Internal heat exchanger for air conditioning system of motor vehicle and such a circuit   

The present invention relates to an internal heat exchanger of coaxial tubular type for a motor vehicle air-conditioning circuit and to a corresponding air-conditioning circuit incorporating this exchanger.

In certain motor vehicle air-conditioning circuits, it is necessary to effect an exchange or transfer of heat between the fluid in the high-pressure portion of the circuit that needs to be cooled and the same fluid from the low-pressure portion of this circuit which acts as the cold source and is heated up in exchange, in order to improve the efficiency of the circuit. To do this, use is made of a heat exchanger known as an internal exchanger because it does not seek to exchange with air external to the vehicle or with air from the cabin.

In the known way, a heat exchanger is of metallic type and is connected to the corresponding pipes of the air-conditioning circuit which, in particular, comprise hoses, via connectors mounted at each of the ends of the exchanger, which may, for example, be of the plate type, consisting of a stack of flat tubes and effecting the heat exchange both by convection with the air external to the exchanger and by conduction, or alternatively may be of the multi-tube type which, in its simplest version, is of the countercurrent coaxial tubular type which then exchanges heat without the abovementioned convection.

In the latter instance, and particularly with fluids such as R134a or R152, this coaxial exchanger generally defines: inside an internal tube of the exchanger, at least one radially internal passage intended to carry the fluid from the low-pressure portion of the circuit, and radially between this internal tube and an external tube that forms the shell of the exchanger, a radially external passage, usually provided with longitudinal fins designed to optimize the transfer of heat between the fluids flowing through the internal passage(s) and the external passage which are distributed around its circumference and may be secured to the internal and/or external tubes or alternatively added in between these two tubes, as illustrated, for example, in document U.S. Pat. No. 6,434,972.

Use is then generally made of at least one metal female connector for the relevant end of the exchanger which is then welded or brazed both to the internal and to the external tubes of the exchanger so as to define passageways for the fluid communicating in a leaktight manner with these internal and external passages.

Patent documents WO-A1-2007/013439 and EP-A1-1 762 806 illustrate such internal heat exchangers which are respectively equipped with two female connectors and with a single female connector, in both instances via three lines of welding or brazing at the corresponding end of the exchanger.

One major disadvantage with these known finned coaxial internal exchangers is that it is necessary to refrain from creating tappings on the external tube in line with these fins for the connection notably of valves or sensor support nozzles, or alternatively that the profiled sections that make up the internal and/or external tubes have to be machined beforehand at the site of the fins that they comprise in that region of the exchanger (usually an end region) that is specifically intended to have these tappings, thus increasing the cost of manufacture of the exchangers.

Another disadvantage with the known coaxial internal exchangers fitted with connectors lies in the relatively high weight of these connectors which have also to be accurately machined and then welded or brazed to secure them to the internal and external tubes of the exchangers, likewise contributing to an increase in the cost of manufacture and assembly thereof.

It is an object of the present invention to propose such an internal exchanger of the coaxial tubular type which comprises two, low-pressure and high-pressure, portions through which a coolant flows, the exchanger defining inside an internal tube at least one radially internal passage preferably for the low-pressure fluid, and a radially external passage preferably for the high-pressure fluid and formed between this internal tube and an external tube, which exchanger is able to address these disadvantages.

To this end, an exchanger according to the invention is such that spacer means of a thermal conductivity lower than that of the internal and external tubes are movably mounted at least in translation between these two tubes and axially extend over just a part of the length of the external passage, at least one region of this latter passage which is devoid of these means being intended to be connected to a tapping, such as a valve body or a sensor mounting nozzle, by a connecting orifice formed in the external tube at right angle with this region.

It will be noted that these spacer means according to the invention which act as spacers (i.e. as distance pieces) between these tubes thus make it possible, because of their thermal conductivity which is lower than that of the latter tubes, to avoid any thermal coupling in the form of thermal bridges between these two, internal and external tubes. By way of example, these spacer means may be made of a metallic material (typically of a thermal conductivity lower than that of aluminum in the case of tubes based on that metal) or made of plastic (e.g. based on a polyamide).

According to another feature of the invention, these spacer means, which are intended to create turbulence in the fluid flowing through the external passage so as to optimize the transfer of heat between the high-pressure and low-pressure fluids, may extend axially continuously or discontinuously over said part of the external passage, ending set back from at least one connecting end of the external tube.

According to a first example of the invention, these spacer means are formed of a plurality of longitudinal ribs connected circumferentially between their respective bases by a substantially cylindrical wall capable of matching the internal tube so that the overall radial height of this wall and of each rib is substantially equal to that of the external passage.

According to a second example of the invention, these spacer means are formed of at least one spiral rib able to match the internal tube, extending in a helix around the latter with a pitch that is either constant or variable.

It will be noted that this added-in and sliding fitting of the spacer means between the internal and external tubes allows these means to be positioned accurately and in anticipation of the or each tapping to be created on the external tube, by causing them to slide axially beforehand out of the or each tapping region in order to create one or more free space(s) allowing this (these) tapping(s) to be made. It is thus possible to dispense entirely with the need felt in the prior art to use internal or external tubes having fins which have been locally machined in the regions intended for the tappings, thus making it possible to lower the cost of manufacture of the exchanger.

It will also be noted that these tappings, which are thus easier to achieve thanks to the adjustable positioning of the spacer means, may, for example, allow bodies of valves for filling the exchanger with coolant, nozzles supporting pressure or temperature sensors, or any other nozzle or radial connecting fitting (i.e. the axis of which is perpendicular to the axial direction of the exchanger) to be connected to the exchanger.

According to another feature of the invention, these spacer means may advantageously be mounted in contact with the internal and external tubes in order to act as radial spacer pieces between these tubes to keep them concentric. Again advantageously, when the exchanger is of the type that has at least one bent or curved portion, these spacer means are preferably inserted at least at the site of this (these) section(s) and, more preferably still, over the majority of the axial length of the external passage.

It will be noted that these spacer means according to the invention thus make it possible to “absorb” the bend radii and/or radii of curvature of the internal and external tubes of the exchanger along the length thereof, making it possible to keep the bore section for fluid in the external passage substantially constant and therefore not impede exchange of heat in the bent or curved sections.

Advantageously, an exchanger according to the invention may incorporate said tapping at right angle with said region of the external passage devoid of these spacer means, which region is situated near one end of the external tube, this tapping being formed of a connecting nozzle of the exchanger which nozzle is intended to carry the fluid coming from or toward the external passage.

According to another feature of the invention, the exchanger may advantageously be devoid of any high-pressure/low-pressure female connector for connecting the internal passage(s) and external passage(s) to the air-conditioning circuit. In other words, this exchanger then consists exclusively of the internal tube, of the external tube and of said spacer means, which do not oppose there being a tapping communicating with the external passage and do not either have to be machined in order to permit this tapping, as explained hereinabove.

It will be noted that this lack of a female connector (usually made of aluminum) allows a significant reduction in the mass of the exchanger according to the invention and, furthermore, in its overall cost of manufacture and assembly which, in the past, was adversely affected by the operations of machining the or each connector.

It will also be noted that the internal and external tubes of the exchanger according to the invention, which no longer have to be machined at the spacer section pieces, can thus be used directly after they have been shaped.

According to a first embodiment of the invention which is made easier by the aforementioned sliding mounting of the spacer means, the internal tube at least one of its ends has a protruding portion which protrudes axially beyond the corresponding end of the external tube being secured to the latter end and which alone—instead of the aforementioned female connector—forms another connecting nozzle of the exchanger intended to carry the fluid from or toward the or each internal passage.

In this case, this end of the external tube may be secured to the internal tube by a simple sinking of this end obtained, for example, by knurling, followed by circumferential attachment of this end to this internal tube performed for example by welding, brazing, magnetoforming (preferably in two stages, although a single stage is conceivable) or bonding.

According to a second embodiment of the invention, likewise made easier by the aforementioned sliding mounting of the spacer means, the external tube is secured, at least at one of its ends, to the internal tube by crimping with previous push-fitting of one end of a flexible hose for connecting to the air-conditioning circuit between the respective ends of these tubes, which hose is optionally mounted so that it butts axially against a ring flange of the internal tube. It will be noted that this single crimping operation therefore allows the two, internal and external, tubes of the exchanger to be connected to the adjacent hose of the air-conditioning circuit.

A motor vehicle air-conditioning circuit according to the invention is such that it comprises an internal heat exchanger as defined hereinabove, which is preferably connected to this circuit with no high-pressure/low-pressure female connector.

Further features, advantages and details of the invention will become apparent from reading the following description of a number of embodiments of the invention which have been given by way of nonlimiting illustration, the description being given with reference to the attached drawings, among which:

FIG. 1 is a schematic view of a motor vehicle air-conditioning circuit incorporating an internal heat exchanger according to the invention,

FIG. 2 is a perspective view of a spacer insert according to a first embodiment of the invention, to be inserted in the internal heat exchanger of FIG. 1,

FIG. 3 is a part view, in longitudinal section and partly in perspective, of a connection end of an exchanger according to this first embodiment of the invention incorporating the insert of FIG. 2,

FIG. 4 is a perspective view of a spacer insert according to a second embodiment of the invention, to be inserted in the exchanger of FIG. 1,

FIG. 5 is a part view, in longitudinal section and partly in perspective, of a connection end of an exchanger according to this second embodiment of the invention, incorporating the insert of FIG. 4,

FIG. 6 is a part view in perspective of a connection end of an internal heat exchanger according to a first embodiment of the invention, notably with reference to the examples of FIGS. 3 and 5, and

FIG. 7 is a partial schematic view in longitudinal half section of a connection end of an internal heat exchanger according to a second embodiment, notably with reference to the examples of FIGS. 3 and 5.

The air-conditioning circuit 1 illustrated in FIG. 1 is, in the known way, a closed circuit or “loop” which comprises, in addition to an internal heat exchanger E, a number of elements distributed inside the engine compartment of the vehicle, notably a compressor 2, a chiller or condenser 3 and an evaporator 4, and through which a coolant such as R134a or R152, by way of nonlimiting examples, flows under pressure. All these elements are connected together by rigid or flexible lines consisting of rigid and/or flexible tubular portions which at each of their ends have means of leaktight connection.

More specifically, the circuit 1 comprises: a low-pressure LP line intended to carry the coolant between the evaporator 4 and the compressor 2 through the exchanger E via an inlet eLP for low-pressure fluid to be heated up, and an outlet sLP for this fluid thus heated, and a high-pressure HP line intended to carry this same fluid downstream of the compressor 2 and of the chiller 3 via an inlet in eHP of high-pressure fluid to be cooled and an outlet sHP of this fluid thus cooled, a pressure relief valve 5 being positioned downstream of this outlet sHP and upstream of the evaporator 4.

The exchanger E is of the coaxial countercurrent type and is intended to cool the fluid from the HP line by conduction upon contact with this same fluid from the LP line which is heated in exchange. To achieve this and as illustrated in the example of FIG. 3, this exchanger E consists of a metallic radially internal tube 10 which in its interior space delimits an internal passage 11 for the fluid from the LP line 4 and which is inserted axially inside a radially external tube 20, likewise metallic, which with the tube 20 delimits an external passage 21 of annular cross section for the fluid from the HP line.

As illustrated in FIGS. 2 and 3, a spacer insert 30 that forms a distance piece according to the first embodiment of the invention and which is intended to optimize transfer of heat between the HP and LP fluids by generating turbulence in the external passage 21, is slidably mounted between the tubes 10 and 20 and in contact therewith, being positioned set back by an adjustable axial distance from the connection end 22 of the external tube 20. Thus, the end region of the external passage 21, which can be accessed entirely freely because it does not have any insert 30, can be connected easily to a tapping 40, such as a body of a filling valve or a pressure sensor mounting nozzle, for example, via a connecting orifice 23 formed in the external tube 20.

The insert 30 is formed of a plurality of ribs 31 connected circumferentially at their respective bases by a cylindrical wall 32 which hugs the wall of the internal tube 10, the overall radial height of the wall 32 and of each rib 31 being substantially equal to that of the external passage (less the mounting clearance needed to allow the insert 30 to slide).

As may be seen in FIGS. 4 and 5, a spacer insert 130 according to the second example of the invention is formed of a spiral rib which matches both the internal tube 10 and the external tube 20 of the exchanger E, extending in a helix about the latter (at a pitch that is constant in this embodiment, it being emphasized that this pitch could vary in the axial direction and the spiral could be discontinuous along the length of the external passage 21).

As mentioned previously, it will be noted that the insert 30, 130 makes it possible both to improve the transfer of heat between the HP and LP fluids and to act as a radial distance piece between these tubes to keep them concentric, particularly in bent or curved sections of the exchanger E.

In the embodiment of FIG. 6, which for example incorporates the insert 30, 130 of FIG. 2 or 4, the internal tube 10 has a protruding portion 12 which protrudes axially beyond the end 22 of the tube 20 being secured thereto and which constitutes the connecting nozzle of the internal passage 11 of the exchanger E to the LP line of the air-conditioning circuit 1. This end 22 of the tube 20 may be secured to the portion 12 of the tube 10 by a tube sinking which is applied to it by knurling, followed by circumferential attachment of the end 22 thus narrowed onto this tube portion 12 preferably by welding or brazing (it being emphasized that other methods such as magnetoforming or even bonding may be used).

In the embodiment of FIG. 7, which also for example incorporates the insert 30, 130 of FIG. 2 or 4, the tube 120 is secured to the tube 110 by crimping with previous push-fitting of one end of a flexible hose 50 for connecting to the circuit 1 between the respective ends 112 and 122 of the tubes 110 and 120, this hose 50 in this example being mounted to butt axially against a ring flange 113 of the tube 110 (the deformations of the respective ends 112 and 122 of the tubes 110 and 120 as a result of this crimping upon contact with the hose 50 have been depicted schematically).

It will be noted that the two embodiments of FIGS. 6 and 7 have the advantage of allowing the corresponding end of the exchanger E to be connected to the rest of the air-conditioning circuit 1 without requiring a welding or brazed connection of one or more female connector(s) the solid structure and requisite prior machining of which are known disadvantages to this connection because of their weight and because of the additional cost of assembly that they represent for the exchanger E.