Patent ID: 6845996

Claim:
A shock absorber for a power wheelchair having a frame, an electrical drive assembly and a pair of rear wheels, where the electrical drive assembly is mounted in the frame and has a drive shaft with two ends respectively extending out of the electrical drive assembly, and the rear wheels are respectively attached to and driven by the ends of the drive shaft; the shock absorber comprising a seat having a base with a top, a front end and a rear end and adapted to couple to the electrical drive assembly; a pivot bracket respectively attached to the top near each of the front and the rear of the base; and a connecting ring secured on the top of the base between the two pivot brackets; a bracket pivotally connected to the connecting ring on the base to pivotally connect the base to the bracket and having a top, a bottom, a front end, a rear end and two opposite sides, the top of the bracket adapted to attach to the frame of the power wheelchair and the bracket further having two through holes respectively defined through the top of the bracket and corresponding to the pivot brackets on the base; and a suspension device mounted between the bottom of the bracket and the top of the base and the suspension device comprising a front suspension rod pivotally mounted in one of the pivot brackets near the front end of the base and having a top end and a bottom end, the bottom end of the front suspension rod pivotally mounted in the pivot bracket and the top end of the front suspension rod extending out of a corresponding one of the through holes in the bracket to be fastened at the top of the bracket; a rear suspension rod pivotally mounted in one of the pivot brackets near the rear end of the base and having a top end and a bottom end, the bottom end of the rear suspension rod pivotally mounted in the pivot bracket and the top end of the rear suspension rod extending out of a corresponding one of the through holes in the bracket to be fastened at the top of the bracket; a front suspension spring mounted around the front suspension rod and having a spring stiffness, a top end and a bottom end supported on the bottom end of the front suspension rod; and a rear suspension spring mounted around the rear suspension rod and having a spring stiffness, a top end and a bottom end supported on the bottom end of the rear suspension rod; wherein the spring stiffness of the front suspension spring is less than the spring stiffness of the rear suspension spring.