Method and system for controlling a hybrid motor vehicle during decelerations

Abstract

The invention relates to a method for controlling a hybrid motor vehicle comprising a disengageable combustion engine, comprising the following steps: - determining the power absorbed by the main electric machine to observe the target torque required at the wheels, - determining the electrical power to be dispensed by the second electric machine to observe the target torque required at the wheels by subtracting the power absorbed by the main electric machine from the charge capacity of the traction battery, - determining a raw value of the minimum rotational speed of the combustion engine, which is a function of the electrical power to be dispensed by the second electric machine, and - determining a minimum rotational speed setpoint of the combustion engine from the minimum rotational speed of the combustion engine as a function of positive and negative gradients.

Description

[0001] DESCRIPTION

[0002] TITLE: Method and system for controlling a hybrid motor vehicle during deceleration

[0003] Technical field

[0004] The invention relates to the control of a hybrid vehicle, equipped with a thermal engine and at least one electric machine, and more particularly the control of such a vehicle during regenerative braking.

[0005] A hybrid vehicle comprising a transmission enabling a 100% electric operating mode is defined as comprising:

[0006] • at least one electric machine, called an electric traction machine, connected to the wheels and

[0007] • a thermal engine that can be decoupled from the wheels and switched off (without combustion, without fuel injection).

[0008] Publication FR3022495A1 in the name of the applicant describes such an architecture.

[0009] A 100% electric operating mode involves decoupling the combustion engine from the wheels, which allows the majority of the vehicle's kinetic energy to be recovered during vehicle deceleration phases. Indeed, the decoupled combustion engine does not dissipate energy through its idle drive and the resulting friction.

[0010] Such an operating mode is then preferred during deceleration for the associated energy gain and for reasons of driving pleasure.

[0011] Such a 100% electric deceleration mode also allows for so-called "regenerative" braking. Furthermore, by coupling the thermal engine to the wheels, and controlling it without fuel injection, the vehicle can be braked by dissipating part of the energy. Such braking is generally called "engine braking", and is commonly used in thermal vehicles. However, it happens that in certain phases of vehicle driving, the battery is no longer able to recover the kinetic energy of the vehicle, due to its charge level. In other words, regenerative braking is not possible because the battery is full. The vehicle then only has braking by the dedicated braking system, which presents a significant and therefore undesirable driving inconvenience.

[0012] In other words, according to the state of the art on such hybrid vehicles, in the event of deceleration in all-electric mode at a time when the battery is already full, there is no longer any engine braking, and the only way to decelerate the vehicle is a mechanical action on the braking system (voluntary pressure by the driver on the brake pedal).

[0013] Such a problem can also occur when the battery is too cold or a malfunction limits its recharging capacity.

[0014] A solution to resolve this problem, known from the state of the art as described in document FR3022495A1, more particularly based on an architecture with two electric machines, consists of selecting another particular state of the kinematic chain, commonly called “series hybrid” and defined as being a mode in which:

[0015] • at least one first electric machine, called an “electric traction machine” is connected to the wheels and

[0016] • a second electric machine is not connected to the wheels,

[0017] • the thermal engine is switched on, controlled by injection cut-off and connected to the second electrical machine

[0018] • the electric traction machine regenerates the kinetic energy of the vehicle into electrical energy, with the destination being the battery via a charge thereof, the electrical consumers via a power supply of the latter and the second electric machine connected to the thermal engine. The second electric machine is powered in order to rotate the thermal engine in injection cut-off so as to dissipate electrical energy into mechanical energy through the friction of the thermal engine. It is thus possible to dissipate the energy that cannot be recovered by the battery or the electrical accessories in order to guarantee the deceleration of the vehicle by means of regenerative braking.

[0019] This energy to be spent by the electric machine can be more or less large depending on the capacity of the battery to recover energy and the will of the driver, it is then necessary to adapt the operating point of the thermal engine and the second electric machine in order to only spend the necessary energy. This operating point being limited to the rotation speed, the thermal engine can only realize its losses, it is then necessary to calculate the minimum rotation speed to meet the desired deceleration constraint of the vehicle.

[0020] There remains a technical problem to be solved linked to the calculation of the rotation speed of the thermal engine to expend the electrical energy necessary to achieve the deceleration of the vehicle by regenerative braking while controlling the associated noise and vibration problem, known as NVH (English acronym for "Noise and Vibration Harshness").

[0021] Previous techniques

[0022] From the state of the prior art, document EP 3 725 616 is known, describing the calculation of a target speed and its trajectory for the case of a hybrid vehicle whose thermal engine and electric machine are connected to the wheel as a function of a desired recharge level.

[0023] Statement of the invention

[0024] The subject of the invention is a method for controlling a motor vehicle comprising a heat engine, a first electric machine and a second electric machine, the heat engine being connected to the wheels by a disengageable connection and to the second electric machine by a connection which is also disengageable, the electric machines being electrically connected to a battery, the control method comprising the following steps:

[0025] - the driver's torque requirement is determined,

[0026] - the power absorbed by the main electric machine is determined to meet the target torque required at the wheels,

[0027] - the electrical power to be expended by the second electric machine to meet the target torque required at the wheels is determined by subtracting the power absorbed by the main electric machine from the charging capacity of the traction battery,

[0028] - the equivalent mechanical power to be produced by the second electrical machine is determined as a function of the electrical power to be expended by the second electrical machine and the average value of electrical efficiency from a mechanical power,

[0029] - a raw value of the minimum rotation speed of the heat engine is determined, modeled by a linear model of the power losses of the heat engine as a function of the equivalent mechanical power to be produced by the second electric machine, and

[0030] - a minimum rotation speed setpoint for the thermal engine is determined from the minimum rotation speed of the thermal engine as a function of positive and negative gradients.

[0031] The raw value of the minimum rotation speed of the thermal engine can be limited to a maximum authorized rotation speed of the thermal engine for decelerations to take into account vibration constraints.

[0032] To determine the raw minimum rotation speed setpoint of the thermal engine, the following sub-steps can be carried out:

[0033] - a minimum rotation speed differential of the heat engine is determined as being equal to the difference between the minimum rotation speed of the heat engine and the raw minimum rotation speed setpoint of the heat engine, - a Boolean state value is determined, based on a comparison between the minimum rotation speed of the heat engine and a rotation speed threshold for a minimum duration,

[0034] - a positive gradient is determined as a function of a first predetermined table receiving as input the minimum rotation speed differential of the heat engine and as a function of said Boolean state value,

[0035] - a negative gradient is determined as a function of a second predetermined table receiving as input the minimum rotation speed differential of the heat engine and as a function of said Boolean state value, and

[0036] - the gross minimum rotation speed setpoint of the thermal engine is then determined as a function of the positive gradient, the negative gradient and the minimum rotation speed of the thermal engine.

[0037] The minimum rotation speed setpoint of the thermal engine can be determined as the minimum value between the raw minimum rotation speed setpoint of the thermal engine and the maximum authorized rotation speed of the thermal engine for decelerations.

[0038] The invention also relates to a system for controlling a motor vehicle comprising a heat engine, a first electric machine and a second electric machine, the heat engine being connected to the wheels by a disengageable connection and to the second electric machine by a connection which is also disengageable, the electric machines being electrically connected to a battery, the control system being characterized in that it comprises a sensor for measuring the target torque required at the wheels, a sensor for measuring the charge capacity of the traction battery, calculation means and memories configured to execute the control method as described above.

[0039] Brief description of the drawings

[0040] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0041] - Figure 1 illustrates the main steps of a control method according to the invention,

[0042] Detailed description

[0043] The control process aims to define a minimum engine rotation speed in order to meet the driver's wishes during deceleration while controlling the evolution and level of this rotation speed in order to limit its impact on the NVH performance (acronym for "Noise Vibration and Harshness").

[0044] The following variables are introduced:

[0045] - WHL TQ TG: target torque required at the wheels developed from the driver's request and third-party functions having an impact on its development (Cruise control, autonomous driving, etc.)

[0046] - WHEEL EL POW TG: power absorbed by the main electrical machine

[0047] - EM SND EL POW: electrical power to be spent by the second electrical machine

[0048] - BAT TRAC CHRG POW: charge capacity of the traction battery

[0049] - EM SND MECA POW: equivalent mechanical power to be achieved by the second electrical machine

[0050] - EM SND MOT EF Y_F AC: average value of electrical efficiency from mechanical power

[0051] - ENG MIN SPD RAW: raw value of the minimum rotation speed of the thermal engine

[0052] - ENG_MIN_SPD_RAW_TG: raw minimum rotation speed setpoint of the thermal engine

[0053] - ENG MAX AUTH SPD: maximum authorized rotation speed of the thermal engine for decelerations, which may be dependent on the speed, the lever position or other HMI (acronym for “human machine interface”) interface having an impact on the level of vehicle deceleration.

[0054] - ENG MIN SPD _TG: Minimum rotation speed setpoint of the thermal engine going towards the rest of the arbitrations having an impact on the choice of the final speed of the thermal engine on a series hybrid state.

[0055] - ENG MIN SPD: minimum rotation speed of the thermal engine

[0056] Sequentially, the control method according to the invention allows:

[0057] - to calculate the electrical power produced by the electric traction machine to meet the “driver’s wishes” (the driver’s wishes correspond to a desire for acceleration of the vehicle, which is translated by a computer into a power / torque setpoint at the wheel),

[0058] - to calculate the electrical power to be dissipated by the second electrical machine connected to the thermal engine to dissipate the electrical power that could not be absorbed by the battery or the electrical accessories,

[0059] - to calculate the associated mechanical power, and

[0060] - to define the minimum rotation speed of the thermal engine to be achieved to dissipate the previous mechanical power.

[0061] The control process is illustrated in Figure 1.

[0062] In a first step 1, we determine the power absorbed by the main electric machine WHEEL EL POW TG (expressed in Watts) to meet the target torque required at the wheels WHL TQ TG. This function is calculated here using a second-order polynomial model of electrical consumption: With :

[0063] - RAT EM: a gear ratio between the main electric traction machine and the wheel,

[0064] - PO (expressed in Watts): the static losses of the main machine, generally a function of the speed and battery voltage,

[0065] - PI (expressed in W / Nm): a coefficient of order 1 of the electrical consumption of the main machine, generally a function of the rotation speed and the battery voltage,

[0066] - P2 (expressed in W / Nm 2): a coefficient of order 2 of the electrical consumption of the main machine, generally a function of the rotation speed and the battery voltage.

[0067] In a second step 2, the power absorbed by the main electric machine WHEEL EL POW TG is then subtracted from the charging capacity of the traction battery BAT TRAC CHRG POW in order to determine the electrical power to be expended by the second electric machine EM SND EL POW to meet the target torque required at the wheels and the associated electrical power:

[0068] [Math 2]

[0069] EM_SND_EL_POW = BAT TRAC _CHRG_POW - WHEEL_EL_POW _TG

[0070] During a third step 3, the electrical power to be spent by the second electrical machine EM SND EL POW is converted into equivalent mechanical power EM SND MECA POW to be produced by the secondary electrical machine.

[0071] [Math 3]

[0072] EM_SND_MECA_POW = EM_SND_EL_POW / EM_SND_MOT_EFY_FAC

[0073] With: EM SND MOT EFY FAC the average value of electrical efficiency from a mechanical power (configurable value). During a fourth step 4, we determine the raw value of the minimum rotation speed of the thermal engine ENG MIN SPD RAW, modeled by a linear model of the power losses of the thermal engine as being equal to the equivalent mechanical power to be achieved by the second electrical machine EM SND MECA POW

[0074] [Math 4]

[0075] (EM_SND_MECA_POW - PO_ENG_LOSS_POW)

[0076] ENG-MIN-SPD-RAW =

[0077] Pl ENG LOSS POW

[0078] With :

[0079] - PO ENG LOS S POW (expressed in Watts): the zero order coefficient of the power of thermal engine losses, this coefficient can be a function of the temperature of the thermal engine coolant.

[0080] - P1 ENG LOS S POW (expressed in W / RPM, RPM for “Rotation Per Minute”): the first order coefficient of the power of thermal engine losses, this coefficient can be a function of the temperature of the thermal engine coolant.

[0081] Since the raw value of the minimum rotation speed of the thermal engine ENG MIN SPD RAW can be subject to significant variations, the latter is consolidated with a maximum authorized rotation speed of the thermal engine for decelerations ENG MAX AUTH SPD to take into account NVH vibration constraints. The minimum rotation speed of the thermal engine ENG MIN SPD is thus limited to the maximum authorized rotation speed of the thermal engine for decelerations ENG MAX AUTH SPD:

[0082] [Math 5]

[0083] ENG_MIN_SPD =

[0084] MIN(ENG_MIN_SPD_RAW ; ENG_MAX_AUTH_SPD) During a fifth step 5, a minimum rotation speed setpoint of the thermal engine ENG MIN SPD TG is determined from the minimum rotation speed of the thermal engine ENG MIN SPD.

[0085] During this step, the dynamic evolution of the raw setpoint is managed by authorizing maximum gradients in order to avoid any jump in rotation speed which would be undesirable for the customer service from an acoustic and vibration point of view (NVH) while guaranteeing high dynamics if required.

[0086] To determine the raw minimum rotation speed setpoint of the thermal engine for braking ENG MIN SPD RAW TG, the following sub-steps are carried out:

[0087] A minimum rotation speed differential of the thermal engine ENG MIN SPD DIF is determined as being equal to the difference between the minimum rotation speed of the thermal engine ENG MIN SPD and the raw minimum rotation speed setpoint of the thermal engine ENG MIN SPD RAW TG.

[0088] [Math 6]

[0089] ENG_MIN_SPD_DIF = ENG_MIN_SPD_RAW_TG - ENG_MIN_SPD

[0090] A Boolean state value is determined, taking a first value if the minimum rotation speed of the thermal engine ENG MIN SPD is lower than a rotation speed threshold ENG MIN AL THD for a minimum duration ENG MIN AL DLY, and taking a second value in other cases.

[0091] A positive gradient ENG MIN SPD POS SLOPE AUTH is determined based on a first predetermined table receiving as input the minimum rotation speed differential of the thermal engine ENG MIN SPD DIF and said Boolean state value. The positive gradient value is that of the table if the Boolean state value has taken the second value and a configurable value if the Boolean state value has taken the first value, this configurable value usually being parameterized with a very large positive value.

[0092] A negative gradient ENG MIN SPD NEG SLOPE AUTH is determined based on a second predetermined table receiving as input the minimum rotation speed differential of the thermal engine ENG MIN SPD DIF and said Boolean state value. The negative gradient value is that of the table if the Boolean state value has taken the second value and a configurable value if the Boolean state value has taken the first value, this configurable value usually being parameterized with a very large negative value.

[0093] The raw minimum rotation speed setpoint of the thermal engine ENG MIN SPD RAW TG is then determined as a function of the positive gradient

[0094] ENG MIN SPD POS SLOPE AUTH, the negative gradient ENG MIN SPD NEG SLOPE AUTH and the minimum rotation speed of the thermal engine ENG MIN SPD.

[0095] This logic makes it possible to return to the minimum rotation speed of the thermal engine ENG MIN SPD at the end of processing while controlling its evolution when a higher value than that usually obtained on series hybrid states is not required in order to allow the thermal engine to return to a neutral rotation speed from an acoustic and vibration NVH point of view for the customer.

[0096] The raw minimum rotation speed setpoint of the thermal engine ENG MIN SPD RAW TG is then consolidated during a sixth step 6 by the maximum authorized rotation speed of the thermal engine for decelerations ENG MAX AUTH SPD to comply with the NVH noise and vibration constraints. The minimum rotation speed setpoint of the thermal engine ENG MIN SPD _TG is then determined as being equal to the minimum value between the raw minimum rotation speed setpoint of the thermal engine ENG MIN SPD RAW TG and the maximum authorized rotation speed of the thermal engine for decelerations ENG MAX AUTH SPD.

[0097] A minimum target rotation speed of the thermal engine is thus developed to allow the target torque required at the wheels to be respected during deceleration with a low battery recharge potential while controlling the associated NVH issues to guarantee the vehicle's performance.

Claims

DEMANDS 1. A method for controlling a motor vehicle comprising a heat engine, a first electric machine and a second electric machine, the heat engine being connected to the wheels by a disengageable connection and to the second electric machine by a similarly disengageable connection, the electric machines being electrically connected to a battery, the control method comprising the following steps: determining the desired torque from the driver, determining the power absorbed by the main electric machine to meet the target torque required at the wheels, determining the electrical power to be expended by the second electric machine to meet the target torque required at the wheels by subtracting the power absorbed by the main electric machine from the charging capacity of the traction battery,The equivalent mechanical power to be produced by the second electrical machine is determined as a function of the electrical power to be expended by the second electrical machine and the average electrical efficiency value. A raw value for the minimum rotational speed of the heat engine is determined, modeled by a linear model of the heat engine's power losses as a function of the equivalent mechanical power to be produced by the second electrical machine. Finally, a minimum rotational speed setpoint for the heat engine is determined based on the minimum rotational speed of the heat engine as a function of positive and negative gradients.

2. A control method according to claim 1, wherein the raw value of the minimum motor rotational speed is limited thermal at a maximum permissible rotational speed of the thermal engine for decelerations to take into account vibration constraints.

3. A control method according to any one of claims 1 or 2, wherein, to determine the raw setpoint for the minimum rotational speed of the heat engine, the following substeps are carried out: a differential for the minimum rotational speed of the heat engine is determined as being equal to the difference between the minimum rotational speed of the heat engine and the raw setpoint for the minimum rotational speed of the heat engine; a Boolean state value is determined, based on a comparison between the minimum rotational speed of the heat engine and a rotational speed threshold over a minimum duration; a positive gradient is determined based on a first predetermined table receiving as input the differential for the minimum rotational speed of the heat engine and based on said Boolean state value.A negative gradient is determined based on a second predetermined table which receives as input the differential of the minimum rotational speed of the heat engine and as a function of said Boolean state value, and the raw setpoint of the minimum rotational speed of the heat engine is then determined as a function of the positive gradient, the negative gradient and the minimum rotational speed of the heat engine.

4. Control method according to claim 3, wherein the minimum rotational speed setpoint of the heat engine is determined as the minimum value between the raw minimum rotational speed setpoint of the heat engine and the maximum permissible rotational speed of the heat engine for decelerations.

5. Control system for a motor vehicle comprising a thermal engine, a first electric machine and a second electric machine, the thermal engine being connected to the wheels by a disengageable connection and to the second electric machine by a similarly disengageable connection, the electric machines being electrically connected to a battery, the control system being characterized in that it comprises a sensor for measuring the target torque required at the wheels, a sensor for measuring the charging capacity of the traction battery, computing means and memories configured to execute the control method according to any one of claims 1 to 4.

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