Hydrostatic.pdf

8/10/2019 Hydrostatic.pdf

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Power Train IICOURSE OVERVIEW

Overview

This course will discuss the methods for transferring power. The

course will begin with machines that are driven with hydraulic

components. This subject is covered in detail in the Hydraulics

courses, so only brief mention is made of them in this course.

This rest of the course will concentrate on the mechanical power

train components that were not covered in Power Train I. These

components include differentials, brakes, final drives and

undercarriage.

Torque converters and transmissions are not part of this course.

Class time is divided between classroom and hands on activities,

such as disassembly, assembly, troubleshooting, testing and

adjusting.

The content of this course should be treated as general information

for power train components in all Caterpillar machines.

The following course curriculum has been developed using the

reference materials and tooling listed on the following pages.

Substitute materials and tooling may be used at the discretion of the

instructor.

Course exercises and lab assignments may require modification(s) if

substitute materials and tooling are used.

2000 Caterpillar Inc.

Revision August 1, 2000Property of Caterpillar Inc.


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Table Of ContentsUnit 1: Hydraulically Driven Machines

Lesson 1: Drive Systems

Unit 2: Differentials

Lesson 1: Basic Components and Theory

Lesson 2: Locking Differentials

Lesson 3: Planetary DifferentialLesson 4: Adjustments

Lesson 5: Differential Steering

Lesson 6: Steering Clutch and Brake

Unit 3: Brakes

Lesson 1: Brake Mechanisms

Lesson 2: Brake Actuation Components

Lesson 3: Brake Systems

Lesson 4: Retarding and Traction Control

Unit 4: Tracks and Undercarriage Components

Lesson 1: Undercarriage Components

Lesson 2: Undercarriage Wear and Operation

Lesson 3: Track Options and Shoe Options

Unit 5: Final Drives and Tire Discussion

Lesson 1: Final Drives

Lesson 2: Miscellaneous Components


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Power Train IICOURSE DESCRIPTION

Description

1. Power Train II

2. Course Number __________

3. Prerequisite: Hydraulics, Power Train I

4. Four lecture and six laboratory hours per week (8 week class)

5. Credit: Three semester hours

Methods of Presentation

1. Lecture and discussion

2. Demonstrations3. Supporting laboratory exercises and lab worksheets

Suggested Evaluation of Student Achievement

1. Unit tests -- _______%

2. Laboratory worksheets -- _______%

3. Quizzes and exercises -- ________%

4. Class and laboratory participation -- ______%


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Power Train IIOBJECTIVES

At the completion of this course, the student will have working

knowledge of the power train components that are included in this

course. Using reference materials, the student will be able to

disassemble, assemble and adjust various power train components.


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REFERENCE MATERIALS (continued)

Miscellaneous:

950G Wheel Loader, 962G Wheel Loader and

IT62G Integrated Toolcarrier Braking System

Specifications Module. SENR1385

Undercarriage Application Guide for Medium Size Track-type

Tractors. PEGP2009

Data Sheet: Sealed and Lubricated Track. PEDP0036

Data Sheet: Extended Life Undercarriage. PEDP7107

Data Sheet: Heavy Duty Track. PEHP5031Data Sheet: Quad and Tri Link Track. PEHP6031

Data Sheet: Positive Pin Retention Track. PEHP7025

Data Sheet: Rotating Bushing Track. PEHP5030

Data Sheet: Mobil-trac System. PEHP7026

Data Sheet: Mobil-trac System Options. PEHP8039

Data Sheet: Chopper Shoe. PEDP1147

Power Train II


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Power Train IITOOLING REQUIREMENTS

Labs and exercises for this course require the following tools.

Substitute tooling may be used at the discretion of the instructor

FT0834 Clutch Test Nozzle 1

FT0957 Adapter Group 4FT0996 Positioning Group 4

FT2214 Adapter 1

FT2615 Bar (Rolling Torque) 1

FT2616 Gauge Block 1

1B-9575 Bolt 1

1D-4716 Nut 1

1D-4717 Nut 3

1P-1863 Pliers 1

1P-2420 Transmission Test Stand 1

1P-3532 Track Block Assembly 11U-6434 Duo-Cone Seal Installer 1

1U-6689 Socket 1

3B-1915 Bolt 3

3K-4897 Spring Pin 8

4B-5270 Washer 2

4B-5271 Washer 2

4C-8345 Spanner Wrench 1

4C-8346 Spanner Wrench 1

5M-2894 Washer 6

6V-4072 Spanner Wrench 1

6V-7820 Torque Multiplier 17X-0851 Nut 1

8B-7548 Bearing Puller Assembly 1

8S-5132 Plate 1

8T-0664 Bolt 1

8T-5096 Dial Indicator 1

9S-7354 Torque Wrench 1

9U-7346 Spanner Wrench 1

120-9877 Spanner Wrench 1


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UNIT 1Hydraulically Driven Machines

Introduction

This unit provides instruction on machines that are driven with

hydraulic components. This unit describes the components and drive

systems of several machines that are driven with hydraulic power.

Unit Objectives

At the completion of this unit, the student will be able to demonstrate

an understnading of drive systems used on various machines and the

similarities between them.

Unit References:

Student Worktext

Tooling:

None Required


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Lesson 1: Drive Systems

Introduction

This lesson will discuss some specific drive systems. The systems

have been chosen to demonstrate a unique feature. All possible

combinations of drive systems are too varied to cover in this course.

Objectives

1. Understand the drive systems of a various machines.

2. Understand the similarities between these different systems.

Fig. 1.1.1 Drive System

TO IMPLEMENT

PILOT SYSTEM

HYDROSTATIC DRIVE

SYSTEM

M1

MHT2PS1

OIL SAMPLINGFILTERGROUP

PUMP MOTOR

G

CREEPER

VALVE

TO BRAKE

CALIPER

BRAKE

MASTER

CYLINDER

TO HYDRAULIC

TANK


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FUNCTIONAL AREAS

Swashplate angle

High pressure side Low pressure side

Fig. 1.1.2

Introduction

In a bi-directional variable displacement pump, a circuit controls theswashplate angle:

A valve controls the amount of signal oil that flows to the

piston that shifts the swashplate. The amount of signal oil is

usually proportional to the amount of lever movement, but not

always.

A valve controls the direction that the output oil should flow

to the motor.

A valve that senses the pressure in the drive loop will cause

the pumps to destroke when the drive loop pressure gradually

rises too high, usually by draining signal pressure. A valve tied to the brake system will cause the pumps to

destroke when the brakes are applied, usually by draining

signal pressure.

In some systems, a valve that is dependent on engine speed

will cause the pumps to destroke when the engine speed is

lugging. This gives priority to the implement system. The

pump is usually destroked by draining signal oil.

Some of these functions are combined and done by one valve.

Unit 1 1-1-2 Power Train II

Lesson 1


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Lesson 1

Fig. 1.1.3 Early Vibratory Compactors

Paving Compactors

The drive system of the earlier models of vibratory compactors

allows the operator to choose high speed or low speed operation.

Both of the hydraulic motors are two-speed motors.

The two-speed bent axis piston motor for the rear wheels sends power

through a gear reducer and a NO-SPIN differential. The axle shafts

then drive the rear wheels.

The drum is driven by a two-speed radial piston motor. The parking

brake is also located at the drum.

Each bi-directional variable displacement piston pump has a servo

piston that is connected to the swashplate through a lever arm. When

the displacement control lever in the cab is moved, oil flows to one

end of the servo piston. The servo piston is shifted by an amount that

is proportional to lever movement.


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SECONDARYBRAKE AND

HIGH/LOW

SHIFT VALVE

PROPEL

COOLINGVALVE

FRONTPROPEL

MOTOR

REAR PROPEL MOTOR

TANDEM

PROPEL PUMP

CS/CP-563 PROPEL SYSTEMREVERSE

FROM STEER &BLADE CIRCUIT

FROM CHARGE

FILTER

TO VIBRATORYCOOLING VALVE

FROM VIBRATORYCOOLING VALVE

DISPLACEMENT

CONTROL SPOOL

DISPLACEMENT

CONTROL SPOOL

CHARGE

RELIEFVALVE

CHARGE

RELIEF

VALVE

SERVO

PISTON

SERVOPISTON

SOLENOIDVALVE

(SEC BRK)

SOLENOID

VALVE(SEC BRK)

Fig. 1.1.5 HIGH REVERSE

The difference between forward speeds and reverse speeds is the side

of the servo piston that is supplied with oil. This changes the

swashplate angle and the direction of flow from the pump.

The high/low shift valve is a solenoid valve. Both of the motors are

2-speed motors. The operator chooses a high speed or low speed.

In low speed (high torque) operation, no oil flows through the

high/low shift valve to the motors. The actuator piston in the rear

motor holds the swashplate at maximum angle. The displacementcontrols spool in the rear motor keeps eight pistons pressurized.

When the operator chooses high speed, the high/low solenoid is

energized. Oil flows through the high/low shift valve. Oil that flows

to the rear motor is directed to the other side of the actuator piston.

Due to a higher effective area, the actuator piston will shift and the

swashplate will move to minimum angle. Oil that flows to the front

motor shifts the displacement selector spool. The front motor will be

driven by four pistons.

The secondary brake requires three solenoid valves. When the

secondary brake is released, the solenoid valve on the left allows oil

to release the spring applied secondary brake near the drum motor.

When the secondary brake is applied, the two solenoid valves in the

pumps connect the two ends of each servo piston to each other so the

pump cannot upstroke.

The propel cooling valve routes some of the return oil to the vibratory

system and the oil cooler when a direction has been chosen.


Lesson 1


16/49

Fig. 1.1.6 Multi-function Valves

Each pump has two sets of multi-function valves. Each set contains a

variable relief valve, a fixed relief valve and 2 check valves.

The variable relief valve on the drive side will destroke the pump

when the drive side pressure gets too high. When high pressure shifts

the valve, oil flows to the opposite side of the servo piston.

The fixed relief valve on the drive side will dump pressure when

pressure spikes raise the pressure too quickly for destroking to be

effective. The oil will be dumped into the charge circuit.

A check valve on the low pressure side allows makeup oil into the

motor return line. This supplements the supply oil to the pump to

make up for normal leakage.

When towing is necessary, these valves can be converted into bypass

valves to prevent the pressure increase from the operation of the

motors as the wheels and the drum turn.


Lesson 1


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Fig. 1.1.7 Compact Wheel Loader

Compact Wheel Loaders

The drive system of the compact Wheel Loaders has a variable

displacement drive motor is mounted to a gear box. Power from the

motor flows into the gear box. The gear box transfers power to the

pinion for the differential in the rear axle. The gear box also transfers

power through a drive shaft to the pinion for the differential in the

front axle. The brake is fastened to the input shaft of the front axle.

The bi-directional variable displacement axial piston pump is

controlled with a servo piston. A valve with two solenoids controls

the direction of flow to the servo piston. The speed sensing valve

controls the amount of flow into the servo piston.


Lesson 1


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CHARGEPUMP

TO IMPLEMENTPILOT SYSTEM

TO HYDRAULICTANK

CHARGERELIEF VALVE

PRESSUREOVERRIDE

VALVE

X1

X2

F-N-RVALVE

FWD

SPEEDSENSING

VALVE

MA

HYDROSTATIC DRIVE SYSTEMPUMP AND FILTER GROUPS

PUMP

MHT2GPS1

TO BRAKEMASTER CYLINDER

AND CREEPER VALVE

TOMOTOR

CROSSOVERRELIEF AND

MAKEUP VALVESORIFICE

OIL FILTER ANDBYPASS SWITCH

OIL SAMPLING VALVE

DIAGNOSTIC VALVE

MB

TOMOTOR

Fig. 1.1.8 Pump

Compact Wheel Loaders

The charge pump supplies the signal pressure for the pump and motor

and supplements the oil at the inlet of the bi-directional variable

displacement piston pump. The filtered charge oil flows to the speed

sensing valve, the crossover relief and makeup valves and the charge

relief valve.

The charge relief valve limits the maximum pressure in the charge

circuit. When the piston pump is in the neutral position, themaximum pressure in both drive loops is also controlled by the

charge relief valve.

The crossover relief and makeup valves allow charge oil into the inlet

side of the pump. The relief portion of the crossover relief and

makeup valve will open when pressure spikes raise the pressure in the

drive loop. The high pressure oil will be dumped into the charge

circuit.

The pressure override valve limits the maximum drive loop pressure.

When the highest drive loop pressure reaches the pressure setting,

some of the signal oil will be drained from the pump control andfrom the motor control.

The speed sensing valve determines the amount of the charge flow

that will become signal pressure to control the pump and the motor.

The signal pressure will vary proportionally to engine speed. The

higher the engine speed, the higher the signal pressure.

The F-N-R valve consists of a spool and two solenoids. When one of

the solenoids is energized, the spool will route the oil from the speed

sensing valve to the correct end of the servo piston that controls the

swashplate angle.


Lesson 1


19/49

FLUSHINGVALVE

SPEED

SELECTORSOLENOID

VALVE

MOTOR DISPLCONTROL

VALVE

HYDROSTATIC DRIVE SYSTEMMOTOR

MIN

M1

FROM PUMP

FROM SPEEDSENSING VALVE

FROM PUMP

REVERSESOLENOID

VALVE

THROTTLEPIN

CREEPERVALVE

TO BRAKEMASTER

CYLINDER

INCHINGVALVE

MOTOR

Fig. 1.1.9 Motor

The signal oil also flows to the speed selector solenoid valve and the

brake master cylinder (or inching valve if equipped). If the brake

pedal is depressed, some of the signal oil will be drained to the tank.

This will cause the pump to destroke as the brake is being applied.

The engine speed will not reduce when the brake is applied, so the

implements can be used at full power.

A high/low switch in the cab allows the operator to indicate that the

drive motor should stay in the low speed, high torque position. Inthis case, the speed selector valve will block signal oil flow to the

motor controls.

If the speed selector valve is not energized, signal oil flows past the

speed selector valve to the end of the motor displacement control

valve. The other end of the motor displacement control valve is open

to the oil in the high pressure side of the drive loop. The reverse

solenoid valve is used to determine which side of the drive loop is

open to the motor displacement control valve. The position of the

reverse solenoid valve is determined by the direction chosen by the

operator.

The motor displacement control valve compares signal pressure to

drive loop pressure to determine the swashplate angle of the motor.

As signal pressure increases, the motor displacement control spool

will send oil to the motor actuator. The swashplate will move toward

minimum angle. The motor will turn faster.

Resistance to motor rotation will increase the drive loop pressure.

When the drive loop pressure increases above the signal pressure, the

motor displacement control valve shifts. Oil will be drained from the

motor actuator. The swashplate will move toward maximum angle.


Lesson 1


20/49

The throttle pin slows down rate that the actuator drains when the

motor swashplate is being moved from minimum angle toward

maximum angle.

The flushing valve continuously drains some oil from the low

pressure side of the drive loop through the motor bearings to casedrain.


Lesson 1

CROSSOVERRELIEF AND

MAKEUPVALVE


TO HYDRAULICTANK

CHARGE RELIEFVALVE

FLUSHINGVALVE

PRESSUREOVERRIDE

VALVE

X2

F-N-RVALVE

FWD

MB

MA

MOTOR DISPL.CONTROL

VALVE

HYDROSTATIC DRIVE SYSTEMFORWARD / LOW

MIN

PUMPGROUP

MHT2GPS1

MOTORGROUP

M1

THROTTLEPIN

SPEEDSENSING

VALVE

SPEEDSELECTORSOLENOID

VALVE

REVERSESOLENOID

VALVE

CREEPERVALVE

TO BRAKECALIPER

BRAKEMASTER

CYLINDER

OIL FILTER ANDBYPASS SWITCH

OIL SAMPLING VALVE

DIAGNOSTIC VALVE

Fig. 1.1.10 FORWARD/LOW

Operation - FORWARD/LOW

When the operator moves the directional control switch to

FORWARD, the F-N-R valve in the pump will shift to the forwardposition and the reverse solenoid valve in the motor will remain open

to the forward side of the drive loop. The signal pressure will not be

high enough to move the machine until the accelerator pedal is

depressed.

When the accelerator pedal is pressed, the speed sensing valve will

control the amount of signal oil that flows through the F-N-R valve to

the control piston in the pump. The swashplate angle will shift by a

proportionate amount. The swashplate angle determines the amount

of pump flow. The pump flow drives the motor.

Several valves in the pump can override the speed sensing valve to

change the signal pressure or the drive loop pressure if necessary.

In Figure 1.1.10, the speed selector valve is energized because the

switch in the cab is in the low position. Signal oil cannot flow to the

end of the motor displacement control valve. The motor actuator will

keep the swashplate at maximum angle. The motor will be in the low

speed, high torque position.

Low speed may be chosen for applications such as truck loading.

More of the available engine power is used for the implement pump

instead of the travel system.


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TO HYDRAULICTANK

CHARGE RELIEFVALVE

FLUSHINGVALVE

PRESSUREOVERRIDE

VALVE

X1

X2

F-N-RVALVE

FWD

MB

MA

MOTOR DISPLCONTROL

VALVE

HYDROSTATIC DRIVE SYSTEMREVERSE / HIGH

MIN

PUMPGROUP

M1

MHT2GPS1

MOTORGROUP

CROSSOVERRELIEF

ANDMAKEUPVALVES

THROTTLEPIN

SPEEDSENSING

VALVE

SPEEDSELECTORSOLENOID

VALVE

REVERSESOLENOID

VALVE

CREEPERVALVE

TO BRAKECALIPER

BRAKEMASTER

CYLINDER

OIL FILTER AND

BYPASS SWITCH

OIL SAMPLING VALVE

DIAGNOSTIC VALVE

Fig. 1.1.11 REVERSE/HIGH

Operation - REVERSE/HIGH

When the operator moves the directional control switch to

REVERSE, the F-N-R valve in the pump will shift to the reverse

position and the reverse solenoid valve in the motor will shift. The

reverse solenoid valve in the motor will be open to the reverse side of

the drive loop.

In Figure 1.1.11, the speed selector valve is not energized because the

switch in the cab is in the HIGH position. Signal oil flows to the

motor displacement control valve. Because of the reverse solenoid

valve, the high pressure side of the drive loop is open to the other end

of the motor displacement control valve.

When the signal pressure and the pump output are low, the motor

displacement valve will be in the LOW position. The motor actuator

will keep the motor swashplate at maximum angle. The motor will

be in the low speed, high torque position.

As the pump output increases, the speed of the motor increases. As

the speed of the motor increases, the machine speed increases.As the accelerator pedal continues to be depressed, the engine speed

and the signal pressure continue to increase. Eventually, the signal

pressure will be high enough to move the motor displacement control

valve. Drive loop oil will flow to the motor actuator and move the

swashplate toward minimum angle. The motor speed will increase.

When the engine speed is at the maximum, the pump swashplate is at

maximum angle and the motor swashplate is at minimum angle, the

machine will move at maximum speed.


Lesson 1


22/49

Resistance to rotation of the motor will increase drive pressure.

When the drive pressure increases and shifts the motor displacement

control valve, oil will be drained from the motor actuator through the

throttle pin. The swashplate will move toward maximum angle.

The motor displacement control valve continuously balances the

signal pressure with the drive pressure. This prevents excessive

engine lug, improves driving response and maximizes system stability

during hydrostatic braking.


Lesson 1

Fig. 1.1.12 C Series Track Loader

C Series Track Loaders

The drive system of the C series Track Loaders has variable speed

link-type piston motors splined to the final drive at the track. The

parking brakes are located at the track motors.

Each bi-directional variable displacement axial piston pump has a

forward servo piston and a reverse servo piston. These servo pistons

are shifted with hydraulic oil by an amount that is determined by the

Electronic Control Module (ECM).


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PARKING BRAKESOLENOID

IMPLEMENT DUAL PRESSURERELIEF SOLENOID

SYNCHRONIZATIONVALVE

BACK-UP ALARM

SERVICE TOOLCONNECTOR

LEFTREVERSE

STEERSOLENOID

LEFT PUMP

LEFTMOTOR

LEFTFORWARD

STEERSOLENOID

CHARGE

PUMP

OVERRIDESOLENOID

DISPLAY /CALIBRATESWITCHES

SERVICE MODE

CLEAR MODE

CALIBRATION

LEFT STEERING PEDAL SENSOR

CENTER PEDAL SENSOR

RIGHT STEERING PEDAL SENSOR

SPEED AND DIRECTIONALLEVER SENSOR

ENGINE SPEED SENSOR

GOVERNOR LEVER SWITCH

TRANSMISSIONECM

CHARGEPRESSURE

SENSOR

PARKING BRAKE SWITCH

TILT LEVER SWITCH

COOLANTTEMPERATURE SENSOR

LEFT TRACK SPEED SENSOR

RIGHT TRACK SPEED SENSOR

AIR INLET HEATER SWITCH

CATERPILLARMONITORING

SYSTEM

AIR INLET

HEATER RELAY

RIGHTREVERSE

STEERSOLENOID

RIGHT PUMP

RIGHTMOTOR

RIGHTFORWARD

STEERSOLENOID

POWER TRAIN ELECTRONIC CONTROL SYSTEM

Fig. 1.1.13 ECM Control


The ECM will energize the synchronization valve when the steering

pedals are not being used. The synchronization valve connects the

two drive loops when the machine is traveling in a straight line or

when the parking brake is engaged. If either of the steering pedal

sensors registers pedal movement, the synchronization valve will

separate the two drive loops.

The four steering solenoid valves are used to control the speed andthe direction of the machine. The steering solenoids are proportional

solenoids.

The ECM monitors the engine speed sensor. When the load begins to

reduce engine speed, the ECM will signal the appropriate steering

solenoids to destroke the pumps. The ECM also monitors the

governor lever switch. If the governor lever is not in high idle, the

ECM will destroke the pumps at a lower engine speed.

The center pedal will cause the steering solenoids to destroke the

pumps proportionately. When the center pedal is completelyengaged, the parking brakes are engaged.

The parking brakes are spring engaged and hydraulically released.

When the speed and direction lever is in the PARK position, the

brake control solenoid is de-energized.

The ECM sends current to the transmission override solenoid. If a

fault occurs, the transmission override solenoid will destroke the

pumps and put the machine in a PARK position.


Lesson 1


24/49

POWER TRAIN HYDRAULIC SYSTEMPARKING BRAKES ENGAGED

SYNCHRONIZATIONMANIFOLD

ECMMANIFOLD

RIGHT

DRIVE PUMP

LEFTDRIVE PUMP

LEFTDRIVE MOTOR

RIGHT DRIVE

MOTOR

CASE DRAINFILTER

CHARGE PRESSURESENSOR

CHARGERELIEF VALVE

OVERRIDESOLENOID

BRAKECONTROLSOLENOID

MAKEUP AND

LINE RELIEFVALVE

Fig. 1.1.14 Parking Brakes Engaged


The charge pump supplies the signal pressure for the pump and motor

and supplements the oil at the inlet of the bi-directional variable

displacement piston pump. The filtered charge oil flows to the charge

pressure sensor, the charge relief valve, the brake control solenoid,

the override solenoid, the makeup and line relief valves and the servo

valves for the pumps and motors.

The charge relief valve limits the maximum pressure in the chargecircuit. When the piston pump is in the neutral position, the

maximum pressure in both drive loops is also controlled by the

charge relief valve.

When the speed and direction lever is in the PARK position, charge

oil will be blocked by the brake control solenoid. Charge oil will not

be sent to release the parking brakes until the speed and direction

lever is moved.

The ECM sends current to the transmission override solenoid. If a

fault occurs, the transmission override solenoid will block charging

system oil flow to the steering solenoids. This causes the pumps to

destroke. The override solenoid will also block charge oil flow to the

steering solenoid valves if a direction has not been chosen.

The makeup and line relief valves allow charge oil into the inlet side

of the pump. The relief portion of the makeup and line relief valve

will open when pressure spikes raise the pressure in the drive loop.

The high pressure oil will be dumped into the charge circuit.


Lesson 1


25/49

LEFT SIDE

RIGHT SIDE

POWER TRAIN HYDRAULIC SYSTEMMAXIMUM FORWARD

ACTUATORPISTON

SERVO

VALVE

SERVOVALVE

SERVOVALVE

CONTROL PISTON

BRAKES

PURGESHUTTLE VALVE

ACTUATORPISTON

PURGERELIEF VALVE

BRAKES

MAKEUP ANDLINE RELIEF VALVE

MAKEUP ANDLINE RELIEF VALVE

SYNCHRONIZATION VALVEAND TOWING VALVES

PILOTSPOOL

RIGHT FORWARDSTEERING SOLENOID

RIGHT REVERSESTEERINGSOLENOID

LEFTREVERSE

STEERINGSOLENOID

LEFTFORWARDSTEERINGSOLENOID

SERVOVALVE

BRAKECONTROLSOLENOID

OVERRIDESOLENOID

CHARGERELIEF VALVE

CHARGE PRESSURESENSOR

Fig. 1.1.15 MAXIMUM FORWARD

Operation - MAXIMUM FORWARD

When a direction has been chosen, the override solenoid will allow

charge oil to flow to the steering solenoids. When the ECM

determines that the swashplate angle(s) of the pump(s) needs to

change, the ECM will energize the steering solenoid(s) that cause the

desired change.

When a steering solenoid is energized, oil flows to one end of the

pilot spool. The oil shifts the pilot spool. The pilot spool shifts the

servo valve. The servo valve controls the oil flow to the control

pistons. The control pistons control the swashplate angle. The

swashplate angle determines the amount of flow and the direction of

flow from the piston pump. Pump output flow drives the motor.

When a steering solenoid is energized, oil also flows beneath the

servo valve for the motor. The pressure of the oil will not be high

enough to shift the servo valve for the motor until the pump has

reached maximum angle. When the pressure below the servo valve

for the motor increases to a certain point, the servo piston will shift

and charge pressure will be rerouted from below the actuator piston

to the top of the actuator piston. When the actuator piston shifts, the

barrel will shift and the swashplate angle will decrease. The motor

will require less pump flow to turn for one revolution.

The purge shuttle valve is shifted by the drive loop pressure. The

purge shuttle valve routes the low pressure side to the drive loop to

the purge relief valve. The purge relief valve continuously drains

some oil from the low pressure side of the drive loop to the case

drain.


Lesson 1


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FORWARD

REVERSE

POWER TRAIN HYDRAULIC SYSTEMRIGHT TURN

Fig. 1.1.16 RIGHT TURN

Operation - RIGHT TURN

When the machine is travelling in the FORWARD direction and the

right steering pedal is partially depressed, the right track will slow

and the left track will maintain the original speed.

The right track slows because the ECM sends a reduced signal to the

right forward steering solenoid valve. This causes the right side

pump to destroke. The pump drives the motor, so the motor on the

right side slows down.

If the machine is travelling at the maximum speed and the steering

pedal is partially depressed, the motor swashplate angle will begin to

increase. This also causes the motor to slow down.

If the operator depresses the right steer pedal completely to perform a

spot turn, the ECM will stop the signal to the right forward steering

solenoid valve and direct an output signal to the right reverse steering

solenoid valve. In this situation, the tracks will move in opposite

directions.

During any type of turn, the synchronization valve will separate thedrive loops and the machine will act as though the synchronization

valve is not part of the system.

The synchronization valve is energized during straight travel. The

right forward drive loop is connected to the left forward drive loop

and the right reverse drive loop is connected to the left reverse drive

loop. This allows for differences between the pump output on the left

and right sides.


Lesson 1


27/49

Additional Information for 953C

The position sensor for the steering pedal is used to determine when

to de-energize the synchronization valve. If the operator notices that

the machine begins to turn right at a different steering pedal positionthan to turn left (or vice versa), calibration of the ECM must be

performed.

If the center pedal is partially depressed, the signal pressure will be

reduced. If the center pedal is fully depressed, the motors will move

to maximum displacement and the pumps will move to minimum

displacement. The machine will stop abruptly and the parking brakes

will engaged.

When the machine load begins to reduce the engine speed, the ECM

will ensure that the implement system has first priority. The ECM

will reduce the signal to the steering solenoids. The pump or motorwill change swashplate angle to slow the machine down. This

underspeed function overrides the operator speed signal as necessary.

The ECM will decrease the machine speed to maintain the engine

speed at a designated set point. The set point is not adjustable.

During high or extreme engine loading, the synchronization valve

automatically de-energizes and the drive loops are separated until the

ECM reduces the load on the engine.

The two towing valves can be mechanically changed into bypass

valves. The flow generated by the motors will be bypassed back to

the input for the drive motors.


Lesson 1


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29/49

OPEN LOOP CIRCUIT

Fig. 1.1.18

Open Loop Circuit

In the Caterpillar product line, Hydraulic Excavators are the most

common example of an open loop circuit. In an open loop circuit, the

pump is not dedicated to one motor. In Hydraulic Excavators, each

pump supplies many cylinders and motors.


Lesson 1

Fig. 1.1.19 Mini Hydraulic Excavator

Mini Hydraulic Excavators

In the mini hydraulic excavator the operator can choose high speed or

low speed operation. Located at the tracks are two-speed orbital

motors that are low speed and high torque.

There is no need for gear reduction final drives.

Two gear pumps supply the swing circuit, all the implements and the

travel system.

If the operator is moving the machine and operating an implement or

swing, a valve will shift causing, the two separate pump flows to

combine and supply the entire system.


30/49

FROMFRONT PUMP

FROMREAR PUMP

PILOT

PUMP

ATTACHMENT

STICKLEFT

TRAVELSTRAIGHT

TRAVEL

RIGHTTRAVEL

BOOMBUCKET

MAIN CONTROL VALVENEUTRAL

UNLOAD

VALVE

FROM

PILOTMANIFOLD

FROMPILOTPUMP

PILOT MANIFOLD

TO/FROM RIGHTTRAVEL MOTOR

TO/FROM LEFTTRAVEL MOTOR

FROM PILOT

MANIFOLD

PILOT

LOGIC NETWORK

Fig. 1.1.20 Portion of the Main Control Valve in Neutral

Mini Hydraulic Excavators

Three gear pumps supply all of the oil to the systems on the 301.5

mini Excavator. The rear pump supplies the left travel, boom and

bucket circuits. The front pump supplies the right travel, stick and

attachment circuits. The pilot pump supplies the swing, blade and

boom swing circuits. The unloading valve is set so that the pilot oil

combines with the front pump oil and flows to the attachment valve.

The straight travel valve is shifted by pilot pressure. When the leftarmrest in the cab is not lowered, pilot oil is blocked to the straight

travel valve. When there is no pilot oil at the straight travel valve,

pump flow is combined and sent to tank.

When the armrest is lowered, pilot pressure will be sent to the

straight travel valve. The straight travel valve shifts to the center and

the passage to tank is blocked. The two pump flows are separated

and supply the travel motor first. If the travel valve is in the neutral

position, pump oil flows through the travel valve and supplies the

implement valves.


Lesson 1


31/49

FROMFRONT PUMP

FROMREAR PUMP

PILOT

LOGIC NETWORK

PILOT PUMP

ATTACHMENT

STICKLEFT

TRAVELSTRAIGHT

TRAVEL

RIGHTTRAVELBUCKET

MAIN CONTROL VALVESTRAIGHT TRAVEL

UNLOAD

VALVE

FROMPILOT

MANIFOLD

FROM

PILOTPUMP

TO/FROM RIGHTTRAVEL MOTOR

TO/FROM LEFTTRAVEL MOTOR

FROM PILOTCONTROL

BOOM

Fig. 1.1.21 Portion of Main Control Valve - Straight Travel

If either travel valve is shifted, pump oil flows to the motor. One line

to the motor drives the machine forward, the other reverse.

Normally, the left side motor is supplied by one pump and the right

side by the other pump. If an implement or swing is used at the same

time, the straight travel valve will shift. Both travel valves and all

implements will be supplied with combined oil flow from the two

gear pumps. The travel motors receive less flow when an implement

or swing is operated at the same time.The straight travel valve shifts because of the pilot logic network.

Some of the pilot oil that flows to the right side of the straight travel

valve also flows through the pilot logic network. When the travel

valves are in the neutral position, some oil is directed to the

implement valves and some to the tank. When the travel spool shifts,

the passage to the tank is blocked.

The implement valves only allow oil to flow through if the implement

valve is in the neutral position. If the implement valve is shifted, the

implement valve blocks the pilot oil. Pressure builds in passage open

to the straight travel valve. The straight travel valve shifts.


Lesson 1


32/49

TO SWING, BOOMSWING AND BLADE

CIRCUITS

PRESSUREREGULATING

VALVE

PILOTREDUCING

VALVE

FROM TRAVELMOTORS

TWO SPEEDVALVE

TO PILOTCONTROLVALVES

HYDRAULICDISABLEVALVE

PILOTMANIFOLD

PILOTPUMP

PILOTACCUMULATOR

PILOT MANIFOLDENGINE ON

Fig. 1.1.22 Pilot Manifold

The pilot system has an accumulator to prevent erratic movement of

controls during multiple implement operation.

The pilot manifold contains four valves. The pressure reducing valvesets the pressure of the pilot oil to the pilot valves for the joystick,

swing park brake, straight travel valve and unloading valve.

The two-speed travel solenoid valve sends a signal to the motor to

cause the motor to be at high or low speed.

The pressure regulating valve is set at a higher pressure than the

pressure reducing valve. The pressure regulating valve supplies oil to

the swing valve, blade valve, boom swing valve and unloading valve.


Lesson 1


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34/49

Hyd LockValve B kt B oo m

AESC

Level S.P.

Brake PRV2-SpdTravel

PilotRelief

L. Travel R. Travel

Swing Stick

Shockless

Valves

(TopPump)

NFC

Back

Pressure

(TopPump)

NFC

Left Travel Right Travel

Boom CylBkt CylStick Cyl Swing

Stick 1 Swing R. Travel St. Travel SwingBrake

L. Travel

Aux. Bkt

Boom 2

P.T.L.

Selector

NFC

Back

Pressure

(BottomPump)

NFC

(BottomPump)

Boom1

Stick 2

MainRelief

Crowd

PS TOPUMPS

E

Fig. 1.1.24 Hydraulic System

300 Series Hydraulic Excavators

Negative flow control valves on the ends of the main control valve

maintain backpressure. The negative flow control valves send signal

oil to the pump controls. The signal pressure is reduced when a spool

shifts and the required backpressure is not present.

The pilot system is equipped with a gear pump, filter and an

accumulator to prevent erratic movement of controls during multiple

implement operation.

The pilot manifold contains. The proportional reducing valve that

modulates pilot pressure. The proportional reducing valve also sends

signal oil to the piston pump controls. The amount of signal oil is

determined by the Electronic Control Unit (ECU).


Lesson 1


35/49

IIIIII

1

2

1

2

GOVERNOR

ACTUATOR

ENGINE

SPEED DIAL

PUMP

SPEED SENSOR

PROPORTIONAL

REDUCING VALVE

ENGINE

ELECTRONICCONTROL CIRCUITS

SPEED DIAL LIMITSPOWER

MODE

SWITCH

MONITOR

ECU FEEDBACKSENSOR(CONTROLLER)

POWER

ll l

l

ll

Fig. 1.1.25 ECU Pump Controls

When more pressure is sent by the proportional reducing valve, less

signal oil from the negative flow control valves is required to

destroke the pump.The ECU monitors the travel pressure switch, implement/swing

pressure switch, engine speed sensor, power mode switch and engine

speed dial.

The travel pressure switch and/or the implement/swing pressure

switch closes when the appropriate valve is shifted and pump oil is

sent to the motor or cylinders.

The power mode switch allows the operator to match the machine

power to the task. Different limits of hydraulic horsepower can be

assigned to implement, swing or travel. Each power mode setting

also corresponds to a maximum engine speed dial position.

In Mode 1, the machine uses up to 60% or 65% of the available

horsepower, depending on the machine model. The engine

speed is limited to dial position 7, even if the dial is set higher.

In Mode 1, the powershift pressure will be constant and high.

In Mode 2, the machine uses up to 85% of the available

horsepower. The engine speed is limited to dial position 9. In

Mode 2, the powershift pressure will be constant, but lower

than Mode 1.

In Mode 3, no horsepower limit is set and no dial position limit

exists. In Mode 3, the powershift pressure will be constant, but

lower than Mode 2.

When Mode 3 is chosen and the engine speed dial is at the highest

setting, the proportional reducing valve will act as an underspeed

valve. As engine speed decreases near full load, more pressure will

be sent to the pump control group to destroke the pump.


Lesson 1


36/49

Hyd LockValve B kt B oo m

AESC

Level S.P.

Brake PRV2-SpdTravel

PilotRelief

L. Travel R. Travel

Swing Stick

Shockless

Valves

(TopPump)

NFC

Back

Pressure

(TopPump)

NFC

Left Travel Right Travel

Boom CylBkt CylStick Cyl Swing

Stick 1 Swing R. Travel St. Travel SwingBrake

L. Travel

Aux. Bkt

Boom 2

P.T.L.

Selector

NFC

Back

Pressure

(BottomPump)

NFC

(BottomPump)

Boom1

Stick 2

MainRelief

Crowd

PS TOPUMPS

E

Fig. 1.1.26 Hydraulic System

The pilot manifold includes the two-speed travel solenoid valve

which determines the swashplate angle of the two-speed travel

motors.

Pilot oil also supplies the pilot valves for the operator controls. If the

operator moves the lever, pilot oil will be sent to the ends of the

appropriate control spool(s) in the main control valve. This shifts the

control spool to allow pump oil to flow to the cylinder or to the

motor.

The pilot logic network activates pressure switches to control the

straight travel control valve, change main relief valve pressure and

release the swing park brake. When control spools are in the neutral

position, pilot oil will flow through the pilot logic network to tank.

When the control spools shift, pilot passages are blocked and pressure

builds in the pilot logic network.


Lesson 1


37/49

PS TO

PUMPS

SELECTOR

SW STK

BKT

BM

M

LT

LT RT

RT

ATCH BOOM 1BUCKETLEFTTRAV

STICK1

BOOM2

ATCH

BY-PASS

STRTRAVEL

PTL

STICK2

STRAIGHT TRAVEL

RTTRAV

SWING

AECSPB

SHOCKLESSVALVE

TOSTICK 1

Fig. 1.1.27 Straight Travel Operation

Normally, the left side travel motor is supplied by one pump and the

right side by the other and, half of the implements are supplied by

one pump and half by the other.

If an implement or swing is used at the same time as both of the

travel valves, the pilot logic network causes the straight travel valve

to shift. Both of the travel control valves will be supplied by the

same pump. The implements and swing will be supplied by the other

pump.The pilot logic network pressure that causes the straight travel valve

to shift also causes the relief pressure to increase. The travel motors

will still receive less flow when an implement or swing is operated at

the same time.


Lesson 1


38/49

Unit 1 - 1 - Power Train II

Lab 1.1.1

MAIN RELIEF VALVE CIRCUITTRAVEL POSITION

FROM

REAR PUMP

FROM

FRONT PUMP

FROM

PILOT

PUMP

TO TRAVEL

PRESSURE SWITCH

MAIN

RELIEF

VALVE

CHECK

VALVES

RIGHT

TRAVEL

CONTROL

VALVE

STRAIGHT

TRAVEL VALVE

LEFT

TRAVEL

CONTROL

VALVE

TRAVEL

SHUTTLE

VALVE

FROM

PILOT

PUMP

LAB 1.1.1: TRAVEL MOTOR AND FINAL DRIVE

The travel motor for this lab is for a 311B Hydraulic Excavator. The 311B Hydraulic Excavator has an

open circuit system. The same two pump sections supply the oil for the entire machine. The travel

motors are not the only output.

Pump oil from a front section pump and from a rear section pump flow into the main control valve.

When the machine is only traveling, the front section of the pump will supply the right travel controlvalve and the rear section of the pump will supply the left travel control valve. Both pump sections

will also supply implement spools and the swing spool. When an implement or the swing is used at the

same time that the machine is traveling, the straight travel valve will shift. The rear pump section will

only supply the travel spools and the front pump section will supply all of the implement spools. This

enables both of the travel spools to continue to have equal pump supply. If one of the pump sections

was also supplying an implement, the pressure through the travel spools would be uneven and the

machine would not travel straight.

The travel spools in the main control valve route pump oil through the swivel to the travel and final

drive groups at the tracks. The travel brake valve has two supply lines. These lines supply different

sides of the motor to enable forward and reverse motor rotation.

Fig. L1.1.1 Main Control Valve (center portion)


39/49


Lab 1.1.1

FROM PUMP

TRAVEL MOTOR BRAKE VALVE

TRAVEL POSITION

LINE RELIEF VALVELINE RELIEF VALVE

BRAKERELEASE

PORT TO CONTROLVALVE

COUNTERBALANCE

VALVE

Fig. L1.1.2 Travel Brake Valve

Fig. L1.1.3 Travel Brake Valve

LAB 1.1.1: TRAVEL MOTOR AND FINAL DRIVE (continued)

The pump oil enters the travel brake valve. The travel brake valve causes oil to flow to the pistons in

the motor. The travel brake valve also routes oil to the parking brake release port.

The line relief valve limits the pressure of the oil into the motor.

The counterbalance valve limits the amount of oil that can leave the motor. The counterbalance valve

makes sure that the amount of oil leaving the motor is not greater than the amount of oil entering the

motor. The counterbalance valve is necessary when the machine travels downhill. The counterbalance

valve makes sure that the motor speed remains at the level that the pump commands.


40/49


Lab 1.1.1

TRAVEL

MOTOR

PARK BRAKE

PARK BRAKE PISTON

BRAKE VALVE

Fig. L1.1.4 Travel Motor and Final Drive


Pump oil comes into the travel brake valve and flows to the parking brake release chamber and into the

port plate to the pistons. The oil to the pistons drives the travel motor. The output shaft of the travel

motor drives the final drive of this machine.

The disc for the parking brake has teeth that fit with teeth around the barrel. When oil pushes the

parking brake piston back, the parking brake will be released. The barrel will rotate freely. When oilis not present, the springs will push the parking brake piston into the parking brake disc. The barrel

will be held by friction and will not rotate.


41/49


Lab 1.1.1

311 TRAVEL MOTORSLOW SPEED

FROM TWOSPEED SOLENOID

TO/FROM TRAVELCONTROL VALVE


311 TRAVEL MOTORSHIGH SPEED

FROM TWOSPEED SOLENOID






This is a two-speed motor. The default for the swashplate angle is the maximum angle. If the switch

in the cab is in the HIGH speed position, it is possible for the swashplate angle to move to the

minimum angle. When high speed is needed, oil will be supplied beneath a valve under the

swashplate. This valve will push the swashplate into a flatter position. The motor will rotate faster

with the same amount of supply oil.


42/49

LAB 1.1.1: TRAVEL MOTOR AND FINAL DRIVE

Reference:

311B Excavator Disassembly & Assembly Hydraulic System

Disassemble and Assemble Travel Motors and Final Drives SENR9235

Perform the following lab:

1. Mount the travel motor on the transmission stand.

2. Skip the disassembly of the travel brake valve. (Step 5 - 11)

3. In Step 13a, what was the visible difference between the brake release port and the other

ports?The orifice

4. What do you think the other ports are for?

Oil to the valves that move the swashplate (one is not used).

5. What is the purpose of the disc that is removed in Step 15?

Parking brake

6. Describe how the pistons in the barrel (that you see in Step 17) pump oil.

Oil comes in through one half of the port plate and fills the pistons.As the pistons move around the swashplate, oil is pushed out through the other half of

the port plate.

7. What is the shaft in Step 23 connected to?

The sun gear in the outer planetary.

8. Is this shaft driving the motor or is this shaft driven by the motor?

This shaft is driven by the motor.

9. What is the purpose of the two steel balls in Step 24?

Pivot point for the swashplate.

10. What is the purpose of the 2 piston assemblies and springs in Step 25?

They push the swashplate to whatever angle is needed (2 speed motor).


Instructor Copy Lab 1.1.1


43/49


Reference:

311B Excavator Disassembly & Assembly Hydraulic System

Disassemble and Assemble Travel Motors and Final Drives SENR9235


1. Mount the final drive on the transmission stand

2. Are the shafts in the planetary gears pressed on?

No

3. Which component was connected to the shaft from the travel motor?The shaft with the outer sun gear on it.

4. How is the first planetary set connected to the second planetary set?

The sun gear on the inner planetary is connected to the carrier on the outer planetary.

5. Which component of the Duo-Cone seal in Step 41 is doing the sealing?

The metal rings.

Assembly

1. What procedure is necessary in Step 45 and Step 47?Do not twist, push in evenly on all sides.

2. When the ring gear is torqued in Step 51, does it continue to rotate?

Yes

3. Why is this adjustment important?

The ring gear moves with the sprocket which drives the tracks.

4. In Step 66, why is it important to push on the swashplate?

It has to be able to tilt. It has to be seated.

5. In Step 67-69, what is the purpose of the spring and the three pins?

Prevent leakage between the barrel and the port plate and to hold barrel to retraction

plate pins push on the bushing by the retraction plate.

6. In Step 74, why are the seals important?

They are on the brake piston the chamber that pushes the brake piston must be sealed.


Instructor Copy Lab 1.1.1


44/49


45/49

LAB 1.1.1: TRAVEL MOTOR AND FINAL DRIVE (continued))

Reference:

311B Excavator Disassembly & Assembly Hydraulic SystemDisassemble and Assemble Travel Motors and Final Drives SENR9235


1. Mount the final drive on the transmission stand

2. Are the shafts in the planetary gears pressed on?

3. Which component was connected to the shaft from the travel motor?

4. How is the first planetary set connected to the second planetary set?

5. Which component of the Duo-Cone seal in Step 41 is doing the sealing?

Assembly

1. What procedure is necessary in Step 45 and Step 47?

2. When the ring gear is torqued in Step 51, does it continue to rotate?

3. Why is this adjustment important?

4. In Step 66, why is it important to push on the swashplate?

5. In Step 67-69, what is the purpose of the spring and the three pins?

6. In Step 74, why are the seals important?


Student Copy Lab 1.1.1


46/49

COMPACT WHEEL LOADER HYDROSTATIC DRIVE SYSTEM COMPONENT LOCATION

Directions: Fill in the blanks next to the terms with the correct letters.

Identify Components:

J Reverse solenoid valve

B Charge pump

G POR valve

D Speed sensing valve

K Motor displacement control valve

F Charge relief valve

C F-N-R valve

L Hydrostatic motor

H Flushing valve

A Hydrostatic drive pump

E Crossover relief and makeup valves

I Speed selector valve

Unit 1 - 1 -

Instructor Copy Test.

HYDROSTATIC DRIVE SYSTEMCOMPACT WHEEL LOADER

PUMP PS1

GT2

TO FAN MOTOR

TO PRIORITY VALVE

X1

X2

D

MH

MOTOR

M1

THROTTLE

PIN

MA

MB

CREEPERVALVE

TO BRAKECALIPER

MIN

BRAKEMASTER

CYLINDER

OIL FILTER AND

BYPASS SWITCH

TO IMPLEMENTPILOT

OIL SAMPLING VALVE

DIAGNOSTIC VALVE FROMFAN MOTOR

TO TANK

TO TANK

B A

C

E

E

F

G

H

K

I

J

L

Fig. 1.1.1 Hydrostatic Drive System - Compact Wheel Loader


47/49


48/49

Unit 1 - 3 -

Student Copy Test.

HYDROSTATIC DRIVE SYSTEMCOMPACT WHEEL LOADER

PUMP PS1

GT2

TO FAN MOTOR

TO PRIORITY VALVE

X1

X2

D

MH

MOTOR

M1

THROTTLE

PIN

MA

MB

CREEPERVALVE

TO BRAKECALIPER

MIN

BRAKEMASTER

CYLINDER

OIL FILTER AND

BYPASS SWITCH

TO IMPLEMENTPILOT

OIL SAMPLING VALVE

DIAGNOSTIC VALVE FROMFAN MOTOR

TO TANK

TO TANK

B A

C

E

E

F

G

H

K

I

J

L

Fig. 1.1.1 Hydrostatic Drive System - Compact Wheel Loader

COMPACT WHEEL LOADER HYDROSTATIC DRIVE SYSTEM COMPONENT LOCATION

Directions: Fill in the blanks next to the terms with the correct letters.

Identify Components:

Reverse solenoid valve

Charge pump

POR valve

Speed sensing valve

Motor displacement control valve

Charge relief valve

F-N-R valve

Hydrostatic motor

Flushing valve

Hydrostatic drive pump

Crossover relief and makeup valves

Speed selector valve


49/49

Documents

Hydrostatic.pdf