SERV1852_02_TXT2.pdf

SERV1852-02August 2008

TECHNICAL PRESENTATION

320D-336D HYDRAULIC EXCAVATORS -TIER III ENGINES

PILOT HYDRAULIC SYSTEM

Service Training Meeting Guide(STMG)

GLOBAL SERVICE LEARNING

320D-336D HYDRAULIC EXCAVATORS -TIER III ENGINESPILOT HYDRAULIC SYSTEM

AUDIENCELevel II - Service personnel who understand the principles of machine systems operation,diagnostic equipment, and procedures for testing and adjusting.

CONTENTThis presentation provides an introduction and describes the components and systems operationof the 320D-336D pilot hydraulic system. Additional presentations will cover the machinewalkaround, engines, pumps and controls, main control valve group, swing system, travelsystem, and tool control systems in more detail. This presentation may be used for self-pacedand self-directed training.

OBJECTIVESAfter learning the information in this presentation, the technician will be able to:

1. identify the components and explain the operation of the 320D-336D hydraulicexcavators pilot system, and

2. diagnose problems in the pilot system.

REFERENCES320D Hydraulic Excavator Specalog AEHQ5856324D Hydraulic Excavator Specalog AEHQ5663325D Hydraulic Excavator Specalog AEHQ5665328D Hydraulic Excavator Specalog AEHQ5706330D Hydraulic Excavator Specalog AEHQ5667Machine Monitoring System - Systems Operation RENR8068Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator, and 365C & 385C Large Hydraulic Excavators SERV7032iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems" SERV2693iTIM "325C Hydraulic Excavators-Hydraulic Systems" SERV2701325D Hydraulic Schematic KENR6157

Estimated Time: 45 minutesIllustrations: 19Form: SERV1852-02Date: August 2008

2008 Caterpillar

TABLE OF CONTENTS

INTRODUCTION ........................................................................................................................5Pilot Manifold .........................................................................................................................9Hydraulic Activation Lever ..................................................................................................14Pilot Controls and Valves ....................................................................................................16

CONCLUSION...........................................................................................................................23

SERV1852-02 - 3 - Text Reference08/08 Pilot System

PREREQUISITES"Fundamentals of Mobile Hydraulics Self Study Course" TEMV3002"Fundamentals of Power Train Self Study Course" TEMV3003"Fundamentals of Electrical Systems Self Study Course" TEMV3004"Fundamentals of Engines Self Study Course" TEMV3001

NOTES

Nomenclature Change: During the fourth quarter of 2008, the 325D and 330Dnomenclature changed. The 325D became the 329D and the 330D became the 336D formost arrangements.

The exceptions are as follows:

- The nomenclature for the 325D MH and 330D MH did not change.

- The nomenclature for the 325D FM and 330D FM did not change.

- The 325D HD HW did not change into 329D HD HW. This model is being discontinued.However, the 330D HD HW changed to the 336D HD HW.


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INTRODUCTION

The oil delivered from the pilot pump performs the following main functions:

- Provides pilot oil pressure to the pilot control valves for implements, swing, and travel inorder to perform machine operations.

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

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

The pilot circuit is classified into the following circuits and each circuit performs one of theabove functions:

- pilot control valve circuit - power shift pressure system

- pressure switch circuits - straight travel valve circuit

- swing parking brake - boom priority

- swing priority - automatic travel speed change

- heavy lift setting of the main relief valve


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This section of the presentation will cover the focus on the pilot manifold, the implementjoysticks (pilot valves), and the travel pilot valves.

NOTE: In the fourth quarter of 2008, the 325D and 330D nomenclature changed. The325D became the 329D and the 330D became the 336D for most arrangements.


A gear-type pilot pump (1) provides oil flow to the pilot system. The pilot pump ismechanically connected to the drive pump.

The oil delivery from the pilot pump flows through the pilot oil filter (2) and into thecomponents in the pilot system.

Pilot relief valve (3) is located on the mounting base for the pilot oil filter. The pilot reliefvalve limits the pressure in the pilot system. The pilot relief valve setting is adjustable.

Pilot system pressure can be checked at the test port (4) on the right side of the filter base.Next to the pilot pressure test port is the hydraulic system SOS port (5).

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The filter element in the pilot oil filter removes contaminants from the pilot oil.

If the pilot oil is extremely cold or if the flow of pilot oil through filter element becomesrestricted by contaminants, the oil bypasses the filter element through the bypass relief valve.

The bypass relief valve is built into the pilot oil filter base.

The pilot oil flows from the pilot pump to inlet port. When the pressure in the pilot oil systemreaches the pressure setting of the pilot relief valve, part of the pilot oil flow is returned to thehydraulic tank. The pressure of the pilot system oil in outlet lines is equal to the pressuresetting of the pilot relief valve.


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Pilot Manifold

The pilot manifold is the same as the "300C" pilot manifold. The pilot manifold is accessibleby removing the cover plate under the machine, behind the swing bearing. The manifold islocated directly below the main control valve.

The hydraulic activation valve (1) and solenoid (2) are located in the pilot manifold along withthe swing brake solenoid (3) and the two-speed travel solenoid (4).

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Oil from the pilot pump enters the pilot manifold to be distributed to the various components ofthe machine. Some of the pilot oil flow is directed to the swing priority valve, to the two speedtravel solenoid valve, and to the straight travel solenoid valve. The rest of the pilot oil flowsthrough the check valve.

Two Speed Travel Solenoid Valve: The two speed travel solenoid valve controls oil flow tothe two-speed travel motors. In the illustration above the solenoid is energized. Pilot oil isdirected to the travel motors to shift the two displacement change valves (not shown). Whenthe displacement change valves shift, the motors will destroke for higher speed.

Check Valve: The pilot manifold also has a check valve. The check valve maintains pilotaccumulator pressure in the pilot circuit when the engine is not running. By maintaining thepilot pressure (for a limited time) when the engine is stopped, the implements can be loweredsafely to the ground.


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Pilot Accumulator: The pilot accumulator is used to release the swing brake and for loweringthe boom and stick in the event of a loss of pilot system pressure or a dead engine. The pilotaccumulator also helps to dampen pressure spikes in the pilot system, which enhances thestability of the machine control systems.

The accumulator stores pilot pressure oil for use at the main control valves. During someoperations, the pilot system needs more oil because there is insufficient flow from the pilotpump.

Implement Hydraulic Lockout Solenoid Valve and Hydraulic Activation Valve: These twovalves work together to either prevent the implement control valves and the motors from beingactivated or to allow them to be activated. In the de-energized position, no pilot oil is availableto operate the implements. Pilot oil is blocked at both valves.

When the hydraulic lockout control lever in the cab is in or moved to the LOCKED position,the plunger of the limit switch is NOT depressed by the control lever. The limit switch is in theOFF position.

When hydraulic activation control lever is in the LOCKED position, the hydraulic activationsolenoid is NOT energized.

The spool is held up by a spring. The spool blocks the pilot supply oil from going to the pilotvalves. The spool also opens a passage to drain from the pilot valves to the tank.

In the locked position, if the joysticks are moved, the cylinders and the motors cannot beactivated.

Swing Brake Solenoid Valve: The swing brake solenoid valve energizes to release the springapplied, hydraulically-released, wet disc swing brake. The swing brake is automaticallyreleased when any joystick function is performed by the operator.

When the swing brake solenoid valve de-energized the swing brake is engaged by springs.


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When the hydraulic lockout control lever in the cab is placed in the UNLOCKED position, thelimit switch closes the circuit path to the lockout solenoid valve. The lockout solenoid valve isenergized.

When the implement hydraulic lockout solenoid valve is energized, pilot oil is directed to movethe hydraulic activation valve down. Pilot oil flows through the hydraulic activation valve tothe swing brake solenoid valve, the left and right joysticks (pilot valves), and the travel pilotvalves. The hydraulic activation valve also supplies pilot oil for the heavy lift solenoid valve.

When an implement is activated the swing brake solenoid is energized by the Machine ECM.Pilot oil is directed through the swing brake solenoid valve to release the swing park brake inthe swing motor group.


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The pilot accumulator (arrow) provides pressure oil to the pilot system when the pilot pumpflow is low or the pilot pump has stopped.

Low 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 controlvalves is stopped.

- Combined implement, swing, and travel operations.

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Hydraulic Activation Lever

The hydraulic lockout lever (arrow) is shown in the LOCKED position.

The engine will not start unless the hydraulic activation lever (3) is in the LOCKED position.

Raise the lever activation lever to the UNLOCKED position to energize the implementhydraulic lockout solenoid valve to allow the operator to move the implements.

If the machine is running, the operator can lockout the implement controls by returning thelever to the LOCKED position.

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A limit switch and plunger are located on a bracket with the hydraulic lockout lever.

When the hydraulic activation control lever is moved forward, the lever pushes the plungerdown to activate the limit switch.

When the hydraulic lockout control lever is shifted to the rear to the LOCKED position, theimplement lockout solenoid valve is NOT energized, so the hydraulic activation valve doesNOT shift to direct pilot oil to the pilot control valves.

The joysticks and/or travel pedals can NOT shift a control valve in the main control valvegroup when the hydraulic activation lever is in the LOCKED position.

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Pilot Controls and Valves

Pilot controls in the cab include:

- left (1) and right (2) travel pedals

- left (3) and right (4) travel levers

- auxiliary foot switch (5) (attachment)

- straight travel (6) (attachment)

- left joystick (7) to control the swing and stick (SAE excavator pattern)

- right joystick (8) to control the bucket and boom (SAE excavator pattern)

- foot rest (9 and 10)

The joysticks shown above are equipped with full electronic control for the tool control system.

NOTE: The switch for one touch low idle is on the right joystick. If the machine isequipped with a magnet, the trigger switch on the front of the right joystick turns themagnet on, while the trigger switch on the front of the left joystick turns the magnet off.


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The resolver block (1) is located under the cab. The resolver block provides a junction betweenthe pilot lines to the joysticks and the pilot lines to the main control valve group as well assensing when an an implement or the swing is activated.

The resolver network in the block, directs the pilot signal pressure to the swing/implementpressure switch (2) for Automatic Engine Control (AEC).

Two travel pressure switches (not shown) and the swing/implement pressure switch (2) areactivated by pilot pressure oil. The switches close at 490 49 kPa (71 7 psi) and open at 290 0 kPa (42 0 psi).

The pressure switches are inputs to the Machine ECM. The Machine ECM uses these inputs todetermine when a hydraulic function has been activated.

If Automatic Engine Control (AEC)/one touch low idle is activated and the machine is at lowidle the Machine ECM and will increase the engine speed to the current speed dial setting.

When only the swing/implement pressure switch is activated, the Machine ECM will release theswing brake. When all three pressure switches are activated at the same time, the MachineECM will energize the straight travel solenoid.

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When one or more of the joysticks are shifted, resolvers in the block direct the highest pilot oilpressure to the the swing/implement pressure switch.

The Machine ECM will cause the engine to increase rpm to match the speed dial position.


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When the pilot joystick lever is shifted, the joystick contacts the plunger and pushes the plungerdown against its spring. The plunger will contact the spool and move the spool down againstits spring. Depending on how far the joystick lever is moved, determines how far the spoolmoves.

As the spool moves down, the spool will close off the drain passage for the oil to the controlvalve and meter pilot pressure oil to the control valve to cause the control spool (not shown) toshift. The greater the pilot oil flow to the control spool, the greater the control spool travel.

As pressure increases in the pilot line to the control valve, the pressure moves the spool up to abalance position against the spool and metering springs to maintain a constant pilot pressure inthe pilot line. This action will maintain the control spool position in the control valve until thejoystick is moved.

In summary, once the pilot joystick is shifted, the pilot valve becomes a pressure reducing valvewhich maintains a downstream pressure equal to the spring forces above the spool.

When the joystick is released, the joystick will return to the NEUTRAL position due to theforce of the return spring moving the spool up. When this action occurs, the pilot oil is blockedby the spool from flowing to the control valve to shift the control spool. Pilot oil at the controlspool is drained to the tank past the spool.


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The travel pilot control valve operates similar as the implement pilot valves.

Depending on how far the the travel pedal or lever is moved, will determine the amount ofpilot oil directed to the respective travel control valve.

A dampening function is built into the travel pilot control valve which allows the operationalspeed of the travel lever/pedal to respond only to intended movements of the operators foot.The dampening function also prevents vibration or harshness when releasing the travel pedal.

When the travel lever/pedal is moved suddenly from the NEUTRAL position, the rod is pusheddownward. The rod moves the dampening piston downward. The hydraulic oil below thedampening piston is pressurized.

An orifice check valve allows the trapped hydraulic oil below the dampening piston togradually flow into into the metering spring chamber, which is open to the tank. The gradualflow of oil through the orifice check valve provides the dampening function.


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The attachment circuits are controlled by proportional solenoids valves. These valves are alsocalled proportional reducing valve or PRV. The valves receive PWM signals from the MachineECM to shift energize the solenoid. The amount of current sent from the Machine ECM willdetermine how far the solenoid spool shifts.

As the solenoid spool shifts, pilot oil is metered from one of the energized solenoid valves tothe attachment circuit to control the position of the control spool for the attachment.

When the solenoid is de-energized the solenoid spool shifts to block the pilot oil. The pilotsupply passage to the control spool is open to the tank.

NOTE: The solenoid valves also act as variable pressure reducing valves. Instead ofusing a spring to control the downstream pressure, the current is varied to the solenoidto control the downstream pressure to the control spool. For a fixed current the pilotpressure to the spool is maintained as it was for the joysticks.


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When the joysticks are operated, the pilot control valves send pilot pump oil through the pilotlines to the pilot ports (arrows) at the main control valve group in order to shift the spools in themain control valve.

Additional pilot lines are located below the main control to shift the control spools in theopposite direction.

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Pilot oil enters a control valve from either end to shift the main control spool.

The control spool will shift in proportion to the amount of pilot oil sent to the control spoolfrom the a pilot valve or solenoid.

For some circuits, proportional solenoid valves are used to direct pilot oil to shift the controlspool.


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CONCLUSION

This presentation has provided information for the Caterpillar 320D-336D HydraulicExcavators.

This presentation covered the pilot control system and pilot control valves.

Additional presentations are available for each system used on these machines.

When used in conjunction with the service manual, the information in this package shouldpermit the technician to do a thorough job of analyzing a problem in these systems.

For service repairs, adjustments, and maintenance, always refer to the Operation andMaintenance Manual, Service Manuals, and other related service publications.

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SERV1852_02_TXT2.pdf

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