Impact sensor

Abstract

An impact sensor for a vehicle. The impact sensor includes at least one strain-sensitive sensor element which comprises a sensor material, and at least two terminals, between which the sensor material is electrically connected. The sensor material is a metal-containing carbon material.

Claims

1. An impact sensor for a vehicle, comprising: at least one strain-sensitive sensor element which comprises a sensor material disposed as a layer on a carrier element, said sensor material being a nickel-containing hydrogenated amorphous carbon material, and at least two terminals disposed at opposite ends of the carrier element, between which the sensor material is electrically connected.

2. The impact sensor according to claim 1, wherein the layer of sensor material has a thickness of 10-100 nm.

3. The impact sensor according to claim 2, wherein the layer is a sputtered layer.

4. The impact sensor according to claim 2, wherein the terminals are screen printed onto said carrier element.

5. The impact sensor according to claim 1, wherein the carrier element is a polymer sheet.

6. The impact sensor according to claim 1, wherein a maximum dimension of the impact sensor is less than 200 mm.

7. An impact detection system for a vehicle, comprising at least one impact sensor, said impact sensor comprising: at least one strain-sensitive sensor element which comprises a sensor material disposed as a layer on a carrier element, said sensor material being a nickel-containing hydrogenated amorphous carbon material, and at least two terminals disposed at opposite ends of the carrier element, between which the sensor material is electrically connected.

8. The impact detection system according to claim 7, further comprising an exterior component for the vehicle, in which the at least one impact sensor is disposed.

9. The impact detection system according to claim 8, a plurality of impact sensors which are staggered along the exterior component.

10. The impact detection system according to claim 7, further comprising a processing unit, which is connected to the at least one impact sensor, said processing unit being configured to identify an impact situation based on a variation of the electrical resistance of the at least one impact sensor.

11. The impact detection system according to claim 10, wherein the processing unit is connected and configured to individually measure the resistance of each of a plurality of subsets of a plurality of impact sensors.

12. The impact detection system according to claim 10, wherein the processing unit is configured to identify an impact location based on a location of at least one impact sensor which shows a variation of its electrical resistance.

13. The impact detection system according to claim 10, wherein the processing unit is configured to determine an impact energy based on a combination of the variations of the electrical resistances of several impact sensors.

14. The impact detection system according to claim 7, wherein the layer of sensor material has a thickness of 10-100 nm.

15. The impact detection system according to claim 14, wherein the layer is a sputtered layer.

16. The impact detection system according to claim 14, wherein the carrier element is a polymer sheet.

17. A method for impact detection for a vehicle, with at least one impact sensor, said impact sensor comprising: at least one strain-sensitive sensor element which comprises a sensor material disposed as a layer on a carrier element, said sensor material being a nickel-containing hydrogenated amorphous carbon material, and at least two terminals disposed at opposite ends of the carrier element, between which the sensor material is electrically connected; the method comprising the steps of: measuring the electrical resistance of the at least one impact sensor; and identifying an impact situation based on a variation said electrical resistance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic representation of an embodiment of an inventive impact sensor;

(3) FIG. 2 is a schematic view of a vehicle front with an embodiment of an inventive impact detection system.

(4) FIG. 3 is a schematic view of the vehicle front of FIG. 2 with an impacting object in a first position.

(5) FIG. 4 is a diagram illustrating the time evolution of the resistance variation of the impact sensors corresponding to FIG. 3;

(6) FIG. 5 is a schematic view of the vehicle front of FIG. 2 with an impacting object in a second position; and

(7) FIG. 6 is a diagram illustrating the time evolution of the resistance variation of the impact sensors corresponding to FIG. 5.

DETAILED DESCRIPTION

(8) FIG. 1 shows a schematic view of an impact sensor 2 according to an embodiment of the present invention. The impact sensor 2 is generally rectangular in shape having a length of approximately 100 mm and a width of 15 mm. It is understood, though, that the size and the shape of the impact sensor 2 could be varied. The shape is generally given by a rectangular polymer sheet 3, which has a thickness of 100 m. In the embodiment shown, the polymer sheet 3 is made of polyimide. On this polymer sheet 3, a layer of sensor material 5 is disposed. The sensor material 5 is Nickel-containing hydrogenated amorphous carbon (Ni:a-C:H), which has been disposed on the polymer sheet 3 by sputtering. The thickness of the layer of sensor material 5 is about 60 nm. The sensor material 5, which is part of a strain-sensitive sensor element 4, is electrically connected between two terminals 6.1, 6.2. These terminals 6.1, 6.2 are made of silver ink and have been disposed on the polymer sheet 3 by screen printing. The thickness of the terminals 6.1, 6.2 is about 20 m.

(9) As can be seen from the dimensions described above, the impact sensor 2 is highly flexible and may be bent easily. When such bending occurs, the electrical resistance of the sensor material 5 undergoes a variation. In the present embodiment, this variation is increased by a meandering structure of the sensor element 4. The variation is easily detectable when a voltage is applied to the terminals 6.1, 6.2 and the current is measured.

(10) In order to protect the thin layers of the sensor element 4 and the terminals 6.1, 6.2, a protective cover layer will generally be added. For sake of simplicity, such a cover layer is not shown in FIG. 1.

(11) FIG. 2 schematically illustrates a vehicle front with a bumper 100, a radiator 101, headlights 102 and number plate holder 103. Five impact sensors 2.1-2.5 are integrated into the bumper 100. The bumper may have a common structure with a hard outer plastic skin and a foam or a plastic absorber filling. In this case, the impact sensors 2.1-2.5 may be integrated immediately underneath the plastic skin, so that they can detect any impact immediately.

(12) The impact sensors 2.1-2.5 are part of an impact detection system 1. They are identical to the impact sensor 2 shown in FIG. 1. Each of them is connected via terminals 6.1, 6.2 to a processing unit 10. For sake of simplicity, the connections are not shown in FIG. 2. The processing unit 10 is configured to apply a voltage to each of the impact sensors 2.1-2.5 and to measure the electrical resistance. During normal operation of the vehicle, the resistance is nearly constant, because the sensor material 5 is practically not influenced by temperature changes or humidity.

(13) As can be seen from FIG. 2, the sensors 2.1-2.5 are disposed in a staggered manner along the bumper 100. In the embodiment shown, the sensors 2.1-2.5 laterally spaced apart, but they might also be disposed next to each other. The third sensor 2.3 is disposed considerably lower than the other sensors 2.1, 2.2, 2.4, 2.5 in order to avoid the radiator 101.

(14) FIG. 3 shows an impact situation, wherein the bumper 100 collides with a stationary pole 110 in the region of the second impact sensor 2.2. The impact leads to a deformation of the bumper 100, and thus to a deformation of the impact sensor 2.2, which in turn leads to a variation of the resistance of the impact sensor 2.2.

(15) FIG. 4 illustrates the resistance variation of the sensors 2.1-2.5 over time. What is shown is actually the variation of electrical resistance of sensor 2.2 vs time. The partial diagrams are labelled with numbers in circles, which corresponds to the numbers shown in FIG. 3. Since the first sensor 2.1 and the third through fifth sensor 2.3-2.5 are unaffected by the impact, there resistance remains constant, wherefore their variation is zero.

(16) The resistance of the second sensor 2.2, however, shows a considerable increase as the pole 110 is hit. The increase is shown by the curve in FIG. 4. Depending on the speed of the vehicle, usually within a few milliseconds, the curve reaches a peak value, marked by the dashed line in FIG. 4. After some time, the deformation of the sensor 2.2 has reached a maximum value, wherefore the resistance variation goes back to zero.

(17) FIG. 5 shows a similar impact situation as FIG. 3. In this case, however, the bumper 100 collides with the stationary pole 110 in between the first impact sensor 2.1 and the second impact sensor 2.2. In this case, the deformation of the bumper 100 leads to a deformation of both impact sensors 2.1, 2.2, which, however, is not as severe as in the scenario shown in FIG. 3, because neither of the impact sensors is hit directly. Again, the deformation of the impact sensors 2.1, 2.2 leads to a variation of their resistance.

(18) FIG. 6, similar to FIG. 4, illustrates the resistance variation of the sensors 2.1-2.5 over time. Again, the third through fifth sensor 2.3-2.5 are unaffected by the impact, wherefore their resistance remains constant and their variation is zero.

(19) The resistance of the first and second sensor 2.2, however, each increase in the process of the impact, shown by the curves in FIG. 6. The overall shape of the curves is similar to the curve shown in FIG. 4. However, since neither of the first and second impact sensor 2.1, 2.2 is deformed as severely as in the previous scenario, each of the curves reaches a peak value that is approximately half as high as the peak value in FIG. 4.

(20) In each of the scenarios shown in FIG. 3 and the FIG. 5, respectively, the processing unit 10 can detect the impact location based on the location of the impact sensors which are responding, i.e. which show a variation of their resistance. Furthermore, the cumulated resistance variation of all impact sensors 2.1-2.5 is calculated and used as a measure for the total energy of the impact. It should be noted that, although the peak value of the individual curves in FIG. 6 is less than in the FIG. 4, the integral of both curves, representing the cumulated resistance variation, is approximately the same as in FIG. 4. Therefore, a realistic estimate of the severity of the impact can be derived.

(21) In order to derive the impact energy from the resistance variation, a calibration process may be performed with a bumper 100 having the same configuration of impact sensors 2.1-2.5. In such a calibration process, several impacts with known energy can be generated and the resistance variation of the impact sensors can be measured. The measured values can be used for database of the processing unit 10.

(22) FIG. 6 represents a situation in which both sensors 2.1, 2.2 are equally affected if the impact location is in the middle between both sensors 2.1, 2.2. If, however, the bumper in the area of the first sensor 2.1 has a greater stiffness then in the area of the second sensor 2.2, this would lead to a minor deformation of the first sensor 2.1. Anyhow, such effects can be accounted for if a calibration process as described above is performed. In calculating the cumulated resistance variation, the processing unit may apply weighting factors to the individual variations instead of simply summing them up.

(23) In any case, the impact detection system 1 can detect and evaluate an impact situation practically without any delay, because the impact sensors 2.1-2.5 are disposed immediately at the location of the impact. Also, since the resistance of the individual sensors 2.1-2.5 is easy to measure and does not depend on temperature or humidity, the system 1 is very reliable.