Friday, November 30, 2012

797F Off-Highway Truck: Hoist Cylinder

Hoist cylinders
(1) Cylinder (first stage)
(2) Cylinder (second stage)(3) Rod assembly

Raising the Dump Body

Hoist cylinder (first stage) to extended length
(1) Cylinder (first stage)
(2) Cylinder (second stage)
(3) Rod assembly
(4) Internal head
(5) Head
(6) Chamber between cylinders (first stage and second stage)
(7) Grooves in the end of the cylinder (second stage)
(8) Piston
(9) Opening to the head end of the hoist cylinder
(10) Opening to the rod end of the hoist cylinder
(11) Chamber between the rod assembly and cylinder (second stage)
(12) Orifices in the rod assembly(13) Chamber in the head end of the hoist cylinder

Two hydraulic cylinders are used to move the dump body. When the hoist control is held in the raise position, the pump oil extends the two-stage cylinders and the dump body is raised to the dump position.

The hoist cylinders raise the dump body in two stages. The pump oil flows into opening (9) to the head ends of the hoist cylinders. The oil flows through a tube in rod assembly (3) and into chamber (13) in the head end of cylinder (1). The force of the pressurized oil moves cylinder (1) .

The oil in chamber (6) will flow through grooves (7) as the cylinder begins to extend. The oil will flow through grooves (7) into chamber (13). When head (5) on the end of cylinder (1) reaches a lip on the end of cylinder (2) the first stage is complete. Chamber (13) will continue to fill with oil. The oil in chamber (11) now flows through orifices (12), through the tube in rod assembly (3), and through opening (10) to the hoist control valve.

Extended hoist cylinder
(1) Cylinder (first stage)
(2) Cylinder (second stage)
(3) Rod assembly
(4) Internal head
(5) Head
(6) Chamber between cylinders (first stage and second stage)
(7) Grooves in the end of the cylinder (second stage)
(8) Piston
(9) Opening to the head end of the hoist cylinder
(10) Opening to the rod end of the hoist cylinder
(11) Chamber between the rod assembly and cylinder (second stage)
(12) Orifices in the rod assembly(13) Chamber in the head end of the hoist cylinder

Cylinder (2) extends until internal head (4) contacts piston (8). This is the second stage. Piston (8) is bolted to the top of rod assembly (3). When cylinder (1) is against the end of cylinder (2) and cylinder (2) is against the end of rod assembly (3), the hoist cylinder is fully extended.

Lowering the Dump Body

Retracted hoist cylinder (second stage)
(1) Cylinder (first stage)
(2) Cylinder (second stage)
(3) Rod assembly
(4) Internal head
(5) Head
(6) Chamber between cylinders (first stage and second stage)
(7) Grooves in the end of the cylinder (second stage)
(8) Piston
(9) Opening to the head end of the hoist cylinder
(10) Opening to the rod end of the hoist cylinder
(11) Chamber between the rod assembly and cylinder (second stage)
(12) Orifices in the rod assembly(13) Chamber in the head end of the hoist cylinder

Move the hoist control to the lower position or to the float position in order to lower the dump body to the truck frame.

When the hoist cylinders are fully extended and the hoist control is moved into the lower position, pump oil retracts only cylinder (2). When cylinder (2) is fully retracted, gravity moves cylinder (1) and the dump body lowers onto the truck frame.

The dump body is lowered when the pump oil flows through opening (10), into rod assembly (3), through orifices (12), and into chamber (11) between the rod assembly and cylinder (2). The oil pushes cylinder (2) and cylinder (1) downward as chamber (11) is filled with pump oil. When the dump body gets to a specified position, flow that is leaving opening (9) will be restricted. This traps oil in chamber (13). The weight of the dump body continues to move cylinder (1) slowly. The weight of the dump body moves cylinder (1) downward until the cylinder is fully retracted. The oil in chamber (13) is pushed through the tube in rod assembly (3) and through opening (9) to the hoist control valve. The hoist control valve routes the oil to the hydraulic tank.

MARYGAR