FR2964612A1 - METHOD AND DEVICE FOR THERMAL PROTECTION OF AN ELECTRICAL COMPONENT OF A MOTOR VEHICLE - Google Patents

Abstract

Device for thermal protection of at least one electric member (2,3,4) of a motor vehicle equipped with an electric motor (3), comprising means (5,6) for measuring a limit temperature of said electric member ( 2) and a rotational speed of the electric motor (3) and a torque limiting means (7) which is adapted to develop a torque limit for the electric motor (3), and which comprises a power determining means ( 9) to determine a maximum mechanical power as a function of the limit temperature, said torque limit being developed as a function of the rotational speed of the electric motor (3) and said determined maximum mechanical power.

Description

B10-0052EN 1 Method and device for thermal protection of an electric component of a motor vehicle

The invention relates to the thermal protection of electrical components of a motor vehicle with a hybrid or all-electric type of motorization. In particular, the invention relates to electrical devices dedicated to the propulsion and / or the production of electrical energy of the motor vehicle.

The electrical components of purely electric or hybrid motor vehicles generally comprise a battery for powering an electric motor via an electronic power unit. In order not to destroy or damage these electrical organs, it is necessary to avoid a heating of the latter beyond a temperature limit. The temperature of these organs can be controlled by limiting the current flowing from the battery to the electric motor (in traction mode, when the electric motor is propelling the vehicle) or conversely (in the energy recovery mode, when the electric motor recovers Energy). But these thermal protection strategies have the disadvantage of generating jolts in the torque delivered or recovered by the electric motor, and are generally badly felt by the driver of the vehicle.

For example, European Patent Application EP 1 084 895 describes a method of controlling the torque of an electric vehicle electric motor from the engine temperature or the battery charge level. European Patent Application EP 2 110 280 can also be mentioned which describes a control system for an electric vehicle of an electric power unit comprising a battery and an electronic power unit for powering an electric motor. This system limits the torque of the electric motor from a torque setpoint and a low consumption setpoint so as to reduce the losses of the driving unit. In addition, this system uses maps stored in memory which give the value of the losses of the power unit as a function of the torque and the speed of rotation of the electric motor. But the torque setpoint is in this case limited to the operating points where the losses do not exceed a certain limit value. One of the aims of the invention is to overcome the drawbacks mentioned above by providing an improved method and an improved device for the thermal protection of the electrical components of a motor vehicle when the temperature of an organ becomes too high. Another object of the invention is to protect the electrical components while ensuring the safety and enjoyment of driving the vehicle. According to one aspect, there is provided a method of thermal protection of at least one electric member of a motor vehicle equipped with an electric motor, in which a limit temperature of said electric member and a speed of rotation of the electric motor are measured and we limit the torque of the electric motor. In this method, a maximum mechanical power is determined as a function of the limit temperature and the torque of the electric motor is limited as a function of the rotational speed of the electric motor and of said determined maximum mechanical power. Thus, limiting the traction torque or energy recovery limit the current consumed or supplied by the electric motor. There is also an improved strategy for the thermal protection of organs because it takes into account the temperature of at least one electrical member and the speed of rotation of the electric motor.

According to one embodiment, a reduction power is developed which is non-zero when the value of the measurement of the limit temperature is greater than a temperature threshold, and otherwise zero, and the maximum mechanical power is determined as a function of a sum between a parameterizable variable representing nominal maximum mechanical power and said elaborated reduction power. Thus, a reduction power is developed as a function of the temperature of an electrical member so as to reduce the torque limit of the electric motor when the temperature increases. This effectively protects the electrical member from overheating. Advantageously, said reduction power is equal to a parameterizable gain that multiplies a difference between said temperature threshold and the value of the measurement of the limit temperature. With the aid of such a parameterizable gain, it is possible to modify the limit of the torque of the electric motor in order to adapt the speed of the device to limit the torque according to the needs, in traction mode or in energy recovery mode.

According to another embodiment, a first maximum torque is calculated as a function of the ratio between the maximum mechanical power and the rotational speed of the electric motor, a second maximum torque is determined from a piecewise affine function of the maximum mechanical power, and limit the torque of the electric motor as a function of the minimum between the first and second maximum torque. Thus, the torque limit of the motor is further reduced when the rotational speed of the motor is low, which makes it possible to reduce the jolts of the electric motor during transitions between a low rotational speed and a high rotational speed in order to avoid surprising the driver during transitions. It is possible to limit the traction torque of the electric motor when it is operating in traction mode to propel the motor vehicle.

It is also possible to limit the energy recovery torque of the electric motor when the latter is operating in energy recovery mode to supply electrical energy to the motor vehicle.

According to another aspect, there is provided a device for thermal protection of at least one electric member of a motor vehicle equipped with an electric motor, comprising means for measuring a limit temperature of said electric member and a rotational speed of the motor electrical and torque limiting means adapted to develop a torque limit for the electric motor. The torque limiting means comprises power determining means for determining a maximum mechanical power as a function of the limit temperature, said torque limit being elaborated as a function of the rotational speed of the electric motor and said determined maximum mechanical power. According to one embodiment, the torque limiting means is configured to calculate a first maximum torque as a function of the ratio between the maximum mechanical power and the rotational speed of the electric motor, to determine a second maximum torque from a function piecewise refining the maximum mechanical power, and to develop the torque limit as a function of the minimum between the first and second maximum torque. According to another embodiment, the means for measuring the limit temperature comprise temperature sensors for respectively measuring the temperatures of the electrical components of the motor vehicle and a comparison means configured to determine the limit temperature which is equal to the maximum value of the temperatures of the electrical organs measured.

According to yet another embodiment, the torque limiting means comprises a limit temperature control loop which is configured to control the torque value of the electric motor from the torque limit and as a function of a difference between a temperature threshold and said limit temperature. Thus, from the torque limit, it is possible to regulate the temperature of the organ to be protected around a temperature threshold. Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example, and with reference to the appended drawings, in which: FIG. 1 schematically illustrates an embodiment of a thermal protection device of a motor vehicle electrical component; FIG. 2 is a graphical representation of the variations of the maximum mechanical power as a function of the temperature; FIG. 3 is a graphical representation of the variations of the maximum torque calculated as a function of the rotational speed of the engine; FIG. 4 illustrates an example of a piecewise affine function; and FIG. 5 is a graphical representation of the variations of the torque limit of the electric motor as a function of the speed of rotation of the electric motor. FIG. 1 diagrammatically shows a first embodiment of a device for thermal protection 1 of electrical components 2, 3, 4 of a motor vehicle. These electrical components generally comprise a battery 2, an electric motor 3 and a power electronics unit 4. The battery 2 supplies the electric motor 3 via the electronic power unit 4.

The device 1 comprises at least one temperature sensor 5, a speed sensor 6 and a torque limiting means 7. The sensors 5, 6 make it possible respectively to measure the limiting temperature T of an electrical component to be protected among the electrical components. 2, 3, 4 and the speed of rotation N of the electric motor 3. By way of nonlimiting example, the limit temperature T of the battery 2 is measured, but it is also possible to measure the temperature of the electronic power unit 4 or the temperature of the electric motor 3 itself.

The torque limiting means 7 generates a Climite torque limit which it transmits, via a connection 8, to the electric motor 3. This Climite torque limit represents a maximum torque setpoint which limits the torque (traction or recovery) of the electric motor 3 to control the limit temperature T of the battery 2. This Climite limit is positive or zero and the principle of its development will be described later. The limiting means 7 comprises a power determination means 9 for determining a maximum mechanical power Pmax, a calculation means 10 for calculating a first maximum torque Cmaxcal, a torque determination module 11 for determining a second maximum torque Cmax_red and a output module 12 for developing the Climite torque limit, said output module 12 being coupled to the motor 3 by the connection 8.

The power determining means 9 receives the measurement of the limit temperature T of the battery 2 by a connection 13 from the temperature sensor 5. It further comprises an adder 14 which makes the difference AT between the measured value T of the temperature limit of the battery 2 and a temperature threshold Tseuil, then transmits this difference AT by a connection 15 to a proportional regulator 16 with variable gain G. The adder 14 calculates the difference AT according to the following equation (1): AT = Tseuil -T (1)

with - T: the limit temperature of an electrical component to be protected in ° C, for example the limit temperature of the battery 2; - Tseuil: threshold of temperature beyond which one limits the torque of the electric motor in ° C.

The proportional regulator 16 with variable gain G develops a reduction power Pred, according to equation (2), which it transmits via a connection 17 to a calculation module 18.

Pred = Min (O; G-AT) (2)

with - Pred: reduction power in Watt; - Min: function that calculates the minimum value between two variables; - G: Variable gain in W / ° C. Pred reduction power can be negative or zero. In addition, the temperature threshold Tseuil and the variable gain G are two adjustable parameters.

The calculation module 18 determines the maximum mechanical power Pmax as a function of the reduction power Pred and of a parameterizable variable Pmax nom representing a maximum nominal mechanical power. The calculation module 18 calculates the maximum mechanical power Pmax according to the following equation (3):

Pmax = Max (O; Pmax name + Pred) (3)

with - Pmax name: nominal maximum mechanical power, parameterizable, in Watt; - Max: function that calculates the maximum value between two variables. The parametric variable Pmax_nom represents the maximum mechanical power of the electric motor in traction mode (or in generator mode) and in a nominal situation, that is to say a situation without defects. This variable Pmax_nom is therefore specific to the type of electric motor used.

The power determination means 9 transmits the maximum mechanical power Pmax via a connection 19 towards the calculation means 10 and towards the torque determination module 11.

The calculation means 10 comprises a divider 20 and a control operator 21. The control operator 21 receives the measurement of the speed of rotation N of the electric motor 3 by a connection 22 from the speed sensor 6 and provides a value strictly Nabs positive to the divider 20 through a connection 23 to prevent division by zero. The calculation means 10 transmits, by a connection 24, the result of the calculation of the first maximum torque Cmaxcal to the output module 12. The calculation means 10 calculates the first maximum torque Cmaxcal according to the following equations (4 and 5): Pmax (4 ) C = max_cal Nc (5) Nc = Max (Nabs; Eps) with - Cmaxcal: first maximum torque, also noted maximum torque, in Nm; - Nc: strictly positive parameter in radians- '; Nabs: absolute value of the speed of rotation N of the electric motor 3 in radians; - Eps: constant equal to 1 in radians- '(to avoid division by 0 when the rotation speed N of the electric motor 3 is zero). The torque determination module 11 determines the second maximum torque Cmax_red which it transmits, by a connection 25 to the output module 12. The torque determination module 11 determines the second maximum torque Cmax_red according to the following equation (6) Cmax_red = f (Pmax) (6)

with - f: affine function (or right) in pieces; - Cmax red: second maximum torque, also noted maximum torque, in N-m. This affine function f makes it possible to associate a vector of n values of an input variable with a vector of n values of an output variable. Each element of the input vector corresponds to the element of the same position of the output vector. The intermediate points of the function f are obtained by interpolation. FIG. 4 shows, by way of example, a curve Fa of a piecewise affine function g.

Let the input vector x1 = (a, b, c, d) with a <b <c <d and the corresponding output vector y1 = (g, h, h, i). The equation function y = g (x) finite is defined by the vectors xl and yl. For the affine function f used by the torque determination module 11, it is possible to define, by way of non-limiting example, the function f by the following vectors

Pmax = (a1, a2, a3, a4, a5) Cmax_red = (bl, b2, b2, b3, b3)

Where the values al, a2, a3, a4, a5 of Pmax are such that al <a2 <a3 <a4 <a5 and are expressed in Watt and those of Cmax_red are such that bl <b2 <b3 and are expressed in N-m.

The output module 12 generates the Climite torque limit according to the following equation (7):

Climite = Min (Cmaxcal; Cmax_red) (7) The second maximum torque CmaxRed makes it possible to add a limitation to the torque of the motor in addition to that established from the first maximum torque Cmax_cal. The first maximum torque Cmaxcal calculated protects the battery 2 from heating due mainly to magnetic losses, also known as hysteresis losses. The second maximum torque CmaxRed makes it possible, in turn, to protect the battery 2 from heating due mainly to losses by Joule effect.

The use of the first and second maximum couples Cmaxcal, CmaxRed can effectively protect the electrical member from overheating. FIG. 2 shows graphically variations of the maximum mechanical power Pmax as a function of the temperature T in the case where Pmax = 45000 Watts and Tseuil = 60 ° C. FIG. 2 shows two curves representing variations of the maximum mechanical power Pmax for two respective values G1, G2 of the variable gain G. The curve A represents the variations of the maximum mechanical power Pmax for a first value G1 of the variable gain with G1 = 5000 W / ° C. Curve B represents the variations of the maximum mechanical power Pmax for a second value G2 of the variable gain with G2 = 10000 W / ° C.

The variable gain G therefore makes it possible to directly adjust the speed of the limitation of the torque as a function of the temperature rise of the battery 2. FIG. 3 shows graphically variations of the first maximum torque Cmax_cal as a function of the speed of rotation of the battery. The three curves C (T1), D (T2), E (T3) are called iso-power curves because they are established for constant values of the maximum mechanical power Pmax.

The curves C (T1), D (T2), E (T3) represent the variations of the first maximum torque Cmax cal for three different temperatures of the member to be protected T1, T2, T3, with T1 <T2 <T3. FIG. 5 graphically shows variations of the torque limit of the Climite electric motor as a function of the rotational speed of the electric motor N. The three curves C (T1), D (T2), E (FIG. T3) described in FIG. 3, two values H, I, for the second maximum torque Cmax red and a limitation zone ZC, represented in FIG. 5 by the hatched area. The values H and I represent the values of the second maximum torque Cmax_red, respectively for the temperatures T1 and T2. For each iso-power curve C (T1), D (T2), E (T3), a second maximum torque Cmax_red is determined. Consequently, for a given temperature T2 greater than the temperature threshold Tseuil, the torque of the electric motor is limited in the limiting zone ZC. The Climite torque limit can be a simple instruction for the electric motor to prevent the torque of the latter can not exceed this limit Climite. According to another embodiment, this Climite torque limit can serve as a basis for developing a torque command for controlling the torque value of the electric motor 3. In this variant, the thermal protection device 1 corresponds to a regulator of the limit temperature T of the organ to be protected. Thus, the torque limiting means 7 comprises a regulation loop BR for regulating the limiting temperature T around the temperature threshold Tseuil. This control loop BR is configured to develop the control of the torque of the electric motor 3 from the Climite torque limit and the difference AT between the temperature threshold Tseuil and said limit temperature T. The variable gain G of the proportional regulator 16 thus makes it possible to adjust the gain of the thermal protection device 1 and thus to adjust the dynamics of the regulation.

According to yet another embodiment, it is possible to use a temperature sensor for each electrical component to be protected and to develop a corresponding limit temperature T, for example at the maximum value or the average of the measured temperatures.

Thus, it is possible to effectively protect a particular electrical component, or several electrical components, of a motor vehicle. Thanks to the present invention, it is possible to control the temperature of at least one electrical element using parameterizable means which offer great freedom of adjustment to adapt the power consumption of the various electrical components according to the needs, and in particular to improve the driving comfort of the driver.

Claims (10)

REVENDICATIONS1. A method of thermal protection of at least one electric member (2,3,4) of a motor vehicle equipped with an electric motor (3), in which a limit temperature (T) of said electric member and a speed of rotation (N) of the electric motor (3) and limiting the torque of the electric motor (3), characterized in that a maximum mechanical power is determined as a function of the limit temperature (T) and the torque of the electric motor is limited (3) depending on the rotational speed (N) of the electric motor (3) and said determined maximum mechanical power. 2. Method according to claim 1, wherein a reduction power is developed which is non-zero when the value of the measurement of the limit temperature (T) is greater than a temperature threshold (Tseuil), and zero otherwise, and determines the maximum mechanical power as a function of a sum between a parameterizable variable (Pmax_nom) representing a maximum nominal mechanical power and said elaborated reduction power. 3. Method according to claim 2, wherein said reduction power is equal to a parameterizable gain (G) multiplied by a difference between said temperature threshold (Tseuil) and the value of the measurement of the limit temperature (T). 4. Method according to one of claims 1 to 3, wherein a first maximum torque is calculated as a function of the ratio between the maximum mechanical power and the rotational speed (N) of the electric motor (3), a second torque is determined. maximum from a piecewise refining function of the maximum mechanical power, and limiting the torque of the electric motor (3) as a function of the minimum between the first and second maximum couples. 5. Method according to one of claims 1 to 4, wherein limiting the traction torque of the electric motor (3) when it operates in traction mode to propel the motor vehicle. 6. Method according to one of claims 1 to 4, wherein limiting the energy recovery torque of the electric motor (3) when it operates in energy recovery mode to provide electrical energy to the motor vehicle. 7. Device for thermal protection of at least one electrical element (2,3,4) of a motor vehicle equipped with an electric motor (3), comprising means (5,6) for measuring a limiting temperature of said organ electric motor (2) and a rotational speed of the electric motor (3) and a torque limiting means (7) adapted to develop a torque limit for the electric motor (3), characterized in that the torque limiting means (7) comprises a power determining means (9) for determining a maximum mechanical power as a function of the limit temperature, said torque limit being elaborated as a function of the rotational speed of the electric motor (3) and said mechanical power maximum determined. 8. Device according to claim 7, wherein the torque limiting means (7) is configured to calculate a first maximum torque as a function of the ratio between the maximum mechanical power and the rotational speed of the electric motor (3), to determine a second maximum torque from a piece-wise refinement function of the maximum mechanical power, and to develop the torque limit as a function of the minimum between the first and second maximum couples. 9. Device according to one of claims 7 or 8, wherein the measuring means (5) of the limit temperature comprise temperature sensors for respectively measuring the temperatures of the electrical components (2,3,4) of the motor vehicle and a comparison means configured to determine the limit temperature which is equal to the maximum value of the temperatures of the electrical components (2,3,4) measured. 10. Device according to one of claims 7 to 9, the torque limiting means (7) comprises a control loop (BR) of the limit temperature which is configured to control the torque value of the electric motor (3) to from the torque limit and a difference between a temperature threshold and said limit temperature.