Method for operating an ultrasonic sensor of a vehicle

Abstract

The present invention relates to a method for operating an ultrasonic sensor of a vehicle, a directional characteristic of the ultrasound sensor being modified as a function of speed in order to minimize a measurement error.

Description

[0001] Description

[0002] title

[0003] Method for operating an ultrasonic sensor of a

[0004] State of the art

[0005] The present invention describes a method for operating an ultrasonic sensor, as well as a device for speed-dependent adaptation of the directional characteristic of the ultrasonic sensor.

[0006] Ultrasonic array-based sensors offer the possibility of angular measurement, i.e., they detect the direction of the incoming echo by analyzing the phase shift of the sound waves between the elements. Of particular interest here is elevation measurement, as it allows discrimination between traversable and non-traversable objects.

[0007] The quality of the angle measurement, i.e. the measurement error, depends crucially on the signal-to-noise ratio of the received echo signals. The relevant noise is caused by the sensor noise near the maximum range of the sensor (typically 4-6 m). At shorter distances, the noise is dominated by ground reflections and exceeds the contribution of the sensor noise by an order of magnitude. This means that ground reflections significantly interfere with the elevation measurement. This severely limits the use of elevation measurements for over-drivability detection. Angle measurement is particularly important for emergency braking. The reduced signal-to-noise ratio has a particularly significant impact at vehicle speeds above approximately 2 km / h, since on the one hand the braking decision is made in the area dominated by ground reflections (> 0.8 m) must be taken, and the number of measurements until the brake is triggered decreases with speed, so that larger individual errors in a measurement have an even greater impact. Disclosure of the invention.

[0008] The inventive method for operating an ultrasonic sensor of a vehicle with the features of claim 1 has the advantage that ground reflections and thus the interference factors for the angle measurement are minimized. In addition, the sensitivity of the sensor with respect to the detection of echoes can be increased. This is achieved according to the invention by changing a directional characteristic of the ultrasonic sensor depending on the speed in order to minimize a measurement error. The speed dependence relates to the vehicle on which the ultrasonic sensor is mounted. The strength of the directional characteristic of the ultrasonic sensor is angle-dependent and preferably has a main direction in which the intensity of the ultrasonic signal is maximum. The sound cone of the directional characteristic preferably has a usable opening angle of 30°.

[0009] The subclaims show preferred developments of the invention.

[0010] Preferably, the directional characteristic of the ultrasonic sensor is aligned essentially parallel to a direction of origin up to a first vehicle speed. The direction of origin refers to the main direction of the directional characteristic. Essentially means that the directional characteristic is aligned parallel to the direction of origin, taking into account usual tolerances. The direction of origin is preferably aligned vertically to a surface of the ultrasonic sensor facing outwards on the vehicle. At low speeds, the brake can only be triggered late, i.e. at object distances of less than 50 cm. In this distance range, a good signal-to-noise ratio can be assumed because the signal amplitude is still sufficiently large due to the low geometric and atmospheric attenuation and because ground reflections only occur at greater distances at typical installation heights of 50 cm.

[0011] Preferably, the origin direction is aligned at a first angle between 0° and 20° to the ground, so that the directional characteristic of the ultrasonic sensor is parallel to the ground or aligned toward the ground. This allows for a good compromise between the detection of low objects and the detection of tall objects at greater distances. The origin direction is usually specified by an installation guideline for the ultrasonic sensor.

[0012] Further preferably, the directional characteristic of the ultrasonic sensor is directed away from the ground up to a second angle relative to the original direction as the vehicle speed increases, particularly in the direction of travel, between the first vehicle speed and a second vehicle speed that is faster than the first vehicle speed. Thus, fewer ground reflections can be received and the angle measurement error is reduced.

[0013] The directional characteristic of the ultrasonic sensor is preferably directed between the second vehicle speed and a third vehicle speed that is faster than the second vehicle speed, as the vehicle speed increases back to the original direction towards the ground. By adjusting the directional characteristic upwards the signal amplitude is reduced. Near the maximum range of the sensor the signal-to-noise ratio is noise dominated, i.e. adjusting the direction upwards causes a deterioration in the signal-to-noise ratio and thus an increase in the measurement error. The distance range relevant for a braking decision increases with increasing speed. Above 2.77 m / s only detections between 2 m and 4.5 m are relevant for braking activation. In this detection range ground reflections have a lesser interference influence.For this reason, it is advantageous to reduce the angle of the sensor again.

[0014] Further preferably, the directional characteristic of the ultrasonic sensor is aligned substantially parallel to the original direction for vehicle speeds faster than the third vehicle speed. Thus, at higher speeds, detections can be recorded at great distances with a good signal-to-noise ratio. The first vehicle speed is preferably between 0.27 and 0.55 m / s. Up to this speed, the brake can only be triggered late at object distances of less than 50 cm. By aligning the directional characteristic in the original direction, low and nearby objects can be detected with a low measurement error.

[0015] More preferably, the second vehicle speed is between 0.56 and 0.83 m / s. This can reduce measurement errors caused by ground reflections for objects slightly further away.

[0016] Particularly preferably, the third vehicle speed is limited by the maximum range of the ultrasonic sensor. Thus, the noise in the range of the maximum range of the ultrasonic sensor can be adjusted depending on the respective ultrasonic sensor.

[0017] In particular, for an ultrasonic sensor with a maximum range of 4.5 m, the third speed is preferably 3.33 m / s.

[0018] Preferably, the second angle is between 10° and 20° in the direction of travel. The second angle is particularly preferably 15°. Thus, at a second vehicle speed, ground reflections can be reduced and the angle measurement error of the ultrasonic sensor can be reduced.

[0019] Furthermore, the invention describes a device for speed-dependent adaptation of the directional characteristic of an ultrasonic sensor, comprising an ultrasonic sensor and a control unit which is configured to carry out a method described above.

[0020] Short description of the drawings

[0021] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing:

[0022] Figure 1 shows a vehicle with a device for speed-dependent adaptation of the directional characteristic of an ultrasonic sensor according to a preferred embodiment, and

[0023] Figure 2 is a line diagram showing a directional characteristic of the

[0024] Ultrasonic sensor as a function of vehicle speed according to the preferred embodiment.

[0025] Embodiments of the invention

[0026] In the following, a method for operating an ultrasonic sensor 100 of a vehicle 101, as well as a device 105 for speed-dependent adaptation of a directional characteristic 104 of the ultrasonic sensor 100 according to a preferred embodiment of the invention are described in detail with reference to Figures 1 and 2.

[0027] Figure 1 shows the vehicle 101 with the device 105 for speed-dependent adaptation of the directional characteristic 104 of the ultrasonic sensor 100. The device 105 comprises the ultrasonic sensor 100 and a control unit 102. The control unit 102 is configured to control the directional characteristic 104 of the ultrasonic sensor 100 and to carry out the method for operating the ultrasonic sensor 100.

[0028] The ultrasonic sensor 100 is mounted on the front of the vehicle 101. A first lobe-shaped directional characteristic 106 and a second lobe-shaped directional characteristic 107 are shown extending from the ultrasonic sensor 100.

[0029] The first directional characteristic 106 is oriented in the direction of origin R1. The origin R1 is oriented vertically to a surface of the ultrasonic sensor 100 oriented in the direction of travel R2. The ultrasonic sensor 100 is arranged obliquely to the ground 200, so that the origin R1 points at a first angle a toward the ground 200.

[0030] The second directional characteristic 107 is angled by a second angle ß to the

[0031] Original direction R1 directed away from the ground 200. The second angle ß lies in a plane that intersects the ultrasonic sensor 100 and is aligned vertically to the ground 200 in the direction of travel R1. Thus, the ultrasonic sensor 100 receives fewer ground reflections from the second directional characteristic 107 than from the first directional characteristic 106. In return, the first directional characteristic 106 has a detection range that can detect closer objects to the vehicle 101. Due to the stronger alignment toward the ground 200, the first directional characteristic 106 has an improved signal-to-noise ratio in the area of ​​the maximum range of the ultrasonic sensor 100.

[0032] The method for operating the ultrasonic sensor 100 changes the directional characteristic 104 of the vehicle such that a measurement error of the ultrasonic sensor 100 when detecting objects is minimized. For this purpose, the ultrasonic sensor 100 has the first directional characteristic 106 up to a first vehicle speed v1. As the vehicle speed 103 increases, the directional characteristic 104 of the ultrasonic sensor 100 is directed away from the ground 200 until, at a second vehicle speed v2, the directional characteristic 104 assumes the second directional characteristic 107, which is arranged at a second angle β to the first directional characteristic 106. As the vehicle speed 103 continues to increase, the directional characteristic 104 is directed towards the ground 200 until, at a third vehicle speed v3, it is again aligned in the original direction R1 and forms the first directional characteristic 106.

[0033] The signal lobe of the first directional characteristic 106 and the second directional characteristic 107 have an opening angle of 30°.

[0034] Figure 2 shows the relationship between the vehicle speed 103 and the angle 108 of the directional characteristic 104 in a line diagram. The vehicle speed 103 is plotted on the abscissa and the angle 108 on the ordinate.

[0035] The angle 108 is measured in a plane which is oriented perpendicular to the ground 200 in the direction of travel R2. The original direction R1 has an angle of 0°. The angle 108 is measured from the ground 200 upwards. For vehicle speeds 103 between the standstill and the first vehicle speed v1, the angle 108 is essentially 0°. The first vehicle speed v1 is preferably 0.4 m / s. At the second vehicle speed v2, the directional characteristic 104 of the ultrasonic sensor 100 has the second angle β. Between the first speed v1 and the second speed v2, the angle 108 increases from 0° to the second angle β. The second vehicle speed v2 is preferably 0.7 m / s.

[0036] Between the second vehicle speed v2 and the third vehicle speed v3, the angle 108 decreases essentially linearly until the angle 108 reaches the original direction R1 at 0° at the third speed v3.

[0037] The third vehicle speed v3 depends on the maximum range of the ultrasonic sensor 100 and the measurement error within this range. With a typical maximum range of 4.5 m, the third vehicle speed v3 is 3.3 m / s.

[0038] For vehicle speeds 103 which are faster than the third vehicle speed v3, the directional characteristic 104 remains aligned in the original direction R1.

[0039] The vehicle speed 103 is to be understood as the amount of the vehicle speed 103, so that the method is also applicable when reversing for rear-facing ultrasonic sensors 100.

Claims

Claims 1. A method for operating an ultrasonic sensor (100) of a vehicle (101), wherein a directional characteristic (104) of the ultrasonic sensor (100) is changed as a function of speed in order to minimize a measurement error.

2. The method according to claim 1, wherein the directional characteristic (104) of the ultrasonic sensor (100) is aligned substantially parallel to an original direction (R1) up to a first vehicle speed (v1).

3. The method according to claim 2, wherein the origin direction (R1) is oriented at a first angle (α) between 0° and 20° to the ground (200).

4. The method according to one of claims 2 or 3, wherein the directional characteristic (104) of the ultrasonic sensor (100) is directed away from the ground (200) between the first vehicle speed (v1) and a second vehicle speed (v2) which is faster than the first vehicle speed (v1) as the vehicle speed (103) increases up to a second angle (ß) to the original direction (R1), in particular is directed away from the ground (200) in the direction of travel (R2).

5. The method according to claim 4, wherein the directional characteristic (104) of the ultrasonic sensor (100) is directed between the second vehicle speed (v2) and a third vehicle speed (v3) which is faster than the second vehicle speed (v2) as the vehicle speed (103) increases up to the original direction (R1) in the direction of the ground (200).

6. The method according to claim 5, wherein the directional characteristic (104) of the ultrasonic sensor (100) for vehicle speeds (103) which are faster than the third vehicle speed (v3) is aligned substantially parallel to the direction of origin (R1).

7. Method according to one of claims 2 to 6, wherein the first vehicle speed (v1) is between 0.27 and 0.55 m / s 8. The method according to any one of claims 4 to 7, wherein the second vehicle speed (v2) is between 0.56 and 0.83 m / s 9. The method according to any one of claims 5 to 8, wherein the third vehicle speed (v3) is limited by the maximum range of the ultrasonic sensor (100).

10. The method according to claim 9, wherein for an ultrasonic sensor (100) with a maximum range of 4.5 m, the third speed (v3) is 3.33 m / s.

11. Method according to one of claims 4 to 10, wherein the second angle (ß) is between 10° and 20°.

12. Device for speed-dependent adaptation of the directional characteristic (104) of an ultrasonic sensor (100), comprising an ultrasonic sensor (100) and a control unit (102) which is configured to carry out a method according to one of claims 1 to 11.

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