HYBRID ELECTRIC VEHICLE AND METHOD FOR CONTROLLING REGENERATIVE BRAKING THEREFON

Abstract

A hybrid electric vehicle capable of more efficient regenerative braking and a control method for regenerative braking are provided.A method for controlling regenerative braking of a hybrid electric vehicle may comprise: determining, upon the occurrence of a braking request, the state of an internal combustion engine clutch (130), which is configured to selectively connect a first electric motor (120), which is directly connected to an internal combustion engine (110), and a second electric motor (140), which is directly connected to an input end of a transmission (150); determining, when the internal combustion engine clutch (130) is in an open state, whether the internal combustion engine clutch (130) should be engaged or not in order to perform additional regenerative braking with the first electric motor (120); and performing regenerative braking based on whether the internal combustion engine clutch (130) should be engaged or not.

Description

Technical field

[0001] The present disclosure and invention relates to a hybrid electric vehicle capable of more efficient regenerative braking and relates to a control method for regenerative braking therefor. background

[0002] Recently, with growing environmental awareness, the demand for environmentally friendly vehicles equipped with electric motors as a power source has increased. Environmentally friendly vehicles are also referred to as electrified vehicles and include, as typical examples, hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0003] A hybrid electric vehicle generally refers to a vehicle that utilizes two types of power sources, such as an internal combustion engine and an electric motor. This type of hybrid electric vehicle offers excellent fuel efficiency and performance, and compared to vehicles equipped solely with internal combustion engines, it is advantageous in reducing exhaust emissions, which is why active development efforts are underway in this area.

[0004] When braking, the hybrid electric vehicle (HEV) is able to convert the vehicle's kinetic energy into electrical energy by operating the electric motor as a generator, in addition to the existing hydraulic friction brakes. This type of braking is called "regenerative braking" (or also "recuperation braking" or "recuperation"). The hybrid electric vehicle performs regenerative braking to maximize the amount of braking power and thus increase fuel efficiency, and the maximum amount of regenerative braking is determined by the maximum power output of the electric motor and the battery's state of charge (SOC).In general hybrid electric vehicles, however, even if two or more electric motors are present, regenerative braking is controlled based on one drive electric motor, and the use of the remaining electric motors to improve the efficiency of regenerative braking is not considered.

[0005] The foregoing description in the background section serves only to provide an understanding of the background of the present disclosure and is not intended to imply that the foregoing description in the background section falls within the related prior art as already known to those skilled in the art. Brief explanation

[0006] The present disclosure relates to a hybrid electric vehicle capable of more efficient regenerative braking and to a control method for regenerative braking therefor.

[0007] In particular, the present disclosure is intended to provide a hybrid electric vehicle capable of more efficiently performing regenerative braking using different electric motors, and to provide a control method for regenerative braking.

[0008] The technical objective of an embodiment of the present disclosure is not limited to the technical objectives mentioned above. Further technical objectives not mentioned should be clearly understood by those skilled in the art to which the present disclosure belongs, based on the following description.

[0009] According to one embodiment of the present disclosure, a method for controlling regenerative braking of a hybrid electric vehicle may comprise: determining, upon the occurrence of a braking demand, the state of an internal combustion engine clutch configured to selectively engage a first electric motor directly connected to an internal combustion engine and a second electric motor directly connected to an input end of a transmission. The method may further comprise: determining, when the internal combustion engine clutch is in an open state, whether the internal combustion engine clutch should be engaged (e.g., coupled / engaged) or not, in order to perform additional regenerative braking with the first electric motor. The method may further comprise: performing regenerative braking based on whether the internal combustion engine clutch should be engaged or not.

[0010] According to one embodiment, determining whether the internal combustion engine clutch should be engaged or not can include: Determining predetermined internal combustion engine clutch engagement conditions.

[0011] According to one embodiment, the specified combustion engine clutch engagement conditions can include a drive load condition, according to which energy recovery is possible or not, and a battery charge level.

[0012] According to one embodiment, the specified combustion engine clutch engagement conditions can include a combustion engine stall prevention condition that depends on the combustion engine speed when the combustion engine clutch is engaged. The specified combustion engine clutch engagement conditions can further include a regenerative braking premature termination prevention condition that depends on the vehicle speed.

[0013] According to one embodiment, the specified combustion engine clutch engagement conditions can include a residual torque condition for a residual torque that can be generated by the additional regenerative braking of the first electric motor, within a regenerative braking permit value according to the braking requirement. The specified combustion engine clutch engagement conditions can further include a charging power limit condition according to a charging value (e.g., charging power and / or charging energy quantity) of the second electric motor during the additional regenerative braking and a charging power limit of a battery.

[0014] According to one embodiment, the specified combustion engine clutch engagement conditions further include, for example, a consumption energy condition according to a predicted power of the first electric motor during the additional regenerative braking and an engagement consumption power for speed synchronization of the combustion engine and the second electric motor.

[0015] According to one embodiment, the method may further comprise: determining the predicted power as a minimum value of (e.g., from / below) a value obtained by subtracting the charge value of the second electric motor from the battery's charge power limit; a value obtained by multiplying a value obtained by subtracting a torque of the second electric motor and a friction torque of the internal combustion engine from the regenerative braking allowance value according to the braking requirement by the speed of the second electric motor; and a charge power limit of the first electric motor. The method may further comprise: predetermining a value of the regeneration power consumption using a speed difference between the internal combustion engine and the second electric motor as a factor.

[0016] According to one embodiment, the specified combustion engine clutch engagement conditions can further include a consumption energy condition according to a predicted charging energy of the first electric motor during the additional regenerative braking and an engagement consumption energy for the speed synchronization of the combustion engine and the second electric motor.

[0017] According to one embodiment, the method may further include: Performing, if all specified combustion engine clutch engagement conditions are met, a control to engage the combustion engine clutch and to perform regenerative braking using both the first and second electric motors.

[0018] According to one embodiment, the control procedure can include: controlling the charging power of the first electric motor to a value obtained by subtracting the charging power of the second electric motor from a battery charging power limit. The control procedure can further include: controlling the torque of the first electric motor to a value obtained by subtracting the torque of the second electric motor and the friction torque of the internal combustion engine from a regenerative braking allowance value as specified in the braking requirement.

[0019] Furthermore, a computer-readable recording medium according to an embodiment of the present disclosure can store a program for executing the above-described method of controlling the regenerative braking of a hybrid electric vehicle.

[0020] Furthermore, according to a further embodiment of the present disclosure, a hybrid electric vehicle may comprise: an internal combustion engine, a first electric motor directly connected to the internal combustion engine, an internal combustion engine clutch, one end of which is connected to the first electric motor, a second electric motor connected to the other end of the internal combustion engine clutch and configured to be selectively connected to the first electric motor via the internal combustion engine clutch, a transmission with an input end directly connected to the second electric motor, and a control device. The control device is configured to determine the state of an internal combustion engine clutch when a braking request occurs.The control unit is further configured to determine, when the combustion engine clutch is in an open state, whether the combustion engine clutch should be engaged to perform additional regenerative braking with the first electric motor, or not. The control unit is further configured to perform regenerative braking based on this determination of whether the combustion engine clutch should be engaged or not.

[0021] According to one embodiment, the control device can further be configured to determine predetermined internal combustion engine clutch engagement conditions in order to determine whether the internal combustion engine clutch should be engaged or not.

[0022] According to one embodiment, the combustion engine clutch engagement conditions can include a drive load condition, according to which energy recovery is possible or not, and a battery charge level.

[0023] According to one embodiment, the internal combustion engine clutch engagement conditions can include an engine stall prevention condition that depends on the engine speed when the clutch is engaged. The internal combustion engine clutch engagement conditions can further include a regenerative braking premature termination prevention condition that depends on the vehicle speed.

[0024] According to one embodiment, the combustion engine clutch engagement conditions can include a residual torque condition for a residual torque that can be generated by the additional regenerative braking of the first electric motor, within a regenerative braking permit value according to the braking requirement. The combustion engine clutch engagement conditions can further include a charging power limit condition according to a charging value (e.g., charging power and / or charging energy quantity) of the second electric motor during the additional regenerative braking and a charging power limit of a battery.

[0025] According to one embodiment, the specified combustion engine clutch engagement conditions further include, for example, a consumption energy condition according to a predicted power of the first electric motor during the additional regenerative braking and an engagement consumption power for speed synchronization of the combustion engine and the second electric motor.

[0026] According to one embodiment, the control device can further be configured to determine the predicted power as a minimum value of (e.g., from / below) a value obtained by subtracting the charge value of the second electric motor from the battery's charge power limit, a value obtained by multiplying a value obtained by subtracting a torque of the second electric motor and a friction torque of the internal combustion engine from the regenerative braking allowance value according to the braking request by the speed of the second electric motor, and a charge power limit of the first electric motor. The control device can further be configured to predetermine a value of the regeneration power consumption using a speed difference between the internal combustion engine and the second electric motor as a factor.

[0027] According to one embodiment, the specified combustion engine clutch engagement conditions can further include a consumption energy condition according to a predicted charging energy of the first electric motor during the additional regenerative braking and an engagement consumption energy for the speed synchronization of the combustion engine and the second electric motor.

[0028] According to one embodiment, the control device can be configured, if all specified combustion engine clutch engagement conditions are met, to perform a control operation to engage the combustion engine clutch and to carry out regenerative braking using both the first and second electric motors.

[0029] According to one embodiment, the control device can further be configured to control the charging power of the first electric motor to a value obtained by subtracting the charging power of the second electric motor from a battery charging power limit. The control device can further be configured to control the torque of the first electric motor to a value obtained by subtracting the torque of the second electric motor and the friction torque of the internal combustion engine from a regenerative braking allowance value as specified in the braking requirement.

[0030] According to numerous embodiments of the present disclosure described above, more efficient regenerative braking is possible in the hybrid electric vehicle.

[0031] In particular, the present disclosure determines, by determining numerous conditions, whether regenerative braking with the first electric motor is to be carried out by actively engaging the combustion engine clutch when the combustion engine clutch is in an open state at the time of the braking request. Thus, additional energy recovery by the first electric motor is enabled on a situation-dependent basis.

[0032] Advantageous effects that can be obtained through this disclosure are not limited to those mentioned above. Further effects, not mentioned here, can be clearly understood from the following descriptions by those skilled in the art to which this disclosure belongs. Brief description of the drawings

[0033] The above and further aspects, properties and advantages of the present disclosure should become clearer from the following detailed description in conjunction with the accompanying drawings, wherein: Fig. Figure 1 shows an example of a powertrain configuration of a hybrid electric vehicle according to an embodiment of the present disclosure. Fig. Figure 2 shows an example of a control system configuration of a hybrid electric vehicle according to an embodiment of the present disclosure. Fig. Figure 3 shows an example in which a braking amount is distributed when a braking request is made, in a hybrid electric vehicle according to an embodiment of the present disclosure. Fig. Figure 4 is a flowchart which illustrates an example of performing regenerative braking in a hybrid electric vehicle according to an embodiment of the present disclosure. Fig. Figure 5 is a flowchart which illustrates an example of performing regenerative braking in a hybrid electric vehicle according to a further embodiment of the present disclosure.

[0034] It should be understood that the attached drawings are not necessarily to scale and represent a somewhat simplified depiction of various properties in order to illustrate the basic principles of this disclosure. The specific design features of this disclosure, including, for example, specific dimensions, orientations, positions, and shapes as disclosed herein, are (at least) partially determined by the respective intended application and usage environment.

[0035] Throughout the figures, the same reference symbols refer to the same or equivalent sections of the present revelation across several figures in the drawings. Detailed description

[0036] The embodiments explained herein are described in detail below with reference to the accompanying drawings, and identical or similar elements in the figures are designated with identical or similar reference numerals, thus avoiding duplicate descriptions. The terms "module" and "unit," used for the elements in the following descriptions, are employed throughout this disclosure for the sake of simplicity and, in themselves, have no distinct meanings or roles. Furthermore, a detailed description of the relevant known technology may be omitted when describing the embodiments disclosed herein if it would unnecessarily obscure the essence of the disclosure. It should also be understood that the accompanying drawings serve only to facilitate understanding of the embodiments presented herein.The technical idea of ​​the present disclosure is not limited to the accompanying drawings and includes all modifications, equivalents or alternatives which fall within the meaning and scope of the present disclosure.

[0037] Terms with ordinal numbers, such as "a first" and "a second," can be used to describe numerous elements, but the elements are not limited by these terms. The above terms are used merely to distinguish one element from other elements.

[0038] When an element is described as "connected" or "coupled / linked" to other elements, it should be understood that not only can the element be directly connected or coupled / linked to the other elements, but that another element may also be present in between. Conversely, when an element is described as "directly connected" or "directly coupled / linked" to another element, it should be assumed that no other element is present in between.

[0039] A singular expression can include a plural expression unless they are defined differently in a context.

[0040] The terms used here, such as "exhibit," "comprise," and "have," are intended to indicate the presence of the mentioned characteristics, numbers, steps, processes, elements, components, or combinations thereof. These terms are to be understood as not excluding the possible presence or addition of one or more further characteristics, numbers, steps, operations, elements, components, or combinations thereof.

[0041] Furthermore, a unit or control unit, such as that found in an electric motor control unit (MCU) and a hybrid control unit (HCU), is simply a commonly used term to describe a control device designed to manage a specific function of a vehicle. The unit or control unit, however, does not refer to a generic functional unit.For example, to control a function for which a control unit is responsible, each control unit may have a communication device configured for communication with a sensor or another control unit, a memory configured for storing an operating system, a logical instruction or input / output information, and at least one processor configured to perform a determination, calculation, decision or the like necessary for controlling the function in question.When a control device, module, component, apparatus, element, part, unit, or the like is described herein as pursuing a purpose or performing an operation, function, or the like, the control device, module, component, apparatus, element, part, unit, or the like shall be considered herein as "configured" to fulfill that purpose or to perform that operation or function. Each control device, module, component, apparatus, element, part, unit, and the like may separately constitute or be provided with a processor and memory, such as non-volatile, computer-readable medium, as part of the apparatus.

[0042] Before describing a control method for regenerative braking according to the embodiments of the present disclosure, a structure and control system of a hybrid electric vehicle applicable to the embodiments will first be explained.

[0043] Fig. Figure 1 represents an example of a powertrain configuration of a hybrid electric vehicle according to an embodiment of the present disclosure.

[0044] Fig. Figure 1 shows a powertrain of a hybrid electric vehicle which uses a parallel hybrid system with two electric motors 120 and 140 and an internal combustion engine clutch 130, which is installed between an internal combustion engine (ICE) 110 and a transmission 150. This parallel hybrid system is also referred to as a "transmission-mounted electric drive hybrid system" (TMED for short), since the electric motor 140 is permanently connected to the input of the transmission 150.

[0045] Of the two electric motors 120 and 140, a first electric motor 120 is arranged here between the internal combustion engine 110 and one end of the internal combustion engine clutch 130. An internal combustion engine shaft of the internal combustion engine 110 and a first electric motor cell of the first electric motor 120 are directly connected to each other and can rotate together at any time.

[0046] One end of a second electric motor shaft of a second electric motor 140 can be connected to the other end of the internal combustion engine clutch 130, and the other end of the second electric motor shaft can be connected to an input end (also e.g. the input side) of the gearbox 150.

[0047] The second electric motor 140 can have a higher output power than the first electric motor 120 and can therefore assume the role of a drive electric motor (also called a "driving electric motor" or "traction electric motor"). In addition, the first electric motor 120 can function as a starter motor (e.g., starter motor), which cranks the internal combustion engine 110 when it is started, can recover the rotational energy of the internal combustion engine 110 by generating power when the internal combustion engine is switched off, and can generate power using the power of the internal combustion engine 110 while the internal combustion engine 110 is running.

[0048] In a hybrid electric vehicle, which is equipped with the in Fig. As the vehicle is equipped with the powertrain shown in Figure 1, when the driver presses the accelerator pedal after starting the vehicle (e.g., Hybrid Electric Vehicle Ready (HEV Ready)), the second electric motor 140 is preferably driven using the power of a battery in the state where the internal combustion engine clutch 130 is open. Accordingly, the power of the second electric motor 140 is transmitted via the transmission 150 and an axle drive (FD) 160, causing the wheels to rotate (i.e., Electric Vehicle Mode (EV Mode)). If greater driving force is required while the vehicle is gradually accelerating, the first electric motor 120 can engage the internal combustion engine 110.

[0049] If, after the combustion engine 110 has been started, the difference in its rotational speed between the combustion engine 110 and the second electric motor 140 falls within a predetermined range, the combustion engine clutch 130 is engaged (e.g., engaged / engaged), so that the combustion engine 110 and the second electric motor 140 rotate together (i.e., transition from EV mode to HEV mode). Accordingly, the output power of the second electric motor 140 decreases and the output power of the combustion engine 110 increases through a torque mixing process (also known as a torque transfer process), so that the torque demanded by the driver is achieved.In HEV mode, the internal combustion engine 110 can cover most of the required torque, and the difference between the internal combustion engine torque and the required torque can be compensated for by at least one of the first electric motors 120 or the second electric motor 140. For example, if the internal combustion engine 110 outputs a higher torque than required, the first electric motor 120 or the second electric motor 140 can generate power corresponding to the excess internal combustion engine torque, taking into account the efficiency of the internal combustion engine 110. Conversely, if the internal combustion engine torque is lower than required, at least one of the first electric motors 120 or the second electric motor 140 can output torque corresponding to the deficiency.

[0050] When a predefined (or preset) combustion engine shutdown condition (e.g., a condition for switching off the combustion engine) is met, for example, when the vehicle decelerates, the combustion engine clutch 130 opens and the combustion engine 110 switches off (i.e., transition from HEV mode to EV mode). During deceleration, the battery is charged by the second electric motor 140 using the driving force of the wheels, a process known as "brake energy recovery" or "regenerative braking" (also "recuperation braking" or "recuperation"). If the combustion engine clutch 130 is engaged during deceleration, the battery can be further charged by regenerative braking of the first electric motor 120.

[0051] The 150 transmission can generally be an automatic transmission or a multi-disc clutch transmission, such as a dual-clutch transmission (DCT).

[0052] Fig. Figure 2 shows an example of a control system configuration of a hybrid electric vehicle according to an embodiment of the present disclosure.

[0053] With reference to Fig. 2 In a hybrid electric vehicle to which the embodiments of the present disclosure are applicable, the internal combustion engine 110 can be controlled by an internal combustion engine control unit 210, the torque of the first electric motor 120 and the second electric motor 140 can be controlled by an electric motor control unit (MCU) 220, and the internal combustion engine clutch 130 can be controlled by a clutch control unit 230. The internal combustion engine control unit 210 is also referred to herein as the “engine management system (EMS)”. In addition, the transmission 150 is controlled by a transmission control unit 250, and a hydraulic brake system 170 is controlled by a brake control unit 270.

[0054] The electric motor control unit 220 can control a gate drive unit with a control signal in the form of pulse width modulation (PWM) based on the motor angle, phase voltage, phase current, and required torque of each electric motor 120 or 140. The gate drive unit can then control an inverter, which drives each electric motor 120 or 140 accordingly. The electric motor control unit 220 can be used for each electric motor 120 or 140.

[0055] The individual control units are connected to a hybrid control unit (HCU) 240 as a higher-level control device, which controls the entire powertrain, including mode switching. This provides the hybrid control unit 240 with information required to control the combustion engine clutch when switching between driving modes and transmission stages, and / or with information required for combustion engine shutdown control under the hybrid control unit 240. An operating process is then carried out according to the control signal.

[0056] For example, the hybrid control unit 240 determines whether a switch between EV mode and HEV mode, or between charge depleting mode (CD mode) and charge sustaining mode (CS mode) (in the case of a plug-in hybrid electric vehicle (PHEV)), should be performed based on the vehicle's driving condition. To this end, the hybrid control unit 240 determines the opening time of the combustion engine clutch 130 and performs hydraulic control when the combustion engine clutch opens. Furthermore, the hybrid control unit 240 can determine the state of the combustion engine clutch 130 (engagement, slippage, open, etc.) and control the fuel injection stop time of the combustion engine 110.Furthermore, the hybrid control unit can transmit a torque command to the electric motor control unit 220 to control the torque of the first electric motor 120 for the combustion engine shutdown control and thus control the rotational energy recuperation of the electric motor. In addition, the hybrid control unit 240 can determine the states of the respective drive sources 110, 120, and 140 in order to fulfill the required torque (e.g., also called the required torque or target torque), determine the required drive forces, which are accordingly distributed among the respective drive sources 110, 120, and 140, and then transmit a torque command to the control units 210 and 220, which control the respective drive sources.

[0057] The brake control unit 270 can determine the total braking amount, which corresponds to a value from the brake pedal position sensor (BPS value), when a braking request (e.g., a driver request to brake) is received, for example, when the driver depresses the brake pedal, thus activating a brake pedal position sensor (BPS). Furthermore, the brake control unit 270 can determine a regenerative braking allowance (or regenerative braking approval value, regenerative braking allocation, etc. – e.g., a braking amount for which regenerative braking is permitted (i.e., allowed, authorized, released, etc.) – within the total braking amount) and transmit this to the hybrid control unit 240.Accordingly, the hybrid control unit 240 can control the electric motor control unit 220 according to the permitted value to execute regenerative braking, determine the execution amount, and transmit this to the brake control unit 270. The brake control unit 270 can then perform a control such that the remaining braking amount, excluding the regenerative braking execution amount from the total braking amount, is executed by the hydraulic brake device 170. A more detailed distribution of the braking amount is described below with reference to [reference to relevant section]. Fig. 3 described.

[0058] It should be clear to experts that the relationships between control units and the functions / areas of the control units described above are only examples and are not limited to their names. For example, the hybrid control unit 240 may be configured so that its functions are provided by one of the other control units, excluding the hybrid control unit 240, or the corresponding functions may be provided by two or more of the other control units for distribution.

[0059] It should be obvious to experts that the configurations described above are in the Fig. 1 and Fig. 2 are only examples of hybrid electric vehicles and that the hybrid electric vehicle applicable to the embodiments is not limited to them.

[0060] Next, with reference to Fig. 3 describes an example where the braking amount is distributed when a braking request is made.

[0061] With reference to Fig. In Figure 3, the horizontal axis of a graph represents time, and the vertical axis represents the wheel reference torque.

[0062] When the driver depresses the brake pedal (BPS ON), the brake control unit 270 can determine the total braking amount and establish a regenerative braking allow value within this range (i.e., within the total braking amount). The hybrid control unit 240 can control the electric motor control unit 220 within the regenerative braking allow value to perform regenerative braking by at least one of the currently available electric motors 120 or 140. The hybrid control unit 240 can transmit information about the regenerative braking execution amount measured by the electric motor control unit 220 to the brake control unit 270. The brake control unit 270 can then perform the control so that the torque, excluding the regenerative braking execution amount from the total braking amount, is applied by the hydraulic brake (i.e., the hydraulic braking amount). If a predetermined condition (e.g.,(Once a predetermined regenerative braking termination speed or less has been reached), regenerative braking is terminated and the vehicle can be brought to a complete stop by hydraulic braking.

[0063] The regenerative braking execution amount is the sum of the execution amount by the first electric motor (120) and the execution amount by the second electric motor (140). Assuming the hybrid electric vehicle's powertrain as described above with reference to... Fig. As described in Figure 1, the second electric motor 140 is permanently connected to the input end of the transmission 150, thus physically connected to the wheel. Therefore, it is able to participate in regenerative braking as long as the input and output ends (e.g., output side) of the transmission 150 are not disconnected. However, the first electric motor 120 is only physically connected to the wheel (the drive shaft) when the combustion engine clutch 130 is engaged, so its contribution to regenerative braking is limited. In other words, when the combustion engine clutch 130 is engaged, both the first electric motor 120 and the second electric motor 140 can each perform regenerative braking within the regenerative braking limit and thus execute a regenerative braking amount that exceeds the charging limit torque (e.g., the maximum generator torque) of the second electric motor 140.However, when the combustion engine clutch 130 is open, only the second electric motor 140 can perform regenerative braking. Consequently, with the combustion engine clutch 130 open, even if the regenerative braking allowance is sufficiently large, the actual amount of regenerative braking that can be performed is limited by the charging limit torque of the second electric motor 140.

[0064] Therefore, in one embodiment of the present disclosure, it is proposed that when a braking request is received, it is determined, based on numerous conditions, whether the combustion engine clutch 130 should be engaged (e.g., brought into engagement) or not, in order to cause the first electric motor 120 to contribute to regenerative braking. If the combustion engine clutch 130 is engaged, an additional amount of regenerative braking can be implemented by the first electric motor 120 in addition to the regenerative braking provided by the second electric motor 140. In this way, more energy is recovered during braking. Furthermore, since the combustion engine clutch 130 is engaged, rapid acceleration can be ensured if a re-acceleration request (e.g., a driver request to accelerate again) is received during braking.

[0065] However, if the combustion engine clutch 130 is already open when the braking request occurs, the participation of the first electric motor 120 in regenerative braking by engaging the combustion engine clutch 130 may not always contribute to improved efficiency. More precisely, in the open state of the combustion engine clutch 130, its engagement based on the start state (or starting state - ON / OFF) of the combustion engine 110 can be taken into account as follows. 1) When driving in EV mode

[0066] When the vehicle is operating in EV mode, the combustion engine 110 is switched off, resulting in an energy loss for starting (e.g., cranking) the combustion engine and fuel injection / ignition through the operation of the first electric motor 120 and through the speed control of the combustion engine 110 to meet an engagement condition of the combustion engine clutch 130 before the combustion engine clutch 130 is engaged (e.g., regulating the combustion engine speed to meet the engagement condition of the combustion engine clutch 130). 2) Idle control situation

[0067] Since the internal combustion engine 110 is started, starting (e.g., cranking) is not necessary, but there is an energy loss to control the speed of the internal combustion engine 110 to engage the internal combustion engine clutch 130.

[0068] Consequently, engaging the combustion engine clutch 130 causes energy losses both when the vehicle is operating in EV mode and when the combustion engine 110 is idling when a braking demand occurs. Therefore, to improve the efficiency of regenerative braking, the combustion engine clutch 130 should only be engaged if the energy recovered by the first electric motor 120 is expected to be equal to or greater than the loss.

[0069] Conditions considered when determining whether the internal combustion engine clutch 130 should engage according to an embodiment may include an energy recovery condition, an internal combustion engine stall prevention condition, a regenerative braking premature termination prevention condition, a regenerative residual torque condition, a battery charging power condition, and the like. For simplicity, the respective conditions considered when determining whether the internal combustion engine clutch 130 is engaged are hereinafter referred to as "internal combustion engine clutch engagement conditions." The internal combustion engine clutch engagement conditions are described in detail below.

[0070] Firstly, the energy-recoverable condition can include a drive load condition and a state-of-charge (SOC) condition.

[0071] The drive load condition (e.g., also driving load condition or driving resistance condition) can be fulfilled if the current drive load (LdLvl) is equal to or less than a predefined threshold drive load (LdLvITh) (i.e., LdLvl <_ LdLvITh). The current drive load (e.g., current driving load or current driving resistance) can be determined by the hybrid control unit 240 by summing at least one gradient load, an air resistance load, a rolling resistance load, or a trailer load. The method for determining the individual loads is generally known in the art, so a detailed description is omitted in this disclosure. Furthermore, the threshold drive load can be a value determined through testing for each type of hybrid electric vehicle.

[0072] The SOC condition can be met if the current SOC of the battery is equal to or less than a predetermined threshold SOC (SOCTh) (i.e., SOC ≤ SOCTh). This is because sufficient regenerative braking is only possible if the battery has a sufficient SOC value. The threshold SOC (SOCTh) could be a value determined by testing, taking into account the energy normally recovered through regenerative braking using both the first electric motor 120 and the second electric motor 140; however, this is just one example and not necessarily limited to this.

[0073] The engine stall prevention condition serves to prevent engine stalling during the synchronization of the rotational speeds between the two ends of the engine clutch 130 in order to engage the engine clutch 130. This stalling can occur when the engine speed 110 is synchronized with the speed of the second electric motor 140, even though the speed of the second electric motor 140 is too low. This engine stall prevention condition can include a second electric motor speed condition and a gear stage condition.

[0074] The second electric motor speed condition can be satisfied if the speed (Np2) of the second electric motor 140 is equal to or greater than a predetermined threshold electric motor speed (Np2Th) (i.e., Np2 ≥ Np2Th). The threshold electric motor speed (Np2Th) can be determined as a value obtained by adding a predetermined allowance (e.g., a safety allowance) to the revolutions per minute (RPM) at which the internal combustion engine 110 stalls, although this is just one example and not necessarily limited to it.

[0075] Furthermore, the gear stage condition can be met if the current gear stage (CurGr) is equal to or greater than a predefined threshold gear stage (GrTh) (i.e., CurGr ≥ GrTh). This is because, if the current gear stage (CurGr) is equal to or greater than the threshold gear stage (GrTh), a downshift according to the shift pattern will occur when the vehicle speed decreases due to braking, and thus the input speed of the transmission will also increase to 150 rpm. This prevents the combustion engine from stalling.Since the shift from second to first gear typically occurs shortly before the vehicle comes to a complete stop, limiting the gear stage can prevent the combustion engine from stalling due to a drop in speed after engagement or any feeling of incongruity due to the forced disengagement of the combustion engine clutch when the combustion engine clutch is engaged with the first electric motor 120 in a low gear such as second gear. Therefore, the threshold gear stage (GrTh) can be third gear or higher; this is just one example and not necessarily limited to this, and the threshold gear stage can be determined through testing depending on the vehicle type and the transmission specifications.

[0076] Next, the regenerative braking premature termination prevention condition may be met if the current vehicle speed (VehSpd) is equal to or greater than a predetermined threshold vehicle speed (SpdTh) (i.e., VehSpd ≥ SpdTh). This is because if the current vehicle speed is close to a predetermined regenerative braking termination speed, regenerative braking will terminate prematurely after the braking process begins, thus limiting the recoverable energy. The threshold vehicle speed (SpdTh) can be determined through testing that considers the regenerative braking termination speed.

[0077] The regenerative residual torque condition can be met if a value obtained by subtracting a charging limit torque (Tp2ca) of the second electric motor 140 from a regenerative braking permissible torque (i.e., regenerative braking allow value) (Tca) is greater than or equal to a predefined threshold torque (Tth) (i.e., Tca - Tp2ca ≥ Tth). This is because, even if the second electric motor 140 performs regenerative braking with the maximum possible regenerative (braking) amount in the current situation, the first electric motor 120 can only output the regenerative torque if a certain amount (e.g., a residual portion) of the regenerative braking allow value remains. The threshold torque (Tth) can also be a value determined through testing.

[0078] The battery charging power condition can be met if a value obtained by subtracting the charging power limit (Pp2cl) of the second electric motor 140 from the battery charging power limit (Pbcl), which is the maximum charging power the battery can accept, is greater than or equal to a predefined threshold power (Pth) (i.e., Pbcl - Pp2cl ≥ Pth). This is because, even if the second electric motor 140 performs regenerative braking with the maximum possible charging power in the current situation, the first electric motor 120 is only able to perform additional regenerative braking if a certain amount (e.g., a residual portion) of remaining available charging power for the battery is still present. The threshold torque (Tth) can also be a value determined through testing. The threshold power (Pth) can likewise be a value determined through testing.

[0079] If all the conditions described above are met, the hybrid control unit 240 can determine to engage the combustion engine clutch 130 in order to perform additional regenerative braking with the first electric motor 120. The hybrid control unit 240 can then perform the following determination to ascertain the operating point of the first electric motor 120 after the combustion engine clutch 130 has been engaged.

[0080] First, the charging power (Pp1) of the first electric motor 120 can be determined as a value obtained by subtracting the charging power (Pp2) of the second electric motor 140 from the charging power limit (Pbcl) of the battery (i.e., Pp1 = Pbcl - Pp2).

[0081] Additionally, a charging torque (Tp1) of the first electric motor 120 can be determined as a value obtained by subtracting the regenerative braking amount (Tp2) of the second electric motor 140 and a friction torque (Tfr) of the internal combustion engine 110 from the regenerative braking allowance value (Tca) (i.e., Tp1 = Tca - (Tp2 + Tfr)).

[0082] However, since the final charging torque of the first electric motor 120 may be limited by the charging power (Pp1), it may be a smaller value of the torque corresponding to the charging power (Pp1) and the speed and the braking torque (Tp1) determined from the regenerative braking allowance value (Tca).

[0083] The control process for regenerative braking according to the embodiment described above can be represented as a flowchart, as shown in Fig. 4 shown, depicted.

[0084] Fig. Figure 4 is a flowchart which illustrates an example of performing regenerative braking in a hybrid electric vehicle according to an embodiment of the present disclosure.

[0085] Referring to Fig. 4. If a braking request exists (“Yes” in S401), the brake control unit 270 can determine a braking amount (S402). The braking request can be “BPS On” indicated by the driver pressing the brake pedal or indicate a situation in which a braking request occurs within a driver assistance function (e.g., an Advanced Driver Assistance System – ADAS) or an autonomous driving function. Furthermore, the braking amount determined by the brake control unit 270 can include a total braking amount and a regenerative braking allowance value within the total braking amount. Information about the regenerative braking allowance value can be transmitted to the hybrid control unit 240.

[0086] If the combustion engine clutch 130 is in an engaged state at the time the braking request occurs (“Yes” in S403), the hybrid control unit 240 can perform a standard regenerative braking control (S410B). Here, the standard regenerative braking control specifies a type of control for regenerative braking: either to perform regenerative braking with the combustion engine clutch 130 engaged, or to disengage the combustion engine clutch 130 and perform regenerative braking without a control to actively engage the combustion engine clutch 130, which is in a disengaged state (i.e., open state), during regenerative braking. A condition for maintaining the engagement (e.g., engaged state) of the combustion engine clutch 130 can be met if a value, which is determined by adding a predetermined increment (e.g.,The torque obtained (a safety margin) to the charging limit torque (Tp2ca) of the second electric motor 140 is less than the lower of the torque values ​​according to the battery's charging power limit and the regenerative braking allowance value (permissible torque) (Tca) of the brake control unit 270. If the condition for maintaining the engagement of the combustion engine clutch 130 is met, the first electric motor 120 participates in regenerative braking together with the second electric motor 140. If the condition is not met, the combustion engine clutch 130 can be disengaged, and regenerative braking can be performed using only the second electric motor 140. If the standard regenerative braking control is performed in the state where the combustion engine clutch 130 is already disengaged, regenerative braking can be performed using only the second electric motor 140.

[0087] If the combustion engine clutch 130 is in a disengaged state at the time the brake request occurs (“No” in S403), the hybrid control unit 240 can determine whether specified (or preset) conditions, i.e. the combustion engine clutch engagement conditions, are met or not, in order to determine whether the combustion engine clutch should be engaged (e.g., coupled / engaged) or not, in order to additionally use the first electric motor 120 for regenerative braking (S404 to S407).

[0088] As described above, the internal combustion engine clutch engagement conditions can include an energy-recoverable condition (i.e., drive load condition and SOC condition, S404), an internal combustion engine stall prevention and regenerative braking premature termination prevention condition (i.e., internal combustion engine stall prevention condition and premature termination prevention condition, S405), a residual torque condition (S406), and a battery charging power condition (S407). Specific criteria for determining whether the respective conditions are met have already been described above, so redundant descriptions have been omitted.

[0089] If all conditions are met, the hybrid control unit 240 can engage the combustion engine clutch 130 and perform regenerative braking using both the first electric motor 120 and the second electric motor 140 (S410A). The operating point of the first electric motor 120 can be determined taking into account the charging power of the battery and the second electric motor 140, the regenerative braking allowance, the regenerative braking amount of the second electric motor 140, the friction torque of the combustion engine 110, and the like.

[0090] On the other hand, if at least one of the conditions is not met, the hybrid control unit 240 can perform standard regenerative braking (S410B).

[0091] Although in Fig. 4. The fact that the respective internal combustion engine clutch engagement conditions (S404 to S407) are determined sequentially is exemplary and not necessarily limited to this. For example, the order in which the respective internal combustion engine clutch engagement conditions are determined can be designed differently than in Fig. 4, and at least some conditions can be determined simultaneously and in parallel.

[0092] Furthermore, according to one embodiment of the present disclosure, the combustion engine clutch engagement conditions are designed to enable energy recovery through regenerative braking using the first electric motor 120. However, even if energy recovery as such is possible through regenerative braking using the first electric motor 120, energy is consumed for combustion engine speed synchronization and the like until the combustion engine clutch 130 is engaged.

[0093] Therefore, in a further embodiment of the present disclosure, a method is proposed in which a condition for the energy consumed to engage the internal combustion engine clutch 130 (hereinafter referred to for simplicity as the “consumption energy condition” - for example also “energy consumption condition”) is added to the internal combustion engine clutch engagement conditions.

[0094] If the energy recovered through additional regenerative braking by the first electric motor 120 is equal to or greater than the energy consumed during the speed synchronization process of the combustion engine 110 and the second electric motor 140, engaging the combustion engine clutch 130 can be advantageous from an efficiency standpoint. Therefore, the energy consumption condition can be met if the predicted charging energy that the first electric motor 120 is expected to generate during the additional regenerative braking is equal to or greater than the energy consumed during speed synchronization. This energy consumption condition can also be interpreted from the perspective of power (e.g., considering power (for example, over time) instead of energy).

[0095] In particular, the energy consumption condition, which improves the overall efficiency of regenerative braking by engaging the combustion engine clutch 130 and subsequently performing the additional regenerative braking by means of the first electric motor 120, can be met if the charging power of the first electric motor is equal to or greater than the power consumed (e.g. required) for engaging the combustion engine clutch 130.

[0096] To determine whether this consumption energy condition is met or not, it is necessary to determine the charging power (i.e., the expected charging power) that is expected to charge the battery by the first electric motor 120, which performs regenerative braking, assuming that the combustion engine clutch 130 is engaged.

[0097] The expected charging power of the first electric motor 120 can be determined as the smallest value of (e.g. from / below) i) the difference between the available charging power of the battery and the charging power of the second electric motor 120 (Pbcl - Pp2), ii) the charging power based on the chargeable torque of the first electric motor 120 using the regenerative braking allowance value, and iii) the charging power limit (Pp1cl) due to the temperature of the first electric motor 120.

[0098] The difference (Pbcl - Pp2) between the available charging power of the battery and the charging power of the second electric motor 120 is taken into account, since the combined charging power of the first electric motor 120 and the second electric motor 140 cannot exceed the charging power limit of the battery.

[0099] Additionally, ii) the charging power based on the chargeable torque of the first electric motor 120 can be a power value obtained by multiplying the value (Tca - (Tp2 + Tfr)), obtained by subtracting the regenerative braking torque (Tp2) of the second electric motor and the friction torque (Tfr) of the internal combustion engine from the regenerative braking permit value (Tca) transmitted by the brake control unit 270, by the rotational speed (Np2) of the second electric motor (i.e., ((Tca - (Tp2 + Tfr)) × Np2)).

[0100] In summary, the expected charging power (Pp1prd) of the first electric motor 120 can be achieved as follows. Pp1prd=Min{(Pbcl−Pp2),((Tca−(Tp2+Tfr))×Np2),Pp1cl}

[0101] Meanwhile, power indicates the amount of work per unit of time, which can be expressed as the amount of energy transferred per hour (i.e., P=dE / dt).

[0102] The energy consumed to control the speed of the internal combustion engine (hereinafter referred to for simplicity as "speed control energy") is a loss energy consumed to synchronize the speed of the internal combustion engine 110 with the speed of the second electric motor 140, and its amount can vary depending on the speed difference between the two power sources. The amount of speed control energy can be predetermined by tests or analytical methods according to the magnitude of the speed difference.

[0103] For example, if the energy loss value in a particular section is Eloss, if the expected charging power of the first electric motor 120 is Pp1prd, and if the reference time for which the first electric motor 120 is expected to continue (e.g., continuously perform) regenerative braking after the engagement of the combustion engine clutch 130 is Tthr, then the amount of expected energy recovery (Eprd) can be defined by the following relationship, assuming that the charging power of the first electric motor 120 is constant.

[0104] The expected energy recovery (Eprd) is the product of the expected charging power (Pp1prd) of the first electric motor and the reference time (Tthr), and its value must be greater than or equal to the value of the energy loss (Eloss). In summary, the equation "Pp1prd x Tthr ≥ Eloss" can be formulated, and dividing both sides of this equation by the reference time Tthr yields "Pp1prd ≥ Eloss / Tthr", allowing both sides to be converted into power units. Here, the energy loss (Eloss) is a function of the speed difference between the second electric motor 140 and the combustion engine 110. Assuming that it has a constant value for a given speed difference, and if the reference time (Tthr) is also predetermined as constant through testing, "Eloss / Tthr" can be expressed as a function of the (e.g.,depending on the) difference between the rotational speed (Np2) of the second electric motor 140 and the rotational speed (Neng) of the internal combustion engine 110 (i.e. Eloss / Tthr = fcn[Np2 - Neng]), which can be represented as a unit of power.

[0105] The function of the speed difference can be replaced by the engagement power consumption (Pth), which is a power calibration value that incorporates the speed difference as a factor. Ultimately, the energy consumption condition can be defined as follows. Pp1prd≥Pth[x:Np2−Neng]

[0106] In other words, if the expected charging power (Pp1prd) of the first electric motor, i.e., “Min{(Pbcl - Pp2), ((Tca - (Tp2 + Tfr)) × Np2), Pp1cl}”, is equal to or greater than the engagement power (Pth), which is a reference power that has the speed difference (Np2 - Neng) as a factor (e.g., as a function argument), then the consumption energy condition can be met.

[0107] The control method for regenerative braking, in which the energy consumption condition is added to the combustion engine clutch engagement conditions, can be represented in the form of a flowchart, which is shown in Fig. As shown in section 5, they will be organized.

[0108] Fig. Figure 5 is a flowchart which illustrates an example of performing regenerative braking in a hybrid electric vehicle according to a further embodiment of the present disclosure.

[0109] With reference to Fig. 5 are the processes from determining whether a braking request occurs or not (S401), to determining whether the battery charging power condition is met or not, which are described in Fig. 4 similar, so redundant descriptions of it have been omitted.

[0110] As described above, if a brake request exists (“Yes” in S401) and the combustion engine clutch 130 is in the disengaged state (“No” in S403), the hybrid control unit 240 can determine whether the respective combustion engine clutch engagement conditions are met or not. In contrast to the case in Fig. 4, the hybrid control unit 240 determines in the control process according to the in Fig. The flowchart shown in section 5 further indicates whether the consumption energy condition is met or not, as well as the internal combustion engine clutch engagement conditions (S408 and S409).

[0111] More precisely, the hybrid control unit 240 can determine whether the expected charging power (Pp1prd) of the first electric motor 120 is equal to or greater than a break-in consumption power (Pth) (S408), and if the expected charging power (Pp1prd) of the first electric motor 120 is equal to or greater than the break-in consumption power (Pth), the hybrid control unit 240 can determine that the consumption energy condition is met (“Yes” in S409).

[0112] When all the combustion engine clutch engagement conditions, including the energy consumption condition, are met, the hybrid control unit 240 can engage the combustion engine clutch 130 and perform regenerative braking using both the first electric motor 120 and the second electric motor 140. The operating procedure for reaching the operating point of the first electric motor 120 is as described above (S410A).

[0113] In the embodiments described above, when the combustion engine clutch 130 is engaged and regenerative braking is performed using both the first electric motor 120 and the second electric motor 140, the hybrid control unit 240, when the regenerative braking execution amount is transmitted to the brake control unit 270, can add the friction torque (Tfr) of the combustion engine to the actual electric motor execution amount (Tp1 + Tp2) and transmit this to the latter. In this case, the brake control unit 270 can exclude the friction torque (Tfr) of the combustion engine during hydraulic braking by means of the difference between the total braking amount and the regenerative braking execution amount.

[0114] According to the control method for regenerative braking of the embodiments described above, additional battery charging can be ensured by performing an additional regenerative braking of the first electric motor 120 by engaging the combustion engine clutch 130, thereby improving energy and / or fuel efficiency.

[0115] When the internal combustion engine clutch 130 is engaged, the frictional torque of the internal combustion engine 110 can be used as a braking force, so that the corresponding hydraulic braking amount can be reduced, thereby reducing the wear of brake pads and brake discs.

[0116] Since the engagement of the combustion engine clutch 130 is maintained, a rapid start-up can also be ensured if a re-acceleration request is received during braking.

[0117] The present disclosure, as described above, can be implemented as computer-readable code on a medium. Computer-readable medium includes all types of recording devices in which data is stored that can be read by a computer system. Examples of computer-readable medium may include a hard disk drive (HDD), a solid-state drive (SSD), a silicon disk drive (SDD), a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical storage device, and the like. Therefore, the above detailed description should not be interpreted restrictively, but rather considered in all aspects as exemplary.The scope of the present disclosure shall be determined by reasonable interpretation of the attached claims, and all variations and modifications within the equivalence range of the present disclosure shall fall within the scope of the present disclosure.

Claims

[1] Methods for controlling regenerative braking of a hybrid electric vehicle, comprising methods: Determine, when a braking request occurs, a state of an internal combustion engine clutch (130) which is configured to selectively connect a first electric motor (120) which is directly connected to an internal combustion engine (110) and a second electric motor (140) which is directly connected to an input end of a transmission (150), In response to the fact that the combustion engine clutch (130) is in an open state, determine whether the combustion engine clutch (130) should be engaged or not in order to perform additional regenerative braking with the first electric motor (120), and Performing regenerative braking based on whether the internal combustion engine clutch (130) needs to be engaged or not. [2] Method according to claim 1, wherein determining whether the internal combustion engine clutch (130) is to be engaged or not comprises: Determining whether predetermined internal combustion engine clutch engagement conditions are met or not. [3] Method according to claim 2, wherein the specified combustion engine clutch engagement conditions include a drive load condition according to which energy recovery is possible or not, and a state of charge of a battery. [4] Method according to claim 2 or 3, wherein the specified internal combustion engine clutch engagement conditions include: a combustion engine stall prevention condition according to the combustion engine speed when the combustion engine clutch (130) is engaged, and a regenerative braking premature termination prevention condition according to vehicle speed. [5] Method according to any one of claims 2 to 4, wherein the specified internal combustion engine clutch engagement conditions include: a residual torque condition for a residual torque which can be executed by the additional regenerative braking using the first electric motor (120), in a regenerative braking allow value according to the braking requirement, and a charging power limit condition according to a charging value of the second electric motor (140) during the additional regenerative braking and a charging power limit of a battery. [6] Method according to claim 5, wherein the specified combustion engine clutch engagement conditions further comprise a consumption energy condition according to a predicted power of the first electric motor (120) during the additional regenerative braking and an engagement consumption power for speed synchronization of the combustion engine (110) and the second electric motor (140). [7] Method according to claim 6, further comprising: Determining the predicted power as a minimum value of (i) a value obtained by subtracting the charge value of the second electric motor (140) from the battery's charge power limit, (ii) a value obtained by multiplying a value obtained by subtracting a torque of the second electric motor (140) and a friction torque of the internal combustion engine (110) from the regenerative braking allowable value (Tca) according to the braking requirement by the speed of the second electric motor (140), and (ii) a charge power limit of the first electric motor (120), and Predetermining a value of the inrush power consumption using a speed difference between the internal combustion engine (110) and the second electric motor (140) as a factor. [8] Method according to claim 5, 6 or 7, wherein the specified internal combustion engine clutch engagement conditions further include a consumption energy condition according to a predicted charging energy of the first electric motor (120) during the additional regenerative braking and an engagement consumption energy for the speed synchronization of the internal combustion engine (110) and the second electric motor (140). [9] Method according to any one of claims 2 to 8, further comprising: When all specified combustion engine clutch engagement conditions are met, a control is performed to engage the combustion engine clutch (130) and to perform regenerative braking using both the first electric motor (120) and the second electric motor (140). [10] Method according to claim 9, wherein the execution of the control comprises: Controlling the charging power of the first electric motor (120) to a value obtained by subtracting the charging power of the second electric motor (140) from a charging power limit of a battery, and Controlling a torque of the first electric motor (120) to a value obtained by subtracting a torque of the second electric motor (140) and a friction torque of the internal combustion engine (110) from a regenerative braking allowance value according to the braking requirement. [11] Hybrid electric vehicle, comprising: an internal combustion engine (110), a first electric motor (120) which is directly connected to the combustion engine (110), a combustion engine clutch (130) with a first end which is connected to the first electric motor (120), a second electric motor (140) which is connected to a second end of the combustion engine coupling (130) and is configured to be selectively connected to the first electric motor (120) via the combustion engine coupling (130), a gearbox (150) with an input end which is directly connected to the second electric motor (140), and a control device which is designed for this purpose to determine the state of the internal combustion engine clutch (130) in response to the occurrence of a braking request, when the combustion engine clutch (130) is in an open state, to determine whether the combustion engine clutch (130) needs to be engaged to perform additional regenerative braking using the first electric motor (120), or not. to control the execution of regenerative braking based on whether the internal combustion engine clutch (130) is to be engaged or not. [12] Hybrid electric vehicle according to claim 11, wherein the control device is further configured to determine whether predetermined combustion engine clutch engagement conditions for engaging the combustion engine clutch (130) are met or not. [13] Hybrid electric vehicle according to claim 12, wherein the specified combustion engine clutch engagement conditions include a drive load condition according to which energy recovery is possible or not, and a state of charge of a battery. [14] Hybrid electric vehicle according to claim 12 or 13, wherein the specified combustion engine clutch engagement conditions are: a combustion engine stall prevention condition according to the combustion engine speed when the combustion engine clutch (130) is engaged, and a regenerative braking premature termination prevention condition according to vehicle speed. [15] Hybrid electric vehicle according to one of claims 12 to 14, wherein the specified combustion engine clutch engagement conditions are: a residual torque condition for a residual torque which can be executed by the additional regenerative braking using the first electric motor (120), in a regenerative braking allow value according to the braking requirement, and a charging power limit condition according to a charging value of the second electric motor (140) during the additional regenerative braking and a charging power limit of a battery. [16] Hybrid electric vehicle according to claim 15, wherein the specified combustion engine clutch engagement conditions further comprise a consumption energy condition according to a predicted power of the first electric motor (120) during the additional regenerative braking and an engagement consumption power for speed synchronization of the combustion engine (110) and the second electric motor (140). [17] Hybrid electric vehicle according to claim 16, wherein the control device is further configured to: to determine the predicted power as a minimum value of (i) a value obtained by subtracting the charge value of the second electric motor (140) from the charge power limit of the battery, (ii) a value obtained by multiplying a value obtained by subtracting a torque of the second electric motor (140) and a friction torque of the internal combustion engine (110) from the regenerative braking allowable value (Tca) according to the braking requirement by the speed of the second electric motor (140), and (ii) a charge power limit of the first electric motor (120), and to predetermine a value of the regeneration power consumption using a speed difference between the internal combustion engine (110) and the second electric motor (140) as a factor. [18] Hybrid electric vehicle according to claim 15, 16 or 17, wherein the specified combustion engine clutch engagement conditions further include a consumption energy condition according to a predicted charging energy of the first electric motor (120) during the additional regenerative braking and an engagement consumption energy for the speed synchronization of the combustion engine (110) and the second electric motor (140). [19] Hybrid electric vehicle according to one of claims 12 to 18, wherein the control device is further configured to perform a control operation to engage the combustion engine clutch (130) and to perform regenerative braking using both the first electric motor (120) and the second electric motor (140) when all predetermined combustion engine clutch engagement conditions are met. [20] Hybrid electric vehicle according to claim 19, wherein the control device is further configured to: to control the charging power of the first electric motor (120) to a value obtained by subtracting the charging power of the second electric motor (140) from a charging power limit of a battery, and to control a torque of the first electric motor (120) to a value obtained by subtracting a torque of the second electric motor (140) and a friction torque of the internal combustion engine (110) from a regenerative braking allowance value according to the braking requirement.

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