As shown by the fine line graph in FIG. 4, the sound pressure level of the 24th harmonic frequency component of the electric motor sound and the sound pressure level of the 48th harmonic frequency component of the electric motor sound are prominent compared to the sound pressure levels of the other frequency components of the electric motor sound. Therefore, the sound of the 24th harmonic frequency component and the sound of the 48th harmonic frequency component are heard noticeably by the occupant of the vehicle, giving the occupant a sense of discomfort. Therefore, the first harmonic sound and the second harmonic sound are generated from the speaker 12, whereby the sound pressure level of the component in the frequency band having the predetermined range centered on the 24th harmonic frequency and the sound pressure level of the component in the frequency band having the predetermined range centered on the 48th harmonic frequency are increased (see the parts indicated by A and B in FIG. 4). In this way, a synthesized sound can be generated that is linked to the fluctuation of the rotational speed of the electric motor and alleviates the prominence of the sound of the 24th harmonic frequency component and the sound of the 48th harmonic frequency component.

The order of the frequency component of the outstanding sound pressure level varies depending on electric motor specifications, transmission specifications, powertrain specifications, or the like. Therefore, the order of the frequency component of the outstanding sound pressure level is not limited to the 24th or 48th. In addition, the number of points where the sound pressure levels stand out varies depending on the electric motor specifications, the transmission specifications, the powertrain specifications, or the like. Therefore, the points where the sound pressure levels stand out are not limited to two points (24th, 48th). For example, when the sound pressure levels are prominent at three locations, a third harmonic-sound signal generating unit (not shown) may be provided in the signal generating unit 18 in addition to the first harmonic-sound signal generating unit 28 and the second harmonic-sound signal generating unit 30 shown in FIG. 2.

In addition, a vehicle body may resonate with the electric motor sound, and the sound pressure level of the component of the resonant frequency of the vehicle body may stand out from the sound pressure levels of the other frequency components. Therefore, the first, second, and third background sounds are generated from the speaker 12, whereby the sound pressure levels of the components in a frequency band having a predetermined range centered on the resonant frequency of the vehicle body are increased (see the portions indicated by C, D, and E in FIG. 4). Thus, the synthesized sound can be made where the prominence of the resonant sound has been alleviated.

Because the resonance frequency varies with the vehicle body, the center frequencies of the first background sound, the second background sound, and the third background sound are adjusted and determined for each vehicle body. Further, because the number of resonant frequencies also varies with the vehicle body, the background sound is not limited to three types of the first background sound, the second background sound, and the third background sound but may be two or less types of background sound or four or more types of background sound. For example, when the types of background sound are two, it is ensured that a state in which the third background sound is not output to the synthesis unit 42 is selected by the selection switch 40h shown in FIG. 2. For example, when the types of background sound are four, a fourth background-sound signal generating unit (not shown) may be provided in the signal generating unit 18 in addition to the first background-sound signal generating unit 32, the second background-sound signal generating unit 34, and the third background-sound signal generating unit 36 shown in FIG. 1.

When the electric motor rotates, a synthesized sound of the first harmonic sound and the second harmonic sound may be output from the speaker 12 into the vehicle as a sound effect. That is, the background sound need not be included in the sound effect.

Sound Effects when Launch Control is Activated

FIG. 5 is a diagram illustrating sound effects when launch control is activated. FIG. 5 shows, from the top, a time chart of brake pedal pressing force, a time chart of accelerator pedal opening, a time chart of flow rate increase completion flag, a time chart of launch control state, a time chart of electric motor torque, and a time chart of vehicle speed.

Launch control enhances the acceleration performance of a vehicle during vehicle startup by the electric motor outputting higher torque than usual while the slip of the driving wheels is suppressed. When the launch control is not activated, i.e., in normal conditions, the torque of the electric motor during vehicle startup is limited to a limit L1. On the other hand, when the launch control is activated, the torque of the electric motor during vehicle startup is allowed up to a limit L2, which is higher than the limit L1. While the vehicle is stopped, the torque of the electric motor is limited to a limit L3. The limit L3 is a torque limit value when the driver simultaneously depresses the brake pedal and the accelerator pedal.

While the vehicle is stopped, if the driver simultaneously depresses the brake pedal and the accelerator pedal, launch control preparation is initiated. When the launch control preparation is started, the flow rate of the cooling water for cooling the electric motor is increased more than usual. While launch control is in operation, the electric motor produces higher torque than usual, resulting in that the heat generation of the electric motor increases. Therefore, the cooling performance of the electric motor is enhanced by increasing the flow rate of the cooling water. When the increase of the flow rate of the cooling water is completed, the flow rate increase completion flag is switched from “0” to “1”. When the driver then eases off the brake pedal, launch control is activated and the vehicle starts moving. When launch control is activated, the electric motor can produce higher torque than usual, resulting in that the acceleration performance during vehicle startup improves compared to the normal conditions in which launch control is not activated.

When the brake pedal pressing force is equal to or greater than a threshold value Bth1 and the accelerator pedal opening is equal to or greater than a threshold value Ath, the determination unit 38 determines that the state of launch control is “in preparation”. When the brake pedal pressing force is less than the threshold Bth1 or the accelerator pedal opening is less than the threshold Ath, the determination unit 38 determines that the state of launch control is “deactivated”.

When the flow rate increase completion flag becomes “1” in a state where the brake pedal pressing force is equal to or greater than the threshold value Bth1 and the accelerator pedal opening is equal to or greater than the threshold value Ath, the determination unit 38 determines that the state of launch control is “ready”. When the brake pedal pressing force becomes equal to or less than the threshold Bth2 after “ready”, the determination unit 38 determines that the state of launch control is “in operation”. When a predetermined time has elapsed since the state of launch control was determined to be “in operation”, the determination unit 38 determines that the state of launch control is “deactivated”.

When the state of launch control is determined to be “in preparation”, the first isolated sound (first sound effect) is output from the speaker 12. The first isolated sound is a sound having a component of relatively low frequency f1 as a principal component. This makes the driver feel the increasing torque.

When the state of launch control is determined to be “ready”, the second isolated sound (second sound effect) is output from the speaker 12. The second isolated sound is a sound having a component of frequency f2, which is higher than frequency f1, as a principal component. Switching from the first sound effect to the second sound effect allows the driver to recognize that launch control is ready and the vehicle can be started at high acceleration if the driver eases off the brake. In addition, by outputting a sound with a relatively high frequency from the speaker 12, it is possible to simulate a state in which a high engine rotational speed is maintained in an engine vehicle.

When the state of launch control is determined to be “in operation”, a third isolated sound (third effect sound) is output from the speaker 12. When the state of launch control is “in operation”, the electric motor is rotating and thus the harmonic sound (fourth sound effect) and the background sound are output from the speaker 12. That is, a synthesized sound acquired by synthesizing the third isolated sound, the harmonic sound, and the background sound is output from the speaker 12. In the following, the synthesized sound acquired by synthesizing the third isolated sound, the harmonic sound, and the background sound may be described as the fifth sound effect.

Thus, a synthesized sound in which the third isolated sound is synthesized in addition to the harmonic sound and the background sound that are output in the normal conditions is output from the speaker 12, and thus the driver can be made to recognize that the acceleration different from the normal is performed. For example, the frequency f3 of the sound that is the principal component of the third isolated sound is made close to the frequency of the wind noise of the vehicle, whereby it is possible to give the driver a sense of acceleration.

Configuration of Isolated-Sound Signal Generating Unit

FIG. 6 is a functional block diagram showing a first isolated-sound signal generating unit 22 in one embodiment. The first isolated-sound signal generating unit 22 includes a reference signal setting unit 44, a gain setting unit 46, and a correction unit 48.

The reference signal setting unit 44 sets a reference signal SA1. The reference signal SA1 is a sound signal having a component of frequency f1 as a principal component.

The gain setting unit 46 sets a gain Ga. The gain Ga is set according to the rotational speed of the electric motor, the output of the electric motor, the torque of the electric motor, the opening degree of the accelerator pedal, and the acceleration/deceleration of the vehicle.

The correction unit 48 outputs a first isolated-sound signal Sa1 obtained by multiplying the reference signal SA1 set by the reference signal setting unit 44 by the gain Ga.

The second isolated-sound signal generating unit 24 is different from the first isolated-sound signal generating unit 22 in that the reference signal set by the reference signal setting unit 44 is a sound signal having a component of the frequency f2 as a principal component, but the other configuration is the same as that of the first isolated-sound signal generating unit 22.

The third isolated-sound signal generating unit 26 is different from the first isolated-sound signal generating unit 22 in that the reference signal set by the reference signal setting unit 44 is a sound signal having a component of the frequency f3 as a principal component, but the other configuration is the same as that of the first isolated-sound signal generating unit 22.

Configuration of Harmonic-Sound Signal Generating Unit

FIG. 7 is a functional block diagram showing a first harmonic-sound signal generating unit 28 in one embodiment. The first harmonic-sound signal generating unit 28 includes a reference signal setting unit 50, a gain setting unit 52, and a correction unit 54.

The reference signal setting unit 50 sets the reference signal SB1 based on the rotational speed of the electric motor. The reference signal SB1 is a sound signal composed of a plurality of frequency components in a frequency band having a predetermined range centered on the 24th harmonic frequency of the rotational speed of the electric motor.

The gain setting unit 52 sets a gain Gb. The gain Gb is set according to the rotational speed of the electric motor, the output of the electric motor, the torque of the electric motor, the opening degree of the accelerator pedal, and the acceleration/deceleration of the vehicle.

The correction unit 54 outputs a first harmonic-sound signal Sb1 obtained by multiplying the reference signal SB1 set by the reference signal setting unit 50 by the gain Gb.

The second harmonic-sound signal generating unit 30 is different from the first harmonic-sound signal generating unit 28 in that the reference signal set by the reference signal setting unit 50 is a sound signal composed of a plurality of frequency components in a frequency band having a predetermined range centered on the 48th harmonic frequency of the rotational speed of the electric motor, but the other configuration is the same as that of the first harmonic-sound signal generating unit 28.

Configuration of Background-Sound Signal Generating Unit

FIG. 8 is a functional block diagram showing the first background-sound signal generating unit 32 in one embodiment. The first background-sound signal generating unit 32 includes a reference signal setting unit 56, a gain setting unit 58, and a correction unit 60.

The reference signal setting unit 56 sets a reference signal SC1. The reference signal SC1 is a sound signal composed of a plurality of frequency components in a frequency band whose center frequency is the frequency f4.

The gain setting unit 58 sets a gain Gc. The gain Gc is set according to the rotational speed of the electric motor, the output of the electric motor, the torque of the electric motor, the opening degree of the accelerator pedal, and the acceleration/deceleration of the vehicle.

The correction unit 60 outputs the first background-sound signal Sc1 obtained by multiplying the reference signal SC1 set by the reference signal setting unit