Abstract:
An electric compressor for compressing a gas, particularly configured for use in a motor vehicle, comprising a control unit, an electric motor controlled by the control unit, a compressor wheel driven by the electric motor, and a housing at least partially surrounding the electric motor. The housing is produced by an encapsulation method such that a cooling structure is formed integrally with the housing, in particular within the housing, for ensuring cooling of the electric motor and of the control unit. A method for producing the electric compressor of this kind is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit and priority of German Application No. DE 102015214788.6, filed on Aug. 3, 2015. The entire disclosure of the above application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates generally to an electric compressor for compressing a gas, and in particular to such an electric compressor for a motor vehicle, and to a method for producing an electric compressor. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]    In general, compressors in the automotive sector are associated especially with the desire for an increase in the power and efficiency of an internal combustion engine of a motor vehicle. 
         [0005]    One of the probably best known embodiments of a compressor is the exhaust turbocharger. The exhaust turbocharger is used to ensure an adequate quantity of combustion air in the cylinders of the internal combustion engine by compressing ambient air or an ambient air/exhaust gas mixture and thus supplying the cylinders with this combustion air at excess pressure. 
         [0006]    In general, exhaust turbochargers consist of an exhaust turbine and a compressor wheel, wherein the exhaust turbine and the compressor wheel are arranged on a common shaft. The exhaust turbine converts the heat and kinetic energy of the exhaust gas from the internal combustion engine into rotational energy. This rotational energy is transferred via the common shaft to the compressor wheel. By means of the compressor wheel, ambient air or a mixture of ambient air and exhaust gas is drawn in and compressed. It is thereby possible to achieve a higher working pressure for the same temperature in the cylinder of the internal combustion engine. 
         [0007]    As long as there is sufficient exhaust gas flowing in on the side of the internal combustion engine and driving the exhaust turbine, the speed of rotation is sufficient to bring about an excess pressure on the intake side. However, when accelerating the motor vehicle, for example, the turbo may respond with a delay (even) at relatively high speeds of rotation—this state being commonly known as “turbo lag”. 
         [0008]    There are many approaches to counteracting the occurrence of turbo lag. For example, the inertia of the exhaust turbine can be reduced by making it smaller. Although this lowers the efficiency of the turbo, the exhaust turbine can be driven even by a weak exhaust gas flow. 
         [0009]    Another approach in this context is the use of an (additional) electrically driven compressor (electric compressor), for example, which is configured to operate independently of the exhaust gas flow of the internal combustion engine. An electrically driven compressor generally likewise has a compressor wheel, although this can be driven by an electric motor. 
         [0010]    The publication WO 99/10654 describes an electrically driven compressor, for example, wherein the compressor and the electric drive motor are arranged coaxially with one another on a shaft and are accommodated in a common housing. In particular, the primary object here is to specify a compressor which is of as small construction as possible. 
         [0011]    In planning an electric compressor, an embodiment of the overall compressor which is, in particular, optimized in terms of components and compact is the primary consideration. 
         [0012]    In the case of high-speed engine components such as an electric compressor, there are high induced electrical voltages owing to the high speeds of rotation. During operation, these high voltages and the applied currents lead to heat generation, which must be dissipated by external cooling to be able to ensure continuous operation at predetermined power levels. 
         [0013]    The publication DE 10 2008 003 784 A1, for example, describes a device and a method for the full encapsulation of stators of electric motors having internal rotors. In the method described, rotation is imparted to the stator during and/or after the introduction of a fluid casting compound, wherein the casting compound is introduced radially from the inside outwards, with the result that the casting compound is distributed so as to fill cavities and in a uniform manner during the rotation process. Owing to the centrifugal forces which the rotation exerts on the casting compound, the casting compound is forced into all the cavities and windings of the stator. In this process, the stator is fully encapsulated. By means of full encapsulation of the stator and, in particular, of the stator windings, the electric motor can be made very compact and, depending on the full encapsulation material used, heat transfer from the stator or stator winding to the housing can be influenced in a positive way—the housing representing the heat sink here. 
       SUMMARY 
       [0014]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0015]    On the one hand, it is an object of the invention to specify an electric compressor which, while being of compact construction, can be operated at high power and, on the other hand, it is an object of the invention to specify a simple method for producing a compressor of this kind. 
         [0016]    The solution of the first aspect of the object is accomplished by an electric compressor for compressing a gas, in particular for a motor vehicle, comprising a control unit, an electric motor, wherein the electric motor can be controlled by means of the control unit, a compressor wheel, wherein the compressor wheel can be driven by means of the electric motor, and a housing, wherein the housing at least partially surrounds the electric motor, wherein the housing is produced in such a way by means of an encapsulation method that a cooling structure is formed integrally with the housing, in particular in the housing, ensuring cooling of the electric motor and of the control unit. 
         [0017]    The solution of the second aspect of the object is accomplished by a method for producing an electric compressor of this kind, wherein the housing is produced in such a way by means of an encapsulation method that a cooling structure is formed integrally with the housing, in particular in the housing. 
         [0018]    The electric compressor according to the invention has a control unit, an electric motor, a compressor wheel and a housing. 
         [0019]    According to the invention, the electric motor can be controlled by means of the control unit and is used for selective driving of the compressor wheel. 
         [0020]    The control unit represents the power and signal electronics for the electric motor and preferably comprises a circuit board, on which various electronic modules, e.g. capacitors, semiconductor chips etc. can be arranged. 
         [0021]    However, the control unit can also be taken to mean a plug connector, in which case the circuit board, including the various electronic modules arranged thereon, is embodied as an external control module. 
         [0022]    The compressor wheel and the electric motor are preferably arranged coaxially on a common shaft, wherein the shaft is formed along a central axis of rotation of the electric motor. 
         [0023]    The electric motor has a rotor and a stator having at least one stator winding but, in general, a plurality of stator windings. 
         [0024]    The control unit is arranged along the central axis of rotation of the electric motor, preferably coaxially with the electric motor, and is connected electrically to the electric motor, more precisely to the stator windings of the stator of the electric motor, by at least one connecting element. 
         [0025]    According to the present invention, the electric motor is used to drive the compressor wheel. 
         [0026]    The rotor of the electric motor is preferably arranged for conjoint rotation on the shaft and/or is formed integrally with the shaft. 
         [0027]    The compressor wheel is preferably arranged for conjoint rotation on the shaft and/or is formed integrally with the shaft. 
         [0028]    The rotational energy generated by the electric motor is transferred to the compressor wheel via the common shaft. 
         [0029]    According to the invention, the housing of the electric compressor according to the invention is used to at least partially accommodate the electric motor, in particular the stator of the electric motor. 
         [0030]    The housing of the electric compressor according to the invention is preferably used to at least partially accommodate the control unit. 
         [0031]    According to the invention, the housing is produced by means of an encapsulation method, wherein a cooling structure is formed integrally with the housing, in particular in the housing. 
         [0032]    The encapsulation method is preferably an injection moulding method or a diecasting method. 
         [0033]    Here, polymeric materials, e.g. thermosetting plastics, thermoplastics etc. are used as casting compounds, for example. In general, these materials are filled with inorganic materials in order to improve certain material properties, e.g. thermal conductivity. 
         [0034]    By means of the embodiment according to the invention of the electric compressor, efficient cooling, particularly of the electric motor and of the control unit, can be achieved. In this way, given appropriate choice of the casting compound used in the encapsulation method, a higher power of the electric motor combined with compact and simple construction can be achieved in a simple manner. Moreover, reliable operation of the electric compressor in a manner which is optimized in terms of service life can be ensured, particularly through the efficient cooling of the control unit. 
         [0035]    The housing at least partially performs the protection of the electric motor from external negative influences, e.g. contaminants, and furthermore performs the cooling function of the electric motor. 
         [0036]    The method according to the invention for producing an electric compressor described above comprises producing the housing by means of an encapsulation method, wherein the encapsulation method is performed in such a way that the cooling structure is formed integrally with the housing, in particular in the housing. 
         [0037]    Through the production, according to the invention, of a housing with an integrated cooling structure for efficient cooling of the electric motor and of the control unit of the electric compressor according to the invention, it is possible to dispense with additional components in this region. 
         [0038]    Moreover, the production according to the invention of the electric compressor also makes it possible to optimize and/or eliminate other components, e.g. in the region of the mounting of the shaft. 
         [0039]    At the same time, the production method can be carried out in a simple manner, and the cooling structure in the housing can be configured on an individual basis, depending on the cooling requirements and design configuration of the electric motor and of the control unit. 
         [0040]    In an advantageous embodiment of the present invention, the cooling structure has a plurality of cooling ducts. 
         [0041]    In this way, appropriate cooling of the electric motor and of the control unit can be accomplished in a simple manner. 
         [0042]    In another advantageous embodiment of the electric compressor according to the invention, the cooling structure is formed at least partially around the outer circumference of the stator of the electric motor. 
         [0043]    The stator has at least one stator winding, preferably a plurality of stator windings. 
         [0044]    Forming the cooling structure at least partially around the outer circumference of the stator allows efficient cooling, especially of the electrically loaded stator winding. 
         [0045]    The stator is preferably of substantially annular design and has a plurality of axially extending recesses uniformly spaced apart along its outer circumference. 
         [0046]    The direction indication “axially” refers to a direction along the central axis of rotation of the electric motor. 
         [0047]    It is advantageous if the cooling structure has a number of cooling ducts corresponding to the number of recesses of the stator. 
         [0048]    However, it is also possible for there to be more or fewer cooling ducts around the stator. 
         [0049]    It is furthermore advantageous if the cooling ducts extend axially along the recesses of the stator. 
         [0050]    Through the configuration of the recesses of the stator and furthermore of the arrangement of one cooling duct of the cooling structure in each recess, an extremely compact construction combined with efficient cooling, particularly of the stator, is achieved. 
         [0051]    In another advantageous variant embodiment of the present invention, the cooling structure is formed at least partially on a rear side of the control unit. 
         [0052]    In this way it is possible to ensure cooling of further high-load electronic components in a simple manner. 
         [0053]    The housing is preferably manufactured from an electrically insulating material of good thermal conductivity. 
         [0054]    The cooling structure is preferably produced by means of internal-pressure injection moulding and/or by the introduction of at least one moulding body. 
         [0055]    Moreover, in an advantageous embodiment of the invention, at least one opening is formed by means of internal-pressure injection moulding and/or by the introduction of at least one opening moulding body. 
         [0056]    Through the formation, for example, of a central opening along the central axis of rotation of the electric motor, within the stator of the electric motor, installation space for the shaft and the rotor can be configured in a simple manner. 
         [0057]    By way of example, the moulding body and the opening moulding body are arranged, together with that part of the electric compressor according to the invention which is to be encapsulated, at least in part the electric motor of the electric compressor according to the invention, in a suitable encapsulation device and encapsulated with casting compound. 
         [0058]    After the encapsulation process, i.e. after the curing of the casting compound, the moulding body and the opening moulding body are preferably removed mechanically and/or vaporized by a chemical reaction and/or a thermal reaction. 
         [0059]    In the case of the formation of the cooling structure and/or of the opening by means of internal-pressure injection moulding, a filler, e.g. water or an inert gas such as nitrogen, is introduced into a gas-tight device partially filled with fluid uncured casting compound. In the device, the filler acts as an internal moulding piece and displaces the casting compound radially from the inside outwards in the direction of the inner walls of the device. In this way, a cavity is created within the casting compound. After the casting compound has cured, the filler can escape from the device, and the cavity created forms the cooling structure. 
         [0060]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0061]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0062]    The invention is described below by way of example with reference to the drawings. 
           [0063]      FIG. 1  shows a longitudinal section through an electric compressor according to the invention. 
           [0064]      FIG. 2  shows one perspective view of a control unit and of a stator of an electric motor of an electric compressor according to the invention. 
           [0065]      FIG. 3  shows a perspective detail view from  FIG. 3 . 
           [0066]      FIG. 4  shows a perspective view of a housing, including a control unit, and of a stator of an electric motor of an electric compressor according to the invention. 
           [0067]      FIG. 5  shows  FIG. 4  in a longitudinal section. 
           [0068]      FIG. 6  shows  FIG. 4  in a cross section. 
           [0069]      FIG. 7  shows  FIG. 4  in another cross section at the interface between the electric motor and the control unit. 
           [0070]      FIG. 8  shows a plan view of the control unit according to  FIG. 4 . 
           [0071]      FIG. 9  shows  FIG. 4  in another longitudinal section, including arranged mould parts. 
           [0072]      FIG. 10  shows a perspective illustration of the electric compressor according to the invention. 
       
    
    
     DESCRIPTION 
       [0073]    One or more example embodiments of an electric compressor are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0074]    An electric compressor, shown in  FIG. 1 , is configured to include a control unit  2 , an electric motor  3 , a compressor wheel  4  and a housing  6  ( FIG. 4 ). The electric motor  3  can be controlled by means of the control unit  2  and is used for selective driving of the compressor wheel  4 . The compressor wheel  4  and the electric motor  3  are arranged coaxially on a common shaft  5 , wherein the shaft  5  is formed along a central axis of rotation  13  of the electric motor  3 . The compressor wheel  4  is arranged in a compressor wheel housing  17 . The compressor wheel housing  17  is formed by the joining together of a first compressor wheel housing part  18  and a second compressor wheel housing part  19 . 
         [0075]    The electric motor  3  is designed as an internal-rotor electric motor and has a rotor  14  with permanent magnets and a stator  9  with six stator windings  15 . The electric motor  3  is used to drive the compressor wheel  4 . The rotor  14  of the electric motor  3  is arranged for conjoint rotation on the shaft  5 . The compressor wheel  4  is arranged for conjoint rotation on the shaft  5 . The rotational energy generated by the electric motor  3  is transferred to the compressor wheel  4  via the common shaft  5 . 
         [0076]    The control unit  2  is arranged coaxially with the electric motor  3  along the central axis of rotation  13  of the electric motor  3  and is connected electrically to the electric motor  3 , more precisely to the stator windings  15  of the stator  9  of the electric motor  3 , by at least one connecting element  16 . 
         [0077]      FIG. 2  shows a perspective view of a control unit  2  and of a stator  9  of an electric motor  3  of an electric compressor  1  according to the invention. The control unit  2  represents the power and signal electronics for the electric motor  3  and comprises a circuit board  20 , on which various electronic modules  21  are arranged, in this case including capacitors  22 , and in this case likewise two plug connectors  23 . The two plug connectors  23  are, on the one hand, a power connector and, on the other hand, a signal connector. 
         [0078]    The stator  9  of the electric motor  3  comprises six individual stator segments  24 , six stator windings  15 , which are arranged on the stator segments  24 , and a stator carrier  25 . The stator carrier  25  is of annular design and surrounds the stator segments  24  and the stator windings  15 . The outer circumference of the stator carrier thus forms the outer circumference  10  of the stator  9  of the electric motor  3 . On the outer circumference  10 , the stator carrier  25  has a plurality of uniformly spaced, axially extending recesses  11 . The direction indication “axially” refers to a direction along the central axis of rotation  13  of the electric motor  3 . In the region between each of the recesses  11 , the stator carrier  25  has projections  26  in the region of a side facing away from the control unit  2 . 
         [0079]    The projections  26  extend radially over a part of the outer circumference  10  of the stator carrier  25  in the region between two recesses  11 . The direction indication “radially” refers to a direction normal to the central axis of rotation  13  of the electric motor  3 . The projections  26  are embodied in such a way that the capacitors  22  of the control unit  2  can extend axially along the stator  9  as far as the projections  26  in the region between two recesses  11 . In this way, a compact and robust arrangement of the electric motor  3  and of the control unit  2  is achieved. 
         [0080]    The perspective view, already described by means of  FIG. 2 , of the control unit  2  and of the stator  9  of an electric motor  3  without the stator carrier is shown in  FIG. 3 . Here, the six stator windings  15  of the stator can be seen. The rotor  14  (not shown;  FIG. 1 ) arranged on the shaft  5  is arranged in the region of the central opening  27  of the stator  9 . 
         [0081]      FIG. 4  shows the perspective view, already described by means of  FIG. 2  and  FIG. 3 , of the control unit  2  and of the stator  9  of an electric motor  3  with the housing of the electric compressor  1  according to the invention.  FIG. 5  shows a longitudinal section through the perspective illustration in  FIG. 4 . The stator  9  of the electric motor  3  and the control unit  2  are arranged in the housing  6  of the electric compressor  1  according to the invention. The housing  6  is produced by an encapsulation method, wherein a cooling structure is formed in the housing  6 , integrally with the housing  6 . 
         [0082]    The cooling structure  7  has a plurality of cooling ducts  8 , wherein the cooling ducts  8  are formed around the outer circumference  10  of the stator of the electric motor  3 , the cooling ducts  8  extending, in particular, axially along the recesses  11  of the stator (of the stator carrier  25 ). The cooling structure  7  of the illustrative electric compressor  1  under consideration has a number of cooling ducts  8  corresponding to the number of recesses  11  of the stator  9 , i.e. six cooling ducts  8 . 
         [0083]    The cooling ducts  8  each extend radially from the recess  11  on the outer circumference  10  of the stator  9  into the region of the capacitors  22  of the control unit  2 , which extend axially along the outer circumference  10  of the stator  9 , in each case between two recesses  11 . Here, the radial extent of the projections  26  is shorter than the radial extent of the cooling ducts  8 . The cooling ducts  8  serve not only to cool the electric motor  3  but are also used to cool the capacitors  22 . Via the cooling duct passages  28 , the rear side  34  of the control unit  2 , namely that side of the control unit  2  which faces away from the electric motor  3 , is also cooled. 
         [0084]    A first cross section through the perspective view, shown in  FIG. 4 , of the control unit  2  and of the stator  9  of an electric motor  3 , together with the housing  6  of the electric compressor  1  according to the invention, is shown in  FIG. 6 . Here, it is possible to see, in particular, the distribution of the projections  26 , of the capacitors  22  and of the cooling ducts  8  along the outer circumference  10  of the stator carrier  25 . 
         [0085]      FIG. 7  shows another cross section through the perspective view, shown in  FIG. 4 , of the control unit, together with the housing  6  of the electric compressor  1  according to the invention, at the interface between the electric motor  3  and the control unit  2 . Here too, the distribution of the capacitors  22  and of the cooling ducts  8  along the outer circumference  10  of the stator carrier  25  can be seen. Moreover, one of three connecting elements  16 , by means of which the electric motor  3  is connected electrically to the control unit  2 , is shown. The connecting elements  16  represent the electrical interface between the electric motor  3 , more precisely the stator windings  15 , and the control unit  2 . 
         [0086]    A plan view of control unit  2 , as it is shown in  FIG. 4 , is shown in  FIG. 8 . In the region of the control unit  2 , the cooling structure  7  of the electric compressor  1  according to the invention has two cooling-duct passages  28 , which serve to cool the rear side  34  of the control unit  2 , namely that side of the control unit  2  which faces away from the electric motor  3 , wherein in this way the cooling of further high-load electronic modules  21  of the control unit  2  is accomplished, in particular. The cooling structure  7  is supplied with cooling fluid via a cooling-fluid inlet  32  and a cooling-fluid outlet  33 . 
         [0087]    The method according to the invention for producing the electric compressor  1  described comprises the production of the housing  6  by means of an encapsulation method, wherein the encapsulation method is performed in such a way that the cooling structure  7 , that is to say in this case the cooling ducts  8 , is (are) formed integrally with the housing  6 , in the housing  6 . Here, the cooling structure  7  is produced by introducing moulding bodies  12 . 
         [0088]      FIG. 9  shows a longitudinal section through the perspective view, shown in  FIG. 4 , with inserted moulding bodies  12  and an opening moulding body  29 . After the encapsulation process, the moulding bodies  12  and the opening moulding body  29  are removed mechanically. 
         [0089]    As shown in  FIG. 9 , the moulding bodies  12  serve to form the cooling ducts  8  of the cooling structure  7  and, in accordance with the illustrative embodiment under consideration, have a trapeziform cross section, resulting in the formation of trapeziform cooling ducts  8  in the housing. However, the moulding bodies  12  and thus the cooling ducts  8  can be configured in any desired shape. The opening moulding body  29  serves to form the central opening  27  and has a substantially circular cross section, resulting in a circular central opening  27  for the arrangement of the shaft  5  and of the rotor  14 . 
         [0090]    In this illustrative embodiment, the stator  9  and the control unit  2  are completely encapsulated by means of the encapsulation method, with only those points at which the moulding bodies  12  and the opening moulding body are inserted remaining free, thus forming the cooling structure  7  and also the central opening  27 . 
         [0091]      FIG. 10  shows the illustrative electric compressor  1  according to the invention, shown in  FIG. 1  in a longitudinal section, in a perspective view, wherein in this case a compressor gas inlet  30  and a compressor gas outlet  31  are formed on the compressor wheel housing  17 . The assembly of the compressor wheel housing  17  and of the housing  6  of the electric compressor  1  is furthermore visible. 
         [0092]    According to the present invention, the compressor wheel housing  17  can also be formed integrally with the housing  6  of the electric compressor  1 . 
         [0093]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
       LIST OF REFERENCE SIGNS 
       [0094]      1 . electric compressor 
         [0095]      2 . control unit 
         [0096]      3 . electric motor 
         [0097]      4 . compressor wheel 
         [0098]      5 . shaft 
         [0099]      6 . housing 
         [0100]      7 . cooling structure 
         [0101]      8 . cooling duct 
         [0102]      9 . stator 
         [0103]      10 . outer circumference (of the stator/stator carrier) 
         [0104]      11 . recess 
         [0105]      12 . moulding body 
         [0106]      13 . central axis of rotation 
         [0107]      14 . rotor 
         [0108]      15 . stator winding 
         [0109]      16 . connecting element 
         [0110]      17 . compressor wheel housing 
         [0111]      18 . first compressor wheel housing part 
         [0112]      19 . second compressor wheel housing part 
         [0113]      20 . circuit board 
         [0114]      21 . electronic modules 
         [0115]      22 . capacitors 
         [0116]      23 . plug connector 
         [0117]      24 . stator segment 
         [0118]      25 . stator carrier 
         [0119]      26 . projection 
         [0120]      27 . opening 
         [0121]      28 . cooling duct passage 
         [0122]      29 . opening moulding body 
         [0123]      30 . compressor gas inlet 
         [0124]      31 . compressor gas outlet 
         [0125]      32 . cooling fluid inlet 
         [0126]      33 . cooling fluid outlet 
         [0127]      34 . rear side (of the control unit)