DE102011015935A1 - Method for determining a correction value for the measurement of a target angle with a radar device, driver assistance system and motor vehicle - Google Patents

Abstract

A solution is to be shown how a correction value (γoff) for the measurement of a target angle (γ) by means of a radar device (3, 4) in a motor vehicle (1) can be determined particularly reliably and precisely during operation of the motor vehicle (1). In a method according to the invention, the radar device (3, 4) transmits a transmission signal (S0) and receives a reception signal (S1, S2). The target angle (γ) is determined based on the received signal (S1, S2) according to a predetermined measuring method, such as the phase monopulse method. An object (29) immovable with respect to an environment of the motor vehicle (1) is detected from the received signal (S1, S2), and a radial velocity (vr) of the motor vehicle (1) with respect to the mobile object (29) is measured. The current radial speed (vr) and a current airspeed (vhost) of the motor vehicle (1) are set in the ratio (vr / vhost). The correction value (γ) is determined depending on the ratio (vr / vhost). There is also provided a driver assistance system (2) as well as a motor vehicle (1).

Description

The invention relates to a method for determining a correction value for the measurement of a target angle by means of a radar device in a motor vehicle. The radar transmits a transmission signal and receives a reception signal which is the transmission signal reflected from an object. The target angle is determined based on the received signal according to a predetermined measuring method (such as phase monopulse method). The invention also relates to a driver assistance system for a motor vehicle, as well as a motor vehicle with a driver assistance system.

In the present case, the interest is particularly the phase monopulse measurement using an automotive radar device. This method serves to determine the target angle of an object and represents a known method in radar technology. For determining the target angle - angle between a reference axis extending through the radar device and a connecting line passing through the radar device and the object - according to the phase monopulse method At least two receiving antenna units, which can be two individual receiving antennas or two receiving antenna groups (arrays), are required. The signals received by the receiving antenna units are processed in two separate receiving channels and processed as digital signals by means of a computing device. The target angle is determined depending on the phase shift between the received signals of the two receiving channels. For this purpose, the relationship of the target angle and the phase difference between the phases of the received signals in the computing device is modeled, namely by a target angle phase difference characteristic (also known as "phase monopulse characteristic").

Such a radar device can be used for a driver assistance system which on the one hand serves to monitor the blind spot area of the motor vehicle and on the other hand is also used as a lane change assistant. Such a driver assistance system warns the driver of the presence of other vehicles in the blind spot area of the motor vehicle; On the other hand, the system was also ahead of vehicles that drive up to 70 m behind their own motor vehicle on the neighboring lane and soon overtake their own motor vehicle. For these applications, the driver assistance system must be able to detect vehicles that are located next to and behind the vehicle. For this purpose, two radars are installed behind the rear bumper in the prior art, namely a radar at the right corner and a radar at the left corner of the rear bumper. With the two radars, the vehicles are detected in the environment, it distance, relative speed, as well as the target angle - azimuth angle - measured. Based on all this information, the other vehicles can be tracked or it can be determined in each case the instantaneous position of these vehicles with respect to their own motor vehicle. From this it is determined whether the vehicles are within the blind spot area or the lane change area.

The lane allocation of distant vehicles requires a particularly high angle measurement accuracy of less than 1 °. For this, the installation angle of the radar device must be known exactly. However, the installation tolerances in series production can be so great that the installation angle tolerance is greater than the required angle measurement accuracy. Installation tolerances, high-frequency properties and the shape of the bumper also influence the directional characteristics of the antennas and also falsify the measurement of the target angle. In addition, the actual target angle phase difference dependency may vary over the life of the motor vehicle, for example, due to deformation of the bumper due to slight collisions often caused when parking the motor vehicle in longitudinal parking spaces. There is thus a particular challenge in correcting systematic errors, for example those which are caused by installation tolerances or else by aging of the components, during the measurement of the target angle.

The actual installation angle of the radar device should be known to the driver assistance system, so that it can determine the target position relative to the own motor vehicle from the measured target angle and the measured distance relative to the sensor coordinate system. During final assembly of the radar on the motor vehicle, the actual installation angle can be determined by means of a calibration. The actual installation angle can then be stored in a non-volatile memory of the driver assistance system. However, such calibration is relatively expensive and takes a relatively long time. Furthermore, a change in the installation angle over the life of the motor vehicle can not be detected.

Methods are already known from the prior art which are used for calibrating the target angle-phase difference characteristic during operation of the motor vehicle-that is to say while driving. The publication DE 10 2009 024 064 A1 describes a driver assistance system and a method from the house of Applicant, in which a distance of an object to the radar device and a distance of the same object are measured to a separate sensor. The target angle is calculated from these measured values by the trilateration method, and the target angle phase difference characteristic is then corrected depending on the result of this calculation.

From the document EP 1 159 638 B1 a method for adjustment detection in a motor vehicle sensor system is known in which reflected electromagnetic waves are received by a stationary object. Based on the transmitted and the received signals, a relative angle and a relative distance between the detected object and a reference axis of the motor vehicle and a relative speed of the object with respect to the motor vehicle are determined. Based on the relative angle, the relative distance and a vehicle's own speed, a correction value for the relative angle is determined. Further, a yaw rate correction value is determined from the relative angle, the correction value, the relative distance, the relative speed, the vehicle airspeed, and a yaw rate.

The publication DE 196 10 351 C2 describes a radar device for a motor vehicle in which a beam emission axis is corrected in accordance with a correction value in order to minimize an error of the beam emission axis relative to a rectilinear trajectory of the motor vehicle in the horizontal direction. To determine this correction value, the radar device transmits a transmission signal to scan a distant object in the horizontal direction.

It is an object of the invention to show a way, as in a method of the type mentioned in the correction value during operation of the motor vehicle can be determined without much effort, so that the target angle can be determined with the highest precision.

This object is achieved by a method with the features according to claim 1, by a driver assistance system having the features of claim 14, as well as by a motor vehicle having the features according to claim 15. Advantageous embodiments of the invention are the subject of the dependent claims and the description.

An inventive method is used to determine a correction offset or correction value for the measurement of a target angle by means of a radar device in a motor vehicle. The radar transmits a transmission signal and receives a reception signal. The received signal is the transmission signal reflected by a target or vehicle-external object. The target angle is determined based on the received signal according to a predetermined measuring method (such as the phase monopulse method). A stationary object relative to an environment of the motor vehicle-that is, stationary relative to the road-is detected on the basis of the received signal. A radial speed of the motor vehicle with respect to the immovable object is measured on the basis of the received signal of the radar device, and the current radial speed and a current intrinsic speed of the motor vehicle are set in relation. The correction value for the measurement of the target angle is then determined as a function of this ratio.

Thus, a basic idea of the present invention is to measure a radial velocity of an immovable, fixed object - such as an infrastructure object - with respect to the motor vehicle and measure this radial velocity with the vehicle's own speed - this is the actual speed of the motor vehicle relative to the road and can for example be measured by means of a wheel speed sensor - to put into proportion. The invention makes use of the fact that the target angle is also dependent on the radial velocity of the immovable object and on the intrinsic speed of the motor vehicle. Namely, the following relationship holds: v _host = v _r * cos (γ), where v _{host is} the airspeed, v _{r is} the radial velocity and γ is the target angle. Based on this relationship, the target angle can thus be determined independently of the actual installation angle of the radar device, so that a target angle determined therefrom can be used to determine the correction value. It is thus possible to automatically determine the correction value during operation of the motor vehicle or while driving and to calibrate the radar device. Systematic errors caused by the aging of the components as well as installation tolerances can thus be corrected and a precise determination of the target angle is ensured.

The invention is also based on the finding that the determination of the target angle according to the predetermined measuring method - such as the phase monopulse method - using a stored target angle-parameter characteristic has a low variance or low measurement noise, but with a systematic error, namely due to the aging of the components or due to the installation tolerances. On the other hand, the target angle values calculated depending on the radial velocity have a high variance, but can be considered to be on the whole faithful to expectations. The error in the calculation of the target angle as a function of the radial velocity is thus a random error - due to the accuracy of the measurement of the radial velocity - and not a systematic error. This error can be approximated to be mean free. It is thus possible to achieve very precise correction values by means of a filtering-for example an averaging-of the ratio of the radial velocity to the own velocity over a specific time and to correct the target angle parameter characteristic or to an average cosine value derived from the values of the ratio. Adjust function. There are no further parameters of the motor vehicle required here, such as the current yaw rate.

Thus, according to the predetermined measurement method, the target angle can be determined based on a parameter of the received signal based on a stored target angle parameter characteristic, and the target angle parameter characteristic can be corrected based on the correction value. This embodiment can be implemented without much effort and also allows a precise measurement of the target angle in different angular ranges.

In principle it can be provided that the radar device has a single receiving antenna unit and at least two transmitting antenna units - at least two individual transmitting antennas or at least two groups of transmitting antennas (arrays) - are used. In this case, the target angle can be determined according to the predetermined measuring method by evaluating the received signals transmitted by two independent transmitting antenna units.

However, it has proven to be particularly advantageous if the radar device comprises at least two receiving antenna units. Then, a separate receiving channel can be provided for each receiving antenna unit, in which the signals received by the associated receiving antenna unit are processed. For the determination of the target angle then signals are available in two independent receiving channels, and it can be the phase monopulse method or the amplitude monopulse method used to determine the target angle. Then, the target angle parameter characteristic is a target angle phase difference characteristic or a target angle amplitude difference characteristic. The radar device can make do with only one transmission antenna unit in this embodiment. The predetermined measuring method is therefore preferably the phase monopulse method in which the target angle is measured as a function of the phase difference between the received signals of different receiving antenna units on the basis of a stored target angle phase difference characteristic. Then, this target angle phase difference characteristic can be corrected based on the correction value. This measuring method in particular has a low measurement noise and thus ensures a very precise measurement of the target angle, in particular if the systematic error due to the aging of the components and the installation tolerances is corrected on the basis of the correction value.

Thus, the radial velocity is measured with respect to an immovable or fixed object. This immovable object may be an infrastructure object located next to a road. An object can then be classified as immovable if, with a predetermined accuracy - approximately ± 1 km / h or ± 2 km / h or ± 3 km / h or ± 4 km / h or ± 5 km / h - the current measured Radial speed is equal to a current reference radial speed, which is calculated from the current airspeed of the motor vehicle and from the current, measured according to the specific measurement method target angle. Thus, if the vehicle's own speed coincides with the relative speed of the object as measured by the radar, that object is classified as an immovable object. This is a very robust and reliable method of classifying objects. This classification method thus uses the target angle determined by the predetermined measuring method (eg phase monopulse measurement). This has the following advantages: On the one hand, the computational effort is reduced to a minimum, because the ratio of the radial velocity to the intrinsic velocity does not have to be converted into the current target angle for each individual measurement or each individual object. On the other hand, the variance of said ratio is relatively high and the conversion to the target angle is much more stable if the said ratio is averaged over a long time.

In one embodiment, at least one value of the ratio is determined for each of a plurality of target angle intervals. The ratio can thus be determined as a (cosine) function as a function of the target angle. Thus, also the correction value - in this case a correction quantity - as a can be determined from the target angle dependent function, and an entire target angle parameter characteristic can be corrected.

If an immovable object is detected, the radar device continuously scans this immovable object while driving, so that the radial velocity and the ratio of the radial velocity to the intrinsic velocity are each obtained for a plurality of target angle values. Thus, for a single immovable object, a plurality of values of the ratio are available, each associated with a different target angular interval. The assignment of a current value of the ratio to a target angular interval may be such that a corresponding value of the target angle measured according to the predetermined measuring method to be calibrated is determined for this current ratio value. The current ratio value is then assigned to that target angle interval into which the corresponding current value of the target angle also falls. Thus, the assignment of the current value of the ratio to a target angular interval is based on the current value of the target angle measured according to the predetermined measuring method. This embodiment also has the advantages already described above: On the one hand, the computational effort can be reduced to a minimum, because the current ratio value does not have to be transformed in a complex manner into the angular range; on the other hand, the variance in the measurement of the ratio is relatively high, and this transformation is much more stable when the ratio values are averaged over a long time. Thus, the assignment of the ratio values can be made very precise and error-free.

For a large number of target angle intervals, in each case at least one value of the ratio is available for the determination of the correction value. In principle, two approaches are usefully possible: For a large number of target angle intervals, different correction values for the measurement of the target angle can be determined in each case. Alternatively it can be provided that from the respective values of the ratio a common correction factor common to a multiplicity of target angle intervals is determined. The latter embodiment may, for example, be such that the "old" target angle parameter characteristic is adapted to the cosine function of the ratio. Here, the correction value corresponds to the displacement or the offset between the "old" characteristic and the cosine function of the ratio. Such a procedure can be carried out without much computational effort.

As already stated, the determination of the ratio is associated with a relatively large measurement variance, since even slight measurement errors in the measurement of the radial velocity cause large errors in the determination of the ratio. The measurement of the radial velocity has a high variance, but can be assumed as expected litter. For precisely this reason, it is provided in one embodiment that the ratio of the radial velocity to the intrinsic velocity is averaged over a predetermined period of time. For each of the plurality of target angle intervals, a plurality of values of the ratio can be respectively collected, and from the respective plurality of the values, an average value for the ratio can be respectively calculated. For each of the plurality of target angle intervals, an average value of the ratio is then available, which was determined from a multiplicity of collected ratio values. In this way, it is possible to determine the correction offset with the highest precision and to ensure overall a highly accurate determination of the target angle according to the predetermined measurement method.

The target angle intervals can each have, for example, an angular width from a value range of 0.5 ° to 3 °. For example, each target angle interval can have an angle width of 1 °.

The averaging of the ratio can be carried out, for example, such that a predetermined number of values of the ratio are collected at each target angle interval-in particular between 10,000 and 100,000, for example 20,000 or 40,000 or 60,000 or 80,000 values-and the mean value from this predetermined number of values is calculated. According to a first alternative, the collected values may be deleted after the calculation of the mean value, and new values may be collected for individual target angle intervals. According to a second alternative it can be provided that for each target angle interval in each case a sliding average of each of the predetermined number of values is calculated. Thus, the correction value can be continuously determined, and the target angle parameter characteristic can be continuously adjusted. It is thus always an accurate characteristic for the measurement of the target angle available.

By determining the correction value, essentially an installation angle error and thus the actual installation angle of the radar device are determined. However, the bumper can distort the directional characteristics of the antennas also angle-dependent. In this case, the measured installation angle error, for example, in the lateral detection range (in addition to the motor vehicle) is a little different than in the rear Detection area (behind the motor vehicle). Because of such an angle-dependent distortion, it makes sense to evaluate only measurements on immovable objects from a partial angle range for determining the correction value, in which the determination of the target angle requires the greatest precision. It is also possible to process different detection areas separately from each other and to determine a separate correction value for each area.

It can therefore be provided that the ratio of the measured radial velocity to the actual airspeed of the motor vehicle is determined exclusively for a predetermined partial angle range of an entire (azimuthal) target angle detection range of the radar device. Consequently, the correction value can be determined exclusively for the predetermined angular range of the entire target angle detection range.

Because the target angle is to be measured particularly precisely, in particular for the application of the lane change assistant, and in this application, those vehicles which are located on a neighboring lane behind the own vehicle are to be detected particularly accurately, the ratio of the radial speed to the airspeed can be determined exclusively for the following angular range If the radar device is arranged in a rear corner region of the motor vehicle, then with respect to a reference axis extending in the vehicle longitudinal direction through the radar device, the genuinely exclusive partial angle range can be determined by a first angular limit value from a value range of 0 ° to 20 ° in the direction of the central longitudinal axis of the Motor vehicle out and on the other hand be limited by a second angle limit from a range of 40 ° to 60 ° in the direction away from the central longitudinal axis. Just then, the target angle of a vehicle located in the adjacent lane can be measured with the utmost precision, and the computational effort is also reduced to a minimum.

The following procedure proves to be particularly advantageous: If the correction value is smaller than a predefined threshold, then the target angle-in particular the target angle-parameter characteristic-is corrected on the basis of the correction value. If, on the other hand, it is determined that the correction value is greater than the predetermined threshold, then the radar device and in particular also the entire driver assistance system is deactivated. In this way it is prevented that the radar device is active even with an unexpectedly large error or too large a deviation of the actual installation angle from the planned installation angle of the radar device.

Depending on the ratio of the radial velocity to the intrinsic speed of the motor vehicle, a measurement error of the intrinsic speed of the motor vehicle can also be determined. This airspeed, measured using a wheel speed sensor, for example, can then be corrected on the basis of the measurement error determined, and the correct airspeed can be displayed to the driver and / or used by the driver assistance system for internal calculations. This embodiment is based on the fact that the ratio of the radial velocity to the intrinsic velocity is in principle a cosine function, ie a function with a minimum of -1 and a maximum of 1. If the actual maximum of the ratio exceeds or falls below the value of one, Thus, the deviation of the actual maximum from the ideal maximum is a measure of the measurement error of the airspeed of the motor vehicle. In this way, the measurement of the airspeed can be made plausible.

A continuous wave radar is preferably used as the radar device, which is designed to emit a frequency-modulated continuous electromagnetic wave (also known as FMCW (Frequency Modulated Continuous Wave) radar). With such a radar device, it is possible to determine the distance of an object from the same radar device, as well as the relative speed of the object with respect to the radar device and the relative position or the target angle. The radar may include one or more transmit antenna units and one or more receive antenna units. The radar device may include a receiver to which the at least one receiving antenna unit is coupled. Such a receiver may include, for example, a mixer, a low-pass filter, an amplifier, and an analog-to-digital converter. The signals received by the at least one receiving antenna unit are then down-converted in the receiver to the baseband, low-pass filtered and analog-to-digital converted. The digital signal is then processed by a computing device, which calculates the distance, the relative speed, as well as the target angle from a target angle parameter characteristic based on the digital signal.

If the radar device comprises at least two receiving antenna units, the receiver for each receiving antenna unit can each have a mixer, a low-pass filter, an amplifier and an analogue antenna. Digital converters include. The signals received by the receiving antenna units are then down-converted in the receiver to the baseband, low-pass filtered and analog-to-digital converted. The computing device can perform on the received signals the Fourier transform, in particular the FFT (Fast Fourier Transformation), the phases or the amplitudes of the received signals detect and compare with each other to determine the target angle.

The radar device preferably uses a separate transmitting antenna unit, be it a single transmitting antenna or a transmitting antenna group, which is fed by means of a local oscillator to generate a transmission signal. The transmit signal may also be applied to the respective mixers in the receiver to down-mix the received signals into the baseband. The transmitting antenna unit can be phased, so as to be able to detect a relatively wide surrounding area with a narrow main lobe of the directional characteristic as a whole.

According to the invention, a driver assistance system for a motor vehicle is also provided. The driver assistance system comprises a radar device, which comprises at least one receiving antenna unit for receiving a received signal. The driver assistance system also includes a computing device, which is designed to determine a target angle based on the received signal according to a predetermined measurement method. The computing device can detect an immovable object based on the received signal, measure a radial velocity of the motor vehicle with respect to the immovable object and determine a correction value for the determination of the target angle as a function of a ratio of the radial velocity to an intrinsic velocity of the motor vehicle.

An inventive motor vehicle includes a driver assistance system according to the invention. The preferred embodiments presented with reference to the method according to the invention and their advantages apply correspondingly to the driver assistance system according to the invention and to the motor vehicle according to the invention.

Further features of the invention will become apparent from the claims, the figures and the description of the figures. All the features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively indicated combination but also in other combinations or alone.

The invention will be explained in more detail below with reference to individual preferred embodiments, as well as with reference to the accompanying drawings.

Show it:

1 a schematic plan view of a motor vehicle according to an embodiment of the invention;

2 a block diagram of a radar device with a computing device;

3 in a schematic representation of a plan view of the motor vehicle according to 1 wherein a method according to an embodiment of the invention is explained in more detail;

4 a plurality of measured values of a ratio of a radial speed to the intrinsic speed of the motor vehicle as a function of a target angle;

5A an ideal and a shifted course of a phase difference between the phases of received signals of different receiving antenna units in dependence on the target angle;

5B an ideal and a distorted course of the phase difference; and

6 in a schematic representation of the motor vehicle according to 1 , wherein a method according to an embodiment of the invention is explained in more detail.

An in 1 illustrated motor vehicle 1 may be, for example, a passenger car. It includes a driver assistance system 2 that the driver while driving the motor vehicle 1 supported. The driver assistance system 2 For example, a system for monitoring the blind spot area of the motor vehicle 1 and / or to assist the driver in changing lanes. The driver assistance system 2 includes a first radar device 3 and a second radar device 4 , The first radar device 3 is located in a left corner of a rear bumper, while the second radar 4 is arranged in a right corner of the same bumper. The radars 3 . 4 are installed behind the bumper.

The first radar device 3 captures a detection area 7 , which is defined by an azimuth angle α, which in 1 through two boundary lines 7a . 7b is limited. Accordingly, the second radar device 4 a detection area 8th which is defined by a corresponding azimuth angle α. The azimuth angle α is defined by two lines 8a . 8b limited.

The azimuth angles α in the exemplary embodiment are each about 170 °. The coverage areas 7 . 8th the radars 3 . 4 overlap, leaving an overlap area 9 given is. The overlap area 9 is through the lines 7b . 8b angular limited. In the exemplary embodiment, an opening angle β of the overlapping area 9 about 70 °.

The first and the second radar device 3 . 4 are with a computing device 5 electrically coupled. Same computing device 5 For example, one may be for the first and second radar devices 3 . 4 common microcontroller 6 include, as well as a digital signal processor, not shown in the figures. Alternatively, you can also use two separate microcontrollers 6 and / or two digital signal processors may be provided, for example, one in the motor vehicle 1 existing communication bus communicate with each other.

In their respective coverage areas 7 . 8th can the radars 3 . 4 Locate objects. In particular, the radar devices 3 . 4 a distance R of an object 10 from the respective radar device 3 . 4 as well as a relative speed of this object 10 with respect to the motor vehicle 1 and determine a target angle γ. The target angle γ is an angle between a reference axis 11 , in the vehicle longitudinal direction by the respective radar device 3 . 4 runs, and a connecting line 12 which the respective radar device 3 . 4 with the object 10 combines.

2 shows a block diagram of a single radar device 3 . 4 including the computing device 5 , The radar device 3 . 4 includes a transmitting antenna unit 13 which may be an antenna array or array and may include a plurality of patch antennas. The transmitting antenna unit 13 is via a feed circuit 14 fed. The transmitting antenna unit 13 is done using a local oscillator 15 fed, which generates a transmission signal S ₀ . This transmission signal S ₀ is a frequency-modulated electromagnetic wave whose frequency has a sawtooth-shaped course in the exemplary embodiment. So the transmission signal S _{0 is} frequency-modulated; For example, its frequency may periodically pass between a first frequency value and a second frequency value. The mean frequency of the transmission signal S ₀ is 24 GHz in the exemplary embodiment.

The local oscillator 15 is through the computing device 5 driven. The oscillator 15 is, for example, a voltage controlled oscillator (Voltage Controlled Oscillator), which generates the transmission signal S ₀ with such a frequency, which depends on the amplitude of one of the computing device 5 on the oscillator 15 provided DC voltage is.

The radar device 3 . 4 comprises in the embodiment two receiving antenna units 17 . 18 , each via a feed circuit 19 . 20 with a receiver 16 are coupled. The receiving antenna unit 17 . 18 In the exemplary embodiment, these include a multiplicity of patch antennas and may be two-dimensional antenna arrays (arrays). The power circuits 19 . 20 each provide a received signal S ₁ , S ₂ ready. The received signals S ₁ , S ₂ are then each using a low-noise amplifier 21 . 22 (Low Noise Amplifier) amplified using a mixer 23 . 24 mixed down, using a low-pass filter 25 . 26 low-pass filtered and using an analog-to-digital converter 27 . 28 analog-digital-converted. For the down-mixing of the received signals S ₁ , S ₂ , the transmission signal S _{0 is} used; it gets to the mixer 23 . 24 guided, namely for example by means of a directional coupler. The received signals S ₁ , S ₂ are then using the computing device 5 processed, which then determines the distance R, the target angle γ, as well as the relative speed of the received signals S ₁ , S ₂ .

2 is a schematic diagram of the radar device 3 . 4 , For example, the respective radar device 3 . 4 also include further receiving antenna units, each with an additional receiving channel; the radar device 3 . 4 may also include multiple transmit antenna units. The invention is not on the in 2 illustrated radar device 3 . 4 limited.

The transmitting antenna unit 13 , and more specifically the supply circuit 14 , can be controlled so that they successively different subareas A to H of the detection area 7 respectively 8th illuminated (see 1 ). For example, a transmitting lobe of the transmitting antenna unit 13 be pivoted electronically in the horizontal direction, namely according to the phase array principle. The receiving antenna units 17 . 18 In this case, in the horizontal direction, they can have a relatively wide reception characteristic, with which the entire detection range 7 respectively 8th is covered. Other configurations can alternatively or additionally realize narrow reception angle ranges in conjunction with broad transmission lobes.

In 1 For the sake of clarity, only the partial areas A to H of the detection area are shown 7 of the first radar device 3 shown. Accordingly, here is the scope 8th of the radar 4 divided into several sub-areas, by the radar device 4 be lit one after the other. The number of subareas A to H is in 1 merely exemplified. Depending on the configuration of the antenna characteristic, this number can vary accordingly.

In a single measurement cycle, the subareas A to H through the radar device 3 respectively 4 recorded consecutively. The measuring cycles are repeated continuously. The radar sends in one measurement cycle 3 respectively. 4 for each subarea A to H (ie per beam) separately in each case a predetermined sequence of frequency-modulated wave pulses (chirps). The radar device 3 . 4 So sends one sequence of frequency-modulated wave pulses per measurement cycle and per sub-area A to H. These wave pulses are then from an object 10 reflected and through the receiving antenna units 17 . 18 receive.

As already stated, the computing device 5 based on the received signals S ₁ , S _2, the target angle γ of the vehicle external object 10 determine, namely an angle between the reference axis 11 and the connecting line 12 , This is in the computing device 5 a target angle phase difference characteristic stored, which reflects the relationship of the target angle γ and a phase difference between the phases of the received signals S ₁ , S ₂ . The computing device 5 thus calculates the phase difference between the received signals S ₁ , S ₂ and then determines the associated value of the target angle γ based on the target angle phase difference characteristic.

Hereinafter, a method for determining a correction value γ _off for the measurement of the target angle γ will be explained in more detail. The stored target angle phase difference characteristic curve is corrected on the basis of the correction value.

Referring to 3 detects the computing device 5 first an immovable or stationary with respect to the road object 29 which may be an infrastructure object, for example. The computing device 5 measures based on the received signals S ₁ , S _2, a radial velocity v _{r of} the immovable object 29 with respect to the motor vehicle 1 , The airspeed v _{host of} the motor vehicle 1 is known; For example, it can be measured using a wheel speed sensor. The airspeed v _host is therefore the speed of the motor vehicle 1 concerning the street. During a passage of the motor vehicle 1 on the immovable object 29 determines the computing device 5 in each case a ratio of the instantaneous radial speed v _r to the instantaneous airspeed v _{host of} the motor vehicle for a multiplicity of target angle values or target angle intervals 1 , This ratio v _r / v _host provides a measure of the current target angle γ, and the in 3 illustrated relationship.

In 4 For example, a plurality of measured values of the ratio v _r / v _{host are} plotted as a function of the target angle γ measured using the target angular phase difference characteristic. These readings were for a variety of immovable objects 29 for a plurality of values of the target angle γ. How out 4 As a result, the ratio v _r / v _{host as} a whole has a course of the cosine function. This method of determining the target angle γ is in principle not suitable for the determination of the respective instantaneous target angle γ with the highest precision. How out 4 In fact, the ratio v _r / v _host is subject to a relatively large variance; the standard deviation is relatively high. In other words, this method has a relatively high measurement noise. However, this method is in principle to be regarded as unbiased and - which is of great advantage - it comes without knowledge of the actual mounting angle of the radar 3 . 4 and can thus be used as a reference method to correct the stored target angle phase difference characteristic. If sufficient measured values of the ratio v _r / v _{host are} collected over time, then the stored target angle phase difference characteristic curve can be corrected. For example, a new characteristic can be defined, namely one that corresponds to the in 4 measured values of the ratio v _r / v _{host is} adjusted or obtained by an interpolation of these measurement points. Out 4 For example, a shift in the Characteristic by about 2 °, which can be seen by the maximum value of the ratio (v _r / v _host ) _max . Therefore, the target angle phase difference characteristic curve can be corrected by this 2 °.

An interpolation of the measuring points is in 4 with a solid line 30 shown.

In principle, all infrastructure destinations can be determined by the radar device 3 . 4 be detected, to determine the ratio v _r / v _host and thus to estimate the installation angle of the radar 3 . 4 to be used. However, the bumper may also distort the antenna characteristics in an angle-dependent manner. Then the measured offset-that is, the correction value-is different in the rear detection range of the radar, for example in the lateral detection range 3 . 4 , It is thus intended that the immovable objects 29 are evaluated exclusively for a partial angle range in which the greatest precision of the determination of the target angle γ is needed.

The 5A and 5B show curves of the phase difference Θ between the phases of the received signals S ₁ , S ₂ as a function of the target angle γ. In the 5A and 5B Thus, the target angle phase difference characteristics are shown. 5A on the one hand shows an ideal target angle phase difference characteristic 31 , which is for the planned target position of the radar 3 . 4 on the motor vehicle 1 would result. On the other hand, the shows 5A a shifted characteristic 32 , which results from the installation angle error or from the correction value. The representation according to 5A So results in a pure rotation of the radar 3 . 4 in a horizontal direction. As already stated, the bumper can also influence the antenna characteristics, so that the characteristic curve is distorted. In 5B is next to the ideal characteristic 31 also a distorted characteristic 33 shown. The estimation of the target angle γ according to 4 and thus the installation angle of the radar 3 . 4 compensates only a pure shift of the characteristic. With an additional distortion - as in 5B - This compensation is correct only for a small angular range.

In the case of the lane change assistant, high precision is at the rear of the vehicle 1 required. So there should be detections on the immovable object 29 be selected and evaluated, located in a predetermined angular range behind the motor vehicle 1 are located. For the sake of simplicity, this selection of the detections can be made on the basis of the phase monopulse measurement to be calibrated.

In 6 is a partial angle range 34 behind the motor vehicle 1 for which the ratio v _r / v _{host is} measured and evaluated. This partial angle range 34 is an angle range of -10 ° to 50 ° with respect to the reference axis 11 , The angle is measured clockwise. For the radar device 4 this partial angle range is correspondingly symmetrical with respect to a central longitudinal axis 35 of the motor vehicle 1 , The partial angle range 34 is thus by a first angle limit of 10 ° in the direction of the central longitudinal axis 35 limited; On the other hand, the partial angle range 34 by a second angle limit of 50 ° in the direction of the central longitudinal axis 35 limited way.

For example, the following algorithm can be implemented:
For a plurality of target angle intervals, a plurality of values of the ratio v _r / v _{host may be} collected over time, respectively. All measured values within a measurement cycle are examined to see if they are from an immovable object 29 come or not. Only those measured values are selected and evaluated which are in the partial angle range 34 according to 6 lie. To determine if the readings from an immovable object 29 The measured radial velocity v _{r is} compared with an estimate of the radial velocity calculated from the airspeed v _host and the target angle γ determined by the phase monopulse method. If these two values of the radial velocity coincide - namely with a given accuracy - the object is classified as an immovable object. The individual values of the ratio v _r / v _host are stored for the plurality of target angle intervals according to the following table: Index i 0 1 N - 2 N - 1 interval γ1 ... γ1 + dγ γ1 + dγ ... γ1 + 2dγ ... γ2 - 2dγ ... γ2 - dγ γ2 - dγ ... γ2 S (i): sum V _r / v _host nm (i): number of measurements

The partial angle range 34 is angularly limited by the angular limits γ1 and γ2, as in 6 shown. This partial angle range 34 is divided into equal target angle intervals dγ. The size of the target angle intervals dγ can be set to 1 °, for example.

In the first row of the table, the individual target angle intervals dγ are consecutively numbered, namely from 0 to N-1, where N denotes the number of target angular intervals dγ. In the second row, the target angle intervals dγ are clearly defined or the respective limits are indicated.

If a value of the ratio v _r / v _{host is} measured, it is checked on the basis of the current value of the target angle γ determined on the basis of the current target angle phase difference characteristic curve into which column or target angle interval the measured ratio v _r / v _host falls. This is done on the basis of the measured according to the phase monopulse process to be calibrated instantaneous target angle γ. If it is determined in which of the target angle intervals dγ the instantaneous value of the ratio v _r / v _host falls, then in the third row the sum S (i) is calculated from all the values of the ratio v _r / v _host present for this interval, and the number of measurements is incremented or incremented by one in the fourth row.

Thus, a plurality of values of the ratio v _r / v _{host are} collected and grouped for the plurality of target angle intervals dγ. For example, for each target angle interval dγ, 20,000 (40,000 or 60,000) values of the ratio v _r / v _{host may be} collected. Then, for each target angle interval, a sum S (i) of 20,000 individual values (40000 or 60000) is available, as well as the respective number nm (i) of the values. Then, for each target angle interval, an average value of the ratio can be calculated: MV (i) = S (i) / nm (i). The mean values MV (i) ideally describe a cosine function: MV (i) = cos (γ (i) + γ _off ), in which: γ (i) = γ1 + dγ / 2 + i · dγ. Here, γ _off denotes the correction value for the target angle phase difference characteristic and corresponds in principle to the unknown angular offset of the installation angle of the radar device 3 . 4 ,

The correction value γ _off can now be evaluated in various ways. For example, a separate correction value γ _off can be calculated for each target angular interval dγ or for any desired groups of target angular intervals dγ. Alternatively, a common correction value γ _off can be calculated for all target angle intervals. In this case, a cosine function can be adapted to the data vector MV. The cosine function can be adapted to the MV record by mean-square optimization.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009024064 A1 [0006]
• EP 1159638 B1 [0007]
• DE 19610351 C2 [0008]

Claims (15)

Method for determining a correction value (γ _off ) for the measurement of a target angle (γ) by means of a radar device ( 3 . 4 ) in a motor vehicle ( 1 ), in which: - the radar device ( 3 . 4 ) transmits a transmission signal (S ₀ ) and receives a reception signal (S ₁ , S ₂ ), and - the target angle (γ) is determined on the basis of the reception signal (S ₁ , S ₂ ) according to a predetermined measurement method, characterized by - detecting one with respect to one Environment of the motor vehicle ( 1 ) immovable object ( 29 ) based on the received signal (S ₁ , S ₂ ), - measuring a relative radial velocity (v _r ) between the motor vehicle ( 1 ) and the immovable object ( 29 ) based on the received signal (S ₁ , S ₂ ), wherein the current radial velocity (v _r ) and a current airspeed (v _host ) of the motor vehicle ( 1 ) (The ratio v _r / v _host) is set, and - determining the correction value (γ _off) as a function of the ratio (v _r / v _host). A method according to claim 1, characterized in that according to the predetermined measuring method, the target angle ( 1 ) is determined as a function of a parameter of the received signal (S ₁ , S ₂ ) on the basis of a stored target angle parameter characteristic, and the target angle parameter characteristic curve is corrected on the basis of the correction value (γ _off ). Method according to claim 1 or 2, characterized in that - at least two receiving antenna units ( 17 . 18 ) of the radar device ( 3 . 4 ) receive in each case a received signal (S ₁ , S ₂ ), - according to the predetermined measuring method, the target angle (γ) as a function of a phase difference between the received signals (S ₁ , S ₂ ) based on a stored target angle phase difference characteristic curve ( 31 ), and - the target angle phase difference characteristic ( 31 ) is corrected on the basis of the correction value (γ _off ). Method according to one of the preceding claims, characterized in that an object ( 29 ) then as immovable object ( 29 ) is classified, when with a predetermined accuracy, the current measured radial velocity (v _r ) is equal to a current reference radial velocity, which is derived from the actual airspeed (v _host ) of the motor vehicle ( 1 ) and from the current, measured according to the predetermined measurement method target angle (γ) is calculated. Method according to one of the preceding claims, characterized in that in each case at least one value of the ratio (v _r / v _host ) is determined for a plurality of target angle intervals (dγ). A method according to claim 5, characterized in that the assignment of a current value of the ratio (v _r / v _host ) to a target angle interval (dγ) based on a current, measured according to the predetermined measurement method value of the target angle (γ) is made. A method according to claim 5 or 6, characterized in that for a plurality of target angle intervals (dγ) respectively different correction values (γ) for the measurement of the target angle (γ) are determined. A method according to claim 5 or 6, characterized in that from the respective values of the ratio (v _r / v _host ) a common correction value (γ _off ) is determined for a plurality of target angle intervals (dγ). Method according to one of Claims 5 to 8, characterized in that a plurality of values of the ratio (v _r / v _host ) are respectively collected for the multiplicity of target angular intervals (dγ) and an average value (MV) of the respective plurality of values the ratio (v _r / v _host ) is calculated. Method according to one of the preceding claims, characterized in that only for a predetermined partial angle range ( 34 ) of an entire target angle detection range ( 7 . 8th ) of the radar device ( 3 . 4 ) the ratio (v _r / v _host ) of the measured radial velocity (v _r ) to the actual airspeed (v _host ) of the motor vehicle ( 1 ) is determined. Method according to claim 10, characterized in that the radar device ( 3 . 4 ) in a rear corner region of the motor vehicle ( 1 ) and that with respect to a reference axis ( 11 ), which in the vehicle longitudinal direction by the radar device ( 3 . 4 ), the ratio (v _r / v _host ) is exclusive to one Partial angle range ( 34 ) of a first angular limit value (γ1) from a value range of 0 ° to 20 ° in the direction of the central longitudinal axis ( 35 ) of the motor vehicle ( 1 ) up to a second angular limit value (γ2) from a value range of 40 ° to 60 ° in the direction of the central longitudinal axis ( 35 ) is determined away. Method according to one of the preceding claims, characterized by - if the correction value (γ _off ) is less than a predetermined threshold, correcting the target angle (γ) based on the correction value (γ _off ), and - if the correction value (γ _off ) greater than that default threshold is to disable the radar ( 3 . 4 ). Method according to one of the preceding claims, characterized in that, depending on the ratio (v _r / v _host ), a measurement error of the airspeed (v _host ) of the motor vehicle ( 1 ) is determined. Driver assistance system ( 2 ) for a motor vehicle ( 1 ), with: - a radar device ( 3 . 4 ) with at least one receiving antenna unit ( 17 . 18 ) for receiving a received signal (S ₁ , S ₂ ) and - a computing device ( 5 ) for determining a target angle (γ) based on the received signal (S ₁ , S _{2 )} according to a predetermined measuring method, characterized in that the computing device ( 5 ) is designed to use the received signal (S ₁ , S ₂ ) an immovable object ( 29 ), a radial velocity (v _r ) of the motor vehicle ( 1 ) with respect to the immovable object ( 29 ) and a correction value (γ _off ) for determining the target angle (γ) as a function of a ratio (v _r / v _host ) of the radial velocity (v _r ) to an intrinsic velocity (v _host ) of the motor vehicle ( 1 ). Motor vehicle ( 1 ) with a driver assistance system ( 2 ) according to claim 14.

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