CAPACITIVE OCCUPANT DETECTION SYSTEM WITH ISOFIX DISCRIMINATION

Abstract

In addition to the loading mode of a capacitive sensing device of a seat occupancy detection and classification system, a second measurement mode is introduced, which allows a discrimination of objects (CRS or human) with and without grounding condition. Depending on the value of the new measurement, the data is allocated to different groups which are subject to different thresholds in the loading mode. This means that if the new measurement indicates a grounding condition of the object, a higher threshold in the loading mode will be applied. In this way CRS with grounding condition will be classified by means of the higher threshold, resulting in a robustness increase. Typical human sitting positions do not show a grounding condition and will be classified by the lower threshold.

Claims

1. A capacitive sensing device for a seat occupancy detection and classification system, including a capacitive sensor that includes at least a first electrically conductive antenna electrode and a second electrically conductive antenna electrode; an impedance measurement circuit, comprising a signal voltage source that is configured for providing, with reference to a ground potential, a periodic electrical measurement signal at an output port, and at least one sense current measurement means that is configured to measure complex sense currents with reference to a reference voltage, wherein the impedance measurement circuit is electrically connectable to said capacitive sensor such that at least the first antenna electrode is electrically connectable to the output port for receiving the electrical measurement signal, the second antenna electrode is electrically connectable via at least one controllable switch member either to the ground potential or to an electric AC potential of the output port, wherein the complex sense currents are being generated in the capacitive sensor by the provided periodic measurement signal, and a signal processing unit that is configured to determine complex impedances from measured currents at least through the first antenna electrode with reference to the complex reference potential, and to provide output signals that are representative of the determined complex impedances.

2. A seat occupancy detection and classification system, including a capacitive sensing device as claimed in claim 1, wherein the capacitive sensor is electrically connectable to the impedance measurement circuit such that a current through the second antenna electrode is measurable by said impedance measurement circuit, and wherein the signal processing unit is further configured to at least determine a complex impedance from a measured current through the second antenna electrode determined with reference to the complex reference potential, and a control and evaluation unit that is configured to receive the output signals provided by the signal processing unit, dependent on a result of the complex impedance from the measured current through the second antenna electrode, to select at least one threshold value out of predetermined threshold values for complex impedance, to compare the complex impedances from the measured current through the first antenna electrode to the at least one selected predetermined threshold value, and, based on the result of the comparing, to determine a seat occupancy class.

3. A seat occupancy detection and classification system, including a capacitive sensing device as claimed in claim 1, wherein the capacitive sensor is electrically connectable to the impedance measurement circuit such that the second antenna electrode is electrically connectable via the at least one controllable switch member either to the ground potential or to the electric AC potential of the output port, and wherein the signal processing unit is further configured to at least determine a first complex impedance from a measured current through the first antenna electrode with the second antenna electrode being electrically connected to the ground potential, and to determine a second complex impedance from a measured current through the first antenna electrode with the second antenna electrode being electrically connected to the electric AC potential of the output port, and a control and evaluation unit that is configured to receive the output signals provided by the signal processing unit, dependent on a relation between the first and the second complex impedance, to select at least one threshold value out of predetermined threshold values for complex impedance, to compare the complex impedances from the measured current through the first antenna electrode to the at least one selected predetermined threshold value, and, based on the result of the comparing, to determine a seat occupancy class.

4. A seat occupancy detection and classification system, including a capacitive sensing device as claimed in claim 1, wherein the capacitive sensor is electrically connectable to the impedance measurement circuit such that the second antenna electrode is electrically connectable via the at least one controllable switch member alternately to the ground potential and to the electric AC potential of the output port, and wherein the signal processing unit is further configured to at least determine a difference between a first complex impedance of the first antenna electrode with the second antenna electrode being electrically connected to the ground potential and a second complex impedance of the first antenna electrode with the second antenna electrode being electrically connected to the electric AC potential of the output port, and a control and evaluation unit that is configured to receive the output signals provided by the signal processing unit, dependent on the difference between the first and the second complex impedance, to select at least one threshold value out of predetermined threshold values for complex impedance, to compare the complex impedances from the measured current through the first antenna electrode to the at least one selected predetermined threshold value, and, based on the result of the comparing, to determine a seat occupancy class.

5. The seat occupancy detection and classification system as claimed in claim 3, wherein the capacitive sensing device comprises at least one remote controllable switch member and the seat occupancy detection and classification system comprises a switch remote control unit for remotely controlling the at least one remote controllable switch member.

6. The capacitive seat occupancy detection and classification system as claimed in claim 5, wherein the switch remote control unit is configured to periodically switch the remote controllable switch member to change an electrical connection of the second antenna electrode from being electrically connected to the electric ground potential to being electrically connected to the electric AC potential of the output port for a predetermined time period and back to being electrically connected to the electric ground potential after the time period has elapsed.

7. The capacitive seat occupancy detection and classification system as claimed in claim 2, further comprising a capacitive sensor, wherein the capacitive sensor is electrically connected at least to the output port of the signal voltage source and to the sense current measurement means.

8. The capacitive seat occupancy detection and classification system as claimed in claim 2, wherein the control and evaluation unit is configured to generate a classification output signal that is indicative of the determined seat occupancy class.

9. The capacitive seat occupancy detection and classification system as claimed in claim 2, wherein the at least one threshold value out of predetermined threshold values for complex impedance can be represented by a line in a two-dimensional graph spanned by a real part and an imaginary part of the complex impedance.

10. A method of operating the capacitive seat occupancy detection and classification system as claimed in claim 2, including steps of providing a periodic electrical measurement signal to the first antenna electrode of the capacitive sensor, determining a complex sense current that is being generated in the second antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, comparing the determined complex sense current to at least one predetermined threshold value for the complex sense current, depending on the result of the step of comparing, selecting at least one threshold value out of predetermined threshold values for complex impedance, determining a complex sense current that is being generated in the first antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, determining a complex impedance from the complex sense current in the first antenna electrode measured with reference to the complex reference potential, comparing the determined complex impedance to the at least one selected predetermined threshold value for complex impedance, and determining a seat occupancy class for the determined complex impedance depending on a relation between the determined complex impedance and the at least one selected predetermined threshold value for complex impedance.

11. A method of operating the capacitive seat occupancy detection and classification system as claimed in claim 3, including steps of providing a periodic electrical measurement signal to the first antenna electrode of the capacitive sensor, electrically connecting the second antenna electrode to the ground potential, determining a first complex sense current that is being generated in the first antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, determining a first complex impedance from the determined first complex sense current in the first antenna electrode measured with reference to the complex reference potential, changing the electrically connection of the second antenna electrode from the ground potential to the electric AC potential of the output port, determining a second complex sense current that is being generated in the first antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, determining a second complex impedance from the determined first complex sense current in the first antenna electrode measured with reference to the complex reference potential, determining a difference of the first complex impedance and the second complex impedance, comparing the determined difference of the first complex impedance and the second complex impedance to at least one predetermined threshold value for the difference of complex impedance, depending on the result of the step of comparing, selecting at least one threshold value out of predetermined threshold values for complex impedance, comparing the determined first complex impedance to the at least one selected predetermined threshold value for complex impedance, determining a seat occupancy class for the determined first complex impedance depending on at least one relation between the determined first complex impedance and the at least one selected predetermined threshold value for complex impedance.

12. A method of operating the capacitive seat occupancy detection and classification system as claimed in claim 4, including steps of providing a periodic electrical measurement signal to the first antenna electrode of the capacitive sensor, alternately connecting the second antenna electrode to the ground potential and to the electric AC potential of the output port, determining a difference between a first complex impedance of the first antenna electrode with the second antenna electrode being electrically connected to the ground potential and second complex impedance of the first antenna electrode with the second antenna electrode being electrically connected to the electric AC potential of the output port, comparing the determined difference of the first complex impedance and the second complex impedance to at least one predetermined threshold value for the difference of complex impedance, depending on the result of the step of comparing, selecting at least one threshold value out of predetermined threshold values for complex impedance, comparing the determined first complex impedance to the at least one selected predetermined threshold value for complex impedance, determining a seat occupancy class for the determined first complex impedance depending on at least one relation between the determined first complex impedance and the at least one selected predetermined threshold value for complex impedance.

13. A vehicle seat, comprising a seat cushion having at least one seat foam member, a seat base configured for receiving at least a portion of the seat cushion, the seat base and the seat cushion being provided for supporting a bottom of a seat occupant, a backrest that is provided for supporting a back of the seat occupant, and a seat occupant detection and classification system as claimed in claim 2, wherein the capacitive sensor is arranged at at least one out of the seat cushion and the backrest.

14. The seat as claimed in claim 13, wherein at least one out of the first antenna electrode and the second antenna electrode is formed by an electrical seat heater member that is installed in the seat.

15. A non-transitory, computer readable medium for carrying out the method as claimed in claim 10, wherein the method steps are stored on the computer readable medium as program code that is executable by a processor unit of the capacitive seat occupancy detection and classification system or a separate control unit.

16. Use of the capacitive seat occupancy detection and classification system as claimed in claim 2 in a vehicle seat that includes a seat structure for erecting the vehicle seat on a passenger cabin floor of the vehicle, a seat cushion having at least one seat foam member, a seat base supported by the seat structure and configured for receiving the seat cushion, the seat base and the seat cushion being provided for supporting a bottom of a seat occupant, a backrest that is provided for supporting a back of the seat occupant, wherein the capacitive sensor member is arranged at at least one out of the seat cushion and the backrest.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0110] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

[0111] FIG. 1 schematically illustrates a vehicle seat with a first installed embodiment of a seat occupancy detection and classification system in accordance with the invention;

[0112] FIG. 2 schematically illustrates details of the functional principle of the seat occupancy detection and classification system in accordance with the invention; and

[0113] FIG. 3 schematically shows details of the first installed embodiment of the seat occupancy detection and classification system in accordance with the invention;

[0114] FIG. 4 schematically shows the vehicle seat with a second installed embodiment of the seat occupancy detection and classification system in accordance with the invention;

[0115] FIGS. 5A to 5C schematically illustrate details of the operating principle of the seat occupancy detection and classification system in accordance with the invention; and

[0116] FIG. 6 is a flowchart of an embodiment of a method in accordance with the invention of operating the seat occupancy detection and classification system pursuant to FIG. 1.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0117] FIG. 1 schematically shows a seat 34 formed as a vehicle seat, comprising a capacitive seat occupancy detection and classification system 10 in accordance with an embodiment of the invention. The vehicle seat is designed as a seat of a passenger car and includes a seat structure (not shown) by which it is erected on a passenger cabin floor of the passenger car, as is well known in the art.

[0118] The seat 34 further includes a seat base 36 supported by the seat structure and configured for receiving a seat cushion 38 for providing comfort to a seat occupant. The seat cushion 38 of the vehicle seat comprises a seat foam member and a fabric cover, which has been omitted in FIG. 1. The seat base 36 and the seat cushion 38 are provided for supporting a bottom of the seat occupant. A backrest 40 of the seat 34 is provided for supporting a back of the seat occupant.

[0119] The vehicle seat occupant detection and classification system 10 includes a capacitive sensor 16, a capacitive sensing device 12 and a control and evaluation unit 26. The capacitive sensor 16 is located on the A-surface of the seat cushion 38, underneath the fabric cover. The capacitive sensing device 12 and the control and evaluation unit 26 are installed in the vehicle, remote from the vehicle seat. An output port of the control and evaluation unit 26 is connected to an airbag control unit 60. The capacitive sensing device 12 comprises an impedance measurement circuit 14 and a signal processing unit 22.

[0120] The impedance measurement circuit 14 includes a signal voltage source that is configured for providing, with reference to a ground potential 64, a periodic electrical measurement signal at an output port, and a sense current measurement means that is configured to measure complex sense currents with reference to a reference voltage. The sense current measurement means may be formed as a transimpedance amplifier, which is connected to a sensing antenna electrode and which converts a current flowing into the sensing antenna electrode into a voltage, which is proportional to the current flowing into the sensing antenna electrode. In principle, any other sense current measurement means could be employed that appears to be suitable to those skilled in the art.

[0121] The capacitive sensor 16 comprises a first electrically conductive antenna electrode 18 and a second electrically conductive antenna electrode 20 that are arranged side by side at the seat cushion A surface, mutually galvanically separate from each other (FIG. 3). The first antenna electrode 18 and the second antenna electrode 20 are capacitively coupled, which is indicated by a capacitor 30 shown as electrically connected to both antenna electrodes 18, 20. An object approaching the antenna electrodes 18, 20 is represented by an unknown capacitor 32 that is connected to the ground potential 64, which for instance may be a vehicle ground potential. If the object approaches the antenna electrodes 18, 20, the respective unknown capacitor 32 changes its capacitance, and a sense current flowing between the antenna electrode 18, 20 and ground potential 64 changes.

[0122] The first antenna electrode 18 and the second antenna electrode 20 are made e.g. from thin aluminum foil or, alternatively, from an aluminized plastic material such as polyethylene terephthalate (PET). The capacitive sensor 16 is electrically connected to the impedance measurement circuit 14 such that the first antenna electrode 18 is electrically connected to the output port for receiving the electrical measurement signal. The second antenna electrode 20 is electrically connectable via a remote controllable switch member either to the ground potential 64 or to an electric AC potential of the output port. For this specific embodiment, it shall be presumed that the second antenna electrode 20 is connected to the impedance measurement circuit 14 such that a current through the second antenna electrode 20 is measurable by said impedance measurement circuit 14.

[0123] In this specific embodiment, both the antenna electrodes 18, 20 are made from thin aluminum foil. In an alternative embodiment, only the first antenna electrode 18 is made from thin aluminum foil, and the second antenna electrode 20 is formed by an electrical seat heater member that is installed in the vehicle seat, as is well known in the art. The operating principle of the capacitive seat occupancy detection and classification system 10 disclosed herein as well applies to such an alternative embodiment.

[0124] The complex sense currents to be sensed by the current measurement means are being generated in first electrically conductive antenna electrode 18 of the capacitive sensor 16 by the provided periodic measurement signal, i.e. the regular operating mode of the capacitive sensor 16 is the loading mode.

[0125] The signal processing unit 22 is configured to determine complex impedances from measured currents through the first antenna electrode 18 with reference to the complex reference potential, which is given by the electrical measurement signal. Moreover, the signal processing unit 22 is configured to provide output signals 24 that are representative of the determined complex impedances.

[0126] The control and evaluation unit 26 is configured to receive the output signals 24 provided by the signal processing unit 22.

[0127] With the second antenna electrode 20 being connected to the impedance measurement circuit 14, the signal processing unit 22 is further configured to determine a complex impedance from a measured complex current through the second antenna electrode 20 determined with reference to the complex reference potential.

[0128] FIG. 2 schematically illustrates details of the functional principle of the seat occupancy detection and classification system 10. The diagrams show the real part (expressed as conductance G) and the imaginary part (expressed as capacitance C) of determined complex impedances. A first zone 42 in the left-hand diagram represents complex impedances to be expected with the seat occupant being a non-grounded human being. A second zone 44 represents complex impedances to be expected with the seat occupant being a grounded CRS 62. A dash-dotted first line 52 in the two-dimensional graph represents predetermined threshold values for the complex current (expressed as complex impedances) to distinguish between the first 42 and the second zone 44.

[0129] Depending on a position of the result of the complex impedance from the measured complex current through the second antenna electrode 20 with regard to the dash-dotted first line 52, the control and evaluation unit 26 is configured to select at least one threshold value out of predetermined threshold values for complex impedance, as is exemplarily shown in the two right-hand diagrams of FIG. 2.

[0130] In the following, an embodiment of a method of operating the capacitive seat occupancy detection and classification system 10 pursuant to FIG. 1 will be described. A flowchart of the method is provided in FIG. 6. In preparation of using the capacitive seat occupancy detection and classification system 10, it shall be understood that all involved units and devices are in an operational state and configured as illustrated in FIG. 1.

[0131] In order to be able to carry out the method, the control and evaluation unit 26 comprises a software module 58. The method steps to be conducted are converted into a program code of the software module 58. The program code is implemented in a digital data memory unit 66 of the control and evaluation unit 26 and is executable by a processor unit 68 of the control and evaluation unit 26. Alternatively, the software module 58 may as well reside in and may be executable by a control unit of the vehicle, for instance by the airbag control unit 60, and established data communication means between the control and evaluation unit 26 and the airbag control unit 60 of the vehicle would be used for enabling mutual transfer of data.

[0132] In a first step 70 of the method, a periodic electrical measurement signal is provided to the first antenna electrode 18 of the capacitive sensor 16. Then, a complex sense current that is being generated in the second antenna electrode 20 of the capacitive sensor 16 in response to the periodic electrical measurement signal provided to the first antenna electrode 18 of the capacitive sensor 16 is determined by the sense current measurement means in another step 72. The determining of the complex sense current with reference to the complex reference potential is followed by a step 74 of determining a corresponding complex impedance by the signal processing unit 22. In the next step 76, the determined complex impedance is compared to the predetermined threshold values for the complex impedance represented by the dash-dotted first line 52 in the left-hand diagram of FIG. 2.

[0133] Depending on the result of the step 76 of comparing, threshold values out of predetermined threshold values for complex impedance are selected in another step 78. If the determined complex impedance lies above the dash-dotted first line 52 in FIG. 2, threshold values that are represented by a dash-dotted second line 54 labeled Low Load are selected by the control and evaluation unit 26. This is shown in the upper part of the right-hand side of FIG. 2.

[0134] If the determined complex impedance lies below the dash-dotted first line 52 in FIG. 2, classification threshold values that are represented by a dash-dotted third line 56 labeled High Load are selected by the control and evaluation unit 26. This is shown in the lower part of the right-hand side of FIG. 2.

[0135] In another step 80, the signal processing unit 22 determines a complex sense current that is being generated in the first antenna electrode 18 of the capacitive sensor 16 in response to the periodic electrical measurement signal provided to the first antenna electrode 18 of the capacitive sensor 16. A complex impedance is determined from the complex sense current with reference to the complex reference potential in the following step 82.

[0136] In the next step 84 then, the control and evaluation unit 26 compares the complex impedance received by the signal processing unit 22 to the selected predetermined classification threshold values. For the sake of argumentation it shall be presumed that the dash-dotted second line 54 labeled Low Load has been selected by the control and evaluation unit 26. The diagram in the upper part of the right-hand side of FIG. 2 includes, besides the first zone 42 and also arranged above the dash-dotted second line 54, a third zone 46 that represents complex impedances to be expected with the seat occupant being a grounded human being. Arranged below the dash-dotted second line 54, the diagram includes a fourth zone 48 that represents complex impedances to be expected with the seat occupant being a non-grounded CRS 62.

[0137] The control and evaluation unit 26 determines a seat occupancy class in a next step 86, based on the result of the preceding step 84 of comparing and depending on a relation between the determined complex impedance and the selected predetermined threshold values for complex impedance. If, for instance, the complex impedance derived from the measured current through the first antenna electrode 18 lies within the third zone 46, the seat occupancy class grounded human being is selected.

[0138] In another step 88, the control and evaluation unit 26 generates a classification output signal 28 that is indicative of the determined seat occupancy class. The classification output signal 28 is transferred to the airbag control unit 60 to serve as a basis for a decision to deploy an air bag system to the vehicle seat.

[0139] The control and evaluation unit 26 is configured to automatically and periodically carry out the above-described method steps 70-88.

[0140] The diagram in the lower part of the right-hand side of FIG. 2 includes the third zone 46 arranged above a dash-dotted third line 56 and the fourth zone 48 arranged below the dash-dotted third line 56. Moreover, arranged below the dash-dotted third line 56 the diagram comprises the second zone 44 that represents complex impedances to be expected with the seat occupant being a grounded CRS 62.

[0141] FIG. 4 shows a second embodiment of the seat occupancy detection and classification system 10 installed in the seat 34. In this embodiment, the first antenna electrode 18 is formed by an electrical seat heater member that is installed in the seat cushion 38 of the vehicle seat. The second antenna electrode 20 is formed by an electrical seat heater member that is installed in the backrest 40 of the vehicle seat. The method for operating the capacitive seat occupancy detection and classification system 10 disclosed herein as well applies to this alternative embodiment of the capacitive seat occupancy detection and classification system 10.

[0142] Without giving a detailed description it is further contemplated that the second antenna electrode 20, with suitable electrical connections to the signal voltage source and to the sense current measurement means, can be employed in at least one operational mode of the seat occupancy detection and classification system 10, 10 as an additional sense antenna electrode in the same way as the first antenna electrode 18, for improving a distinction performance regarding seat occupancy.

[0143] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0144] Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.