Locking lift arms safety mechanism for a hydraulic floor jack

A safety mechanism for a power unit, including a rectangular frame having a forward end, a rearward end, a bottom sides, and a pair of longitudinal side flanges extending upward from the frame, with the rearward end having a tubular control handle pivotally attached and extending with a rotatable control knob at the upper end of the handle;

• a pivotal lifting system mounted on the frame including a pair of parallel lift arms having rearward ends interconnected by a lateral push bar and having forward ends interconnected by a rectangular lifting plate pivotally mounted thereon, and rotatable upward for lifting a load;
• a pair of longitudinal U channel tracks attached to the inner side flanges within the frame and retaining the ends of the lateral push bar therein;
• a hydraulic cylinder, actuated by pumping the control handle, having an extendable ram for pushing the lateral push bar forward along the tracks for raising the forward ends of the lift arms, and a releasable control valve for retracting the ram for lowering the forward ends of the lift arms;
• the tubular handle enclosing a control shaft extending from the control knob to the rearward end of the frame and including a U-joint and coupling interconnecting the shaft to the releasable control valve;
• the control valve being fully closed from 0 to about 60° of counterclockwise rotation, then releasable from about 60° to 90°;
• and the safety mechanism comprising:
• a pair of parallel guide rails fixed to the bottom of the rearward end of the frame and extending longitudinally to a distance corresponding to that of the fully extended push bar;
• a pair of slidable rack bars each having forward ratcheting teeth and a forward end pivotally linked to the push bar for traversing along said guide rails as the push bar is advanced and retracted;
• a pair of dogs positioned and extended above said rack bars, each having a rearward end pivotally attached to the frame, and having a forward end with a downward lug for engaging a respective tooth of said rack bar, as said rack bar is advanced with the push bar,
• a lateral cam tube rotatably attached to the side flanges of the frame and positioned above the forward ends of said dogs, having a generally V shaped slotted opening in the cylindrical underside thereof;
• and having a pair of lever arms extending downwardly and forwardly near the forward ends of said dogs;
• a pair of lifting links pivotally interconnecting the distal ends of the lever arms of said cam tube to the forward ends of said dogs;
• the control shaft coupling having a swing arm extending forwardly therefrom, with a swing arm pin extending generally perpendicularly and downwardly from the distal end thereof;
• a forward pivot pin attached to the frame and extending generally vertically at a position forward of said cam tube and near the longitudinal center of the frame;
• a swing plate positioned generally horizontally and adjacently below said cam tube, and having a forward end pivotally attached to said forward pivot pin, and having a slotted rearward end pivotally and slideably engaged around the swing arm pin of said swing arm;
• said swing plate further having an upwardly extended cam follower stud positioned and slideably engaged within the V slotted opening of said cam tube;
• and
• the V slotted opening in said cam tube having a right side corresponding to the position of the cam follower stud when the valve is in the fully closed position;
• the opening is then angled in a direction from the right side thereof, laterally inwardly corresponding to the position of the stud with a rotation of the valve of about 30°, and longitudinally from the right side thereof, corresponding to a rotation of the cam tube sufficiently to elevate the forward ends of said dogs from engagement with said rack bars, to an apex of the V slotted opening;
• and from the apex, further laterally inwardly in an arc corresponding to the radius from said pivot pin to the cam follower stud, to the left side of the V slotted opening, corresponding to the position of the cam follower stud when the control valve is in the fully open position.