Lid construction for breathing apparatus

1. A breathing assistance apparatus comprising:

a main body comprising a cavity;

a lid configured to rotate between an opened position and a closed position closing the cavity;

a hinge assembly that connects the lid to the main body, the hinge assembly comprising:

a post mounted to the lid or the main body;

a support mounted to the other of the lid or the main body, the support comprising a recess configured to receive at least a portion of the post, the recess having:

a mouth and an end surface that is defined by a curve having a radius from a center point;

an axis between the mouth and the end surface, the post is moved along the axis toward the end surface as the lid is moved from a detached state to an attached state;

a cam structure that includes a first contact point and a second contact point located on a sloped surface, a first distance between the first contact point and the center point, a second distance between the second contact point and the center point, the first distance is smaller than the second distance; and

a guide structure configured to contact the cam structure from the first contact point to the second contact point as the lid is moved from a detached state to an attached state.

2. The breathing assistance apparatus of claim 1 , wherein the lid moves from the detached state to the attached state by rotation of the lid from the opened position to the closed position.

3. The breathing assistance apparatus of claim 1 , wherein the end surface is semi-circular.

4. The breathing assistance apparatus of claim 1 , wherein the axis of the recess is horizontal.

5. The breathing assistance apparatus of claim 1 , wherein the mouth is rearwardly facing.

6. The breathing assistance apparatus of claim 1 , wherein the support comprises an upper guide portion and a lower guide portion extending between the mouth and the end surface, and the upper guide portion forms a retention surface that contacts the post to retain the lid on the main body in response to forces tending to separate the lid from the main body.

7. The breathing assistance apparatus of claim 1 , wherein the post is circular in cross-section and comprises a post center point and a post radius, around which the lid rotates during normal opening and closing of the lid.

8. The breathing assistance apparatus of claim 7 , wherein a third distance travelled by the post center point within the recess as the lid is moved from the detached state to the attached state is equal to a difference between the second distance and the first distance.

9. The breathing assistance apparatus of claim 1 , wherein the radius of the post is substantially equal to the radius of the end surface such that the post is positioned against the end surface, in use.

10. The breathing assistance apparatus of claim 1 , wherein in normal opening and closing movement, sliding of the post within the recess does not occur.

11. The breathing assistance apparatus of claim 1 , wherein interaction of the guide structure and the cam structure only occurs during reattachment of the lid.

12. The breathing assistance apparatus of claim 1 , wherein the cam structure is on the main body, and guide structure is on the lid.

13. The breathing assistance apparatus of claim 1 , wherein the guide structure is on the main body, and cam structure is on the lid.