Fluid transfer pipe with corrugated portion(s) and method for manufacturing same

The invention provides a fluid transfer pipe for filling a cooling circuit of a motor vehicle, and the method for manufacturing said pipe. This pipe includes at least one corrugated bendable portion based on at least one thermoplastic material and which includes a succession of radial reliefs axially spaced so as to form hollows between them, each relief having two frontal regions linked together by an intermediate region, the frontal regions of each relief each having one and the same overall polygonal contour defining at least three straight sections forming flats for this relief and interlinked by rounded sections forming bulges, and the contours of the successive reliefs being adapted to allow for the stripping of the corrugated portion from two hemicylindrical shells of a mold along a single axial stripping plane.

FIELD OF THE INVENTION

The present invention relates to a fluid transfer pipe in particular for filling a motor vehicle cooling circuit, this pipe comprising at least one corrugated bendable portion, and a method for manufacturing this pipe. The invention applies generally to bendable pipes made of at least one thermoplastic material and being able to transfer all liquid fluids (e.g. water or a coolant for heat engine) or gaseous fluids (e.g. air).

BACKGROUND

As is known, the motor vehicle manufacturers demand that the cooling circuit filling pipes should withstand displacements in all three directions as well as vibrations, which is obtained by the presence of undulations or corrugations defining reliefs and hollows on the outer face of these pipes, which are conventionally made of rubber for reasons of flexibility in response to the displacements, and of resistance to the fluid conveyed and to its temperature and circulation pressure.

Recently, and in particular for economic reasons, research has been conducted into producing such corrugated pipes using thermoplastic materials for its regions that are fixed in relation to the displacements, while retaining rubber for the regions subject to these displacements, or even entirely of one or more thermoplastic materials in order to further reduce their cost of manufacture.

The document U.S. Pat. No. 6,021,816 can, for example, be cited for the description of such a corrugated pipe which is entirely thermoplastic, whose ring-shaped reliefs have overall rounded contours of elliptical, oval or circular type, with angular offsets between these reliefs.

A major drawback in the known corrugated thermoplastic pipes lies in these rounded geometries for the contours of these annular reliefs which, if they favour the flexibility of the pipe for its displacements, have the undesirable effect of resulting in a flattening and therefore an elongation of these reliefs in the axial direction of the pipe, because of the high operating temperatures and/or pressures.

SUMMARY OF THE INVENTION

One aim of the present invention is to propose a fluid transfer pipe in particular for filling a cooling circuit of a motor vehicle heat engine which makes it possible to remedy these drawbacks, this pipe comprising at least one single-layer or multilayer corrugated bendable portion which is based on at least one thermoplastic material and which comprises a succession of radial reliefs which are axially spaced so as to form hollows between them, each relief having two frontal regions linked together by an intermediate region, the frontal regions of each relief each having one and the same overall polygonal contour defining at least three straight sections interlinked by rounded sections, and the contours of these successive reliefs being adapted to allow for the stripping of said at least one corrugated portion from two hemicylindrical shells of a mould along a single axial stripping plane.

To this end, a pipe according to the invention is such that, at the level of said rounded sections of each relief, said two frontal regions meet in said intermediate region by forming, for each relief, n (n being an integer equal to or greater than 3) discontinuous convex bulges which are substantially in the form of a circular arc in the circumferential and axial directions.

The expression “overall polygonal” contour should be understood in the present description to mean a contour in which the straight sections have a length greater than that of the rounded sections.

It will be noted that these straight sections associated for each relief with these rounded sections formed by these discontinuous convex bulges (this convexity of the bulges being not only circumferential but also axial) make it possible to provide a satisfactory trade-off between, on the one hand, the flexibility of the pipe in its bent portion or portions subject to displacements by virtue of the presence of these rounded sections and, on the other hand, an effective resistance to elongation of the reliefs in the axial direction of the pipe by virtue of these straight sections, unlike the overall rounded reliefs of the prior art which are the seat of axial elongations.

According to another characteristic of the invention relating to said or each corrugated portion, the respective contours of said reliefs are identical and angularly offset from one relief to another.

It will be noted that the abovementioned essential condition for each contour, which is to allow for the stripping of the pipe along a single stripping plane between the two identical shells of the mould, implies that the respective contours of the reliefs are axisymmetrical.

According to another characteristic of the invention, the contour of each relief substantially may define a convex regular polygon with n sides (n being an integer equal to or greater than 3) and with n truncated summits formed by said rounded sections, and the reliefs follow one another in alternation according to one and the same angular offset of π/n radians by defining two angular positions for the polygons of all of these reliefs.

It will thus be noted that an angular offset between two consecutive reliefs corresponding to an angle different to π/n radians—for example π/8 radians for a truncated regular polygon other than an octagon—cannot be used to produce the or each corrugated portion of a pipe according to the invention by moulding by means of an extrusion blow-moulding of at least one plastomer and/or thermoplastic elastomer from an extruding machine to a mould with two mobile hemicylindrical shells, these shells defining an axial stripping plane for the pipe.

Preferably, this contour in the form of a truncated regular polygon is chosen such that n is inclusively between 3 and 8, i.e. a contour in the form of an equilateral triangle, a square, a pentagon, a hexagon, a heptagon or an octagon, all of them regular.

As indicated previously, these truncated summits ensure the flexibility of the or each corrugated portion, whereas the sides of each duly truncated polygon make it possible to minimize the axial elongation of the reliefs after a given duration of use.

Preferably, the contours of said reliefs each have an even number n of sides, being, for example, truncated squares offset in alternation according to an angle of π/4 radians or else truncated regular hexagons offset according to an angle of π/6 radians.

It will be noted that these polygons with an even number of sides advantageously facilitate the bending of the pipe.

According to another characteristic of the invention, at the level of said straight sections, the frontal regions of each relief are coplanar and form flats defining n discontinuous bottoms of each hollow separating two said consecutive bulges from one another in the circumferential direction (whereas, as indicated above, the two frontal regions of each relief are both convex in the axial direction at the level of said rounded sections to form these bulges).

According to another characteristic of the invention, said reliefs may be separated two-by-two from one another by an interstitial peripheral smooth portion of said at least one corrugated portion, these reliefs not having any axial bridges linking them together two-by-two.

It will be noted that the n bulges formed in this way on each relief are formed discontinuously, in other words that the or each corrugated portion does not comprise any ringlet-shaped circumferentially continuous bulge, unlike in the prior art.

Advantageously, a pipe according to the invention can be moulded by extrusion blow-moulding of at least one plastomer and/or thermoplastic elastomer in a mould with two shells defining an axial stripping plane for the pipe.

According to an exemplary embodiment of the invention, said at least one corrugated portion comprises an internal layer for example made of a thermoplastic elastomer and an external layer for example made of a plastomer, all the layers having said reliefs and said hollows in this corrugated portion.

According to a variant of the invention, said at least one corrugated portion may include a smooth internal tubular portion and a corrugated external tubular portion which defines said reliefs and said hollows and which covers said internal portion by being attached thereto (for example, by a fusion-type assembly).

The manufacturing method according to the invention for a pipe as defined hereinabove comprises a moulding by extrusion blow-moulding of at least one plastomer and/or thermoplastic elastomer from an extruding machine to a mould with two mobile hemicylindrical shells, these shells defining an axial stripping plane for the pipe.

Examples of plastomers that may for example be used are polyamides (e.g. PA6, PA11 or PA12), polyesters (e.g. PET or PBT), polyolefins (e.g. polyethylenes), polyurethanes or polytetrafluoroethylenes (PTFE), as non-limiting examples.

Examples of thermoplastic elastomers (TPE) that may for example be used are olefinic thermoplastic elastomers (TPO), thermoplastic vulcanizates (TPV) or thermoplastic polyurethanes (TPU), to give a few non-limiting examples.

According to one embodiment of the invention common to all of the abovementioned characteristics for the pipe, said reliefs are each centred on a transversal plane perpendicular to the longitudinal axis of symmetry of the pipe (i.e. each relief forms an angle of π/2 radians with this axis).

As a variant, these reliefs according to the invention may each be centred on a plane forming with the longitudinal axis of symmetry of the pipe an angle of between π/6 and π/2 radians, so that the profile chosen for these reliefs makes it possible, as indicated hereinabove, to produce the pipe by this extrusion blow-moulding from an extruding machine to a mould with two mobile hemicylindrical shells defining an axial stripping plane for the pipe.

DETAILED DESCRIPTION

A pipe1according to the invention is illustrated inFIG. 10, this pipe preferably being made by an extrusion blow-moulding of at least one thermoplastic material and comprising in this example a number of corrugated and bent or bendable portions2,3,4,5which are interlinked by smooth and straight portions6,7,8and each of which can be seen precisely inFIGS. 1 to 9. This pipe1is of single-layer or multilayer type, being able to comprise in the latter case a radially internal layer based on a thermoplastic elastomer, such as a TPV, and a radially outer layer based on a plastomer, such as a polyamide, as a non-limiting example.

As can be seen inFIGS. 1,5and6, each corrugated portion2to5of the pipe1defines a tubular structure10having a plurality of radial reliefs11which follow one another axially by being separated in pairs from one another by substantially flat hollows12and which are each discontinuous in the circumferential direction. More specifically, each relief11has two frontal regions, respectively front13and rear14, which each have one and the same contour15in the form of a convex regular polygon with n flat sides16, truncated at its summits by n rounded sections17(n being an integer equal to or greater than 3), these regions13and14being joined together by a circumferential intermediate region18.

As illustrated inFIGS. 2 to 4, the respective contours15of the reliefs11are identical but angularly offset between the reliefs11, two-by-two consecutively, by one and the same angle α of π/n radians by thus defining, in alternation over the length of the portion10, two unique angular positions for these polygons15, which allows for the stripping of the pipe along a single joint plane between the two shells of the extrusion blow-moulding mould (seeFIGS. 12 and 13). In this example ofFIGS. 2 to 4, the contours15are squares (n=4) truncated by four slightly rounded and convex summits17, that is an angle of offset between the contours15of π/4 radians (or 45°).

It can be seen in particular inFIGS. 1 and 4that, in each relief11, the rounded sections17form between them n discontinuous convex bulges19(seeFIG. 5for this convexity in the axial direction) with a section in the form of a circular arc (both in the axial and circumferential directions) which are linked together in pairs in the circumferential direction by flats20defined by the sides16of each polygon15. These flats20, also discontinuous over the circumference of each relief11, thus form an axially central part of the bottom of each hollow12, which is complemented on either side of these flats20by two continuous circumferential smooth portions21of small axial width (seeFIG. 1).

As a non-limiting illustration,FIGS. 3 and 5show the distance separating two opposite flat sides16of the square15(16.5 mm) and that separating two opposite bulges19(20 mm, or the diagonal of the truncated square15). As for the thickness e of the smooth portions21, it is, in the example ofFIG. 1, approximately 1.75 mm.

The variant corrugated portions10′,10″,10″′ according toFIGS. 7,8and9respectively illustrate reliefs which are in the form of:

regular pentagons with n=5 flats20′ linked together by as many bulges19′ (or α=π/5 radians),

regular hexagons with n=6 flats20″ linked together by as many bulges19″ (or α=π/6 radians), and

To manufacture a pipe1incorporating such corrugated portions10to10″′ such as the portions2to5ofFIG. 10, an extrusion blow-moulding installation30such as that ofFIG. 11is advantageously used, with, upstream, an extruding machine31intended to feed extrudate32in the direction A in a machine33capable of forming corrugations on a pipe (“corrugator”) and formed by two chains of hemicylindrical shells33aand33b(“mould chains”) which are mobile on endless conveyors in opposite directions of rotation and which form, one against the other, a cylindrical mould, to obtain each corrugated portion10to10″′ after cutting in a cutting unit34situated downstream of the machine33.

FIGS. 12 and 13schematically illustrate a possible geometry of the die35of the extruding machine31with an axis of rotation X, in relation to a shell33aof the extrusion blow-moulding mould receiving the extrudate32.

The Applicant has subjected multilayer pipes1(notably with an inner layer based on TPV (“Santoprene”) and with an outer layer based on PA12) incorporating corrugated portions such as those ofFIGS. 1 to 9to tests in normal conditions of displacements and temperature and pressure of the cooling fluids conveyed, tests which have in particular demonstrated the improved resistance to axial elongation of the reliefs of these corrugated portions via dimensional stability tests (implemented after an ageing of 2 hours at 118° C. then 30 minutes at 135° C. at 1.4 bar of pressure, with a fluid consisting of a 50/50 mixture of glycol and water) compared to known corrugated pipes, and have also resulted in an improved resistance to the pressure of the fluid for these pipes1(bursting pressure at 118° C.: approximately 7.8 bar) compared to these known pipes.