Patent Publication Number: US-2023150505-A1

Title: Method and device for controlling regenerative braking of hybrid vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on claims the benefit of Korean Patent Application No. 10-2021-0159340 filed in the Korean Intellectual Property Office on Nov. 18, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate to a vehicle, and more particularly, to a method and a device for controlling regenerative braking of a hybrid vehicle. 
     DESCRIPTION OF THE RELATED ART 
     In general, a hybrid vehicle, which is a kind of eco-friendly vehicle, is a vehicle that efficiently combines and uses two or more different types of power sources, and means a vehicle driven by an engine which combusts fuel to obtain rotational force and a motor which obtains rotational force from power of a battery. 
     The hybrid vehicle may be formed in various structures by using two or more power sources formed of the engine and the motor. The motor provided in the hybrid vehicle serves to assist the power of the engine during acceleration or hill driving. 
     A driving mode of the hybrid vehicle includes an Electric Vehicle (EV) mode, which is a pure electric vehicle mode that uses only motor power, a Hybrid Electric Vehicle (HEV) mode using the engine as the main power and using the motor as the auxiliary power, and a regenerative braking mode in which braking energy of the vehicle is collected through power generation in the motor and charged in the battery when the vehicle is driven by braking. 
     The regenerative braking is the technology in which electric energy is generated in a motor by applying reverse torque to an electric motor by using energy generated during braking in order to maximize fuel efficiency of an eco-friendly vehicle, the generated electric energy is stored in a high-voltage battery and is re-usable during the driving of the vehicle, and is applied to eco-friendly vehicles, such as a hybrid vehicle, an electric vehicle, or a fuel cell vehicle. 
     The regenerative braking is the technology for converting energy to electric energy during braking, and is directly connected with fuel efficiency, and the increase in the amount of regenerative braking means improvement of fuel efficiency. In the case of hybrid vehicles, compared to a general vehicle, regenerative braking plays a major role in improving fuel efficiency to the extent that regenerative braking exhibits most of the effect of improving fuel efficiency. 
     SUMMARY 
     Embodiments of the present disclosure have been made in an effort to provide a method and a device for controlling regenerative braking of a hybrid vehicle, which improve fuel efficiency of a hybrid vehicle by regenerative braking of motors included in the hybrid vehicle. 
     An exemplary embodiment of the present disclosure provides a method of controlling regenerative braking of a hybrid vehicle, the method including: controlling, by a controller, the hybrid vehicle to start a braking operation in response to a brake pedal operation signal; and after the braking operation of the hybrid vehicle is started, controlling, by the controller, a second motor that is connected to an input shaft of a transmission of the hybrid vehicle to perform regenerative braking. 
     The method may further include determining, by the controller, whether a speed of the hybrid vehicle is less than a vehicle speed reference value, in which when the speed of the hybrid vehicle is less than the vehicle speed reference value, the controller may control the second motor to perform the regenerative braking so that the amount of regenerative braking of the second motor is the amount of demanded braking of the hybrid vehicle corresponding to the brake pedal operation signal. In certain aspects, the speed of the hybrid vehicle may be determined to be at least 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 kilometers per hour less than a vehicle speed reference value. 
     The method may further include, when the speed of the hybrid vehicle is equal to or greater than the vehicle speed reference value, determining, by the controller, whether the second motor generates the maximum amount of regenerative braking, and whether the maximum amount of regenerative braking of the second motor is less than the amount of demanded braking of the hybrid vehicle, in which when the second motor does not generate the maximum amount of regenerative braking, the controller may control the second motor to perform the regenerative braking so that the amount of regenerative braking of the second motor is the amount of demanded braking of the hybrid vehicle. In certain aspects, the speed of the hybrid vehicle may be determined to be at least 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 kilometers per hour greater than a vehicle speed reference value. 
     The method may further include: when the second motor generates the maximum amount of regenerative braking and the maximum amount of regenerative braking of the second motor is less than the amount of demanded braking of the hybrid vehicle, engaging, by the controller, the engine clutch that connects or disconnects an engine and the second motor of the hybrid vehicle; after the engine clutch is engaged, calculating, by the controller, the amount of regenerative braking of the first motor that starts the engine based on the amount of demanded braking of the hybrid vehicle, friction force of the transmission, the maximum amount of regenerative braking of the second motor, and friction force of the engine; and controlling, by the controller, the first motor to perform the regenerative braking based on the amount of regenerative braking of the first motor. 
     Another exemplary embodiment of the present disclosure provides a device for controlling regenerative braking of a hybrid vehicle, the device including: a second motor connected to an input shaft of a transmission of the hybrid vehicle; and a controller configured to control the hybrid vehicle to start a braking operation in response to a brake pedal operation signal, in which after the braking operation of the hybrid vehicle is started, the controller may control the second motor to perform regenerative braking. 
     The controller may determine whether a speed of the hybrid vehicle is less than a vehicle speed reference value, and when the speed of the hybrid vehicle is less than the vehicle speed reference value, the controller may control the second motor to perform the regenerative braking so that the amount of regenerative braking of the second motor is the amount of demanded braking of the hybrid vehicle corresponding to the brake pedal operation signal. In certain aspects, the speed of the hybrid vehicle may be determined to be at least 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 kilometers per hour less than a vehicle speed reference value. 
     When the speed of the hybrid vehicle is equal to or greater than the vehicle speed reference value, the controller may determine whether the second motor generates the maximum amount of regenerative braking, and whether the maximum amount of regenerative braking of the second motor is less than the amount of demanded braking of the hybrid vehicle, and when the second motor does not generate the maximum amount of regenerative braking, the controller may control the second motor to perform the regenerative braking so that the amount of regenerative braking of the second motor is the amount of demanded braking of the hybrid vehicle. In certain aspects, the speed of the hybrid vehicle may be determined to be at least 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 kilometers per hour greater than a vehicle speed reference value. 
     The device may further include a first motor configured to start an engine of the hybrid vehicle, in which when the second motor generates the maximum amount of regenerative braking and the maximum amount of regenerative braking of the second motor is less than the amount of demanded braking of the hybrid vehicle, the controller may engage an engine clutch that connects or disconnects the engine and the second motor, and after the engine clutch is engaged, the controller may calculate the amount of regenerative braking of the first motor based on the amount of demanded braking of the hybrid vehicle, friction force of the transmission, the maximum amount of regenerative braking of the second motor, and friction force of the engine, and the controller may control the first motor to perform the regenerative braking based on the amount of regenerative braking of the first motor. 
     The method and the device for controlling regenerative braking of the hybrid vehicle according to the exemplary embodiments of the present disclosure may improve fuel efficiency of a hybrid vehicle by regenerative braking of the motors included in the hybrid vehicle. 
     As discussed, the method and system suitably include use of a controller or processer. 
     In another aspect, vehicles are provided that comprise an apparatus as disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to help more full understanding of the drawings used in the detailed description of embodiments of the present disclosure, a brief description of each drawing is provided. 
         FIG.  1    is a flowchart for describing a method of controlling regenerative braking of a hybrid vehicle according to an exemplary embodiment of the present disclosure. 
         FIG.  2    is a block diagram illustrating a device for controlling regenerative braking of a hybrid vehicle to which the method of controlling regenerative braking of the hybrid vehicle illustrated in  FIG.  1    is applied. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In order to fully understand the present disclosure and the object achieved by the implementation of the present disclosure, reference should be made to the accompanying drawings illustrating the exemplary embodiment of the present disclosure and the contents described in the accompanying drawings. 
     Hereinafter, the present disclosure will be described in detail by describing the exemplary embodiment of the present disclosure with reference to the accompanying drawings. In the following description of the exemplary embodiment, a detailed description of known configurations or functions incorporated herein will be omitted when it is judged that the detailed description may make the subject matter of the present disclosure unclear. Like reference numerals presented in each drawing designate like elements throughout the specification. 
     It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. These terms are merely intended to distinguish one component from another component, and the terms do not limit the nature, sequence or order of the constituent components. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, the terms “unit”, “-er”, “-or”, and “module” described in the specification mean units for processing at least one function and operation and can be implemented by hardware components or software components and combinations thereof. 
     Although exemplary embodiment is described as using a plurality of units to perform the exemplary process, it is understood that the exemplary processes may also be performed by one or plurality of modules. Additionally, it is understood that the term controller/control unit refers to a hardware device that includes a memory and a processor and is specifically programmed to execute the processes described herein. The memory is configured to store the modules and the processor is specifically configured to execute said modules to perform one or more processes which are described further below. 
     Further, the control logic of the present disclosure may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN). 
     The term used in the present specification is simply used for describing a specific embodiment and does not intend to limit the present disclosure. A singular expression includes a plural expression unless it is specifically described to the contrary in the context. In the present specification, it should be appreciated that terms “including” and “having” are intended to designate the existence of characteristics, numbers, steps, operations, constituent elements, and components described in the specification or a combination thereof, and do not exclude a possibility of the existence or addition of one or more other characteristics, numbers, steps, operations, constituent elements, and components, or a combination thereof in advance. 
     Throughout this specification, when it is described that an element is “coupled” to another element, the element may be “directly coupled” to the another element or “electrically or mechanically coupled” to the another element a still another element interposed therebetween. 
     All terms used herein including technical or scientific terms have the same meanings as meanings which are generally understood by those skilled in the art to which the present disclosure pertains unless they are differently defined. Terms defined in generally used dictionary shall be construed to have meanings matching those in the context of a related art and shall not be construed as ideal or excessively formal meanings unless they are clearly defined in the present application. 
       FIG.  1    is a flowchart for describing a method of controlling regenerative braking of a hybrid vehicle according to an exemplary embodiment of the present disclosure.  FIG.  2    is a block diagram illustrating a device for controlling regenerative braking of a hybrid vehicle to which the method of controlling regenerative braking of the hybrid vehicle illustrated in  FIG.  1    is applied. 
     Referring to  FIGS.  1  and  2   , in a determination operation  105 , a controller  205  may control a hybrid vehicle  200  to start a braking operation in response to a brake pedal operation signal. The brake pedal operation signal may be generated when a driver of the hybrid vehicle  200  depresses the brake pedal of the hybrid vehicle. 
     As illustrated in  FIG.  2   , the hybrid vehicle  200  may include the controller  205 , an engine  210 , a first motor  215 , an engine clutch  220 , a second motor  225 , a transmission  230 , a final reduction gear device  235  that is a decelerator, driving wheels  240 , and a battery  245 . The device for controlling regenerative braking of the hybrid vehicle may include the controller  205 , the first motor  215 , and the second motor  225 . 
     The controller  205  may control the overall operation of the hybrid vehicle  200  as an electronic control unit (ECU). For example, the controller  205  may be one or more microprocessors operated by a program (control logic) or hardware (for example, a microcomputer) including the microprocessor, and the program may include a series of instructions for performing the method of controlling regenerative braking of the hybrid vehicle according to the exemplary embodiment of the present disclosure. The instruction may be stored in a memory of the hybrid vehicle  200 . 
     The controller  205  may include a hybrid control unit (HCU), a motor control unit (MCU), an engine control unit (ECU), and a transmission control unit (TCU). 
     The hybrid vehicle  200  is a hybrid electric vehicle, and may use the engine  210  and the second motor  225  as power sources, and the engine clutch  220  is present between the second motor  225  and the engine  210 , so that the vehicle is operated in an Electric Vehicle (EV) mode in which the vehicle travels by the second motor  225  in the state where the engine clutch  220  is opened, and the vehicle is operated in a Hybrid Electric Vehicle (HEV) mode in which the vehicle is capable of travelling by both the engine  210  and the second motor  225  in the state where the engine clutch  220  is closed. 
     The first motor  215  is operated as an electric motor or a generator, and the first motor  215  may be operated as an electric motor according to a control signal output from the controller  205  to start the engine  210  and is operated as a generator in the state where the starting of the engine  210  is maintained to generate voltage and provide the generated voltage to the battery  245  as charging voltage. The first motor  215  may be operated as a generator in regenerative braking to supply regenerative energy to the battery  245 . The first motor  215  may be installed (disposed) between the engine  210  and the engine clutch  220 , and may also be mentioned as a P1 motor. 
     The second motor  225  is a driving motor and is connected to an input shaft of the transmission  230 , and may also be mentioned as a P2 motor. The second motor  225  may be installed (disposed) between the engine clutch  220  and the transmission  230 . The second motor  225  may be operated as a generator in coasting drive or regenerative braking to supply regenerative energy to the battery  245 . 
     The battery  245  is formed of a plurality of unit cells, and for example, a high direct-current voltage of 260 Volt to 450 V may be stored in the battery  245  for providing a voltage to the first motor  215  or the second motor  225 . 
     According to an operation  110  illustrated in  FIG.  1   , after the braking operation of the hybrid vehicle  200  starts, the controller  205  may control the second motor  225  connected to the input shaft of the transmission  230  of the hybrid vehicle to first perform regenerative braking. The second motor  225  is connected to the driving wheel  240  through the transmission  230 , so that a regenerative braking loss of the second motor  225  may be smaller than a regenerative braking loss of the first motor  215 . For instance, in certain aspects, the regenerative braking loss of the second motor  225  may be about at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 or 25 percent less than a regenerative braking loss of the first motor  215 . Therefore, regenerative braking efficiency of the second motor  225  is larger than regenerative braking efficiency of the first motor  215 , so that the controller  205  may control the second motor  225  to first perform the regenerative braking. 
     The regenerative braking may be performed by the driving wheels  240 , the final reduction gear device  235 , the transmission  230 , the first motor  215 , and the battery  245 . 
     According to an operation  115 , after the operation  110 , the controller  205  may determine whether a speed of the hybrid vehicle  200  is less than a vehicle speed reference value. The vehicle speed reference value may be determined by a test (or experiment), or determined by other selection. 
     When the speed of the hybrid vehicle  200  is less than the vehicle speed reference value, the method of controlling regenerative braking of the hybrid vehicle performs an operation  120 , and when the speed of the hybrid vehicle  200  is equal to or greater than the vehicle speed reference value, the method of controlling regenerative braking of the hybrid vehicle performs an operation  125 . 
     According to the operation  120 , the controller  205  may control the second motor  225  to perform the regenerative braking so that the amount of regenerative braking of the second motor  225  is the amount of demanded braking of the hybrid vehicle  200  corresponding to the brake pedal operation signal. 
     According to the operation  125 , the controller  205  may determine whether the second motor  225  generates the maximum amount of regenerative braking. Further, the controller  205  may determine whether the maximum amount of regenerative braking of the second motor  225  is less than the amount of demanded braking of the hybrid vehicle  200  corresponding to the brake pedal operation signal. The maximum amount of regenerative braking of the second motor  225  may be determined by an output (capacity or output capacity) of the second motor. 
     When the second motor  225  generates the maximum amount of regenerative braking and the maximum amount of regenerative braking of the second motor  225  is less than the amount of demanded braking of the hybrid vehicle  200 , the process of the method of controlling regenerative braking of the hybrid vehicle may perform an operation  135 , and when the second motor  225  does not generate the maximum amount of regenerative braking, the process of the method of controlling regenerative braking of the hybrid vehicle may perform an operation  130 . 
     According to the operation  130 , the controller  205  may control the second motor  225  to perform the regenerative braking so that the amount of regenerative braking of the second motor  225  is the amount of demanded braking of the hybrid vehicle  200  corresponding to the brake pedal operation signal. 
     According to the operation  135 , the controller  205  may engage the engine clutch  220  that connects or disconnects the engine  210  and the second motor  225 . In another exemplary embodiment of the present disclosure, before the engine clutch  220  is engaged, the controller  205  may control the speed of the engine to be the same as the speed of the second motor  225  by operating the engine  210  to control the fuel not to be supplied to the engine. 
     According to an operation  140 , after the engine clutch  220  is engaged, the controller  205  may calculate the amount of regenerative braking of the first motor  215  based on the amount of demanded braking of the hybrid vehicle  200  corresponding to the brake pedal operation signal, friction force (or the amount of friction) of the transmission  230 , the maximum amount of regenerative braking of the second motor  225 , and friction force (or the amount of friction) of the engine  210 . For example, the controller  205  may calculate the amount of regenerative braking of the first motor  215  by subtracting the friction force of the transmission  230 , the maximum amount of regenerative braking of the second motor  225 , and the friction force of the engine  210  from the amount of demanded braking of the hybrid vehicle  200 . The controller  205  may control the first motor  215  to perform the regenerative braking based on the amount of regenerative braking of the first motor  215 . The regenerative braking may be performed by the driving wheels  240 , the final reduction gear device  235 , the transmission  230 , the engine clutch  220 , the engine  210 , the first motor  215 , and the battery  245 . 
     The constituent element, “˜ unit”, a block, or a module used in the exemplary embodiment of the present disclosure may be implemented by software, such as a task, class, subroutine, process, object, execution thread, and program performed in a predetermined area of a memory, or hardware, such as field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), and may also be implemented by a combination of the software and the hardware. The constituent element, “˜ unit” or the like may also be included in a computer readable storage medium, and a part thereof may be distributed in the plurality of computers. 
     As described above, the exemplary embodiments have been disclosed in the drawings and the specification. The specific terms are used herein but are only used for the purpose of describing the present disclosure and are not used to limit the meaning or the scope of the present disclosure described in the claims. Accordingly, those skilled in the art will appreciate that various modifications and equivalent embodiments may be made without departing from the scope and spirit of the present disclosure. Therefore, the true technical protection scope of the present disclosure will be defined by the technical spirit of the accompanying claims.