Vehicle proximity detection device

Abstract

Vehicle approach warning device (1) for indicating a vehicle approach by emitting a warning tone from a loudspeaker (2) with which a vehicle is equipped, the vehicle approach warning device (1) comprising: a reference voltage generating circuit (12) which generates a reference voltage (Vref) obtained by dividing a power supply voltage applied to a power supply terminal (Vt) by a plurality of resistors (12a, 12b); a sound emission signal generating section (10) having a digital / analog converter (10b) which generates a sound emission signal by means of the digital / analog converter (10b); a power amplifier (14) which outputs an amplified signal at an output terminal (OUT) of the power amplifier (14), the amplified signal being generated by amplifying a differential voltage between the reference voltage (Vref) and the voltage of the sound emission signal; a coupling capacitor (15) placed between the output terminal (OUT) of the power amplifier (14) and an output terminal for a loudspeaker (2); and a rise delay capacitor (16) placed between a connection point connecting the plurality of resistors (12a, 12b) generating the reference voltage (Vref) and a ground terminal, the rise delay capacitor (16) generating a rise time of the reference voltage (Vref) to delay it at a start of the power supply to the power supply terminal (Vt), where The tone emission signal generation section (10) increases the tone emission signal to a voltage level substantially equal to the reference voltage (Vref) such that a variation of the differential voltage between the reference voltage (Vref) and the voltage of the tone emission signal lies within a predetermined range.

Description

[0001] The present disclosure relates to a vehicle approach notification device for notifying the approach of a vehicle by outputting an alert sound from a speaker equipped in a vehicle.

[0002] DE 693 17 135 T2 discloses a circuit of a radio receiver for preventing a crackling sound from a loudspeaker, wherein the receiver contains an intermediate frequency audio amplifier which controls an amplifier feeding the loudspeaker, and wherein the circuit generates a ramp-shaped operating voltage from a first DC voltage source via a collector / emitter path of a transistor with three electrodes, the collector, the emitter and the base, characterized in that the intermediate frequency audio amplifier is designed in the form of an integrated circuit with an output feeding the amplifier of the loudspeaker and an operating voltage terminal connected to the collector / emitter path of the transistor (T1), wherein a second operating voltage source is connected to the base of the transistor via an RC integrating network and the base is connected directly to earth via a Zener diode.

[0003] An electric vehicle equipped only with an electric motor as its power source emits a significantly low-pitched noise when traveling at low speeds. Similarly, a hybrid vehicle equipped with an electric motor and an internal combustion engine as power sources also emits a significantly low-pitched noise when traveling at low speeds using only the power of the electric motor. Accordingly, a pedestrian or other person may not be able to detect the approach of such a vehicle.

[0004] In view of this, a vehicle approach notification device equipped in such a low-noise vehicle is practically used, for example, as described in JP 2012-17071 A. The vehicle approach notification device generates an alert sound whose frequency changes according to a vehicle speed, and emits an alert sound based on the alert sound to the exterior of the vehicle to notify a pedestrian or the like around the vehicle of the existence of the vehicle.

[0005] The vehicle approach detection device as described above starts operating when the vehicle approach detection device is supplied with electric power via an ignition (IG) power supply of the vehicle battery after operation of a start switch or the like. When the vehicle approach detection device starts operating, a popping sound or the like generated in a speaker causes a reduction in commercial value.

[0006] It is an object of the present disclosure to provide a vehicle proximity detection device that reduces the occurrence of a popping or cracking noise.

[0007] This object is achieved by the vehicle approach detection device having the features of claim 1. Advantageous further developments thereof can be found in the subclaims.

[0008] According to one aspect of the present disclosure, a vehicle approach notification device for notifying a vehicle approach by emitting a notification sound from a speaker installed in a vehicle includes (i) a reference voltage generation circuit, (ii) a sound emission signal generation section, (iii) a power amplifier, (iv) a coupling capacitor, and (v) a rise delay capacitor. The reference voltage generation circuit generates a reference voltage obtained by dividing a power supply voltage applied to a power supply terminal by a plurality of resistors. The sound emission signal generation section generates a sound emission signal. The power amplifier outputs an amplified signal from an output terminal of the power amplifier.The amplified signal is generated by amplifying a differential voltage between the reference voltage and the voltage of the sound emission signal. The coupling capacitor is placed between the output terminal of the power amplifier and the speaker. The rise-delay capacitor is placed between a junction point connecting the plurality of resistors that generate the reference voltage and a ground terminal. The rise-delay capacitor causes a rise time of the reference voltage to delay a start of power supply to the power supply terminal. The sound emission signal generating section boosts the sound emission signal with the voltage level substantially equal to the reference voltage so that a variation in the differential voltage between the reference voltage and the voltage of the sound emission signal is within a predetermined value range.

[0009] According to the above vehicle approach detection device, it is possible to reduce the occurrence of a cracking noise.

[0010] The above object, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings.

[0011] It shows: Fig. 1 is a circuit diagram illustrating a vehicle approach detection device of an embodiment; Fig. 2 is a circuit diagram illustrating a digital-to-analog converter (DAC); Fig. 3 is a graph each showing a waveform of a power supply voltage, a reference voltage, a sound emission signal, and a speaker current of the vehicle approach detection device of the present embodiment; Fig. 4 is a graph showing a waveform of a sound emission signal from a control unit and an output signal from a power amplifier (AMP), respectively; Fig. 5 is a circuit diagram illustrating a vehicle approach detection device of a comparative embodiment; and Fig. 6 is a graph showing a waveform of a power supply voltage, a reference voltage, a sound emission signal and a speaker current, respectively. Fig. 5 represents.

[0012] For example, a configuration of the vehicle proximity detection device in Fig. 5. We will be referring to Fig. 5 describes a generation mechanism of a clicking sound. The vehicle approach detection device includes a control unit 10 that outputs a sound emission signal, a low-pass filter (LPF) 11 that extracts a low-frequency component of the sound emission signal to remove a high-frequency component from the sound emission signal, a power amplifier (AMP) 14, and a coupling capacitor 15. The AMP 14 outputs an amplified signal, which is a differential voltage between a reference voltage Vref and a sound emission signal voltage Vin. The reference voltage Vref is obtained by dividing a power supply voltage applied to a power supply terminal Vt by resistors 12a, 12b. The sound emission signal voltage Vin is input from the control unit 10 through the LPF 11. The coupling capacitor 15 connects the AMP 14 to a speaker 2 via AC coupling.

[0013] In Fig. 6 shows a waveform of the power supply voltage, the reference voltage, the sound emission signal, and a speaker current of the vehicle approach detection device shown in Fig. 5. A characteristic of the vehicle speed is also shown in Fig. 6. In cases where the vehicle proximity detection device is also supplied with the electric power of the IG power supply after the vehicle starter switch or the like is operated, the power supply voltage and the reference voltage increase or increase together with the waveforms in Fig. 6.

[0014] The control unit 10 is set to start after a predetermined interval after the power supply is turned on. The sound emission signal is output from the control unit 10 slightly later after the power supply voltage increases or rises from 0V until the value of the sound emission signal reaches the neutral voltage, which is equal to the reference voltage. When the control unit 10 judges that the vehicle is starting to move based on the vehicle speed signal, the control unit 10 outputs an AC sound emission signal having the neutral voltage as the central value. The AMP 14 outputs the amplified signal, which is the differential voltage between the sound emission signal and the reference voltage.

[0015] In a transition period immediately after the start of power supply to the power supply terminal Vt, a relatively large speaker current (charging current) flows from the AMP 14 into the coupling capacitor 15. The charging current generates a cracking sound.

[0016] It is effective to provide a switching circuit on one side of the output terminal of the AMP 14 and connect the output of the AMP 14 to the speaker at a predetermined interval from the start of the power supply, thus reducing the clicking noise. However, this is undesirable because it may increase the number of parts. (Embodiment)

[0017] A circuit diagram of the vehicle approach detection device 1 in the present embodiment is shown in Fig. 1. The vehicle proximity notification device 1 notifies a pedestrian or the like of a vehicle near the vehicle by emitting an notification sound from the speaker 2 installed in the vehicle.

[0018] The vehicle proximity detection device 1 includes the control unit 10, the LPF 11, resistors 12a, 12b, the AMP 14, the coupling capacitor 15, and a capacitor 16. Both the coupling capacitor 15 and the capacitor 16 connect the power amplifier 14 and the speaker 2 through AC coupling.

[0019] The control unit 10 includes a microcomputer including a CPU 10a and a digital-to-analog converter (DAC) 10b. The control unit 10 includes a sound emission signal generation section that generates the sound emission signal and outputs it to the LPF 11 so that the speaker 2 outputs the notification sound. The LPF 11 receives a vehicle speed signal from a vehicle speed sensor (not shown).

[0020] In the present embodiment, the control unit 10 may correspond to an example of a sound emission signal generation section. In addition, the capacitor 16 may correspond to an example of a ramp-up capacitor.

[0021] The control unit 10 includes a RAM, a ROM, an I / O device, and the like (not shown in detail). The CPU 10a executes a program stored in the ROM.

[0022] As in Fig. As shown in Figure 2, data output terminals D0 to D10 of CPU 10a are connected to DAC 10b. CPU 10a outputs a digital signal from 000f to 3ffh in hexadecimal notation through data output terminals D0 to D10. Data output terminal D0 serves the least significant bit (LSB). Data output terminal D10 serves the most significant bit (MSB).

[0023] The DAC 10b includes an R-2R ladder resistor network or a resistor divider network with a plurality of ladder resistors 100, a capacitor 101, an operational amplifier 102, and resistors 103, 104. The level shift circuit allows a change of the voltage level according to the combined resistance of the R-2R ladder resistor network.

[0024] An output terminal SOUT outputs a voltage according to the voltage level of the data output terminals D0 to D10 of the CPU 10a, that is, according to the combined resistance value of the R-2R ladder resistor network.

[0025] The LPF 11 extracts a low-frequency component from an audio emission signal to remove a high-frequency component such as higher harmonics. The LPF 11 in the present embodiment includes a resistor R and a capacitor C, which are combined with the AMP.

[0026] A reference voltage generating circuit 12 generates a reference voltage Vref obtained by dividing a power supply voltage applied to a power supply terminal Vt by the resistors 12a, 12b.

[0027] The AMP 14 is a differential amplifier that amplifies a differential voltage between the reference voltage Vref and a voltage Vin. The reference voltage Vref is applied to an input terminal Vin1. The voltage Vin is applied to an input terminal Vin2.

[0028] The coupling capacitor 15 removes a DC component contained in the output signal of the AMP 14 to extract an AC component from the output signal. The coupling capacitor 15 connects the AMP 14 to the speaker 2 through AC coupling.

[0029] The speaker 2 outputs the notification sound from the AMP 14 via the coupling capacitor 15 according to an input signal.

[0030] In the above-described embodiment, when the power supply terminal Vt is supplied with electric power from a vehicle battery according to an operation of a starter switch or the like, the reference voltage Vref is input to the input terminal Vin1 of the AMP 14. The reference voltage Vref is obtained by dividing the power supply voltage applied to the power supply terminal Vt by the resistors 12a, 12b. The sound emission signal generated in the control unit 10 is input to the input terminal Vin2 of the AMP 14 via the LPF 11. The AMP 14 outputs a signal obtained by amplifying the differential voltage between the reference voltage Vref and the sound emission signal. The output signal from the AMP 14 is input to the speaker 2 installed in the vehicle via the coupling capacitor 15.Then, the speaker 2 outputs the alarm tone according to the output signal from the AMP 14.

[0031] A charging current flowing from the AMP 14 to the coupling capacitor 15 causes a cracking noise when the power supply is started. To prevent this charging current, the control unit 10 in the present embodiment includes the capacitor 16 arranged between a connection point where the resistors 12a, 12b are connected and a ground terminal. In addition, the control unit 10 boosts the sound emission signal in such a way that, upon starting the power supply to the power supply terminal, the voltage of the sound emission signal rises in phase with the reference voltage such that the variation in the difference voltage between the reference voltage and the voltage of the sound emission signal is lower than a predetermined value.

[0032] The capacitor 16 is arranged such that a rise time of the reference voltage at the start of the power supply is longer than a period of, for example, 25 ms, which corresponds to a frequency much lower than a resonance frequency of the speaker.

[0033] The rise time of the reference voltage Vref is varied with a time constant based on the resistance values ​​of resistors 12a, 12b and the capacitance value of capacitor 16. Generally, a minimum audible frequency is approximately 20 Hz. A rise time of a 20 Hz waveform corresponds to 25 ms in a case where the minimum audible frequency is 20 Hz.

[0034] In the present embodiment, the capacitance value of the capacitor 16 is determined such that the rise time of the reference voltage is much longer than the period of 25 ms corresponding to the minimum audible frequency.

[0035] In the present embodiment, at the start of the power supply, a rising characteristic (e.g., time) of the reference voltage becomes moderate, and in addition, the sound emission signal is gradually increased to a neutral voltage along an ascending curve of the reference voltage at the start of the power supply.

[0036] Fig. 3 shows a waveform of a power supply voltage, a power amplifier input reference voltage, a sound emission signal output from the control unit, and a speaker current (a charging current) flowing through the speaker 2 of the vehicle approach detection device, respectively. In cases where the vehicle approach detection device is supplied with electric power from a vehicle battery via an IG power supply, the rises of the power supply voltage have the waveform of Fig. 3 on.

[0037] In the present embodiment, since the capacitor is arranged between the connection point to which the resistors 12a, 12b are connected and the ground terminal, the reference voltage Vref has a gradually increasing waveform as shown in Fig. 3 shown.

[0038] The control unit 10 of the present embodiment outputs the sound emission signal according to a program prestored in a memory. Specifically, when power is supplied to the power supply terminal Vt, the control unit 10 gradually increases the sound emission signal along the rising curve of the reference voltage until the sound emission signal reaches a neutral voltage. When the control unit 10 judges that the vehicle starts traveling based on the vehicle speed signal, the control unit 10 outputs the AC sound emission signal whose center value is the neutral voltage.

[0039] As described above, the rise characteristic (time) of the reference voltage at the start of power supply is gradually increased by placing the capacitor 16 between the junction point to which the resistors 12a, 12b are connected and the ground terminal. The control unit 10 gradually increases the sound emission signal along the rising curve of the reference voltage until the sound emission signal reaches a neutral voltage at the start of power supply to the power supply terminal Vt. In this way, the charging current can be reduced, which causes a popping sound in the speaker 2 when it flows through the coupling capacitor 15.

[0040] Fig. 4 shows a waveform of the AC tone emission signal output from the control unit 10 and the output signal of the AMP 14 after the vehicle starts driving. As shown in Fig.As shown in Figure 4, the AMP 14 outputs an amplified signal corresponding to the differential voltage between the reference voltage and the audio emission signal. The amplified signal has the neutral voltage at its midpoint. The speaker 2, connected to the output terminal OUT, receives the output signal from the AMP 14 through the coupling capacitor 15. The speaker 2 emits the notification tone according to the audio emission signal.

[0041] In the manner described above, the capacitor 16 is arranged between the connection point where the resistors 12a, 12b are connected and the ground terminal. The capacitor 16 delays the rise of the reference voltage at the start of power supply to the power supply terminal. At the start of power supply to the power supply terminal, the control unit 10 increases the sound emission signal at the level substantially equal to the reference voltage, so that the variation of the differential voltage between the reference voltage and the voltage of the sound emission signal is within a range of a predetermined value. The charging current flowing into the coupling capacitor at the start of power supply to the power supply terminal is reduced. Occurrence of the click noise can be avoided without adding a switching circuit that changes the output level of the power amplifier.

[0042] It should be noted that the present disclosure is not limited to the present embodiment. It should be understood that various modifications may be made.

[0043] For example, in the configuration of the embodiment illustrated above, the sound emission signal is generated by changing the combined resistance of the R-2R ladder resistor network including the plurality of ladder resistors 100, and the sound emission signal is increased according to the rising characteristic of the reference voltage before the start of power supply. However, this configuration does not limit the embodiment. For example, in another configuration, the vehicle approach detection device 1 may include an RC circuit for providing such a rising characteristic to the sound emission signal as it causes the sound emission signal to rise, and in addition, at the start of power supply, the sound emission signal may be increased according to the rising characteristic of the reference voltage.

[0044] Furthermore, in the present embodiment, the control unit 10 increases the sound emission signal along the rising curve of the reference voltage at the start of power supply to the power supply terminal Vt until the sound emission signal reaches a neutral voltage. However, it may not be necessary for the sound emission signal to be increased to the neutral voltage along the rising curve of the reference voltage. Thus, it may be sufficient that the sound emission signal and the reference voltage can rise to the same level to such an extent that the variation in the difference voltage between the reference voltage and the voltage of the sound emission signal falls within a range that prevents the occurrence of a click noise at the start of power supply.

[0045] In summary of the above embodiment, a vehicle approach notification device for notifying the proximity of the vehicle outputs the notification sound from the speaker 2 installed in the vehicle. The reference voltage generation circuit generates the reference voltage Vref obtained by dividing the power supply voltage applied to the power supply terminal Vt by a plurality of resistors 12a, 12b. The sound emission signal generation section 10 generates the sound emission signal. The AMP 14 outputs the amplified signal from the output terminal OUT. The amplified signal is generated by amplifying the differential voltage between the reference voltage and the sound emission signal. The coupling capacitor is arranged between the output terminal OUT of the AMP 14 and the speaker 2.Capacitor 16 is arranged between the junction point where resistors 12a, 12b are connected and the ground terminal to increase the rise of the reference voltage at the start of power supply to the power supply terminal. The sound emission signal generating section 10 increases the sound emission signal to the same level as the reference voltage, so that the variation in the differential voltage between the reference voltage and the sound emission signal voltage falls within a predetermined range.

[0046] In the present structure, the capacitor 16 is arranged between the connection point where the resistors 12a, 12b are connected and the ground terminal, so that it increases the rise of the reference voltage at the start of power supply to the power supply terminal. The sound emission signal generating section 10 increases the sound emission signal to be at the same level as the reference voltage, so that the variation of the differential voltage between the reference voltage and the voltage of the sound emission signal falls to the predetermined value. Therefore, the charging current flowing into the coupling capacitor at the start of power supply to the power supply terminal can be reduced, thus reducing the occurrence of the click noise, without adding a switching circuit that changes the output of the power amplifier.

[0047] The occurrence of the clicking noise when starting the power supply to the power supply terminal Vt can be further reduced by setting the rise time of the reference voltage to a period or time period longer than the time period corresponding to the minimum audible frequency.

Claims

[1] Vehicle approach warning device (1) for indicating a vehicle approach by emitting a warning tone from a loudspeaker (2) with which a vehicle is equipped, the vehicle approach warning device (1) comprising: a reference voltage generating circuit (12) which generates a reference voltage (Vref) obtained by dividing a power supply voltage applied to a power supply terminal (Vt) by a plurality of resistors (12a, 12b); a sound emission signal generating section (10) having a digital / analog converter (10b) which generates a sound emission signal by means of the digital / analog converter (10b); a power amplifier (14) which outputs an amplified signal at an output terminal (OUT) of the power amplifier (14), the amplified signal being generated by amplifying a differential voltage between the reference voltage (Vref) and the voltage of the sound emission signal; a coupling capacitor (15) placed between the output terminal (OUT) of the power amplifier (14) and an output terminal for a loudspeaker (2); and a rise delay capacitor (16) placed between a connection point connecting the plurality of resistors (12a, 12b) generating the reference voltage (Vref) and a ground terminal, the rise delay capacitor (16) generating a rise time of the reference voltage (Vref) to delay it at a start of the power supply to the power supply terminal (Vt), where the sound emission signal generating section (10) increases the sound emission signal with a voltage level substantially equal to the reference voltage (Vref) such that a variation of the differential voltage between the reference voltage (Vref) and the voltage of the sound emission signal is within a predetermined range. [2] The vehicle approach detection device (1) according to claim 1, wherein the vehicle approach detection device (1) is configured such that: a rise time of the reference voltage (Vref) at the start of the power supply to the power supply terminal (Vt) is longer than a time period corresponding to a minimum audible frequency. [3] Vehicle approach detection device (1) according to claims 1 or 2, wherein the vehicle approach detection device (1) is configured such that: the power supply to the power supply terminal (Vt) starts in response to the supply of electric power from a vehicle battery to the vehicle approach detection device (1); and the reference voltage (Vref) and the sound emission signal rise while having substantially the same voltage level. [4] Vehicle approach detection device (1) according to one of claims 1 to 3, wherein: a capacitance of the rise delay capacitor (16) is determined such that the rise time of the reference voltage (Vref) at the start of the power supply to the power supply terminal (Vt) is longer than 25ms, which corresponds to the minimum audible frequency.

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