JPH02140682A - Detector for distance between vehicles - Google Patents

Abstract

PURPOSE:To accurately detect the distance between a vehicle and the preceeding or backward vehicle by transmitting a laser beam to the forward or backward direction of the vehicle and extracting only the signal reflected from the preceeding or backward vehicle among received reflection signals. CONSTITUTION:A signal (laser beam) S0 with the 1st frequency f0 is transmitted to the forward or backward direction of the vehicle by transmission means 2. The reflected signals of the signal transmitted by the means 2, i.e. reflected lights from the preceeding (backward) vehicle or any other objects, are received by receiving means 4, and the light signals are converted to electrical signals by a photodiode 22. A reference signal with the 2nd frequency f0+DELTAf which has a difference of a specified frequency DELTAf from the frequency f0, is generated by reference signal generating means 6. The reflection signal and the reference signal are mixed by mixing means 8 consisting of a half mirror. The signal outputted from the means 8 is inputted to filter means 10, whereby only the frequency components adjacent to the specified frequency DELTAf are passed among the electrical signals converted by the photodiode 22. The distance is calculated by distance calculation means 12 in accordance with the signal outputted from the means 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a vehicle inter-vehicle distance detection device for detecting the inter-vehicle distance between one's own troops and a preceding vehicle or a following vehicle.

(Prior Art) Conventionally, for example, as described in Japanese Patent Application Laid-open No. 82-54189, signals such as radio waves, laser light, and ultrasonic waves are transmitted forward from the own military, and the signals are transmitted to the front by the own military. The inter-vehicle distance detection device receives the reflected signal that is reflected back from the preceding vehicle located in front, and calculates the inter-vehicle distance between the own force and the preceding vehicle based on the signal round trip time (delay time) from transmission to reception. Are known.

(Problem to be Solved by the Invention) However, in the above-mentioned inter-vehicle distance detection device, the signal transmitted from the own vehicle is not necessarily reflected back only to the preceding vehicle; For example, when driving on a curve, there are many cases where the signal is reflected back from a guardrail, etc., and the reflected signal that is reflected from something other than the vehicle in front causes a malfunction. There is a problem in that the distance between the vehicle and the preceding vehicle is detected as the inter-vehicle distance. Such a problem similarly exists when a signal is transmitted from the own army to the rear to detect the inter-vehicle distance between the own army and a trailing vehicle located behind the own army.

In view of the above circumstances, an object of the present invention is to extract only the reflected signals reflected by the preceding vehicle and the following vehicle from among the received signals, and to accurately detect the inter-vehicle distance between the preceding vehicle and the following vehicle. An object of the present invention is to provide a vehicle inter-vehicle distance detection device that is capable of detecting an inter-vehicle distance.

(Means for Solving the Problems) In order to achieve the above object, the inter-vehicle distance detection device for a vehicle according to the present invention includes a transmitting means for transmitting a signal of a first frequency;
a receiving means for receiving a reflected signal of the signal transmitted by the transmitting means; a reference signal generating means for generating a reference signal of a second frequency different from the first frequency by a predetermined frequency;
mixing means for mixing the reflected signal and the reference signal; filter means for passing only frequency components below the predetermined frequency of the signal output from the mixing means; and a signal output from the filter means. and distance calculation means for calculating the distance based on the following.

As the signal, radio waves such as microwaves, light such as laser light, or sound waves such as ultrasonic waves can be used.

The filter that only passes frequency components below the vicinity of the predetermined frequency means a filter that cuts frequency components that are higher than the vicinity of the predetermined frequency, for example, a bandpass filter that only passes frequency components near the predetermined frequency. Alternatively, it may be a low-pass filter that passes only frequency components near or below the predetermined frequency.

(Function) The signal S0 of the first frequency fo is transmitted from the transmitting means to the front of the vehicle (self-army). The signal SO hits the preceding vehicle to be measured and objects other than the preceding vehicle and is reflected. The reflected signal St (frequency fo
+fl) and the reflected signal Sz (frequency fo+f2) reflected from an object other than the preceding vehicle are both received by the receiving means. Therefore, the signal S1+82 received by the receiving means has frequencies (fo +fr) and (fo
+fz), and this has a first frequency f. A second frequency (f
. +Δf) When mixing the reference signal, the frequency 1f
A signal having 5-Δf1 components and a frequency 1fz-Δf1 component is generated.

By the way, the preceding vehicle has almost no relative speed with respect to the own force, and objects other than the preceding vehicle, such as guardrails, usually have relative speed with respect to the own force. Therefore, the reflected signal Sl
The Doppler shift (frequency shift) fx is f 14g
Q, but the Doppler shift molecule 2 of the reflected signal S2 has a somewhat large value.

Therefore, by passing the signal generated by the above-mentioned mixing through a filter means that passes only the frequency components below the predetermined frequency 1Δf1, the frequency component 1f
Only 1-Δf1 passes through, and the frequency component 1fz-Δf1 is cut. Therefore, when the distance calculation means calculates the distance based on the signal that has passed through the filter means, the filter means calculates the frequency component lf! Since only −Δf1, that is, only the above-mentioned signal S1 is allowed to pass, it is possible to accurately detect the inter-vehicle distance to the preceding vehicle without being affected by reflected signals reflected by objects other than the preceding vehicle. .

The above-mentioned effect is the same when transmitting a signal toward the rear and receiving the reflected signal to detect the inter-vehicle distance to the following vehicle.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an inter-vehicle distance detection device for a vehicle according to the present invention. The illustrated embodiment uses a laser beam as a signal, and includes a transmitting means 2, a receiving means 4, a reference signal generating means 6, a mixing means 8, a filter means IO, and a distance calculating means 12.

The transmitting means 2 transmits a signal (laser light) So at a first frequency f towards the front of a vehicle (self-army) equipped with this device, and specifically transmits a signal (laser light) So at a first frequency f, using a semiconductor laser 14 as a light source.
, a drive circuit 16 that drives the semiconductor laser 14, and a transmission lens L8 that irradiates laser light forward.

The receiving means 4 receives the reflected signal of the signal transmitted by the transmitting means 2, that is, the reflected light that has hit the preceding vehicle or other objects, and specifically collects the reflected light. It is composed of a receiving lens 20, a photodiode 22 that converts an optical signal into an electrical signal, and an amplifier 24.

The reference signal generating means 6 has the first frequency f.

It generates a reference signal of a second frequency (Cfo+Δf) different from a predetermined frequency Δf from the semiconductor laser 14, and specifically includes a half mirror 26 for branching and extracting the laser beam of frequency f0 emitted from the semiconductor laser 14; a frequency shifter 2 that shifts the laser beam extracted by the frequency Δf and outputs a laser beam of a second frequency (fo+Δf);
It consists of 8.

The mixing means 8 mixes the reflected signal and the reference signal, and is specifically constituted by a half mirror.

The filter means 1O receives the signal outputted from the mixing means 8, and passes only the frequency components in the vicinity of the predetermined frequency Δf of the input signal. The predetermined frequency 1Δf1 of the electrical signal converted by the diode
It is composed of an electric bandpass filter that passes only nearby frequency components.

The distance calculation means 12 calculates the distance based on the signal output from the filter means IO, and specifically, the information indicating that the signal has been transmitted from the drive circuit 1B is inputted. Then the filter means I
Time until the signal passing through O is input (delay time)
It is composed of a counter section (not shown) that measures the distance, and a calculation section (not shown) that calculates the distance based on the measured value of the counter section.

Next, the operation of the above embodiment will be explained.

First, the drive circuit 1G causes the semiconductor laser 14 to
A laser beam (signal S.) with a frequency fo is emitted as a pulse, and the signal So is transmitted through the transmission lens 18 toward the object to be measured in front of the own troops.

Simultaneously with the transmission of this signal So, the signal So is sent from the drive circuit 1B.
A start signal, which is information indicating that the distance has been transmitted, is manually input to the distance calculation means 12. Further, the signal So is branched and taken out by the half mirror 2B, and the taken out signal of the first frequency f0 is inputted to the frequency shifter 28, and from the frequency shifter 28, the second frequency is shifted by a predetermined frequency Δf. A reference signal of (fo+Δf) is output.

On the other hand, the transmitted signal So hits the preceding vehicle or an object other than the preceding vehicle, such as a guardrail, and is reflected, and the reflected signals are collected by the receiving lens 20. In this case, the reflected signal reflected by the preceding vehicle is converted to Ss.
(frequency; fo + fl), and the reflected signal reflected by objects other than the preceding vehicle is Sz (frequency; fo + fz
). The signal (Sl+32) collected by the receiving lens 20 is mixed with the reference signal by the half mirror 8, and converted into an electrical signal by the photodiode 22. The optical signal converted by this photodiode 22 is the reflected signal J (f□ + fl ) and Sz (fo + fz
) and the reference signal (fo+Δf), therefore, the electrical signal output from the photodiode 22 is lf! It has two frequency components -Δf1 and If2-Δf.

Incidentally, the preceding vehicle is normally traveling at approximately the same speed as the own force, and therefore the relative speed between the preceding vehicle and the own force is approximately zero, and therefore the Doppler shift numerator 1 in the reflected signal SX from the preceding vehicle is approximately zero.

On the other hand, most of the reflectors other than the preceding vehicle are stationary objects such as guardrails, and therefore the relative speed between the reflector other than the preceding vehicle and the own vehicle is approximately to the extent that it corresponds to the traveling speed of the own vehicle. This is a large value, and therefore, the Doppler shift molecule 2 in the reflected signal S2 from a vehicle other than the preceding vehicle has a somewhat large value. That is, in the two frequency components 1-Δf1 and 1fz-Δf1 of the electrical signal, f is approximately zero, and f2 is a somewhat large value.

The electrical signal obtained by the photoelectric conversion is amplified by the amplifier 24, and passed through a bandpass filter lO that passes only the frequency components near the 1Δf1,
As a result, only the frequency component of 1fs-Δf1, that is, the reflected signal S reflected from the preceding vehicle! only are extracted. This is because as mentioned above (f1'+0, so lft
-Δfl&vlΔf1, so the frequency component of 1fr-Δf1 passes through the band-pass filter IO, but since f2 is a somewhat large value, the frequency component of 1fz-Δf is cut by the filter IO.

The reflected signal Sl that has passed through the filter 10 is input to the distance calculating means 12, and the reflected signal S1 is input to the distance calculating means 12.
The distance calculation means measures the time (signal delay time) from the start signal inputted from the drive circuit 1B to the stop signal, and calculates the distance accordingly.

FIG. 2(a) shows the waveform of the above signal S, FIG. 2(b) shows the waveform of the above signal S1, FIG. 2(e) shows the waveform of the above signal S2, and FIG. 3 shows the waveform of the above signal S. The difference in frequency between the signal 5onSl+S2 and the reference signal is shown, and FIG. 4 is a diagram showing the frequency components of the photoelectrically converted electric signal.

In addition, as can be easily understood from FIG. 4, the frequency component 1fz-Δf1 is the frequency component 1f1-Δf1+1Δf
1, so even if a low-pass filter that passes only frequency components below 1Δf1 is used in place of the above-mentioned band-pass filter, the signal S2 will be cut and the signal S! It is possible to extract only

Further, in the above embodiment, the predetermined frequency Δf in the reference signal was Δf≠0, but the Δf may be zero. That is, it is also possible to use a signal with frequency fo as the reference signal.

Although laser light is used as the signal in the above embodiment, it is also possible to use microwaves or ultrasonic waves, and FIG. 5 is a block diagram showing an embodiment in which microwaves are used.
FIG. 6 is a block diagram showing an embodiment in which ultrasonic waves are used. In either case, the basic configuration and operation of the device are the same as those using the laser beam described above, so detailed explanations will be omitted. In both figures, the mixing means 8 consists of a mixer, the reference signal generating means 6 consists of a local oscillator, and in FIG.
Accordingly, in FIG. 6, transmission and reception are performed by the transmitting/receiving ultrasonic transducer 30. The other components, such as the amplifier 24, filter IO, and distance calculation means 12, are the same as those shown in FIG.

Further, in the above embodiment, a pulse modulation method is used in which the laser beam is pulse-modulated and the distance is calculated based on the time difference between the transmitted laser beam S0 and the reflected signal Sl, but the present invention also provides other distance detection methods, For example, it is effective in AM modulation, FM modulation, and even so-called triangulation methods.

(Effects of the Invention) As described above, the present invention provides that the Doppler shift of reflected signals from the preceding vehicle and the following vehicle is approximately zero since the relative speed between the preceding vehicle and the own troops is approximately zero; Therefore, since the system is configured to calculate the distance based on the signal whose Doppler shift component is less than near zero in the received signal, it extracts only the reflected signal from the preceding vehicle, etc., and uses it to determine the distance between the preceding vehicle, etc. and the own force. The distance between vehicles can be accurately detected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the device according to the present invention, Fig. 2 (a), (b), and (c) are diagrams showing the waveforms of each signal, and Fig. 3 shows the frequency of each signal. FIG. 4 is a diagram showing the frequency components of the signal output from the mixing means, and FIGS. 5 and 6 are diagrams showing other embodiments. 2... Transmitting means 6... Reference signal generating means lO... Filtering means 4... Receiving means 8... Mixing means 12... Distance calculating means

Claims (1)

[Claims] a transmitting means for transmitting a signal of a first frequency; a receiving means for receiving a reflected signal of the signal transmitted by the transmitting means; and a reference signal generator for generating a reference signal of a second frequency different from the first frequency by a predetermined frequency. a mixing means for mixing the reflected signal and the reference signal; a filter means for passing only frequency components in the vicinity of the predetermined frequency or less among the signals output from the mixing means; and an output from the filter means. 1. An inter-vehicle distance detection device for a vehicle, comprising: distance calculation means for calculating a distance based on a signal obtained by the vehicle.