Protective helmet with integrated rotational limiter

1. A helmet comprising:

an outer liner having an interior surface comprising a shelf extending inward from the interior surface of the outer liner proximate a perimeter of an opening at a lower edge of the outer liner, the shelf comprising an arresting surface; and

an inner liner having an exterior surface, an interior surface and an edge connecting the exterior surface of the inner liner to the interior surface of the inner liner, the edge facing the arresting surf ace of the shelf;

wherein the inner liner is slidably coupled to the interior surface of the outer liner and slidably movable relative to the outer liner between a first position in which the edge of the inner liner is separated from the arresting surface of the shelf by a first gap, and an arrested position in which a portion of the edge of the inner liner is in contact with a portion of the arresting surface of the shelf in response to movement of the outer liner relative to the inner liner caused by an impact to the helmet,

wherein at least one of the outer liner and the inner liner comprise an energy management material;

further comprising at least one return spring coupling the outer liner with the inner liner and biasing the inner liner toward the first position from the arrested position after the inner liner moves from the first position to the arrested position in response to the impact to the helmet, wherein the at least one return spring is composed of an elastomer material.

2. The helmet of claim 1 , wherein the energy management material comprises at least one of expanded polystyrene (EPS), expanded polyurethane (EPU), expanded polyolefin (EPO), and expanded polypropylene (EPP).

3. The helmet of claim 1 , wherein the interior surface of the outer liner proximate a majority of the perimeter of the opening includes the shelf.

4. The helmet of claim 1 , wherein the shelf further comprises a material having a different elasticity from a material of a portion of the outer liner.

5. The helmet of claim 1 , wherein the shelf comprises a plurality of shelf pieces, and at least two of the plurality of shelf pieces are separate and distinct from each other.

6. The helmet of claim 1 , wherein the outer liner further comprises a front, a rear, and two sides opposite each other and connecting the front and the rear, and wherein a first portion of the shelf is located proximate the rear of the outer liner, a second portion of the shelf is located proximate one of the two sides of the outer liner, and a third portion of the shelf is located proximate the other of the two sides of the outer liner.

7. The helmet of claim 1 , wherein the first gap is substantially uniform across the arresting surface when the inner liner is in the first position.

8. The helmet of claim 1 :

wherein the outer liner comprises a plurality of vents passing through the outer liner;

wherein the inner liner comprises a plurality of channels passing through the inner liner; and

wherein the plurality of channels at least partially overlap with the plurality of vents to form a plurality of apertures from outside the helmet to inside the helmet.

9. The helmet of claim 8 :

wherein each of the plurality of vents is beveled at the interior surface of the outer liner; and

wherein each of the plurality of channels is beveled at the exterior surface of the inner liner.

10. The helmet of claim 1 , wherein at least one of the interior surface of the outer liner and the exterior surface of the inner liner comprises a surface treated with a friction-reducing material comprising in-molded polycarbonate (PC) or in-molded polypropylene (PP).

11. The helmet of claim 1 , wherein an air gap exists between a majority of the exterior surface of the inner liner and the interior surface of the outer liner.