JP5433338B2 - Vehicle operating sound control device - Google Patents

Description

  The present invention relates to vehicle operating sound control.

  Patent Document 1 discloses a technique for reducing noise generated by an electric motor by controlling a driving current of the electric motor. In Patent Document 1, the amplitude and phase of a high-order current superimposed according to operating conditions are set optimally, thereby reducing the excitation force and reducing the noise generated by the motor.

JP 2000-13066 A

  In the above invention, it is possible to reduce the noise generated by the electric motor, but there is a problem that the feeling of acceleration felt by the driver during acceleration of the vehicle is reduced.

  The present invention was invented to solve such problems, and it is an object of the present invention to increase the feeling of acceleration during acceleration traveling and to improve sound quality during acceleration traveling.

  The present invention relates to a vehicle operating sound control device. A vehicle operation sound control device includes a motor, a rotation angle detection unit that detects a rotation angle of the motor, and a rotation angle extraction that extracts a rotation angle a predetermined time based on the rotation angle detected by the rotation angle detection unit. Means. In addition, the first signal having an electrical angle order component that becomes an operation sound of the motor from the rotation angle extracted by the rotation angle extraction means a predetermined time ago and the first signal having an electrical angle order component that becomes the operation sound of the motor from the current rotation angle. An operation sound signal calculating means for calculating two signals is provided. Furthermore, a voltage command value generating means for generating a voltage command value based on a value obtained by multiplying the first signal and the second signal calculated by the operating sound signal calculating means, and a voltage command value generated by the voltage command value generating means And a control means for controlling the inverter based on the above.

  According to the present invention, a sound having a time delay is generated and a delay effect is added to the original sound generated by the motor, so that the sound quality during acceleration traveling can be improved.

It is a schematic structure figure of vehicles of a 1st embodiment. It is a figure which shows the sound quality evaluation result of 1st Embodiment. It is a figure which shows the relationship between a sound pressure when there is no delay effect, or a sound pressure when there is a delay effect, and a frequency. It is a schematic sectional drawing of the motor of 1st Embodiment. It is a figure which shows the relationship between an electrical angle and the electric current of a motor. It is a figure which shows the relationship of the basic current of a motor with respect to an electrical angle, a correction coefficient, and a drive current. It is a figure which shows the magnetic characteristic of a drive current and an exciting force. It is a figure which shows the excitation force characteristic with respect to the coefficient decided by vehicle driving conditions. It is a figure which shows the sound quality evaluation result of 2nd Embodiment. It is a figure which shows the exciting force characteristic with respect to time delay. It is a schematic block diagram of the external operation part of 3rd Embodiment.

  The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a vehicle according to the present embodiment.

  The vehicle 1 according to this embodiment includes a battery 2 that stores electric power supplied from an external power source, an inverter 4 that converts a direct current of the battery 2 into a three-phase alternating current based on a command from the controller 3, and a three-phase alternating current. And a motor 5 that is driven to rotate.

  The inverter 4 converts a direct current supplied from the battery 2 into a three-phase alternating current. The current converted into the three-phase alternating current is supplied to the motor 5 as a drive current.

  Although the motor 5 will be described in detail later, it is constituted by a synchronous AC motor 5. The rotation of the motor 5 is transmitted to the wheels 8 via the speed reducer 6 and the differential gear 7.

  The controller 3 includes a microcomputer having a central processing unit (CPU) 20, a read only memory (ROM) 21, a random access memory (RAM) 22, and an input / output interface (I / O interface) 23. . It is also possible to configure the controller 3 with a plurality of microcomputers. The controller 3 calculates a basic current, a drive current instruction value, and the like by executing a program stored in the ROM 21 and controls the inverter 4 and the like.

  The controller 3 calculates a basic current and a drive current instruction value according to the driving state of the vehicle 1. The controller 3 outputs a predetermined three-phase alternating current from the inverter 4 based on a comparison between the drive current instruction value and the actual current value detected by the current sensor 9 that detects the actual current value flowing in each phase. Current feedback control. The controller 3 controls the inverter 4 so that a drive current based on the drive current instruction value is supplied to the motor 5. That is, the controller 3 calculates a voltage command value in the inverter 4 based on the drive current command value, and controls the inverter 4 based on the voltage command value.

  The acceleration of the vehicle 1 generally means that the driver has a positive intention to accelerate. Therefore, when the vehicle 1 is traveling at an accelerated speed, the operating sound of the motor 5 that is a driving source is changed to a sound quality that allows the driver to feel acceleration, and the changed sound is actively heard by the driver. The ring can be improved.

  By actively generating the operation sound of the motor 5 in this way, the operation sound originally generated by the motor 5 (hereinafter referred to as the original sound) becomes inconspicuous. As a result, for example, an effect of eliminating an operation sound reducing member such as a sound insulation cover can be expected.

  FIG. 2 shows that when the delay effect of adding a sound with a time delay to the original sound during steady driving and the original sound during acceleration driving is added as the steady driving sound and the acceleration traveling sound, the inventors This is a result of sound quality evaluation by SD method (semantic scale method) by letting the driver know the driver. The application of the SD method to sound quality evaluation is described in “Psychological Measurement Method for Sound Evaluation” (by Seichiro Namba and Sonoko Kuwano, Corona, ISBN: 978-4-339-01104-3), pages 107-133 It is known.

  The evaluation result is a case where it is equivalent to the original sound having no reference delay effect, and the higher the value, the more positive the answer. The evaluation results are averages obtained when the delay effect is added under various conditions. Comparing the steady running sound and the accelerated running sound, the accelerated running sound has a better score by adding a delay effect as a whole. The subject feels particularly strongly in the acceleration running sound such as “interesting”, “creative”, “innovative”, “futuristic”, “sounding”, “remaining in the ear”. In addition, the test subject does not feel the feeling of “uncomfortable” and “bad” felt by the steady running sound with the accelerated running sound. In this way, by adding a delay effect to the original sound at the time of acceleration driving of an electric vehicle, it is possible to create a new and fun sound that has never existed before, and the sound quality during acceleration driving Can be improved.

  Since the original sound generated from the motor 5 becomes the rotation order component, it has a frequency component proportional to the rotation speed. However, since the speed is not completely constant in steady running, the frequency of the original sound and the frequency of the sound having a time delay are close to each other, and a low frequency beat is generated. Such beats affect the subject as a beat sound, and the subject feels “uncomfortable” and “bad” during steady running. Therefore, there is a risk that the subject may feel uncomfortable.

  Therefore, it is desirable to add a delay effect to the original sound generated by the motor 5 by generating a sound with a time delay during acceleration traveling. On the other hand, it is desirable not to add a delay effect to the original sound generated by the motor 5 during steady running. In order to realize these, the controller 3 switches whether to add a delay effect to the original sound emitted by the motor 5.

  FIG. 3 shows the relationship between the sound pressure when there is no delay effect or the sound pressure and frequency when there is a delay effect. FIG. 3A is a diagram showing the relationship between sound pressure and frequency when there is no delay effect. FIG. 3B is a diagram showing the relationship between sound pressure and frequency when there is a delay effect. In FIG. 3, the sound pressure level increases as the thickness of the line increases. When there is a delay effect, as shown in FIG. 3B, a sound having a time delay with respect to the original sound without the delay effect is generated. By generating a sound with a time delay, the original sound and the sound with a time delay are overlapped to create a reverberant sound. Therefore, in order to add a delay effect to the original sound, it is necessary to generate a sound having a time delay, and it is necessary to generate a sound corresponding to the motor sound a predetermined time ago.

  In the present embodiment, a high-order component of the basic current is added to the basic current of the drive current of the motor 5 to generate a sound having the main noise frequency of the motor a predetermined time ago. Thereby, a sound corresponding to the motor sound a predetermined time ago is generated.

  Here, the motor 5 will be described in detail with reference to FIG. FIG. 4 is a schematic sectional view of the motor 5 of the present embodiment.

  The motor 5 includes a stator 10 and a rotor 11. The stator 10 includes twelve coils 13 in which three phases U, V, and W are alternately wound around the teeth 12. The coil 13 is concentrated winding. The rotor 11 includes eight permanent magnets 14 arranged at equal angular intervals along the outer periphery. The permanent magnet 14 constitutes a four-pole pair of permanent magnets by alternately arranging the permanent magnet 14 magnetized with the N pole on the outer peripheral side and the permanent magnet 14 magnetized with the S pole on the outer peripheral side. Further, the motor 5 includes a resolver 15 that detects the rotation angle of the rotor 11.

  The concentrated winding motor 5 of 4 pole pairs 12 slots is comprised by the above structure. In the case of a 4-pole motor, the permanent magnet 14 of the 1-pole pair of the rotor 11 corresponds to the three slots of the stator 10 at a mechanical angle of 90 degrees.

  FIG. 5A shows a current phase when the motor 5 is driven by applying a sinusoidal basic current having a mechanical angle of 90 degrees as one cycle to the coil 13. In FIG. 5A, the mechanical angle 90 degrees of the motor 5 corresponds to an electrical angle of 360 degrees. The current phase of the sinusoidal basic current (drive current) supplied to the motor 5 is determined based on the rotation angle detected by the resolver 15.

  At this time, the radial component of the electromagnetic force acting between the rotor 11 and the stator 10 is all at the frequency of the electrical angle 6th order and mechanical angle 24th order which is the least common multiple of the number of poles of the rotor 11 and the number of slots 3 of the stator 10 This is a so-called circular zero-order mode that acts on the teeth 12 in the same phase. In the circular 0th-order mode, the stator 10 expands and contracts uniformly in the radial direction, and the breathing spherical vibration that is most likely to generate sound is generated, so that the operating sound is the largest.

  FIG. 5B shows a current phase when the driving current is calculated by adding a high-order component to the basic current of the motor 5 and the motor 5 is driven by applying the driving current to the coil 13. As a result of the electromagnetic conversion of the current, the order of the generated electromagnetic excitation force is ± 1st order with respect to the order of higher order components included in the drive current. Therefore, it is possible to generate an excitation force having a desired frequency by adding an electrical angle ± primary higher-order current to the basic current with respect to the frequency of the electromagnetic excitation force to be generated.

In the present embodiment, it is held until the rotation angle theta _-.DELTA.t of the rotation angle theta as an electrical angle detected by the resolver 15 Delta] t seconds before the RAM22 of the controller 3 (predetermined time before). The rotation angle θ- _Δt is not limited to the RAM 22 and may be held in another memory. The controller 3 uses the rotation angle θ _−Δt before Δt seconds to correct the electrical angle 6th order which is the main order of the operating sound of the motor 5 with respect to the correction coefficient (first signal) having the electrical angle 6th order component before Δt seconds. ) K is calculated based on equation (1).

_{K = 1 + qsin (6θ -Δt} ) ··· formula (1)
q: Coefficient determined by vehicle driving conditions (for example, accelerator opening)

  The coefficient q determined by the vehicle operating condition indicates the amplitude of the electrical angle sixth-order component of the motor 5 corresponding to the frequency of the main sound of the motor 5 before Δt seconds.

Then, the controller 3 multiplies the calculated correction coefficient K by the basic current calculated according to the driving condition of the vehicle 1 based on the equation (2), thereby providing a drive current instruction value having an electrical angle ± primary component. (Current instruction values) I _u , I _v , I _w are calculated. The basic current is a signal (second signal) having an electrical angle sixth-order component that is an operation sound of the motor 5 from the current rotation angle θ.

I _u = KI ₀ sin (θ + θ ₀ )
I _v = KI ₀ sin (θ + θ ₀ − (2π / 3))
_{I w = KI 0 sin (θ} + θ 0 - (4π / 3)) ··· (2)
I ₀ : Amplitude of basic current determined by operating conditions, θ ₀ : Phase of basic current determined by operating conditions

The controller 3 controls the inverter 4 based on the calculated drive current instruction value. That is, the controller 3 multiplies the basic current waveform shown in FIG. 6A by the correction coefficient K shown in FIG. 6B to obtain the drive current instruction values I _u , I _v , and I _w shown in FIG. calculate. Then, the controller 3 calculates a voltage command value in the inverter 4 based on the drive current instruction values I _u , I _v , and I _w and controls the inverter 4 based on the voltage command value.

  As a result, a drive current based on the drive current instruction value is applied to the coil 13 of the motor 5 to drive the motor 5. The motor 5 generates an excitation force with a time delay of Δt seconds.

  Thus, by multiplying the basic current by the correction coefficient K having a sixth-order electrical angle component Δt seconds before, the basic current is corrected to calculate the driving current instruction value, thereby obtaining the driving current in FIG. As shown in a) (± 6th order before Δt seconds) ± first order higher order component current is added. As a result, as shown in FIG. 7B, a 6th-order electrical angle component Δt seconds before appears newly in the excitation force generated by the motor 5. That is, a sound in which a sound having a time delay of Δt is added to the original sound is generated from the motor 5. Thereby, a delay effect can be obtained.

  In this embodiment, Δt is 0.5 seconds. As a result of driving the motor 5 based on the calculated drive current instruction value, the excitation force generated by the motor 5 is in addition to the electrical angle 6th order excitation force originally possessed, and the electrical angle 6th order addition of Δt seconds ago. Vibration force is generated. As shown in FIG. 8, a sound with a time delay is generated in addition to the original sound by the sound generated by these two excitation forces, and a delay effect is obtained.

  In the present embodiment, the coefficient q determined by the vehicle operating condition of Equation (1) is changed according to the accelerator opening, and the coefficient q determined by the vehicle operating condition increases as the accelerator opening increases. As the coefficient q determined by the vehicle operating conditions increases, the excitation force of the sound with a time delay increases as shown in FIG. As a result, the driver feels the delay effect more strongly as the accelerator opening is larger.

  However, the frequency of the sound having the time delay is not a frequency having a proportional relationship with the frequency of the sound of the electrical angle 6th order component and its harmonic component which are the original sound. For this reason, when the level of the time-delayed sound increases, the time-delayed sound and the original sound are combined to form a dissonant sound, which gives driver discomfort. Such a dissonance occurs when the time-delayed sound is approximately equal to or larger than the original sound, and therefore the time-delayed sound must be smaller than the original sound. Therefore, in the present embodiment, the coefficient q determined by the vehicle driving conditions is changed in the range of coefficient q ≦ 0.2 determined by the vehicle driving conditions shown in FIG.

  Further, under driving conditions other than when the vehicle 1 is accelerating, there is a case where the driver is uncomfortable by adding the delay effect as described above. Therefore, the coefficient q determined by the vehicle driving conditions is set to “0” and the higher order. The component current is not added and the delay effect is not obtained. The controller 3 determines, for example, whether the vehicle is in acceleration traveling or steady traveling by detecting acceleration, and switches whether to multiply the basic current by the correction coefficient K.

  As described above, by changing the delay effect according to the accelerator opening, it is possible to improve the sound quality, prevent deterioration of sound quality due to discomfort, and create a novel and fun acceleration sound of an electric vehicle by the delay effect.

  The effect of 1st Embodiment of this invention is demonstrated.

  During acceleration traveling, a correction coefficient K having a sixth-order electrical angle component Δt seconds before is calculated, and the basic current is multiplied by the correction coefficient K to calculate a drive current instruction value. A voltage command value in the inverter 4 is calculated based on the drive current instruction value, and the inverter 4 is controlled based on the voltage command value. As a result, a sound having a time delay of Δt seconds can be generated, and the sound quality during acceleration traveling can be improved by the delay effect.

The rotation angle theta _-.DELTA.t before Δt seconds detected by the resolver 15 by storing in the RAM 22, can be read Δt seconds before the rotation angle theta _-.DELTA.t precisely, the sound quality during accelerated running by delay effect accurately Can be improved.

  As the accelerator opening of the vehicle 1 is larger, the delay effect can be increased and the sound quality during acceleration traveling can be further improved by increasing the excitation force of the sound having a time delay of Δt seconds.

  By making the volume of the sound with time delay smaller than the volume of the original sound, it is possible to prevent the generation of dissonance and to prevent the deterioration of the sound quality.

  When the traveling state of the vehicle is accelerated traveling, the sound quality during accelerated traveling can be improved by multiplying the basic current by the correction coefficient K and obtaining a delay effect. Further, when the vehicle is in steady running, the delay coefficient is not obtained without multiplying the basic coefficient by the correction coefficient K, thereby preventing beats from occurring and deterioration of sound quality during steady running. Can be prevented.

  Next, a second embodiment of the present invention will be described.

This embodiment is obtained by the seek to the first embodiment, by calculating the Δt seconds before rotation angle .theta.1 _-.DELTA.t. In the present embodiment, the controller 3 calculates the rotation angular velocity dθ / dt by differentiating the rotation angle θ as the electrical angle detected by the resolver 15 by the first order time, and differentiates the rotation angle θ by the second order time to obtain the rotation angle. The acceleration d ² θ / dt ² is calculated. Moreover, to calculate the Δt seconds before rotation angle .theta.1 _-.DELTA.t based calculated rotation angle d [theta] / dt, from ^{d 2 θ} / dt ² and the time delay Δt in equation (3).

Moreover, to calculate a correction factor K based on Equation (4) using the rotation angle .theta.1 _-.DELTA.t previous calculated Δt seconds.

_{K = 1 + qsin (6θ1 -Δt} ) ··· formula (4)

  Then, similarly to the first embodiment, the basic current is multiplied by the calculated correction coefficient K to calculate the drive current instruction value. Based on this drive current instruction value, the controller 3 controls the inverter 4. As a result, a drive current is supplied to the motor 5, and the same delay effect as in the first embodiment can be obtained.

  This eliminates the need to hold the rotation angle up to Δt seconds before in the RAM 22 of the controller 3, so that the load on the controller 3 can be reduced.

  In this embodiment, the time delay Δt is changed according to the accelerator opening. FIG. 9 shows the sound quality evaluation results when the time delay Δt is changed. Referring to FIG. 9, it can be seen that the smaller the time delay Δt, the better the evaluation. Therefore, in the present embodiment, the time delay Δt is decreased as the accelerator opening is increased, so that the driver feels the delay effect more strongly.

  However, the frequency of the sound having the time delay and the frequency of the sound of the electrical angle 6th order component which is the original sound are a constant frequency difference if the acceleration is constant, and the smaller the time delay Δt as shown in FIG. The frequency difference is also reduced. If this frequency difference becomes too small, a beat with a constant frequency occurs. The roar gives driver discomfort. Since the beat becomes felt when the frequency difference is about 30 Hz or less, in this embodiment, the time delay Δt is changed in a range where the frequency difference Δf is larger than 30 Hz. Note that the frequency difference Δf is not limited to 30 Hz, and is set in a range that does not cause discomfort to the driver.

  The frequency difference Δf and the time delay Δt have the relationship shown in the equation (5).

  Therefore, in order for the frequency difference Δf to be greater than 30 Hz, the relationship of Expression (6) may be satisfied.

  Further, in driving conditions other than during acceleration traveling of the vehicle 1, there may be an unpleasant feeling due to the beat sound as described above. Therefore, in driving conditions other than during acceleration traveling, the basic current is returned to the same as in the first embodiment. No higher order component current is added, and no beat sound is generated.

  As described above, the delay effect is changed according to the accelerator opening while reducing the load on the controller 3, thereby improving the sound quality and preventing the deterioration of the sound quality due to the uncomfortable feeling. Can create sound.

  The effect of 2nd Embodiment of this invention is demonstrated.

By calculating the rotation angle .theta.1 _-.DELTA.t based on the time lag Delta] t, without storing the rotation angle of the previous Delta] t seconds RAM22 of the controller 3 can calculate the drive current command value. As a result, the load on the controller 3 can be reduced.

  By reducing the time delay Δt as the accelerator opening is larger, the delay effect can be made stronger for the driver when the accelerator opening is larger, and the sound quality during acceleration traveling can be further improved.

  The time delay Δt is set so that the frequency difference between the frequency of the sound with time delay and the frequency of the original sound is 30 Hz or more. As a result, the frequency difference between the frequency of the sound having a time delay and the frequency of the original sound is reduced, and it is possible to prevent the beat from occurring. Therefore, it is possible to prevent deterioration in sound quality during acceleration traveling.

  A third embodiment of the present invention will be described with reference to FIG. FIG. 11 is a configuration diagram of the external operation unit of the present embodiment.

  This embodiment is obtained by adding an external operation unit 16 that allows the driver to arbitrarily set the delay effect with respect to the second embodiment. The external operation unit 16 is provided near the driver's seat of the vehicle 1. The external operation unit 16 includes a delay effect ON / OFF switch 17, a time delay change knob 18, and a delay strength change knob 19.

  The delay effect ON / OFF switch 17 can be selected from three positions of OFF / AUTO / MANUAL.

  When OFF is selected, the controller 3 does not add the high-order component current to the basic current, and no delay effect occurs even when the drive current is supplied to the motor 5. Therefore, no beat sound is generated.

  When AUTO is selected, the drive current supplied to the motor 5 is controlled based on an instruction from the controller 3 as in the first or second embodiment, and the sound quality is improved by the delay effect.

  When MANUAL is selected, the delay effect is adjusted based on the settings of the time delay change knob 18 and the delay strength change knob 19 to improve the sound quality. In this case, the time delay Δt increases as the time delay change knob 18 is turned to the right, and the coefficient q determined by the vehicle operating condition of the equation (4) increases as the delay strength change knob 19 is turned to the right. You can increase the loudness you have.

By enabling manual setting of the delay effect as described above, the driver can create an arbitrary delay effect, and can create a sound quality according to the preference of the driver. Effects of the third embodiment of the present invention explain.

  By providing the delay effect ON / OFF switch 18, the sound quality change due to the delay effect can be switched by the operation of the driver, and the sound quality can be switched according to the preference of the driver.

  By providing the delay strength changing knob 19, the volume of the sound having a time delay can be changed, and the sound quality suitable for the driver's preference can be created.

  It goes without saying that the present invention is not limited to the above-described embodiments, and includes various modifications and improvements that can be made within the scope of the technical idea.

1 Vehicle 2 Battery 3 Controller (Rotation angle extraction means, operation sound signal calculation means, voltage command value creation means, control means)
4 Inverter 5 Motor 9 Current sensor 15 Resolver (Rotation angle detection means)
16 External operation section 17 Delay effect ON / OFF switch (switching means)
18 hours delay change knob (change means)
19 Delay strength change knob (change means)
22 Random access memory (RAM, rotation angle storage means)

Claims (12)

A motor,
Rotation angle detection means for detecting the rotation angle of the motor;
Based on the rotation angle detected by the rotation angle detection means, a rotation angle extraction means for extracting a rotation angle a predetermined time ago;
A first signal having an electrical angle order component that becomes an operation sound of the motor from the rotation angle extracted by the rotation angle extraction means and the electrical angle order component that becomes an operation sound of the motor from the current rotation angle. Operating sound signal calculating means for calculating a second signal having;
Voltage command value generating means for generating a voltage command value based on a value obtained by multiplying the first signal and the second signal calculated by the operating sound signal calculating means;
And a control unit that controls an inverter based on the voltage command value generated by the voltage command value generation unit. A rotation angle storage means for storing the rotation angle detected by the rotation angle detection means;
2. The vehicle operating sound control device according to claim 1, wherein the rotation angle extraction unit extracts a rotation angle of the predetermined time from the rotation angle storage unit.   The vehicle operating sound control device according to claim 1, wherein the rotation angle extraction unit calculates a rotation angle before the predetermined time based on the rotation angle detected by the rotation angle detection unit.   The said operation sound signal calculation means enlarges the said 1st signal, so that the accelerator opening degree of the said vehicle is large, The operation sound control apparatus of the vehicle as described in any one of Claim 1 to 3 characterized by the above-mentioned.   The operating sound signal calculation means calculates the amplitude of the electrical angle order component of the motor corresponding to the frequency of the sound of the motor before the predetermined time included in the first signal as the accelerator opening of the vehicle increases. The operation sound control device for a vehicle according to claim 4, wherein the operation sound control device is increased.   The vehicle operating sound control device according to any one of claims 1 to 5, further comprising switching means for switching whether to multiply the second signal by the first signal.   The vehicle operating sound control device according to any one of claims 1 to 6, further comprising changing means for changing at least one of the magnitudes of the first signals for the predetermined time.   8. The vehicle operating sound control device according to claim 1, wherein the predetermined time is shorter as the accelerator opening of the vehicle is larger.   The vehicle according to any one of claims 1 to 8, wherein the predetermined time is a time when a frequency difference between the frequency of the second signal and the frequency of the first signal is equal to or greater than a predetermined value. Operating sound control device.   The vehicle operating sound control device according to claim 9, wherein the predetermined value is 30 Hz.   The vehicle operating sound control device according to any one of claims 1 to 10, wherein the magnitude of the first signal is smaller than the magnitude of the second signal.   12. The vehicle according to claim 1, wherein the operation sound signal calculation unit does not calculate the first signal when the vehicle is traveling at a substantially constant speed. Operating sound control device.

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