Piston Motor
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| Illustration 1 | g01229464 |
Left Front Propel Motor (1) Loop line (2) Flushing valve (3) Loop line (4) Case drain line (5) Charge inlet line (6) Minimum angle stop (7) Brake inlet line | |
Each track is equipped with a propel motor. The propel motors receive supply oil from the propel pump. The propel motors return low pressure oil to the propel pump through loop lines (1) and (3). Brake inlet line (7) on each motor provides oil from the auxiliary hydraulic system in order to release the parking brake.
Each propel motor contains flushing valve (2). The flushing valves direct oil from the low pressure side of the propel loop to the flushing relief valves. The flushing relief valve opens when the pressure in the low pressure side of the loop is 345 ± 172 kPa (50 ± 25 psi) less than the charge pressure. The flushing action directs oil from the low pressure side of the loop into the motor case drain. Case drain line (4) on each motor directs oil from the motor cases to the pump case. The case drain line of each front motor directs oil from the motor case drain to the hydraulic tank.
When the machine is in the high speed range, the shift solenoid (center manifold) is energized. Charge oil then enters the propel motors through charge inlet line (5). Under these conditions, the propel motors operate at the minimum angle.
Note: Illustration 1 shows minimum angle stop (6). The maximum angle stop is not shown. The propel motors are against the maximum angle stop when the machine is operating in the low speed range.
Cross Section of Propel Motor
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| Illustration 2 | g01229709 |
When the propel pump generates flow, a pressure differential exists between the forward and reverse sides of the motor. The pressure differential causes the motor to turn.
Low Speed Operation
When the shift switch is in the L position, the shift port is open to the case drain. The control spool spring moves the spool to the right. In this condition, the control spool directs oil from the high pressure side of the propel loop and into the chamber which is at the top of the actuator piston. This oil causes the piston and the control plate to shift down. The bottom of the actuator piston is open to the motor case.
Note: In order to shift the motor into the HIGH SPEED position, charge oil is routed to the shift port. This oil shifts the control spool against the force of a spring. When the control spool shifts, oil from the high pressure side of the propel loop is directed into the chamber which is at the bottom of the actuator piston. During this time, high pressure oil remains in the chamber which is at the top of the actuator piston. Since the effective area of the bottom of the actuator piston is greater than the effective area of the top of the piston, the piston and control plate shift up.
When the propel pump produces flow, flushing of the circuit occurs. Oil in the high pressure circuit flows past the shuttle spool, and the spool shifts to the left. Oil in the low pressure circuit now flows to the flushing relief valve.
The flushing relief valve is set to open at a pressure that is less than charge pressure. Therefore, loop flushing occurs when the machine is moving.
The orifice in the flushing relief valve allows 5 L/min (1,3 US gpm) of flow through the relief valve when the valve is opened. The orifice is a sharp edged type. This type of orifice allows a constant amount of oil to flow regardless of the viscosity of the oil. The flushed oil is directed to the motor case. Eventually, the flushed oil flows through the oil cooler and into the hydraulic tank.
Note: The flushing relief valve is adjustable by using a shim. However, an adjustment is not typically required in normal service.