Load sensor for measuring engine cylinder pressure and seat occupant weight

• US 6,134,947 A
• Filed: 09/12/1997
• Issued: 10/24/2000
• Est. Priority Date: 09/12/1997
• Status: Expired due to Term

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Kwun, Hegeon
• Primary Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US08/928,051
• Time in Patent Office: 1,138 Days
• Field of Search: 73/35.07, 73/35.12, 73/115, 73/116, 73/117.3, 324/393, 280/735, 340/665, 340/666, 340/667
• US Class Current: 73/35.12
• CPC Class Codes: G01L 1/14 by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
• CPC Class Codes: G01L 23/14 by electromagnetic elements
• CPC Class Codes: G01L 5/243 using washers

Abstract

A load sensor for measuring engine cylinder pressure and vehicle seat occupant weight in a nonintrusive manner that is easily adaptable to existing vehicle components and occupancy support structures. The sensor of the invention provides a toroidal-shaped ferromagnetic steel core that defines a hollow space within which an excitation coil and a detection coil are wound. For engine cylinder pressure sensing, this toroidal sensor is placed on a spark plug, much in the nature of a washer, and is clamped between the spark plug and the spark plug seat in the chamber. For seat occupant weight sensing, the sensor is placed under a seat leg around a fastening bolt, again much in the nature of a washer, and is clamped between the bolt and the floor of the vehicle. Changes in the load or force produced by the cylinder pressure or the occupant weight, alters the stress in the steel core of the sensor. These stress changes in turn induce changes in the magnetic properties of the steel core. Non-linear harmonic analysis of the stress induced magnetic property changes is made and derives the cylinder pressure or occupant weight after suitable calibrations. The cylinder pressure measurements can then be used to facilitate an efficient operation of the internal combustion engine through the modification of timing, fuel mixture, etc. The use of the device in conjunction with occupant safety systems would provide a weight value sufficient to characterize the appropriate or inappropriate activation of an air bag system or the like.

Claims

1. A sensor device for measuring changes in a clamping force exerted on said device, said sensor device comprising:

a toroidal-shaped ferromagnetic core, said core having an inner cylindrical wall and an outer cylindrical wall and defining an internal volume between said cylindrical walls, said inner cylindrical wall further defining a central, coaxial, cylindrical hole in said toroidal-shaped ferromagnetic core;

an electromagnetic excitation coil positioned within said internal volume of said ferromagnetic core between said cylindrical walls and coaxial with said hole, said electromagnetic excitation coil for generating an alternating magnetic field within said ferromagnetic core when said coil is subjected to an alternating electric current; and

an electromagnetic detection coil positioned within said internal volume of said ferromagnetic core adjacent to said excitation coil between said cylindrical walls and coaxial with said hole, said electromagnetic detection coil for detecting a magnetic field response within said ferromagnetic core.

2. The device of claim 1, wherein said ferromagnetic core comprises:

an open ring, said open ring having a U-shaped cross-section and defining a circular groove for receiving said excitation coil and said detection coil; and

a circular washer sized and positioned on said ring, said circular washer serving to close said circular groove as to form said internal volume.

3. The device of claim 1 having a geometry and size suitable for use in conjunction with standard-sized spark plug devices, wherein said device is positioned between said spark plug device and a spark plug seat on an internal combustion engine.

4. The device of claim 1, having a geometry and size appropriate for use in conjunction with bolts for the attachment of vehicular occupant seat support systems, wherein said device is sized to receive one of said attachment bolts through said central hole in said toroidal core, said device and said attachment bolt being positioned between said seat support system and a floor structure of said vehicle and serving to measure force changes brought about by occupancy weight variations.

5. A method for measuring changes in a clamping force exerted on a material, said method comprising:

applying an alternating magnetic field to said material by supplying an alternating electric current to an excitation coil positioned adjacent said material, said field having a field frequency;

detecting a magnetic response of said material by measuring an electric voltage induced in a detection coil positioned adjacent said material;

extracting non-linear harmonic components of said applied field frequency from said detected magnetic response; and

correlating a magnitude of said non-linear harmonic components with quantitative changes in said clamping force.

6. The method of claim 5, wherein said step of extracting non-linear harmonic components of said applied field frequency comprises extracting the third harmonic of the applied field frequency.

7. The method of claim 6, wherein said step of extracting non-linear harmonic components of said applied field frequency further comprises extracting the fundamental frequency and other frequency components as a means for enhancing force measurement accuracy.