Abstract:
An electric motor for driving a motor vehicle component, in particular a fan impeller for cooling cooling water, having an electronics unit that includes a lead frame around which injection-molded plastic is provided and which has a current path conducting the motor current, and having two spaced-apart current path ends that form an interruption point bridged by a thermal fuse in the form of a spring-biased contact bridge. The contact bridge is mounted so as to be pivotable about an axis of rotation extending perpendicular to the plane of the interruption point. An abutment contour, against which the contact bridge pivots as a result of the restoring force of a spring element when the thermal fuse is triggered, limits the pivoting range of the contact bridge.

Description:
[0001]    This nonprovisional application is a continuation of International Application No. PCT/EP2015/063136, which was filed on Jun. 12, 2015, and which claims priority to German Patent Application No. 20 2014 004 732.4, which was filed in Germany on Jun. 12, 2014, and which are both herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The invention relates to an especially brushless electric motor for driving a motor vehicle component, comprising an electronics unit that includes a lead frame, which is provided with plastic encapsulation and has a current path conducting the motor current, and having two spaced-apart current path ends that form an interruption point bridged by a thermal fuse in the form of a spring-biased contact bridge. A motor vehicle component is understood to be in particular a fan impeller for cooling the cooling water. 
         [0004]    Description of the Background Art 
         [0005]    DE 20 2010 002 664 U1, which corresponds to U.S. Pat. No. 8,633,621, which is incorporated herein by reference, and which discloses a DC motor for driving a motor vehicle component, in particular a fan impeller for cooling the cooling water, with a rotor and a commutator, against which carbon brushes rest in a contacting manner. A plastic-encapsulated lead frame forms a current path which is embossed in an electrical insulation and is connected in an electrically conductive manner to one of the carbon brushes. The current path, which conducts the motor current, is interrupted with the formation of two spaced-apart current path ends and the interruption point is bridged by a contact spring as the thermal fuse. 
         [0006]    DE 10 2009 036 578 B3 relates to a thermal fuse, in particular for a power module of a motor vehicle, with a conductive strip, which is arranged on a circuit board and is interrupted by an interruption point, and which has a first conductive strip section and a second conductive strip section adjacent to the interruption point. A contact bridge, which is arranged in the area of the interruption point, has a first contact section and a second contact section arranged opposite to one another. The contact sections in a first position are attached to conductive strip sections by solder at soldering sites. The contact bridge in the first contact position is acted upon by a spring force in such a way that, when the melting point of the solder is reached, the contact sections of the corresponding conductive strip sections are separated. Further, the thermal fuse has a spring element which, when the melting point of the solder is reached, brings about a movement of the contact bridge, which extends parallel to the circuit board. In the second or triggering position, the contact bridge is held in a cage without contacting the first conductive strip section. 
         [0007]    DE 10 2009 036 578 B3 discloses a thermal fuse with a spring-biased contact bridge, whose triggering movement in the event of triggering is oriented parallel to a circuit board, on which conductive strip sections run which are adjacent to a separation site and with which the contact bridge is contacted by means of solder melting in the event of triggering. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the invention is to provide an especially brushless electric motor for driving a motor vehicle component, in particular a fan impeller for cooling the cooling water, with a space-saving and reliably triggering thermal fuse. 
         [0009]    To this end, the electric motor has in an exemplary embodiment, in addition to a rotor mounted so as to be rotatable relative to a stator, an electronics unit that includes a lead frame, which is provided with plastic encapsulation and has a current path conducting the motor current, and two spaced-apart current path ends, forming an interruption point, and a thermal fuse with a spring-biased contact bridge for the interruption point. The contact bridge, which has contact surfaces corresponding to the current path ends, is mounted so as to be pivotable about an axis, which extends perpendicular to the plane in which the interruption point is located. An abutment contour limiting the pivoting range of the contact bridge is used as a stop for the contact bridge when the thermal fuse is triggered. 
         [0010]    In the case of triggering, the contact bridge pivots in the plane of the interruption point. As a result, a space-saving configuration option for the thermal fuse including the contact bridge and the spring element is made possible. 
         [0011]    The abutment contour, acting as an end stop for the contact bridge when the thermal fuse is triggered, is suitably formed from the plastic encapsulation. Advantageously the contact bridge moreover is arranged overall in a circle segment-like guide slot formed from the plastic encapsulation. The interruption point is arranged along one of the circle radii and the abutment contour in the area of the other circle radius of the circle segment-like guide slot. 
         [0012]    The circle segment shape of the guide slot makes it possible in a simple and reliable manner to limit the pivoting range of the contact bridge at at least one of the circle radii and to guide the contact bridge expediently also along an arcuate web contour of the guide slot. To this end, the contact bridge, suitably formed as or in the manner of a stamped/bent part, has a number of bent sections, which form a raised bridge section between the contact surfaces. As a result, the desired mechanical and/or electrical properties of the contact bridge can be established in a simple way. In particular, the contact bridge can be adapted to different current strengths. 
         [0013]    The contact bridge has a free bridge end and a holding end opposite to it. The contact bridge sits with this end on a pivot pin, which is suitably formed from the plastic encapsulation and forms the rotation axis and which passes through a corresponding opening in the holding end of the contact bridge. In the area of the free bridge end there is a first contact surface, which in the normal state when the thermal fuse is not triggered is soldered to one of the current path ends. A second contact surface, which is in contact with the other current path end and can also be soldered to it, is located advantageously between the first contact surface and the rotation axis on the interruption point side facing it. 
         [0014]    The spring element is formed particularly preferably as a leg spring with a spring eye and two spring legs. The spring eye in the assembled state coaxially surrounds the rotation axis, in particular the pivot pin. Thereby, in a simple and reliable manner there is a mutual pivoting of the spring element or its spring legs, acting jointly with the contact bridge, and of the contact bridge about the same rotation or pivot axis. 
         [0015]    One of the spring legs of the leg spring is held on a stop-side extension arm and there suitably in an undercut contour, whereas the other spring leg lies under spring bias against the contact bridge on its long bridge side facing away from the stop contour. There, the contact bridge expediently has extensions, which extend in the pivot direction and are gripped above and below by the bridge-side spring leg. 
         [0016]    When the thermal fuse is triggered, the spring element exerts furthermore a spring force on the contact bridge in the direction of the abutment contour. As a result, it is assured especially reliably that neither the contact bridge nor the spring element becomes detached from their fixation point in the area of the rotation axis. The spring legs of the spring element in this regard in the original state run spread at a suitable angle to one another in such a way that both in the bridged installed state and in the triggered state of the contact bridge the spring legs preferably run at an acute angle to one another and therefore a sufficient spring force always acts on the contact bridge. Suitably, the spring element is made of round wire. Therefore, this provides a cost-effective option for producing the spring element. 
         [0017]    The contact bridge, suitably made as or in the manner of a stamped/bent part with a number of bent sections, forms a raised bridge section in the area of the rotation axis and between the contact surfaces. In addition, the contact bridge preferably has a bent depression, which is directed toward the contact surface facing the rotation axis. Because said contact surface of the rotation axis is placed radially upstream in the direction of the interruption point, only one correspondingly shortened radial bridge section of the contact bridge carries current. 
         [0018]    When the thermal fuse is triggered, i.e., in the case of overheating, the solder melts in the area of the or each current path end, so that the contact bridge in the triggered case can pivot unimpeded about the rotation axis and in the plane of the interruption point. The melted solder connections are thereby practically protected, which assures a reliable interruption of the interruption point or contact point bridged by the thermal fuse or its contact bridge. 
         [0019]    The advantages associated with the invention incle, in particular in that by triggering the thermal fuse in the plane of the interruption point a simple, advantageous, and space-saving option is provided for integrating the thermal fuse in an electric motor preferably constructed with the saving of space. 
         [0020]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0022]      FIG. 1  shows in an exploded illustration a radiator fan for a motor vehicle with a brushless inner rotor motor with integrated inverter electronics; 
           [0023]      FIG. 2  shows an electronics compartment with an electronics unit of the electric motor, with a printed circuit board populated with electrical or electronic components, and with a lead frame provided with plastic encapsulation, and with a thermal fuse; 
           [0024]      FIG. 3  shows the lead frame with the plastic encapsulation including an interruption point to be bridged by the thermal fuse in a perspective illustration; and 
           [0025]      FIG. 4  shows in a detail in a perspective illustration the thermal fuse with a spring-biased contact bridge in the contact position within a guide slot with an abutment contour as the end stop for the contact bridge in the case of thermal fuse triggering. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a fan  1  for the radiator of a motor vehicle in an exploded illustration. Fan  1  comprises a fan impeller  2  with a central cap  3 , around whose outer circumference (only shown to some extent) air guide blades  4  are arranged evenly distributed. Fan  1  comprises furthermore an electric motor  5  which is also referred to as a fan motor and by which fan impeller  2  is rotationally driven. 
         [0027]    Electric motor  5  is formed substantially by a stator  6 , which is wound with a three-phase rotating field winding  7  in the form of coils. Motor  5  comprises furthermore a permanently excited rotor  8 , which is mounted so as to be rotatable about a motor axis  9  in the interior of stator  6 . To mount rotor  8 , motor  5  comprises two roller bearings  10  and  11 , which engage from axially opposite sides in rotor  8 . The axial play of rotor  8  between the two roller bearings  10  and  11  is spring-biased in this case by a spring ring  12 . 
         [0028]    Motor  5  comprises furthermore an approximately disc- or half-shell-shaped motor support  13 . At an end face facing away from fan impeller  2 , an electronics compartment  14 , into which inverter electronics  15  is inserted, is introduced into motor support  13 . To tightly close electronics compartment  14 , motor  5  comprises an electronics compartment cover  16  referred to as a housing cover hereafter. 
         [0029]    Rotor  8  is formed by a lamination stack (not shown in greater detail), in which permanent magnets are inserted to generate an excitation field, whereby the lamination stack together with the inserted permanent magnets are encapsulated by a plastic sheath. In a similar way, stator  6  also has a lamination stack, which is encapsulated by a plastic sheath. 
         [0030]    Motor support  13  is formed in particular by a one-piece die cast part made of aluminum. Electronics compartment cover  16  preferably is an injection-molded part made of plastic. 
         [0031]    On its front side, rotor  8  is provided with four screw domes  18 , by means of which rotor  8  in the assembled state is screwed onto fan impeller  2 . Motor  5  and thereby the entire fan  1  is attached to the vehicle via motor support  13 , which is provided for this purpose with three screw plates  19 , protruding from its outer circumference. Motor  5  is a brushless, self-cooled inner rotor motor. 
         [0032]    In  FIG. 2 , a perspective illustration shows a slightly modified motor support  13  with electronics unit  15  which is inserted into the corresponding electronics compartment  14  and, in contrast to the embodiment according to  FIG. 1 , for example, is assigned only three capacitors. Electronics unit  15  comprises a plastic-encapsulated lead frame  20  and a circuit board or printed circuit board  21  populated with electrical components. Electric motor  5  is driven by a bridge circuit (B6 circuit), which is implemented in the encapsulated lead frame  20 . To this end, encapsulated lead frame  20  has a number of switchable semiconductor elements  22 , by means of which three phase windings of field winding  7  of electric motor  5  are alternately supplied with current. The electrical current used for this purpose is provided by a DC source which is not shown in a more detailed manner. 
         [0033]    The three phase windings of field winding  7  of electric motor  5  are connected, e.g., in a delta circuit via capacitors  23 . In other words, two electrically adjacent phase windings are electrically connected at a motor-side contact point, and the windings in turn are electrically contacted via a bridge-side contact point in each case with a bridge branch of the bridge circuit. The windings are produced from enameled copper wire and rolled centrally to form a coil. 
         [0034]    A thermal fuse  24  can be seen in  FIG. 2  in addition to encapsulated lead frame  20  and semiconductor elements  22  and capacitors  23 . Thermal fuse  24  protects electric motor  5  from overheating and the risk of fire. If motor  5  overheats, thus thermal fuse  24  is triggered and current can no longer flow to or from motor  5 . Terminals  25 ,  26 , and  27  form an input terminal and an output terminal for the motor current or two sensor signal outputs, e.g., for measurements of the rotational speed (number of revolutions), the rotation direction, and/or the position of motor  5 . 
         [0035]    As is evident relatively clearly from  FIG. 3 , lead frame  28 , which realizes the traces and which or the traces of which conduct the motor current, is provided by a plastic encapsulation  29  and electrically insulated. In the area of the thermal fuse removed here, current path ends  30 ,  31  can be seen, which conduct the motor current and between which an interruption point  32  is formed in lead frame  28 . Current path ends  30 ,  31  and interruption point  32  are located in guide slot  33 , which is formed from plastic encapsulation  29  and which is configured in the shape of a circle segment at least on the inside. 
         [0036]    As is evident relatively clearly from  FIG. 4 , thermal fuse  24  is formed from a contact bridge  34 , which in the bridged state connects current path ends  30  and  31  of lead frame  28 . Contact bridge  34  has contact surfaces  35  and  36 , of which at least contact surface  36  associated with a free bridge end  37  of contact bridge  34  is connected by a solder connection to the corresponding current path end  31  of lead frame  28 . The or each soldering site contacts current path ends  30  and  31  with one another electrically via contact bridge  34  and connects contact bridge  34  mechanically to the particular current path end  30 ,  31  of lead frame  28  to form a mechanically stable connection. 
         [0037]    To realize the function of thermal fuse  24 , a separate spring element  38  is provided in the form of a leg spring, which is held with a first spring leg  39  on an extension arm  40 , formed from plastic encapsulation  29 , and there in a rear undercut contour  42  in terms of pivot direction  41  of contact bridge  34 . Second spring leg  43  abuts contact bridge  34  on its front side in terms of pivot direction  41  under spring bias. Spring legs  42 ,  43  of spring element  38  are situated at an acute angle to one another and are connected to one another via a spring or leg loop  45 , forming a spring eye  44  and having a number of spring turns. Spring element  38  sits with said spring eye  44  on a pivot pin  46 , which is formed advantageously also from plastic encapsulation  29  and forms rotation axis  47  for contact bridge  34 . 
         [0038]    Contact bridge  34  with its holding end  48 , which faces away from free bridge end  37  and in which a bored hole (not visible) for receiving pivot pin  46  is introduced, is mounted so as to be rotatable about rotation axis  47  which is perpendicular to the plane in which interruption point  32  lies. Spring loop  45  of spring element  38  and thereby its spring eye  44  are arranged coaxially relative to pin  46  and therefore relative to rotation axis  47 . 
         [0039]    Contact bridge  34  is made in the manner of a stamped/bent part with a number of bent sections, which form a central, raised bridge section  34   a.  Second contact surface  35  of contact bridge  34 , said surface being provided between rotation axis  47  at holding end  48  and interruption point  32 , is situated on the underside of a bent depression  34   b,  said underside facing lead frame  28  and plastic encapsulation  29 , and both middle bridge section  34   a  and holding end  48  of contact bridge  34  are raised relative to the depression. In contrast, both contact surfaces  35  and  36  of contact bridge  34  are located at the same height level based on the plane of interruption point  32 . In this case, contact surface  36  associated with free bridge end  37  is situated underneath a bridge section  34   c,  which is lower relative to raised bridge section  34   a.    
         [0040]    The contact-bridge-side spring leg  43  of spring element  38 , suitably made of round wire, is held by means of two extensions  49 ,  50 , which are formed on contact bridge  34  and extend in the opposite direction to the drawn pivot direction  41 . In this case, this spring leg  43  engages below extension  49 , provided on the middle raised bridge section  34   a,  and engages above extension  50 , provided on the free bridge end  37 . 
         [0041]    The circle segment-like guide slot  33  in the area of its circle radius, facing away from interruption point  32  in pivot direction  41 , forms an abutment contour  51 . This abutment or stop contour  51  serves as a stop for contact bridge  34  when thermal fuse  24  is triggered and therefore as an end stop for the pivoting movement of contact bridge  34  about rotation axis  47 . Interruption point  32  is located accordingly in the area of the opposite or other circle radius or at least adjoins it. 
         [0042]    A slot wall  52 , following the circular arc of circle segment-like guide slot  33 , is also formed from plastic encapsulation  29  and there delimits the partial area of a circular area, said partial area being formed by guide slot  33  and rotation axis  47  being in the center of the circular area. Within guide slot  33 , arcuate slots  53 ,  54  are introduced in plastic encapsulation  29  and in the underlying lead frame  28 . An arcuate guide contour  55  is formed on the inner side, facing rotation axis  47 , of arcuate slot  54  from plastic encapsulation  29  within guide slot  33 . It is located in the transitional region between the middle, raised bridge section  34   a  and bent depression  34   b.  Said guide contour  55  is used additionally for pivoting guidance or sliding guidance of contact bridge  34  when thermal fuse  24  is triggered. 
         [0043]    In the event of triggering after melting of the solder of the soldering sites, contact bridge  34  and the bridge-side spring leg  43  of spring element  38  pivot about pin  46  and therefore about axis  47 . Contact surface  35  of contact bridge  34  is in fact located in the vicinity of rotation axis  47 , but is intentionally arranged spaced apart from it. Thermal fuse  24  is triggered in particular at an excessive temperature in that the solder melts and contact bridge  34  pivots due to the spring force of spring element  38  by a combined rotational and shearing movement, so that interruption point  32  bridged by the biased contact bridge  34  is interrupted. Contact bridge  34  in the case of triggering pivots from a first position (contact position) to a second position (triggering position), whereby the pivoting movement occurs about rotation axis  47  and in the plane of interruption point  32 . In this case, the pivoting movement of contact bridge  34  in pivot direction  41  is limited by abutment contour  51  in that contact bridge  34  strikes it and advantageously furthermore is under spring bias by means of spring element  38 . Contact bridge  34  and in particular spring element  38  in both positions (contact and triggering position) are held securely as a result. During the pivoting, contact spring  34  is securely guided within guide slot  33  also without a guide contour  55 , because contact spring  34  with its contact surfaces  35 ,  36  can slide along the corresponding circle segment-like surface section (surface region) of plastic encapsulation  29 . 
         [0044]    The invention is not limited to the exemplary embodiments described above. Rather, other variants of the invention can also be derived herefrom by the skilled artisan, without going beyond the subject of the invention. Particularly, further all individual features described in relation to the individual exemplary embodiments can also be combined with one another in a different manner, without going beyond the subject of the invention. 
         [0045]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.