JP3360434B2 - 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 device for measuring an inter-vehicle distance between a host vehicle and a preceding vehicle, and more particularly to a technique for improving measurement accuracy.

[0002]

2. Description of the Related Art Along with recent remarkable advances in automobile technology, an inter-vehicle distance measuring apparatus which automatically measures the inter-vehicle distance between a host vehicle and a preceding vehicle while the automobile is running, and issues an alarm when the inter-vehicle distance becomes short. Is being developed. As a conventional example of such an inter-vehicle distance measuring apparatus, for example, the one shown in FIG. 8 is known.

This device calculates an inter-vehicle distance based on a measurement result of a time from when a pulse signal such as a radio wave or a laser is transmitted in front of a host vehicle to when a pulse signal reflected from a preceding vehicle is received. Is what you do.

[0004] The pulse signal transmitting means 11 transmits a pulse signal such as a radio wave or a laser toward a preceding vehicle ahead, and the reflected pulse signal receiving means 12 transmits a pulse signal such as a radio wave or a laser reflected from the preceding vehicle ahead. And converts it into an electric signal. The control means 13 controls the transmission timing of the pulse signal, and the time measurement means 14 counts and measures the time from the pulse transmission time to the reception of the reflected pulse signal based on the command from the control means 13.

FIG. 9 is a timing chart of various signals. The trigger signal (1) is a signal repeatedly output at predetermined intervals Tr. The transmission pulse signal (2) is a signal output from the pulse signal transmission unit 11 controlled by the control unit 13, and is output in synchronization with the trigger signal (1). The reception pulse signal (3) is a signal reflected and received from an external obstacle by the reflection pulse signal receiving means 12, and when the amplitude of the reception pulse signal (3) exceeds a predetermined threshold value Vth, The reflected pulse signal receiving means 12 outputs a detection signal. On the other hand, the clock pulse (4)
This is a signal for counting the time from when the pulse signal (2) is transmitted by the time measuring means 14 to when the detection signal is output, and is output at regular intervals Δt for a certain period.

However, such a conventional signal detection method has the following problems. That is, the reception output of the reflected pulse usually contains internal noise and external noise,
The threshold value for detecting the reflected pulse signal needs to be set to a relatively high value so as to prevent erroneous detection due to such noise. In general, noise may be regarded as random noise following a Gaussian distribution, and if the instantaneous amplitude of the noise is n,
As shown in FIG. 10, the probability distribution P (n) is a probability density constant having a mean value of zero and a Gaussian distribution having a variance of σ ² . Here, σ is a standard deviation. The probability density function P (n) at this time is represented by Expression (1).

[0007]

(Equation 1) In the above equation (1), σ ² corresponds to noise power, and σ corresponds to its effective value. The probability density function P (ns) when the noise as described above is added to the signal having the amplitude s is represented by the following equation (2).
It is represented by

[0008]

(Equation 2) Therefore, in order to correctly detect the reflected signal from the desired distance with a probability of 99.85%, the threshold is set to 3σ as shown in FIG.
The pulse signal output to be transmitted may be set so as to obtain a peak signal that is σ higher, that is, six times (15 to 16 dB in SN ratio) higher than the effective value σ of noise. However, in the case of radar, it is known that the level of the received signal attenuates in proportion to the fourth power of the distance from the so-called radar equation, and in order to increase the distance (detection) distance, a large output and extremely high cost are required. High special oscillation devices are required. In addition, to increase the reception intensity instead of increasing the output power, it is necessary to increase the aperture area or light reception area of the antenna, which increases both the shape and weight of the radar head, and is particularly applicable to radars for detecting the distance between vehicles. If this is attempted, there is a problem that the mountability on the vehicle is extremely poor. Furthermore, from the viewpoint of ensuring safety when the human body is irradiated, the output is limited to the safety standard or less, so that it is difficult to obtain a desired detection capability.

On the other hand, in order to detect a weak signal, Japanese Patent Publication No.
A method as shown in Japanese Patent Publication No. 2-2106 has been proposed. In this method, a received signal having a constant repetition cycle such as a Loran C signal is converted into a binary signal indicating whether the signal is positive or negative, and is sampled. After the addition and storage, the presence / absence of a signal, the S / N ratio, and the time position thereof are detected from the memory contents. The detectable S / N can be greatly improved by addition, and the detection of a weak reception signal can be performed. Will be possible.

However, the configuration of this conventional example is suitable for a case where the repetition period is relatively long, such as the Loran C signal, and the time required for signal detection can be relatively long.
There are the following problems when trying to apply to radar signal reception.

That is, since the reception intensity of the radar signal attenuates in proportion to the fourth power of the distance as described above, it is necessary to improve the sensitivity 16 times in order to double the detection distance. However, the sensitivity improvement amount by calculation is proportional to the 1/2 power of the number of additions.
^It is necessary to increase ² = 256 times. The radar pulse transmission repetition cycle must be as short as possible, but in the conventional method, the microcomputer controls the RAM memory for addition and storage, so the clock time and instruction cycle of the microcomputer determine the time required for sampling and addition. As a result, the transmission repetition period of the radar pulse is limited, and there is a limit to the improvement of high sensitivity by greatly increasing the number of additions.

Further, when the above-described radar device is applied to a rear-end collision warning device for an automobile, the following problem occurs.
That is, when an oncoming vehicle equipped with the same radar device transmits the vehicle facing the vehicle, the pulse signal transmitted from the own vehicle and the pulse signal transmitted from the oncoming vehicle interfere with each other,
Normal distance measurement may not be performed.

It is not only the pulse signal of the oncoming vehicle that impairs the normal distance measurement, but also the spark noise of the engine of the own vehicle and the noise due to the turning on and off of the power supply of electrical components such as headlights, air conditioners, and wipers. Alternatively, noise due to fluctuations in the power supply voltage, environmental changes such as changes in sunshine, entry into a tunnel, and the like may occur. That is, the noise of the own vehicle resonates with external noise, for example, to increase the detection level, and exceeds a preset threshold value. is there.

On the other hand, the applicant of the present application has filed Japanese Patent Application No. 3-171.
As shown at 380, when an alarm is issued in accordance with the proximity to the vehicle in front, not only the inter-vehicle distance but also the relative speed is required. There's a problem. That is, in general, a pulse radar can measure only the distance to the colliding object, so that it is necessary to increase the distance measurement accuracy and measure the time change rate in order to accurately determine the relative speed. In order to increase the accuracy, it is necessary to shorten the light transmission pulse width and increase the number of sampling points. However, in order to obtain a distance measuring accuracy of 1 m in a section of a distance measuring range of 130 m, for example, 130 sampling points are required for every 1 m, and it takes an extremely long time for the adding process. Further, since the light transmission pulse width needs to be about several nS, the light transmission unit becomes complicated and expensive, and there is a problem that the features of the conventional example are lost.

On the other hand, when the pulse signal transmitting means 11 is driven, the duty ratio of the pulse is reduced in order to ensure the durability and reliability of the light emitting element. I will. Naturally, shortening the repetition time of the light transmission pulse and speeding up the distance measurement will decrease the durability and reliability of the light emitting element. Conversely, increasing the repetition time of the light transmission pulse will speed up the distance measurement. Will be harmed.

Therefore, in order to solve such a problem,
The one described in Japanese Patent Application No. 6-146752 filed by the present applicant has been proposed.

FIG. 5 is a block diagram showing the configuration of the apparatus described in Japanese Patent Application No. 6-146755, in which a distance sensor head 1 mounted on a front portion of a vehicle and a signal processing section 3 are shown.
And an inter-vehicle distance calculation unit 2. The distance sensor head 1 transmits an optical pulse toward a vehicle ahead.
D, LD, etc., a transmission circuit 4 for supplying a drive voltage to the transmission unit 4, a reception circuit including a photodiode for receiving light pulses reflected by a preceding vehicle in time series, and the like. It comprises a unit 6 and a signal amplifying circuit 7 for amplifying a received analog optical pulse.

The signal processing section 3 converts the amplified analog optical pulse signal into a digital signal, and further samples this digital signal at a predetermined sampling cycle.
The synchronous addition value of the time-series data for each transmission of the optical pulse is counted.

The inter-vehicle distance calculation unit 2 includes the signal processing circuit 3
Is obtained from the synchronous addition value obtained in (1), and the inter-vehicle distance is obtained based on this time and the propagation speed of the transmitted optical pulse.

The operation will be described below. First,
Light emitting diode (LED) and laser diode (LD)
The optical pulse is directed forward from the transmitting unit 4 composed of an optical semiconductor device such as a predetermined pulse width (for example, 130 ns).
c) and a predetermined number of transmissions within a predetermined period of time at a pulse interval (for example, 6 μsec), and the reflected light from the vehicle ahead is received by the receiving unit 6 including a light receiving element such as a photodiode (PD). FIG. 6 shows a flow of signal processing from reception of reflected light to distance calculation.

FIG. 2A shows the analog level of the received pulse signal, and the signal value is increased at the portion indicated by P1 in the figure. That is, since the horizontal axis is time t,
It can be expected that a vehicle ahead is present at a distance corresponding to this time (the speed of the light pulse is known, so that the distance can be obtained by time and speed). Also, FIG.
3 is a diagram in which the analog signal shown in FIG. 3 is converted into a digital signal. The portion corresponding to S1 is "1", and the other portions repeat "1" and "0" vibrations.

FIG. 2C shows data obtained when the digital signal shown in FIG. 1B is sampled at a sampling period Δt, and this data is obtained by the number of times of distance measurement. FIG. 4D shows a synchronous addition result obtained by adding the sampling data.

First, the amplitude-amplified reception signal shown in (a) is binarized into "0" and "1" by comparison with a predetermined reference value, and becomes digital data as shown in (b). The signal obtained is converted to a certain period Δt (for example, 67 nsec:
By sampling at a distance of 10m),
As shown in (c), digital data of a predetermined number of bits is obtained. This operation is performed a large number of times (for example, 8192 times) during one distance measurement, and a plurality of digital data groups (for example, 8192 times) consecutive in time obtained during each operation are synchronously added. The characteristic of the added value level with respect to the distance shown in (d) can be obtained. Based on this added value level characteristic, for example, as disclosed in Japanese Patent Application No. 5-233091, four surrounding points (v1 to v4) including a sampling point at which the added value becomes a peak are divided into two sets, and the two points of each set are connected. The distance is calculated from the intersection of the straight lines.

[0024]

However, the apparatus described in Japanese Patent Application No. 6-146755 has the following improvements. That is, since the signal intensity is too strong especially at the time of detecting a short distance, FIG.
In the diagram shown in FIG. 5, the sum at the peak sampling point is substantially equal to the total number of times of addition (for example, 8192 times) (addition value saturation), and as a result, the sum is obtained from the method described above, that is, from the intersection of two straight lines. The value of the distance may cause an error with respect to the actual distance, and the distance may not be measured accurately. That is, FIG.
If the sampling point is saturated as shown in (b), the method shown in FIG. 6D cannot be used.
Conversely, even when the light receiving signal is weak, the distance detection accuracy is reduced due to the deterioration of the S / N ratio. To solve such a problem, a method of controlling the added value to an optimum value by changing the light transmission power or changing the amplification degree of the receiving circuit after one distance measurement is completed can be considered. . However, in this method, each distance measurement (about 50 msec: 6 μsec × 81)
(For example, 92 times), the transmission power or amplification control can be performed. For example, when the added value is saturated or the distance calculation is not enough, the distance cannot be calculated in the current distance measurement. At least about 50 msec after the control, the distance cannot be obtained. Further, if the power or the amplification degree cannot be controlled to the optimum value at one time, a time delay will be caused in obtaining a further distance. If the distance measurement is delayed in this way, for example, when this radar is used in an inter-vehicle distance warning device, the determination of a warning is delayed, and the generation of a warning lacks timeliness.

The present invention focuses on such a conventional problem. In the course of one distance measurement, the distance measurement is temporarily interrupted, and the total number of additions up to that point and the added value which becomes a peak are obtained. To determine whether the added value is saturated or insufficient, and if it is saturated or insufficient at that time, it is added even when distance measurement is completely terminated. It is predicted that the value will be saturated or insufficient, and even if the distance measurement is in progress, the distance measurement is terminated and the transmitted light power or the amplification degree of the receiving circuit is changed, so that the added value is saturated or insufficient. It is an object of the present invention to solve the above-described problem that a delay occurs in the time until distance data is acquired by the above method.

[0026]

In order to achieve the above object, the present invention provides a transmitting means for repeatedly transmitting a predetermined pulse signal toward the front of a vehicle, and a reflection means for reflecting the pulse signal by an object located ahead. Receiving means for receiving a signal, amplifying means for amplifying the received reflected signal, data converting means for converting the signal amplified by the amplifying means into digital data, sampling the digital data at a predetermined cycle, and A time-series data generating means for forming the time-series data, a synchronous addition means for synchronously adding the time-series data a predetermined number of times consecutively, and a synchronous addition value from the peak value of the synchronous addition value by the synchronous addition means to the object. Distance calculating means for calculating the distance between the two, and extracting the peak value from the intermediate result before the synchronous adding means completes the predetermined number of synchronous additions. Means, determining means for determining whether or not the peak value extracted by the extracting means is within a predetermined range, and gain control for controlling the gain of the amplifying means based on the determination result by the determining means. And means.

[0027]

According to the present invention constructed as described above, when the number of times of distance measurement becomes a predetermined number (for example, half of the total number), the distance measurement is temporarily interrupted and the synchronous addition value of the time-series data is checked. I do. When the synchronous addition value exceeds a predetermined range and becomes equal to or more than the upper limit value, the amplification factor of the amplifying means is reduced to reduce the number of measurement pulses, thereby preventing the saturation of the synchronous addition value. When the value falls below the predetermined range and falls below the lower limit, the amplification factor of the amplifying means is increased to increase the synchronous addition value. That is, before the total number of distance measurement ends, it is determined whether the synchronous addition value is too large or too small, and the amplification factor of the amplifying means is adjusted. Therefore, there is no large time delay in measuring the distance to the vehicle ahead.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an inter-vehicle distance measuring apparatus according to one embodiment of the present invention. The inter-vehicle distance measuring device shown in the figure is the same as the conventional device shown in FIG. 5 in that it comprises a distance sensor head 1, an inter-vehicle distance calculating unit 2 and a signal processing unit 3, but the distance sensor head 1 Has an amplification factor control circuit 8. That is, the configuration of the amplification factor control circuit 8 will be described, and other description will be omitted.

The amplification factor control circuit 8 is composed of, for example, a variable amplification factor amplifier and controls the amplification factor of the signal amplification circuit 7 under the control of the following distance calculation unit 2.

Next, the operation of this embodiment will be described with reference to the flowchart shown in FIG.

First, the addition number data N is cleared to 0 (S1). When the distance measurement is started (S2), 1 is added to the number-of-additions data N (S3), and light is directed forward from the light transmitting unit 4 to a predetermined pulse width (for example, 130 nsec) and a pulse interval (for example, 6 μsec). (S4), and the reflected light from the target is received by the receiving unit 6 including a light receiving element such as a photodiode (PD) (S5). The flow from the reception of the reflected light to the addition processing will be described with reference to FIG.
First, the amplitude-amplified analog reception signal shown in FIG. 3A is changed to “0” and “1” by comparison with a predetermined reference value.
The digital signal is converted into a digital signal as shown in (b), and the binarized signal is sampled at a certain fixed period Δt (for example, 67 nsec: equivalent to a distance of 1 m), so that a digital signal having a predetermined number of bits shown in (c) is obtained. Get the data. This operation is performed many times during one distance measurement (for example, 8192/2).
Times), and a plurality of (for example, 8192/2) digital data groups that are temporally continuous and obtained during each operation are synchronously added (S6). The total number of additions in this embodiment is eight.
192 times, but just at the midpoint, 4096 (=
At the time when the addition has been completed (8192/2) times (repeated from S3 to S7), the distance measurement is temporarily stopped (S8), and the added peak value Pk is obtained.
Is inspected (S9). Here, the distance measurement is interrupted at the intermediate point. However, the distance measurement may be interrupted, for example, when a quarter is completed, that is, at the time when 2048 (= 8192/4) times are added. Step S1
At 0, it is determined whether Pk exceeds 3950 (= 7900/2). When Pk exceeds 3950, after the addition of 8192 times, which is the end of distance measurement, there is a high possibility that the added value will be saturated or infinitely close (added value exceeds 7900), so the added value at four sampling points will be high. In the distance calculation method using, it is not possible to calculate the distance accurately, and the process proceeds to step S11 to investigate the added value saturation point number. For example, if the saturation point number is only one as shown in FIG. If the number of saturation points is two as shown in FIG. 7B, the amplification is reduced by two steps (S1).
2), distance measurement is stopped (S13). And step S
Return to 1 and start ranging again from the beginning.

On the other hand, if Pk is 3950 or less, the process proceeds to step S14, where Pk is 2500 (= 5
000/2) is determined. FIG.
FIG. 3 illustrates a relationship between a peak addition value (Pk) and a distance calculation accuracy. For example, the required distance calculation accuracy is ± 1 m.
In the case of the following, Pk needs to be 5000 or more at the time after the completion of the addition of 8192 times (the end of the distance measurement). That is, the number of additions 4096 (= 8192/2)
If Pk is less than 2500 after the end of the measurement (after the distance measurement is interrupted), the distance cannot be calculated with high accuracy.
For example, if the added peak value Pk is 2000 to 2250, the amplification is increased by two steps, and if the added peak value Pk is 2251 to 2499, the amplification is increased by one step (S15), and the distance measurement is stopped (S1).
6). Then, the process returns to step S1, and the distance measurement is performed again. If Pk is equal to or greater than 2500, a result of addition sufficient for distance calculation can be finally expected, so that distance measurement is restarted (S17: restart from the 4097th number of additions). When the distance measurement is restarted, 1 is added to the number of additions N (S18), and the light is directed forward from the light transmitting unit to a predetermined pulse width (for example, 13).
0 nsec) and a pulse interval (for example, 6 μsec) (S19), and the light reflected from the target is received by the light receiving unit 6 (S20). A series of operations from the reception of the reflected light to the addition processing (S18 to S22) are the same as described above, and are repeated until the number of additions N reaches 8192, and when the number of additions reaches 8192, the distance measurement ends (S23). . Then, the surrounding four points including the sampling point at which the added value becomes a peak are divided into two sets, and the distance is obtained from the intersection of the straight line connecting the two points of each set (S24). Here, the distance calculation is performed by an arithmetic expression shown in the following expression (1).

[0033]

D = (v1 × 2−v2 × 1−v3 × 4 + v4 × 3) / (v1−v2−v3 + v4) (3) where D is a calculation distance, and x1 to x4 are distances at sampling points (for example, 30, 40, 50, 60m), v1
To v4 are added values at sampling points x1 to x4 (see FIG. 6D). After completing the distance calculation,
The process immediately returns to step S1. By doing so, even if the added value level characteristic is not suitable for distance calculation, it is possible to change to the optimum receiving circuit amplification factor in a much shorter time than in the past.

In this embodiment, when the added peak value Pk exceeds 3950 (= 7900/2) or falls below 2500 (= 5000/2), the amplification degree of the receiving circuit is changed. Although Pk is set to fall within 2500 to 3950, the light transmission power may be changed, or the compatibility between the light transmission power and the amplification degree of the receiving circuit may be changed.

[0035]

As described above, according to the present invention,
When the synchronous addition value of the time-series data becomes larger than the upper limit value, the amplification factor of the amplifying unit is reduced to decrease the synchronous addition value, thereby preventing the synchronous addition value from being saturated. If the synchronous addition value is smaller than the lower limit value, the amplification factor of the amplifying means is increased to increase the synchronous addition value.
Therefore, an effect is obtained that the distance between vehicles can always be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an inter-vehicle distance measuring apparatus according to the present invention.

FIG. 2 is a flowchart illustrating the operation of the present embodiment.

FIG. 3 is an explanatory diagram showing stages of amplification degree.

FIG. 4 is an explanatory diagram showing a relationship between a distance calculation accuracy and a peak addition value.

FIG. 5 is a block diagram showing a configuration of a conventional inter-vehicle distance measuring device.

FIG. 6 is an explanatory diagram showing a procedure up to obtaining an inter-vehicle distance from a received light pulse.

FIG. 7 is an explanatory diagram showing a synchronous addition result of time-series data.

FIG. 8 is a block diagram showing a configuration of a conventional inter-vehicle distance measuring device.

FIG. 9 is a timing chart showing a conventional operation.

FIG. 10 is a diagram showing a probability density function.

[Explanation of symbols]

1 distance sensor head 2 inter-vehicle distance calculation unit 3
Signal processing unit 4 Transmission unit 5 Drive circuit 6 Light receiving unit 7 Signal amplification circuit 8 Gain control circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-172285 (JP, A) JP-A-58-158672 (JP, A) JP-A-59-99376 (JP, A) 62883 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/64 G01S 13/00-17/95 G01C 3/00-3/32

Claims (5)

(57) [Claims] 1. A transmitting means for repeatedly transmitting a predetermined pulse signal toward the front of a vehicle; a receiving means for receiving a reflected signal of the pulse signal reflected by an object existing ahead; and amplifying the received reflected signal. Amplifying means, a data converting means for converting a signal amplified by the amplifying means into digital data, a time-series data creating means for sampling the digital data at a predetermined cycle and forming predetermined time-series data, Synchronous addition means for synchronously adding the time series data of a predetermined number of consecutive times, distance calculation means for calculating the distance to the object from the peak value of the synchronization addition value by the synchronization addition means, and the synchronous addition means Extracting means for extracting a peak value from an intermediate result before completing the predetermined number of synchronous additions; and a peak extracted by the extracting means. A distance determining means for determining whether or not the distance is within a predetermined range, and an amplification rate controlling means for controlling an amplification rate of the amplifying means based on a determination result by the determining means. apparatus. 2. The amplification factor control means, when the judgment means judges that the peak value exceeds a predetermined range, reduces the amplification factor in accordance with the magnitude of the peak value, and sets the peak value Is determined to be below the predetermined range,
2. The inter-vehicle distance measuring apparatus according to claim 1, wherein the amplification factor is increased in accordance with the magnitude of the decrease. 3. The method according to claim 1, wherein the extracting unit is configured to perform a half of the predetermined number.
3. The inter-vehicle distance measuring apparatus according to claim 2, wherein a peak value is extracted when the synchronous addition of the number of times is completed. 4. The inter-vehicle distance measuring apparatus according to claim 1, wherein the pulse signal is an optical pulse. 5. The inter-vehicle distance measuring apparatus according to claim 1, wherein the pulse signal is an ultrasonic pulse.