Hệ thống thủy lực máy đào CATERPILLAR SERIE D - P4

SERV1852-02
August 2008

GLOBAL SERVICE LEARNING
TECHNICAL PRESENTATION

320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES
PILOT HYDRAULIC SYSTEM

Service Training Meeting Guide
(STMG)


320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES
PILOT HYDRAULIC SYSTEM
AUDIENCE
Level II - Service personnel who understand the principles of machine systems operation,
diagnostic equipment, and procedures for testing and adjusting.

CONTENT
This presentation provides an introduction and describes the components and systems operation
of the 320D-336D pilot hydraulic system. Additional presentations will cover the machine
walkaround, engines, pumps and controls, main control valve group, swing system, travel
system, and tool control systems in more detail. This presentation may be used for self-paced
and self-directed training.

OBJECTIVES
After learning the information in this presentation, the technician will be able to:
1. identify the components and explain the operation of the 320D-336D hydraulic
excavators pilot system, and
2. diagnose problems in the pilot system.

REFERENCES
320D Hydraulic Excavator Specalog
324D Hydraulic Excavator Specalog
325D Hydraulic Excavator Specalog
328D Hydraulic Excavator Specalog
330D Hydraulic Excavator Specalog
Machine Monitoring System - Systems Operation
Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator,
and 365C & 385C Large Hydraulic Excavators
iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems"
iTIM "325C Hydraulic Excavators-Hydraulic Systems"
325D Hydraulic Schematic

Estimated Time: 45 minutes
Illustrations: 19
Form: SERV1852-02
Date: August 2008
© 2008 Caterpillar

AEHQ5856
AEHQ5663
AEHQ5665
AEHQ5706
AEHQ5667
RENR8068
SERV7032
SERV2693
SERV2701
KENR6157

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Text Reference
Pilot System

TABLE OF CONTENTS
INTRODUCTION ........................................................................................................................5
Pilot Manifold .........................................................................................................................9
Hydraulic Activation Lever ..................................................................................................14
Pilot Controls and Valves ....................................................................................................16
CONCLUSION...........................................................................................................................23


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Pilot System

PREREQUISITES
"Fundamentals of Mobile Hydraulics Self Study Course"
"Fundamentals of Power Train Self Study Course"
"Fundamentals of Electrical Systems Self Study Course"

"Fundamentals of Engines Self Study Course"

TEMV3002
TEMV3003
TEMV3004
TEMV3001

NOTES
Nomenclature Change: During the fourth quarter of 2008, the 325D and 330D
nomenclature changed. The 325D became the 329D and the 330D became the 336D for
most 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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Text Reference
Pilot System

PILOT HYDRAULIC SYSTEM
Stick Cylinder
Bucket Cylinder
Swing Motor

Main Control Valve Group

Pilot
Control
Valves

Priority
Valves

Pilot Manifold

Pilot
Pump
Fan
Motor

Boom Cylinders

Travel Motors

Main
Hydraulic
Pumps

M
Fan
Pump

Tank

The Fan Motor and Pump are only used on the 330D and 336E

1

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 in
order 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 the
above 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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Pilot System

This section of the presentation will cover the focus on the pilot manifold, the implement
joysticks (pilot valves), and the travel pilot valves.
NOTE: In the fourth quarter of 2008, the 325D and 330D nomenclature changed. The
325D became the 329D and the 330D became the 336D for most arrangements.


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Text Reference
Pilot System

3
4

1

5

2

2

A gear-type pilot pump (1) provides oil flow to the pilot system. The pilot pump is
mechanically connected to the drive pump.
The oil delivery from the pilot pump flows through the pilot oil filter (2) and into the
components in the pilot system.
Pilot relief valve (3) 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.
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 S•O•S port (5).


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Pilot System

PILOT SYSTEM FILTER
FILTER RELIEF VALVE
AND
PILOT SYSTEM
RELIEF VALVE
Pilot System
Relief Valve

Pilot Filter
Relief Valve
Pilot System
Filter
Pilot System
Relief Valve

Pilot Filter
Relief Valve

Pilot System
Filter

SOS

3

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 becomes
restricted 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 system
reaches the pressure setting of the pilot relief valve, part of the pilot oil flow is returned to the
hydraulic tank. The pressure of the pilot system oil in outlet lines is equal to the pressure
setting of the pilot relief valve.


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Pilot System

4
3
1

2

4

Pilot Manifold
The pilot manifold is the same as the "300C" pilot manifold. The pilot manifold is accessible
by removing the cover plate under the machine, behind the swing bearing. The manifold is
located directly below the main control valve.
The hydraulic activation valve (1) and solenoid (2) are located in the pilot manifold along with
the swing brake solenoid (3) and the two-speed travel solenoid (4).


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Pilot System

PILOT MANIFOLD

LOCKED - HIGH SPEED TRAVEL
SWING BRAKE ENGAGED
Straight
Travel
Solenoid

Heavy Lift
Solenoid

Pilot
Pump

Hydraulic
Activation
Valve

Pilot
Valves

Tank

Hydraulic
Activation Valve

Travel
Motors

Pilot Pump
Two Speed

Travel
Solenoid

Swing
Brake
Solenoid
Hydraulic
Activation
Valve

Swing
Priority
Valve

Implement
Hydraulic
Lockout
Solenoid

Check
Valve

Swing
Brake

5

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

through the check valve.
Two Speed Travel Solenoid Valve: The two speed travel solenoid valve controls oil flow to
the two-speed travel motors. In the illustration above the solenoid is energized. Pilot oil is
directed to the travel motors to shift the two displacement change valves (not shown). When
the 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 pilot
accumulator pressure in the pilot circuit when the engine is not running. By maintaining the
pilot pressure (for a limited time) when the engine is stopped, the implements can be lowered
safely to the ground.


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Text Reference
Pilot System

Pilot Accumulator: The pilot accumulator is used to release the swing brake and for lowering
the boom and stick in the event of a loss of pilot system pressure or a dead engine. The pilot
accumulator also helps to dampen pressure spikes in the pilot system, which enhances the
stability of the machine control systems.
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.
Implement Hydraulic Lockout Solenoid Valve and Hydraulic Activation Valve: These two
valves work together to either prevent the implement control valves and the motors from being
activated or to allow them to be activated. In the de-energized position, no pilot oil is available
to 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 the
OFF position.
When hydraulic activation control lever is in the LOCKED position, the hydraulic activation
solenoid is NOT energized.
The spool is held up by a spring. The spool blocks the pilot supply oil from going to the pilot
valves. 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 be
activated.
Swing Brake Solenoid Valve: The swing brake solenoid valve energizes to release the spring
applied, hydraulically-released, wet disc swing brake. The swing brake is automatically
released 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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Text Reference
Pilot System
Implement Hydraulic
Lockout Solenoid

PILOT MANIFOLD

UNLOCKED - SWING BRAKE RELEASED

Tank

Hydraulic
Activation
Valve

Straight
Travel
Solenoid

Heavy Lift
Solenoid

Pilot
Pump

Hydraulic
Activation Valve

Pilot
Valves

Pilot Pump

Travel
Motors
Two Speed
Travel
Solenoid

Swing
Brake

Solenoid
Hydraulic
Activation
Valve

Swing
Priority
Valve

Implement
Hydraulic
Lockout
Solenoid

Check
Valve

Swing
Brake

6

When the hydraulic lockout control lever in the cab is placed in the UNLOCKED position, the
limit switch closes the circuit path to the lockout solenoid valve. The lockout solenoid valve is
energized.
When the implement hydraulic lockout solenoid valve is energized, pilot oil is directed to move
the hydraulic activation valve down. Pilot oil flows through the hydraulic activation valve to
the swing brake solenoid valve, the left and right joysticks (pilot valves), and the travel pilot
valves. 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 in
the swing motor group.


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Text Reference
Pilot System

7

The pilot accumulator (arrow) provides pressure oil to the pilot system when the pilot pump
flow 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 control
valves is stopped.
- Combined implement, swing, and travel operations.


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Text Reference
Pilot System

8

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 implement
hydraulic 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 the
lever to the LOCKED position.


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Text Reference
Pilot System

HYDRAULIC
ACTIVATION LEVER

Hydraulic Activation
Lever

Lever

Plunger

Limit Switch

9

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 plunger
down to activate the limit switch.
When the hydraulic lockout control lever is shifted to the rear to the LOCKED position, the
implement lockout solenoid valve is NOT energized, so the hydraulic activation valve does
NOT 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 valve
group when the hydraulic activation lever is in the LOCKED position.


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Text Reference
Pilot System

4

3

1

8
6
2

5
7

10

9

10

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 is
equipped with a magnet, the trigger switch on the front of the right joystick turns the
magnet on, while the trigger switch on the front of the left joystick turns the magnet off.


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Text Reference
Pilot System

1

2

11

The resolver block (1) is located under the cab. The resolver block provides a junction between
the pilot lines to the joysticks and the pilot lines to the main control valve group as well as
sensing when an an implement or the swing is activated.
The resolver network in the block, directs the pilot signal pressure to the swing/implement
pressure switch (2) for Automatic Engine Control (AEC).
Two travel pressure switches (not shown) and the swing/implement pressure switch (2) are
activated 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 to
determine when a hydraulic function has been activated.
If Automatic Engine Control (AEC)/one touch low idle is activated and the machine is at low
idle 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 the
swing brake. When all three pressure switches are activated at the same time, the Machine
ECM will energize the straight travel solenoid.


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Text Reference
Pilot System

Travel Pilot Valves

Pilot Manifold
Travel Pilot Valves

Stick

Bucket

Swing

OUT

IN

R

L

OPEN

Boom

CLOSE

aR4

DOWN

UP

Resolver
Block

Swing/Implement
Pressure
Switch

aR3

IMPLEMENT PILOT
JOYSTICKS

bR3

bR4

bL3

bL2

bL4

aL2

12

When one or more of the joysticks are shifted, resolvers in the block direct the highest pilot oil
pressure 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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Text Reference
Pilot System

PILOT CONTROL VALVE
SECTION A-A

Pilot
Pilot
Manifold Manifold

Joystick
Plate
Plunger
Metering
Spring
Seat
Port B

Port A

Return
Spring

Return
Chamber

A

Spool

Supply
Pilot Oil

A

Port A

Port B

13

When the pilot joystick lever is shifted, the joystick contacts the plunger and pushes the plunger
down against its spring. The plunger will contact the spool and move the spool down against
its spring. Depending on how far the joystick lever is moved, determines how far the spool
moves.
As the spool moves down, the spool will close off the drain passage for the oil to the control
valve and meter pilot pressure oil to the control valve to cause the control spool (not shown) to
shift. 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 a

balance position against the spool and metering springs to maintain a constant pilot pressure in
the pilot line. This action will maintain the control spool position in the control valve until the
joystick is moved.
In summary, once the pilot joystick is shifted, the pilot valve becomes a pressure reducing valve
which 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 the
force of the return spring moving the spool up. When this action occurs, the pilot oil is blocked
by the spool from flowing to the control valve to shift the control spool. Pilot oil at the control
spool is drained to the tank past the spool.


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Pilot System

TRAVEL PILOT CONTROL VALVE
Pedal

Rod

Orifice
Check
Valve

Dampening
Piston

Dampening
Piston

Pilot Supply

Left

Right

Tank
Metering
Spring

Spool

Return
Spring

Pilot
Supply

REV

FWD
aL1

bL1

FWD

bR1

Travel Pressure
Switch (AEC)
Travel
Valve

REV
aR1
Resolver

Travel
Valve

14

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 of
pilot oil directed to the respective travel control valve.
A dampening function is built into the travel pilot control valve which allows the operational
speed 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 pushed
downward. The rod moves the dampening piston downward. The hydraulic oil below the
dampening piston is pressurized.
An orifice check valve allows the trapped hydraulic oil below the dampening piston to
gradually flow into into the metering spring chamber, which is open to the tank. The gradual
flow of oil through the orifice check valve provides the dampening function.

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Pilot System

PWM SOLENOID VALVE
PWM SIGNAL DECREASE

PWM SIGNAL INCREASE

Solenoid

Plunger
Spring

Spring

Tank

Tank

Control Spool

Control Spool

Pilot Oil

Pilot Oil

15

The attachment circuits are controlled by proportional solenoids valves. These valves are also
called proportional reducing valve or PRV. The valves receive PWM signals from the Machine
ECM to shift energize the solenoid. The amount of current sent from the Machine ECM will
determine how far the solenoid spool shifts.
As the solenoid spool shifts, pilot oil is metered from one of the energized solenoid valves to
the 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 pilot
supply passage to the control spool is open to the tank.
NOTE: The solenoid valves also act as variable pressure reducing valves. Instead of
using a spring to control the downstream pressure, the current is varied to the solenoid
to control the downstream pressure to the control spool. For a fixed current the pilot
pressure to the spool is maintained as it was for the joysticks.


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Pilot System

16

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

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


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Load Check
Valve
Parallel Feeder
Passage

Port A

Port B

Text Reference
Pilot System

CONTROL VALVE
FULL SHIFT

Line Relief and
Makeup Valve

Pilot Valve
or

Solenoid

Passage to
Next Valve
Center Bypass
Passage

17

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 spool
from the a pilot valve or solenoid.
For some circuits, proportional solenoid valves are used to direct pilot oil to shift the control
spool.


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Pilot System

18

CONCLUSION
This presentation has provided information for the Caterpillar 320D-336D Hydraulic
Excavators.
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 should
permit 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 and
Maintenance Manual, Service Manuals, and other related service publications.