Course Overview
This module will discuss the basic components and operations of
power train systems used in Caterpillar Inc. machines. Included will
be basic components, clutches, manual shift transmissions and power
shift transmissions.
Basic components and component functions are explained as they
relate to the operation of various power train systems.
Unit1: Power Train: Course Overview
Power Train
NOTES
UNIT 1: Power Train
Lesson 1: Introduction to Power Train
Lesson 2: Power Train Basic Components
Lesson 3: Power Train Drive Systems
UNIT 2: Couplings
Lesson 1: Flywheel Clutch
Lesson 2: Power Train Basic Components
UNIT 3: Transmissions
Lesson 1: Manual Shift Transmission
Lesson 2: Power Shift Transmission
Lesson 3: Controls for Power Shift Transmission
© 2000 Caterpillar Inc.
Unit 1: Table of Contents
TABLE OF
CONTENTS
NOTES
Course Description
Description
1. Power Train I Course
2. Course Number ___________
3. Prerequisite: None
4. Four lecture and six laboratory hours per week.
5. Credit: Three semester hours
Methods of Presentation
1. Lecture and discussion
2. Demonstrations
3. Supporting laboratory exercises and lab worksheets
Suggested Evaluation of Student Achievement
1. Unit tests--______%
2. Laboratory worksheets--______%
3. Final exam--______%
4. Class and laboratory participation--_______%
Unit 1: Course Objectives
Power Train
NOTES
Objectives
At the completion of this course, the student will have working
knowledge of basic power train theory, components and power train
systems. Using special tooling and reference literature, the student
will be able to disassemble and assemble torque converters, torque
dividers, clutches, manual shift and power shift transmissions.
Unit 1: Objectives
Power Train
NOTES
Tooling Requirements
Labs and exercises for this course require the following tools. This
list will support 1 workstation. Substitute tooling may be used at the
discretion of the instructor
1P0510 Driver Gp
1P0511 Plate
1P0520 Driver Gp
1P0531 Handle
1P1862 Pliers
1P1863 Pliers
1P1864 Pliers
1P2321 Puller As
1P2322 Puller As
2P8312 Pliers
5P4758 Pliers
5P9736 Link Bracket (3)
4C3652 Spring Compressor
4C6136 Lifting Bracket
4C6137 Lifting Bracket
4C6142 Spacer-Brg Installer
4C6143 Clutch Piston Installer
4C6399 Spring Compressor
4C6402 Spring Compressor
6V2156 Link Bracket (2)
8B7548 Push/Puller
8B7551 Bearing Puller As
8B7556 Adapter (2)
8B7560 Step Plate
8H0684 Ratchet Box Wrench
8S2328 Dial Indicator Gp
9S9154 Step Plate
FT2343 Plexiglass Cover
FT0833 Clamp (2)
FT0834 Clutch Test Nozzle
FT0947 Clamp (2)
Unit 1: Course Tooling Requirements
Power Train
NOTES
Reference Materials
The reference materials listed below should be ordered before
conducting the course. Other reference materials may be used at the
discretion of the instructor.
Disassembly and Assembly Manuals:
970F Wheel Loader Power Train SENR6627-01
D6R Track-Type Tractor Power Train SENR8357
924F Wheel Loader & IT24F Integrated Toolcarrier Power Train
SENR6726
416B, 426B, 428B, 436B & 438B Backhoe Loaders Power Train
SENR5803-01
Series II Wheel Loader Power Train SENR5918-01
Miscellaneous:
An Introduction to Bearings SEBV0507
An Introduction to Seals and Gaskets SEBV0511
The Gear Book SEBV0533
Unit 1: Course Reference Materials
Power Train
NOTES
Power Train I
Introduction
This unit provides an introduction to the power train. The unit
begins with the theory of how a power train works. This unit also
covers basic power train components and the types of power train
drive systems.
Objectives
After completing this unit, the student will be able to: identify
common anti-friction bearings, gears,seals and gaskets and explain
the theory of how a power train works.
Unit 1: Introduction to Power Train I
UNIT 1
NOTES
Fig. 1.1.1 Power Train
Introduction
This lesson covers power train theory of operation, types of power
trains, components and power flow through the power train.
Objectives
After completing this lesson the student will be able to explain the
basic operation of a power train.
Reference Materials
Student workbook
The Gear Book SEBV0533
Unit 1: Power Train Theory of Operation
Lesson 1: Power Train Theory of
Operation
Unit 1
Lesson 1
1-1-2
Power Train I
Fig. 1.1.2 Water Wheel
Power Train Theory of Operation
A power train is a group of components that work together to transfer
power from the source where it is produced to a point where it is used
to perform work. This definition might be compared to a "freight
train." A freight train is a group of components, a locomotive and
cars, that transfers freight from where it is produced to where it is
needed. The term power train is not new. It has been used since the
earliest times to describe the components that transfer power from
one place to another. For example, in early water-powered mills
(Figure 1.1.1) used in colonial times, the term power train was used
to describe the machinery that carried power from the water wheel to
perform work such as milling flour, weaving cloth or sawing lumber.
PURPOSE OF A POWER TRAIN
1. Connect and Disconnect Power from the Engine
2. Modify Speed and Torque
3. Provide a Means for Reverse
4. Equalize Power Distribution to the Drive Wheels
Fig. 1.1.3 Power Train Functions
Power Train Functions
In a typical modern industrial machine, the power train transfers
power from the rotating flywheel of an engine to the road wheels or
tracks that do the work of propelling the machine. But it does more
than just transfer power. If an engine were coupled directly to the
drive wheels of a vehicle, the vehicle would run constantly at engine
speed.
Unit 1
Lesson 1
1-1-3
Power Train I
The power train provides a means of disconnecting and controlling
engine power. The basic functions of the power train are to:
¥ Connect and disconnect power from the engine to the drive
wheel(s)
¥ Modify speed and torque
¥ Provide a means for reverse
¥ Equalize power distribution to the drive wheels (enables the
vehicle to turn)
Power =
Work
Time
Fig. 1.1.4 Power Principle
Power Train Principles
Power is a term used to describe the relationship between work and
time. Power is defined as the rate of performing work or transferring
energy. In other words, power measures how quickly work is done.
Power is equal to the work done divided by the amount of time it
takes to do the work or P=W/t.
Unit 1
Lesson 1
1-1-4
Power Train I
Work = Force x Distance
Fig. 1.1.5 Work and Force
Work and Force
Work is equal to the force applied to move an object multiplied by
the distance the object travels. Force is a measure of the pushing
power exerted by one object against another.
According to physicist Isaac NewtonÕs laws of motion, work equals
force multiplied by the distance an object is moved. W = F x d.
Power =
Force x Distance
Time
Fig. 1.1.6 Power
Power
Substituting the definition of work into the definition of power shows
that power is equal to the force applied to move an object multiplied
by the speed that the object travels. P = F x d/t
Unit 1
Lesson 1
1-1-5
Power Train I
LEVER
OBJECT
TORQUE
FULCRUM
Fig. 1.1.7 Torque
Torque
Torque is a twisting effort applied to an object that tends to make the
object turn about its axis of rotation. The amount of torque is equal
to the magnitude of the applied force multiplied by the distance
between the object's axis of rotation and the point where the force is
applied. Just as a force applied to an object tends to change the linear
rate of motion of the object, a torque applied to an object tends to
change the object's rate of rotational motion.
The amount of torque available from a source of power is
proportional to the distance from the center at which it is applied. In
Figure 1.1.7 the lever has more torque as the fulcrum gets closer to
the object of power application (right diagram). But the lever must
also be rotated farther to get this torque.
Types of Power Trains
The power trains used in most of todayÕs construction machinery can
be classified into three basic types:
- Mechanical
- Hydrostatic
- Electric Drive
Unit 1
Lesson 1
1-1-6
Power Train I
FINAL
DRIVE
ENGINE
TC
TRANS
DIFF
FINAL
DRIVE
Fig. 1.1.8 Mechanical Power Train
In a mechanical power train, power from the engine is transferred
through a coupling (clutch or torque converter) to the transmission.
From the transmission power is transferred to the differential, final
drive and to the wheels or tracks.
MECHANICAL POWER TRAIN COMPONENTS
• Engine
• Coupling
• Transmission
• Differential
• Final Drive
• Ground Engagement
Fig. 1.1.9 Mechanical Power Train Components
Mechanical Power Train Components
The major components of a typical mechanical power train are as
follows:
Engine: Provides the power to operate the vehicle and the coupling
device
Coupling: Connects the engine power to the rest of the power train.
Flywheel clutch couplings may disconnect the engine power from the
rest of the power train. This allows the engine to run while the
machine is not moving. Torque converters and torque dividers
always provide a fluid coupling to connect the engine to the
remainder of the power train. The connection can be direct if the
machine is equipped with a lockup clutch.
Transmission: Controls output speed, direction and torque of the
power delivered to the remainder of the power train.
Unit 1
Lesson 1
1-1-7
Power Train I
Differential: Transmits power to the final drive and wheels while
allowing each wheel to rotate at a different speed.
Final drive: Connects power to the wheels or tracks.
Ground engagement: Propels the machine through wheels or tracks.
Fig. 1.1.10 Caterpillar 826G Compactor with
Mechanical Power Train Components
Fig. 1.1.11 Caterpillar D11R Tractor with Mechanical
Power Train Components
The machines shown in Figures 1.1.10 and 1.1.11 are equipped with
mechanical power trains.
Unit 1
Lesson 1
1-1-8
HYDRAULIC
PUMP
ENGINE
Power Train I
HYDRAULIC
MOTOR
TRANSMISSION
OR
DIFFERENTIAL
FINAL
DRIVE
HYDRAULIC CONNECTION
ENGINE
HYDRAULIC
MOTOR
FINAL
DRIVE
HYDRAULIC
MOTOR
FINAL
DRIVE
HYDRAULIC
PUMP
Fig. 1.1.12
Hydrostatic Drives
In hydrostatic drives, as the name implies, fluid is used to transmit
engine power to the machineÕs final drive. Power from the engine is
transferred to a hydraulic pump. The hydraulic pump provides oil
flow to a drive motor. The drive motor transfers power to the
transmission or directly to the final drive.
HYDROSTATIC POWER TRAIN COMPONENTS
• Engine
• Hydraulic Pump(s)
• Hydraulic Motor(s)
• Transmission (if equipped)
• Differential (if equipped)
• Final Drive
• Ground Engagement
Fig. 1.1.13 Hydrostatic Power Train Components
Hydrostatic Power Train Components
The major components of a typical hydrostatic power train are as
follows:
Engine: Provides the power to operate the vehicle and the hydraulic
pump(s)
Pump(s): Produce fluid flow to power the drive motor(s)
Motor(s): Provide power to the transmission or final drive
Transmission (if equipped): Controls the output speed, direction and
torque of the power delivered to the remainder of the power train..
Differential (if equipped): Transmits power to the final drive and
wheels while allowing each wheel to rotate at a different speed.
Unit 1
Lesson 1
1-1-9
Power Train I
Final drive: Connects power to the wheels or tracks.
Ground engagement: Propels the machine through wheels or tracks.
Fig. 1.1.14 Caterpillar 953C Track Loader with
Hydrostatic Power Train Components
Fig. 1.1.15 Caterpillar Small Wheel Loader with
Hydrostatic Power Train Components
The machines shown in Figures 1.1.14 and 1.1.15 are equipped with
hydrostatic power trains.
Unit 1
Lesson 1
1-1-10
Power Train I
In electric drive, electricity is used to transmit engine power to the
machine final drive. Power from the engine is transferred to an AC
generator. The electricity from the AC generator is used to power the
motors at the final drive.
CONTROLS
AC
GEN
DC
MOTOR
RECTIFIER
MOTOR
FIELD
EXCITER
Fig. 1.1.16 DC Electrical Drive Components
DC Electric Drive
•
•
•
•
•
•
•
Engine
AC Generator
Rectifier
Field Exciter
DC Motors
Final Drive
Ground Engagement
Fig. 1.1.17 DC Electrical Drive Components
DC Electrical Drive Components
Engine: Provides the power to operate the vehicle.
AC Generator: Converts the mechanical power from the engine into
electricity.
Rectifier: Converts the AC into DC.
Field Exciter: Controls speed of motors.
DC Motors: Provide power to the final drive.
Final Drive: Connects power to the wheels.
Ground Engagement: Propels the machine through the wheels.
Unit 1
Lesson 1
1-1-11
AC
GEN
RECTIFIER
Power Train I
DC to
VARIABLE AC
INVERTER
AC
MOTOR
Fig. 1.1.18 AC Electrical Drive Components
AC Electric Drive
•
•
•
•
•
•
•
Engine
AC Generator
Rectifier
DC to Variable AC Inverter
AC Motors
Final Drive
Ground Engagement
Fig. 1.1.19 AC Electrical Drive Components
AC Electrical Drive Components
Engine: Provides the power to operate the vehicle.
AC Generator: Converts the mechanical power from the engine into
electricity.
Rectifier: Converts the AC into DC.
DC to Variable AC Inverter: Controls speed of motors.
AC Motors: Provide power to the final drive.
Final Drive: Connects power to the wheels.
Ground Engagement: Propels the machine through the wheels.
Unit 1
Lesson 1
1-1-12
Power Train I
Fig. 1.1.20 Typical Location of AC Electric Drive
Electric drives are used on some competitive mining trucks. Most
competitive mining trucks have a DC electric drive, but recent larger
mining trucks have an AC electric drive.
Caterpillar does not manufacture any machines with electric drive.
Mining trucks with mechanical drives have been shown to have a
higher power train efficiency and higher operating speed on an uphill
grade. Competitive mining trucks also rely on dynamic braking
instead of using oil cooled disc brakes.
Because Caterpillar does not manufacture any machines with electric
drives, the remainder of the material in this course will exclude them.
Unit 1
Lesson 1
1-1-13
Power Train I
Power Transfer Drives
While the functions of all power trains are basically the same, a
variety of methods have been devised to achieve those functions. The
principal methods used for transferring power in machinery can be
classified into the following types:
- Gear
- Chain
- Friction
Fig. 1.1.21 Gears
Gear Drive
By definition, a gear is a toothed wheel or cylinder used to transmit
rotary or reciprocating motion from one part of a machine to another.
Gears are the most common elements used in modern power trains.
This is because gears represent one of the most efficient and costeffective means of transferring engine power to the drive wheels of a
machine. By varying the size and number of gears it is also possible
to modify the power produced by an engine to suit the work being
performed.
Unit 1
Lesson 1
1-1-14
Power Train I
Fig. 1.1.22 Rotating in Opposite Directions
Rotating in Opposite Directions
Gear teeth in mesh act as multiple levers that transfer torque from the
engine flywheel to the other gears in the power train. When only two
gears are used, the countershafts rotate in opposite directions (Figure
1.1.22).
Fig. 1.1.23 Idler gear
Idler Gear
Two gears in mesh are called a gear set. A third gear or idler gear
(Figure 1.1.23) is sometimes used between the drive gear and the
driven gear. The idler gear changes the direction of the driven gear
so it turns in the same direction as the drive gear.
Unit 1
Lesson 1
1-1-15
Power Train I
Fig. 1.1.24 Gear Train
Gear Train
Three or more gears in mesh together are called a gear train (Figure
1.1.24).
Fig. 1.1.25 Pinion Gear
Pinion Gear
When one gear is considerably smaller than another the smaller gear
is called a pinion (Figure 1.1.25).
Unit 1
Lesson 1
1-1-16
Power Train I
Fig. 1.1.26 Gear Splines
Gear Splines
Gears are usually mounted on shafts. Power is transferred to and
from gears by shafts, and gears must be firmly fastened to shafts.
Various methods are used to fasten gears to the shafts. Grooves
known as splines may be machined on the surface of the shaft and in
the gear hub. When the gear is pushed into the shaft, the splines hold
the gear so that it turns the shaft without slipping. Sometimes,
splines are engineered so that the gear can slide sideways on the
shaft. This sliding gear feature is often used in transmissions.
Fig. 1.1.27 Gear Keys
Gear Keys
Keys are another method used to prevent gears from slipping on their
shafts. In a simple key arrangement, a single slot or keyway is
machined in the shaft and another in the hub of the gear. When the
key, a square piece of metal, is inserted it locks the gear and shaft
together. A more elaborate variation of the key is a semi-circular type
known as a Woodruff key, named for the inventor.
Unit 1
Lesson 1
1-1-17
Power Train I
SPEED
ADVANTAGE
or a
TORQUE
ADVANTAGE
Fig. 1.1.28 Gear Mechanical Advantage
Gear Mechanical Advantage
Gears in machinery are frequently used to provide a speed advantage
or a torque advantage. Gears cannot provide a power advantage. The
actual power of a machine is determined by the capacity of the
engine. However, the use of different size gears permits engine
power and speed to be used most efficiently to operate a machine
under various load conditions. When gears are used to increase
torque, output speed is reduced. When output speed is increased
through gearing, torque is reduced.
24
48
2:1
Fig. 1.1.29 2:1 Gear Ratio
2:1 Gear Ratio
The rotational speed of gear-driven shafts depends on the number of
teeth in each gear.
A pinion gear with 24 teeth driving a gear with 48 teeth will revolve
twice as fast as the gear it is driving. The gear ratio is 2:1 (Figure
1.1.29).
Unit 1
Lesson 1
1-1-18
Power Train I
24
48
1:2
Fig. 1.1.30 1:2 Gear Ratio
1:2 Gear Ratio
If the power flow is reversed, so that the larger gear is driving the
smaller gear, the gear ratio is also reversed to 1:2 (Figure 1.1.30). By
using a train of several gears, the ratio of driving to driven speed may
be varied within wide limits.
12
48
48
1:1
48
48
48
1:1
Fig. 1.1.31 Idler Gear Ratios
Idler Gear Ratios
A single idler gear used to change the direction of rotation does not
change the gear ratio (Figure 1.1.31). The idler gear can have any
number of teeth. So if a small idler wheel with 12 teeth is used
between two gears with 48 teeth the ratio remains 1:1. The same is
true if the idler gear has 48 teeth.
Unit 1
Lesson 1
1-1-19
EXTERNAL GEAR
Power Train I
INTERNAL GEAR
Fig. 1.1.32 External and Internal Gear Teeth
External and Internal Gear Teeth
A gear with teeth around the outside circumference is called an
external tooth gear. A gear with teeth machined around the inside
diameter is called an internal gear.
Fig. 1.1.33 Gear Face Width
Gear Face Width
The width of a gear across the teeth is called the face width. Wider
gears have more contact area and can transmit more power.
Unit 1
Lesson 1
1-1-20
Power Train I
INVOLUTE CURVE
Fig. 1.1.34 Involute Curve
Involute Curve
For a power train to operate properly, all gears in a gear train must
have teeth that are compatible with one another in size and shape.
The sides of gear teeth are not straight. Instead, gear teeth are
machined with a profile that is designed to obtain maximum power
transfer efficiency from the gear as it meshes with other gears. The
sides of each tooth follow the shape of what is known as an involute
curve (Figure 1.1.34). The curved shape provides a rolling contact as
opposed to sliding against other teeth in mesh.
PRESSURE
ANGLE
Fig. 1.1.35 Pressure Angle
Pressure Angle
Gears teeth are cut with a profile so that when teeth mesh they
produce a pressure angle that is calculated to allow smooth, full-depth
engagement (Figure 1.1.35).
Unit 1
Lesson 1
1-1-21
Power Train I
Fig. 1.1.36 Gear Tooth Clearance
Gear Tooth Clearance
Smooth gear mesh is critical to proper gear operation. If gears mesh
too tightly, binding occurs producing excessive friction and power
loss. If the mesh is too loose, gears will be noisy and inefficient. A
small amount of clearance (Figure 1.1.36) is required between teeth
to allow for lubrication and smooth, efficient operation. The
clearance allows a slight backward movement of the gears that is
called backlash.
Excessive backlash is usually an indication of wear in the gear teeth
or the bearings that support the gears. Excessive backlash can result
in broken gear teeth or gears bouncing under load. During equipment
service operations it is often necessary to measure and adjust
backlash to proper specification, using shims designed for that
purpose.
BENEFITS OF GEAR DRIVE
No Slippage
Can Handle Very High Loads
Fig. 1.1.37 Gear Drive Benefits
Gear Drive Benefits
The benefits of gear drives are no slippage and they can handle very
high loads. However they are heavier than other types of drives and
the distance between the input and output shafts is fixed by the
diameter of the gears.
Unit 1
Lesson 1
1-1-22
Power Train I
Fig. 1.1.38 Gear Drive in an Axle
Gear Drive in an Axle
The axle pictured in Figure 1.1.38 is an example of gear drive. In
this particular application, the gears are able to handle very high
torque loads at the final drive.
Fig. 1.1.39 Chain Drive
Chain Drive
A chain drive is a variation of a gear drive that is also used to
transmit power from one rotating shaft to another. The gears, usually
called sprockets, are not in mesh but instead are connected by a
linked chain. The links of the chain mesh with the teeth of the
sprockets so that the driven sprocket maintains a constant speed ratio
with the drive sprocket. Track drives operate under the same
principles as a chain drive.
Like gears, chains drives virtually eliminate slippage. Sprockets
connected to the same side of the chain rotate in the same direction.
Sprockets connected on different sides of the chain move in opposite
directions. To avoid excessive wear, sprockets for roller chain drives
should have 10 or more teeth. If a chain has an even number of
spaces between links the sprockets should have an odd number of
teeth.
Unit 1
Lesson 1
1-1-23
Power Train I
Fig. 1.1.40 Roller Chain Components
Roller Chain Components
Roller chains are the types most commonly seen on heavy machinery.
They provide an efficient means of carrying heavy loads at low
speeds between shafts that are far apart. The roller chain is made up
of alternate roller links and pin links. Roller links have two roller
link side plates, two bushings and two rollers. Pin links consist of
two pin link plates and two pins. The side plates of the roller chain
determine the pitch of the chain.
Fig. 1.1.41 Chain Tensioning
Chain Tensioning
Like gears, chain sprockets are often mounted on shafts with splines
and keys. The slack side of a chain should be on the bottom
whenever possible. On longer chain drives an idler wheel or sprocket
is often used on the slack side to maintain proper tension between the
driving sprocket and the driven sprocket. Chains do stretch in use so
chain tension must sometimes be adjusted (Figure 1.1.41). This may
be accomplished by moving one of the main sprockets or adjusting
the idler sprocket, if equipped.
Unit 1
Lesson 1
1-1-24
Power Train I
BENEFITS OF CHAIN DRIVE
Little or No Slippage
Relatively Inexpensive
Can Maintain Fixed Ratio Between Shafts
Resist Heat, Dirt and Bad Weather
More Powerful than Belt Drives
Fig. 1.1.42 Benefits of Chain Drives
Benefits of Chain Drives
The benefits of chain drives are:
- Little or no slippage
- Relatively inexpensive
- Can maintain fixed ratio between rotating shafts
- Resist heat, dirt and bad weather
- More powerful than belt drives
Disadvanges of Chain Drives
Chain sprockets and shafts must be very carefully aligned to ensure
full service life and correct tracking. Chains drives must be
lubricated regularly to reduce wear, protect against corrosion and
prevent the link pins or roller bushings from galling or seizing.
Unit 1
Lesson 1
1-1-25
Power Train I
Fig. 1.1.43 Chain Drive in a Track-type Tractor
Chain Drive
Large machines use different types of chain drives. The tractor
pictured in Figure 1.1.43 uses a version of a chain (called a track) to
propel the machine. The track is driven by a sprocket.
Fig. 1.1.44 Chain Drive in a Skid Steer Loader
Chain Drive in a Skid Steer Loader
Smaller machines, such as the Skid Steer Loader shown in Figure
1.1.44, use a chain to transfer power to the final drive and drive
wheels. The chain is driven by a hydraulic motor through a sprocket
as shown in Figure 1.1.39.
Unit 1
Lesson 1
1-1-26
Power Train I
Fig. 1.1.45 Friction Between Wheel and Ground
Friction Drive
Friction occurs when the surfaces of two objects rub together. This
friction can be used to transmit motion and power from one object to
another. The amount of friction depends on the surface materials, the
force with which the objects touch and the temperature of the
surfaces. Unlike gears and chains, friction drives allow some
slippage to occur between components. This slippage is useful when
a more gradual transfer of power is desirable.
One of the most common uses of friction is in a wheel. The friction
between a driven wheel and the ground propels the wheel and the
machine attached to it in the same direction the wheel is turning
(Figure 1.1.45).
Unit 1
Lesson 1
1-1-27
Power Train I
Fig. 1.1.46 Friction Between Two Wheels (wheel to
Friction Between Two Wheels
Using this same friction, power can be transmitted by bringing a
driven wheel into contact with the surface circumference a second
wheel (Figure 1.1.46). The second wheel will rotate in the opposite
direction. Wheels used to transmit power in this manner are
sometimes referred to as friction gears even though the wheels have
no teeth.
The speed and torque of friction wheel drives depends on the size of
each wheel. The same speed and torque principle explained earlier
regarding gears also applies to friction wheel drives. A small wheel
driving a large wheel results in less speed and more torque. A large
wheel driving a small wheel results in less torque and more speed.
Unit 1
Lesson 1
1-1-28
Power Train I
Fig. 1.1.47 Disc or Clutch Drive (friction disc)
Disc or Clutch Drive
Another common friction drive is the disc or clutch. Clutches are
used to cause two components to rotate together. When the clutch is
engaged, the discs and plates are held together by springs or by
hydraulic pressure. Friction causes the discs and plates to rotate
together. In a flywheel clutch, two disks are mounted on a shaft.
One disc is connected to the engine, the other to the power train,
usually at the transmission. When the discs are not touching, the disc
connected to the engine runs freely (Figure 1.1.47, top diagram)
while the disc connected to the power train is unaffected. When the
discs are brought together, engine rotation is transferred by friction to
the power train disc, which then turns in the same direction (Figure
1.1.47, bottom diagram). The speed and torque of each friction disc is
the same.
Clutches are used in planetary transmissions to change the speed ratio
between the input shaft and the output shaft. Clutches are also used
in torque converters with lockup clutches to provide a direct
connection between the input shaft and the output shaft.
Unit 1
Lesson 1
1-1-29
Power Train I
Fig. 1.1.48 Belt Drive
Belt Drive
Belts are a common means of transferring power from one wheel to
another. In a belt drive (Figure 1.1.48) the wheels are referred to as
pulleys. Unlike wheels driven by direct friction contact, pulleys
rotate in the same direction. Also belts provide a more efficient power
transfer than friction wheels because the belt contacts more of the
pulley surface.
The speed and torque of belt drives depends on the size of each
pulley. The same speed and torque principle explained earlier
regarding gears and friction wheel drives, also applies to belt drives.
A small pulley driving a large pulley results in less speed and more
torque. A large pulley driving a small pulley results in less torque
and more speed.
Unit 1
Lesson 1
1-1-30
Power Train I
BENEFITS OF FRICTION DRIVE
Intentional Slippage Can be Built into Machine
A Wide Range of Different Materials can be Used
Fig. 1.1.49 Benefits of Friction Drive
Benefits of Friction Drive
The benefits of friction drives (Figure 1.1.49) include the ability to
intentionally build slippage into the machine and a wide range of
different materials can be used. The contact area should be a
minimum of 180ûon the driver. Friction drives are expensive and
excessive slippage can cause accelerated wear and premature failure.
Fig. 1.1.50 Belt Drive
Belt Drive
The drive belts on the Challenger tractor pictured in Figure 1.1.50 use
friction to transfer power from the final drive to the ground.
Unit 1
Lesson 1
1-1-31
Power Train I
Fig. 1.1.51 Disc Drive
Disc Drive
The clutch discs and plates shown in Figure 1.1.51 use friction to
engage the clutch pack which transfers power to a transmission.
Fig. 1.1.52 Fluid Drive--Water Wheel
Fluid Drive
Fluid drives have been in use since the earliest developments in
machinery. One of the most basic forms of fluid drive is the water
wheel (Figure 1.1.52). Many of the mills and factories of Colonial
America were powered very efficiently by water wheels. Fluid drives
are now used in the some of the most sophisticated modern
machinery such as hydrostatic drives.
Unit 1
Lesson 1
1-1-32
Power Train I
Fig. 1.1.53 Hydraulic Pump
Fig. 1.1.54 Motor
Hydraulic Pump and Motor
Fluid drive in a machine power train converts the mechanical power
of the engine to hydraulic power and then converts the hydraulic
power back to mechanical power to move the machine. This
conversion of power is done using a hydrostatic system or by
hydrodynamics.
A hydrostatic system is a closed loop hydraulic system that uses fluid
under high pressure and low velocity to transmit power. A hydraulic
pump, driven by the engine (Figure 1.1.53), provides oil flow to a
motor (Figure 1.1.54) which propels the machine.
Unit 1
Lesson 1
1-1-33
Power Train I
Fig. 1.1.55 Fluid Coupling
Fluid Coupling
Hydrodynamics use low oil pressure at a high velocity to transmit
power through the use of a fluid coupling . A fluid coupling (Figure
1.1.55) consists of an impeller (or pump) and a turbine. The impeller
(driven by the engine) forces oil into the turbine, which transfers
power to the transmission.
Fig. 1.1.56 Liquids Have No Shape of Their Own
Liquids Have No Shape of Their Own
Two principles of hydraulics are required to understand a hydrostatic
drive system:
- Liquids have no shape of their own and therefore, assume the
shape of any container they are placed in (Figure 1.1.56).
Unit 1
Lesson 1
1-1-34
Power Train I
Fig. 1.1.57 Pascal's Law (Pascal's law)
PascalÕs Law
- Liquids do not compress. PascalÕs Law of fluids states: "Change
in pressure applied to an enclosed fluid is transmitted
undiminished to every point of the fluid and to the walls
containing the fluid." (Figure 1.1.57)
MECHANICAL ADVANTAGE
100 lbs
50 lbs
50 psi x 2 sq. in.
= 100 lbs.
6 in.
50 psi
12 in.
2 sq. in.
1 sq. in.
Flow
50 lbs. x 1 sq. in. = 50 psi
Fig. 1.1.58 Mechanical Advantage
Mechanical Advantage
In practice, these principles mean that oil in a hydraulic system will
flow in any direction and into passages of any size or shape. When
pressure is applied to the fluid, instead of compressing, it pushes
through the passages of the device it is contained in. The applied
pressure can be transmitted in all directions to perform work.
Unit 1
Lesson 1
1-1-35
Power Train I
For instance, if two identical cylinders are connected by a tube and
partially filled with oil, compressing the fluid in one cylinder will
cause the fluid to rise by a corresponding and equal amount in the
connected cylinder. This is the basic operating principal used in
hydraulics.
Say the identical cylinders have areas of one square inch and pistons
of the same size are placed in each cylinder. If a force of one pound
is applied to the piston in one cylinder a force of one pound will be
applied throughout the liquid. So, an equal force of one pound will
be applied to the second cylinder.
Now, say the first cylinder has an area of one square inch and the
second cylinder has an area of two square inches. Again a pressure
of one pound is applied to the first cylinder. Since the second
cylinder has an area of two square inches, now a force of 2 pounds is
applied to the second piston. This is called mechanical advantage
(Figure 1.1.58). The force exerted by a piston can be determined by
multiplying the piston area by the pressure
BENEFITS OF FLUID DRIVE
Fewer Moving Parts
Less Wear
Infinite Speed Ranges
Fig. 1.1.59 Fluid Drive Benefits
Fluid Drive Benefits
In a hydrostatic drive system, a number of pistons are used to
transmit power. A group of pistons in the pump send power to
another group of pistons in the motor. In a pump motor type
hydraulic drive, the rate of oil flow determines speed. The amount of
torque is determined by oil pressure. The direction of the oil flow
controls the direction of power flow.
The benefits of a fluid drive system include fewer parts, less wear
and infinite speed ranges.
Fluid drive systems are susceptible to leakage and temperature related
problems.
NOTES
NOTES
NOTES