JPH0915332A - Detecting device of vehicle ground speed - Google Patents

Abstract

PURPOSE: To prevent a detected vehicle speed from being affected by the state of a road surface and thereby to always detect a vehicle speed with high accuracy. CONSTITUTION: A signal of a prescribed frequency is transmitted to a road surface at a prescribed angle by a sensor means M1, the signal reflected on the road surface is received thereby and the speed of a vehicle to the ground is computed from the deviation of the frequency of the received signal from that of the transmitted signal by an arithmetic means M2. A road surface state detecting means M3 detects the state of the road surface on the basis of the strength of the received signal. Based on the detected state of the road surface, an angle correcting means M4 corrects an angle of reception of the signal reflected on the road surface, which is used for computation of the speed to the ground.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground vehicle speed detecting device, and more particularly to a Doppler type ground vehicle speed detecting device.

[0002]

2. Description of the Related Art ABS (anti-lock brake system) and TRC (truncation control system)
Accurate ground vehicle speed data is required for vehicle control such as, and a Doppler type ground vehicle speed detection apparatus using ultrasonic waves or microwaves has been developed.

An example of such a ground vehicle speed detecting device is disclosed in Japanese Patent Laid-Open No. 2-307087. This is a ground vehicle speed detection device that uses the Doppler effect of ultrasonic waves, and the reflection point on the road surface of the ultrasonic waves to be transmitted is the passing position of the wheels, which eliminates water on the road surface during rainfall by passing the wheels, and By attaching a tire tread pattern to the road surface when it freezes, the reflection of ultrasonic waves on the road surface is increased and the detection of the vehicle speed to ground is ensured.

[0004]

However, although the intensity of the reflected wave on the road surface at the wheel passing position is higher than that of the other parts, the intensity of the reflected wave depends on the road surface condition, and therefore the road surface may not necessarily be the wheel depending on the road surface condition. It is not always possible to obtain the maximum intensity of the reflected wave at the passage position of.

Further, the angle formed by the center of the reflected wave and the road surface and the frequency of the reflected wave change depending on whether the road surface is rough or smooth. The smoother the road surface, the larger the angle and the frequency of the reflected wave. Get lower. There is a problem in that an error that causes the calculated vehicle speed to decrease is generated. Furthermore, because the position of the ultrasonic transmission / reception sensor is limited,
There are problems such as restrictions on the design of the device.
The present invention has been made in view of the above points, by detecting the road surface situation, by correcting the angle to receive a signal based on the road surface situation, to prevent the detection vehicle speed is affected by the road surface situation, An object of the present invention is to provide a vehicle speed detection device that can always detect a vehicle speed with high accuracy.

[0006]

According to the present invention, as shown in FIG. 1, a sensor means M1 transmits a signal having a predetermined frequency toward a road surface at a predetermined angle, receives a signal reflected on the road surface, and calculates a means M2. In the ground vehicle speed detecting device for calculating the ground vehicle speed of the vehicle from the deviation of the frequency between the transmitted signal and the received signal, the road surface condition detecting means M3 for detecting the road surface condition whether the road surface is rough or smooth, and the detected road surface condition. And an angle correction means M4 for correcting the angle at which the signal reflected on the road surface is received, which is used for the calculation of the ground speed.

[0007]

According to the present invention, the vehicle speed is obtained by detecting the road surface condition whether the road surface is rough or smooth, and correcting the angle at which the signal reflected on the road surface is received, that is, the scattered beam angle, based on the detected road surface condition. Therefore, the smoother the road surface, the lower the strength of the received signal, the larger the scattered beam angle, and the lower the vehicle speed can be corrected, and the vehicle speed can be detected with high accuracy.

[0008]

FIG. 2 shows a block diagram of an embodiment of the device of the present invention. In the figure, the radar sensor 1 as the sensor means M1
Reference numeral 0 denotes a Doppler system, which irradiates a radar beam at an angle (elevation angle) θ with respect to the road surface in the direction opposite to the traveling direction of the vehicle, and receives a reflected radar beam on the road surface. The radar sensor 10 generates and outputs beat signals of the irradiation radar beam and the reflected radar beam.

When the vehicle travels at the vehicle speed V, the road surface moves at the speed -V relative to the radar sensor 10, and the frequency of the beat signal becomes the Doppler frequency fd due to the Doppler effect. The beat signal of the Doppler frequency fd output from the radar sensor 10 is amplified by the amplifier 12, and then supplied to the waveform shaper 14 and the detector 16.

The waveform shaper 14 is composed of a comparator 20, as shown in FIG. In the figure, the beat signal output from the amplifier 12 enters the terminal 21 and the comparator 2
0 is supplied to the non-inverting input terminal. To the inverting input terminal of the comparator 20, the power supply voltage + Vss, -Vss is applied to the resistor R ₁ ,
The reference voltage Vref divided by R ₂ is applied. The comparator 20 generates a rectangular wave signal which becomes a high level when the level of the beat signal is equal to or higher than the reference voltage Vref and becomes a low level when the beat signal is lower than the reference voltage Vref, and outputs from the terminal 22. The beat signal rectangularized by the waveform shaper 14 is supplied to a vehicle speed calculation ECU (electronic control circuit) 18.

As shown in FIG. 4, the detector 16 is composed of a diode D ₁ , a capacitor C ₁ and a resistor R ₃ . In the figure, the beat signal output from the amplifier 12 enters the terminal 25 and is supplied to the anode of the diode D ₁ . The diode D ₁ conducts in the positive polarity portion of the beat signal and takes out a positive half wave. This positive half-wave is the capacitor C ₁
By being smoothed by the resistance R ₃ and the resistance R ₃ , the intensity signal S of the voltage corresponding to the peak level in the positive half wave of the beat signal is obtained.
r is generated and output from the terminal 26. This intensity signal Sr
Is supplied to the vehicle speed calculation ECU 18.

Of course, the detector 16 may perform full-wave rectification. Further, the detector 16 detects the strength of the beat signal. Since the strength of this beat signal is determined by the strength of the received signal of the reflected radar beam, the strength of the received signal at the radar sensor 10 is directly detected. Is equivalent to doing.

Here, as shown in FIG.
Even if the central axis of the radar beam from the radar sensor 10 fixed to is set to an elevation angle θ and a depression angle ψ (ψ = 90 ° −θ) with respect to the road surface, the radar beam spreads to some extent,
It has a beam width that gives the maximum elevation angle θ ′ and the minimum elevation angle θ ″ on the road surface.

The scattering coefficient, which is the probability of reflecting the radar beam toward the radar sensor 10, greatly differs depending on the road surface condition, as shown in FIG. 5 (B). When the road surface is rough, a large scattering coefficient can be obtained regardless of the depression angle ψ as shown by the solid line Ia. As the smoothness of the road surface increases, the alternate long and short dash line I
The scattering coefficient decreases in the order of b and the broken line Ic. When the road surface becomes smooth, the scattering coefficient tends to decrease as the depression angle ψ increases, and the tendency increases as the road surface becomes smoother.

As a result, the scattered beam angle, which is the angle at which the radar sensor receives the radar beam reflected on the road surface, becomes larger than the elevation angle θ as the road surface becomes smoother. Looking at this phenomenon in the signal spectrum of the Doppler frequency, as the road surface becomes smoother, the solid line in FIG.
The peak frequency decreases in the order of IIa, the alternate long and short dash line IIb, and the broken line IIc, and the peak level (reflected beam intensity) decreases.

Here, conventionally, the vehicle speed V is calculated using the equation (1).

[0017]

(Equation 1)

However, fd is the Doppler frequency, f ₀ is the transmission frequency, C is the speed of light, and θ is the elevation angle. However, although the scattered beam angle changes depending on the road surface condition, if the fixed elevation angle θ is used, the calculated vehicle speed will have an error on the low vehicle speed side as the road surface becomes slippery. In this embodiment, the above error is detected according to the reflected beam intensity, that is, the intensity signal, and the error is corrected.

The reason why the peak frequency becomes lower as the road surface becomes smoother will be described. A formula (1 ′) obtained by modifying the formula (1) is obtained.

[0020]

(Equation 2)

When the elevation angle θ becomes large, the denominator on the right side of the equation (1 ') can be regarded as constant, and the cos of the numerator on the right side can be considered.
Since the θ is reduced, the Doppler frequency fd is lowered.
FIG. 6 shows a flowchart of an embodiment of the vehicle speed calculation processing executed by the vehicle speed calculation ECU 18. This process is repeatedly executed at predetermined time intervals. In the figure, in step S10, the intensity signal Sr is read. Of course, the intensity signal Sr is E
The value is A / D converted by the input circuit incorporated in the CU 18.

Next, in step S20 corresponding to the road surface condition detecting means M3 and the angle correcting means M4, the scattered beam angle φ is detected by referring to the map shown in FIG. 7 by using the read intensity signal Sr. As described above, if the road surface is smooth, the Doppler signal intensity Sr is small, the scattered beam angle φ is larger than the elevation angle θ, and if the road surface is rough, the Doppler signal intensity Sr is large and the scattered beam angle φ is small, and the elevation angle θ is small. Approach θ. From this, the map shown in FIG. 7 is formed. Of course, this map may be linear or non-linear.

Next, in step S30, the frequency of the beat signal supplied from the waveform shaper 14, that is, the Doppler frequency fd is calculated, and the process proceeds to step S50. Computing means M2
In step S40 corresponding to, the vehicle speed V is calculated using the equation (2).
Is calculated.

[0024]

(Equation 3)

However, fd is the Doppler frequency, f ₀ is the transmission frequency, C is the speed of light, and φ is the scattered beam angle. After the vehicle speed V is calculated in step S50, the process ends. In this way, the road surface condition of whether the road surface is rough or smooth is detected based on the intensity of the received signal, and the angle at which the signal reflected on the road surface is received based on the detected road surface condition, that is, the scattered beam angle is corrected. Since the vehicle speed is obtained, the error that the received signal strength decreases as the road surface becomes smoother, the scattered beam angle increases, and the vehicle speed decreases can be corrected, and the vehicle speed can be detected with high accuracy.

Although the road surface condition is detected based on the intensity of the received signal in the above embodiment, the road surface condition is detected using, for example, an optical sensor, or the vehicle height value detected by the vehicle height sensor is displaced. You may detect the road condition from the situation,
It is not limited to the above embodiment.

[0027]

As described above, according to the present invention, the angle at which the road surface condition is detected whether the road surface is rough or smooth, and the signal reflected by the road surface is received based on the detected road surface condition, that is, the scattered beam angle. Since the vehicle speed is calculated by correcting the error, the intensity of the received signal decreases as the road surface becomes smoother, the error that the scattered beam angle increases and the vehicle speed decreases can be corrected, and the vehicle speed can be detected with high accuracy. It is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram of the device of the present invention.

FIG. 3 is a circuit diagram (example) of a waveform shaper.

FIG. 4 is a circuit diagram (one example) of a detector.

FIG. 5 is a diagram for explaining the present invention.

FIG. 6 is a flowchart of vehicle speed calculation processing.

FIG. 7 is a diagram showing a map of scattered beam angles.

[Explanation of symbols]

10 radar sensor 12 amplifier 14 waveform shaper 16 detector 18 ECU 20 comparator C ₁ capacitor D ₁ diode R _{1 to} R ₃ resistance M1 sensor means M2 calculation means M3 road surface condition detection means M4 angle correction means

Claims (1)

[Claims] 1. A ground vehicle speed detection, which transmits a signal of a predetermined frequency to a road surface at a predetermined angle, receives a signal reflected on the road surface, and calculates a vehicle ground speed of the vehicle from a frequency difference between the transmitted signal and the received signal. In the device, a road surface condition detecting means for detecting a road surface condition whether the road surface is rough or smooth, and an angle for receiving a signal reflected on the road surface, which is used for calculating the ground speed based on the detected road surface condition. A vehicle speed detecting device for ground, comprising: