Abstract:
A cooling element ( 2 ) for power electronic devices comprises heat-exchange fluid inlet and outlet apparatus ( 29 ) and an interior volume in which said fluid circulates. The element ( 2 ) is made from an electrically insulative material and comprises at least one opening ( 28 ) connecting the internal volume (V) to the exterior of the element, a perimeter ( 24 ) of the at least one opening ( 28 ) forming a seat receiving at least one base ( 38 A) of the power electronic device ( 36 ) to be cooled with sealing apparatus ( 43 ) between them. The element has a small volume compared to those of the prior art.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cooling element for power electronic components. 
     Such cooling elements are usually made of metal, in particular of aluminum or copper, and comprise a volume in which a heat-exchange fluid circulates and whose two ends respectively constitute a fluid inlet and a fluid outlet. The walls defining the circulation volume can be provided with fins cooled by a natural or forced flow of air. The circulation volume can equally be fed with water or any other cooling liquid. 
     Power electronic modules are fixed to the metal cooling element, for example bolted to it. Other units enabling the electronic power component to operate correctly are also attached, for example starters, capacitors and one or more phase bars in the case of a phase inverter. 
     The cooling elements referred to above have a number of drawbacks, however. Most of the component parts of the power component must be electrically insulated from one another, leading to the use of complex mechanical assemblies. In the case of an inverter phase, insulating parts are used to fix the capacitors, starters, and phase bars, for example. The metal cooling element must also be kept away from live components. 
     The use of these mechanical assemblies therefore makes the whole of the power electronic component very complex, which contributes to increasing its cost. The overall volume and the weight of such power components are also relatively high. 
     The invention proposes to provide a cooling element which can alleviate the drawbacks of the prior art referred to above. To this end, it provides a cooling element for power electronic devices, in particular for phases inverter, the element comprising heat-exchange fluid inlet and outlet means and an interior volume in which the fluid circulates, characterized in that the cooling element is made from an electrically insulative material and comprises at least one opening connecting the internal volume to the exterior of the element, a perimeter of the at least one opening forming a seat receiving at least one base of the power electronic device to be cooled with sealing means between them. 
     According to other features of the invention: 
     the cooling element is made from a material that can be molded; 
     the cooling element comprises two identical half-bodies assembled together; 
     the cooling element includes a number of openings corresponding to the number of bases received on the element; 
     the intermediate space between two openings which are adjacent in the fluid flow direction includes at least two passages extending in the fluid flow direction and separated by at least one rib on the cooling element; and 
     the longitudinal axis of the rib is inclined to the fluid flow direction. 
     The invention also provides a power electronic device, in particular a phase inverter, comprising a cooling element, a plurality of power modules fixed to the cooling element and complementary functions of the device, in particular starters, characterized in that the cooling element is a cooling element as described hereinabove. 
     According to other features of the invention: 
     each base received on the perimeter of the at least one opening is integral with one of the power modules; 
     the base has fins extending in the fluid flow direction; 
     the modules are fixed in pairs at corresponding openings disposed symmetrically with respect to the median plane of the cooling element and an insert is immobilized between the adjacent ends of the facing modules of each pair, or the end of a first module extends towards a second module facing it at or beyond the end of the latter; 
     the power modules are fixed to the cooling element by a clamp on their face opposite the interior fluid circulation volume; 
     the clamp is electrically conductive and is common to two power modules which are adjacent in the fluid flow direction; 
     the cooling element comprises two half-bodies assembled together and the clamp member is fixed to the cooling element by fixing means which also fasten the two half-bodies together; and 
     the base comprises at least one plate attached at least one of the openings of the cooling element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below with reference to the accompanying drawings, which are given by way of non-limiting example only and in which: 
     FIG. 1 is a perspective view of two half-bodies for constructing a cooling element according to the invention before the two half-bodies are assembled together, 
     FIGS. 2 and 3 are views of the assembled cooling element in section respectively taken along the lines II—II and III—III in FIG. 1, 
     FIG. 4 is a perspective view of an inverter phase constructed on the assembled cooling element shown in FIG. 1, 
     FIG. 5 is a view in section taken along the line V—V in FIG. 4, 
     FIG. 6 is a partial sectional view to a larger scale, analogous to that of FIG. 5, showing a variant of the fins of a power module of the inverter phase shown in FIG. 4, and 
     FIG. 7 is a diagrammatic partial top view showing the mounting of two successive power modules equipping the inverter phase shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 to  3 , the cooling element according to the invention consists of two half-bodies  2 A and  2 B made from an electrically insulative material that can be molded, for example a polyphenylene oxide (PPO) resin which can be injection molded. The half-bodies are substantially identical. 
     Each elongate half-body  2 A,  2 B has a back  4  which is hollowed out over the greater part of its surface to define a peripheral strip  6  which surrounds the hollowed out part. The strip  6  incorporates several holes  8  for screws  9  for fastening the two half-bodies together, as shown in FIG.  3 . The strip  6 A also has a peripheral groove  10  adapted to receive a seal  11  which can be seen in FIGS. 2 and 3. 
     The cavities formed in the respective backs of the two facing half-bodies define within the assembled cooling element  2  a volume V in which a heat-exchange fluid circulates, as can be seen in FIGS. 2 and 3 in particular. 
     Two lateral walls  12 A and  12 B extend from the peripheral strip  6 . The wall  12 A has a continuous longitudinal rim  14  provided with a succession of notches  16  through which control connections of the assembled phase inverter pass. The other lateral wall  12 B has a discontinuous border  18  from which extend a multiplicity of transverse projections  20  adapted to house spacers for connecting power modules of the assembled inverter phase. 
     The lateral walls  12 A,  12 B of each half-body are joined together at a face  22  opposite the back  4 . The face  22  includes a series of lands  24  along the main axis of each half-body  2 A,  2 B and between the rim  14  of the lateral wall  12 A and the border  18  of the lateral wall  12 B. Two consecutive lands are separated by partitions  26  onto which the screw holes  8  open. An opening  28  adapted to receive a power module is formed at the center of each land  24 . The openings  28  connect the circulation volume V to the exterior of the cooling element  2 . 
     At each longitudinal end of each half-body  2 A,  2 B, the face  22  opposite the back  4  forms a setback  22 A so that the assembled cooling element  2  has heat-exchange fluid inlet and outlet spaces at respective opposite ends. Those spaces are connected to the exterior of the cooling element by respective orifices  29  adapted to be connected to respective fluid inlet and outlet lines. Fins  29 A project outward from each end of the wall  22  and are used to fix a phase bar, as explained below. 
     As shown in FIG. 3, the circulation volume V defined by the facing partitions  26  and the lateral walls  12  does not communicate with the outside of the cooling element in the intermediate space between two successive openings. The volume V is formed by two passages  30  extending in the fluid flow direction. The passages are separated from each other by ribs  32  projecting from the partitions  26  towards the back  4 . The ribs  32  are in mutual contact in the assembled cooling element, which imparts satisfactory mechanical strength to the cooling element  2 . 
     The longitudinal axis of each rib can be inclined to the fluid flow direction. This procures an agitated flow of fluid between two successive openings  28 , which has the advantage of mixing streams of water at different temperatures. This is particularly important if the ribs  32  are not in mutual contact, enabling the fluid to pass from one passage to the other. The axial end of each passage is connected to the adjacent land  24  via an inclined plane  34  which can be seen in FIGS. 1 and 2 and is inclined away from the base  4  and towards each opening  28 . 
     In the example shown, the two half-bodies  2 A,  2 B are fixed together by means of screws and a seal. Other fixing means can be used, such as gluing, elastic clipping or ultrasound welding. 
     FIG. 4 shows a phase inverter  36  based on the assembled cooling element shown in FIGS. 1 to  3 . The phase inverter  36  comprises power modules  38  attached to the cooling element  2  at each opening  28 . The cooling element also carries starters  40 , capacitors  41  and a phase bar  42 . 
     To be more precise, and referring to FIG. 5 in particular, each power module  38  is an insulated gate bipolar transistor (IGBT), for example, and has a base  38 A which is made of copper, for example. The base bears on the inside perimeter of one of the lands  24 , with a seal  43  between them. Sealing means can equally be formed by an intimate co-operation of shapes between the module and the opening which receives it, for example by molding the material of the cooling element around the module. 
     The end of the base  38 A opposite the module body  38  has fins  44  which penetrate into the circulation volume V through each opening  28 . Two identical power modules face each other across a median plane (P) of the cooling element. Thus each land  24  forms a seat for receiving the base  38 A of a corresponding power module  38 . 
     An insert  46  made from foam or silicone, for example, is immobilized between the adjacent ends of the fins  44  of each power module  38 . This prevents an unwanted flow of water around the fins  44 , which optimizes the exchange of heat via the fins. The heat-exchange fluid is constrained to flow in interstitial volumes V′ formed between each pair of adjacent fins of the same power module. 
     As shown in FIG. 6, the fins  144  of a first power module  138  can equally extend beyond the ends of the fins  144 ′ of the facing module  138 ′. This also guarantees the maximum exchange of heat. 
     FIG. 7 shows the fixing of the power modules  38  to the cooling element  2 . Two successive modules  38  are fixed to the same half-body  2 A by a single clamp  48  covering the facing ends of the two modules. The clamp  48  is made from an electrically conductive material and is fixed to the half-body  2 A by screws  9  which also fasten the two half-bodies together. The screws  9  enter holes  48 A in the clamp in line with the holes  8  in each half-body  2 A,  2 B. 
     Referring again to FIG. 5, the two facing power modules  38  are electrically connected by means of conductive members  50  which are braced by spacers  52  bearing on the projections  20  on each border  18 . The control connections of the power modules are twisted wires which connect to conductive members  54 , for example. 
     The phase bar  42  is fixed to the cooling element  2  by pins  29 A on the cooling element which enter corresponding orifices in the phase bar. The phase bar is electrically connected to one or more power modules  38  by a conductive member  56 . 
     The starters  40  are attached to the cooling element  2  at the borders  18  of each half-body  2 A,  2 B. They are fixed by bosses  58  integral with the cooling element. 
     The invention achieves the objectives previously stated. The insulative material cooling element with openings to receive power modules has a three-fold function of mechanical support, cooling and electrical insulation. 
     Assemblies which have to be insulated from each other can therefore be assembled to the cooling element without using the complex mechanical assemblies known in the art. 
     The cooling element of the invention is therefore of much simpler design and has a much smaller volume than prior art cooling elements, and the estimated reduction is from 30% to 50%. Moreover, using an insulative material reduces the overall weight of the cooling element compared to using a conductive metal. 
     Using a material that can be molded makes it extremely simple to form all of the complex shapes needed to implement the functions of the cooling element according to the invention, for example the bosses  58 . What is more, all of those functions can be provided by a single component. 
     Assembling two half-bodies together to form the cooling element according to the invention guarantees easy molding, especially if the half-bodies are identical. 
     The use of power modules fixed directly to the openings of the cooling element procures direct contact between the power module and the heat-exchange fluid so that it is possible to use a smaller volume of silicon than is used in the prior art, which represents an economic saving of approximately 30% for each power module. 
     Fixing two adjacent power modules by means of a common clamp enables the number of fixing members used to be significantly reduced compared to the prior art. Moreover, the two adjacent modules are at the same potential if the common clamp is made from a conductive material. Because a smaller number of fixing members is used, it is possible to employ a greater number of power modules than in the prior art without increasing assembly costs, with the result that the resulting inverter phase is more modular and more compact than those of the prior art. The reduction in the number of fixing members employed is particularly important when, in the case of a cooling element made from two half-bodies, the same fixing members not only fasten the two half-bodies together but also fix each clamp to the respective half-body. 
     The power modules can equally be fixed to at least one plate attached at one or more of the openings in the cooling element. For example, it is possible to use a single conductive plate to which different power modules are attached, and are therefore at the same potential, enabling the use of standard power modules. It is equally possible to use a plurality of insulative plates to each of which a corresponding power module is fixed, enabling the various modules to be insulated from each other. 
     The use of one or more such plates enables the use of prior art fixing means in combination with the benefits of an electrically insulative material cooling element.