Patent Publication Number: US-2023155447-A1

Title: Cover for a rotating electric machine

Description:
The invention relates, in particular, to a cover for a rotating electric machine. 
     The invention is particularly advantageously applicable in the field of rotating electric machines such as alternators, starter-alternators, or even reversible machines or electric motors. By way of a reminder, a reversible machine is a rotating electric machine capable of working in a reversible manner, on the one hand, as an electric generator in the alternator function and, on the other hand, as an electric motor, for example, in order to start the heat engine of the vehicle such as a motor vehicle. 
     A rotating electric machine comprises a rotor that is free to rotate about an axis, and a fixed stator. In alternator mode, when the rotor is rotating, it induces a magnetic field at the stator, which converts it into electric current in order to supply power to the electrical consumers of the vehicle and to recharge the battery. In motor mode, the stator is electrically powered and induces a magnetic field that rotates the rotor, for example, in order to start the heat engine. 
     The assembly formed by the rotor and the stator is arranged in a casing on which an inverter is arranged. The inverter, which forms an electronic assembly of the machine, is conventionally protected by a cover. The cover has a plate extending in a radial direction to cover an axial end surface of the inverter and a skirt extending in an axial direction from the plate to cover a circumferential periphery of the inverter. The plate and/or the skirt may have openings allowing a cooling air flow to pass through. 
     Such a cover does not have an optimized shape helping to protect the elements of the rotating electric machine without degrading performances in terms of cooling said elements. 
     The aim of the present invention is to help avoid the drawbacks of the prior art by proposing an optimized cover shape. 
     To this end, the present invention therefore relates to a cover for a rotating electric machine comprising an axis of rotation. The cover is intended to be arranged on an inverter of said machine and comprises a skirt extending in an axial direction and forming a perimeter of the cover, the perimeter defining an inner portion of the cover and an open region arranged in the inner portion and comprising at least one axial opening. According to the present invention, the open region extends over at least 50% of the inner portion of the cover. 
     The presence of such an open region on the cover helps considerably improve the passage of the cooling air flow, thus allowing better cooling of the inverter without affecting the mechanical strength of the cover or the protection of the elements of the machine against the external environment. Indeed, enlarging the area of the opening in the cover makes it possible, inter alia, to facilitate the circulation of the air flow between the cover and the inverter and, in particular, on the axial end surface of the inverter. Moreover, this novel cover shape also helps to reduce the axial space requirement of the machine, as well as its weight, and to simplify the arrangement of the inverter and in particular of the connector for connecting the inverter to the general computer of the vehicle in which the machine is mounted. 
     According to one embodiment, the open region extends over at least 70% of the inner portion of the cover and in particular 84%. This increase in the dimensions of the open region helps further optimize the shape of the cover in order to improve the cooling of the inverter. 
     According to one embodiment, the open region extends over the whole of the area of the inner portion. 
     According to one embodiment, the axial opening of the open region extends over at least 50% of the inner portion of the cover. It should be understood here that the cover has at least one opening extending over at least 50% of the inner portion of the cover. The cover may also have other openings. 
     According to one embodiment, the open region comprises several axial openings. This makes it possible to enlarge the open region while maintaining the possibility of adding elements such as protection, gripping or mechanical strength elements in the inner portion. Alternatively, the open region may be formed from a single axial opening. 
     According to one embodiment, the cover comprises at least one axial protection portion intended to be arranged axially opposite at least one phase connection of the machine, the axial protection portion extending into the inner portion. The axial protection portion helps protect the electrical connection between the phases of the stator and the inverter from the external environment in order to ensure safe operation of the machine. 
     For example, the axial protection portion extends from the skirt. 
     According to one embodiment, the skirt comprises at least one radial protection portion intended to be arranged radially opposite at least one phase connection of the machine. This radial protection portion helps protect the phase connection of the machine from the external environment. 
     According to one embodiment, the skirt comprises at least two radial protection portions, each being intended to be arranged radially opposite at least one phase connection of the machine, and at least one connecting portion extending circumferentially between said two radial protection portions, the connecting portion having a height, in an axial direction, less than the height, in an axial direction, of the radial protection portions. The difference in height between the radial protection portions and the connecting portion makes it possible to arrange a primary radial opening region in the cover. The radial opening helps improve the cooling of the inverter. For example, the primary radial opening region is formed from one or more primary radial openings. 
     According to one embodiment, the height of the connecting portion is less than half the height of a radial protection portion. In other words, the height of the primary radial opening region, in an axial direction, is greater than half the axial thickness of the radial protection portion. 
     According to one embodiment, the skirt is formed from a succession of radial protection portions and connecting portions. 
     According to one embodiment, each radial protection portion comprises a secondary radial opening region. This also helps improve the cooling of the machine. For example, the secondary radial opening region is formed from one or more secondary radial openings. 
     For example, the area of the secondary radial opening region is between 15% and 25% of the area of the associated protection portion. This helps improve the cooling of the machine while ensuring the mechanical strength of the cover and protecting the machine from the external environment. 
     According to one embodiment, the skirt forms a closed perimeter. This helps improve the mechanical strength of the cover. 
     According to one embodiment, the cover further comprises at least one fastening portion, the fastening portion being intended to cooperate with a fastening element in order to mount the cover on an inverter of the rotating electric machine, the fastening portion extending into the inner portion. 
     For example, the axial fastening portion extends from the skirt or from the axial protection portion or from the gripping means. 
     According to one embodiment, the fastening portion extends in a radial direction and comprises an opening through which the fastening element can pass. 
     According to one embodiment, the cover further comprises at least one gripping means extending into the inner portion. This gripping means makes it possible, during the process of assembling the machine, to simplify the arrangement of the cover on the inverter before they are fastened together. 
     For example, the gripping means extends from the skirt or from the fastening portion or from the axial protection portion. 
     According to one embodiment, the gripping means is formed from a planar portion extending in a radial plane. This makes it possible to move the cover without increasing the axial space requirement of the machine. This may also provide a labelling area for recording the references of the machine. 
     According to one embodiment, a set-back portion is formed at at least one end of the gripping means so that said means extends axially at a distance from the skirt. This helps reduce the axial height of the skirt in order to improve the cooling of the machine. 
     The present invention also relates to a rotating electric machine comprising an inverter and a cover as previously described, the cover being mounted on the inverter. The rotating electric machine can, advantageously, form an alternator, a starter-alternator, a reversible machine or an electric motor. 
     According to one embodiment, the inverter comprises a power stage for supplying power to the phases of a stator of the machine and/or for rectifying the current leaving said phases. The inverter further comprises a control stage for controlling the machine. 
     According to one embodiment, the inverter comprises at least one heat sink plate, said plate forming, at least partially, one axial end of said inverter and being arranged at least partially facing the open region. The heat sink plate helps to protect the elements of the inverter from the external environment and also to improve the cooling of the inverter by conduction. 
     According to one embodiment, the inverter comprises a capacitor bank and the open region is arranged so as to be at least partially axially aligned with the capacitor bank. 
     According to one embodiment, the machine comprises a casing arranged to at least partially surround a stator and a rotor of said machine, the inverter being arranged axially between the cover and the casing. 
     According to one embodiment, the rotating electric machine further comprises a shutter arranged at one axial end of the inverter, the shutter comprising a radially extending portion arranged opposite a capacitor bank of the inverter. The radially extending portion helps to protect the capacitor bank from the external environment. 
     According to one embodiment, the machine comprises a casing arranged to at least partially surround a stator and a rotor of said machine, the shutter being arranged axially between the casing and the inverter. The shutter makes it possible to at least partially cover axial openings arranged in the casing. The shutter therefore helps prevent a cooling air flow that has already been heated by the rotor or the stator from circulating in the inverter. 
     According to one embodiment, the power stage and the control stage are axially superposed so as to define a cooling passage between them, the primary radial opening region being in particular at least partially arranged facing said cooling passage. 
     According to one embodiment, the machine comprises a stator comprising at least one phase terminal and the inverter comprises at least one power module comprising at least one power terminal, the power terminal being electrically connected to the phase terminal in order to form a phase connection. 
    
    
     
       The present invention may be better understood upon reading the following detailed description of nonlimiting exemplary embodiments of the invention and upon studying the appended drawings. 
       [ FIG.  1   ] shows a schematic and partial sectional view of a rotating electric machine according to one example of the invention. 
       [ FIG.  2   ] shows a schematic and partial perspective view of an example of a cover according to the invention mounted on an inverter. 
       [ FIG.  3   ] shows a schematic and partial perspective view of the cover shown in  FIG.  2   . 
       [ FIG.  4   ] shows a schematic and partial perspective view of an example of a shutter according to the invention. 
       [ FIG.  5   ] shows a schematic and partial perspective view of another example of a cover according to the invention. 
     
    
    
     Identical, similar or comparable elements use the same reference signs from one figure to the next. It also should be noted that the various figures are not necessarily to the same scale. In addition, the embodiments which are described hereinafter are in no way limiting. In particular, it is possible to conceive of variants of the invention comprising only a selection of features described hereinafter, in isolation from the other features described. 
       FIG.  1    depicts an example of a compact and polyphase rotating electric machine  10 , in particular for a vehicle such as a motor vehicle or a drone. This machine  10  converts mechanical energy into electrical energy, in alternator mode, and can operate in motor mode in order to convert electrical energy into mechanical energy. This rotating electric machine  10  is, for example, an alternator, a starter-alternator, a reversible machine or an electric motor. 
     In this example, the machine  10  comprises a casing  11  on which an inverter  36  is mounted. Inside this casing  11 , it further has a shaft  13 , a rotor  12  which rotates as one with the shaft  13  and a stator  15  surrounding the rotor  12 . The rotational movement of the rotor  12  takes place about an axis X. In the rest of the description, the axial direction corresponds to the axis X, which passes through the shaft  13  at the center thereof, while the radial orientations correspond to planes that are concurrent with, and in particular perpendicular to, the axis X. For the radial directions, the term inner corresponds to an element oriented toward the axis, or closer to the axis than a second element, and the term outer denotes distance from the axis. 
     In this example, the casing  11  comprises a front end plate  16  and a rear end plate  17  which are joined together. These end plates  16 ,  17  are hollow in form and each centrally bear a bearing carrier coupled to a respective ball bearing  18 ,  19  for the rotational mounting of the shaft  13 . Moreover, the casing  11  has fastening means (not shown) for mounting the rotating electric machine  10  in the vehicle. 
     A drive member such as a pulley  20  may be fastened to a front end of the shaft  13 . This member makes it possible to transmit the rotational movement to the shaft or allows the shaft to transmit its rotational movement to the belt. In the rest of the description, the terms front/rear refer to this member. Thus, a front face is a face oriented in the direction of the member, while a rear face is a face oriented in the direction away from said member. 
     The rear end of the shaft  13  bears, in this case, slip rings  21  belonging to a commutator  22 . A brush holder (not shown) comprises brushes arranged in such a way as to rub on the slip rings  21 . The brush holder is connected to the inverter  36  and, in particular, to a control module  23  of the inverter. 
     The front end plate  16  and the rear end plate  17  may have substantially lateral openings for the passage of an air flow in order to allow the machine  10  to be cooled by air circulation brought about by the rotation of a front fan  25  arranged on a front axial face of the rotor  12  and of a rear fan  26  arranged on a rear axial face of said rotor. 
     In this example, the rotor  12  is a claw-pole rotor comprising two pole wheels  31 . Each pole wheel  31  is formed from a plate oriented transversely, a plurality of claws forming magnetic poles, and a cylindrical core. The rotor has a coil  35  wound around the core. For example, the slip rings  21  belonging to the commutator  22  are connected by wire connections to said coil  35 . The rotor  12  may also comprise magnetic elements  32 , such as permanent magnets, interposed between two adjacent claws. Alternatively, the rotor may be formed from a stack of laminations housing permanent magnets forming the magnetic poles. 
     In this exemplary embodiment, the stator  15  has a body  27  formed from a stack of laminations provided with slots, equipped with a slot insulator for the mounting of an electric winding  28 . The winding passes through the slots in the body  27  and forms a front overhang and a rear overhang on either side of the body of the stator. Furthermore, the winding  28  is formed from one or more phases comprising at least one electrical conductor. Each phase comprises an end forming a phase output  33  which is electrically connected to the inverter  36 . 
     The inverter  36 , which is in this instance mounted on the casing  11 , forms the electronic assembly of the machine. The inverter comprises a power stage used to receive or supply an electric power signal from or to the electrical phases of the winding  28 . The power stage comprises at least one power module  24  comprising a power terminal  37  arranged to be electrically connected to a phase output  33  in order to form a phase connection  38 . The power module forms a bridge voltage rectifier for converting the AC voltage generated by the phases of the stator into a DC voltage and/or, conversely, for converting a DC voltage into an AC voltage to be fed to the phases of the stator. The inverter also comprises a control stage comprising a control module  23  making it possible, in particular, to regulate the voltage injected via the brush holder to rotor  12  and providing the interface with a computer external to the vehicle. 
     In the example shown in  FIGS.  1  and  2   , the power stage and the control stage are stacked on each other in an axial direction. More particularly in this example, the power stage comprises a heat sink, referred to as the first heat sink  39 , mounted on the casing  11 , the power module  24  being mounted on said first heat sink. Moreover, the control stage comprises a heat sink, referred to as the second heat sink  40 , mounted on the first heat sink  39 , the control module  23  being mounted on said second heat sink. For example, the two heat sinks are each formed from a thermally conductive material such as metal. 
     The inverter  36  also comprises at least one capacitor (not shown) for filtering electrical signals from the inverter. The capacitor is arranged in a capacitor bank  34  which may contain one or more capacitors. The capacitor bank is arranged, for example, in a recess in the first heat sink  39 . Said recess may be closed by the second heat sink  40 . The capacitor bank  34  is, in this instance, arranged between the two heat sinks in order to improve the cooling of said bank. 
     The machine  10  further comprises a cover  42  mounted on the inverter  36 . For example, the cover is formed from an electrically insulating material such as plastic. By way of further example, the cover is a one-piece component and is, in particular, formed as a single part, for example by molding. 
     The cover  42  comprises a skirt  43  extending in an axial direction and forming a perimeter of the cover. In other words, the perimeter forms an outer periphery inside which an inner portion of the cover is defined. The cover  42  has an open region  44  arranged in the inner portion. The open region  44  extends over at least 50%, and in particular at least 70%, of an axial end area of the inner portion of the cover  42 . The axial end area of the inner portion of the cover is defined as being the area delimited by the perimeter of the skirt. In other words, the cover  42  is closed axially over an area covering less than half the total axial end area of said cover. 
     In the example shown in  FIG.  2   , the open region  44  extends over an area equal to 84% of the axial end area of the inner portion of the cover  42 . The temperature of the inverter  36  at a given speed is, on average, with this example of the opening percentage of the open region, approximately 143.2° C., whereas the temperature of an inverter of the prior art comprising a conventional cover that has an opening percentage of less than 20% is approximately 147° C. With this exemplary embodiment of the invention, the temperature of the inverter  36  at a given speed has therefore dropped by 3.8° C. compared to a cover of the prior art. 
     The open region  44  may be arranged in such a way as to be at least partially axially aligned with the capacitor bank  34 . Moreover, in this example, the inverter  36  comprises a heat sink plate  41  arranged to cover the control stage. For example, the heat sink plate  41  is formed from a metal material. More specifically, a thermal adhesive may be arranged between the part of the second heat sink  40  in contact with the capacitor bank  34  and the heat sink plate  41 . This helps improve the cooling of the capacitor bank by conduction. The fact that the cover  42  is axially open over at least 50% of its area and in particular above the capacitor bank  34  helps further improve the cooling of said bank. Indeed, the rear axial end surface of the heat sink plate  41  is exposed to a greater quantity of cooling air flow, and this also helps prevent hot air from stagnating axially between the cover  42  and said plate  41 . 
     The open region  44  is arranged facing the heat sink plate  41 . Moreover, in this instance, a signal connector  46  is arranged to pass through said plate  41  and the open region  44  in order to connect the control module  23  to a computer external to the vehicle for controlling the machine. 
     The open region  44  is formed from at least one axial opening  45 . In the example shown in  FIGS.  2  and  3   , the open region comprises three axial openings  45 . The openings  45  are in this instance of different shapes and sizes. 
     The cover  42  may comprise at least one axial protection portion  47  arranged axially opposite at least one phase connection  38 . The axial protection portion extends into the inner portion from the skirt  43 . Said portion  47  extends in a radial direction. In the example shown in  FIG.  2   , the stator  15  comprises six phase outputs  33  grouped into pairs along the circumference of the machine. Therefore, in this instance, the cover  42  comprises three axial protection portions  47 , each being arranged axially opposite two phase connections  38 . Alternatively, each axial protection portion could be arranged opposite a single phase connection or a number of phase connections greater than two. 
     The skirt  43  extends circumferentially so as to at least partially surround the inverter  36  and, in particular, the control stage. The skirt  43  comprises at least two radial protection portions  48  and at least one connecting portion  49 . Each radial protection portion  48  is arranged radially opposite at least one phase connection  38  of the machine. Preferably, each axial protection portion  47  extends from a radial protection portion  48 . In the example shown in  FIG.  2   , the skirt  43  comprises three radial protection portions  48 , each being arranged radially opposite two phase connections  38 . Alternatively, each radial protection portion could be arranged opposite a single phase connection or a number of phase connections greater than two. 
     The connecting portion  39  extends circumferentially between two radial protection portions  48 . Therefore, the skirt is formed from a succession of radial protection portions  48  and connecting portions  49 . The connecting portions  49  extend, in particular, in such a way as to be aligned axially in relation to each other. For example, in this instance, the skirt  43  forms a closed annular perimeter. 
     As shown in  FIG.  3   , the connecting portion  49  has, in this instance, a height H2 less than the respective height H 1  of the radial protection portions  48 , the heights H1, H2 being measured in an axial direction. An axial end of the connecting portion  49  is, preferably, arranged so as to be aligned in a radial plane with an axial end of the adjacent radial protection portions  48 . 
     In the example shown in  FIG.  2   , the height H2 of the connecting portion  49  is less than half the height H 1  of the radial protection portions  48 . 
     The difference in height between the radial protection portions  48  and the connecting portion  49  makes it possible to form a primary radial opening region in the cover  42 . For example, the primary radial opening region is formed from one or more primary radial openings  50 . Two radial protection portions  48  are separated from each other both by a connecting portion  49  and by a primary radial opening  50 . The stack of the power stage and the control stage defines a cooling passage  52  between said stages, which can be seen in  FIG.  2   . Each primary radial opening  50  is arranged at least partially facing said cooling passage  52 . 
     In the example of  FIGS.  2  and  3   , each radial protection portion  48  may comprise a secondary radial opening region, for example formed from one or more secondary radial openings  51 . The secondary radial openings help improve the cooling of the inverter  36  and the phase connections  38  while allowing said connections to be protected from the external environment of the machine. For example, the area of the secondary radial opening region is between 15% and 25% of the area of the associated protection portion  48 . 
     More specifically, in the example shown here, each secondary radial opening  51  extends from an axial end of the skirt and, in particular, from the associated axial protection portion  47 . With continuing reference to this example, the secondary radial opening region is formed from three secondary radial openings  51 . Two of said openings  51  are, in this instance, arranged axially between a respective phase connection  38  and the axial protection portion  47 . The other opening  51  is, in this instance, arranged radially between two phase connections  38 . 
     The cover  42  may comprise several fastening portions  53  arranged to mount said cover on the inverter  36 . For this purpose, each fastening portion has, for example, an opening through which a fastening element  54  is inserted. The cover and the inverter are assembled together, in particular, by screwing or clip-fastening. In the example shown in  FIG.  3   , each fastening portion  53  extends radially from the skirt  43  into the inner portion of the cover  42  and, in particular, from a connecting portion  49 . Each fastening portion  53  may be partially surrounded by a rim  56  extending axially in particular to stiffen said fastening portion. 
     The cover  42  may comprise a gripping means  55  making it possible, during the process of assembling the machine, to simplify the arrangement of the cover on the inverter  36  before they are fastened together. In the example shown in  FIG.  3   , the gripping means  55  is formed from a planar portion extending in a radial plane into the inner portion of the cover  42 . This makes it possible, in particular, to use an automatic gripping device to position the cover  42  on the inverter  36 . More specifically in this example, the cover comprises two gripping means  55 . The first gripping means extends between two fastening portions  53  and the second gripping means extends between a fastening portion  53  and an axial protection portion  47 . For example, each gripping means  55  extends axially at a non-zero axial distance from the skirt  43 . In other words, in this instance, each gripping means  55  extends in a radial plane not comprising the skirt  43 . For this purpose, each gripping means  55  extends more particularly from an axial end of the rim  56  partially surrounding the associated fastening portion  53  or from an axial set-back portion  57  formed between the axial protection portion  47  and said means  55 . 
     A shown in  FIG.  2   , the axial end of the machine  10  is formed locally by several elements arranged in different radial planes: the signal connector  46 , the heat sink plate  41 , the cover  42  and, in particular, the gripping means  55  of the cover. 
     As shown in  FIGS.  1  and  4   , the rotating electric machine  10  further comprises a shutter  58  arranged axially between the inverter  36  and the casing  11 . More specifically in this instance, the shutter is mounted sandwiched between the rear end plate  17  and the first heat sink  39  and may comprise openings for the passage of an element for fastening the inverter  36  with the casing  11 . The shutter may, moreover, comprise at least one damper  60  in order to help assemble the shutter in a more solid manner. 
     For example, the shutter  58  has an annular shape and is arranged in such a way as to at least partially cover axial openings formed in the rear end plate  17 . The shutter  58  comprises openings  59  through which the phase outputs  33  of the stator can pass. 
     In the example shown in  FIG.  4   , the shutter  58  comprises a radially extending portion  61  arranged so as to be aligned in an axial direction with the capacitor bank  34  of the inverter  36 . The radially extending portion  61  extends, in particular, in a radial direction, in such a way as to form an external radial projection of the shutter. For example, the radially extending portion  61  is surrounded on its outer periphery by a rim  62  extending axially. 
     The shutter is in particular formed from an electrically insulating material such as plastic. For example, at least one portion of the shutter  58  comprises a grooved area helping to stiffen said shutter. The grooved area extends in particular over the radially extending portion  61 . 
       FIG.  5    shows another example of a cover  42  not comprising a portion specifically forming a gripping means  55 . The other features and elements forming this cover are identical or essentially identical to those disclosed in the description of the first example of a cover described with reference to  FIGS.  2  and  3   . 
     Thus, in this second example of a cover  42 , the open region  44  extends over at least 95% of the axial end area of the inner portion of the cover  42 . In other words, in this instance, the entire area of the inner portion is open, apart from the areas forming the axial protection portions  47  and the areas forming the fastening portions  53 . In this example, the open region  44  is formed from a single axial opening  45 . 
     In one variant of this second exemplary embodiment, which is not shown, it is conceivable to modify the fastening portions  53  and the axial protection portions  47  so that they do not extend into the inner portion of the cover and to therefore further increase the opening percentage of the open region in order to obtain an opening percentage equal to 100%. 
     The present invention is applicable in particular in the field of alternators, starter-alternators or reversible machines, but it could also apply to any type of rotating machine. 
     Naturally, the preceding description has been given only by way of example and does not limit the field of the present invention, from which a departure would not be made by replacing the various elements with any other equivalents.