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| Illustration 1 | g00538682 |
Hydraulic schematic (S/N: 3MR1-49784MR1-715) (1) Swing motor (2) Left travel motor (3) Right travel motor (4) Stick cylinder (5) Left travel brake valve (6) Right travel brake valve (7) Bucket cylinder (8) Boom cylinders (9) Stick drift reduction valve (10) Swivel (11) Main control valve (12) Pressure switch (implement or swing) (13) Pressure switch (travel) (14) Boom drift reduction valve (15) Main relief valve (16) Pressure switch (boom raise) (17) Pilot control valve (travel) (18) Pilot control valve (swing and stick) (19) Solenoid valve (fine control) (20) Solenoid valve (travel speed) (21) Solenoid valve (trenching) (22) Solenoid valve (proportional reducing) (23) Pilot control valve (boom and bucket) (24) Hydraulic activation control valve (25) Accumulator (26) Pilot relief valve (27) Shock reducing valve (28) Front pump (29) Rear pump (30) Automatic travel speed change valve (31) Pilot pump (32) Pilot oil manifold (33) Pilot filter (34) Drain filter (35) Slow return check valve (36) Oil cooler (37) Bypass check valve (38) Return filter (39) Hydraulic tank | |
Introduction
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| Illustration 2 | g00630150 |
Pump compartment (28) Front pump (29) Rear pump (30) Pilot pump | |
This machine is driven and controlled by the following systems.
- The main hydraulic system supplies oil to the cylinders and motors of the machine.
- The pilot hydraulic system supplies oil to the control circuits.
- The electronic control system controls the output from the engine and the pump.
Main Hydraulic System
The main hydraulic system oil is supplied by front pump (28) and rear pump (29). Pumps (28) and (29) are variable displacement piston pumps. Pumps (28) and (29) are identical in performance. Front pump (28) is directly connected to the engine by a flexible coupling. Pumps (28) and (29) are mechanically connected by a spline coupling.
Gear type pilot pump (30) supplies oil to the pilot hydraulic system. Gear type pilot pump (30) is directly connected to rear pump (29) by a shaft. All engine output is used to drive these three pumps.
When the load on the machine increases, the delivery pressure of pumps (28) and (29) increases. When the delivery pressure of pumps (28) and (29) increases the flow rate decreases. The hydraulic horsepower remains constant even though the oil pressure and the flow rates change. The hydraulic horsepower is approximately identical to the engine horsepower.
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| Illustration 3 | g00466332 |
Main control valve compartment (15) Main relief valve (44) Right control valve body (45) Left control valve body | |
The oil from front pump (28) flows into right valve body (44). The oil from rear pump (29) flows into left valve body (45). Main control valve (11) is made up of right valve body (44) and left valve body (45) .
When no work is being performed, pump oil flows through main control valve (11) and into hydraulic tank (39). This creates a negative flow control signal. The main control valve sends this negative flow control signal to each main pump in order to destroke the pump to the minimum output flow.
If an operation is being performed, main control valve (11) directs pump oil to the respective cylinders (boom, bucket, and stick) and/or motors (swing and travel). Main control valve (11) contains numerous valve stems, passages, check valves, and orifices in order to carry out a single operation or a combined operation. The working pressure of the main hydraulic system is restricted by main relief valve (15) .
Pilot Hydraulic System
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| Illustration 4 | g00368679 |
Cab (49) Monitor panel (50) Control lever (stick and swing) (51) Control lever (boom and bucket) (52) Travel pedal (left) (53) Travel pedal (right) (54) Engine speed dial | |
The pilot pump delivers a constant flow of oil pressure to the pilot circuit. The pilot circuit performs the following functions:
- The pilot circuit operates main control valve (11). When control levers (50) and (51) or pedals (52) and (53) are operated, pilot oil flows to main control valve (11) through pilot control valves (18), (23), and (17). The pilot oil pressure shifts the stems in main control valve (11) in order to send the main pump oil to the required circuits. The circuits include cylinder (4), cylinder (7), cylinders (8), motor (1), motor (2) and motor (3) .
- The pilot circuit controls the output of pumps (28) and (29). Solenoid valve (22) receives an electronic signal. Solenoid valve (22) uses the pilot system oil to develop a hydraulic signal pressure. The hydraulic signal pressure flows to the regulators in pumps (28) and (29). The regulators control the output flow of pumps (28) and (29) .
- The pilot circuit activates the Automatic Engine Speed Control (AEC) system. This causes functions to automatically reduce the engine speed when no hydraulic operation is called for.
- The pilot circuit develops a pilot signal pressure in the pilot circuit in order to release the swing motor parking brake.
- The pilot circuit automatically changes the travel speed to the HIGH or LOW position. The travel speed depends on the load of the machine.
- The pilot circuit operates the straight travel control valve. This maintains straight travel during the operation of an implement.
- The pilot circuit controls the operation of the valves that can be used during a loading operation or a trenching operation.
Electronic Control System
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| Illustration 5 | g00368680 |
Controller compartment (55) Controller | |
The electronic control system controls the outputs from the engine and the pumps through controller (55). Controller (55) senses the position of the governor lever which is selected by engine speed dial (54). Controller (55) senses the power mode position which is selected by the power mode switch. The power mode switch is located on monitor panel (49). The controller processes the information. The controller sends a pressure signal to the pump. The pump supplies the optimum output that matches the machine loading and the engine speed.
The electronic control system has the following four major functions.
- When a large load is placed on the machine, the system allows the pumps to destroke. The system utilizes the maximum horsepower from the engine.
- The load of the machine controls the output of the pumps. The output is based on two power modes and three work modes. The machine operates at optimum efficiency which helps to reduce fuel consumption.
- When there is a very small load condition or no load condition, the system automatically decreases the engine speed. This improves the fuel consumption and this reduces the noise level.
- The system causes the activation of solenoid valve (19), solenoid valve (20), and solenoid valve (21). The activation of the valves allows easier levelling of the ground surface, vertical finishing of ditches and tamping. The activation of solenoid valve (20) changes the travel speed.