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| Illustration 1 | g00563691 |
Drum Drive Motor (1) Drive shaft. (2) Motor case. (3) Retainer. (4) Pistons. (5) Spring. (6) Barrel. (7) Minimum displacement adjustment screw. (8) Head. (9) Valve spool. (10) Flushing valve. (11) Swivel pin. (12) Control piston. (13) Maximum displacement adjustment screw. (14) Control lens. (15) Control slot. (16) Control slot. (17) Pivot pin. | |
The drum drive motor is a variable displacement axial piston motor with a bent axis. The drum drive motor in LOW speed has the following characteristics:
- High torque
- Large displacement
The drum drive motor in HIGH speed has the following characteristics:
- Low torque
- Small displacement
In LOW speed, the motor has a displacement of 55 cc/rev (3.35 cu in/rev). In HIGH speed, the motor has a displacement of 28 cc/rev (1.71 cu in/rev). When the machine is shifted from LOW to HIGH, the displacement and the torque of the drum drive motor are decreased by one half. At the same time, the rotating speed is doubled. The drum drive motor can operate in either direction.
Four lines are connected to the motor:
- Two high pressure loop lines
- One displacement selector pilot line
- One case drain line
Oil is supplied to the drum drive motor by the drum propel pump. The direction of the motor rotation is controlled by the oil flow direction from the propel pump. The displacement and the speed are controlled by the shift valve.
The components of the drum drive motor that rotate are drive shaft (1), retainer (3), pistons (4), and barrel (6). The components of the drum drive motor that do not rotate are motor case (2), head (8), and control lens (14). Spring (5) pushes barrel (6) against control lens (14). This makes a high pressure seal between the barrel and the control lens. A seal is also made between the control lens and the head.
When high pressure oil flows through the high pressure loop line, the oil also flows to control slot (15). Oil in the control slot goes into the cylinders of barrel (6) that are over the control slot.
The spherical piston heads are held in the sockets in drive shaft (1) by retainer (3). Seven pistons (4) are held by barrel (6). The barrel rotates around pivot pin (17) which is at an angle to the axis of the drive shaft (1). The design of the bent axis between the barrel and the shaft causes each piston to move. The pistons, the barrel, and the drive shaft rotate as pressure oil enters the cylinders.
The pistons are fully retracted when the pistons are in the top center position. The cylinder overlaps control slot (15) on the low pressure side of the loop at this point. When the piston starts to move down, the oil is pushed out of the cylinder. The oil also moves out of the control slot, the other high pressure loop port and exits to the low pressure side of the loop.
The drum drive motor is lubricated by oil leakage from the pistons and the barrel.
The drum drive motor operates at either a large displacement or at a small displacement. When the propel motor operates at a large displacement, the barrel and the shaft are at the maximum angle. At this point, the barrel and the shaft are against the maximum displacement adjustment screw (13). When the propel motor operates at a small displacement, the barrel and the control lens are at the minimum angle against minimum displacement adjustment screw (7).
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| Illustration 2 | g00563692 |
Hydraulic Schematic for the Drum Drive Motor (2) Motor case. (9) Valve spool. (10) Flushing valve. (12) Control piston. (18) Shift valve. (19) Cavity for pilot oil. (20) Drum propel pump. (21) Drum brake. (22) Drum drive motor. (23) Line to thermal bypass valve. (24) Line from charge circuit. (25) Line from charge circuit. | |
The cavity for pilot oil (19) does not receive control pressure when the propel motor is in LOW speed. When the valve spool (9) is shifted to the left, high pressure oil flows to the left side of control piston (12). At this point, the control lens (14) and the barrel are held at the maximum displacement angle.
The cavity for pilot oil (19) receives control pressure when the propel motor is in HIGH speed. When the valve spool (9) is shifted to the right, high pressure oil flows to the right side of control piston (12). At this point, the control lens (14) and the barrel are held at the minimum displacement angle.