2. Inlet manifold according to Claim 1, characterized in that each tube (12a, 12b) is made of a synthetic material, preferably a moldable one, such as a thermoplastic, and is preferably of circular section.
3. Inlet manifold according to either of Claims 1 and 2, characterized in that the ringed external face (14) of each tube (12a, 12b) is a cylindrical surface of revolution with a wavy generatrix before the tube is bent into the desired shape.
4. Inlet manifold according to any one of Claims 1 to 3, characterized in that the envelope (1) consists of two half shells (2, 3) of complementary shapes corresponding to the shape of the envelope (1) and which are molded, preferably of a moldable synthetic material, preferably thermoplastic, with attachment flanges (4, 5) on their peripheral edges in a parting plane (P), the half shells (2, 3) being closed and fixed together at their attachment flanges (4, 5), for example by welding, preferably vibration welding, and each tube (12a, 12b) is fixed to the half shells (2, 3) only by its ends (15a, 16a, 16b).
5. Inlet manifold according to Claim 4, characterized in that at least one of the ends (15a, 16a) of each tube (12a) is fixed to a half shell (2, 3) using a sleeve (17a, 18a) which is partly (19a, 23a) force-fitted into the corresponding end (15a, 16a) of the tube and held on the said half shell (2, 3) by a sleeve part (20a, 24a) external to the tube (12a).
6. Inlet manifold according to Claim 5, characterized in that on the external face of its part (23a) that is pushed into a corresponding end (16a) of the tube (12a), the sleeve (18a) has at least one peripheral anchoring tooth (26a) which is formed at the axial end pointing toward the said end (16a) of the tube (12a), with a more or less frustoconical surface (27a) with the small base pointing toward the central part of the tube (12a).
7. Inlet manifold according to either of Claims 5 and 6, characterized in that the sleeve (18a) has at least one stop (25a) projecting more or less radially outward to limit the extent to which it can be pushed into a corresponding end (16a) of the tube (12a).
8. Inlet manifold according to one of Claims 5 to 7, characterized in that the sleeve (17a, 18a, 18b) is molded of a synthetic material, preferably a thermoset.
9. Inlet manifold according to any one of Claims 5 to 8, characterized in that at least one air inlet sleeve (17a) pushed (19a) into an inlet end (15a) of a tube (12a) is shaped, in its part external to the said inlet end (15a) of the tube (12a) as a bell housing (20a) that converges toward the inside of the tube (12a) and is equipped with at least one lug (21a) for attaching it to that one (2) of the two half shells (2, 3) which does not have the attachment flange (6) with the supply opening (7) to which the said tube (12a) is connected by its outlet (16a).
10. Inlet manifold according to any one of Claims 5 to 9, characterized in that each tube (12a) is connected by an air outlet sleeve (18a) pushed (23a) into the outlet end (16a) of the tube (12a) to that one (3) of the half shells (2, 3) which has the said attachment flange (6) with the said supply opening (7) to which the said tube (12a) is connected in leaktight fashion by its outlet (16a), the said leaktight connection means comprising a tubular manifold end piece (29a - 31a) projecting from the said flange (6) on the opposite side to the cylinder head, in line with the said corresponding supply opening (7) and in which end piece part (24a) of the said outlet sleeve (18a), external to the tube (12a), is held with the insertion of at least one flexible seal (28) between the said external part (24a) of the outlet sleeve (18a) and the said manifold end piece (29a - 31a).
11. Inlet manifold according to Claim 10, characterized in that the said manifold end piece comprises:

    a cradle (29a) molded as a single piece with the said half shell (3) and the said corresponding attachment flange (6), and of a more or less semicylindrical shape, of which the end internal to the said half shell (3) has a U-shaped bottom (30a) forming a stop projecting toward the inside of the cradle (29a), and

    an attached cover (31a) for holding the outlet sleeve (18a) and the seal or seals (28) which are mounted on the latter in the cradle (29a), the said cover (31a) having a stop (32a) projecting toward the inside of the cradle (29a) opposite the U-shaped bottom (30a) of the cradle (29a) and being fixed to the edges of the cradle (29a) preferably by ultrasound welding.
12. Inlet manifold according to Claim 11, characterized in that it comprises, for each tube (12a), a single flexible seal (28) mounted around that part (24a) of the corresponding outlet sleeve (18a) which is external to the tube (12a) and held in the corresponding manifold end piece (29a - 31a) and molded into a shape, preferably from elastomer, with a cross section that corresponds to that of the space available between, on the one hand, the said outlet sleeve (18a) and, on the other hand, the said cradle (29a) and the said cover (31a) and so that the seal (28) is compressed radially between these three components.
13. Inlet manifold according to any one of Claims 10 to 12, characterized in that each manifold end piece (29a - 31a) has a cross section which is more or less the same shape as the corresponding supply opening (7) and in that the corresponding outlet sleeve (18a) has a central passage which has a cross section of changeable shape, this shape varying progressively from the cross-sectional shape of the manifold end piece (29a - 31a), in that part (24a) of the outlet sleeve (18a) which is external to the tube (12a), to the cross-sectional shape of the tube (12a), in that part (23a) of the outlet sleeve (18a) which is pushed into the outlet end (16a) of the tube (12a).
14. Inlet manifold according to any one of Claims 1 to 13, characterized in that in the envelope (1) the tubes (12a, 12b) are grouped at least in pairs of tubes that touch over at least part of their length, and the transverse displacements of the groups of touching tubes in the envelope (1) are limited by housings delimited by recesses in the internal face of the envelope (1) and in which touching parts of the tubes (12a, 12b) are housed.

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