JP3290547B2 - Inter-vehicle distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-vehicle distance measuring apparatus for measuring a distance between vehicles by identifying a peak frequency obtained by performing Fast Fourier Transformation of a millimeter wave radar signal. Relates to the calculation of the threshold value for the peak frequency.

[0002]

2. Description of the Related Art Conventionally, there is the following technology in such a field. FIG. 20 is a diagram schematically illustrating a conventional FM-CW (continuous wave) type millimeter wave radar. As shown in the figure, the millimeter wave radar has an antenna 1 that transmits a radio wave of a frequency f to an object and receives a reflected wave f + fd from the object. An FM-CW transmitter 2 is connected to the antenna 1. Further, a mixer 3 is connected to the antenna 1, and the mixer 3 outputs a beat signal fb (positive, negative) = fr ± fd of the reception signal and the transmission signal for each half cycle of the FM modulation.
To form The processor 4 connected to the mixer 3 analyzes the frequency of the beat signal by the fast Fourier transform unit, and fr = {fb (positive) + fb (negative)} / 2 (1) fd = {fb (positive) −fb (negative)｝ / 2 (2), and the distance R to the object and the relative velocity v are calculated using the following equations. The display unit 5 displays the distance from the Doppler processor 4 and the relative speed. Here, fr = 4R · fm · Δf / C (3) fd = 2v · f / C (4) fm: FM repetition frequency, f: transmission frequency, C: light speed, Δf: frequency shift .

When a raw beat signal is subjected to frequency analysis by a fast Fourier transform unit, a large number of peak frequencies are generated due to noise, and it becomes difficult to identify a peak frequency for an object. At the subsequent stage of the fast Fourier transform unit, a threshold index detecting means for identifying a peak frequency for the object is provided.The threshold index detecting means, for example, from the result of the frequency analysis, the power of the peak frequency having the maximum power. Half is detected as a threshold index. Or
When there are a plurality of peak frequencies, the power average value of the peak frequency having the highest power to the middle power is detected as a threshold index. When the power is lower than the threshold, the corresponding peak frequency is removed, and when the power exceeds the threshold, the corresponding peak frequency is identified as the peak frequency of the object. The reason why the threshold value is made to depend on the measured power is to limit the number of objects to be identified to a certain fixed number to facilitate confirmation. Furthermore, this threshold is averaged over time. In the temporal averaging of the threshold value, when the power of the peak frequency having the maximum power changes, the threshold value changes. In other words, the peak frequency of other powers is affected by the fluctuation of the maximum power, even if there is no change in its own power, and it becomes an object of identification, becomes unstable, or becomes unstable. This is to prevent stability. Temporal averaging of the power at the peak frequency to average the threshold is performed using a low pass filter. As a result, those with large fluctuations in the maximum power are excluded from the formation of the threshold. In this way, the threshold value is stabilized so that the target does not suddenly appear or be removed due to the change in the threshold value, thereby preventing unstable display.

[0004]

In the above inter-vehicle distance measuring apparatus, for example, when the own vehicle is traveling at a low speed, the level of the received signal changes slowly, but when the own vehicle is traveling at a high speed. In this case, the level of the received signal greatly changes, and accordingly, the power of the peak frequency greatly changes. The cutoff frequency of the low-pass filter is commonly used in high-speed running and low-speed running. For this reason,
In the case of high-speed running, there is a problem that threshold stability is lower than in the case of low-speed running.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an inter-vehicle distance measuring apparatus which can stabilize a threshold value at the same level as in the case of low-speed running even during high-speed running.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a vehicle-mounted distance measuring device having the following configuration. That is, in the first configuration, an inter-vehicle distance measuring device that measures a distance between vehicles from a peak frequency obtained by frequency-analyzing a millimeter-wave radar signal detects a power-dependent threshold index corresponding to the peak frequency. In order to form a threshold by controlling a time-dependent change in the index of the threshold with respect to the fluctuation of the power, the cut-off frequency is reduced as the speed of the vehicle increases from low to high. And a peak frequency detecting means for detecting a peak frequency having a power exceeding a threshold value formed by the low-pass filter. In addition to directly depending on the speed of the own vehicle, a plurality of conditions, that is, the relative speed with the vehicle in front, the relative distance with the vehicle in front, the acceleration of the own vehicle,
Using any one of the relative acceleration with the vehicle in front, the rotation angle by the steering angle sensor, the rotation angle by the yaw rate, the number of vehicles in front, and the ratio of the presence or absence of the vehicle in front within a certain period of time, the speed of the own vehicle The filter coefficient of the low-pass filter is made variable so that the cutoff frequency decreases as the speed increases from low to high.

In the second configuration, an inter-vehicle distance measuring device that measures a distance between vehicles from a peak frequency obtained by frequency-analyzing a millimeter-wave radar signal is provided with an index of a threshold value depending on power corresponding to the peak frequency. In order to form a threshold by controlling the time-dependent change of the threshold index with respect to the fluctuation of the power, the cutoff frequency decreases as the speed of the host vehicle increases from low to high. A plurality of low-pass filters, selecting means for selecting one from the plurality of low-pass filters according to the speed of the vehicle, and one of the plurality of low-pass filters selected by the selecting means. And a peak frequency detecting means for detecting a peak frequency having a power exceeding a threshold value formed based on the peak frequency. In addition to directly depending on the speed of the own vehicle, there are a plurality of conditions, that is, the relative speed with the vehicle in front, the relative distance with the vehicle in front, the acceleration of the own vehicle, the relative acceleration with the vehicle in front, the steering angle sensor. Using any one of the rotation angle according to the yaw rate, the rotation angle according to the yaw rate, the number of preceding vehicles, and the ratio of the presence or absence of the preceding vehicle within a certain time, the cutoff frequency decreases as the speed of the own vehicle changes from low to high. In this case, a plurality of low-pass filters are provided. Then, the magnitude of the relative speed with the vehicle in front, the magnitude of the relative distance with the vehicle in front, the magnitude of the acceleration of the own vehicle, the magnitude of the relative acceleration with the vehicle in front,
Multiple low-passes according to any one of the magnitude of the rotation angle by the steering angle sensor, the magnitude of the rotation angle by the yaw rate, the number of vehicles in front, and the ratio of the presence or absence of vehicles in front within a certain time Select a filter.

In the third configuration, an inter-vehicle distance measuring device that measures a distance between vehicles from a peak frequency obtained by frequency-analyzing a millimeter-wave radar signal is provided with an index of a threshold value dependent on power corresponding to the peak frequency. An index detecting means for detecting a threshold, and a plurality of conditions dividing a condition for changing the speed of the own vehicle from a low speed to a high speed in order to form a threshold by controlling a temporal change of the threshold index with respect to the fluctuation of the power. Each of the groups has a low-pass filter, and the filter coefficient is changed according to one condition of each of the plurality of condition groups, that is, the filter coefficient is reduced so that the cutoff frequency decreases as the speed of the own vehicle changes from low to high. A plurality of low-pass filters, a selecting unit for selecting one from the plurality of low-pass filters according to one of the plurality of condition groups, and the plurality of low-pass filters selected by the selecting unit. Peak frequency detection means for detecting a peak frequency having a power exceeding the threshold value to be formed on the basis of one of the pass filter is provided. At least one of the plurality of low-pass filters includes one of the plurality of condition groups.
As one condition, in addition to directly depending on the speed of the own vehicle, a plurality of conditions, that is, the relative speed with the vehicle in front, the relative distance with the vehicle in front, the acceleration of the own vehicle, the relative acceleration with the vehicle in front, Using any one of the rotation angle detected by the steering angle sensor, the rotation angle determined by the yaw rate, the number of vehicles in front, and the ratio of the presence or absence of the vehicle in front within a certain period of time, cut as the speed of the vehicle changes from low to high. The filter coefficient of the low-pass filter is made variable so that the off-frequency becomes small. Then, the magnitude of the relative speed with the vehicle in front, the magnitude of the relative distance with the vehicle in front, the magnitude of the acceleration of the own vehicle, the magnitude of the relative acceleration with the vehicle in front,
Multiple low-passes according to any one of the magnitude of the rotation angle by the steering angle sensor, the magnitude of the rotation angle by the yaw rate, the number of vehicles in front, and the ratio of the presence or absence of vehicles in front within a certain time Select one from the filters.

[0009]

According to the inter-vehicle distance measuring apparatus of the present invention, in order to form the threshold value by controlling the temporal change of the index of the threshold value with respect to the fluctuation of the power, in the first configuration, the speed of the own vehicle is low. As the vehicle speed increases, the cutoff frequency of the lowpass filter decreases, that is, the averaging time constant increases, as the vehicle speed increases. . For this reason, it is possible to stabilize the threshold of the degree of identification as compared with the case of low-speed running even during high-speed running. As a result, even when the vehicle is traveling at low speed or traveling at high speed, the object can be secured without being removed or added due to a problem in data processing.

Further, in the second configuration, one of the plurality of low-pass filters having different cutoff frequencies and one of the plurality of low-pass filters is selected according to the running condition of the vehicle, and the speed of the own vehicle is selected. And the selection means for selecting one of the selected cutoff frequencies so as to decrease as the speed increases from low speed to high speed.
The same operation and effect as those of the configuration can be obtained, but the responsiveness can be particularly improved.

Further, in the third configuration, a low-pass filter is provided in each of a plurality of condition groups that divide the condition of the speed of the vehicle from low speed to high speed, and one condition of each of the plurality of condition groups is provided. A plurality of low-pass filters that vary the filter coefficient so that the cutoff frequency decreases as the speed of the vehicle increases from low to high, and a plurality of low-pass filters according to one of the plurality of condition groups. With the selection means for selecting one of the low-pass filters, the same operation and effect as those of the first configuration can be obtained, the responsiveness is good, and the scale can be made appropriate.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating threshold value determining means in a vehicle distance measuring device according to a first embodiment of the present invention. As shown in the figure, the threshold value determining means is provided in the processing unit 4 of FIG. 20, and is provided with a fast Fourier transform unit 100 (FFT) for inputting a beat signal from the mixer 3. In the subsequent stage of the fast Fourier transform unit 100, a threshold index detecting means 10 is provided.
1 is provided. As described above, the threshold index detecting means 101 detects about half of the power of the peak frequency having the maximum power as the threshold index from the result of the frequency analysis. Also, when there are multiple peak frequencies,
The average of the power of the peak frequency in the half order from the largest power is detected as the index of the threshold. A low-pass filter 102 having a variable cutoff frequency is provided at a stage subsequent to the threshold index detecting means 101. The characteristic changing unit 103 changes the cut frequency of the low-pass filter 102. The condition determining unit 104 inputs a plurality of vehicle conditions and determines a change in the characteristics by the characteristic changing unit 103 based on the conditions. The conditions for this multiple vehicle include:
Own vehicle speed, relative speed to the vehicle in front, relative distance to the vehicle in front, acceleration of the own vehicle, relative acceleration to the vehicle in front, steering angle sensor, rotation angle by yaw rate, number of vehicles in front There are conditions such as the ratio of the presence or absence of a preceding vehicle within a certain time.

Further, the peak frequency detecting section 105 includes a threshold from the low-pass filter and the fast Fourier transform section 10.
A peak frequency from 0 and its power are input, and a peak frequency exceeding a threshold is detected. Then, the above equation (1)
The distance R and the relative speed v are obtained based on (4), and output to the display unit 5. FIG. 2 is a diagram illustrating the configuration of the low-pass filter 102 and the configuration of the characteristic changing unit 103 in FIG.
As shown in FIG. 2A, the low-pass filter 102
It is composed of a second-order IIR (Infinite Impulse Response) digital filter, and the coefficients a0, a of the digital filter
1, a2, b1, b2 are constants for determining the characteristics of the filter as described below, and by changing these, the filter can be changed.

A0 = 1 / (1 + 1 / ω0) a1 = a2 b1 = (− 1 + 1 / ω0) / (1 + 1 / ω0) a2 = b2 = 0 ω0 = tan (π · fd / fs) where fd is a filter And the cutoff frequency of f
s is the reciprocal of the operation cycle of the digital filter.

In FIG. 1A, the characteristic changing means 103
Is a microcomputer 300 and a memory ROM 400
(Read Only Memory). The microcomputer 300 inputs a vehicle speed signal from the condition determining means 104. This speed signal is input to the condition determining means by a normal sensor having wheels attached. Memory ROM
400 includes, for example, filter coefficients a0, a1,
a2, b1, and b2 patterns are stored,
As shown in FIG. 4B, these filter coefficient patterns are divided into a case where the vehicle is at low speed, a case where the vehicle is at medium speed, and a case where the vehicle is at high speed. It is formed so as to be small.
The microcomputer 300 determines a low speed, a medium speed, and a high speed based on the speed signal of the vehicle, and determines the RO as follows.
A filter coefficient pattern is read from M400 to set and control the filter coefficient of the low-pass filter 102.

FIG. 3 shows the microcomputer 300 of FIG.
4 is a flowchart for explaining the control operation of FIG. In step S1, the microcomputer 300 inputs a speed signal from the condition determining means 104. In step S2, it is determined whether the speed is low.

In step S3, the above determination is made as "Y E
If "S", a low-speed filter coefficient is selected from the ROM 400, and the process proceeds to step S7 described later. In step S4, if the determination in step S2 is "NO", it is determined whether or not the vehicle is at the middle speed. In step S5, the determination is "YE
If "S", a filter coefficient for medium speed is selected from the ROM 400, and the process proceeds to step S7 described later.

In step S6, if the judgment in step S4 is "NO", a filter coefficient for a high-speed case is selected.
The process proceeds to step S7 described below. In step S7, the filter coefficient is changed and set to the low-pass filter 102.
The above is the change setting of the filter coefficient according to the speed of the own vehicle. However, the present invention is not limited to this, and the speed information may be obtained from the following parameters.

As a first modified example, the filter coefficient of the low-pass filter 102 is updated and set based on the relative speed with respect to the vehicle ahead in place of the own vehicle speed. The relative speed obtained by the above equation (4) may be used. In this case, the update setting is performed so that the cutoff frequency of the low-pass filter decreases as the relative speed decreases. This is because when the relative speed is high, the own vehicle is in a low-speed running state, and when the relative speed is low, the own vehicle is in a high-speed running state.

Further, as a second modification, the filter coefficient of the low-pass filter 102 is updated and set based on the relative distance to the vehicle ahead in place of the own vehicle speed. The relative speed obtained by the above equation (3) may be used. In this case, the update setting is performed so that the cutoff frequency of the low-pass filter decreases as the relative distance increases. This is because when the relative distance is small, the own vehicle is traveling at a low speed, and when the relative distance is large, the own vehicle is traveling at a high speed.

Further, as a third modified example, the low-pass filter 10 is changed by the acceleration of the own vehicle instead of the speed of the own vehicle.
The filter coefficient of 2 is updated and set. The acceleration obtained by the throttle opening signal may be used. In this case, the update setting is performed such that the cutoff frequency of the low-pass filter 102 decreases as the speed of the own vehicle increases as the acceleration decreases. further,
As a fourth modification, the filter coefficient of the low-pass filter 102 is updated and set in accordance with the relative acceleration with respect to the vehicle ahead in place of the host vehicle speed in the same manner as described above. The relative acceleration obtained by the time change of the relative speed may be used.

Further, as a fifth modification, a low-pass filter 10 is used in accordance with the rotation angle of the own vehicle instead of the own vehicle speed.
The filter coefficient of 2 is updated and set. The rotation angle obtained by the steering angle sensor may be used. In this case, the cutoff frequency of the low-pass filter 102 is reduced as the rotation angle decreases. This is because when the rotation angle is large, the own vehicle is traveling at low speed, and when the rotation angle is small, the own vehicle is traveling at high speed.

Further, as a sixth modification, the filter coefficient of the low-pass filter 102 is updated and set in accordance with the rotation angle of the vehicle based on the yaw rate of the vehicle in place of the vehicle speed in the same manner as described above. This yaw rate is obtained by a yaw rate sensor that detects the rotational angular velocity of the vehicle in the vertical axis direction. Further, as a seventh modified example, the filter coefficient of the low-pass filter 102 is updated and set based on the number of vehicles ahead within a predetermined time recognized by the present apparatus, instead of the vehicle speed. In this update setting, when the number of vehicles in front is large, it is determined that the vehicle speed is low because there is a traffic jam, and when the number of vehicles in front is small, it is determined that the vehicle speed is high because there is no traffic jam. Then, the cutoff frequency of the low-pass filter 102 is reduced as the number of vehicles ahead decreases.

Further, as an eighth modification, the filter coefficient of the low-pass filter 102 is updated and set based on the ratio of the presence or absence of a preceding vehicle within a predetermined time recognized by the present apparatus, instead of the own vehicle speed. In this update setting, when the ratio of the vehicles in front is high, the vehicle speed is low because the traffic is in a congestion state, and when the ratio of vehicles without the front vehicles is low, the vehicle speed is high because there is no traffic in the congestion state. It is determined that the cutoff frequency of the low-pass filter 102 becomes smaller as the proportion of the preceding vehicle gradually decreases.

Further, as a ninth modification, the filter coefficient of the low-pass filter 102 is changed according to the conditions obtained by combining the first embodiment and the first to eighth modifications. Make the update settings as follows. FIG. 4 is a diagram showing an example in which a plurality of conditions are combined. As shown in FIG. 3A, the microcomputer 3 of the characteristic changing unit 104
At 00, the vehicle speed signal and the relative speed signal of the vehicle ahead are input from the condition determining means 104. As shown in FIG. 3B, the ROM 400 stores filter coefficient patterns, whose cutoff frequency gradually decreases. The microcomputer 300 reads the low-pass filter 102 from the filter coefficient pattern in the ROM 400 based on the speed signal of the vehicle and the relative speed of the vehicle ahead.
Set the filter coefficient to. These filter coefficients are set, for example, by combining the vehicle speeds “low”, “medium”, and “high” with the relative speeds “low”, “medium”, and “high” of the vehicle ahead as follows. Done.

FIG. 5 shows the microcomputer 300 of FIG.
It is a figure explaining the control operation of. In step S10, the microcomputer 300 inputs a speed signal. In step S11, the microcomputer 3
00 inputs a relative speed signal.

In step S12, a filter coefficient pattern to be selected is obtained. For example, as shown in FIG. 4B, a filter coefficient pattern is selected based on the vehicle speed signals “low” and “medium” and the relative speed “low” of the vehicle.
Similarly, a filter coefficient pattern is selected based on the vehicle speed signal “high” and the vehicle relative speed “high”.

In step S13, the coefficients of the low-pass filter 102 are changed. Further, as a tenth modification, when the condition for changing the filter coefficient changes continuously for a certain period of time, a hysteresis characteristic for performing the change may be provided as follows.

FIG. 6 is a flowchart for providing the control operation of the microcomputer 300 with a hysteresis characteristic. In step S14, conditions are input. In step S15, a filter coefficient pattern corresponding to the given condition is selected.

In step S16, it is determined whether the filter coefficient pattern is the same as the set filter coefficient pattern. If this determination is "YES", the process returns to step S14 and waits. In step S17, if the above determination is "NO", it is determined whether the state where the next new filter coefficient pattern is selected has continued for a certain period of time. If this determination is "NO", the process returns to step S14 and waits.

In step S18, the above determination is made as "Y
If "ES", a new filter coefficient pattern is set. For this reason, stability is further increased at high speed running. Therefore, according to the present embodiment, as the vehicle speed increases, the cutoff frequency of the low-pass filter 102 decreases, that is, the averaging time constant increases. For this reason, it is possible to stabilize the threshold of the degree of identification as compared with the case of low-speed running even during high-speed running. As a result, the stability of identification can be ensured without suddenly removing or adding an object even at low speed traveling or high speed traveling.

In the above, a case has been described in which a plurality of cutoff frequencies are changed by changing the coefficient of one filter. However, the changing process is complicated and the response is poor. Therefore, another configuration for improving the coefficient changing process and the response will be described. FIG. 7 is a diagram for explaining a threshold value determining means in the vehicle distance measuring device according to the second embodiment of the present invention. As shown in this figure, the configuration different from that of the first embodiment of FIG. 1 is that low-pass filters each connected to a threshold index detecting means 101 and having a plurality of different cutoff frequencies,...
And a selection means for selecting a filter having any one cut-off frequency from the plurality of low-pass filter groups 106 according to a plurality of external conditions similar to the first embodiment. 107. The selecting means 107 is connected to the peak frequency detecting means 105.

FIG. 8 is a diagram showing a partial configuration showing a more specific example of the second embodiment of FIG. As shown in the figure, the low-pass filter group 106 is provided with three low-pass filters for low speed, medium speed, and high speed. The cut-off frequency of these low-speed low-pass filters decreases as the speed changes from low to high. The selection means 107 is a switch for switching the above three low-pass filters,
Controls this switching. The microcomputer 300 determines low speed, medium speed, and high speed based on the input speed signal, and performs filter selection control as described below.

FIG. 9 shows the microcomputer 300 of FIG.
4 is a flowchart for explaining the control operation of FIG. In step S21, the microcomputer 300 inputs a speed signal. In step S22, it is determined whether the speed is low.

In step S23, the above judgment is made as "Y
If "ES", a filter for a low speed is selected, and the process proceeds to step S27 described later. In step S24, if the determination in step S22 is "NO", it is determined whether or not the vehicle is at the middle speed.
If the determination is "YES" in step S25, a filter for the case of medium speed is selected, and a step S27 described later is performed.
Proceed to.

In step S26, step S24
If the determination is "NO", a high-speed filter is selected, and the process proceeds to step S27 described later. In step S27, the filter is changed. FIG. 10 shows the selecting means 1 of FIG.
It is a figure which shows the deformation of 07. As shown in this figure, the selection means 107 is replaced with the switch,
A variable multiplication means for changing the multiplication coefficient to “1” or “0” is provided for high speed, and the microcomputer 300 sets only one of these multiplication coefficients to “1” and the other to “0”. The control is performed as follows. The microcomputer 300, based on the speed signal of the vehicle, as shown in FIG.
The low-pass filter group 106 is changed.

The above is the change setting of the filter coefficient caused by the speed of the own vehicle. However, the present invention is not limited to this, and various modifications similar to those in the first embodiment according to the driving situation will be described below.
As a first modification, the selection means 107 selects the cutoff frequency of the low-pass filter group 106 as the relative speed of the vehicle with respect to the vehicle in front decreases from high speed to low speed. It is done to be.

Further, as a second modification, the selection means 107 selects the low-pass filter group as the traveling distance of the vehicle changes from a short distance to a long distance with respect to a vehicle ahead. This is performed so that the cutoff frequency of the signal 106 becomes smaller. Further, as a third modified example, the selection of the selecting means 107 is performed such that the cutoff frequency of the low-pass filter group 106 decreases as the acceleration of the own vehicle decreases as the traveling state of the vehicle increases. Further, as a fourth modified example, the selection of the selecting means 107 is performed as the relative acceleration of the traveling condition of the vehicle with respect to the vehicle in front decreases from large to small. So that the cutoff frequency of
Further, as a fifth modified example, the selection of the selection means 107 is performed by changing the low-pass filter group 106 according to the running condition of the vehicle as the rotation angle of the own vehicle by the steering angle sensor decreases. Is performed such that the cutoff frequency of

Further, as a sixth modification, the selection means 107 selects the low-pass filter group 106 as the rotation angle of the own vehicle according to the yaw rate decreases from large to small. The off-frequency is reduced. Further, as a seventh modified example, the selection by the selection means 107 is performed by changing the low-pass frequency as the number of vehicles in front of the vehicle decreases from a large number to a small number. Filter group 10
6 is performed so that the cut-off frequency of the sixth signal becomes small.

[0040] Further, as a modified example of the eighth, the selection of the selection unit 107, according to proportion the vehicle is in front of the fixed time as the travel condition of the vehicle is from the large to the small,
The dividing line as the cut-off frequency of the low pass filter group 106 is reduced. Further, as a ninth modified example, the selection by the selection means 107 is performed when the traveling state of the vehicle continuously changes for a certain period of time.

Further, as a tenth modification, the second
The low-pass filter group 106 is selected and changed as in the following example under the conditions obtained by combining the embodiment with the first to eighth modifications. FIG. 11 is a diagram illustrating an example in which a plurality of conditions are combined. As shown in FIG. 3A, the microcomputer 300 inputs a vehicle speed signal and a relative speed signal of a vehicle ahead. As shown in FIG. 6B, the low-pass filter group 106 includes filters whose cutoff frequency gradually decreases. The microcomputer 300 switches the selection means 107 as described below based on a combination of the speed signal of the vehicle and the relative speed of the vehicle ahead, and selectively changes the filter of the low-pass filter 102 as follows.

FIG. 12 shows the microcomputer 3 of FIG.
It is a figure explaining the control operation of 00. In step S30, the microcomputer 300 inputs a speed signal. In step S31, the microcomputer 300 inputs a relative speed signal.

In step S32, a filter to be selected is determined. For example, as shown in FIG.
Vehicle speed signal "low", "medium" and relative speed of vehicle "low"
, A filter is selected, and similarly, a filter coefficient pattern is selected based on the vehicle speed signal “high” and the vehicle relative speed “high”. In step S33, a filter selection signal is output and the low-pass filter 10
Select and change 6.

Further, as an eleventh modification, the first
The hysteresis characteristics performed when the conditions in the modified examples to the ninth modified example are continuously changed for a certain period of time may be provided as follows. FIG. 13 is a flowchart for giving the control operation of the microcomputer 300 a hysteresis characteristic.

In step S34, conditions are input. In step S35, a filter corresponding to the given condition is selected. In step S36, it is determined whether the filter is the same as the currently set filter. If this determination is "YES", the process returns to step S34 and waits.
If the determination is "NO" in the step S37, it is determined whether or not the state where the next new filter is selected has continued for a predetermined time. If this determination is "NO", step S3 is performed.
Return to step 4 and wait.

In step S38, the above judgment is made that "Y
If "ES", a new filter is set. Therefore, the stability is further increased at high speed. Further, as a twelfth modification, the selection by the selection means 107 is performed by multiplying the output of the low-pass filter group 106 before and after switching by a weight gradually as follows.

FIG. 14 is a diagram showing an example of a configuration for gradually performing filter switching. As shown in the figure, the selecting means 107 for inputting the output of each of the filters of the low-pass filter group 106 into two is provided with a switch. ,... Are selectively selected, and each of the outputs is provided with variable multiplying means 200 and 201. The output of each of the variable multiplication means 200 and 201 is provided with an addition means 202, and the output is connected to the peak frequency detection means 105.

The microcomputer 300 controls the switching so as to switch, for example, from a filter to a filter.
The setting of the multiplication coefficients a and b of 0 and 201 is controlled as follows. FIG. 15 is a diagram for explaining control of the variable multiplication means 200 and 201 of the microcomputer 300 in FIG. The microcomputer 300 includes the variable multiplication unit 20
Weights are controlled so that the multiplication coefficients a and b of 0 and 201 change with time in the relationship shown in FIG.

[0049] Thus, according to this embodiment, according to the speed of the vehicle increases, the cutoff frequency of the low pass filter 106 is reduced, i.e., the constant is increased when the average during high-speed travel, the threshold Also changes gradually and stabilizes, and the stability of identification can be secured without suddenly removing or adding an object. Compared to the first embodiment,
Since a plurality of filters are provided for a plurality of cutoff frequencies and an arbitrary one is selected, the scale is increased, but the processing is simple and the responsiveness is improved.

Next, a description will be given of a combined configuration of the first and second embodiments in order to make the size of these filters appropriate. FIG. 16 is a diagram for explaining the threshold value determining means in the vehicle distance measuring device according to the third embodiment of the present invention. As shown in the drawing, the configuration of this embodiment is a combination of the first embodiment of FIG. 1 and the second embodiment of FIG.
A plurality of low-pass filter groups 108 including a low-pass filter, a characteristic changing unit, a condition determining unit, a condition group similar to that of the first embodiment, a low-pass filter, a characteristic changing unit, a condition determining unit, The same condition group as in the first embodiment is provided. The filter characteristics of each of the low-pass filters are varied according to the state of the vehicle, are varied so as to have mutually different characteristics, and are varied according to different conditions. Further, the condition judging means 109 for inputting the condition group,... And for inputting the external condition group x as in the first embodiment, outputs a low-pass filter,. The selection means 107 is switched to select one arbitrarily. A condition group used for changing the filter characteristic may be different from a condition group for switching the filter.

FIG. 17 is a diagram showing a partial configuration showing a more specific example of the third embodiment of FIG. As shown in the figure, the low-pass filter group 108 has two low-pass filters whose cutoff frequency is variable. These low-pass filters are composed of IIR digital filters. The characteristic change, condition judgment, characteristic change, condition judgment, and condition judgment 109 corresponding to FIG.
The microcomputer 300 has a vehicle speed, a relative distance,
Information on the ratio of the presence or absence of a preceding vehicle within a certain time is input. The microcomputer 300 of the controller determines the driving situation based on the own vehicle speed, the relative distance, and the ratio information of the presence or absence of the preceding vehicle, and changes the filter coefficient pattern of the low-pass filter and the switching of the filter as follows. Do.

FIG. 18 shows the microcomputer 3 of FIG.
It is a figure explaining the control operation of 00. In step S40, a speed signal of the own vehicle is input. In step S41, a relative distance from a preceding vehicle is input. Step S4
In step 2, ratio information indicating the presence or absence of a preceding vehicle within a predetermined time is input.

In step S43, the microcomputer 300 determines, for example, a high speed, a medium speed, and a low speed under the condition of the vehicle speed, and determines the selection of a filter coefficient for the cutoff frequency of the low-pass filter.
Under the condition of the relative distance, for example, a long distance, a medium distance, and a short distance are determined, and the selection of the cutoff frequency of the low-pass filter is determined. Further, the microcomputer 300
If there is a preceding vehicle at a certain ratio or more within a certain period of time, it is determined to switch to the low-pass filter. This is because, when there are many vehicles ahead, it is preferable to determine the threshold value based on the relative distance rather than the speed of the own vehicle.

In step S43, a filter selection signal is output to the selection means 107, and a filter coefficient is output to a low-pass filter. FIG. 19 shows R in FIG.
FIG. 4 is a diagram illustrating filter coefficients of a low-pass filter stored in OM400. As shown in FIG.
In 0, a filter coefficient pattern for a low-pass filter corresponding to the vehicle speed, low speed, medium speed, and high speed is stored, and further, a low-pass filter corresponding to a relative distance, a short distance, a medium distance, and a long distance. Filter coefficients are stored.

Hereinafter, various modifications of the switching of the low-pass filter group 108 according to the driving situation will be described. As a first modification, the filter coefficients of the plurality of low-pass filter groups 108 are variable so that their cutoff frequencies are different from each other. Further, as a second modified example, each of the filter coefficients of the plurality of low-pass filter groups 108 is variable according to the condition that the cutoff frequency is different from each other.

Further, as a third modified example, the condition for making the cutoff frequency characteristic variable for each filter coefficient of the plurality of low-pass filter groups 108 and the selecting means 1
07 is different from the switching condition. further,
As a fourth modification, at least one of the low-pass filter groups 108 has a filter so that its cutoff frequency decreases as the speed of the own vehicle changes from low to high as the running condition of the vehicle. The coefficient becomes variable.

Further, as a fifth modified example, at least one of the low-pass filter groups 108 has a cut-off frequency whose relative speed with a vehicle ahead in the running condition of the vehicle is high to low. , The filter coefficient becomes variable so as to become smaller. In addition, the sixth
As a modified example, at least one of the low-pass filter groups 108 has a cutoff frequency that becomes smaller as the relative distance of a vehicle ahead in the traveling state of the vehicle changes from a short distance to a long distance. Thus, the filter coefficient becomes variable.

Further, as a seventh modified example, at least one of the low-pass filter groups 108 has a cut-off frequency which changes as the acceleration of the own vehicle decreases from large to small as the running condition of the vehicle. The filter coefficient is variable so as to be smaller. Further, as an eighth modification, at least one of the low-pass filter groups 108 includes:
The filter coefficient is variable so that the cutoff frequency becomes smaller as the relative acceleration of the vehicle with respect to the vehicle in front of the vehicle decreases from large to small.

Further, as a ninth modified example, at least one of the low-pass filter groups 108 has a cut-off frequency whose rotation angle by the steering angle sensor of the own vehicle is large as the running condition of the vehicle. Becomes smaller, the filter coefficient becomes variable so as to become smaller. Further, as a tenth modified example, at least one of the low-pass filter groups 108 has a cutoff frequency, as the rotation angle of the own vehicle according to the yaw rate decreases from large to small as the traveling condition of the vehicle, It is variable so that it becomes smaller.

Further, as an eleventh modified example, at least one of the low-pass filter groups 108 has a cut-off frequency whose number of vehicles ahead is reduced from a large number to a small number as the traveling state of the vehicle. , The filter coefficient is variable so as to be smaller. Further, as a twelfth modification, at least one of the low-pass filter groups 108 has a cut-off frequency whose ratio of a vehicle in front within a certain time as a running condition of the vehicle is reduced from large to small. As the filter coefficient becomes smaller, the filter coefficient becomes variable so as to become smaller.

Further, as a thirteenth modification, at least one of the low-pass filter groups 108 has its cutoff frequency changed from the fourth modification to the twelfth modification.
When the running condition of the vehicle in the modified example of the above changes continuously for a certain period of time, the filter coefficient becomes variable. Next, various modifications of the selection by the selection unit 107 according to the driving situation will be described.

As a first modification, the selection means 10
The selection of 7 is performed such that the cutoff frequency of the low-pass filter group 108 decreases as the relative speed of the vehicle with respect to the vehicle in front decreases from high speed to low speed. Further, as a second modified example, the selection of the selection means 107 is performed by cutting the low-pass filter group 108 as the relative distance of the traveling condition of the vehicle from a vehicle in front of the vehicle changes from a short distance to a long distance. This is performed so that the off-frequency becomes small.

Further, as a third modification, the selection means 107 selects the cut-off frequency of the low-pass filter group 108 as the acceleration of the vehicle changes from large to small as the running condition of the vehicle. Further, as a fourth modified example, the selection of the selecting means 107 is performed as the relative acceleration with respect to the vehicle ahead in the traveling state of the vehicle decreases from large to small. To reduce the cutoff frequency of the filter group 108,
Further, as a fifth modified example, the selection by the selection means 107 is performed by changing the low-pass filter group 108 as the rotation angle of the own vehicle as measured by the steering angle sensor becomes smaller. Is performed such that the cutoff frequency of

Further, as a sixth modification, the selection of the selection means 107 is performed by cutting the low-pass filter group 108 as the rotation angle of the own vehicle according to the yaw rate decreases from large to small. The off-frequency is reduced. Further, as a seventh modified example, the selection by the selection means 107 is performed by changing the low-pass frequency as the number of vehicles in front of the vehicle decreases from a large number to a small number. Filter group 10
8 is performed so that the cutoff frequency becomes smaller.

Further, as an eighth modification, the selection of the selection means 107 is performed in such a manner that the ratio of the presence of the preceding vehicle within a certain time as the running condition of the vehicle changes from large to small.
The processing is performed so that the cutoff frequency of the low-pass filter group 108 is reduced. Further, as a ninth modified example, the selection by the selection means 107 is performed when the traveling state of the vehicle continuously changes for a certain period of time.

Further, as a tenth modification, the second
The low-pass filter group 108 is selectively changed as in the above-described example, under the conditions obtained by combining the embodiment with the first to eighth modified examples. Further, as an eleventh modification, the hysteresis characteristic performed when the conditions in the first to tenth modifications continuously change for a certain period of time may be provided as described above .

Further, as a twelfth modification, the selection of the selecting means 107 is gradually performed by multiplying the output of the low-pass filter group 108 before and after the switching by a weight. Therefore, according to the present embodiment, as the speed of the vehicle increases, the cutoff frequency of the low-pass filter 106 decreases, that is, the time constant of the averaging becomes large during high-speed running, so that the threshold also changes gradually. Therefore, the stability of the identification can be ensured without removing or adding the object. Compared to the second embodiment, and to allow changes characteristics for filters, and reduce a size is increased while securing the responsiveness.

[0068]

As described above, according to the present invention, in order to form the threshold value by controlling the temporal change of the index value of the threshold value with respect to the fluctuation of the power, as the speed of the own vehicle changes from low to high, Since the low-pass filter that reduces the cut-off frequency is provided, as the speed of the vehicle increases, the cut-off frequency of the low-pass filter decreases, that is, the time constant of averaging increases. For this reason, it is possible to stabilize the threshold of the degree of identification as compared with the case of low-speed running even during high-speed running. This allows
Even at low speeds and high speeds, stable identification can be ensured without suddenly removing or adding objects. In addition, a plurality of low-pass filters having different cutoff frequencies, and one of a plurality of low-pass filters is selected according to the traveling state of the vehicle, and is selected as the speed of the own vehicle increases from low to high. Further, since the selection means for selecting such one of the cut-off frequencies is reduced, the responsiveness can be further improved. In addition, each of a plurality of condition groups that divide the condition of increasing the speed of the own vehicle from low speed to high speed has a low-pass filter, and according to one condition of each of the plurality of condition groups, that is, the speed of the own vehicle is increased. Select one from a plurality of low-pass filters that vary the filter coefficient so that the cutoff frequency decreases as the speed increases from low to high, and a plurality of low-pass filters according to one of each of a plurality of condition groups Since the selection means is provided, not only the responsiveness but also the scale can be made appropriate.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a threshold value determining unit in an inter-vehicle distance measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a low-pass filter 102 and a configuration of a characteristic changing unit 103 in FIG.

FIG. 3 is a flowchart illustrating a control operation of the microcomputer 300 of FIG. 2;

FIG. 4 is a diagram showing an example in which a plurality of conditions are combined.

FIG. 5 is a flowchart illustrating a control operation of the microcomputer 300 of FIG. 4;

FIG. 6 is a flowchart for giving a hysteresis characteristic to the control operation of the microcomputer 300.

FIG. 7 is a diagram illustrating a threshold value determining unit in the following distance measuring apparatus according to the second embodiment of the present invention.

8 is a diagram showing a partial configuration showing a more specific example of the second embodiment in FIG. 7;

9 is a diagram illustrating a control operation of the microcomputer 300 in FIG.

FIG. 10 is a diagram showing a modification of the selection means 107 of FIG.

FIG. 11 is a diagram showing an example in which a plurality of conditions are combined.

12 is a diagram illustrating a control operation of the microcomputer 300 in FIG.

FIG. 13 is a flowchart for giving a hysteresis characteristic to the control operation of the microcomputer 300.

FIG. 14 is a diagram showing a configuration for gradually performing filter switching.

15 is a diagram illustrating control of variable multiplication means 200 and 201 of microcomputer 300 in FIG.

FIG. 16 is a diagram illustrating threshold value determining means in the following distance measuring apparatus according to the third embodiment of the present invention.

FIG. 17 is a diagram showing a partial configuration showing a more specific example of the third embodiment in FIG. 16;

18 is a flowchart illustrating a control operation of the microcomputer 300 in FIG.

19 is a diagram illustrating filter coefficients of a low-pass filter stored in a ROM 400 of FIG.

FIG. 20 is a diagram schematically illustrating a conventional FM-CM type millimeter wave radar.

[Explanation of symbols]

 Reference Signs List 100 fast Fourier transform unit 101 threshold index detecting means 102, 106, 108 low-pass filter 105 peak frequency detecting means 107 selecting means 300 microcomputer 400 ROM

Continuation of the front page (72) Inventor Tokio Shinagawa 1-2-2, Goshodori, Hyogo-ku, Kobe-shi, Hyogo Prefecture Inside Fujitsu Ten Co., Ltd. (56) References JP-A-6-187599 (JP, A) JP-A-4 JP-A-348293 (JP, A) JP-A-4-315080 (JP, A) JP-A-3-191890 (JP, A) JP-A-59-79872 (JP, A) JP-A-58-44369 (JP, A) JP-A-57-128871 (JP, A) Patent 2788189 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S ⁷ /00-17/88 B60R 21/00 621

Claims (52)

(57) [Claims] An inter-vehicle distance measuring device for measuring a distance between vehicles from a peak frequency obtained by frequency-analyzing a millimeter-wave radar signal, comprising: a threshold for detecting an index of a threshold depending on power corresponding to the peak frequency; An index detecting means (101) for controlling a temporal change of the index of the threshold with respect to the fluctuation of the power so as to form a threshold, so that the cutoff frequency decreases as the speed of the vehicle increases from low to high. Low-pass filter (10
2) and a peak frequency detecting means (105) for detecting a peak frequency having a power exceeding a threshold value formed by the low-pass filter (102). 2. The low-pass filter (102) alternatively controls the temporal change of the threshold index with respect to the power variation to form a threshold with a vehicle ahead. 2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is variable so that the cutoff frequency decreases as the relative speed decreases from high speed to low speed. 3. The low-pass filter (102) may alternatively control the temporal change of the threshold index with respect to the power variation to form a threshold with a vehicle ahead. The inter-vehicle distance measuring device according to claim 1, wherein the filter coefficient is made variable so that the cutoff frequency decreases as the relative distance increases from a short distance to a long distance. 4. The low-pass filter (102), instead, controls the temporal change of the index of the threshold value with respect to the fluctuation of the power to form a threshold value. 2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is made variable so that the cutoff frequency becomes smaller as the distance becomes smaller. 5. The low-pass filter (102) may alternatively control the temporal change of the threshold index with respect to the power variation to form a threshold with a vehicle ahead. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is made variable so that the cutoff frequency becomes smaller as the relative acceleration becomes smaller. 6. The low-pass filter (102), instead, controls the temporal change of the index of the threshold with respect to the fluctuation of the power to form a threshold. 2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is variable so that the cutoff frequency decreases as the rotation angle of the sensor decreases from large to small. 7. The low-pass filter (102), instead, controls the temporal change of the threshold index with respect to the power fluctuation to form a threshold, and the rotation of the host vehicle at a yaw rate. 2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is made variable so that the cutoff frequency becomes smaller as the angle becomes smaller. 8. The low-pass filter (102), instead, controls the temporal change of the threshold index with respect to the power variation to form a threshold, so that the number of vehicles ahead is reduced. 2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is made variable so that the cutoff frequency becomes smaller as the number decreases from a large number to a small number. 9. The low-pass filter (102), instead, controls the temporal change in the index of the threshold value with respect to the power variation to form a threshold value. 2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the filter coefficient is made variable so that the cutoff frequency becomes smaller as the ratio of the presence of the vehicle becomes smaller. 10. The low-pass filter (102)
Instead, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, the speed of the own vehicle is changed from a low speed to a high speed, and the relative speed with the vehicle in front is high. And the relative distance to the vehicle in front of the vehicle changes from short to long, the acceleration of the vehicle decreases from large to small, and the relative acceleration to the vehicle in front decreases from large to small. The rotation angle by the steering angle sensor of the vehicle decreases from large to small, the rotation angle by the yaw rate of the own vehicle decreases from large to small, the number of vehicles in front decreases from many to few, Characterized in that the filter coefficient is made variable so that the cutoff frequency is reduced according to a combination of a plurality of conditions in which the ratio is changed from large to small,
The inter-vehicle distance measuring device according to claim 1. 11. The method according to claim 11, wherein the change of the cutoff frequency of the low-pass filter is performed when a running state of the vehicle continuously changes for a certain period of time.
An inter-vehicle distance measuring device according to any one of claims 1 to 10. 12. An inter-vehicle distance measuring apparatus for measuring a distance between vehicles from a peak frequency obtained by frequency-analyzing a millimeter-wave radar signal, comprising: a threshold for detecting an index of a threshold depending on power corresponding to the peak frequency; An index detecting means (101) for controlling a temporal change of the index of the threshold with respect to the fluctuation of the power to form a threshold, wherein a cutoff frequency decreases as the speed of the vehicle increases from a low speed to a high speed. And a plurality of low-pass filters (10) according to the speed of the vehicle.
6) a selection means (107) for selecting one of the plurality of low-pass filters (106) selected by the selection means (107); And a peak frequency detecting means (105) for detecting a peak frequency of the vehicle. 13. The plurality of low-pass filters (10).
6) Alternatively, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, a cutoff is performed as the relative speed with respect to the vehicle in front decreases from high speed to low speed. The frequency decreases, and the selecting means (107) instead selects one of the plurality of low-pass filters (106) according to the magnitude of the relative speed with respect to the vehicle in front of the vehicle. Characterized by
An in-vehicle distance measuring device according to claim 12. 14. The plurality of low-pass filters (10).
6) Instead, in order to form a threshold value by controlling the temporal change of the index of the threshold value with respect to the fluctuation of the power, the cutoff frequency becomes smaller as the acceleration of the vehicle becomes smaller. 13. The method according to claim 12, wherein the selecting means (107) instead selects one of the plurality of low-pass filters (106) according to the magnitude of the acceleration of the vehicle. The in-vehicle distance measuring device according to the above. 15. The plurality of low-pass filters (10).
6) Alternatively, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, a cutoff is performed as the relative acceleration with the vehicle in front decreases from large to small. As the frequency decreases, the selecting means (107) may instead select one of the plurality of low-pass filters (106) according to the magnitude of the relative acceleration with the vehicle in front. 13. The on-vehicle distance measuring device according to claim 12, wherein: 16. The plurality of low-pass filters (10).
6) Instead of this, in order to form a threshold value by controlling the temporal change of the index of the threshold value with respect to the fluctuation of the power, as the rotation angle of the own vehicle by the steering angle sensor decreases from large to small. Cutoff frequency becomes smaller,
Alternatively, the selecting means (107) selects one from the plurality of low-pass filters (106) according to the magnitude of the rotation angle of the own vehicle by the steering angle sensor. An in-vehicle distance measuring device according to claim 12. 17. The low-pass filter (10)
6) Instead of this, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, the cut-off frequency becomes smaller as the rotation angle of the own vehicle according to the yaw rate decreases from large to small. And the selection means (107) instead selects one from the plurality of low-pass filters (106) according to the magnitude of the rotation angle of the own vehicle according to the yaw rate. The in-vehicle distance measuring device according to claim 12, which performs the measurement. 18. The low-pass filter (10).
6) Alternatively, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, the cutoff frequency becomes smaller as the number of vehicles in front decreases from a large number to a small number. The selection means (107)
13. The in-vehicle distance measuring device according to claim 12, wherein, instead of this, one of the plurality of low-pass filters is selected according to the number of vehicles ahead. . 19. The method of claim 19, wherein the plurality of low-pass filters (10).
6) Instead of this, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, the ratio of the presence of a vehicle in front within a certain period of time decreases from large to small. The cutoff frequency is reduced, and the selecting means (107) instead selects one from the plurality of low-pass filters (106) according to the ratio of the presence of a vehicle in front within a predetermined time. The in-vehicle distance measuring device according to claim 12, characterized in that: 20. The plurality of low-pass filters (10).
6) Instead of this, in order to form a threshold by controlling the temporal change of the index of the threshold with respect to the fluctuation of the power, the ratio of the presence of a vehicle in front within a certain period of time decreases from large to small. The cutoff frequency is reduced, and the selecting means (107) instead selects one from the plurality of low-pass filters (106) according to the ratio of the presence of a vehicle in front within a predetermined time. The in-vehicle distance measuring device according to claim 12, characterized in that: 21. The method according to claim 12, wherein the selection by the selection unit is performed when a traveling state of the vehicle continuously changes for a certain period of time. Inter-vehicle distance measuring device. 22. Alternatively, the selecting means (107) may control a temporal change of the index of the threshold value with respect to the fluctuation of the power to form a threshold value. The speed increases from low to high, the relative speed with the vehicle ahead decreases from high to low, the relative distance with the vehicle ahead decreases from short to long, and the acceleration of the vehicle decreases from large to small. The relative acceleration with the vehicle in front becomes large to small, the rotation angle of the own vehicle by the steering angle sensor becomes large to small, the rotation angle of the own vehicle by the yaw rate becomes large to small, From a large number to a small number, and the plurality of low-pass filters ( 106) 13. The inter-vehicle distance measuring device according to claim 12, wherein the device is selected. 23. Instead of this, the selecting means (107) multiplies the outputs of the plurality of low-pass filters (106) before and after the switching by a weight and performs the switching gradually. An inter-vehicle distance measuring device according to claim 12. 24. An inter-vehicle distance measuring apparatus for measuring a distance between vehicles from a peak frequency obtained by frequency-analyzing a millimeter-wave radar signal, comprising: a threshold for detecting a power-dependent threshold index corresponding to the peak frequency; An index detecting means (101); and a plurality of condition groups for dividing a condition for changing the speed of the own vehicle from a low speed to a high speed in order to form a threshold by controlling a temporal change of the threshold index with respect to the power fluctuation. Have a low-pass filter, and make the filter coefficient variable according to one condition of each of the plurality of condition groups, that is, so that the cutoff frequency decreases as the speed of the own vehicle changes from low to high. A plurality of low-pass filters (108); and a selecting means (107) for selecting one from the plurality of low-pass filters (108) according to one of the plurality of condition groups.
And a peak frequency detecting means (105) for detecting a peak frequency having a power exceeding a threshold formed based on one of the plurality of low-pass filters (108) selected by the selecting means (107). An inter-vehicle distance measuring device comprising: 25. The plurality of low-pass filters (10).
8) At least one of the plurality of condition groups is to make the filter coefficient variable so that the cutoff frequency decreases as the relative speed with respect to the vehicle in front decreases from high speed to low speed. The on-vehicle distance measuring device according to claim 24, characterized in that: 26. The low-pass filter (10).
At least one of 8) includes, as one of the plurality of condition groups, a low-pass filter that varies a filter coefficient so that the cutoff frequency decreases as the acceleration of the vehicle decreases from large to small. The on-vehicle distance measuring device according to claim 24, wherein: 27. The plurality of low-pass filters (10).
At least one of 8) is one of the plurality of condition groups, in which the filter coefficient is variable so that the cutoff frequency decreases as the relative acceleration with the vehicle in front decreases from large to small. The in-vehicle distance measuring device according to claim 24, further comprising a pass filter. 28. The low-pass filter (10).
At least one of 8), as one condition of each of the plurality of condition groups, makes the filter coefficient variable so that the cutoff frequency decreases as the rotation angle of the own vehicle by the steering angle sensor decreases from large to small. 25. The in-vehicle distance measurement device according to claim 24, further comprising a low-pass filter. 29. The plurality of low-pass filters (10).
8) At least one of the plurality of condition groups is one of the plurality of condition groups, in which the filter coefficient is variable so that the cutoff frequency decreases as the rotation angle of the own vehicle at the yaw rate decreases from large to small. The in-vehicle distance measuring device according to claim 24, further comprising a filter. 30. The plurality of low-pass filters (10).
8) At least one of the plurality of condition groups is a low-pass filter that changes a filter coefficient so that the cutoff frequency decreases as the number of vehicles in front decreases from a large number to a small number. Characterized by having
An in-vehicle distance measuring device according to claim 24. 31. The plurality of low-pass filters (10).
At least one of 8), as one condition of each of the plurality of condition groups, makes the filter coefficient variable so that the cutoff frequency becomes smaller as the ratio of the presence of the vehicle in front within a certain period of time becomes smaller. 25. The in-vehicle distance measurement device according to claim 24, further comprising a low-pass filter. 32. The plurality of low-pass filters (10).
At least one of 8), as one condition of each of the plurality of condition groups, makes the filter coefficient variable so that the cutoff frequency becomes smaller as the ratio of the presence of the vehicle in front within a certain period of time becomes smaller. 25. The in-vehicle distance measurement device according to claim 24, further comprising a low-pass filter. 33. The plurality of low-pass filters (10).
At least one of 8) is one of the plurality of condition groups, in which the speed of the own vehicle changes from low to high, the relative speed with the vehicle in front changes from high to low, and The relative distance of the vehicle changes from a short distance to a long distance, the acceleration of the own vehicle decreases from large to small, the relative acceleration with the vehicle in front decreases from large to small, and the rotation angle of the own vehicle steering angle sensor increases. From a large to a small number, the number of vehicles ahead is reduced from a large number to a small number, and the ratio of vehicles in front within a certain period of time is large to small. 25. The inter-vehicle distance measuring apparatus according to claim 24, wherein the filter coefficient is made variable so that the cutoff frequency is reduced according to the combination of the following. 34. The plurality of low-pass filters (10).
The change of at least one of the cut-off frequencies in the item (8) is variable when the running condition of the vehicle continuously changes for a certain period of time.
The inter-vehicle distance measuring device according to any one of the above. 35. The plurality of low-pass filters (10).
25. The inter-vehicle distance measuring apparatus according to claim 24, wherein the cutoff frequencies in 8) are variable so as to be different from each other. 36. The plurality of low-pass filters (10).
25. The inter-vehicle distance measuring apparatus according to claim 24, wherein each cutoff frequency of 8) is variable under different conditions. 37. The plurality of low-pass filters (10).
25. The inter-vehicle distance measuring apparatus according to claim 24, wherein the condition for changing the cutoff frequency characteristic in 8) is made different from the condition for switching the selection means (107). 38. The selecting means (107) selects one of the plurality of low-pass filters (108) according to a speed of a vehicle as one condition of each of the plurality of condition groups. An in-vehicle distance measuring device according to claim 24. 39. The selecting means (107) selects one of the plurality of low-pass filters (108) according to a relative speed with respect to a vehicle ahead as one of the plurality of condition groups. The on-vehicle distance measuring device according to claim 24, wherein: 40. The selecting means (107) selects one from the plurality of low-pass filters (108) according to one of the plurality of condition groups according to a relative distance to a vehicle ahead. The on-vehicle distance measuring device according to claim 24, wherein: 41. The selection means (107) selects one from the plurality of low-pass filters (108) according to the acceleration of the vehicle as one of the plurality of condition groups. The in-vehicle distance measuring device according to claim 24, which performs the measurement. 42. The selecting means (107) selects one of the plurality of low-pass filters (108) according to a relative addition to a vehicle ahead as one of the plurality of condition groups. The in-vehicle distance measuring device according to claim 24, characterized in that: 43. The selecting means (107) selects one of the plurality of low-pass filters (108) as one of the plurality of condition groups according to the rotation angle of the own vehicle by a steering angle sensor. The in-vehicle distance measuring device according to claim 24, wherein the device is selected. 44. The selecting means (107) selects one of the plurality of low-pass filters (108) according to a rotation angle of the own vehicle at a yaw rate as one of the plurality of condition groups. The in-vehicle distance measuring device according to claim 24, characterized in that: 45. The selection means (107) selects one from the plurality of low-pass filters (108) according to the number of vehicles ahead as one of the plurality of condition groups. The in-vehicle distance measuring device according to claim 24, wherein: 46. The plurality of low-pass filters (108) according to one condition of each of the plurality of condition groups, according to a proportion of vehicles ahead in a predetermined time.
The in-vehicle distance measuring device according to claim 24, wherein one is selected from the following. 47. The plurality of low-pass filters (108) according to one of each of the plurality of condition groups, according to a proportion of vehicles ahead in a predetermined time.
The in-vehicle distance measuring device according to claim 24, wherein one is selected from the following. 48. The method according to claim 24, wherein the selection by the selection unit is performed when one of the plurality of condition groups continuously changes for a certain period of time.
The inter-vehicle distance measuring device according to any one of the above. 49. The selecting means (107) includes: a speed of the own vehicle, a relative speed with respect to the vehicle in front, a relative distance with the vehicle in front, an acceleration of the own vehicle, a relative acceleration with respect to the vehicle in front, The plurality of low frequencies according to a combination of a plurality of conditions including a rotation angle of the own vehicle's steering rudder angle sensor, a rotation angle of the own vehicle according to a yaw rate, the number of vehicles ahead, and a ratio of presence of a preceding vehicle within a predetermined time. 26. The on-vehicle distance measuring device according to claim 24, characterized in that one of the pass filters (108) is selected. 50. The selection of the selection means (107) is such that the change of the cutoff frequency of the low-pass filter (108) is performed when the running condition of the vehicle continuously changes for a certain period of time. The inter-vehicle distance measuring device according to claim 24, characterized in that: 51. The selection of the selection means (107) is performed after a lapse of a fixed time from a change of a cutoff frequency of the low-pass filter (108).
An inter-vehicle distance measuring device according to claim 24. 52. The method according to claim 2, wherein the selection by the selection means is performed gradually by multiplying the output of the low-pass filter before and after the switching by a weight.
5. The inter-vehicle distance measuring device according to 4.