Hydraulic Schematic (Neutral)
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| Illustration 1 | g01197722 |
The front propel hydraulic circuit consists of the following:
- A closed loop hydrostatic drive circuit with one main propel pump
- A flow divider valve
- Two piston motors
- A pressure circuit from the auxiliary pump for shifting the front motors
When the engine is running, the propel and charge pumps rotate.
The charge pump provides a constant supply of oil to the hydraulic system. The charge pump draws oil from the tank and sends it through the charge filter.
Output charge pump oil then flows to the following components:
- The charge relief valve
- The multifunction control valves
- The EDC metering spool
- The pressure control pilot valve
Charge oil entering the multifunction valves, seats the check valves and acts against the makeup valves. Since the propel pump rotates while the engine is running, normal leakage occurs in the propel circuit. When the pressure in the propel circuit falls below charge pressure, the makeup valves open and the propel circuit fills with charge oil.
When front propel pump charge pressure increases to 2830 ± 210 kPa (410 ± 30 psi), the charge relief valve opens, dumping charge oil into the pump case drain. For machines equipped with optional all wheel drive, the rear propel pump charge pressure relief setting 2410 ± 206 kPa (350 ± 30 psi). The rear propel pump charge pressure is lower than the setting of the front propel pump charge pressure.
When the propel lever is in theNEUTRAL position (or the machine ECM has disengaged the propel lever), neither the forward nor the reverse EDC are energized. This causes the center envelope of the pressure control pilot valve to be active. In this case, the center envelope of the EDC metering spool is also active.
When the center envelope of the EDC metering spool is active, the metering spool blocks charge oil. The EDC metering spool also opens a passage between the propel pump's servo pistons and the case drain. The pump swashplate moves to zero angle.
Hydraulic Schematic (Forward at Low Speed)
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| Illustration 2 | g01197723 |
The normal working mode for all machines has the front propel system operating with the propel lever in the FORWARD direction, at LOW speed.
When the machine is traveling forward, the bottom envelope of the pressure control pilot valve is active. The position of the pressure control pilot valve is determined by the duty cycle of the signal that is sent from the machine ECM. The machine ECM analyzes the input signals in order to determine the magnitude of the output signal which is sent to the pressure control pilot valve.
Charge pressure flows across the pressure control pilot valve. This oil acts against the top of the EDC metering spool. The EDC metering spool moves down. Charge oil is metered across the spool to the forward servo piston. The charge oil causes the forward servo piston to shift. This shift changes the angle of the swashplate in the pump. As a result, the pump generates flow in the forward circuit.
Forward circuit oil flows to the forward multifunction valve and to the front flow divider. Forward circuit oil in the forward multifunction valve closes the makeup valve and acts against the pressure limiter and the main relief valves. If pressure in the forward circuit reaches 40710 ± 690 kPa (5900 ± 100 psi), the pressure limiter valve opens. This directs oil from the forward circuit to the reverse servo piston. This causes the pump to destroke. If the pressure in the reverse servo piston chamber is greater than the charge pressure, the check valve in the pump end housing opens. As a result, the excess oil pressure in the reverse servo piston is vented into the charge circuit. If the pressure in the forward circuit rises to approximately 44850 ± 690 kPa (6500 ± 100 psi), the main relief valve opens. This directs oil from the forward circuit into the charge circuit.
Oil in the forward circuit causes the motors to turn. After the motors are turned, the pressure of the oil is reduced. Oil at a reduced pressure then enters the reverse circuit. Reverse circuit oil flows to the reverse multifunction valve and back to the propel pump, completing the drive circuit.
Since reverse circuit oil is at a lower pressure than forward circuit oil, forward circuit oil causes the flushing valves to shift. These shifts allow oil from the reverse circuit to act on the flushing relief valves. When the pressure that is acting against the flushing valves is greater than 2208 kPa (320 psi), the flushing relief valves open. In this case, oil from the reverse circuit is directed into the case drains of the motors.
Reverse circuit oil acts against the makeup valve, the relief valve, and the pressure limiter valve in the reverse multifunction valve. As the flushing valves remove oil from the reverse circuit, the pressure in the reverse circuit decreases. When the pressure in the reverse circuit is less than the pressure in the charge circuit, charge pressure unseats the makeup valve. Flow from the charge pump enters the reverse circuit. This action allows cool, filtered oil from the charge circuit to flush the propel circuit.
When the propel mode shift switch is in the LOW SPEED position, the shift cylinders in the propel motors are driven to the low speed position by the oil in the low pressure side of the propel loop. The high side of the servo piston chamber is open to the tank. The motor swashplate moves to the maximum angle. As a result, the motor operates in the low speed range.
Hydraulic Schematic (Reverse at High Speed with Traction Control)
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| Illustration 3 | g01197726 |
When the machine is traveling in reverse, the top envelope of the pressure control pilot valve is active. The position of the pressure control pilot valve is determined by the duty cycle of the signal that is sent from the propel ECM. The propel ECM analyzes the input signals in order to determine the magnitude of the output signal that is sent to the pressure control pilot valve.
Charge oil flows through the orifice and to the EDC metering spool. Charge oil is then metered across the EDC metering spool to the reverse servo piston. The charge oil causes the reverse servo piston to shift. This shift changes the angle of the swashplate in the pump, and the pump generates flow in the reverse circuit.
While the machine is traveling in reverse, the reverse multifunction valve limits system pressure. Oil from the forward circuit flows through the flushing relief valve. The makeup valve in the forward multifunction valve allows charge oil to flow into the forward circuit.
When the shift switch is in the HIGH SPEED position, the front motor shift solenoid is energized. When the front motor shift solenoid is energized, reduced pressure oil from the auxiliary pump flows into the high side of the servo piston chamber. The pressure of this oil is 4820 kPa (700 psi). Oil from the low pressure side of the propel loop is directed into the low side of the servo piston chamber. The pressure differential between the two sides of the servo piston causes the swashplate in the motor to move to the minimum angle. In this case, the motor operates in the high speed range.
The traction control system for the front propel system engages an electric solenoid. This solenoid engages a flow divider. Normal operating conditions allow differential wheel rotation and tire slippage based on underfoot conditions. Under normal operating conditions oil flows through the flow divider shuttle spools and around the flow divider valve. When the front flow divider solenoid is energized, the solenoid causes charge pressure oil to pass to the pilot circuit of the flow divider shuttle spools. The flow divider spools move out. In this case, an equal volume of oil is sent to the left propel motor and to the right propel motor, regardless of the pressure demand of the individual front wheels.
Hydraulic Schematic (Forward with Traction Control)
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| Illustration 4 | g01197732 |
Machines equipped with optional rear wheel assist have a rear propel hydraulic circuit. The rear propel hydraulic circuit consists of a closed loop hydrostatic drive circuit with one pump, two motors and a freewheel manifold with open loop electrical control. The rear propel pump and control solenoid EDC are identical to the front propel pump and control solenoid EDC. When the engine is running, the rear propel and rear charge pumps rotate along with the front propel, front charge, and auxiliary pumps. The machine ECM controls the front propel system and the rear propel system in parallel. Forward, reverse, and traction control operation of the front and rear propel systems coincide with each other.
The rear traction control system is a slave to the front traction control system. The machine ECM causes the front and rear flow divider solenoids to energize in parallel based on the input from the traction control switch. The operation of the rear flow divider is the same as the front flow divider. The oil passing through the PAV port of the rear freewheel valve is the metered oil in the rear flow divider circuit. The rear flow divider controls the volume of the reduced pressure oil returning from right and left rear propel motors causing equal flow volume to pass through the flow divider regardless of the pressure demand at the individual rear wheels.
Machines equipped with optional all wheel drive have orificed balance lines between the front and rear propel pump high pressure and reduced pressure return lines.
Hydraulic Schematic (Freewheel)
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| Illustration 5 | g01197734 |
Inside the freewheel manifold, charge oil entering port "G" branches in three directions. Charge oil is delivered to the freewheel solenoid valve through the first branch. Charge oil is delivered to the flow divider solenoid valve through the second branch. Charge oil is delivered to an orifice in port "CD1" through the third branch. When the rear wheel assist switch is in the OFF position, the freewheel solenoid is de-energized. Charge oil is blocked at the spool of the freewheel valve and at the spool of the flow divider solenoid valve.
When rear wheel assist is off, all charge oil in the freewheel manifold is forced through the orifice in port "CD1". The orifice directs 7.6 L/min (2 US gpm) flow of oil into the side case drain ports on the rear propel motors.
The rear propel pump charge oil flows through the cases of both rear motors and is directed out the top case drain ports to the "CD2" port of the rear freewheel manifold. Inside the rear freewheel manifold, the oil is split into two branches. One branch delivers charge oil to the pilot opened check valve. The other branch delivers oil to the freewheel check valve. Pilot pressure is not available in order to open the pilot opened check valve. As a result, the valve remains seated. This blocks charge oil in that branch. Therefore all return oil from the motor case drain lines is forced to the rear freewheel check valve.
The rear freewheel check valve is held closed by a spring. The rear freewheel check valve maintains a back pressure of 450 kPa (65 psi) in the rear propel motor case drain lines. At 450 kPa (65 psi) of case drain pressure, the pistons in the rear propel motors are held off of the cam ring and the motors turn freely.