Liquid cooled power inductor

A vehicle electrical power system includes a variable voltage converter. The variable voltage converter includes an inductor assembly having a housing that defines a chamber containing dielectric fluid. An inductor is disposed within the chamber and is in contact with the fluid. The power system also includes a pump configured to circulate the dielectric fluid to cool the inductor.

TECHNICAL FIELD

This disclosure relates to an inductor assembly of a DC-DC converter, and components for thermal management of the inductor assembly.

BACKGROUND

The term “electric vehicle” as used herein, includes vehicles having an electric machine for vehicle propulsion, such as battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV). A BEV includes an electric machine, wherein the energy source for the electric machine is a battery that is re-chargeable from an external electric grid. In a BEV, the battery is the source of energy for vehicle propulsion. A HEV includes an internal combustion engine and one or more electric machines, wherein the energy source for the engine is fuel and the energy source for the electric machine is a battery. In a HEV, the engine is the main source of energy for vehicle propulsion with the battery providing supplemental energy for vehicle propulsion (the battery buffers fuel energy and recovers kinematic energy in electric form). A PHEV is like a HEV, but the PHEV has a larger capacity battery that is rechargeable from the external electric grid. In a PHEV, the battery is the main source of energy for vehicle propulsion until the battery depletes to a low energy level, at which time the PHEV operates like a HEV for vehicle propulsion.

Electric vehicles may include a voltage converter (DC-DC converter) connected between the battery and the electric machine. Electric vehicles that have AC electric machines also include an inverter connected between the DC-DC converter and each electric machine. A voltage converter increases (“boosts”) or decreases (“bucks”) the voltage potential to facilitate torque capability optimization. The DC-DC converter includes an inductor (or reactor) assembly, switches and diodes. A typical inductor assembly includes a conductive coil that is wound around a magnetic core. The inductor assembly generates heat as current flows through the coil.

SUMMARY

In one embodiment, a transmission includes a housing defining a chamber and an inductor assembly including a coil having exterior surface portions exposed to an interior of the chamber. At least one gear is disposed within the housing and is configured to rotate relative to the housing and splash fluid onto the exterior surface portions to cool the inductor assembly.

In another embodiment, a vehicle comprises a transmission including gears lubricated by transmission fluid and a variable voltage converter including an inductor arranged such that the transmission fluid contacts the inductor to cool the inductor.

In yet another embodiment, a vehicle electrical power system includes a variable voltage converter. The variable voltage converter includes an inductor assembly having a housing that defines a chamber containing dielectric fluid. An inductor is disposed within the chamber and is in contact with the fluid. The power system also includes a pump configured to circulate the dielectric fluid to cool the inductor.

DETAILED DESCRIPTION

Referring toFIG. 1, a transmission12is depicted within a plug-in hybrid electric vehicle (PHEV)16, which is an electric vehicle propelled by an electric machine18with assistance from an internal combustion engine20and connectable to an external power grid. The electric machine18may be an AC electric motor depicted as “motor”18inFIG. 1. The electric machine18receives electrical power and provides drive torque for vehicle propulsion. The electric machine18also functions as a generator for converting mechanical power into electrical power through regenerative braking.

The transmission12may have a power-split configuration. The transmission12includes the first electric machine18and a second electric machine24. The second electric machine24may be an AC electric motor depicted as “generator”24inFIG. 1. Like the first electric machine18, the second electric machine24receives electrical power and provides output torque. The second electric machine24also functions as a generator for converting mechanical power into electrical power and optimizing power flow through the transmission12.

The transmission12includes a planetary gear unit26, which includes a sun gear28, a planet carrier30and a ring gear32. The sun gear28is connected to an output shaft of the second electric machine24for receiving generator torque. The planet carrier30is connected to an output shaft of the engine20for receiving engine torque. The planetary gear unit26combines the generator torque and the engine torque and provides a combined output torque about the ring gear32. The planetary gear unit26functions as a continuously variable transmission, without any fixed or “step” ratios.

The transmission12may also include a one-way clutch (O.W.C.) and a generator brake33. The O.W.C. is coupled to the output shaft of the engine20to only allow the output shaft to rotate in one direction. The O.W.C. prevents the transmission12from back-driving the engine20. The generator brake33is coupled to the output shaft of the second electric machine24. The generator brake33may be activated to “brake” or prevent rotation of the output shaft of the second electric machine24and of the sun gear28. Alternatively, the O.W.C. and the generator brake33may be eliminated and replaced by control strategies for the engine20and the second electric machine24.

The transmission12includes a countershaft having intermediate gears including a first gear34, a second gear36and a third gear38. A planetary output gear40is connected to the ring gear32. The planetary output gear40meshes with the first gear34for transferring torque between the planetary gear unit26and the countershaft. An output gear42is connected to an output shaft of the first electric machine18. The output gear42meshes with the second gear36for transferring torque between the first electric machine18and the countershaft. A transmission output gear44is connected to a driveshaft46. The driveshaft46is coupled to a pair of driven wheels48through a differential50. The transmission output gear44meshes with the third gear38for transferring torque between the transmission12and the driven wheels48. The transmission also includes a heat exchanger or automatic transmission fluid cooler49for cooling the transmission fluid.

The vehicle16includes an energy storage device, such as a battery52for storing electrical energy. The battery52is a high voltage battery that is capable of outputting electrical power to operate the first electric machine18and the second electric machine24. The battery52also receives electrical power from the first electric machine18and the second electric machine24when they are operating as generators. The battery52is a battery pack made up of several battery modules (not shown), where each battery module contains a plurality of battery cells (not shown). Other embodiments of the vehicle16contemplate different types of energy storage devices, such as capacitors and fuel cells (not shown) that supplement or replace the battery52. A high voltage bus electrically connects the battery52to the first electric machine18and to the second electric machine24.

The vehicle includes a battery energy control module (BECM)54for controlling the battery52. The BECM54receives input that is indicative of vehicle conditions and battery conditions, such as battery temperature, voltage and current. The BECM54calculates and estimates battery parameters, such as battery state of charge and the battery power capability. The BECM54provides output (BSOC, Pcap) that is indicative of a battery state of charge (BSOC) and a battery power capability to other vehicle systems and controllers.

The transmission12includes a DC-DC converter or variable voltage converter (VVC)10and an inverter56. The VVC10and the inverter56are electrically connected between the main battery52and the first electric machine18; and between the battery52and the second electric machine24. The VVC10“boosts” or increases the voltage potential of the electrical power provided by the battery52. The VVC10also “bucks” or decreases the voltage potential of the electrical power provided to the battery52, according to one or more embodiments. The inverter56inverts the DC power supplied by the main battery52(through the VVC10) to AC power for operating the electric machines18,24. The inverter56also rectifies AC power provided by the electric machines18,24, to DC for charging the main battery52. Other embodiments of the transmission12include multiple inverters (not shown), such as one invertor associated with each electric machine18,24. The VVC10includes an inductor assembly14.

The transmission12includes a transmission control module (TCM)58for controlling the electric machines18,24, the VVC10and the inverter56. The TCM58is configured to monitor, among other things, the position, speed, and power consumption of the electric machines18,24. The TCM58also monitors electrical parameters (e.g., voltage and current) at various locations within the VVC10and the inverter56. The TCM58provides output signals corresponding to this information to other vehicle systems.

The vehicle16includes a vehicle system controller (VSC)60that communicates with other vehicle systems and controllers for coordinating their function. Although it is shown as a single controller, the VSC60may include multiple controllers that may be used to control multiple vehicle systems according to an overall vehicle control logic, or software.

The vehicle controllers, including the VSC60and the TCM58generally includes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM, EPROM and/or EEPROM) and software code to co-act with one another to perform a series of operations. The controllers also include predetermined data, or “look up tables” that are based on calculations and test data and stored within the memory. The VSC60communicates with other vehicle systems and controllers (e.g., the BECM54and the TCM58) over one or more wired or wireless vehicle connections using common bus protocols (e.g., CAN and LIN). The VSC60receives input (PRND) that represents a current position of the transmission12(e.g., park, reverse, neutral or drive). The VSC60also receives input (APP) that represents an accelerator pedal position. The VSC60provides output that represents a desired wheel torque, desired engine speed, and generator brake command to the TCM58; and contactor control to the BECM54.

The vehicle16includes a braking system (not shown) which includes a brake pedal, a booster, a master cylinder, as well as mechanical connections to the driven wheels48, to effect friction braking. The braking system also includes position sensors, pressure sensors, or some combination thereof for providing information such as brake pedal position (BPP) that corresponds to a driver request for brake torque. The braking system also includes a brake system control module (BSCM)62that communicates with the VSC60to coordinate regenerative braking and friction braking. The BSCM62may provide a regenerative braking command to the VSC60.

The vehicle16includes an engine control module (ECM)64for controlling the engine20. The VSC60provides output (desired engine torque) to the ECM64that is based on a number of input signals including APP, and corresponds to a driver's request for vehicle propulsion.

The vehicle16may be configured as a plug-in hybrid electric vehicle (PHEV). The battery52periodically receives AC energy from an external power supply or grid, via a charge port66. The vehicle16also includes an on-board charger68, which receives the AC energy from the charge port66. The charger68is an AC/DC converter which converts the received AC energy into DC energy suitable for charging the battery52. In turn, the charger68supplies the DC energy to the battery52during recharging.

Although illustrated and described in the context of a PHEV16, it is understood that the VVC10may be implemented on other types of electric vehicles, such as a HEV or a BEV.

Referring toFIG. 2, a front view of the transmission12and the VVC10is shown. The transmission12includes a transmission housing90, which is illustrated without a cover to show internal components. As described above, the engine20, the motor18and the generator24include output gears that mesh with corresponding gears of the planetary gear unit26. These mechanical connections occur within an internal chamber92of the transmission housing90. A power electronics housing94is mounted to an external surface of the transmission12. The inverter56and the TCM58are mounted within the power electronics housing94.

The VVC10is an assembly with components that may be mounted both inside and/or outside of a transmission12. The VVC10includes an inductor assembly14. In this embodiment, the inductor assembly14is located within the transmission housing90. In other embodiments the inductor assembly14may be located outside of the transmission. The VVC10also includes a number of switches and diodes (shown inFIG. 4) that are mounted in the power electronics housing94, which is outside of the transmission12, and are operably coupled to the inductor assembly14. By mounting the inductor assembly14within the transmission12, the exposed surface area of the inductor assembly14may be directly cooled by transmission fluid which allows for improved thermal performance. The transmission12includes additional structure for supporting the inductor assembly14while allowing the transmission fluid to flow through the structure to contact the exposed surface area.

The transmission12includes a fluid96such as oil or automatic transmission fluid (ATF), for lubricating and cooling the gears located within the transmission chamber92(e.g., the intermediate gears34,36,38). The transmission chamber92is sealed to retain the fluid96. The transmission12may also include valves, pumps and conduits (not shown) for circulating the fluid96through the chamber92. A heat exchanger or ATF cooler49may be used to cool the fluid96. The fluid96may also be used to cool the inductor assembly14.

Rotating elements (e.g., gears and shafts) may displace or “splash” fluid96on other components. Such a “splash” region is referenced by letter “A” inFIG. 2and is located in an upper portion of the chamber92. If the inductor assembly14is disposed in region A, the inductor assembly14may be cooled by transmission fluid96that splashes off of the rotating elements (e.g., the second intermediate gear36and the differential50) as they rotate.

The transmission12may include nozzles98for directly spraying transmission fluid96on components within the housing90, according to one or more embodiments. Such a “spray” region is referenced by letter “B” inFIG. 2and is located in an intermediate portion of the chamber92. The inductor assembly14may be mounted within region B and cooled by transmission fluid96that sprays from the nozzle98. The inductor assembly14may also receive transmission fluid96that splashes off of proximate rotating elements (e.g., the planetary gear unit26). Other embodiments of the transmission12contemplate multiple nozzles and nozzles mounted in other locations of the chamber92(e.g., a nozzle mounted in region A).

Further, the transmission fluid96accumulates within a lower portion, also known as a reservoir or sump99of the chamber92. Such an “immersion” region is referenced by letter “C” inFIG. 2and is located in a lower portion99of the chamber92. The inductor assembly14may be mounted within region C and immersed in the transmission fluid96.

Referring toFIG. 3, a power electronics housing94is shown in an alternative embodiment. In this embodiment, the VVC10, the inverter56, the TCM58, and the inductor assembly108are all disposed within the housing94. The housing94includes a first aperture100and a second aperture102. An inlet fluid line104is received through the first aperture100and provides fluid to the inductor assembly108. An outlet fluid line106is received through the second aperture102and provides a return for the fluid. The fluid is circulated through the inductor assembly108to cool the inductor assembly108. The inductor assembly108is sealed to prevent fluid from damaging the other electrical components inside the housing94. The inlet and outlet fluid lines104,106may be connected with the transmission plumbing or may be part of an independent fluid loop. If an independent fluid loop is used, additional pumps and heat exchangers may need to be provided.

Alternatively, the inductor108may be disposed in its own dedicated housing. The dedicated housing may also contain splash, spray and submersion cooling zones similar to the zones A, B and C in the transmission12as described above.

Referring toFIG. 4, the VVC10includes a first switching unit78and a second switching unit80for boosting the input voltage (Vbat) to provide output voltage (Vdc). The first switching unit78includes a first transistor82connected in parallel to a first diode84, but with their polarities switched (anti-parallel). The second switching unit80includes a second transistor86connected anti-parallel to a second diode88. Each transistor82,86may be any type of controllable switch (e.g., an insulated gate bipolar transistor (IGBT) or field-effect transistor (FET)). Additionally, each transistor82,86is individually controlled by the TCM58. The inductor assembly14is depicted as an input inductor that is connected in series between the main battery52and the switching units78,80. The inductor14generates magnetic flux when a current is supplied. When the current flowing through the inductor14changes, a time-varying magnetic field is created, and a voltage is induced. The VVC10may also include different circuit configurations (e.g., more than two switches).

Referring toFIG. 5, a schematic of an open loop inductor cooling system110is depicted. The system110includes a hydraulic pump112for circulating a dielectric fluid114such as ATF. A first supply line116is attached to the pump112and connects the pump112with a heat exchanger or ATF cooler118. A second supply line120is connected to the heat exchanger118at a first end122. A second end124of the second supply line120is positioned proximate a top126of the inductor assembly128. In operation, the fluid114is pumped out of at least one opening130in the second end124and drips onto the top126of the inductor assembly128. The top126is either open or contains openings, such as holes or slots, for allowing the fluid114to drip inside of the assembly128and make contact with the internal components of the inductor assembly128. The fluid114then flows across the inductor assembly128due to gravity. The inductor assembly128is cooled as the fluid114flows around and through the inductor assembly128. An optional secondary object132may be disposed under the inductor assembly114. The fluid114drips from the inductor assembly128onto the secondary object132to cool the secondary object132. The secondary object132may be a component inside the transmission12or may be any other component that is contained within the housing that contains the inductor assembly128and requires cooling. Fluid114that drips off of the inductor128and/or the secondary cooling object132is collected in a reservoir or sump134. A pickup tube136is provided in the sump134and connects with the pump112to supply fluid114to the pump112for recirculation though the system110.

At least one valve assembly138may be provided in one or more of the fluid lines. The valve assembly138is used to control the fluid flow. The valve assembly may include an actuator and a valve. The actuator may be in electrical communication with one or more controllers and configured to open and close the valve according to signals sent by the one or more controllers. A bypass line140may be provided to supply fluid114to the reservoir134or secondary object132when the valve assembly138is at least partially closed.

The open loop inductor cooling system110may be integrated into the transmission plumbing or may be an independent fluid loop. Integrating the system110into the transmission plumbing may provide cost savings by reducing the number of parts required due to part sharing. For example, integrating system110with the transmission12allows the system110to use the ATF, transmission pump, heat exchanger and reservoir to reduce redundant parts.

Referring toFIG. 6, a schematic view of a spray inductor cooling system150is shown. The system150includes a hydraulic pump152for circulating a fluid154. A first supply line156is attached to the pump152and connects the pump152with a heat exchanger or ATF cooler158. A second supply line160is connected to the heat exchanger158at a first end162. A second end164of the supply line160is positioned proximate a top168of the inductor assembly170. At least one nozzle166is attached to the second end164. In operation, the fluid154is pumped out of the at least one nozzle and sprayed on to the top168of the inductor assembly170. The top168is either open or contains openings, such as holes or slots, for allowing the fluid154to drip inside of the assembly170and make contact with the internal components of the inductor assembly168. The droplets of fluid accumulate on the inductor assembly170and drip across the inductor assembly170due to gravity. The inductor assembly170is cooled as the fluid154flows around and through the inductor assembly170. An optional secondary object174may be disposed under the inductor assembly170. The fluid154drips from the inductor assembly128onto the secondary object174to cool the secondary object174. The secondary object174may be a component inside the transmission12or may be any other component that is contained within the housing that contains the inductor assembly170. Fluid154that drips off of the inductor170and/or the secondary cooling object174is collected in a reservoir or sump176. A pickup tube178is provided in the sump176and connects with the pump152to supply fluid154to the pump152for recirculation though the system150.

At least one valve assembly179may be provided in one or more of the fluid lines. The valve assembly179may be similar to valve assembly138. The valve assembly179is used to control the fluid flow. The valve179assembly may be electrically connected to a controller for opening and closing the valve, as similarly described above with respect to valve assembly138. A bypass line177may be provided to supply fluid154to the reservoir176or secondary object174when the valve assembly179is at least partially closed.

The spray inductor cooling system150, like the cooling system110, may be integrated into the transmission plumbing or may be an independent fluid loop. Integrating the system150into the transmission plumbing may provide cost savings by reducing the number of parts required due to part sharing.

Alternatively, the spray nozzles166many spray the fluid154on a rotating object, such as one of the transmission gears. The transmission gears may cool the inductor assembly170by splashing the fluid154on the inductor assembly170.

Referring toFIG. 7, a schematic view of a closed loop inductor cooling system180is shown. The system180includes a hydraulic pump181for circulating a fluid182. A first supply line183is attached to the pump181and connects the pump181with a heat exchanger or ATF cooler185. A second supply line186is connected to the heat exchanger185at a first end187. A second end188of the second supply line186is coupled to the inductor assembly189. The inductor assembly189includes an inlet aperture190for receiving fluid182from the second supply line186into the inductor assembly189. An outlet aperture191is provided in the inductor assembly189. An intermediate line192is coupled to the inductor assembly189at the outlet aperture191to receive fluid182from the outlet aperture191. The inductor assembly189may be sealed to prevent fluid leakage. The inductor assembly189is cooled as the fluid182circulates through the inductor assembly189. The intermediate line192may be coupled with an optional secondary object193. The secondary object193may be the transmission12or any other component that needs cooling. A return line194may connect the secondary object to a reservoir195. If the secondary object is the transmission12, the return line may be omitted and the fluid182may be allowed to freely flow within the transmission and gravity drain into the reservoir or sump195. A pickup tube196is provided in the reservoir195and connects with the pump182to supply fluid182to the pump181for recirculation through the system180.

At least one valve assembly198may be provided in one or more of the fluid lines. The valve assembly198is used to control the fluid flow. The valve assembly198may be the same as valve assemblies138and/or179. A bypass line184may be provided to supply fluid182to the reservoir195or the secondary object193when the valve assembly138is at least partially closed.

The closed loop inductor cooling system180is a self-contained system and has the advantage of allowing the inductor assembly189to be placed within oil free housings or compartments. For example the inductor assembly189may be placed within the power electronics housing94. Similar to the open loop cooling system110and the spray cooling system150, the closed loop system180may be integrated into the transmission plumbing or may be an independent coolant loop.

FIG. 8illustrates the inductor assembly200according to one or more embodiments. The inductor assembly may be placed in various locations on the vehicle such as within the transmission housing90, the power electronics housing94or any other suitable location. The inductor assembly14includes a conductor210that is formed into two adjacent tubular coils, a core212and an insulator214. The inductor assembly200includes the insulator214, which is formed as a two-piece bracket and supports the conductor210and the core212. Additionally, the insulator214physically separates the conductor210from the core212and is formed of an electrically insulating polymeric material, such as Polyphenylene sulfide (PPS).

Referring toFIGS. 8-10, the conductor210is formed of a conductive material, such as copper or aluminum, and wound into two adjacent helical coils, a first coil211and a second coil213. The coils may be formed using a rectangular (or flat) type conductive wire by an edgewise process. Input and output leads extend from the conductor210and connect to other components.

The core212may be formed in a dual “C” configuration. The core212includes a first end216and a second end218that are each formed in a curved shape. The core212also includes a first leg220and a second leg222for interconnecting the first end216to the second end218to collectively form a ring shaped core212. Each leg220,222includes a plurality of core elements224that are spaced apart to define air gaps. (FIG. 9). The core212may be formed of a magnetic material, such as an iron silicon alloy powder. Ceramic spacers226may be placed between the core elements224to maintain the air gaps. An adhesive may be applied to the core212to maintain the position of the ends216,218and the legs220,222including the core elements224and the spacers226. Alternatively, a strap228, as shown in phantom view inFIG. 8, may be secured about an outer circumference of the core212to maintain the position of the ends216,218and legs220,222.

Referring toFIG. 10, the insulator214may be formed as a bobbin structure with a first half portion230and a second half portion230′ that are generally symmetrical to each other. Each half portion230,230′ includes a base234,234′ for attachment of the assembly14. The base234,234′ includes apertures236,236′ for receiving fasteners (not shown) for mounting the inductor assembly14to a supporting structure such as a transmission or other housing. A support238,238′ extends transversely from the base234,234′. A pair of spools, including a first spool240, and a second spool242, extend from the support238of the first half portion230, to engage a corresponding first spool240′ and a corresponding second spool242′ that extend from the support238′ of the second half portion230′. In one embodiment, the first spools240,240′ are coaxially aligned along a first longitudinal axis (not shown), and the second spools242,242′ are coaxially aligned along a second longitudinal axis (not shown) that is parallel to the first longitudinal axis. The spools240,240′,242,242′ are each formed in a tubular shape with a generally square shaped cross section.

As shown inFIG. 10, the insulator214supports the conductor210and the core212. The first spools240,240′ engage each other to collectively provide an external surface244for supporting the first coil211. The first spools240,240′ also define a cavity246for receiving the first leg220of the core212. Similarly, the second spools242,242′ engage each other to collectively provide an external surface248for supporting the second coil213, and define a cavity250for receiving the second leg222of the core212. According to the illustrated embodiment, the spools240,240′,242,242′ include a plurality of holes252for facilitating heat transfer from the legs220,222by allowing the fluid96to easily pass through the spools240,240′,242,242′. Other embodiments of the insulator214include nonsymmetrical half portions (not shown). For example, the spools may extend from one of the half portions and are received by the support of the other half portion (not shown).

Referring toFIG. 11, an alternative inductor assembly251is shown for use with the closed loop inductor cooling system180. The inductor assembly251includes a housing253. The housing253includes sidewalls254and a bottom wall256cooperating to define an enclosure258. The inductor260is disposed within the enclosure258. A potting compound may be provided to partially fill the enclosure258. Holes may be provided through the potting compound to facilitate circulation of the fluid. A cover (removed and not shown) is configured to be disposed on a top portion262of the sidewalls254. The cover may be sealed onto the housing253with a gasket or other sealant to form a fluid tight enclosure258. The sidewall254includes an aperture266. An inlet fluid line268is coupled to the aperture266to allow pumped fluid into the enclosure258. The bottom wall256also includes an aperture270. An outlet fluid line272is coupled to the aperture270to allow fluid to exit the enclosure258. The outlet fluid line272and aperture270may be provided in the sidewall254instead of in the bottom wall256. As the fluid96is circulated through the enclosure258the inductor260is cooled. A temperature sensor274may be provided to measure the temperature of the inductor260and the temperature of the fluid. If potting compound is provided, the temperature sensor274may be embedded in the potting compound.

The fluid may be ATF supplied from the transmission12. Alternatively, the fluid may be another suitable oil and may be supplied by an independent fluid loop. In this case, an additional pump, reservoir and heat exchanger may be provided for the independent fluid loop. The inductor assembly251is a sealed unit which does not have any fluid leakage. Thus, the inductor assembly251has the advantage of allowing the inductor assembly189to be placed within oil free housings or compartments.

Referring toFIG. 12, a flow chart300is shown for controlling any of the above described inductor cooling systems. The flow chart is implemented using software code contained within one or more of the controllers such as the VSC60, TCM58, and/or ECM64. At operation302, current is applied to the inductor. At operation304, the controller determines if the inductor temperature is greater than a threshold temperature. The controller may determine the inductor temperature by receiving a temperature signal from an inductor temperature sensor indicative of the inductor temperature. The measured inductor temperature can then be compared to a threshold temperature. The threshold temperature may be stored in a look up table or other memory within the controller.

At operation306, it is determined whether current is still being applied to the inductor. If current is still being applied, the loop continues to run and operation304is repeated as necessary. If current is not still being applied, then the controller signals the pump to turn off and the valve to close at operation308.

If the inductor temperature is greater than the threshold temperature, the system proceeds to operation312. At operation312, the controller determines the position of the valve. The valve position may be determined by having the controller receiving a signal from the valve indicative of the valve position. If at operation312, it is determined that the valve is closed, then the valve is opened one step at operation314and the pump is activated at operation316. If it is determined at operation312that the valve is open, then at operation310the valve opening is increased. The controller will continue to monitor the inductor temperature and further increase the valve opening, up to a maximum, so long as the inductor temperature is above the threshold temperature.