JP3399197B2 - Distance detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a distance detecting device, and more particularly to a distance detecting device for detecting a distance from a detection target in a vehicle cabin using an ultrasonic sensor. About. 2. Description of the Related Art Conventionally, as a distance detecting device, there has been known a device for detecting a distance from an occupant seated in a driver's seat of an automobile, an example of which is disclosed in Japanese Patent Application Laid-Open No. 5-270351. ing. [0003] As shown in FIG. 5, this device comprises a steering wheel 72 provided in front of a driver's seat 70 in the vehicle.
A device for deploying an airbag bag 74 folded and stored at the time of rapid deceleration of a vehicle, using a distance sensor 76, 78 comprising an ultrasonic sensor provided on a dashboard to store the airbag bag 74. The distance from the position to the upper body of the occupant 80 seated on the driver's seat 70 is detected. However, in such a distance detecting device using an ultrasonic sensor, a wind noise of a vehicle, an air inflow noise when a window is opened, or an air blowing noise of an air conditioner. It is conceivable that distance detection accuracy is degraded due to a specific frequency noise included in, for example,. That is, the frequency used in the ultrasonic sensor is 20,000 Hz or more (often about 40,000 to 2,000,000 Hz) which exceeds the audible range of humans. However, even if the frequency is other than these (it is natural because noise in the audible range is heard), the ultrasonic receiving element is vibrated so that the original signal is buried or the arithmetic processing is affected. As a typical distance detecting method using ultrasonic waves, there is a pulse method. This measures the time difference between the transmission time of the ultrasonic wave and the reception time of the reflected wave,
The reciprocating distance is determined from the ultrasonic wave propagation velocity (C = 340 m / s: at 15 ° C.), and half of the distance is defined as the distance from the sensor to the detection target. Here, the measurement process in which the influence of noise occurs is detection of a received wave in measurement of a reception time. In general, a predetermined detection threshold is set for detection, and when there is a received output exceeding that value, the time is measured. [0007] If the noise level exceeds the detection threshold, clocking is performed at the noise reception timing before receiving the reflected wave, and the original position cannot be detected. In order to cope with such a case, a method called AGC (auto gain control) is conventionally used. In this method, the initial threshold value is set high so that the intensity of the received wave is not hidden by the detection threshold, and the transmission output is increased by one step when the received wave does not reach the detection threshold at the time of detection. Therefore, if the reception wave does not reach the detection threshold, the procedure of increasing the transmission one more stage is repeated until the reception wave exceeds the detection threshold. In this method, it is necessary to make settings that assume the maximum level of noise so that the noise does not exceed the detection threshold and is detected.
If the noise is small, a large transmission output is required, and if there is no detection target, the reflected wave from the target will not be received even if the transmission output is increased. Is sent. such as,
There are problems such as waste of power consumption and shortening of the life of the ultrasonic transmission element. In addition, when noise exceeding a detection threshold set at a high level occurs, as described above, there occurs a problem that appropriate reception wave detection (distance measurement) cannot be performed. [0008] SUMMARY OF THE INVENTION In view of the above, can be set and optimize the transmission output of the detection threshold and will in accordance with the noise level, a certain distance detecting device that can prevent a decrease in distance detection accuracy due to the frequency noise The goal is to obtain According to the present invention, there is provided a distance detecting apparatus provided in a vehicle interior of an automobile for detecting a distance from a detection target using an ultrasonic sensor.
It is working from ultrasonic transmission time, through the maximum detection distance round-trip time
And the noise level measuring means from the point of Tsu measuring the noise level during the time until the next transmission, compares the measured noise level and the detection threshold value by said noise level measuring means,
Adjusting means for adjusting at least one of the detection threshold value and the transmission output according to the noise level. [0010] Therefore, the noise level measuring means measures the object to be detected in the vehicle cabin by using the ultrasonic sensor disposed in the cabin of the automobile, and after the ultrasonic wave transmission time, it has passed the maximum detection distance round trip time . Measure the noise level during the time from the point of time to the next transmission, compare the noise level measured by the adjusting means with the detection threshold, and determine at least one of the detection threshold and the transmission output according to the noise level. Make adjustments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a distance detecting device according to the present invention will be described with reference to FIGS. As shown in FIG. 3, the distance detecting device 10 of the present embodiment includes an ultrasonic sensor 12 for transmission and an ultrasonic sensor 14 for reception.
4, the control circuit 13 controls the situation on the passenger seat 16 of the automobile 14 (the presence or absence of the occupant 18, the proximity of the occupant 18 to the airbag device 20 disposed on the dashboard, and the child seat (not shown)). The operation of the airbag device 20 is optimally controlled by detecting the mounting direction. As shown in FIG. 1, the control circuit 13 includes an ultrasonic sensor unit 22, an occupant detection operation unit 24, and an airbag control operation unit 26. The ultrasonic sensor unit 22 includes a reference pulse oscillation circuit 22A as adjustment means and a detection threshold calculation unit 22B. Further, the ultrasonic sensor unit 22 includes a reflection time counter circuit 22C, a distance calculation unit 22D, and a noise level detection / calculation unit 22E as a noise level measurement unit. The noise level during the time is measured, the measured noise level is compared with a detection threshold, and the detection threshold and the transmission output are adjusted according to the noise level. The occupant detection / calculation section 24 includes an occupant seating presence / absence calculation section 24A and an occupant position / posture calculation section 24B. The transmission ultrasonic sensor 12 includes a pulse transmission circuit 2
8 is connected, and based on a signal from the ultrasonic sensor unit 22, an ultrasonic signal is transmitted from the ultrasonic sensor 12 to the occupant 18.
Irradiation is performed on a detection target such as the above. On the other hand, the reception ultrasonic sensor 14 includes a reception detection circuit 30.
Are connected, and a signal from the ultrasonic sensor unit 14 is input to the ultrasonic sensor unit 22. The control circuit 13 includes whether or not a passenger is seated,
A seat position sensor 32 and a seat belt switch 34 for calculating the occupant position and posture, and an airbag control circuit 36 for controlling the operation of the airbag device 20.
And a display unit 38 for displaying the wearing state of the seat belt. As shown in FIG. 3, the ultrasonic sensors 12, 14 are mounted on a dash panel 26,
The detection surfaces (signal emission surfaces and signal reception surfaces) of the ultrasonic sensors 12 and 14 are directed toward the chest 18A of the occupant 18. Next, the operation of this embodiment will be described with reference to the flowcharts of FIGS. In a device such as the distance detection device 10 of the present embodiment, the minimum period of the transmission pulse is
The maximum detection distance is obtained from the ultrasonic wave reciprocating time + distance calculation time. When measuring up to 1 m, the reciprocating time is 5.9 m.
It is often set to about 7 to 10 ms in s + calculation time. One ultrasonic pulse has a length of about 1 ms. That is, the receiving ultrasonic sensor 14 only receives a signal having a time length of about 10% of the cycle in one measurement cycle, and receives the noise in the others. Therefore, in the distance detecting apparatus 10 of the present embodiment, the noise level is measured between the maximum detection distance round-trip time and the time until the next transmission. That is, in step (hereinafter referred to as S) 100, while transmitting the ultrasonic wave,
The timer T is reset (T = 0), and in S102, it is determined whether or not the time T after the transmission of the ultrasonic wave is less than or equal to the range for measuring the distance (the maximum detection distance reciprocation time) t1. When it is determined that the time T is equal to or less than the maximum detection distance reciprocation time t1, it is determined in S104 whether the reception intensity of the ultrasonic wave is greater than the detection threshold Th. S1
If it is determined in 04 that the reception intensity of the ultrasonic wave is not greater than the detection threshold Th, the process returns to S102. on the other hand,
If it is determined in step S104 that the reception intensity of the ultrasonic wave is greater than the detection threshold Th, the processing proceeds to step S106.
The wave round-trip time TL is defined as a timer T (TL = T). Next, in S108, leaving calculate the distance L between a sense target and (L = C · TL / 2 ), in S110, the time T after ultrasonic transmission maximum detection distance round-trip time t1
If the time T after ultrasonic transmission is determined to be less than or equal to the maximum detection distance round trip time t1,
The process of S110 is repeated. On the other hand, in S110,
If it is determined that the time T after the transmission of the ultrasonic wave is not less than the maximum detection distance round trip time t1, the process proceeds to S112. Also, S
If it is determined in step 102 that the time T after the transmission of the ultrasonic wave is not shorter than the maximum detection distance reciprocation time t1, the process also proceeds to S112. In S112, the counter i is reset,
In S114, the reception intensity Pi due to noise is measured. Next, in S116, the time T after the ultrasonic transmission
Is smaller than the sum of the maximum detection distance reciprocating time t1 and the noise level detection range t2, and the time T after the transmission of the ultrasonic wave is equal to the maximum detection distance reciprocation time t1 and the noise level detection range t2. If it is determined to be smaller than the sum,
In S118, the counter i is incremented (i
= I + 1), and returns to S114. At S116, the time T after the transmission of the ultrasonic wave
Is not smaller than the sum of the maximum detection distance round trip time t1 and the noise level detection range t2, S11
In step 8, the noise reception intensity P is set to the maximum value of the noise reception intensity Pi (P = MAX (Pi)). Next, in S120, based on the noise reception intensity P, the new detection threshold Th is set to k1 · P, and the new transmission output PO is set to k2 · P. That is, as shown in FIG. 2, the noise level at t2 is measured during the time τ from the maximum detection distance round trip time t1 to the next transmission, the measured noise level is compared with the detection threshold Th, and the detection threshold is compared with the detection threshold Th. The transmission output is adjusted according to the noise level. Next, in S122, it is determined whether or not the time T after the transmission of the ultrasonic wave is smaller than the transmission period τ of the ultrasonic wave.
When it is determined that the time is smaller than the time, the process of S122 is repeated, and when it is determined that the time T after the transmission of the ultrasonic wave is not smaller than the transmission period τ of the ultrasonic wave, the process returns to S100. Accordingly, in the distance detecting apparatus 10 of the present embodiment, if the noise level exceeds the detection threshold, control is performed so as to increase the detection threshold and also increase the transmission output. This makes it possible to take measures corresponding to the noise level at that time (setting a detection threshold and optimizing the transmission output), thereby preventing a decrease in distance detection accuracy due to a specific frequency noise. On the other hand, under running conditions with little noise, the detection threshold value can be lowered, and only the transmission intensity corresponding to the detection threshold value can be reduced.
By C, the transmission intensity can be prevented from increasing more than necessary. In the above, the present invention has been described in detail with respect to a specific embodiment. However, the present invention is not limited to such an embodiment, and various other embodiments are within the scope of the present invention. It is clear to a person skilled in the art that is possible. For example, in the present embodiment, when the noise level exceeds the detection threshold, the control is performed to increase the detection threshold and also increase the transmission output, but instead, only one of the detection threshold or the transmission output is used as necessary. May be increased. Further, the detection device using the ultrasonic sensor of the present invention is applicable to a passenger detection device for a rear seat, a corner sensor, and the like, in addition to a passenger detection device for a front passenger seat. [0027] According to the present invention according to claim 1, disposed in the passenger compartment of a motor vehicle, the distance detecting device for detecting a distance between the detection object using the ultrasonic sensor, ultrasonic transmission time Yo
Ri aim, compares the noise level measuring means, the measured noise level at the noise level measuring means and detection threshold to measure the noise level during the period from when the maximum detection distance has passed a round trip time until the next transmission And adjusting means for adjusting at least one of the detection threshold value and the transmission output according to the noise level, so that the detection threshold value according to the noise level at that time and the appropriate transmission output are set. This has an excellent effect that the distance detection accuracy can be prevented from lowering due to a specific frequency noise.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing main members of a distance detection device according to one embodiment of the present invention. FIG. 2 is an explanatory diagram showing a relationship between a transmission signal and a reception signal of the distance detection device according to one embodiment of the present invention. FIG. 3 is a schematic side view showing an occupant detection device to which the distance detection device according to one embodiment of the present invention is applied. FIG. 4 is a flowchart illustrating control of a distance detection device according to an embodiment of the present invention. FIG. 5 is a perspective view showing a distance detecting device according to a conventional embodiment. [Description of Signs] 10 Distance detection device 12 Ultrasonic sensor 13 for transmission 13 Control circuit 14 Ultrasonic sensor 16 for reception 16 Passenger seat 18 Occupant 20 Airbag device 22 Ultrasonic sensor unit 22A Reference pulse oscillation circuit (adjustment means) 22B Detection threshold calculation unit (adjustment unit) 22E Noise level detection / calculation unit (noise level measurement unit)

Continuation of front page (56) References JP-A-8-201514 (JP, A) JP-A-7-83747 (JP, A) JP-A 9-145836 (JP, A) JP-A-5-232240 (JP) JP-A-53-145231 (JP, A) JP-A-7-196006 (JP, A) JP-A-7-159531 (JP, A) JP-A-3-96885 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B60R 21/32 G01S 15/06

Claims (1)

(57) [Claims 1] A distance detecting device disposed in a vehicle interior of an automobile and detecting a distance from a detection target using an ultrasonic sensor, the distance being measured from the time of ultrasonic transmission. , after the maximum detection distance round-trip time
And the noise level measuring means from the point of Tsu measuring the noise level during the time until the next transmission, compares the measured noise level and the detection threshold value by said noise level measuring means, the transmission output and the detection threshold Adjusting means for adjusting at least one of them according to the noise level.