EP1399698A1

EP1399698A1 - Heat exchanger, especially for an air conditioning device in a motor vehicle

Info

Publication number: EP1399698A1
Application number: EP02767529A
Authority: EP
Inventors: Christophe Chevallier; Ivan Le Bouteiller; Jean-Marie Pelletier
Original assignee: Valeo Climatisation SA
Current assignee: Valeo Climatisation SA
Priority date: 2001-06-27
Filing date: 2002-06-24
Publication date: 2004-03-24
Also published as: WO2003002920A1; CZ20033557A3; CN1537214A; FR2826711A1; FR2826711B1

Abstract

A heat exchanger for heating air comprising a plurality of tubes (10a, 10b) for circulating a heat-carrying fluid, a plurality of electric heating bars (30) having resistive elements disposed between the electrodes of the electricity supply, and a set of radiating elements (20) associated with the tubes and heating bars. The radiating elements are made up of crossed blades (20) with contact via the tubes (10a, 10b) and heating bars (30). The bars are engaged with constraint in the openings (28) of the blades in such a way that they can be kept in contact with the blades and in order to apply the electrodes with pressure against the resistive elements.

Description

Heat exchanger, in particular for a motor vehicle air conditioning device.

Invention background

The invention relates to a heat exchanger for air heating, in particular, but not exclusively, for a motor vehicle air conditioning device.

Traditionally, in a motor vehicle with an internal combustion engine, air heating for heating the passenger compartment, demisting or defrosting is provided by a heat exchanger through which the engine coolant flows.

More particularly with certain type of engine, a relatively long time may elapse between the start of the engine and the time when the coolant provides the calories necessary for efficient heating of the air. This is all the more annoying that, in very cold weather, the air conditioning device is asked not only to quickly heat the passenger compartment, but also to ensure effective defrosting or demisting immediately after starting. To overcome this drawback, it is known to add an electric heating device capable of supplying the calories required as soon as it is switched on. The operation of the electric heating device is interrupted when the heat requirements can be satisfied by the heat transfer fluid, in this case the engine coolant. Such an electric heating device is commonly formed of electric heating bars associated with radiant elements and is arranged in the air circulation duct to be heated, downstream of the heat exchanger through which the engine coolant flows. Heating rods generally include resistive elements formed from resistors with positive temperature coefficient (PTC) which have the advantage of providing self-protection against excessive heating.

The addition of such an electric heating device results in an increase in the size and cost of the air conditioning device, even when, for mounting convenience, it is pre- assembled with the liquid heat exchanger, as described in document EP 0 919409.

It has been proposed in document EP 0 857 922 A2 to integrate the additional electric heating in the liquid heat exchanger by replacing some of the pipes traversed by the heat-transfer liquid by heating bars. Dividers interposed between the heating pipes or bars act as radiant elements situated, with the pipes and heating bars, on the path of the air passing through the exchanger. The efficiency of the exchanger is reduced when the electric heating is not in operation due to the inactive presence of the bars in place of pipes traversed by the heat transfer fluid.

In addition, good heat transfer between the heating rods and the spacers is difficult to achieve.

Subject and summary of the invention

The object of the invention is to reduce the cost and size of an air heating assembly formed by a heat exchanger with heat transfer fluid and an electric heating device without however affecting its efficiency, whatever operating mode.

This object is achieved thanks to a heat exchanger for air heating comprising a plurality of pipes for the circulation of a heat transfer fluid, a plurality of electric heating rods having resistive elements arranged between electric supply electrodes, and a set of radiant elements associated with the heating pipes and bars, exchanger in which the radiant elements consist of fins traversed by contact by the pipes and the heating bars, the bars being engaged with stress in the openings of the heating fins so as to be kept in close contact with the fins and to apply the electrodes with pressure against the resistive elements.

The invention is remarkable in that the heating rods are integrated in the heat exchanger with heat transfer fluid, sharing the same fins and without replacing the pipes through which the heat transfer fluid passes, while the electrical contact and The thermal resistance of the heating rods is ensured by mounting under stress in the openings of the fins. The result is a simple and compact structure, therefore low cost and space, with good heating efficiency. Advantageously, the heat exchanger comprises at least one row of pipes and at least one row of heating bars, and the heating bars and the pipes located in two parallel rows are offset from one another. It is thus possible, in the available space, to move the heating bars away from the pipes as much as possible.

According to another feature of the exchanger, the heating rods are arranged downstream of the pipes in the direction of flow of air to be heated through the exchanger. The possibility of a significant transfer of calories between the heating rods and the fluid passing through the pipes, when this fluid has a fairly low temperature, is therefore reduced.

The mounting of the heating bars in the openings of the fins can be carried out in different ways. Thus, the openings may have a substantially D shape with two opposite sides forming elastically deformable wings which extend substantially in the plane of the fins and between which the heating bars are engaged with constraint. Alternatively, the openings of the fins traversed by the heating bars have flanges which are folded out of the plane of the fins and between which the heating bars are engaged with constraint.

The heating bars can be made in different ways.

Thus, in one embodiment, each heating rod comprises first, second and third electrodes in the form of conductive strips arranged parallel to one another, resistive elements arranged between the first electrode and one face of the second electrode, and resistive elements disposed between the other face of the second electrode and the third electrode, the first and third electrodes being in pressure contact with two opposite sides of the openings formed in the fins. In another embodiment, each heating rod comprises first and second electrodes in the form of parallel conductive strips, resistive elements arranged between the first electrode and one face of the second electrode, and an insulator arranged on the other face of the second electrode, the first electrode and the insulator being in pressure contact with two opposite sides of the openings formed in the fins.

In yet another embodiment, the heating rods are housed in tubes held with stress in the openings of the fins. The tube of a heating rod can constitute a first supply electrode, the other, or second, supply electrode being in the form of a conductive strip housed inside the tube being separated from the wall of the tube, on one side by resistive elements and, on the other side, by resistive elements or an insulator. Heat and electrically conductive parts can be interposed between the resistive elements and the side of the internal wall of the tube with which they are in electrical contact, said parts conforming to the shape of the internal wall of the tube.

The tubes of the heating rods can have a generally flattened or oval cross section.

The tubes can be opened along their entire length along a generator, which gives them an elastic deformation capacity, or can be closed. In the latter case, preferably, the tubes of the heating rods are applied with pressure against the edges of the openings in which they are engaged, and wedging pieces are engaged in the tubes to exert a contact pressure between the resistive elements and the electrodes.

The invention also relates to a motor vehicle air conditioning device provided with a heat exchanger as defined above.

Brief description of the drawings

The invention will be better understood on reading the description given below, by way of indication but not limitation, with reference to the appended drawings in which: - Figure 1 is a partial perspective view of a heat exchanger according to a first embodiment of the invention; - Figure 2 is a partial sectional view, on an enlarged scale, along the plane 11-11 of Figure 1;

- Figure 3 is a partial sectional view along the plane III-III of Figure 2; - Figure 4 is a partial plan view of a radiant element of the exchanger of Figures 1 to 3;

- Figure 5 is a sectional view along the plane V-V of Figure 4;

- Figure 6 is a sectional view on an enlarged scale of an alternative embodiment of a heating rod for a heat exchanger such as that of Figures 1 to 5;

- Figures 7A and 7B are partial plan views of alternative embodiments of a heat exchanger according to the invention;

- Figure 8 is a partial sectional view of a second embodiment of a heat exchanger according to the invention;

- Figure 9 is a partial view of a heating rod of the exchanger of Figure 8 before its integration into the heat exchanger;

- Figure 10 is an enlarged view illustrating the engagement with stress of a heating bar of the exchanger of Figure 8;

- Figure 11 is a partial view of an alternative embodiment of a heating rod for a heat exchanger similar to that of Figures 8 to 10; - Figure 12 is a sectional view of an alternative embodiment of the heat exchanger of Figure 8;

- Figure 13 is a partial sectional view, on an enlarged scale, along the plane XIII-XIII of Figure 12;

- Figure 14 is a sectional view of another alternative embodiment of the heat exchanger of Figure 8;

- Figure 15 is a partial sectional view of another embodiment of a heat exchanger according to the invention;

- Figure 16 is an enlarged view of a detail of Figure 15; and - Figure 17 is a partial exploded view of a heating rod of the exchanger of Figures 16 and 17. Detailed description of embodiments of the invention

In the description which follows, we place ourselves within the framework of the application of the invention to the air conditioning devices of motor vehicles with thermal engine. The invention is however not limited to this application and can be used for any heating system associating a heat exchanger with circulation of heat-transfer fluid and an electric heating device.

A first embodiment of a heat exchanger according to the invention is illustrated in FIGS. 1 to 5.

It comprises an air / heat transfer liquid heat exchanger with a row of ducts 10, intended to be traversed by a coolant of a heat engine, and radiant elements 20 in the form of fins of generally rectangular shape traversed by the ducts 10.

Each conduit 10 comprises a first section 10a_forming a rectilinear tube which crosses all of the fins 20, substantially perpendicular to the latter, and a second section 10b forming a rectilinear tube which likewise crosses all of the fins 20.

At a first end of the exchanger, the pipes 10a are connected in common to a manifold (not shown) supplying the exchanger supplying the engine coolant coming from the engine and, at this same end of the exchanger , the pipes 10b are connected in common to an evacuation manifold (not shown) returning the coolant to the engine.

At the second end of the exchanger, the pipes 10a and 10b are connected by elbows 10c, or pins.

This arrangement, well known, makes it possible to have the supply and discharge collectors of the exchanger at the same end thereof, which facilitates its mounting in an air conditioning assembly. We could of course adopt another arrangement according to which the supply and discharge collectors are situated at two opposite ends of the exchanger. Furthermore, several rows of pipes 10 could be provided. The fins 20 are formed by metal sheets, for example aluminum, arranged parallel to each other and provide between them spaces for the circulation of the air to be heated. Cut-outs are made in areas of the surface of the fins to form lamellae 22 which are deformed out of the plane of the fins in order to form louvers 24 (shown only in FIGS. 3 to 5) improving the heat exchange with the air. crossing the exchanger.

The tubes 10a, 10b are forcibly housed in openings 26 made in the fins for the passage of the tubes (Figure 4).

This can be achieved by engaging the tubes 10a, 10b by force in the openings 26 or by deformation by inflation under pressure of the lines 10 after their establishment.

An air / liquid exchanger as described above is well known and commonly used in air conditioners of motor vehicles.

According to the invention, heating bars 30 with electrical resistances are integrated into the heat exchanger by being constrained to engage in additional openings 28 of the fins 20. In the embodiment of FIGS. 1 to 3, the bars 30 comprise a stack formed by a first external electrode 32a, resistive elements 34, a second internal electrode 36, resistive elements 38, and a third external electrode 32b.

The electrodes 32a, 36 and 32b are formed by metal strips, for example aluminum. They extend over the entire length of the heating rods and protrude at one end of the heat exchanger, to form terminals 33a, 37, 33b for connection to an electrical supply circuit (not shown).

In each heating rod, several resistive elements 34 spaced from one another are interposed between the electrode 32a and one face of the electrode 36, and several resistive elements 38 spaced from each other are interposed between the other face of the electrode 36 and the electrode

32b.

The resistive elements 34, 38 are for example resistors with a positive temperature coefficient in the form of blocks or "stones" parallelepiped. The stack formed by the electrodes 32a, 36, 32b and the resistive elements 34, 38 is kept compressed by force engagement of the heating rod in the openings 28.

As shown in Figures 3 and 4, the openings 28 have two opposite edges 28a, 28b against which the electrodes 32a, 32b are applied with pressure by their external face.

The openings 28 advantageously have a D shape so that the edges 28a, 28b form wings which can deform elastically during the engagement of a bar 30, while remaining substantially in the plane of the fin. The total thickness of the bar is chosen to be slightly greater than the width of the opening 28 between the edges 28a, 28b.

In this way, pressure is exerted by the edges of the openings 28 on the bars 30. This engagement of the bars 30 with stress in the openings 28 guarantees good thermal contact between the bars 30 and the fins 20 and good electrical contact between the resistive elements and electrodes.

The electrodes 32a, 32b in contact with the fins 20 are brought to the same potential, preferably the reference potential (ground), while the electrode 36 is brought to a positive potential during the operation of the electric heating.

Figure 6 shows an alternative embodiment of a heating rod 30 '. This comprises a stack formed by an external electrode 32 ', resistive elements 34', an internal electrode 36 'and an electrical insulator 39' in the form of a strip. The electrode 36 'has one face in contact with the resistive elements 34' and the other face in contact with the strip 39 '. The electrodes 32 'and 36' are in the form of metal strips, for example aluminum. The strip 39 ′ is made of an electrically insulating but heat conductive material, for example of alumina. The bar 30 'is engaged with stress between the opposite edges 28a, 28b of openings 28 of the fins, which guarantees good thermal contact between the bar and the fins and good electrical contact between the resistive elements and the electrodes.

Figure 3 shows that the pipes 10a, 10b and the bars 30 form rows parallel to each other. The bars 30 have positions offset relative to those of the pipes 10a, 10b, along rows. In the example of Figure 3, the pipes 10a, 10b and bars 30 have, in section, a staggered arrangement. The offset between pipes and bars makes it possible to separate them as much as possible in the available space. This limits the transfer of calories between the bars and a fluid flowing in the pipes. Such a transfer would indeed be detrimental when the bars are in operation to compensate for an insufficiency of caloric intake by the fluid circulating in the pipes.

In an alternative embodiment shown in FIG. 7A, and again with the aim of limiting the transfer of calories from the bars to the pipes, the bars 30 are arranged downstream of the pipes 10a, 10b in the direction (arrow F) of flow air to be heated through the exchanger.

Figure 7B illustrates an alternative embodiment similar to that of Figure 7A, with two additional rows of tubing 10'a, 10'b.

Figures 8 to 11 show another embodiment of a heat exchanger according to the invention. This embodiment differs from that of FIGS. 1 to 5 by the production of the heating bars, the other elements being similar and being designated by the same references.

In the embodiment of FIGS. 8 to 10, the heating bars 130 comprise a longitudinally split tube 132 with a flattened section having an opening or slot 131 over the entire length of a generator in a part of the tube connecting two substantially parallel planar faces opposite 132a, 132b.

The tube 132 contains a supply electrode 136 in the form of a conductive strip extending over the entire length of the tube. Resistive elements 134 are interposed between one face of the electrode 136 and the internal wall of one of the planar faces (132a) of the tube 132 while an insulating strip 137 is interposed between the other face of the electrode 136 and the other flat face (132b) of the tube 132. The tube 132 constitutes the other supply electrode for the resistive elements 134.

Before insertion into the openings 28 of the fins 20, each tube 132 is slightly open (FIG. 9), the total thickness of the resistive elements 134, of the electrode 136 and of the insulation 137 being slightly greater than the distance measured between the internal faces of the walls 132a, 132b when the lips 131a, 131b of the opening 131 are brought together.

The dimensions of the tube 132 and the openings 28 (FIG. 10) are chosen so that the constrained engagement of the tube 132 between the edges 28a, 28b of the openings 28 brings the lips 131a, 131b closer together. In this way, an effective contact pressure is exerted to ensure good thermal transmission between the bar and the fins and good electrical contact between the resistive elements and the electrodes (see detail in FIG. 8). FIG. 11 illustrates an alternative embodiment of the heating rod 130. According to this alternative, the tube 132 forming an electrode contains resistive elements 134 interposed between one face of the electrode 136 and the internal wall of one of the planar faces (132a) of the tube 132 and other resistive elements 138 interposed between the other face of the electrode 136 and the internal wall of the other flat face (132b) of the tube 132. We find an arrangement of resistive elements similar to that of the bar 30 of Figures 1 to 3.

Figures 12 and 13 illustrate an alternative embodiment of the heat exchanger of Figure 8 which differs from it by the fact that the openings 128 of the fins 20 in which the tubes 132 are engaged have a shape corresponding to that tubes 132 with their slot 131 substantially closed. The openings 128 have flanges 128a, 128b folded substantially perpendicular to the plane of the fin 20 (Figure 13). The flanges 128a, 128b bear on the opposite flat faces 132a, 132b of the tube 132, which ensures good thermal contact between the bar 130 and the fin 20, as well as good electrical contact between the resistive elements 134 and the electrodes 132, 136.

In the embodiment of Figure 12 (as in that of Figure 8), the substantially planar faces of the tubes 132 are parallel to the direction of flow (arrow F) of the air through the exchanger. According to the variant illustrated in FIG. 14, these substantially planar faces can be inclined relative to the direction of flow in order to favor the heat exchange with the air. The openings 128 of the fins are correspondingly oriented. Figures 15 to 17 illustrate yet another embodiment of a heat exchanger according to the invention, which is distinguished from that of FIG. 8 by the production of the heating bars.

As shown in Figures 15 and 16, the heating rods 230 are housed in closed tubes 232 with an oval or elliptical section. The bars are engaged in apertures 228 of corresponding shape formed in the fins 20.

The tubes 232 are applied with pressure to the edges of the openings 228. To this end, in a manner known per se, the tubes may be deformed by inflation under pressure after engagement in the openings 228, so that intimate contact is established between the tubes 232 and the fins 20.

The tube 232 contains a frame 240 in the form of a profile extending longitudinally in the tube with edges 240a, 240b which substantially match the shape of the wall of the tube in its opposite zones 232c, 232d of section with a smaller radius of curvature. The framework

240 is made of an electrical insulating material, for example a plastic material and has housings 242 spaced apart from one another by dividing walls 244, or by ribs 246.

Resistive elements 234 are arranged in the housings 242 and are applied, on one side, to one face of an electrode 236 in the form of a strip, and, on the other side, to adapter pieces 235 made of a material electrical and thermal conductor, for example aluminum.

The adapter pieces 235 have a face 235b in contact with the resistive elements and an opposite face 235a in contact with a part of the inner wall of the tube 232 in an area 232a of section with a larger radius of curvature, taking the form of this part of the inner wall. One or more longitudinal shims 237 are interposed between the other face of the electrode 236 and the wall part of the tube 232 in an area 232b opposite the area 232a. Or the shims 237 have a face 237a in contact with the electrode 236 and an opposite face in contact with the internal wall of the tube by means of ribs 237b, the envelope of which conforms to the shape of this internal wall.

The shims 237 are made of electrical insulating material, for example of alumina. After insertion of the frame 240 with the resistive elements 234, they are inserted, adaptation pieces 235 and the electrode 236, in the tube 232 previously engaged and blocked in the openings 238.

The shims 237 have in section a dimension such that they are engaged in the tube 232 with stress, possibly with slight deformation of the ribs 237 ^ to exert a pressure promoting the electrical contact of the resistive elements 234 with the electrode

236 and the tube 232 forming an electrode (via the adapter parts 235).

In FIGS. 8, 12, 14 and 15, the heating rods occupy with respect to the pipes 10a, 10b, the same positions as in FIG. 3. We can of course adopt another arrangement, for example such as that of FIG. 6.

In the above examples, a single row of heating bars is provided, with a bar located opposite the gap between two pipes 10a or 10b of a row of neighboring pipes. Of course, and in particular according to the needs for electric heating, the number of bars in a row may be different, not necessarily in relation to the number of pipes, and several rows of bars may be provided.

Claims

1. Heat exchanger for air heating comprising a plurality of pipes (10a, 10b) for the circulation of a heat transfer fluid, a plurality of electric heating rods (30; 30 '; 130; 230) having elements resistors arranged between electrical supply electrodes, and a set of radiant elements (20) associated with the pipes and heating rods, characterized in that the radiant elements consist of fins (20) traversed by contact by the pipes ( 10a, 10b) and the heating bars (30; 30 '; 130; 230), the bars being forcedly engaged in openings (28; 128; 228) of the fins so as to be kept in close contact with the fins and applying the electrodes with pressure against the resistive elements.

2. Heat exchanger according to claim 1, comprising at least one row of pipes and at least one row of heating bars, characterized in that the heating bars (30; 130) and the pipes (10a, 10b) located in two parallel rows are offset from each other.

3. Heat exchanger according to any one of claims 1 and 2, characterized in that the heating bars are arranged downstream of the pipes in the direction (F) of air flow to be heated through the exchanger.

4. Heat exchanger according to any one of claims 1 to 3, characterized in that the openings (28) of the fins

(20) traversed by the heating bars (30; 30 '; 130) have substantially a D shape with two opposite sides (28a, 28b) forming elastically deformable wings which extend substantially in the plane of the fins and between which the heating bars are engaged with constraint.

5. Heat exchanger according to any one of claims 1 to 3, characterized in that the openings (128) of the fins (20) through which the heating bars (130) have flanges (128a, 128b) folded out of the plane of the fins between which the heating bars are engaged with constraint.

6. Heat exchanger according to any one of claims 1 to 5, characterized in that each heating rod (30) comprises first, second and third electrodes (32a, 36, 32b) in the form of conductive strips arranged parallel to each other, resistive elements (34) disposed between the first electrode and one face of the second electrode, and resistive elements (38) disposed between the other face of the second electrode and the third electrode, the first and the third electrode being in pressure contact with two opposite sides of the openings (28) formed in the fins (20).

7. Heat exchanger according to any one of claims 1 to 5, characterized in that each heating rod (30 ') comprises first and second electrodes (32', 36 ') in the form of parallel conductive strips, resistive elements (34 ') disposed between the first electrode and one face of the second electrode, and an insulator (39') disposed on the other face of the second electrode, the first electrode and the insulator being in pressure contact with two opposite sides of the openings formed in the fins.

8. Heat exchanger according to any one of claims 1 to 7, characterized in that the heating rods

(130; 230) are housed in tubes (132; 232) held with constraint in the openings of the fins (20).

9. Heat exchanger according to claim 8, characterized in that the tube (132; 232) of a heating rod (130; 230) constitutes a first supply electrode, the other, or second, electrode supply being in the form of a conductive strip (136; 236) housed inside the tube.

10. Heat exchanger according to claim 9, characterized in that the resistive elements (134; 234) are arranged between one face of the second electrode (136; 236) and a first side of the internal wall of the tube (132; 232 ), an insulator (137; 237) being interposed between the other face of the second electrode and the side of the internal wall of the tube opposite the first side.

11. Heat exchanger according to claim 9, characterized in that resistive elements (134, 138) are interposed between each face of the second electrode (136) and opposite sides of the inner wall of the tube (132).

12. Heat exchanger according to any one of claims 9 and 10, characterized in that parts (235) conductive of heat and electricity are interposed between the resistive elements (234) and the side of the internal wall of the tube (232) with which they are in electrical contact, said parts conforming to the shape of the internal wall of the tube.

13. Heat exchanger according to any one of claims 8 to 12, characterized in that the tubes (132) of the heating rods (130) have a cross section of flattened shape.

14. Heat exchanger according to any one of claims 8 to 12, characterized in that the tubes (232) of the heating rods (230) have a cross section of oval shape.

15. Heat exchanger according to any one of claims 8 to 14, characterized in that the tubes (132) of the heating bars (130) are open over their entire length along a generator.

16. Heat exchanger according to any one of claims 8 to 14, characterized in that the tubes (232) of the heating rods (230) are closed and are applied with pressure against the edges of the openings (228) in which they are engaged, and shims (237) are engaged in the tubes to exert contact pressure between the resistive elements (234) and the electrodes (232, 236).

17. Motor vehicle air conditioning device, characterized in that it comprises a heat exchanger according to any one of claims 1 to 16.