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| Illustration 1 | g03317349 |
(1) Pilot Gear Pump (2) Rear Pump (3) Servo Pilot Hose (4) Front Pump | |
The main hydraulic pump is located on the right rear side of the machine.
The main hydraulic pump is made of two piston-type variable displacement pumps constructed in tandem. The pump is driven by the engine from the flange plate. The pump uses pressure compensation, an electronically controlled solenoid, and a negative control system to manage pump output.
As the load pressure increases during operating conditions, the tandem pumps increase the delivery pressure, and the pumps decrease the flow rate. As the engine load increases, the machine ECM reduces ESS shift pressure, and the pumps decrease the flow rate. In these two cases, the hydraulic horsepower remains constant even though the delivery pressure, and the flow rates change.
When no operation is being performed, pump oil flows through the main control valve, through a control orifice, and into the hydraulic tank. The pressure upstream from the orifice becomes a negative flow control signal. The main control valve sends the negative flow control signal to each pump in order to destroke the pump to the minimum output flow.
The front pump provides a maximum flow rate of 243 L/min (64 US gpm). This pump provides oil flow to the following functions: boom control, grapple rotate, stick one control. The rear pump provides a maximum flow rate of 178 L/min (47 US gpm). This pump provides flow to the following functions: swing control, grapple open and close, and stick two controls.
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| Illustration 2 | g03693569 |
(5) Pressure Tap "a4" (6) Port "A2" (7) Pressure Tap "a2" (8) Pilot Pump (9) Servo Pilot Hose (10) Port a3 (11) Pilot Pressure Tap Port "A3" (12) Filter Screen (13) Pilot Relief Valve (14) Port "B3" (15) Rear Pump (16) Port "B1" (17) Front Pump (18) Port "Dr" (19) Pressure Tap "a1" (20) ESS Control Valve (21) Port "A1" (22) Port "Psv" | |
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| Illustration 3 | g03269318 |
(20) ESS Control Valve (23) Swashplate (24) Pistons (25) Cylinder Block (26) Servo Piston | |
The pilot pump draws oil from the hydraulic tank through port B3 (14). When the engine is operating, pilot oil flows out port A3 (11) to the pilot shutoff manifold. Pilot oil also flows out port a3 (10) to the ESS control valve (20) through the servo pilot hose (9) and into port Psv (22) .
The pilot relief valve (13) limits the maximum pressure in the pilot system.
Port A1 (21) is the outlet port for the front pump (17). Port A2 (6) is the outlet port for the rear pump (15). Supply pressure from front pump can be measured at pressure tap a1 (19). Supply pressure from rear pump can be measured at the pressure tap a2 (7) .
The tandem pumps of the main hydraulic pump draw oil from the hydraulic tank through port B1 (16). Case drain oil is directed out port Dr (18) .
The ESS control valve (20) is located on the rear face of the implement hydraulic pump. Pilot oil is delivered to this valve through the servo pilot hose. The main pump solenoid is part of the power-shift control valve.
The ESS control valve (20) also contains a solenoid operated variable pressure reducing valve. The main pump solenoid and the pressure reducing valve work in conjunction to control the ESS command pressure. The ESS command pressure, along with the negative control signal pressure, controls the pump output. ESS pressure can be measured at the pressure tap a4 (5) of the pump.
The machine ECM controls the ESS control valve solenoid. The solenoid modifies the setting of the pressure reducing valve in the ESS control valve. The ECM allows the operator to set one of three desired power modes. The ECM also uses the solenoid to change pump output with changing engine loads. The greater the output signal to the main pump solenoid, the greater the pump output.
The main pump is destroked at start-up by the pilot pump (8). Oil flows through servo pilot hose (9) that leads from the pilot pump (8) to the main pump servo chamber. The engine turns the pump rotating group, which contains a ring of pistons. At one end of the cylinder block the pistons (24) ride on a tilted swashplate (23). The tilted swashplate causes the pistons to move back and forth to pump the fluid. The pressurized fluid is ported out of the pump to provide power to the system. The swashplate angle is varied by the control servo piston (26). Altering the swashplate angle changes the stroke of the pistons and the flow rate of the pump. A larger angle gives a greater flow rate and a lesser angle gives a smaller flow rate.