DE102006047605A1 - Angle-resolving radar sensor for motor vehicles - Google Patents

Abstract

Angle-resolving radar sensor for motor vehicles, comprising a plurality of antenna elements (12) which differ in their main sensitivity direction, and an evaluation device (22) having a plurality of channels (24) which respectively evaluate the signals of an antenna element (12), characterized in that the number of Antenna elements (12) is greater than that of the channels (24) and that a channel selection module (20) is provided to switch the antenna elements (12) in response to the operating condition of the vehicle in different ways to the channels (24).

Description

State of the art

The The invention relates to an angle-resolving radar sensor for motor vehicles, with multiple antenna elements that are in their main sensitivity direction distinguish, and a multi-channel evaluation, the each evaluate the signals of an antenna element.

motor vehicles are increasingly equipped with so-called ACC systems (Adaptive Cruise Control), the allow the distance of one's own vehicle to a preceding one To automatically control the vehicle. To this end, help with of the radar sensor, for example an FMCW LRR sensor (Frequency Modulated Wave Long Range Radar) the distances and azimuth angles as well measured the relative speeds of preceding vehicles.

The previously used in this context radar sensors have For example, four antenna elements or antenna patches, the in the horizontal offset to the optical axis of the radar sensor are arranged in front of a radar lens, so that their Hauptempfindlichkeitsrichtungen slight differ from each other. If, as is often the case, to send the Radar signal and to receive the radar echo the same antenna elements are used, also have the main emission directions of the antenna elements a corresponding deviation.

In a first evaluation stage of the evaluation is each Antenna element assigned to exactly one channel, in which that of the respective Antenna element received signal is evaluated. For example is used in an FMCW radar, where the frequency of the transmitted radar signal is periodically modulated, received at each antenna element Signal mixed with the signal sent at the time of reception, so that one receives an intermediate frequency signal, whose frequency is the frequency difference between the sent and the received signal. In the channel in question The evaluation device then becomes a frequency spectrum in each measurement period recorded the intermediate frequency signal. In this frequency spectrum plots each located object by a peak whose frequency position the distance and the relative speed of the object in question dependent is. By modulating the transmitted frequency with different ones Ramp slopes can be calculated from the obtained frequency positions of the Calculate distance and relative speed.

each Antenna element radiates the radar power with one according to a certain characteristic varying intensity in a certain solid angle range from. The amplitude and phase of the received signal is from Azimuth angle of the located object dependent. This dependence let yourself for a Standard object at a given distance and with a given reflectivity in an antenna diagram. By matching the of the obtained different antenna elements for the same object Amplitudes and / or phases with the corresponding antenna diagrams let yourself then in a second evaluation stage the azimuth angle of the relevant Determine object.

at The previously used LRR sensors are intended to drive vehicles ahead already in a relatively large Distance of, for example, 100 m or more can be located. The Main sensitivity directions of the antenna elements are therefore only a relatively small one Angular offset on, so that the Radar beams of the various antenna elements even at a great distance in the first place only the width of the carriageway and a sufficient intensity for locating objects at greater distances to Available. However, it must be accepted that achieve only a limited angular resolution leaves and that at low Distances left and to the right of the radar lobe arise dead corners in which no objects can be located. If, for example, at low speed, more accurate monitoring short range sensors are therefore additionally required For example, video sensors, lidar sensors or SRR sensors (Short Range Radar) used.

Disclosure of the invention

task The invention is the application of a radar sensor to expand the type mentioned above and thereby the required To limit processing effort in the signal evaluation.

These Task is inventively characterized solved, that the Number of antenna elements is larger than the channels and that one Channel selection module is provided to the antenna elements in dependence on the operating condition of the vehicle in different ways the channels to switch.

For example, the number of antenna elements can be increased from four to six, while only four channels are available for the evaluation. The channel selection module then determines, among the total of six antenna elements based on the operating state of the vehicle, the four antenna elements whose signals be evaluated. Thus, for example, in an operating state of the vehicle in which a high angular resolution and / or monitoring of a larger angular range in the near range is desired, the four "outer" antenna elements are used for the evaluation, ie the antenna elements whose main sensitivity directions are the strongest of the optical Deviate axis of the sensor. In another operating state of the vehicle, in which the widest possible range of the radar sensor is required, for example, when driving at high speed, however, the four "inner" antenna elements are evaluated, so that the mode of operation corresponds to that of a conventional LRR radar. In general, the selection of the antenna elements used for the evaluation can thus be optimized for every conceivable operating state of the vehicle. In this case, for example in curves, an asymmetric selection is also conceivable, so that a preceding vehicle can be tracked better in the curve.

It are also angle-resolving Radar sensors known in which only a single Auswertekanal is provided and the determination of the azimuth angle thereby takes place that the different antenna elements are controlled in succession, So that the Radar lobe constantly across the lane width oscillates. In contrast, However, the radar sensor proposed here has the special feature on that to the Determination of the azimuth angle always a parallel evaluation in multiple channels and also the channel selection is dependent on the operating state of the vehicle.

Under "antenna elements" in the sense of this application should also be understood so-called phased array elements, which consist of several subelements and in which the directional characteristic not primarily by the position relative to the optical axis, but rather through the phase relations between the individual Subelements is determined.

The "number of channels" in terms of this Registration does not relate to the hardware of the sensor, but rather, the type of signal evaluation. That's the way it is, for example quite conceivable that the Hardware of the radar sensor for certain special purposes has as many evaluation channels as antenna elements. It is crucial, however, that according to the invention in the Software of the sensor implemented at least one operating mode is, in which only a part of the existing antenna elements for evaluation is used.

advantageous Embodiments and developments of the invention are specified in the subclaims.

In an advantageous embodiment is the channel selection module designed so that it is not just the evaluation the received signals, but also the control of the relevant Antenna elements affected. So can in each case those antenna elements that are not used for the evaluation be switched off completely, so that they do not send radar signals. This has the advantage that of Radar reflections are generated to these antenna elements, the could interfere with the evaluation in the active antenna elements. at the same time is limited in this way the total radiated radar power.

Prefers include the operating states that determine the channel selection, different ranges of the speed of your own vehicle. So can for example, at high speed, the inner antenna elements be activated in order to achieve a long range, while activated at low speed, the outer antenna elements so that one larger detection angle range and achieved a higher angular resolution become. It is also a mixed operation conceivable, approximately in the middle Velocity range, from measuring cycle to measuring cycle a periodic change of the channel selection pattern takes place.

In certain applications, for example, if the ACC system a so-called stop-and-go Has function that allows the vehicle when driving around to brake on a jam in the state and possibly automatically one To control the restart process when the fore vehicle returns in motion, it is necessary that the radar sensor also during the Standstill of the vehicle is in operation. In this case, the allowed during the Vehicle standstill radiated radar power certain limits do not exceed. This requirement can be meet in a particularly elegant way, when the outer antenna elements have a lower power than the inner antenna elements. When the vehicle is stationary then the outer antenna elements are activated and the inner deactivated, which on the one hand a large Ortungswinkelbereich receives which makes sense in this state, and at the same time the radiation power is reduced.

Brief description of the drawings

One embodiment The invention is illustrated in the drawings and in the following Description closer explained.

It demonstrate:

1 a block diagram of the radar sensor according to the invention in conjunction with a ACC system;

2 a sketch illustrating different sensitivity characteristics of different antenna elements of the radar sensor;

3 to 5 Sketches analogous to 2 to illustrate different operating modes of the radar sensor; and

6 a diagram illustrating an example of the selection of different operating modes as a function of the vehicle speed.

Embodiments of the invention

The in 1 shown radar sensor 10 has six antenna elements 12 on. The radar beams or "beams" generated by these antenna elements are with 1 - 6 numbered. Each antenna element 12 is from a local oscillator 14 over a mixer 16 supplied with a radar signal transmitted from the respective antenna element. The signal received by this antenna element of a radar echo is in the mixer 16 mixed with the transmitted signal, so that one an intermediate frequency signal 18 that receives a channel selection module 20 is supplied. This channel selection module 20 Thus, a total of six intermediate frequency signals 18 fed. Among these six intermediate frequency signals are provided by the channel selector module 20 four signals selected and an evaluation 22 fed. In a first stage of the evaluation 22 The four selected signals are in separate channels 24 preprocessed.

According to the functional principle of an FMCW radar, the frequencies are those of the oscillators 14 radar signals ramped modulated, each cycle containing at least one rising ramp and one falling ramp. During preprocessing in the channels 24 The intermediate frequency signals obtained on each ramp are recorded and converted into a frequency spectrum by Fast Fourier Transformation. The peaks corresponding to the located objects are then identified in this spectrum. Based on the frequency positions of the peaks obtained for each object on the rising and the falling ramps, the distance and the relative speed of the object in question can then be calculated in a known manner. In addition, the preprocessing peaks in the channels become 24 standardized so that their amplitudes can be compared with each other.

In a second stage 26 the evaluation device 22 Then the normalized amplitudes and / or phases of the intermediate frequency signals with corresponding antenna diagrams for the antenna elements 12 adjusted, so that can be determined based on the known angular dependence of the amplitudes and / or phases, the azimuth angle of the located objects. The location data obtained for each object, ie the distances, relative speeds and azimuth angle, are then from the radar sensor 10 to a driver assistance system, for example an ACC system 28 outputted, which then based on the location data, the speed of the radar sensor 10 equipped vehicle regulates. This will be done in the ACC system 28 also the dynamic data of the own vehicle evaluated, in particular its current speed V and the yaw rate dφ / dt. The ACC system 28 is thus also able to differentiate between different operating conditions of the vehicle, such as standstill, driving at low, medium or high speed and cornering. The operating state of the vehicle categorized in this way is provided by the ACC system 28 to the channel selection module 20 reported there and determines the selection of intermediate frequency signals 18 that in the channels 24 are processed.

Although the radar sensor 10 in this example six antenna elements 12 thus, need of the evaluation 22 only the signals of four antenna elements are evaluated in each measurement cycle. In this way, the required processing effort is limited while, on the other hand, by proper selection of the antenna elements 12 or the intermediate frequency signals 18 in the channel selection module 20 the possibility exists to optimally adapt the location and sensitivity range of the radar sensor to the respective operating state of the vehicle.

In the example shown, the channel selection module takes over 20 also the activation or activation of the local oscillators 14 representing the individual antenna elements 12 assigned. This creates the possibility to activate only those antenna elements whose output signals from the channel selection module 20 be selected for the evaluation. This has the advantage of reducing the risk of misinterpretations which might otherwise result from the signals sent from the unnecessary antenna elements and reflected at the objects being received by the active antenna elements (cross echoes) and there the evaluation complicate the signals.

In addition, it can be assumed in the example shown that the different oscillators 14 generate identical signals. In a modified embodiment, however, it is also possible that the six oscillators 14 or at least the four ever because active oscillators work in mutually offset frequency bands. This avoids, on the one hand, the above-mentioned problem of cross echoes between the various antenna elements. In addition, depending on the operating state between frequency offset or synchronous operation of the oscillators can be switched, so that can be varied by targeted utilization of interference effects, the directional characteristic of the radar sensor as needed, as in the earlier patent application DE 10 2006 032 539 is proposed.

In 2 are the six antenna elements 12 in the image plane of a lens 30 represented by the radar sensor. The associated beams 1 - 6 are through the corresponding antenna lobes 30 . 32 and the main sensitivity directions 34 (dashed lines) represents.

As an example, it can be assumed that the six beams together cover an angular range of ± 8 °. With uniform angular distances between the beam this corresponds to an angular distance of 3.2 ° from beam to beam. For comparison, the four beams of a conventional radar sensor have angular intervals of 4 °, so that together they cover an angular range of ± 6 °. Corresponding to the smaller angular distances in the radar sensor according to the invention, the individual beams can be bundled sharper, so that the antenna lobes 30 . 32 have a slimmer shape than a conventional radar sensor. This can be achieved by suitable dimensioning and arrangement of the antenna elements 12 (Patches) and the lens 30 to reach. The sharper focusing of the beams has the advantage that a greater angular resolution is achieved, although on the other hand, the total covered angular range is greater than in the prior art.

The total of each antenna element 12 radiated radar power can from the two central beams 3 and 4 decrease towards the outer beams. In 2 this is symbolized by the fact that the antenna lobes 30 for the outer beams 1 and 6 have smaller dimensions.

It is understood that the in 1 and 2 shown arrangement is to be understood only as an example and that the total available number of antenna elements 12 and the configuration of the beams as well as the number of channels available for evaluation 24 may vary depending on the embodiment.

3 illustrates an operating mode where only the four inner beams 2 - 5 are active and evaluated while the two outer beams 1 and 6 through the sewer car module 20 are disabled. The entire radar radiation is thus radiated forward in a relatively narrow angular range, at the same time the radiation energy is maximum, since the four strongest beams are active. This operating mode is therefore particularly suitable for locating objects at a relatively large distance and is therefore preferably selected in the upper speed range.

In contrast illustrated 4 a mode of operation in which the two central beams 3 and 4 are turned off and only the signals of the four outer beams 1 . 2 . 5 and 6 be evaluated. Here, therefore, the largest possible detection angle range is achieved, so that, for example, from the left or right side lane ago einscherende vehicles using the antenna lobes 30 the two outer beams 1 . 6 can be detected early. On the other hand, here is the near the optical axis of the lens 30 zone in which the beams with sufficient signal strength overlap, compared to the mode 3 reduced, so that the range of the radar sensor is reduced accordingly. This mode is therefore particularly suitable for the lower speed range. The total emitted beam power is minimal here, since only the four weakest beams are active.

5 Finally, it illustrates an operating mode with an asymmetrical activation pattern in which only the four "right" beams 3 - 6 are activated. This mode of operation is particularly suited to track vehicles ahead in a right turn, and is therefore chosen, for example, when the ACC system 28 ( 1 ) using the yaw rate dφ / dt detects that a right turn is passed. Optionally, this operating mode can be activated even before entering the curve, for example, in the operating mode after 3 shows that a preceding vehicle, which is tracked in the distance control as a target, to the right out of the detection range of the beams 2 - 5 emigrates.

6 illustrates possible modes of operation for three different ranges of the speed V of the vehicle. These speed ranges are referred to as "high" (eg V> 60 km / h) "medium" (30 km / h ≤ V ≥ 60 km / h) and "low" (V <30 km / h). For each of these operating states, the successive measuring cycles of the radar sensor over time are indicated by rectangles 36 symbolizes. Each of the beams 1 - 6 In this case, a row of rectangles is assigned and the measuring cycles in which a beam is active are symbolized by hatched rectangles.

In the operating state "high" is from the channel selector module 20 in each measuring cycle, the operating mode according to 3 chosen, ie, they are each four inner beams 2 - 5 active. Since each of these beams is activated in each cycle, the temporal resolution at the location of the preceding vehicles is maximum, as it makes sense for high-speed travel.

In the "medium" operating mode, the measuring cycle to the measuring cycle periodically fades between the operating modes 3 and 4 changed. The temporal density in the monitoring of objects with a large distance and a small azimuth angle is therefore somewhat reduced, at least as far as locating with all four inner beams 2 - 5 and consequently with maximum angular resolution, while on the other hand every other cycle with the help of the beams 1 and 6 also the fringes can be monitored. Of course, in this context, other activation patterns are conceivable, for example, an activation of the beams 1 . 2 . 4 and 6 in the first cycle and the Beams 1 . 3 . 5 and 6 in the second cycle. Similarly, a periodic change between three or four different activation patterns is conceivable.

In the "low" operating state, the mode is set in each cycle according to 4 chosen, so that in the vicinity of the vehicle a large angular range can be monitored with maximum temporal resolution.

Because the two outer beams 1 and 6 also in the area of the optical axis of the lens 30 still overlap, for example, in vehicle standstill, an operating mode is conceivable in which only the two outer beams 1 and 6 be activated and the more powerful inner antenna elements 2 - 5 are constantly switched off.

Claims (7)

Angle-resolving radar sensor for motor vehicles, having a plurality of antenna elements ( 12 ), which are in their main sensitivity ( 34 ) and an evaluation device ( 22 ) with several channels ( 24 ), each of which receives the signals of an antenna element ( 12 ), characterized in that the number of antenna elements ( 12 ) is greater than that of the channels ( 24 ) and that a channel selection module ( 20 ) is provided, the antenna elements ( 12 ) depending on the operating condition of the vehicle in different ways on the channels ( 24 ) to switch. Radar sensor according to claim 1, characterized in that that of the channel selection module ( 20 ) distinguishable operating conditions of the vehicle with respect to the vehicle speed (V). Radar sensor according to claim 1 or 2, characterized in that the signal from the channel selection module ( 20 ) distinguishable operating conditions of the vehicle comprise at least one cornering condition. Radar sensor according to one of the preceding claims, characterized in that the channel selection module ( 20 ) is designed to also feed the radar signals to be transmitted into the antenna elements ( 12 ) and to activate only the antenna elements whose signals are transmitted to the channels ( 24 ). Radar sensor according to one of the preceding claims, characterized in that the operating states of the vehicle comprise at least one state in which those antenna elements are placed on the channels ( 24 ) whose beams ( 1 . 2 . 5 . 6 ) deviate most strongly from the optical axis of the radar sensor, as well as at least one operating state in which those antenna elements are placed on the channels ( 24 ) whose beams ( 2 . 4 . 5 . 6 ) are the least different from the optical axis. Radar sensor according to one of the preceding claims, characterized in that the antenna elements ( 12 ) differ in their transmission power and that the transmission power with increasing angular distance of the main sensitivity direction ( 34 ) decreases from the optical axis of the sensor. Radar sensor according to one of the preceding claims, characterized in that the channel selection module ( 20 ) is designed, in at least one operating state, the pattern of the association between the antenna elements ( 12 ) and the channels ( 24 ) periodically from measuring cycle to measuring cycle.