Vehicle obstacle detection device

A vehicle obstacle detection device includes a sensor that transmits and receives ultrasonic waves, and a controller that instructs the sensor to transmit the ultrasonic waves. The controller compares amplitude of reflected waves received by the sensor with a threshold to determine presence or absence of an obstacle. The controller includes a voltage monitoring unit that detects a power supply voltage. The controller more reduces the threshold as the power supply voltage detected by the voltage monitoring unit is lower.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2012/079806, filed on Nov. 16, 2012, which in turn claims the benefit of Japanese Application No. 2011-254464, filed on Nov. 21, 2011, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

This invention relates to a vehicle obstacle detection device which detects, with sound waves or ultrasonic waves, an obstacle around a vehicle.

BACKGROUND ART

Conventionally, there has been provided a vehicle obstacle detection device which detects, with sound waves or ultrasonic waves, an obstacle around a vehicle (e.g., see WO 2009/119577 A1). The document discloses the vehicle obstacle detection device which detects the obstacle around the vehicle, with a sensor transmitting and receiving the ultrasonic waves, thereby assisting parking of the vehicle. In the vehicle obstacle detection device described in the document, the sensor transmits transmission waves, and receives reflected waves that are reflected by an obstacle, and then the vehicle obstacle detection device detects the obstacle around the vehicle, based on a time period between a timing of when the sensor transmits the transmission waves and a timing of when the sensor receives the reflected waves. The sensor of such a vehicle obstacle detection device generally includes a piezo element.

This kind of vehicle obstacle detection device receives power supply from a battery that is installed in the vehicle. The power supply from the battery is also used for other apparatuses that are installed in the vehicle, and accordingly the voltage fluctuates, depending on use situations of other apparatuses. Here, because the sensor including the piezo element outputs sound waves or ultrasonic waves with a sound pressure depending on the supplied voltage, the output sound pressure is changed together with the fluctuation of the supplied voltage. Therefore, the conventional vehicle obstacle detection device keeps constant the output of the transmission waves by the sensor, using a stabilization power supply circuit that keeps constant the voltage to be supplied to the sensor.

However, an output voltage becomes lower than an input voltage, due to using the stabilization power supply circuit. Accordingly, when using the stabilization power supply circuit to keep constant the voltage to be supplied to the sensor, there is a case where the output sound pressure from the sensor becomes smaller than a desired sound pressure. In this case, there is a problem that a distance at which the vehicle obstacle detection device can detect the obstacle is reduced.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a vehicle obstacle detection device which can relatively increase a distance at which the vehicle obstacle detection device is able to detect an obstacle even when a voltage supplied from a power supply to a sensor fluctuates.

A vehicle obstacle detection device according to one aspect of the present invention includes a sensor and a controller. The sensor is configured to intermittently transmit transmission waves and receive reflected waves that are generated by reflection of the transmission waves. The controller is configured to output a transmission signal for instructing the sensor to transmit the transmission waves. The controller is configured to evaluate, when the sensor receives the reflected waves with amplitude that is a prescribed threshold or more, a time period between a timing of outputting the transmission signal and a timing of reception of the reflected waves by the sensor, to detect presence or absence of an obstacle. The sensor is configured to be driven with a power supply voltage to output the transmission waves. The controller includes a voltage monitoring unit that is configured to detect the power supply voltage. The controller is configured to more reduce the prescribed threshold as the power supply voltage detected by the voltage monitoring unit is lower.

In the vehicle obstacle detection device, preferably, the controller is configured to change the prescribed threshold, in stages, according to the power supply voltage detected by the voltage monitoring unit.

In the vehicle obstacle detection device, preferably, the prescribed threshold includes a first threshold and a second threshold that is more than the first threshold, and the controller is configured to detect, when the power supply voltage is equal to or more than a first reference value and is less than a second reference value, the presence or absence of the obstacle with the first threshold, and the controller is configured to detect, when the power supply voltage is equal to or more than the second reference value and is less than a third reference value, the presence or absence of the obstacle with the second threshold.

In the vehicle obstacle detection device, preferably, the controller is configured not to allow, when the power supply voltage is less than the first reference value or is equal to or more than the third reference value, the sensor to transmit the transmission waves.

According to the aspect of the present invention, it is possible to relatively increase a distance at which the vehicle obstacle detection device is able to detect the obstacle even when a voltage supplied from a power supply to the sensor fluctuates.

BEST MODE FOR CARRYING OUT THE INVENTION

A vehicle obstacle detection device of the present embodiment, as shown inFIG. 1, includes a sensor1and a controller2. The sensor1includes a piezo element and is configured to transmit and receive ultrasonic waves. The controller2is configured to instruct the sensor1to transmit transmission waves, and determine presence or absence of an obstacle, with a sensor signal that is output by the sensor1due to reception of reflected waves. As shown inFIG. 2, the sensor1is installed to at least one of front and back ends of a vehicle10, and the vehicle obstacle detection device detects an obstacle around the vehicle10. Hereinafter, as one example, a case will be described, where the sensor1is installed in the front side of the vehicle10, so that a detection range A1 is set in a front direction of the vehicle10.

As shown inFIG. 1, the controller2of the present embodiment includes a microcomputer24, and is configured as part of an ECU (Electric Control Unit) that performs electronic control for various units in the vehicle10. The controller2receives power supply from an in-vehicle battery3. The controller2includes a wave transmission circuit21that is configured to drive the sensor1to transmit the transmission waves, in addition to the microcomputer24. Further, the controller2includes a wave reception circuit22and a wave detection circuit23. The wave reception circuit22is configured to extract, from the sensor signal, a signal that has a frequency within a predetermined frequency band including a frequency of the transmission wave, as a reception signal. The wave detection circuit23is configured to output a detection signal that corresponds to an envelope component of the reception signal. The microcomputer24receives power supply stabilized by a power supply circuit25.

Here, as shown inFIG. 1, only the microcomputer24receives the stabilized power supply from the power supply circuit25, and the wave transmission circuit21receives a power supply voltage directly from the battery3. That is, because the wave transmission circuit21receives the power supply voltage that fluctuates depending on use situations of other apparatuses, also amplitude of a transmission signal output from the wave transmission circuit21fluctuates depending on the power supply voltage.

Next, a basic operation of the vehicle obstacle detection device will be described. When the vehicle obstacle detection device starts the operation, the microcomputer24, as shown in A ofFIG. 3, intermittently transmits, to the wave transmission circuit21, a pulse signal that includes rectangular waves having constant periods. A single pulse signal includes several rectangular waves, each of which has the same period as the ultrasonic wave output from the sensor1. When this pulse signal is input to the wave transmission circuit21, the wave transmission circuit21outputs the transmission signal with the amplitude depending on the power supply voltage received from the battery3, as shown in B ofFIG. 3. The sensor1is driven by the transmission signal, and intermittently transmits the ultrasonic waves, each of which has a sound pressure depending on the amplitude of the transmission signal.

On the other hand, the wave reception circuit22receives, for a little while from the output of the transmission signal, the transmission signal that turns around from the wave transmission circuit21and a signal that is generated due to reverberation of the sensor1. After that, when the sensor1receives the reflected waves, the wave reception circuit22receives also a signal by the reflected waves. Therefore, the wave reception circuit22outputs the reception signal as shown in C ofFIG. 3. Further, the wave detection circuit23, as shown in D ofFIG. 3, outputs the detection signal that has a voltage value corresponding to the envelope component of the reception signal. When a signal level of the detection signal is a prescribed threshold Th or more, the microcomputer24evaluates a time period between a timing of outputting the pulse signal and a timing of detecting the detection signal, to detect presence or absence of the obstacle.

Here, it is assumed that the microcomputer24outputs the pulse signal at a time t1shown inFIG. 3and the detection signal is obtained at a time t2shown inFIG. 3. In the example of the drawing, a component232including reverberation is also obtained as the detection signal, in addition to the detection signal at the time t2(a component231by the reflected wave). Here, in order to remove this component232including the reverberation, the microcomputer24is out of a state of determining the presence or absence of the obstacle during a time period between the time t1at which the pulse signal is output and a prescribed time ts, as a non-detection period. Then, the microcomputer24defines a predetermined time period after the prescribed time ts, as a detection period for determining the presence or absence of the obstacle, and determines the presence or absence of the obstacle, based on the detection signal during the detection period. The above-mentioned detection range A1is defined during this detection period.

As described above, the wave transmission circuit21is driven with the power supply voltage from the battery3, and accordingly, the amplitude of the transmission signal output from the wave transmission circuit21is also changed with the fluctuation of the power supply voltage. That is, as the power supply voltage is lower, the amplitude of the transmission signal output from the wave transmission circuit21is reduced and therefore the sound pressure of the transmission wave is also reduced.

In order to adapt to such a change of the sound pressure, the controller2of the present embodiment further includes a voltage monitoring unit26that detects the power supply voltage, and is configured to change the above-mentioned threshold Th, depending on the power supply voltage detected by the voltage monitoring unit26. The voltage monitoring unit26is configured by an A/D input part27that is included in the microcomputer24and a voltage monitoring circuit28that reduces the power supply voltage to a voltage to be applied to the A/D input part27. The voltage monitoring circuit28includes a voltage dividing circuit for example, and applies a voltage proportional to the power supply voltage to the A/D input part27. The A/D input part27converts, to a digital value, the voltage applied from the voltage monitoring circuit28. Accordingly, the microcomputer24obtains a power supply voltage value Vs through the digital value from the voltage monitoring unit26.

The microcomputer24is configured to change the threshold Th, in stages, according to the power supply voltage value Vs. In the present embodiment, the threshold includes a first threshold Th1and a second threshold Th2, as two stages. That is, the microcomputer24selects, as the threshold Th, any one of the first and second thresholds Th1and Th2, according to the power supply voltage value Vs. The first threshold Th1is set to be less than the second threshold Th2(Th1<Th2) (seeFIG. 5). InFIG. 5, a direction of a magnitude of a signal level faces a downward direction, and accordingly, the wave form more extends in the downward direction as a voltage value (absolute value) of the detection signal is more increased, similarly to D ofFIG. 3.

The threshold selected from the first and second thresholds Th1and Th2is determined by comparing the power supply voltage value Vs with three stages of reference values (first to third reference values V1, V2and V3). That is, as shown inFIG. 4, the microcomputer24selects, when the power supply voltage value Vs is equal to or more than the first reference value V1and is less than the second reference value V2(V1<=Vs<V2), the first threshold Th1, as the threshold Th. The microcomputer24selects, when the power supply voltage value Vs is equal to or more than the second reference value V2and is less than the third reference value V3(V2<=Vs<V3), the second threshold Th2, as the threshold Th. The microcomputer24sets, when the power supply voltage value Vs is less than the first reference value V1(Vs<V1) or is equal to or more than the third reference value V3(Vs>=V3), no threshold Th, and accordingly, the vehicle obstacle detection device is out of the operation of detecting the obstacle.

In this way, it is possible to drive the wave transmission circuit21with the power supply voltage by changing the threshold Th, in stages, according to the power supply voltage value Vs, to detect the presence or absence of the obstacle, and as a result, it is possible to increase the sound pressure of the transmission wave. Therefore, the vehicle obstacle detection device can detect the farther obstacle, compared with a conventional vehicle obstacle detection device.

The operation of the above microcomputer24is summarized and shown inFIG. 6.

When the vehicle obstacle detection device starts the operation, the microcomputer24acquires a power supply voltage value Vs through the A/D input part27(S10). The microcomputer24compares the power supply voltage value Vs with the first to third reference values V1, V2and V3(S11, S12and S17).

When the power supply voltage value Vs is less than the first reference value V1(S11: Yes) or is equal to or more than the third reference value V3(S17: Yes), the microcomputer24acquires a new power supply voltage value Vs without outputting the pulse signal (S10). That is, because the microcomputer24outputs no pulse signal to the wave transmission circuit21, the vehicle obstacle detection device is out of the state of determining presence or absence of the obstacle. Therefore, in this case, it is preferred that the microcomputer separately performs an error processing to inform a user.

On the other hand, when the power supply voltage value Vs is equal to or more than the first reference value V1and is less than the second reference value V2(S12: Yes), the microcomputer24selects the first threshold Th1, as the threshold Th (S13). After that, the microcomputer24outputs the pulse signal to make the sensor1transmit the transmission waves (S14). When the signal level of the detection signal depending on the reflected waves is equal to or more than the first threshold Th1(S15: Yes), the microcomputer24determines that the obstacle is present, and performs notification operation (S16). The microcomputer24may perform auditory notification operation with a buzzer or the like, or perform visual notification operation with a lamp. Then, the microcomputer24acquires a new power supply voltage value Vs (S10), and repeats the above-mentioned operation.

On the other hand, when the power supply voltage value Vs is equal to or more than the second reference value V2and is less than the third reference value V3(S17: No), the microcomputer24selects the second threshold Th2, as the threshold Th (S18). After that, the microcomputer24outputs the pulse signal to the wave transmission circuit21to make the sensor1transmit the transmission waves (S19). When the signal level of the detection signal depending on the reflected waves is equal to or more than the second threshold Th2(S20: Yes), the microcomputer24determines that the obstacle is present, and performs the notification operation (S16). Here, time intervals of acquiring the power supply voltage value Vs are set to be equal to time intervals of outputting the pulse signal.

In the present embodiment, the vehicle obstacle detection device includes the sensor1that transmits and receives the ultrasonic waves, but may include a sensor that transmits and receives sound waves in an audible range instead of the sensor1.

Although the present invention has been described with reference to certain preferred embodiments, numerous modifications and variations can be made by those skilled in the art without departing from the true spirit and scope of this invention, namely claims.