330C_Hyd_Sys-Op

Systems Operation

330C Excavator Hydraulic System

CYA1-Up (Machine) HAA1-Up (Machine) MCA1-Up (Machine) JAB1-Up (Machine) KDD1-Up (Machine) GAG1-Up (Machine) RBH1-Up (Machine) BTM1-Up (Machine) CAP1-Up (Machine) GKX1-Up (Machine) DKY1-Up (Machine) CGZ1-Up (Machine)

Most accidents that involve product operation, maintenance and repair are caused by failure to observe basic safety rules or precautions. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs. A person must be alert to potential hazards. This person should also have the necessary training, skills and tools to perform these functions properly.

Improper operation, lubrication, maintenance or repair of this product can be dangerous and could result in injury or death.

Do not operate or perform any lubrication, maintenance or repair on this product, until you have read and understood the operation, lubrication, maintenance and repair information.

Safety precautions and warnings are provided in this manual and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons.

The hazards are identified by the “Safety Alert Symbol” and followed by a “Signal Word” such as “DANGER”, “WARNING” or “CAUTION”. The Safety Alert “WARNING” label is shown below.

The meaning of this safety alert symbol is as follows:

Attention! Become Alert! Your Safety is Involved.

The message that appears under the warning explains the hazard and can be either written or pictorially presented.

Operations that may cause product damage are identified by “NOTICE” labels on the product and in this publication.

Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The warnings in this publication and on the product are, therefore, not all inclusive. If a tool, procedure, work method or operating technique that is not specifically recommended by Caterpillar is used, you must satisfy yourself that it is safe for you and for others. You should also ensure that the product will not be damaged or be made unsafe by the operation, lubrication, maintenance or repair procedures that you choose.

The information, specifications, and illustrations in this publication are on the basis of information that was available at the time that the publication was written. The specifications, torques, pressures, measurements, adjustments, illustrations, and other items can change at any time. These changes can affect the service that is given to the product. Obtain the complete and most current information before you start any job. Caterpillar dealers have the most current information available. For a list of the most current publication form numbers available, see the Service Manual Contents Microfiche, REG1139F.

When replacement parts are required for this product Caterpillar recommends using Caterpil-lar replacement parts or parts with equivalent specifications including, but not limited to, phys-ical dimensions, type, strength and material. Failure to heed this warning can lead to prema-ture failures, product damage, personal injury or death.

Table of Contents

Systems Operation Section

General Information

General Information ... 4

Main Hydraulic System ... 4

Electronic Control System ... 9

Pilot System Pilot Hydraulic System ... 10

Gear Pump (Pilot) ... 17

Hydraulic Filter (Pilot) ... 17

Relief Valve (Pilot) ... 18

Accumulator (Pilot) ... 19

Solenoid Valve (Hydraulic Activation) ... 21

Pilot Valve (Joystick) ... 23

Solenoid Valve (Proportional Reducing) (Power Shift System) ... 26

Pump System Main Hydraulic Pump ... 28

Pump Control (Main Hydraulic) ... 31

Main Control Valve Main Control Valve ... 38

Relief Valve (Main) ... 48

Relief Valve (Line) ... 50

Check Valve (Load) ... 53

Negative Flow Control System ... 55

Boom System Boom Hydraulic System ... 63

Boom Drift Reduction Valve ... 73

Stick System Stick Hydraulic System ... 75

Stick Drift Reduction Valve ... 84

Bucket System Bucket Hydraulic System ... 86

Cylinders Cylinders (Boom, Stick and Bucket) ... 90

Travel System Travel Hydraulic System ... 91

Pilot Valve (Travel and Steering) ... 98

Travel Motor ... 100

Travel Parking Brake ... 103

Displacement Change Valve ... 106

Travel Counterbalance Valve ... 109

Oil Makeup (Travel System) ... 116

Final Drive ... 117

Swivel ... 120

Swing System Swing Hydraulic System ... 122

Swing Motor ... 132

Pilot Valve (Swing Parking Brake) ... 134

Relief Valve (Swing) ... 137

Oil Makeup (Swing System) ... 140

Relief Valve (Cushion Crossover) (Anti-Reaction Valves) ... 141

Swing Drive ... 148

Return System Return Hydraulic System ... 151

Check Valve (Return Makeup) (Slow Return Check Valve) ... 152

Bypass Valve (Return) (Bypass Check Valve) .... 153

Hydraulic Tank and Filter ... 155

Oil Filter (Return) (Case Drain Filter) ... 156

Hydraulic Oil Cooler ... 156

Gear Pump (Fan Motor) ... 156

Reference Graphic Color Codes ... 157

Index Section

Index ... 160

Systems Operation Section

General Information

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General Information

SMCS Code:4000; 4250; 4265; 4284; 4300; 4801; 5050

Reference:For testing and adjusting of the hydraulic system, refer to Testing and Adjusting, “Excavator Hydraulic System” for your machine.

Reference:For systems operation of the electronic control unit and electronic system, refer to Systems Operation/Testing and Adjusting, “Excavator Engine and Pump Control” for your machine.

Reference:For more information on specifications with illustrations, refer to Specifications, “Excavator Machine System Specifications” for your machine.

Reference:For more information on the hydraulic schematics, refer to Schematic, “Excavator Hydraulic System” for your machine.

Reference:For more information on electrical schematics, refer to Schematic, “Excavator Electrical System” for your machine.

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Main Hydraulic System

SMCS Code:5050; 5051; 5069; 5117; 5472

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(1) Swing motor (2) Left travel motor (3) Right travel motor (4) Stick cylinder

(5) Travel brake valve (left) (6) Travel brake valve (right) (7) Bucket cylinder (8) Boom cylinder (9) Swivel

(10) Pilot control valve (travel) (11) Stick drift reduction valve (12) Main control valve (13) Boom drift reduction valve (14) Pressure switch

(15) Pressure switch

(16) Pilot control valve (swing and stick) (17) Pilot control valve (boom and bucket) (18) Main relief valve

(19) Pressure switch (20) Accumulator

(21) Reducing valve (boom priority mode or swing priority mode) (22) Pressure sensor (drive pump)

(23) Swing parking brake solenoid valve (24) Valve

(25) Solenoid valve (hydraulic activation) (26) Drive pump (view from shaft end) (27) Travel speed solenoid valve (28) Pilot oil manifold

(29) Drain filter (30) Pilot relief valve (31) Pilot filter

(32) Idler pump (view from shaft end) (33) Pilot pump

(34) Slow return check valve (35) Bypass check valve (36) Pressure sensor (idler pump)

(37) Proportional reducing valve (power shift pressure) (38) Oil cooler

(39) Return filter (40) Hydraulic tank (41) Gear pump (fan motor) (42) Relief valve (fan pump) (43) Fan motor (hydraulic oil cooler)

Hydraulic Pump Flow and Pressure

Control System

g00847825 Illustration 2 Pump compartment (26) Drive pump (32) Idler pump

(37) Proportional reducing valve (power shift pressure) (44) Delivery line (idler pump)

(45) Delivery line (drive 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 pumps, the main control valve, the swing brake and the travel motors.

•

The electronic control system controls the outputs of the engine and pump.

•

The hydraulic oil cooling system provides oil to the fan motor in order to cool the hydraulic oil.

The main hydraulic system delivers oil flow from idler pump (32) and drive pump (26) in order to control the following components: bucket cylinder (7), stick cylinder (4), boom cylinders (8), right travel motor (3), left travel motor (2), and swing motor (1).

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Illustration 3 Main control valve (18) Main relief valve (45) Right control valve body (46) Left control valve body

Idler pump (32) and drive pump (26) are bent axial piston type pumps. The performance of both pumps is equal.

Drive pump (26) is directly connected to the engine by a flexible coupling. The drive pump delivers oil to the left control valve body (46) of the main control valve. Idler pump (32) is mechanically connected to the drive pump through gears. The idler pump delivers oil to the right control valve body (45) of the main control valve. Gear type pilot pump (33) supplies oil to the pilot hydraulic system. Gear type pilot pump (33) is mechanically connected to idler pump (32) through gears. Gear type fan pump (41) supplies oil to the oil cooling system. Gear pump (41) is mechanically connected to the engine through gears. 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 approximately identical to the engine horsepower.

When no work is being performed, pump oil flows through main control valve (12) and into hydraulic tank (40). The main control valve sends a negative flow control 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 (12) directs pump oil to the respective cylinders (boom, bucket, and stick) and/or motors (swing and travel). Main control valve (12) 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 regulated by main relief valve (18).

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Illustration 4 Cab

(47) Monitor panel

(48) Joystick (stick and swing) (49) Joystick (boom and bucket) (50) Left travel lever/pedal (51) Right travel lever/pedal (52) Engine speed dial

The pilot hydraulic system receives oil flow from pilot pump (33). The pilot hydraulic system controls the following functions.

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

Pilot oil flows from pilot pump (33) through pilot manifold (28). The pilot oil then flows to the pilot control valves for machine operation (implement operations, swing operations and travel operation). These pilot control valves are activated by the joysticks and the travel levers/pedals.

When joystick (48), joystick (49), left travel lever/pedal (50) and/or right travel lever/pedal (51) are moved from the NEUTRAL position, the pilot oil flows through the pilot control valves to the corresponding spools at the main control valve (12).

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 (32) or drive pump (26) to the cylinders and motors.

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

2. The pilot hydraulic system controls the output flow of the main pumps.

During machine operation, pilot pressure is sent to the main pump regulators as a signal pressure. This signal pressure is called power shift pressure. The engine and pump controller receives input signals from various components on the machine. The engine and pump controller processes the input signals. The engine and pump controller then sends an electrical signal to proportional reducing valve (37) at the idler pump regulator in order to regulate the power shift pressure. The power shift pressure controls the output flow of idler pump (32) and drive pump (26). Power shift pressure adjusts the output flow of the main pumps in accordance with the engine speed. For more information concerning power shift pressure, refer to Systems Operation, “Pilot Hydraulic System”.

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

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

b. Pilot signal pressure releases the swing parking brake.

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

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

e. Pilot signal pressure controls the operation of the valves that can be used during a loading operation or a trenching operation.

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

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Electronic Control System

SMCS Code:1900

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Illustration 5

(1) Engine and pump controller (2) Fuse panel

(3) Engine

(4) Engine speed sensor (5) Main pumps (6) Governor lever (7) Engine start switch (8) Battery (9) Backup switch (10) Governor actuator (11) Feedback sensor (12) Monitor (13) Action alarm (14) Engine speed dial (15) Switch panel

(16) Engine coolant temperature sensor (17) Hydraulic oil temperature sensor (18) Alternator

(19) Fuel level sensor

(20) Engine oil pressure sensor (21) Manual low idle switch (22) Engine oil level switch (23) Hydraulic oil level switch (24) Water separator

(25) Implement/swing pressure switch (26) Right travel pressure switch (27) Left travel pressure switch (28) Straight travel pressure switch (29) Pressure sensor (idler pump) (30) Pressure sensor (drive pump)

(31) Power shift solenoid (32) Straight travel solenoid (33) Travel speed solenoid

(34) Swing parking brake solenoid valve (35) Travel alarm

(36) Restricted air filter switch (37) Restricted hydraulic return filter

indicator

(38) Air heater indicator (39) Engine coolant level switch (40) Pressure switch (attachment pump) (41) Attachment pedal pressure switch (1) (42) Attachment pedal pressure switch (2) (43) Proportional reducing valve for auxiliary

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Illustration 6

(1) Engine and pump controller

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Illustration 7 (12) Monitor

The electronic control system consists of monitor (12) in the cab and the engine and pump controller (1) that is located in the compartment behind the cab. The electronic control system controls the engine speed and the pumps through the engine and pump controller.

Engine and pump controller (1) receives input signals from various components on the machine. The engine and pump controller continuously monitors the input signals in order to control the output flow rate of the main pumps, engine speed and various components of the machine hydraulic systems.

The electronic control system has the following three major functions.

•

The electronic control system controls the output flow rate of the main pumps. The engine and pump controller sends an electrical signal to the power shift solenoid that is based on engine speed and the position of the engine speed dial. This allows the main pumps to supply the optimum output that matches the hydraulic load to the machine and the engine speed. When a large load is placed on the machine, the system allows the pumps to destroke. The system utilizes the available maximum engine horsepower.

•

The electronic control system controls the engine speed. This is called Automatic Engine Speed Control (AEC). When there is a very small load condition or no load condition, the system automatically decreases the engine speed. The AEC system is designed to reduce fuel consumption and noise.

•

The electronic control system controls various components of the machine hydraulic systems. The engine and pump controller sends output signals to the swing parking brake solenoid valve, the travel speed solenoid valve and the straight travel solenoid.

Note:If a problem occurs in the electronic control system, temporary operation of the machine is possible by use of the backup switches that are located in the cab. For more information concerning the backup system, refer to Operation and Maintenance Manual, “Backup Controls”.

Reference:For more information concerning the operation of the electronic control system, refer to Systems Operation/Testing and Adjusting, “Engine and Pump Electronic Control System”.

Pilot System

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Pilot Hydraulic System

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(1) Swing parking brake

(2) Displacement change valve (left travel motor) (3) Displacement change valve (right travel motor) (4) Line (pilot oil from swing parking brake solenoid valve) (5) Travel pilot control valve

(6) Pilot line (BOOM LOWER)

(7) Pilot line (boom drift reduction valve) (8) Pilot line (STICK IN)

(9) Pilot line (stick drift reduction valve) (10) Stick drift reduction valve (11) Main control valve (12) Boom drift reduction valve (13) Solenoid valve (straight travel)

(14) Pilot line (pilot pressure to left travel pressure switch) (15) Pilot line (pilot oil to travel pilot control valve) (16) Right travel control valve

(17) Boom I control valve (18) Straight travel control valve (19) Travel pressure switch (left)

(20) Pilot line (pilot pressure to right travel pressure switch) (21) Travel pressure switch (right)

(22) Pilot line (pilot oil to pilot control valve for stick and swing) (23) Pilot line (pilot oil to pilot control valve for boom and bucket) (24) Left travel control valve

(25) Pilot control valve for stick and swing (26) Pilot control valve for boom and bucket (27) Variable swing priority valve

(28) Pilot line (STICK OUT) (29) Pilot line (STICK IN) (30) Pilot line (SWING RIGHT) (31) Pilot line (SWING LEFT) (32) Pilot line (BUCKET CLOSE) (33) Pilot line (BOOM RAISE) (34) Pilot line (BOOM LOWER) (35) Pilot line (BUCKET OPEN)

(36) Pilot line (pilot oil from boom pilot control valve) (37) Pilot line (BOOM RAISE)

(38) Pilot line (pilot oil to the pressure reducing valve for boom priority)

(39) Pilot line (pilot pressure to implement/swing pressure switch) (40) Implement/swing pressure switch

(41) Pilot line (pilot pressure to displacement change valves) (42) Pilot line (pilot oil to pressure reducing valve for swing priority) (43) Pilot line (pilot oil to pilot control valves)

(44) Pilot line (pilot oil to straight travel control valve) (45) Swing parking brake solenoid valve

(46) Valve (hydraulic activation)

(47) Pressure reducing valve for swing priority (48) Pressure reducing valve for boom priority (49) Drive pump

(50) Passage (power shift pressure) (51) Pilot manifold

(52) Travel speed solenoid valve (53) Passage

(54) Hydraulic activation solenoid valve (55) Passage

(56) Passage (57) Passage (58) Idler pump (59) Pilot pump

(60) Pilot line (pilot oil flow to pilot oil manifold) (61) Pilot filter

(62) Passage (power shift pressure)

(63) Proportional reducing valve (power shift pressure) (64) Pilot relief valve

(65) Passage

(66) Pilot line (pilot oil flow from pilot pump to pilot oil filter) (67) Pilot line (pilot oil flow to pump regulators)

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Illustration 9

Ports and solenoids at pilot manifold (45) Swing parking brake solenoid valve (46) Valve (hydraulic activation)

(52) Travel speed solenoid valve (54) Hydraulic activation solenoid valve

Pilot Oil Circuit

The pilot circuit pressure is limited by pilot relief valve (64).

The oil delivery from pilot pump (59) performs the following main functions.

•

Create pilot oil pressure in order to control the output flows of the main pumps.

•

Provide pilot oil pressure to the pilot control valves for implements, swing and travel in order to perform machine operations.

•

Create pilot oil pressure in order to automatically operate the control devices.

The pilot circuit is classified into the following circuits and each circuit performs one of the above functions.

•

Power shift pressure system

•

Pilot control valve circuit

•

Pressure switch circuits

•

Straight travel valve circuit

•

Swing parking brake

•

Boom priority

•

Swing priority

Power Shift Pressure System

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Illustration 10 (49) Drive pump (58) Idler pump

(63) Proportional reducing valve (PS pressure)

(59) Pilot pump

(68) Engine and pump controller (69) Monitor

(70) Engine speed dial (71) Idler pump pressure sensor (72) Drive pump pressure sensor

(73) Feedback sensor (74) Governor actuator

(75) Engine speed sensor (flywheel housing)

During machine operation, engine and pump controller (68) receives input signals from the following components:

•

Engine speed dial (70)

•

Engine speed sensor (75) that is located on the flywheel housing

•

Idler pump pressure sensor (71)

•

Drive pump pressure sensor (72)

•

Monitor in the cab (69)

•

Feedback sensor (73) at governor actuator (74) The engine and pump controller (68) continually monitors all of the input signals. The input signals are processed by the engine and pump controller and an output signal is sent to proportional reducing valve (63) at the pump regulator. The proportional reducing valve assists in controlling the output flow of idler pump (58) and drive pump (49).

The oil delivery from pilot pump (59) flows through the pilot filter to proportional reducing valve (63) at the pump regulator. The electrical signal that is sent from engine and pump controller (68) causes proportional reducing valve (63) to regulate the pilot pressure to a reduced pressure. This reduced pressure is called power shift pressure (PS). The proportional reducing valve sends the reduced pilot oil pressure through the idler pump regulator and through the drive pump regulator. The output flow of idler pump (58) and drive pump (49) is controlled in accordance with the power shift pressure. The power shift pressure is used to regulate the maximum allowable hydraulic pump output.

The output signal that is sent from the engine and pump controller to the proportional reducing valve will change when the engine and pump controller detects a change in any of the input signals. The power shift pressure that is sent to the regulators at the idler pump and the drive pump will change in order to regulate the maximum allowable hydraulic pump output. The desired engine speed is maintained.

A decrease in engine speed increases the power shift pressure. An increase in power shift pressure causes destroke condition of the idler pump and the drive pump. The maximum allowable hydraulic power output is decreased.

An increase in engine speed decreases the power shift pressure. A decrease in power shift pressure causes an upstroke condition of the idler pump and the drive pump. The maximum allowable hydraulic power output is increased.

Note:For more information concerning the operation of the engine and pump controller, refer to Systems Operation/Testing and Adjusting, “Engine and Pump Electronic Control System”.

Pilot Control Valve Circuits

Oil from pilot pump (59) flows through pilot line (66), pilot filter (61) and pilot line (60) to pilot manifold (51). When the hydraulic activation control lever is shifted to the UNLOCKED position, the engine and pump controller energizes the hydraulic activation solenoid valve (54). The pilot oil then shifts valve (46). The pilot oil now flows through valve (46) and pilot line (43). The pilot oil now flows to pilot control valves (5), (25) and (26) for implements, swing and travel in order to perform machine operations. When the joysticks and/or travel levers/pedals are moved, the pilot oil flows to main control valve (11) in order to control the machine functions.

The following example is given for the BOOM LOWER operation and the BOOM RAISE operation. Machine operations for a stick operation, bucket operation, travel operation and swing operation are accomplished in the same manner as the boom operation.

When the joystick for the boom is moved to the BOOM RAISE position, pilot oil from pilot control valve (26) flows through pilot line (37) to boom I control valve (17). The pilot pressure shifts the boom I control valve. The oil delivery from the idler pump flows to the head end of the boom cylinders in order to perform the BOOM RAISE operation.

When the joystick for the boom is moved to the BOOM LOWER position, pilot oil from pilot control valve (26) flows through pilot line (6) to boom I control valve (17). The pilot pressure shifts the boom I control valve. The pilot oil also flows through pilot line (7) in order to open boom drift reduction valve (12). The return oil from the head end of the boom cylinders flows through the boom drift reduction valve and the boom I control valve to the hydraulic tank. The BOOM LOWER operation is now performed.

Pressure Switch Circuits

Pressure switches (19) and (21) are connected to travel pilot control valve (5). Pressure switch (40) is connected to pilot control valve (25) and pilot control valve (26). When all of the joysticks and/or travel levers/pedals are in the NEUTRAL position, the pilot oil pressure to the pressure switches is low. Pressure switches (19), (21) and (40) are OFF. The engine and pump controller recognizes the OFF condition of all of the pressure switches. The AEC system is activated in order to lower the engine rpm.

If any of the joysticks and/or travel levers/pedals are moved from the NEUTRAL position, the increased pilot oil pressure is sent to the pressure switches. If pressure switch (19), (21) and/or (40) is ON, the engine and pump controller activates the AEC system in order to increase the engine rpm.

Straight Travel Valve Circuit

When a swing operation and/or implement operation is performed during a travel operation, the increase of pilot pressure in pilot line (39) activates implement/swing pressure switch (40). The implement/swing pressure switch sends an electrical signal to the engine and pump controller. The engine and pump controller energizes straight travel solenoid (13). Pilot pressure now activates straight travel control valve (18). The straight travel control valve maintains straight travel even though there is a swing operation or an implement operation during travel. For more information concerning the operation of the straight travel control valve, refer to Systems Operation, “Control Valve (Straight Travel)”.

Swing Parking Brake

When the hydraulic activation control lever is placed in the UNLOCKED position, pilot oil in passage (57) flows through valve (46) and passage (53) to swing parking brake solenoid valve (45). When any of the joysticks are moved from the NEUTRAL position, the increase of pilot pressure in pilot line (39) activates implement/swing pressure switch (40). The implement/swing pressure switch sends an electrical signal to the engine and pump controller. An electrical signal from the engine and pump controller energizes the swing parking brake solenoid valve (45). Pilot oil in line (4) flows to swing parking brake (1). This oil releases the swing parking brakes. For more information concerning the operation of the swing parking brake, refer to Systems Operation, “Pilot Valve (Swing Parking Brake)”.

Boom Priority

During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure in pilot line (36) and pilot line (38) activates the pressure reducing valve for boom priority. The pressure reducing valve for boom priority allows priority flow to the head end of the boom cylinders during these combined hydraulic operations by disabling the stick II control valve. For more information concerning the pressure reducing valve for boom priority, refer to Systems Operation, “Boom Hydraulic System”.

Swing Priority

During a swing operation, pilot oil flows from pilot control valve (25) to the pressure reducing valve for swing priority (47). The pressure reducing valve for swing priority shifts. The pilot oil flow in pilot line (42) from pilot oil manifold (51) is blocked by the pressure reducing valve for swing priority. Most of the drive pump delivery flow goes to the swing motor. For more information concerning the pressure reducing valve for swing priority, refer to Systems Operation, “Swing Hydraulic System”.

Automatic Travel Speed Change

Valve

Pilot oil in passage (56) flows to travel speed solenoid valve (52). When the travel speed switch on the right console is set at the HIGH SPEED position, the travel speed solenoid valve opens. This allows pilot oil to flow through travel speed solenoid valve (52) and through line (41). The oil then flows to the displacement change valve for the left travel motor (2) and the displacement change valve for the right travel motor (3). As the displacement change valve operates, the travel speed is maintained at the HIGH SPEED position.

When the travel speed switch on the right console is set at the HIGH SPEED position, the pressure sensors for the pump delivery pressure control the travel speed in accordance with the travel load. For example, low speed during a high load condition and high speed during a low load condition.

For more information concerning the operation of the displacement change valves, refer to Systems Operation, “Displacement Change Valve”.

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Gear Pump (Pilot)

SMCS Code:5073; 5085

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Illustration 11 Pilot pump

The pilot pump is a gear type pump that supplies oil flow to the pilot system. The pilot pump is located inside the main pump housing. The pilot pump is mechanically connected to the drive pump. The pump delivery rate with load is approximately 34 L/min (9.0 US gpm).

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Hydraulic Filter (Pilot)

SMCS Code:5068; 5092

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Illustration 12 (1) Pilot oil filter

The oil delivery from the pilot pump flows through pilot oil filter (1) and into the components in the pilot system.

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Illustration 13 (1) Pilot oil filter (2) Filter element (3) Bypass relief valve

Filter element (2) in pilot oil filter (1) removes contaminants from the pilot oil.

If the pilot oil is extremely cold or if the flow of pilot oil through filter element (2) becomes restricted by contaminants, the oil bypasses filter element (2) through bypass relief valve (3). Bypass relief valve (3) is built into the base for the pilot oil filter.

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Relief Valve (Pilot)

SMCS Code:5072

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Illustration 14

(1) Inlet port (oil flow from pilot pump) (2) Pilot relief valve

(3) Port (oil flow to hydraulic tank)

(4) Outlet lines (regulated pilot oil pressure)

Pilot relief valve (2) is located on the mounting base for the pilot oil filter. The pilot relief valve limits the pressure in the pilot system. The pilot relief valve setting is adjustable.

The pilot oil flows from the pilot pump to inlet port (1). When the pressure in the pilot oil system reaches the pressure setting of pilot relief valve (2), part of the pilot oil flow is returned to the hydraulic tank through port (3). The pressure of the pilot system oil in outlet lines (4) is equal to the pressure setting of the pilot relief valve.

Reference:For more information concerning the pilot relief valve setting, refer to Testing and Adjusting, “Relief Valve (Pilot) - Test and Adjust”.

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Accumulator (Pilot)

SMCS Code:5077 g00681745 Illustration 15 (5) Accumulator

(16) Line (pilot oil from pilot oil manifold) (17) Mounting block

The accumulator stores pilot pressure oil for use at the main control valves. During some operations, the pilot system needs more oil because there is insufficient flow from the pilot pump. Accumulator (5) will provide pilot pressure oil to the pilot system when the pilot pump flow is inadequate. Insufficient supply of pilot oil flow to the pilot system may be caused by the following two reasons:

•

Implements are lowered while the engine is stopped and oil supply to the main control valves is stopped.

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Illustration 16 Accumulator (5) Accumulator

(16) Line (pilot oil flow from pilot oil manifold to the mounting block for the accumulator)

(17) Mounting block (18) Passage

(19) Inlet port

(20) Pressure oil chamber (21) Vessel (22) Bladder (23) Gas chamber (24) Passage (25) Passage (26) Passage

(27) Inlet port (pilot oil manifold) (28) Passage

(29) Check valve

Pilot oil from the pilot filter enters inlet port (27) of the pilot oil manifold. Pilot oil flows through passage (28) and opens check valve (29). Pilot oil now flows through passages (24) and (26) to the pilot control valves (joysticks and travel levers/pedals).

The pilot oil also flows through passage (25) and line (16) to the mounting block for the accumulator. The pilot oil now flows through passage (18) and inlet port (19) into pressure oil chamber (20). The pilot oil acts against bladder (22) and the nitrogen gas in gas chamber (23) is compressed. Check valve (29) prevents a backflow of the stored oil in the accumulator. The stored oil is used for solely operating the stems of the main control valve.

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Solenoid Valve (Hydraulic

Activation)

SMCS Code:5479

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Illustration 17 Pilot oil manifold (1) Pilot oil manifold

(2) Hydraulic activation solenoid valve

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Illustration 18 Cab

(3) Hydraulic activation control lever (LOCKED position)

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Illustration 19 Cab

(3) Hydraulic activation control lever (UNLOCKED position)

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Illustration 20

(3) Hydraulic activation control lever (4) Limit switch

(5) Plunger (6) Box

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Illustration 21 Cab (bottom view) (6) Box

Limit switch (4) and plunger (5) are contained in box (6). The limit switch is activated by hydraulic activation control lever (3).

When hydraulic activation control lever (3) is shifted to the LOCKED position, solenoid valve (2) of pilot oil manifold (1) is not energized. Pilot oil is not supplied to the pilot control valves. Thus when the joysticks and/or the travel levers/pedals are operated, the cylinders or the motors are not activated.

The engine will not start unless hydraulic activation control lever (3) is in the LOCKED position. If some one unexpectedly operates the machine, the machine will not operate.

When hydraulic activation control lever (3) is placed in the UNLOCKED position, solenoid valve (2) is energized and pilot oil passes through the solenoid valve. Pilot oil now flows to the pilot control valves.

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Illustration 22

Partial diagram of solenoid valve (hydraulic activation) (UNLOCKED circuit) (2) Hydraulic activation solenoid valve

(7) Solenoid (8) Spring (9) Spool (10) Control valve (11) Passage (12) Passage (13) Passage

(14) Passage (return oil)

(15) Passage (pilot oil to swing parking brake solenoid valve)

(16) Swing parking brake solenoid valve

(17) Pilot oil flow to pilot valves (joysticks) (18) Valve (hydraulic activation)

(19) Passage

When hydraulic activation control lever (3) is placed in the UNLOCKED position, plunger (5) of limit switch (4) is depressed by control lever (3). Limit switch (4) is in the ON state.

The hydraulic activation solenoid valve (2) consists of solenoid (7) and control valve (10). When hydraulic activation control lever (3) is in the UNLOCKED position, solenoid (7) controls valve (10). When solenoid (7) is energized, spool (9) moves in a downward direction against the force of spring (8). Passage (12) opens. Pilot pressure oil from passage (13) flows through passage (11) to valve (18). The spool in valve (18) moves in a downward direction. Pilot pressure oil in passage (19) flows through valve (18). Pilot oil is now delivered through passage (15) to swing parking brake solenoid valve (16). Pilot pressure oil in passage (19) is also delivered to the pilot control valves (joysticks and travel levers/pedals) through line (17).

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Illustration 23

Partial drawing of solenoid valve (hydraulic activation) (LOCKED position) (1) Hydraulic activation solenoid valve

(7) Solenoid (8) Spring (9) Spool (11) Passage (12) Passage (13) Passage

(14) Passage (return oil) (20) Passage

When hydraulic activation control lever (3) is moved to the LOCKED position, plunger (5) of limit switch (4) is not depressed by control lever (3). Limit switch (4) is in the OFF state.

When hydraulic activation control lever (3) is in the LOCKED position, solenoid (7) is not energized. Spool (9) is forced upward by spring (8). Passage (20) opens and passage (12) closes. Passage (13) is not open to passage (11). Pilot oil supply to line (17) is stopped. Pilot oil supply to the pilot control valves (joysticks and travel levers/pedals) is blocked. The cylinders and the motors can not be activated.

i01579519

Pilot Valve (Joystick)

SMCS Code:5705-V4

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Illustration 24 Cab

(1) Joystick (stick and swing) (2) Joystick (boom and bucket)

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Illustration 25

Pilot lines at the main control valve (top view)

When joystick (1) and/or joystick (2) are operated, the pilot control valves send pilot pump oil through the pilot lines to pilot ports at the main control valve in order to shift the spools in the main control valve. Refer to Illustration 25 and Table 1 for the location of the pilot lines and machine operations.

Table 1

Pilot line Control Valve Machine Operation (3) Boom I control valve BOOM LOWER (4) Bucket control valve BUCKET CLOSE (5) Swing control valve SWING LEFT (6) Boom II control valve BOOM RAISE (7) Stick II control valve STICK IN (8) Right travel control valve REVERSE RIGHT TRAVEL (9) Left travel control

valve REVERSE LEFT TRAVEL (10) Stick I control valve STICK IN

Pilot oil from the pilot control valves flows through pilot lines to the ports on the bottom of the main control valve in order to perform the opposite operation.

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Illustration 26

Pilot control valve (stick and swing) (1) Joystick (2) Rod (3) Return passage (4) Passage (5) Spool (6) Plate (7) Rod (8) Spring (9) Seat (10) Seat (11) Spring (12) Spring (13) Return chamber (14) Return passage (15) Passage (16) Spool

(17) Port (return pressure to valve) (18) Passage (pilot supply pressure) (19) Port (reduced pressure to valve) (20) Port (pilot supply)

(21) Port (tank)

When joystick (1) is moved to the right, plate (6) tilts to the right. Plate (6) pushes down on rod (7). Seat (10) moves down against the force of metering spring (11) and spring (12). The force of metering spring (11) shifts spool (16) downward. Passage (15) opens. The pilot oil flows through passage (20), passage (18), passage (15) and port (19) to the main control valve. The pilot oil pressure shifts the spool of the main control valve. This enables the implement operation or swing operation.

The return pilot oil at the opposite end of the spool in the main control valve returns to the pilot control valve through port (17). Since rod (2) is not pushed down by plate (6), return passage (3) is open and passage (4) is closed. The return pilot oil flows through return passage (3), return chamber (13) and port (21) to the hydraulic tank.

The force of metering spring (11) varies with the position of the joystick. Since spool (16) is moved by the force of metering spring (11), the pilot oil pressure that flows through passage (15) to the main control valve directly corresponds with the position of the joystick. Spool modulation in the main control valve directly corresponds with the amount of movement of the joystick.

When the joystick is moved slightly from the NEUTRAL position, metering spring (11) moves spool (16) slightly. Low pilot oil pressure is sent to the spool of the main control valve. The main control valve spool shifts a slight amount. The volume of oil delivery to the cylinders and/or motors is small. The speed of the cylinders and/or motors is slow. As the joystick is moved farther from the NEUTRAL position, the force of metering spring (11) on spool (16) increases. The pilot oil pressure that is sent to the main control valve increases. The spool in the main control valve shifts farther and the speed of the cylinders and/or motors increases. Thus, cylinder speed and motor speed is controlled by the amount of movement and the position of the joystick.

When the joystick is moved slightly from the NEUTRAL position, only metering spring (11) acts on spool (16). Fine control of the cylinders and/or motors is accomplished since the pilot oil pressure that is sent to the main control valve is decreased. As the joystick is moved farther from the NEUTRAL position, the bottom of rod (7) comes in contact with spring (8). Now, the combined force of metering spring (11) and spring (8) act on spool (16). The pilot oil pressure increases rapidly. The cylinders and/or motors respond more rapidly.

When the joystick is released, the joystick will return to the NEUTRAL position due to the force of spring (12).

i01630751

Solenoid Valve (Proportional

Reducing)

(Power Shift System)

SMCS Code:5479

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Illustration 27

Proportional reducing valve (power shift solenoid) (1) Solenoid

(3) Body (main pump) (9) Line (pilot oil flow)

The proportional reducing valve for the power shift pressure is located on the main pump housing. The proportional reducing valve is a solenoid operated control valve. The proportional reducing valve receives supply oil from the pilot pump. The solenoid receives a pulse width modulated signal (PWM signal) from the engine and pump controller. The PWM signal that is sent from the engine and pump controller causes the proportional reducing valve to regulate the pilot pressure to a reduced pressure. This reduced pressure is called power shift pressure (PS). The proportional reducing valve sends the reduced pilot oil pressure to the regulators at the idler pump and the drive pump. The output flow of the idler pump and the drive pump is controlled in accordance with the power shift pressure. The power shift pressure is used to control the maximum allowable hydraulic pump output.

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Illustration 28

Proportional reducing valve (increase in PWM signal) (1) Solenoid

(2) Spring (3) Valve body (4) Spool

(5) Passage (return oil flow)

(6) Passage (power shift pressure to pump regulators) (7) Spool chamber

(8) Passage (pilot oil flow)

A decrease in engine speed causes an increase in power shift pressure and a decrease in pump flow.

While the engine is operating, the engine and pump controller senses a decrease in engine speed. A decrease in engine speed causes the engine and pump controller to increase the PWM signal that is sent to solenoid (1). The magnetic force of the solenoid increases. As the magnetic force of the solenoid becomes greater than the force of spring (2), spool (3) moves in a downward direction against the force of the spring. The downward movement of spool (3) blocks the flow of oil from passage (6) to passage (5). Pilot oil in line (9) now flows through passage (8), into spool chamber (7) and into passage (6) at a reduced pressure (power shift pressure). The increased power shift pressure in passage (6) acts on the idler pump regulator and the drive pump regulator. The idler pump and the drive pump destroke as a result of an increase in power shift pressure.

g00678719

Illustration 29

Proportional reducing valve (decrease in PWM signal) (1) Solenoid

(2) Spring (3) Valve body (4) Spool

(5) Passage (return oil flow)

(6) Passage (power shift pressure to pump regulators) (7) Spool chamber

(8) Passage (pilot oil flow)

An increase in engine speed causes a decrease in power shift pressure and an increase in pump flow.

While the engine is operating, the engine and pump controller senses an increase in engine speed. An increase in engine speed causes the engine and pump controller to decrease the PWM signal that is sent to solenoid (1). The magnetic force of the solenoid decreases. As the force of spring (2) becomes greater than the magnetic force of the solenoid, spool (3) moves in an upward direction. The upward movement of spool (3) blocks the flow of pilot oil from passage (8). Power shift pressure oil in passage (6) now drains into spool chamber (7) and into passage (5). The decreased power shift pressure in passage (6) that is acting on the idler pump regulator and the drive pump regulator causes the idler pump and the drive pump to move to an upstroke position. The idler pump and the drive pump upstroke as a result of a decrease in power shift pressure.

Reference:For more information concerning power shift pressure (PS), refer to Systems Operation, “Pilot Hydraulic System”.

Pump System

i01638366

Main Hydraulic Pump

SMCS Code:5070-MV

Construction

g00700449

Illustration 30 Main pumps

(1) Port (negative flow control pressure) (2) Outlet port (pilot pump)

(3) Idler pump

(4) Outlet port (idler pump)

(5) Inlet port

(6) Port (power shift pressure)

(7) Port (negative flow control pressure) (8) Drive pump

(9) Outlet port (drive pump) (10) Housing

(11) Pilot pump

The main pumps consist of idler pump (3) and drive pump (8). The main pumps and the port block are bolted together in order to form one assembly. The idler pump and the drive pump are identical in construction and identical in operation. The pumps have identical control systems.

Oil from the hydraulic tank flows into inlet port (5) of the port block. Idler pump (3) delivers oil through outlet port (4). Drive pump (8) delivers oil through outlet port (9). Pilot pump (11) draws oil through inlet port (5). Pilot pump (11) delivers oil through outlet port (2).

The power shift pressure is determined by the electronic controller. The power shift pressure flows into the main pumps through port (6). The negative flow control (NFC) pressure from the main control valve flows into idler pump (3) through port (1). The NFC pressure from the main control valve flows into drive pump (8) through port (7).

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Illustration 31

Main pumps (sectional views) (4) Outlet port (idler pump) (5) Inlet port

(9) Outlet port (drive pump) (10) Housing

(11) Pilot pump (12) Gear (pilot pump) (13) Plate

(14) Pin (17) Regulator

(18) Drive shaft (drive pump)

(19) Center line (20) Trunnion (21) Housing (22) Center line (23) Gear (drive pump) (24) Piston

(25) Cylinder (26) Valve plate (27) Piston

(28) Gear (idler pump)

(29) Shaft (idler pump) (30) Cylinder passage (31) Inlet passage (32) Inlet passage (33) Center hole (34) Outlet passage (35) Outlet passage (C) Radial direction (D) Radial direction

Idler pump (3) and drive pump (8) are bent axial piston type pumps. The term “bent axial” describes the angular movement of the piston pump assembly. This movement is around the point of intersection of center lines (19) and (22). The output of the pumps changes depending on the angle of cylinder (25).

Drive shaft (18) of the drive pump is coupled with the engine flywheel. Gear (23) of drive shaft (18) engages with gear (28) of shaft (29). When shaft (18) is driven by the engine flywheel, shaft (29) is driven through a mechanical linkage between gear (23) and gear (28). Gear (23) has the same number of teeth as gear (28). Therefore, both pumps rotate at the same speed as the engine.

Because gear (23) engages with gear (12) of the pilot pump, pilot pump (11) rotates with the main pumps.

Main Pump Operation

The idler pump (3) and drive pump (8) are identical in operation. The drive pump is described below.

Drive shaft (18) is driven by the engine. Drive shaft (18) turns seven pistons (24). Therefore, angle cylinder (25) rotates. Angle cylinder (25) is in contact with valve plate (26). Angle cylinder (25) rotates on valve plate (26). Angle cylinder (25) pivots on pin (14). Gear (23) has plate (13) that retains the heads of pistons (24). Therefore, pistons (24) swivel in the sockets.

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Illustration 32

(4) Outlet port (idler pump) (5) Inlet port

(9) Outlet port (drive pump) (20) Trunnion (21) Housing (26) Valve plate (31) Inlet passage (33) Center hole (35) Outlet passage (36) Grooves

Oil from the hydraulic tank goes into pump housing (21) through inlet port (5). The oil goes through inlet passages (32) and (31) in plate (26). The oil then enters cylinder passage (30) of angle cylinder (25). Cylinder passage (30) is positioned over inlet passage (31). Angle cylinder (25) turns. The openings of passage (30) in angle cylinder (25) rotate. The openings line up with the position of passage (31).

The displacement of pistons (24) changes depending on the position of angle cylinder (25). The piston draws oil by moving out of the bore of angle cylinder (25). Oil is pushed ahead of the piston as the piston moves through the bore. The oil that is pushed ahead of the piston goes through passage (30) and then through outlet passage (35) in valve plate (26). The oil passes through the drive pump through outlet port (9). The oil flows to the hydraulic circuit.

g00293030

Illustration 33

(26) Valve plate (drive pump) (37) Valve plate (idler pump)

Valve plate (26) moves on machined grooves (36) of housing (21). Housing (21) has a circular contour. Center hole (33) of valve plate (26) holds one end of trunnion (20). The other end of the trunnion is held to piston (27) of regulator (17). Piston (27) moves in and out during regulator operation. Trunnion (20) is connected to valve plate (26). Therefore, the angle cylinder will move to a new position. Valve plate (26) moves in radial direction (C), and the angle cylinder decreases the angle of position. The stroke of pistons (24) decreases, and the pump output will decrease. When valve plate (26) moves in radial direction (D), pump output will increase.

Inlet oil is sealed from outlet oil by a metal seal. The seal is formed between the face of valve plate (26) and the face of angle cylinder (25). On the opposite side of valve plate (26), a seal is made with the face of grooves (36). The sealing faces are made with precision in order to protect the faces from damage during disassembly and assembly.

Valve plate (26) in the drive pump is not similar to valve plate (37) in the idler pump. Use extra care to install valve plates (26) and (37) in the correct position.

i01638292

Pump Control (Main Hydraulic)

Main Pump Regulator

g00704757

Illustration 34 Regulator (Idler Pump) (5) Passage

(7) Passage (8) Housing

(9) Outlet port (idler pump) (10) Outlet passage

(11) Negative flow control line (idler pump) (12) Port (13) Piston (14) Control piston (15) Passage (17) Passage (18) Spring (19) Bushing (20) Passage (21) Pin (22) Spring

(23) Line (power shift pressure) (24) Control piston (25) Passage (26) Spring chamber (27) Spring (28) Spring (29) Spring spacer (30) Spring (31) Trunnion (32) Piston (33) Bolt (34) Ring (35) Passage (37) Piston chamber (38) Bolt

(57) Idler pump delivery pressure (58) Drive pump delivery pressure (59) Negative flow control pressure (60) Power shift pressure

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Illustration 35 Pump Compartment

(11) Negative flow control line (idler pump) (23) Line (power shift pressure)

(39) Regulator (idler pump) (41) Regulator (drive pump)

(42) Negative flow control line (drive pump)

See the following list for the pump regulator operation.

•

The pump regulator receives power shift pressure (60) from the electronic control system. The pump regulator controls the pump flow.

•

The pump regulator maintains a constant horsepower between the engine and the pump. The pump regulator receives a summation of idler pump delivery pressure (57) and drive pump delivery pressure (58). This operation is called the horsepower control characteristic.

•

When the control levers are in NEUTRAL position or in PARTIAL position, the pump regulator receives the negative flow control pressure (59). Negative flow control pressure (59) controls the pump output flow. This is called the negative flow control.

The pump regulator of the idler pump and drive pump are identical in construction and in operation. The following description identifies the idler pump regulator.

Oil from the idler pump flows to pump regulator (39). Oil from the idler pump goes through passages (10) and (7) in housing (8) to passages (15) and (17). Oil through passage (15) controls piston (14). Oil through passage (17) goes to passage (25). Also, oil goes to piston chamber (37) through passage (35). Oil from the drive pump goes through passage (5) to control piston (14).

Power shift pressure (60) goes through line (23) to a port on the pump regulator. The port is common to idler pump regulator (39) and drive pump regulator (41).

During the horsepower control characteristic, both idler pump delivery pressure (57) and drive pump delivery pressure (58) act against the rings of control piston (14) while power shift pressure (60) is acting against the top end face of control piston (14). Control piston (14), pin (21), and control piston (24) shift in order to control the pump output.

During negative flow control, negative flow control pressure (59) from line (11) acts against the top surface of piston (13). Control piston (14) shifts in order to move control piston (24) for pump flow control.

Note:For further information on the horsepower control characteristic and negative flow control, refer to the “Regulator Operation” section in this module.

Regulator Operation

Horsepower Control Characteristic

(Period Before Decreased Pump Stroke)

g00704758 Illustration 36 Regulator Operation (5) Passage (14) Control piston (15) Passage (17) Passage (21) Pin (22) Spring (24) Control piston (25) Passage (26) Spring chamber (27) Spring (30) Spring (31) Trunnion (32) Piston (33) Bolt (34) Ring (35) Passage (37) Piston chamber (38) Bolt (45) Idler pump

(57) Idler pump delivery pressure (58) Drive pump delivery pressure (60) Power shift pressure

g00704760

Illustration 37

Regulator Operation (Partial View) (5) Passage (14) Control piston (15) Passage (17) Passage (20) Passage (21) Pin (22) Spring (24) Control piston (25) Passage (26) Spring chamber (27) Spring (47) Top surface (48) Passage (49) Passage

(57) Idler pump delivery pressure (58) Drive pump delivery pressure (60) Power shift pressure

When the machine operates with a low load, pump pressure acts on control piston (14). Idler pump delivery pressure (57) from passage (15) and drive pump delivery pressure (58) from passage (5) act on the ring grooves of control piston (14). Control piston (14) pushes down against pin (21). The force tries to move control piston (24) in the downward direction. Control piston (24) does not move down because the total forces of idler pump delivery pressure (57), drive pump delivery pressure (58) and power shift pressure (60) are less than the combined forces of springs (22), (27) and (30). The force of spring (30) is less than spring (27). Spring (30) is compressed before spring (27) is compressed. Passage (48) closes and passage (49) opens making an open connection between passage (25) and spring chamber (26). Tank pressure in spring chamber (26) acts on the bottom surface of ring (34). Idler pump delivery pressure (57) in piston chamber (37) pushes down piston (32) and ring (34). When bolt (33) comes in contact with bolt (38) movement stops. The mechanical linkage of piston (32) and the cylinder through trunnion (31) hold the cylinder at the maximum angle position. This allows the pump to maintain the maximum output flow.

Horsepower Control Characteristic

(Period Before Destroke)

g00704761

Illustration 38 Regulator Operation

(5) Passage (14) Control piston (15) Passage (17) Passage (20) Passage (21) Pin (22) Spring (24) Control piston (25) Passage (26) Spring chamber (27) Spring (28) Spring (30) Spring (31) Trunnion (32) Piston (34) Ring (35) Passage (37) Piston chamber (45) Idler pump (50) Set screw

(57) Idler pump delivery pressure (58) Drive pump delivery pressure (60) Power shift pressure

g00704762

Illustration 39

Regulator Operation (Partial View) (5) Passage (14) Control piston (15) Passage (17) Passage (20) Passage (21) Pin (22) Spring (24) Control piston (25) Passage (26) Spring chamber (27) Spring (47) Top surface (48) Passage (49) Passage (50) Set screw

(57) Idler pump delivery pressure (58) Drive pump delivery pressure (60) Power shift pressure

An increased load on the main pump increases idler pump delivery pressure (57) from passage (15) and increases drive pump delivery pressure (58) from passage (5). The force acts on ring grooves of piston (14).

The combined forces of increased power shift pressure (60) through passage (20) acts on top surface (47) of control piston (14) to overcome the total forces of springs (22) and (30). Control piston (14) pushes down on control piston (24) through pin (21). Passage (49) closes and passage (48) opens. Therefore, idler pump delivery pressure (57) from passage (17) goes through passage (25) to the bottom surface of ring (34).

Idler pump delivery pressure (57) acts on the top surface of ring (34). Therefore, oil is supplied to piston chamber (37) through passage (35). Idler pump delivery pressure (57) is common to both top and bottom surfaces of ring (34). The bottom surface area of ring (34) is larger than the top surface area. Therefore, ring (34) pushes up piston (32) against the forces of springs (30) and (28). The mechanical linkage of piston (32) and the cylinder through trunnion (31) cause the cylinder to move in a smaller angular direction. Therefore, the pump stroke decreases.

As piston (32) moves up, spring (30) compresses. Spring (30) pushes up on control piston (24). Passage (48) closes and passage (49) partially opens. Therefore, oil flows from passage (25) to spring chamber (26). Because spring chamber (26) is open to tank pressure, the pressure on the bottom surface of ring (34) becomes less than idler pump delivery pressure (57). Piston (32) starts to stop upward movement. When the force of idler pump delivery pressure (57) on the top surface of ring (34) becomes more than the force on the bottom surface, piston (32) starts to move down. Because of the decreased compression force of spring (30), control piston (24) also starts to move down. Passage (49) now closes and passage (48) partially opens. Piston (32) now starts to move up again because of idler pump delivery pressure (57) through passage (25) to the bottom surface of the ring.

When the idler pump delivery pressure (57) compresses spring (27), pistons (24) and (32) operate.

Idler pump delivery pressure (57) is equal to the combined force of springs (28), (30), and (27). Piston (32) is in a balanced position and the angle of the cylinder is held at this point. Control piston (24) is held at a balanced position by keeping the openings slightly opened at passages (48) and (49).

Turning set screw (50) changes the compression force of spring (22) which changes the pump output flow. Increased compression force of the spring increases the pump output flow.

Negative Flow Control

g00704763

Illustration 40

(11) Negative flow control line (idler pump) (12) Port (13) Piston (14) Control piston (17) Passage (19) Bushing (21) Pin (24) Control piston (27) Spring (28) Spring (30) Spring (32) Piston (45) Idler pump (47) Top surface (48) Passage (49) Passage (51) Passage

(52) Center bypass passage (53) Negative flow control orifice (54) Main control valve (55) Spring spacer (56) Spring spacer

(57) Idler pump delivery pressure (58) Drive pump delivery pressure (59) Negative flow control pressure (60) Power shift pressure

The rate of oil flow through center bypass passage (52) in main control valve (54) is maximum when all control levers are in NEUTRAL position. When the control levers are partially moved for a leveling operation, part of idler pump oil flows to passage (51) in order to decrease the rate of oil flow in passage (52).

The oil flow in center bypass passage (52) is then restricted at negative flow control orifice (53). Negative flow control pressure (59) now develops in line (11). Negative flow control pressure (59) is dependent on the rate of oil flow through center bypass passage (52). Negative flow control pressure (59) is maximum when all control levers are in NEUTRAL position. The pump output flow is minimum.

Note:For more information on negative flow control pressure (59), see Systems Operation, “Main Control Valve”.

Negative flow control pressure (59) in line (11) enters the regulator through port (12). The force acts on the top surface of piston (13). Piston (13) tries to move down. Power shift pressure (60) acts on top surface (47) of control piston (14). Idler pump delivery pressure (57) and drive pump delivery pressure (58) act on the body of control piston (14). The combination acts on the inner surface of bushing (19). Bushing (19) tries to push up on piston (13).

Negative flow control pressure (59) acts on piston (13). The force which acts on piston (13) becomes greater than the force which acts on bushing (19). Piston (13) moves down allowing the negative flow control to function. When piston (13) moves down, bushing (19) is pushed down. Bushing (19) pushes down control piston (14). The cylinder decreases the angle of the cam which destrokes the pump. This operation is similar to the horsepower control characteristic.

All control levers are in NEUTRAL position because negative flow control pressure (59) is maximum. Control piston (14) pushes down against pin (21). Pin (21) moves control piston (24) down opening passage (48). Idler pump delivery pressure (57) or drive pump delivery pressure (58) from passage (17) pushes piston (32) upward. The movement of piston (32) compresses springs (27), (28) and (30). When the top surface of spring spacer (56) comes in contact with spring spacer (55), control piston (24) and piston (32) are pushed up by the force of idler pump delivery pressure (57) or drive pump delivery pressure (58). A pressure balance is attained. Control piston (24) remains in the balance position in order to keep the openings of passages (48) and (49) slightly open. This operation is similar to the horsepower control characteristic. The cylinder is now held at the minimum angle position for minimum pump output flow.

When the control levers are partially moved, negative flow control pressure (59) gradually decreases force on piston (13). The forces of compressed springs (27) and (30) overcome the force of the decreased negative flow control pressure (59). Therefore, control piston (24) moves up before spring spacer (56) comes in contact with spring spacer (55). During a leveling operation, the pump output flow is controlled between a minimum and a maximum. The flow depends on negative flow control pressure (59).

When piston (13) moves up due to a lower negative flow control pressure (59), the total horsepower control functions.

Pressure/Flow Characteristic

Curves

g00297449 Illustration 41 P-Q Characteristic Curves (1) Destroked position (2) Horsepower characteristics

The output characteristics of each pump depends on the following four pressures.

•

Pump output circuit pressure of top pump

•

Pump output circuit pressure of bottom pump

•

Power shift pressure

•

Negative flow control pressure

After a pump starts to operate, each pump has a set of pressure/flow characteristic curves. The pressure/flow characteristic curve represents a set of flow rates for distinct pump circuit pressures. Each point on horsepower characteristic (2) represents the respective flow rate and the respective pressure in order to maintain a constant output from the pump.

Main Control Valve

i01630775

Main Control Valve

g00847201

Hydraulic schematic (1) Stick drift reduction valve

(2) Line relief valve (stick cylinder rod end) (3) Boom drift reduction valve

(4) Line relief valve (boom cylinder head end) (5) Return port

(6) Main control valve (7) Stick regeneration valve (8) Load check valve (9) Parallel feeder passage (10) Straight travel solenoid valve (11) Right travel control valve (12) Attachment control valve (13) Bucket control valve (14) Center bypass passage (15) Boom I control valve (16) Stick II control valve (17) Relief valve (negative flow) (18) Straight travel control valve (19) Relief valve (negative flow) (20) Negative flow control orifice (21) Boom II control valve (22) Stick I control valve (23) Center bypass passage (24) Swing control valve (25) Left travel control valve (26) Load check valve (27) Boom regeneration valve

(28) Line relief valve (boom cylinder rod end) (29) Negative flow control orifice

(30) Line relief valve (stick cylinder head end) (31) Variable swing priority valve

(32) Main relief valve (33) Stick unloading valve

(34) Line relief valve (bucket cylinder rod end) (35) Line relief valve (bucket cylinder head end) (36) Parallel feeder passage

(37) Inlet port (drive pump)

(38) Negative flow control line (drive pump) (39) Inlet port (Idler pump)

(40) Negative flow control line (idler pump) (41) Drive pump

(42) Pilot pump (43) Idler pump (44) Hydraulic tank

g00689563

Illustration 43

(AR1) Right travel control valve (REVERSE TRAVEL)

(AR2) Attachment control valve (port) (AR3) Bucket control valve (BUCKET

CLOSE)

(AR4) Boom I control valve (BOOM LOWER) (AR5) Stick II control valve (STICK IN) (BR1) Right travel control valve (FORWARD

TRAVEL)

(BR2) Attachment control valve (port) (BR3) Bucket control valve (BUCKET OPEN) (BR4) Boom I control valve (BOOM RAISE) (BR5) Stick II control valve (STICK OUT) (AL1) Left travel control (REVERSE

TRAVEL)

(AL2) Swing control valve (SWING LEFT) (AL3) Stick I control valve (STICK IN) (AL4) Boom II control valve (BOOM RAISE) (BL1) Left travel control valve (FORWARD

TRAVEL)

(BL2) Swing control valve (SWING RIGHT) (BL3) Stick I control valve (STICK OUT) (aR1) Pilot port at right travel control valve

(REVERSE TRAVEL)

(aR2) Pilot port at attachment control valve (aR3) Pilot port at bucket control valve

(BUCKET CLOSE)

(aR4) Pilot port at boom I control valve (BOOM LOWER)

(aR5) Pilot port at stick II control valve (STICK IN)

(aL1) Pilot port at left travel control valve (REVERSE TRAVEL)

(aL2) Pilot port at swing control valve (SWING LEFT)

(aL3) Pilot port at stick I control valve (STICK IN)

(aL4) Pilot port at boom II control valve (BOOM RAISE)

(bR1) Pilot port at right travel control valve (FORWARD TRAVEL)

(bR2) Pilot port at attachment control valve (bR3) Pilot port at bucket control valve

(BUCKET OPEN)

(bR4) Pilot port at boom I control valve (BOOM RAISE)

(bR5) Pilot port at stick II control valve (STICK OUT)

(bL1) Pilot port at left travel control valve (FORWARD TRAVEL)

(bL2) Pilot port at swing control valve (SWING RIGHT)

(bL3) Pilot port at stick I control valve (STICK OUT)

(bL4) Pilot port at boom II control valve (STICK IN)

(DST) Drain port (straight travel control valve)

(HL) Negative flow signal pressure port (drive pump)

(HR) Negative flow signal pressure port (idler pump)

(Pi1) Pilot port (boom regeneration valve) (Pi2) Pilot port (stick regeneration valve) (Pi3) Pilot port (variable swing priority valve) (Pi4) Pilot port (straight travel solenoid valve) (R2) Return port

(R3) Return port

Introduction

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Illustration 44

(10) Straight travel solenoid valve (11) Right travel control valve (12) Attachment control valve (13) Bucket control valve (15) Boom I control valve (16) Stick II control valve (18) Straight travel control valve (21) Boom II control valve (22) Stick I control valve (24) Swing control valve (25) Left travel control valve

(28) Line relief valve (boom cylinder rod end) (30) Line relief valve (stick cylinder head end) (32) Main relief valve

(34) Line relief valve (bucket cylinder rod end) (45) Right body

(46) Left body

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Illustration 45

Main control valve (bottom view) (3) Boom drift reduction valve

(4) Line relief valve (boom cylinder head end)

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Illustration 46

Bottom view of main control valve (1) Stick drift reduction valve