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Caterpillar hydraulic excavators serie D

320D336D HYDRAULIC EXCAVATORS TIER III ENGINES

This presentation provides an introduction and describes the components and systems operation

of the 320D - 336D hydraulic excavator Travel Systems Additional presentations will coverthe machine walkaround, engines, pilot system, pumps and controls, main control valve group,swing 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 correct operation of the Travel Systems on the 320D-336D hydraulic

excavators, and

2 diagnose problems in the Travel Systems

REFERENCES

Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator,

iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems" SERV2693iTIM "325C Hydraulic Excavators-Hydraulic Systems" SERV2701

Estimated Time: 1 Hour

Illustrations: 30

Form: SERV1852-02

Date: August 2008

© 2008 Caterpillar

TABLE OF CONTENTS

INTRODUCTION 5

TRAVEL SYSTEMS COMPONENTS 6

320D-329D TRAVEL SYSTEMS OPERATION 13

Travel Motor 13

Travel Parking Brake and .20

320D Travel Brake Valve 22

Makeup Operation 28

330D/336D TRAVEL SYSTEMS OPERATION 29

Travel Motor 29

Travel Parking Brake .36

321D-336D Travel Brake Valve 38

Makeup Operation

STRAIGHT TRAVEL VALVE 45

SWIVEL 53

FINAL DRIVE 55

CONCLUSION 54

"Fundamentals of Mobile Hydraulics Self Study Course" TEMV3002

"Fundamentals of Power Train Self Study Course" TEMV3003

"Fundamentals of Electrical Systems Self Study Course" TEMV3004

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.

- travel pilot valves

- left and right travel control valves

- straight travel valve and solenoid

- two travel motors

- travel park brake

- two speed travel solenoid valve

NOTE: The 330D and 336D travel motor is slightly different in operation than the

travel motors used in the smaller machines The 330D and 336D travel motor will be covered in a revision to this section.

Main Hydraulic Pumps M

Pilot Pump Fan

Motor

Pilot Manifold

Main Control Valve Group

Fan Pump Tank

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

TRAVEL SYSTEMS

TRAVEL SYSTEMS COMPONENTS

The idler pump and drive pump supplies oil flow to the travel control valve circuit, whichcontrols pump flow to the two travel motors

When the travel control valves are in NEUTRAL, pump supply oil from the pumps flowsthrough the center bypass passage in the travel valves through all other control valves (notshown) to the NFC valves (also not shown) The return oil from the pumps through the bypasspassages (neutral envelopes of the valve) creates NFC signals used to destroke the pumps.Pilot oil is available at the travel speed solenoid valve

Since the implement hydraulic lockout solenoid has been energized, the hydraulic activationvalve has shifted Pilot oil is directed to the travel pilot valves

TRAVEL HYDRAULIC SYSTEM

NEUTRAL

Travel Speed Solenoid Valve

Swing Brake Solenoid Hydraulic Activation Valve Pilot

Manifold

Implement Hydraulic Lockout Solenoid

Swivel

Straight Travel Control Valve

Right Travel Valve Main

Relief Valve

Straight Travel Solenoid

Left Travel Valve

M Drive

Idler Pump Pilot Pump

Travel Pilot Valves

REV FWD FWD REV

AEC Right Travel

Motor Left Travel Motor

Some of the major components of the Travel Systems include:

Two Speed Travel Solenoid Valve: This solenoid valve is controlled by the Machine ECM.

The valve controls the position of the displacement change valve in each motor to select slow

or fast travel speed

Travel Pilot Valves: The valves direct pilot oil to shift the travel valves in the main control

valve group The pilot valves are shifted by either pedals or levers

Straight travel control valve and solenoid: When both travel control valves are shifted or

one travel valve and an implement/swing circuit are activated, the solenoid is energized toprovide flow priority to the travel motors

Slow Return Check Valve: The back pressure created by the slow return check valve ensures

that makeup oil is present at the travel motor and the various makeup valves in the hydraulicsystem

Left travel valve (1) and right travel valve (2) are used to control the travel motors The

straight travel valve (3) provides flow priority for the Travel Systems during a travel condition

The slow return check valve is part of the slow return check valve and cooler bypass

Each track is driven by a travel motor (1) A counterbalance valve (2) prevents overspeed whilethe machine is traveling downhill, prevents shocks to the system when travel is stopped, andhelps to prevent motor cavitation.

Crossover relief valves (3 & 4) are used to protect the travel motor from pressure spikes The upper supply line (5) directs supply oil to the motor for reverse travel, while the lowersupply line (6) directs supply oil to the motor for forward travel

The final drive is composed of a three-stage planetary gear reduction to reduce the motor speed

to drive the track Fill (8) and drain (9) plugs are in the outer cover

4

5

6

8 9

The two speed travel solenoid valve (1) is part of the pilot manifold The manifold is locateddirectly below the main control valve

The hydraulic activation solenoid (2) must energize to shift the hydraulic activation valve (3)

If the hydraulic activation valve is not shifted there is no pilot oil to the the travel pilot valves

3 1

2

When the two-speed travel soft switch (1) is located on the soft switch panel (2)

When the two-speed travel switch is pushed , the travel speed is toggled between the Slow andFast Speed Modes

- The rabbit indicator is for fast or high speed

- The tortoise indicator is for slow or low speed

The Fast Speed Mode is also called the Automatic Mode The Machine ECM senses the drivepressure and will automatically change the travel speed from the Fast Speed Mode to the SlowSpeed Mode, when the drive pressure exceeds a predetermined limit

For instance, by putting the machine automatically into the Slow Speed Mode, more torque isavailable for climbing slopes

Once the drive pressure drops again below the predetermined limit, the Machine ECM willautomatically return the machine to the Fast Speed Mode

1

2

The travel pilot control valve operates similar as the implement pilot valves (joysticks)

Depending on how far the travel pedal or lever is moved will determine the amount of pilot oildirected 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 the vibration that occurs when the travel lever/pedal isreleased

When the travel lever/pedal is moved from the NEUTRAL position, the rod is pushed

downward 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 to

gradually flow 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

Pilot Supply

Dampening Piston

Travel Pressure

TRAVEL PILOT CONTROL VALVE

Pedal

Pilot Supply

Due to the travel valves being the first control valves to receive supply oil, the valves receivesupply oil directly off of the center bypass passage through the feeder passage and into thebridge passage The travel valve blocks the oil in the bridge passage.

Since the travel valve is not shifted, supply oil through the center bypass passage flows tothrough main valve group Some of this supply oil is used to destroke one of the hydraulicpumps

NOTE: The illustration above is for the left travel control valve only The right travel

control valve should operate similarly, but the drawings shown in the Parts Manual and other publications makes the valve appear to function differently.

Feeder

Passage

Center Bypass Passage

NFC Signal

Bridge Passage

Travel Spool

LEFT TRAVEL CONTROL VALVE

NEUTRAL

NFC Signal

Bridge Passage

320D-329D TRAVEL SYSTEMS OPERATION

Travel Motor

Some of the major components of the travel motor include:

Crossover Relief Valves: These valves dampen pressure spikes in the Travel Systems

whenever the travel is stopped The valves also prevent or reduce travel motor cavitation

Brake Pilot Valve: This valve controls the parking brake Some of the supply oil is directed

to the brake pilot valve to release the park brake for machine travel The valve also providesfor a gradual engagement of the parking brake when travel is returned to NEUTRAL

Counterbalance Valve: This valve prevents overspeed while the machine is traveling downhill,

prevents shocks to the system when travel is stopped, and helps to prevent motor cavitation

In NEUTRAL the counterbalance valve blocks the oil in the passages to the motor to preventthe motor from rotating

Slow Return Check Valve

U

Output Pressure Sensor

Power Shift PRV Solenoid Valve

Machine ECM

Displacement Change Valve

Pilot Pump

Two Speed Travel Solenoid Valve

Parking Brake Actuator

Brake Pilot Valve

Two Speed Travel Switch

320D - 329D LEFT TRAVEL MOTOR

Min

Displacement Change Valve: The displacement change valve is controlled by the two speed

travel solenoid valves The displacement change valve controls the supply oil to shift one ofthe motor actuators

Motor Actuator Pistons: Two actuators are used to control the angle of the motor swashplate.

If the maximum actuator is shifted, the machine is in the Slow Speed Mode for travel If theminimum actuator is shifted, then the machine is in the Fast Speed Mode for travel

03/06

Output Pressure Sensor

Power Shift PRV Solenoid Valve

Machine ECM

Displacement Change Valve

Pilot Pump

Two Speed Travel Solenoid Valve

Parking Brake Actuator

Brake Pilot Valve

Two Speed Travel Switch

320D - 329D LEFT TRAVEL MOTOR

Min

The travel valves in the main control valve group direct oil to and from the motors.

Parking Brake Piston

Separator Plates and Friction Disks Piston

Piston and Barrel Assembly

Max Min

Min Actuator

Piston

Spring

Displacement Change Valve

DISPLACEMENT CHANGE VALVE

MAXIMUM ANGLE - SLOW SPEED

Left Drive Loop Right Drive Loop

The Machine ECM receives feedback from the output pressure sensor If the drive pressure istoo high, the Machine ECM will de-energize the two speed travel valve to put the machine intothe Slow Speed Mode.

With the two speed travel valve de-energized, the displacement change valve moves back to theright and directs supply oil to the maximum angle actuator and drains the oil to the minimumangle actuator to upstroke the motor for slower speed and higher torque

As the drive pressure decreases the Machine ECM will automatically return the machine to theFast Speed Mode

Crossover Relief Valves

Displacement Change Valve

Parking Brake Actuator

Brake Pilot Valve

Counterbalance

Valve

Machine ECM Pilot

Pump

Two Speed Travel Solenoid Valve

Two Speed Travel Switch

320D - 329D LEFT TRAVEL MOTOR

FAST SPEED

Slow Return Check Valve

Travel Valve

Actuator Max Min

Pilot Pump

U

Output Pressure Sensor

Power Shift PRV Solenoid Valve

When the displacement change valve shifts due to the two speed travel solenoid being

energized, the displacement change valve sends some of the supply oil to the minimum angleactuator piston to decrease the swashplate angle

With a decreased swashplate angle, the motor pistons displace less flow as the piston and barrelassembly rotate The motor now turns faster resulting in higher machine speed, with less torquethan at low speed

Minimum Angle Actuator Piston Max

Min

When the two speed travel solenoid valve is energized, pilot oil is directed to the displacementchange valve

The displacement change valve shifts and directs some of the supply oil to the minimum

actuator piston on the left to decrease the swashplate angle

The maximum actuator piston is open to the tank through the displacement change valve

Left Drive Loop Right Drive Loop

Displacement Change Valve

DISPLACEMENT CHANGE VALVE

MINIMUM ANGLE - FAST SPEED

Two Speed Travel

Solenoid Valve

Pilot

Oil

Piston Piston Chamber

Swashplate

When both travel levers or pedals are shifted and at least one of the implements or the swing isselected, both travel pressure switches (AEC) and the implement pressure switch close TheMachine ECM then will energize the straight travel solenoid valve

When the straight travel valve shifts all of the drive pump flow is directed equally to the travelcontrol valves

The idler pump flow is directed into the parallel feeder passages and to the activated implementcircuit In the illustration above the bucket has been shifted to close

At the travel motors, the counterbalance valves shift and direct drive pump supply oil to themotors At the same time some of the supply oil is used to release the parking brake

Because the travel speed solenoid valve has been energized, the travel motor displacement ischanged to upstroke the motors to provide slow speed Return oil from the motors flows backpast the counterbalance valves and the travel valves to the tank

NOTE: The straight travel solenoid valve is only energized when both travel pressure

switches are closed and the implement pressure switch is closed at the same time.

320D-329D TRAVEL HYDRAULIC SYSTEM

FORWARD TRAVEL - FAST SPEED STRAIGHT TRAVEL - BUCKET CLOSE

Pilot

Manifold

Implement Hydraulic Lockout Solenoid

Swivel

Left Travel Motor

Right Travel

Motor

Straight Travel Control Valve

Right Travel Valve

Main Relief Valve

Straight Travel Solenoid

Left Travel Valve

M Drive

Idler Pump Pilot Pump

Travel Pilot Valves

REV FWD FWD REV

AEC

Bucket Valve

Bucket Cylinder

Bucket Pilot Valve AEC

Pilot Oil

Hydraulic Activation Valve

Travel Parking Brake

The travel parking brake is located in the travel motor The travel parking brake consists of thefollowing components: the brake spring, the brake piston, the separator plates, and the frictionplates The friction plates are splined to the cylinder barrel The separator plates are splined tothe motor housing

When the travel pedals or levers are moved from the NEUTRAL position, supply oil from thepump flows to the inlet port of the travel motor from the travel control valve in the main controlvalve group

A portion of the supply oil enters the motor and unseats the brake pilot check valve The oilthen flows to the brake piston As pressure builds in the brake piston, the piston moves to theleft against the brake spring

The separator plates and friction plates are no longer pressed together and the motor is able torotate

Drive

Brake Spring

Brake Piston

Piston Guide

Separator Plate

Friction Plate Barrel

Check Valve

Brake Piston

Piston Guide

Separator Plate

Friction Plate Barrel

320D Travel Brake Valve

The travel brake valve consists of the counterbalance valve, two check valves, and two

crossover relief valves The orifice check valves are internal to the counterbalance spool

In NEUTRAL, the counterbalance valves block the passages to the motor The check valvesseat The passages from the travel valve are open to the tank

NOTE: The travel brake valve for the 321D-329D is covered later in this presentation.

These machines use the same brake valve as the 330D/336D.

A A

Crossover Relief Valve

Check Valve

Orifice Check

Valve

Travel Valve

Counterbalance Valve

Parking Brake

Parking

Brake

Motor Motor

320D TRAVEL BRAKE VALVE

NEUTRAL

Section A-A Check Valve

During normal travel, supply oil from the travel control valve enters the travel brake valve andflows to the counterbalance valve

Some of the supply oil flows through the orifice check valve to the right end to shift the

counterbalance valve to the left As the counterbalance initially shifts to the left, some of thesupply oil is used to release the parking brake

As the counterbalance continues to move to the left, a return passage from the motor is opened

The supply pressure unseats one of the check valves and flows past the check valve to themotor Return oil from the motor flows around the counterbalance valve, to the travel controlvalve, and back to the tank The check valve (section A-A) on the return side remains seated

At the beginning of travel, one of the crossover relief valves will open to dampen the shock ofstarting to travel

NOTE: The travel brake valve shown is from the 320D and the "C" Series For the

325D-336D, the valve is functionally the same The two check valves shown are inside the counterbalance valve along with the orifice check valve.

A A

Crossover Relief Valve

Check Valve

Orifice Check

Valve

Travel Valve

Counterbalance Valve

Parking Brake

Parking

Brake

Motor Motor

320D TRAVEL BRAKE VALVE

TRAVEL

Section A-A

B B

reduced motor cavitation.

One of the crossover reliefs valve may open to send the high pressure return oil into the supplyside to help prevent motor cavitation

Section A-A

Check Valve

A A

320D TRAVEL BRAKE VALVE

COUNTERBALANCE

Check Valve

Orifice Check

Valve

Travel Valve

Counterbalance Valve

Parking Brake

Crossover Relief Valve

Parking

Brake

Motor Motor

Section B-B Check Valve

B B

When the travel pedals/levers are returned to NEUTRAL, the supply oil is blocked by the travelcontrol valve

The pressure drops in the spring chamber on one end of the counterbalance valve The

counterbalance shifts to restrict the return oil

The crossover relief valve opens to dampen the shock of the stop and send some of the highpressure oil in the return passage to the supply passage to prevent motor cavitation

A A

320D TRAVEL BRAKE VALVE

STOPPING

Check Valve

Orifice Check

Valve

Travel Valve

Counterbalance Valve

Parking Brake

Crossover Relief Valve

Parking

Brake

Motor Motor

Section A-A

B B