JP5533795B2 - Vehicle approach notification device - Google Patents

Description

  The present invention relates to a vehicle approach notification device that notifies the surroundings that a vehicle is approaching by generating sound from the vehicle.

  In recent years, electric vehicles (EV cars), hybrid cars (HV cars), etc. have structurally low noise, and it is difficult for pedestrians to notice the approach of these vehicles. In order to raise the recognition level that the vehicle is in the vehicle, a vehicle approach notification device that generates a simulated running sound is being installed (see, for example, Patent Documents 1 to 3). In this vehicle approach notification device, as a sound generation method, data such as PCM (Pulse Code Modulation) stored in the memory of a microcomputer, that is, a voice code converted into a data code, is encoded for each sampling period. A method is used in which sound is generated by being set in a / A converter or PWM output device. In addition, the vehicle approach notification device generates a simulated running sound when driving at low speed with low road noise. However, processing such as changing the pitch and sound pressure generated depending on the running state of the vehicle and the accelerator operation state of the driver is performed. In addition, it enables the pedestrian to recall the running state of the vehicle.

JP 2005-215544 A JP 2007-38937 A JP 2009-101895 A

  Increasing the pitch produced by the conventional method as described above can be realized by making the period for setting the PCM data stored in the memory of the microcomputer in the D / A converter or the PWM output unit shorter than the sampling period. However, it is necessary to execute an operation for increasing / decreasing the size of the PCM data in this period, and the processing load of the microcomputer exceeds the processing capacity of the microcomputer, which causes a problem that sound quality is deteriorated. Also, when using the PWM output device built in the microcomputer to increase the pitch, it is necessary to shorten the PWM carrier cycle. However, the PWM data bit is a factor of PWM LSB (minimum unit of PWM cycle). There is a problem that the resolution is lowered, and as a result, the sound quality is lowered.

  Hereinafter, this problem will be described with reference to the drawings. FIGS. 9A and 9B are diagrams showing the relationship between the PWM waveform and the variable width when the pitch is not increased (during the reference pitch) and when the pitch is increased in the conventional PWM method. (D) is the elements on larger scale of Drawing 9 (a) and (b). In the actual PWM system, the PWM resolution is controlled at a high resolution such as 10 bits (1024 steps), but here, for the sake of simplicity of explanation, the PWM resolution is expressed by 5 bits (32 steps), Further, the sound pressure is also shown as a case where the sound pressure is constant. In addition, as the pitch up amount, a case where the pitch is increased by 50% with respect to the reference pitch is shown.

  When the pitch is not increased, the carrier cycle is set to 32 times the PWM LSB, and the PWM pulse width (duty) is changed stepwise from 1 to 32 times the LSB to increase the amplitude of the PCM data. A PWM output that matches this is generated. Therefore, a variable range of 32 steps can be realized at the reference pitch.

  On the other hand, when the pitch is increased, the carrier cycle is set to a time shorter than the carrier cycle at the reference pitch according to the pitch increase amount. For example, when the pitch increase amount is 50%, a time obtained by multiplying 100/150 times the carrier cycle 100% at the reference pitch is an approximate carrier cycle at the time of the pitch increase. For this reason, the carrier frequency at the reference pitch is 32 times the LSB of PWM, whereas the carrier frequency at the time of pitch up is a value multiplied by 100/150 (= 21.33...) For example, it is set to 20 times the LSB of PWM. For this reason, when the pitch is increased by 50%, the PWM pulse width can be changed only by a stepwise change from 1 to 20 times the PWM LSB.

  Furthermore, the PWM pulse width that was set in 32 steps will be changed to 20 steps, and the variable width that can be expressed does not correspond one-to-one, so when the pitch is raised, it can only be set to an approximate pulse width. Disappear. Specifically, as shown in FIG. 9C, the PWM pulse width changes by one step in 32 steps, whereas the same pulse width is expressed in 20 steps. As shown in the figure, there are cases where the stage does not change. This leads to a reduction in the bit resolution of the PWM data, resulting in a reduction in sound quality. Furthermore, as described above, when the carrier period is set in accordance with the pitch up rate, it cannot be set to the carrier cycle at the exact pitch up rate. For example, as described above, when the pitch-up amount is 50%, the carrier period is originally 21, 33... Times the PWM LSB, but is set to 20 times approximate to it. . For this reason, since the carrier period is not set accurately, this also causes a decrease in sound quality.

  In addition, such a pitch variable control by the PWM method is performed by executing the following control processing. However, since there is an arithmetic routine in this control processing, the processing load on the microcomputer is large. Therefore, there is a problem that the sound quality cannot be processed during the control processing cycle, and the sound quality is affected.

  FIG. 10 is a flowchart of a sound generation control process including a pitch variable control and a sound pressure variable control in the conventional PWM method. In addition, although sound pressure variable control is not demonstrated above, the case where sound pressure variable control is also performed here is demonstrated. The sound generation control process is executed for each predetermined carrier period set during the process when the vehicle starts to travel and the vehicle speed is equal to or lower than the predetermined speed.

  First, in step 400, the carrier frequency corresponding to the pitch increase amount is converted from the vehicle speed. The carrier frequency is a frequency for updating the duty ratio of the PWM output, and is a value corresponding to the amount of pitch increase. The reciprocal of the carrier frequency (1 / carrier cycle) is the carrier cycle, which is the time for updating the duty ratio of the PWM output. Regarding the carrier frequency (pitch increase amount), a table showing the relationship of the pitch increase amount with respect to the vehicle speed is stored in the microcomputer in advance, and the carrier frequency corresponding to the detected vehicle speed is obtained using the table. Looking for.

  Next, in step 410, the PWM resolution ratio (stage number ratio) is converted from the vehicle speed (or the corresponding pitch increase amount). Specifically, the bit resolution (number of stages) of the PWM data when the pitch is increased is calculated with respect to the resolution (32 stages) of the PWM data bits at the reference pitch. As described above, when the pitch-up amount is 50%, the number of steps is 20 steps.

  Subsequently, in step 420, the PWM data to be generated is read. This process is performed by reading PCM data stored in the memory of the microcomputer. In step 430, the sounding data PWM value is calculated, and the PWM data is updated to the sounding data PWM value calculated this time. Specifically, the sounding data PWM value is calculated by multiplying the PWM data read out in step 420 by the PWM resolution ratio calculated in step 410. This sounding data PWM value becomes PWM data when the carrier period of PWM is changed in consideration of pitch up. For this reason, by updating the PWM data to this sound generation data PWM value, it is possible to obtain PWM data that takes into account a pitch increase in accordance with the vehicle speed.

  Further, in step 440, the sound pressure increase amount (PWM magnification) is converted from the accelerator opening. For the sound pressure increase amount, a table showing the relationship of the sound pressure increase amount with respect to the accelerator opening degree is stored in advance in the microcomputer, and the sound pressure increase amount corresponding to the detected accelerator opening amount is stored using the table. Seeking by acquiring.

  Next, in step 450, the PWM value to be output is calculated by multiplying the PWM data updated in step 430 by the sound pressure increase amount (PWM magnification) calculated in step 440, and the previous control cycle is calculated. The PWM value calculated at this time is updated to the value calculated this time. In step 460, the PWM value calculated in step 450 is set in the PWM output device and output as a sound output. Thereafter, in step 470, the current carrier cycle is updated to the carrier cycle calculated in step 400 and used as the next carrier cycle. Thus, the pitch variable control by the PWM method is executed.

  In the method of variable pitch control by the PWM method as described above, since a calculation routine exists in step 430 and step 450, the processing load on the microcomputer increases, and processing cannot be performed during the control processing cycle, which affects the sound quality. The problem of the occurrence of a problem can also occur.

  In view of the above points, an object of the present invention is to provide a vehicle approach notification device capable of reducing deterioration in sound quality.

  In order to achieve the above object, according to the first to third aspects of the present invention, in the vehicle approach notification device for reporting the approach of the vehicle by controlling the pitch of the sound from the sound generator (3) mounted on the vehicle. The means for storing the relationship between the vehicle speed and the carrier cycle corresponding to the pitch and the sound generation data, the detection signal indicating the vehicle speed being input, and the carrier cycle corresponding to the vehicle speed indicated by the detection signal corresponding to the stored vehicle speed and pitch Means (100 to 130) for executing a process of reading sound generation data for each acquired carrier period and storing the read sound data as a PWM value in a sound data buffer after acquiring from the relationship with the carrier cycle At each re-sampling period set to a fixed period, the PWM value stored in the sound data buffer is read and the PWM value is output as a PWM output. A microcomputer (21) having a means (200, 210) for executing processing and a PWM output device (21b) for outputting a PWM output, and a current corresponding to the PWM output generated from the microcomputer (21). The sound generator (3) is provided with an amplifier (24) that causes the sound generator (3) to generate a sound having a pitch corresponding to the vehicle speed.

  As described above, the sound generation data is read out and stored in the sound generation data buffer, and the sound generation data stored in the sound generation data buffer is read at every short resampling cycle to generate a PWM value corresponding to the pitch corresponding to the vehicle speed. Yes. Therefore, even if the pitch is increased, the PWM value can be set without changing the PWM resolution.

  In addition, since the carrier cycle when reading the sounding data changes, the time for updating the duty ratio of the PWM output changes. However, since the resampling cycle when reading the PWM value data is fixed, it is simply stored in the sounding data buffer. What is necessary is just to read the stored PWM value. Therefore, the variable pitch control according to the vehicle speed can be executed without performing any processing such as multiplying the sound generation data by the PWM resolution ratio as in the prior art. For this reason, the processing load on the microcomputer (21) can be reduced, the processing can be surely completed during the control processing cycle, and the sound quality can be prevented from deteriorating.

  According to the second aspect of the present invention, the microcomputer (21) receives a means for storing the relationship between the accelerator opening and the sound pressure amount in association with the accelerator opening, and a detection signal indicating the accelerator opening. In addition, after obtaining the sound pressure amount corresponding to the accelerator opening indicated by the detection signal for each fixed period from the relationship between the accelerator opening and the sound pressure amount, a process of outputting a control signal corresponding to the sound pressure amount And a control signal output unit (21a) for outputting a control signal. Based on a control signal generated from the microcomputer (21), a PWM output device (21b) is provided. The voltage control unit (22) that adjusts and outputs the voltage level of the PWM output from the amplifier (24), and the amplifier (24) is based on the PWM output after the voltage level is adjusted by the voltage control unit (22). Pronunciation by sound generator (3) It is characterized in that to perform.

  Thus, by adjusting the voltage level of the PWM output by the voltage control unit (22), the sound pressure of the sound produced by the sound producing body (3) can be changed corresponding to the accelerator opening. The sound pressure amount can also be acquired from the relationship of the sound pressure amount with respect to the accelerator opening. For this reason, the processing load on the microcomputer (21) can be reduced, the processing can be surely completed during the control processing cycle, and the sound quality can be prevented from deteriorating.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

1 is a block diagram of a vehicle approach notification system including a vehicle approach notification device according to a first embodiment of the present invention. 1 is an overall view of a vehicle approach notification system showing an example of a specific block configuration and circuit configuration of a vehicle approach notification device 2. FIG. It is the flowchart which showed the detail of the timer control routine which 21d of pitch variable control parts perform as a pitch variable control process. It is the flowchart which showed the detail of the timer control routine which 21d of pitch variable control parts perform as a pitch variable control process. It is the flowchart which showed the detail of the timer control routine which the sound pressure variable control part 21c performs. It is the figure which showed the mode of the production | generation of the PWM output waveform based on a pitch variable control. (A), (b) is the figure which showed the relationship between the PWM waveform when a pitch does not rise in the sound pressure variable control (at the time of a reference pitch), and a pitch up, and a variable width, (c), (d) ) Is a partially enlarged view of (a) and (b). It is the figure which showed the mode of the production | generation of the PWM output waveform when performing pitch variable control by the conventional PWM system. (A), (b) is the figure which showed the relationship between the PWM waveform when a pitch does not rise in the conventional PWM system (at the time of a reference pitch), and a pitch up, and a variable width, (c), (d) ) Is a partially enlarged view of (a) and (b). It is a flowchart of a sound generation control process including a pitch variable control and a sound pressure variable control in a conventional PWM system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
FIG. 1 is a block diagram of a vehicle approach notification system including a vehicle approach notification device according to the present embodiment. With reference to this figure, the vehicle approach notification system including the vehicle approach notification apparatus according to the present embodiment will be described.

  As shown in FIG. 1, the vehicle approach notification system includes various sensors 1 a and 1 b, a vehicle approach notification device 2, and a speaker 3. In the vehicle approach notification system, the vehicle approach notification device 2 generates a sound from the speaker 3 that is a sounding body based on the driving state detection signals transmitted from the various sensors 1a and 1b, thereby indicating the approach of the vehicle to the surrounding pedestrian. Report to Here, the vehicle approach notification device 2 is separated from the speaker 3, but the speaker 3 may be integrated with the vehicle approach notification device 2.

  The various sensors 1a and 1b constitute vehicle running state acquisition means. As the various sensors 1a and 1b, a vehicle speed sensor 1a and an accelerator opening sensor 1b are provided. The vehicle speed sensor 1a outputs a detection signal indicating the vehicle speed as a vehicle traveling state detection signal, and the accelerator opening sensor 1b outputs a detection signal indicating the accelerator opening as a vehicle traveling state detection signal. For this reason, the vehicle approach notification device 2 inputs a detection signal indicating the vehicle speed and the accelerator opening as a traveling state detection signal, and generates a sounding pitch and a sound pressure according to the traveling state of the vehicle such as the vehicle speed and the accelerator opening. Perform sound control to control.

  The vehicle approach notification device 2 includes a microcomputer 21, a voltage control unit 22, a low-pass filter (hereinafter referred to as LPF) 23, and a power amplifier (hereinafter referred to as AMP) 24.

  The microcomputer 21 has a memory (not shown) and a digital / analog converter (hereinafter referred to as DAC) 21a and a PWM output device 21b. The memory stores a sound generation control program, sound generation data such as PCM data, a pitch up amount and sound pressure amount table associated with the vehicle running state indicated by the running state detection signal, and the like. Using this stored content, the microcomputer 21 outputs, from the DAC 21a and the PWM output device 21b, an output for setting a sound volume amount corresponding to the vehicle speed indicated by the traveling state detection signal and a sound pressure amount corresponding to the accelerator opening. Specifically, a control signal for setting the sound pressure amount corresponding to the accelerator opening is output from the DAC 21a, and a PWM output having a pitch level corresponding to the vehicle speed is output from the PWM output device 21b. Basically, the pitch-up amount is set to increase as the vehicle speed increases, and the sound pressure amount is set to increase as the accelerator opening increases. In other words, the faster the vehicle approaches a pedestrian or the like, the greater the amount of pitch increase, and the greater the driver's operation amount, the higher the sound pressure level, so that the vehicle approaches the pedestrian or the like. It makes it easy to detect.

  The voltage control unit 22 adjusts the voltage level of the PWM output based on the control signal transmitted from the DAC 21a, and changes the voltage level of the PWM output to the voltage level indicated by the control signal. Specifically, a control signal corresponding to the amount of sound pressure is generated from the DAC 21a, and when the sound pressure amount to be generated increases, the voltage level generated by the voltage control unit 22 increases, and the sound pressure to be generated is increased. As the amount decreases, the control signal of the DAC 21a is changed so that the voltage level generated by the voltage control unit 22 decreases. Therefore, the voltage control unit 22 decreases the voltage level of the PWM output as the sound pressure amount to be generated decreases, and increases the voltage level of the PWM output as the sound pressure amount increases.

  The LPF 23 corresponds to filter means, and removes high frequency noise components and generates an output corresponding to the output of the PWM output device 21 b transmitted via the voltage control unit 22. For example, the LPF 23 stores a voltage corresponding to the output of the voltage control unit 22 in a built-in capacitor and outputs it to the AMP 24.

  The AMP 24 supplies a current corresponding to the output of the LPF 23 to the speaker 3 based on voltage application from a constant voltage source (not shown). The sound pressure generated by the speaker 3 is determined according to the magnitude (amplitude) of the current supplied from the AMP 24, and the magnitude of the current supplied from the AMP 24 is determined by the output waveform of the LPF 23 corresponding to the PWM output. For this reason, the current flowing through the AMP 24 is changed based on the adjustment of the voltage level in the voltage control unit 22. At this time, if the voltage control unit 22 does not adjust the voltage level, the current flowing through the AMP 24 is changed only by the pulse width of the PWM output of the PWM output device 21b. The pulse width becomes too small. However, since the voltage level of the PWM output is made variable by the voltage control unit 22, even when the current flowing through the AMP 24 is small, the pulse width of the PWM output does not need to be extremely reduced.

  FIG. 2 is an overall view of a vehicle approach notification system showing an example of a specific block configuration and circuit configuration of the vehicle approach notification device 2.

  As the microcomputer 21, for example, a microcomputer clock having a period of 0.03125 μs and a frequency of 32 MHz is used. A PWM clock has a period of 0.09375 μs, a frequency of 10.67 MHz, and an 8-bit PWM period [× 256 clocks] has a period of 24 μs. A frequency of 41.67 kHz is used. The PWM clock has a frequency obtained by multiplying the microcomputer clock. In the conventional PWM system, a microcomputer clock having a period of 0.03125 μs and a frequency of 32 MHz is used. A PWM clock has a period of 0.03125 μs, a frequency of 32 MHz, and a 10-bit PWM period [× 1024 clock] has a period of 32 μs and a frequency of 31. A cycle of 21.3125 μs and a frequency of 46.92 kHz were used for .25 kHz, 10-bit PWM cycle [× 682 clocks]. As described above, in the present embodiment, the 8-bit PWM cycle is used instead of the conventional 10-bit PWM cycle, but this performs sound pressure variable control processing and pitch variable control processing as sound generation control processing as will be described later. By executing these separately, the PWM cycle can be set to 8 bits, and the clock can be rotated more slowly than in the case of 10 bits.

  Specifically, as shown in FIG. 2, the microcomputer 21 includes a sound pressure variable control unit 21c that executes a sound pressure variable control process and a pitch variable control unit 21d that executes a pitch variable control process. Yes.

  The sound pressure variable control unit 21c converts the sound pressure amount based on the accelerator opening, and outputs an output corresponding to the sound pressure amount from the DAC 21a. For example, the sound pressure variable control unit 21c controls the voltage level output from the voltage control unit 22 by outputting a voltage corresponding to the amount of sound pressure as a control signal from the DAC 21a. Details of the sound pressure variable control process executed by the sound pressure variable control unit 21c will be described later.

  The pitch variable control unit 21d updates the timer control time data, sets the timer control timer, updates the pitch up amount by executing each routine set as the timer control routine, and according to the pitch up amount. The PWM output is output from the PWM output device 21b. For example, the pitch variable control unit 21d obtains a carrier frequency corresponding to the pitch increase amount according to the vehicle speed, and sets a timer control time corresponding to the carrier frequency, or sets a count value of the timer control timer as the timer control time. And perform processing such as measurement. In addition, as one of the timer control routines, the variable pitch control unit 21d performs the process of reading the sounding PWM data and storing the PWM value of the read PWM data in the sounding data buffer. Then, a process for reading the PWM value stored in the sound data buffer and generating a PWM output corresponding to the PWM value is performed. Details of the pitch variable control process executed by the pitch variable control unit 21d will be described later.

  For example, as shown in FIG. 2, the voltage control unit 22 includes a buffer 22a and a switch unit 22b. The buffer 22a generates an output voltage corresponding to the voltage output from the DAC 21a. The switch unit 22b includes an NPN transistor 22ba, an input resistor 22bb, and a resistor 22bc provided between the base and the emitter. The NPN transistor 22ba is turned on / off based on the output of the PWM output device 21b, whereby the output of the buffer 22a. A voltage is input to the LPF 23.

  Thus, after the high frequency noise component is removed from the output of the voltage control unit 22 by the LPF 23, the signal after the noise component removal is input to the AMP 24. As a result, a current for generating a desired pitch and sound pressure is supplied from the AMP 24 to the speaker 3, and the pitch and sound pressure are generated from the speaker 3.

  Next, the sound generation control process, that is, the pitch variable control process and the sound pressure variable control process will be described. Of the sound generation control processes, the pitch variable control process is executed by the above-described pitch variable control part 21d, and the sound pressure variable control process is executed by the sound pressure variable control part 21c.

  3 and 4 are flowcharts showing details of a timer control routine executed by the pitch variable control unit 21d as a pitch variable control process. The timer control routine shown in FIG. 3 is executed for each carrier cycle. Since the carrier cycle is updated every time this routine is executed, the control cycle of this routine varies corresponding to the updated carrier cycle. For example, the carrier frequency (= 1 / carrier cycle) varies between 15.626 and 23.4375 kHz, and the control cycle of this routine also varies correspondingly. The control cycle of the timer control routine shown in FIG. 4 is a fixed cycle. For example, the control cycle of this routine is set to a fixed cycle of 1 / 41.67 kHz. FIG. 5 is a flowchart showing details of a timer control routine executed by the sound pressure variable control unit 21c. The control cycle of the timer control routine shown in this figure is also a fixed cycle. For example, the control cycle of this routine is a fixed cycle of 1/50 Hz. Although this control cycle is longer than the control cycle used for the variable pitch control, it is not necessary to change the sound pressure abruptly.

  First, two timer control routines executed by the pitch variable control unit 21d will be described. As shown in FIG. 3, in step 100, the carrier frequency corresponding to the pitch increase amount is converted from the vehicle speed. For the pitch up amount, a table showing the relationship of the carrier frequency (pitch up amount) with respect to the vehicle speed is stored in the microcomputer 21 in advance, and the carrier frequency corresponding to the detected vehicle speed is obtained using the table. Looking for.

  Subsequently, in step 110, the PWM data to be generated is read. The PWM data is read by reading the PCM data stored in the memory of the microcomputer 21 at every control cycle of this routine. For example, PCM data is stored as 8-bit data, and the PCM data is sequentially read for each control period. The read value becomes a PWM value in the control cycle.

  In step 120, the PWM value is stored as PWM data in the sound generation data buffer. That is, the PWM data is read out every control cycle of this routine, that is, every carrier cycle. Since the carrier period obtained in step 100 is set to a time corresponding to the pitch-up amount, if the PWM value is sequentially read and stored in the sounding data buffer for each carrier period, the sounding data buffer Since the stored PWM value is updated every carrier period, the value is changed in accordance with the change in pitch.

  Thereafter, in step 130, the current carrier cycle is updated to the carrier cycle calculated in step 100. At this time, the updated carrier period is used as the carrier period in the next control period. In this way, the timer control routine shown in FIG. 3 is executed.

  In the timer control routine shown in FIG. 4, the PWM value is resampled. Specifically, the processing of steps 200 and 210 is executed for each resampling cycle, with the above-described fixed cycle control cycle as the resampling cycle. First, in step 200, the PWM value is read from the sound generation data buffer. That is, since the PWM value is stored in the sound generation data buffer in step 120 of FIG. 3, the stored PWM value is read out. The PWM value at this time has already changed in response to the pitch change. Since the control cycle of the routine shown in FIG. 4 is set to a time shorter than the control cycle of the routine shown in FIG. 3, the PWM value stored in the routine shown in FIG. It can be read out periodically. In step 210, the PWM value read in step 200 is set in the PWM output device 21b and output as a sound output. In this way, the timer control routine shown in FIG. 4 is executed. Thus, the two timer control routines executed by the pitch variable control unit 21d are completed.

  Next, a timer control routine executed by the sound pressure variable control unit 21c as the sound pressure variable control process will be described. First, in step 300, the DAC amount corresponding to the sound pressure increase amount from the accelerator opening, that is, the output value of the control signal output from the DAC 21a, for example, the output voltage value in the configuration shown in FIG. For the DAC amount (sound pressure increase amount), a table indicating the relationship of the DAC amount to the accelerator opening is stored in advance in the microcomputer, and the DAC amount corresponding to the detected accelerator opening is obtained using the table. By seeking. In step 310, a control signal corresponding to the DAC amount acquired in step 300 from the DAC 21a is output. Accordingly, the voltage control unit 22 can change the PWM output output from the PWM output device 21b to a voltage level corresponding to the control signal of the DAC 21a. Thereby, the sound pressure of the sound produced by the speaker 3 can be changed corresponding to the accelerator opening. In this way, the timer control routine shown in FIG. 5 is executed, and the timer control routine executed by the sound pressure variable control unit 21c is completed.

  As described above, the sound generation control process, that is, the pitch variable control and the sound pressure variable control are performed. When the sound generation control process is executed by such a method, the following effects can be obtained. This effect will be described with reference to FIG.

  FIG. 6 is a diagram showing how the PWM output waveform is generated based on the pitch variable control. The sounding data stored as PCM data, the sounding data buffer stored value (stored PWM value), the PWM output value ( PWM value to be output).

  FIG. 6A shows a state where the pitch is 100%, that is, the pitch-up amount is 0%. The PCM data (sound generation data) shown in FIG. 6A is read for each carrier cycle, and the data is stored in the sound generation data buffer. At this time, since the pitch is 100% and there is no pitch increase, the carrier period is 64 μs (carrier frequency 15.625 kHz). Then, the PWM value is read from the sounding data buffer at every fixed resampling period, and the PWM value stored in the sounding data buffer is read at a resampling period of 24 μs (resampling frequency 41.67 kHz). As a result, it is possible to read from the sound generation data buffer with a resampling period that is shorter than the reading of the PCM data.

  FIG. 6B shows a state where the pitch is 120%, that is, the pitch-up amount is 20%. Also in this case, the PCM data is read for each carrier period, and the data is stored in the sound generation data buffer. At this time, since the pitch is 120% and the pitch increase is 20%, the carrier period is 53.33 μs (carrier frequency 18.75 kHz). Then, the PWM value is read from the sounding data buffer at every fixed resampling period, and the PWM value stored in the sounding data buffer is read at a resampling period of 24 μs (resampling frequency 41.67 kHz).

  FIG. 6C shows a state in which the pitch is 150%, that is, the pitch increase amount is 50%. Also in this case, the PCM data is read for each carrier period, and the data is stored in the sound generation data buffer. At this time, since the pitch is 150% and the pitch increase is 50%, the carrier period is 42.67 μs (carrier frequency 23.4375 kHz). Then, the PWM value is read from the sounding data buffer at every fixed resampling period, and the PWM value stored in the sounding data buffer is read at a resampling period of 24 μs (resampling frequency 41.67 kHz).

  In this way, the PCM data is read out and stored in the sound generation data buffer, and the PCM data stored in the sound generation data buffer is read out every short resampling period, thereby generating a PWM value corresponding to the pitch increase amount. Therefore, when the pitch is 100% (pitch increase amount = 0%), and when the pitch is 120%, 150% (pitch increase amount = 20%, 50%), the PWM value is changed without changing the PWM resolution. It becomes possible to set.

  FIGS. 7A and 7B are diagrams showing the relationship between the PWM waveform and the variable width when the pitch is not increased (during the reference pitch) and when the pitch is increased in the sound pressure variable control of the present embodiment. 7C and 7D are partial enlarged views of FIGS. 7A and 7B. In the actual PWM system, the PWM resolution is controlled at a high resolution such as 8 bits (256 levels), but here, for the sake of simplicity of explanation, the PWM resolution is expressed by 5 bits (32 levels). Further, the sound pressure is also shown as a case where the sound pressure is constant. In addition, as the pitch up amount, a case where the pitch is increased by 50% with respect to the reference pitch is shown.

  In the present embodiment, the carrier frequency for reading PCM data at the reference pitch is 15.625 kHz, and the resampling frequency is 41.67 kHz. Therefore, the resampling frequency is about 2.7 times the carrier frequency. Therefore, at the time of the reference pitch, the carrier frequency is set to 15.625 kHz and reading from the PCM data is performed, and when it is resampled, data of the same PWM value is continuously read for about three cycles. When the pitch increase amount is 50%, the carrier frequency for reading PCM data is set to 23.4375 kHz, and the resampling frequency is 41.67 kHz. Therefore, the resampling frequency is about the carrier frequency. 1.8 times. Therefore, at the time of the reference pitch, the carrier frequency is set to 15.625 kHz and reading from the PCM data is performed, and when it is resampled, data of the same PWM value is continuously read for about two cycles.

  In this way, the carrier period when PCM data is read changes due to the pitch increase, but the resampling period when PWM value data is read is fixed, so the PWM value stored in the sound data buffer can be simply read. The PWM resolution may be 5 bits (32 steps). Also, since the carrier cycle does not have to be set to a value that matches the PWM LSB, the carrier cycle can be set accurately. Therefore, it is possible to prevent a decrease in sound quality based on these.

  Although not reflected in FIG. 6, the sound pressure increase amount can also be set simply by conversion using a table showing the relationship of the sound pressure amount (DAC amount) to the accelerator opening. Therefore, even if the processing such as multiplying the PCM data by the PWM resolution ratio (step 430 in FIG. 9) or multiplying the PWM data by the sound pressure increase amount (PWM magnification) as in the prior art is not performed. It is possible to execute variable pitch control and variable sound pressure control according to the vehicle speed and the accelerator opening. For this reason, the processing load on the microcomputer 21 can be reduced, the processing can be surely completed during the control processing cycle, and the sound quality can be prevented from being deteriorated.

  For reference, FIG. 8 shows how a PWM output waveform is generated when variable pitch control is performed using the conventional PWM method. The sound output data and PWM output values (output PWM values) stored as PCM data and the like are shown. Show.

  FIG. 8A shows a state where the pitch is 100%, that is, the pitch-up amount is 0%. As shown in FIG. 5A, when the pitch is 100%, the carrier period is set to 32 times the LSB, and the PWM resolution remains at 5 bits (32 steps). Can be set. On the other hand, FIGS. 8B and 8C show a state in which the pitch is 120% and 150% (pitch increase amount is 20% and 50%). In these cases, since the resolution ratio is converted from the vehicle speed and the PWM data is updated by multiplying the PCM data by the PWM resolution ratio, the resolution is lowered and the carrier period is also accurately set. Disappear. For this reason, a deviation occurs in the value of the actually output PWM output value with respect to the ideal PWM output value to be output indicated by dots in the figure. This affects the sound quality of pronunciation.

  On the other hand, as shown in FIG. 6, according to the pitch variable control of the present application, the value of the PWM output value that is actually output with respect to the ideal PWM output value that is desired to be output indicated by the dots in the figure. Match. For this reason, it is possible to prevent the sound quality from being deteriorated.

(Other embodiments)
In the above embodiment, the sound pressure is changed according to the accelerator opening, and the pitch is changed according to the vehicle speed. However, these are merely examples. For example, both the sound pressure and the sound generation pitch may be changed according to the vehicle speed or the accelerator opening. In this case, as the vehicle speed or accelerator opening increases, the sound pressure increase amount and the pitch increase amount can be increased.

  In the microcomputer 21, the DAC 21a is used as the control signal output unit, and the voltage control of the voltage control unit 22 is performed by generating a DAC output for changing the sound pressure from the DAC 21a. The voltage control unit 22 may be used to control the voltage. When using the PWM controller and changing the sound pressure according to the vehicle speed or the accelerator opening, for example, changing the on / off duty ratio of the PWM output according to the vehicle speed or the accelerator opening, and changing the sampling period of the PWM output Change it.

DESCRIPTION OF SYMBOLS 1a Vehicle speed sensor 1b Accelerator opening sensor 2 Vehicle approach notification apparatus 3 Speaker 21 Microcomputer 21a DAC
21b PWM output device 21c sound pressure variable control unit 21d pitch variable control unit 22 voltage control unit 23 LPF
24 AMP

Claims (3)

In the vehicle approach notification device for reporting the approach of the vehicle by controlling the pitch of the sound from the sound generator (3) mounted on the vehicle,
The means for storing the relationship between the vehicle speed and the carrier cycle corresponding to the pitch and the sound generation data, the detection signal indicating the vehicle speed being input, and the carrier cycle corresponding to the vehicle speed indicated by the detection signal corresponding to the stored vehicle speed and pitch Means (100 to 130) for executing the process of reading the sounding data for each acquired carrier period and storing the read sounding data in the sounding data buffer as a PWM value after acquiring from the relationship with the carrier period And means (200, 210) for executing a process of reading out the PWM value stored in the sound generation data buffer and outputting the PWM value as a PWM output at every re-sampling period set as a fixed period, and the PWM output A microcomputer (21) having a PWM output device (21b) for outputting
An amplifier (24) which causes the sounding body (3) to generate a sound corresponding to the vehicle speed by causing a current corresponding to the PWM output generated from the microcomputer (21) to flow through the sounding body (3). And a vehicle approach notification device. The microcomputer (21) is input with means for storing the relationship between the accelerator opening and the sound pressure in association with the accelerator opening, and a detection signal indicating the accelerator opening, and at regular intervals. Means (300) for obtaining a sound pressure amount corresponding to the accelerator opening degree indicated by the detection signal from the relationship between the accelerator opening degree and the sound pressure amount and outputting a control signal corresponding to the sound pressure amount (300) 310) and a control signal output unit (21a) for outputting the control signal,
Based on the control signal generated from the microcomputer (21), a voltage control unit (22) for adjusting and outputting the voltage level of the PWM output from the PWM output device (21b),
The amplifier (24) causes the sounding body (3) to perform sound generation based on the PWM output after the voltage level is adjusted by the voltage control unit (22). The vehicle approach notification device described.   The vehicle approach notification device according to claim 1, wherein the resampling period is shorter than the carrier period.

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