Abstract:
The present invention deals with a transverse flux machine of the switched reluctance variety. The transverse flux machine consists of multiple phases where each phase is spaced axially along the shaft. Axial spacing provides many benefits including a decreased weight and a capability to use simple wound bobbin coils for the windings. An embedded cooling loop is provided within the coils themselves. This cooling loop provides internal temperature regulation for the windings and allows for a higher efficiency among other benefits.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to an improved motor, wherein the stator windings of a multi-phase motor are spaced axially along a rotational axis of the motor. In addition, a cooling fluid is circulated through the stator windings. 
         [0002]    Traction motors are often required to provide electrical to mechanical conversion for commercial vehicle drive trains. Typically the traction motors used in drive train applications have been three phase AC induction machines. A three phase AC induction machine is a machine that utilizes an induction motor to turn three phase electrical energy into mechanical motion. The primary reason for the use of AC induction machines as traction motors is that AC induction machines are easy to build and use well established technology. The fact that the technology behind AC induction machines is well established and has a large infrastructure allows them to be produced relatively cheaply. 
         [0003]    On the other hand, large cost, size, and weight penalties are incurred when standard AC induction machines are adapted to vehicle drive trains. As such, much research has been put into developing new motor designs that can satisfy the cost, size and weight requirements of commercial vehicles. 
         [0004]    Typically a goal has been to make induction machines more effective by increasing the output torque while decreasing the overall weight and cost of the machine. Transverse flux machines are the most viable method to fulfill this goal. Two types of transverse flux machines are known in the art, the permanent magnet transverse flux machine and the switched reluctance transverse flux machine. Permanent magnet transverse flux machines are transverse flux machines which utilize a permanent magnet, usually constructed out of rare-earth materials, as part of their rotor construction. Permanent magnet transverse flux machines achieve a high torque per weight ratio. However, permanent magnet transverse flux machines are not optimal. They are difficult to manufacture due to the complex magnet mounting methods used to construct the windings required for machine construction. Also, the torque output of a machine is temperature dependant, and they are highly intolerant of electrical fault conditions. 
         [0005]    Switched reluctance machines have several distinct advantages over permanent magnet machines. First, switched reluctance machines provide relatively temperature independent torque, and second, switched reluctance machines are more tolerant of fault conditions. Switched reluctance motors work on the principle that a rotor pole pair has a tendency to align with a charged stator pole pair. By sequentially energizing stator windings the rotor is turned as it realigns itself with the newly energized stator poles in each energization. This allows the production of mechanical movement within the machine without the use of rare-earth materials. Switched reluctance machines have not been developed as much as permanent magnet machines due to, among other reasons, high investment costs in the electronic controls development Current switched reluctance machines use radially spaced phases and have multiple windings per phase that are more difficult to assemble. 
       SUMMARY OF THE INVENTION 
       [0006]    The goal of the current invention is to design a switched reluctance transverse flux machine that is lighter in weight and produces higher torque. Additionally the goal of the present invention is to reduce assembly costs, and reduce the space required for the machine. 
         [0007]    The invention relates to an axially spaced, transverse flux, switched reluctance, traction motor utilizing a single simple wound bobbin coil for each phase winding. As a separate inventive feature, an integral cooling loop is built into each phase winding. Transverse flux, switched reluctance machines are known in the art and provide a variety of benefits including simple design and an acceptable power to weight ratio. Some downsides of using switched reluctance machines are that they have a difficult assembly processes, do not have as high a power efficiency as permanent magnet transverse flux machines, and have high assembly costs. 
         [0008]    It is known in the art to create a switched reluctance machine by spacing the phases radially around the rotor. The present invention spaces the phases axially along the rotor. Axial spacing allows the switched reluctance machine to be arranged in such a way that the machine can be constructed using a modular construction technique. The modular construction technique allows each phase to be assembled individually and then be “snapped” together with the other phases. Additional construction techniques not using modular assembly are possible with axially spaced phases, all of which are easier than the assembly techniques of the prior art switched reluctance machines. 
         [0009]    A feature of the phase winding construction is made possible by the axial spacing and contributes to the ease in assembly. Known switched reluctance machines, as well as permanent magnet systems, use ‘daisy chained’ windings, or even more complex and intricate coil winding arrangements. The axial spaced windings with only one coil per phase allows a simple wound bobbin coil to be used for the windings. In this case the windings are circular and easy to assemble. This simple wound bobbin coil not only aids in ease of assembly but uses less copper wire, and reduces the overall weight of the switched reluctance machine. A third benefit resulting from the simple wound bobbin coils is the possibility of adding an integrated cooling loop within the electrical windings. 
         [0010]    An integrated cooling loop is a hollow loop wound around the bobbin and embedded within the coil. The loop can be constructed of any material capable of being formed into a tube, having good heat transfer characteristics, and being capable of containing a refrigerant gas or liquid without leakage. The material would also provide benefits if non-conductive to electricity. The embedded cooling loop allows a refrigerant to be pumped through the coil while the switched reluctance machine is in operation. While the refrigerant is pumped through the coils heat is transferred from the coils to the refrigerant, thus cooling the overall system. The hot refrigerant then flows outside the coils. Once outside the coils, the refrigerant is cooled via a heat exchanger and pumped back through the embedded cooling loop. This allows temperature regulation within the coils themselves, providing for higher efficiency and a higher torque output. It is also envisioned that a similar effect could be accomplished using hollow wires to create the winding and pumping the cooling refrigerant directly through the winding wires themselves. 
         [0011]    An integrated cooling loop is possible in any motor/generator system implementing simple wound bobbin coils and all motor/generator systems known in the art can benefit from the internal temperature regulation provided by an integrated cooling loop. The benefits provided by an internal temperature regulation system include, but are not limited to, a steadier torque output level due to a constant temperature, the capability of placing the motor/generator in locations where a typical motor/generator would be subject to overheating, and increased efficiency. 
         [0012]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates a possible use for and deployment of an embodiment of the present invention. 
           [0014]      FIG. 2  illustrates a simple radially spaced switched reluctance machine as found in the prior art. 
           [0015]      FIG. 3  illustrates an embodiment of the present invention utilizing C shaped stators and C shaped rotors 
           [0016]      FIG. 4  illustrates a potential layout of phases around the rotor shaft for a three phase embodiment of the present invention. 
           [0017]      FIG. 5  illustrates a toroidal core for one phase of an axially spaced switched reluctance machine. 
           [0018]      FIG. 6  illustrates multiple views of a single wound bobbin coil contained within the toroidal core of  FIG. 3 . 
           [0019]      FIG. 7  illustrates a modular assembly embodiment of the present invention. 
           [0020]      FIG. 8  illustrates an embodiment of the present invention utilizing C shaped stators and I shaped rotors. 
           [0021]      FIG. 9  illustrates a cooling circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    The embodiment of  FIG. 1  relates to a traction motor for use in an electric drive train for an automobile. Traction motor  10  is placed on a shaft  30  near each of four wheels  20 . In the illustrated example the motor is being used in a hybrid electromechanical braking system. The current invention could be utilized in any number of different applications, and provides benefits anywhere a switched reluctance transverse flux machine would be beneficial. 
         [0023]    As shown in  FIG. 2 , known standard switched reluctance motors in the prior art are composed of a set of three phase windings  53 ,  54 ,  55 , each of which is wound on a stator pole  51 . Each switched reluctance machine design has a certain number of suitable combinations of stator poles  51  and rotor poles  52 . The motor is excited (caused to move) by a sequence of current pulses applied at each phase winding  53 ,  54 ,  55 . The individual phase windings  53 ,  54 ,  55  are consequentially energized, forcing the electric field within the switched reluctance machine to change alignment. The rotor poles  52  then shift to align themselves with the newly changed electric field and rotational motion is created. 
         [0024]    When each new phase charges up, the electric field within the switched reluctance machine realigns itself with the stators that correspond with the charged phase causing the rotor poles  52  to shift and realign themselves with the electric field. Using this process the rotor  56  can be made to sequentially shift alignment from one phase to the next; causing a full 360 degrees of rotation after each phase has been activated twice. If the phase windings  53 ,  54 ,  55  are sequentially charged and discharged fast enough then the rotation can reach sufficient speeds and generate sufficient torque for most applications. Typically the phases are spread radially in a single ring around the shaft as illustrated in  FIG. 2 . This design introduces downsides including a very harsh fault intolerance, and the necessity of intricate phase windings to accommodate for adjacent phases. 
         [0025]    In the present invention the phases  530 ,  540 ,  550  are spaced axially along the shaft  590  as illustrated  FIG. 3 . In a design such as the illustrated embodiment each phase  530 ,  540 ,  550  consists of its own toroidal core  580  around the rotor shaft  590 . The stators  510 ,  511 ,  512  for each phase  530 ,  540 ,  550  are aligned with each other, and the rotors  520 ,  521   522  on the shaft  590  are offset for each phase  530 ,  540 ,  550  as illustrated in  FIG. 4 . The number of rotors  520 ,  521 ,  522  and stators  510 ,  511 ,  512  per phase in  FIG. 4  is reduced for illustration purposes. Each phase  530 ,  540 ,  550  is fired up sequentially as in a radially spaced switched reluctance machine. This forces a mechanical rotation similar to the rotation in a radially spaced transverse flux machine. 
         [0026]      FIG. 4  shows a three dimensional view of how the stators  510  and rotors  520  could be positioned to allow for this effect. Each stator  510  is lined up with the other phase&#39;s stators  511 ,  512  in a column parallel to the rotor shaft  590 . The rotors  520  for phase  530  start lined up with the stators  510 . The next phase placed axially on the shaft  590  has its rotors  521  offset from the first phase&#39;s  530  rotors  520 . The third phase  550  placed axially along the shaft  590  has its stators  512  offset from both the first phase  530  and the second phase,  540 . The pattern can be modified to allow for any number of phases. However, the industry standard is to use three phases. 
         [0027]      FIG. 5  illustrates a toroidal core  580  utilized in each phase of the illustrated embodiment of the invention. The toroidal core consists of a ring shaped housing containing individual simple wound bobbin coils  320  about which the stators are placed. The toroidal core contains one simple wound bobbin coil  320  for each stator  520 ,  521 ,  522  which will be placed around the toroid. The coils are connected to each other essentially creating one coil that runs throughout the housing. This connection scheme can be accomplished using a simple input and output connection within the housing for each winding. This setup would connect the input of a given coil with the output of the coil immediately before it in the circle. The first and last coil in the toroid would not be connected to each other, but would instead be connected to an input and output of the core. The coils could also be connected to each other through some other means known in the art to provide a similar effect of connecting the coils together. The stators are placed outside a toroidal core housing  310  and are typically U, or C shaped. 
         [0028]    The axial spacing of the three phases  530 ,  540 ,  550  allows the machine to be built out of less material, and dramatically reduces the complexity of the windings. Radially spaced windings (like the ones utilized in  FIG. 2 ) needed to be complex for the phase windings  53 ,  54 ,  55  to accommodate each of the phases immediately adjacent to them. In the present invention the windings can be constructed of simple wound bobbin coils dramatically reducing the complexity. This allows for a lighter design as less material in the windings is wasted in non-essential winding components, such as end turn windings. Lighter design and the simpler winding allows additional features to be implemented that were previously impractical or impossible. 
         [0029]    Additionally made possible by the axial spacing of the phases is a modular assembly design.  FIG. 7  illustrates a modular assembly consisting of three phases  610 ,  611 ,  612 . Each phase  610 ,  611 ,  612  is assembled in an identical fashion and then the phases are “snapped” together to form the three phase switched reluctance machine. The modular assembly consists of a housing  620  containing the stator poles  621  which are C shaped. Contained within the center of the C of the stator poles  621  are the coils  622 . Attached to the rotor  623  is a rotor pole  624 . The rotor pole  624  is I shaped, and attached to the motor shaft  680 . Once each phase  610 ,  611 ,  612  has been assembled they are offset around the shaft  680  as described above and fixed into place. This method provides for an easier and faster method of assembling the switched reluctance machine than has previously been available, allowing for a quicker and cheaper manufacturing process. 
         [0030]    It is additionally possible to construct an axially spaced switched reluctance machine using non-modular assembly. A non-modular assembly requires the switched reluctance machine to be assembled as one step. A benefit provided by a non-modular assembly is that the switched reluctance machine can be built smaller. This is made possible because certain components built into each module which are necessary for a modular design are not necessary and can be removed. Removing the modular components allows a smaller construction and a lighter weight. Additionally non-modular assemblies can be “tailor made” to specific applications much easier than modular assemblies.  FIG. 3  and  FIG. 8  illustrate two possible non-modular designs.  FIG. 8  uses a standard rotor shaft  700  with C shaped rotors  702  attached corresponding to each phase. Also, a C shaped stator  704  design is used. The design of  FIG. 8  results in both a radial and an axial air gap. 
         [0031]      FIG. 3  uses a standard rotor shaft with I shaped rotors  520 ,  521 ,  522  and C shaped stators  510 ,  511 ,  512 . The design of  FIG. 3  results in a radial air gap. The advantages and disadvantages of each design vary dependant on the particular application. A person skilled in the art would be capable of determining an appropriate stator/rotor configuration for any given application. Radial gaps are more tolerant of axial runnout. Axial gaps are more tolerant of radial runnout. 
         [0032]    Axial spacing of the phase windings also allows for the use of toroidal cores  580  containing simple wound bobbin coils  320 . Because each phase is axially spaced along the shaft, each phase has its own toroidal core  580 . This design allows for the windings to be simple wound bobbin coils as the windings do not need to accommodate adjacent phases. An illustration of a toroidal core using simple wound bobbin coils is shown in  FIG. 6 .  FIG. 6  illustrates a section of the toroidal core with three separate views. View A shows the placement of a simple wound bobbin coil  410  within the toroidal core housing  470 . A bobbin is placed in the middle of each C shaped stator  420 , resulting in the coil  450  being centered in the middle of the stator  420 . In an embodiment using a toroidal core, the toroidal core is placed around the rotor shaft and then the C shaped stators  420  are put into place around each of the simple wound bobbin coils  410 . The rotor poles  430  do not need to be aligned at this step as they will automatically align when the motor is turned on. View B illustrates the positioning and orientation of the simple wound bobbin coil  410  relative to the toroidal core housing  310 . The windings are arranged such that each wire in the winding runs parallel to the toroidal core housing  470  in the plane formed by the X-axis and the Y-axis and perpendicular to the toroidal core housing  470  in the Z-axis. This orientation aligns the electric field to properly induce motion when the simple wound bobbin coils  410  are charged. View C illustrates a single stator  420  and rotor pole  430  with a simple wound bobbin coil  410  within the C shape of the stator  420 . View C is rotated 90 degrees about the Y-axis relative to the rest of the drawing. As shown in view C the coil  450  is wrapped around a bobbin  460 , which is snapped into place inside the toroidal core housing  470 . An integrated cooling loop  440  is contained within the coils  450  to ensure sufficient temperature regulation. The axial or radial gaps can occur at any points around a closed circuit path form by section of the C and I laminations. 
         [0033]    In the present invention a cooling loop  440  may be integrated in the coils  450 . Alternatively, a dedicated cooling tube may be included in the coils  450 . This is made possible because of the reduced weight and the simple winding design. The cooling loop  440  may consist of any flexible non permeable hollow tubing with adequate heat transfer characteristics. A refrigerant can then be pumped through the cooling loop  440  using any number of available means. 
         [0034]    As illustrated schematically in  FIG. 9 , a cooling circuit can be provided with fluid path  804 , and a pump  802  removing cooling fluid through the coils  450 , and outwardly to a heat exchanger  800 . Heat is taken out of the refrigerant circulated through the circuit  804  at heat exchanger  800 . Any number of methods for taking heat out of the refrigerant can be utilized. As an example, the heat exchanger could be placed in the path of a fan driven by the motor shaft. Also, more elaborate refrigerant systems including a compressor, an expansion device, etc. can be utilized. Again, a worker of ordinary skill in the art would recognize how to prepare an appropriate refrigerant system. The present invention is directed to the application of a refrigerant system within the coils of an electric motor. 
         [0035]    If the coils  450  are constructed out of hollow wires, a similar system can be achieved without the use of an embedded cooling loop. In such a case the refrigerant would be cycled through the hollow wires instead of a cooling loop using a similar method and system as the system used for the embedded cooling loop described above. This would provide for better heat regulation than an embedded cooling loop as the cooled refrigerant would be distributed evenly throughout the coil  450 . Additionally this would distribute the cooling refrigerant throughout a larger area and reduce the quantity of materials required for construction of the coils. 
         [0036]    Although several embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.