Capacitance type seat occupant sensor system

• US 7,796,017 B2
• Filed: 10/23/2007
• Issued: 09/14/2010
• Est. Priority Date: 10/31/2006
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Kiribayashi, Shinichi
• Primary Examiner(s): Zimmerman; Brian A
• Assistant Examiner(s): Lau; Kevin
• Application Number:
  US11/977,139
• Publication Number:
  US 20080100425A1
• Time in Patent Office: 1,057 Days
• Field of Search: 340/425.5, 340/457.1, 340/438, 340/562, 340/561, 340/541, 340/540, 340/500, 701/45, 280/735, 280/734
• US Class Current: 340/425.5
• CPC Class Codes: B60N 2/002 Seats provided with an occupancy detection means mounted therein or thereon detection means responsive to presence or absence of children B60N2/266
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors
• CPC Class Codes: G01V 3/088 operating with electric fields G01V3/082 takes precedence

Abstract

A capacitance type seat occupant sensor system of a vehicle includes an AC electric power source, a main electrode disposed at a seat of the vehicle to form an electric field between the main electrode and the body of the vehicle, a guard electrode disposed between a seat frame and the main electrode, a switch unit for establishing connection of the guard electrode to have the same potential as the main electrode to provide a seat occupant sensing mode, an impedance calculating unit for calculating an impedance of a sensing circuit based on the AC voltage and an amount of current flowing through the sensing circuit, a real-part-and-imaginary-part calculating unit and judging unit for discriminating an occupant on the seat based on at least the imaginary part of the first impedance. The impedance calculating unit calculates a first impedance of an electric circuit including the main electrode when the switch means provides the seat occupant sensing mode, and the real-part-and-imaginary-part calculating unit calculates the real part and the imaginary part of the impedance.

Claims

1. A capacitance type seat occupant sensor system of a vehicle having a vehicle body, a seat frame that is fixed to and electrically connected with the vehicle body and a seat fixed to the seat frame, the system comprising:

an electric power source for providing AC voltage;

a main electrode disposed at the seat to form an electric field between the main electrode and the vehicle body;

a main wire connecting the electric power source and the main electrode;

a guard electrode disposed between the seat frame and the main electrode;

means for establishing a sensing circuit to provide at least a seat occupant sensing mode;

means for calculating an impedance of the sensing circuit based on the AC voltage and an amount of current flowing through the sensing circuit;

means for calculating the real part and the imaginary part of the impedance; and

means for judging an occupant on the seat based on at least the imaginary part of the impedance, wherein;

when the establishing means provides the seat occupant sensing mode, the establishing means forms the main wire and the main electrode into the sensing circuit and renders the guard electrode to have the same potential as the main electrode;

the judging means judges that there is an occupant according to a position indicated by the real part and the imaginary part of the first impedance in a rectangular coordinate having one axis of the real value and the other axis of the imaginary value compared to a preset position in the rectangular coordinate;

the judging means judges that there is an occupant by comparing the position indicated by the real part and the imaginary part with a threshold line in the rectangular coordinate;

assuming that the first impedance is Z1, the real part of the first impedance is Re, and the imaginary part of the first impedance is Im, when the resistive component is defined by R, when the capacitive component is defined by C, and when the angular frequency is defined by ω

, 1/Z1=Re(1/Z1)+Im(1/Z1)·

j=1/R+Cω

·

j;

the real part is an inverse number of a resistive component of the first impedance and the imaginary part is a capacitive component of the first impedance; and

the threshold line is a linear function of the real part and the imaginary part.

2. A seat occupant sensor system as in claim 1 further comprising a sub-electrode disposed at a side of the main electrode and a sub-wire for connecting the sub-electrode to the vehicle body, wherein:

when the establishing means provides a wet-seat sensing mode, the establishing means forms the main electrode and the sub-electrode into the sensing circuit; and

the judging means judges whether the seat is wetted by water or not by comparing the imaginary part of the impedance with a threshold level.

3. A seat occupant sensor system as in claim 2, wherein the judging means judges whether the seat is wetted by water or not by further comparing the real part of the impedance with a threshold level.

4. A seat occupant sensor system as in claim 2, wherein the judging means judges whether there is a malfunction in one of the main electrode, the main wire, the sub-electrode, the sub-wire or not by further comparing the imaginary part of the impedance with a threshold level.

5. A seat occupant sensor system as in claim 4, wherein the judging means judges that there is a malfunction in one of the main electrode, the main wire, the sub-electrode, the sub-wire if the imaginary part of the impedance is smaller than the threshold level.

6. A seat occupant sensor system as in claim 5, wherein the malfunction to be judged includes short-circuiting of the main electrode, short-circuiting of the sub-electrode and break down of the sub-wire.

19. A seat occupant sensor as in claim 1, wherein if there is an occupant, the real and imaginary parts are plotted above the threshold line in the rectangular coordinate having the ordinate axis of the real value and the abscissa axis of the Imaginary value.

20. A seat occupant sensor as in claim 19, wherein the threshold line is a linear function in which the real part increases as the imaginary part increases.

7. A capacitance type seat occupant sensor system of a vehicle having a vehicle body, a seat frame that is fixed to and electrically connected with the vehicle body and a seat fixed to the seat frame, the system comprising:

an electric power source for providing AC voltage;

a main electrode disposed at the seat to form an electric field between the main electrode and the vehicle body;

a main wire connecting the electric power source and the main electrode;

a guard electrode disposed between the seat frame and the main electrode;

means for establishing a sensing circuit to provide a seat occupant sensing mode and a malfunction sensing mode;

means for calculating an impedance of the sensing circuit based on the AC voltage and an amount of current flowing through the sensing circuit;

means for calculating the real part and the imaginary part of the impedance;

means for judging an occupant on the seat based on at least the imaginary part of the impedance, and

a guard wire connecting the guard electrode with the vehicle body, wherein;

when the establishing means provides the seat occupant sensing mode, the establishing means forms the main wire and the main electrode into the sensing circuit and renders the guard electrode to have the same potential as the main electrode, and

when the establishing means provides the malfunction sensing mode, the establishing means forms the main electrode, the guard electrode and the guard wire into the sensing circuit;

the judging means judges whether there is a malfunction or not in the sensing circuit by comparing a position of the real part of the impedance and the imaginary part thereof in a rectangular coordinate having one axis of the real value and the other axis of the imaginary value compared with a threshold level in the rectangular coordinate;

the judging means judges that there is an occupant by comparing the position indicated by the real part and the imaginary part with a threshold line in the rectangular coordinate;

assuming that the first impedance is Z1, the real part of the first impedance is Re, and the imaginary part of the first impedance is Im, when the resistive component is defined by R, when the capacitive component is defined by C, and when the angular frequency is defined by ω

, 1/Z1=Re(1/Z1)+Im(1/Z1)·

j=1/R+Cω

·

j;

the real part is an inverse number of a resistive component of the first impedance and the imaginary part is a capacitive component of the first impedance; and

the threshold line is a linear function of the real part and the imaginary part.

8. A seat occupant sensor system as in claim 7, wherein the judging means judges that there is a malfunction in one of the main electrode, the main wire, the guard electrode, the guard wire if the real part of the impedance is smaller than the threshold level.

9. A seat occupant sensor system as in claim 8, wherein the malfunction to be judged includes break down of the main wire and break down of the guard wire.

10. A capacitance type seat occupant sensor system of a vehicle having a vehicle body, a seat frame that is fixed to and electrically connected with the vehicle body and a seat fixed to the seat frame, the system comprising:

an electric power source for providing AC voltage;

a main electrode disposed at the seat to form an electric field between the main electrode and the vehicle body;

a main wire connecting the electric power source and the main electrode;

a sub-electrode disposed at a side of the main electrode;

a sub-wire connected with a ground;

means for connecting the sub-electrode with the sub-wire to form an electric field between the main electrode and the sub-electrode, thereby providing a wet seat sensing mode;

means for calculating an impedance between the main electrode and the sub-electrode when the connecting means provides the wet seat sensing mode;

means for calculating the real part and the imaginary part of the impedance; and

means for judging a wet seat based on at least the imaginary part of the impedance;

wherein

the judging means judges that there is a wet seat according to a position indicated by the real part and the imaginary part of the impedance in a rectangular coordinate having one axis of the real value and the other axis of the imaginary value compared to a preset threshold line in the rectangular coordinate;

the judging means judges that there is an occupant by comparing the position indicated by the real part and the imaginary part with a threshold line in the rectangular coordinate;

assuming that the first impedance is Z1, the real part of the first impedance is Re, and the imaginary part of the first impedance is Im, when the resistive component is defined by R, when the capacitive component is defined by C, and when the angular frequency is defined by ω

, 1/Z1=Re(1/Z1)+Im(1/Z1)·

j=1/R+Cω

·

j;

the real part is an inverse number of a resistive component of the first impedance and the imaginary part is a capacitive component of the first impedance; and

the threshold line is a linear function of the real part and the imaginary part.

11. A capacitance type seat occupant sensor system as in claim 10, wherein the judging means discriminates the wet seat based on both the real part and the imaginary part.

12. A seat occupant sensor system as in claim 11, wherein the judging means judges whether there is a malfunction in one of the main electrode, the main wire, the sub-electrode and the sub-wire or not by further comparing the imaginary part of the impedance with a threshold level.

13. A seat occupant sensor system as in claim 11, wherein the judging means judges that there is a malfunction in one of the main electrode, the main wire, the sub-electrode and the sub-wire if the imaginary part of the impedance is smaller than the threshold level.

14. A seat occupant sensor system as in claim 13, wherein the malfunction to be judged includes short-circuiting of the main electrode, short-circuiting of the sub-electrode, and break down of the sub-wire.

15. A capacitance type seat occupant sensor system of a vehicle having a vehicle body, a seat frame that is fixed to and electrically connected with the vehicle body and a seat fixed to the seat frame, the system comprising:

an electric power source for providing AC voltage;

a main electrode disposed at the seat to form an electric field between the main electrode and the vehicle body;

a main wire connecting the electric power source and the main electrode;

a guard electrode disposed between the seat frame and the main electrode;

a guard wire electrically connected with the vehicle body;

means for switching connection of the guard electrode from the electric power source to provide a seat occupant sensing mode to connection of the guard electrode with the guard wire to provide a malfunction sensing mode;

means for calculating an impedance of an electric circuit including the main wire, the main electrode and the guard wire when the switch means provides the malfunction sensing mode;

means for calculating the real part and the imaginary part of the impedance (Z3); and

means for judging a malfunction of one of the main wire, the main electrode, the guard wire and the guard electrode based on at least one of the real part of the first impedance and the imaginary part of the first impedance;

wherein

the judging means judges that there is a malfunction according to a position indicated by the real part and the imaginary part of the impedance in a rectangular coordinate having one axis of the real value and the other axis of the imaginary value compared to a preset value in the rectangular coordinate;

the judging means judges that there is an occupant by comparing the position indicated by the real part and the imaginary part with a threshold line in the rectangular coordinate;

assuming that the first impedance is Z1, the real part of the first impedance is Re, and the imaginary part of the first impedance is Im, when the resistive component is defined by R, when the capacitive component is defined by C, and when the angular frequency is defined by ω

, 1/Z1=Re(1/Z1)+Im(1/Z1)·

j=1/R+Cω

·

j;

the real part is an inverse number of a resistive component of the first impedance and the imaginary part is a capacitive component of the first impedance; and

the threshold line is a linear function of the real part and the imaginary part.

16. A seat occupant sensor system as in claim 15, wherein the judging means judges that there is a malfunction in one of the main electrode, the main wire, the guard electrode and the guard wire if the imaginary part of the impedance is smaller than a threshold level.

17. A seat occupant sensor system as in claim 16, wherein the malfunction to be judged includes break down of the main electrode, and break down of the guard wire.

18. A capacitance type seat occupant sensor system of a vehicle having a vehicle body, a seat frame that is fixed to and electrically connected with the vehicle body and a seat fixed to the seat frame, the system comprising:

an electric power source for providing AC voltage;

a main electrode disposed at the seat to form an electric field between the main electrode and the vehicle body;

a main wire connecting the electric power source and the main electrode;

a sub-electrode disposed at a side of the main electrode;

a sub-wire connected with the vehicle body;

a guard electrode disposed between the seat frame and the main electrode to confront the main electrode at a distance;

a guard wire connected to the vehicle body;

means for providing a seat occupant sensing mode, a wet-seat sensing mode and a malfunction sensing mode, the switching mode establishing connection of the guard electrode to have the same potential to provide the seat occupant sensing mode, connecting the sub-electrode with the sub-wire to form an electric field between the main electrode and the sub-electrode to provide the wet seat sensing mode and connecting the guard electrode with the guard wire to form an electric field between the main electrode and the guard electrode to provide the malfunction sensing mode;

means for calculating a first impedance of an electric circuit including the main wire and the main electrode when the providing means provides the seat occupant sensing mode, a second impedance of an electric circuit including the main electrode and the sub-electrode when the providing means provides the wet seat sensing mode and a third impedance of an electric circuit including the main electrode and the guard electrode;

means for calculating the real part and the imaginary part of one of the impedances; and

means for judging a seat occupant, a wet seat and a malfunction based on at least one of the real part of the first, second and third impedances and the imaginary part thereof according to respective positions indicated by the real part and the imaginary part of the first, second and third impedances in a rectangular coordinate having one axis of the real value and the other axis of the imaginary value compared to preset positions in the rectangular coordinate;

wherein

the judging means judges that there is the seat occupant by comparing the position indicated by the real part and the imaginary part with a threshold line in the rectangular coordinate;

assuming that the first impedance is Z1, the real part of the first impedance is Re, and the imaginary part of the first impedance is Im, when the resistive component is defined by R, when the capacitive component is defined by C, and when the angular frequency is defined by ω

, 1/Z1=Re(1/Z1)+Im(1/Z1)·

j=1/R+Cω

·

j;

the real part is an inverse number of a resistive component of the first impedance and the imaginary part is a capacitive component of the first impedance; and

the threshold line is a linear function of the real part and the imaginary part.