Passenger detection system

• US 6,161,070 A
• Filed: 08/31/1998
• Issued: 12/12/2000
• Est. Priority Date: 02/23/1996
• Status: Expired due to Term

• Current Assignee: Nidec Elesys Americas Corporation (Nidec Corporation)
• Original Assignee: NEC Home Electronics Incorporated (NEC Corporation)
• Inventors: Jinno, Kazunori, Ofuji, Masahiro
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Pipala, Edward
• Application Number:
  US09/145,309
• Time in Patent Office: 834 Days
• Field of Search: 701/45, 701/46, 701/47, 280/728.1, 280/732, 280/734, 280/735, 180/268, 180/271, 180/272, 340/438, 340/457.1, 340/500
• US Class Current: 701/45
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors

Abstract

A passenger detection system including a single antenna electrode mounted on a surface of a passenger seat in an automobile. An oscillator generates an AC current having a predetermined voltage amplitude that is transmitted to the antenna electrode to produce a minute electric field around the antenna electrode. An amplitude control circuit is used to control the voltage amplitude of the output signal from the oscillator. The electrical characteristics of an object on the passenger seat alter the current and phase of the signal in the antenna electrode. A current detection circuit detects the amount of current flowing from the oscillator to the antenna electrode. In addition, a phase differential detection circuit detects a phase differential between the output signal from the oscillator and the signal on the antenna electrode. A control circuit detects the presence or absence of a passenger seated in the seat based on a current signal output from the current detection circuit and a phase differential signal output from the phase differential detection circuit. A control unit including the oscillator, the amplitude control circuit, the current detection circuit, the phase differential detection circuit and the control circuit, is contained in a single housing that is mounted under the passenger seat.

Claims

1. A passenger detection system comprising:

a seat,

at least one antenna electrode mounted on a surface of the seat,

an oscillation circuit for transmitting an alternating current output signal to the antenna electrode, thereby generating an electric field adjacent to the antenna electrode,

a current detection circuit connected between the oscillation circuit and the antenna electrode for generating a current signal indicating an amount of current flowing from the oscillation circuit to the antenna electrode,

a phase differential detection circuit connected to the oscillation circuit and to the antenna electrode for generating a phase differential signal indicating a difference between a phase of the output signal sent from the oscillation circuit and a phase of the signal on the antenna electrode, and

a control circuit for generating a safety restraint system control signal in response to the current signal and the phase differential signal.

2. A passenger detection system according to claim 1, wherein the oscillation circuit, the current detection circuit, the phase differential detection circuit, and the control circuit are mounted in a single housing attached to the seat.

3. A passenger detection system according to claim 1, wherein the phase differential detection circuit includes a first wave rectifier connected to the oscillation circuit, a first flip flop circuit having a first input terminal connected to an output of the first wave rectifier, a second wave rectifier connected to the antenna electrode, a second flip flop having an input terminal connected to an output of the second wave rectifier and an output terminal connected to a second input terminal of the first flip flop circuit, and an integrating circuit connected to an output of the first flip flop circuit.

4. A passenger detection system according to claim 3, wherein a rising edge of the output signal from the first wave rectifier causes the first flip flop circuit to generate a high output signal, and a rising edge of the output signal from the second wave rectifier is inverted by the second flip flop such that the first flip flop is switched to generate a low output signal.

5. A passenger detection system according to claim 3, wherein a falling edge of the output signal from the first wave rectifier causes the first flip flop circuit to generate a high output signal, and a falling edge of the output signal from the second wave rectifier is inverted by the second flip flop such that the first flip flop is switched to generate a low output signal.

6. A passenger detection system according to claim 1, wherein the oscillation control circuit comprises a variable oscillation circuit that alters the voltage amplitude of the output signal in response to a amplitude adjustment control signal, and a detection circuit for detecting the voltage amplitude output from the variable oscillation circuit, wherein the detection circuit transmits a voltage amplitude signal to the control circuit, and the control circuit generates the amplitude adjustment control signal in accordance with a comparison between the voltage amplitude signal and a stored value such that the variable oscillation circuit generates an output signal having a predetermined voltage amplitude.

7. A passenger detection system according to claim 1, wherein the antenna electrode includes an antenna having a first portion mounted on a base portion of the seat and a second portion mounted on a back portion of the seat, a conductor formed from a part of the first portion of the antenna, and a connector mounted on the conductor.

8. A passenger detection system according to claim 1, wherein a connecting structure is connected between the current detection circuit and the antenna electrode.

9. A passenger detection system according to claim 1, wherein the control circuit compares the current signal with a first threshold value and the phase differential signal with a second threshold value, and generates a safety restraint system control signal when the current signal is greater than the first threshold value and the phase differential signal is greater than the second threshold value.

10. A passenger detection system comprising:

a seat,

at least one antenna electrode mounted on a surface of the seat,

an oscillator for generating an alternating current (AC) signal,

an amplitude control circuit for adjusting a voltage amplitude of the AC signal in response to an amplitude adjustment control signal such that the voltage amplitude is maintained at a predetermined value, wherein the adjusted AC signal is transmitted from the amplitude control circuit to the antenna electrode, thereby causing the antenna electrode to generate a minute electric field,

a current detection circuit connected between the amplitude control circuit and the antenna electrode for generating a current signal indicating an amount of current flowing from the amplitude control circuit to the antenna electrode,

a phase differential detection circuit connected to the amplitude control circuit and to the antenna electrode for generating a phase differential signal indicating a difference between a phase of the adjusted AC signal sent from the amplitude control circuit and a phase of the signal on the antenna electrode, and

a control circuit for generating the amplitude adjustment control signal, and for generating a safety restraint system control signal in response to the current signal and the phase differential signal.

11. A passenger detection system according to claim 10, wherein the oscillator, the amplitude control circuit, the current detection circuit, the phase differential detection circuit, and the control circuit are mounted in a single housing attached to the seat.

12. A passenger detection system according to claim 10, wherein the phase differential detection circuit includes a first wave rectifier connected to the oscillation circuit, a first flip flop circuit having a first input terminal connected to an output of the first wave rectifier, a second wave rectifier connected to the antenna electrode, a second flip flop having an input terminal connected to an output of the second wave rectifier and an output terminal connected to a second input terminal of the first flip flop circuit, and an integrating circuit connected to an output of the first flip flop circuit.

13. A passenger detection system according to claim 12, wherein a rising edge of the output signal from the first wave rectifier causes the first flip flop circuit to generate a high output signal, and a rising edge of the output signal from the second wave rectifier is inverted by the second flip flop such that the first flip flop is switched to generate a low output signal.

14. A passenger detection system according to claim 12, wherein a falling edge of the output signal from the first wave rectifier causes the first flip flop circuit to generate a high output signal, and a falling edge of the output signal from the second wave rectifier is inverted by the second flip flop such that the first flip flop is switched to generate a low output signal.

15. A passenger detection system according to claim 10, wherein the oscillation control circuit comprises a variable oscillation circuit that alters the voltage amplitude of the output signal in response to a amplitude adjustment control signal, and a detection circuit for detecting the voltage amplitude output from the variable oscillation circuit, wherein the detection circuit transmits a voltage amplitude signal to the control circuit, and the control circuit generates the amplitude adjustment control signal in accordance with a comparison between the voltage amplitude signal and a stored value such that the variable oscillation circuit generates an output signal having a predetermined voltage amplitude.

16. A passenger detection system according to claim 10, wherein the antenna electrode includes an antenna having a first portion mounted on a base portion of the seat and a second portion mounted on a back portion of the seat, a conductor formed from a part of the first portion of the antenna, and a connector mounted on the conductor.

17. A passenger detection system according to claim 10, wherein a connecting structure is connected between the current detection circuit and the antenna electrode.

18. A passenger detection system according to claim 10, wherein the control circuit compares the current signal with a first threshold value and the phase differential signal with a second threshold value, and generates a safety restraint system control signal when the current signal is greater than the first threshold value and the phase differential signal is greater than the second threshold value.