Capacitance-based sensor and occupant sensing system

• US 20060164254A1
• Filed: 01/23/2006
• Published: 07/27/2006
• Est. Priority Date: 01/24/2005
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc.
• Original Assignee: DENSO Corporation, Nippon Soken, Inc.
• Inventors: Kamizono, Tsutomu, Ando, Shinji, Wanami, Shingo
• Granted Patent: US 7,575,085 B2
• Time in Patent Office: Days
• US Class Current: 340/667
• 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

Abstract

An occupant sensing electrode is embedded in a seat. An empty seat capacitance reducing electrode is placed between the occupant sensing electrode and a seat frame of the seat in an opposed relationship to the occupant sensing electrode. A dielectric base film may be interposed between the occupant sensing electrode and the empty seat capacitance reducing electrode. The occupant sensing electrode may include a plurality of electrode portions. The electrode portions may include high potential electrode portions and low potential electrode portions.

Claims

1. A capacitance-based sensor that is arranged in a seat of a vehicle and senses presence of an occupant in the seat, the capacitance-based sensor comprising:

an occupant sensing electrode that is embedded in the seat;

an empty seat capacitance reducing electrode that is opposed to the occupant sensing electrode and is positioned between the occupant sensing electrode and a seat frame of the seat, which is electrically connected to a vehicle ground;

an electric current sensing device that measures an electric current and is placed in one of;

a first position that is interposed and electrically connected between;

the occupant sensing electrode; and

the empty seat capacitance reducing electrode; and

a second position that is interposed and electrically connected between;

the vehicle ground; and

the empty seat capacitance reducing electrode and the first position; and

a drive device that generates a drive voltage and is positioned in the other one of the first and second positions.

2. The capacitance-based sensor according to claim 1, wherein:

the electric current sensing device is placed in the first position; and

the drive device is placed in the second position.

3. The capacitance-based sensor according to claim 2, wherein the occupant sensing electrode has the same electric potential as that of the empty seat capacitance reducing electrode upon operation of the drive device.

4. The capacitance-based sensor according to claim 1, wherein:

the electric current sensing device is placed in the second position; and

the drive device is placed in the first position.

5. The capacitance-based sensor according to claim 4, wherein the empty seat capacitance reducing electrode has the same electric potential as that of the vehicle ground upon operation of the drive device.

6. The capacitance-based sensor according to claim 1, wherein the electric current sensing device includes an operational amplifier, which keeps the same electric potential and electric insulation between corresponding two of the occupant sensing electrode, the empty seat capacitance reducing electrode and the vehicle ground, between which the electric current sensing device is connected.

7. The capacitance-based sensor according to claim 1, wherein:

the occupant sensing electrode and one of the electric current sensing device and the drive device, which is interposed between the occupant sensing electrode and the empty seat capacitance reducing electrode, are electrically connected to each other through a first conductive line;

the vehicle ground and the other one of the electric current sensing device and the drive device are electrically connected to each other through a second conductive line;

at least a portion of the first conductive line and at least a portion of the second conductive line are formed as a shielded line that has a shield portion, which has the same electric potential as that of the empty seat capacitance reducing electrode upon operation of the drive device.

8. The capacitance-based sensor according to claim 7, wherein the empty seat capacitance reducing electrode is electrically connected to the electric current sensing device and the drive device through the shield portion of the shielded line.

9. The capacitance-based sensor according to claim 1, further comprising a dielectric layer, wherein the occupant sensing electrode is provided on a first side of the dielectric layer, and the empty seat capacitance reducing electrode is provided on a second side of the dielectric layer, which is opposite from the first side of the dielectric layer.

10. The capacitance-based sensor according to claim 9, wherein a surface of the occupant sensing electrode and a surface of the empty seat capacitance reducing electrode are coated with a dielectric material.

11. The capacitance-based sensor according to claim 1, wherein a surface area of the empty seat capacitance reducing electrode is smaller than a surface area of the occupant sensing electrode.

12. The capacitance-based sensor according to claim 1, wherein a surface area of the empty seat capacitance reducing electrode is larger than a surface area of the occupant sensing electrode.

13. The capacitance-based sensor according to claim 1, wherein:

in an occupant state sensing operational mode of the capacitance-based sensor, the drive device applies a voltage between the occupant sensing electrode and the vehicle ground, and the electric current sensing device measures an electric current between the occupant sensing electrode and the vehicle ground; and

in a malfunction sensing operational mode of the capacitance-based sensor, the drive device applies a voltage between the occupant sensing electrode and the empty seat capacitance reducing electrode, and the electric current sensing device measures an electric current between the occupant sensing electrode and the empty seat capacitance reducing electrode.

14. The capacitance-based sensor according to claim 13, wherein:

in the occupant state sensing operational mode of the capacitance-based sensor, the drive device and the electric current sensing device are connected in series between the occupant sensing electrode and the vehicle ground in this order, and the empty seat capacitance reducing electrode has the same electric potential as that of the vehicle ground; and

in the malfunction sensing operational mode of the capacitance-based sensor, the drive device and the electric current sensing device are connected in series between the occupant sensing electrode and the empty seat capacitance reducing electrode in this order.

15. The capacitance-based sensor according to claim 14, wherein in each of the occupant state sensing operational mode and the malfunction sensing operational mode of the capacitance-based sensor, the occupant sensing electrode has a relatively high electric potential, and the empty seat capacitance reducing electrode and the vehicle ground has a relatively low electric potential.

16. The capacitance-based sensor according to claim 15, further comprising:

a first conductive line that has the drive device, which is interposed between a first end and a second end of the first conductive line, wherein the first end of the first conductive line is directly connected to the occupant sensing electrode;

a second conductive line that has the electric current sensing device, which is interposed between a first end and a second end of the second conductive line, wherein the first end of the second conductive line is directly connected to vehicle ground, and the second end of the second conductive line is connected to the second end of the first conductive line;

a third conductive line that has a first end, which is directly connected to the empty seat capacitance reducing electrode, and a second end, which is connected to the second end of the first conductive line and the second end of the second conductive line; and

a line selecting switch device that executes switching for the second conductive line and the third conductive line, wherein;

the line selecting switch device divides the second conductive line into;

a first part that includes the first end of the second conductive line, which is directly connected to the vehicle ground; and

a second part that includes the second end of the second conductive line and the electric current sensing device;

the line selecting switch device divides the third conductive line into;

a first part that includes the first end of the third conductive line, which is directly connected to the empty seat capacitance reducing electrode; and

a second part that includes the second end of the third conductive line, which is connected to the second end of the first conductive line and the second end of the second conductive line;

in the occupant state sensing operational mode of the capacitance-based sensor, the line selecting switch device electrically connects between the first part of the second conductive line and the second part of the second conductive line and also electrically connects between the first part of the third conductive line and the second part of the third conductive line; and

in the malfunction sensing operational mode of the capacitance-based sensor, the line selecting switch device electrically connects between the first part of the third conductive line and the second part of the second conductive line, so that the occupant sensing electrode is electrically connected to the empty seat capacitance reducing electrode through the drive device and the electric current sensing device.

17. The capacitance-based sensor according to claim 13, wherein:

in the occupant state sensing operational mode of the capacitance-based sensor, the electric current sensing device and the drive device are connected in series between the occupant sensing electrode and the vehicle ground in this order, and the occupant sensing electrode has the same electric potential as that of the empty seat capacitance reducing electrode; and

in the malfunction sensing operational mode of the capacitance-based sensor, the electric current sensing device and the drive device are connected in series between the occupant sensing electrode and the empty seat capacitance reducing electrode in this order.

18. The capacitance-based sensor according to claim 17, wherein:

in the occupant state sensing operational mode of the capacitance-based sensor, the vehicle ground has a relatively high electric potential, and the occupant sensing electrode and the empty seat capacitance reducing electrode have a relatively low electric potential;

in the malfunction sensing operational mode of the capacitance-based sensor, the occupant sensing electrode and the vehicle ground have a relatively low electric potential, and the empty seat capacitance reducing electrode has a relatively high electric potential.

19. The capacitance-based sensor according to claim 18, further comprising:

a first conductive line that has the electric current sensing device, which is interposed between a first end and a second end of the first conductive line, wherein the first end of the first conductive line is directly connected to the occupant sensing electrode;

a second conductive line that has the drive device, which is interposed between a first end and a second end of the second conductive line, wherein the first end of the second conductive line is directly connected to the vehicle ground, and the second end of the second conductive line is connected to the second end of the first conductive line;

a third conductive line that has a first end, which is directly connected to the empty seat capacitance reducing electrode, and a second end, which is connected to the second end of the first conductive line and the second end of the second conductive line; and

a line selecting switch device that executes switching for the second conductive line and the third conductive line, wherein;

the line selecting switch device divides the second conductive line into;

a first part that includes the first end of the second conductive line, which is directly connected to the vehicle ground; and

a second part that includes the second end of the second conductive line and the drive device;

the line selecting switch device divides the third conductive line into;

a first part that includes the first end of the third conductive line, which is directly connected to the empty seat capacitance reducing electrode; and

a second part that includes the second end of the third conductive line, which is connected to the second end of the first conductive line and the second end of the second conductive line;

in the occupant state sensing operational mode of the capacitance-based sensor, the line selecting switch device electrically connects between the first part of the second conductive line and the second part of the second conductive line and also electrically connects between the first part of the third conductive line and the second part of the third conductive line; and

in the malfunction sensing operational mode of the capacitance-based sensor, the line selecting switch device electrically connects between the first part of the third conductive line and the second part of the second conductive line, so that the occupant sensing electrode is electrically connected to the empty seat capacitance reducing electrode through the electric current sensing device and the drive device.

20. The capacitance-based sensor according to claim 1, wherein:

the occupant sensing electrode includes a group of electrode portions, each of which is electrically separated from the rest of the electrode portions of the group; and

the capacitance-based sensor further comprising an electrode portion selecting switch device, which electrically connects one of the electrode portions of the group to the drive device and the electric current sensing device.

21. The capacitance-based sensor according to claim 20, wherein upon operation of the drive device, the empty seat capacitance reducing electrode has an electrical potential that is the same as that of the vehicle ground.

22. The capacitance-based sensor according to claim 20, wherein the electrode portions of the group are arranged in parallel and are spaced from one another in one of a fore-and-aft direction of the vehicle and a transverse direction of the vehicle.

34. An occupant sensing system comprising:

the capacitance-based sensor according to claim 1;

and

an occupant sensing ECU that determines an occupant state of the seat based on an output of the capacitance-based sensor.

35. The occupant sensing system according to claim 34, wherein:

the occupant sensing ECU receives an output of a belt buckle switch device of the seat; and

when the occupant sensing ECU senses an unbuckled state of a seat belt of the seat based on the output of the belt buckle switch device, the occupant sensing ECU determines that the seat is empty and has no child restraint system installed therein.

23. A capacitance-based sensor that is arranged in a seat of a vehicle and senses presence of an occupant in the seat, the capacitance-based sensor comprising:

a dielectric layer that is embedded in the seat;

an occupant sensing electrode that includes a first group of electrode portions and a second group of electrode portions, which are arranged on a first side of the dielectric layer;

an empty seat capacitance reducing electrode that is arranged on a second side of the dielectric layer in an opposed relationship to the occupant sensing electrode, so that the empty seat capacitance reducing electrode is interposed between the occupant sensing electrode and a seat frame of the seat;

a drive device, which applies a voltage between;

one of at least one of the electrode portions of the first group and at least one of the electrode portions of the second group; and

the empty seat capacitance reducing electrode and the other one of the at least one of the electrode portions of the first group and the at least one of the electrode portions of the second group; and

an electric current sensing device that measures an electric current between the at least one of the electrode portions of the first group and the at least one of the electrode portions of the second group.

24. The capacitance-based sensor according to claim 23, wherein upon operation of the drive device, the empty seat capacitance reducing electrode has an electric potential that is the same as that of the other one of the at least one of the electrode portions of the first group and the at least one of the electrode portions of the second group.

25. The capacitance-based sensor according to claim 23, wherein the electrode portions of the first group and the electrode portions of the second group are arranged in parallel and are spaced from one another in one of a fore-and-aft direction of the vehicle and a transverse direction of the vehicle.

26. The capacitance-based sensor according to claim 23, wherein:

each of the electrode portions of the first group is electrically connected to the rest of the electrode portions of the first group; and

each of the electrode portions of the second group is electrically connected to the rest of the electrode portions of the second group.

27. The capacitance-based sensor according to claim 23, further comprising first and second pressure sensitive electrodes, which form a pressure sensitive switch device, wherein:

a plurality of through holes extends in the dielectric layer from the first side to the second side of the dielectric layer;

the first pressure sensitive electrode is arranged over the plurality of through holes on the first side of the dielectric layer; and

the second pressure sensitive electrode is arranged over the plurality of through holes on the second side of the dielectric layer.

28. The capacitance-based sensor according to claim 23, further comprising first and second electrode selecting switch devices, wherein:

each of the electrode portions of the first group is electrically separated from the rest of the electrode portions of the first group;

each of the electrode portions of the second group is electrically separated from the rest of the electrode portions of the second group;

the firs electrode portion selecting switch device electrically connects one of the electrode portions of the first group to the drive device and the electric current sensing device; and

the second electrode selecting switch device electrically connects one of the electrode portions of the second group to the drive device and the electric current sensing device.

29. The capacitance-based sensor according to claim 28, wherein upon operation of the drive device, an electric potential of the empty seat capacitance reducing electrode is the same as that of the one of the electrode portions of the second group.

30. The capacitance-based sensor according to claim 28, wherein the electrode portions of the first group and the electrode portions of the second group are arranged in parallel and are spaced from one another in one of a fore-and-aft direction of the vehicle and a transverse direction of the vehicle.

31. The capacitance-based sensor according to claim 28, wherein:

the electrode portions of the first group are located in one of a front side and a rear side of a seat bottom of the seat; and

the electrode portions of the second group are located in the other one of the front side and the rear side of the seat bottom of the seat.

32. The capacitance-based sensor according to claim 28, wherein the electrode portions of the first group and the electrode portions of the second group are alternately arranged.

33. A capacitance-based sensor that is arranged in a seat of a vehicle and senses presence of an occupant in the seat, the capacitance-based sensor comprising:

a dielectric layer that is embedded in the seat;

an occupant sensing electrode that includes a first group of electrode portions and a second group of electrode portions, which are arranged on a first side of the dielectric layer, wherein the electrode portions of the first group and the electrode portions of the second group are alternately arranged;

an auxiliary electrode that extends between each of the electrode portions of the first group and an adjacent one of the electrode portions of the second group without electrically contacting the electrode portions of the first group and the electrode portions of the second group on the first side of the dielectric layer;

an empty seat capacitance reducing electrode that is arranged on a second side of the dielectric layer in an opposed relationship to the occupant sensing electrode and the auxiliary electrode, so that the empty seat capacitance reducing electrode is interposed between the occupant sensing electrode and a seat frame of the seat;

a drive device, which applies a voltage between the occupant sensing electrode and the auxiliary electrode; and

an electric current sensing device that measures an electric current between the occupant sensing electrode and the auxiliary electrode.