Dual cylinder actuated boom arm

A road maintenance vehicle construction comprising:

• a support housing including a means for securing the housing to a vehicle;
• a mast which is rotatably secured to said housing;
• a frame fixedly secured to said mast;
• a boom member attached at one end to said frame and adapted to hold a road maintenance tool at another end;
• a first hydraulic cylinder having a piston rod end and a cylinder end, said piston rod end being pivotably secured to a first side of said mast and said cylinder end being secured to a first side of said support housing;
• a second hydraulic cylinder having a piston rod end and a cylinder end, said second hydraulic cylinder piston rod end being pivotably secured to a second side of said mast, and said cylinder end being secured to a second side of said support housing;
• a hydraulic control circuit in fluid communication with and controlling an operation of said first and second hydraulic cylinders;
• an overload protection circuit in fluid communication with at least one of said first and second cylinders;
• and,
• a means for selectively disabling said overload protection circuit, said means for selectively disabling being in fluid communication with said overload protection circuit, wherein said means for selectively disabling comprises a piston of said at least one of said first and second cylinders, a movement of said piston past a preselected point disabling said overload protection circuit.

An actuating mechanism which allows a substantially 180.degree. pivoting motion of a frame, and hence a boom arm secured to the frame, around the frame's pivot axis, the frame being pivotably secured to a vehicle, the actuating mechanism comprising:

• a mast to which the frame is fixedly secured, said mast being rotatably secured on one side of the vehicle;
• a first hydraulic cylinder having a piston rod end and a cylinder end, one end of said first cylinder being pivotably secured to a first side of said mast and another end being operatively secured to the vehicle;
• a second hydraulic cylinder having a piston rod end and a cylinder end, one end of said second cylinder being pivotably secured to a second side of said mast and another end being operatively secured to the vehicle;
• a hydraulic overload protection circuit for said first and second hydraulic cylinders, said overload protection circuit having one end in fluid communication with said
• at least one of said first and second hydraulic cylinders wherein said overload protection circuit engages and disengages depending on an orientation of the boom arm in relation to a longitudinal axis of the vehicle;
• and,
• a hydraulic control means connected to said first and second hydraulic cylinders for effecting a linear movement of a piston located in each of said first and second cylinders and hence a pivotal movement of the mast, and the boom arm secured to the frame, about the mast's pivot axis, wherein said control means comprises:
• a first hydraulic line communicating at one end with one of said first and second hydraulic cylinders;
• a second hydraulic line communication at one end with another of said first and second hydraulic cylinders;
• a pump for pressurizing hydraulic fluid;
• and,
• a valve interposed in said first and second lines for selectively allowing pressurized hydraulic fluid to flow from said pump to said first and second hydraulic cylinders through said first and second hydraulic lines;
• wherein said hydraulic overload protection circuit comprises a third hydraulic fluid line terminating at one end in a port located on said at least one of said first and second hydraulic cylinders, wherein a movement of said piston of said at least one of said first and second hydraulic cylinders in one direction past said port blocks a flow of hydraulic fluid in said hydraulic overload protection circuit thereby disengaging said hydraulic overload protection circuit.