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| Illustration 1 | g06193031 |
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View of the hoist system (1) Control lever and position sensor (2) Pump (3) Hydraulic oil tank (4) Cylinders (5) Control valve (6) Screens and bypass switches | |
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| Illustration 2 | g06193073 |
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Hoist system overview (1) Control lever and position sensor (2) Pump (5) Control valve (6) Screens and bypass switches (7) Park brake valve (8) Electronic proportional reducing valve (Lower) (9) Cylinder head end (10) Rear brake oil coolers (11) Cylinder rod end (12) Electronic proportional reducing valve (Raise) (13) Hydraulic oil tank | |
The hoist system on the 785G truck is electronically controlled by the Chassis (ECM). The main components in the hoist system are: Hoist control lever and position sensor (1), gear pump (2), hydraulic tank (3), cylinders (4), control valve (5), and screens and bypass switches (6).
Pump (2) draws oil from hydraulic oil tank (3). Pump (2) sends the oil through screens (6) and the oil continues to flow to control valve (5).
Control valve (5) uses pilot pressure oil from park brake valve (7) to shift the control valve main spool inside the valve body. When Electronic Proportional Reducing Valve (EPRV) (8) and EPRV (12) are de-energized to pressurize the main spool in the HOLD position. When EPRV (12) on the left is energized by the Chassis ECM to drain pilot pressure, the main spool moves to the RAISE position. causing the body to raise. When EPRV (8) on the right is energized to move the body in the LOWER position and to hold the main spool in the FLOAT, SNUB, or HOLD positions.
When the main spool is moved in the (LOWER) position, high-pressure oil is sent from control valve (5) to cylinder rod ends (11) and cylinder head end oil (9) returns to the valve, then to hydraulic oil tank (13). When the main spool is moved in the RAISE position, high-pressure oil is sent from control valve (5) to cylinder head ends (9) and cylinder rod end (11) oil returns to the valve, then to hydraulic oil tank (13).
Hydraulic cylinders (4) are used to raise and lower the body from and onto the frame of the truck. When control lever (1) is held in the RAISE position, supply oil flows to the cylinder head ends (4) and moves the two-stage cylinders toward the extended lengths.
When control lever (4) is moved to the LOWER position or FLOAT position and the cylinders are extended, supply oil enters the rod ends of the cylinders and lowers the second stage of the cylinders. The oil from the head end of the cylinders flows through the control valve (5) to the hydraulic oil tank (13).
Some of pump (2) oil is used for cooling the rear brakes and is directed to the rear brake oil coolers (10). Some return oil is used for the rear brake cooling oil pressure in all hoist conditions, to protect the coolers and the seals in the brake housings.