PIEZOELECTRIC VEHICLE IMPACT SENSOR

• US 3,701,903 A
• Filed: 10/29/1970
• Issued: 10/31/1972
• Est. Priority Date: 10/29/1970
• Status: Expired due to Term

• Current Assignee: Donald M. Merhar
• Original Assignee: Donald M. Merhar
• Inventors: Merhar, Donald M.
• Primary Examiner(s): Lewis H. Myers
• Assistant Examiner(s): Stanley J. Witkowski
• Application Number:
  US05/085,123
• Time in Patent Office: 733 Days
• Field of Search: 310/8,8.1,8.4,8.7,9.1 318/116,118,120-133 73/67.1,67.2 323/22SC,22Z 307/251,252R,9,10 340/52H 180/82,103,104 280/150AB 102/70.2
• US Class Current: 307/9.1
• CPC Class Codes: B60R 21/01 Electrical circuits for triggering passive safety arrangements, e.g. airbags, safety belt tighteners, in case of vehicle accidents or impending vehicle accidents electrical circuits for transmission of signals between steering wheel and the vehicle itself B60R16/027; for electrically actuating belt retractor locking means B60R22/343
• CPC Class Codes: G01P 15/09 by piezoelectric pick-up

Abstract

A piezoelectric vehicle impact sensor which is responsive to changes in the vehicle'"'"''"'"'s velocity caused by particular impacts upon the vehicle from predetermined directions relative to the vehicle. A piezoelectric crystal which has a sensitive axis is firmly attached within the vehicle. A mass is mounted within the vehicle for compressing the crystal along the sensitive axis in response to an impact from the predetermined directions, thereby causing the crystal to generate a voltage as a function of the impact. A voltage limiter limits the amplitude of the voltage to a predetermined level. An integrating circuit receives the voltage from the voltage limiter and produces a signal which is an integral of that voltage. A detecting circuit is responsive to a particular value of the signal from the integrating circuit for activating an apparatus such as an inflatable passenger restraining system.

Claims

1. A piezoelectric vehicle impact sensor responsive to changes in the vehicle'"'"''"'"'s velocity caused by particular impacts upon the vehicle from predetermined directions relative to the vehicle comprising:

a piezoelectric crystal having a sensitive axis, said crystal being attached to said vehicle;

compressing means attached to said vehicle for compressing said crystal along said sensitive axis in response to impacts upon said vehicle from said predetermined directions, thereby causing said crystal to generate a voltage as a function of said impacts;

voltage limiting means connected to said crystal for limiting the amplitude of said voltage to a predetermined level;

integrating means connected to said voltage limiting means for producing a signal which is an integral of said voltage received from said voltage limiting means;

first and second input terminals for connection to a voltage source;

first and second output terminals; and

detecting means connected to said integrating means, said output terminals, and said input terminals, said detecting means being responsive to a particular value of said signal for conducting a current through said output terminals.

2. The piezoelectric vehicle impact sensor of claim 1 wherein a plurality of piezoelectric crystals and compressing means are used, each of said crystals being positioned to sense impacts from different directions.

3. The piezoelectric vehicle impact sensor of claim 2 wherein said voltage limiting means comprises a zener diode.

4. The piezoelectric vehicle impact sensor of claim 3 wherein said integrating means comprises:

a first impedance;

a capacitor connected to said first impedance, said capacitor and said first impedance being connected in parallel with said zener diode; and

a second impedance connected in parallel with said capacitor and said first impedance.

5. The piezoelectric vehicle impact sensor of claim 4 wherein said detecting means comprises:

first semiconductor switching means connected to said capacitor in said integrating means, said first semiconductor switching means being responsive to a particular value of said signal for becomIng conductive;

a third impedance connected between said first semiconductor switching means and said first input terminal;

a fourth impedance connected to said second input terminal;

second semiconductor switching means connected between said first and second input terminals and further connected to said first semiconductor switching means and to said fourth impedance, said second semiconductor switching means being responsive to said first semiconductor switching means becoming conductive for conducting a current through said fourth impedance;

a fifth impedance connected to said first input terminal;

capacitive storage means connected in series with said fifth impedance between said first input terminal and said second output terminal;

means connecting said second input terminal to said first semiconductor switching means and to said second output terminal; and

third semiconductor switching means connected to said capacitive storage means, to said first output terminal, and to said fourth impedance, said third semiconductor switching means being responsive to a current through said fourth impedance to conduct a current from said capacitive storage means through said first and second output terminals.

6. The piezoelectric vehicle impact sensor of claim 5 wherein said first, second, and third semiconductor switching means comprise an N-channel field effect transistor, a pair of opposite conductivity type field effect transistors, and a silicon controlled rectifier, respectively.