JPH0248073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a collision prevention device that uses two radar devices and can reliably determine the risk of collision with a simple circuit configuration.

In the past, various collision prevention devices have been proposed that detect and warn of obstacles and other vehicles in the vicinity of the vehicle, especially in front (hereinafter referred to as "targets"). One example is the collision prediction method. Figure 1 shows the basic idea of this system, where 1 is an oscillator, 2a and 2b are antennas attached to the front of the vehicle, and 3a and 3b are
is a detector, 4a and 4b are amplifiers, 5a and 5b are frequency/voltage converters, and 6 is a divider. In Fig. 2, if C is a vehicle and D is a target, the sound waves or radio waves radiated from the antennas 2a and 2b of the vehicle C are reflected by the target D, and this reflected wave signal is received by the antennas 2a and 2b. Obtain the Doppler signal from the frequencies of both signals. The frequency of the Doppler signal is the second
Compare with v _R (=vcosθ _R ) and v _L (=vcosθ _L ) shown in the figure. Depending on the position of target D and its moving direction, v _R
Since the relationship between and v _L changes, it is determined that there is a risk of collision when these ratios, that is, the frequency ratio of the two Doppler signals, are within a certain range.

By the way, in such a collision prediction method, the target object is usually located at a distance of several tens of meters to 100 meters in front of the vehicle, so the frequencies of the two Doppler signals are very close to each other.

For example, as shown in Figure 3A, targets D ₁ and D ₂
is 10 meters ahead of vehicle C in the straight direction, D ₁ :v _R /v _L = cosθ _R /cosθ _L = 0.98749 D ₂ :v _R /v _L = 1.01267, and v _R /v _L are 0.98749 and 1.01267. It is determined that there is a risk of collision if the vehicle gets between the vehicle and the vehicle. Furthermore, as shown in Figure 3B, when approaching oblique targets D ₁ and D ₂ and target D ₁ is 1 m off to the left of vehicle C, D ₁ :v _R /v _L = cosθ _R /cosθ _L =0.98811 D ₂ :v _R /v _L =1.01282, and if v _R /v _L falls between 0.98811 and 1.01282, it is determined to be dangerous.

In either case, an extremely narrow range of change in v _R /v _L will be detected, so an accuracy of 1% or more is required, and therefore v _R and v _L require the same degree of accuracy. Become. For example, the frequency of the Doppler signal is "0" (that is, the relative speed is 0) when the vehicle is following the vehicle in front. If the other vehicle is approaching at 100 km/h, the carrier frequency of the radar is 10 GHz.
Since it is 3.7KHz, it is necessary to maintain the above-mentioned accuracy of 1% or more over this frequency range. In order to accurately determine the frequencies of two Doppler signals in such a short time, a complicated circuit configuration is required.

The present invention has been made in view of the above points, and in order to reliably determine the risk of collision with a simple circuit configuration, two Doppler signals are obtained by two radar devices mounted on a vehicle, and these signals are used. The risk of collision is determined by differentiating the phase difference of the Doppler signal with respect to the distance between the vehicle and the target object, and comparing the differential value with a predetermined value.

The present invention will be explained below based on the drawings.

FIG. 4 shows an embodiment of the collision prevention device according to the present invention, in which reference numerals 11 and 21 are oscillators;
2 is a pulse modulator, 13 and 23 are antennas, 1
4 and 24 are transmitting trigger circuits, and 15 and 25 are receiving circuits, which provide two systems of pulse Doppler radars 100 and 200 (shown surrounded by broken lines in the figure).
It consists of 7 is a phase comparison circuit, 8 is a differentiation circuit, 9 is a comparison circuit, and 10 is an alarm circuit.

In the above circuit configuration, the pulse Doppler radar
100 outputs a Doppler signal S _{1 with a frequency f 1 proportional} to the magnitude of v _R in FIG. 2 and a signal S ₂ corresponding to the distance between the own vehicle and the target object. The pulsed Doppler radar 200 also outputs a Doppler signal _S3 with a frequency _f2 proportional to the magnitude of _vL in FIG. The phase comparison circuit 7 compares the phases of the Doppler signal S ₁ and the Doppler signal S ₃ and outputs a signal S ₄ corresponding to the phase difference. This phase difference signal S ₄ is differentiated with respect to the distance detected by the pulsed Doppler radar 1 by a differentiating circuit 8 . This differential value will be analyzed below.

In Fig. 5, when the target approaches directly from the center of the vehicle as shown by D ₁ , v _R = v _L , and therefore f ₁
= _f2 . Therefore, two Doppler signals S ₁ and S ₂
The phase difference remains constant, so the differential value becomes "0". Further, when the target object _D2 approaches along the hyperbola _L1 with the two antennas 2a and 2b as focal points, the differential value becomes "0". However, when targets D ₃ and D ₄ cross the hyperbolas L ₂ and L ₃ , the differential value does not become "0", and especially targets D ₄
The larger the deviation from the hyperbola L ₃ , the larger the differential value becomes. As is clear from the figure, the target
In the case of D ₄ , the risk of collision is small because the vehicle often crosses in front of the vehicle, but in the case of targets D ₁ and D ₂ , the risk of collision is high. Therefore, the risk of collision can be determined based on the differential value of the phase difference between the two Doppler signals S ₁ and S ₂ .

Therefore, the comparison circuit 9 uses two Doppler signals S ₁ ,
Compare the differential value of the phase difference of _S3 with a predetermined reference value R,
When the differential value is less than the reference value R, "1" is output and the alarm circuit 10 is activated.

For example, if the carrier frequency of the pulse Doppler radars 100 and 200 is 10 GHz, the antenna spacing is 1.5 m, and the vehicle width is 1.7 m, the reference value R is approximately 20 deg/m when converted to the differential value of the phase difference. It can be a value.

FIG. 6 shows another embodiment of the collision prevention device according to the invention, in which the same reference numerals as in the embodiment shown in FIG. 4 indicate the same components.

In this embodiment, the reference value R, which is compared with the differential value of the phase difference between the two Doppler signals S ₁ and S ₃ , is changed in accordance with the distance between the target object and the host vehicle to perform more accurate determination. . The arithmetic circuit 16 is a circuit that calculates a reference value R based on the distance signal S ₂ representing the distance detected by the receiving circuit 15 of the pulse Doppler radar 1 . Ideally, the input/output characteristics of the arithmetic circuit 16 should change as shown by a curve a shown in FIG. 7, but in order to simplify the circuit configuration, they may change as shown by a straight line b.

FIG. 8 shows still another embodiment of the present invention, in which the same reference numerals as in the previous embodiment indicate the same components. As can be seen from FIG. 9, when the vehicle C is traveling straight, the target D approaches in the direction of the relative feed rate v.
is considered to cross in front of the own vehicle as shown by the broken line, but when vehicle C is traveling on a circular path, target D approaches with a trajectory like the solid line,
Collision is likely. Therefore, in this embodiment, in order to avoid such a danger, the reference value R to be compared with the differential value is changed according to the amount of steering operation (steering angle) of the vehicle using a steering angle sensor 17 and an arithmetic circuit 18. This is what I did. FIG. 10 shows an example of the relationship between the reference value calculated by the calculation circuit 18 and the steering angle in this embodiment. That is, the larger the steering angle is, the larger the reference value R is.

Differentiating circuit 8 of the first, second and third embodiments,
It is also possible to implement the functions of comparison circuit 9, arithmetic circuits 16 and 18, etc. using a microcomputer. In this case, by theoretically calculating reference values for comparison based on values such as the distance from the own vehicle to the target, the steering angle, and the distance between the antennas, it is possible to make a highly accurate risk determination. FIG. 11 is an isomorphic curve showing an example of the relationship between the distance and the reference value when the steering angle in that case is used as a parameter.

In the embodiment described above, an alarm is generated when it is determined that there is a risk of collision, but driving control such as applying braking (or follow-up driving) may be performed.

As explained above, in the present invention, two Doppler signals and a distance signal are obtained by two systems of radar devices installed in a vehicle, and the risk of collision is determined based on the value obtained by differentiating the phase difference of the Doppler signals with respect to distance. As a result, accurate risk judgment can be made with a relatively simple circuit configuration. Furthermore, by changing the reference value for determining danger according to the distance between the host vehicle and the target object, the steering angle, etc., more accurate determination can be made.

[Brief explanation of the drawing]

Figure 1 shows the basic circuit of the conventional collision prediction system using two radar devices, Figure 2 shows the principle of detecting the movement of a target with two radar devices, and Figure 3 A and B show the basic circuit of the conventional collision prediction system using two radar devices. FIG. 4 is a block diagram showing the first embodiment of the collision prevention device according to the present invention, and FIG. An explanatory diagram of the danger judgment method based on the differential value of the phase difference of signals, FIG. 6 is a block diagram of the second embodiment of the present invention, and FIG. 7 is a reference value based on distance of the embodiment shown in FIG. 6. FIG. 8 is a block diagram of the third embodiment of the present invention, FIG. 9 is an explanatory diagram of the third embodiment of the present invention shown in FIG. 8, and FIG. FIG. 11 is a characteristic diagram showing the change in the reference value depending on the steering angle, and FIG. 11 is a characteristic diagram showing the relationship between the distance and the reference value. 1... Oscillator, 12, 22... Pulse modulator,
13...Antenna, 14...Transmission trigger circuit, 1
5... Receiving circuit, 2... Oscillator, 21... Oscillator, 22... Pulse modulator, 23... Antenna,
24... Transmission trigger circuit, 25... Receiving circuit, 7
... Phase comparison circuit, 8 ... Differentiation circuit, 9 ... Comparison circuit, 10 ... Alarm generating circuit, 16 ... Arithmetic circuit, 17 ... Steering angle sensor, 18 ... Arithmetic circuit.

Claims (1)

[Claims] 1 Two radar devices mounted on a vehicle, which detect the distance between the vehicle and an object and output a distance signal, and output two Doppler signals based on the movement of the object around the vehicle; means for calculating a phase difference; means for calculating a distance change rate of the phase difference based on the distance signal and the phase difference; A collision prevention device comprising means for determining the possibility of approaching.