Patent Publication Number: US-7592786-B2

Title: Aircraft engine starter/generator

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to engine starters and generators and, more particularly, to combined engine starter/generators. 
     In the aerospace industry, electric engine start technology has become a de facto standard for engine starters and generators. According to an aspect of this technology, a starter and a generator may be combined in a single starter/generator device. Such a design may be advantageous in terms of weight and size. 
     A starter/generator device may include three generators: a permanent magnet generator, an exciter generator, and a main generator. Each generator may include a stator and a rotor. Each rotor may include a winding. 
     A starter/generator device may be a synchronous, brushless electric device. A starter/generator device may be said to be synchronous when the frequency of the starter/generator device is proportional to an input speed when the starter/generator device is in a generate mode. A starter/generator device may be said to be brushless when, instead of using brushes to transfer current to main rotor, an exciter may be used to provide excitation current to the main field when the starter/generator device is in a generate mode. 
     In order to effectively start an engine, torque is necessary. When a conventional starter/generator device is placed in a start mode, a start controller unit may be used to provide electrical power to create torque of the starter/generator device. The start controller unit may add significant weight and volume to a starting system. Depending on the application, the start controller unit can range, for example, from 50% to more than 100% of the weight of the generator itself. Additionally, the starter/generator device may be located at a distance from the start controller unit requiring unwanted additional wiring. 
     As can be seen, there is a need for an aircraft engine starter/generator device not requiring a start controller unit. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a starter/generator device may include an exciter stator, a main stator, and a rotor portion. The rotor portion may include an exciter rotor winding, a main rotor winding, and a resistor and switch combination positioned between the exciter rotor winding and the main rotor winding to control a flow of current in the main rotor winding during a start mode of the starter/generator. 
     In another aspect of the present invention, a rotor portion of a starter/generator device may include an exciter rotor winding, a main rotor winding, and a device forming an isolated closed circuit with the main rotor winding during a start mode. 
     In another aspect of the present invention, a method of optimizing starting torque of a starter/generator device without a start controller unit during a start mode may include providing a main rotor winding of the starter/generator device, and providing a control to control the flow of current in the main rotor winding of the starter/generator device during the start mode. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a starter/generator device according to an embodiment of the present invention; 
         FIG. 2  is a schematic representation of a starter/generator device according to an embodiment of the present invention; and 
         FIG. 3  is a flowchart of a method of optimizing starting torque of a starter/generator device without a start controller unit according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Broadly, embodiments of the present invention may relate to a starter/generator device including a switch and resistor to form a closed circuit with the main rotor winding during a start mode. Embodiments may be useful in a variety of applications, such as aircraft or other vehicles using starter/generators. A switch and a resistor may cause the starter/generator device to function as an asynchronous device when in start mode. Thus, starting torque may result. 
     Embodiments of the present invention may differ from conventional starter/generators at least by not requiring a start controller unit. Embodiments of the present invention may differ from conventional starter/generators at least by adding a switch and resistor. Embodiments of the present invention may differ from conventional starter/generators at least by causing a starter/generator to function as an asynchronous device when in start mode. 
       FIG. 1  is a schematic representation of a starter/generator device  100  according to an embodiment of the present invention. The starter/generator device  100  may include an exciter stator  102 , a main stator  104 , and a rotor portion  106 . The exciter stator  102  may include an exciter controller  108 . The rotor portion  106  may include an exciter rotor winding  110 , a main rotor winding  112 , a diode rectifier assembly  114 , a resistor  118 , and a switch  127 . 
     The starter/generator device  100  may operate in a generate mode and a start mode. In generate mode, the exciter controller  108  may excite the exciter stator  102 . A magnetic field may be coupled into the exciter rotor winding  110 . The exciter rotor winding  110  may output a voltage which may be rectified by the diode rectifier assembly  114  and passed through the switch  127 , which may be closed. In an embodiment, the exciter rotor winding may be poly-phase windings. 
     The voltage that may be rectified by the diode rectifier assembly  114  may be supplied to the main rotor winding  112 . This voltage may establish a direct current (“DC”) which in turn may establish a DC magnetic field flux which may be rotating at the shaft speed and may be coupled in the main stator  104 . This may induce in the main stator  104  the main voltages that may be used by a vehicle such as an aircraft. 
     With respect to the start mode of the starter/generator device  100 , the rotor portion  106  may include the switch  127  and the resistor  118 . The switch  127  and the resistor  118  may be positioned between the exciter rotor winding  110  and the main rotor winding  112 . In an embodiment, the switch  127  and the resistor  118  may be positioned between the diode rectifier assembly  114  and the main rotor winding  112 . 
     When in a start mode, power may be supplied from a vehicle auxiliary power unit (APU) or ground power supply. The switch  127  and the resistor  118  may form an isolated closed circuit with the main rotor winding  112  with the switch  127  open when the starter/generator device  100  is in the start mode. The starter/generator device  100 , which may be a synchronous device when in the generate mode, may function as an asynchronous device when in the start mode due to the switch  127  and the resistor  118 . That is, the starter/generator  100  may act as an asynchronous induction motor during the start mode. Conceptually, the switch  127  and the resistor  118  may cause the main rotor winding  112  to function similar to bars of a squirrel cage of an induction machine. Thus, starting torque may result. 
     The resistor  118  may form an isolated closed circuit with the main rotor winding  112  and the switch  127  may prevent current from flowing into the exciter rotor winding  110 . In an embodiment, the resistor  118  may be a damper resistor. The optimum resistor value that produces maximum torque may be dependent upon machine parameters. The design of the damper bars included in the starter/generator device may also have an impact on the starting torque. 
       FIG. 2  is a schematic representation of a starter/generator device  200  according to an embodiment of the present invention. The starter/generator device  200  may include an exciter stator  202 , a main stator  204 , and a rotor portion  206 . The exciter stator  202  may include an exciter controller  208 . The rotor portion  206  may include an exciter rotor winding  210 , a main rotor winding  212 , a diode rectifier assembly  214 , a resistor switch  220 , a resistor  218 , and an isolating switch  227 . In the description of the embodiment of  FIG. 2 , redundant discussions of aspects of features similar to those already discussed are omitted for clarity. 
     The resistor  218 ; resistor switch  220 , and the isolating switch  227  may form an isolated closed circuit with the main rotor winding  212  when the starter/generator device  200  is in a start mode. The resistor switch  220  may connect the resistor  218  when the starter/generator device  200  is in the start mode and disconnect the resistor  218  when the starter/generator device  200  is in a generate mode. The isolating switch  227  may disconnect the main rotor winding  212  from the exciter rotor winding  210  during the start mode, and connect the main rotor winding  212  and the exciter rotor winding  210  in the generate mode. 
     The resistor switch  220  may be controlled using a voltage signal from the main rotor winding  212 . The isolating switch  227  may be controlled using a voltage signal from the exciter rotor winding  210 . Alternatively the switches  220  and  227  may be controlled by centrifugal forces which may be proportional to the rotor speed. In an alternative embodiment, the resistor switch  220  may be eliminated by using an eddy current mechanism to vary the value of the resistor  218 . 
       FIG. 3  is a flowchart of a method  300  of optimizing starting torque of a starter/generator device without a start controller unit according to an embodiment of the present invention. The method  300  may include providing  302  a main rotor winding of a starter/generator device. The method may include providing  304  a control to control the flow of current in the main rotor winding of the starter generator device during a start mode. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.