Patent Application
20150336677
1. Field of the Invention
The present invention relates to an in-flight refueling device of an electrically propelled aircraft which comprises an on-board electrical storage system, an aircraft equipped with such a device and a method for recharging batteries of an electrically propelled aircraft. The device provides for charging aircraft, aircraft likely to be recharged and appropriate connection means.
2. Technological Background
Since the launch of lithium-based batteries on the market, there has been an increasing emergence of airplane or helicopter demonstrators operating with electrical energy stored in electrochemical form in batteries.
It is clear that the power of the electric motors involved is very significant so there is therefore a need for a very significant input of on-board electrical energy.
The problem is that, in the short and even medium-term, the battery technologies do not allow the electric aircraft to achieve endurance levels similar to their counterparts that use gas or kerosene.
To increase the action radius of such aircraft, the American company Flight of the Century proposes producing an aircraft of mother vessel type with electric propulsion flying continually and capable of accommodating flying devices in the form of drones supporting batteries which complement the mother vessel and power it.
Once discharged, the drone is separated from the mother vessel and flies to a recharging station while another drone takes its place for the continuation of the flight.
Another solution envisaged by this company is to propose aircraft provided with battery packs in a plurality of parts that can be separated and jettisoned which increases the action radius of the supporting craft by progressively reducing its weight.
Other studies focus on laser or microwave-based remote energy transfer technologies.
In-flight refuelings are known in the field of aircraft with heat propulsion: an aircraft will serve as refueller and a second will come to be served. The refueller is generally an airplane with high capacities to have the maximum of fuel available for the airplanes which meet it. It drags behind it an in-flight refueling device which can take two different forms: either a rigid boom which will be controlled from the charging aircraft, or a basket at the end of a flexible pipe in which the airplane to be refueled will be refueled via a refueling boom. The latter is the system retained by the French airforce.
The present invention envisages, for a determined mission type, increasing the power reserve of an electrically propelled craft via an in-flight recharging process. This operation could be repeated, in the same flight, a number of times.
The present invention notably makes it possible to extend the mission times of the aircraft without increasing the weight of the on-board batteries and without producing a complex structure for jettisoning or mooring an additional vehicle.
For this, the present invention proposes a system for recharging on-board batteries in an electrically propelled aircraft, characterized in that it comprises a charging aircraft, means for temporarily electrically connecting the charging aircraft to the electrically propelled aircraft and a charge regulation device in the electrically propelled aircraft.
Advantageously, the charging aircraft and the temporary connection means are adapted to supply and transport a power supply current for the engine or engines of the electrically propelled aircraft in addition to the battery recharging current.
The on-board batteries preferably comprise fast-charge batteries that are the object of the recharging by the recharging system.
The temporary connection means are preferably designed to withstand the turbulences while being suitable for being disconnected safely in case of emergency and at the end of refueling.
The temporary connection means advantageously comprise two complementary plug-in connectors one borne by a flexible cable or a boom from the charging aircraft, the other borne by a junction device of the electrically propelled aircraft, and comprise an electromagnetic device for connecting the two complementary plug-in connectors.
The charge regulation device advantageously comprises a circuit for balancing the charges on packs and cells of the on-board batteries.
According to a first embodiment, the charging aircraft is equipped with an electrical energy production system suitable for recharging the propulsion batteries of the electrically propelled aircraft.
According to an advantageous embodiment, the charge regulation device is a device for controlling the batteries which monitors, during the charging, the current, the voltage and the temperatures of the battery cells, is adapted to decide to disconnect from the charger or alert the pilot to do so in the case of overvoltage, overcharging of the cells or excessively high temperature, and is adapted to communicate with the charger of the refueling airplane in order to itself control the battery charging current.
The electrical energy production system can comprise a heat engine coupled to a generator and/or a fuel cell.
According to an alternative or complementary embodiment, the electrical energy production system comprises batteries or a hybrid system with a plurality of sources.
According to a particular embodiment, the charging aircraft is a drone.
The electrically propelled aircraft can further comprise an on-board system for generating electrical energy from kerosene or hydrogen as backup system for example.
According to a particularly advantageous embodiment, the charging aircraft, the temporary electrical connection means for connecting the charging aircraft to the electrically propelled aircraft and the charge regulation device in the electrically propelled aircraft are adapted to recharge all the packs of the on-board batteries at one time.
According to an alternative or complementary embodiment, the charging aircraft is itself electrically propelled.
The invention also relates to a method for recharging batteries of an electrically propelled aircraft by means of a system as claimed in any one of the preceding claims, for which:
Other features and advantages of the invention will become apparent on reading the following description of a nonlimiting exemplary embodiment of the invention with reference to the drawings which represent:
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The present invention proposes a system for recharging on-board batteries 6 in an electrically propelled aircraft 10 that can be recharged in flight.
The system schematically represented in
The temporary electrical connection means comprise, according to the example, a flexible electrical cable 2 dragged by the charging aircraft, here a reaction airplane, a first connector element 3a at the end of the cable, a second connector element 3b arranged at the end of a boom 4 from the aircraft 10 whose batteries are to be recharged.
The electric cable can be a flexible cable placed in the eye of the wind of the charging aircraft and can, as in the prior art of refueling with kerosene, comprise a basket to stabilize it and form a guiding cone for the second connector element 3b arranged at the end of the boom 4 from the electrically propelled aircraft 10 whose batteries are to be recharged.
The electrical cable can also be replaced by a boom controlled by an operator in the charging aircraft.
The temporary connection means comprise two complementary plug-in connectors 3a, 3b detailed more particularly in
As represented in
For this, the complementary plug-in connectors 3a, 3b here comprise an electromagnetic device for coupling the two plug-in connectors comprising electromagnets 35 linked to a control device in the aircraft by wires 351.
According to the example, the complementary plug-in connectors comprise self-centering tapered coupling profiles 36, 37 and end-connecting coaxial annular contacts 31a, 31b, 31c.
On the charging aircraft side, the contacts are linked by electrical conductors 311a, 331b, 311c to the charging device.
On the side of the aircraft to be recharged, the contacts are linked by conductors 312a, 312b, 312c to the charge balancing device 5 and, possibly, to the power supply circuit of the engine or engines of the aircraft.
Here, the contacts 31a can be mass contacts jointly recharging the batteries and supplying power to the engine or engines, the contacts 31b being the battery charging contacts and the contacts 31c being the contacts supplying power to the electric engines of the aircraft during the charging.
It is also possible to consider four contacts, two for the recharging of the batteries and two for supplying power to the engines during the recharging.
The connection must be robust to turbulences, ensure safe locking and unlocking after refueling and allow for a rapid decoupling in case of emergency during the recharging. Here, this is made possible by the electromagnetic coupling means.
The mounting of one of the contact supports on a plate suspended by springs 38 here ensures that the contacts bear upon one another.
The electrical recharging plug-in connector 3b of the electrically propelled aircraft is here arranged on an arm 4, but could be arranged on the nose of the aircraft.
To recharge all the on-board battery packs at one time, the circuit 5 for balancing the charge on the battery packs and the cells is an on-board circuit in the electrically propelled aircraft.
The charging aircraft and the temporary connection means are adapted to supply and transport a power supply current for the engine or engines 7 of the electrically propelled aircraft in addition to the recharging current for the on-board batteries 6 of the electrically propelled aircraft. As seen above, this can be done with one or more additional contacts.
The charge regulation device 5 comprises a circuit for balancing the charges on the packs and the cells 61 of the on-board batteries. This makes it possible to simplify the wiring of the temporary links although this increases the on-board weight in the rechargeable electrically propelled aircraft.
The charge regulation device is for example of BMS (battery management system) type, which is a device for controlling the batteries which makes it possible to envisage more functionalities in the battery charge regulation device.
Typically, the BMS is a so-called smart device which monitors, during the charging, the current, the voltage and the temperatures of the battery cells.
The BMS can decide to disconnect from the charger or alert the pilot to do so in the case of overvoltage, overcharging of the cells or of excessively high temperature.
The BMS also makes it possible to communicate with the charger of the refueling airplane in order to itself control the battery charging current. This can be done by means of a computer bus (CAN bus for example) or by analogue control. It finally incorporates active or passive balancing means between the cells that make up the battery pack.
Ideally, the charging aircraft 1, the means 2, 3a, 3b, 4 for temporarily electrically connecting the charging aircraft to the electrically propelled aircraft and the charge regulation device 5 in the electrically propelled aircraft are adapted to recharge all the packs of the on-board batteries at one time.
To recharge the batteries of his or her craft, during the flight of the electrically propelled aircraft, the pilot decides to connect to a charging aircraft which makes it possible to recharge its batteries rapidly.
Based on the current batteries, an estimation for an aircraft having 2×10 kW engines, a recharging of the 2×30 kW batteries (250V×120 A) and a rate of charge of 3 C, the recharging time is estimated to be of the order of 15 minutes for an 80% recharge.
As seen above, the charging aircraft can also supply power to the engines of the electrically propelled aircraft during the recharging phase.
This supply of power can notably be provided through dedicated cables and contacts 31b in order to convey the necessary current and deliver the necessary voltage.
The charging aircraft can be an airplane equipped with an electrical energy production system 100 which can be a heat engine coupled to a generator, a fuel cell, batteries or a hybrid system with a plurality of sources.
It can also be a drone equipped with the same type of energy production system. The drone would make it possible to have more space and weight available for the production of electrical power.
The charging aircraft can itself be an electrically propelled aircraft.
As in the case of a conventional kerosene refueling, the refueling area must be determined and known in advance and, consequently, the safety in case of failure of the recharging for whatever reason, is taken into account by at least three factors:
The system of the invention requires two pilots trained for this purpose or automatic piloting functions adapted to this task.
Moreover, the system of the invention is designed in the context of fast-recharge batteries which do, however, have a lower energy density than the slow-recharge batteries which means that the weight budget of the airplane can be affected thereby.
The fast-charge batteries can handle phases with high power demand such as taking off and climbing. Once recharged, these batteries make it possible to continue the flight after recharging.
It is, however, possible to combine batteries with high energy density, but in this case with slow recharging, for the take-off and flight start phases that are strong consumers, and fast-recharge batteries for the rest of the flight.
The recharging steps will then be conducted on the fast-recharge batteries which have to supply less energy than the batteries handling the take-off.
The invention makes it possible to optimize the choice of the batteries according to the missions to be carried out.
The implementation of the invention is broken down into a plurality of steps:
The electrically propelled aircraft of the invention can further comprise an on-board system which makes it possible to generate electrical energy from kerosene, for example a turbogenerator or a small heat engine coupled to a generator which makes it possible to generate electrical energy from hydrogen, for example a fuel cell. This system makes it possible to improve the power reserve of the aircraft or provide backup in case of complete discharging of the batteries, but it adds to the on-board weight and adds complexity to the propulsion system.
Currently, the battery capacities are of the order of 200 Wh/kg with a recharging rate of 2 to 4 C, but it is possible to consider being able to design a regional airplane with 1000 Wh/kg batteries and a recharging rate of 10 C which would give, for an engine power of 2 MW and a battery capacity of 1.6 MWh, a flight time of one hour with a reserve of 10% and recharging times of 6 to 7 minutes.
It is also possible to envisage using cables and engines operating at superconductor temperature.
The invention is applicable to all types of electrically propelled aircraft, airplanes, helicopters, drones. This invention notably makes it possible to propose drones of reasonable dimensions, capable of handling medium distance missions, even long distance missions, but in this case managed by an on-board automatic system linked with a charging aircraft which could itself be automatic.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1262655 | Dec 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/077306 | 12/19/2013 | WO | 00 |
