Method and system for controlling hybrid motor vehicle during deceleration

Abstract

The invention relates to a control method for a hybrid motor vehicle, the vehicle comprising a separable internal combustion engine, the control method comprising the steps of:-determining the power absorbed by a main electric machine in order to meet the target torque required for the wheels; -determining the electrical power consumed by the second electric machine to meet the target torque required by the wheels by subtracting the power absorbed by the main electric machine from the charge capacity of the traction battery; determining an original value for the minimum rotational speed of the internal combustion engine as a function of the electrical power consumed by the second electric machine; and determining a minimum rotational speed setpoint of the internal combustion engine from a minimum rotational speed of the internal combustion engine as a function of the positive gradient and the negative gradient.

Description

Technical Field

[0001] The present invention relates to the control of hybrid vehicles equipped with an internal combustion engine and at least one electric machine, and more particularly to the control of such vehicles during regenerative braking.

[0002] A hybrid vehicle including a transmission capable of a 100% electric operating mode is defined as including:

[0003] - at least one electric motor, called an electric traction machine, connected to the wheels, and

[0004] - An internal combustion engine that can be decoupled from the wheels and shut down (without combustion or fuel injection).

[0005] Publication FR 3 022 495 A1 in the name of the applicant describes such an architecture.

[0006] 100% electric operating mode involves decoupling the internal combustion engine from the wheels, which means that a large part of the vehicle's kinetic energy can be recovered during vehicle deceleration. With the internal combustion engine uncoupled, no energy is dissipated through its idling drive and the resulting friction.

[0007] This operating mode is preferred during deceleration for reasons of associated energy savings and driving pleasure. This 100% electric deceleration mode also enables "regenerative" braking. Furthermore, by coupling the internal combustion engine to the wheels and controlling it without injecting fuel, the vehicle can be braked by dissipating some of the energy. This type of braking is often referred to as "engine braking" and is commonly used in gasoline vehicles.

[0008] However, at certain stages of the vehicle's travel, the battery may no longer be able to recover the vehicle's kinetic energy due to its charge level. In other words, regenerative braking is not possible due to the full battery. The vehicle is then braked only by the dedicated braking system, which is a great inconvenience for driving and is therefore undesirable.

[0009] In other words, according to the prior art of such hybrid vehicles, when decelerating in full electric mode when the battery is already full, there is no longer any engine braking and the only way to slow the vehicle is through mechanical action on the braking system (the driver voluntarily depresses the brake pedal).

[0010] Such problems may also occur when the battery is too cold or when a fault limits its ability to charge.

[0011] From the prior art described in FR 3 022 495 A1, more specifically based on an architecture with two electric machines, the solution to this problem consists in choosing another specific state of the drive train, generally called “series hybrid” and defined as the following mode:

[0012] - at least one first electric machine (called "traction motor") connected to the wheels, and

[0013] - the second motor is not connected to the wheels,

[0014] - the internal combustion engine is switched on, controlled in injection cut-off mode and connected to the second electric machine,

[0015] - The electric traction machine regenerates the vehicle's kinetic energy into electrical energy for the following purposes:

[0016] - Batteries, through which they are charged,

[0017] - power consuming devices, by supplying the latter with electricity, and

[0018] - A second electric machine is connected to the internal combustion engine.

[0019] When the injection is cut off, the second electric machine is powered to rotate the internal combustion engine, thereby dissipating the electrical energy into mechanical energy through the friction of the internal combustion engine. In this way, energy that cannot be recovered by the battery or electrical accessories can be dissipated to ensure that the vehicle is decelerated through regenerative braking.

[0020] Since the electric motor can consume more or less energy depending on the capacity of the battery to recover energy and the driver's wishes, it is necessary to adjust the operating point of the internal combustion engine and the second electric motor so that only the necessary energy is consumed. Since this operating point is limited by the speed, since the internal combustion engine can only make losses, it is necessary to calculate the minimum speed to meet the required deceleration requirements of the vehicle.

[0021] There are still unresolved technical issues in calculating the rotational speed of an internal combustion engine while controlling the associated noise and vibration harshness (NVH). Background Art

[0022] Prior art includes EP 3 725 616, which describes the calculation of a target speed and its trajectory for a hybrid vehicle, in which an internal combustion engine and an electric machine are connected to the wheels according to the required charge level. Summary of the invention

[0023] The invention relates to a control method for a motor vehicle, the motor vehicle comprising an internal combustion engine, a first motor and a second motor, the internal combustion engine being connected to the wheels via a detachable connection and to the second motor via a detachable connection, the motor being electrically connected to a battery, the control method comprising the following steps:

[0024] - determine the driver's torque request,

[0025] - determine the power absorbed by the main electric motor to meet the target torque required at the wheels,

[0026] - determining the electric power that the second electric machine must consume to meet 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,

[0027] - determining the equivalent mechanical power produced by the second electric machine according to the average electrical efficiency value of the electrical power and the mechanical power consumed by the second electric machine,

[0028] - determining an overall value for the minimum speed of the internal combustion engine based on the equivalent mechanical power produced by the second electric machine, the overall value being modeled by a linear model of the power losses of the internal combustion engine, and

[0029] -Determining a minimum engine speed setpoint from the minimum engine speed based on the positive gradient and the negative gradient.

[0030] Taking into account the vibration constraints, the overall value of the minimum speed of the internal combustion engine can be limited to the maximum authorized speed of the internal combustion engine for deceleration.

[0031] The following sub-steps may be performed to determine the overall minimum speed set point for the internal combustion engine:

[0032] the minimum speed difference of the internal combustion engine is determined to be equal to the difference between the minimum speed of the internal combustion engine and the overall minimum speed set point of the internal combustion engine,

[0033] - determining a Boolean status value as a function of a comparison between a minimum rotational speed of the internal combustion engine and a rotational speed threshold value for a minimum duration,

[0034] - determining the positive gradient according to a first predetermined table which receives as input a minimum speed difference of the internal combustion engine and according to a Boolean state value,

[0035] - determining the negative gradient according to a second predetermined table which receives as input the minimum speed difference of the internal combustion engine and according to the Boolean state value, and

[0036] - An overall minimum speed setpoint for the internal combustion engine is then determined based on the positive gradient, the negative gradient and the minimum speed of the internal combustion engine.

[0037] The minimum speed setpoint of the internal combustion engine can be determined as the minimum value between the overall minimum speed setpoint of the internal combustion engine and a maximum authorized speed of the internal combustion engine for deceleration.

[0038] Another object of the invention is a control system for a motor vehicle comprising an internal combustion engine connected to the wheels by a detachable connection and to the second electric machine by a connection also capable of being detached, 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 for the wheels, a sensor for measuring the charge capacity of the traction battery, a computing device and a memory configured to execute the control method described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other objects, features and advantages of the present invention will become apparent from the following description, which is given by way of non-limiting example only and is made with reference to the accompanying drawings, in which:

[0040] - Figure 1 The main stages of the control process according to the invention are shown. DETAILED DESCRIPTION

[0041] The purpose of the control process is to define the minimum engine speed in order to respond to the driver's wishes during the deceleration phases, while controlling the development and level of this speed in order to limit the impact on the NVH (noise and vibration harshness) performance.

[0042] The following variables were introduced:

[0043] - WHL_TQ_TG: Target torque required at the wheels based on the driver's request and third-party functions that have an influence on their development (cruise control, automated driving, etc.).

[0044] -WHEEL_EL_POW_TG: Power absorbed by the main motor

[0045] -EM_SND_EL_POW: electrical power to be consumed by the second electric machine

[0046] -BAT_TRAC_CHRG_POW: Traction battery charge capacity

[0047] -EM_SND_MECA_POW: Equivalent mechanical power to be generated by the second electric machine

[0048] -EM_SND_MOT_EFY_FAC: Average value of electrical efficiency of mechanical power

[0049] -ENG_MIN_SPD_RAW: Total value of the minimum speed of the internal combustion engine

[0050] -ENG_MIN_SPD_RAW_TG: Overall minimum speed set point for the internal combustion engine

[0051] -ENG_MAX_AUTH_SPD: Maximum permissible speed of the internal combustion engine for deceleration, which may depend on speed, joystick position or other human machine interface (HMI) that influences the level of vehicle deceleration.

[0052] ENG_MIN_SPD_TG: minimum speed setpoint of the internal combustion engine for the remaining arbitrations, which has an influence on the selection of the final engine speed of the internal combustion engine in the series hybrid state.

[0053] -ENG_MIN_SPD: Minimum speed of the internal combustion engine.

[0054] Next, the control method according to the invention allows:

[0055] - calculation of the electric power produced by the electric traction machine in response to the "driver's will" (the driver's will corresponds to the desire to accelerate the vehicle, which is converted by the computer into a power / torque setting at the wheels),

[0056] - calculating the electric power to be dissipated by the second electric machine connected to the internal combustion engine in order to dissipate the electric power that cannot be absorbed by the battery or the electrical accessories,

[0057] - Calculate the associated mechanical power, and

[0058] - Limiting the minimum speed of the internal combustion engine required to dissipate the above-mentioned mechanical power.

[0059] Control process such as Figure 1 shown.

[0060] In a first step 1, the power (expressed in Watts) absorbed by the main electric machine WHEL_EL_POW_TG is determined in order to meet the target torque WHL_TQ_TG required at the wheels. This function uses a second-order polynomial electric power consumption model calculation:

[0061] [Formula 1]

[0062]

[0063] in:

[0064] - RAT_EM: transmission ratio between the main electric traction machine and the wheels,

[0065] -P0 (in Watts): The static power consumption of the host, which is usually a function of speed and battery voltage.

[0066] P1 (expressed in W / Nm): The first-order coefficient of the host's power consumption, usually a function of the speed and battery voltage.

[0067] -P2 (expressed in W / Nm²): The second-order coefficient of the host's power consumption, usually a function of the speed and battery voltage.

[0068] In a second step 2, the power absorbed by the main electric machine WHEEL_EL_POW_TG is subtracted from the charge capacity of the traction battery BAT_TRAC_CHRG_POW in order to determine the electric power that the second electric machine must consume EM_SND_EL_POW in order to meet the target torque and the associated electric power required by the wheels:

[0069] [Formula 2]

[0070]

[0071] In a third step 3 , the electrical power EM_SND_EL_POW consumed by the second electrical machine is converted into an equivalent mechanical power EM_SND_MECA_POW produced by the secondary electrical machine.

[0072] [Formula 3]

[0073]

[0074] Among them: EM_SND_MOT_EFY_FAC is the average electrical efficiency value of mechanical power (parameterizable value).

[0075] In a fourth step 4 , an overall value ENG_MIN_SPD_RAW of the minimum speed of the internal combustion engine is determined, which is modeled by a linear model of the power losses of the internal combustion engine and is equal to the equivalent mechanical power EM_SND_MECA_POW produced by the second electric machine.

[0076] [Formula 4]

[0077]

[0078] in:

[0079] - P0_ENG_LOSS_POW (expressed in Watts): 0th order coefficient of the engine power loss, which may be a function of the engine coolant temperature.

[0080] - P1_ENG_LOSS_POW (expressed in W / RPM, RPM being "revolutions per minute"): first order coefficient of the hot engine loss power, which may be a function of the hot engine coolant temperature.

[0081] Since the total value of the minimum speed of the internal combustion engine ENG_MIN_SPD_RAW may vary greatly, it is combined with the maximum authorized speed of the internal combustion engine for deceleration ENG_MAX_AUTH_SPD taking into account the NVH vibration constraints. This limits the minimum speed of the internal combustion engine ENG_MIN_SPD to the maximum speed of the internal combustion engine that is allowed to decelerate ENG_MAX_AUTH_SPD.

[0082] [Formula 5]

[0083]

[0084] In a fifth step 5 , a minimum speed setpoint ENG_MIN_SPD_TG of the internal combustion engine is determined from the minimum speed ENG_MIN_SPD of the internal combustion engine.

[0085] During this phase, the dynamic evolution of the overall set point is managed by authorizing a maximum gradient in order to avoid speed jumps that would be detrimental to customer service from an acoustics and vibration (NVH) point of view, while guaranteeing high dynamics when required.

[0086] In order to determine the overall minimum speed setpoint ENG_MIN_SPD_RAW_TG of the internal combustion engine for braking, the following substeps are performed:

[0087] The minimum speed difference ENG_MIN_SPD_DIF of the internal combustion engine is determined to be equal to the difference between the minimum speed ENG_MIN_SPD of the internal combustion engine and the overall minimum speed setpoint ENG_MIN_SPD_RAW_TG of the internal combustion engine.

[0088] [Formula 6]

[0089]

[0090] - a Boolean state value is determined which assumes a first value if the minimum speed ENG_MIN_SPD of the internal combustion engine is less than the speed threshold value ENG_MIN_AL_THD for a minimum duration ENG_MIN_AL_DLY and a second value otherwise.

[0091] - The positive gradient ENG_MIN_SPD_POS_SLOPE_AUTH is determined according to a first predetermined table which receives as input the difference between the minimum speed ENG_MIN_SPD_DIF of the internal combustion engine and a Boolean state value. If the Boolean state value has assumed the second value, the positive gradient value is the gradient value of the table, and if the Boolean state value has assumed the first value, the positive gradient value is the parameterizable value which is usually parameterized with a very large positive value.

[0092] - The negative gradient ENG_MIN_SPD_NEG_SLOPE_AUTH is determined according to a second predetermined table which receives as input the difference between the minimum speed ENG_MIN_SPD_DIF of the internal combustion engine and the Boolean state value. If the Boolean state value has the second value, the negative gradient value is the gradient value of the table, and if the Boolean state value has the first value, the negative gradient value is the parameterizable value which is usually parameterized with a very large negative value.

[0093] - An overall minimum speed setpoint ENG_MIN_SPD_RAW_TG for the internal combustion engine is then determined as a function of the positive gradient ENG_MIN_SPD_POS_SLOPE_AUTH, the negative gradient ENG_MIN_SPD_NEG_SLOPE_AUTH and the minimum speed ENG_MIN_SPD of the internal combustion engine.

[0094] This logic makes it possible to return to the minimum speed ENG_MIN_SPD of the internal combustion engine at the end of the process, while controlling its evolution when higher values ​​than those normally obtained in the series hybrid state are not needed, in order to allow the internal combustion engine to return to a neutral speed for the customer from an acoustics and vibrations NVH point of view.

[0095] Then, in a sixth step 6, the overall minimum speed setpoint ENG_MIN_SPD_RAW_TG of the internal combustion engine is merged by the maximum authorized speed ENG_MAX_AUTH_SPD of the internal combustion engine for deceleration in order to comply with the NVH noise and vibration constraints. Then, the minimum speed setpoint ENG_MIN_SPD_TG of the internal combustion engine is determined to be equal to the minimum value between the overall minimum speed setpoint ENG_MIN_SPD_RAW_TG of the internal combustion engine and the maximum authorized speed ENG_MAX_AUTH_SPD of the internal combustion engine for deceleration.

[0096] A minimum target speed for the internal combustion engine has been developed to be able to meet the target torque required to the wheels during deceleration at low battery charging potential, while controlling associated NVH issues to ensure vehicle performance.

Claims

1. A control method for a motor vehicle, the motor vehicle comprising an internal combustion engine, a first electric machine and a second electric machine, the internal combustion engine being connected to the wheels by a detachable connection and to the second electric machine by a connection also capable of being detached, the electric machine being electrically connected to a battery, the control method comprising the following steps: - determine the driver's torque request, - determining the power absorbed by the main electric machine to meet the target torque required by said wheels, the electric power consumed by the second electric machine to meet the target torque required by the wheels is determined by subtracting the power absorbed by the main electric machine from the charge capacity of the traction battery, - determining the equivalent mechanical power generated by the second electric machine according to the average electrical efficiency value of the electrical power and the mechanical power consumed by the second electric machine, - determining a total value for the minimum rotational speed of the internal combustion engine as a function of the equivalent mechanical power produced by the second electric machine, said total value being modelled by a linear model of the power losses of the internal combustion engine, and - determining a setpoint for the minimum speed of the internal combustion engine from the minimum speed of the internal combustion engine as a function of the positive gradient and the negative gradient.

2. The control method according to claim 1, wherein: Taking vibration constraints into account, the overall value of the minimum speed of the internal combustion engine is limited to the maximum authorized speed of the internal combustion engine for deceleration.

3. The control method according to claim 1 or 2, wherein: In order to determine the overall setpoint for the minimum rotational speed of the internal combustion engine, the following sub-steps are performed: the minimum speed difference of the internal combustion engine is determined to be equal to the difference between the minimum speed of the internal combustion engine and the overall minimum speed setpoint of the internal combustion engine, - determining a Boolean state value as a function of a comparison between a minimum rotational speed of the internal combustion engine and a rotational speed threshold value for a minimum duration, - determining the positive gradient according to a first predetermined table which receives as input the minimum speed difference of the internal combustion engine and according to the Boolean state value, - determining the negative gradient according to a second predetermined table receiving as input the minimum speed difference of the internal combustion engine and according to the Boolean state value, and - A global setpoint for the minimum speed of the internal combustion engine is then determined as a function of the positive gradient, the negative gradient and the minimum speed of the internal combustion engine.

4. The control method according to claim 3, wherein: The minimum speed setpoint of the internal combustion engine is determined as the minimum value between the overall minimum speed setpoint of the internal combustion engine and the maximum permissible speed of the internal combustion engine for deceleration.

5. A control system for a motor vehicle comprising an internal combustion engine, a first electric machine and a second electric machine, the internal combustion engine being connected to the wheels by a detachable connection and to the second electric machine by a connection also capable of being detached, 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 for the wheels, a sensor for measuring the charge capacity of the traction battery, a computing device and a memory configured to execute a control method according to any one of claims 1 to 4.

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