Patent Publication Number: US-10319360-B1

Title: Active masking of tonal noise using motor-based acoustic generator to improve sound quality

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to vehicles, and more particularly relates to methods and systems for masking tonal noise in vehicles, particularly in electric or hybrid electric vehicles having an electric motor. 
     INTRODUCTION 
     Drivers and other occupants of vehicles may have a desire to hear vehicle noises in a certain manner, for example with an improved sound quality with respect to certain types of tonal noises that may be experienced within a vehicle. In particular, certain electric vehicles have highly tonal noise sources from electric motor(s) and transmission gears, while the overall masking noise level is low due to a lack of engine noise (for battery electric vehicles or hybrid vehicles operating at Electric Vehicle mode). This may raise tonal noise concerns, which may adversely affect the noise quality or acoustic rating of electric vehicle. 
     Accordingly, it is desirable to provide techniques for masking potentially unpleasant tonal electric vehicle sounds. It is also desirable to provide methods, systems, and vehicles utilizing such techniques. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description of exemplary embodiments and the appended claims, taken in conjunction with the accompanying drawings. 
     SUMMARY 
     In accordance with certain exemplary embodiments, a method is provided that includes: identifying a tonal noise of a motor; and masking the tonal noise, by introducing a complementary harmonic tone, injecting dithering into the motor, or both, using the motor as a speaker to create the complementary tone, the dithering, or both. 
     Also in certain embodiments, the step of masking the tonal noise includes masking the tonal noise, by injecting dithering into the motor. 
     Also in certain embodiments, the step of injecting dithering into the motor includes: 
     injecting dithering into the motor, thereby increasing a noise floor for the motor and decreasing a tone-to-noise ratio for the motor. 
     Also in certain embodiments, the step of masking the tonal noise includes introducing a complementary harmonic control signal voltage for the motor. 
     Also in certain embodiments, the step of introducing a complementary harmonic tone includes introducing a complementary harmonic tone for the motor, wherein the complementary harmonic tone includes a low-order harmonic tone that enriches a complexity of the tonal noise of the motor. 
     Also in certain embodiments, the step of introducing a complementary harmonic tone includes introducing a low order harmonic tone with respect to the tonal noise of the motor. 
     Also in certain embodiments, the method further includes incrementing a sound pitch for the tonal noise as a function of motor speed. 
     Also in certain embodiments, the method further includes incrementing a sound pitch for the tonal noise as a function of motor torque. 
     Also in certain embodiments, the motor includes an electric motor; and the method is implemented as part of an electric vehicle or hybrid electric vehicle. 
     In certain other embodiments, a system includes a motor and an active masking acoustic signal generator (AMAG). The motor generates a tonal noise. The active masking acoustic signal generator (AMAG) is configured to at least facilitate masking the tonal noise, by introducing a complementary harmonic tone, injecting dithering into the motor, or both. 
     Also in certain embodiments, the AMAG is configured to at least facilitate masking the tonal noise by injecting dithering into the motor. 
     Also in certain embodiments, the AMAG is configured to at least facilitate masking the tonal noise by introducing a complementary harmonic tone for the motor. 
     Also in certain embodiments, the AMAG is configured to at least facilitate masking the tonal noise by injecting dithering into the motor; and introducing a complementary harmonic tone for the motor. 
     Also in certain embodiments, the motor includes an electric motor; and the system is implemented as part of an electric vehicle or hybrid electric vehicle. 
     In certain other embodiments, a vehicle includes a drive system and an active masking acoustic signal generator (AMAG). The drive system includes a motor generating a tonal noise. The AMAG is configured to at least facilitate masking the tonal noise, by introducing a complementary harmonic tone, injecting dithering into the motor, or both 
     Also in certain embodiments, the AMAG is configured to at least facilitate masking the tonal noise by injecting dithering into the motor. 
     Also in certain embodiments, the AMAG is configured to at least facilitate masking the tonal noise by introducing a complementary harmonic tone for the motor. 
     Also in certain embodiments, the AMAG is configured to at least facilitate masking the tonal noise by injecting dithering into the motor; and introducing a complementary harmonic tone for the motor. 
     Also in certain embodiments, the motor includes an electric motor; and the vehicle includes an electric vehicle or hybrid electric vehicle. 
     Also in certain embodiments, the AMAG includes a processor onboard the vehicle; and the vehicle further includes a sensor array that is configured to at least facilitate identifying the tonal noise of the motor. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a functional block diagram of a vehicle that includes a motor drive system for masking vehicle sound, in accordance with exemplary embodiments; 
         FIG. 2  provides a functional diagram of the motor drive system of the vehicle of  FIG. 1 , in accordance with exemplary embodiments; 
         FIG. 3  provides a functional diagram of an exemplary implementation of a motor-based acoustic signal generator in the motor drive system of  FIG. 2 , in accordance with exemplary embodiments. 
         FIG. 4  is a block diagram of a process for masking vehicle sound, and that can be used in connection with the motor drive system and vehicle of  FIG. 1  and the components of  FIGS. 2 and 3 , in accordance with exemplary embodiments; 
         FIGS. 5-7  are graphical representations of an exemplary case study of sound masking utilizing the techniques of the motor drive system and vehicle of  FIG. 1  and components of  FIGS. 2 and 3 , and the process of  FIG. 4 , including the use of dithering techniques ( FIG. 5 ); complementary tones ( FIG. 6 ), and combinations thereof ( FIG. 7 ), in accordance with exemplary embodiments, for sound masking when the electric motor is operating at a specific exemplary speed and torque condition; 
         FIG. 8  provides a graphical representation of exemplary test results using sound masking utilizing the techniques of the motor drive system and vehicle of  FIG. 1 , in accordance with exemplary embodiments, for sound masking when the electric motor is operating over a run-up transient event corresponding to a vehicle drive-away condition; 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
       FIG. 1  illustrates a vehicle  100 , or automobile, according to an exemplary embodiment. The vehicle  100  may be any one of a number of different types of automobiles, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD) or all-wheel drive (AWD), and/or other types of vehicles and/or mobile platforms (e.g., aircraft, spacecraft, watercraft, locomotive, train, personal movement apparatus, robot, and so on). 
     While the motor drive system  102  is depicted in  FIG. 1  as being part of the vehicle  100 , it will be appreciated that in other embodiments the drive system  102  may be a stand-alone system, and/or may be part of one or more other systems, separate from or in addition to any vehicles. Additional details of the motor drive system  102  are depicted in  FIGS. 7 and 8  and described in detail further below in connection therewith. The motor drive system  102  as depicted in  FIGS. 1, 7, and 8  and described herein may be implemented in various embodiments as a stand-alone system and/or in connection with any number of vehicles, mobile platforms, and/or other systems. 
     As described in greater detail further below in connection with the example of a vehicle  100  of  FIG. 1 , the vehicle  100  includes a motor drive system  102  for masking vehicle sound. In various embodiments, the motor drive system  102  masks vehicle sound in accordance with the steps set forth further below in connection with the process  400  of  FIG. 4  and the exemplary implementations of  FIGS. 2-8 , also discussed further below. 
     In various embodiments, as depicted in  FIG. 1 , vehicle  100  also includes, in addition to the above-referenced motor drive system  102 , a body  104 , a chassis  106 , and four wheels  108 . The body  104  is arranged on the chassis  106  and substantially encloses the other components of the vehicle  100 . The body  104  and the chassis  106  may jointly form a frame. The wheels  108  are each rotationally coupled to the chassis  106  near a respective corner of the body  104 . In various embodiments, the vehicle  100  may differ from that depicted in  FIG. 1 . For example, in certain embodiments the number of wheels  108  may vary. 
     In various embodiments, the motor drive system  102  is disposed within the body  104  of the vehicle  100 , and is mounted on the chassis  106 . As depicted in  FIG. 1  discussed further below, in various embodiments, the motor drive system  102  includes a motor  110 , a power source  112 , an inverter module  114 , and a control system  116 . 
     In various embodiments, the motor  110  includes one or more electric motors. In certain embodiments, the motor  110  may include one or more other types of motors (e.g., gas combustion engines). Also in various embodiments, the motor  110  is utilized as part of a powertrain and/or actuator assembly for powering movement of the vehicle  100 , for example by powering one or more wheels  108  of the vehicle  100  via engagement of one or more drive shafts (e.g., axles)  118  of the vehicle  100 . 
     Also in various embodiments, the power source  112  includes one or more vehicle batteries, direct current (DC) power sources, and/or other vehicle power sources. In addition, in various embodiments, the inverter module  114  receives direct current from the power source  112 , and converts the direct current to alternating current (AC) for use by the motor  110 . 
     In various embodiments, the control system  116  controls operation of the motor drive system  102 , including operation of the motor  110  thereof. In addition, in various embodiments, the control system  116  provides masking for certain vehicle sounds through the control of the motor  110 , for example in accordance with the steps set forth further below in connection with the process  400  of  FIG. 4  and the exemplary implementations of  FIGS. 3-8 , also discussed further below. 
     As depicted in  FIG. 1 , the control system  116  comprises a sensor array  118  and a computer system  120 . In various embodiments, the sensor array  118  includes one or more sensors (e.g., voltage sensors, current sensors, motor position sensors, and/or other sensors) for use in controlling the motor  110  and/or other components of the motor drive system  102 . In the depicted embodiment, the computer system  120  of the control system  116  includes a processor  122 , a memory  124 , an interface  126 , a storage device  128 , and a bus  130 . The processor  122  performs the computation and control functions of the control system  116 , and may comprise any type of processor or multiple processors, single integrated circuits such as a microprocessor, or any suitable number of integrated circuit devices and/or circuit boards working in cooperation to accomplish the functions of a processing unit. During operation, the processor  122  executes one or more programs  132  contained within the memory  124  and, as such, controls the general operation of the control system  116  and the computer system of the control system  116 , generally in executing the processes described herein, such as the process  400  described further below in connection with  FIG. 4  and the exemplary implementations of  FIGS. 5-8 . 
     The memory  124  can be any type of suitable memory. For example, the memory  124  may include various types of dynamic random access memory (DRAM) such as SDRAM, the various types of static RAM (SRAM), and the various types of non-volatile memory (PROM, EPROM, and flash). In certain examples, the memory  124  is located on and/or co-located on the same computer chip as the processor  122 . In the depicted embodiment, the memory  124  stores the above-referenced program  132  along with one or more stored values  134 . 
     The bus  130  serves to transmit programs, data, status and other information or signals between the various components of the computer system of the control system  116 . The interface  126  allows communication to the computer system of the control system  116 , for example from a system driver and/or another computer system, and can be implemented using any suitable method and apparatus. In one embodiment, the interface  126  obtains the various data from the sensors of the sensor array  104 . The interface  126  can include one or more network interfaces to communicate with other systems or components. The interface  126  may also include one or more network interfaces to communicate with technicians, and/or one or more storage interfaces to connect to storage apparatuses, such as the storage device  128 . 
     The storage device  128  can be any suitable type of storage apparatus, including direct access storage devices such as hard disk drives, flash systems, floppy disk drives and optical disk drives. In one exemplary embodiment, the storage device  128  comprises a program product from which memory  124  can receive a program  132  that executes one or more embodiments of one or more processes of the present disclosure, such as the steps of the process  400  (and any sub-processes thereof) described further below in connection with  FIG. 4  and the exemplary implementations of  FIGS. 3-8 . In another exemplary embodiment, the program product may be directly stored in and/or otherwise accessed by the memory  124  and/or a disk (e.g., disk  136 ), such as that referenced below. 
     The bus  130  can be any suitable physical or logical means of connecting computer systems and components. This includes, but is not limited to, direct hard-wired connections, fiber optics, infrared and wireless bus technologies. During operation, the program  132  is stored in the memory  124  and executed by the processor  122 . 
     It will be appreciated that while this exemplary embodiment is described in the context of a fully functioning computer system, those skilled in the art will recognize that the mechanisms of the present disclosure are capable of being distributed as a program product with one or more types of non-transitory computer-readable signal bearing media used to store the program and the instructions thereof and carry out the distribution thereof, such as a non-transitory computer readable medium bearing the program and containing computer instructions stored therein for causing a computer processor (such as the processor  122 ) to perform and execute the program. Such a program product may take a variety of forms, and the present disclosure applies equally regardless of the particular type of computer-readable signal bearing media used to carry out the distribution. Examples of signal bearing media include: recordable media such as floppy disks, hard drives, memory cards and optical disks, and transmission media such as digital and analog communication links. It will be appreciated that cloud-based storage and/or other techniques may also be utilized in certain embodiments. It will similarly be appreciated that the computer system of the control system  116  may also otherwise differ from the embodiment depicted in  FIG. 1 , for example in that the computer system of the control system  116  may be coupled to or may otherwise utilize one or more remote computer systems and/or other systems. 
       FIG. 2  provides a functional diagram of the motor drive system  102  of the vehicle  100  of  FIG. 1 , in accordance with exemplary embodiments. Specifically, in various embodiments,  FIG. 2  shows a three-phase AC motor drive system  102  using the inverter from a DC power supply as the power source  112 . In various embodiments, the control system  116  uses the motor position θ r  and speed ω r , and synthesize the output voltage using the IGBT input S ap ˜S cn  (for example, as discussed further below) to control the output current i a , i b  and i c  in order to deliver the function such as torque generation or speed control. As noted above, in various embodiments, the motor drive system  102  may be implemented in various embodiments as a stand-alone system and/or in connection with any number of vehicles, mobile platforms, and/or other systems. 
     With continued reference to  FIG. 2 , in various embodiments the motor drive system  102  comprises a multi-phase electric motor drive system. Also in various embodiments, the motor drive system  102  comprises the motor  110 , power source  112 , inverter module  114 , and control system  116  of  FIG. 1 . Also in various embodiments, the inverter module  114  is disposed between the power source  112  (e.g., a direct current (DC) power source) and the motor  110 . In certain embodiments, the inverter module  114  includes the control system  116  (in whole or in part), along with an inverter power circuit  202 , which can be collocated in a single package in certain embodiments. 
     In various embodiments, the motor  110  may be configured as a three-phase permanent magnet device that includes a rotor  204  that is disposed within a stator  206 . Also in certain embodiments, one or more position sensors  208  (e.g., of the sensor array  118  of  FIG. 1 ) may be utilized to monitor a rotational position θ r  and rotational speed ω r  of the rotor  204 . In various embodiments, the position sensors  208  may be physically part of, and/or physically separate from, the control system  116 . In certain embodiments, the position sensors  208  comprise one or more Hall effect sensors. In certain other embodiments, the position and/or speed may be monitored via one or more other types of sensors (e.g., of the sensor array  118  of  FIG. 1 ), and/or from a resolver of the motor  110 , and/or from one or more motor commands (e.g., as may be obtained via the processor  122  of  FIG. 1 ). 
     In various embodiments, the power source  112  is electrically connected to the inverter power circuit  202  via a high-voltage bus  211 . In certain embodiments, the high-voltage bus  211  includes a positive high-voltage bus link (HV+)  212  and a negative high-voltage bus link (HV−  213 . In certain embodiments, a voltage sensor  216  (e.g., which may be part of the sensor array  121  of  FIG. 1  in certain embodiments) monitors electric potential across positive high voltage bus link  212  and negative high voltage bus link  213 . 
     In various embodiments, various power conductors  218  are utilized to electrically connect the power source  112  to the inverter power circuit  202  via the high-voltage DC bus  211 . Also in various embodiments, in this manner high-voltage DC electric power is transferred from the power source  112  to the motor  110  via the power conductors  218  in response to control signals provided by the control system  116 . 
     In various embodiments, the inverter power circuit  202  includes various control circuits, such as power transistors  210  (e.g., paired power transistors  210 , such as Integrated Gate Bipolar Transistors (IGBTs)) for transforming high-voltage direct current (DC) electric power to high-voltage alternating current (AC) electric power and transforming high-voltage AC electric power to high-voltage DC electric power. Also in various embodiments, the power transistors  210  of the inverter module  114  are electrically connected to the motor  110  via the power conductors  218 . In addition, in various embodiments, one or more current sensors  212  (e.g., which may be part of the sensor array  118  of  FIG. 1  in certain embodiments) are disposed to monitor electrical current in each of the power conductors. In certain embodiments, the inverter power circuit  202  and control system  116  are configured as a three-phase voltage-source pulse width modulated (PWM) converter that can operate in either a linear mode or a non-linear mode. 
     In certain embodiments, the control system  116  controls the power transistors  210  of the inverter power circuit  202  to convert stored DC electric power originating in the power source  112  to AC electric power to drive the motor  110  to generate torque. Similarly, the control system  116  can control the power transistors  210  of the inverter power circuit  202  to convert mechanical power transferred to the motor  110  to DC electric power to generate electric energy that is storable in the DC power source  20 , including as part of a regenerative control strategy. The control system  116  can control the power transistors  210  employing linear and/or non-linear pulse width modulating (PWM) control strategies. 
     In certain embodiments, the control system  116  receives motor control commands and controls inverter states of the inverter power circuit  202  to provide motor drive and regenerative power functionalities. Signal inputs from the position sensor  208 , the power conductors  218  and the voltage sensor  35  are monitored by the control system  116 . The control system  116  communicates via control lines  214  to individual ones of the power transistors  210  of the inverter power circuit  202 . The control system  116  includes control circuits, algorithms and other control elements to generate transistor control inputs S ap ˜S cn  which are communicated via the control lines  214  to the power transistors  210  of the inverter power circuit  202 . The power transistors  210  control the output currents i a , i b  and i c , which are transferred via the power conductors  218  to the motor  110  to generate power in the form of torque and/or rotational speed based upon the motor position θ r  and speed ω r . 
     Also in various embodiments, the control system  116  receives and implements motor control commands in a manner that masks vehicle sound in accordance with the steps set forth further below in connection with the process  400  of  FIG. 4  and the exemplary implementations of  FIGS. 3-8 , also discussed below. 
       FIG. 3  schematically shows an embodiment of the motor controller  116  and inverter power circuit  114  of  FIG. 2 , which control operation of the electric motor of  FIGS. 1 and 2 , in various embodiments. As depicted in various embodiments, the motor controller  116  includes a first controller  302  and an acoustic signal generator  304 , which combine to generate input signals Vdi and Vqi that are converted to the transistor control inputs S ap ˜S cn    270  of  FIG. 2  to control the power transistors  210  of the inverter power circuit  114  of  FIG. 2 . 
     The first controller  302  generates commands to control operation of the electric motor  110  based upon operating conditions, such as a torque command  306 , motor speed  308 , electrical potential  310 , and/or other operating conditions. 
     The acoustic signal generator  304  generates a control output that injects an acoustic sound element in the form of a sound injection voltage  312  into the first controller  302 . In various embodiments, the acoustic signal generator  304  comprises a sound pattern generator  308  that generates an instantaneous audio signal V i    332 , and a rotational transformation element  310 . 
     In various embodiments, the acoustic signal generator  304  can be in the form of a dedicated hardware circuit, an algorithm or another suitable form. The sound injection voltages  312  from the acoustic signal generator  304  and the initial output voltages V d ** and V q **  314  combine to form voltage signals for controlling the motor output voltage that controls the electric motor  110  to generate a suitable acoustic signal coincident with generating and controlling torque and/or speed, and that marks certain tonal sounds, for example in accordance with the process  400  described further below. As employed herein, the term ‘sound’ refers to audible acoustic sound. 
     In various embodiments, the first controller  302  comprises a torque-to-current converter  316 , a current regulator  318 , an inverse Park transformation operation T −1 (θ) (dq-αβ) 320, an inverse Clarke transformation (αβ-abc) operation  322 , a Clarke transformation operation (abc-αβ)  324 , and a Park transformation operation T(θ) (αβ-dq)  326 . 
     The torque-to-current converter  316  converts the torque command  306  into a pair of current commands i d * and i q *  330 , which are input to the current regulator  318 . Monitored 3-phase AC currents from the power conductors  218 , i.e., i a , i b  and is 328 are reduced to stationary reference frame currents in the form of a pair of sinusoidal currents i α  and i β    336  by the Clarke transformation operation (abc-αβ)  324 , and then transformed into currents i d  and i q    334  by the Park transformation operation T(θ) (αβ-dq)  326  in the rotating reference domain using the motor position and motor speed information from the position sensor  208 . The current regulator  318  uses the pair of current commands i d * and i q *  330  from the torque-to-current converter  316  and feedback from the Park transformation operation T(θ) (αβ-dq)  326  to generate a pair of initial output voltages V d ** and V q **  314  for operating the electric motor  110  to generate torque. 
     The acoustic signal generator  304  is composed of a sound pattern generator  308  that generates an instantaneous audio signal V i    332 , and a rotational transformation element  310  that generates sound injection voltages V di  and V qi    312  based upon the instantaneous audio signal V i    332 . The term ‘generator’ as employed in the terms ‘acoustic signal generator’ and ‘sound pattern generator’ can include hardware, software, and/or firmware components that have been configured to perform the associated specified functions that have been described. The sound injection voltages V di  and V qi    312  are injected to the initial output voltages V d ** and V q **  314  for operating the electric motor  110  to generate torque. The instantaneous audio signal V i    332  from the sound pattern generator  308  is generated and decomposed by the rotational transformation element  310  so as to vary the sound injection. The rotational transformation  310  is executed to locate the sound injection voltages V di  and V qi    312  into the correct angular location γ in the electromagnetic circuit of the electric motor  110 , and can be expressed as follows: 
     
       
         
           
             
               
                 
                   
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     wherein γ represents the correct angular location. 
     The sound injection voltages V di  and V qi    312  are added to the initial output voltages V d ** and V q **  314  that are output from the current regulator  318  to generate the signal that is input to the inverse rotational transformation operation T −1 (θ) (dq-αβ)  320 , i.e., V d * and V q *. As such, the sound injection voltages V di  and V qi    312  are added to the corresponding initial output voltages V d ** and V q **  314  of the current regulator  318  of the motor controller  116 . The combination of the initial output voltages  314  and the sound injection voltages  312 , i.e., V d *=V d **+V di  and V q *=V q **+V qi  are inverse-transformed back to the stationary reference frame voltage commands V α * and V β *  126  in the inverse rotational transformation operation T −1 (θ) (dq-αβ)  320  using the position information from the position sensor  208 . The stationary reference frame voltage commands V α * and V β *  126  are decomposed into output voltage commands V a , V b  and V c    171  in the inverse Clarke transformation (αβ-abc) operation  322 , and finally converted to the transistor control inputs S ap ˜S cn    270 , which are communicated via the control lines  214  to the power transistors  210  of the inverter power circuit  114  to cause the electric motor  110  to generate audible acoustic sound, wherein the audible acoustic sound can be sensed by a pedestrian when the electric motor  110  is employed on an electric vehicle application. 
     Accordingly, in various embodiments, the control of the 3-phase AC motor is composed of elements  316 ,  318 ,  320 ,  322 , and  114  of  FIG. 3 ; depending on the operating condition (torque command T e *, motor speed N r  and the inverter input voltage V dc ), the torque conversion unit  316  converts the torque command into a pair of current commands i d * and i q * for the current regulator  318 . Also in various embodiments, 3-phase AC currents (i a , i b  and i c  from  328 ) are reduced to a pair of sinusoidal current i α  and i β  (called as stationary reference frame currents) in conversion unit  324 , and then transformed into i d  and i q  by transformation unit  326  in the rotating reference domain using the motor position and speed information from the sensor  208 . The current regulator  318  uses the current command from the torque conversion unit  316  and feedback from the transformation unit  326  to make a pair of output voltages V d ** and V q ** for the motor. Without a new function, output voltages V d *=V d ** and V q *=V q **are inverse-transformed back to the stationary reference frame voltage V α * and V β * in  320  using the position information from  208 . Then they are decomposed into V a , V b  and V c  in conversion box  322 , and finally converted to the IGBT command S ap ˜S cn  of  FIG. 2 , which are communicated via the control lines  214  to the power transistors  210  of the inverter power circuit  114  to cause the electric motor  110  to generate audible acoustic sound, including the desired masking for the tonal motor sound, for example as discussed in greater detail further below in connection with the process  400  of  FIG. 4  and the exemplary implementations of  FIGS. 5-8 . 
       FIG. 4  is a block diagram of a process  400  for masking vehicle sounds, in accordance with exemplary embodiments. The process  400  can be implemented in connection with the vehicle  100 , including the motor drive system  102  and components thereof of  FIGS. 2 and 3 , in accordance with exemplary embodiments. The process  400  is also discussed further below in connection with  FIGS. 5-7 , which provide graphical representations of an exemplary case study of sound masking utilizing the techniques of the motor drive system and vehicle of  FIGS. 1-3  and the process of  FIG. 4 , including the use of dithering techniques ( FIG. 5 ); complementary tones ( FIG. 6 ), and combinations thereof ( FIG. 7 ), in accordance with exemplary embodiments. The process  400  is also discussed further below in connection with  FIG. 8 , which provides a graphical representation of exemplary test results using sound masking utilizing the techniques of the motor drive system and vehicle of  FIGS. 1-3 , in accordance with exemplary embodiments. 
     In various embodiment, the process  400  may be initiated any time when the vehicle  100  encounters a tonal noise issue. In certain embodiments, the process  400  continues throughout the vehicle drive, or as long as the tonal noise issue is present. 
     In various embodiments, the process  400  masks vehicle noises, such as relatively high pitch tonal noises from the motor  110  of  FIG. 1  (e.g., from an electric motor) that could otherwise be uncomfortable for a driver or other user of the vehicle, and that could otherwise raise possible sound quality issues for electrified propulsion systems. Also in various embodiments, in general, the process  400  ( i ) controls the motor  110  (e.g., an electric motor) in order to create complementary low order tones to enrich sound complexity and achieve distraction of high pitch tonal noise targets; (ii) controls the motor  110  to generate random dithering noise to raise masking noise floor around tonal targets and reduce tone-to-noise ratio for active masking; (iii) combines both complementary injection (at low freq/rpm) and dithering (at high freq/rpm) for effective masking; and (iv) enables control of masking noise level, frequency, order and bandwidth as a function of motor torque/rpm for effective masking. 
     With continued reference to  FIG. 4 , an exemplary implementation of the process  400  for the proposed active masking technology using a motor-based acoustic generator is provided. In various embodiments, block  399  of  FIG. 4 , the playback speed of the sound is determined as a function of motor speed N r , which is received as input  308  from  FIG. 3  (e.g., from one or more motor sensors of the sensor array  121  of  FIG. 1 , for from one or more motor commands from the processor  122  of  FIG. 1 , or the like, in various embodiments). 
     In various embodiments, one or more tonal sounds are created at block  403 . In certain embodiments, a single tonal sound is generated at block  403 . However, this may vary in other embodiments. Also in certain embodiments, the tonal sound(s) at block  403  comprise one or more complementary tones to help with masking one or more vehicle and/or motor sounds for which masking may be desired. Also in various embodiments, a sinusoidal signal generator  402  obtains the input from the playback speed K n , and a predetermined frequency f comp1  and angle corresponding to the time “t” via operator  401 , in accordance with Equation (2) below:
 
 V   1   =V   comp1  sin( K   n   ·f   comp1 ·2π t )  (2)
 
     Similarly, in various embodiments, a second tonal sound at block  412  can be obtained from blocks  410  and/or  411 . Also in certain embodiments, the tonal sound(s) at block  412  comprise one or more complementary tones to help with masking one or more vehicle and/or motor sounds for which masking may be desired. In certain embodiments, in  FIG. 4 , only two complementary tonal sounds are shown (i.e., at  403  and  412 ). However, in various other embodiments, additional tonal sounds can be added as needed. In various embodiments, at block  419 , the output of each tonal sound source is collected and summed. In various embodiments, the tonal sounds are used to create the complementary tones. 
     In various embodiments, the sound from block  418  is used to create the dither sound. In various embodiments, a random number generator  414  generates a number between −1 and 1, and the output is multiplied with ½ f span  at operator  415 , which creates the frequency variation between −½f span  and +½f span . In various embodiments, the output of operator  415  is combined with center frequency inputs at operator  413 , to generate an updated frequency at operator  416 . Also in various embodiments, this frequency is then dithered (Δf) at operator  413 , and is added to the center frequency f center  for the input of the sine signal generator  417 . Later, the output is multiplied with the amplitude V dither , and added in block  419 . The summed output at block  419  goes through controlled amplifier  404  and  405  to adjust the sound volume as a function of the motor speed and torque. Block  408  is used to scale the overall sound volume to the voltage for the final implementation, and block  409  limits the final output voltage. Later, the output of block  409  goes to the input of block  312  in  FIG. 3 , to be blended in the motor control. 
     In certain embodiments, torque-based derating is provided at block  407 , using a motor torque value  430  as an input. In various embodiments, during block  407 , the motor torque value  430  is utilized to generate a torque-based gain, resulting in torque-based derating of the motor sound as provided as an output to block  405 . 
     Also in certain embodiments, speed-based derating is provided at block  406 , using the motor speed  308  as an input. In various embodiments, during block  406 , the motor speed value  308  is utilized to generate a speed-based gain, resulting in speed-based derating of the electric motor sound as provided as an output to block  404 . 
     With continued reference to block  419  and the preceding blocks feeding into block  419 , the steps utilized to determine the complementary tones and dither tones are explained in further detail below. 
     First, in various embodiments, at steps  413 - 416 , the dithering frequency is defined in span to be wider than Critical Bandwidth (CB) for effective masking of high pitch tones at center frequency. Estimate Critical Bandwidth of auditory filter use Moore&#39;s empirical model for ERB (Equivalent Rectangular Bandwidth), such as in B. Moore&#39;s publication entitled “Frequency analysis and Masking, Chapter 4”, in Handbook of Perception and Cognition, 2 nd  Edition, Academic Press, 1995, p. 176, incorporated by reference herein. For instance, in order to mask 72nd order motor whine at 1500 rpm, the CB of 1.8 kHz center frequency is estimated to be 219 Hz. The dithering frequency span is created to cover the entire CB. 
     Second, also in various embodiments, at steps  416 - 418 , the dithering magnitude level is defined in accordance with requirements using Critical Masking Ratio (CMR) curve. For instance, estimate the CMR about 17 dB for tonal frequency of 1.8 kHz (72nd order at 1500 rpm) using known reference curves, such as in Kinsler &amp; Frey&#39;s published article “Fundamentals of Acoustics”, J. Wiley &amp; Sons, 1962, at p. 412, incorporated by reference herein. In various embodiments, the motor is controlled via dithering in order to generate random dithering noise to raise the floor around tonal targets and to reduce the tone-to-noise ratio for active masking (i.e., to mask the tone). 
     For example, with further reference to  FIG. 5 , a case study is provided to demonstrate the masking concept using vehicle noise measured at 3000 rpm with 90 Nm motor torque. Specifically, a graph  500  is provided, using frequency (in Hz) along the x-axis and sound (in Db) along the y-axis. The baseline noise (denoted in solid lines, at exemplary locations  501  of  FIG. 5 ) in frequency domain shows high levels of potentially undesirable high pitch tonal noise proximate region  502  as represented in the graph  500  of  FIG. 5 , around 72 nd  order (masking targets) between 3 to 4 kHz, which causes EV sound quality problems due to very little masking in this frequency range. In various embodiments, the dithered noise is denoted in dashed lines, at exemplary locations  503  of  FIG. 5 . In various embodiments, measured noise data associated with dithering of the motor (represented in region  504  of  FIG. 5 ) raised noise floor around the masking targets (CB selected to be 600 Hz) by using the dithering technology with motor-based acoustic generator as explained above. 
     Third, also in various embodiments, at steps  401 - 412 , complementary tones are defined as low-order overlapping-harmonics, for example as complementary music tones. For example, in certain embodiments, the same frequency ratio is utilized as a music major triad; 4th and 12th harmonics are selected for 8 pole Permanent Magnet motor) to produce a more consonant sound, and to distract from unpleasant high pitch tones. In various embodiments, this more complex sound masks the natural occurring single tone. For example, in certain embodiments, one or more complementary low-order harmonic sounds are used with respect to the motor tonal sound in order to enrich the sound complexity and achieve distraction of high pitch tonal noise targets. 
     For example, with further reference to  FIG. 6 , a case study is provided that demonstrates the injection of 4 th  and 12 th  harmonics to mask a vehicle motor noise as distracting low order tones, with effectiveness confirmed by user tests. Specifically, a graph  600  is provided, using frequency (in Hz) along the x-axis and sound (in Db) along the y-axis. The baseline noise is denoted in solid lines, at exemplary locations  601  of  FIG. 6 , and include masking targets, for example as denoted in region  602  of  FIG. 6 . In various embodiments, the complementary sounds are denoted in dashed lines, at exemplary locations  603  of  FIG. 6 . In various embodiments, the complementary tones  603  (e.g., including the 4 th  and 12 th  harmonics with respect to the motor tonal noise that is desired to be masked) help to enrich the sound complexity and achieve distraction of high pitch tonal noise targets (e.g., the depicted tonal masking target  602  of  FIG. 6 ). 
     Fourth, at steps  419 ,  404 - 409  voltage signals of dithering and/or complementary tones are injected at current regulator output. In certain embodiments, the dithering may be utilized instead of the complementary tones. In other embodiments, the complementary tones may be utilized instead of the dithering. In yet other embodiments, the dithering and complementary tones may be used together for maximum effectiveness. Accordingly, in various embodiments, the dithering and complementary tones can be activated individually or together to achieve the maximum masking of motor tonal noise targets pending feedback from motor/electric vehicle test results. 
     For example, with further reference to  FIG. 7 , a case study is provided that demonstrates both dithering and complementary tone techniques activated at the same time to achieve maximum masking of the high pitch tonal noise. Specifically, a graph  700  is provided, using frequency (in Hz) along the x-axis and sound (in dB) along the y-axis. The baseline noise is denoted in solid lines, at exemplary locations  701  of  FIG. 7 . In various embodiments, the dithered motor sounds are denoted in dashed lines in region  702  of  FIG. 7  (i.e., on the right side of  FIG. 7 ). Also in various embodiments, the complementary sounds are denoted in dashed lines in region  703  of  FIG. 7  (i.e., on the left side of  FIG. 7 ). In various embodiments, the dithered sounds  702  and the complementary sounds  703  work together to mask the tonal noise  701  and to provide a measure pleasing sound for the occupants inside the vehicle  100 . 
     Fifth, in various embodiments, at step  406 , a tracking of motor tonal orders is enabled by incrementing sound pitch as a function of motor speed  308  (for example, as discussed above in connection with step  406 ). In various embodiments, harmonic injection frequency and bandwith are both defined proportional to the motor speed, and thus this allows for the tracking of a specific tonal noise order at varying operating speeds of the motor vehicle. 
     Sixth, in various embodiments, an identification is made as to a minimum voltage injection (e.g., using available voltage without disturbing motor control) to achieve tonal masking and reduce motor efficiency loss. In accordance with various embodiments, the available voltage control is shown by the Amplitude Limit of  409 . 
     For example, with further reference to  FIG. 8 , graphical representations are provided of exemplary test results using sound masking utilizing the techniques of the motor drive system and vehicle of  FIG. 1  and components of  FIGS. 2 and 3 , the process of  FIG. 4 , and the implementations of  FIGS. 5-7 , in accordance with exemplary embodiments. In various embodiments, the graphical representations of  FIG. 8  compare measured vehicle cabin noise data before and after both dithering and commentary tones injected over the 0 to 60 mph drive-away event. Specifically, in various embodiments, first graph  802  shows baseline motor noise levels for a vehicle, for example an electrical vehicle (with motor revolutions per minute on the x-axis and frequency, in Hz, on the y-axis). Second graph  804  shows revised motor noise levels for a vehicle, for example an electrical vehicle (with motor revolutions per minute on the x-axis and frequency, in Hz, on the y-axis). 
     In the example of  FIG. 8 , dither noises were created at region  803  to raise the noise floor around 72 nd  tonal target. In addition, also as shown in  FIG. 8 , low order harmonics at 4 th  and 12 th  orders are also injected as complementary tones at region  804  to distract passengers&#39; attention of the high pitch noise. In addition, it is noted that user test results confirm effectiveness of active masking: (i) 93.3% (14 out of 15) feel difference before and after injection; (ii) 86.7% (13 out of 15) feel injection makes motor noise less tonal/sharp; (iii) 73.3% (11 out of 15) feel injection improves sound quality (i.e., less displeasing). 
     Accordingly, the systems, vehicles, and methods described herein provide for masking of vehicle noises. In various embodiments, complementary tones, dithering of tonal noises, or both are utilized for masking certain vehicle tonal noises, for example in order to provide an improved experience for the driver and/or other users of the vehicle. 
     It will be appreciated that the disclosed methods, systems, and vehicles may vary from those depicted in the Figures and described herein. For example, the vehicle  100 , the motor driver system  102 , and/or various components thereof may vary from that depicted in  FIGS. 1-3  and/or described in connection therewith. In addition, it will be appreciated that certain steps of the process  400  may vary from those depicted in  FIG. 4  and/or described above in connection therewith. It will similarly be appreciated that certain steps of the methods described above may occur simultaneously or in a different order than that depicted in  FIG. 4  and/or described above in connection therewith. It will similarly be appreciated that the various implementations of  FIGS. 5-8  may also differ from those depicted in  FIGS. 5-8  may differ from those depicted therein and/or described herein, and so on. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.