METHOD FOR THE GRADUAL HEATING OF A LITHIUM-ION BATTERY MOUNTED ON A HYBRID MOTOR VEHICLE

Abstract

The invention relates to a method for progressively heating a lithium-ion battery mounted on a hybrid motor vehicle comprising a step of determining a setpoint torque applied to the primary shaft; a step of regulating the second torque; a step of measuring the battery power (PB); a step of measuring the cumulative battery power (IPB) over time (t) as a function of the battery power (PB); a step of forcing the discharge phase (PhD) when the cumulative battery power (IPB) is greater than a second predetermined threshold value (V2), said second threshold value (V2) being less than said first threshold value (V1), said second torque being positive; a step of progressively heating the battery without risk of plating the lithium by a succession of discharge phases (PhD) and charging phases (PhC). Figure 1

Description

Title of the invention: METHOD FOR PROGRESSIVE HEATING OF A LITHIUM-ION BATTERY MOUNTED ON A HYBRID MOTOR VEHICLE

[0001] The invention relates to the field of hybrid motor vehicles, and more particularly to the batteries of these vehicles.

[0002] Known from the prior art is a patent application CN112428881 which describes a battery heating device and method for a hybrid motor vehicle. The vehicle comprises an electric motor, a heat engine and a battery. The vehicle is configured to control the charging and discharging of said battery. The vehicle generates alternating cycles of charging and discharging the battery in order to produce heat by Joule effect. Thus, the heat increases the temperature of the battery until it reaches a predefined target value. The invention aims to optimize the heating of the battery by adjusting the alternating cycles according to the temperature in order to maintain said battery in an optimal operating state. When the temperature of the battery is lower than the target value, the vehicle alternately enters into charging and discharging.When the battery has a state of charge above a first power threshold, the vehicle enters the discharge phase. When the vehicle has a state of charge below a second power threshold, the vehicle exits the discharge phase. However, a drawback remains. The described device and the associated method do not take into account the risk of lithium plating. Thus, if the target value is not reached, the vehicle continues to generate charge and discharge cycles, which is likely to cause lithium plating, reducing the performance of the battery and reducing the lifespan of said battery.

[0003] The objective of the present invention is to remedy these drawbacks and to allow gradual heating of the battery without causing the detection of a risk of lithium plating.

[0004] To achieve this objective, the invention proposes a method for progressively heating a lithium-ion battery mounted on a motor vehicle, said vehicle comprising an accelerator pedal, wheels, an electric motor and a heat engine, the electric motor and the heat engine being connected to the wheels by a primary shaft configured to transmit the mechanical energy generated by the heat engine and the electric motor to said wheels to move said vehicle, said electric motor being connected to said battery via a DC / AC converter configured to control a discharge phase of the battery during wherein said DC / AC converter transforms a direct current from said battery into an alternating current to power said electric motor and an AC / DC converter configured to control a charging phase of the battery during which said AC / DC converter transforms the alternating current from the electric motor into direct current to power said battery, the discharge phase and the charging phase being carried out alternately so as to generate heat dissipation by Joule effect to heat said battery, a first torque being applied to the heat engine and a second torque being applied to the electric motor, said battery comprising an anode and a cathode, said battery comprising lithium capable of moving from the anode to the cathode during the discharge phase and from the cathode to the anode during the charging phase,a first threshold value for which the charging phase is interrupted to avoid the risk of lithium plating, lithium plating being the deposition of lithium in solid form on the surface of the anode during the charging phase, remarkable in that said method comprises the following steps: , - a step of determining a target torque applied to the primary shaft as a function of the state of depression of the accelerator pedal by the driver, the target torque being equal to the sum of the first torque and the second torque, said battery being in the discharge phase when said second torque is positive, said battery being in the charge phase when said second torque is negative; - a step of measuring the power of the battery; - a step of measuring the cumulative battery power over time as a function of the battery power measured during the step of measuring the battery power when the battery power is greater than a predetermined continuous recharge power, said continuous recharge power corresponding to the power admissible by said battery without time limitation and without generating the risk of lithium plating; - a step of forced execution of the discharge phase when the cumulative battery power is greater than a second predetermined threshold value, said second threshold value being less than said first threshold value, said second torque being positive; - a step of progressive heating of the battery without risk of plating the lithium by a succession of discharge phases and charging phases, the cumulative battery power remaining lower than said second threshold value.

[0005] Thanks to the invention, the battery operates optimally by avoiding the detection of a risk of lithium plating. The temperature of the battery increases gradually.

[0006] Advantageously, the battery comprises a temperature measurement sensor, said method comprising a stopping step when the temperature measured by said temperature measuring sensor reaches a predetermined temperature threshold value.

[0007] Preferably, during the stopping step, the battery power is greater than the predetermined continuous recharge power.

[0008] The invention also relates to a heating device configured to implement said method for progressively heating a lithium-ion battery mounted on a hybrid motor vehicle previously described, characterized in that said device comprises a means for determining the setpoint torque, a means for regulating the second torque, a means for measuring the power of the battery, a means for measuring the cumulative power of the battery and a means for forcing execution of the discharge phase when the cumulative power of the battery is greater than the second predetermined threshold value.

[0009] Furthermore, the invention relates to a hybrid motor vehicle comprising a heating device according to the invention.

[0010] The invention will be further detailed by the description of a non-limiting embodiment, and on the basis of the appended figure illustrating the invention, in which [Fig.l] schematically illustrates a graphical representation of the power of a lithium-ion battery mounted on a hybrid motor vehicle as a function of time, correlated with a graphical representation of the cumulative battery power as a function of time.

[0011] Schematically illustrated in [Fig.l] is a graphical representation of the power of a lithium-ion battery PB mounted on a hybrid motor vehicle as a function of time t, correlated with a graphical representation of the cumulative battery power IPB as a function of time t. The graphical representations illustrate a first period A during which the battery presents a risk of lithium plating and a second period B during which the battery implements the method of progressive heating of a lithium-ion battery mounted on a hybrid motor vehicle according to the present invention. The lithium-ion battery is a type of rechargeable battery in which lithium moves from the anode to the cathode during discharge and from the cathode to the anode during charging.The lithium-ion battery is capable of providing stable power over a long period of time t, which is an advantage when used in electric or hybrid motor vehicles. Lithium plating is a phenomenon that can occur in the lithium-ion battery when the charging or discharging conditions are not optimal. Indeed, lithium plating is the phenomenon during which lithium is deposited on the surface of the anode in solid form during charging. Lithium plating occurs when the battery is overcharged, when the battery is discharged at a particularly low temperature or when the said battery . is subjected to excessively high charging currents. Lithium plating is likely to cause short circuits within said battery, thus reducing the performance of said battery and consequently of the vehicle. Furthermore, lithium plating is likely to cause premature deterioration of the battery, thus reducing the lifespan of said battery. In addition, said vehicle has wheels, an electric motor and a heat engine. The electric motor and the heat engine are connected to the wheels by a primary shaft configured to transmit the mechanical energy generated by the heat engine and by the electric motor to the wheels of the vehicle to enable its movement.The vehicle comprises a DC / AC converter (acronym meaning Alternating Current / Direct Current) and an AC / DC converter (acronym meaning Direct Current / Alternating Current), the DC / AC converter and the AC / DC converter each connecting the electric motor to said battery. The DC / AC converter is configured to control a PhD discharge phase of the battery. The AC / DC converter is configured to control a PhC charge phase of the battery. The PhD discharge phase is characterized by a phase during which the DC / AC converter transforms a direct current into an alternating current. The direct current is emitted by said battery. The direct current is transformed into alternating current to power said electric motor.The PhC charging phase of the battery is a phase during which the AC / DC converter transforms the alternating current of said electric motor into direct current to power said battery. The PhD discharging phase and the PhC charging phase are carried out alternately in a cyclic manner. Such a cycle of PhD discharging phase and PhC charging phase generates heat dissipation by Joule effect. The Joule effect is a thermal phenomenon that occurs when an electric current passes through an electrically conductive material. Indeed, when an electric current passes through the electrically conductive material, the electrical energy is converted into heat. In the PhC charging phase, said battery is likely to undergo a lithium plating phenomenon if the power of the PB battery is too high or if the duration of the PhC charging phase is too long.To reduce the risk of battery deterioration, a first threshold value VI is predefined. In other words, the first threshold value VI is the value for which the charging phase PhC is interrupted to limit the risk of lithium plating. Over the period A illustrated in [Fig.l], the graphical representation illustrates the battery power PB, alternately in the discharge phase PhD and in the charging phase PhC, as a function of time t when the battery presents a risk of lithium plating. The first curve PB A is the curve representing the expected battery power over time t. The expected battery power is the power allowing optimal operation of the vehicle. A second curve PBR re . shows the actual battery power. The actual battery power takes into account the impact of lithium plating. In the PhC charging phase, and in the case of lithium plating, the actual battery power is lower than the expected battery power. The vehicle performance is therefore not optimal. In the graphical representation illustrating the cumulative battery power IPB as a function of time t, the first threshold value V1 is shown. During period A, the cumulative battery power IPB quickly reaches the first threshold value VI, which causes the premature interruption of the PhC charging phase and therefore less heat dissipation by Joule effect, which results in reduced battery performance. In this way, the cumulative battery power IPB gradually decreases after two cycles of PhC charging phase and PhD discharging phase.The main consequence of the embodiment illustrated in period A is a stationary temperature of said battery. Indeed, the difference between the power of the battery PB in the charging phase PhC and the power of the battery PB in the discharging phase does not generate sufficient heat dissipation by Joule effect to increase the temperature of said battery. Period A illustrates the consequences of the battery heating methods according to the prior art. Period B represents the results perceived when said method of progressive heating of the battery, the subject of the present patent application, is implemented. The method comprises a step of determining a target torque applied to the primary shaft according to the wishes of a driver of the vehicle. The torque is a measure of the rotational force that the electric motor and / or the thermal engine can produce.The driver's desire is interpreted based on the driver's depressed state of the accelerator pedal. Indeed, if the pedal is depressed 90% for example, this is interpreted as a significant power demand. A first torque is applied to the combustion engine and a second torque is applied to the electric motor. The second torque is alternately positive or negative. The battery is in the discharge phase PhD when the second torque is positive. Conversely, the battery is in the charge phase PhC when the second torque is negative. The second torque is always the opposite of the first torque. Thus, the sum of the first torque and the second torque is equal to the target torque. The method includes a step of measuring the power of the battery PB as shown in the graphical representation illustrating the power of the battery PB as a function of time t.In practice, the PB battery power varies between - 20000 W and 15000 W. In a cumulative IPB battery power measurement step, the cumulative IPB battery power is measured from the PB battery power measured in the PB battery power measurement step. The cumulative IPB battery power measurement step is only implemented when the . battery PB is greater than a continuous recharge power PRC. The continuous recharge power PRC is the power admissible by the battery without time limitation and without generating the risk of lithium plating. During a forced execution step, the discharge phase PhD is triggered when the cumulative battery power IPB is greater than a second predetermined threshold value V2. The second threshold value V2 is lower than the first threshold value VL The difference between the first threshold value VI and the second threshold value V2 is a protection margin which drastically reduces, or even eliminates, the risk of lithium plating. During a gradual heating step, said battery increases its temperature gradually without inducing a risk of lithium plating because the cumulative battery power IPB remains lower than said second threshold value V2.The battery therefore gradually heats up through a succession of discharge phases PhD and charge phases PhC. Advantageously, said battery comprises a temperature measurement sensor and the method comprises a stopping step when the temperature measured by said battery temperature measurement sensor reaches a predetermined temperature threshold value. In other words, when the battery has a temperature at least equal to said predetermined temperature threshold value, the battery is no longer subjected to the charge phase PhC and discharge phase PhD cycles. Preferably, during the stopping step, the power of the battery PB is greater than the predetermined continuous recharge power PRC.Indeed, when the power of the battery PB is greater than the continuous recharge power PRC, the power of the battery PB is sufficient to allow the thermal engine to operate efficiently, including when the driver's will is low or even negative, for example during deceleration when said thermal engine is in operating condition. In addition, when the power of the battery PB is greater than the continuous recharge power PRC, the battery is able to recover the kinetic energy when the vehicle brakes from a high speed until the vehicle stops, without this causing the lithium plating.

[0012] Furthermore, the invention relates to a device configured to implement said method for progressively heating a lithium-ion battery mounted on a hybrid motor vehicle. The device comprises a means for measuring the power of the battery PB, a means for calculating the cumulative power of the battery IPB and an inverter configured to interrupt the charging phase PhC and activate the discharging phase PhD when the battery is in the charging phase PhC and when the cumulative power of the battery IPB is greater than the second predetermined threshold value V2. The invention also relates to a hybrid motor vehicle comprising such a device previously described.

Claims

1. Claims A method for gradually heating a lithium-ion battery mounted on a motor vehicle, said vehicle comprising an accelerator pedal, wheels, an electric motor and a heat engine, the electric motor and the heat engine being connected to the wheels by a primary shaft configured to transmit the mechanical energy generated by the heat engine and the electric motor to said wheels to move said vehicle,said electric motor being connected to said battery via a DC / AC converter configured to control a discharge phase (PhD) of the battery during which said DC / AC converter transforms a direct current from said battery into an alternating current to power said electric motor and an AC / DC converter configured to control a charge phase (PhC) of the battery during which said AC / DC converter transforms the alternating current from the electric motor into direct current to power said battery, the discharge phase (PhD) and the charge phase (PhC) being carried out alternately so as to generate heat dissipation by the Joule effect to heat said battery, a first torque being applied to the heat engine and a second torque being applied to the electric motor, said battery comprising an anode and a cathode,said battery comprising lithium capable of moving from the anode to the cathode during the discharge phase (PhD) and from the cathode to the anode during the charge phase (PhC), a first threshold value (VI) for which the charge phase (PhC) is interrupted to avoid the risk of lithium plating, lithium plating being the deposition of lithium in solid form on the surface of the anode during the charge phase (PhC), characterized in that said method comprises the following steps:, - a step of determining a setpoint torque applied to the primary shaft as a function of the state of depression of the accelerator pedal by the driver, the setpoint torque being equal to the sum of the first torque and the second torque, said battery being in the discharge phase (PhD) when said second torque is positive, said battery being in the charge phase (PhC) when said second torque is negative; - a step of measuring the battery power (PB); - a step of measuring the cumulative battery power (IPB) over time (t) as a function of the battery power (PB) measured during the step of measuring the battery power (PB) when the battery power (PB) is greater than a predetermined continuous recharge power (PRC), said continuous recharge power (PRC) corresponding to the power admissible by said battery without time limitation and without causing the risk of lithium plating; - a step of forced execution of the discharge phase (PhD) when the cumulative battery power (IPB) is greater than a second predetermined threshold value (V2), said second threshold value (V2) being less than said first threshold value (VI), said second torque being positive;- a step of progressive heating of the battery without risk of plating the lithium by a succession of discharge phases (PhD) and charge phases (PhC), the cumulative battery power (IPB) remaining lower than said second threshold value (V2).;

2. Method according to claim 1 characterized in that the battery comprises a temperature measuring sensor, said method comprising a stopping step when the temperature measured by said temperature measuring sensor reaches a predetermined temperature threshold value.

3. Method according to claim 2 characterized in that, during the stopping step, the power of the battery (PB) is greater than the predetermined continuous recharge power (PRC).

4. Heating device configured to implement said method of progressive heating of a lithium-ion battery mounted on a hybrid motor vehicle according to any one of claims 1 to 3, characterized in that said device comprises a means for determining the setpoint torque, a means for regulating the second torque, a means for measuring the battery power (PB), a means for measuring the cumulative battery power (IPB) and a means for forcing execution of the discharge phase (PhD) when the cumulative battery power (IPB) is greater than the second predetermined threshold value (V2).

5. A hybrid motor vehicle comprising a heating device according to claim 4.

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