DE10316313A1 - Automatic distance control system - Google Patents

Abstract

For the longitudinal guidance of motor vehicles, a number of different systems are known which relieve the driver by automatic braking and acceleration interventions or increase traffic safety. The most elementary example is the cruise control, which keeps a driver-selected speed constant. At higher traffic density, however, the intervention of the driver remains necessary in order to react to slower vehicles driving ahead or changing their lane. Further developments include "intelligent cruise control", "cruise control", ICC ("intelligent cruise control"), ACC ("adaptive cruise control") or AICC ("autonomous intelligent cruise control"). The sensor principle is essentially infrared laser or millimeter-wave radar is used, which detects the area in front of the vehicle in a distance range up to 100 ... 150 m to detect there objects located and their distance, speed and angular deviation with respect to to determine your own vehicle. It is an automatic distance control, which can be realized without high technical complexity with low-cost system components proposed. In the method, an electromagnetic signal is emitted by a transmitter located on the motor vehicle and receive this signal after reflection by a sensor on the motor vehicle again. On the basis of the evaluation of the sensor signal, the following distance of the motor vehicle is then converted into a ...

Description

The The invention relates to a method and a device for automatic Distance control according to the preamble of claims 1 and 12th

For the longitudinal guidance of Motor vehicles are known a number of different systems that by automatic braking and acceleration interventions the driver relieve or increase traffic safety. Elementary example is the cruise control, which maintains a driver-selected speed comply. At higher Traffic density, however, remains the driver's intervention necessary, slower vehicles ahead or changing their lane to react.

A Further development, which has been described numerous in the literature is, added the classic cruise control by a sensor for detection ahead vehicles at their own speed to be able to adapt. designations therefor are "smarter Cruise control "," cruise cruise control "," intelligent cruise control "," ACC "(adaptive cruise control) or AICC (" autonomous intelligent cruise control "). The sensor principle is essentially infrared laser or millimeter-wave radar used to the area in front of the vehicle in a distance range detected up to about 150 m to detect there objects located and their distance, speed and angle with respect to to determine your own vehicle. Suitable evaluation methods must now the relevance of the detected objects with regard to their own lane rate. Therefor becomes common also the steering angle of the vehicle used.

• 1. Freie Fahrt mit eingestellter Geschwindigkeit, wobei der Frontbereich permanent überwacht wird, um vorausfahrende Fahrzeuge zu identifizieren;
• 2. Geregelte Folgefahrt hinter einem aufgefassten langsameren Fahrzeug, wobei der Abstand im Sinne eines Sicherheitsabstandes anzupassen ist.

The operation of an adaptive cruise control is described by two modes:

• 1. Free travel at set speed, with the front area permanently monitored to identify vehicles in front;
• 2. Regulated follow-up drive behind a slower vehicle understood, wherein the distance in the sense of a safety distance is to be adjusted.

mode 1 represents much higher Sensor requirements as Mode 2 in terms of sensitivity, spatial Resolving power and measuring accuracy, because of the high possible differential speeds Already at a distance of about 100 m, a reliable track assignment done got to. Typical measuring accuracies of the sensors used are: 0.5 m at a distance and 0.3 ° m in azimuth angle; Sensitivity: 1 sqm backscatter cross section in 150 m Distance.

At the Example of a radar sensor can be the required measurement accuracy achieve only by physical resolution. For the Azimuth angle, this means the presence of several sharply focused Antenna directions. resolution in distance sets spectral bandwidth in pulse signals or frequency modulation ahead. In addition to the high technical effort and the associated Cost also results in a considerable Size for the sensor.

A corresponding millimeter-wave radar system is from the patent US 5 680 137 A1 known. This is an automotive radar system for distance control, which can be operated both in the long-range and at close range. In the far range, the radar system is operated as an FM-CW radar to estimate the distance to a moving in front of the vehicle other vehicle by means of a runtime analysis. While the own motor vehicle approaches the vehicle in front, the actual absolute distance is continuously estimated by means of FM-CW radar method. In the event, however, that the distance to the vehicle in front is too low for a distance measurement to be sensibly carried out, the radar system changes to a phase difference mode and, based on the last measured absolute distance, considers the relative distance changes. This as long as useful again to the actually desired FM-CW radar method can be switched.

The The object of the invention is a method and an implementation of this Method to find suitable device, which allows an automatic Distance control without high technical complexity with cost-effective To realize system components.

The The object is achieved by a method and a device having the features of the claims 1 and 12 solved. Advantageous embodiments and modifications of the invention are achieved by the dependent claims described.

In the method for automatic distance control for a motor vehicle, an electromagnetic signal is emitted by a transmitter located on the motor vehicle and this signal is received again after reflection by a sensor on the motor vehicle. On the basis of the evaluation of the sensor signal, the following distance of the motor vehicle to a preceding vehicle is then adjusted to a specific one Set distance controlled. In a particularly inventive manner, the control process is initiated by a targeted activation of the distance control and this at the time of the targeted activation existing sequence distance at least initially used as a target distance. Characterized in that when activating the distance control of einzuregelnde target distance already prevails, can be dispensed in a particularly profitable manner to a complex and usually costly determination of an absolute distance of the motor vehicle to the vehicle driving this ahead. Advantageously, only the change of the distance to the vehicle in front must be measured from the time the activation of the distance control, which then serves the distance control as a controlled variable. In many situations in traffic, such as congestion, slow-moving traffic or inner-city traffic, a motor vehicle is already at the time when the driver activates the automatic distance control, in the desired desired distance to the preceding vehicle. In this case, measurement of the absolute distance to the preceding vehicle is unnecessary. It is therefore omitted in the inventive distance control on the usual in the art autonomous detection of newly appearing in the field of vision vehicles. Instead, in the event that the motor vehicle is at a desired distance from a preceding vehicle, the vehicle driver himself activates the automatic distance control to specify this distance as the desired distance. the function of the inventive system can thus be referred to as a kind of "electronic coupling rod" for the realization of automated column rides.

In Particularly advantageously, the invention provides an automatic Distance control system, which is to follow a motor vehicle solely with the measurement and observation of the relative distance to a preceding vehicle gets along. This is preferably done the emitted electromagnetic signal is considered to be substantially formed continuous signal. This is how it is done in a simple way possible, the evaluation of the sensor signal according to the Doppler sensor / Doppler radar principle perform, wherein the phase variation or the frequency offset between the Transmission signal and the reflected transmission signal (received signal) as Measure of the change the relative distance between the motor vehicle and the preceding this Vehicle is evaluated. In such a measurement in which the temporal change of the distance (ΔR / Δt) - so only a relative speed - measured is also called Range Rating. This innovative significant simplification of those known in the art Automated distance control systems allow a dramatic simplification the necessary sensors, which is particularly positive in terms on the complexity the system structure, the size and the Production costs.

Of course you can it is also the case of the substantially continuous signal a modulation oscillation modulated onto another signal act.

In particular to avoid a malfunction of the system is automatic Distance control system designed so that the control process only then can be activated when the intensity of the received from the sensor reflected signal exceeds a certain signal level. On this way it is avoided by activating too weak Sensor signal, for example, due to unfavorable reflection geometries of the preceding vehicle or poor propagation conditions for the Transmission signal (fog or rain), the control process early is aborted, because by the sensor no reflected signal more can be detected. This functionality thus also serves to increase comfort and thus the acceptance of the system by the driver.

There as described above, the successful activation of the system of certain parameters, such as the intensity intensity of the received from the sensor Signal dependent especially if the distance control system was to be designed that the leader of the motor vehicle is displayed when its distance control is activated.

Different conditions are conceivable under which the automatic distance control process is aborted. Thus, advantageously, the control process should be stopped when the reflected signal registered by the sensor drops in intensity below a certain threshold. This situation could occur, for example, when the preceding vehicle changes lane. It is also advantageous if the automatic control then hands over control of the motor vehicle completely to the vehicle driver when the setpoint distance can no longer be corrected automatically (too high acceleration or deceleration). In order to avoid malfunctions of the automatic distance control, the control process should preferably be stopped even if the determined frequency shift in the waveform between emitted and reflected signal is not continuous. Such a discontinuity could be the case, for example, by the collapse of another vehicle in the area between the motor vehicle and the vehicle originally pursued. As part of the he In the case of the inventive method, no absolute distances can be measured, the set distance can not be automatically adjusted with respect to this newly retracted vehicle.

It is also conceivable that the control process for automatic distance control is then canceled as soon as the driver of the vehicle the brake or the accelerator pedal is pressed. Such interventions in the driving operation can be regarded as signs, that the automatic distance control in the prevailing traffic situation no longer meets the driver's sense of security, so it should be better stopped.

On In any case, the driver should, especially on acoustic or optical way, about be notified of the termination of the automatic distance control, so that he can regain control of the vehicle in good time can.

There the in traffic safety distance to be maintained by vehicles in front, too strongly on the currently driven absolute speed of the vehicles depends should preferably also provide information about the automatic distance control Absolute speed of the motor vehicle are supplied. This will it is possible dependent on the change the absolute velocity to change the nominal distance, where is increased with increasing absolute speed of the desired distance.

Out security considerations the distance control system can profitably be designed that the control process is interrupted at least temporarily, when the preceding vehicle exceeds a predeterminable speed. The speed of the preceding vehicle may be known the own speed and the tracking of the changes of the relative speeds be estimated to the preceding vehicle. falls below the preceding vehicle again the predeterminable speed, It is conceivable that the automatic distance control system then the prevailing distance to this vehicle as a new nominal distance and automatically again takes the distance control. The nominal distance has then compared to the previously set by the driver set distance increases Driver is not coerced into to interfere with the control process.

to Entering the predeterminable speed can be profitable a cruise control or speed limiter already in the vehicle (Speed Limit Assistant) can be used. It is conceivable at the time of activation of the automatic distance control system the by means of cruise control or speed limiter last selected speed as a predetermined maximum speed in the distance control. Anyway should be in profitable Way the control element for activation of the inventive pitch control system in the control unit of a cruise control located in the motor vehicle to get integrated.

To the understanding The invention will be described below with reference to an implementation of Distance control system based on a millimeter-wave radar advantageous system structure will be explained in detail.

at The use of a millimeter-wave radar sensor can be assumed be that the antenna only a single spatial direction with lesser bundling must capture and thus have a small aperture. to Speed measurement is sufficient the Doppler analysis of an unmodulated continuous wave signal (, contiuous wave ', CW), which for noise reduction and increase in the immunity can be filtered very narrowband. A possible, advantageous realization Such a CW Doppler radar is very simple in terms of circuitry possible. The figure shows a corresponding circuit of such a radar frontend according to the homodyne principle, those with a single antenna and even without a circulator or duplexer gets along. The received signal has in-phase and quadrature components I and Q on to the required sign evaluation in the Doppler analysis to enable. With the adjustment elements r is the amount and phase of the coupled Oscillator signal adjusted to the necessary for the mixing 90 ° phase shift to obtain.

The Doppler analysis itself can be performed by numerical Fourier transformation (FFT) the I / Q signals occur, resulting in a gain in sensitivity accordingly the FFT block length results, or by a zero crossing counter, in which case the phase position from I and Q the counting direction pretends.

In a particularly advantageous manner, the millimeter-wave radar is designed so that it is operated in the released for automotive applications frequency range 76 ... 77 GHz. We get a Doppler frequency analysis based on a 128-point FFT. The determination of the global maximum in the magnitude spectrum of the FFT then supplies the relative speed of the vehicle ahead of the motor vehicle. With an advantageous sampling rate for the I / Q values of the received signal of 10 kHz, which satisfies the sampling theorem according to Nyquist, the relative speed can be resolved in the range of 0.08 m / s; this with a uniqueness range of +/- 10 m / s. These frame values are for use of the automatic distance control in the road ßenverkehr particularly with regard to the relative speeds and relative accelerations occurring there before geous selected. Assuming that the radar backscatter cross section associated with the motor vehicle is at least 5 dBsm and the antenna of the radar system has a gain of 25 dBi, it can be assumed that the system has a range and thus functionality for distances of up to 120 m Assuming the total system losses do not exceed 10dB. The minimum required signal-to-noise ratio for error-free detection is assumed to be 15 dB. A range of 120 m is certainly sufficient for use in traffic and is therefore an indication of the feasibility of the inventive simplification of the known from the prior art automotive distance control systems. The realization of the radar antenna advantageously has a fixed radiation characteristic of approximately 10 ° in azimuth and 5 ° in elevation and is realized profitably by a microstrip patch array.

Next The millimeter-wave radar is also suitable for other sensor principles for easy Doppler measurement. So while the short wavelengths of (IR) laser no direct Doppler analysis of the reflected laser signal practical, but the one example, sinusoidal amplitude modulation.

on the other hand It is also conceivable, for example, the emitted light a motor vehicle headlight (eg xenon headlights) to modulate with a modulation oscillation and the phase curve observe and evaluate this modulation oscillation.

The with the Doppler analysis in cyclic intervals .DELTA.t determined relative velocity v is a direct measure of the change in distance ΔR / Δt, which is immediate as the variable to be controlled for the vehicle's governor to disposal can be made to control signals for the operation of Derive brake or throttle. In the case that the preceding one Vehicle changes its speed is the - as above described - regulated distance adapt in the sense of a safety distance. This is, however only in relation to the original chosen by the driver Desired distance possible. The adaptation is based on the actual airspeed, which is available elsewhere in the vehicle (ABS, ESP, electronic Speedometer etc.). Based on a safety margin, the depends linearly on the speed ("half-speed rule"), even that of the Doppler sensor is sufficient directly supplied information about the relative velocity, since their measured change then a measure of the distance to be changed is.

Claims (15)

A method for automatic distance control for a motor vehicle, in which an electromagnetic signal is emitted by a transmitter located on the motor vehicle and this signal is received after reflection by a sensor on the motor vehicle, based on the evaluation of the sensor signal of the following distance of the motor vehicle to a this driving ahead Vehicle is controlled to a desired distance, characterized in that the control process is initiated by a targeted activation of the distance control, and that the existing at the time of the targeted activation following distance at least initially serves as a target distance. Method according to claim 1, characterized in that that the emitted electromagnetic signal is a substantially continuous one Signal is, and that the evaluation of the sensor signal after the Doppler sensor / Doppler radar principle, where the phase variation or the frequency offset between the transmission signal and the reflected transmit signal (received signal) as a measure of the change in distance is evaluated. Method according to one of the preceding claims, characterized characterized in that the control process is activated only then can if the intensity of the reflected signal received by the sensor has a certain one Exceeds signal level. Method according to one of the preceding claims, characterized that marked the leader of the motor vehicle is displayed when its distance control is activated. Method according to one of the preceding claims, characterized in that the regulation information about the Absolute speed of the motor vehicle is supplied and that in dependence the change the absolute velocity of the nominal distance is changed, being with increasing absolute speed of the desired distance is increased. Method according to one of the preceding claims, characterized characterized in that the control process is interrupted at least temporarily, when the preceding vehicle exceeds a predeterminable speed. Method according to Claim 6, characterized that the predeterminable speed by the driver of the motor vehicle Predeterminable by a cruise control or speed limiter is. Method according to claim 7, characterized in that that for the case that the control process for automatic distance control is interrupted, the speed of the usual cruise control function is regulated. Method according to one of the preceding claims, characterized characterized in that the control process for automatic distance control is canceled as soon as the driver of the vehicle the brake or the accelerator pedal is pressed. Method according to one of the preceding claims, characterized characterized in that the control process for automatic distance control is canceled when reflected by the sensor Signal in its intensity falls below a certain threshold, which is typically lower chosen is as the threshold as the threshold of claim 3 or the target distance can not be automatically compensated or the determined frequency shift in the waveform between emitted and reflected signal is not steady. Method according to claim 10, characterized in that that the driver, in particular on an acoustic or optical way, on the Information on canceling the control procedure for the automatic distance control becomes. Apparatus for operating the method according to one the claims 1 to 11 in a motor vehicle, consisting of a transmitter for emitting electromagnetic waves and a sensor for reception these waves after a reflection, in particular on a motor vehicle preceding vehicle, and consisting of a signal processing unit, for evaluating the sensor signal, based on which the following distance of the motor vehicle to a preceding this vehicle a constant desired distance is regulated, characterized that the combination of transmitter and sensor and the associated signal processing unit are designed so that only the phase variation or the frequency offset between a continuous transmit and a received signal reflected from a preceding vehicle as a measure of the change in distance can be evaluated. Device according to claim 12, characterized in that that the transmitter is designed so that the radiated from him Signal is emitted at a relatively wide opening angle. Device according to one of claims 12 or 13, characterized that the transmitter is a micro or millimeter wave transmitter is. Device according to one of claims 12 or 13, characterized that the transmitter is an infrared or visible light emit emitters.