Constant force impact protection device
A protective impact device is provided that produces an approximately constant force during compression. The device distinguishes several structural features. First, the cross-sectional area in between two impact surfaces increases over the stroke distance when compression takes place. Second, a compressible fluid containing vessel, held in between two impact surfaces, defines an outer shape with a positive second derivative slope defined from one impact surface towards the other impact surface. Third, orifices allow the fluid to bleed out from the compressible vessel when an impact force causes compression of the protective impact device. The resulting approximately constant force scales more or less linearly with impact energy, regardless of impact velocity caused by the impact force. Applications include athletic equipment, automotive bumpers, aircraft landing gear, and any other application that would benefit from maximum energy absorption during an impact.
1. A protective impact device, comprising:
(a) a first impact surface;
(b) a second impact surface substantially parallel to the first impact surface;
wherein the area of the first impact surface is smaller than the area of the second impact surface,
wherein a perpendicular distance between the first and second impact surface defines a stroke distance;
(c) a compressible vessel held in between the first and second impact surfaces, wherein a cross-sectional area defined by the compressible vessel increases in a continuous fashion over the stroke distance from the first impact surface towards the second impact surface and wherein the compressible vessel in between the first and second impact surfaces defines an inner wall shape with a positive second derivative slope defined over the stroke distance, defined over the entire inner wall and defined from the first impact surface towards the second impact surface, wherein the compressible vessel has reinforcement fibers to prevent the compressible vessel bulging;
(d) a fluid contained within the compressible vessel; and
(e) one or more orifices to allow the fluid to bleed out from the compressible vessel when an impact force causes compression of the protective impact device, wherein the compression is defined by the first impact surface moving towards the second impact surface along the stroke distance.
2. The protective impact device as set forth in claim 1 , wherein the area of the second impact surface is at least 20% greater than the area of the first impact surface.
3. The protective impact device as set forth in claim 1 , wherein the wall shape is a continuous shape for at least 90% of the stroke distance.
4. The protective impact device as set forth in claim 1 , further comprising a fluid collection chamber fluidly connected with the compressible vessel via the one or more orifices.
5. The protective impact device as set forth in claim 1 , further comprising one or more one-way valves to allow the fluid to return to the compressible vessel back into the compressible vessel after the compression.
6. The protective impact device as set forth in claim 1 , wherein the protective impact device produces an approximately constant force during the compression.
7. The protective impact device as set forth in claim 1 , wherein the protective impact device produces an approximately constant force established by the bleeding liquid through the one or more orifices during the compression.
8. The protective impact device as set forth in claim 1 , wherein the protective impact device produces an approximately constant force that scales substantially linearly with impact energy, regardless of impact velocity caused by the impact force.
9. The protective impact device as set forth in claim 1 , wherein the reinforcement fibers are axial fibers.