FR3104515A1 - METHOD OF CONTROL OF AN ELECTRIC MACHINE OF A HYBRID VEHICLE - Google Patents

Abstract

Method for controlling an electric machine (4) of a hybrid vehicle (10) able to be propelled by a heat engine (2) and by the electric machine, said machine being able to operate either in alternator mode to recharge a battery (8 ), or in engine mode to contribute to propelling the vehicle, the method comprising:- switching the electric machine to alternator mode when a state of charge of the battery is less than or equal to a first minimum threshold, and- switching the electric machine in engine mode when said state of charge of the battery is greater than or equal to a second minimum threshold, characterized in that said switching of the electric machine in engine mode is also dependent on an instantaneous speed of the vehicle and does not is authorized only if the instantaneous speed is less than or equal to a critical speed. Figure 1

Description

METHOD FOR CONTROLLING AN ELECTRIC MACHINE OF A HYBRID VEHICLE

The present invention generally relates to the field of electric machines for hybrid vehicles, in particular for motor vehicles, which can be propelled by a heat engine and by at least one such electric machine.

Today, hybrid vehicles fall into two main categories. On the one hand, there are PHEV type vehicles, an English acronym meaning "Plug-in Hybrid Electric Vehicle", and EREV type vehicles, meaning "Extended Range Electric Vehicle". The so-called PHEV models have two engines, one thermal and the other electric, which act together to propel the vehicle. On the other hand, the so-called EREV models are vehicles whose wheels can only be driven by the electric motor. In this case, the heat engine is a booster engine coupled to an electricity generator which is used to recharge the storage battery when the latter reaches a critical discharge threshold.

The present invention relates to vehicles of the PHEV type and relates to a method for controlling or controlling an electric machine of a hybrid vehicle which can be propelled not only by a combustion engine but also by such an electric machine. The invention also relates to a device for implementing this method, as well as to a vehicle comprising such a device.

PHEV-type vehicles have an electric machine that can operate either in an alternator mode, to recharge an electric storage battery, or in an electric motor mode, to propel the vehicle. In this latter mode, the electric machine is powered by the storage battery.

When the electric machine operates in alternator mode, it recharges the battery through a coupling that connects it to the heat engine. In this mode of operation, the electric machine then draws part of the power supplied by the internal combustion engine to recharge the battery. At the same time, this heat engine provides the remaining power it has to move the vehicle.

When the battery reaches a sufficient charge threshold, it too becomes capable of supplying power again to the powertrain to help move the vehicle. This takes place via the electric machine which then operates in its electric motor mode. On the other hand, as soon as the battery charge level drops to a critical discharge threshold, the electric machine switches its operating mode to switch to alternator mode, which makes it possible to recharge the battery again.

This battery charging and discharging cycle repeats indefinitely. The battery charging threshold which is considered to be sufficient for the electric machine to switch to electric motor mode is typically equivalent to 17% of the maximum state of charge of the battery. This state of charge is often identified by the acronym SOC, meaning "State Of Charge" in English. The critical level of battery discharge is typically close to 15% of the SOC. The small difference between these two values implies that the electric machine switches frequently between the alternator and electric motor operating modes.

When the electric machine operates in electric motor mode, the powertrain benefits from the combination of the powers provided by the internal combustion engine and by the electric motor. As a result, the vehicle can benefit from increased power and can reach a higher speed than that which can be reached when the power is delivered only by the internal combustion engine. However, at this speed, the battery discharges rapidly and the electrical machine quickly switches to its alternator operating mode. In this mode, the internal combustion engine becomes the sole source of energy for moving the vehicle. The power of this source being lower than that delivered simultaneously by the two motors, it follows that the vehicle decelerates as soon as the electric machine no longer contributes to supplying power to the powertrain. This deceleration occurring shortly after the acceleration provided by the electric motor to the powertrain, the switchings of the electric machine between the alternator and motor modes are then felt by the users of the vehicle as annoying jerks and which can lead to believe a malfunction of the powertrain.

Document US 9,623,757 B2 describes an electrical power supply device for a vehicle. This device comprises an electrical storage device, a "boost" converter configured to increase the voltage of the electrical storage device and supply the boosted voltage to an electrical load of the vehicle, and a controller configured to control the operation of the converter according to a continuous operating mode and an intermittent operating mode. According to this document, the controller further restricts a charge/discharge request of the electric storage device, so that a charge/discharge request of the electric storage device, when the boost converter operates according to the mode of intermittent boost is more restricted than a charge/discharge request from the electrical storage device when the boost converter is operating in the continuous boost mode. However, this strategy does not make it possible to solve the problem relating to the aforementioned jerks.

Consequently, there is an interest in finding an efficient solution which makes it possible at least in part to resolve the aforementioned drawbacks.

To this end, the present invention relates, in a first aspect, to a method for controlling an electric machine of a hybrid vehicle which can be propelled by a heat engine and by the electric machine, said electric machine being able to operate either in alternator mode to recharge a battery of electric accumulators, or in motor mode powered by the battery to contribute to propelling the vehicle, the method comprising:
- a step of switching the electric machine to alternator mode when a state of charge of the battery is less than or equal to a first minimum threshold, and
- a step of switching the electric machine to motor mode when said state of charge of the battery is greater than or equal to a second minimum threshold,
characterized in that said switching of the electric machine to motor mode is also dependent on an instantaneous speed of the vehicle and is authorized only if the instantaneous speed is less than or equal to a critical speed.

Advantageously, due to the fact that the switching of the electric machine (between its two modes of operation) is dependent on a critical speed (which can be determined in advance), the heat engine is always in a regime which allows the vehicle to ensure at least maintaining this speed. In other words, the power developed by the heat engine at the aforementioned critical speed, or below the latter, is lower than the maximum power of the heat engine. Consequently, the power of the heat engine alone is sufficient to maintain the vehicle at least at this critical speed, which eliminates any uncontrolled deceleration of the vehicle when the electric machine switches from electric motor mode to alternator mode. It follows that the switchings of the electric machine between its two operating modes no longer cause jerks, which improves the comfort of the users of the vehicle and eliminates any suspicion of malfunction of the electromotor unit.

It will be noted that the switchings between the two aforementioned operating modes comprise both a switching from the alternator mode to the motor mode and a reverse switching, namely a switching from the motor mode to the alternator mode.

In a preferred embodiment of the invention, the critical speed is defined as a function of a nominal power of the heat engine.

In another embodiment of the invention, the first and second minimum thresholds have a difference not exceeding 10% of a capacity of the battery, preferably not exceeding 7%, 5% or 2% of the battery capacity.

Preferably, the second minimum threshold does not exceed 25% of the capacity of the battery, preferably 20% of the capacity of the battery, more preferably 17% of the capacity of the battery.

In a preferred embodiment, the first minimum threshold does not exceed 20% of the capacity of the battery, preferably 17% of the capacity of the battery, more preferably 15% of the capacity of the battery.

In another embodiment of the invention, said critical speed of the vehicle is less than or equal to 80 km/h, preferably less than or equal to 60 km/h, more preferably less than or equal to 50 km/h.

In one embodiment, the capacity of the battery relates to a nominal capacity or to a state of seniority of said battery.

In one embodiment, at least one datum among the instantaneous speed of the vehicle, the state of charge of the battery, the first minimum threshold and the second minimum threshold, is derived from at least one parameter which is preferably representative of this data.

In a second aspect, the invention relates to a device for implementing the method according to any one of the embodiments or variants of said method, this device comprising:
- a control unit configured to control a switching device of the electric machine according to parameters representative of: the state of charge of the battery of electric accumulators, and
- a communication interface configured to receive at least a part of said parameters and transmit at least one command to the switching member of the electric machine in order to allow switching between said operating modes.

In a last aspect, the invention also relates to a vehicle, in particular a motor vehicle, comprising the aforementioned device.

The invention will be better understood in the light of the appended figures, given by way of non-limiting illustrations and examples, in which:

is a schematic illustration of an example of architecture of a powertrain of a hybrid vehicle incorporating a control device;

is a representation of a first graph illustrating the problem which the present invention aims to solve;

is a representation of a second graph also illustrating this issue through other quantities;

is a representation of a third graph highlighting the improvements provided by the invention; And

is a representation of a fourth graph also highlighting these improvements through said other quantities.

With reference to FIG. 1, this represents, in its upper part, the architecture of a powertrain 1 configured for driving a hybrid vehicle 10 of the PHEV type. This architecture notably represents the main entities which constitute the traction chain of such a powertrain. Among these entities, one will recognize a combustion engine 2, a clutch device 3, at least one electric machine 4, a transmission box 5 and an axle shaft 6, in particular of the front axle of the vehicle 10. This vehicle further comprises at least one battery 8 of electric accumulators which is electrically connected to the electric machine 4.

The heat engine 2 is, with the electric machine 4, located at the input of the transmission box 5. The latter is typically an automatic gearbox connected to the front axle of the vehicle. From the architecture illustrated in FIG. 1, it will be understood that the hybrid vehicle 10 can be propelled by the combustion engine 2 and by the electric machine 4. These two entities 2, 4 can therefore operate simultaneously, to each provide their power to the transmission box 5, and at least one of these two entities, typically the heat engine 2, can be used alone to move the vehicle. In other words, the electric machine 4 and the heat engine 2 can bring their energy to the axle of the driving wheels (typically the front axle) until reaching a maximum speed thanks to the transmission box 5 which allows adapt the operating point of the heat engine 2 and of the electric machine 4. The vehicle 10 can therefore be propelled, together, by the heat engine 2 and by the electric machine 4.

The electric machine 4 has two modes of operation. The first mode of operation of this machine is defined as being an alternator mode making it possible to recharge the battery 8. The second mode of operation of the electric machine 4 is called motor mode and makes it possible at least to contribute to the propulsion of the vehicle. More specifically, the electric machine 4 can operate either in its alternator mode or in its motor mode, being in the latter case powered by the battery.

Figs. 2a and 2b represent two graphs illustrating the problem which the present invention aims to solve. The first graph shown in Fig. 2a simultaneously represents three curves on a system of Cartesian coordinate systems having the time (in seconds) on the abscissa and a common scale on the ordinate reflecting the magnitudes of each of the three curves. The first curve denoted D is illustrated in dotted lines and refers to the distance (for example in km) traveled by the vehicle 10. The second curve denoted SOC (an English acronym meaning "State Of Charge") represents the level or the state of charge of the battery 4 over time when the vehicle travels the distance D. The third curve denoted V represents the instantaneous speed (for example in km/h) of the vehicle over time.

The second graph which is shown in Fig. 2b provides other information for a system of Cartesian coordinate systems similar to that of FIG. 2a in which on the abscissa is also represented the time, and on the ordinate are represented the magnitudes of the two curves illustrated in this figure. The first curve CMT, shown in bold, illustrates the torque (in Nm) of the heat engine 2, while the second curve CME illustrates the torque (in Nm) of the electric machine 4 over time in its engine mode. It will be noted that the abscissa scales of FIGS. 2a and 2b are identical so that these two figures can be assessed in mutual agreement.

As illustrated in Figs. 2a and 2b, battery 8 is successively charged during a time interval T1 and discharged during a time interval T2. This is particularly noticeable in Fig. 2a through the SOC curve which increases very slightly in the time intervals T1 and which decreases in the time intervals T2. During the recharging phases of the battery 8 (intervals T1), it is also noted in FIG. 2b that the torque CME of the electric machine 4 is negative and constant, which indicates that this electric machine does not supply any engine torque but is in its alternator mode to recharge the battery 8. On the other hand, in the time intervals T2, the electric machine 4 provides torque to the powertrain 1 and therefore contributes to the propulsion of the vehicle 10.

When the battery 8 is recharged by the electric machine 4 during the time interval T1, this electric machine 4 extracts energy from the heat engine 2 which, during this time interval T1, constitutes the only source of energy for the vehicle. 10. In this case, the power supplied by the heat engine 2 must be shared, on the one hand, to propel the vehicle and, on the other hand, to recharge the battery. However, if the vehicle requires a large part of this power for its movement, the power or the torque of the heat engine will peak at a maximum value, as illustrated in the time intervals T1 in FIG. 2b. This type of scenario can typically appear in the case where, for example, the instantaneous speed of the vehicle (curve V in FIG. 2a) is relatively high.

In this scenario, the heat engine 2 develops its maximum power and its torque is therefore also maximum. When the battery charge level or state reaches a minimum threshold (SOC2) which is considered sufficient to switch the electric machine from alternator mode to motor mode, the power input developed by the electric machine in its motor generates a acceleration which results in an increase in speed as shown in Fig. 2a in time intervals T2. However, this increase in speed remains relatively brief because the battery, severely stressed, quickly discharges to reach a minimum critical threshold (SOC1) which forces the electric machine to switch back to its alternator mode. The speed of the vehicle V decelerates because the electric machine can no longer be used as an additional source of energy. The increasing and decreasing speed variation, during the brief acceleration followed by the deceleration, is felt by the users of the vehicle as a jerk marked by the letter A on the speed curve V of FIG. 2a. Without reducing the power or the torque requested from the heat engine, these jerks are repeated cyclically and are mainly punctuated by the duration of the interval T1 which is necessary to recharge the battery.

The method of the invention aims to overcome this problem and in particular to eliminate the jolts A which may lead one to believe in a malfunction of the powertrain 1. To do this, the invention suggests a method for controlling at least one electric machine 4 of a hybrid vehicle 10 capable of being propelled (i) by a heat engine 2 and (ii) by the electric machine 4. This electric machine 4 can operate either in alternator mode to recharge the battery 8 of electric accumulators , or in motor mode (powered by the battery) to at least contribute to propelling the vehicle 10.

This process includes the following steps:
- switching of the electric machine 4 in alternator mode when a state of charge SOC of the battery 8 is less than or equal to a first minimum threshold SOC1,
- Switching of the electric machine 4 to motor mode when the state of charge SOC of the battery 8 is greater than or equal to a second minimum threshold SOC2, and
in that the switching of the electric machine 2 to motor mode is also dependent on an instantaneous speed Vi of the vehicle 10 and is only authorized if the instantaneous speed Vi is less than or equal to a critical speed Vc (FIG. 3a ).

Fig. 3a is similar to FIG. 2a in the sense that it shows the same magnitudes in the same system of reference marks as that of FIG. 2a. In Fig. 3a, it can be seen that the jerks A on the speed curve V have advantageously been eliminated. This mainly stems from the fact that the switching of the electric machine 2 to motor mode no longer depends only on the state of charge of the battery SOC with respect to the second minimum threshold SOC2, but also depends on the instantaneous speed Vi of the vehicle 10.

When the heat engine 2 is strongly or sufficiently stressed, as is the case in the example of FIG. 3a to maintain the speed of the vehicle at a high level, the switching of the electric machine from the alternator mode to the motor mode is prevented despite the fact that the state of charge of the battery may be greater than or equal to the second minimum threshold SOC2. In Figs. 3a and 3b, the first time interval T1 corresponds to the time required (t ₂ -t ₁ ) for the battery 8 for its state of charge SOC to reach the second minimum threshold SOC2 at time t ₂ .

Note in these figures that, despite the fact that the instantaneous speed Vi ₁ of the vehicle at time t ₁ is greater than the critical speed Vc, the battery recharging phase remains when the state of charge of the battery SOC is less than or equal to the first minimum threshold SOC1. However, once the state of charge of the battery reaches the second minimum threshold SOC2, the switching of the electric machine 4 into its motor mode is deliberately prevented due to the fact that the instantaneous speed Vi ₂ at the instant t ₂ is greater at the critical speed Vc.

As illustrated in the graph of Fig. 3b, during the interval T1, the torque CME of the electric machine 2 is negative because this machine absorbs part of the power supplied by the heat engine 2 to recharge the battery 8. At time t ₂ , the Switching of the electrical machine to motor mode is prevented, which causes the value of the torque CME to rise to a negative value close to zero. Because this electric machine cannot function as an electric motor as long as the instantaneous speed of the vehicle remains greater than or equal to the critical speed Vc, the torque CME of the electric machine cannot therefore be positive.

The critical speed Vc is preferably a predefined constant speed, for example according to at least one criterion which can typically be specific to the heat engine 2. In a preferred embodiment, the critical speed Vc is defined according to the power nominal heat engine. The higher the nominal power of the heat engine, the higher this critical speed could also rise. In another embodiment, the critical speed Vc of the vehicle is less than or equal to 80 km/h, preferably less than or equal to 60 km/h or even less than or equal to 50 km/h as illustrated in FIG. 3a.

In one embodiment, the first and second minimum thresholds SOC1, SOC2 of the state of charge of the battery 8 preferably have a difference not exceeding 10% of the capacity of the battery, preferably of the maximum capacity of this battery. Preferably again, this SOC2-SOC1 difference does not exceed 7%, 5% or 2% of this capacity.

In one embodiment, the second minimum threshold SOC2 does not exceed 25% of the (preferably maximum) capacity of the battery. Preferably again, this second minimum threshold SOC2 does not exceed 20% or 17% of this capacity. Preferably, this second minimum threshold SOC2 is set at 17% of the capacity of the battery.

The first minimum threshold SOC1 for its part preferably does not exceed 20%, 17% or 15% of the capacity of the battery. Preferably, this first minimum threshold SOC1 is set at 15% of the capacity of the battery.

In one embodiment of the invention, the (preferably maximum) capacity of the battery relates to its nominal capacity or to a state of age of the battery 8. This state of age could correspond to the new state drums.

Preferably, at least one datum among the instantaneous speed Vi of the vehicle, the state of charge SOC of the battery, the first minimum threshold SOC1 and the second minimum threshold SOC2, is derived from at least one parameter, preferably d at least one parameter representative of this datum. In other words, at least one datum among those mentioned above could be obtained indirectly, namely deduced or derived from one or more parameters. By way of example, the instantaneous speed Vi could be derived from the speed of the heat engine (for example in revolutions/min) as well as from the engaged gear ratio of the gearbox 5. As another example, the state of loading SOC of the battery could be determined by the voltage across the battery terminals. Alternatively, the SOC state of charge of the battery could be determined by the application of a more complex methodology which could for example resort to the application of a series of current pulses before taking the voltage measurement of the battery at its terminals.

In a second aspect, the invention also relates to a device 20 for implementing the method according to any one of the embodiments described in the present description or according to any variant of this method.

With reference to FIG. 1, this device 20 is typically a control device that can be embarked in the vehicle 10. As shown schematically in this figure, the device 20 comprises a control unit 21 configured to control a switching device 14 of the electric machine 4 according to different parameters which can, at least in part, come from the powertrain 1, either directly or indirectly, or from a storage unit 28 such as an internal memory in the control device 20. These different parameters are preferably representative of:
- the state of charge SOC of the battery 8 of electric accumulators,
- first and second minimum thresholds SOC1 and SOC2, and
- instantaneous speeds Vi and critical speeds Vc of the vehicle 10.

The device 20 also comprises a communication interface 25 configured to receive at least some of the aforementioned parameters and transmit at least one command to the switching member 14 of the electric machine 4, in order to allow the switching of this machine between its two operating modes, i.e. between alternator mode and engine mode. In Fig. 1, the parameters transmitted to the control unit 21, via the communication interface 25 or coming from the storage unit 28, are represented schematically by an envelope denoted P, whereas the command intended to the switching device 14 is represented by an envelope denoted Cmd.

It will be noted that the switching device 14 can be integrated or associated with the electric machine 4 and can therefore form part of the powertrain 1 or be located outside the latter as shown schematically in FIG. 1. Furthermore, the links between the different units or entities within the control unit 20 can of course be two-way communication channels. Other units not shown in FIG. 1 could also be part of the control device 20.

In a last aspect, the invention also relates to a vehicle 10, in particular a motor vehicle, comprising a device such as the control device 20. This vehicle is therefore a hybrid vehicle, more specifically a hybrid vehicle of the PHEV type. .

It will be understood that various modifications and/or improvements obvious to those skilled in the art can be made to the various embodiments of the invention described in the present description without departing from the scope of the invention.

Claims (10)

Method for controlling an electric machine (4) of a hybrid vehicle (10) able to be propelled by a heat engine (2) and by the electric machine, said electric machine (4) being able to operate either in alternator mode to recharge a battery (8) of electric accumulators, either in motor mode powered by the battery (8) to contribute to propelling the vehicle (10),
the method comprising:
- a step of switching the electric machine (4) to alternator mode when a state of charge (SOC) of the battery (8) is less than or equal to a first minimum threshold (SOC1), and
- a step of switching the electric machine (4) to motor mode when said state of charge (SOC) of the battery (8) is greater than or equal to a second minimum threshold (SOC2),
characterized in that said switching of the electric machine (4) to motor mode is furthermore dependent on an instantaneous speed (Vi) of the vehicle (10) and is authorized only if the instantaneous speed (Vi) is less than or equal at a critical speed (Vc). Method according to Claim 1, characterized in that the said critical speed (Vc) is defined as a function of a nominal power of the heat engine (2). Method according to Claim 1 or 2, characterized in that the first and second minimum thresholds (SOC1, SOC2) have a difference not exceeding 10% of a capacity of the battery, preferably not exceeding 7%, 5 % or 2% of battery capacity (8). Method according to one of the preceding claims, characterized in that the second minimum threshold (SOC2) does not exceed 25% of the capacity of the battery, preferably 20% of the capacity of the battery, more preferably 17% of battery capacity (8). Method according to one of the preceding claims, characterized in that the first minimum threshold (SOC1) does not exceed 20% of the capacity of the battery, preferably 17% of the capacity of the battery, more preferably 15% of battery capacity (8). Method according to one of the preceding claims, characterized in that the said critical speed (Vc) of the vehicle (10) is less than or equal to 80 km/h, preferably less than or equal to 60 km/h, more preferably less than or equal to 50 km/h. Method according to one of the preceding claims, characterized in that the capacity of the battery (8) relates to a nominal capacity or to a state of age of the said battery. Method according to one of the preceding claims, characterized in that at least one datum among the instantaneous speed (Vi) of the vehicle (10), the state of charge (SOC) of the battery (8), the first minimum threshold (SOC1) and the second minimum threshold (SOC2), is derived from at least one parameter representative of this datum. Device (20) for implementing the method according to one of Claims 1 to 8, comprising:
- a control unit (21) configured to control a switching device (14) of the electric machine (4) according to parameters representative of: the state of charge (SOC) of the battery (8) of electric accumulators , said first and second minimum thresholds (SOC1, SOC2), and the instantaneous (Vi) and critical (Vc) speeds of the vehicle (10),
- a communication interface (25) configured to receive at least a part of said parameters and transmit at least one command to the switching device (14) of the electric machine (4) in order to allow switching between said operating modes. A vehicle (10), comprising a device (20) according to claim 9.