초록 ▼

The purpose of this invention is to sense the presence of a seated occupant in a vehicle such as an automobile, plane, train or bus, or in a room or location where it is desirable to detect if seats are occupied. The occupant presence detection device consists of a single seat-mounted electrode, an

The purpose of this invention is to sense the presence of a seated occupant in a vehicle such as an automobile, plane, train or bus, or in a room or location where it is desirable to detect if seats are occupied. The occupant presence detection device consists of a single seat-mounted electrode, an oscillator circuit, a bridge circuit, a detection circuit and a circuit for processing the detected signals. The oscillator circuit excites the electrode. If an occupant is present on the seat, additional capacitance from the human body is introduced into the bridge via the electrode. This created differences in the voltage and phase of the waveform in each arm of the bridge circuit which are amplified by a differential amplifier. The signal is then converted to a DC voltage that, when above a predetermined threshold, causes the device to outputs a signal that indicates the presence of an occupant. Using a bridge configuration and a differential amplifier allows the circuit to be operated over a wide range of supply voltages. It also reduces the need for high precision components and the need to regulate the amplitude of the waveform produced by the oscillator. The net result is a capacitive occupant sensing device that is less complex and less expensive that previous capacitive occupant sensing devices, yet is tolerant of power supply fluctuations, is able to function over a wide range of operating voltage and still provides failsafe functionality.

대표청구항 ▼

What is claimed is: 1. An occupant presence detector comprising: a bridge circuit including a first electrode, the bridge circuit including a sensing arm and a reference arm, the sensor arm including the first electrode, the bridge circuit being balanced when no occupant is detected near the first

What is claimed is: 1. An occupant presence detector comprising: a bridge circuit including a first electrode, the bridge circuit including a sensing arm and a reference arm, the sensor arm including the first electrode, the bridge circuit being balanced when no occupant is detected near the first electrode, the bridge circuit becoming unbalanced based upon the presence of an occupant near the first electrode; and a differential amplifier determining when the bridge circuit is unbalanced. 2. The occupant presence detector of claim 1 further including an oscillator exciting the bridge circuit. 3. The occupant presence detector of claim 1 wherein the first electrode comprises a conductive thread. 4. The occupant presence detector of claim 3 wherein the first electrode is sewn into a vehicle seat. 5. The occupant presence detector of claim 1 wherein the first electrode comprises a conductive thread in a vehicle seat. 6. The occupant presence detector of claim 5 wherein the bridge circuit includes a sensing arm and a reference arm, the sensor arm including the first electrode. 7. The occupant presence detector of claim 6 wherein the reference arm includes a reference wire for canceling noise received by the first electrode. 8. The occupant presence detector of claim 6 wherein the sensing arm and the reference arm are inputs to the differential amplifier. 9. The occupant presence detector of claim 1 wherein the first electrode is mounted adjacent a seating surface, the detector further including a pressure sensor determining a force applied to the seating surface. 10. The occupant presence detector of claim 9 wherein the pressure sensor comprises a capacitor having a pair of spaced-apart electrodes, the space between the electrodes varying based upon the force applied to the seating surface, thereby changing a capacitance of the capacitor. 11. The occupant presence detector of claim 10 installed in a vehicle with an occupant safety system, the occupant safety system being disabled if the pressure sensor indicates that the force is less than a threshold and being enabled only if the force exceeds the threshold. 12. The occupant presence detector of claim 11 wherein the occupant safety system is disabled based upon an indication by the occupant presence detector that no occupant is present even when the pressure sensor exceeds the threshold. 13. The occupant presence detector of claim 10 wherein the pressure sensor further includes a compressible material between the pair of spaced-apart electrodes, the compressible material being compressed upon the application of force to the seating surface. 14. The occupant presence detector of claim 1 wherein the differential amplifier has a first input connected to the reference node and a second input connected to the sensor node. 15. The occupant presence detector of claim 14 further including a signal source connected to a first node in the bridge circuit, the first node connecting the reference arm and the sensor arm. 16. The occupant presence detector of claim 15 further including a first resistor between the first node and the reference node and a second resistor between the first node and the sensor node. 17. The occupant presence detector of claim 1 wherein the reference arm includes a reference wire for canceling noise received by the first electrode. 18. An occupant presence detector comprising: a bridge circuit including a first electrode, the bridge circuit being balanced when no occupant is detected near the first electrode, the bridge circuit becoming unbalanced based upon the presence of an occupant near the first electrode; a differential amplifier determining when the bridge circuit is unbalanced; and a fault detection circuit monitoring the first electrode and configured to generate a fault signal based upon detection of a fault in the first electrode. 19. The occupant presence detector of claim 18 wherein the fault detection circuit monitors current through the first electrode and generates a first fault signal based upon detection of current through the first electrode exceeding a high current threshold. 20. The occupant presence detector of claim 19 wherein the fault detection circuit further generates a second fault signal based upon detection of current through the first electrode dropping below a low current threshold. 21. The occupant presence detector of claim 20 further including an oscillator exciting the bridge circuit and wherein the fault detection circuit further includes an oscillator failure detection circuit monitoring an output of the oscillator and generating an oscillator fault signal based upon detection of a failure of the oscillator. 22. An occupant presence detector comprising: a bridge circuit including a sensing arm and a reference arm, the sensor arm including a first electrode, the reference arm including a reference wire for canceling noise received by the first electrode, wherein the reference wire is twisted with a wire in the sensing arm, the bridge circuit being balanced when no occupant is detected near the first electrode, the bridge circuit becoming unbalanced based upon the presence of an occupant near the first electrode; and a differential amplifier determining when the bridge circuit is unbalanced. 23. An occupant presence detector comprising: an oscillating circuit including an amplifier; an electrode forming an input to the amplifier, the capacitance of the electrode varying based upon a presence or absence of an occupant near the electrode, the frequency of the oscillating circuit changing based upon the capacitance of the electrode; and a fault detection circuit monitoring the electrode and configured to generate a fault signal based upon detection of a fault in the electrode. 24. An occupant presence detector comprising: a bridge circuit including a first electrode, the bridge circuit being balanced when no occupant is detected near the first electrode, the bridge circuit becoming unbalanced based upon the presence of an occupant near the first electrode; and a differential amplifier determining when the bridge circuit is unbalanced, the first electrode is mounted adjacent a seating surface, the detector further including a pressure sensor determining a force applied to the seating surface wherein the occupant presence detector is installed in a vehicle with an occupant safety system, the occupant safety system being disabled if the pressure sensor indicates that the force is less than a threshold and being enabled only if the force exceeds the threshold. 25. The occupant presence detector of claim 24 wherein the occupant safety system is disabled based upon an indication by the occupant presence detector that no occupant is present even when the pressure sensor exceeds the threshold.