JP2778300B2 - Ultrasonic distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic distance measurement for measuring a distance to a preceding vehicle based on a propagation delay time from the transmission of an ultrasonic signal in front of the vehicle to the reception of a reflected signal by the preceding vehicle. Related to the device.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a conventional example of an ultrasonic distance measuring device, and FIG. 6 is a diagram showing an operation timing chart of the conventional example.

[0003] This device is based on an ultrasonic signal transmitted from an ultrasonic transmitter 55 at a constant period (see FIG. 6 (a)) to a vehicle ahead under the control of a drive signal generator 51 and a driver 53. 5 (d) is received by the ultrasonic wave receiver 57, and the reflected signal is processed by the amplifier 59, the bandpass filter 61, the detection circuit 63, the gate circuit 65, and the comparator 67. The inter-vehicle distance to the preceding vehicle is measured based on the propagation delay time from transmission of the ultrasonic signal to reception of the ultrasonic signal, and the distance is displayed on the distance display 71. In the above device, the bandpass filter 61 extracts only a reflected signal component of a specific frequency from the received signal, and the detection circuit 63 performs processing such as envelope detection on the extracted signal component. The comparator 67 compares the signal subjected to the detection processing with a threshold set by the threshold setting unit 73, and outputs a signal reflected by the preceding vehicle to the CPU 69 when the signal exceeds the threshold.

[0004]

In the above-described conventional apparatus, however, since the influence of noise and the like is reduced and only the reflected signal from the preceding vehicle is detected, once the reflected signal from the preceding vehicle is received. The CPU 69 sets a gate time (ΔT) at which the reflected signal can be received according to the reception timing, and the gate circuit 65 opens and closes accordingly (see FIG. 6D). . Therefore, as long as there is no preceding vehicle and no reflected signal is received, the gate circuit 65 is kept open (see FIG. 6C).

However, if another vehicle interrupts the preceding vehicle, the interrupted vehicle becomes a new preceding vehicle. Therefore, the distance to the interrupted vehicle must be measured. Since the reflected signal from the vehicle is received outside the gate time, there is a problem to be solved that the distance to the interrupting vehicle cannot be measured immediately despite the reflected signal being received.

The present invention has been made in view of the above, and an object of the present invention is to provide an ultrasonic distance measuring apparatus capable of always accurately measuring a distance to a preceding vehicle.

[0007]

In order to achieve the above object, a distance to a preceding vehicle is measured based on a propagation delay time from transmission of an ultrasonic signal in front of the vehicle to reception of a reflected signal by the preceding vehicle. According to the present invention, as shown in FIG. 1, according to the present invention, a first gate time having a predetermined time width for enabling a reflected signal to be received is set in accordance with a timing of receiving a reflected signal by a preceding vehicle once received. First gate setting means 1
A second gate setting means 3 for setting a second gate time for enabling a reflected signal to be received from the elapse of a predetermined time after the transmission of the ultrasonic signal to the rise of the first gate time; When a reflected signal from another vehicle different from the preceding vehicle is received within the second gate time, the first gate correction setting means 5 for newly setting the first gate time according to the reception timing. It is the gist to have.

[0008]

In the ultrasonic distance measuring device according to the present invention,
In addition to the first gate time, a second gate time for detecting the presence or absence of an interrupted vehicle is set, and when the interrupted vehicle is detected, the interrupted vehicle is used to measure the distance as the new preceding vehicle. The first gate time is newly set in accordance with the reception timing of the reflected signal from.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a configuration of an ultrasonic distance measuring apparatus according to one embodiment of the present invention. As the configuration, a gate circuit (hereinafter, referred to as a “first gate circuit”) 65, a comparator (hereinafter, referred to as a “first comparator”) 67, and a threshold setting unit (hereinafter, referred to as “first gate circuit”) are different from the configuration in FIG. The second gate circuit 15, the second comparator 17, and the second threshold setting unit 23 having the same functions as those of the “first threshold setting unit” 73 are connected in parallel to the detection circuit 63. And the processing function of the CPU 19 differs accordingly.

Next, the operation of this embodiment will be described with reference to FIG.
And the timing chart of FIG.

First, the CPU 19 sets the first and second gate circuits 65 and 15 to the fully open state and the fully closed state, respectively, and starts transmitting ultrasonic waves at a constant cycle (FIG. 4A).
) And start the measurement. Here, the fully opened and fully closed states mean that the reflected signal comparators 17 and 67 are in a period from the passage of a fixed reflected wave undetectable time after the transmission of the ultrasonic signal to the transmission of the next ultrasonic signal. (See FIGS. 4 (a) to 4 (c)).

When there is no preceding vehicle, the CPU 19 cannot set the gate time according to the reflection signal, and the first and second gate circuits 65 and 15 hold the fully open state and the fully closed state, respectively (step 10).
0, 110, 150, 170).

When a preceding vehicle is detected from this state, the process is performed as described in the conventional example of FIG. 5, so that the distance to the preceding vehicle is measured, and accurate measurement is continuously performed without being affected by noise. As shown in FIG. 4D, a predetermined first gate time (ΔT) is set in the first gate circuit 6.
5 (steps 100 to 130). Accordingly, the CPU 19 sets the time from the passage of the reflected wave undetectable time to the rise of the first gate time to the second gate time (see FIG. 4E) for detecting the interrupted vehicle. Is set for the second gate circuit 15 (steps 140 and 240).

In this state, if another vehicle interrupts during the distance measurement to the preceding vehicle, regardless of the presence or absence of the reflected signal from the preceding vehicle, at least the reflected signal from the interrupted vehicle is output during the second gate time. (Step 140). The CPU 19 determines from the value of the register N whether the first or second wave reception within the second gate time is performed (steps 180 and 190). And
If it is the first time, a new second gate time is set according to the reception timing as shown in FIG. 4F (step 250). If it is the second time, in order to perform the subsequent distance measurement using the interrupted vehicle as a new preceding vehicle, the distance is measured and output based on the second reflected signal, and the value of the register N is cleared. , (H) as shown in FIG.
A new first gate time and a new second gate time are set according to the reception timing of the second reflection signal (steps 200 to 230).

In the above embodiment, step 130 is the first gate setting means, and step 250 is the second gate setting means.
Gate setting means, step 230, constitutes first gate correction setting means.

Further, the first and second gate times set in accordance with the reception timing of the reflected signal may be changed according to the moving speed of the preceding vehicle. If the maximum value of the distance change can be expected to some extent, it may be fixed.

Therefore, according to the present embodiment, the second gate time for detecting the interrupted vehicle with respect to the conventional device is set separately from the first gate time, so that there is a sudden interrupted vehicle. Even when the interrupted vehicle is used as a new preceding vehicle, the object to be measured can be quickly changed to continue accurate distance measurement.

[0019]

As described above, according to the present invention, in addition to the first gate time, a second gate time for detecting the presence or absence of an interrupted vehicle is set. Since the first gate time is newly set in accordance with the reception timing of the reflected signal from the interrupted vehicle in order to measure the distance as the new preceding vehicle, the distance to the preceding vehicle is always accurately determined. Can be measured.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is a diagram showing a configuration of one embodiment of the present invention.

FIG. 3 is a flowchart illustrating a process according to the embodiment;

FIG. 4 is a timing chart for explaining the operation of the embodiment.

FIG. 5 is a diagram showing a configuration of a conventional example.

FIG. 6 is a timing chart for explaining the operation of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st gate setting means 3 2nd gate setting means 5 1st gate correction setting means 15 2nd gate circuit 17 2nd comparator 19 CPU 23 2nd threshold value setting part 51 drive signal generator 53 driver 55 ultrasonic transmission Wave receiver 57 Ultrasonic wave receiver 59 Amplifier 61 Bandpass filter 63 Detection circuit 65 Gate circuit 67 Comparator 69 CPU 71 Distance indicator 73 Threshold setting unit

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01S 15/00-15/93

Claims (1)

(57) [Claims] An apparatus for measuring a distance to a preceding vehicle based on a propagation delay time from transmission of an ultrasonic signal to the front of the vehicle to reception of a reflected signal by the preceding vehicle, the preceding vehicle receiving the signal once. First gate setting means for setting a first gate time of a predetermined time width for enabling the reflection signal to be received in accordance with the reception timing of the reflection signal by the ultrasonic signal; A second gate setting means for setting a second gate time for allowing a reflected signal to be received until the rise of the first gate time, and a second vehicle which is different from the preceding vehicle within the second gate time When a reflected signal is received, the first
And a first gate correction setting means for newly setting the gate time of the ultrasonic distance.