Method and System for Controlling a Hybrid Vehicle During Deceleration

Abstract

A method of controlling a hybrid vehicle equipped with a detachable combustion engine, comprising the following steps: determining the power absorbed by the main electric machine to meet the target torque required at the wheels; determining the power consumed 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; determining a gross value as a function of the power consumed by the second electric machine for the minimum rotational speed of the combustion engine; and determining a setpoint for the minimum rotational speed of the combustion engine from the minimum rotational speed of the combustion engine as a function of a positive gradient and a negative gradient.

Description

Technical Field

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

Background Art

[0002] A hybrid vehicle equipped with a transmission enabling operation in 100% electric mode includes at least one electromechanical machine known as an electric traction machine connected to the wheels, a combustion engine that can be disconnected from the wheels (without combustion or fuel injection) and turned off, and is defined as comprising. Patent Document 1 in the name of the present applicant describes such an architecture.

[0003] Operation in 100% electric mode involves disconnecting the combustion engine from the wheels, which means that most of the vehicle's kinetic energy can be recovered during vehicle deceleration. With the combustion engine not engaged, the combustion engine does not dissipate energy through its idling drive and resulting friction.

[0004] This mode of operation is preferred during deceleration for the associated energy savings and driving pleasure.

[0005] Such a 100% electric deceleration mode also enables "regenerative" braking. Furthermore, by coupling the combustion engine to the wheels and controlling the combustion engine without fuel injection, the vehicle can be braked by dissipating part of the energy. This type of braking is generally known as "engine braking" and is commonly used in combustion-engine vehicles.

[0006] However, during certain stages of vehicle operation, the battery may become unable to recover the vehicle's kinetic energy due to its charge level. In other words, regenerative braking becomes impossible when the battery is fully charged. And the vehicle then has only the braking provided by the dedicated braking system, which causes significant and thus undesirable driving inconveniences.

[0007] In other words, according to the prior art of such hybrid vehicles, when decelerating in all-electric mode when the battery is already fully charged, the engine brake ceases to function, and the only way to decelerate the vehicle is by mechanical action on the braking system (the driver's spontaneous depression of the brake pedal).

[0008] This type of problem can also occur when the battery temperature is too low or when its recharge capacity is limited due to a defect.

[0009] The solution to this problem known in the prior art based on an architecture using two electromechanical machines, more specifically as described in Patent Document 1, lies in selecting other specific states of the drive train, generally referred to as "series hybrids" and defined as the following modes. At least one first electromechanical machine known as the "traction electromechanical machine" is connected to the wheels, The second electromechanical machine is not connected to the wheels, The combustion engine is turned on, controlled in injection cut-off mode, and connected to the second electromechanical machine, The electric traction machine regenerates the vehicle's kinetic energy into electrical energy for the following purposes. The purposes are, Charging the battery with electrical energy, Supplying electrical energy to electrical loads via the power source, and Supplying electrical energy to the second electromechanical machine connected to the combustion engine.

[0010] The second electric machine is powered when injection is interrupted to rotate the combustion engine, thereby dissipating electrical energy as mechanical energy through the friction of the combustion engine. In this way, the energy that cannot be recovered by the battery or electrical accessories can be dissipated to ensure that the vehicle decelerates by regenerative braking.

[0011] Since the energy consumed by the electric machine can increase or decrease according to the capacity of the battery that recovers energy and the driver's intention, in order to consume only the necessary energy, it is necessary to adapt the operating points of the combustion engine and the second electric machine. Since this operating point is limited with respect to the rotational speed, the combustion engine can only generate its losses, and it is necessary to calculate the minimum rotational speed to meet the desired deceleration requirements of the vehicle.

[0012] When calculating the rotational speed of the combustion engine while controlling the related noise, vibration, and harshness (NVH), technical problems to be solved remain.

[0013] The prior art includes Patent Document 2, which describes calculating the target speed and its trajectory of a hybrid vehicle in which a combustion engine and an electric machine are connected to wheels as a function of a desired recharge level.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Summary of the Invention

[0015] The present invention relates to a control method for an automobile including a combustion engine, a first electric machine, and a second electric machine, wherein the combustion engine is connected to wheels by a separable connection and to the second electric machine by a disconnectable connection, the first and second electric machines are electrically connected to a battery, and the control method includes the following: determining a torque requirement of a driver; determining power absorbed by a main electric machine to satisfy a target torque required at the wheels; determining power that must be consumed by the second electric machine to satisfy the target torque required at the wheels by subtracting the power absorbed by the main electric machine from a charge capacity of a traction battery; determining an equivalent mechanical force generated by the second electric machine as a function of the power consumed by the second electric machine and an average electrical efficiency value from the mechanical force; determining a gross value for a minimum rotational speed of the combustion engine modeled by a linear model of power losses of the combustion engine as a function of the equivalent mechanical force generated by the second electric machine; determining a minimum engine speed setpoint from the minimum engine speed as a function of a positive gradient and a negative gradient.

[0016] The gross value of the minimum rotational speed of the combustion engine may be limited to a maximum allowable rotational speed of the combustion engine for deceleration in order to consider vibration constraints.

[0017] To determine a gross minimum rotational speed setpoint of the combustion engine, the following: determining a differential value of the minimum rotational speed of the combustion engine as equal to a difference between the minimum rotational speed of the combustion engine and the gross minimum rotational speed setpoint of the combustion engine; determining a boolean state value as a function of a comparison between the minimum rotational speed of the combustion engine and a rotational speed threshold for a minimum duration; A sub-step in which a positive gradient is determined as a function of a first predetermined table that receives the minimum rotational speed derivative value of the combustion engine as an input and as a function of the boolean state value, A sub-step in which a negative gradient is determined as a function of a second predetermined table that receives the minimum rotational speed derivative value of the combustion engine as an input and as a function of the boolean state value, A sub-step in which the gross minimum rotational speed setpoint of the combustion engine is then determined as a function of the positive gradient, the negative gradient, and the minimum rotational speed of the combustion engine can be executed.

[0018] The minimum rotational speed setpoint of the combustion engine can be determined as the minimum value between the gross minimum rotational speed setpoint of the combustion engine for deceleration and the maximum allowable rotational speed of the combustion engine.

[0019] Another object of the present invention is a control system for an automobile including a combustion engine, a first electric machine, and a second electric machine, wherein the combustion engine is connected to wheels by a detachable connection and is connected to the second electric machine by a detachable connection, the first and second electric machines are electrically connected to a battery, and the control system includes a sensor for detecting a target torque required at the wheels, a sensor for detecting a charge capacity of a traction battery, and computing means and a memory configured to execute the control method described above.

[0020] Other objects, features, and advantageous effects of the present invention should become apparent from the following description, which is given merely as a non-limiting example and is made with reference to the accompanying drawings.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] The purpose of the control process is to define the minimum engine speed in order to respond to the driver's intention during the deceleration phase, while controlling the transition and level of that speed in order to limit the impact on NVH (noise, vibration, harshness) performance.

[0023] The following variables are introduced. WHL_TQ_TG: The target torque required at the wheels, depending on the driver's request and third-party functions (such as cruise control, autonomous driving, etc.) that affect the generation of the target torque. WHEEL_EL_POW_TG: The power absorbed by the main electric machine EM_SND_EL_POW: The power consumed by the second electric machine BAT_TRAC_CHRG_POW: The traction battery charge capacity EM_SND_MECA_POW: The equivalent mechanical force generated by the second electric machine EM_SND_MOT_EFY_FAC: The average value of the electrical efficiency from the mechanical force ENG_MIN_SPD_RAW: The gross value of the minimum speed of the combustion engine ENG_MIN_SPD_RAW_TG: The setpoint of the gross minimum speed of the combustion engine ENG_MAX_AUTH_SPD: The maximum allowable speed of the combustion engine for deceleration, which may depend on the speed, lever position, or other HMIs (human machine interfaces) that affect the level of vehicle deceleration. ENG_MIN_SPD_TG: The setpoint of the minimum speed of the combustion engine for the remaining arbitration that affects the selection of the final engine speed of the combustion engine in the series hybrid state ENG_MIN_SPD: The minimum speed of the combustion engine

[0024] The control method according to the present invention is, successively: Calculating the power generated by the electric traction machine according to the "driver's intention" (the driver's intention corresponds to a request for vehicle acceleration, which is converted by a computer into a power / torque setting at the wheels), Calculating the power to be dissipated by a second electric machine connected to the combustion engine in order to dissipate the power not absorbable by the battery or the electrical accessories, calculating the associated mechanical force, and defining the minimum rotational speed of the combustion engine necessary to dissipate the said mechanical force are made possible. The control process is shown in Figure 1.

[0025] In a first step 1, the power WHEEL_EL_POW_TG (expressed in watts) absorbed by the main electric machine in order to supply the target torque WHL_TQ_TG required at the wheels is determined. This function is calculated using a quadratic polynomial model of the electricity consumption.

[0026] [Equation 1] WHEEL_EL_POW_TG = P0 + P1 * WHL_TQ_TG * RAT_EM + P2 * (WHL_TQ_TG * RAT_EM) 2 where RAT_EM: the gear ratio between the main electric traction machine and the wheels, P0 (expressed in watts): the static losses of the main machine, generally a function of the speed and the battery voltage, P1 (expressed in W / Nm): the first order coefficient of the power consumption of the main machine, generally a function of the rotational speed and the battery voltage, P2 (expressed in W / Nm 2 ): the second order coefficient of the electricity consumption of the main machine, generally a function of the rotational speed and the battery voltage.

[0027] In a second step 2, the power WHEEL_EL_POW_TG absorbed by the main electric machine is subtracted from the charging capacity BAT_TRAC_CHRG_POW of the traction battery in order to determine the power EM_SND_EL_POW that must be consumed by the second electric machine in order to supply the target torque required at the wheels and the associated power.

[0028] [Equation 2] EM_SND_EL_POW = BAT_TRAC_CHRG_POW - WHEEL_EL_POW_TG

[0029] In the third step 3, the electric power EM_SND_EL_POW consumed by the second electromechanical machine is converted into the equivalent mechanical power EM_SND_MECA_POW generated by the second electromechanical machine.

[0030] [Equation 3] EM_SND_MECA_POW = EM_SND_EL_POW / EM_SND_MOT_EFY_FAC However, EM_SND_MOT_EFY_FAC: Average electrical efficiency value from mechanical force (parameterizable value).

[0031] In the fourth step 4, the gross value ENG_MIN_SPD_RAW of the minimum rotational speed of the combustion engine modeled by the linear model of the power loss of the combustion engine is determined as being equal to the equivalent mechanical power EM_SND_MECA_POW generated by the second electromechanical machine.

[0032] [Equation 4] ENG_MIN_SPD_RAW = (EM_SND_MECA_POW - P0_ENG_LOSS_POW) / P1_ENG_LOSS_POW However, P0_ENG_LOSS_POW (expressed in watts): Zero - order coefficient of the loss power of the combustion engine, and this coefficient can be a function of the combustion engine refrigerant temperature. P1_ENG_LOSS_POW (expressed in W / RPM, where RPM is "revolutions per minute"): First - order coefficient of the loss power of the heat engine, and this can be a function of the heat engine refrigerant temperature.

[0033] The gross value of the minimum rotational speed of the combustion engine, ENG_MIN_SPD_RAW, can vary significantly. Therefore, it is integrated by the maximum permitted rotational speed of the combustion engine during deceleration, ENG_MAX_AUTH_SPD, in order to consider NVH vibration constraints. As a result, the minimum rotational speed of the combustion engine, ENG_MIN_SPD, is limited by the maximum permitted rotational speed of the combustion engine for deceleration, ENG_MAX_AUTH_SPD.

[0034] [Equation 5] ENG_MIN_SPD = MIN(ENG_MIN_SPD_RAW; ENG_MAX_AUTH_SPD)

[0035] In the fifth step 5, the minimum rotational speed setpoint of the combustion engine, ENG_MIN_SPD_TG, is determined from the minimum rotational speed of the combustion engine, ENG_MIN_SPD.

[0036] During this stage, the dynamic transition of the gross setpoint is managed by allowing a maximum gradient so as not to cause jumps in rotational speed that are undesirable for customer service from an acoustic and vibration (NVH) perspective while ensuring a high operating state as required.

[0037] To determine the gross minimum rotational speed setpoint of the combustion engine for braking, ENG_MIN_SPD_RAW_TG, the following sub-steps are performed: The differential value of the minimum rotational speed of the combustion engine, ENG_MIN_SPD_DIF, is determined to be equal to the difference between the minimum rotational speed of the combustion engine, ENG_MIN_SPD, and the gross minimum rotational speed setpoint of the combustion engine, ENG_MIN_SPD_RAW_TG.

[0038] [Equation 6] ENG_MIN_SPD_DIF = ENG_MIN_SPD_RAW_TG - ENG_MIN_SPD

[0039] The Boolean state value is determined. When the minimum rotational speed ENG_MIN_SPD of the combustion engine is less than the rotational speed threshold ENG_MIN_AL_THD for the minimum continuous period ENG_MIN_AL_DLY, it takes the first value; in other cases, it takes the second value.

[0040] The positive gradient ENG_MIN_SPD_POS_SLOPE_AUTH is determined as a function of a first predetermined table that receives the differential value ENG_MIN_SPD_DIF of the minimum rotational speed of the combustion engine as input and the above Boolean state value. The positive gradient value becomes that of the table when the Boolean state value takes the second value, and becomes a parameterizable value when the Boolean state value takes the first value. This parameterizable value is usually parameterized with a very large positive value.

[0041] The negative gradient ENG_MIN_SPD_NEG_SLOPE_AUTH is determined as a function of a second predetermined table that receives the differential value ENG_MIN_SPD_DIF of the minimum rotational speed of the combustion engine as input and the above Boolean state value. The negative gradient value becomes that of the table when the Boolean state value takes the second value, and becomes a parameterizable value when the Boolean state value takes the first value. This parameterizable value is usually parameterized with a very large negative value.

[0042] Thereafter, the gross minimum rotational speed setpoint ENG_MIN_SPD_RAW_TG of the combustion engine is 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 rotational speed ENG_MIN_SPD of the combustion engine.

[0043] This logic enables returning to the minimum rotational speed ENG_MIN_SPD of the combustion engine at the end of the process. On the other hand, when a value higher than that usually obtained in the serial hybrid state is not required, it controls the transition of the minimum rotational speed to enable the combustion engine to return to an intermediate rotational speed from the perspective of acoustic and vibration NVH for the customer.

[0044] Thereafter, in a sixth step 6, the gross minimum engine speed setpoint ENG_MIN_SPD_RAW_TG of the combustion engine is integrated by the maximum allowable engine speed ENG_MAX_AUTH_SPD of the combustion engine for deceleration so as to comply with the NVH noise and vibration constraints. Thereafter, the minimum engine speed setpoint ENG_MIN_SPD_TG of the combustion engine is determined to be equal to the minimum value between the gross minimum engine speed setpoint ENG_MIN_SPD_RAW_TG of the combustion engine and the maximum allowable engine speed ENG_MAX_AUTH_SPD of the combustion engine for deceleration.

[0045] The minimum target engine speed for the combustion engine transitions such that the target torque required at the wheels during deceleration at a low battery recharge potential can be satisfied, while at the same time controlling the associated NVH problems to ensure the performance of the vehicle.

Claims

1. A method for controlling a motor vehicle comprising a combustion engine, a first electrical machine, and a second electrical machine, wherein the combustion engine is connected to a wheel by a disconnectable connection and to the second electrical machine by a disconnectable connection, and the first and second electrical machines are electrically connected to a battery, the method comprising the following steps: Determining a torque requirement of a driver; Determining power absorbed by a main electrical machine to meet a target torque required at the wheel; Determining power consumed by the second electrical machine to meet the target torque required at the wheel by subtracting the power absorbed by the main electrical machine from a charge capacity of a traction battery; Determining an equivalent mechanical force generated by the second electrical machine as a function of the power consumed by the second electrical machine and an average electrical efficiency value from the equivalent mechanical force; Determining a gross value for a minimum rotational speed of the combustion engine modeled by a linear model of power losses of the combustion engine as a function of the equivalent mechanical force generated by the second electrical machine; Determining a setpoint for the minimum rotational speed of the combustion engine from the minimum rotational speed of the combustion engine as a function of a positive gradient and a negative gradient; A control method comprising the above steps.

2. The control method according to claim 1, wherein the gross value of the minimum rotational speed of the combustion engine is limited to a maximum allowable rotational speed of the combustion engine for deceleration in order to take into account vibration constraints.

3. In order to determine a gross setpoint for the minimum rotational speed of the combustion engine, the following steps are included: A sub-step of determining that a differential value of the minimum rotational speed of the combustion engine is equal to a difference between the minimum rotational speed of the combustion engine and a gross minimum rotational speed setpoint of the combustion engine; A sub-step of determining a boolean state value as a function of a comparison between the minimum rotational speed of the combustion engine and a rotational speed threshold for a minimum duration; A sub-step of determining a positive gradient as a function of a first predetermined table receiving the differential value of the minimum rotational speed of the combustion engine as an input and as a function of the boolean state value; A sub-step of determining a negative gradient as a function of a second predetermined table receiving the differential value of the minimum rotational speed of the combustion engine as an input and as a function of the boolean state value; The sub-step in which the gross setpoint for the minimum rotational speed of the combustion engine is subsequently determined as a function of the positive gradient, the negative gradient, and the minimum rotational speed of the combustion engine is executed, the control method according to claim 1 or 2.

4. The control method according to claim 3, wherein the minimum rotational speed setpoint of the combustion engine is determined as the minimum value between the gross minimum rotational speed setpoint of the combustion engine for deceleration and the maximum allowable rotational speed of the combustion engine.

5. A control system for an automobile comprising a combustion engine, a first electric machine, and a second electric machine, wherein the combustion engine is connected to wheels by a disconnectable connection and is connected to the second electric machine by a connection that can be disconnected, and the first and second electric machines are electrically connected to a battery. A control system comprising a sensor for detecting a target torque required at the wheels, a sensor for detecting the charge capacity of a traction battery, and computing means and a memory configured to execute the control method according to any one of claims 1 to 4.

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