1. Field of the Invention
The present invention is generally related to a switched reluctance or variable reluctance machine used both as a starter motor and a generator and, more particularly, to the use of a switched reluctance starter motor and generator system in conjunction with a marine propulsion device, such as an outboard motor.
2. Description of the Prior Art
Switched reluctance machines have been known to those skilled in the art for many years. These machines can be used either as an electric motor or as an electric generator.
U.S. Pat. No. 5,864,477, which issued to Webster on Jan. 26, 1999, describes a converter circuit for a polyphase switched inductive load. A converter circuit for an inductive load, such as the phase windings of a switched reluctance motor, uses only n-switches for n-phases. In a four phase machine, each of the three of the phases is serially connected with a switch across one voltage source. The remaining phase is serially connected with a switch across another voltage source which receives the inductive energy returned by the other three phases. This returned energy is used to energize the fourth phase. A generator converter is also disclosed in which the energy in the fourth phase is used to provide the excitation for the other three phases.
U.S. Pat. No. 5,075,610, which issued to Harris on Dec. 24, 1991, describes a switched reluctance motor control circuit with energy recovery capability. A control circuit for a switched reluctance motor is provided with a connection between a second end of each stator winding and a first end of an associated other winding. The purpose of this connection is to permit the flow of current from a phase winding to an energy storage device following the disconnection of the phase winding from a primary power source. Because of the inductive characteristics of the phase winding in a switched reluctance motor, the current flow through the winding does not immediately cease when the winding is disconnected from the power source. Instead, the inductive characteristic resists the immediate cessation of current flow following the opening of an associated switch. That continued current flow is directed to an energy storage device, such as a capacitor, for the purpose of raising the voltage at the first, or input, end of another stator winding. This increased voltage potential at the first end of the other stator winding assists the initiation of current flow through that stator winding when its switch is later closed for the purpose of energizing the winding. Alternative embodiments of the invention include the directing of the continued current flow to more than one other winding to permit bi-directional rotation of the motor rotor.
U.S. Pat. No. 5,736,828, which issued to Turner et al on Apr. 7, 1998, describes an electric machine controller. The controller for a switch reluctance machine, especially a switch reluctance motor, takes timing information from a rotor position transducer to generate a switch-off output at a point near maximum phase inductance in a phase inductance cycle. A switch-on signal is generated after a delay but still within the phase inductance cycle. A simple form of single pulse control is thereby achieved. A comparator is also provided which monitors phase winding current. A pulse generator is actuated by the comparator when the winding current exceeds a reference level and is used to control the motor in a chopping mode at low speeds and is disabled by the comparator at higher speeds when the single-pulse control is used.
U.S. Pat. No. 5,446,359, which issued to Horst on Aug. 29, 1995, describes a current decay control in a switched reluctance motor. A control circuit for controlling the residual or tail current decay in a single phase or polyphase switched reluctance motor winding when a phase is switched from active to inactive is described. A Hall-effect type sensor senses rotor position of the switched reluctance motor. Current flows through a winding of the motor when the motor phase winding is active; and, current flow into the windings decays to zero when the phase becomes inactive. Semiconductor switches direct current flow into the winding when the phase is active and then redirect residual energy into winding between an energy recovery circuit and an energy dissipation circuit when the phase becomes inactive. A pulse width modulated signal generator provides pulse width modulated operating signals to the switches to control current flow first into the winding and then between the recovery and dissipation circuits. A control module or microprocessor with a pulse width modulated output is responsive to rotor position information for controlling operation of the pulse width modulated signal generator. The signal generator provides pulse width modulated signals having one set of signal characteristics when there is current flow to the winding and a different set of characteristics when there is not. This produces alternative intervals of zero voltage and forced commutation residual current decay while the phase is inactive. During the decay interval, both pulse width modulated frequency and the pulse duty cycle are variable to produce a current decay scheme which eliminates ringing and motor noise.
U.S. Pat. No. 5,373,206, which issued to Lim on Dec. 13, 1994, describes a position detection of rotors for switched reluctance motors. A position detection apparatus for a switched reluctance motor is disclosed wherein a single sensor is used for detecting a rotor position and thus driving the motor. A sensing unit is provided with a single sensor for detecting a position of a rotor, a start signal generation circuit, for generating a start signal for aligning the rotor with a stator upon starting, a position detection signal input circuit for passing the position detection signal following the start signal, a drive control pulse generation circuit, for receiving an output signal from the position detection signal input signal as a clock signal, sequentially shifting driving signals for respective phases and generating drive control pulses for respective phases, and a phase excitation circuit for logically combining phase drive control pulses from the drive control pulse generator with the start signal from the start, signal generation circuit and exciting the phases sequentially.
U.S. Pat. No. 5,012,177, which issued to Dhyanchand et al on Apr. 30, 1991, describes a power conversion system using a switched reluctance motor/generator. Prior power conversion systems operable in generating and starting modes have utilized brushless generators which are suitable for only certain applications. In order to overcome this problem, a power conversion system operable in generating and starting modes utilizes a switched reluctance motor/generator which is reliable and inexpensive and which can be used in a variety of environments.
U.S. Pat. No. 5,012,172, which issued to Sember on Apr. 30, 1991, describes a control system for a switched reluctance motor operating as a power generator. A method for operating a multi-phase switched reluctance motor in a generator mode includes gating switches connected in series with selected ones of the phase windings of the motor into conduction to establish current flow in a selected one of the windings. The switches are thereafter disabled and current is forced to commutate into flyback diodes whereby the current is returned to an associated DC bus. The instant at which the conducting switches are gated out of conduction is selected or measured in angular displacement between an associated stator pole and a corresponding rotor pole by establishing a preselected magnitude of current such that when the current in the winding reaches that magnitude, the switches are disabled. The voltage at the DC bus is regulated during generator mode operation by adjusting the phase angle measured between a stator pole and a corresponding rotor pole at which the switches are gated into conduction. The voltage is alternatively regulated at the DC bus by adjusting the phase angle at which the switches are disabled if the generated current does not reach the preselected magnitude. Overcurrent protection is included to reduce the turn-on angle if the current in the DC bus exceeds another preselected magnitude.
U.S. Pat. No. 6,351,094, which issued to Green on Feb. 26, 2002, describes the control of switched reluctance machines. A switched reluctance drive include a reluctance machine, a controller, power switches actuated by the controller and a current transducer for monitoring the current in each phase winding. The controller employs a sensorless rotor position detection technique by injecting voltage pulses into the idle period of each phase winding in a chopping mode. Acoustic noise associated with the injected pulses is concealed by varying the frequency at which the pulses are injected according to rotor speed. In an alternative embodiment the frequency is varied pseudo-randomly.
U.S. Pat. No. 6,255,756 which issued to Richter on Jul. 3, 2001, describes a winding arrangement for a switched reluctance machine based internal starter generator. A stator coil winding arrangement comprises an inner layer and an outer layer, which define the two layers of the coil. A first turn of the inner layer is positioned directly over the outer layer. All subsequent turns of the inner layer return to the inner layer to be positioned over the inner layer. With this winding arrangement, total losses in the stator coil are reduced by approximately a factor of two.
U.S. Pat. No. 5,654,601, which issued to Fulton on Aug. 5, 1997, describes a switched reluctance machine. The machine comprises a rotor, defining rotor poles and a stator defining stator poles. Each stator pole pair, creating a flux path through the rotor includes only one winding mounted on one of the stator poles. The invention is particularly applicable to a machine having a four-pole field pattern and an odd number of phases. The coils are placed on alternate stator poles such that the space between the stator poles can be used exclusively for a single winding. The single winding is made larger to compensate for the lack of a winding on its associated pole.
U.S. Pat. No. 5,523,635, which issued to Ferreira et al on Jun. 4, 1996, describes a switched reluctance starter/generator. A switch reluctance starter/generator is presented which has a stator mounted within a housing having an outer periphery and a plurality of salient poles defining an inner periphery, the salient poles further defining slots therebetween. A stator cooling sleeve is press fit on the outer periphery of the stator and defines a plurality of cooling channels between the outer periphery of the stator cooling sleeve and the housing. A plurality of phase windings are wound on the plurality of salient stator poles, and phase winding retainers are positioned within the slots for securing the phase windings on the salient stator poles. The winding retainers comprise a triangular base separator, a quasi-dove-tailed retaining member, and two opposing wedge shaped expanders. A rotor assembly is rotatably positioned within the stator, and comprises a hollow shaft assembly and a rotor core having a plurality of salient poles press fit on the outer periphery of the shaft. The hollow shaft assembly comprises an outer sleeve and an inner cooling sleeve. The inner periphery of the inner cooling sleeve defines an interior void of the shaft. The outer periphery of the inner cooling sleeve is press fit on the inner periphery of the outer sleeve and defines a plurality of cooling channels between the inner periphery of the outer sleeve and the outer periphery of the inner cooling sleeve. The stator windings are wound from hollow core conductors, and are coupled to external sources of cooling fluid and electrical energy by electrical/hydraulic terminal connectors.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Switched reluctance machines comprise a stator, with a number of stator poles, and a rotor, with a number of rotor poles. The number of stator poles does not equal the number of rotor poles. The stator poles are provided with a number of stator windings through which current can be induced to flow. When operating as a motor, the stator windings are energized at appropriate times to attract adjacent rotor poles toward them to produce torque. A switching control system then switches off the current flow in certain stator poles as the rotor poles approach them, in coordination with the energization of other stator poles to further attract rotor poles. When operating as a generator, the rotor is mechanically driven by some power source, such as an internal combustion engine, and the stator poles are energized to produce a magnetic field. As the rotor poles move into the proximity of the magnetic field, various switches are activated to cause the resulting generated current in the stator coils to flow in a preselected direction for the purpose of charging an electrical energy storage device, such as a battery. Switched reluctance machines have been used as both motors and generators and the control of such machines for these purposes is well known to those skilled in the art.
A marine propulsion device, made in accordance with the preferred embodiment of the present invention, comprises an internal combustion engine and a crankshaft supported within the internal combustion engine for rotation about a generally vertical axis. It also comprises a switched reluctance device comprising a rotor and a stator, wherein the rotor is attached in torque transmitting relation with the crankshaft and is rotatable relative to the stator. A stator winding structure is associated with the stator and a source of electrical power is provided. The source of electrical power is alternatively connectable in electrical communication with the stator winding in accordance with a motoring mode of operation and an electrical power generating mode of operation. The marine propulsion device further comprises a switching circuit that is connected in signal communication with the stator winding and the source of electrical power for connecting and disconnecting the stator winding and the source of electrical power in coordination with rotation of the crankshaft about the generally vertical axis. The present invention also comprises a controller that is connected in signal communication with the switching circuit and configured to select the motoring mode of operation when the internal combustion engine is being started and to select the electrical power generating mode of operation when the internal combustion engine is operating above a preselected operating speed.
A preferred embodiment of the present invention further comprises a position sensor connected in signal communication with the switching circuit for determining the rotational position of the rotor. The rotor can be attached directly to the crankshaft for rotation about the generally vertical axis. The rotor can be disposed radially inwardly from the stator or radially outwardly from the stator. The source of electrical power can be a 36 volt battery system for providing DC current to the switched reluctance device. It can also be a 12 VDC or 24 VDC supply. In one particular embodiment of the present invention, the stator has 18 poles and the rotor has 12 poles. The rotor operates as a flywheel of the internal combustion engine. The switching circuit can comprise a plurality of metal oxide semiconductor field effect transistors (MOSFET""s).