966G Series II Wheel Loader and 972G Series II Wheel Loader Hydraulic System Implement System - Electrohydraulic System Caterpillar


Implement System - Electrohydraulic System
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1.1. Pilot System
2.1. Main Hydraulic System
3.1. Quick Coupler (If Equipped)



Illustration 1g00990277

Schematic of the Main Hydraulic System

(1) Main control valve

(2) Auxiliary cylinders

(3) Tilt cylinder

(4) Lift cylinders

(5) Manifold

(6) Main relief valve

(7) Line relief valve (auxiliary)

(8) Line relief valve (tilt)

(9) Check valve (float)

(10) Line relief valve (auxiliary)

(11) Line relief valve (tilt)

(12) Check valve (load)

(13) Stem (auxiliary)

(14) Check valve (load)

(15) Stem (tilt)

(16) Check valve (load)

(17) Stem (lift)

(18) Shuttle valve (ball resolver)

(19) Screen (pilot)

(20) Orifice (1.7 mm)

(21) Orifice (1.2 mm)

(22) Primary reducing valve

(23) Solenoid valve (pilot proportioning)

(24) Solenoid valve (pilot proportioning)

(25) Solenoid valve (pilot proportioning)

(26) Solenoid valve (hydraulic lockout)

(27) Pilot valve (oil manifold)

(28) Screen (pilot valve)

(29) Ball valve (dead engine lower)

(30) Solenoid valve (pilot proportioning)

(31) Solenoid valve (pilot proportioning)

(32) Solenoid valve (pilot proportioning)

(33) Shuttle valve

(34) Float valve

(35) Secondary reducing valve

(36) Implement pump

(37) Hydraulic tank

(38) Steering pump

(39) Pilot/brake pump

(40) Breaker relief valve

Note: Illustration 1 is the schematic for a machine with an auxiliary function. Machines without auxiliary functions (logging fork, side dump bucket, multipurpose bucket, etc) will not have the following components: the auxiliary cylinders (2), line relief valves (7, 10), the check valve (load) (12), the stem (auxiliary valve) (13) and the solenoid valves (pilot proportioning) (23, 30)

The implement system is composed of the following systems: pilot control system and the main hydraulic system. Hydraulic tank (37) is common to the systems.

The pilot control system is made up of the following components: screen (19), orifices (20, 21), the pilot valve (oil manifold) (27), screen (28), the ball valve (dead engine lower) (29) and pilot/brake pump (39) .

The main hydraulic system is made up of the following components: main control valve (1), auxiliary cylinders (2), tilt cylinder (3), lift cylinders (4), manifold (5), main relief valve (6), the shuttle valve (ball resolver) (18) and implement pump (36) .

Pilot System

The pilot system is a combination of pilot pressure and electrical commands. In the pilot system, pilot/brake pump (35) draws oil from hydraulic tank (37). The pilot/brake pump (36) also supplies oil for the hydraulic braking system.

The oil from pilot/brake pump (38) is filtered by screen group (28). Screen group (28) is installed in the pilot valve (oil manifold) (27).

Pilot oil from the pilot/brake pump (37) flows into the primary reducing valve (22). Primary reducing valve (22) will reduce the pressure of the pilot oil to 3450 ± 200 kPa (500 ± 30 psi) at a flow of 21 ± 3 L/min (5.5 ± 0.8 US gpm). When the adjustment of the primary reducing valve is greater than the adjustment of the secondary reducing valve, the pilot oil from the primary reducing valve (22) will shift shuttle valve (33) to the DOWN position. From the output of shuttle valve (33), the pilot oil flows to the solenoid valve (hydraulic lockout) (26). When the engine is running and as one of the control levers is moved, the solenoid valve opens and oil can flow to solenoid valves (23, 24, 25, 30, 31, 32). At this point, the electrical commands will control the movement of the solenoid valve. This controls the amount of pressurized pilot oil that is flowing to the main control valve.




Illustration 2g00916699

Electrohydraulic control




Illustration 3g01032828

Joystick control

The electronic control is located on the panel at the right side of the operator's seat. The implement ECM interprets the amount of movement by either the control lever or the joystick control. The electrohydraulic control consists of control levers, position sensors, and detent coils. The joystick control consists of one handle, position sensors and soft detents.

As one of the control levers or the joystick handle is moved, the position sensor is rotated about the axis. As the position sensor is rotated, an electronic signal is sent to the implement ECM. The implement ECM interprets the amount of rotation of the position sensor. Then, the implement ECM sends a proportional amount of current to one of the appropriate solenoid valves (pilot proportioning) (23, 24, 25, 30, 31, 32). The solenoid valve is energized proportionally by the amount of current that is sent by the implement ECM. Pilot oil flows from the solenoid valve to the end cap of the stem in main control valve (1) .

The electrohydraulic control is equipped with detent coils. When the control lever is placed at the end of travel, the control lever is held in position until the current to the coils is interrupted. Then, the control lever returns to the HOLD position.

The joystick control is not equipped with detent coils. The detents in the joystick control are soft detents. The soft detents are controlled by the software within the ECM. As the joystick control is moved into the detent position and the joystick control is released, the linkage will travel to the kickout position that is preprogrammed. The joystick control will return to the HOLD position. The linkage movement will continue until the kickout is reached. Any 6° movement of the joystick control from the HOLD position will disable the detent. The soft detents will not be activated if the joystick control is held in the detent position for more than 1 second.

Reference: For information about solenoid valves, refer to the Service Manual module Systems Operation, "Solenoid Valves (Implement)" for the machine that is being serviced.

Reference: For more information about modulation current for the solenoid valves, refer to the Service Manual module Systems Operation, "Implement Electronic Control System" for the machine that is being serviced.

Reference: For information about calibrating the control levers or the joystick control, refer to the Service Manual module Testing and Adjusting, RENR$#97, "Position Sensor for the Control Lever (Electronic Technican) or Position Sensor for the Joystick Control (Electronic Technican)" for the machine that is being serviced.

Reference: For information about calibrating the control levers or the joystick control, refer to the Service Manual module Testing and Adjusting, RENR4397, "Position Sensor for the Control Lever (AVSpare Monitoring System) or Position Sensor for the Joystick Control (AVSpare Monitoring System)" for the machine that is being serviced.

If the engine is not running and the lift cylinders are in a RAISED position, oil from the head end of lift cylinders (4) will flow back to the pilot valve (oil manifold) (27). Screen group (19) will filter oil that flows from the shuttle valve (ball resolver) (18). The pressurized oil from the head end of the lift cylinders is used for the dead engine lower. The oil pressure will flow through secondary reducing valve (35). The pressure at primary reducing valve (22) will be less than the pressure in secondary reducing valve (35). Shuttle valve (33) will shift to the UP position and the oil that is coming from the head end of the lift cylinders will supply the oil to the pilot system. The oil will stop at the solenoid valve.

With the key start switch in the ON position and a nonrunning engine, the operator will be able to lower the work tool.

In a case of a battery failure and the lift arms in the RAISED position, the lift arms can be lowered by the ball valve (dead engine lower) (29). The oil from the shuttle valve (ball resolver) (18) flows through secondary reducing valve (35). Ball valve (29) is connected to the output of secondary reducing valve (35). As ball valve (29) is opened, the oil from the head end of lift cylinders (4) will flow through secondary reducing valve (35). Then, the oil will be relieved to hydraulic tank (36). The lift arms will lower.

Main Hydraulic System

In the main hydraulic system, implement pump (36) provides supply oil to main control valve (1). Main relief valve (6) is installed into main control valve (1) in order to control the pressure in the main hydraulic system. Main relief valve (6) regulates the pressure that flows into main control valve (1). Main relief valve (6) opens when the oil pressure in the hydraulic system rises above the relief valve setting. Oil will be relieved to the hydraulic tank. The relief valve setting is 20700 ± 340 kPa (3000 ± 50 psi) at approximately 268 ± 4 L/min (71 ± 1 US gpm).

Reference: For more information about the main relief valve, refer to the Service Manual module Systems Operation, "Relief Valve" for the machine that is being serviced.

The 966G Series II Wheel Loader or the 972G Series II Wheel Loader can be equipped with a two-section valve or a three-section main control valve. The three sections control the lift function, the tilt function, and the auxiliary function of the work tool.

The two-section valve controls the lift function, and the tilt function of the work tool. Main control valve (1) has an open center. When the engine is running and the control lever or the joystick control is in the CENTER position, the oil that is flowing into main control valve (1) flows through the valve and back to hydraulic tank (37). The return oil will pass through the filter group within hydraulic tank (37).




Illustration 4g00990467

Main Control Valve

(1) Main control valve. (38) Auxiliary control valve. (39) Tilt control valve. (40) Lift control valve.

When pilot oil is sent to an end cap of main control valve (1) the affected stem will shift and the pump supply oil is directed to the appropriate implement cylinder.

Valve stems (13), (15), and (17) control the flow of oil to auxiliary cylinders (2), tilt cylinder (3), and lift cylinder (4). The movement of the valve stems are controlled by pilot oil pressure from the pilot valve (oil manifold) (27) .

Tilt stem (15) has three positions: TILT BACK position, HOLD position and DUMP position. When tilt stem (15) moves to the TILT BACK position, high pressure oil flows through the tilt valve (39) to the head end of the tilt cylinder. Oil from the rod end of the tilt cylinder flows through tilt valve (38) back to the hydraulic oil tank.

When the tilt control lever or the joystick control is in the HOLD position, all of the oil flow returns to hydraulic tank (37). When tilt stem (15) moves to the DUMP position, pump supply oil flows through the tilt valve (39) to the rod end of the tilt cylinder. Oil from the head end of tilt cylinder (3) will flow to hydraulic tank (36) .

Lift stem (17) has four positions: RAISE position, HOLD position, LOWER position and FLOAT position. In the RAISE position, high pressure oil flows to the head end of the lift cylinders. As lift cylinders (4) are moving the oil that is in the rod end of the lift cylinders (4) will flow through lift control valve (40) back to hydraulic tank (37). When the lift lever or the joystick control is placed in the HOLD position, stem (17) will return to the CENTER position. The high pressure oil returns to hydraulic tank (37). When the operator moves the lift control lever or the joystick control to the LOWER position, stem (17) will shift. Pump supply oil flows to the rod end of lift cylinders (4). Lift cylinder (4) will retract and the oil in the head end of lift cylinder (4) will flow through lift control valve (40) back to hydraulic tank (36) .

When the lift control lever or the joystick control is placed in the FLOAT position the lift valve spool remains in the LOWER position. Float valve (34) vents the high pressure oil that is in the rod end of lift cylinder (4). The pump supply oil will drain back to hydraulic tank (37) through float valve (34). The bucket will follow the contour of the terrain.

The flow of oil through the main control valve changes when the machine has an auxiliary circuit. The oil from implement pump (36) first flows to auxiliary stem (13). The auxiliary stem has three positions: OPEN position, HOLD position and CLOSE position.

In the OPEN position, pump supply oil flows through auxiliary control valve (38) to the rod end of the auxiliary cylinder. In the HOLD position, all of the oil flow returns to the hydraulic oil tank. In the CLOSE position, high pressure oil flows to the head end of the auxiliary cylinder.

The auxiliary circuit, the tilt circuit, and the lift circuit have check valves that are located inside the main control valve. Load check valves (12), (14) and (16) prevent reverse oil flow through main control valve (1). Check valves (12, 14, 16) are built into the control valves. The check valves prevent oil from flowing back to implement pump (36) from a load that may be developed in the one or more of the cylinders.

The tilt function and the auxiliary functions are equipped with line relief valves. If the work tool is met by an outside source, a pressure spike can be induced into the main control valve. If the pressure spike is higher than the setting of the line relief valve, the line relief valve will allow the pressure to dump to hydraulic tank (37) .

Reference: For more information about the operation of the main control valve, refer to the Service Manual module Systems Operation, "Main Control Valve" for the machine that is being serviced.

Reference: For information about calibration of the main control valve, refer to the Service Manual module Testing and Adjusting, RENR4397, "Main Control Valve (Electonic Technician) or Main Control Valve (AVSpare Monitoring System)".

Quick Coupler (If Equipped)

If a machine is equipped with an optional quick coupler, the operator has the ability to change work tools without leaving the cab. The quick coupler is controlled from a switch in the cab. Illustration 5 shows the location on the panel. In order to activate the pins for the quick coupler, press the bottom of the switch. In order to disengage the pins from the work tool, activate the red button on the switch as the top of the switch is pressed. The red button is a locking feature of the switch that prevents disengaging the quick coupler during operation.




Illustration 5g00990764

Location of the Switch (Quick Coupler)




Illustration 6g00992409

Lines Group (Quick Coupler)

(41) Charge valve. (42) Accumulator. (43) Hose between the ball valve and the accumulator. (44) Hose between the ball valve and the diverter valve (quick coupler). (45) Hose between the diverter valve and the hydraulic tank. (46) Hose between the solenoid valve and the ball valve on the lift arm (retract pins). (47) Hose between solenoid valve and the ball valve on the lift arm (extend pins). (48) Ball valve. (49) Solenoid valve (quick coupler). (50) Relief valve (quick coupler). (51) Diverter valve (quick coupler). (52) Ball valve. (53) Connector (extend pins). (54) Rear frame. (55) Loader frame. (56) Connector (retract pins)

In the operation of the quick coupler, diverter valve (51) controls the engagement or the disengagement of the coupler pins.

The oil that is used by the quick coupler is provided by the pilot/brake pump. The pressure line for the quick coupler is attached to a tee on brake accumulator (42) for the rear brakes. From brake accumulator (42), the oil flows through hose (43) to ball valve (48). Then, the oil flows from ball valve (48) through hose (44) to diverter valve (51). The return oil flows from diverter valve (51) through hose (45) and back to the hydraulic tank.

As the switch for the quick coupler in Illustration 5 is in the DOWN position, solenoid valve (49) is energized in order to retract the coupler pins. The oil flows from diverter valve (51) through hose (46). The oil flows out of hose (46) to ball valve (52) on the lift arm. The hose for the rod end of the cylinder (quick coupler) is connected to connector (56) at ball valve (52).

When the switch is placed in the UPPER position, the oil flows out of diverter valve (51) through hose (47). Hose (47) is connected to the other ball valve on the lift arm. The hose for the head end of the cylinder (quick coupler) is connected to connector (53) at ball valve (52). The oil flows to the head end of the cylinder. The cylinder will extend the coupler pins. The work tool will be attached to the coupler frame.




Illustration 7g00992412

Frame (Quick Coupler)

(57) Cylinder (quick coupler). (58) Locking area of the frame. ( 59) Pins.

From ball valve (52), the hoses are connected to coupler cylinder (57). When the boss of the work tool is positioned in area (58) of the frame and the operator presses the top of the switch, coupler pins (59) will advance. The work tool will be firmly attached to the frame.

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