Passenger detection system

• US 6,208,249 B1
• Filed: 09/03/1998
• Issued: 03/27/2001
• Est. Priority Date: 09/03/1997
• Status: Expired due to Term

• Current Assignee: Honda Elesys Co., Ltd. (Nidec Corporation)
• Original Assignee: NEC Corporation
• Inventors: Saito, Takashi, Jinno, Kazunori, Ofuji, Masahiro
• Primary Examiner(s): TRIEU, VAN THANH
• Application Number:
  US09/146,231
• Time in Patent Office: 936 Days
• Field of Search: 340/435, 340/561, 340/562, 340/565, 340/870.37, 340/573.4, 340/436, 324/663, 324/671, 324/687, 280/728.1, 280/728.2, 280/734, 280/735, 180/271, 180/273
• US Class Current: 340/561
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors

Abstract

A passenger detection system comprises an antenna electrode, an oscillation circuit, a current detection circuit, a phase difference detection circuit, and a control circuit. The antenna electrode is placed on the upper side of a seat. The oscillation circuit generates a high frequency low voltage oscillation signal in order to generate a weak alternating electric field around the antenna electrode. The current detection circuit detects a transmission current which passes between the oscillation circuit and the antenna electrode according to the weak alternating electric field which is generated around the antenna electrode. The phase difference detection circuit detects the phase difference between the oscillation signal supplied from the oscillation circuit and an output signal which is supplied to the antenna electrode. And the presence or absence of a passenger seated on the seat is judged by the control circuit based on the outputs of the current detection circuit and the phase difference detection circuit. Especially, the passenger detection system needs only one antenna electrode, therefore judgment on the presence or absence of a passenger seated on the seat can be executed with simplified circuit composition and low cost.

Claims

1. A passenger detection system comprising:

an antenna electrode which is placed on the upper side of a seat;

an oscillation means for generating a high frequency low voltage oscillation signal in order to generate a weak alternating electric field around the antenna electrode;

a current detection means for detecting a transmission current which passes between the oscillation means and the antenna electrode according to the weak alternating electric field which is generated around the antenna electrode; and

a judgment means for judging the presence or absence of a passenger seated on the seat based on the output of the current detection means.

2. A passenger detection system as claimed in claim 1, further comprising an amplitude control means for controlling the voltage amplitude of the oscillation signal which is supplied by the oscillation means to the antenna electrode at an almost constant value.

3. A passenger detection system as claimed in claim 2, wherein the amplitude control means includes an amplitude detection circuit for detecting the voltage amplitude of the oscillation signal and an amplitude variation circuit for varying and controlling the voltage amplitude of the oscillation signal, and variations of the voltage amplitude of the oscillation signal is controlled by the amplitude variation circuit based on the output of the amplitude detection circuit so that the voltage amplitude will be almost constant.

4. A passenger detection system as claimed in claim 1, wherein the antenna electrode is composed of:

an antenna section which is provided to the cushion section and/or the back section of the seat;

a conduction section which is formed by extending part of the antenna section; and

a connector which is provided to the end of the conduction section.

5. A passenger detection system as claimed in claim 1, wherein a control unit is made up by enclosing the oscillation means, the current detection means and the judgment means in a common housing, and the control unit is provided to the seat.

6. A passenger detection system as claimed in claim 5, wherein the housing of the control unit is provided with a connector which is connected with the oscillation means via the current detection means, and the connector on the housing of the control unit is electrically connected to a connector which is provided to the end of the antenna electrode.

7. A passenger detection system as claimed in claim 1, wherein the judgment means executes the judgment on the presence or absence of a passenger seated on the seat, by comparing the transmission current detected by the current detection means with a prestored threshold value concerning the transmission current.

8. A passenger detection system as claimed in claim 1, further comprising a power circuit for generating a single uniform DC voltage utilizing power derived from a car battery, in which the single uniform DC voltage supplied by the power circuit is utilized as the system power source for circuits in the passenger detection system including the oscillation means, the current detection means and the judgment means.

9. A passenger detection system as claimed in claim 1, wherein the antenna electrode is placed on the upper side of the seat so as to cover almost the entire upper side of the cushion section of the seat.

10. A passenger detection system as claimed in claim 1, wherein the antenna electrode is designed to be provided to both the cushion section and the back section of the seat.

11. A passenger detection system as claimed in claim 1, wherein the antenna electrode is fixed to one or more components of the seat.

12. A passenger detection system comprising:

an antenna electrode which is placed on the upper side of a seat;

an oscillation means for generating a high frequency low voltage oscillation signal in order to generate a weak alternating electric field around the antenna electrode;

a current detection means for detecting a transmission current which passes between the oscillation means and the antenna electrode according to the weak alternating electric field which is generated around the antenna electrode;

a phase difference detection means for detecting the phase difference between the oscillation signal supplied from the oscillation means and an output signal which is supplied to the antenna electrode; and

a judgment means for judging the presence or absence of a passenger seated on the seat based on the outputs of the current detection means and the phase difference detection means.

13. A passenger detection system as claimed in claim 12, further comprising an amplitude control means for controlling the voltage amplitude of the oscillation signal which is supplied by the oscillation means to the antenna electrode at an almost constant value.

14. A passenger detection system as claimed in claim 13, wherein the amplitude control means includes an amplitude detection circuit for detecting the voltage amplitude of the oscillation signal and an amplitude variation circuit for varying and controlling the voltage amplitude of the oscillation signal, and variations of the voltage amplitude of the oscillation signal is controlled by the amplitude variation circuit based on the output of the amplitude detection circuit so that the voltage amplitude will be almost constant.

15. A passenger detection system as claimed in claim 12, herein the antenna electrode is composed of:

an antenna section which is provided to the cushion section and/or the back section of the seat;

a conduction section which is formed by extending part of the antenna section; and

a connector which is provided to the end of the conduction section.

16. A passenger detection system as claimed in claim 12, wherein a control unit is made up by enclosing the oscillation means, the current detection means, the phase difference detection means and the judgment means in a common housing, and the control unit is provided to the seat.

17. A passenger detection system as claimed in claim 16, wherein the housing of the control unit is provided with a connector which is connected with the oscillation means via the current detection means, and the connector on the housing of the control unit is electrically connected to a connector which is provided to the end of the antenna electrode.

18. A passenger detection system as claimed in claim 12, wherein the judgment means executes the judgment on the presence or absence of a passenger seated on the seat, by comparing the transmission current detected by the current detection means with a prestored threshold value concerning the transmission current and comparing the phase difference detected by the phase difference detection means with a prestored threshold value concerning the phase difference.

19. A passenger detection system as claimed in claim 12, further comprising a power circuit for generating a single uniform DC voltage utilizing power derived from a car battery, in which the single uniform DC voltage supplied by the power circuit is utilized as the system power source for circuits in the passenger detection system including the oscillation means, the current detection means, the phase difference detection means and the judgment means.

20. A passenger detection system as claimed in claim 12, wherein the antenna electrode is placed on the upper side of the seat so as to cover almost the entire upper side of the cushion section of the seat.

21. A passenger detection system as claimed in claim 12, wherein the antenna electrode is designed to be provided to both the cushion section and the back section of the seat.

22. A passenger detection system as claimed in claim 12, wherein the antenna electrode is fixed to one or more components of the seat.

23. A passenger detection system as claimed in claim 12, wherein the phase difference detection means detects the phase difference between signals at both ends of the current detection means.

24. A passenger detection system as claimed in claim 12, wherein the phase difference detection means detects the phase difference between the oscillation signal and the output signal, by detecting the phase difference between a rising/falling edge of a square wave signal corresponding to the oscillation signal and a rising/falling edge of a square wave signal corresponding to the output signal.

25. A passenger detection system as claimed in claim 12, wherein the oscillation means generates the high frequency low voltage oscillation signal substantially in the form of a square wave.

26. A passenger detection system as claimed in claim 25, wherein an MPU (MicroProcessor Unit) is utilized as the oscillation means for generating the high frequency low voltage oscillation in the form of a square wave.

27. A passenger detection system comprising:

an antenna electrode which is placed on the upper side of a seat;

an oscillation means for generating a high frequency low voltage oscillation signal in order to generate a weak alternating electric field around the antenna electrode;

a resistance which is placed between the oscillation means and the antenna electrode;

a phase difference detection means for detecting the phase difference between the oscillation signal supplied from the oscillation means and an output signal which is supplied to the antenna electrode; and

a judgment means for judging the presence or absence of a passenger seated on the seat based on the output of the phase difference detection means.