Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-02-01
2002-10-29
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S179000, C310S184000, C310S198000
Reexamination Certificate
active
06472790
ABSTRACT:
BACKGROUND OF THE INTENTION
The present invention relates to a stator for a polyphase electric motor/generator and, particularly, to a stator for a three-phase motor/generator having three phase windings with each phase winding including two groups of coils electrically connected in parallel.
Three-phase induction motors are important and popular motors used for a variety of applications. Three-phase motors are popular because the horsepower rating of a three-phase induction motor is typically 167 percent more than a single-phase induction motor having the same weight. An exemplary use for a three-phase motor is using the motor as a starter motor for an internal combustion engine. The starter motor assists the internal combustion engine during engine starting until the engine can sufficiently operate without the assistance of the starter motor. The internal combustion engine can be an engine for a lawn mower, tractor, automobile, power-generation system, or the like.
One of the problems with a three-phase induction starter motor of the prior art is having the motor generate enough torque to start or “turn over” the engine. The problem arises because the power source for the starter motor is typically a twelve volt direct current (DC) battery. By capping the power source at twelve volts, the starter motor of the prior art typically cannot generate enough torque by itself to turn over the engine. One solution to this problem is to provide gearing between the starter motor and a crankshaft of the internal combustion engine. The gear ratio of the gears between the motor and the crankshaft is designed to be a ratio sufficient to allow the motor to start the engine. However, the gears are subject to wear and, therefore, have a limited operational life. Accordingly, there is a need for an improved three-phase electric motor that is capable of generating enough torque to start an internal combustion engine without the use of gears.
SUMMARY OF THE INVENTION
The invention provides a polyphase electric motor/generator and a controller. The polyphase motor is typically a three-phase motor/generator having a rotor and a stator. The rotor is interconnected with a drive shaft of the engine such that when the rotor rotates the drive shaft also rotates. The stator includes a core having slots for receiving electrical wire. The stator further includes three phase windings. The three phase windings include wire that is wound in the slots of the core and are electrically connected to the controller. The controller provides a substantially alternating current (AC) three-phase signal to the phase windings resulting in a magnetic field being induced within the core. The interaction of the induced magnetic field with a rotor magnetic field causes the rotor to rotate, which in turn causes the drive shaft to rotate.
The amount of torque a three-phase electric motor generates is dependent upon the amount of electric current flowing in the phase windings. The flow of electric current in the phase windings induces the magnetic field within the stator core for interaction with the rotor magnetic field, resulting in the rotation of the rotor. Assuming everything else is equal, the larger the current in the phase windings, the stronger the magnetic field within the stator core and, consequently, the greater the amount of torque that is generated by the rotor.
One way to increase current flow in the phase windings is to increase the voltage applied by the power source. However, if the voltage of the power source is fixed, such as is the case with an engine having a twelve-volt DC battery, then this is not a practical solution. An alternative way to increase current flow in the phase windings is to use the stator of the invention. The stator of the invention reduces the impedance of the phase windings as seen from the power source. Reducing the impedance of the phase windings increases the amount of current flowing to the phase windings and, therefore, increases the amount of current flow in the phase windings.
Accordingly, a stator of the invention provides a stator core having a plurality of slots that receives electrical wire. The stator further includes a first phase winding wound on the stator including first and second wires electrically connected in parallel. The first wire forms a first group of coils having a first pattern, and the second wire forms a second group of coils having a second pattern. For example, the first wire may form four coils according to a first pattern where the first coil is wound clockwise, the second coil is wound counter-clockwise, the third coil is wound clockwise, and the fourth coil is wound counter-clockwise. Furthermore, for example, the second wire may form four coils according to a second pattern where the first coil is wound counter-clockwise, the second coil is wound clockwise, the third coil is wound counter-clockwise, and the fourth coil is wound clockwise. Thus, the first and second groups of coils have different winding patterns. The stator further includes a second phase winding wound on the stator including third and fourth wires electrically connected in parallel. The third wire forms a third group of coils having the first pattern and the fourth wire forms a fourth group of coils having the second pattern. The stator further includes a third phase winding wound on the stator comprising fifth and sixth wires electrically connected in parallel. The fifth wire forms a fifth group of coils having the first pattern and the sixth wire forms a sixth group of coils having the second pattern. Of course, each pattern could be extended to include additional coils.
The stator of the invention further provides that the first phase winding is wound such that an end of the first wire and an end of the second wire are disposed in the same slot and are electrically connected together, the second phase winding is wound such that an end of the third wire and an end of the fourth wire are disposed in the same slot and are electrically connected together, and the third phase winding is wound such that an end of the fifth wire and an end of the sixth wire are disposed in the same slot and are electrically connected together. Additionally, the invention further provides that the remaining ends of the first, second, third, fourth, fifth and sixth wires are electrically connected together.
By connecting the first group of coils in parallel with the second group of coils, the resultant impedance as seen from the power source is reduced in half when compared to connecting the first and second group of coils in series. Similarly, by connecting the third group of coils in parallel with the fourth group of coils, the resultant impedance as seen from the power source is reduced in half when compared to connecting the third and fourth group of coils in series. In addition, by connecting the fifth group of coils in parallel with the sixth group of coils, the resultant impedance as seen from the power source is reduced in half when compared to connecting the fifth and sixth group of coils in series. Thus, the overall impedance of the stator windings as seen from the power source is substantially reduced by the parallel connection. Reducing the overall impedance increases the amount of current flowing to the phase windings and, therefore, the overall torque of the motor is increased.
One of the potential drawbacks to increasing the current flowing to the stator is that the amount of heat being generated by the windings increases. However, another advantage of electrically connecting two groups of coils for each phase winding in parallel is that the current flowing to the stator splits between the two groups of coils. Splitting the current flow results in less heat being generated by the phase windings when compared to connecting two groups of coils for each phase winding in series.
The stator of the invention further provides that each coil has one or more turns. Assuming that the wire for each phase winding has the same cross-sectional area (e.g., if the wire for each phase winding is round,
Briggs & Stratton Corporation
Lam Thanh
Michael & Best & Friedrich LLP
Waks Joseph
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