FR 3097819 A1 20210101 FR 2006402 A 20200618 Description Title of Invention: VEHICLE APPROACH NOTIFICATION DE VICE Technical Field [0001] The present invention relates to a vehicle approach notification device. Background Art [0002] For example, an elcctric automobile driven by an clectric motor cmits a vcry quiet traveling sound during low speed traveling. When such a vehicle of small traveling sound travels in close proximity to a pedestrian or the like, there is the possibility of the pedestrian being unawai-e of the approach of the vehicle. As disclosed, for example, in Patent Literature 1, a vehicle is known in which an approach notification device is mounted in order to notify the pedestrian or the like of the approach of the vehicle. [0003] The device disclosed in Patent Literature 1 is equipped with a first sound production signal generating portion varying the frequency and output of a first sound production signal in accordance with variation in vehicle speed, and a second sound production signal generating portion varying the output in accordance with vehicle speed while maintaining the frequency of a second sound production signal at a fixed level, synthesizing a notification sound signal. [0004] [Patent Literature 1] JP 2015-067029 A Summary [0005] [Problems to bc Solved by the Invention] [0006] However, in the abovementioned notification device, in the case in which the variation in the frequency of the first sound production signal takcs place in a low/ medium frequency band (approximately 20 to 800 Hz), the first sound production signal undergoes transition through a frequency band in which the response scnsitivity of the vehicle body is high. The variation in frequency and the variation in output of the first sound production signal giving a pcak feeling undcrgo transition through a frequency band in which the response scnsitivity of the vehicle body is high. so that in a case in which there is room for improvement in tcrms of the sound insulation performance of the vehicle body. a sufficicnt sound insulation effect by the vehicle body is not exertcd, and the sound produccd is allowcd to bc transmitted to the interior of the vehicle. which nacans there is the possibility of discomfort bcing impartcd to the occupant. [0007] It is casy for the human car to perceive a sound of. for example, around 1 kHz. As is known, relative displacement in frequency (transition in frequency) cxhibits sufficicnt perceptibility without training. By allotting the first sound production signal capable of 2 variation in frequency in this medium/high frequency band, it is possible to notify the pedestrian or the like of the existence of the vehicle. However, the sound production frequency in this band is simultancously audible to the occupant, which mcans the possibility of discomfort. That is, the abovc-described example leaves room for improvement in tcrms of perception of the vehicle approach by the pedestrian or the like and sccuring quietness for the occupant. [0008] The present invention has hem made in vicw of the abovementioned problem. Tt is an object of the present invention to providc a vehicle approach notification &vice capable of efficiently notifying a pedestrian or the likc of approach of a vehicle whilc sccuring quietness for the occupant of the vehicle. [0009] [Mcans for Solving the Problems] [0010] To achievc the abovementioned object, there is providcd, in accordance with the present invention, a vehicle approach notification &vice which is equipped with a notification sound generating portion having a first notification sound and a second notification sound that arc audible. In the vehicle approach notification &vice, a first sound pressure of the first notification sound has, in a frequency band of 800 Hz or more and 1.6 kHz or lcss, a first pcak, which is a maximum pcak, and a second peak lowcr than the first peak; a first frequency of the first notification sound is set to be a fixcd level independently of a vehicle speed; the first sound pressure k set to he variable in accordance with the vehicle speed; a second sound pressure of the second notification sound has a third peak, which is a maximum peak; the third peak is set to be on the higher frequency sicle of the first peak and the second peak of the first sound pressure; and a second frequency of the second notification sound is set to be variable in accordance with the vehicle speed. [0011] According to an embodiment, the third peak is set to be variable within a frequency band of more than 2 kHz and less than 6 kHz. [0012] According to an embodiment, the first peak and the second peak are set in a frequency band of 800 Hz or more and 1.6 kHz or les s, are spaced away from each other by 200 Hz or more, and are spaced away from the third peak by 500 Hz or more. [0013] According to an embodiment, a frequency band width of the first peak and the second peak is set to be wider than a frequency band width of the third peak. [0014] According to an embodiment, in a vehicle speed range of zero to 20 km/h, the first sound pressure is set to be higher than the second sound pressure. [0015] According to an embodiment, a rate of change of the third peak with respect to the vehicle seed is set to 1.5 to 3.5%/(km/h) [0016] According to an embodiment, the second frequency is maintained in a fixed state in a vehicle speed range of zero to a predetermined speed; and the second frequency is set to vary in accordance with the vehicle speed in a vehicle speed range in excess of the 3 predetermined speed. [0017] According to an embodi ment, the second sound pressure of the second notification sound is set to be variable in accordance with the vehicle speed; the predetermined speed is set to be more than zero and less than 20 km/h; and in the vehicle speed range of from the predetermined speed to 20 km/h, a rate of change of the first sound pressure is set to be greatcr than a rate of change of the second sound pressure. [0018] According to an embodiment, when the vehicle speed is 20 km/h or more, the second sound pressure is set to he maintaincd in a fixed state independently of the vehicle speed. [0019] [Advantagcous Effect of Invention] [0020] According to the present invention, it is possible to efficicntly notify the pedestrian or the likc of approach of the vehicle whilc sccuring the quietness for the occupant of the vehicle. Brief Description of Drawings [0021] Other fcatures, dctails and advantages will be shown in the following detailed de- scription and on the figures, on which: Fig. 1 100221 Ifig.11 is a graph illustrating the characteristics of the first notification sound and the second notification sound of a vehicle approach notification device according to the present invention, of which the horizontal axis indicates frequency and the vertical axis indicates sound pressure, with the vehicle speed being 5 km/h. Fig. 2 100231 I fie.21 is a graph illustrating the characteristics of the first notification sound and the second notification sound when the vehicle speed is 15 km/h, with regard to the first notification sound and the second notification sound shown in Figure I. Fig. 3 100241 Ifie.31 is an enlareed view of region Z of the first peak of Figure 1. Fig. 4 [0025] [fie.4] illustrates propagation rate with respect to frequency with regard to the first notification sound and the second notification sound of Figure 1, etc. The horizontal axis indicates liequency, and the vertical axis indicates propagation rate. Fig. 5 [0026] [fig.5] is a graph comparing the first notification sound and the second notification sound of Figure 1 with the conventional notification sound. Fig. 6 [0027] [fig.6] is a graph comparing the first notification sound and the second notification sound of Figure 2 with the conventional notification sound. Fig. 7 100281 Ifig.71 is a eraph illustrating the change rate of the first frequency and the second frequency of Figures 1 and 2 with respect to the vehicle speed. The horizontal axis indicates the vehicle speed, and the vertical axis indicates the frequency. Fig. 8 [0029] [fig.81 is a eraph illustrating the sound pressure level with respect to the vehicle speed with regard to the first sound pressure level and the second sound pressure level of Figures 1 and 2. The horizontal axis indicates the vehicle speed, and the vertical axis indicates the sound pressure. Description of Embodiments [0030] In the following, a vehicle approach notification device according to an embodiment of the present invention will be described with reference to the drawings (Figures 1 through 8). The vehicle approach notification device of the present embodiment is mounted in a hybrid car, an electric automobile or the like in which the traveling sound during low speed traveling is very quiet. [0031] The vehicle approach notification device of the present embodiment is capable of outputting two kinds of audible notification sound, that is, a first notification sound Si and a second notification sound S2. The first notification sound Si has a first frequency and a first sound pressure, and the second notification sound S2 has a second frequency and a second sound pressure. Here, the first notification sound SI and the second notification sound 52 are audible, and are sounds set to a frequency and of approximately 20 Hz to 20 kHz. The first sound pressure and the second sound pressure may be set, for example, to a range of 30 dB to 70 dB. This, however, should not be construed restrictively. 100321 The first notification sound SI and the second notification sound S2 will be described with reference to Figures I and 2. Figure I illustrates the characteristics of the first notification sound SI and the second notification sound S2 when the vehicle is at a vehicle speed immediately after traveling (low speed). In the present embodiment, there are illustrated the characteristics of the first notification sound SI and the second notification sound S2 at a vehicle speed of 5 km/h. Figure 2 illustrates the characteristics of the first notification sound SI and the second notification sound S2 during traveling at a vehicle speed higher than the vehicle speed of Figure I. In the present embodiment, Figure 2 illustrates the characteristics of the first notification sound SI and the second notification sound 52 at a vehicle speed of 15 km/h. 100331 The band of the first frequency of the first notification sound SI exists between a value somewhat higher than 0 Hz and a value somewhat lower than 2 kHz. The first sound pressure of the first notification sound S1 has a first peak Pl which is maximum in a frequency band of 800 Hz or more and 1.6 kHz or less, and a second peak P2 which is lower than the first peak PI. Furthermore, the band of the first frequency of the first notification sound Si has the first peak P1 which is maximum in a frequency band of 1.1 kHz or more, and the second peak P2 which is lower than the first peak Pl in the low frequency band of less than 1.1 kHz. As shown in Figures 1 and 2, in the present embodiment, the second peak P2 is set to be around 0.9 kHz, and the first peak P1 is set to be around 1.2 kHz. As shown in Figure 3, in more detail, the first peak P1 is set to lie 1230 Hz. [0034] The first frequency of the first notification sound Si is set to be a fixed level inde- pendently of the vehicle speed, and the first sound pressure is set so as to be variable in accordancc with the vehicle speed. The second sound pressure of the second notification sound S2 has a third peak P3, which is a maximum peak, and the third peak P3 is set on the higher frequency sidc of the first peak Pl and the second peak P2 of the first sound pressure. The second frequency of the second notification sound S2 is set so as to be variable in accordancc with the vehicle speed. [0035] As described above, the first sound pressure is variable in accordancc with the vehicle speed, so that the first sound pressure at 15 km/h shown in Figure 2 is higher than the first sound pressure at the vehicle speed of 5 km/h shown in Figure 1. The wavcform of the first notification sound Si shown in Figure 1 is of the same configuration as the waveform of the fu-st notification sound Si shown in Figure 2. That is, with respect to the variation in vehicle speed, the wavefonn remains constant in the direction of arrow Al of Figure 2, with solely the sound pressure varying. [0036] The band of the second frequency of the second notification sound is set to be on the higher frequency sicle of the first frequency of the first notification sound Si, and, for example, as shown in Figure 1, at the vehicle speed of 5 km/h, it exists between a value somewhat higher than 2 kHz and a value somewhat lower than 4 kHz. Furthennore, as shown in Figure 2, at the vehicle speed of 15 km/h, the frequency band exists somewhere between 3 and 4 kHz. At the vehicle speed of 5 km/h shown in Figure 1, the third peak P3 is set to be substantially 3 kHz, and at the vehicle speed of 15 km/h shown in Figure 2, it moves in the direction of arrow A2 with respect to the third peak P3 of Figure 1, that is, to the high frequency sicle, and is set to be around 3.7 to 3.8 kHz. [0037] The first peak Pl and the second peak P2 of the sound pressure levet of the first noti- fication sound Si are set in the frequency band of less than 1 kHz and the frequency band of 800 Hz or more and 1.6 kHz or less, whereby it is possible to notify the pedestrian of the approach of the vehicle. By using a frequency of 800 Hz or more, it is possible to suppress solid propagation of the vehicle body, making it possible to reduce 6 discomfort for the occupant and, furthcr, to achieve an improvement in terms of vehicle perception performance for the pedestrian. [0038] The first notification sound S1 is varicd solely in sound pressure in accordancc with the vehicle speed, whercby it is possible to suppress the first notification sound Si from exceeding a frequency of high vehicle body sensitivity. In the band in which die sound insulation performance of the vehicle body is casily exerted, it is possible to keep the frequency characteristic of the first notification sound Si at a fixcd level, making it possible to reduce the notification sound intruding die vehicle interior. The band in which the vehicle body scnsitivity must lie kcpt low is fixed, so that it is casy to specify the range in which the vehicle body sensitivity is selectively reduced. [0039] The third peak P3 of the second notification sound S2 moves to the high frequency sidc in output and frequency in accordancc with thc vehicle speed, and movcs to the frequency band on the highcr frequency side of the first pcak Pl, so that the frequency band of the third peak P3 does not overlap the frequency band of the first peak Pl, and an unnecessary incrcase in the first sound pressure of the first notification sound 51 is preventcd. Furthermore, duc to the change in frequency in the third peak P3, it is possible to simulatc the acceleration/deceleration feeling, and even in the case of a vehicle body leaving room for an improvement in terris of sound insulation performance, a frequency band in which sound insulation performance is easily exerted can be attaincd, so that it is possible to mitigatc the discomfort of the occupant. [0040] The first notification sound Si outputs the first frequency which is in a frequency band that is lower than that of the second notification sound 52, so that in the case in which the vehicle accelerates, the first notification sound SI does not easily generate space attenuation, so that it is possible to cause a pedestrian or the like further in the distance to perceive the approach of the vehicle. [0041] As shown in Figure 4, the third peak P3 of the second notification sound S2 is set so as to vary within a frequency band of more than 2 kHz and less than 6 kHz. Figure 4 is a graph illustrating propagation rate with respect to frequency, showing that propagation rate decreases as frequency increases. That is, the graph of Figure 4 shows that propagation becomes gradually more difficult as frequency increases. In Figure 4, the first peak PI and the second peak P2 of the first notification sound SI are set in a frequency band indicated by FI, and the third peak P3 is set in the frequency band indic ated by F2. [0042] In the frequency band of 2 to 6 kHz, audibility performance with respect to envi- ronmental noise is high, and tlu-ough further movement of the third peak P3 within the frequency band, it is possible to evoke the approach of a vehicle or the like. Transition from low frequency to high frequency can evoke the acceleration feeling of the vehicle, and transition from high frequency to low frequency can evoke the de- 7 celcration feeling of the vehicle. [0043] At the first peak Pl and the second peak P2 of the first notification sound SI, the pedestrian is causcd to recognize the vehicle, and further, the second notification sound S2 is set to the above-mentioned frequency band, whereby it is possible to achieve an improvement in ternis of rccognizability in the amblent environment. With respect to the frequency band of the third peak P3, the vehicle body has sound insulation property, so that the vehicle body can reducc the second notification sound S2 having the third peak P3, with the result that the vehicle body providcs a sound insulation effect for the occupant. [0044] In the prescnt embodiment, the first peak Pl and the second peak P2 is set to a frequency band of 800 Hz or more and 1.6 kHz or less. Thcy arc spaced away from each other by 200 Hz or more, and arc spaced away from the third peak P3 by 1 kHz or more. [0045] When the frequencies of the first peak and the second peak arc close to each other, there is the possibility of generation of a beat duc to a difference in sound, and, in this case, the transmissivity of the vehicle body is high, so that there is the possibility of the sound insulation effect not bcing exerted. In contrast, in the prcsent embodiment, in the first notification sound S1 and the second notification sound S2, the first peak Pl which is the maximum peak and the second peak P2 which is the second highest peak arc spaced away from each other by 200 Hz or more so that thcy may concord as a scale, whereby a sufficient frequency difference is provided, a concordant sound results, and an improvement is achieved in terms of the acceptability of the tone. Furthermore, with respect to the th-st peak P1 and the second peak P2, the third peak P3 is spaced away by 500 Hz or more, so that sound production is possible with the third peak P3 not interfering with the first peak PI and the second peak P2 making it possible to achieve an improvement in tenus of perceptibility for the pedestrian. Furthermore, by spacing away the third peak P3 by 1 kHz, no concordant sound relationship is established, making it possible to achieve a further improvement in terms of perceptibility. [0046] Furthermore, as shown in Figure 3, in the present embodiment, the frequency band width of each of the first peak P1 and the second peak P2 is set to be wider than the frequency band width of the third peak P3. In this example, as shown in Figure 3, the frequency band width at a sound pressure levet lower than the peak value of the first peak PI by 6 dB is set to 30 Hz (5 Hz/dB). [0047] In the case of a peak of a narrow frequency band width, the directivity of the central frequency is a problem. Due to the directivity, variation in sound pressure is generated. In the case in which this variation is generated and in which the volume is below the level audible to the pedestrian, some measure must be taken to enhance the sound 8 pressure, rcsulting in an increase in the levet of the notification sound intruding the vehicle intcrior. In the case in which the volume is M'ove the supposcd level, the pedestrian is unnecessarily notificd of the approach of the vehicle, so that there is the possibility of generating discomfort. [0048] Dash une S'IO in the characteristic chart of Figure 5 shows the sound pressure with respect to the frequency of the conventional notification sound when the vehicle speed is 5 km/h. Dash une 510 in the characteristic chart of Figure 6 shows the sound pressure with respect to the frequency of the conventional notification sound when the vehicle speed is 15 km/h. The frequency band of the conventional notification sound 510 in Figure 6 is nioved to the high frequency side (in the direction of arrow A3 of Figure 6) with respect to the frequency band of the conventional notification sound 510 of Figure 5. The rate of change of the conventional notification sound 510 is approximately 0.8%/(km/h), so that the frequency band of the conventional notification sound 510 of Figure 6 is tnoved to the high frequency side with respect to the frequency band indicated by dash line 510 of Figure 5 by 8%. On the other hand, the characteristics indicatcd by the solid linos of Figures 5 and 6 arc the characteristics of the first notification sound Si and the second notification sound 52 of Figures 1 and 2. [0049] The conventional notification sound 510 has a plurality of peaks, and cach peak is of a narrowcr frequency band width as comparcd with the first peak P1 and the second peak P2 of the first notification sound Si. Furthermore, as shown in Figures 5 and 6, when the vehicle speed increases, ail the peaks move to the high frequency side, so that the pedestrian and the occupant can easily feel fluctuation in the notification sound. As a result, the fluctuation feeling of the notification sound becomes too strong, so that there is the possibility of the pedestrian and the occupant experiencing discomfort. [0050] In contrast, in the present embodiment, the frequency band width is set as described above, so that a frequency band of a frequency band width is added to the center frequency of each peak, with the result that it is possible to suppress the directivity of the frequency. As a result, in the case in which the first peak PI and the second peak P2 reach the pedestrian, it is possible to reduce the generation of variation in sound pressure. That is, with respect to the first notification sound Si and the second notification sound S2, it is possible for the requisite sound pressure to be set appropriately, making it possible to provide compatibility between vehicle perception performance and quietness. [0051] In the present embodiment, the rate of change of the second frequency with respect to the vehicle speed is set to 1.5 to 3.5%/(km/h) Here, the rate of change means the rate of change in frequency with respect to a change (increase/decrease) in vehicle speed. The vertical axis in Figure 7 indicates the rate of change (%) in frequency, and line Li indicates the characteristics of the first frequency. In this example, for instance, the 9 first peak P1 is shown as the typical value of the first frequency. The typical value may be the second pcak P2. [0052] Lincs L2 through L6 of Figure 7 indicate examples of the characteristics of the second frequency. Line L2 indicatcs the characteristics when the rate of change in the second frequency is 1.5%/(km/h). Si milady, line L3 indicates the characteristics when the rate of change in the second frequency is 2.2%/(krn/h), line L4 indicatcs the characteristics when the rate of change in the second frequency is 2.7%/(lan/h), line L5 indicatcs the characteristics when the rate of change in the second frequency is 3.0%/(km/h), and line L6 indicatcs the characteristics when the rate of change in the second frequency is 3.5%/(km/h). Line L7 indicates the conventional notification sound, and the rate of change is 0.8%/(km/h). [0053] As described above, the rate of change in the second frequency of the present cm- bodiment is set to be 1.5 to 3.5%/(km/h). That is, it is possible to set the rate of change in the rcgion above line 2 and below line L6 in Figure 7. The rate of change of the present embodi ment is set to 2.5%/(krn/h), which is between line L3 and line L4. [0054] The rate of change of 2.5%/(km/h) will be described with regard to the second noti- fication sound S2 in Figures 1 and 2. As described above. Figure 1 shows a state in which the vehicle speed is 5 km/h, and Figure 2 shows a state in which the vehicle speed is 15 km/h. Thus, comparison of the state of Figure 1 and that of Figure 2 shows an increase in speed of 10 km/h. The rate of change is 2.5%/(km/h), so that as compared with the second notification sound S2 of Figure 1, the second notification sound S2 of Figure 2 is increased by 25%. Assuming that the typical value of the second notification sound S2 is the third peak P3, the third peak P3 of the second notification sound of Figure 2 increases tiom 3 kHz of the third peak P3 of the third peak P3 of the second notification sound of Figure 1 in the direction of arrow A2 of Figure 2 by approximately 25% to attain 3.7 to 18 kHz. [0055] Furthermore, the rate of change in the frequency of the third peak P3 has the effect of evoking the vehicle state and of calling attention. A high rate of change helps to achieve an improvement in terms of vehicle perception perfmmance. In the case of a relative change in sound (change in frequency), it can be recognized without any audibility training. As compared with the conventionally prescribed rate of change of 0.8%/(km/h) indicated by line L7 of Figure 3, the rate of change set in the present embodiment is superior in terms of sensing the movement of the vehicle, that is, simulating the feeling of movement. [0056] In the present embodiment, the rate of change is set to 1.5 to 3.5%/(km/h) hi this range, recognition is easy. Furthermore, when the rate of change is set to 1.5 to 2.7%/(km/h), there is provided a speed feeling in which the acceleration sound due to transition of the third peak P3 is coincident with the vehicle speed. When the rate of change is set to 2.2 to 3.0%/(km/h), it is possible to rnakc the pedestrian awarc of an abrupt change in the vehicle state through rapid pcak transition in a range allowing recognition. Furthermore, it is possible to reducc comfort for the occupant. Thus, in the present embodi ment, the rate of change is set to 2.5%/(kni/h) within the range of 2.2 to 2.7%/(km/h). [0057] When the first notification sound S1 is being produccd, if the rate of change of the second notification sound S2 is 1.5% or more, an improvement in ternis of perception rate is achieved. The ground for the determination that the perception rate is cnhanced is as follows. As a prerequisite, in the present embodiment, the change in vehicle speed is set to bc within 5 km/h, and the change in frequency is set to 6% or more. That is, the rate of change is set to 1.2%/(krn/h) or more. [0058] The rcason for this is that in the frequency band of around 3 kHz, when the frequency is increased by 6%, the frequency is enhanced by a halftonc relative to the reference sound. It is, for example, the rclationship between sol and sol# in the scalc. In the case of such a musical interval, one can recognizc the difference in sound without training. [0059] On the other hand, when the rate of change is 1%/(km/h), a change in vehicle speed of 6 km/h is required to attain a change in frequency of 6%. In this case, there is the possibility of the vehicle speed being increased too much before the change in the second notification sound S2 is recognized. In vicw of this, in the present embodiment, the lower limit is 1.5%/(km/h), which is somewhat larger than 1.2%/(km/h) [0060] When the rate of change is larger than 3.5%/(km/h), the sound may be distoned, so that the abovementioned value is set as the upper Huait [0061] As described above, the third peak P3 is set for the second frequency of the second notification sound S2. Furthermore, the second frequency is set such that it maintains a fixed state in the vehicle speed range of zero to 5 km/h (predetennined speed), and that it undergoes a change in accordance with the vehicle speed in the vehicle speed range of in excess of 5 km/h In this example, in the vehicle speed range of 5 to 20 km/h, the second frequency moves to the high frequency side as the vehicle speed increases. [0062] Through the generation of the second notification sound S2, it is possible to evoke the movement of the vehicle. That is, the second notification sound S2 is the sound for evoking vehicle movement. The frequency is set to a fixed level in accordance with the vehicle speed, and then the second frequency is changed when the speed of 5 km/h is exceeded, whereby it is possible to notify the pedestrian of the change in vehicle position using the sound of the statt from resting as the reference sound. [0063] It is also possible to notify the occupant of the change in the vehicle state. In this example, the second frequency varies using the speed of 5 km/h as the reference, which, however, should not be construed restrictively. The vehicle speed at which the 11 change in the second frequency starts can Ir set to more than zero and less than 20 km/ ni and, more preferably, to more than zero and legs than 10 km/m. [0064] Here, the change in the first sound pressure of the first notification sound Si and in the second sound pressure of the second notification sound S2 with respect to the vehicle speed will be described. As described above, the first sound pressure is variable in accordancc with the vehicle speed. As shown in Figures 1 and 2, the first sound pressure is higher when the vehicle speed is 15 km/h as shown in Figure 2 than when it is 5 km/h as shown in Figure 1. Furthermore, in the present embodiment, the second sound pressure is also set to Ir variable in accordancc with the vehicle speed. [0065] Figure 8 is a graph illustrating sound pressure level with respect to vehicle speed. The horizontal axis indicatcs vehicle speed, and the vertical axis indicates sound pressure. Line L11 indicatcs the characteristics of the first sound pressure, and line L12 indicatcs the characteristics of the second sound pressure. Here, the first peak P1 of the first sound pressure or the second peak P2 thereof may be used as the typical value of line Ll I. In this example, the first pcak Pl is uscd as the typical value. [0066] As shown in Figure 8, the first sound pressure is set to hc higher than the second sound pressure. In the vehicle speed range of zero to 20 km/h, the first sound pressure varies in accordance with the variation in the vehicle speed. That is, in the vehicle speed range, as the vehicle speed increases, the first sound pressure increases. In the vehicle speed range higher than 20 km/h, the first sound pressure is at a fixcd level with respect to the vehicle speed. [0067] In the vehicle speed range of 5 to 20 km/h, the second sound pressure varies in cone- spondence with the change in the vehicle speed. That is, in the above-mentioned vehicle speed range, the second sound pressure increases as the vehicle speed increases. In this example, the rate of increase of the second sound pressure decreases as the vehicle speed approaches 20 km/h The rate of increase of the second sound pressure decreases at a vehicle speed of around 13 to 14 km/h, and is at a fixed level in the vehicle speed range higher than 20 km/h [0068] When the vehicle speed is 10 km/h the first sound pressure XldB is higher than the second sound pressure YldB, and when the vehicle speed is 20 km/h, the first sound pressure X2dB is higher than the second sound pressure Y2dB. Furthermore, in the vehicle speed range of 5 to 20 km/h, the rate of change of the first sound pressure is set to be higher than the rate of change of the second sound pressure. In the vehicle speed range, the inclination of line LI 1 in Figure 8 is set to be greater than the inclination of line L12. [0069] As the vehicle speed increases, it is necessary to increase the loudness of the noti- fication sound having characteristics advantageous in terms of space attenuation. The first peak PI and the second peak P2 of the first notification sound 51 give a sound not 12 easily attenuated by space, so that even in the case in which the vehicle and the pedestrian are spaced away from each other, it can be easily recognized by the pedestrian, and the first peak Pl and the second peak P2 are easily recognized by a pedestrian in the distance at the lime of acceleration. Thus, as shown in Figure 8, the rate of change of the first sound pressure is made greater than that of the second sound pressure, whereby, due to the first peak Pl and the second peak P2, the vehicle is perceived by a pedestrian further spaced away from the vehicle, makine it possible to recoenize the acceleration/deceleration of the vehicle throueh the second notification sound S2. [0070] Furthermore, as shown in Figure 8, whcn the vehicle speed is 20 km/h or more, the second sound pressure is set to maintain a fixcd state independently of the vehicle speed. As a result, it is possible to cause the occupant to recognize the sufficicntly accelerated state. [0071] Furthermore, as described above, in the vehicle spced range of zero to 20 km/h, the first sound pressure is set to be highcr than the second sound pressure. As a result, it is casier for a low frequency Flot casily attcnuated through the enhancement of thc sound pressure of the first pcak P1 and the second peak P2 to rcach a position at thc distance. Furthermore, in the case in which the vehicle speed is high, it is possible to cause a pedestrian in the distance to recognize thc approach of the vehicle. [0072] The embodi ment described abovc has been presented by way of example in order to illustrate the present invention, and does not limit the invention as claimed in the appended claims. Furthermore, the structure of each portion of the present invention is not limited to that of the above-described embodiment but allows various modifications without departing from the technical scope of the claims. Reference Signs List [0073] - SI: first notification sound - S2: second notification sound - S10: conventional notification sound - PI: first peak - P2: second peak - P3: third peak - Li: une illustrating the characteristics of first frequency - L2: une illustrating the characteristics when the rate of change of the second frequency is 1.5%/(km/h) - L3: une illustrating the characteristics when the rate of change of the second frequency is 2.2%/(km/h) - L4: une illustrating the characteristics when the rate of change of the second 13 frequency is 2.7%/(km/h) - L5: une illustrating the characteristics when the rate of change of the second frequency is 3.0%/(km/h) - L6: une illustrating the characteristics when the rate of change of the second frequency is 3.5%/(km/h) - L7: une indicating the frequency of the conventional notification sound - Lil: une indicating the sound pressure level of the first sound pressure - L12: une indicating the sound pressure level of the second sound pressure - Fi: frequency band of the first notification sound - F2: frequency band of the second notification sound Citation List Patent Literature Documents [0074] For any purpose, the following patent document(s) is (are) cited: - palciti: REVENDICATIONS1. A vehicle approach notification &vice which is equipped with a notification sound generating portion having a first notification sound (SI) and a second notification sound (S2) that arc audible, characterized in that a first sound pressure of the first notification sound lias, in a frequency band (FI) of 800 Hz or more and 1.6 kHz or less, a first peak (PI), which is a maximum peak, and a second pcak (P2) Iowa than the first peak, a first frequency of the first notification sound is set to be a fixcd level independently of a vehicle speed, with the first sound pressure being set to be variable in accordance with the vehicle speed, a second sound pressure of the second notification sound has a third peak (P3), which is a maximum peak, the third peak being set to be on the higher frequency side of the first peak and the second peak of the first sound pressure, and a second frequency of the second notification sound is set to be variable in accordance with the vehicle speed. 2. The vehicle approach notification device according to claim 1, wherein the third peak (P3) is set to be variable within a frequency band (F2) of more than 2 kHz and less than 6 kHz. 3. The vehicle approach notification device according to claim 1 or 2, wherein the first peak (P1) and the second peak (P2) are set in a frequency band (F1) of 800 Hz or more and 1.6 kHz or less, are spaced away from each other by 200 Hz or more, and are spaced away from the third peak (P3) by 500 Hz or more. 4. The vehicle approach notification device according to any one of claims 1 to 3, wherein a frequency band width of the first peak (Pl) and the second peak (P2) is set to be wider than a frequency band width of the third peak (P3). 5. The vehicle approach notification device according to any one of claims 1 to 4, wherein in a vehicle speed range of zero to 20 km/h, the first sound pressure is set to be higher than the second sound pressure. 6. The vehicle approach notification device according to any one of claims 1 to 5, wherein a rate of change of the third peak (P3) with respect to the vehicle seed is set to 1.5 to 3.5%/(km/h) 7. The vehicle approach notification device according to any one of claims 1 to 6, wherein the second frequency is maintained in a fixed state in a vehicle speed range of zero to a predetermined speed; and the second frequency is set to vary in accordance with the vehicle speed in a vehicle speed range in excess of the predeterrnined speed. 8. The vehicle approach notification device according to claim 7, wherein the second sound pressure of the second notification sound (S2) is set to be variable in accordancc with the vehicle speed; the predetermined speed is set to be more than zero and lcss than 20 km/h; and in the vehicle speed range of from the predetermined speed to 20 km/h, a rate of change of the first sound pressure is set to be grcatcr than a rate of change of the second sound pressure. 9. The vehicle approach notification device according to any one of claims 1 to 8. whercin when the vehicle speed is 20 km/h or more, the second sound pressure is set to he maintaincd in a fixed state independently of the vehicle speed.