Front-wheel drive motor vehicle including a battery cooling system

Abstract

An electrically powered motor vehicle comprising a battery (1), a cooling system (SR) for cooling the battery, at least during charging from the external power source, the cooling system comprising a first Stirling-type machine (MS1) configured as a Stirling refrigeration machine for cooling the battery, in which work is supplied to the flywheel of the first machine at least in part by an electric motor (M3), the cooling system comprising a second Stirling-type machine (MS2) configured as a Stirling engine, with a second portion of the battery as its hot source and ambient air as its cold source, with a second flywheel (32) mechanically coupled to the first flywheel (31) to deliver work received by the second flywheel to the first flywheel. Figure 1

Description

Title of the invention: Front-wheel drive motor vehicle comprising a battery cooling system

[0001] The invention relates to a plug-in hybrid or 100% electric motor vehicle. In this type of vehicle, it is necessary to recharge the batteries, otherwise referred to here as electrical energy storage means, from time to time from a charging station or an electrical outlet available in the usual residence of the vehicle user.

[0002] Batteries used for electric or plug-in hybrid motor vehicles are generally an assembly of elementary electrochemical cells, for example Ni-MH, Ni-Cd, Lithium-Ion, without excluding other electrochemical solutions.

[0003] For fast charging, it is desirable to be able to quickly recharge the vehicle's battery using "fast charging stations" made available to the public, for example, at motorway service areas. These fast charging stations can deliver high power outputs, e.g., several tens of kW, a few hundred kW, up to 350 kW.

[0004] A charging operation at several hundred kW generates significant heat in the core of the battery. It is therefore necessary to dissipate the heat as efficiently as possible as it is generated in the battery, to avoid excessive heating of the materials composing the battery cells.

[0005] Heat pipe systems for heat removal have already been proposed. Phase-change fluid systems for heat removal have also already been proposed. Furthermore, forced-air systems for heat removal have already been proposed.

[0006] However, the performance of these systems is limited, and the power dissipated is not sufficiently controllable.

[0007] The present invention aims to remedy at least one of these drawbacks.

[0008] To achieve this objective, the invention proposes, in its broadest sense, an electric motor vehicle comprising an electrochemical battery for electrical energy storage, connection means for enabling the battery to be recharged from an external power source, a cooling system for cooling the battery, at least during charging from the external power source, the cooling system comprising a first Stirling-type machine configured as a Stirling refrigeration machine, the first machine comprising: - a portion of heat extraction using thermal coupling with a first portion of the battery, - a portion of the heat rejection system configured to release heat into the ambient air, - a first piston, a second piston and a first flywheel connected to the first and second pistons by a first connecting rod, in which work is supplied to the first flywheel at least in part by an electric motor, characterized in that the cooling system comprises a second Stirling-type machine configured as a Stirling engine, with as a hot source a second portion of the battery coupled to a heat receiving portion of the second Stirling-type machine, and as a cold source ambient air coupled to a cooling portion of the second Stirling-type machine, with a third piston, a fourth piston and a second flywheel connected to the third and fourth pistons by a second connecting rod, and in that the second flywheel is mechanically coupled to the first flywheel to deliver work received by the second flywheel to the first flywheel.

[0009] We are interested here in the case of charging on a fast charging station, with a high intensity direct current charging current, typically greater than 100 amps.

[0010] Thanks to these arrangements, the first Stirling-type machine, configured as a Stirling refrigeration machine, can remove large quantities of heat, particularly in a rapid recharging situation where significant currents are involved. Furthermore, the heat flow can be controlled by means of the rotational speed of the first flywheel of the first Stirling machine. This speed can be controlled by means of the electric motor. Moreover, the second Stirling machine operates as a motor, and the work available on the second flywheel is fed back onto the shaft of the first flywheel, thus reducing the energy required to operate the first Stirling machine.

[0011] This provides a very efficient solution in terms of heat flow evacuation while minimizing the energy taken from the electrical charging line to carry out this heat evacuation.

[0012] In this document, the term "Stirling engine" refers to a thermodynamic machine known as an external combustion engine, named after its inventor, since the mid-19th century. This machine was initially conceived to provide mechanical energy, namely to function as a motor. However, this thermodynamic machine is reversible, and its use as a refrigeration machine is more recent, having developed during the second half of the 20th century.

[0013] The operating principle of a Stirling engine is assumed to be known to the reader as well as the usual constructive variants of embodiment.

[0014] Each Stirling machine considered here can be formed as a set of two cylinders (type Alpha and Gamma) each cylinder containing a piston, with flywheel-connecting rod assembly or each Stirling machine considered here can be formed as a single-cylinder type combination with two pistons one above the other with a flywheel-connecting rod assembly (this is type Beta).

[0015] The pistons are mobile in the cylinders and delimit gas chambers as will be seen below.

[0016] According to an advantageous option, a thermal bridge plate may be provided to collect the calories generated in the battery, the thermal bridge plate being thermally connected to the portion of the heat collection of the first Stirling engine.

[0017] This promotes the transmission of calories from a large surface to the location of the portion of the first Stirling engine that extracts calories.

[0018] Any system enabling the heat generated in the battery to be conveyed to the heat extraction portion of the first Stirling engine is considered within the scope of the present invention.

[0019] It is noted that, said motor vehicle having a frame of reference in space comprising a longitudinal axis following a direction of movement of said motor vehicle, a transverse axis perpendicular to the longitudinal axis, and a vertical axis perpendicular to the longitudinal axis and to the transverse axis, the vertical axis being directed from bottom to top, the plate forming a thermal bridge can contain a heat transfer fluid or even a thermodynamic fluid with phase change, in order to offer the lowest possible thermal resistance.

[0020] According to an advantageous option, the thermal bridge plate is arranged under the battery. Thus, the plate forms a physical support for the arrangement of the plurality of electrochemical cells forming the battery, said cells being in firm and gravitational contact with said plate.

[0021] According to one embodiment, the battery is at least partly immersed in a dielectric liquid and the portion that extracts heat is in thermal coupling with the dielectric liquid.

[0022] According to another embodiment, the heat-absorbing portion is thermally coupled to the first portion of the battery by means of heat pipes. The heat pipes can have various shapes facilitating thermal contact between the electrochemical cells and the heat-absorbing portion of the first Stirling engine.

[0023] According to an advantageous option, a fan may be provided to induce forced convection in contact with the heat rejection portion. Preferably, this may be forced-air convection, although convection by a liquid fluid is not excluded. This improves the transfer of heat to the ambient air from the portion of calorie rejection from the first Stirling engine.

[0024] Depending on one option, the first Stirling-type machine can be of a type chosen from among the following Stirling machine configurations: Alpha, Beta, Gamma, or a membrane Stirling machine. Depending on the available space and the footprint required for installing the Stirling machine, one of the three aforementioned available types can be chosen.

[0025] Depending on one option, the second Stirling engine can be of a type chosen from among the following Stirling engine configurations: Alpha, Beta, Gamma, or a membrane Stirling engine. Similarly, depending on the available space and the footprint required for installing the Stirling engine, one of the three aforementioned available types can be chosen. It should be noted that the two Stirling engines do not have to be of the same type.

[0026] In practice, one can choose an Alpha type for the first Stirling machine and a Gamma type for the second Stirling machine.

[0027] According to one option, the first Stirling-type machine is chosen to be of the Alpha type, with a first cylinder housing the first piston and defining a first chamber with variable volume, the first chamber forming part of the heat extraction portion, and with a second cylinder housing the second piston and defining a second chamber with variable volume, the second chamber forming part of the heat rejection portion. The Alpha-type machine is particularly well suited to operation as a refrigeration machine of the Stirling cycle.

[0028] According to one option, the second flywheel is mechanically coupled to the first flywheel by means of a reducer or a multiplier. This allows for a different rotational speed between the two Stirling engines.

[0029] According to one option, the electric motor is mechanically coupled to the first flywheel by means of a reduction gear. This allows the use of a small motor which, in practice, will rotate faster than the rotational speed of the first Stirling engine.

[0030] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: - [Fig.l] schematically illustrates a cooling system for an electric vehicle battery based on two Stirling machines, one operating as a refrigeration machine and the other as a motor, the Stirling machines being of the Alpha type; - [Fig.2] schematically illustrates a battery cooling system electric vehicles based on two Stirling machines, one operating as a refrigeration machine and the other as a motor, the Stirling machines being of the Beta type; - [Fig.3] illustrates a variant of [Fig.1], with the battery elements in an immersive configuration; - [Fig.4] illustrates an example of a mechanical coupling solution between the second steering wheel and first steering wheel.

[0031] In the various figures, the same reference numerals designate identical or similar elements. For the sake of clarity, some elements are not necessarily shown to scale.

[0032] A hybrid or electric vehicle includes at least one BATT electrochemical type battery capable of storing a large amount of electrical energy and at least one electric traction motor.

[0033] Here, the term battery means any electrical energy storage device on board an electric or hybrid vehicle, of electrochemical type (Ni-MH, Li-Ion, etc.) or even partially purely electrical (supercapacitors).

[0034] We are particularly interested here in batteries having an energy storage capacity of at least 40 kW.

[0035] In practice, a battery is a set of individual electrochemical cells mechanically and electrically assembled to form a module or battery pack. There may be several subsets of battery modules arranged in different locations, but functionally grouped from an electrical point of view. As another example, the entire battery may be housed in the vehicle floor.

[0036] The vehicle includes connection means designed to allow rapid battery charging from an external power source. For charging of a few hundred kilowatts, this involves direct current charging available at public charging stations.

[0037] The charging process causes significant heating inside the battery due to the currents involved. The vehicle is therefore equipped with a cooling system designed to dissipate the large amount of heat generated within the battery during the charging process, particularly through the Joule effect.

[0038] The SR cooling system comprises a first Stirling type MS 1 machine configured as a Stirling refrigeration machine and a second Stirling type MS2 machine operating as a motor.

[0039] The first Stirling-type machine, MS 1, operates as a Stirling refrigeration machine. Its role is to extract heat from the battery and release it into the outside air. As we will see later, mechanical work must be supplied to this first Stirling machine.

[0040] Conversely, the second Stirling-type machine (MS2) operates as an engine Stirling, it uses calories from the battery to form its hot source and the ambient air forms its cold source.

[0041] In the first example shown in [Fig.1], both machines are of the Stirling Alpha type.

[0042] First machine

[0043] The first Stirling machine MSI includes a heat-absorbing portion 21 in thermal coupling with a first portion 81 of the battery, and a heat-rejecting portion 22 configured to reject heat into the environment in the ambient air.

[0044] The first Stirling machine MSI comprises a first piston 71 mounted sliding in a first cylinder 11, a second piston 72 mounted sliding in a second cylinder 12.

[0045] The first Stirling MSI machine includes a flywheel 31, called the first flywheel, connected to the first and second pistons by a first connecting rod 41, detailed later.

[0046] It is noted that one of the cylinders is geometrically offset by 90° relative to the other cylinder, which simplifies the connecting rod assembly (single crankpin) required for the connecting rod assembly.

[0047] This constructive arrangement reflects one of the main characteristics of Stirling machines, namely the quadrature offset of one piston relative to the other.

[0048] The first connecting rod 41 is articulated from a crankpin 49 attached to the flywheel 31. An intermediate connecting rod 42 is attached on one side to the crankpin 49 and on the other side to a rod end 43 of the first piston 71. Another intermediate connecting rod 45 is attached on one side to the crankpin 49 and on the other side to a rod end 44 of the second piston 72.

[0049] The first flywheel 31 is mounted pivoting around an axis XI relative to a machine housing.

[0050] The first piston 71, together with the first cylinder 11, defines a first gas chamber Cl above the piston. The first gas chamber has an orifice at its upper end. This orifice is fluidly connected by a conduit to a regenerator 91, on its cold side.

[0051] Similarly, the second piston 72, together with the cylinder 12, defines a second gas chamber C2 above the second piston. Here too, an upper end orifice allows the second gas chamber C2 to be fluidly connected to the regenerator, on the hot end side.

[0052] In the first chamber Cl, the phenomenon of relaxation is predominant, whereas in the second chamber C2, the phenomenon of compression is predominant.

[0053] The heat flux extracted from the battery by the extraction portion is denoted Q1. The heat flux rejected into the surrounding air by the heat rejection portion 22 is denoted Q2.

[0054] Fins 19 may be provided as schematically represented in the figures to improve the exchange coefficients at the intake and discharge portions.

[0055] To operate this machine in refrigeration mode, mechanical work must be supplied to the first flywheel 31. To this end, a coupling of the flywheel 31 with an electric motor M3 is provided.

[0056] The direction of rotation of the flywheel is the opposite direction to the case where the machine is operating as a motor.

[0057] The average temperature Tl of the first gas chamber Cl is lower than the average temperature T2 of the second gas chamber C2.

[0058] The electric motor M3 is controlled by a computer responsible for monitoring the charging of the vehicle's battery. The rotational speed of the flywheel 31 can range from a few tens of revolutions per minute to a few hundred revolutions per minute, depending on the heat dissipation requirements.

[0059] For example, the control of M3 can be such that the average temperature Tl on the portion of the sampling is close to 0°C, without going lower to avoid the formation of ice.

[0060] The fluid used in the first Stirling engine may be air, CO2, ethanol, hydrogen, helium, without excluding other gases.

[0061] As is known per se and not described in detail here, the regenerator 91 exchanges energy with the gas flowing through it cyclically and in both directions. There is a significant temperature gradient inside the regenerator between the hot end and the cold end.

[0062] Second machine

[0063] The second Stirling engine MS2 operates as a Stirling engine, with a second portion of the battery coupled to a heat-receiving portion 23 of the second Stirling engine as its heat source. The cold source is ambient air coupled to a cooling portion 24 of the second Stirling engine. The heat-receiving portion 23 of the second engine is thermally coupled to a second portion 82 of the battery.

[0064] Preferably, this second portion 82 of the battery is away from the first portion 81 of the battery which benefits from the cooling provided by the first Stirling engine.

[0065] The second Stirling engine MS2 includes a third piston 73 mounted sliding in a third cylinder 13 and a fourth piston 74 mounted sliding in a fourth cylinder 14.

[0066] The second Stirling machine MS2 includes a flywheel 32, called the second flywheel, connected to the third and third pistons by a second connecting rod 42.

[0067] The second connecting rod 42 is similar or identical to the first connecting rod 41 and therefore not described again here for the sake of brevity.

[0068] Here too the cylinders are offset by 90° from each other, according to the Alpha configuration.

[0069] The second flywheel 32 is mechanically coupled to the first flywheel 31 to deliver work received by the second flywheel to the first flywheel.

[0070] The second flywheel 32 is mounted pivoting around an axis X2 relative to the machine housing.

[0071] The third piston 73, together with the third cylinder 13, defines a third gas chamber C3 above the piston. The third gas chamber has an orifice at its upper end. This orifice is fluidly connected by a conduit to a regenerator 92, on its hot end side.

[0072] Similarly, the fourth piston 74, together with the fourth cylinder 14, defines a fourth gas chamber C4 above the fourth piston. Here too, an upper end orifice allows the second gas chamber to be fluidly connected to the regenerator on its cold side.

[0073] In the third chamber C3, the expansion phenomenon is predominant, while in the fourth chamber C4, the compression phenomenon is predominant. Compared to the first machine, the direction of rotation of the second flywheel 32 is reversed.

[0074] The heat flux extracted from the battery by the extraction portion 23 is denoted Q3. The heat flux rejected into the surrounding air by the heat rejection portion 24 is denoted Q4.

[0075] The average temperature T3 of the third gas chamber C3 is higher than the average temperature T4 of the fourth gas chamber C4.

[0076] To improve thermal performance, a thermal bridge plate, denoted 8, may be provided in close interface with the electrochemical cells of the battery.

[0077] According to one option, the thermal bridge plate 8 is arranged under the battery, i.e. the electrochemical elements of the battery rest on said plate 8.

[0078] On the side of the heat rejection portion, a fan 87 may be provided to generate forced convection that blows against the fins of the rejection portion 22. Any other system promoting heat exchange to extract heat since the rejection portion 22 can also be used.

[0079] The rotation speed of the electric motor M3 can be controlled by the BMS computer in charge of monitoring the charging process.

[0080] According to a particular option, the fan 87 is driven proportionally with respect to the rotational speed of the motor M3, the fan can be driven via a reducer from the return shaft of the motor M3.

[0081] Stirling Beta variant

[0082] Figure 2 illustrates another embodiment with Beta-type Stirling engines. This configuration is generally more compact in terms of geometric dimensions.

[0083] Compared to the Alpha configuration described above, only the different elements will be shown below, the other functions and characteristics being assumed to be identical or similar to those of Alpha type machines.

[0084] Here too, the first Stirling-type machine MSI operates as a Stirling refrigeration machine, drawing a heat flux Q1 from the battery and releasing a heat flux Q2 into the ambient air. Conversely, the second Stirling-type machine MS2 operates as a Stirling engine; it uses heat from the battery to form its hot source and the ambient air forms its cold source.

[0085] According to this configuration, chambers Cl and C2 are located in one and the same cylinder 15.

[0086] In the first cylinder 15, the first piston 75 is located above the second piston 76. The rod of the first piston passes through the second piston with a sealing gasket at this point.

[0087] According to this configuration, chambers C3 and C4 are located in one and the same cylinder 16.

[0088] In the second cylinder 16, the third piston 77 is located above the piston 78. The rod of the third piston passes through the second piston with the fourth with a sealing joint at this point.

[0089] Each flywheel 31 32 is equipped with two crankpins, the two crankpins 36 37 are angularly offset by 90°, which produces the result of having respective piston movements in quadrature.

[0090] Other features

[0091] Advantageously, according to the present invention, a mechanical coupling 9 is provided between the second flywheel 32 and the first flywheel 31 in order to reinject the work recovered by the second Stirling engine MS2 into the first Stirling engine MSI. In this way, the electric motor M3 is relieved of the load, which then only has to supply part of the work required for the operation of the first engine in a refrigeration cycle.

[0092] The mechanical coupling 9 between the second flywheel and the first flywheel can be direct or indirect.

[0093] In one example, axes XI and X2 may coincide. However, in practice, a connecting tree is provided, with angle reference(s) where appropriate.

[0094] For example, as schematically illustrated in [Fig. 4], the mechanical coupling may involve a reduction stage 92, or conversely a multiplication stage, via a gear train. Different rotational speeds may indeed be required between the first and second machines in order to optimize energy recovery from the second machine MS2 to the first machine MSI.

[0095] According to an alternative embodiment shown in [Fig. 3], the electrochemical cells of the battery are immersed at least partially in a dielectric liquid 3. The heat-absorbing portion 21 of the first MSI machine is thermally coupled to the dielectric liquid 3. Advantageously, the liquid permeates all the spaces between the electrochemical cells and absorbs heat there. Furthermore, the dielectric liquid 3 also allows for good heat conduction to the hot source of the second MS2 machine, namely the heat-receiving portion 23 of the second Stirling-type machine.

[0096] An agitator or circulator may be provided to homogenize the temperature inside the dielectric liquid. The dielectric liquid solution effectively homogenizes the prevailing temperature in the electrochemical cells of the battery.

[0097] According to another embodiment, heat pipes are used, and the heat-absorbing portion 21 is then thermally coupled to the first portion of the battery by means of said heat pipes. The heat pipes can have various shapes to facilitate thermal contact between the electrochemical cells and the heat-absorbing portion of the first Stirling engine. The heat pipes can be passive (capillary) or thermosiphons (using gravity).

[0098] It is noted that the quantities of heat flux Q1 and Q2 are generally greater than the quantities of heat flux Q3 and Q4.

[0099] Any heat exchange system that allows the heat fluxes Q1, Q2, Q3, Q4 to be transferred in the best possible way can be used, either a fin system as shown in the figures, or any other system.

[0100] According to a non-limiting example, the average temperature of the battery during a fast charge can be close to 75°C, the average temperature T1 close to 5°C, the average temperature T2 close to 80°C, the average temperature T3 close to 65°C and the average temperature T4 close to 20°C (ambient temperature).

[0101] Instead of Alpha or Beta types, Stirling machines could also be Gamma type machines (not shown in the figures) or membrane Stirling machines.

[0102] It is noted that Stirling machines are discreet, their silent operation is an advantage in avoiding disturbing a vehicle user while fast charging is taking place.

Claims

Claims

1. An electrically powered motor vehicle comprising an electrochemical type battery (1) for storing electrical energy, connection means intended to enable the battery to be recharged from an external current source, a cooling system (SR) for cooling the battery, at least during recharging from the external current source, the cooling system comprising a first Stirling type machine (MSI) configured as a Stirling refrigeration machine, the first machine comprising: - a heat extraction portion (21) in thermal coupling with a first portion of the battery (81), - a heat rejection portion (22) configured to reject heat into the environment in the ambient air, - a first piston (71), a second piston (72) and a first flywheel (31) connected to the first and second pistons by a first connecting rod (41),wherein work is supplied to the first flywheel at least in part by an electric motor (M3), characterized in that the cooling system comprises a second Stirling-type machine (MS2) configured as a Stirling engine, with as a heat source a second portion of the battery (82) coupled to a heat receiving portion (23) of the second Stirling-type machine, and as a cold source the ambient air coupled to a cooling portion (24) of the second Stirling-type machine, with a third piston (73), a fourth piston (74) and a second flywheel (32) connected to the third and fourth pistons by a second connecting rod (42), and in that the second flywheel (32) is mechanically coupled to the first flywheel (31) to deliver work received by the second flywheel to the first flywheel.,

2. Motor vehicle according to claim 1, characterized in that a thermal bridge plate (8) is provided for collecting the calories generated in the battery, the thermal bridge plate being thermally connected to the calorie collection portion (21) of the first Stirling engine.

3. Motor vehicle according to claim 2, said motor vehicle having a reference frame in space comprising a longitudinal axis (X) along a direction of movement of said motor vehicle, a transverse axis (Y) perpendicular to the longitudinal axis (X), and an axis vertical (Z) perpendicular to the longitudinal axis (X) and to the transverse axis (Y), the vertical axis being directed from bottom to top, characterized in that the thermal bridge plate (8) is arranged under the battery.

4. Motor vehicle according to claim 1, characterized in that the battery is at least partly immersed in a dielectric liquid (3) and the heat collection portion is thermally coupled with the dielectric liquid.

5. Motor vehicle according to claim 1, characterized in that the calorie collection portion (21) is thermally coupled with the first portion of the battery by means of heat pipes.

6. Motor vehicle according to any one of claims 1 to 5, characterized in that it comprises a fan (87) to cause forced convection in contact with the heat discharge portion.

7. Motor vehicle according to any one of claims 1 to 6, characterized in that the first Stirling type machine (MSI) is of a type chosen from the Stirling machine configurations: Alpha, Beta, Gamma or a membrane Stirling machine.

8. Motor vehicle according to any one of claims 1 to 7, characterized in that the second Stirling type machine (MS2) is of a type chosen from the Stirling machine configurations: Alpha, Beta, Gamma or a membrane Stirling machine.

9. Motor vehicle according to any one of claims 1 to 6, characterized in that the first Stirling type machine (MSI) is of the Alpha type, with a first cylinder (11) housing the first piston and delimiting a first chamber (Cl) with variable volume, the first chamber forming part of the calorie collection portion (21), and with a second cylinder (12) housing the second piston and delimiting a second chamber (C2) with variable volume, the second chamber forming part of the calorie rejection portion (22).

10. Motor vehicle according to any one of claims 1 to 9, characterized in that the second flywheel (32) is mechanically coupled to the first flywheel (31) by means of a reducer or a multiplier.

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