Weight sensors having centralized loose tolerance universal force and Mx/My moments overload stops

• US 20030106723A1
• Filed: 12/06/2002
• Published: 06/12/2003
• Est. Priority Date: 12/07/2001
• Status: Active Grant

• Current Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Original Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Inventors: Lee, Darren, Thakur, Rajeev, Golshteyn, Alexander, Das, Rajesh, Watts, Russ
• Granted Patent: US 6,916,997 B2
• Time in Patent Office: Days
• US Class Current: 177/144
• CPC Class Codes: B60R 21/01516 using force or pressure sensing means
• CPC Class Codes: B60R 21/0152 using strain gauges
• CPC Class Codes: G01G 19/4142 for controlling activation of safety devices, e.g. airbag systems electrical circuits for triggering safety arrangements in case of vehicle accidents B60R21/015
• CPC Class Codes: G01G 23/002 Means for correcting for obliquity of mounting for pendulum-weight apparatus G01G1/16

Abstract

Automotive load cells having centralized, multi-axis, loose tolerance overload/limit stops provide improved strain gauge response. The modular, integrated stop assemblies magnify sensor substrate deflection by use of opposed concave (Belleville) springs are used in direct contact with the substrate to accommodate ±Z axis deflection and Mx/My moment angular rotation. A flanged guide member on the load stud permits a wide range of geometries. The substrate is thickened around the load stud hole and the outboard support bolt holes. Hollow rivets assist in design modularity. Strain gauges are placed at the yield zones symmetrically with respect to the X axis. The substrate hole Mx/My gap is larger than the stop bracket hole to insure a positive stop for Mx/My moments prior to yield. The inventive multi-axis stop assembly is used in any type load cell, including rectangular, thinned, notched, necked/dogbone, or cantilever substrates with any strain gauge layout configuration.

Claims

1. Automotive seat weight sensor system comprising in operative combination:

a) a thin steel, generally planar substrate member having spaced, opposed ends, a longitudinal X axis, a lateral Y axis, and a vertical Z axis;

b) said substrate having an array of strain gauges arrayed thereon to determine the amount of load in the Z axis of said substrate;

c) a load stud mounted through a hole in said substrate medial of its ends with concave springs disposed directly in contact with said substrate;

d) said medial substrate hole is configured with loose tolerance with respect to said stud to provide an Mx/My gap there between;

e) a limit stop bracket having an upper and a lower surface mounted spaced from and in association with said substrate, and having a hole through which said load stud passes;

f) stop elements carried by said stud to engage at least one of said upper surface, said lower surface and a wall of said limit stop bracket hole to provide Fz, Fx, FY stops and an Mx/My moment stop; and

g) said limit stop bracket hole having a tolerance configured with respect to said stud to provide a gap smaller than said Mx/My gap so that said Mx/My stop is engaged before moment-induced yield of said substrate occurs.

2. Automotive seat weight sensor system as in claim 1 wherein said limit stop bracket is the same part used as a stop for all loads and moments, and said substrate is configured with thin and thick sections as seen in cross section and said medial substrate hole is located in a thick section.

3. Automotive seat weight sensor system as in claim 2 wherein the concave side of each of said springs is facing a surface of said substrate.

4. Automotive seat weight sensor system as in claim 3 wherein said stop elements include spaced upper and lower flanges associated with said stud with a flange being spaced from each side of said stop bracket.

5. Automotive seat weight sensor system as in claim 3 wherein said concave spring is softer than said substrate.

6. Automotive seat weight sensor system as in claim 4 wherein said stud includes a guide member mounted thereon, said guide member is configured with at least one of said flanges, and said Mx/My gap is defined between an outside surface of said guide and the surface of said medial substrate hole.

7. Automotive seat weight sensor system as in claim 6 wherein said substrate is mounted to said limit stop bracket by at least one hollow rivet passing through a hole in a thickened end section of said substrate disposed spaced from said medial thickened section, said thickened sections being separated by at least one thin section.

8. Automotive seat weight sensor system as in claim 1 wherein the geometry of the loose tolerance of said system is selected to provide a modular unit that is easy to mount and replace in connection with an automotive seat.

9. Automotive seat weight sensor system as in claim 1 wherein the stops are central to the load stud and located above or below said concave springs to provide an efficient and direct path for transferring overload to one or more of said stops while permitting extended travel of said load stud in Z axis and angularly in rotation around at least one of the X and the Y axis.

10. Automotive seat weight sensor system as in claim 1 wherein said springs are Belleville-type springs.

11. Automotive seat weight sensor system as in claim 2 wherein said strain gauges are disposed in onset of yield zones of said substrate.

12. Automotive seat weight sensor system as in claim 11 wherein said onset of yield zones are defined by areas of transition between thick and thin sections of said substrate.

13. Automotive seat weight sensor system as in claim 6 wherein said guide is selected from a unitary and a multi-part member.

14. An improved load cell for automotive seat weight determination including presence of a passenger load, wherein said load cell is a load-stop or a non-load-stop design and includes at least one load bearing stud and a substrate plate carrying sensors thereon, the improvement comprising in operative combination:

securing said load stud to said substrate with concave springs in contact with said substrate, said concave springs having a stiffness less than said substrate, and said load stud being configured with loose tolerance with respect to said substrate.

15. Improved load cell for automotive seat weight determination as in claim 14 wherein the concave side of at least one of said springs is facing and in direct contact with said substrate.

16. Improved load cell for automotive seat weight determination as in claim 15 wherein said load cell includes at least one moment stop Mx or My that engages before yield of said substrate.

17. Improved load cell for automotive seat weight determination as in claim 16 wherein said load cell includes stops for Fz, Fx and Fy.

18. Method of reducing load cell substrate misreading or failure due to Mx and/or My moment-induced yield, comprising the steps of:

a) mounting a load stud to a sensor substrate with concave spring having stiffness less than said substrate;

b) disposing said springs to compress differentially upon moments Mx and/or My being applied to said stud; and

c) configuring a moment gap between said substrate and said load stud that is larger that a gap to a moment stop associated with said stud so that there is stop engagement under a moment before yield strength of said substrate is exceeded.