Method and apparatus for testing the functionality of a sensor device

Abstract

Method for testing the functionality of a sensor device (3) for detecting a pedestrian impact on a motor vehicle (1), which has a flexible container (4) on which at least one pressure sensor (5, 6) for detecting an internal container pressure is arranged, wherein the container (4) has at least one air-permeable membrane (10) for pressure equalization with the environment, characterized in that the frequency response, in particular low-pass response, of the pressure sensor (5, 6) is monitored for a change, and that a decision is made regarding damage to the container (4) if the change exceeds a predefinable limit value.

Description

[0001] The invention relates to a method for testing the functionality of a sensor device for detecting a pedestrian impact, which has a flexible container on which at least one pressure sensor for detecting pressure in the container is arranged, wherein the hose has at least one air-permeable membrane for pressure equalization.

[0002] Furthermore, the invention relates to a device for carrying out the aforementioned method. State of the art

[0003] Methods and devices of the type mentioned above are known from the prior art. The sensor devices described above are used in particular in pedestrian protection systems of motor vehicles, and especially in the front bumper of a motor vehicle. The container extends in a tube-like shape across the width of the bumper in order to detect a pedestrian impact at any point. The impact elastically deforms the tube, which changes the pressure detected by the at least one pressure sensor. The tube is usually filled with air, and under normal circumstances the internal pressure, i.e., the pressure inside the tube, corresponds to the ambient pressure because air exchange is provided by a pressure equalization element, in particular an air-permeable membrane. The membrane prevents water and dirt from penetrating the interior of the tube.If a pressure sensor is arranged at each end of the hose, in the event of an impact that occurs off-center on the hose between the two pressure sensors, it is also possible to determine where the impact took place due to the time-separated detection of a pressure change by the two pressure sensors.

[0004] However, if the container is damaged, allowing direct pressure equalization with the environment (for example, if the container ruptures), the pressure measured by the pressure sensor will be distorted. In such a case, an impact might not be detected correctly, and a safety measure, such as raising the hood, could not be initiated. To avoid this problem, it is known, for example, from DE 10 2011 083 027 A1, to use a hose without a pressure equalization element and to measure the temperature in the hose. This allows the system to determine the expected pressure change in the hose based on a temperature change, thus indicating whether a temperature change will lead to a corresponding pressure change or not. Disclosure of the invention

[0005] The method according to the invention, with the features of claim 1, has the advantage that it eliminates the need for an additional temperature sensor and retains the existing operating principle of the sensor device, thus avoiding any additional effort. According to the invention, the frequency response, in particular the low-pass response of the pressure sensor, is monitored for changes, and damage to the sensor device is inferred if the change exceeds a predefinable limit. It is assumed that pressure equalization with the environment occurs more slowly than a pressure change caused by an impact.For pressure equalization, the frequency response or low-pass behavior of at least one pressure sensor is therefore crucial and can thus also be used to determine the functionality of the sensor device and, in particular, the integrity of the container.

[0006] According to a preferred embodiment of the invention, an output signal from the pressure sensor is acquired to determine the low-pass or frequency response. This can be achieved by a simple evaluation of the sensor signal. In particular, the low-pass response is determined by means of a fast Fourier transform (FFT) or a high-pass filter.

[0007] Furthermore, it is preferably provided that a gradient of the frequency response is monitored to determine the low-pass filter behavior. In particular, the gradient is compared with a predefined limit value. If the gradient exceeds the predefined limit value, it is recognized that damage must be present. The limit value is selected specifically based on the air permeability of the membrane, such that a gradient corresponding to pressure equalization according to the air permeability of the membrane is recognized as permissible.

[0008] Furthermore, it is preferably provided that a pressure change in the vicinity of the sensor device is induced or detected to determine the frequency response or low-pass filter behavior. Depending on the induced and detected pressure change, the pressure response or measurement behavior of the pressure sensor can then be assessed, and the low-pass filter behavior can be compared with an actual pressure change.

[0009] Optionally, the pressure change can be detected by an external pressure sensor. A pressure sensor located externally to the sensor device, particularly to the container, thus detects the ambient pressure, allowing both the ambient pressure and the pressure inside the container to be measured. If a change in the ambient pressure is detected, the frequency response / low-pass filter of the pressure sensor is monitored to determine whether it detects pressure equalization according to the membrane's properties, or whether the gradient of the change is so large that direct pressure equalization occurs, bypassing the membrane, for example, through a hole or crack in the container.

[0010] It is further preferably provided that the pressure change is caused by a motor vehicle equipped with the sensor device entering or exiting a tunnel. For testing purposes, data from the motor vehicle's navigation system is used. The navigation system is used to determine, in particular, whether the motor vehicle is entering or exiting a tunnel. This allows a comparison with the data acquired by the at least one pressure sensor to verify the plausibility of the data. If the pressure sensor signal from the pressure sensor device does not correspond to this pressure change, it is then recognized that the container is damaged.

[0011] Furthermore, it is preferably intended that the pressure change is caused by driving uphill. The driver is guided, for example, by the navigation system, to drive on an uphill or downhill slope, thus changing the ambient air pressure. The behavior of the pressure sensor is then checked based on this change in air pressure in order to detect any damage to the container.

[0012] Furthermore, it is preferably provided that a pressure change caused by driving uphill or entering and / or exiting a tunnel is detected. For this purpose, data from a navigation system or environmental sensors, particularly those with a camera system, are used to detect whether the vehicle is entering or exiting a tunnel, or driving uphill or downhill. This allows an expected change in ambient air pressure and / or an expected pressure change within the container to be calculated and compared with the actual pressure behavior in order to confirm the container's condition.

[0013] The device according to the invention, with the features of claim 10, is characterized by a specially designed control unit that carries out the method according to the invention when used as intended. This results in the advantages already mentioned.

[0014] The invention will now be explained in more detail with reference to the drawing. To this end, we show Fig. 1 a motor vehicle with a sensor device for detecting a pedestrian impact in a simplified top view and Fig. 2 a simplified model for carrying out a procedure for detecting damage to the sensor device.

[0015] Fig. Figure 1 shows a simplified top view of a motor vehicle 1, which has a sensor device 3 in its front bumper 2 for detecting a pedestrian impact. The sensor device 3 has a tubular container 4, which is elastically deformable. A pressure sensor 5 or 6 is assigned to each of its two ends of the container 4. The two pressure sensors are designed and arranged to monitor the pressure inside the container 4. Both pressure sensors 5 and 6 are connected to a control unit 7. The control unit 7 is also optionally connected to an ambient pressure sensor 8 and to a navigation system 9.

[0016] The control unit 7 monitors the output signals of the pressure sensors 5, 6 and in particular detects the low-pass behavior of the pressure sensors 5, 6 as a function of a pressure change in the environment of the motor vehicle 1.

[0017] Fig.Figure 2 shows a simplified representation of a module for monitoring the low-pass behavior of the pressure sensors 5 and 6. The input values ​​are the ambient pressure p and, optionally, an external mechanical force F, which is generated, for example, by a pedestrian impacting the front bumper 2. The module has three parts: I, II, and III. Part I comprises the sensor assembly 3. Part II includes an analog signal evaluation of the exclusion signals supplied by the pressure sensors 5 and 6 by the control unit 7. Part III includes an anti-aliasing filter, an analog-to-digital converter, a digital filter, and a digital down-converter (DDC). The low-pass behavior of the pressure sensors 5 and 6 is determined by means of frequency analysis, in particular frequency conversion, for example, by a fast Fourier transform and a high-pass filter.It is assumed that output signals U. L and U RThe low-pass behavior of the pressure sensors 5, 6 is dominated by the connection between the volume connected in the container 4 and the environment. In this case, this connection is realized by at least one air-permeable membrane 10, which in particular forms a section of the outer wall of the container 4. A significant change in the low-pass behavior is expected if the container 4 is damaged, resulting in a faster pressure equalization between the container interior and the environment. Thus, an undamaged container 4 can be distinguished from a damaged container 4 by monitoring the frequency response or the low-pass behavior of the sensor device 3.As soon as the output signals of the pressure sensors 5, 6 are no longer dominated by the low-pass behavior, it can be assumed that the container 4 has a hole or a crack through which pressure equalization with the environment takes place.

[0018] To monitor the low-pass behavior of the sensor device 3, it is advantageous to excite or change the input value, namely the ambient pressure p. This is the case, for example, when the vehicle 1 enters a tunnel or drives up or down a steep incline. This changes the ambient pressure acting on the container 4, and thus, depending on the air permeability of the membrane 10 and the integrity of the container 4, the pressure in the container 4, which is detected by the pressure sensors 5, 6, changes.To prevent a sudden pressure change, detected by pressure sensors 5 and 6 (for example, when entering a tunnel, the ambient pressure also changes suddenly), from being interpreted as a pedestrian impact on the bumper 2, the low-pass filter behavior is compared to a predefined limit value, which specifically concerns the gradient of the change in the low-pass filter behavior. Unlike a pedestrian impact, a very slow change in the low-pass filter behavior is expected.

[0019] Entering a tunnel or driving up an incline is detected, in particular, using data from the navigation system 9. Based on this data, for example, an expected pressure change is calculated and compared with the actual pressure change detected by pressure sensors 5 and 6. The ambient pressure detected by pressure sensor 8 can also be directly compared with the internal pressures detected by pressure sensors 5 and 6 to determine the low-pass filter response of pressure sensors 5 and 6 to changes in ambient pressure.

Claims

[1] Method for testing the functionality of a sensor device (3) for detecting a pedestrian impact on a motor vehicle (1), which has a flexible container (4) on which at least one pressure sensor (5, 6) is arranged for detecting an internal container pressure, wherein the container (4) has at least one air-permeable membrane (10) for pressure equalization with the environment, characterized by , that the frequency response, in particular the low-pass response, of the pressure sensor (5,6) is monitored for changes, and that a decision is made regarding damage to the container (4) if the change exceeds a predefinable limit. [2] Method according to claim 1, characterized by , that to determine the low-pass behavior or frequency behavior, an output signal from the pressure sensor (5,6) is recorded. [3] Method according to any one of the preceding claims, characterized by, that a gradient of the frequency response is recorded to determine the frequency response or low-pass behavior. [4] Method according to any one of the preceding claims, characterized by , that to determine the low-pass behavior a pressure change is caused or detected in the environment of the sensor device (3). [5] Method according to any one of the preceding claims, characterized by , that the pressure change is detected by an external pressure sensor (8). [6] Method according to any one of the preceding claims, characterized by , that the pressure change is caused by entering or exiting a tunnel with the motor vehicle (1) having the sensor device (3). [7] Method according to any one of the preceding claims, characterized by that the pressure change is caused by driving uphill. [8] Method according to any one of the preceding claims, characterized by, that a pressure change is detected when driving uphill and / or entering or exiting a tunnel. [9] Method according to any one of the preceding claims, characterized by , that entering or exiting and / or driving on an incline is detected by means of a satellite-based navigation system (9) or environmental sensors of the motor vehicle. [10] Device for testing the functionality of a sensor device (3) for detecting a pedestrian impact on a motor vehicle, which has a flexible container to which at least one pressure sensor (5, 6) is arranged for detecting an internal pressure of the container (4), wherein the container (4) has at least one air-permeable membrane for pressure equalization with the environment, characterized by a control unit which, when used as intended, performs the method according to any one of claims 1 to 9.

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