Patent Publication Number: US-10778070-B2

Title: Automotive electric motor

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2016/065983, filed on Jul. 6, 2016. The International Application was published in English on Jan. 11, 2018 as WO 2018/006953 A1 under PCT Article 21(2). 
     FIELD 
     The present invention relates to an automotive electric motor with a mechanical commutation. 
     BACKGROUND 
     The present invention in particular relates to an automotive electric motor for driving components or devices of an automobile. Such components or devices could, for example, be auxiliary units, actuators or pumps. The automotive electric motor according to the present invention is accordingly not an engine of the automobile for driving the vehicle. The automotive electric motor is mechanically commutated so that commutator brushes are necessary which are in permanent contact with a commutator ring. The automotive electric motor comprises a coil wire for electrically connecting the commutator brushes with a power source. 
     A common automotive electric motor for driving auxiliary units, actuators or pumps has an electric performance of up to approximately 500 W so that an electric current of 10 of up to 40 A with an on-board voltage of 12 or 24 V is required. The wire consequently has a diameter of at least a couple of millimeters in order to reduce the electric resistance of the coil wire. The coil wire, which can define, for example, a choke coil, therefore has a high stiffness so that it cannot be directly mechanically connected to the commutator brushes. A flexible braid wire is provided between the commutator brushes and the stiff coil wire to allow for movements of the brushes and vibrations of the coil wire. The braid wire is provided with a wire end which is electrically and mechanically connected to the coil wire by welding. The flexible braid wire can be a brush wire electrically connecting the coil wire with the commutator brush. 
     The stiff coil wire end is in practice defined by a machine cutting so that a burr and/or a sharp edge can result at the end surface which has been cut. The burr or sharp edge can damage the braid wire, which is connected to the coil wire, during the lifetime of the automotive electric motor. The braid wire is defined by a multiple number of thin wires each of which is sensitive to be cut by the burr or sharp edge of the coil wire. A failure of the electric motor can occur in case the braid wire is substantially severed. A failure could also occur if merely a majority of the thin wires are cut. The remaining thin wires are in this case fused due to the high electric current. The lifetime and the reliability of the automotive electric motor is consequently limited. In order to prevent such damage, additional complex manufacturing steps are necessary in order to remove the burr and sharp edges. Manufacturing costs are accordingly increased. 
     SUMMARY 
     An aspect of the present invention is to provide a reliable automotive electric motor with a mechanical commutation where manufacturing costs are reduced. 
     In an embodiment, the present invention provides an automotive electric motor with a mechanical commutation. The automotive electric motor includes a stiff coil wire comprising a welding portion and an end portion which is arranged adjacent to the welding portion, and a flexible braid wire comprising a wire end which is electrically and mechanically connected to the stiff coil wire at the welding portion via a welding. The end portion of the stiff coil wire comprises an end surface. The end portion of the stiff coil wire is bent in relation to the welding portion so that the end portion is bent away from the flexible braid wire and the end surface of the end portion of the stiff coil wire does not face the flexible braid wire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a schematic drawing of an automotive electric motor according to the present invention; and 
         FIG. 2  shows an enlarged section of  FIG. 1  of the connection between the braid wire and the coil wire of the commutator of the electric motor. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides that a stiff coil wire is provided with a welding portion and an end portion adjacent to the welding portion. The wire end portion is bent in relation to the wire welding portion and is thereby bent away from the braid wire so that a wire end surface of the wire end portion of the coil wire does not face the braid wire. The term “welding” according to the present invention is not limited to the welding process as such, but may also be a soldering process. The welding portion according to the present invention is an axial section of the coil wire where the braid wire is allowed and intended to be welded to the coil wire. In this axial section, the braid wire can be connected to the coil wire by spot-welding or by welding over a defined longitudinal section. Between the welding portion and the end portion, which is provided adjacent to the welding portion, the coil wire is bent and thereby changes the axial direction. The end portion is therefore bent in relation to the welding portion. The end surface according to the present invention is the surface of the coil wire which is generated by the cutting process. 
     According to the present invention, the end surface does not face the braid wire if a projected longitudinal axis of the wire end axis does not cross the braid wire. By bending the end portion according to the present invention, a sharp edge of the wire end surface will always be provided in a distance to the braid wire so that abrasion, kinking and breaking of the braid wire can be excluded. Damages of the braid wire during the mounting process or during operation due to vibrations will also no longer occur. The lifetime and reliability of the automotive electric motor will thereby be increased. 
     The complex manufacturing step of deburring the sharp edges of the wire end surface can also be omitted. Manufacturing costs can thereby also be decreased. 
     In an embodiment of the present invention, a bending angle between the wire welding portion and the wire end portion of the coil wire can, for example, be in the range of 60°-120°. The axial direction of the wire welding portion and the axial direction of the end portion enclose and define the bending angle. The specified bending angle has the effect that the end surface of the wire end portion does not face the braid wire so that damage of the braid wire is securely prevented. 
     In an embodiment of the present invention, a welding area can, for example, face to a direction which is substantially orthogonal to a longitudinal direction of the wire end portion of the coil wire. The welding area according to the present invention is the area where the coil wire is materially bonded to the braid wire. The welding area, which is at least a part of an outer circumferential surface of the coil wire, which is facing to a lateral direction, is substantially orthogonal to the direction of the welding portion of the coil wire. The welding area is therefore facing to a direction which is substantially orthogonal to the plane, which is defined by the longitudinal axis of the wire end portion of the coil wire and by the longitudinal axis of the welding portion of the coil wire. The specified arrangement has the effect that the mounting space in the axis of the wire end portion can be kept small. 
     In an embodiment of the present invention, the coil wire end surface can, for example, be inserted into a pocket. According to the present invention, the pocket can be formed like a hopper or a concave portion. The pocket can, for example, be defined by a part of the motor housing or frame or by a part supporting the coil wire, for example, a brush card. The pocket restricts the freedom of movement of the coil wire end portion. As the movement of the coil wire is restricted, the dynamic load on the welding connection between the braid wire and the coil wire is reduced so that the lifetime of the welding connection is increased. 
     The coil wire end portion can be inserted loose into the pocket. The wire end surface is alternatively fixed in the pocket. According to the present invention, the term “fixed” means that the wire end surface is tightly provided and fixed in the pocket. A mechanical load acting on the welding between braid wire and coil wire generated, for example, by vibrations is thereby significantly reduced. The lifetime and reliability of the electric motor will thereby be accordingly increased. 
     In an embodiment of the present invention, the end portion of the coil wire can, for example, be provided with a sharp edge. The sharp edge, such as a burr, which results from the cutting process of the coil wire does not need to be removed. The manufacturing step of removing the sharp edge is accordingly omitted. The automotive electric motor can accordingly be manufactured more economically. 
     The coil wire can, for example, define a choke coil. Electromagnetic interferences generated by the brush sparking can be minimized with the choke coil. Electromagnetic emissions, which can disturb other electronic devices in the automobile, can consequently be significantly reduced. 
     In an embodiment of the present invention, the flexible braid wire can, for example, define a brush wire of a mechanical commutator arrangement. The braid wire has a high flexibility so that relative movements of the brushes in relation to the coil wire can be compensated without a fatigue break of the braid wire. 
     A detailed description of an embodiment of the present invention is set forth below under reference to the drawings. 
       FIG. 1  shows a schematic drawing of an automotive electric motor  10  with a mechanical commutation. The electric motor  10  comprises a motor housing  14  which houses a motor stator  18 , a motor rotor  22 , and a commutator arrangement  26 . The motor rotor  22  is arranged on a rotor shaft  30  which is rotatably supported at the motor housing  14  via a first and a second bearing  34 ,  38 . The motor stator  18  is arranged inside the motor housing  14  surrounding the motor rotor  22 . The commutator arrangement  26  comprises a commutator ring  40  which is arranged on the rotor shaft  30 . The commutator ring  40  is electrically connected by electrical connections  42  to rotor windings of the motor rotor  22 . The commutator arrangement  26  further comprises two commutator brushes  46 . The commutator brushes  46  are provided in radial electrical contact with the commutator ring  40  and are arranged on radial opposing sides of the commutator ring  40 . Each commutator brush  46  is electrically connected to a respective choke coil  50  in order to minimize electromagnetic interference generated by the brush sparking of the commutator brushes  46 . 
       FIG. 2  shows an enlarged view of the electrical connection between the commutator brush  46  and the choke coil  50  of  FIG. 1 . The commutator brush  46  is electrically connected to a coil wire  58  by a flexible braid wire  54 . The flexible braid wire  54  comprises multiple thin filament wires, which are braided to define a ribbon-shaped braid wire  54 . The braid wire  54  is electrically and mechanically connected to the stiff coil wire  58 , which has a diameter of a couple of millimeters, via welding a wire end  62  of the braid wire  54  to a welding portion  66  of the coil wire  58 . The welding portion  66  is an axial section of the coil wire  58 , where the braid wire  54  is intended to be welded to the coil wire  58 . 
     The coil wire  58  comprises a wire end portion  70  which is arranged adjacent to the welding portion  66  of the coil wire  58 . Due to the cutting process of the stiff coil wire  58 , the wire end portion  70  is provided with a sharp edge  74  like, for example, a burr. The wire end portion  70  is bent in relation to the welding portion  66  and is thereby bent away from the braid wire  54  so that a wire end surface  78  of the wire end portion  70  is not facing the braid wire  54 . A welding area  82 , where the coil wire  58  is materially bonded to the braid wire  54 , faces in a direction which is substantially orthogonal to a longitudinal direction  86  of the wire end portion  70  of the coil wire  58 . An angle α between the welding portion  66  and the wire end portion  70  of the coil wire  58  is 90°. It is thereby prevented that the sharp edge  74  of the coil wire  58  comes into contact with the braid wire  54 . The braid wire  54  cannot thus be damaged by the sharp edge  74  of the coil wire  58 . 
     The wire end surface  78  is inserted into a pocket  90  which has a concave shape. The pocket  90  is defined by a frame  94  of the motor housing  14 . The pocket  90  restricts the lateral freedom of movement of the end portion  70  so that vibrations of the coil wire  58  are reduced. The dynamic load on the welding connection is also consequently decreased. 
     It should be clear from the above that the automotive electric motor with a mechanical commutation is not limited to the above described embodiment. Other designs of the pocket can in particular be used. Other bending angles and other designs of the welding area are also conceivable. Reference should also be had to the appended claims. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               10  automotive electric motor 
               14  motor housing 
               18  motor stator 
               22  motor rotor 
               26  commutator arrangement 
               30  rotor shaft 
               34  first bearing 
               38  second bearing 
               40  commutator ring 
               42  electrical connection 
               46  commutator brush 
               50  choke coil 
               54  flexible braid wire 
               58  coil wire 
               62  wire end 
               66  welding portion 
               70  wire end portion 
               74  sharp edge 
               78  wire end surface 
               82  welding area 
               86  longitudinal direction of the wire end portion 
               90  pocket 
               94  frame 
             α angle