OPTIMIZED ELECTRODE SHAPE FOR CAPACITIVE OCCUPANT CLASSIFICATION SYSTEM

Abstract

A capacitive sensor member of a seat occupant classification device for use in seats, in particular in vehicle seats. The capacitive sensor member includes at least one electrically conductive sense electrode that has an optimized shape for use in vehicle seats equipped with child restraint system anchorages. A capacitive seat occupant classification system is provided that includes the capacitive sensor member.

Claims

1. A capacitive sensor member of a seat occupant classification device for use in vehicle seats, the capacitive sensor member comprising at least one electrically conductive sense electrode that has an optimized shape for use in vehicle seats equipped with child restraint system anchorages.

2. The capacitive sensor member as claimed in claim 1, wherein the at least one sense electrode is electrically connectable to a capacitance measurement circuit that is configured for determining a physical quantity which is indicative of a capacitance of the at least one sense electrode with regard to a reference potential, and wherein the at least one sense electrode is designed to have at least a substantially rectangular main portion having a width (w) such that the at least one sense electrode in an operational state is positionable with a minimum gap of 20 mm to virtual planes that are arrangeable perpendicular to a floor on which the seat is erected, and are each alignable with one of inner surfaces of arms of a metal frame of the child restraint system that are facing each other.

3. The capacitive sensor member as claimed in claim 1, wherein the at least one sense electrode has at least one extension portion that in the operational state is positionable to overlap, in a direction perpendicular to the floor, at least one opening in the metal frame of the child restraint system being connected to the vehicle anchorages.

4. The capacitive sensor member as claimed in claim 1, wherein the at least one sense electrode comprises two extension portions that in the operational state are each positionable to overlap, in the direction perpendicular to the vehicle floor, at least one opening in the metal frame of the child restraint system being connected to the vehicle anchorages, wherein the two extension portions are arranged in a spaced relationship to each other and extend from a front end of the main portion.

5. The capacitive sensor member as claimed in claim 1, wherein the main portion of the at least one sense electrode in an operational state is positionable to overlap, in the direction perpendicular to the floor, at least 30% of a length of a seat base cushion of the seat as measured in a direction that is arranged in parallel with arms of the child restraint system without overlapping the metal frame of the child restraint system in the direction perpendicular to the floor.

6. The capacitive sensor member as claimed in claim 1, wherein the at least one sense electrode is made from thin metal foil.

7. A capacitive seat occupant classification system, comprising at least one capacitive sensor member as claimed in claim 1, a capacitance measurement circuit that is configured for generating a time-varying output signal, for providing the time-varying output signal to the at least one capacitive sensor member and for determining a physical quantity which is indicative of a capacitance of the sense electrode with regard to a reference potential, and an evaluation unit that is configured for generating an output signal that is indicative of at least one out of detecting and of classifying a seat occupant, the output signal being based on the determined physical quantity and a comparison of the determined physical quantity to at least one predetermined value for the determined physical quantity.

8. A vehicle seat, with an installed seat occupant classification device as claimed in claim 7, the seat comprising a seat base configured for taking up a seat base cushion, the seat base and the seat base cushion being provided for supporting a bottom of a seat occupant, a backrest configured for taking up a backrest cushion provided for supporting a lumbar and back region of the seat occupant, and at least a pair of anchorages configured for mechanically engaging with corresponding fixation members of a child restraint system, wherein the at least one sense electrode is arranged at an A surface of the seat base cushion.

9. (canceled)

10. A method of occupant seat classification for an occupant sitting in the vehicle seat claimed in claim 8, comprising the steps of: determining the physical quantity using the capacitance measurement circuit and, based on the physical quantity, generating the output signal indicative of the detection or classification of a seat occupant using the evaluation unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] 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:

[0050] FIG. 1 schematically shows a top view of a seating surface (A surface) of a vehicle seat;

[0051] FIG. 2 schematically illustrates the vehicle seat pursuant to FIG. 1 with a sketch of a dummy CRS capacitive footprint;

[0052] FIG. 3 schematically shows a top view of the vehicle seat pursuant to FIG. 1 and a capacitive footprint of a MaxiCosi? EasyFix child restraint system;

[0053] FIG. 4 schematically shows a top view of the vehicle seat pursuant to FIG. 1 and a capacitive footprint of a BeSafe? iZi Kid child restraint system;

[0054] FIG. 5 schematically shows a top view of the vehicle seat pursuant to FIG. 1 and superposed capacitive footprints of the MaxiCosi? EasyFix and the BeSafe? iZi Kid child restraint systems and a sense electrode of a capacitive sensor member in accordance with the invention; and

[0055] FIG. 6 schematically shows a top view of the vehicle seat and superposed capacitive footprints of the MaxiCosi? EasyFix and the BeSafe? iZi Kid child restraint systems pursuant to FIG. 5 and an alternative sense electrode of a capacitive sensor member in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] FIG. 1 schematically shows a top view of a seating surface (A surface) of a seat base cushion 12 of a seat 10. The seat 10 is formed in particular as a vehicle seat and, more specific, as a passenger car seat.

[0057] The seat 10 comprises a seat structure (not shown) for erecting the seat 10 on a passenger cabin floor of the vehicle. A seat base is configured for taking up a seat base cushion 12. The seat base and the seat base cushion 12 are provided for supporting a bottom of a human seat occupant. The seat 10 further includes a backrest 14 configured for taking up a backrest cushion provided for supporting a lumbar and back region of the seat occupant. The backrest 14, which is only shown in FIG. 1 for clarity reasons, is arranged at a rear edge 16 of the seat base cushion 12 shown on the left-hand side of FIG. 1.

[0058] The vehicle seat is furnished with a pair of anchorages 18, 20 that are fixedly attached at locations arranged between the rear edge 16 of the seat base cushion 12 and a bottom edge of the backrest 14. The anchorages 18, 20 are designed as mounting brackets made from 6 mm diameter round bar steel and are compatible with the ISOFIX standard ISO 13216. The anchorages 18, 20 are spaced from each other at a distance between 230 mm and 330 mm. The anchorages 18, 20 are configured for mechanically engaging with corresponding fixation members of a child restraint system (CRS).

[0059] When an ISOFIX CRS is installed at the vehicle seat, its inner metal frame comes close to the seat A-surface. By analogy to pressure distribution, a proximity of grounded metal parts induces a capacitive footprint on the A-surface. FIG. 2 schematically illustrates the seat 10 pursuant to FIG. 1 with a sketch of a dummy CRS capacitive footprint 22.

[0060] It is important to note that the capacitive footprint 22 is mainly due to metal bars of the inner metal frame, which can be grounded from outside. All metal bars located inside the CRS and electrically insulated from the outside should not be considered.

[0061] FIG. 3 schematically shows a top view of the seat 10 pursuant to FIG. 1 and a capacitive footprint 24 of a MaxiCosi? EasyFix child restraint system. The metal frame of the MaxiCosi? EasyFix child restraint system comprises two metal beam-shaped arms 26, 28 that are mechanically and electrically connected to the vehicle seat anchorages 18, 20, and a traverse member 30 having two square-shaped openings 32, 34.

[0062] FIG. 4 schematically shows a top view of the seat 10 pursuant to FIG. 1 and a capacitive footprint 36 of a BeSafe? iZi Kid child restraint system. The metal frame of the MaxiCosi? EasyFix child restraint system comprises just two metal beam-shaped arms 38, 40 that are mechanically and electrically connected to the vehicle seat anchorages 18, 20. FIG. 5 schematically shows a top view of the seat 10 pursuant to FIG. 1 and superposed capacitive footprints 42 of the MaxiCosi? EasyFix and the BeSafe? iZi Kid child restraint systems pursuant to FIGS. 4 and 5.

[0063] The seat 10 shown in FIG. 5 further includes an installed seat occupant classification device in accordance with the invention. The seat occupant classification device comprises a capacitive sensor member with an electrically conductive sense electrode 52 that has an optimized shape for use in vehicle seats equipped with CRS anchorages 18, 20. The sense electrode 52 is arranged at the A surface of the seat base cushion 12.

[0064] In order to accomplish good classification properties between human seat occupants arranged directly on the vehicle seat and an ISOFIX CRS, two guidelines have been considered in the design of the sense electrode 52 of the capacitive sensor member: [0065] on the one hand, the sense electrode 52 should be as large as possible in order to maximize a signal caused by humans sitting directly on the vehicle seat; [0066] on the other hand, the sense electrode 52 should be kept away from the CRS capacitive foot print 42 in order to minimize a CRS activation.

[0067] The sense electrode 52 of the capacitive sensor member in accordance with the invention is electrically connectable to a capacitance measurement circuit (not shown) that is configured for determining a physical quantity, namely an electric current through the sense electrode 52, which is indicative of a capacitance of the sense electrode 52 with regard to a reference potential that is given by the electric potential of the vehicle chassis.

[0068] The capacitance measurement circuit is configured for generating a time-varying output signal, namely a sinusoidal voltage, and for providing the time-varying output signal to the capacitive sensor member. Further, the capacitance measurement circuit is configured for determining the electric current through the sense electrode 52.

[0069] An output signal of the capacitance measurement circuit can be transferred to an evaluation unit (not shown) of the capacitive seat occupant classification system. The evaluation unit is configured for generating an output signal that is indicative of classifying a seat occupant. The output signal is based on the determined electric current through the sense electrode and a comparison of the determined electric current to predetermined values for the electric current. As this part does not belong to the core of the invention and is well known in the art, it is not necessary to describe it in more detail herein.

[0070] The sense electrode 52 is designed to have a substantially rectangular main portion 54 having a width w of about 220 mm, so that the sense electrode 52, as in the operational state shown in FIG. 5, is positionable with a minimum gap of 20 mm, and is actually positioned with a gap of about 22 mm, to virtual planes 56, 58 that are arrangeable perpendicular to the passenger cabin floor that the seat 10 is erected on, and are each aligned with one of inner surfaces of the arms 44,46 of the metal frame of the CRS that are facing each other. In FIG. 5, the virtual planes 56, 58 show as straight lines.

[0071] As will be appreciated by those skilled in the art, the substantially rectangular shaped main portion 54 of the sense electrode 52 may have rounded edges to prevent increased values for an electric field strength at corners of the sense electrode 52.

[0072] The sense electrode 52 is made from thin aluminum foil or, alternatively, from an aluminized plastic material such as polyethylene terephthalate (PET), with a length l of about 135 mm, as measured in a direction 48 that is arranged in parallel with metal arms 44, 46 of the child restraint systems, and thus overlaps more than 40% of a length of the seat base cushion 12 of the vehicle seat. In a direction 50 perpendicular to the floor, the metal frame of the child restraint system is not overlapped at all by the sense electrode 52. The length l of the sense electrode 52 is adapted such that the main portion 54 covers substantially an entire back region of the seating surface without extending under the traverse member 30 of the MaxiCosi? EasyFix CRS.

[0073] FIG. 6 schematically shows a top view of the seat 10 and superposed capacitive footprints 42 of the MaxiCosi? EasyFix and the BeSafe? iZi Kid child restraint systems pursuant to FIG. 5 and an alternative sense electrode 60 of a capacitive sensor member in accordance with the invention. For the sake of brevity, only differences to the embodiment disclosed beforehand will be described.

[0074] The alternative sense electrode 60 comprises two extension portions 62, 64 of about 30?75 mm size with rounded edges. The overall length of the sense electrode 60 in the region of the extension portions is thus about 210 mm. The extension portions 62, 64 and the main portion 54 of the sense electrode 60 are integrally formed. In the operational state shown in FIG. 6, each one of the extension portions 62, 64 is positioned to overlap, in the direction 50 perpendicular to the vehicle floor, one of the two openings 32, 34 in the metal frame of the CRS being directly connected to the vehicle anchorages 18, 20. The two extension portions 62, 64 are arranged in a spaced relationship to each other and extend from a front end 66 of the main portion 54 of the sense electrode 60.

[0075] The alternative sense electrode 60 is especially beneficial for adding robustness for classifying human beings sitting on the seat 10 in a position that is front-shifted relative to a nominal sitting position.

[0076] 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.

[0077] 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.