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| Illustration 1 | g00920900 |
Typical Example (1) Saw motor. (2) Disc saw. | |
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| Illustration 2 | g00919723 |
Schematic of the Saw Motor (3) Rotating group. (4) Check valve. (5) Displacement control valve. (6) Orificed check valve. (7) Spring loaded check valve. (8) Check valve. (9) Control piston. (AA) Pressure tap (upstroke pressure). (BB) Pressure tap (saw pump). (CC) Case drain port. (X1) Pressure line from the machine. (X2) Drain line to the machine. | |
Saw motor (1) is a variable displacement bent axis motor.
Saw motor (1) is mounted to an adapter plate and coupled to the output shaft by a splined adapter. The output shaft is driven by saw motor (1). The output shaft is connected to disc saw (2) .
The hydraulic oil flows from the pump on the machine to port "X1" of saw motor (1). This causes the saw motor to rotate. The return oil flows from port "X2" of saw motor (1) back to the machine. The saw motor starts at maximum displacement. When the saw pump that is on the machine has fully upstroked, the saw motor will begin to destroke.
At start-up, the system pressure is high. The saw pump is at minimum displacement. As the system pressure decreases, the saw pump will move to maximum displacement. When system pressure decreases to a certain amount, the saw motor will start moving toward minimum displacement.
Pressure oil from the saw pump flows into the head end of the saw motor. Pressure oil then flows through rotating group (3) and check valve (4). Oil will then react against the spring that is located on displacement control valve (5). Displacement control valve (5) controls the pressure that shifts the motor to minimum displacement. Displacement control valve (5) is adjustable. Pressure oil will also be present at port (BB) .
As pressure oil shifts the displacement control valve (5) to the right against spring force, pressure oil will flow through displacement control valve (5) to orificed check valve (6). Check valve (6) contains an orifice that will prevent control piston (9) from reaching maximum displacement too quickly. Pressure oil will shift control piston (9) to the left. This moves the motor to maximum displacement and this increases the torque of disc saw (2) .
When the disc saw (2) has reached the maximum speed, the oil demand is lower until a tree is cut. Saw motor (1) will begin to move to minimum displacement, as the oil demand drops. Saw motor (1) will move to minimum displacement when the system pressure decreases due to no load on disc saw (2). Displacement control valve (5) will gradually shift to the left with spring force. System pressure and spring force will become equal forces on displacement control valve (5). Control piston (9) will gradually shift to the right as a result of pressure oil passing through displacement control valve (5). As a result, disc saw (2) will be at high speed and the torque will be low.
When a tree is cut, the speed of saw motor (1) will decrease. This will cause oil pressure to increase at port (X1). Displacement control valve (5) will begin to shift to the right against spring force. While displacement control valve (5) is open, oil will pass from displacement control valve (5) to the right side of control piston (9). Oil from the left side of control piston (9) will drain out and the oil will join the system oil that holds displacement control valve (5) in the shifted position. System pressure on control piston (9) will move rotating group (3) toward maximum displacement. This will upstroke saw motor (1) which increases the torque in order to meet the demands of disc saw (2). Saw motor (1) will remain at maximum displacement until the demand on saw motor (1) no longer exists.
When the pressure at port (X1) from the machine is shut off, disc saw (2) continues to spin freely. Pressure oil will circulate internally from the outlet side of rotating group (3) through spring loaded check valve (7) and through the inlet side of rotating group (3). This allows system oil that remains inside the motor to circulate freely as disc saw (2) slows down.
The oil flow from the saw pump on the machine to the saw motor must be 115 L/min (30 US gpm) at 27600 kPa (4000 psi).
The swashplate angle of saw motor (1) determines the displacement of saw motor (1). Saw motor (1) uses a bushing to hold the displacement of the motor to 115 L/min (30 US gpm).