Electrical circuit for providing a reduced average voltage

Information

  • Patent Grant
  • 6744146
  • Patent Number
    6,744,146
  • Date Filed
    Thursday, September 5, 2002
    22 years ago
  • Date Issued
    Tuesday, June 1, 2004
    20 years ago
Abstract
Systems and methods of the invention may utilize integrated starter-alternator (ISA) electronics to drive a conventional DC starter coupled to a start-stop ISA system providing a voltage higher than that at which the starter is rated. The DC starter may cold crank an internal combustion engine, while a poly-phase starter alternator warn cranks the engine and converts mechanical energy to an AC current. The AC current may be converted to a DC current to provide charging functions. A reduced average voltage is provided to the DC starter and an adjustable-frequency alternating current may be provided to the starter alternator.
Description




TECHNICAL FIELD




The present invention generally relates to electrical systems. More particularly, the invention involves enabling an electrical device rated at a particular voltage to function in a system supplying a higher voltage. In one implementation, the invention may involve using integrated starter-alternator electronics as a pulse-width modulation drive for a conventional starter of an internal combustion engine.




DESCRIPTION OF THE RELATED ART




Several integrated starter-alternator (ISA) systems have been proposed for providing starting and charging functions to an internal combustion engine. Such ISA systems are often driven by a crankshaft, belt, or chain. One configuration of a typical belt driven ISA system is illustrated in system


10


of FIG.


1


. As illustrated, system


10


may include an inverter (


102


), which is connected to a direct current (DC) voltage source (e.g., battery


105


), that drives an alternating current (AC) electrical device, such as starter-alternator


115


, during engine cranking. After the engine (


101


) starts, the same electronics provide rectification for charging the DC voltage source.




Often, ISA systems are vital to engine stop-start systems. A stop-start system may be used to shut off an engine during prolonged idle periods and restart the engine in response to changes in throttle or clutch position. Consequently, start-stop systems can be used to reduce emissions and fuel consumption. However, a typical start-stop system for an internal combustion engine in a vehicle may start an engine 500,000 times over a 150,000 mile lifetime. This high cycle requirement is prohibitive for cranking with a conventional starter. In contrast, ISA systems are well suited to the task since they are brushless and designed for continuous operation.




In addition to durability, stop-start systems typically require ISAs to have high crank speeds to keep start-up emissions low. High crank speeds are also needed to minimize starting times and to avoid noticeable lag times in, for example, traffic flow. This high crank speed requirement translates into a high starter power output requirement.




In automotive applications, conventional starters output between 1.4 to 1.7 kW. However, stop-start systems require ISAs that output 4 to 8 kW. Thus, despite the higher efficiency of ISAs (typically 75-85% compared to 50% for conventional starters), higher battery power is required for start-stop systems. A start-stop ISA system may require a battery with three times the available power of a conventional starter. A typical ISA battery is 36 volts (V), compared to 12V for a conventional starter. The higher voltage system allows more power to be delivered at the same current using the same cable size.




There are, however, several difficulties involved in using ISAs (especially belt driven systems) for cold engine cranking. It is difficult, due to size, to package ISAs, which can provide adequate cold crank torque, as an accessory on existing engines. Also, the mass moment of inertia of a large rotor in such an ISA system produces high belt loads and increased fuel consumption during acceleration. Additionally, in order to transmit cold crank torque, a higher than normal belt tension is required. As a result, a wider belt and larger bearings are required in the engine and belt loop components.




A conventional starter can be added to a start-stop ISA system to provide the cold cranking ability. The number of cold starts over the life of a vehicle is well within the durability limit of a conventional starter. As

FIG. 2

illustrates, a conventional starter


210


can be coupled to, or included in, system


10


. The conventional starter is used for cold cranking and is powered by a standard 12V cranking battery with relatively high cold cranking amps and low reserve capacity (e.g., battery


209


). For warm cranking, when cranking torque is low, the ISA is used with a high power 36V battery (e.g., battery


105


).




As depicted in

FIG. 2

, start-stop ISA systems employing conventional starters often include a 12V battery (


209


) to drive the starter. However, a typical 12V battery has low reserve capacity, which is prohibitive for powering certain loads, such as lamps and radios. Further, an extra 12V battery adds weight to a vehicle and consumes valuable space. There are system architectures in which the 12V battery is eliminated and all loads are powered by a 36V battery. However, powering a conventional starter directly from a 36V requires matching the battery power to the power rating of the starter.




Moreover, it is not possible to make an equivalent size conventional starter capable of handling a 36V battery sized for a stop-start ISA system. Even if the conventional 12V starter were rewound for 36V, the resulting high current draw would damage the starter by overheating, demagnetization, and/or contact welding. For these and other reasons, it is beneficial to utilize ISA electronics to drive a conventional starter.




SUMMARY




The present invention is directed to methods and systems that substantially obviate one or more of the above problems and other problems by enabling an electrical device rated at a particular voltage to operate in an electrical system providing a higher voltage. This may be accomplished without an additional low power battery and without matching the existing battery power to the power rating of the device. Although the present invention, in its broadest sense, is not restricted to start-stop ISA systems, such systems are used here to convey aspects of the invention.




One aspect of the instant invention involves generating a reduced average voltage from an electrical system. The instant invention may, for example, enable a conventional 12V starter to operate in a start-stop ISA system having a 36V voltage source.




Systems consistent with principles of the instant invention may comprise a combination of elements including an electrical device rated at a particular voltage, an AC load, and a voltage source supplying a voltage higher than that at which the electrical device Is rated. In one implementation, the electrical device could be a starter mechanism coupled to, or included in, a start-stop ISA system and used for cold cranking an internal combustion engine. The starter mechanism may include a DC motor rated at a particular voltage, for example,


12


volts. Consistent with one implementation, the AC load could be a poly-phase starter-alternator mechanism configured for warm cranking the engine, i.e., cranking the engine after periods of extended Idle in response to changes in clutch or throttle position. The starter-alternator may also convert rotational energy produced by the engine into an AC current in order to charge the voltage source and/or provide power to other devices. The starter-alternator mechanism may require, and therefore the voltage source may provide, a voltage higher than that at which the starter is rated (e.g., 36V).




Consistent with principles of the present invention, a reduced average voltage may be provided to the electrical device by way of an electrical circuit. For instance, the voltage source may supply 36 volts and the electrical circuit may provide 12 volts to the device. This reduced average voltage may be produced via one or more switching devices. In one configuration, the switching devices may be included in an inverter/converter circuit coupled to an ISA system. In addition, the electrical circuit may provide the reduced average voltage in response to a switch (e.g., an electromechanical switch) triggered by a key-driven or push-button starter switch.




In addition to providing the reduced average voltage, the electrical circuit may be configured to drive an AC load of a chosen frequency and phase. That is, the circuit may be configured to provide an adjustable-frequency alternating current to the AC load from the DC voltage source. In one configuration, the circuit may, in response to the switch opening, cease to provide the reduced average voltage to the electrical device and transfer energy from the DC voltage source to the AC load. Consistent with one implementation, where the AC load is a starter-alternator device, the electrical circuit may also enable the DC voltage source to be charged via AC current obtained from the engine rotation.




Additional aspects related to the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or maybe learned by practice of the invention. Aspects of the invention may be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.




It is to be understood that both the foregoing and the following descriptions are exemplary and explanatory only and are not intended to limit the claimed invention in any manner whatsoever.











BRIEF DESCRIPTION OF THE DRAWINGS




The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the present invention and, together with the description, serve to explain principles of the invention.





FIG. 1

is an exemplary block diagram of a conventional system;





FIG. 2

is an exemplary block diagram of another conventional system;





FIG. 3

is an exemplary block diagram of an electrical system in which the present invention may be practiced;





FIG. 3A

is an electrical circuit diagram of one embodiment of a starter motor assembly consistent with the present invention;





FIG. 4

is an exemplary block diagram of another electrical system in which the present invention may be practiced;





FIG. 4A

is an exemplary block diagram of yet another electrical system in which the present invention may be practiced;





FIG. 5

is a flowchart graphically depicting steps of a method consistent with an exemplary implementation of the present invention;





FIG. 5A

is another flowchart graphically depicting steps of a method consistent with an exemplary implementation of the present invention;





FIG. 6

is an exemplary block diagram depicting an operation of the present invention; and





FIG. 7

is another exemplary block diagram depicting an operation of the present invention.











DETAILED DESCRIPTION




In the following detailed description reference will be made to the accompanying drawings in which is shown by way of illustration specific implementations consistent of the instant invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other implementations may be utilized and that structural changes may be made without departing from the scope of present invention. The following detailed description is, therefore, not to be construed in a limited sense whatsoever.




The present invention may enable an electrical device to operate in an electrical system providing a voltage higher than that at which the electrical device is rated. In one implementation, the invention may provide a reduced average voltage to a DC starter motor coupled to, or included in, a start-stop ISA system. Accordingly, systems consistent with principles of the instant invention may include an electrical device rated at a particular voltage (e.g., 12V), an AC load, and a voltage source. In one implementation, the electrical device could be a DC starter motor for cold cranking an internal combustion engine. Consistent with such an implementation, the AC load could be a poly-phase starter alternator mechanism for warm cranking the engine and converting mechanical energy produced by the engine into an AC current.




In one configuration, the AC load may require, and the voltage source may therefore provide, a voltage higher than that at which the electrical device is rated (e.g., 36V). Accordingly, an electrical circuit may be provided for driving the electrical device with the voltage source by way of a reduced average voltage. In accordance with principles of the invention, the circuit may generate the reduced average voltage via one or more switching devices. In one configuration, the reduced average voltage may be provided in response to an electromechanical switch closing.




Consistent with principles of the invention, the switching devices may be sequentially switched to provide an adjustable-frequency alternating current to the AC load. This may involve generating a set of voltages substantially equal in magnitude and respectively displaced by a phase angle. For example, the circuit may generate a set of the three voltages, each displaced by a phase voltage of 120 degrees. The circuit may also be configured to convert mechanical (e.g., rotational) energy into an AC current, which may in turn be converted to a DC current for charging the voltage source.




Referring now to the drawings, in which like numerals represent like elements throughout the figures, the invention Will be described.




In one exemplary implementation, the invention may be practiced in a start-stop ISA system, such as system


30


of FIG.


3


. System


30


may comprise an engine


301


, a voltage source


305


, a starter


310


, a starter-alternator


315


, and an electrical circuit


320


. Engine


301


may be any device, mechanism, or machine for converting energy into force. For example, engine


301


may be a diesel or gas-fueled internal combustion engine including a throttle and a clutch. Starter


310


may be coupled to engine


301


and configured for cold cranking the engine. Starter


310


may, in one configuration, be a conventional DC starter motor assembly rated at a particular voltage (e.g., 12V). It should, however, be understood that starter


310


may be any DC device, mechanism, or machine capable of cranking engine


301


by way of mechanical force.




One example of a conventional starter assembly Is illustrated in FIG.


3


A. As shown in

FIG. 3A

, a solenoid assembly


390


may include a battery “B” contact and a solenoid “S” contact fixed to a pinion housing. Energization of solenoid assembly


390


may utilize coils including a pull-in coil


392


and a hold-in coil


394


. As

FIG. 3A

illustrates, the assembly may also include a plunger


395


, which may be shifted axially when pull-in coil


392


and hold-in coil


394


are energized. In operation, energizing coils


392


and


394


may cause plunger


395


to shift in a direction which causes a moveable contact


397


to engage a pair of fixed electrical contacts


399




a


,


399




b


. The movement of plunger


395


may cause a pinion to engage with an engine flywheel.




As

FIG. 3

illustrates, starter-alternator


315


may also be coupled to engine


301


. Starter-alternator


315


may be any device, mechanism, or machine capable of starting engine


301


by way of electrical and/or mechanical force and/or converting energy produced by engine


301


into an AC current. Starter-alternator


315


may be driven by a crankshaft, belt, chain, or any other medium. In exemplary implementations, starter-alternator


315


may be poly-phase and may require more power than starter


310


. For example, as

FIG. 3

illustrates, starter-alternator


315


may be a 36V, three-phase ISA.




In one implementation, starter-alternator


315


may be configured for “warm cranking” engine


301


. As used herein, the term “warm cranking” refers to starting engine


301


, by way of mechanical force (e.g., rotary motion), after periods of extended idle in response to changes in clutch and/or throttle position. Thus, starter-alternator


315


may be capable of performing substantially more starts than starter


310


. Starter-alternator


315


may also be configured to convert energy produced by engine


301


into an AC current in order to charge voltage source


305


. This AC current may, in one configuration, be derived from rotational energy.




Voltage source


305


may be any mechanism capable of generating electrical energy. In one implementation, voltage source


305


may include one or more series-connected chemical cells for producing a DC voltage. Voltage source


305


may provide an amount of voltage compatible with the requirement of starter-alternator


315


, for example, 36V.




As depicted in

FIG. 3

, electrical circuit


320


may be coupled to voltage source


305


, starter


310


, and starter-alternator


315


. Consistent with principles of the invention, circuit


320


may comprise one or more switching devices (e.g.,


331


,


332


,


341


,


342


,


351


, and


352


). Switching devices


331


,


332


,


341


,


342


,


351


, and


352


may each be any mechanism for connecting, disconnecting, and/or diverting electrical current, such as a bipolar junction transistor (BJT), a metal oxide semiconductor field-effect transistor (MOSFET), a junction field-effect transistor (JFET), a thyristor, a power field-effect transistor (VMOS), or any other switching component. One skilled in the art will realize that electrical circuit


320


may comprise any number and combination of such switching devices.




Electrical circuit


320


may also comprise one or more heat sinks for transferring heat from the switching devices. The heat sink(s) (not illustrated) may transfer heat from the switching devices via conduction, convection, and/or radiation.




As illustrated in

FIG. 3

, switching devices


331


,


332


,


341


,


342


,


351


, and


352


may be coupled to each phase of starter-alternator


315


via terminals


335


,


345


, and


355


. In one implementation, the switching devices may be arranged in a bridge configuration. However, one skilled in the art will realize that switching devices


331


,


332


,


341


,


342


,


351


, and


352


may be arranged in other alternative configurations known in the art, such as are commonly employed with permanent magnetic synchronous, multi-phase induction, and switch reluctance machines. In addition, it should be understood that the number of switching devices included in electrical circuit


320


may vary with the number of phases accommodated by the system. For example, in a four-phase implementation electrical circuit


320


may comprise eight switching devices arranged in a bridge (or other) configuration.




In exemplary implementations, circuit


320


may provide power to starter-alternator


315


. Since starter-alternator


315


may be poly-phase, electrical circuit


320


may be configured to transfer energy from voltage source


305


to an AC load of arbitrary frequency and phase. That is, electrical circuit


320


may be configured to generate an adjustable-frequency alternating current from DC voltage source


305


. Electrical circuit


320


may transfer energy to an n-phase load by way of providing a set of n voltages substantially equal in magnitude and respectively displaced by a phase angle of 360°/n. For example, circuit


320


may provide starter-alternator


315


with a set of three voltages, each displaced by a phase angle of 120 degrees. In one configuration, switching devices


331


,


332


,


341


,


342


,


351


, and


352


may be sequentially switched to provide the adjustable-frequency alternating current. A skilled artisan will realize that a controller mechanism may be coupled to electrical circuit


320


for setting the chosen frequency and/or voltage.




In addition to driving starter-alternator


315


, electrical circuit


320


may be configured to provide starter


310


with a reduced average voltage. That is, circuit


320


may serve as a DC chopper, enabling a high power battery to drive a low power device. As previously explained, starter


310


may require less power than starter-alternator


315


. For example, starter


310


may be rated at 12V, while starter-alternator


315


may require, and voltage source


305


may therefore provide, 36V. Accordingly, electrical circuit


320


may generate and provide starter


310


with a reduced average voltage (e.g. 12V) from voltage source


305


.




In one implementation, the reduced average voltage may be generated via switching devices


331


,


332


,.


341


,


342


,


351


, and


352


and may be pulse-width modulated (PWM). The reduced average voltage may also be hysteretic and/or may be generated by any other chopper technique. Thus, in addition to serving as an inverter/converter for starter-alternator


315


, switching devices


331


,


332


,


341


,


342


,


351


, and


352


may function as a DC chopper having three output terminals (


330


,


340


,


350


).




As

FIG. 3

illustrates, the output terminals


330


,


340


, and


350


may be connected at a single point coupled to switch


360


. As also illustrated, switch


360


may, in turn, be coupled to starter


310


. In addition, switch


360


may be coupled to voltage source


305


.




Switch


360


may be any mechanism for connecting, disconnecting, and/or diverting electrical current in response to an electromagnetic field. In one configuration, depicted in

FIG. 3

, switch


360


may be any type of electromechanical switch, such as a SPST (Single Pole, Single Throw) magnetic switch. Consistent with such a configuration, diodes


333


,


343


, and


353


may be coupled in series with output terminals


330


,


340


, and


350


, respectively, in order to prevent circuit


320


from short-circuiting when switch


360


opens (i.e., when driving starter-alternator


315


). Although

FIG. 3

illustrates three diodes, it should be understood that any number of diodes may be included in electrical circuit


320


, depending on the number phases of the system and the configuration of the switching devices. In addition, any other device, mechanism, or element for preventing current from flowing may be used in place of any of the diodes illustrated.




In alternative implementations, switch


360


may include a single moving contact along with one or more independent stationary contacts. Such an implementation is illustrated in FIG.


4


. As illustrated, output terminals


330


,


340


, and


350


may each be coupled to three of the stationary contacts while starter


310


could be coupled to a fourth stationary contact. This configuration may prevent electrical circuit


320


from short-circuiting when switch


360


opens and may therefore render diodes


333


,


343


,


353


unnecessary.




As

FIG. 4A

Illustrates, switch


360


may optionally include or be coupled to a diode


363


(or any other current-preventing element) connected in parallel with starter


310


. In operation, diode


363


may be used to protect switching devices


331


,


332


,


341


,


342


,


351


, and


352


from high voltage transients. Additional details associated with the functionality of diode


363


will be described below in connection with the flowchart of FIG.


5


.




In one implementation, switch


360


may be coupled to voltage source


305


and mechanical switch


365


. Mechanical switch


365


may be any type of switching device for connecting and disconnecting electrical current in response to a user action (i.e., a user-controlled switch). For example, mechanical switch


365


may be a key-driven switch or a push button switch and may cause current to flow in response to a key turning or a contact button being pushed.




A skilled artisan will realize that all of the components discussed in the foregoing and following description may be coupled via any combination of media capable of conducting electricity. Thus, all of the connections and terminals depicted in the accompanying Figures may be charge-transporting media.




For clarity of explanation, the foregoing description refers to

FIG. 3

, in which starter


310


, starter-alternator


315


, and engine


301


are depicted. It should, however, be understood that circuit


320


may be used to drive any low power device, mechanism or machine coupled to system


30


instead of starter


310


. In addition, there may be any number of such electrical devices included in system


30


. Likewise, instead of starter-alternator mechanism


315


, any type and number of AC loads may be included in the system. Further, in alternative configurations, system


30


may not include starter-alternator


315


or any other AC load whatsoever. Similarly, in certain configurations, engine


310


could be absent from system


30


. Accordingly, circuit


320


may be primarily used to provide a reduced average voltage.




In one exemplary implementation, operation of the invention may be consistent with the steps illustrated in the flowchart of FIG.


5


. It should, however, be understood that other alternative method steps may be employed, and even with the method depicted in

FIG. 5

, the particular order of events may vary without departing from the scope of the invention. Further, certain steps may not be present and additional steps may be added without departing from the scope and spirit of the invention, as claimed.




As indicated by step


501


, mechanical switch


365


is switched closed. As explained above, this may involve a user turning a key or pushing a contact button. Consistent with principles of the invention, the user may dose switch


365


in order to cold crank engine


301


. Once switch


365


is closed, an electrical current will flow into switch


360


, thereby creating an electromagnetic field which activates switch


360


(step


505


). During a cold crank, switching devices


332


,


342


, and


352


can be off or open, while switching devices


331


,


341


, and


351


are simultaneously pulsed to deliver the reduced average voltage to starter


310


(step


510


). The reduced average voltage is provided via output terminals


330


,


340


, and


350


and routed through switch


360


to starter


310


. In this fashion, electrical circuit


320


serves as a DC chopper allowing a high power battery to drive a low power starter. This action is graphically depicted in FIG.


6


. At this point, starter-alternator


315


is not a load on-voltage source


305


, since its terminals are maintained at equal potential.




After the engine starts (step


515


), mechanical switch


365


, and therefore switch


360


, are switched open (step


520


). At this point, the stored energy in the coils of starter


315


may produce an inductive voltage spike as coil currents decay, due to the L(dl/dt) effect. Accordingly, as previously indicated, diode


363


could be included in or coupled to switch


360


to short circuit any generated coil voltage, allowing current to continue to flow through the coils after switch


360


opens. This short circuiting will minimize the peak voltage applied to switching devices


331


,


332


,


341


,


342


,


351


, and


352


, and could be used to protect certain types of switching devices vulnerable to such voltages. For example, the inclusion of diode


363


may be desired to prevent certain semiconductor switching devices, having breakdown voltages which could be exceeded by a high applied voltage, from failing or causing other components to fail. A skilled artisan, however, will appreciate that, depending on the structure and properties of the switching devices, the inclusion of diode


363


may be unnecessary.




In response to mechanical switch


365


and/or switch


360


opening, circuit


320


will cease to provide the reduced average voltage and will operate as an inverter for starter-alternator


315


. That is, circuit


320


will change modes of operation from a DC chopper mode to an AC inverter mode. Operation of circuit


320


as an inverter is graphically depicted in FIG.


7


. As explained above, switching devices


331


,


332


,


341


,


342


,


351


, and


352


may be sequentially switched to provide an adjustable-frequency alternating current to starter-alternator


315


. In exemplary configurations, voltage and frequency (and therefore the switching devices) are controlled via a controller module.




After engine


301


is initially started by starter


310


, starter-alternator


315


is enabled (step


525


) and may operate as an alternator, as illustrated in step


530


of FIG.


5


A. Starter-alternator


315


may convert energy produced by engine


301


(e.g., rotational energy) into an AC current, which can be converted to a DC current and used to-charge voltage source


305


. The AC current may additionally or alternatively be used for powering other electrical devices residing in, or coupled to, system


30


.




As explained above, engine


301


may be shut down (step


535


) after extended periods of idle in order to, for example, reduce emissions and fuel consumption. In exemplary implementations, engine


301


may be shut down after a predetermined period of time (e.g., 10-60 seconds). Additionally or alternatively, the user may be able to set and adjust the time period and/or control when engine


301


is cut off. Further, in operation, the time period after which engine


301


is shut down may change with each instance.




After being shut down due to, for example, a prolonged idle period, engine


301


may be re-started (warm cranked) by starter-alternator


315


, as illustrated in step


540


. In operation, starter-alternator


315


may warm crank engine


301


in response to changes in the throttle and/ or clutch position. After warm cranking


301


, starter-alternator may resume operation as an alternator (step


530


). As the flowchart of

FIG. 5A

illustrates, starter-alternator


315


may continually serve as an alternator and starter until the start-stop ISA system is shut down. One skilled in the art will realize that the start-stop ISA system could be shut down by, for example, turning a key switch which could optionally cause a controller to generate a shut-down signal. A skilled artisan should also realize that engine


301


may be shut down and warm cranked any number of times before the start-stop ISA system is finally shut down.




It should be understood that processes described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein.




It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the invention as well as in the construction of this invention without departing from the scope of or spirit of the invention.




The invention has been described in relation to particular examples which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention.




Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only. To this end, it is to be understood that inventive aspects lie in less than all features of a single foregoing disclosed implementation or configuration. Thus, the true scope and spirit of the invention is indicated by the following claims.



Claims
  • 1. An electrical system comprising:a direct current (DC) voltage source providing a first voltage; an alternating current (AC) starter-alternator mechanism configured for warm cranking an engine and converting rotational energy from the engine into an AC current; a starter mechanism, rated at a second voltage which is lower than the first voltage, for cold cranking the engine; and a circuit coupled to the voltage source for: providing the second voltage to the starter mechanism in response to a switch closing; and in response to the switch opening, ceasing to provide the second voltage to the starter mechanism; transferring energy from the DC voltage source to the AC starter-alternator mechanism; and converting the AC current, converted from the engine by the starter-alternator, to a DC current in order to charge the voltage source.
  • 2. The system of claim 1, wherein the circuit comprises at least one switching device.
  • 3. The system of claim 1, wherein the AC starter-alternator mechanism includes n phases and wherein the circuit transfers energy by way of providing a set of n voltages substantially equal in magnitude and respectively displaced by a phase angle of 360°/n.
  • 4. The system of claim 3, wherein each of the n phases are coupled to at least one switching device residing in the circuit.
  • 5. The system of claim 2, wherein the at least one switching device is arranged in a converter configuration.
  • 6. The system of claim 4, wherein the at least one switching device is arranged in a converter configuration.
  • 7. The system of claim 2 further comprising a control mechanism for controlling the at least one switching device.
  • 8. The system of claim 7, wherein the control mechanism sets an adjustable frequency at which the energy is transferred from the DC voltage source to the AC starter-alternator mechanism.
  • 9. The system of claim 2, wherein the at least one switching device includes at least one of a MOSFET, a JFET, a BJT, and a thyristor.
  • 10. The system of claim 1, wherein the switch is a magnetic switch.
  • 11. The system of claim 1, wherein the switch is a single pole single throw magnetic switch and wherein the circuit comprises at least diode coupled to said switch.
  • 12. The system of claim 2, wherein the at least one switching device is cooled via a heat sink.
  • 13. The system of claim 12, wherein the heat sink transfers heat from the switching device via at least one of conduction, convection, and radiation.
  • 14. The system of claim 1, wherein the first voltage is 36V and the second voltage is 12V.
  • 15. The system of claim 1, wherein the switch is closed and opened in response to at least one of a key-driven starter switch and a push button starter switch.
  • 16. An electrical circuit comprising:at least one switching device coupled to a direct current (DC) voltage source providing a first voltage; a first terminal set coupled to a switch, the first terminal set comprising at least one terminal coupled to the at least one switching device; and a second terminal set coupled to an AC load having at least one phase, the second terminal set comprising at least one terminal coupled to the at least one switching device, wherein the at least one switching device is pulsed in response to the switch closing, thereby providing, via the first terminal set, a reduced average voltage from the DC voltage source to a DC device; and wherein the at least one switch, in response to the switch opening, provides via the second terminal set, energy from the DC voltage source to the AC load.
  • 17. The circuit of claim 16, wherein the AC load is a starter-alternator device for warm cranking an engine and converting rotational energy produced by the engine into an AC current.
  • 18. The circuit of claim 17, wherein the circuit converts the AC current to a DC current and charges the DC voltage source.
  • 19. The circuit of claim 16, wherein the DC device is a starter for cold cranking an engine.
  • 20. The circuit of claim 16, wherein the AC load is an n-phase load and wherein the circuit provides energy to the n-phase load by way of providing a set of n voltages substantially equal in magnitude and respectively displaced by a phase angle of 360°/n.
  • 21. The circuit of claim 16, wherein the at least one switching device is arranged in a converter configuration.
  • 22. The circuit of claim 16, wherein the at least one switching device includes at least one of a MOSFET, a JFET, a BJT, and a thyristor.
  • 23. The circuit of claim 16 further comprising at least one heat sink for cooling the at least one switching device.
  • 24. The circuit of claim 23, wherein the at least one heat sink transfers heat from the at least one switching device via at least one of conduction, convection, and radiation.
  • 25. The circuit of claim 16, wherein the switch is a magnetic switch.
  • 26. The circuit of claim 25, wherein the magnetic switch is a single pole single throw magnetic switch.
  • 27. The circuit of claim 26 further comprising at least one diode coupled in series to the at least one terminal included in the first terminal set.
  • 28. The circuit of claim 16, wherein the switch is activated by at least one of a key-driven starter switch and a push button starter switch coupled to the voltage source.
  • 29. The circuit of claim 16, wherein the first voltage is 36V and the reduced average voltage is 12V.
  • 30. The circuit of claim 16, wherein the reduced average voltage is at least one of a pulse width modulated, hysteretic, and a chopped voltage.
  • 31. An electrical system comprising:a voltage source providing a first voltage; an electrical device requiring a second voltage lower than the first voltage; an alternating current.(AC) machine, having at least one phase, for converting rotational energy from an engine into an AC current; a circuit coupled to the voltage source, the AC machine, and a switch; wherein the circuit: causes, in response to the switch closing, a reduced average voltage substantially equivalent to the second voltage to be provided from the voltage source to the electrical device; and in response to the switch opening, causes energy to be transferred from the voltage source to the AC machine and enables the voltage source to be charged via the AC current.
  • 32. In a system having a voltage source providing a first voltage, a starter motor rated at a second voltage lower than the first voltage, a starter-alternator device, and an engine including a throttle and a clutch, a method comprising the steps of:providing, in response to a user-controlled switch closing, a reduced average voltage substantially equal to the second voltage to the starter motor from the voltage source; starting the engine via the starter motor; providing, in response to the user controlled switch opening, the first voltage to the starter-alternator device from the voltage source; charging the voltage source from the engine via the starter-alternator device; stopping the engine after a predetermined period of time; re-starting the engine via the starter-alternator device in response to a change in position of the throttle or clutch.
  • 33. The method of claim 32, wherein providing the reduced average voltage to the starter motor from the voltage source comprises providing at least one of a pulse-width modulated and hysteretic voltage via at least one switching device.
  • 34. The method of claim 32, wherein providing the first voltage to the starter-alternator device from the voltage source comprises providing a set of n voltages substantially equal in magnitude and respectively displaced by a phase angle of 360°/n.
  • 35. The method of claim 33, wherein providing the reduced average voltage to the starter motor comprises providing the reduced average voltage via at least one of a MOSFET, a JFET, a BJT, and a thyristor.
  • 36. In a system having a voltage source supplying a first voltage, a DC device, and AC load having a plurality of phases, a method comprising the steps of:providing a reduced average voltage from: the voltage source to the DC device in response to a switch closing, wherein the reduced average voltage is lower than the first voltage; and transferring a plurality of voltages substantially equal in magnitude, each displaced by a phase angle, to the AC load from the voltage source in response to the switch opening.
  • 37. The method of claim 36, wherein the providing step comprises providing the reduced average voltage from the voltage source to a DC starter motor rated at 12 volts.
  • 38. The method of claim 36, wherein the transferring step comprises transferring a plurality of voltages to a starter-alternator device operating at 36 volts.
  • 39. The method of claim 36, wherein the providing step comprises providing the reduced average voltage to the DC device by way of pulsing at least one switching device.
  • 40. The method of claim 36, wherein the switch is a magnetic switch.
  • 41. The method of claim 40, wherein the switch closes and opens in response to a user turning a key.
  • 42. The method of claim 40, wherein the switch closes and opens in response to a user pushing a button.
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