JPH063447A - Speed detector for vehicle - Google Patents

Abstract

PURPOSE:To obtain a speed detector which enables not only increase in frequency of measurement as much as possible but also improvement in measuring accuracy. CONSTITUTION:An ultrasonic pulse transmitted from an ultrasonic transducer 201 is reflected on an object 250 and subjected to a Doppler modulation. An ultrasonic pulse received passes through a bandpass filter 205 and a counter comparator 207 counts the frequency of inversion with a counter 210 centered on a threshold generated with a threshold generating section 209. To judge whether an ultrasonic pulse is received or not, the ultrasonic pulse received is compared with a threshold set with a control section 211 after detected in envelop with a detection section 213 and the results of comparison are transmitted to the control section 211. A pre-excitation command before transmission from an ultrasonic transducer, are ultrasonic pulse transmission command for measuring a speed and a pre-excitation command for reception are outputted from the control section 211. An ultrasonic pulse with frequency and amplitude set immediately after transmission is outputted by the pre-excitation and a correct signal is detected immediately after the reception.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed detecting device for a vehicle such as an automobile, and more particularly to a speed detecting device for a vehicle to which the Doppler effect is applied.

[0002]

2. Description of the Related Art As an apparatus for detecting the speed of a vehicle such as an automobile, a Doppler speed detecting apparatus utilizing the Doppler effect generated between an ultrasonic wave oscillated from a transmitter and an ultrasonic wave reflected from an object. It has been known. Such a Doppler velocity detecting device is roughly classified into a method of continuously generating ultrasonic waves and a method of intermittently generating ultrasonic waves, but when the reflected wave is weak as in a snowy road or an ice road. In general, a method of intermittently generating ultrasonic waves is generally used to enable reliable detection (see, for example, JP-A-58-39971).

[0003]

In the pulse system for intermittently generating ultrasonic waves, the transmission period and the reception period can be temporally separated, but reliable detection is possible. Since the operation of the transmitter and the receiver is also intermittent, a delay occurs when the transmitter and the receiver transmit and receive the wave.

FIG. 6 is a graph showing the results of frequency analysis of the waveform of the ultrasonic pulse transmitted from the ultrasonic transducer and the received ultrasonic pulse. The horizontal axis represents time or frequency and the vertical axis represents amplitude. Take (A) is a frequency analysis of the transmitted waveform (a) when a transmission command is given to the ultrasonic transducer which has been stationary until then and the received waveform when the ultrasonic transducer which has been stationary until then receives. The results are shown.

That is, from the moment when the transmission is started, for a while,
The frequency and amplitude of the transmitted ultrasonic waves are unstable and fluctuate.
In addition, since the detected frequency is not stable for a certain time even when receiving the wave, the peak of the frequency analysis result of the received ultrasonic signal is not steep and the Doppler frequency cannot be accurately identified.

Here, even when a transmission command is given to the ultrasonic transducer which transmits and receives the ultrasonic wave, the ultrasonic wave is actually emitted and there is a delay time of several milliseconds until the ultrasonic wave is stabilized. There is a delay of several milliseconds from the time the wave reaches the ultrasonic transducer until the stable received signal is output. It is almost the same as the time from when the sound wave is emitted to when it returns to the ultrasonic transducer again.

That is, the time t until the ultrasonic pulse is emitted from the ultrasonic transducer, propagates in the air for the distance L, is reflected on the road surface, propagates again for the distance L, and is received by the ultrasonic transducer again is as follows. It is represented by a formula. t = 2 · L / C where C is the speed of sound. For example, L = 0.6 (m), C =
If it is 340 (m / sec), t = 3.5 milliseconds.

That is, when the ultrasonic pulse emitted within about 1.7 milliseconds is stable and the accurate frequency cannot be detected within about 1.7 milliseconds, the time required for one measurement is long. The measurement frequency cannot be reduced. Furthermore, since the Doppler frequency cannot be recognized accurately, the measurement accuracy also decreases. The present invention has been made in view of the above problems, and an object of the present invention is to provide a speed detection device capable of not only increasing the measurement frequency but also improving the measurement accuracy.

[0009]

FIG. 1 is a basic configuration diagram of a vehicle speed detecting device according to a first invention, in which an ultrasonic pulse is transmitted at a predetermined time interval and reflected by an object Doppler. Ultrasonic wave transmitting / receiving means 101 mounted on a vehicle for receiving the modulated ultrasonic wave pulse, and ultrasonic wave transmitting / receiving means 101
Speed calculation means 102 for calculating the vehicle speed by detecting the Doppler modulation degree of the ultrasonic pulse received by
Before the ultrasonic pulse is transmitted, the ultrasonic wave transmitting / receiving means 101 is pre-excited at a first predetermined frequency for a predetermined time and before the ultrasonic pulse is received, the ultrasonic wave transmitting / receiving means 101 is moved for a predetermined time at a second predetermined frequency. And a pre-excitation means 103 for pre-exciting.

In the vehicle speed detecting device according to the second aspect of the present invention, the ultrasonic wave transmitting / receiving means 101 at the time of the previous measurement of the second predetermined frequency used in the pre-excitation pre-excitation performed by the pre-excitation means 103. It has pre-reception pre-excitation frequency determining means 104 for setting the frequency equal to the frequency of the Doppler-modulated ultrasonic pulse received in (1). In the vehicle speed detecting device according to the third aspect of the invention, the frequency of the ultrasonic pulse transmitted from the ultrasonic wave transmitting / receiving means 101 is the ultrasonic wave transmitting / receiving means 1.
The pre-transmission pre-excitation frequency scanning unit 105 scans in a predetermined range around the resonance frequency of 01.

[0011]

According to the first aspect of the invention, since the ultrasonic wave transmitting / receiving means is preliminarily excited, the ultrasonic wave having an accurate frequency is transmitted in a shorter dead time, and the ultrasonic wave subjected to the Doppler modulation is transmitted. The detection signal is output in a shorter dead time when the sound wave pulse is received. According to the second aspect of the present invention, the pre-excitation pre-excitation frequency is selected as the frequency of the ultrasonic pulse that has undergone the Doppler modulation at the time of the previous measurement, so detection is performed after receiving the ultrasonic pulse that has undergone the Doppler modulation. The dead time until the signal is output is further reduced.

According to the third invention, the selectivity Q of the ultrasonic wave transmitting / receiving means at the time of reception can be set higher.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a vehicle speed detecting device 1 according to the present invention.
It is a block diagram of an Example, and is an ultrasonic transducer 20.
1 is used for transmitting and receiving ultrasonic pulses. The ultrasonic pulse to be transmitted is generated by the pulse generator 202, amplified by the drive amplifier 203, and emitted from the ultrasonic transducer 201.

The ultrasonic pulse emitted into the atmosphere is reflected by the object 250 which is, for example, the road surface, and is received again by the ultrasonic transducer 201. The received ultrasonic pulse is amplified by the preamplifier 204, then the bandpass filter 205 extracts only a signal having a predetermined frequency component, and the main amplifier 206 amplifies the signal.

The output of the main amplifier 206 is branched into two, one of which is supplied to a count comparator 207 and the other of which is supplied to an input terminal of a detection comparator 208. In the counter comparator 207, the count threshold generated by the threshold generator 209 is compared with the output of the main amplifier 206, and the counter 210 counts the number of inversions centered on the count threshold.

In the detection comparator 208, the detection threshold value set by the controller 211 and the main amplifier 2 are set.
It is used to detect the presence or absence of a signal, the signal level, etc. by comparing with the output of 06. The count value of the counter 210 or the output of the detection comparator 208 is processed by the control unit 211 using a microcomputer, for example.

The control unit 211 is composed of a CPU 211b, a memory 211c, an input interface 211d and an output interface 211e centering on a bus 211a. That is, the count value counted by the counter 210 and the output of the detection comparator 208 are the control unit 21.
1 is guided to the input interface 211d of the controller 21
Read in 1.

Output interface 21 of control unit 211
From 1e, the detection threshold value and the oscillation frequency setting signal and oscillation control signal from the ultrasonic transducer 201 are output. The detection threshold value is converted into an analog signal by the D / A converter 212, and the output of the main amplifier 206 is envelope-detected by the detection unit 213 to be detected by the detection comparator 208.
Is supplied to.

The oscillation frequency setting signal is sent to the pulse generator 202.
And determines the frequency of the ultrasonic pulse supplied from the ultrasonic transducer 201 and transmitted from the ultrasonic transducer 201. The oscillation control signal is supplied to the pulse generator 202 and the drive amplifier 203, and the pre-excitation timing, transmission timing, and strength of the ultrasonic pulse from the ultrasonic transducer 201 are determined.

FIG. 3 is a flowchart of a wave transmission control routine for transmitting an ultrasonic pulse, which is executed at predetermined time intervals T. The time interval T is defined as a time interval sufficient to execute one wave transmission control routine and the subsequent wave reception routine. In step 31, the transmission frequency fsn is determined.

The transmission frequency fsn is determined by scanning a predetermined band centered on the resonance frequency ft of the ultrasonic transducer 201. That is, step 31 constitutes the pre-excitation pre-excitation frequency scanning means 105. By thus determining the transmission frequency fsn, the selectivity Q of the bandpass filter 205 can be set high,
It is possible to improve the sensitivity.

In step 32, Tq pre-excitation is performed for a predetermined time at the frequency fsn. The amplitude at the time of pre-excitation is set to a fraction of the amplitude at the time of transmission by narrowing down the attenuator (not shown) incorporated in the drive amplifier 203.
At step 33, the setting of the attenuator is returned to the original,
An ultrasonic pulse having a frequency fsn is transmitted from the Ts ultrasonic transducer 201 for a predetermined time.

In step 34, the pre-excitation frequency fpn at the time of reception is determined. It is effective in order to enhance the effect of pre-excitation that the pre-excitation frequency fpn at the time of this reception is set equal to the frequency fr (n-1) of the ultrasonic pulse received by the ultrasonic transducer 201 at the time of the previous measurement. is there. In step 35, the ultrasonic transducer 201 is pre-excited at the frequency fpn.

Pre-excitation during wave reception is interrupted when the wave reception routine described below is started. That is, step 32
And step 35 constitute pre-excitation means 103. FIG. 4 is a flowchart of a wave receiving routine for receiving the ultrasonic pulse, which is executed when the ultrasonic transducer 201 receives an ultrasonic pulse of a predetermined level or higher.

That is, in step 41, the frequency frn of the received ultrasonic pulse counted by the counter 210 is read. In step 42, the transmission frequency fsn and the reception frequency f
The absolute value frequency Δf of the difference from rn is calculated. Step 4
In 3, the vehicle speed v is determined from the absolute frequency Δf of the difference.

That is, steps 42 and 43 constitute the speed calculating means 102. In step 44, the reception frequency frn is set to the reception pre-excitation frequency fp (n + 1) for the next measurement, and this routine ends. That is, step 44 constitutes the pre-reception pre-excitation means 104. FIG. 5 is a timing chart for explaining the operation of the vehicle speed detecting device according to the present invention, in which the horizontal axis represents time and the vertical axis represents amplitude, where (a) is a transmitted pulse and (b) is a received pulse. Represents

That is, if it is measured at each time interval T,
Prior to the transmission, the ultrasonic transducer is pre-excited at the frequency fs1 for Tq time, and then the ultrasonic pulse having the same frequency and the increased amplitude is transmitted for Ts time. Then, immediately after the completion of the wave transmission or after a predetermined time interval, the pre-excitation at the reception frequency fr0 detected in the previous measurement is started.

It is judged that the reflected wave is received when the received signal by the ultrasonic transducer becomes equal to or more than a predetermined threshold value after Tm time after the start of transmission, and Tr time reception is performed to measure the received frequency. I do. The measurement time interval T is determined as a time longer than the time from the start of pre-excitation for transmitting the wave to the reception of the reflected wave.

FIG. 6B is a frequency analysis result (b) of the transmitted wave (a) and the received wave when the pre-excitation according to the present invention is applied. As is clear from this graph, the ultrasonic wave having the frequency and amplitude set from the beginning of the transmission is transmitted, and the Doppler frequency can be accurately identified from the frequency analysis result of the received signal.

[0030]

According to the first aspect of the invention, since the ultrasonic transducer is pre-excited before transmitting or receiving waves,
At the time of transmission, not only can ultrasonic waves of the frequency and amplitude set from the beginning be transmitted to enable accurate measurement, but at the time of reception, the detection signal should be processed immediately after receiving the reflected wave. It is possible to increase the measurement frequency.

According to the second aspect of the invention, the pre-excitation pre-excitation frequency is selected as the frequency at the time of the previous reception, so that the dead time after the reception can be shortened. According to the third aspect, since the transmission frequency is scanned within a predetermined range, it is possible to set the selectivity of the wave receiving means to be high.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a vehicle speed detection device according to the present invention.

FIG. 2 is a configuration diagram of an embodiment of a vehicle speed detection device according to the present invention.

FIG. 3 is a flowchart of a wave transmission control routine.

FIG. 4 is a flowchart of a wave reception routine.

FIG. 5 is a timing diagram illustrating an operation.

FIG. 6 is a result of frequency analysis of transmitted ultrasonic pulses and received ultrasonic pulses.

[Explanation of symbols]

 101 ... Ultrasonic wave transmitting / receiving means 102 ... Velocity calculation means 103 ... Preliminary excitation means 104 ... Pre-wave reception pre-excitation means 105 ... Pre-transmission pre-excitation frequency scanning means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiwa Takagi, 1-1, Showa-cho, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Shinji Ikeda, Toyota-cho, Aichi prefecture Toyota city Within

Claims (3)

[Claims] 1. An ultrasonic wave transmitting / receiving unit mounted on a vehicle, which transmits an ultrasonic wave pulse at a predetermined time interval and receives an ultrasonic wave pulse reflected by an object and Doppler modulated, and the ultrasonic wave. In a vehicle speed detection device comprising a speed calculation means for calculating the vehicle speed by detecting the Doppler modulation degree of the ultrasonic pulse received by the transmission / reception means, before transmitting the ultrasonic pulse. Pre-excitation means for pre-exciting the ultrasonic wave transmitting / receiving means at a first predetermined frequency for a predetermined time, and pre-exciting the ultrasonic wave transmitting / receiving means for a predetermined time at the second predetermined frequency before receiving an ultrasonic pulse; A vehicle speed detection device comprising: 2. The frequency of a Doppler-modulated ultrasonic pulse received by the ultrasonic wave transmitting / receiving means at the time of the previous measurement of the second predetermined frequency used in the pre-excitation pre-excitation performed by the preliminary excitation means. The vehicle speed detection device according to claim 1, further comprising pre-reception pre-excitation frequency determination means that is set equal to 3. Pre-transmission pre-excitation frequency scanning means for scanning the frequency of an ultrasonic pulse transmitted from said ultrasonic wave transmitting / receiving means within a predetermined range centered on the resonance frequency of said ultrasonic wave transmitting / receiving means. The vehicle speed detection device according to claim 1 or 2.