JPH04278487A - Radar for vehicle - Google Patents

Abstract

PURPOSE:To lower the detection threshold of a short distance frequency side to enlarge the width of a radar beam in the device for using a frequency modulated wave. CONSTITUTION:A triangular wave generated in a modulated signal generation circuit 10 is transmitted from a transmission antenna 12a and a reflected wave from a target is received in an antenna 12b. An obtained beat signal is frequency-analyzed in an FFT processing circuit 13, a modulated noise component having a known frequency is eliminated in a modulation noise elimination circuit 14, and a relative distance and speed up to the target are detected in a target detection circuit 15 and a distance speed operation circuit 16. In a triangular amplitude period generation circuit 18 the frequency deflection width of the triangular wave is changed and the beat signal frequency of a target echo signal existing in a modulated noise frequency is changed to detect.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a vehicle radar device, in particular, a vehicle radar device that emits frequency-modulated transmission waves toward a detected object, and
The present invention relates to a radar device that detects the distance and speed of an object from its reflected waves and transmitted waves.

0002

[Prior Art] Radar devices that detect obstacles around a vehicle, such as a vehicle in front, have been developed for the purpose of performing automatic steering such as following driving.
Alternatively, a method using laser light has been proposed.

For example, in the radar device disclosed in Japanese Patent Application Laid-Open No. 2-198379, a frequency modulated wave whose frequency changes over time is used as a transmission signal, and a reflected wave reflected by an object to be detected and this frequency modulation are used. A configuration is disclosed in which the distance and speed to a detected object are detected using waves.

[0004] This conventional radar device will be explained in detail below. FIG. 6A shows a diagram of the relationship between frequency and time of a frequency modulated wave and its reflected wave. As shown in the figure,
The transmitted wave is a triangular modulated wave with a period Tm (=1/fm) and a frequency deviation width Δf. If there is no relative velocity between the object to be detected and the detected object, the waveform indicating the change in the received wave is the waveform of the transmitted wave in the right direction on the horizontal axis over a period of time determined by the distance R to the object to be detected and the speed C of the radio wave. It has been translated by 2R/C, and therefore, the relative distance can be calculated by finding the difference between these transmitting and receiving frequencies.

FIG. 6B shows a temporal change in the absolute value of the difference in frequency between these transmitted and received waves, and a beat signal with a frequency deviation width of Δf/c·fm·R is obtained. however,
Δf is the frequency deviation width of the triangular wave in FIG. 6(A), and fm is the modulation frequency. In addition, when the relative distance to the detected object changes, that is, when the relative velocity is not 0, the frequency of the transmitted wave changes in proportion to the relative velocity during reception due to the Doppler effect. As shown, the received waveform is a waveform obtained by translating the transmitted waveform to the right on the horizontal axis and parallel to the vertical axis.

[0006] Therefore, when calculating the difference in transmitting and receiving frequencies, the result is as shown in Fig. 6.
As shown in (D), a beat signal in which frequencies fd1 and fd2 appear alternately is obtained. Then, the relative distance R and relative velocity V to the detected object are determined from the beat signal obtained in this way, with proportionality constants K1 and K2, R=
It can be calculated by K1·(fd1+fd2)/2 V=K2·(fd1−fd2)/2.

However, there is a problem in that modulation noise fm is generated in the beat signal obtained in this way, especially in the vicinity of the short-range target detection frequency, as shown in FIG. This caused erroneous speed detection.

Therefore, as shown in FIG. 7, in the past, the detection threshold level at short distances was set higher than at long distances (the broken line in the figure) to prevent false detection due to modulation noise fm. Ta. Since this modulation noise fm has almost no effect on the detection frequency of a long-distance target, the detection threshold at long distances has been set low to increase sensitivity and extend the maximum detection distance.

[0009]

[Problems to be Solved by the Invention] Conventionally, the detection threshold was raised to remove modulation noise fm at short distances where the echo signal level was high. When mounted on a vehicle, a highly directional antenna is used, so if the short-range detection threshold is set high, the horizontal detection width becomes extremely narrow, making it difficult to detect two-wheeled vehicles such as motorcycles in close proximity. There was a problem that this could not be detected even if the

This will be explained below using FIGS. 7 to 9. First, in the spectrum of Fig. 7, if we consider the case where a target with the same radar reflection cross section moves from a short distance to a long distance, the level of the beat signal shown in Fig. 6 (D) will be attenuated with distance. It gradually becomes smaller. Here, if the detection threshold of the beat signal is made constant with respect to frequency, the dynamic range of a long-distance target becomes relatively smaller than the dynamic range of a short-distance target. Therefore, in the antenna pattern shown in FIG. 8, what was cut at level Th2 at a short distance will be cut at level Th1 at a long distance.

Therefore, if the detection threshold at short distances is increased as in the prior art described above, the detection threshold at short distances will be cut at Th3, and the width of the detection area at short distances will be reduced as shown by the shaded area in FIG. As a result, it becomes impossible to obtain a large amount.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an in-vehicle device that can expand the detection area at short distances and detect targets with high precision from short distances to long distances. Its purpose is to provide radar equipment.

[0013]

[Means for Solving the Problems] In order to achieve the above object, an in-vehicle radar device according to the present invention includes a transmitting means for transmitting a frequency modulated wave, and a frequency deviation for changing the frequency deviation width of the frequency modulated wave. width control means, reception means for receiving a reflected wave from a detected object (target), and a frequency modulated wave having a first frequency deviation width set by the frequency deviation width control means and its reflected wave. and a beat signal obtained by combining a frequency modulated wave having a second frequency deviation width set by the frequency deviation width control means and its reflected wave. The present invention is characterized by comprising a filter means for removing noise components, and a detection means for detecting the relative distance and relative velocity from the frequency of the beat signal from which the modulated noise components have been removed to the target.

[0014]

[Operation] The vehicle radar device of the present invention has such a configuration, and instead of removing modulation noise by raising the detection threshold in the low frequency region where modulation noise occurs as in the past, it The filter means removes only the modulation noise for which is known in advance.

[0015] Then, the modulation noise component is removed, but
The target echo signal generated at the frequency where this modulated noise component occurs will also be removed at the same time.
By changing the frequency deviation width of the frequency modulated wave from the first frequency deviation width to the second frequency deviation width by the frequency deviation width control means to obtain a beat signal, the echo signal from the target is converted into modulated noise. This makes it possible to detect the target echo signal, which appears at a frequency different from the target echo signal and which is removed together with the modulation noise by the filter means.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a vehicle radar apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of the configuration of the radar device of this embodiment, and FIG.
shows a processing flowchart of the same embodiment. In FIG. 1, a triangular wave having a predetermined frequency deviation width and period is generated by a triangular wave amplitude cycle generating circuit 18 in a modulation signal generating circuit 10, and after being converted into an analog signal by a D/A converter 19, the RF section 11 to transmitting antenna 12
A triangular wave frequency modulation signal is output through the . The frequency modulated wave transmitted from the transmitting antenna 12a is reflected by a detected object in front of the vehicle, such as a preceding vehicle on the same lane, and is input to the receiving antenna 12b.

The reflected wave received by the receiving antenna 12b passes through the RF section 11 and is subjected to FFT as a composite beat signal.
It is output to the processing circuit 13. Here, the beat signal is shown in Figure 6.
As shown in (B) or (D), the difference frequency between the transmitted wave and the received wave is detected by passing it through a mixer, and such a beat signal is input to the FFT processing circuit 13 and Fourier transform processing is performed (S102 ).

As is well known, by obtaining the Fourier transform of a beat signal that changes over time, the spectrum of the frequency components contained in this beat signal is calculated, and as already mentioned in FIG. Echoes will appear on the low frequency side of the frequency spectrum, and target echoes located far away will appear on the high frequency side of the frequency spectrum.

The beat signal whose frequency spectrum has been calculated by the FFT processing circuit 13 is further processed by the modulation noise removal circuit 1.
4 is output. Based on the information from the triangular wave amplitude cycle generating circuit 18, this modulation noise removal circuit 14 is a BEF which has the function of removing only the frequency region of modulation noise, that is, the frequency region corresponding to the modulation frequency of the triangular wave, and transmitting other frequency regions. (Band elimination filter: Band-El
(S103), which transmits and outputs frequency components other than modulation noise components.

In this way, by focusing on the fact that modulation noise consists of the frequency component of the triangular wave modulation signal and its harmonic components, and by removing only this modulation noise with a filter, the detection threshold on the low frequency side can be reduced as in the conventional method. It becomes possible to detect the target without having to set it high.

That is, the signal output from the modulation noise removal circuit 14 is input to the target detection circuit 15, where the target is detected at a desired detection threshold, and further, the signal is sent to the distance/velocity calculation circuit 16 to perform the above-mentioned (1) and (2). Relative distance and relative velocity are calculated according to the formula (S104, S1
05).

In this way, the target detection circuit 15 detects targets at short and long distances with high sensitivity, but the signal input to the target detection circuit 15 is a signal from which the frequency component of modulation noise has been removed, and therefore There is a problem in that if a target detection signal arrives at a frequency component of modulated noise, it cannot be detected.

Therefore, in this embodiment, the frequency fb of the beat signal is changed by fb=Δf/c·fm·R. Therefore, by changing Δf, the beat signal frequency component of the target existing at the same distance R can be adjusted to a desired value. By focusing on the fact that the target can be set to a value of , it is possible to detect the target by shifting the detection signal of the target located at the frequency component of the modulation noise to another frequency component.

That is, since Δf can be changed almost linearly by changing the frequency deviation width of the triangular wave modulation signal, the frequency deviation width of the triangular wave is changed by the triangular wave amplitude number period generating circuit 18 in a certain fixed cycle. change (S106). Then, as described above, the signal transmitted to the front of the vehicle via the transmitting antenna 12a, reflected from the target and returned is received by the receiving antenna 12b, and the beat signal is sent back to the FFT processing circuit 13 and the modulation noise removal circuit 14. Enter the information in sequence.

Here, by changing the frequency deviation width of the frequency modulated wave in this way, the target echo signal located at the frequency component of the modulation noise is shifted to another frequency component, so that the modulation noise can be removed. circuit 1
In step 4, this target echo signal is not removed, and the target detection circuit 15 and distance speed calculation circuit 16 calculate the relative distance and relative speed.

Of course, when the distance and speed calculation circuit 16 calculates the relative distance and relative speed, information regarding the frequency deviation width of the frequency modulated wave is input from the triangular wave amplitude cycle generation circuit 18, and it is possible to calculate the relative distance and relative speed accurately from the beat signal frequency. Relative distance and relative velocity are calculated.

[0027] Then, the dead band removal circuit 17 performs an averaging process between cycles of these changes in the triangular wave frequency deviation width to remove the target detection dead band, and outputs the result to the logic circuit 113 (S107), and calculates the target detection dead band. A warning and vehicle speed control are performed according to the relative distance and relative speed determined (S108).

As explained above, in this embodiment, the beat signal detection threshold at a short distance can be set to a desired low value by removing the modulation noise component that occurs at a short distance. The detection level in the antenna pattern is reduced from conventional Th2 to Th4, and the beam width can be expanded to θ4. Note that if the detection threshold is set to such a low value and detected at medium distances, the beam width may be too wide, causing the problem of detecting targets such as vehicles in front located in adjacent lanes that should not have been detected. In this embodiment, as shown by the dashed line in FIG. 3, the detection threshold is set high for frequencies near the middle distance to prevent the beam from spreading and to detect only targets in the vehicle's lane. ing.

Furthermore, as the signal level becomes attenuated as described above, the detection threshold is lowered again to extend the detection distance. Note that at long distances, even if the detection threshold is lowered as shown in the antenna pattern of FIG. 8, the beam width will not widen so much and no problem will occur.

FIG. 4 shows the detection range of the radar device of this embodiment with diagonal lines. Detection range of conventional radar equipment (see Figure 9)
It is understood that the short-distance detection range is expanded compared to the previous model, and it is possible to reliably detect objects such as motorcycles.

In this embodiment, as shown in the block diagram of FIG.
is provided, and a configuration is adopted in which feedback is provided to the modulation signal generation circuit 10. The configuration of this circuit and its operation will be explained below. The radar device of this embodiment uses a triangular modulated wave, but as is well known, in the FM-CW system, as shown in FIG.
As shown in (A), a problem of modulation distortion may occur in which the oscillation frequency does not change linearly with respect to the modulation voltage of the triangular wave. When modulation distortion occurs in this way, the oscillation frequency changes with respect to the triangular wave modulation voltage, as shown by the solid line in FIG. If the frequency changes accurately in the form of a triangular wave (dashed line in Figure 6(B)), the detected beat frequency will have a waveform as shown in Figure 6(B) when the relative speed is 0. Because of the presence of modulation distortion, the beat frequency becomes low near the top of the triangular wave, and becomes high near the bottom of the triangular wave, as shown in FIG. 5C. For this reason, the relative distance and relative speed to the target cannot be detected correctly.

Therefore, in this embodiment, in order to solve this problem, the triangular wave amplitude cycle generating circuit 18 is initialized so as to detect this modulation distortion and correct this distortion. In other words, when set to distortion correction mode (S
109) The beat signal from the RF section 11 is input to the beat signal pulsing circuit 110, and is pulsed according to the frequency (S110). Figure 5 (D) shows a raw waveform in which the frequency deviation width of the beat signal is plotted against time t, and when this raw waveform is converted into pulses using a predetermined threshold, it is shown in Figure 5 (E). A pulse signal that looks like this can be obtained. By counting the period of this pulse signal (S111), it is possible to detect the amount of modulation distortion shown in (A) and (B) of the figure. In other words, if the pulse periods of each triangular wave are approximately equal, the frequency is changing linearly, but if there is a difference in the pulse periods, it is non-linear and modulation distortion can be detected. (S112).

When modulation distortion is detected in the modulation distortion detection circuit 111 by counting the pulse period of the pulsed beat signal, the distortion correction circuit 112 is set so that the detected distortion becomes 0. The modulation voltage is reversely corrected (FIG. 5(F)), and the distortion is eliminated so that the frequency changes correctly in the form of a triangular wave (S113).

As described above, in this embodiment, modulation distortion can also be eliminated and the relative distance and relative velocity to the target can be detected with high precision. It also becomes possible to control with high precision.

[0035]

As explained above, according to the vehicle radar device according to the present invention, the detection range of the beam can be increased by removing the modulation noise included in the beat signal and lowering the detection threshold on the low frequency side. It can be enlarged and targets in front of the vehicle can be reliably detected.

Therefore, it is possible to construct an extremely reliable system by incorporating the radar device of the present invention into, for example, an automatic tracking system.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of an embodiment of a vehicle radar device according to the present invention.

FIG. 2 is a signal processing flowchart diagram of the same embodiment.

FIG. 3 is an explanatory diagram of detection threshold levels in the same embodiment.

FIG. 4 is an explanatory diagram of the detection range of the radar device in the same embodiment.

FIG. 5 is an explanatory diagram of modulation distortion correction in the same embodiment.

FIG. 6 is a diagram explaining the principle of a radar device using frequency modulated waves.

FIG. 7 is an explanatory diagram of a beat signal spectrum of a radar device using frequency modulated waves.

FIG. 8 is an explanatory diagram of an antenna pattern of a radar device using frequency modulated waves.

FIG. 9 is an explanatory diagram of a detection range of a conventional radar device using frequency modulated waves.

[Explanation of symbols]

10 Modulation signal generation circuit 11 RF section 12a Transmission antenna 12b Receiving antenna 13 FFT processing circuit 14 Modulation noise removal circuit 15 Target detection circuit 16 Distance speed calculation circuit 17 Dead band removal circuit 18 Triangular wave amplitude cycle generation circuit

Claims (1)

[Claims] 1. Transmitting means for transmitting a frequency modulated wave; frequency deviation width control means for changing the frequency deviation width of the frequency modulated wave; receiving means for receiving a reflected wave from a detected object; A beat signal obtained by combining a frequency modulated wave having a first frequency deviation width set by the deviation width control means and its reflected wave, and a second frequency deviation width set by the frequency deviation width control means. a filter means for removing a modulated noise component included in a beat signal obtained by combining a frequency modulated wave having a frequency deviation width and its reflected wave; and a filter means to be detected from the frequency of the beat signal from which the modulated noise component has been removed. A vehicle radar device comprising: detection means for detecting relative distance and relative speed to an object.