Linear load limiter apparatus and method

• US 20040227403A1
• Filed: 05/16/2003
• Published: 11/18/2004
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Wang, Jenne-Tai
• Granted Patent: US 7,063,353 B2
• Time in Patent Office: Days
• US Class Current: 307/10.1
• CPC Class Codes: B60R 2021/01034 Controlling a plurality of restraint devices
• CPC Class Codes: B60R 2021/01279 Load limiters
• CPC Class Codes: B60R 2022/286 using deformation of material
• CPC Class Codes: B60R 21/16 Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags protective garments with automatically inflatable shock-absorbing means A41D13/018; connection of valves to inflatable elastic bodies B60C29/00
• CPC Class Codes: B60R 22/1952 Transmission of tensioning power by cable; Return motion locking means therefor
• CPC Class Codes: B60R 22/28 incorporating energy-absorbing devices belt anchors provided with energy-absorbing means for protecting the occupants in case of physical contact therewith B60R21/055; belt retractors comprising energy-absorbing means B60R22/341, B60R22/4676

Abstract

A method for coordinating the restraint forces provided by a seat belt load limiter and a vehicle airbag is provided. The method includes determining a desired total restraint force profile, determining the airbag force profile, and determining a desired seat belt force profile from the desired total restraint force profile and the airbag profile. The method preferably includes determining a load-limiting force profile sufficient to substantially achieve the desired seat belt force profile, and determining the profile of a load limiter system variable sufficient to substantially achieve the load-limiting force profile. A load limiter is also provided that is characterized by a variable load-limiting force. The load-limiter includes a tube characterized by a tube wall thickness, and a deformation apparatus slidably engaged in the tube for linear translation therein. The deformation apparatus is configured to plastically deform the tube during linear translation to generate a load-limiting force. The tube wall thickness varies over the length of the tube such that the load-limiting force varies during linear translation of the piston.

Claims

1. A load limiter apparatus for a motor vehicle seat belt comprising:

a tube characterized by a tube wall thickness (t) and a yield strength (σ

₀); and

a deformation apparatus slidably engaged in the tube for linear translation therein, the deformation apparatus being configured to plastically deform the tube during said linear translation and thereby generate a load-limiting force;

wherein the tube wall thickness varies over the length of the tube such that the load-limiting force varies during said linear translation.

2. The load limiter apparatus of claim 1, wherein the deformation apparatus includes a piston supported in the tube for linear translation within the tube;

at least one ramp on the piston, and a quantity (n) of rolling elements having radius (r) located between said at least one ramp and said tube;

the load limiting force being attributable to each of the quantity of rolling elements penetrating the tube by a penetration depth (p) and plastically deforming the tube by plowing a groove therein, and by friction between the tube and the quantity of rolling elements.

3. The load limiter apparatus of claim 2, wherein the tube and the quantity of rolling elements have a coefficient of friction (μ

); and

wherein the value of at least one of the yield strength, quantity of rolling elements, radius of rolling elements, penetration depth, tube wall thickness, and coefficient of friction is selected according to the relationship

4. The load limiter apparatus of claim 2, wherein the tube wall thickness was calculated according to the relationship

5. A method for optimizing the interaction between an airbag, a seat belt, and a seat belt load limiter in a vehicle impact, the method comprising:

determining a desired total restraint force profile, the desired total restraint force profile describing a desired total restraint force exerted on a vehicle occupant for each of a plurality of values of an impact-related variable;

determining an airbag force profile, the airbag force profile describing the force exerted by the airbag on the occupant for each of the plurality of values of the impact-related variable; and

determining a desired seat belt force profile describing a desired seat belt force exerted on the occupant for each of the plurality of values of the impact-related variable, the step of determining the desired seat belt force profile including, for each of the plurality of values of the impact-related variable, subtracting the corresponding airbag force from the corresponding desired total restraint force.

6. The method of claim 5, wherein the method further comprises determining a desired load-limiting force profile for the seat belt load limiter, the desired load-limiting force profile describing a desired load limiting force magnitude (F) exerted on the seat belt by the load limiter for each of the plurality of values of the impact-related variable, the desired load limiting force being a component of the corresponding desired seat belt force.

7. The method of claim 6, wherein the load limiter includes a tube characterized by a tube wall thickness (t) and comprised of a material having a yield strength (σ

₀);

a piston supported in the tube for linear translation within the tube between a plurality of positions relative to the tube during an energy absorbing stroke;

at least one ramp on the piston; and

a quantity (n) of rolling elements having radius (r) located between said at least one ramp and said tube;

wherein the load limiting force is attributable to, during the energy absorbing stroke of the piston, each of the quantity of rolling elements plastically deforming the tube by plowing a groove therein at a penetration depth (p), and friction between the tube and the quantity of rolling elements, the tube and the quantity of rolling elements having a coefficient of friction (μ

).

8. The method of claim 7, wherein the impact-related variable is the displacement of the piston during the energy absorbing stroke;

wherein each of the plurality of values of the impact-related variable corresponds to a piston position relative to the tube; and

wherein the method further comprises determining a system variable profile that describes a value of a load-limiter system variable at each of the plurality of piston positions sufficient to substantially achieve the corresponding desired load limiting force.

9. The method of claim 8, wherein the system variable is tube wall thickness.

10. The method of claim 9, wherein said determining a load-limiter system variable profile includes calculating the tube wall thickness at each of the plurality of piston positions according to the relationship

11. The method of claim 10, further comprising assembling a load limiter apparatus having a tube conforming to the tube wall thickness profile.

12. A method for designing a load-limiter apparatus, the method comprising:

determining a desired load-limiting force magnitude (F) for the load-limiter apparatus, the load-limiter apparatus having a tube characterized by a tube wall thickness (t) and comprised of a material having a yield strength (σ

₀);

a piston supported in the tube for linear translation within the tube;

at least one ramp on the piston; and

a quantity (n) of rolling elements having radius (r) located between said at least one ramp and said tube;

wherein the load limiting force is attributable to, during the energy absorbing stroke of the piston, each of the quantity of rolling elements plastically deforming the tube by plowing a groove therein at a penetration depth (p), and friction between the tube and the quantity of rolling elements, the tube and the quantity of rolling elements having a coefficient of friction (μ

); and

selecting the value of at least one of the yield strength, quantity of rolling elements, radius of rolling elements, penetration depth, tube wall thickness, and coefficient of friction such that the relationship

$F=\frac{2<br><br>n<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\sigma <br><br>}}_0<br><br>t<br><br>\left[\mathrm{\theta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t+r<br><br>\left(\mathrm{\theta <br><br>}-\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\theta <br><br>}\right)\right]}{g<br><br>\left(\mathrm{\theta <br><br>},\mathrm{\mu <br><br>}\right)},$

where

$g<br><br>\left(\mathrm{\theta <br><br>},\mathrm{\mu <br><br>}\right)=1-\frac{1}{\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\mathrm{\theta <br><br>}}{2}+\frac{1}{\mathrm{\mu <br><br>}}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\mathrm{\theta <br><br>}}{2}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\theta <br><br>}={\cos }^{-1}<br><br>\left[1-\frac{p}{r}\right],$

is substantially satisfied.