Occupancy detector apparatus for automotive safety system

• US 3,898,472 A
• Filed: 10/23/1973
• Issued: 08/05/1975
• Est. Priority Date: 10/23/1973
• Status: Expired due to Term

• Current Assignee: David K. Long
• Original Assignee: David K. Long
• Inventors: Long, David K.
• Primary Examiner(s): Hohauser, Herman J.
• Application Number:
  US05/408,681
• Time in Patent Office: 651 Days
• Field of Search: 180/82C 340/52E,258C,278 317/DIG.2 307/1SB
• US Class Current: 180/270
• CPC Class Codes: B60R 2022/4816 for sensing locking of buckle
• CPC Class Codes: B60R 2022/4858 for sensing pressure on seat
• CPC Class Codes: B60R 22/48 Control systems, alarms, or interlock systems, for the correct application of the belt or harness

Abstract

Occupancy detector apparatus including a metallic electrode disposed to cooperate with the body of an automobile to form an occupant sensing capacitor, a reference capacitor, and an IC capacitance detecting and logic generating circuit. The IC includes a current source for continuously supplying charging current to the sensing capacitor and the reference capacitor, a first charge detecting circuit for detecting the charge on the sensing capacitor, a second charge detecting circuit for detecting the charge on the reference capacitor, and a comparator circuit for comparing the output signals developed by the first and second charge detecting circuits and for developing a logic output commensurate with the relationship between the capacitances of the sensing capacitor and the reference capacitor.

Claims

1. In an automotive safety system including a seat occupancy detector, other automotive function detectors and electronic logic responsive to signals developed thereby for preventing operation of the automobile unless the detectors develop output signals in a predetermined sequence, an improved occupancy detector comprising:

means forming an occupant sensing capacitor having a first capacitance when a particular seat is occupied and a second capacitance when said seat is not occupied;

a reference capacitor;

means for charging said occupant sensing capacitor and said reference capacitor;

first charge detecting means coupled to said occupant sensing capacitor and operative to develop a first signal commensurate with the capacitance of said occupant sensing capacitor;

second charge detecting means coupled to said reference capacitor and operative to develop a second signal commensurate with the capacitance of said reference capacitor; and

comparator means responsive to said first signal and second signal and operative to compare said signals and develop an output signal representative of the relationship therebetween.

2. In an automotive safety system as recited in claim 1 wherein said first charge detecting means includes first impedance means and means responsive to a switching signal and operative to discharge said occupant sensing capacitor through said first impedance means to develop said first signal thereacross.

3. In an automotive safety system as recited in claim 1 and further comprising signal generating means for developing a switching signal for causing said first charge detecting means and said second charge detecting means to periodically measure the charges on said occupant sensing capacitor and said reference capacitor and develop said first and second signals respectively.

4. In an automotive safety system as recited in claim 3 wherein said first charge detecting means includes first impedance means and means responsive to said switching signal and operative to discharge said occupant sensing capacitor through said impedance means to develop said first signal thereacross.

5. In an automotive safety system as recited in claim 4 wherein said first charge detecting means includes second inpedance means and means responsive to said switching signal and operative to discharge said reference capacitor through said second impedance means to develop said second signal thereacross.

6. In an automotive safety system as recited in claim 1 wherein said first charge detecting means includes a first transistor having a first electrode coupled to said occupant sensing capacitor, a second electrode for receiving a switching signal and a third electrode, and first impedance means coupled to said third electrode, whereby a switching signal applied to said second electrode causes said occupant sensing capacitor to be discharged through said first impedance means to develop said first signal thereacross.

7. In an automotive safety system as recited in claim 6 wherein said second charge detecting means includes a second transistor having a fourth electrode coupled to said reference capacitor, a fifth electrode for receiving a switching signal and a sixth electrode, and second impedance means coupled to said sixth electrode, whereby a switching signal applied to said fifth electrode causes said reference capacitor to be discharged through said second impedance means to develop said second signal thereacross.

8. In an automotive safety system as recited in claim 7 and further comprising signal generating means for periodically developing said switching signal, said switching signal including a train of pulses for causing said first charge detecting means and said second charge detecting means to periodically measure the charge on said occupant sensing capacitor and said reference capacitor.

9. In an automotive safety system as recited in claim 1 wherein said occupant sensing capacitor includes a metallic electrode positioned beneath said seat to form one capacitive plate, the metallic body of the automobile forming the other capacitive plate of said occupant sensing capacitor.