Thermal regulation of batteries

A battery thermal management system for an air vehicle includes a liquid heat exchange circuit, an air heat exchange circuit in selective fluid communication with ram air, a liquid-air heat exchanger positioned on the liquid heat exchange circuit and the air heat exchange circuit to exchange heat therebetween. The system includes at least one battery in thermal communication with the liquid heat exchange circuit. The at least one battery is configured to charge and/or discharge to heat the at least one battery above a pre-determined minimum battery temperature. A method for controlling a thermal management system for an air vehicle includes determining if at least one battery is within a thermal range of operation for heating. The method includes charging and/or discharging the at least one battery to heat the at least one battery if the at least one battery is within the thermal range of operation for heating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to thermal management and more particularly to thermal management for aircraft batteries.

2. Description of Related Art

Aircraft batteries need thermal management to avoid damage due to overheating and overcooling. During cruise, the batteries on an aircraft may experience cold soak in which they run the risk of a substantial loss of capacity and a reduction in vehicle range. This is especially true for batteries that are idle, and therefore are not generating any heat on their own, which occurs during charge and discharge.

Depending on the storage location for the batteries, some areas may be climate-controlled and some may not be. Idle batteries that are not located in climate-controlled compartments may experience cold soak due to protracted exposure to subfreezing conditions common at cruising altitude. Even when batteries are located in a climate-controlled compartment, they may experience cold soak if a loss of fuselage pressure results in ambient air entering the compartment. Furthermore, cold soak may occur on cold days on the ground (e.g. overnight parking in cold climates).

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved thermal management for batteries. This disclosure provides a solution for this need.

SUMMARY OF THE INVENTION

A battery thermal management system for an air vehicle includes a liquid heat exchange circuit, an air heat exchange circuit in selective fluid communication with ram air, a liquid-air heat exchanger positioned on the liquid heat exchange circuit and the air heat exchange circuit to exchange heat therebetween. The system includes at least one battery in thermal communication with the liquid heat exchange circuit. The at least one battery is configured to at least one of charge or discharge to heat the at least one battery above a pre-determined minimum battery temperature.

In certain embodiments, the system includes a battery temperature sensor operatively connected to the at least one battery. The system can include a state-of-charge sensor operatively connected to the at least one battery. The system can include at least one of a motor or a generator operatively connected to the at least one battery to receive electric power therefrom or provide power thereto. The system can include a battery resistance heater electrically coupled to the at least one battery. The system can include an auxiliary load circuit electrically coupled to the at least one battery. The system can include a battery heat exchanger positioned on the liquid heat exchange circuit in thermal communication with the at least one battery and the liquid heat exchange circuit.

In some embodiments, the system includes a bypass valve positioned in the liquid heat exchange circuit upstream from the liquid-air heat exchanger. The system can include a bypass line branching from the liquid heat exchange circuit upstream from the liquid-air heat exchanger and reconnecting to the liquid heat exchange circuit downstream from the liquid-air heat exchanger. The system can include a bypass line valve positioned on the bypass line.

In accordance with another aspect, a method for controlling a thermal management system for an air vehicle includes determining if at least one battery is within a thermal range of operation for heating. The method includes at least one of charging or discharging the at least one battery to heat the at least one battery if the at least one battery is within the thermal range of operation for heating.

Determining if the at least one battery is within the thermal range of operation for heating can include sensing a temperature of at least one battery with a temperature sensor. At least one of charging or discharging the at least one battery can include at least one of charging or discharging the at least one battery if the temperature is below a pre-determined threshold. Determining if the at least one battery is within the thermal range of operation for heating can include referencing a pre-determined operating schedule that corresponds with a phase of flight.

The method can include closing a bypass valve positioned in a liquid heat exchange circuit upstream from a liquid-air heat exchanger if the at least one battery is within the thermal range of operation for heating. The method can include opening a bypass line valve in a bypass line branching from a liquid heat exchange circuit upstream from a liquid-air heat exchanger and reconnecting to the liquid heat exchange circuit downstream from the liquid-air heat exchanger if the at least one battery is within the thermal range of operation for heating. At least one of charging or discharging can include charging the at least one battery when a state-of-charge of the at least one battery is below a pre-determined state-of-charge threshold. Charging the at least one battery can include charging the at least one battery with energy generated with an engine. At least one of charging or discharging can include discharging the at least one battery when a state-of-charge of the at least one battery is above a pre-determined state-of-charge threshold. Discharging can include discharging energy generated from the at least one battery to an electric load such as a motor operatively coupled to a to an engine and/or to a battery resistance heater.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a schematic view of an exemplary embodiment of the battery thermal management system in accordance with the disclosure is shown inFIG.1and is designated generally by reference character100. Other embodiments of the battery thermal management system in accordance with the disclosure, or aspects thereof, are provided inFIG.2as will be described. The systems and methods described herein can be used to keep batteries warm in order to promote quick charging, avoid capacity loss and the concomitant reduction of vehicle range, or avoid other degradation during cold soak. The systems and methods described herein utilize existing hardware on aircraft, or a minimal addition of hardware, for an efficient and cost-effective approach.

As shown inFIG.1, a battery thermal management system100for an air vehicle includes a controller102, a liquid heat exchange circuit116, an air heat exchange circuit114, and a liquid-air heat exchanger112. Signals to and from the controller102can be routed to and from dedicated ports on the controller102, or the sensors and actuators (described below) can be networked together with each device having its own address. In some embodiments, the components may communicate with the controller via a standard communication protocol involving the transfer of digital information. The system100includes a battery heat exchanger106positioned on the liquid heat exchange circuit116in thermal communication with a bank of batteries104. The bank of batteries104are in thermal communication with the liquid heat exchange circuit116by way of battery heat exchanger106. The battery heat exchanger106is positioned on the liquid heat exchange circuit116in thermal communication with the at least one battery and the liquid heat exchange circuit116. The batteries104are configured to charge and/or discharge to heat themselves above a pre-determined minimum battery temperature.

Batteries104, for example, without limitation, can be depleted batteries, reserve batteries, or batteries of a hybrid electric aircraft propulsion system where the batteries and electric motors assist with takeoff and climb, but are inoperative during cruise. The batteries104could be positioned in a variety of locations throughout the aircraft, for example, in the wings (e.g. in wing roots). In some embodiments, batteries104can furnish energy to a hybrid-electric or all-electric propulsion system for propulsion power or for transient operation (e.g. to avoid stall) or for other applications. In some embodiments, batteries104can be stored in a compartment, rack or housing of some kind. The system100assists in avoiding drastic battery storage capacity loss that occurs at low temperature, thereby maintaining vehicle range (or diminishing range loss). In addition, some battery types cannot be recharged quickly at low temperatures, so by keeping batteries above a given temperature, embodiments of the present invention can reduce the time required to recharge batteries.

With continued reference toFIG.1, the system100includes a battery temperature sensor107operatively connected to the batteries104. The temperature sensor107is operatively connected to the batteries104and controller102. Those skilled in the art will readily appreciate that, due to the complexities involved in obtaining a battery temperature, the temperature sensor107may be operatively connected to the heat transfer fluid exiting the battery heat exchanger106in liquid heat exchange circuit116as a proxy for battery temperature. Those skilled in the art will readily appreciate that referring to “battery temperature,” “battery heat load” or other singular reference to battery, could mean the temperature/heat load of an individual battery104or group of batteries104. Controller102is configured to receive information about battery temperature from temperature sensor107and relay a command, if needed, to one or more of motor111, pump109, or valves110and120(described below). Those skilled in the art will readily appreciate that referring to “battery temperature,” “battery heat load” or other singular reference to battery, could mean the temperature/heat load of an individual battery104or group of batteries104. In some embodiments, it is also contemplated that controller could send a command to temperature sensor107. The system100includes a state-of-charge sensor121operatively connected to the batteries104. State-of-charge sensor121is operatively connected to controller102for sending and/or receiving data or commands thereto. The system100includes a generator device124(e.g. a motor/generator device) operatively connected to the batteries104to provide power to batteries. In some embodiments, the generator may be configured to function as a motor as well, in which the motor/generator device is operatively connected to the batteries104to provide electric power thereto to recharge the batteries in generator mode, but can also serve as a motor by receiving electric power input from the batteries104. Generator device124is operatively connected to an engine126, e.g. a reciprocating combustion engine, a turbomachine, or the like. A power electronics interface122is disposed between the generator124and the batteries104. The circuit between batteries104and the power electronics interface122can include a relay switch119. Power electronics interface122can include one or more rectifiers, inverters, or the like.

As shown inFIG.1, generator device124and engine126offer a charging source for batteries104. For example, if system100was on a hybrid electric aircraft, batteries104could be charged by the generator124of the combustion engine126. In some embodiments, this charging occurs during cruise where batteries are typically idle (and potentially cold) and where batteries104can take advantage of the excess power that aircraft engines typically have (as they are no longer accelerating, due to lower density of air at elevated altitude, and due to fuel weight loss that results in less propulsive thrust required from aircraft engines). In some embodiments, charging batteries104during cruise allows landing approach with batteries at an elevated state-of-charge beyond which is required for aborted landings (go-around) and reserve missions. In other words, in these embodiments, the state-of-charge threshold includes sufficient power to supplement these go-around and/or reserve missions. Also, warm batteries can charge more quickly, so pre-heating batteries104during cruise may lead to a quicker turn-around time on the ground. In some scenarios, charging the battery to recover some of the energy may offer advantages over powering resistance heaters to warm the battery (described below).

The system100includes a battery resistance heater108electrically coupled to the batteries104. The resistance heater108is located in close proximity to batteries104along a heat conduction path and includes a battery heat resistance relay switch119. As an alternative, resistance heater108can warm a heat transfer fluid that is circulated through the batteries104(or their corresponding compartment). The system100includes an auxiliary load circuit117electrically coupled with the batteries104. Auxiliary load circuit117and resistance heater108offer two options for battery discharge. Auxiliary load circuit117also includes a relay switch119. In circumstances where charging is not available, it is contemplated that discharging the batteries104is also an option. Charge and discharge of the batteries104tends to generate waste heat due to the internal resistances of the batteries104that serves to keep the batteries104warm. Batteries104may be charged and discharged continuously or intermittently for thermal regulation. Any suitable electric load served by the battery (propulsion motor, lighting, avionics, entertainment system, etc.) will generate heat. The electricity can be routed to resistance heaters108which warm the batteries. In some embodiments, batteries104may also discharge to a motor such as generator124configured as a motor/generator to offer additional power to the corresponding propulsion system for propulsion power, or for transient operation, or for other applications.

With continued reference toFIG.1, a coolant pump109is upstream from the battery heat exchanger106. The coolant is a heat transfer fluid flowing through liquid heat exchange circuit116used for thermal regulation of the batteries104which includes both heating and cooling. The heat transfer fluid can be any of a number of fluids, including but not limited to water and other aqueous fluids, as well as polar and non-polar organic fluids. In some embodiments, the heat transfer fluid can be in liquid form, but can also be in gaseous form as well as including gas or liquid form such as in a vapor compression heat transfer loop. Examples of heat transfer fluids include but are not limited to glycols such as ethylene glycol or propylene glycol, alcohols such as methanol or ethanol, water and aqueous solutions such as heat transfer brines, and other organic fluids such as propane, butane, and substituted hydrocarbons (e.g., fluoro-substituted) and other organic compounds such as 2,2,3,3-tetrafluoropropene or 1,1,1,2-tetrafluoroethane. A motor111is operatively connected to the coolant pump109to drive coolant pump109. The controller102is in operative communication with pump109and motor111. Pump109circulate heat transfer fluid to heat the batteries104downstream. Pump109and its corresponding liquid heat exchange circuit116are used to provide cooling to batteries104. However, where the temperature sensor107, the state-of-charge sensor121, and/or pre-determined reference table indicate to controller102that heating is required, controller102relays a shut-off command, if needed, to one or more of motor111, pump109, or valves110and120(described below). The pre-determined reference table may be located in electronic storage of controller102, or located in the electronic storage of another device that transmits a signal to controller102. Flight-critical components of a propulsion system100, such as a coolant circulation pump109, may be present in duplicate on an aircraft for redundancy. In view of this, there can be two pumps109that can operate on their own or in conjunction with one another. Moreover, it is contemplated that more than two pumps109can be used in system100. Those skilled in the art will readily appreciate that pump109can be a centrifugal pump, a reciprocating pump, a screw pump, a diaphragm pump, or any other suitable mechanical pump.

The system100includes a bypass valve120positioned in the liquid heat exchange circuit116upstream from the liquid-air heat exchanger112. The system100includes a bypass line118branching from the liquid heat exchange circuit116upstream from the liquid-air heat exchanger112and reconnecting to the liquid heat exchange circuit116downstream from the liquid-air heat exchanger112. The system100includes a bypass line valve110positioned on the bypass line118. Bypass line valve110and bypass valve120include respective motors105in operative communication with controller102to receive open/close commands therefrom. In some embodiments, valves110and120can be combined into a three-way valve that directs flow either to liquid-air-heat exchanger112or to bypass line118. Bypass line118assists in diverting around the liquid-air heat exchanger112to avoid cooling the fluid during cold soak conditions. Depending on the data from the pre-determined operating schedule, the state-of-charge of the batteries, and whether the temperature is below a second pre-determined threshold, which can be the same or different from the pre-determined minimum battery temperature threshold described above, controller102operates to command valve110open and valve120closed (e.g. by way of their respective motors105). Motors105receive a command from controller and, in turn, operate to open or close their respective valves110or120. The reverse command can be executed once the temperature rises back up above the second pre-determined threshold. Valves120and/or110can be a gate valve, a globe valve, a needle valve, or any other proportional valve.

With continued reference toFIG.1, the liquid-air heat exchanger112is positioned on the liquid heat exchange circuit116and the air heat exchange circuit114to exchange heat therebetween. The air heat exchange circuit114is in fluid communication with a ram air door115for providing cooling air (ram air) during non-idle conditions. Ram air is air outside of the fuselage of an aircraft. While the heat sink for air heat exchange circuit114is described herein as ram air, those skilled in the art will readily appreciate that heat exchange circuit114can be operatively connected to other ducts to receive fan duct bypass air, cabin outflow air, conditioned air from an environmental control system, or the like. Air heat exchange circuit114can also include a fan or the like for idle conditions. In the systems and embodiments of the present invention, the flow of cooling air can be curtailed or eliminated during cold soak conditions by closing the ram air door115either partially or fully. Ram air door115can similarly be operatively connected to controller102and can receive a close or open command therefrom depending on the data from the pre-determined operating schedule, the temperature measured at the temperature sensor107and/or the state-of-charge of the batteries measured with the state-of-charge sensor121. Since it is common for several heat exchangers to share a common ram air duct, the air heat exchange circuit114may be optionally outfitted with an air splitter (not shown) to branch the flow of ram air to individual heat exchangers. In this case, a flow control valve such as a butterfly valve can be located upstream of liquid-air heat exchanger112to restrict flow.

As shown inFIG.3, system100, for example, can be used even on a hot day. On a hot day, as the altitude increases, the temperature of the atmospheric air still decreases to temperatures that can be below the batteries' preferred minimum temperature of operation. Line302represents the air temperature, line304represents the minimum battery temperature and line306represents the maximum battery temperature. Those skilled in the art will readily appreciate that the temperatures shown herein may vary depending on battery chemistry, weather, time of day, or the like. Where, for example, the minimum battery temperature is approximately 5 degrees Celsius, heating to prevent cold soak at those high altitudes may be needed. The pre-determined threshold for the temperature, described above, can be set based on the minimum battery temperature for a given battery chemistry.

As shown inFIG.2, another embodiment of a battery thermal management system100for an air vehicle is shown. The system100ofFIG.2is the same as the system100ofFIG.1, except that, instead of a generator124and an engine126, system100ofFIG.2only includes a motor224that is configured to be driven by batteries. In other words, the power generation function (e.g. charging) provided by engine126and generator portion of motor/generator124is not present in system100ofFIG.2. Discharging, similar to that described above relative toFIG.1, may still be formed by system100ofFIG.2. Charging of system100ofFIG.2can also occur if a power source is provided.

A method for controlling a thermal management system, e.g. system100, for an air vehicle includes determining if batteries, e.g. batteries104, are within a thermal range of operation for heating. The method includes charging and/or discharging the batteries to heat the batteries if the batteries are within the thermal range of operation for heating. Determining whether to charge or discharge the batteries is determined by measuring a state-of-charge of the batteries with a state-of-charge sensor, e.g. state-of-charge sensor121.

In some embodiments, determining if the batteries are within the thermal range of operation for heating includes sensing a temperature of the batteries with a temperature sensor, e.g. temperature sensor107. If the temperature is below a pre-determined threshold, the method includes charging and/or discharging the batteries to generate heat. The controller compares the battery temperature, T_bat, with a threshold temperature (e.g. 5° C.). For example, if T_bat<5° C., heating can be initiated by charging and/or discharging.

If the state-of-charge of the batteries is below a pre-determined state-of-charge threshold (e.g. with the capacity to recharge), and the batteries can actually be charged (such as pure electric propulsion plugged into charging, hybrid electric propulsion during cruise with turbofan/prop), the method includes charging the batteries. The method includes comparing the battery state-of-charge with a maximum condition (e.g. <99.9%) which, if less than the maximum condition results in the controller actuating battery charging. Otherwise the controller actuates battery discharging (e.g. resistance heaters). The method may include a prediction of the state of charge of batteries in lieu of a measurement.

If the state-of-charge of the batteries is above a pre-determined state-of-charge threshold, e.g. without the capacity to charge, or generally cannot be charged (e.g. electric aircraft in flight or unplugged on ground), the method includes discharging the batteries. The method can include comparing the battery state-of-charge with a minimum condition (e.g. some energy may be required in reserve) with the controller. If the temperature is sufficiently low, and if the battery has sufficient state-of-charge, then the method includes actuating a load to be drawn/discharged from the batteries to a motor such as one that assists a propulsor (if batteries are part of hybrid/electric propulsion) and/or to a battery resistance heater. (e.g. resistance heaters to warm the battery). For a battery that is already cold-soaked, it may be necessary to heat the battery before it can be charged or discharged.

In some embodiments, determining if the batteries are within the thermal range of operation for heating includes referencing a pre-determined operating schedule that corresponds with a phase of flight. For example, certain durations at cruise (where the batteries may be idle) may be linked to charging and/or discharging the batteries in order to keep them above a given minimum battery temperature.

When allowed by the state-of-charge, temperature of the batteries, and/or pre-determined operating schedule, charging the batteries includes charging the batteries with energy generated with an engineer. The rate of charging can be adjusted to provide the desired heat generation as well as charge state. For example, a trickle charge will warm the batteries, store some charge, and allow faster charging on the ground. Charging on the ground, in some embodiments, may be preferred in order to utilize renewable energy sources. Battery temperature is a function of several variables including battery mass, battery heat capacity, initial battery temperature, heat sink temperature, and thermal loads due to charging, discharging, and environmental conditions. The expected temperature of a battery can be calculated according to standard methods by those who are skilled in the art in order to determine the best rate at which to charge or discharge a battery in order to maintain a desired minimum temperature.

In accordance with some embodiments, the method includes charging batteries on the ground on a cold day for pre-heating purposes. This generates heat that warms the batteries and thereby increases their capacity and thus vehicle range. If ground power is available to charge, then the electricity can also feed a battery resistance heater, e.g. battery resistance heater108, to further warm the batteries to a target temperature. In one embodiment, the electricity is provided to an electrical bus that charges the batteries as well as supplies power to the resistance heaters.

Where charging the batteries is not available, e.g. in the embodiment ofFIG.2or where the state-of-charge of the battery does not permit, the method includes discharging the batteries to at least one of a motor, e.g. motor/generator124or motor224, a battery resistance heater, e.g. battery resistance heater108, and/or an auxiliary load circuit, e.g. auxiliary load circuit117. The method includes closing a bypass valve, e.g. bypass valve120, positioned in a liquid heat exchange circuit, e.g. liquid heat exchange circuit116, upstream from a liquid-air heat exchanger, e.g. liquid-air heat exchanger112, if the batteries are within the thermal range of operation for heating. The method includes opening a bypass line valve, e.g. bypass line valve110, in a bypass line, e.g. bypass line118, branching from a liquid heat exchange circuit upstream from the liquid-air heat exchanger and reconnecting to the liquid heat exchange circuit downstream from the liquid-air heat exchanger if the batteries are within the thermal range of operation for heating. The method further includes restricting the flow of a heat sink, e.g. closing ram air door115or a closing a valve that regulates ram air flow, when the batteries are within the thermal range of operation for heating.

The methods and systems of the present disclosure, as described above and shown in the drawings, provide for thermal battery control with superior properties including reduced battery storage capacity loss, decreased recharging time, maintained vehicle range, and/or diminished vehicle range loss. The systems and methods of the present invention can apply to automotive batteries, aircraft batteries, terrestrial batteries, or the like. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.