JPH07280933A - Vehicle-speed measuring apparatus for mounting on vehicle - Google Patents

Abstract

PURPOSE:To obtain a precise vehicle speed by eliminating the influence of a water splash generated from a submerged road surface. CONSTITUTION:A detection circuit 7 detects a reflected-wave signal (c) which is received via a reception amplifier circuit 5, and it obtains a reflected-wave signal (f) which is obtained by binary-coding a detected signal (d) with a level comparison circuit 8. A reception-gate generation circuit 6 generates a pulse (e) which synchronizes with the pulse of a transmission-pulse generation circuit 4. A reception mask circuit 9 obtains a pulse (g) which is triggered by the pulse (e) of the reception-gate generation circuit 6 when reflected waves due to a water splash exist. Individual outputs from the level comparison circuit 8, the reception-gate generation circuit 6 and the reception mask circuit 9 obtain an output signal (h) by the logical product of a gate circuit 10, and it takes a logical product by a gate circuit 11 together with the reflected-wave signal (c) from the reception amplifier circuit 5. An output (i) is obtained, it is input to a frequency measuring circuit 12, an arithmetic circuit 13 extracts its Doppler frequency component on the basis of a frequency obtained by the frequency measuring circuit 12, and a vehicle speed V is operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle speed measuring device mounted on a vehicle and using various speed information such as a navigation system, a vehicle speed detecting device, an ABS device, etc. The present invention relates to an in-vehicle vehicle speed measuring device used.

[0002]

2. Description of the Related Art As a velocity measuring device using ultrasonic waves of this type, there is a technique disclosed in Japanese Utility Model Laid-Open No. 57-68574. The technology disclosed in this publication continuously transmits ultrasonic waves from a separate wave transmitter, continuously receives reflected waves obtained by reflecting from a reflector, and calculates the difference between the transmitted wave and the received wave. It is for detecting the Doppler frequency and is a well-known technique at present.

Further, as a velocity measuring device using this kind of ultrasonic wave, there is a technique disclosed in JP-A-59-203973. The technique disclosed in this publication has a wave transmitter and a wave receiver which are separate bodies, as in the case of the above-mentioned publication, and in particular, the number of wave receivers is two, and vertical vibration of the vehicle body, nose up, This is to reduce the error due to nose down.

In these techniques, since ultrasonic waves are continuously transmitted and received, it is difficult to identify the reflector and it is difficult to remove noise such as multiple reflected waves.

As another velocity measuring device using this kind of ultrasonic wave, there is a technique disclosed in Japanese Patent Laid-Open No. 58-39971. The technology disclosed in this publication transmits ultrasonic waves in a pulse shape, opens a reception gate corresponding to the pulse width at the time when the ultrasonic waves are reflected and received from a road surface which is a specific reflective object, and a predetermined wavelength of the received wave. The Doppler shift amount is obtained by measuring the minutes, and the vehicle speed is measured.

Further, as a vehicle speed measuring device of this type, there is a technique disclosed in Japanese Patent Laid-Open No. 3-269388.

According to this technique, ultrasonic waves are radiated from a wave transmitter / receiver on a road surface in the front or front direction of a vehicle at a predetermined depression angle, and from the received signal of the radiated ultrasonic waves and the reflected wave of the projection on the road surface to the projection. Is measured, and the signal level of the reflected wave of the road surface projection is compared with a predetermined threshold value to detect the presence and size of the road surface projection in front of the vehicle. Then, the vehicle height is detected from the straight line distance and the emission angle of the ultrasonic wave when the reflected wave returns from the road surface, and the vehicle speed is detected based on the obtained Doppler frequency.

Particularly, in the technique disclosed in the above publication, ultrasonic waves are radiated at the same radiation angle in the front-back direction of the vehicle body, and the Doppler frequency of the received signal of each reflected wave is detected.
By obtaining the Doppler frequency of the difference, the vehicle speed at which the vertical speed component of the vehicle body is canceled is detected. The vehicle height is detected by measuring the time until the reflected wave is received.

In this way, the ultrasonic waves are used to detect the protrusions and the like on the front road surface when the vehicle is running, and also to detect the vehicle height, the vehicle speed, and the like.

[0010]

An in-vehicle vehicle speed measuring device which transmits an ultrasonic wave of this kind to a road surface and receives a reflected wave from the road surface is compared with a speed sensor which detects a vehicle speed from a wheel speed. Then, the vehicle speed can be detected without being affected by wheel air pressure and load, tire size, slip, etc.
A reliable vehicle speed can be obtained. However, when the vehicle travels on a submerged road surface, a reflected signal due to water splashes generated from the submerged road surface is mixed, which makes it difficult to accurately detect the road surface, which is a cause of deterioration in accuracy. This phenomenon has the same effect not only on water droplets rising from the flooded road surface but also on muddy water droplets, snow, sand, and dust.

Therefore, an object of the present invention is to provide an on-vehicle vehicle speed measuring device capable of removing the influence of water splashes generated from a flooded road surface and detecting an accurate vehicle speed.

[0012]

An on-vehicle vehicle speed measuring apparatus according to the present invention transmits an ultrasonic signal intermittently output with a predetermined depression angle gradient to a road surface and receives the reflected wave. An ultrasonic wave transmitter / receiver, a frequency measuring circuit for measuring the frequency of a reflected wave signal received by the ultrasonic wave transmitter / receiver, an arithmetic circuit for extracting the Doppler frequency component from the frequency measuring circuit, and calculating a vehicle speed. The vehicle-mounted vehicle speed measuring device having the above-mentioned means is provided with a reflected wave signal introduction prohibiting means for prohibiting the introduction of the reflected wave signal guided to the frequency measurement circuit for a predetermined time from the timing of transmitting the ultrasonic signal.

[0013]

In the present invention, an ultrasonic signal which is intermittently output with a predetermined depression angle gradient is transmitted to the road surface, and the reflected wave is received by the ultrasonic wave transmitter / receiver, and the ultrasonic wave transmitter / receiver is used. The frequency of the reflected wave signal received by the instrument is measured by the frequency measurement circuit,
The Doppler frequency component is extracted from the frequency measuring circuit and the vehicle speed is calculated. At this time, by prohibiting the introduction of the reflected wave signal guided to the frequency measurement circuit for a predetermined time from the timing of transmitting the ultrasonic signal by the introduction prohibiting means, the reflected wave of the water droplet is early in time, Correspond to the detection of the reflected wave being late.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An on-vehicle vehicle speed measuring device according to an embodiment of the present invention will be described below.

<Description of Basic Operation> FIG. 1 is an explanatory view of the basic operation of an in-vehicle vehicle speed measuring apparatus according to an embodiment of the present invention. FIG. 1 (a) is a side view of an in-vehicle vehicle speed measuring apparatus of a single beam system.
(B) is a basic operation explanatory view of an in-vehicle vehicle speed measuring device by a single beam method, and (c) is an explanatory view showing a reflection condition between water droplets and a road surface.

In FIG. 1, an ultrasonic transducer TR, which is parallel to the traveling direction of the vehicle 100 and whose depression angle is set to 45 degrees with respect to the opposite traveling direction, transmits ultrasonic vibration in the 200 [KHz] band to a predetermined ultrasonic wave. It transmits to the road surface with a sound wave beam width, receives the reflected wave, and obtains a vehicle speed (speed vector) V parallel to the traveling direction of the vehicle 100. Specifically, the ultrasonic wave transmitter / receiver TR is disposed in the front center of the vehicle 100, in front of the front wheels or rear wheels, and on the side of the front wheels or rear wheels.

As shown in FIG. 1A, the ultrasonic wave transmitter / receiver TR is housed and integrated in a housing HA together with a printed circuit board and the like. Then, as shown in FIG. 1B, the housing HA is attached to the lower surface of the vehicle 100. Further, the height of radiating ultrasonic waves in this embodiment is H
[M].

That is, as shown in the operation principle diagram in the case of transmitting and receiving by the ultrasonic wave transmitter / receiver TR of FIG. 1 (b), the distance until the road surface is radiated by the ultrasonic wave is L [ m], its height is H [m], and its radiation angle is φ degrees, then L = H / sin φ (1)

Further, an ultrasonic wave having a frequency f [Hz] is intermittently transmitted to the road surface, reflected, and then received by a frequency fo = f−d.
When the Doppler frequency df [Hz] is calculated from f [Hz], df = 2f · (V / 3.6) · cos φ / C [Hz] ··· (2) where V: vehicle speed [Km / h ] C: speed of sound [m / s], which results in V = 1.8 C · df / f · cos φ ··· (3).

In this way, the vehicle 10 is generated using ultrasonic waves.
The vehicle speed of 0 is detected.

Further, as shown in FIG. 1 (c), at the time A when the reflected wave before reaching the road surface is obtained from the ultrasonic wave transmitter / receiver TR, the water splash rather than the influence of the reflected wave from the flooded road surface E is obtained. The speed of W will be measured. Further, at the time B when the reflected wave reaching the road surface E is obtained from the ultrasonic wave transmitter / receiver TR, the reflected wave from the road surface E affected by the water droplet W is measured. Then, at the time C when the reflected wave reaching the road surface E is obtained from the ultrasonic wave transmitter / receiver TR, the reflected wave from the road surface E that is least affected by the water droplet W is measured.

The relationship between the time and the reflected wave output at this time is as follows.

FIG. 2 is an explanatory diagram showing the output conditions of the reflected waves of the water droplets and the road surface, which shows the principle of the vehicle-mounted vehicle speed measuring device of the present invention.

In FIG. 2, the water splash reflected wave N is shown in FIG.
As shown in (c), since the water droplet W is generated at a position closer to the ultrasonic transducer TR than the surface of the flooded road surface E, the reflected wave signal has a peak value at a position earlier in time. It becomes the characteristic to do. The reflected wave from the submerged road surface E is generated at a position farther from the ultrasonic wave transmitter / receiver TR than the water droplet W, so that the signal of the road surface reflected wave S has a peak value at a position which is later in time. Become. That is, in the reflected wave from the flooded road surface E, as shown in FIG. 2, the water splash reflected wave N and the road surface reflected wave S overlap each other, and in order to reduce the vehicle speed error of the vehicle 100, the road surface reflected wave S It is necessary to maximize the ratio S / N between the signal level of the above and the signal level of the water splash reflected wave N.

At time A when the reflected wave before reaching the road surface is obtained from the ultrasonic wave transmitter / receiver TR, the ratio S / N of the signal level of the road surface reflected wave S and the water splash reflected wave N is S / N = S
A / NA, and the road surface E from the ultrasonic transducer TR
At the time B for obtaining the reflected wave reaching the position S, the ratio S / N between the road surface reflected wave S and the signal level of the water splash reflected wave N is S
/ N = SB / NB, and the ultrasonic transducer TR
At time C when the reflected wave reaching the road surface E from is obtained,
Ratio S between the road surface reflected wave S and the signal level of the water splash reflected wave N
/ N is S / N = SC / NC. Here, SA / NA <SB / NB <SC / NC. Therefore, the ratio S / N between the road surface reflected wave S and the signal level of the water splash reflected wave N is reduced at the leading edge portion of the reflected wave. Therefore, the S / N ratio can be improved by removing the reflected wave at the front edge. Therefore, by adjusting the timing of opening the reception gate for each ultrasonic wave transmitter / receiver TR, it is possible to accurately capture the target reflected wave, thereby calculating the Doppler frequency and obtaining an accurate vehicle speed.

In particular, the time A from which the reflected wave reaching the road surface E is obtained from the ultrasonic wave transceiver TR is obtained from the time regions A to C where the reflected wave reaching the road surface E is obtained from the ultrasonic wave transmitter / receiver TR shown in FIG. It is preferable to measure the reflected wave from the road surface E by removing the part.

<Circuit Configuration of the Embodiment> FIG. 3 is a circuit configuration diagram of the vehicle-mounted vehicle speed measuring device according to the embodiment of the present invention.

In FIG. 3, the transmitter 3 is 200 [KHz].
It outputs the ultrasonic vibration of the band, and the repetition frequency of the transmission pulse generation circuit 4 receives the output of the pulse signal of the pulse width of 1 [msec] every 10 [msec], and the ultrasonic wave of the 200 [KHz] band is received. Vibration is output as intermittent ultrasonic waves for a duration of 1 [msec] every 10 [msec]. The ultrasonic wave transmitter / receiver 1 (TR) produces ultrasonic vibration in the 200 [KHz] band for a duration of 1 [msec].
The intermittent ultrasonic waves are transmitted and received with a predetermined ultrasonic beam width transmitted every 10 [msec]. Also,
The transmission / reception switching circuit 2 performs switching when outputting or receiving an ultrasonic wave from the ultrasonic wave transmitter / receiver 1. That is, the transmission / reception switching circuit 2 outputs a signal from the ultrasonic wave transmitter / receiver 1 during transmission and protects the reception circuit at that time. On the other hand, it is switched so that the reception signal is output to the reception amplification circuit 5 during reception. The detection circuit 7 detects the reflected wave signal received via the reception amplification circuit 5. The level comparison circuit 8 is composed of a Schmitt circuit or a comparison circuit which sets the output to "1" when the level of the reflected wave signal is equal to or higher than a predetermined threshold value and sets the output to "0" when the level is not higher than the predetermined threshold value.

The reception gate generation circuit 6 is a monostable circuit including a monostable multivibrator which is triggered by the rising edge of the pulse of the transmission pulse generation circuit 4 and generates a pulse having a pulse width Tb after a delay time Ta. The delay time Ta is set around the time A at which the reflected wave reaching the road surface E is obtained from the ultrasonic transducer 1 (TR) shown in FIG.
Considering the vehicle height variation, Ta + Tb is set to the maximum time associated with the vehicle height variation of the possibility of receiving the reflected wave signal from the rise of the pulse of 1 [msec] of the transmission pulse generation circuit 4.
Further, the reception mask circuit 9 is triggered by the rising edge of the pulse of the reception gate generation circuit 6, and its pulse width Tc is the time A for obtaining the reflected wave reaching the road surface E from the ultrasonic wave transmitter / receiver 1 (TR) shown in FIG. It is a monostable circuit including a monostable multivibrator or the like set for a time period from to B. When the output of the level comparison circuit 8 is "0", the reception mask circuit 9 is in the reset state and does not generate the reception mask signal.

The outputs of the level comparison circuit 8, the reception gate generation circuit 6, and the reception mask circuit 9 are input to a gate circuit 10 which takes a logical product, and the output of the gate circuit 10 also takes a gate circuit 11 which takes a logical product. Is input to the receiver together with the output of the reception amplifier circuit 5. The output of the gate circuit 11 is input to the frequency measuring circuit 12.

The frequency measuring circuit 12 is composed of a counter for measuring the frequency of the reflected wave signal taken out by the gate circuit 11. Further, the arithmetic circuit 13 extracts the Doppler frequency component based on the frequency obtained from the frequency measuring circuit 12, and calculates the vehicle speed V from the Doppler frequency component.
Usually, since the relationship between the Doppler frequency component and the vehicle speed V is in a proportional relationship, the output of a predetermined counter is code-converted or the displayed vehicle speed is obtained by D / A conversion. Of course,
The calculation may be performed by a microcomputer.
In the case of performing calculation with this microcomputer, the functions of the frequency measuring circuit 12 and the calculating circuit 13 can be provided.

In the known pair beam system,
Although a pair of circuits of this type is provided, the description thereof is omitted here.

<Operation of Circuit Configuration> The vehicle-mounted vehicle speed measuring device of this embodiment operates as follows.

FIG. 4 is a timing chart of the vehicle-mounted vehicle speed measuring apparatus according to the embodiment of the present invention.

The pulse signal a of the transmission pulse generation circuit 4 causes the transmitter 3 to generate a frequency of 200 [KHz] and a duration of 1
The intermittent ultrasonic signal a is generated every [msec] for [msec], and the transmission / reception switching circuit 2 changes the output of the transmitter 3 to ultrasonic transmission / reception only at each generation timing of the intermittent ultrasonic waves for a duration of 1 [msec]. Connected to the side of the ultrasonic wave transmitter / receiver 1 to 200 [KH
The burst wave signal b in the [z] band is intermittently output.

When the transmission / reception switching circuit 2 is not output from the transmitter 3, the transmission / reception switching circuit 2 guides the reflected wave received by the generated ultrasonic wave transmitter / receiver 1 to the reception amplification circuit 5, and obtains a reflected wave signal c. The detection circuit 7 detects the reflected wave signal c received via the reception amplification circuit 5, and obtains a detection signal d. The level comparing circuit 8 sets the output to "1" when the level of the reflected wave signal is equal to or higher than the predetermined threshold value Ev, and sets the output to "0" when the level is equal to or higher than the predetermined threshold value Ev to obtain the reflected wave signal f.

The reception gate generation circuit 6 is triggered by the rising edge of the pulse of the transmission pulse generation circuit 4 and generates the pulse e having the pulse width Tb after the delay time Ta. Also,
The reception mask circuit 9 is triggered by the rising edge of the pulse e of the reception gate generation circuit 6 to obtain a pulse g having a negative pulse width Tc.

The outputs of the reflected wave signal f of the level comparison circuit 8, the pulse e of the reception gate generation circuit 6 and the pulse g of the reception mask circuit 9 are ANDed by the gate circuit 10 to obtain the output signal h, The gate circuit 11 logically ANDs it with the reflected wave signal c from the reception amplification circuit 5, and the gate circuit 1
Obtain an output i of 1. The output i of the gate circuit 11 is input to the frequency measuring circuit 12, the frequency measuring circuit 12 measures the frequency of the output i taken out from the gate circuit 11, and
The calculation circuit 13 extracts the Doppler frequency component based on the frequency obtained from the frequency measurement circuit 12, calculates the vehicle speed V from the Doppler frequency component, and outputs it.

The road on which water droplets are not scattered, that is,
When traveling on a dry road surface, the reflected wave signal c received by the generated ultrasonic wave transmitter / receiver 1 and guided to the reception amplification circuit 5
, The reflected wave signal c received through the reception amplification circuit 5 becomes a reflected wave signal c ′, and the detection signal d detected by the detection circuit 7 becomes a detection signal d ′, and the level comparison is performed. The reflected wave signal f of the circuit 8 is the reflected wave signal f ′.
Becomes Also in this case, the normal vehicle speed can be detected.

As described above, the vehicle-mounted vehicle speed measuring apparatus of this embodiment transmits the ultrasonic signal intermittently output with a predetermined depression angle gradient to the road surface and receives the reflected wave. A transceiver 1 (TR), a frequency measuring circuit 12 for measuring the frequency of the reflected wave signal received by the ultrasonic transducer 1.
In a vehicle-mounted vehicle speed measuring device having a calculation circuit 13 for calculating the vehicle speed V by extracting the Doppler frequency component from the frequency measurement circuit 12, a predetermined timing is set from the timing at which the ultrasonic wave transmitter / receiver 1 transmits an ultrasonic wave signal. The frequency measuring circuit 12 is provided with an introduction inhibiting means including a reception gate generation circuit 6 and a reception mask circuit 9, a detection circuit 7, a level comparison circuit 8, a gate circuit 10 and a gate circuit 11 for inhibiting introduction of the reflected wave signal into the frequency measurement circuit 12. To do.

Therefore, the transmission pulse generating circuit 4 causes the transmitter 3 to generate an intermittent ultrasonic signal a, and the ultrasonic transmitter / receiver 1 intermittently outputs a burst wave signal b in the 200 [KHz] band. The reflected wave received by the generated ultrasonic wave transmitter / receiver 1 is guided to the reception amplification circuit 5, and the reflected wave signal c is obtained. The detection circuit 7 receives the reflected wave signal c received via the reception amplification circuit 5.
Is detected to obtain a detection signal d, and the level comparison circuit 8 binarizes the detection signal d to obtain a binarized reflected wave signal f. Further, the reception gate generation circuit 6 generates a pulse e synchronized with the pulse of the transmission pulse generation circuit 4. Further, the reception mask circuit 9 is triggered by the rising edge of the pulse e of the reception gate generation circuit 6 to obtain the pulse g.

The outputs of the reflected wave signal f of the level comparison circuit 8, the pulse e of the reception gate generation circuit 6 and the pulse g of the reception mask circuit 9 are ANDed by the gate circuit 10 to obtain the output signal h, The gate circuit 11 logically ANDs it with the reflected wave signal c from the reception amplification circuit 5, and the gate circuit 1
Obtain an output i of 1. The output i of the gate circuit 11 is input to the frequency measuring circuit 12, the frequency measuring circuit 12 measures the frequency of the output i taken out from the gate circuit 11, and
The arithmetic circuit 13 extracts the Doppler frequency component based on the frequency obtained from the frequency measuring circuit 12, calculates the vehicle speed V from the Doppler frequency component, and outputs it.

This corresponds to the fact that the reflected waves of water droplets are detected earlier in time and the reflected waves on the road surface are detected later. Even if the reflected waves from the submerged road surface E are compared, the road surface reflection is reflected. The ratio S / N between the signal level of the wave S and the signal level of the water splash reflected wave N can be detected as large as possible, and the reflected wave from the road surface E can be accurately obtained.

Therefore, even if noise is generated in the vicinity of the ultrasonic wave transmitter / receiver TR due to water splash W or muddy water splashing from the road surface, snow, sand, or dust, the noise component is converted to the reflected wave obtained from the road surface. Since the vehicle speed V is obtained by removing from the included noise component, it is possible to accurately detect the vehicle speed V when traveling on any road.

By the way, the introduction prohibiting means in the above embodiment is
The reception gate generation circuit 6, the reception mask circuit 9, the detection circuit 7, the level comparison circuit 8, the gate circuit 10, and the gate circuit 11 are included. However, the reception gate generation circuit 6 and the reception mask circuit 9 are for obtaining the time C for obtaining the reflected wave from the time B for obtaining the reflected wave reaching the road surface E from the ultrasonic wave transmitter / receiver TR shown in FIG. Therefore, when the time limit is set only by the reception gate generation circuit 6, the reception mask circuit 9 can be omitted. In the present embodiment, the reception gate generating circuit 6 is used for the ultrasonic transducer TR.
The time A for obtaining the reflected wave that reaches the road surface E from the vehicle is set in advance, and a slight time difference that varies depending on the vehicle type is set in the reception mask circuit 9, which has the advantage of facilitating the setting of the time limit. . Of course, if the time limit is set only by the reception gate generation circuit 6, one circuit is not required, and the unit price of the device can be reduced.

Further, the detection circuit 7 and the level comparison circuit 8 of the above-mentioned embodiment perform the envelope detection to facilitate the comparison processing. Since it is only necessary to detect the level of the wave signal equal to or higher than the predetermined threshold value Ev, it is possible to configure the level comparison circuit 8 and the retrigger type monostable circuit, the level comparison circuit 8 and the integration circuit. That is, in the case of implementing the present invention, any circuit may be used as long as it is a circuit that extracts a predetermined or more signal from the received reflected wave signal.

Although the gate circuit 10 and the gate circuit 11 of the above embodiment use two AND circuits, when implementing the present invention, the logical configuration and the number of circuits are not specified. .

As a result, the introduction prohibiting means of the above embodiment is
It is composed of a reception gate generation circuit 6, a reception mask circuit 9, a detection circuit 7 and a level comparison circuit 8. However, in the case of implementing the present invention, the timing at which the ultrasonic wave transmitter / receiver 1 transmits an ultrasonic wave signal. Frequency measurement circuit 1 for a predetermined time from
Any circuit can be used as long as it can prohibit the introduction of the reflected wave signal.

Incidentally, the vehicle-mounted vehicle speed measuring device of the above-described embodiment can eventually calculate the distance and the acceleration by integrating and differentiating the vehicle speed vector, and can be used in the measuring device and the control device. That is, by using the obtained speed component, various speed information such as the correction of the travel distance and the travel direction of the navigation system, the ABS device, the suspension device for adjusting the vehicle height between the road surface on the left and right wheel sides and the vehicle 100, and the like. It can be used for measuring devices and control devices that use

[0050]

As described above, the vehicle speed measuring device according to the present invention transmits the ultrasonic signal intermittently output with a predetermined depression angle gradient to the road surface and receives the reflected wave. An ultrasonic wave transmitter / receiver, a frequency measuring circuit for measuring the frequency of a reflected wave signal received by the ultrasonic wave transmitter / receiver, an arithmetic circuit for extracting the Doppler frequency component from the frequency measuring circuit, and calculating a vehicle speed. Further, the introduction prohibiting means prohibits the introduction of the reflected wave signal into the frequency measuring circuit for a predetermined time from the timing of transmitting the ultrasonic signal by the ultrasonic transmitter / receiver.

Therefore, the reflected wave of the water droplet is early in time and the reflected wave of the road surface is detected late, and even if the reflected wave from the submerged road surface is detected, The detection can be performed with the ratio of the signal level and the signal level of the water splash reflected wave as large as possible, and the reflected wave from the road surface can be accurately obtained. Therefore, even if noise is generated near the ultrasonic transducer due to water splashes or muddy water splashes from the road surface, snow, sand, or dust, the noise component contained in the reflected wave obtained from the road surface. Removed from the ingredients,
Since the vehicle speed is obtained, it is possible to accurately detect the vehicle speed when traveling on any road.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic principle of an in-vehicle vehicle speed measuring device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an output condition of reflected waves from water droplets and a road surface, which shows the principle of the vehicle-mounted vehicle speed measuring device of the invention.

FIG. 3 is a circuit configuration diagram of an in-vehicle vehicle speed measuring device according to an embodiment of the present invention.

FIG. 4 is a timing chart in the vehicle-mounted vehicle speed measuring device according to the embodiment of the present invention.

[Explanation of symbols]

 W Water splash E Flooded road surface 1 (TR) Ultrasonic wave transmitter / receiver 6 Reception gate generation circuit 7 Detection circuit 8 Level comparison circuit 9 Reception mask circuit 10, 11 Gate circuit 12 Frequency measurement circuit 13 Arithmetic circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuyuki Aoki 2-1-1 Asahi-cho, Kariya city, Aichi, Aisin Seiki Co., Ltd. (72) Inventor Shinji Ikeda 1-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. Within

Claims (1)

[Claims] 1. An ultrasonic wave transmitter / receiver which transmits an ultrasonic wave signal intermittently output with a predetermined depression angle gradient to a road surface and receives the reflected wave, and an ultrasonic wave transmitter / receiver. An in-vehicle vehicle speed measuring device having a frequency measuring circuit for measuring the frequency of a reflected wave signal that has undulated, and an arithmetic circuit for extracting a Doppler frequency component from the frequency measuring circuit to calculate a vehicle speed, wherein the ultrasonic transducer 2. An in-vehicle vehicle speed measuring device comprising an introduction prohibiting means for prohibiting introduction of a reflected wave signal into the frequency measuring circuit for a predetermined time from the timing of transmitting an ultrasonic wave signal.