TECHNICAL SECTOR The present invention relates to a supply assembly for an air conditioning circuit of a motor vehicle comprising a fitting, for example for connecting a pressure sensor or a charging valve .

STATE OF THE PRIOR ART

Air conditioning systems for motor vehicles are circuits traversed by a coolant ^" and are formed by a plurality of components, comprising in particular a compressor, a condenser, a drying tank, an expansion system, and an evaporator. All these components are connected to one another by means of tubular elements that have, at their ends, fixing elements and fitting means capable of guaranteeing fluid tightness.

The components that make up the air conditioning system are housed within the engine compartment of the vehicle, with the compressor driven by the same drive shaft as that of the vehicle, whilst the other components are fixed to portions of the bodywork. In the air conditioning system there exist low- pressure elements and high-pressure elements. The latter can be subject in use to pressures of the coolant in the region of 30 bar.

For a long time the Freon gas known as "R- 134" has been used as coolant for motor vehicles . To overcome the pollutant properties of said gas, it is particularly important that a tube designed for conveying it should be substantially impermeable thereto. In addition, a low permeability is also desired in order for the system to maintain its functionality and efficiency over time. However, international standards of an environmental nature impose the need to find solutions alternative to Freon R- 134 that have a lower GWP (global warming potential) . Amongst these, the gas 1234 YS proposed by Honeywell and Dupont has proven effective. Even using as coolant a gas with lower GWP, however, it remains of fundamental importance for the elements, i.e., pipes and fittings, designed to convey it to present a permeability that is as low as possible in regard thereto, combined with satisfactory mechanical properties at a high pressure, in particular after prolonged ageing and substantially for the entire life cycle of the motor vehicle.

In particular, automobile manufacturers impose the requirement for the lines formed by pipes and fittings designed for use in conveying the coolant in the air conditioning system to pass a multiplicity of experimental tests, for example, hot-burst tests for verifying the mechanical characteristics thereof, tests for resistance to cyclic pressure variations, tests of permeability to the fluid to be conveyed, and tests for resistance to chemical agents .

Generally, in air conditioning systems in the automotive sector, said requirements are satisfied by using, for conveying the coolant , aluminium pipes , provided at the ends of which are brazed flanges, and intermediate rubber pipes with bell- shaped fittings or fast couplings moulded on the rubber itself, said metal possibly being used in combination with multilayer rubber pipes.

However, the general tendency in the automotive field is that of replacing, wherever possible, metal or rubber pipes with equivalent structures made of plastic so as to favour a reduction of the production costs in addition to the overall weight of the resulting air conditioning system and the corresponding benefit in terms of CO ₂ emissions in the engine thanks to the lower consumption levels. In addition, in the automotive sector there has always been felt the need to reduce the times and costs for production of the components .

OBJECT OF THE INVENTION

The aim of the present invention is consequently to provide a supply assembly capable of replacing effectively the elements based upon use of aluminium that are currently employed in air conditioning systems in the automotive sector. A further aim of the present invention is to provide a supply assembly that is able to satisfy all the requirements necessary for type approval and entails reduced production costs and times.

Provided according to the present invention is a supply assembly comprising a fitting for an air conditioning circuit according to Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, the latter will be described more fully with reference to the attached figures; namely:

Figure 1 is a diagram of an air conditioning circuit;

Figure 2 is a view of a portion of a supply assembly according to the present invention; and

Figures 3 is a cross section according to the line III- III of

Figure 2.

BEST MODE FOR CARRYING OUT THE INVENTION In Figure 1 designated as a whole by 1 is an air conditioning system for a motor vehicle, comprising a condenser 2, a drying tank 3, an expansion system 4, an evaporator 5, and a compressor 6. A low-pressure section BP is identified in Figure 1 by a dashed-and-dotted line. A solid line indicates, instead, a high-pressure section AP, which can be identified substantially between the compressor 6 and the expansion system 4. In the high-pressure section AP the coolant (R-134) has in use a temperature of around 100 ⁰ C with a pressure in the region of 20 bar. The components of the air conditioning system shown schematically ^• in Figure 1 are connected to one another by a plurality of hollow components, i.e., tubes 7 and respective fittings. A tube -7 is connected to one from among the condenser 2, the drying tank 3, the expansion system 4, the evaporator 5, and the compressor 6 via a fitting 8 (Figure 2) having a body made of thermoplastic or elastomeric- thermoplastic material.

The fitting 8 comprises a connection portion 9, which defines a through hole 10 having a transverse axis that is skew with respect to that of the tube 7. In particular, the connection portion 9 comprises a tubular insert 11, which is preferably made of metal material and defines the through hole 10. The fitting 8 is fixed to one of the devices of the air conditioning system, for example to the condenser 2, via a screw inserted in the through hole 10 and screwed on a supporting wall of one of said components.

The fitting 8 moreover has a fitting outlet 12 (Figure 3) , which is fluidically connected to the tube 7 and defines a seat for a seal ring 13 so as to define a fluid-tight connection with a hole (not illustrated) for coupling one of the components referred to above of the air conditioning system.

Preferably, the fitting 8 moreover comprises two further connection portions 14 and 15 for fixing a charging valve and a pressure sensor (neither of which is illustrated) , respectively .

The connection portion 14 comprises a metal insert 16 embedded in the body of the fitting and defining an internal thread 17 for connection to the charging valve . The internal thread delimits a cavity 18 having an axis parallel and coinciding with that of the tube 7. The cavity 18 is fluidically connected to the tube 7 via a through hole 19 defined by an end wall of the metal insert 16, and a further through hole 20 -defined by the body of the fitting 8.

The connection portion 15 is identical or altogether similar, except for the dimensions, to the connection portion 14. In fact, the connection portion 15 comprises a metal insert 21, which is embedded in the body of the fitting 8 and defines a threaded cavity 22 that has an axis perpendicular to that of the tube 7 and is fluidically connected to the latter via a through hole 23.

According to an important aspect of the present invention, the body of the fitting 8 is comoulded on the tube 7 together with the inserts 11, 16, 21. In order to carry out comoulding, the fitting 8 comprises an internal hollow element 24 that fluidically connects the outlet 12 to the tube 7.

In particular, comoulding requires a pair of half-moulds, set within which are an end portion 25 of the tube 7, the hollow element 24, and the inserts 11, 16, 21. Next, the thermoplastic material that embeds the inserts 11, 16, 21 and the hollow element 24 for connecting them rigidly to the end portion 25 is injected. The inserts 11, 16, 21 and the hollow element 24 are held in a precise and pre-defined relative position by purposely provided mobile cores, which are extracted prior to comoulding and are subsequently retracted for extracting the finished piece after comoulding. Conveniently, the mobile cores are shaped so as to support the inserts 16, 21 and to be inserted in purposely provided through holes of the hollow insert 24, said holes defining respective stretches of the holes 20, 23. According to a preferred embodiment, the hollow element 23 is driven into the end portion 25 before the latter is mounted in the comoulding half-mould, and the body of the fitting 8 adheres to and sui-rounds the external circumference of the end portion 25 to define with the latter a rigid connection that cannot be dismantled.

The internal element 23 performs the function of preventing ^' the tube 7 from being obstructed and of holding the tube 7 in position inside the half-mould of the body of the fitting 8 via the mobile cores of the half-moulds during the comoulding operation and has an internal diameter smaller than that of the tube 7. In some cases, such as for example in that of an elbow, the internal element 23 avoids the need for undercuts.

•According to a preferred embodiment, the tube 7 and the body of the fitting 8 include a layer, which comprises one and the same thermoplastic copolymer. For example, the thermoplastic material comprises a polyamide 6/10 or a polyamide 6/12.

Preferably, the layer comprising the polyamide 6/10 comprises more than 60% of polyamide 6/10. More preferably, the layer comprises more than 90% of polyamide 6/10. Even more preferably, the layer is made entirely of polyamide 6/10.

Preferably, the polyamide 6/10 comprises more than 60% of a copolymer obtained starting from a first monomer comprising sebacic-acid units and by a second monomer comprising hexamethylenediamine units . More preferably, the polyamide 6/10 comprises more than 90% of a copolymer obtained starting from a first monomer comprising sebacic-acid units and from a second monomer comprising hexamethylenediamine units . Even more preferably, the polyamide 6/10 consists of a copolymer obtained starting from a first monomer comprising sebacic-acid units and a second monomer comprising hexamethylenediamine units . Preferably, a resin of the Grilamid ^® S series produced by EMS is used. For example, the resin Grilamid ^® S can be used.

Said resin, having a density of approximately 1.07 g/cm ³ , has a melting point of approximately 220 ⁰ C and a Young's modulus of approximately 2.3 GPa. An element made of said resin possesses, in addition to distinct properties of chemical resistance to oils (for example PAG2 or POE) , fuels, water, and saline solutions, good properties of short-term thermal resistance and of resistance to hydrolysis, reduced tendency to absorbing water, and a better mechanical stability and resistance to abrasion, as compared to tubes made of other polyamides such as PA6 and PA12.

In addition, since one of the monomeric units that make up the resin is mainly sebacic acid, a compound that is abundantly available in nature in so far as it can be obtained from castor oil, its use advantageously constitutes a form of use of renewable resources. Preferably, the fitting 8 comprises a fibre filler, more preferably a glass-fibre filler, or a mixture of glass fibres and mineral fibres.

Preferably, glass fibres are added in a weight percentage, with respect to the polyamide, of between 10 wt% and 60 wt%. Optimal results in the tests were obtained with a weight percentage of between 20 wt% and 40 wt%, for example 30 wt%.

According to a preferred embodiment of the invention, the glass fibres have a length comprised between 0.05 mm and 1.0 mm, but even more preferably a length of between 0.1 mm and 0.5 mm .

In addition, said fibres preferably have a diameter comprised between 5 μm and 20 μm, and more preferably a diameter of between 6 μm and 14 μm. Preferably, the fitting 8 comprises at least 60% of said polyamide 6/10 with glass-fibre fillers. More preferably, the fitting 8 comprises at least 90% of said polyamide 6/10 with glass-fibre fillers. Even more preferably it is entirely made of said polyamide 6/10 with glass-fibre fillers.

According to one embodiment, the tube 7 is constituted by a single layer comprising polyamide 6/10, preferably with glass- fibre fillers according to what is described in the foregoing paragraphs and preferably has a thickness of between 1.5 and 3 mm.

According to an alternative embodiment of the invention, the tube 7 can include a second layer, which comprises a polyamide resin preferably selected from between polyamide 6/12 and a copolyamide obtained starting from dicarboxylic units, which are terephthalic acid or isophthalic acid for more than 60%.

In the case where the tube 7 is a multilayer tube, the fitting 8 is made of the same thermoplastic material as that of the outermost layer of the tube 7.

Preferably, the second layer comprises at least 60% of said polyamide resin. More preferably, the second layer comprises at least 90% of said polyamide resin. Even more preferably, the second layer is entirely made of said polyamide resin.

According to one embodiment of the invention, said polyamide resin is a polyamide 6/12 modified for resisting cold impact. Preferably, the polyamide 6/12 is selected so as to have a melting point of between 170 ⁰ C and 176°C, a tensile strength of between 25 and 35 MPa, a bending strength of between 20 and 30 MPa, a bending modulus of between 400 and 600 MPa, a resistance to impact of between 100 and 120 kJ/m ² at 23 ⁰ C and between 10 and 20 kJ/m ² at -40 ⁰ C. Preferably, the tube 7 includes a first layer which comprises polyamide 6/10, and a second layer which comprises polyamide 6/12, the first layer being internal to the second layer.

According to a further embodiment of the invention, said copolyamide is a polyphthamide (PPA) .

Preferably, said copolyamide is a copolymer obtained starting from carboxylic units that are terephthalic acid for more than 60% and diamine units that are 1, 9-nonanediamine or 2 -methyl- 1, 8-octanediamine for more than 60%.

More preferably, the dicarboxylic units are terephthalic acid for more than 90%. Even more preferably, terephthalic acid constitutes 100% of the dicarboxylic units.

Preferably, the diamine units are 1, 9-nonanediamine or 2- methyl-1, 8-octanediamine for more than 60%. More preferably, the diamine units are 1, 9-nonanediamine or 2-methyl-l, 8- octanediamine for more than 90%. Even more preferably 1,9- nonanediamine or 2-methyl-l, 8-octanediamine constitute 100% of the diamine units .

Examples of dicarboxylic units different from terephthalic acid comprise aliphatic dicarboxylic acids, such as malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, 2, 2-dimethylglutaric acid, 3 , 3-diethylsuccinic acid, azelaic acid, sebacic acid and suberic acid; alicyclic dicarboxylic acids, such as 1, 3-cyclopentanedicarboxylic acid and 1, 4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids, such as isophthalic acid, 2, 6 -naphthalene dicarboxylic acid, 2, 7 -naphthalene dicarboxylic acid, 1, 3-phenylene dioxydiacetic acid, diphenic acid, 4 , 4' -oxydibenzoic acid, diphenylmethane-4, 4' -dicarboxylic acid, diphenylsulphone-4 , 4 ' - dicarboxylic acid, and 4 , 4 ' -biphenyldicarboxilic acid; or a mixture thereof .

Amongst these, aromatic dicarboxylic acids are preferred.

Examples of diamine units different from the aforementioned 1, 9-nonanediamine and 2-methyl-l, 8 -octanediamine comprise aliphatic diamines, such as ethylenediamine, propylenediamine, 1, 4-buthanediamine, 1, 6-hexanediamine, 1, 8-octanediamine, 1, 10-decanediamine, 3-methyl-l, 5-pentanediamine; alicyclic diamines, such as cyclohexanediamine, methylcyclohexanediamine and isophoronediamine; aromatic diamines, such as p- phenylenediamine , m-phenylenediamine, p-xylenediamine, m- xylenediamine , 4,4' -diaminodiphenyl methane , 4,4'- diaminodiphenyl sulphone, 4 , 4' -diaminodiphenyl ether; and an arbitrary mixture thereof .

Said polyamide is preferably P9T of the type described in the patent No. US6989198. More preferably, the polyamide resin is a Genestar ^® resin produced by Kuraray. Even more preferably, it is a Genestar ^® resin produced by Kuraray, for example Genestar 1001 U03, U83.

The supply assembly comprising the fitting 8 and the tube 7 according to the foregoing paragraphs, satisfies the requirements imposed by automobile manufacturers for use in air conditioning systems. In particular, the PA6/10 layer is able to satisfy the requirements of permeability and resistance to pressure oscillations, even after ageing. In addition, the coupling of the PA6/10 layer to an outer layer made of PA12 , PPA or else P9T enables the problems linked to resistance to chemical attack to be overcome, thus eliminating flaking and failure to occur in the areas of bonding.

Example 1 A mono-layer tube made of Grilamid S FE 5347 7x11 (approx.) mounted on a fitting 8 made of Grilamid S FE 5351 7x11 with 30% glass fibre.

HOT-BURST TESTS

The tests were conducted at a temperature of 120 °C , after stabilization for Ih at the testing temperature. An increasing hydraulic pressure was applied on the tube described previously, with an increment of 5 bar/s up to bursting of the tube. The pressure at which bursting occurs was then compared with the values specified for use for example by an automobile manufacturer.

The test was moreover conducted after pulsating-pressure tests (described in what follows) , recording a value of 89-92 bar, still clearly above the 30 bar prescribed.

PERMEABILITY TESTS

Said tests have the purpose of measuring, through the loss of weight, the amount of fluid that comes out through the wall of the tubes. To obtain a statistically significant datum, the tests were conducted simultaneously on four pipes.

First of all, the lengths (Li, L ₂ ... L ₄ ) of the tubes undergoing testing, excluding the fittings, were measured at atmospheric pressure. Mounted on the ends of the tubes were two closing devices, one of which was provided with a filling valve.

The internal theoretical volume of the first three tubes was calculated, and 0.55 g/cm ³ of HFC134 were introduced therein, which was equivalent to approximately 50% of the internal volume of the tube being tested. By means of a halogen detector, the absence of leakage from the closing devices was verified.

The four tubes (three full tubes plus the blank standard tube) were introduced into the environmental chamber at the temperature of 100 ⁰ C for 1 h; then the check with the halogen detector was repeated. At this point, the four tubes were subjected to a conditioning step in environmental chamber at 100 ⁰ C for 24 h.

Once this conditioning step was through, the tubes were weighed, and the values Pi, P ₂ , ... P ₄ thereof were recorded.

Then, the tubes 7 were subjected to a conditioning step once again at 100 ⁰ C for 72 h, after which they were weighed, and the individual losses of weight ΔPi were determined. The loss of weight of the tubes charged with the coolant was then evaluated as mean value over the three tubes, and the value detected for the blank tube was subtracted therefrom. The resulting difference constitutes the index of permeability expressed in g/m ² /72 h.

For the tube according to the invention a value of lower than 1.82 g/m ² /72 h was recorded.

TESTS OF RESISTANCE TO PULSATING PRESSURE

The tubes 7 under examination were mounted on a test bench equipped with a device capable of sending pressure pulses . The tubes , mounted to form a U shape with radius of curvature equal to the minimum one envisaged for the tube under examination, were charged with the lubricant envisaged for the compressor or else with a silicone oil; the environment in which the tests were conducted contained air. The internal fluid and the air were brought up to the temperature of 100- 120 ⁰ C and subjected to cycles with a testing pressure of 0 ± 3.5 MPa (or else between 0 and 1 MPa, according to the type of tube) , with a testing frequency of 15 cycles per minute. At least 150 000 cycles were performed to be continued up to failure if no failure occurred within 150 000 cycles.

At the end, a verification cycle was carried out, removing the tube from the test bench, immersing it in water, and sending an air pressure of 3.5 MPa for 30 s, controlling absence of leakages . In the case where the presence of bubbles was detected, the pressure was maintained for five minutes in order to ascertain that it was effectively due to a leakage and not, for example, to air that had possibly got trapped between the- layers of the tube (in the case of a multilayer tube) .

Upon completion of the analysis, the specimens of tube were sectioned at their end area provided with the fitting and examined visually to ascertain the absence of any tearing on the internal duct . The presence of this type of defect would constitute a reason for the test not being passed.

For the tube according to the invention no failures were found after 150 000 cycles.

Only the supply assemblies according to the invention passed all the tests necessary for ensuring a sufficient duration of the tube according to the requirements of automobile manufacturers .

The advantages that the fitting and the supply assembly according to the present invention affords are described in what follows .

The fitting 8 comoulded on the tube 7 reduces the production costs and meets the reliability requirements of automobile manufacturers for type approval .

Finally, it is clear that variations and modifications may be made to the supply assembly described and illustrated herein, without thereby departing from the sphere of protection defined by the annexed claims.