336E H Excavator Hydraulic System Caterpillar

Main Hydraulic Schematic

Illustration 1	g03300438
(31) Travel left pilot pressure sensor (32) Travel right pilot pressure sensor (33) Accumulator oil pressure sensor (36) Idler pump displacement sensor (37) Drive pump displacement sensor (40) Accumulator charge PHMV (41) Accumulator discharge PHMV (48) Pump control solenoid (drive pump) (49) Pump control solenoid (idler pump) (50) Swing brake solenoid valve (51) Swing relief solenoid valve (52) Travel speed solenoid valve (53) Solenoid valve (hydraulic lockout) (54) Accumulator drain valve (55) Heavy lift solenoid valve (56) Makeup accumulator oil pressure sensor (58) Stick cylinder (59) Bucket cylinder (60) Boom cylinders (61) Swing motor (62) Left travel motor (63) Right travel motor (64) Main control valve (65) Slow return check valve (66) Bypass check valve (67) Oil cooler (68) Swivel (69) Drive pump (70) Idler pump (71) Pilot pump (72) Pilot control valve (travel) (73) Drain filter (74) Pilot relief valve (75) Pilot filter (76) Pilot oil manifold (77) Valve (78) Accumulator (79) Return filter (80) Hydraulic tank

Illustration 2	g06057149
(1) Boom HE P-C PHMV (2) Boom HE C-T PHMV (3) Boom RE P-C PHMV (4) Boom RE C-T PHMV (5) Boom HE pressure sensor (6) Boom RE pressure sensor (7) Bucket HE P-C PHMV (8) Bucket HE C-T PHMV (9) Bucket RE P-C PHMV (10) Bucket RE C-T PHMV (11) Bucket HE pressure sensor (12) Bucket RE pressure sensor (13) Stick HE P-C PHMV (14) Stick HE C-T PHMV (15) Stick RE P-C PHMV (16) Stick RE C-T PHMV (17) Stick HE pressure sensor (18) Stick RE pressure sensor (19) Swing right P-M PHMV (20) Swing right M-T PHMV (21) Swing left P-M PHMV (22) Swing left M-T PHMV (23) Swing right pressure sensor (24) Swing left pressure sensor (29) Main relief valve (34) Drive pump pressure sensor (35) Idler pump pressure sensor (38) Boom drift reduction solenoid valve (39) Stick drift reduction solenoid valve (42) Boom side warm-up solenoid (43) Stick side warm-up solenoid (44) Flow combiner PHMV (45) Straight travel PHMV (46) Idler pump bypass cut PHMV (47) Drive pump bypass cut PHMV (57) Pilot pressure sensor (64) Main control valve (81) Bypass cut spool (drive pump) (82) Bypass cut spool (idler pump) (83) Stick drift reduction valve (84) Boom drift reduction valve (94) Flow combiner spool

Hydraulic Pump Flow and Pressure Control System

Illustration 3	g02797762
Pump compartment (69) Drive pump (70) Idler pump (95) Delivery line (drive pump) (96) Delivery line (idler pump)

This machine is driven and controlled by the following systems.

• The main hydraulic system controls the cylinders, the travel motors, and the swing motor.

• The pilot hydraulic system supplies oil to the main control valve, swing energy recovery valve, the swing brake, and the travel motors.

• The electronic control system controls the outputs of the engine, pumps, and main control valve.

The main hydraulic system delivers oil flow from idler pump (70) and drive pump (69) in order to control the following components: bucket cylinder (59), stick cylinder (58), boom cylinders (60), right travel motor (63), left travel motor (62) and swing motor (61).

Illustration 4	g03124698
Main control valve (29) Main relief valve (85) Swing and stick IMV section (86) Main control valve center manifold (87) Bucket and boom IMV section

Main control valve (29) is an Adaptive Control System (ACS) valve. The ACS valve is an electronically controlled hydraulic system that adjusts performance through software. The main control valve consists of several Independent Metering Valves (IMV), a center manifold, and two end plates. Each IMV section contains two, pump-to-cylinder (P-C) proportional hydraulic modulation valves (PHMV) and two, cylinder-to-tank (C-T) PHMV's which are electrically controlled. The machine software adjusts pump-to-cylinder and cylinder-to-tank ports to provide optimum efficiency and control for different front linkage weights and operating conditions. The end plates contain valves that are used for the automatic warm-up procedure.

For more information concerning the ACS main control valve, refer to Systems Operation, "Main Control Valve".

Drive pump (69) and idler pump (70) are electronically controlled variable displacement piston pumps. The performance of both pumps is equal.

Drive pump (69) is directly connected to the engine by a flexible coupling. Idler pump (70) is mechanically connected to the drive pump through gears. The drive pump and the idler pump deliver oil to main control valve center manifold (86). The drive pump delivers oil to the right travel control valve, the stick independent metering control valve, and the swing independent metering control valve. The idler pump delivers oil to the left travel control valve, the bucket independent metering control valve, and the boom independent metering control valve. Pilot pump (71) is a gear pump that supplies oil to the pilot hydraulic system. Pilot pump (71) is mechanically connected to idler pump (70) through a splined shaft. All engine output is used to drive these three pumps.

As the load pressure increases during working conditions, the main pumps increase the delivery pressure and the pumps decrease the flow rate. The hydraulic horsepower remains constant even though the delivery pressure and the flow rates change. The hydraulic horsepower is identical to the engine horsepower.

When no work is being performed, pump oil flows to the main control valve and through the bypass cut spool (81) and bypass cut spool (82). From the bypass cut spools the pump oil returns to hydraulic tank (80). The machine ECM sends a signal to each main pump regulator in order to destroke the pump to the minimum output flow.

If an operation is being performed, main control valve (64) directs pump oil to the respective cylinders (boom, bucket, and stick) and/or motors (swing and travel). Main control valve (64) contains numerous valve stems, passages, check valves, orifices, and electronic solenoids in order to carry out a single operation or a combined operation. The working pressure of the main hydraulic system is regulated by main relief valve (29).

Illustration 5	g02803660
Cab (88) Monitor panel (89) Joystick (stick and swing) (90) Joystick (bucket and boom) (91) Left travel lever/pedal (92) Right travel lever/pedal (93) Engine speed dial

The pilot hydraulic system receives oil flow from pilot pump (71). The pilot hydraulic system controls the following functions.

1. The pilot hydraulic system controls the operation of the travel control valves.

   Pilot oil flows from pilot pump (71) through pilot manifold (76). The pilot oil then flows to the pilot control valves for machine travel operation. These travel pilot control valves are activated by the travel levers/pedals.

   When the left travel lever/pedal and/or the right travel lever/pedal are moved from the NEUTRAL position, the pilot oil flows through the pilot control valves to the right or left travel spools at the main control valve (64).

   The pilot pressure oil at that end of the valve spool forces the valve spool to shift. The pilot oil on the other end of the valve spool drains to the hydraulic tank. When the valve spool shifts, oil is then delivered from idler pump (70) or drive pump (69) to the travel motors.

   Thus, pilot oil drives the travel system of the main control valve.

2. The pilot hydraulic system generates signal pressure in order to perform the following operations.

   1. Pilot oil is supplied to the main control valve which is used to shift the individual spools. The respective pump-to-cylinder or cylinder-to-tank PHMVs use this pilot oil to control implement functions.

   2. Pilot signal pressure activates the Automatic Engine Speed Control (AEC) system. This action causes functions to automatically reduce the engine speed when no hydraulic operation is called for.

   3. Pilot signal pressure releases the swing parking brake.

   4. Pilot signal pressure will automatically change the travel speed to either HIGH or LOW in accordance with the hydraulic system load.

   5. Pilot signal pressure operates the straight travel control valve. This valve maintains straight travel during the operation of an implement.

   6. Pilot signal pressure operates flow combiner valve (94). This controls one pump or two pump flow depending on the operation.

   7. Pilot signal pressure operates bypass cutoff spools (81) and (82). This controls whether the main pump oil is directed to the hydraulic tank or the implement function being performed.

   8. Pilot signal pressure controls the heavy lift operation in order to temporary increase the lifting capacity of the machine.

   9. Pilot signal pressure controls the swing dual set crossover relief valve. This action increases the swing relief valve pressure setting.

For more information concerning the pilot hydraulic system, refer to Systems Operation, "Pilot Hydraulic System".