Abstract:
The present disclosure provides an apparatus and a method for active vibration control of a hybrid electric vehicle. In particular, the method may include: detecting an engine speed or a motor speed; selecting a reference angle signal based on the detected; setting up a period of a fast Fourier transform (FFT) and performing FFT of the engine speed or the motor speed for the period of the FFT from the reference angle signal; setting up a reference spectrum; extracting vibration components based on the reference spectrum; summing vibration components to be removed based on the frequencies and performing inverse FFT; determining a basic amplitude ratio based on the engine speed and an engine load and an adjustable ratio based on a SOC; and performing active vibration control of each frequency based on the the basic amplitude ratio, the adjustable ratio and the engine torque.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0176324, filed on Dec. 10, 2015, which is incorporated herein by reference in its entirety. 
       FIELD 
       [0002]    The present disclosure relates to an apparatus and a method for active vibration control of a hybrid electric vehicle. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    A hybrid vehicle is a vehicle using two or more different kinds of power sources, and is generally a vehicle that is driven by an engine that obtains a driving torque by burning fuel and a motor that obtains a driving torque with battery power. 
         [0005]    Hybrid electric vehicles can be provided with optimum output torque, depending on how the engine and the motor are operated while the vehicles are driven by the two power sources, that is, the engine and the motor. 
         [0006]    Hybrid electric vehicles may form various structures using the engine and the motor as power sources, and hybrid electric vehicles are classified as a TMED (Transmission Mounted Electric Device) type, in which the engine and the motor are connected by an engine clutch and the motor is connected to the transmission, and an FMED (Flywheel Mounted Electric Device) type, in which the motor is directly connected to a crankshaft of the engine and connected to the transmission through a flywheel. 
         [0007]    From among these, since the FMED type of the hybrid electric vehicle is very noisy and has severe vibration, vibration reduction thereof is being studied. A method of frequency analysis which extracts the vibration component is normally used for this. 
         [0008]    An analog method using a band pass filter has been used in a conventional frequency analysis, and the analog method of analysis determines whether or not a frequency is abnormal based on an amplitude of each expected point of a frequency band. 
         [0009]    However, distinguishing between the vibration component of the engine and the vibration of the noise component is difficult, and unnecessary over-control of the vibration negatively affects control efficiency and energy management. Further, because it is only possible to create and synchronize a reference signal with respect to a specific frequency in the conventional frequency analysis, comprehensive and active control of other frequencies which may be additionally generated is not performed. 
       SUMMARY 
       [0010]    The present disclosure provides an apparatus and a method for active vibration control of a hybrid electric vehicle, having advantages of elaborately controlling an abnormal vibration component through an entire frequency spectrum analysis using FFT (fast Fourier transform) and reflecting a change of a surrounding frequency component in real time by feedback. 
         [0011]    A method for active vibration control of a hybrid electric vehicle according to one form of the present disclosure may include: detecting an engine speed or a motor speed; selecting a reference angle signal based on position information of a motor or an engine; setting up a period of fast Fourier transform (FFT) and performing FFT of the engine speed or the motor speed corresponding to the period of the FFT from the reference angle signal; setting up a reference spectrum based on an engine speed and an engine load; extracting vibration components to be removed based on information of the reference spectrum; summing vibration components to be removed based on the frequencies and performing inverse FFT; determining a basic amplitude ratio based on an engine speed and an engine load and an adjustable ratio based on a SOC; and performing active vibration control of each frequency based on the information of the basic amplitude ratio, the adjustable ratio and the engine torque. 
         [0012]    The reference angle signal may be set by dividing by a number (m) of resolver poles based on information of the position of the motor or set up the reference angle between top dead center (TDC) of the number one cylinder and bottom dead center (BDC) of the number four cylinder based on information of the position of the engine. 
         [0013]    The FFT period may be set in consideration of a cylinder and a stroke of the engine. 
         [0014]    The analysis of the FFT signal may calculate a magnitude and phase information of each frequency. 
         [0015]    The frequency component that the FFT signal is greater than the reference spectrum may be selected as the vibration component to be removed. 
         [0016]    The vibration component to be removed may be removed by outputting the motor torque corresponding to an inverse value which may be calculated by multiplying the reference signal created by inverse FFT, the engine torque, the basic amplitude ratio, and the adjustable ratio. 
         [0017]    The adjustable ratio based on the SOC may be determined such that an antiphase torque is decreased when the SOC is low, and the antiphase torque is increased when the SOC is high. 
         [0018]    An apparatus for active vibration control of a hybrid electric vehicle including an engine and a motor as a power source according to another form of the present disclosure may include: a position sensor configured to detect position information of the engine or the motor; and a controller configured to select a reference angle signal on the basis of a signal from the position sensor, perform fast Fourier transform (FFT) of engine speed or motor speed, extract a vibration component to be removed through the FFT analysis, and generates a reference signal by performing inverse FFT, and performs active vibration control of each frequency by reflecting the reference signal, a basic amplitude ratio based on an engine speed and an engine load, an adjustable ratio based on a SOC (state of charge), and an engine torque. 
         [0019]    The controller may set up a reference spectrum based on an engine speed and an engine load, and extract the vibration component to be removed by comparing the reference spectrum with the FFT signal. 
         [0020]    The controller may sum the vibration components to be removed based on frequencies, and generate a reference signal by performing inverse FFT. 
         [0021]    The controller may remove the vibration component by outputting the motor torque corresponding to an inverse value. The inverse value can be obtained by multiplying the reference signal created by inverse FFT, the engine torque, the basic amplitude ratio, and the adjustable ratio. 
         [0022]    The controller may set up the reference angle signal by dividing by a number (m) of resolver poles based on information of the position of the motor or sets up the reference angle signal between top dead center (TDC) of a number one cylinder and bottom dead center (BDC) of a number four cylinder based on information of the position of the engine. 
         [0023]    The controller may set up an FFT period in consideration of a cylinder and stroke of the engine, and analyzes the FFT signal by a calculated magnitude and phase information of each frequency. 
         [0024]    As described above, the vibration may be actively controlled because the exact vibration component of each frequency may be extracted through FFT frequency spectrum analysis. Therefore, since the determination system of the reference angle of the engine and the motor may be utilized as it is, an additional device or an algorithm for signal synchronization as used in the conventional art may be eliminated. 
         [0025]    In addition, the adjustment amounts of vibration and a frequency which is an object of the vibration control may be controlled individually, so it is possible to avoid inefficiency which is from the control when the vibration is over-removed and the fuel consumption may be improved as the motor torque is increased when the engine is accelerated. Particularly, it is possible to constantly maintain the SOC of the battery within the predetermined range by using the adjustable ratio. 
         [0026]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0027]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a schematic diagram of an apparatus for active vibration control of a hybrid electric vehicle; 
           [0029]      FIG. 2  is a flowchart illustrating a method for active vibration control of a hybrid electric vehicle; 
           [0030]      FIG. 3  is a drawing illustrating vibration reduction to which a method for active vibration control of a hybrid electric vehicle is applied when a SOC of a battery is low; 
           [0031]      FIG. 4  is a drawing illustrating vibration reduction to which a method for active vibration control of a hybrid electric vehicle is applied when a SOC of a battery is high; and 
           [0032]      FIG. 5A to 5F  are graphs for explaining a method for active vibration control of a hybrid electric vehicle. 
       
    
    
       [0033]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0034]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0035]    As those skilled in the art would realize, the described forms may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
         [0036]    Throughout this specification and the claims which follow, 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. 
         [0037]    It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general including hybrid vehicles, plug-in hybrid electric vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid electric vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
         [0038]    Additionally, it is understood that some of the methods may be executed by at least one controller. The term “controller” refers to a hardware device that includes a memory and a processor configured to execute one or more steps that should be interpreted as its algorithmic structure. The memory is configured to store algorithmic steps and the processor is specifically configured to execute said algorithmic steps to perform one or more processes which are described further below. 
         [0039]    Furthermore, 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, a 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 recording medium can also be distributed in network coupled computer systems so that the computer readable media are stored and executed in a distributed fashion, e.g., by a telematics server or a controller area network (CAN). 
         [0040]      FIG. 1  is a schematic block diagram of an apparatus for active vibration control of a hybrid electric vehicle according to one form of the present disclosure. 
         [0041]    As shown in  FIG. 1 , an apparatus for active vibration control of a hybrid electric vehicle includes an engine  10 , a motor  20 , a position sensor  25 , a clutch  30 , a transmission  40 , a battery  50 , and a controller  60 . 
         [0042]    The engine  10  outputs driving power by burning fuel as a power source while turned on. The engine  10  may be various engines such as a gasoline engine or a diesel engine using conventional fossil fuel. The rotation power generated from the engine  10  is transmitted to the transmission  40  through the clutch  30 . 
         [0043]    The motor  20  is operated by a  3 -phase AC voltage applied from the battery  50  through an inverter to generate torque, and operates as a power generator and supplies regenerative energy to the battery  50  in a coast-down mode. 
         [0044]    In one form, the motor  20  may be directly connected to the crankshaft of the engine  10 . 
         [0045]    The position sensor  25  acquires position information of the engine  10  or the motor  20 . The position information of the engine  10  or the motor  20  are transmitted to the controller  60 . The position sensor  25  may include a crankshaft position sensor that detects a phase of the crankshaft or a motor position sensor that detects a position of a stator and a rotor of the motor. The controller  60  may calculate an engine speed by differentiating the rotation angle detected by the crankshaft position sensor, and a motor speed may be calculated by differentiating the position of the stator and the rotor of the motor detected by the motor position sensor. The position sensor  25  may be a speed sensor (not shown) for measuring the engine speed or the motor speed. 
         [0046]    The clutch  30  is disposed between the motor  20  connected to the crankshaft of the engine  10  and the transmission  40 , and switches power delivery to the transmission  40 . The clutch  30  may be applied as a hydraulic pressure type of clutch or dry-type clutch. 
         [0047]    The transmission  40  adjusts a shift ratio based on a vehicle speed and a running condition, distributes an output torque based on the shift ratio, and transfers the output torque to the driving wheel, thereby enabling the vehicle to run. The transmission  40  may be an automatic transmission (AMT) or a dual clutch transmission (DCT). 
         [0048]    The battery  50  is formed with a plurality of unit cells, and a high voltage for providing a driving voltage to the motor  20  is stored at the battery  50 . The battery  50  supplies the driving voltage to the motor  20  depending on the driving mode, and is charged by the voltage generated from the motor  20  in the regenerative braking. 
         [0049]    The controller  60  selects a reference angle signal on the basis of a signal from the position sensor, performs fast Fourier transform (FFT), extracts a vibration component to be removed via the FFT analysis, and performs active vibration control of each frequency by performing inverse FFT. The reference signal may mean an inverse FFT signal of the vibration components to be removed based on frequencies. 
         [0050]    After that, the controller  60  performs an active vibration control of each frequency by reflecting the reference signal, a basic amplitude ratio based on an engine speed and an engine load, an adjustable ratio based on a SOC (state of charge), and an engine torque. 
         [0051]    For these purposes, the controller  60  may be implemented as at least one processor that is operated by a predetermined program, and the predetermined program may be programmed in order to perform each step of a method for active vibration control of a hybrid electric vehicle. 
         [0052]    Various forms described herein may be implemented within a recording medium that may be read by a computer or a similar device by using software, hardware, or a combination thereof, for example. 
         [0053]    According to hardware implementation, the forms described herein may be implemented by 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, micro-controllers, microprocessors, and electric units designed to perform any other functions. 
         [0054]    According to software implementation, forms such as procedures and functions described in the present forms 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. A software code may be implemented by a software application written in an appropriate program language. 
         [0055]    Hereinafter, a method for active vibration control of the hybrid electric vehicle according to one form of the present disclosure will be described in detail with reference to  FIG. 2  to  FIG. 6 . 
         [0056]      FIG. 2  is a flowchart illustrating a method for active vibration control of a hybrid electric vehicle. 
         [0057]      FIG. 3  is a drawing illustrating vibration reduction to which a method for active vibration control of a hybrid electric vehicle is applied when a SOC of a battery low.  FIG. 4  is a drawing illustrating vibration reduction to which a method for active vibration control of a hybrid electric vehicle is applied when a SOC of a battery high.  FIG. 5A to 5F  are graphs for explaining a method for active vibration control of a hybrid electric vehicle. 
         [0058]    As shown in  FIG. 2 , an active vibration control method of the hybrid electric vehicle is started when the position sensor  25  obtains position information of the engine  10  or the motor  20  at step S 100 , and the controller  60  may acquire engine speed or motor speed using the position information of the engine  10  or the motor  20  at step S 100  (refer to  FIG. 5A ). 
         [0059]    The controller  60  selects the reference angle signal based on the signal of the position sensor  25  at step S 120 . That is, the controller  60  selects the reference angle signal according to information of positions of the engine  10  and the motor  30 (refer to  FIG. 5A ). 
         [0060]    The controller  60  may set up the reference angle signal by dividing a number (m) of resolver poles based on information of the position of the motor  20 , or may set up the reference angle signal between top dead center (TDC) and bottom dead center (BDC) of the number one cylinder or the number four cylinder based on information of the position of the engine  10 . For example, the controller  60  may select the reference angle signal based on the information of the position of the motor  20 , and may create the reference angle signal by dividing 16 poles signal into eight (8). The reference angle signal means a start point for performing FFT. 
         [0061]    After that, the controller  60  sets up a period of the FFT for performing the FFT at step S 120 . The controller  60  may set up the entire period in consideration of a number of cylinders and stroke of the engine  10 . For example, if the engine  10  has four cylinders and four strokes, the crank angle may be 720 degrees. 
         [0062]    When the FFT period is set up in the step S 120 , the controller  60  performs the FFT at step S 130 . That is, the controller  60  performs the FFT of the engine speed or the motor speed corresponding to the period of the FFT from the reference angle signal (refer to  FIG. 5B ). The controller  60  may calculate magnitude and phase information of each frequency by analyzing the FFT signal. 
         [0063]    In addition, the controller  60  sets up a reference spectrum according to the engine speed and load at step S 140  (refer to  FIG. 5B ). That is, the controller  60  may set up a vibration reference value of each frequency according to an operating point of the engine. 
         [0064]    When the reference spectrum is set up in the step S 140 , the controller  60  extracts a vibration component to be removed at step by comparing the FFT signal with the reference spectrum at step S 150 . That is, the controller  60  may select an object requiring vibration control in a compared result value of the FFT analysis and the predetermined vibration reference value. The controller  60  may extract the frequency component of which the FFT signal is greater than the reference spectrum as the vibration component to be removed. 
         [0065]    Since the reference spectrum means normal vibration components according to the engine speed and load, the controller  60  determines the frequency component of which the FFT signal is greater than the reference spectrum as abnormal vibration components to be removed. For example, referring to  FIG. 4B , f 2  frequency component may be selected as a frequency component to be removed. 
         [0066]    Referring to  FIG. 3  and  FIG. 4 , a magnitude and a phase of vibration components of each frequency calculated by performing FFT analysis is illustrated in left upper side of the drawing. 
         [0067]    When the vibration components to be removed is selected in the step S 150 , the controller  60  sums the vibration components to be removed according to frequencies, and performs inverse FFT to create a reference signal at step S 160  (refer to  FIG. 4C ). As described above, the reference signal means inverse FFT signal of the vibration components to be removed. 
         [0068]    The controller  60  determines a basic amplitude ratio according to an engine speed and an engine load, and an adjustable ratio according to the SOC (state of charge) at step S 170 . The amplitude ratio according to the engine speed and the engine load may be determined in advance by a predetermined map. The adjustable ratio according to the SOC may be determined such that an antiphase torque is decreased when the SOC is low, and the antiphase torque is increased when the SOC is high. 
         [0069]    Referring to  FIG. 3  and  FIG. 4 , an antiphase torque values which overlap the component of vibration to be removed as indicated is illustrated in left lower side of the drawing (refer to dotted line). As shown in solid line of  FIG. 3 , the adjustable ratio may be determined such that the antiphase torque is decreased in order to charge the battery when the SOC is low. 
         [0070]    On the contrary, as shown in solid line of  FIG. 4 , the adjustable ratio may be determined such that the antiphase torque is increased in order to discharge the battery when the SOC is high. 
         [0071]    After that, controller  60  performs active vibration control of each frequency based on the basic amplitude ratio, the adjustable ratio, and the engine torque at step S 180 . That is, the controller  60  may remove all the positive components and negative components of the vibration components by outputting the motor torque (antiphase torque) corresponding to an inverse value which is calculated by multiplying the reference signal created by inverse FFT, the engine torque, the adjustable ratio and the basic amplitude ratio (refer to  FIG. 5D ). 
         [0072]    Referring to  FIG. 3  and  FIG. 4 , the antiphase torque is applied to the vibration components of each frequency as described in left side are reflected, thereby it can be controlled such that the vibration component to be removed is removed and a desired vibration component remains as described in right side of the drawings. 
         [0073]    In order words, since the reference signal is expressed as speed according to time, the controller  60  removes the vibration components to be removed by reflecting the engine torque and the basic amplitude ratio to the reference signal and transforming the reference signal to torque component. That is, as shown in  FIG. 5E and 5F , it is possible to control the engine speed or the motor speed that the frequency components corresponding to the reference spectrum are remained. 
         [0074]    In order to manage the SOC of the battery, charging amount or discharging amount of the battery should be controlled when the vibration component is controlled. That is, it needs to maintain the SOC of the battery within a predetermined range by performing the active vibration control and the battery control (i.e., charge depleting control or charge sustaining control) simultaneously. Therefore, when the adjustable ratio according to the SOC is applied, it is possible to constantly maintain final torque as the SOC of the battery constantly maintains within the predetermined range. 
         [0075]    As described above, the vibration may be actively controlled because the exact vibration component of each frequency may be extracted through FFT frequency spectrum analysis. Therefore, since the determination system of the reference angle of the engine and the motor may be utilized as it is, an additional device or an algorithm for signal synchronization as used in the conventional art may be eliminated. 
         [0076]    In addition, the adjustment amounts of vibration and a frequency which is an object of the vibration control may be controlled individually, so it is possible to reduce or avoid inefficiency which is from the control when the vibration is over-removed and the fuel consumption may be improved as the motor torque is increased when the engine is accelerated. Particularly, it is possible to constantly maintain the SOC of the battery within the predetermined range by using the adjustable ratio. 
         [0077]    While this present disclosure has been described in connection with what is presently considered to be practical exemplary forms, it is to be understood that the present disclosure is not limited to the disclosed forms. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure.