Stair-climbing apparatus for wheelchair

An apparatus for moving a wheelchair on a flight of steps, the apparatus comprising:

• a support adapted to engage underneath the wheelchair in an upright condition of same, the wheelchair being pivotal on the support between erect and inclined positions;
• two endless tracks on the support and supporting same and the wheelchair carried thereon, whereby the tracks allow the wheelchair to move over uneven terrain and on stairs;
• a frame element pivotal on the support about a horizontal axis transverse to the tracks;
• a coupling element on the frame element for securing same to the wheelchair and thereby securing the wheelchair to the support;
• latch means on the support including a latch element displaceable between a holding position for securing the wheelchair in the inclined position and a freeing position for permitting the wheelchair to move freely between its positions, the latch element being pivotal on the support about a latch axis between the latch positions and being operatively connected to the frame element;
• means connected to the latch element, responsive to the inclination of the tracks relative to the horizontal, and including
• a retaining dog movable into a position directly juxtaposed with the latch element
• a pivot spaced on the support a fixed radial distance from the latch axis, and
• a weight eccentric to and pivoted on the pivot, the retaining dog being fixed to the weight and latchingly engageable with the latch element when directly juxtaposed therewith, the weight and dog being relatively positioned such that when the forward end of the support and tracks are inclined downwardly at more than a predetermined angle to the horizontal the dog latchingly engages and rotationally arrests the latch element for blocking the latch element from moving into the freeing position when the tracks are inclined at more than a predetermined angle to the horizontal, whereby the wheelchair cannot be released from the support when same is moving on an incline;
• and
• stop means limiting pivoting of the dog to a small arc relative to its pivot.