FR3146435A1 - Front-wheel drive motor vehicle including a battery cooling system - Google Patents

Abstract

An electrically powered motor vehicle comprising a battery (1), a cooling system (SR) for cooling the battery, at least during recharging 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 provided 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 a hot source and ambient air as a cold source, with a second flywheel (32) mechanically coupled to the first flywheel (31) for delivering work received by the second flywheel to the first flywheel. Figure 1

Description

Front-wheel drive motor vehicle including a battery cooling system

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

The 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.

To perform a fast charge, it is desirable to be able to quickly recharge the vehicle battery from "fast charging stations" made available to the public, for example at motorway service stations. These fast charging stations can deliver high power, e.g. several tens of kW, a few hundred kW up to 350 kW.

A recharge operation under several hundred kW generates significant heating at the heart of the battery. It is therefore advisable to evacuate the calories as efficiently as possible as these calories are generated in the battery, to avoid excessive heating of the materials making up the battery cells.

Heat pipe systems have already been proposed to evacuate calories. Phase change fluid systems have also already been proposed to evacuate calories. Also, pulsed air systems have already been proposed to evacuate calories.

The performance of these systems is, however, limited, and the power output is not sufficiently controllable.

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

To achieve this objective, the invention proposes, in its broadest sense, an electrically-driven motor vehicle comprising an electrochemical type battery for storing electrical energy, connection means intended to enable the battery to be recharged from an external current source, a cooling system for cooling the battery, at least during recharging from the external current source, the cooling system comprising a first Stirling type machine configured as a Stirling refrigeration machine, the first machine comprising:
- a portion of calorie collection in thermal coupling with a first portion of the battery,
- a calorie discharge portion configured to discharge calories into the environment in 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 provided 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 calorie receiving portion of the second Stirling-type machine, and as a cold source the 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.

We are interested here in the case of recharging at a fast charging station, with a high-intensity continuous charging current, typically greater than 100 amps.

Thanks to these provisions, the first Stirling-type machine configured as a Stirling refrigeration machine can evacuate calories in large quantities, particularly in a rapid recharging situation where significant currents are involved. In addition, the heat flux treated can be controlled by means of the rotation speed of the first flywheel of the first Stirling machine. This speed can be controlled by means of the electric motor. Furthermore, the second Stirling machine operates as a motor and the work that is available on the second flywheel is reinjected onto the shaft of the first flywheel, which makes it possible to reduce the energy required to operate the first Stirling machine.

This provides a very effective solution in terms of heat flow evacuation while minimizing the energy drawn from the electric charging line to carry out this heat evacuation.

In this document, the term "Stirling engine" refers to a thermodynamic machine called external combustion, named after its inventor, since the middle of the 19th century. This machine was first designed to provide mechanical energy, namely to act as an engine. But it turns out that this thermodynamic machine is reversible, and its use as a refrigerating machine is more recent, it developed during the second half of the 20th century.

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

Each Stirling engine considered here can be formed as a two-cylinder assembly (Alpha and Gamma type) each cylinder containing a piston, with flywheel-connecting rod assembly or each Stirling engine 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 the Beta type).

The pistons move in the cylinders and define gas chambers as will be seen below.

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 calorie collection portion of the first Stirling engine.

This promotes the transmission of calories from a large surface to the location of the calorie collection portion of the first Stirling engine.

Any system for conveying the calories generated in the battery to the calorie collection portion of the first Stirling engine is considered within the scope of the present invention.

It is noted that, said motor vehicle having a reference point 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 may contain a heat transfer liquid or even a phase-change thermodynamic fluid, to offer the lowest possible thermal resistance.

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.

According to one variant, the battery is at least partly immersed in a dielectric liquid and the heat collection portion is thermally coupled with the dielectric liquid.

According to another variant, the calorie collection portion is thermally coupled with 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 calorie collection portion of the first Stirling engine.

According to an advantageous option, a fan may be provided to cause forced convection in contact with the heat discharge portion. Preferably, this may be convection by pulsed air, without however excluding convection by a liquid fluid. This improves the transfer of calories to the ambient air from the heat discharge portion of the first Stirling engine.

As an option, the first Stirling machine can be of a type chosen from the Stirling machine configurations: Alpha, Beta, Gamma or a membrane Stirling machine. Depending on the space available and the footprint required for the installation of the Stirling machine, one of the three available types mentioned above can be chosen.

Alternatively, the second Stirling machine may be of a type selected from the Stirling machine configurations: Alpha, Beta, Gamma or a membrane Stirling machine. Similarly, depending on the space available and the footprint required for the installation of the Stirling machine, one of the three available types mentioned above may be chosen. Note that it is not necessary for the two Stirling machines to be of the same type.

In practice, one can choose an Alpha type for the first Stirling engine and a Gamma type for the second Stirling engine.

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 delimiting a first variable-volume chamber, the first chamber forming part of the calorie collection portion, and with a second cylinder housing the second piston and delimiting a second variable-volume chamber, the second chamber forming part of the calorie rejection portion. The Alpha-type machine is particularly well suited to operation as a Stirling cycle refrigeration machine.

Alternatively, the second flywheel is mechanically coupled to the first flywheel by means of a reducer or a multiplier. It is thus possible to choose to have a different rotation speed between the two Stirling engines.

Alternatively, the electric motor is mechanically coupled to the first flywheel by means of a reducer. This allows a small motor to be used which will in practice rotate faster than the rotation speed of the first Stirling engine.

• illustre schématiquement un système de refroidissement d'une batterie de véhicules électriques à base de deux machines Stirling, l'une fonctionnant en machine frigorifique et l'autre en moteur, les machines Stirling étant de type Alpha ;
• illustre schématiquement un système de refroidissement d'une batterie de véhicules électriques à base de deux machines Stirling, l'une fonctionnant en machine frigorifique et l'autre en moteur, les machines Stirling étant de type Beta ;
• illustre une variante de la , avec les éléments de la batterie dans une configuration immersive ;
• illustre un exemple de solution de couplage mécanique entre le deuxième volant et le premier volant.

The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which:

• schematically illustrates a cooling system for an electric vehicle battery based on two Stirling engines, one operating as a refrigeration machine and the other as a motor, the Stirling engines being of the Alpha type;
• schematically illustrates a cooling system for an electric vehicle battery based on two Stirling engines, one operating as a refrigeration machine and the other as a motor, the Stirling engines being of the Beta type;
• illustrates a variant of the , with the battery elements in an immersive configuration;
• illustrates an example of a mechanical coupling solution between the second flywheel and the first flywheel.

In the various figures, the same references designate identical or similar elements. For reasons of clarity of the presentation, certain elements are not necessarily shown to scale.

A hybrid or electric vehicle comprises at least one BATT battery of electrochemical types capable of storing a large quantity of electrical energy and at least one electric traction motor.

Here, the term battery means any electrical energy storage device embedded in an electric or hybrid vehicle, of the electrochemical type (Ni-MH, Li-Ion, etc.) or even partially purely electric (super capacitors).

Of particular interest here are batteries with an energy storage capacity of at least 40 kW.

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

The vehicle has connection means intended to allow rapid recharging of the battery from an external power source. For recharging of a few hundred kilowatts, this involves direct current recharging available at public charging stations.

The recharging process causes significant heating inside the battery, given the currents involved. The vehicle is therefore equipped with a cooling system designed to evacuate a large quantity of calories which form in the heart of the battery during the recharging process, in particular by the Joule effect.

The SR cooling system comprises a first Stirling MS1 type machine configured as a Stirling refrigeration machine and a second Stirling MS2 type machine operating as an engine.

The first Stirling MS1 type machine works as a Stirling refrigeration machine. Its role is to be the actor of the collection of calories coming from the battery and their rejection in the outside air. As we will see if later, it is necessary to provide mechanical work to this first Stirling machine.

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

In the first example presented in the , both machines are of the Stirling Alpha type.

First machine

The first Stirling engine MS1 comprises a calorie collection portion 21 in thermal coupling with a first portion 81 of the battery, and a calorie rejection portion 22 configured to reject calories into the environment in the ambient air.

The first Stirling engine MS1 comprises a first piston 71 slidably mounted in a first cylinder 11, a second piston 72 slidably mounted in a second cylinder 12.

The first Stirling engine MS1 includes a flywheel 31, called the first flywheel, connected to the first and second pistons by a first connecting rod 41, detailed later.

We note that one of the cylinders is geometrically offset by 90° relative to the other cylinder, which simplifies the connecting rod assembly (single crank pin) required for the connecting rod assembly.

This constructive arrangement reflects one of the main characteristics of Stirling engines, namely the quadrature offset of one piston relative to the other.

The first connecting rod 41 is articulated from a crank pin 49 attached to the flywheel 31. An intermediate connecting rod 42 is attached on one side to the crank pin 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 crank pin 49 and on the other side to a rod end 44 of the second piston 72.

The first flywheel 31 is pivotally mounted around an axis X1 relative to a machine casing.

The first piston 71 delimits with the first cylinder 11 a first gas chamber C1 above the piston. The first gas chamber has an orifice at its upper end. This orifice is fluidically connected by a pipe to a regenerator 91, on the side of its cold part.

Similarly, the second piston 72 delimits with the cylinder 12 a second gas chamber C2 above the second piston. Here too an upper end orifice makes it possible to fluidly connect the second gas chamber C2 to the regenerator, on the side of its hot part.

In the first chamber C1, it is the phenomenon of relaxation which is preponderant whereas in the second chamber C2 it is the phenomenon of compression which is preponderant.

The heat flow taken from the battery by the collection portion is noted Q1. The heat flow rejected into the surrounding air by the calorie rejection portion 22 is noted Q2.

Fins 19 may be provided as shown schematically in the figures to improve the exchange coefficients at the level of the collection and discharge portions.

To operate this machine in refrigeration mode, mechanical work must be provided on the first flywheel 31. For this purpose, a coupling of the flywheel 31 with an electric motor M3 is provided.

The direction of rotation of the flywheel is the opposite direction to the case where the machine operates as a motor.

The average temperature T1 of the first gas chamber C1 is lower than the average temperature T2 of the second gas chamber C2.

The M3 electric motor is controlled by a computer responsible for supervising the recharging of the vehicle's battery. The rotation speed of the flywheel 31 can be between a few dozen revolutions per minute and a few hundred revolutions per minute depending on the heat evacuation needs.

For example, the control of M3 can be such that the average temperature T1 on the sampling portion is close to 0°C, without going lower to avoid the formation of ice.

The fluid used in the first Stirling engine could be air, CO2, ethanol, hydrogen, helium, but not excluding other gases.

As known per se and not described in detail herein, the regenerator 91 exchanges energy with the gas flowing therein and this cyclically and in both directions. There is a significant temperature gradient inside the regenerator between the hot end and the cold end.

Second machine

The second Stirling type machine MS2 operates as a Stirling engine, with as a hot source a second portion of the battery coupled to a calorie receiving portion 23 of the second Stirling type machine. The cold source is formed by the ambient air coupled at a cooling portion 24 of the second Stirling type machine. The calorie receiving portion 23 of the second machine is thermally coupled to a second portion 82 of the battery.

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

The second Stirling engine MS2 comprises a third piston 73 slidably mounted in a third cylinder 13 and a fourth piston 74 slidably mounted in a fourth cylinder 14.

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

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.

Here too the cylinders are offset by 90° relative to each other, according to the Alpha configuration.

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

The second flywheel 32 is pivotally mounted around an axis X2 relative to the machine casing.

The third piston 73 delimits with the third cylinder 13 a third gas chamber C3 above the piston. The third gas chamber has an orifice at its upper end. This orifice is fluidically connected by a pipe to a regenerator 92, on the side of its hot part.

Similarly, the fourth piston 74 delimits with the fourth cylinder 14 a fourth gas chamber C4 above the fourth piston. Here too an upper end orifice makes it possible to fluidically connect the second gas chamber to the regenerator on the side of its cold part.

In the third chamber C3, it is the expansion phenomenon which is predominant while in the fourth chamber C4, it is the compression phenomenon which is predominant. Compared to the first machine, the direction of rotation of the second flywheel 32 is the opposite.

The heat flow taken from the battery by the sampling portion 23 is noted Q3. The heat flow rejected into the surrounding air by the calorie rejection portion 24 is noted Q4.

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

To improve thermal performance, a thermal bridge plate, marked 8, may be provided as an intimate interface with the electrochemical cells of the battery.

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.

On the side of the heat discharge portion, a fan 87 may be provided to generate forced convection which licks the fins of the discharge portion 22. Any other system promoting heat exchanges to extract heat from the discharge portion 22 may also be used.

The rotation speed of the M3 electric motor can be controlled by the BMS calculator responsible for monitoring the charging process.

According to a particular option, the fan 87 is driven proportionally to the rotation speed of the motor M3, the fan can be driven via a reducer from the return shaft of the motor M3.

Variant to Stirling Beta

To the , another example of realization with Beta type Stirling machines is illustrated. This configuration is generally more compact in terms of geometric size.

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

Here too, the first Stirling type machine MS1 operates as a Stirling refrigeration machine, taking a heat flow Q1 from the battery and rejecting heat flow Q2 into the ambient air. Conversely, the second Stirling type machine MS2 operates as a Stirling engine, it uses calories from the battery to form its hot source and its and the ambient air forms its cold source.

According to this configuration, chambers C1 and C2 are located in a single cylinder 15.

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 seal at this location.

In this configuration, chambers C3 and C4 are located in a single cylinder 16.

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 seal at this location.

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

Other features

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 machine MS2 into the first Stirling machine MS1. In this way, the electric motor M3 is relieved, which only has to provide part of the work necessary for the operation of the first machine in the refrigeration cycle.

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

In one example, the X1 and X2 axes can be merged. However, in practice, a connecting shaft is provided with, if necessary, angle transmission(s).

For example, as schematically illustrated in , the mechanical coupling can involve a reduction stage 92, or conversely a multiplication stage, via a gear train. It may indeed be necessary to have different rotation speeds between the first machine and the second machine, so as to optimize the energy recovery from the second machine MS2 to the first machine MS1.

According to an embodiment variant presented at the , the electrochemical cells of the battery are immersed at least in part in a dielectric liquid 3. The calorie collection portion 21 of the first machine MS1 is thermally coupled with the dielectric liquid 3. Advantageously, the liquid penetrates everywhere in the intervals between the electrochemical cells and captures calories there. In addition, the dielectric liquid 3 also allows good conduction of calories to the hot source of the second machine MS2, namely here the calorie reception portion 23 of the second Stirling-type machine.

A stirrer or circulator may be provided to homogenize the temperature inside the dielectric liquid. The dielectric liquid solution effectively homogenizes the temperature prevailing in the electrochemical cells of the battery.

According to another embodiment variant, heat pipes are used, the calorie collection portion 21 is then thermally coupled with the first portion of the battery by means of said heat pipes. The heat pipes can have various shapes facilitating thermal contact between the electrochemical cells and the calorie collection portion of the first Stirling engine. The heat pipes can be passive (capillary) or thermosyphons (using gravity).

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

Any heat exchange system that allows the thermal flows Q1, Q2, Q3, Q4 to be transmitted as best as possible can be used, either a fin system as shown in the figures, or any other system.

According to a non-limiting example, the average temperature of the battery during a rapid recharge may be around 75°C, the average temperature T1 around 5°C, the average temperature T2 around 80°C, the average temperature T3 around 65°C and the average temperature T4 around 20°C (ambient temperature).

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

It is noted that Stirling engines are discreet, their silent operation is an advantage to avoid worrying a vehicle user while the rapid recharge takes place.

Claims (10)

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 (MS1) configured as a Stirling refrigeration machine, the first machine comprising:
- a calorie collection portion (21) in thermal coupling with a first portion of the battery (81),
- a calorie discharge portion (22) configured to discharge calories 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), in which work is provided 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 hot source a second portion of the battery (82) coupled to a calorie 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. 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. Motor vehicle according to claim 2, said motor vehicle having a reference point in space comprising a longitudinal axis (X) following a direction of movement of said motor vehicle, a transverse axis (Y) perpendicular to the longitudinal axis (X), and a vertical axis (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. 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. 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. Motor vehicle according to any one of claims 1 to 5, characterized in that it comprises a fan (87) to cause forced convection on contact with the heat discharge portion. Motor vehicle according to any one of claims 1 to 6, characterized in that the first Stirling type machine (MS1) is of a type chosen from the Stirling machine configurations: Alpha, Beta, Gamma or a membrane Stirling machine. 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. Motor vehicle according to any one of claims 1 to 6, characterized in that the first Stirling-type machine (MS1) is of the Alpha type, with a first cylinder (11) housing the first piston and delimiting a first chamber (C1) 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). 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.