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| Illustration 1 | g01823715 |
Right Side of Rear Drum (1) Case drain line (2) Shift valve line (3) Flushing relief valve (4) Flushing valve (5) Propel motor (6) Brake inlet line (7) Speed sensor | |
Rear drum motor (5) is located on the right side of the rear drum. The front drum motor is located on the left side of the front drum. The front drum motor and the rear drum motor are similar. The front drum motor is not equipped with speed sensor (7) or a shift valve.
The rear drum motor is a piston motor with two speeds. The motors drive the corresponding drum through a planetary gear reducer. The planetary gear reducer contains an integral parking brake.
The parking brake is spring applied and is hydraulically released. Brake inlet line (6) on the motor provides charge oil in order to release the parking brake.
The drum motors receive supply oil from the drum propel pump and return low pressure oil to the drum propel pump, through the forward and reverse circuit lines.
When the machine is in the high speed range, the shift solenoid is energized. In this case, charge oil enters the propel motor through shift valve line (2). In the high speed range, the propel motor operates at the minimum angle.
The drum motor contains flushing valve (4). The flushing valve spool directs oil from the low pressure side of the drum propel loop to flushing relief valve (3). When the pressure in the low pressure side of the propel loop is greater than 1800 kPa (261 psi), the flushing relief valve opens. The flushing relief valve directs oil from the low pressure side of the drum propel loop into the drum motor case drain.
The drum motor case drain line (1) directs oil that is from drum motor (5) to the return manifold.
Rear drum motor (5) is equipped with speed sensor (7). The speed sensor is a proximity sensor. Each time that a gear tooth passes by the tip of the sensor, an electrical impulse is sent to the speedometer. The speedometer converts the frequency of the electrical impulses to the machine speed.
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| Illustration 2 | g01823716 |
Hydraulic Motor Cross Section - Neutral (8) Piston (9) Barrel assembly (10) Minimum displacement limiter (11) Control spool (12) Flushing relief valve (13) Shift port (14) Check valve (15) Flushing spool (16) Flushing block (17) Rod (18) Actuator piston (19) Maximum displacement limiter (20) Control plate | |
The drum motor has a bent axis. The speed of this type of motor shifts when the bend angle of the motor is changed. The motor can be operated against either the minimum displacement limiter or the maximum displacement limiter. The minimum displacement limiter or the maximum displacement limiter can be adjusted in order to control the minimum and maximum motor speeds.
A pressure differential between the forward port and the reverse port of the motor causes the motor to rotate. When the supply pump is not generating flow, pressure in the forward circuit and pressure in the reverse circuit is equal to charge pressure. In this case, a pressure differential does not exist, and the motor will not turn.
When the motor is not operating, the springs of the flushing spool move the spool into the center position. Also, the flushing relief valve is closed. In this condition, oil is trapped between the inner lands of the shuttle spool and the relief valve, and no flushing flow occurs.
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| Illustration 3 | g01823717 |
Hydraulic Motor Cross Section - Forward, Low Speed (8) Piston (9) Barrel assembly (10) Minimum displacement limiter (11) Control spool (12) Flushing relief valve (13) Shift port (14) Check valve (15) Flushing spool (16) Flushing block (17) Rod (18) Actuator piston (19) Maximum displacement limiter (20) Control plate | |
When the supply pump is generating flow, supply oil enters the motor. Supply oil is directed to the inlet port of the control plate. The control plate directs oil into the piston chamber in the barrel assembly. This pressure forces the pistons which are aligned with the inlet port to move out of the cylinder block.
As the pistons are forced out of the barrel assembly, the barrel assembly and pistons rotate. Since the pistons are connected to the output shaft, the output shaft also rotates.
As the barrel assembly rotates, pistons align with the outlet port in the control plate. The rotation of the barrel assembly forces oil out of the piston chambers and into the low pressure side of the hydrostatic loop. The low pressure oil then returns to the inlet side of the hydraulic pump, which completes the hydrostatic circuit.
When the hydraulic system is in the LOW SPEED condition, the shift port is connected to the tank. The springs of the control spool move the spool. In this condition, the control spool directs oil from the high pressure circuit to the top of the actuator piston. This action shifts the actuator piston and control plate down. The bottom of the actuator piston is vented to the motor case.
Note: In order to shift the motor to the HIGH SPEED condition, charge oil is routed to the shift port. Charge oil then shifts the control spool against the spring force. With the control spool shift, the top of the actuator piston will be open to the motor case, and oil from the high pressure circuit will be directed to the bottom of the actuator piston. The piston and control plate will shift up.
When the supply pump produces flow, oil flushes through the circuit. Oil in the high pressure circuit causes the flushing spool to shift. Oil in the low pressure circuit now flows to the relief valve.
The flushing relief valve opens at 1800 kPa (261 psi). This pressure is lower than the setting of the charge relief valve in the supply pump. Therefore, the flushing relief valve opens when the supply pumps are producing flow. This results in oil being flushed through the hydrostatic circuit.
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| Illustration 4 | g01823719 |
Left Side of Front Drum (21) Front propel motor (22) Brake inlet line (23) Case drain line | |
Front propel motor (21) is a bent axis motor with a fixed displacement. The motor is located on the left side of the front drum.
Front propel motor (21) drives the front drum through a planetary gear reducer. The planetary gear reducer contains an integral parking brake. Brake inlet line (22) on the motor provides charge oil in order to release the parking brake. The drum motor case drain line (23) directs oil from drum motor (21) to the return manifold.