Abstract:
An electric motor for driving a motor vehicle component, particularly a fan wheel for cooling coolant water, contains a rotor that is rotatably mounted opposite a stator, and an electronic system. The electronic system contains a punched grid provided with a plastic over-mold and a current path which conducts the motor current and has two current path ends spaced apart from one another forming an interruption point that is bridged by a thermal fuse. The thermal fuse has a spring-loaded contact bridge which is held so as to pivot about an axis that extends perpendicularly to the plane in which the interruption point lies.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation application, under 35 U.S.C. §120, of copending international application No. PCT/EP2013/076638, filed Dec. 16, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application Nos. DE 10 2012 024 604.8, filed Dec. 15, 2012, and DE 10 2013 002 155.3, filed Feb. 7, 2013; the prior applications are herewith incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an electric motor, in particular a brushless electric motor, for driving a motor vehicle component. The electric motor contains a rotor mounted rotatably relative to a stator and an electronics system, which has a punched grid provided with a plastic over-mold and a current path which conducts the motor current and has two current path ends spaced apart from one another forming an interruption point that is bridged by a thermal fuse. The thermal fuse has a spring-loaded contact bridge. In particular, a vehicle component is understood to be a fan wheel for cooling coolant water. 
     German utility model DE 20 2010 002 664 U1 discloses an electric motor, in particular a DC motor, for driving a motor vehicle component, particularly a fan motor for cooling coolant water, having a rotor and a commutator, against which a brush bears with contact. A punched grid over-molded with plastic forms a current path impressed into an electrical isolation, the current path being connected to a brush. The current path, which conducts the motor current, is interrupted so as to form two current path ends spaced apart from one another, and the interruption point is bridged by a contact spring as thermal fuse. 
     German patent DE 10 2009 036 578 B3 relates to a thermal fuse, in particular for a power module of a motor vehicle. The thermal fuse has a conductive path, which is arranged on a circuit board and is interrupted by an interruption point, and which has a first conductive path portion and a second conductive path portion in each case adjacent to the interruption point. A contact bridge, which is arranged in the region of the interruption point, has a first contact portion and a second contact portion arranged opposite one another. The contact portions are secured in a first position to the conductive path portions by solder at soldered points. The contact bridge is acted on in the first contact position by a spring force, in such a way that the contact portions are separated from the corresponding conductive path portions when the melting point of the solder is reached. The thermal fuse also has a spring element, which, when the melting point of the solder is reached, causes a movement of the contact bridge, which extends parallel to the circuit board. In the second or tripped position the contact bridge is held in a cage without contacting the first conductive path portion. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to specify an electric motor, in particular a brushless electric motor, for driving a motor vehicle component, particularly a fan wheel for cooling coolant water containing a thermal fuse, which on the one hand requires a low component part outlay, and with which on the other hand a simple and/or effective arrangement of the component parts in the manufacturing process is enabled. 
     For this purpose, the electric motor has a rotor that is mounted rotatably relative to a stator, an electronics system with a punched grid provided with a plastic over-mold having a current path which conducts the motor current. The current path has two current path ends spaced apart from one another forming an interruption point. A thermal fuse has a spring-loaded contact bridge for bridging the interruption point, wherein the contact bridge is held pivotably about an axis that extends perpendicularly to the plane in which the interruption point lies. 
     In an advantageous embodiment of the electric motor the contact bridge pivots about the pivot axis in the plane of the interruption point. A possibility for the space-saving arrangement of the thermal fuse inclusive of the contact bridge and of the spring element and contact bridge is thus made possible. 
     In accordance with an expedient development the contact bridge is associated with a separate spring element having a first spring leg and having a second spring leg extending at least approximately at right angles hereto. A structurally simple and particularly effective spring element can thus be provided and placed in the arrangement. 
     In accordance with a preferred variant the spring legs transition into one another via a spring or leg eyelet, which in particular is open. The spring can thus be arranged pivotably in an axis on a shaft element, for example a pin or the like, and a favorable configuration of the spring can be produced. In the assembled state the spring eyelet of the spring element surrounds the pivot axis coaxially. A joint pivoting of the spring element, or spring leg thereof cooperating with the contact bridge, and the contact bridge about the same pivot axis is thus provided easily and also reliably. 
     In a further favorable embodiment the first spring leg lies in a storage compartment of the plastic over-mold, whereas the second spring leg bears against the contact bridge under a spring preload. In the starting state the spring legs of the spring element are arranged relative to one another at a suitable angle, such that in the installed state the spring legs are preferably arranged perpendicularly to one another when the second spring leg bears against the contact bridge. The preload of the contact bridge by the spring element is thus produced in a simple and also reliable manner. The separate spring element is suitably fabricated from round wire or flat wire in the manner of a leg spring. An economical possibility is thus provided for producing the spring element. 
     In accordance with an expedient development the spring element and the contact bridge are coupled via a guide element. The contact bridge is thus guided reliably while it passes through the pivot path. For this purpose, the guide element is suitably formed by a groove in the first spring leg and a spring on the contact bridge. A favorable and practical implementation of the spring element is thus provided, which also enables simple handling with regard to the assembly of the component parts. 
     In accordance with a suitable embodiment the first spring leg of the spring element is bent at the leg end. A stable hold of the spring element on the contact bridge is thus provided. 
     In a further advantageous embodiment the pivot axis is shaped in the form of a pin from the plastic over-mold. As a result of this structure, the possibility is created that the spring element, in contrast to the contact bridge, itself is not an active component of the thermal fuse or is only insignificantly an active component of the thermal fuse, such that an electrical current flow is provided only via the contact bridge. The current flow therefore is not influenced by the mechanical properties of the contact bridge. 
     The contact bridge advantageously has, at both ends, contact surfaces contacted with the respective current path ends, wherein the pivot axis lies in the region of the contact surfaces. The possibility is thus created of bridging the interruption point for conduction, soldering the contact bridge at the current path ends, and at the same time also producing the pivotability of the contact bridge. 
     Both contact surfaces of the contact bridge are suitably soldered to the current path ends. On the one hand a particularly reliable electrical transfer capability of the current via the contact bridge is thus provided. On the other hand the contact bridge is fixed to the current path ends mechanically reliably. In the case of overheating the solder in the region of both current path ends melts practically at the same time, such that the contact bridge in the event of tripping can be pivoted out about the pivot axis and in the plane of the interruption point. The melted solder joints are practically sheared off during this process, which ensures a reliable interruption of the interruption or contact point bridged by the thermal fuse or contact bridge thereof. 
     In an expedient variant the contact bridge is configured as, or in the manner of a punched and bent part having a number of bends, which form a middle raised bridge portion. The desired mechanical and/or electrical properties of the contact bridge can thus be provided in a simple manner. In particular, the contact bridge can be adapted to different amperages. 
     The advantages associated with the invention in particular lie in the fact that a simple, favorable and space-saving possibility for integration of the thermal fuse in the electric motor is created by a tripping of the thermal fuse in the plane of the interruption point. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in an electric motor having a thermal fuse, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic, exploded perspective view of a cooler fan for a motor vehicle with a brushless internal rotor motor with integrated converter electronics system according to the invention; 
         FIG. 2  is a perspective view of an electronics compartment with an electronics system of an electric motor, with a printed circuit board and a punched grid provided with a plastic over-mold, and with a thermal fuse; 
         FIGS. 3A and 3B  are perspective views of a punched grid before and after the plastic over-mold inclusive of an interruption point to be bridged by the thermal fuse; 
         FIG. 4  is a perspective view of a detail of the electronics system with the thermal fuse; and 
         FIGS. 5A to 5C  are top plan views showing the thermal fuse with a spring-loaded contact bridge in a contact position, in a pivoted position and in a tripped position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Parts corresponding to one another are provided in all figures with the same reference signs. 
     Referring now to the figures of the drawings in detail and first, particularly to  FIG. 1  thereof, there is shown a fan  1  for a radiator of a motor vehicle in a state removed from one another. The fan  1  includes a fan wheel  2  with a central cap  3 , around an outer circumference of which air-guiding blades  4  (illustrated only in part) are arranged in an evenly distributed manner. The fan  1  also has an electric motor  5 , also referred to as a fan motor, by which the fan wheel  2  is driven in rotation. 
     The motor  5  is formed generally by a stator  6 , which is wound with a three-phase rotary field winding  7  in the form of coils. The motor  5  also includes a permanently excited rotor  8 , which is mounted rotatably about a motor axis  9  in an interior of the stator  6 . In order to mount the rotor  8 , the motor  5  has two rolling bearings  10  and  11 , which act on the rotor  8  from axially opposite sides. The axial play of the rotor  8  between the two rolling bearings  10  and  11  is spring-loaded here by a spring ring  12 . 
     The motor  5  also has an approximately disk-shaped motor mount  13 . An electronics compartment  14  is formed in the motor mount  13  on an end face facing away from the fan wheel  2 , a converter electronics system  15  being inserted into the electronics compartment  14 . In order to tightly close the electronics compartment  14 , the motor  5  contains an electronics compartment lid  16 , also referred to hereinafter as a housing lid. 
     The rotor  8  is formed (in a manner not illustrated in greater detail) by a laminated core, into which permanent magnets are inserted in order to generate an exciting field, wherein the laminated core together with the inserted permanent magnets is over-molded by a plastic coating. Similarly, the stator  6  also consists of a laminated core that is over-molded by a plastic coating. 
     The motor mount  13  is formed in particular by a one-piece die-cast part made of aluminum. The electronics compartment lid  16  is preferably an injection molded part made of plastic. 
     On the front side thereof, the rotor  8  is provided with four screw domes  18 , by which the rotor  8  is screwed to the fan wheel  2  in the assembled state. The motor  5  and therefore the entire fan  1  is secured to the vehicle via the motor mount  13 , which for this purpose is provided with three screw tabs  19  protruding from the outer circumference of the mount. The motor  5  is a brushless, self-cooled internal rotor motor. 
       FIG. 2  shows a perspective illustration of the electronics compartment  14  with inserted electronics system  15 . The electronic system  15  has an over-molded punched grid  20  and a circuit board or printed circuit board  21  fitted with electrical component parts. The electric motor  5  is operated by a bridge circuit (B 6  circuit), which is implemented in the over-molded punched grid  20 . For this purpose the over-molded punched grid  20  has a number of switchable semiconductor components  22 , by which current is supplied alternately to the three phase windings of the field winding  7  of the electric motor  5 . The electrical current used for this purpose is provided by a DC source in a manner not illustrated in greater detail. 
     The three phase windings of the field winding  7  of the electric motor  5  are connected for example in a delta connection via capacitors  23 . In other words each two electrically adjacent phase windings are electrically connected to one another at a motor-side contact point and in each case are in turn electrically contacted via a bridge-side contact point to a bridge branch of the bridge circuit. The windings are produced from a lacquered copper wire and are wound centrally to form a coil. 
     The over-molded punched grid  20 , additionally to the semiconductor components  22  and the capacitors  23 , also has a thermal fuse  24 . The thermal fuse  24  protects the electric motor  5  against overheating and fire risk. If the motor  5  overheats, the thermal fuse  24  thus trips, and current can no longer flow to or from the motor  5 . Connections  25 ,  26  and  27  form an input connection and an output connection for the motor current and two sensor signal outputs, for example for the measurements of the rotational speed (number of revolutions), the direction of rotation and/or the position of the motor  5 . 
     As is shown in  FIG. 2  together with  FIGS. 3A, 3B , the input connection  25  is connected to the semiconductor components  22  via the capacitors  23 . A punched grid  28  (see  FIG. 3A ) provides conductive paths and is electrically insulated by a plastic over-mold  29  (see  FIG. 3B ). The punched grid  28  or these conductive paths conducts/conduct the motor current I M . 
       FIG. 4  shows the thermal fuse  24  in an enlarged illustration. The thermal fuse  24  connects the current path ends  30 ,  31  conducting the motor current I M  to one another via an interruption point  32  of the punched grid  28 . The thermal fuse  24  is formed from a contact bridge  33 , which connects two contact points  34 ,  35  of the punched grid  28  to one another. The contact bridge  33  itself has contact points  36  and  37 , which are connected by a soldered joint to the contact points  34 ,  35  of the punched grid  28 . The soldered points contact the current path ends  30  and  31  to one another electrically via the contact bridge  33  and connect the contact bridge  33  mechanically to the contact points  34  and  35  to form a mechanically fixed connection. 
     In order to provide the function of the thermal fuse  24 , a separate spring element  38  is provided, which preloads the contact bridge  33  by a first spring leg  39  and is inserted in a storage compartment  41  of the plastic over-mold  29  by a second spring leg  40 . The spring element  38  is deformed in this position in such a way that the spring legs  39  and  40  are arranged practically at right angles relative to one another. Both spring legs  39  and  40  are interconnected via a leg eyelet  42 . 
     The spring element  38  and the contact bridge  33  are also mounted rotatably about an axis  43 , which is perpendicular to the plane in which the interruption point  32  lies. The axis  43  is formed from the over-mold  29  as a rotary or pivot pin  44 . Here, the leg eyelet  42  is arranged coaxially with respect to the pin  44  and thus with respect to the pivot axis  43 . 
     The contact bridge  33  is formed in the manner of a punched and bent part having a number of bends, which form a middle raised bridge portion. The spring element  38  can be produced from round wire or also flat wire. No current flows via the spring element  38 , since the pin  44  is formed from the insulating over-mold and the spring element  38  is fitted thereon. 
     The first spring leg  39  of the spring element  38  has a bend  45  at the leg end, which bend guides the contact bridge  33  in the event of tripping. In addition, the thermal fuse  24  also contains a guide element  46  in the form of a groove/spring connection. Here, the spring element  38  in the event of tripping guides the contact bridge  33  during the pivot over the pivot path thereof. The groove  46   a  is formed here on the contact bridge  33 , and the spring  46   b  is located on the first spring leg  39  of the spring element  38 . 
     On the basis of  FIGS. 5A to 5C  it is shown how, in the event of tripping once the solder of the soldered points has melted, the contact bridge  33  and also the spring element  38  pivot about the pin  44  and thus about the axis. The pivot axis  43  lies here in the vicinity of the contact surface  37 . There, the contact bridge  33  has a bore, through which the pin  44  is passed. 
     The thermal fuse  24  trips in particular in the event of an over-temperature, in that the solder melts and the contact bridge pivots through a combined rotary and shearing movement on account of the spring force of the spring element  38 , such that the interruption point  32  bridged by the preloaded contact bridge  33  is interrupted. The contact bridge  33  pivots in the event of tripping from a first position (contact position) into a second position (tripped position), wherein the pivot movement is performed about the pivot axis  43  and in the plane of the interruption point  32 . 
     The invention is not limited to the above-described exemplary embodiments. Rather, other variants of the invention can also be derived herefrom by a person skilled in the art without departing from the subject matter of the invention. In particular, all individual features described in conjunction with the individual exemplary embodiments can also be combined with one another in a different way without departing from the subject matter of the invention. 
     The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
       1  fan     2  fan wheel     3  cap     4  air-guiding blade     5  fan/motor     6  stator     7  rotary field winding     8  rotor     9  motor axis     10  rolling bearing     11  rolling bearing     12  spring ring     13  motor mount     14  electronics compartment     15  converter/electronics     16  electronics compartment lid     17  axis pin     18  screw dome     19  end face     20  overmolded punched grid     21  printed circuit board     22  semiconductor component     23  capacitors     24  thermal fuse     25  input connection     26  output connection     27  sensor signal outputs     28  punched grid     29  plastic overmold     30  first current path end     31  second current path end     32  interruption point     33  contact bridge     34  first contact point of the punched grid     35  second contact point of the punched grid     36  first contact point of the contact bridge     37  second contact point of the contact bridge     38  spring element     39  first spring leg     40  second spring leg     41  receiving compartment of the plastic overmold     42  leg/spring eyelet     43  pivot axis     44  pin     45  bend     46  guide element     46   a  groove     46   b  spring