System and method for controlling torque split of a hybrid electric vehicle

Abstract

A system for controlling the torque split of a hybrid electric vehicle having an electric motor (24) and an internal combustion engine (20) as drive sources, comprising: a driving information detector that detects the driving state of the vehicle and request information of the driver of the vehicle; a transmission control unit (TCU) (16) that requests a torque reduction when changing gears of the vehicle based on a signal from the driving information detector; a traction control system (TCS) (32) that requests torque reduction by outputting a split torque to prevent the vehicle's wheels from slipping; and a controller (11) that controls the torque split by dividing a requested amount of torque reduction between the internal combustion engine (20) and the electric motor (24) when it receives the torque reduction request from the TCU (16) or the TCS (32), wherein the controller (11) first reduces an assist torque of the electric motor (24) when the state of the electric motor (24) before the torque split is an assist state, maintains the charging torque of the electric motor (24) when the state of the electric motor (24) before the torque split is a charging state, and divides an additionally requested reduction proportionally to an available reduction range of the internal combustion engine (20) and an available reduction range of the electric motor (24), and wherein the controller (11) sets the available reduction range of the internal combustion engine (20) from the torque of the internal combustion engine (20) before the torque split to a torque 0 and the available reduction range of the electric motor (24) from a charging torque before the torque split to the charging limit value when the state of the electric motor (24) before the torque split is the charging state.

Description

BACKGROUND OF THE DISCLOSURE(a) Technical field

[0001] The present disclosure generally relates to a system and method for controlling torque split of a hybrid electric vehicle. More specifically, the present disclosure relates to a system and method for controlling torque split of a hybrid electric vehicle that, when torque split is requested, splits the requested amount of torque reduction taking into account the state of the electric motor and the ratio of an available reduction range. (b) Description of the related art

[0002] As is well known, a hybrid electric vehicle is powered by an internal combustion engine, whose torque is generated by the combustion of fuel, and an electric motor, whose torque is generated by an electric battery. The hybrid electric vehicle typically includes a hybrid control unit (HCU) for controlling the operation of an internal combustion engine of the hybrid electric vehicle, an engine control unit (ECU) for controlling the operation of an internal combustion engine, an electric motor control unit (MCU) for controlling the operation of the electric drive motor, a transmission control unit (TCU) for controlling the operation of the transmission, and a battery management system (BMS) for managing the condition of a battery.In addition, a traction control system (TCS), which is a safety system that prevents the drive wheels from spinning and improves driving stability by controlling the brakes and the combustion engine during starting and acceleration, can be installed in the hybrid electric vehicle.

[0003] The hybrid electric vehicle typically performs torque split control to distribute a requested amount of torque reduction between an internal combustion engine and an electric motor when the TCU or TCS requests torque reduction. Fig. Figure 1 is a graph illustrating, for example, a conventional method for controlling the torque split of a hybrid electric vehicle, in which the engine torque is first reduced and the electric motor torque is additionally reduced in the event of insufficient power. However, if a continuous torque reduction is requested, the battery's state of charge (SOC) may become depleted and the electric motor's performance may deteriorate.

[0004] Fig. Figure 2 is a graph of a conventional method for controlling the torque split of a hybrid electric vehicle, in which the electric motor torque is first reduced and the engine torque is additionally reduced in the case of insufficient power. However, the engine torque does not change even though torque split is requested, and excessive engine noise and a deterioration of noise, vibration, and harshness (NVH) characteristics may occur.

[0005] Furthermore, DE 10 2014 210 537 A1 discloses a method for operating a hybrid vehicle having an internal combustion engine and an electric machine, wherein a total wheel drive torque is composed of a wheel drive torque of the internal combustion engine and a wheel drive torque of the electric machine, wherein the electric machine can be operated in a motor operating mode, wherein the total wheel drive torque is increased by the wheel drive torque of the electric machine, orwherein the electric machine can be operated in a generator operating mode, wherein the total wheel drive torque is reduced by the wheel drive torque of the electric machine, wherein it is monitored whether a wheel drive torque-increasing safety measure or a wheel drive torque-reducing safety measure is to be carried out, wherein the electric machine is operated in such a way that the sum of the wheel drive torque of the electric machine and the wheel drive torque of the safety measure is constant when the electric machine is operated in the generator operating mode and the wheel drive torque-reducing safety measure is to be carried out, or when the electric machine is operated in the motor operating mode and the wheel drive torque-increasing safety measure is to be carried out.

[0006] Furthermore, DE 197 24 681 C2 discloses a device for controlling a hybrid drive system of a motor vehicle, which comprises an internal combustion engine driven by combustion of a fuel, an electric motor / generator and a transmission arranged between a vehicle drive wheel and the set consisting of the internal combustion engine and the electric motor / generator, the device comprising a torque reduction control device for reducing a transmission input torque during a transmission shift action under a certain torque reduction condition, characterized in that the torque reduction control device comprises: a first torque reduction device for reducing the transmission input torque by controlling the internal combustion engine, a second torque reduction device for reducing the transmission input torque by controlling the electric motor / generator,and a torque reduction mode selection device that enables the operation of at least the first or second torque reduction device to reduce the input torque depending on a specific selection condition, wherein the torque reduction mode selection device comprises an energy quantity determination device for determining whether the amount of electrical energy stored in an electrical storage device is above a specific threshold, and operates the second torque reduction device to control the electric motor / generator to reduce the input torque when the energy quantity determination device determines that the amount of electrical energy is above the specific threshold.

[0007] The above statements in this background section serve only to better understand the background of the disclosure and may therefore contain information that is not part of the prior art already known to the average person skilled in the art in this country. OVERVIEW OF REVELATION

[0008] The present disclosure has been developed in an effort to provide a system and method for controlling torque split of a hybrid electric vehicle that offers the advantages of ensuring the SOC of a battery and NVH characteristics by apportioning a requested amount of torque derating depending on the state of the electric motor and the ratio of the available derating range when torque split is requested.

[0009] Embodiments of the present disclosure provide a system for controlling the torque split of a hybrid electric vehicle having an electric motor and an internal combustion engine as drive sources, including: a driving information detector that detects the driving state of the vehicle and request information from the driver of the vehicle; a transmission control unit (TCU) that requests torque reduction when the vehicle is shifting gears based on a signal from the driving information detector; a traction control system (TCS) that requests torque reduction by outputting a split torque to prevent the wheels of the vehicle from slipping; and a controller that controls the torque split by dividing a requested amount of torque reduction between the internal combustion engine and the electric motor when receiving the torque reduction request from the TCU or the TCS.The controller first reduces the assist torque of the electric motor when the state of the electric motor before torque splitting is an assist state, maintains the charging torque of the electric motor when the state of the electric motor before torque splitting is a charging state, and divides an additional requested reduction proportionally between an available reduction range of the internal combustion engine and an available reduction range of the electric motor. The controller sets the available reduction range of the internal combustion engine from the torque of the internal combustion engine before torque splitting to a torque of 0, and the available reduction range of the electric motor from a charging torque before torque splitting to the charging limit when the state of the electric motor before torque splitting is the charging state.

[0010] The controller may, when the state of the electric motor before torque split is the assist state, set the available reduction range of the internal combustion engine from a torque of the internal combustion engine before torque split to a torque of 0 and set the available reduction range of the electric motor from a torque of 0 to a charging limit.

[0011] The controller may, when the state of the electric motor before torque split is the assist state, calculate the additional requested torque reduction by subtracting the requested amount of torque reduction and the torque of the electric motor before torque split from a total requested torque amount before torque split.

[0012] The controller may set the available reduction range of the internal combustion engine from the torque of the internal combustion engine before torque split to the torque 0 and the available reduction range of the electric motor from a charging torque before torque split to the charging limit when the state of the electric motor before torque split is the charging state.

[0013] The controller may calculate the additional requested reduction by subtracting the requested amount of torque reduction split from the total requested torque before torque split when the state of the electric motor before torque split is the state of charge.

[0014] The controller may determine the torque of the internal combustion engine after torque split and the torque of the electric motor after torque split as equivalent to the torque of the internal combustion engine before torque split and the torque of the electric motor before torque split, respectively, when the requested amount of torque reduction is greater than or equal to the total requested torque before torque split.

[0015] According to embodiments of the present disclosure, a method for controlling torque split of a hybrid electric vehicle having an electric motor and an internal combustion engine as power sources includes: detecting data for controlling torque split when a torque reduction is requested from a transmission control unit (TCU) of the vehicle or a traction control system (TCS) of the vehicle; determining the state of the electric motor before torque split; first reducing the assist torque of the electric motor when the state of the electric motor before torque split is the assist state, and maintaining the charging torque of the electric motor when the state of the electric motor before torque split is the charging state; calculating an additional requested reduction depending on the state of the electric motor before torque split;and adjusting the available reduction range of the internal combustion engine and the available reduction range of the electric motor depending on the state of the electric motor before torque splitting, and dividing the additional required reduction proportionally to the available reduction ranges of the internal combustion engine and the electric motor. The available reduction range of the internal combustion engine is set from the torque of the internal combustion engine before torque splitting to a torque of 0, and the available reduction range of the electric motor is set from a charging torque before torque splitting to the charging limit when the state of the electric motor before torque splitting is the charging state.

[0016] The data may include the engine torque before torque split, the electric motor torque before torque split, the requested amount of torque reduction, and an electric motor charging limit.

[0017] The method may further include determining the post-torque-split internal combustion engine torque and the post-torque-split electric motor torque as equivalent to the pre-torque-split internal combustion engine torque and the pre-torque-split electric motor torque, respectively, when the requested amount of torque reduction is greater than or equal to the total pre-torque-split requested torque, which is the sum of the pre-torque-split internal combustion engine torque and the pre-torque-split electric motor torque.

[0018] The method may further include, when the electric motor is in the assist state before torque split: comparing a value obtained by subtracting the requested amount of torque reduction from the requested total torque before torque split with the torque of the electric motor before torque split; determining the torque of the internal combustion engine after torque split as equivalent to the torque of the internal combustion engine before torque split; and determining the torque of the electric motor after torque split as a value obtained by subtracting the torque of the internal combustion engine before torque split from the requested amount of torque reduction when the value of the requested amount of torque reduction is less than the torque of the electric motor before torque split.

[0019] The requested amount of torque reduction can be calculated by subtracting the requested amount of torque reduction and the torque of the electric motor before torque split from the total requested torque before torque split when the value of the requested amount of torque reduction is greater than or equal to the torque of the electric motor before torque split.

[0020] When the state of the electric motor before torque split is the assist state, the available reduction range of the internal combustion engine can be set from the torque of the internal combustion engine before torque split to 0 torque, and the available reduction range of the electric motor is set from 0 torque to the charging limit.

[0021] The requested amount of torque reduction can be calculated by subtracting the requested amount of torque reduction from the total requested torque before torque split when the state of the electric motor before torque split is the state of charge.

[0022] The available reduction range of the internal combustion engine can be set from the torque of the internal combustion engine before torque split to the torque 0, and the available reduction range of the electric motor is set from the charging torque before torque split to the charging limit when the state of the electric motor before torque split is the charging state.

[0023] According to embodiments of the present disclosure, the hybrid electric vehicle first reduces the assist torque of the electric motor before torque splitting as described above, and divides the additional required reduction in proportion to the available reduction range of the engine and the available reduction range of the electric motor, thereby preventing depletion of the battery's state of charge (SOC). Furthermore, the charging torque of the electric motor is maintained when the state of the electric motor before torque splitting is the state of charge, thereby improving the charging amount of the electric motor. Furthermore, the torque of the engine is reduced along with the torque of the electric motor, so that engine noise can be reduced and NVH characteristics can be improved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a graph of a conventional method for controlling the torque split of a hybrid electric vehicle that first reduces the torque of the internal combustion engine. Fig. Figure 2 is a graph of a conventional method for controlling the torque split of a hybrid electric vehicle, which first reduces the torque of the electric motor. Fig. 3 is a schematic diagram of a hybrid system employing a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure. Fig. 4 is a block diagram of a system for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure. Fig. 5 is a graph showing torque according to a method for controlling torque split of a hybrid electric vehicle that simultaneously reduces engine torque and electric motor torque. Fig. 6 is a graph of torque to which a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure is applied when the state of the electric motor is an assist state. Fig. 7 is a graph of torque applying a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure when the state of the electric motor is a state of charge. Fig. 8 and Fig. 9 are flowcharts of a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure. <Beschreibung der Bezugszeichen> 10 HCU 12 ECU 14 MCU 16 TCU 20 combustion engine 22 Clutch of the combustion engine 24 electric motor 26 gearboxes 28 Battery 11 Control 30 Driving information detector 32 TCS DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In the following detailed description, only certain embodiments of the present disclosure are shown and explained by way of example only. It will be understood by those skilled in the art that the described embodiments may be modified in various ways without departing from the spirit or scope of the present disclosure. Accordingly, the drawings are to be considered as illustrative and not restrictive. Throughout the description, like reference numerals indicate like elements.

[0025] Unless otherwise expressly stated, throughout the specification and the subsequent claims, the term "comprise" and "comprising" shall be construed as including the specified elements but not excluding other elements. Furthermore, the word endings "-er," "-or," and the term "module" throughout the specification refer to units for performing at least one function and operation, and may be implemented by hardware or software components, and combinations thereof.

[0026] It is understood that the term "vehicle" or "vehicular" or other similar terms used herein generally refer to motor vehicles, including hybrid vehicles, plug-in hybrid electric vehicles (plug-in charging), and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As used herein, a hybrid vehicle is a vehicle with two or more power sources, such as both gasoline and electric vehicles.

[0027] Furthermore, it is understood that one or more of the following methods, or aspects thereof, may be performed by at least one controller. The term "controller" may refer to a hardware device having a memory and a processor. The memory is configured to store program instructions, and the processor is specifically programmed to execute the program instructions to perform one or more of the processes described below. Furthermore, it is understood that the following methods may be performed by an apparatus including the controller along with one or more other components, as will be known to one of ordinary skill in the art.

[0028] Furthermore, the control logic of the present invention may be embodied as non-transitory computer-readable media on a computer-readable medium with executable program instructions executed by a processor, controller, and the like. Examples of computer-readable media include ROMs, RAMs, compact disc (CD)-ROMs, magnetic tapes, floppy disks, USB flash drives, smart cards, and optical data storage devices. The computer-readable recording medium may also be distributed in network-coupled computer systems so that the computer-readable medium is stored and executed in a distributed manner, e.g., by a telematics server or a controller area network (CAN).

[0029] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0030] Fig. 3 is a schematic diagram of a hybrid system employing a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure.

[0031] The Fig. 3 is provided for better understanding and ease of description. Therefore, a method for controlling the torque split of a hybrid electric vehicle according to embodiments of the present disclosure may not only be applied to the hybrid system of Fig. 3, but also to all other hybrid systems.

[0032] As in Fig. 3, the hybrid system to which a method for controlling the torque split of a hybrid electric vehicle according to the present disclosure is applied includes, for example, a hybrid control unit (HCU) 10, an electronic control unit (ECU) 12, a motor control unit (MCU) 14, a transmission control unit (TCU) 16, an engine 20, an engine clutch 22, an electric motor 24, a transmission 26, and a battery 28.

[0033] The HCU 10 controls the operation of other controllers that mutually exchange information about the overall operation of a hybrid electric vehicle, so that the HCU 10, in cooperation with the other controllers, controls the output torque of the internal combustion engine 20 and the electric motor 24.

[0034] The ECU 12 controls the overall operation of the internal combustion engine 20 depending on the conditions of the internal combustion engine 20 such as a torque requested by the driver, the coolant temperature and the torque of the internal combustion engine.

[0035] The MCU 14 controls the overall operation of the electric motor 24 depending on the torque requested by the driver, the driving mode of the hybrid electric vehicle, and the SOC of the battery 28.

[0036] The TCU 16 controls the overall operation of the transmission 26 such as the gear ratio of the transmission 26 depending on the output torque of the internal combustion engine 20 and the electric motor 24 as well as the regenerative braking amount.

[0037] The internal combustion engine 20 as a drive source delivers power when switched on.

[0038] The engine clutch 22 is arranged between the engine 20 and the electric motor 24 and receives a control signal from the HCU 10 and selectively connects the engine 20 and the electric motor 24 according to the driving mode of the hybrid electric vehicle.

[0039] The electric motor 24 is driven by a 3-phase alternating voltage supplied from the battery 28 via an inverter to generate torque and operates as a power generator that supplies regenerative energy to the battery 28 in follow-on mode.

[0040] The transmission 26 supplies the sum of the output torque of the internal combustion engine 20 and the output torque of the electric motor 24, which is determined by engaging and releasing the clutch 22 of the internal combustion engine, as input torque, and selects the appropriate gear stage according to the vehicle speed and driving condition to transmit the driving power to the drive wheels and maintain driving operation.

[0041] The battery 28 consists of a plurality of cell units and stores a high voltage to supply the electric motor 24, e.g., 400 V or 450 V DC.

[0042] A detailed description of the hybrid system explained above is omitted because it is not required for the present disclosure.

[0043] Fig. 4 is a block diagram of a system for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure.

[0044] As in Fig. 4, a system for controlling the torque split of a hybrid electric vehicle according to the present disclosure includes a driving information detector 30, a TCU 16, a TCS 32, a controller 11, an engine 20, and an electric motor 24.

[0045] Some processes of the torque split control method of the hybrid electric vehicle according to embodiments of the present disclosure to be described later may be executed by the ECU 12 and the MCU 14, and other processes by the HCU 10. For simplicity, in this specification and the claims, the controllers provided in the hybrid electric vehicle, such as the ECU 12, the MCU 14, and the HCU 10, are referred to as the controller 11.

[0046] The hybrid electric vehicle to which embodiments of the present disclosure are applied includes at least one internal combustion engine 20 and at least one electric motor 24. Furthermore, the hybrid electric vehicle provides a driving mode in which the internal combustion engine 20 and the electric motor 24 operate separately or simultaneously as a power source. For this purpose, the internal combustion engine clutch is arranged between the internal combustion engine 20 and the electric motor 24 to selectively connect the internal combustion engine 20 and the electric motor 24.

[0047] The driving information detector 30 detects the driving state of the hybrid electric vehicle and the driver's request information through signals from a vehicle speed sensor that detects the speed of the vehicle, an electric motor speed sensor that detects the speed of the electric motor, an accelerator pedal position sensor (APS) that detects a position value of the accelerator pedal, and a battery management system (BMS) that detects the state of charge of the battery.

[0048] The controller 11 can determine whether the hybrid electric vehicle is in electric vehicle (EV) mode or hybrid electric vehicle (HEV) mode depending on the coupling of the clutch 22 of the internal combustion engine based on a signal from the driving information detector 30.

[0049] When changing gears, the TCU 16 requests a torque reduction from the control unit 11 to ensure drivability.

[0050] The TCS 32 calls for torque reduction by outputting a split torque when wheel slippage occurs because the hybrid electric vehicle is starting or accelerating on slippery road surfaces.

[0051] The controller 11 controls the torque split to distribute the requested amount of torque reduction between the engine 20 and the electric motor 24 when it receives the torque reduction request from the TCU 16 or the TCS 32.

[0052] Fig. 5 is a graph of torque according to a method for controlling the torque split of a hybrid electric vehicle in which, for example, the torque of an internal combustion engine and the torque of an electric motor are reduced simultaneously. Fig. 5 shows that when a torque reduction of the hybrid electric vehicle is required, the controller 11 controls the torque distribution such that the torque of the combustion engine and the torque of the electric motor are reduced simultaneously in the same ratio.

[0053] The method of simultaneously reducing the engine torque and the electric motor torque can reduce the engine noise compared to the conventional method; however, the battery SOC may be depleted if the torque reduction is continuously requested.

[0054] To solve this problem, according to embodiments of the present disclosure, the controller 11 confirms the state of the electric motor 24 (i.e., "electric motor state") before torque split and splits the requested amount of torque reduction between the engine 20 and the electric motor 24 depending on the state of the electric motor before torque split. That is, the controller 11 first reduces an assist torque of the electric motor when the state of the electric motor before torque split is the assist state. Conversely, when the state of the electric motor before torque split is the charging state, the controller 11 maintains the charging torque of the electric motor.Thereafter, the controller 11 controls the torque split in which an additional requested reduction is divided proportionally to an available reduction range of the internal combustion engine and an available reduction range of the electric motor.

[0055] Controlling the torque split by the controller 11 according to embodiments of the present disclosure is described with reference to Fig. 6 and Fig. 7 described in more detail.

[0056] Fig. 6 is a graph of torque to which a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure is applied when the state of the electric motor is the assist state.

[0057] As in Fig. 6, the controller 11 according to the present disclosure confirms the state of the electric motor prior to torque split when it receives a torque reduction request from the TCU 16 or the TCS 32.

[0058] If the state of the electric motor before torque split is the assist state, the controller 11 first reduces the assist torque of the electric motor until the assist torque of the electric motor is exhausted. If the requested amount of torque reduction is not met by the assist torque of the electric motor, the controller 11 divides an additional requested reduction proportional to the available reduction range of the internal combustion engine and the available reduction range of the electric motor. Here, the internal combustion engine 20 can be controlled from 0 torque to an internal combustion engine torque before torque split such that the available reduction range of the internal combustion engine is set from the internal combustion engine torque before torque split to a 0 torque.

[0059] However, the electric motor 24 can also be controlled from a charging limit to a torque of 0, so that the available reduction range of the electric motor is set from a torque of 0 to the charging limit. In addition, as in Fig. 6, an available reduction ratio between the internal combustion engine 20 and the electric motor 24 is determined as 2:1. The controller 11 therefore first reduces the assist torque of the electric motor and divides the additional required reduction depending on the available reduction ratio of 2:1.

[0060] Fig. 7 is a graph of torque applying a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure when the state of the electric motor is the state of charge.

[0061] As in Fig. 7, according to embodiments of the present disclosure, the controller 11 maintains the charging torque of the electric motor when the state of the electric motor before torque split is the charging state, and splits the requested amount of torque reduction proportionally to an available reduction range of the engine and an available reduction range of the electric motor.

[0062] In this case, the internal combustion engine 20 can be controlled from a torque of 0 to a pre-torque-split engine torque, so that the available reduction range of the internal combustion engine can be set from the pre-torque-split engine torque to a torque of 0. On the other hand, the electric motor 24 can be controlled from a charging limit to a charging torque before torque split, so that the available reduction range of the electric motor can be set from the charging torque before torque split to the charging limit.

[0063] In addition, as in Fig. 7, an available derating ratio between the engine 20 and the electric motor 24 is determined to be 3:1. Therefore, the controller 11 maintains the charging torque of the electric motor before torque splitting and divides the requested amount of torque reduction depending on the available derating ratio 3:1. That is, the controller 11 can meet three-quarters of the requested amount of torque reduction by decreasing the engine torque and one-quarter of the requested amount of torque reduction by increasing the charging torque of the electric motor.

[0064] As described above, when the state of the electric motor before torque splitting is the state of charge, the charging torque of the electric motor is maintained, thereby improving the charging amount of the electric motor. Thus, the SOC of the battery can be efficiently managed. To this end, the controller 11 may be implemented as at least one processor operated by a predetermined program as described above, and the predetermined program may be programmed to execute each step of a method for controlling torque split of a hybrid electric vehicle according to an embodiment of the present disclosure.

[0065] Various embodiments described herein may be implemented within the context of a recording medium that can be read by a computer or similar device, for example, using hardware, software, or a combination. In a hardware implementation, the embodiments described herein may be implemented using at least one of application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and electrical devices configured to perform other functions. In a software implementation, embodiments such as procedures and functions described in the present embodiments may be implemented by separate software modules.Each of the software modules may perform one or more functions and operations described in the present disclosure. The software code may be implemented by a software application written in a suitable programming language.

[0066] In the following, a method for controlling the torque split of the hybrid electric vehicle according to embodiments of the present disclosure will be described with reference to Fig. 8 and Fig. 9 described in detail.

[0067] The Fig. 8 and Fig. 9 are flowcharts of a method for controlling torque split of a hybrid electric vehicle according to embodiments of the present disclosure.

[0068] As the Fig. 8 and Fig. 9, a method for controlling torque split of a hybrid electric vehicle according to the present disclosure begins with detecting torque split control data in step S101 when a torque reduction is requested by the TCU 16 or the TCS 32. That is, the controller 11 may detect the pre-torque split engine torque EngTq, the pre-torque split motor torque MotTq, the requested torque reduction amount RedTgt, and the motor charge limit ChgLmt.

[0069] When the data has been detected in step S101, the controller 11 calculates the requested total torque before torque split DmdTq by adding the engine torque before torque split EngTq and the motor torque before torque split MotTq in step S102.

[0070] Thereafter, in step S103, the controller 11 compares the requested total torque before torque split DmdTq with the requested amount of torque reduction RedTgt when torque split is requested.

[0071] If the requested total torque before torque split DmdTq in step S103 is less than or equal to the requested amount of torque reduction RedTgt, the controller 11 determines in step S104 that the engine torque after torque split EngTqInt and the motor torque after torque split MotTqInt are equal to the engine torque before torque split EngTq and the motor torque before torque split MotTq.

[0072] On the other hand, when the requested total torque before torque split DmdTq in step S103 is greater than the requested amount of torque reduction RedTgt, the controller 11 determines in step S105 whether the state of the electric motor before torque split is the assist state or the charging state.

[0073] When the state of the electric motor before the torque split in step S105 is the assist state, the controller 11 determines in step S106 whether the requested amount of torque reduction RedTgt is satisfied by the assist torque of the electric motor.

[0074] If a value obtained by subtracting the requested torque reduction amount RedTgt from the requested total torque before torque split DmdTq is less than or equal to the electric motor torque before torque split MotTq, the controller 11 determines in step S106 that the requested torque reduction amount RedTgt is satisfied by the electric motor torque before torque split MotTq. Thus, in step S107, the controller 11 determines an engine torque after torque split and an electric motor torque after torque split.That is, the controller 11 may determine that the engine torque after torque split EngTqInt is equal to the engine torque before torque split EngTq and that the motor torque after torque split MotTqInt is equal to the value obtained by subtracting the engine torque before torque split EngTq from the requested torque reduction amount RedTgt.

[0075] On the other hand, if a value obtained by subtracting the requested torque reduction amount RedTgt from the total requested torque before torque split DmdTq in step S106 is greater than the torque of the electric motor before torque split MotTq, the controller 11 determines that the requested torque reduction amount RedTgt is not satisfied by the torque of the electric motor before torque split MotTq alone. Therefore, the controller 11 first reduces the torque of the electric motor before torque split MotTq and calculates an additional requested reduction according to the following equation 1 in step S108. RedRq+(DmdTq−RedTqt)−MotTq

[0076] The additional required reduction RedRq can be calculated by subtracting the torque of the electric motor before torque splitting MotTq from a value obtained by subtracting the required amount of torque reduction RedTgt from the total requested torque before torque splitting DmdTq.

[0077] Thereafter, in step S109, the controller 11 sets an available reduction range of the engine and an available reduction range of the electric motor when the state of the electric motor before the torque split is the assist state.

[0078] Herein, the available reduction range of the internal combustion engine and the electric motor refers to the available amount of torque reduction of the internal combustion engine 20 and the electric motor 24 before torque splitting. The internal combustion engine 20 can reduce the total torque before torque splitting, so that the available reduction range of the internal combustion engine EngCap can be set equal to the torque of the internal combustion engine before torque splitting EngTq (EngCap = EngTq).

[0079] In addition, the electric motor 24 reduces the assist torque of the electric motor to 0 torque in advance, and the available reduction range of the electric motor MotCap can be set from 0 torque to the charging limit (MotCap = 0 - ChgLmt).

[0080] The controller 11 determines the torque of the internal combustion engine after the torque split and the torque of the electric motor after the torque split to divide the additional required reduction RedTq in proportion to the available reduction range of the internal combustion engine EngCap and the available reduction range of the electric motor MotCap in step S110. At this time, the torque of the internal combustion engine after the torque split EngTqInt can be calculated according to Equation 2 below. EngTaInt=EngTq−RedRq×EngCap / (EngCap+MotCap)

[0081] Where EngTqInt is the torque of the combustion engine after torque splitting, EngTq is the torque of the combustion engine before torque splitting, RedRq is the additional required derating, EngCap is the available derating range of the combustion engine and MotCap is the available derating range of the electric motor.

[0082] In addition, the torque of the electric motor can be calculated after the torque split MotTqInt according to the following equation 3. MotTqInt=0−RedRq×MotCap / (EngCap+MotCap)

[0083] Thereafter, in step S114, the controller 11 executes the torque reduction depending on the determined torque of the internal combustion engine after the torque split and the torque of the electric motor after the torque split.

[0084] The case will now be examined on the basis of Fig. 9, in which the state of the electric motor before torque splitting is the charging state in step S105. The controller 11 maintains the charging torque of the electric motor and calculates the additional required reduction according to Equation 4 below in step S111. RedRq+(DmdTq−RedTqt)−0

[0085] The additional required reduction RedRq can be calculated by subtracting 0 from a value obtained by subtracting the requested amount of torque reduction RedTgt from the requested total torque before torque split DmdTq.

[0086] The controller 11 sets the available reduction range of the engine and the available reduction range of the electric motor in step S112 when the state of the electric motor before torque split is the state of charge. The engine 20 can reduce the total torque before torque split, so the available reduction range of the engine EngCap can be set equal to the torque of the engine before torque split EngTq (EngCap = EngTq).

[0087] In addition, the electric motor 24 can reduce the torque up to the charging limit, so that the available reduction range of the electric motor MotCap is set from the charging torque before the torque split MotTq (< 0) to the charging limit ChgLmt (MotCap = MotTq < 0 - ChgLmt).

[0088] The controller 11 determines the torque of the internal combustion engine after the torque split and the torque of the electric motor after the torque split to set the additional requested reduction RedTq proportional to the available reduction range of the internal combustion engine EngCap and the available reduction range of the electric motor MotCap in step S113.

[0089] The torque of the internal combustion engine after the torque split EngTqInt can be calculated by the above equation 2. In addition, the torque of the electric motor after the torque split MotTqInt can be calculated according to the following equation 5. MotTqInt=MotTq(<0)−RedRq×MotCap / (EngCap+MotCap)

[0090] Thereafter, in step S114, the controller 11 executes the torque reduction depending on the determined torque of the internal combustion engine after the torque split and the torque of the electric motor after the torque split.

[0091] As described above, the hybrid electric vehicle according to embodiments of the present disclosure first reduces the assist torque of the electric motor before torque splitting and divides the additional required reduction in proportion to the available reduction range of the engine and the available reduction range of the electric motor, thereby preventing depletion of the battery SOC. Furthermore, the charging torque of the electric motor is maintained when the state of the electric motor before torque splitting is the state of charge, thereby improving the charging amount of the electric motor. Furthermore, the torque of the engine is reduced along with the torque of the electric motor, so that engine noise can be reduced and NVH characteristics can be improved.

Claims

[1] A system for controlling the torque split of a hybrid electric vehicle having an electric motor (24) and an internal combustion engine (20) as drive sources, comprising: a driving information detector that detects the driving state of the vehicle and request information of the driver of the vehicle; a transmission control unit (TCU) (16) that requests a torque reduction when changing gears of the vehicle based on a signal from the driving information detector; a traction control system (TCS) (32) that requests torque reduction by outputting a split torque to prevent the vehicle's wheels from slipping; and a controller (11) that controls the torque split by dividing a requested amount of torque reduction between the internal combustion engine (20) and the electric motor (24) when it receives the torque reduction request from the TCU (16) or the TCS (32), wherein the controller (11) first reduces an assist torque of the electric motor (24) when the state of the electric motor (24) before the torque split is an assist state, maintains the charging torque of the electric motor (24) when the state of the electric motor (24) before the torque split is a charging state, and divides an additionally requested reduction proportionally to an available reduction range of the internal combustion engine (20) and an available reduction range of the electric motor (24), and wherein the controller (11) sets the available reduction range of the internal combustion engine (20) from the torque of the internal combustion engine (20) before the torque split to a torque 0 and the available reduction range of the electric motor (24) from a charging torque before the torque split to the charging limit value when the state of the electric motor (24) before the torque split is the charging state. [2] The system of claim 1, wherein, when the state of the engine before the torque intervention is the assist state, the controller (11) sets the available reduction range of the internal combustion engine (20) from torque of the internal combustion engine (20) before the torque split to a torque of 0 and the available reduction range of the electric motor (24) from torque of 0 to a charging limit. [3] The system of claim 1, wherein, when the state of the electric motor (24) before torque split is the assist state, the controller (11) calculates the additional requested reduction by subtracting the requested amount of torque reduction and the torque of the electric motor (24) before torque split from the total requested torque before torque split. [4] The system of claim 1, wherein the controller (11) calculates the additional requested reduction by subtracting the requested amount of split torque reduction from the total requested torque before torque split when the state of the electric motor (24) before torque split is the state of charge. [5] The system of claim 1, wherein the controller (11) determines the torque of the internal combustion engine (20) after the torque split and the torque of the electric motor (24) after the torque split as equivalent to the torque of the internal combustion engine (20) before the torque split and the torque of the electric motor (24) before the torque split, respectively, when the requested amount of torque reduction is greater than or equal to the requested total torque before the torque split. [6] A method for controlling the torque distribution of a hybrid electric vehicle having an electric motor (24) and an internal combustion engine (20) as drive sources, comprising: Detecting data for controlling the torque split when a torque reduction is requested by a transmission control unit (TCU) (16) of the vehicle or a traction control system (TCS) (32) of the vehicle; Determining the state of the electric motor (24) before torque splitting; first reducing the assist torque of the electric motor (24) when the state of the electric motor (24) before the torque split is the assist state, and maintaining the charging torque of the electric motor (24) when the state of the electric motor (24) before the torque split is the charging state; Calculating an additional required reduction depending on the state of the electric motor (24) before the torque split; and Setting the available reduction range of the internal combustion engine (20) and the available reduction range of the electric motor (24) depending on the state of the electric motor (24) before the torque split and splitting the additional required reduction proportionally to the available reduction ranges of the internal combustion engine (20) and the electric motor (24), wherein the available reduction range of the internal combustion engine (20) is set from the torque of the internal combustion engine (20) before the torque split to a torque 0 and the available reduction range of the electric motor (24) is set from a charging torque before the torque split to the charging limit when the state of the electric motor (24) before the torque split is the charging state. [7] The method of claim 6, wherein the data includes the torque of the internal combustion engine (20) before torque splitting, the torque of the electric motor (24) before torque splitting, the requested amount of torque reduction, and the charging limit of the electric motor (24). [8] The method of claim 6, further comprising: Determining the torque of the internal combustion engine (20) after the torque split and the torque of the electric motor (24) after the torque split as equivalent to the torque of the internal combustion engine (20) before the torque split or to the torque of the electric motor (24) before the torque split, when the requested amount of torque reduction is greater than or equal to the requested total torque before torque split, which is the sum of the torque of the internal combustion engine (20) before torque split and the torque of the electric motor (24) before torque split. [9] The method of claim 6, further comprising, when the electric motor (24) is in the assist state prior to torque splitting: Comparing a value obtained by subtracting the requested amount of torque reduction from the requested total torque before torque splitting with the torque of the electric motor (24) before torque splitting; Determining the torque of the internal combustion engine (20) after the torque split as equivalent to the torque of the internal combustion engine (20) before the torque split; and Determining the torque of the electric motor (24) after the torque split as a value resulting from subtracting the torque of the internal combustion engine (20) before the torque split from the requested amount of torque reduction if the value of the requested amount of torque reduction is less than the torque of the electric motor (24) before the torque split. [10] The method of claim 9, wherein the requested amount of torque reduction is calculated by subtracting the requested amount of torque reduction and the torque of the electric motor (24) before torque split from the total requested torque before torque split when the value of the requested amount of torque reduction is greater than or equal to the torque of the electric motor (24) before torque split. [11] The method of claim 6, wherein, when the state of the electric motor (24) before the torque split is the assist state, the available reduction range of the internal combustion engine (20) is set from the torque of the internal combustion engine (20) before the torque split to a torque of 0 and the available reduction range of the electric motor (24) is set from a torque of 0 to the charging limit. [12] The method of claim 6, wherein the requested amount of torque reduction is calculated by subtracting the requested amount of torque reduction from the total requested torque before torque split when the state of the electric motor (24) before torque split is the state of charge.

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