Drive Trains and Power Systems

Drive Trains and Power
Systems

Learning Objectives

●Name the components of a power train

●Understand the differences among transmission types

●Know how a power train transmits power to output sources

●Discuss the ways power can be harnessed for applications other
than driving wheels

●Know how to calculate torque and RPM

Power Trains

●Transmit power to output sources such as drive wheels and power take-offs (PTOs)

●Connect and disconnect the power source and PTO

●Determine speed: torque ratios

●Equalize drive wheel power

●Allow reverse travel

Multiple Choice

______ transmit power to output sources such as drive wheels and power takeoffs (PTOs)?

• hydraulics

• clutches

• power trains

• sprockets

Power Trains

●Components

○Clutch

○Transmission

○Differential

○Final drive

Match

Match the following

• transmits power from the transmission to the final drive

• gives operators the ability to select directional travel

• couples and decouples the engine and transmission

• transmits power to the drive wheels

differential

transmission

clutch

final drive

• differential

• transmission

• clutch

• final drive

Power Train: Clutch

●Friction disc assembly that engages and disengages the engine flywheel from the
transmission to transfer power through gear sets

●Usually engaged and disengaged with a foot pedal

○Mechanical clutch: pedal is connected to linkages, cables, and springs

○Hydraulic clutch: uses fluid power to aid in engagement and disengagement

Power Train: Clutch

Clutch components include the flywheel, pressure plate, and friction disc

Multiple Choice

Parts of a clutch include the flywheel, pressure plate, and _____.

• final drive

• gear ratio

• friction disc

• sprocket

Power Train—Transmission

●Consists of gears that allow the power source to propel the final drive wheels in
multiple forward and reverse speeds

○A gear is a disc- or cone-shaped object with a series of teeth cut into its edge

○Varying arrangements of gears provide multiple speed and torque options

○Gears selected by the operator

●Types

○Automatic, hydrostatic, mechanical

Multiple Choice

A _____ is a disc or cone shaped object with a series of teeth cut into its edge.

• gear

• flywheel

• clutch

• transmission

Power Train—Transmission

●Gearing

○Smaller drive gears turn larger gears for more torque and lower speeds

○Larger drive gears turn smaller gears for more speed and lower torque

●Gear ratio

○The difference between the two gears

○A 10” gear drives a 5” gear

○10:5 equals a 2:1 gear ratio

Fill in the Blank

The difference between a small driver gear and a larger driven gear is called the gear _____.

Multiple Choice

What is the gear ratio if one gear has 40 teeth and the other gear has 16 teeth?

• 2:1

• 3:1

• 1:1

• 2.5:1

Power Train—Gearing

In two-gear systems, both gears rotate in opposite directions

Power Train—Gearing

In three-gear systems, the two outer gears spin in the same direction, and the center gear
spins in the opposite direction

Power Train—Gearing

This alternating pattern of rotation is consistent, no matter how many gears are in the path
or the point of contact between gear pairs

Multiple Choice

If there are three gears, the gears on the end rotate in the same direction, but the gear in the middle rotates in the opposite direction.

• True

• False

Power Train—Transmission

●Automatic transmission

○Gear ratio changes are activated without direct operator input

○Operator selects forward or reverse but not the gearing

○Hydraulic valves direct flow of fluid to adjust gearing

○Convenient

○Lower power-handling ability

○Not prevalent in agricultural machinery

Power Train—Transmission

●Hydrostatic transmission

○Mechanical power is converted to hydraulic power through a pump/motor
combination that modulates fluid pressure

○Hydrostatic is the ability to transfer power through fluids at rest or under
pressure

○Energy transfer is accomplished through the pump/motor

○Speed is controlled through fluid flow rates

○Direction of travel manipulated using internal valves to direct the flow of the fluid

Power Train—Transmission

●Mechanical transmission

○Operator physically selects gear

○Must depress a clutch manually while selecting gears

○Most reliable and most efficient

○Also referred to as manual or standard transmission

Multiple Choice

A basic type of transmission used in agricultural mechanics is a(n) _____.

• automatic

• hydrostatic

• manual

• all of these

Match

Match the following

• Transmission in which the gear ratio changes are activated without direct operator input

• Transmission with a hand-operated selector lever that allows the operator's choice of gear ratios to be transmitted through the transmission

• Transmission with the ability to transfer power through fluids at rest or under pressure

automatic

mechanical

hydrostatic

• automatic

• mechanical

• hydrostatic

Power Train

●Driveline

○Connects transmission to final drive

○Usually a straight metal shaft or tube

○Universal joints and a slip yoke allow movement of the rear end flex in the system

○U-joints allow the driveline to pivot and rotate without binding

Fill in the Blank

A(n) _____ connects the transmission to the final drive.

Power Train

●In some systems, the differential is considered the final drive transmitting power from
the transmission to the drive wheels

○An assembly of gears

○May be connected with or without a driveline

○Allows the drive wheels to turn at different speeds

●Differential types include

○Standard or open

○Limited-slip

Power Systems

●Power systems are used for many applications

○Driving wheels and tires

○Operating equipment such as wood chippers, generators, mixers, and tillers

○Powering power take-off

○Powering hydraulic pumps

Transmitting Power

●Power train components include

○Pulley systems

○Belts and chains

○Power take-off (PTO)

○Hydrostatic drives

Belt Systems

●May use multiple belts in heavy-duty situations

●Materials include rubber, synthetics, and leather

○Proper alignment with adequate friction must be maintained

○Larger driver pulley means higher RPM for the driven pulley but less torque

○Smaller driver pulley means lower RPM for driven pulley but higher torque

Calculating Power

●The ratio between pulley diameters determines the torque and speed

●Both the driver and driven pulleys rotate in the same direction

Calculating Power

●In a gear system, the number of teeth on the driver and driven gears determines the
speed and torque

●The gears rotate in opposite directions

Chain Systems

●More efficient than belts because they have

●little or no slip

○Sprockets (toothed wheels) replace pulleys

○May damage equipment if placed in a bind

○Links are added and removed to adjust length

○Long service life and minimal maintenance

Power Take-Off (PTO)

●Gear-driven shaft that normally extends past the differential on the rear of equipment

●Driven by the power source

●High torque at 540 or 1000 RPM

●Splined output shaft provides connection point for implement

Multiple Choice

A _____ is a gear driven shaft that normally extends past the differential on the rear of the equipment. It is driven by the power source and has a splined output shaft that turns with great torque.

• drive train

• power take-off

• pulley

• output shaft

Hydrostatic Drives

●Hydraulics is the use of a liquid to perform work

●A hydrostatic drive is a hydraulic system that consists of a pump, motors, valves, and
oil lines, which replace the traditional clutch and transmission

Hydrostatic Drives

●Oil flow and pressure drive wheels

●The engine powers the pump, providing high pressure to the drive motors

●Drive direction and power can be done quickly and efficiently

●All motors can be controlled independently

Multiple Choice

_____ is the use of a liquid to perform work, such as extending a cylinder to lift a heavy load.

• drive train

• power take-off

• pulley

• hydraulics