EP0839273B1 - Intake manifold for internal combustion engine - Google Patents

Abstract

Between the two half-molds (2, 3) fixed against each other in order to form an envelope (1), one-piece blow-molded air tubes (12a, 12b) are mounted; the outlet (14a, 14b) of the tubes is held in a half-mold (3) by means of a fixing clamp (6) to the cylinder-head of the engine while being sealingly connected to an opening (7) of the clamp (6) for supplying one cylinder by means of a tubular nozzle formed of a cradle (20a, 20b) molded with the clamp (6) and the half-mold (3), and a staple (22a, 22b) fixed to the cradle to hold a ring (17) on the outlet of the tube while compressing a seal (18) between the tubes (12a, 12b) and the nozzle. Application particularly to intake manifolds of engines with multipoint injection and 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 par une vanne à débit variable, telle qu'un corps de papillon, et munie d'au moins une bride de fixation à 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 à la forme voulue, 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 que le tube reçoit par son entrée dans le plenum et que le tube transmet à une ouverture correspondante d'une bride par sa sortie reliée à ladite ouverture d'alimentation par des moyens de raccordement étanches comprenant un embout tubulaire dans lequel la partie d'extrémité de sortie dudit tube est retenue dans ladite enveloppe, avec interposition d'au moins un joint d'étanchéité souple entre le tube et l'embout.

More specifically, the invention relates to such an intake manifold, more particularly intended to equip a spark-ignition engine, and which comprises, as known by US-A-5,003,933:

• an envelope, delimiting a plenum intended to be supplied with air supplying the engine by a variable flow valve, such as a throttle body, and provided with at least one clamp for fixing to a cylinder head of the engine, the or said flanges 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 face for fixing the flange to said cylinder head , and
• curved air suction tubes, each in one piece with the desired shape, in number at least equal to that of the engine cylinders, and mounted in the envelope, so that each tube feeds a corresponding cylinder in air which the tube receives by its entry into the plenum and which the tube transmits to a corresponding opening of a flange by its outlet connected to said supply opening by sealed connection means comprising a tubular end piece in which the part of outlet end of said tube is retained in said envelope, with the interposition of at least one flexible seal between the tube and the end piece.

We already know how to manufacture similar collectors 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 can be formed by 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 can be formed by the bottoms molded imprints in two molded inserts, in general in the same material as the half-shells, for example in polyamide loaded with reinforcing fibers, and each reported in one of the half-shells respectively, so that the imprints of the inserts also extend during the joining of the half-shells one against the other. This process therefore 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, good tightness, especially at the air tubes, be assured.

For this purpose, a seal must be made between the inserts and the half-shells by laying strings of polymerizable material appropriate, which is a long and delicate operation, adding to the difficulty of realization with low tolerances of the four parts to be assembled for precisely define the air tubes.

In the case of a collector according to US-A-5,003,933, each tube air is either in one piece with the desired shape, as already mentioned above, either made by assembling two complementary halves molded into shape. But this assembly, despite the precautions taken, does not generally not allow to obtain an internal surface of each tube which be completely smooth and continuous, without roughness, from its entry to its exit, except to finish this surface by a special machining, when the geometry of the tubes permits.

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

The problem underlying the invention is to propose a collector of an advantageous structure, in particular for the connection of each tube to the manifold fixing flange to the engine cylinder head, the structure being essentially in a thermomouldable, semi-modular plastic, because acoustically adaptable to a whole family of displacement engines different by dimensional adjustment, and capable of being carried out by a more economical manufacturing process.

To this end, the intake manifold according to the invention, of the type presented above, is characterized in that the internal surface of each tube is smooth, and continues from its entry to its exit and in that each end piece is made with, on the one hand, a cradle in one piece with said mounting flange, and projecting from the side opposite the cylinder head, in the extension of said corresponding feed opening, the cradle being of substantially semi-cylindrical shape, the end internal to said envelope has an annular bottom forming an inwardly projecting stop of the cradle, and, on the other hand, a jumper for holding said tube in said cradle, the rider having a stop protruding towards the inside of the cradle and opposite the annular bottom of the cradle, a ring being attached and fixed around said tube, near its air outlet, said flexible seal being attached around said tube, between said ring and said air outlet of the tube, the outlet end portion of said tube with said ring and said seal sealing being in place in said corresponding cradle, so that the ring or the seal is retained by abutment against said annular bottom of the cradle, said rider being attached to said cradle and the part of the tube housed in the latter, and being fixed on the edges of the cradle.

The characteristic that the internal surface of each tube is smooth and continuous from entry to exit should be understood as meaning that this internal surface has no roughness or unevenness, between two adjacent parts of internal surface, which is greater than about 200ìm.

Monoblock air tubes being inherently sealed, the need to make seams of joints or welds of connection between two complementary halves disappears.

The intake manifold according to the invention is distinguished essentially state-of-the-art collectors by manufacturing air intake tubes and by the connection of each tube to the fixing flange from the manifold to the engine cylinder head.

The intake manifold according to the invention is advantageously such that its envelope includes two molded half-shells, of shapes complementary to the shape of the envelope, and arranged one against each other and joined to each other by their peripheral rim, in a joint plane, to form the envelope with the tubes between them, each tube being blow molded, and preferably by suction-blowing, in a material thermally moldable plastic, and said fixing flange being in one piece with one of the half-shells.

Advantageously, the collector is further such that each tube is made with a section gradually decreasing downstream on at least part of its length and / or with a converging air inlet, shaped tulip; each tube can be made with a section having substantially the same shape from entry to exit air, and which can be a circular section or, advantageously as specified below, an oblong section.

Advantageously, 'in addition, to facilitate the fixing the air tubes in the half-shells, the tubes are grouped at least in pairs of tubes attached to at at least part of their length, and the tubes of each group of tubes are fixed in the same half-shell provided a mounting flange with supply openings to which the tubes of said group are connected with sealing, using at least a second jumper which transversely overlaps the joined tubes of said group, in their adjoining part, which is fixed by its ends on said half-shell.

For this purpose, it is advantageous that each tube is made with an oblong section and parallel flats to the major axis of its section, on its opposite opposite faces, and the tubes are grouped together by being joined by their flats.

In a simple way, the half-shells with their bases, on the one hand, and the second jumpers, on the other hand, may be molded plastic parts, and the second jumpers can be fixed on a half-shell corresponding by welding or gluing.

Advantageously, the tubes can be made curved with a radius of curvature, in the plane containing their axis, lower than that of the envelope, the envelope half-shells being molded of material plastic with clamps on their edges in the joint plane, and the half-shells are secured together to form the envelope by welding, preferably by vibration, at the clamps. Indeed, this geometry of the tubes bent by relation to the geometry of the envelope, as well as the mode of fixing of the tubes in the half-shells, which avoid contact points, and therefore friction between the tubes and the half-shells, allow the half-shells to be joined together economically, by vibration welding at the level of their fastening flanges, a known manner, without risk of rupture of the tubes.

Advantageously, in addition, each end piece ensures the retaining a corresponding tube on one of the half-shells which each cradle is integral with.

In particular, when the tubes are of section transverse circular, sealing can be ensured between the outlet end portion of each tube and the corresponding end piece by axial compression of said seal sealing, which is cylindrical, by its planar faces end between a flat radial face, facing the tube outlet, tube ring and a radial face flat, facing inward of said envelope, cradle and said flange, said radial faces being substantially perpendicular to the axis of the tube at its exit.

However, when the air tubes have advantageously an oblong cross section, as specified above, it is advantageous that each cradle and the corresponding jumper are molded so that the tip formed by the cradle and the rider has a cross section gradually evolving from a shape circular, on the side of the mounting flange and its circular feed opening, oblong in shape, complementary to that of the tubes.

In this case, the seal between the end part outlet of each tube and the corresponding nozzle is advantageously provided by radial compression of said seal sealing between, on the one hand, the tube, and, on the other hand, the cradle and the corresponding rider.

• 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 ou inférieure du collecteur de la figure 1, avec une des deux paires de tubes qui sont regroupés et retenus dans cette demi-coquille,
• les figures 3, 4 et 5 sont des coupes transversales respectivement selon III-III, IV-IV, V-V de la figure 1,
• la figure 6 est une vue en coupe axiale d'un tube d'air,
• la figure 7 est une vue en partie en coupe et en partie en élévation verticale de la paire des deux tubes regroupés représentés sur la figure 2, avant son montage dans la demi-coquille correspondante,
• la figure 8 est une vue schématique de face des entrées d'air des deux tubes de la figure 7, vues selon la flèche de la figure 6,
• les figures 9, 10 et 11 sont une vue et deux demi-vues schématiques représentant trois exemples de joints d'étanchéité souples comprimés radialement entre un tube et l'embout du collecteur correspondant,
• les figures 12 et 13 sont des vues correspondant respectivement aux figures 1 et 2 pour un second exemple de réalisation,
• les figures 14 et 15 sont des coupes transversales respectivement selon XIV-XIV et XV-XV de la figure 12, et
• la figure 16 est une demi-vue en coupe schématique d'un joint d'étanchéité cylindrique comprimé axialement et monté entre un tube et l'embout du collecteur correspondant.

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 or lower half-shell of the collector of Figure 1, with one of the two pairs of tubes which are grouped and retained in this half shell,
• FIGS. 3, 4 and 5 are cross sections respectively along III-III, IV-IV, VV of FIG. 1,
• FIG. 6 is a view in axial section of an air tube,
• FIG. 7 is a view partly in section and partly in vertical elevation of the pair of the two grouped tubes represented in FIG. 2, before its mounting in the corresponding half-shell,
• FIG. 8 is a schematic front view of the air inlets of the two tubes of FIG. 7, seen along the arrow in FIG. 6,
• FIGS. 9, 10 and 11 are a schematic view and two half-views showing three examples of flexible seals compressed radially between a tube and the end of the corresponding manifold,
• FIGS. 12 and 13 are views corresponding respectively to FIGS. 1 and 2 for a second example of embodiment,
• FIGS. 14 and 15 are cross sections respectively along XIV-XIV and XV-XV of FIG. 12, and
• Figure 16 is a schematic half-sectional view of a cylindrical seal axially compressed and mounted between a tube and the tip of the corresponding manifold.

The manifold of Figures 1 and 2, for a motor with four cylinders in line, includes a rigid casing 1, made of moldable and heat-sealable plastic of two half-shells 2 and 3, each molded in this material, having complementary shapes which correspond to the shape of the envelope 1. The two half-shells 2 and 3 close against each other, by their edges peripherals, to reconstruct the shape of envelope 1, and are joined to each other in a joint plane P, defined by fastening flanges 4 and 5, in protruding outwards on their edges, by welding vibrations at these flanges 4 and 5, after assembly in the half-shells 2 and 3 of four suction tubes air (one per engine cylinder), grouped in two pairs of attached tubes, as shown in Figure 2 and described below with reference to Figures 6 to 8.

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 cross section, which opens on one side into the flat face 8 for fixing the flange 6 to the cylinder head of the motor and, on the other side, inside the half-shell 3, lower in FIG. 1 and called the half-shell downstream, since it is intended to house the downstream parts of the air tubes, as opposed to the upper half-shell 2 in the figure 1, called the upstream half-shell, since it is intended to house the upstream parts of the air tubes. The flange 6 also has, for each cylinder, a housing 9 for an injector of fuel, 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, on the one hand, 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 tube 12 in Figure 6, is a curved tube molded in one piece from a material blow molded plastic, or more precisely by the known process of suction-blowing. We realize thus a light, relatively rigid, thin-walled tube 12 and waterproof, with smooth internal and external surfaces. In in particular, the internal surface of the tube 12 is smooth and continues from entry to exit. By smooth and continuous, it should be understood that this internal surface does not have roughness or unevenness between two adjacent parts with a surface that is greater than about 200 µm.

In this example, each tube such as 12 is molded with a volute or tulip shaped air inlet 13 converging downstream, and the cross-sectional area of the tube gradually decreases from its entry 13 to its exit 14, from preferably around 10% of its input cross-section, while that the shape of the section of the tube is constant input 13 to its output 14, and, in this example, is a oblong shape, visible in FIGS. 7 and 8, the wall of each tube having two opposite flats 15 parallel to the major axis 16 of the oblong section of the tube. Each tube as that 12 is bent in an almost complete loop in the plane of Figure 6, over most of its length from its entry 13, and its downstream part is more bent or bent in a direction perpendicular to the plan of Figure 6, as shown in Figures 2 and 7. Thanks to the 15 flats and their curved shapes, two tubes such as 12a and 12b, grouped into a pair of tubes to supply each one of two cylinders respectively adjacent, can be joined by their flats 15 on the most of their length from their entrances 13a and 13b (see Figure 8), while their outputs 14a and 14b (see Figure 7) are separated from each other to be each tightly connected to one respectively two adjacent supply openings 7 one of the other in the flange 8 to supply the two cylinders correspondents.

A ring 17, for example made of plastic heat-sealable, with an internal section corresponding to the shape and on the surface at the external section of each tube such as 12 to near its outlet 14, is attached and fixed by heat sealing, for example by the known method of welding said "by mirror", around the tube near its outlet 14, to form an annular shoulder projecting radially towards outside. Then a flexible and annular seal 18, which may, by way of nonlimiting examples, be lip seal 18a of FIG. 9, the section seal cruciform 18b of Figure 10 or the O-ring 18c of the Figure 11, is mounted around the end portion of outlet of each tube such as 12, between its ring 17 and its outlet 14. The two tubes 12a and 12b grouped in pairs of joined tubes, as in FIG. 7, with their ring 17 and their seal 18 (not shown in Figure 7) are then placed in the downstream half-shell 3. The end outlet, with ring 17 and seal 18, of each of the tubes 12a and 12b is introduced into a cradle 20a and 20b respectively molded in one piece with the half-shell 3 and the flange 6. This cradle 20a, 20b 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 and delimiting 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, each cradle 20a, 20b has an annular chamber delimited by an annular bottom 21a, 21b projecting radially towards the inside of the cradle 20a, 20b, to form a stop opposing the axial exit of the ring 17 and the seal 18 on the outlet end of the tube 12a, 12b. During this positioning of the outlet end of the tube 12a or 12b in the cradle 20a or 20b, the seal 18 (such as 18a, 18b or 18c), around the tube is compressed radially between the tube and the cradle 20a, 20b. Restraint of each of the tubes 12a and 12b in the cradle 20a or 20b of the half-shell 3 and its tight connection at the opening 7 corresponding, thanks to the seal, are completed by a jumper 22a or 22b reported transversely on the end part of the tube engaged in the cradle 20a or 20b, and bearing by its periphery against the edges of this cradle, the rider 22a, 22b having a rim 23a, 23b in the form of an annular bottom projecting inwards of the cradle 20a, 20b, and opposite the flange 21a, 21b of this latest. This jumper 22a, 22b is molded in plastic material and welded by ultrasound on its periphery on the edges of the cradle 20a or 20b. Maintaining the tube and sealing its connection to the corresponding opening 7 are thus ensured thanks to the gasket and a manifold tip, formed by the cradle 20a or 20b and the rider 22a or 22b corresponding, the latter having, as shown on the sections Figures 4 and 5, a recess complementary to that of cradle 20a or 20b to define a section duct progressively variable connecting the oblong outlet 14a or 14b from the tube to the circular section of the opening 7 corresponding, as represented by the section of the figure 3. The cradle 20a, 20b as well as the rider 22a, 22b corresponding are molded so that their recesses present this corresponding section evolution.

The two tubes 12a and 12b are also retained in the downstream half-shell 3 by a second jumper 24, also molded from plastic, which overlaps transversely these two tubes 12a and 12b in their part attached, and is preferably fixed by stoppers in plastic material 25, projecting towards the joint plane P in the half-shell 3, and engaged in orifices at ends of the second jumper 24, to then be crushed thermally on the latter. Thus, the jumper 24 maintains the tubes 12a and 12b applied against a base 26 of support, formed by an extra thickness of the half-shell 3, projecting towards the interior of the latter.

As tubes 12a and 12b were molded by blowing with a general radius of curvature which is less at the radius of curvature of the rounded parts of the half-shells 2 and 3 of envelope 1, this avoids contacts and friction between the tubes and the half-shell upstream 2, during vibration welding of the two half-shells 2 and 3 against each other, which imposes small relative alternating displacements of the half-shells 2 and 3 causing friction between the flanges 4 and 5 leading to a heat seal. We note, moreover, that the contacts between the tubes and the downstream half-shell 3 are limited to contact with the jumper 24 and the base 25 and in contact with the ring 17 of the outlet end of the tubes 12a, 12b with the tubular end piece constituted by the cradle 20a or 20b and the jumper 22a or 22b, so that we avoid any possible source of disruptive friction between tubes and the two parts of the envelope, which can lead to ruptures during the vibration welding phase, which constitutes the final assembly phase of the collector.

A collector is thus obtained, the envelope 1 of which delimits an internal chamber 27, called plenum, which is supplied with engine feed air through an opening (not shown) for example formed in the center of a end face of the envelope 2 parallel to the plane of Figure 1, this opening being connected to a body of butterfly. Each tube such as 12a or 12b mounted in the envelope 1 draws air into plenum 27 through its inlet 13a or 13b and transmits this air through its outlet 14a or 14b to a supply opening 7 of the flange 6 for supplying a corresponding cylinder. We understand that envelope 1 contains, in its half not shown in Figure 2, two other symmetrical air intake tubes 12a and 12b and mounted in the same way.

The example of an intake manifold in Figures 12 and 13 has many features in common with the one just described, so the elements analogs are identified by the same reference numbers assigned a prime symbol, and which we are satisfied with below to describe the differences presented by this second example compared to the first.

First, the tubes 12'a and 12'b are of section transverse circular. However, they are also joined for part of their length and are applied by a jumper 24 'against a support base 26' to inside the downstream half-shell 3 ', the jumper 24' being, as in the previous example, fixed by bolting or heat sealing on pins 25 'of this half-shell 3 '.

Similarly, the outlet ends of the tubes 12'a and 12'b are surrounded by a 17 'ring and a seal flexible 18 'and are each connected so watertight at a corresponding opening 7 'of the flange of fixing 6 'to the cylinder head by a tubular end piece. But in this example, the latter consists of a cradle 20'a or 20'b of U-shaped cross section and value constant, with an annular bottom forming a radial stop internal 21'a or 21'b, on the side of the half-shell 3 ', thus than a basically flat rider 22'a or 22'b with a 23'a or 23'b arc-shaped abutment projecting inwards of the cradle 20'a or 20'b and opposite the annular bottom 21'a or 21'b of the latter. The manifold tip as well made for each outlet end of a 12'a tube or 12'b is preferably of circular cross-section of diameter constant, with one face, oriented towards the corresponding tube which is flat and perpendicular to the axis of the tube in its outlet end part. The cylindrical seal 18 'is, in this example, compressed axially by its two radial and planar end faces between, of a side, the planar radial face of the ring 17 'which is turned towards the flange 6 'and, on the other side, a radial face flat, facing inward of the 3 'half-shell, in the bottom of the corresponding cradle 20'a or 20'b, on the flange 6 ', these different radial faces being substantially perpendicular to the axis of the tube 12'a or 12'b at its outlet.

In the two examples described above, the tubes as the half-shells can be made in one plastic material such as polyamide, loaded with fibers reinforcement.

Claims (12)

1. Inlet manifold for an internal combustion engine, preferably a fuel-injected engine, particularly one with multipoint injection, the manifold comprising:

   an envelope (1, 1') delimiting a plenum chamber (27, 27') intended to be supplied with air for supplying the engine via a variable-delivery valve, such as a butterfly valve, and equipped with at least one flange (6, 6') for attaching it to a cylinder head of the engine, said flange or flanges having at least one opening (7, 7') for supplying each cylinder of the engine, each supply opening (7, 7') opening, on the one hand, into the envelope (1, 1') and, on the other hand, into a face (8, 8') for attaching the flange (6, 6') to said cylinder head, and

   curved air-induction tubes (12a, 12b, 12'a, 12'b) each made as a single piece with the desired shape, and of which there are at least as many as there are cylinders in the engine, and which are mounted in the envelope (1, 1') so that each tube supplies a corresponding cylinder with air which the tube receives via its inlet (13a, 13b, 13'a, 13'b) in the plenum chamber (27, 27') and which the tube transmits to a corresponding opening (7, 7') in a flange (6, 6') via its outlet (14a, 14b, 14'a, 14'b) connected to said supply opening (7, 7') by leaktight connection means comprising a tubular end piece (20a-22a, 20b-22b, 20'a-22'a, 20'b-22'b) in which the outlet end part of said tube is held in said envelope (1, 1') with the insertion of at least one flexible seal (18a, 18b, 18c, 18') between the tube and the end piece,

   characterized in that the internal surface of each tube (12a, 12b, 12'a, 12'b) is smooth and continuous from its inlet (13a, 13b, 13'a, 13'b) to its outlet (14a, 14b, 14'a, 14'b), and in that each end piece is made with, on the one hand, a cradle (20a, 20'a) integral with said attachment flange (6, 6') and projecting from the opposite side to the cylinder head, in line with said corresponding supply opening (7, 7'), the cradle being of a more or less semi-cylindrical shape, of which the end inside said envelope (1, 1') has an annular end wall (21a, 21'a) forming a stop projecting toward the inside of the cradle (20a, 20'a) and, on the other hand, a stirrup piece (22a, 22'a) for holding said tube (12a, 12'a) in said cradle (20a, 20'a), said stirrup piece (22a, 22'a) having a stop (23a, 23'a) projecting toward the inside of the cradle (20a, 20'a) and facing the annular end wall (21a, 21'a) of the cradle, a ring (17, 17') being attached and fixed around said tube (12a, 12'a) close to its air outlet (14a, 14'a), said flexible seal (18a, 18b, 18c, 18') being attached around said tube (12a, 12'a) between said ring (17, 17') and said air outlet (14a, 14'a) of the tube (12a, 12'a), the outlet end part of said tube (12a, 12'a) with said ring (17, 17') and said seal being in place in said corresponding cradle (20a, 20'a) in such a way that the ring (17, 17') or the seal (18, 18') is retained by butting against said annular end wall (21a, 21'a) of the cradle (20a, 20'a), said stirrup piece (22a, 22'a) being attached to said cradle (20a, 20'a) and that part of the tube (12a, 12'a) which is held therein, and being fixed to the edges of the cradle (20a, 20'a).
2. Inlet manifold according to Claim 1 characterized in that the envelope (1, 1') comprises two molded half shells (2, 3; 2', 3') with complementary shapes corresponding to the shape of the envelope (1, 1') and arranged one against the other and secured together via their peripheral edges (4, 5; 4', 5') in a parting plane (P), to form the envelope with the tubes (12a, 12b, 12'a, 12'b) between them, each tube being blow molded, and preferably suction blow-molded, from a thermomoldable plastic, and said attachment flange (6, 6') being integral with one of said half shells (3, 3').
3. Inlet manifold according to one of Claims 1 and 2, characterized in that each tube (12) is made with a section that decreases progressively in the downstream direction over at least part of its length and/or with a convergent bell-socket-shaped air inlet (13).
4. Inlet manifold according to one of Claims 1 to 3, characterized in that each tube (12) is made with a section that has more or less the same shape from its air inlet (13) to its air outlet (14).
5. Inlet manifold according to one of Claims 2 to 4, characterized in that the tubes are grouped at least in pairs of tubes (12a-12b; 12'a-12'b) that touch over at least part of their length, and the tubes of each group of tubes (12a-12b; 12'a-12'b) are fixed into one and the same half shell (3, 3') which has an attachment flange (6, 6') with supply openings (7, 7') to which the tubes of said group are connected in leaktight manner, using at least one second stirrup piece (24, 24') which transversely straddles the touching tubes (12a, 12b; 12'a, 12'b) of said group, in their touching part, and which is attached via its ends to said half shell (3, 3').
6. Inlet manifold according to Claim 5, characterized in that each tube (12) is made with an oval section and flats (15), parallel to the major axis (16) of its section, on its opposed facing faces, and the tubes (12a-12b) are grouped together, touching along their flats (15).
7. Inlet manifold according to either of Claims 5 and 6, characterized in that the half shells (2, 3; 2', 3') with their bases (26, 26'), on the one hand, and the stirrup pieces (24, 24'), on the other hand, are components molded from plastic, and the second stirrup pieces (24, 24') are fixed to the corresponding half shells (2, 3; 2', 3') by welding or snap riveting.
8. Inlet manifold according to one of Claims 2 to 7, characterized in that the tubes (12) are made curved with a radius of curvature, in the plane containing their axis, smaller than that of the envelope (1), the half shells (2, 3) of the envelope (1) are molded of plastic with securing flanges (4, 5) along their edges in the parting plane (P), and the half shells (2, 3) are secured together to form the envelope (1) by welding, preferably vibration welding, at the securing flanges (4, 5).
9. Inlet manifold according to any one of Claims 2 to 8, characterized in that each end piece (20a-22a) holds a corresponding tube (12a) on one of the half shells (3) to which each cradle (20a, 20'a) is secured.
10. Inlet manifold according to one of Claims 1 to 9, characterized in that the seal between the outlet end part (14a) of each tube (12a) and the corresponding end piece (20'a-22'a) is provided by axially compressing said seal (18), which is cylindrical, via its flat end faces between a flat radial face, pointing toward the outlet (14'a) of the tube (12'a), of the ring (17') of the tube (12'a) and a flat radial face, pointing toward the inside of said envelope (1'), of the cradle (20'a) and of said flange (6'), said radial faces being more or less perpendicular to the axis of the tube (12'a) at its outlet (14'a).
11. Inlet manifold according to one of Claims 1 to 9, characterized in that each cradle (20a) and the corresponding stirrup piece (22a) are molded in such a way that the end piece formed by the cradle and the stirrup piece has a cross section that changes progressively from a circular shape, on the same side as the attachment flange (6) and its circular supply opening (7), to an oval shape which complements that of the tubes (12a).
12. Inlet manifold according to Claim 11, characterized in that the seal between the outlet end part (14a) of each tube (12a) and the corresponding end piece (20a-22a) is provided by radially compressing said seal (18a, 18b, 18c) between, on the one hand, the tube (12a) and, on the other hand, the cradle (20a) and the corresponding stirrup piece (22a).

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