IMS Operation and Service of Power Trains

Principles of Power Transfer

• The most convenient method to move something is often found using simple machines, like levers.
  • Early humans used branches as levers to move large rocks. A small rock acted as a fulcrum (pivot point).
• Torque is the turning effort causing rotation.
  • Measured by force (pounds) multiplied by the distance from the pivot point (feet).
    • Example: 100 lbs of force applied 6 feet from the pivot point equals 600 ft-lbs of torque.
• Mechanical advantage of a lever is the ratio of the force side to the resistance side of the pivot.
  • Closer to the resistance, the more increased the mechanical advantage.
  • The further the force is applied from the resistance, the slower the action is to move the resistance = increased effort.
• Simple machines were developed over time.
  • Wheel and axle, pulleys, inclined plane, screw, wedge

Introduction to Power Trains

• Most modern engines operate most efficiently at about 2,200 RPM.
  • A 150-horsepower engine produces about 300 foot-pounds of continuous torque.
• A power train converts high-speed, low-torque rotation to low-speed, high-torque rotation of the wheels to pull a load.
  • Connects and disconnects engine power.
  • Allows selection of different speed ratios.
  • Provides a means for reversing vehicle direction.
  • Equalizes power to all drive wheels.
  • Starts and stops the PTO shaft.
• Power transfer methods include friction, moving fluids, and gears.

Friction Drives

• Children using a tricycle is an example of friction transfer.
• Applied force through the pedals is transmitted to the wheel by friction.
• Friction between the wheel and the floor is necessary for the tricycle to move.
• Slippage occurs when there is less friction, like on slick surfaces.

Fluid Drives

• Water wheels are a simple form of fluid power transfer.
• Water force causes paddles to turn the wheel.
• Modern fluid drives include fluid couplings, torque converters, and hydrostatic transmissions.
  • Fluid drives use hydraulic oil movement to turn turbine wheels.

Gear Drives

• Gears are the most common way to transfer power.
  • Gears meshing eliminates slippage.
• Gears change speed and direction of power; also, increase or decrease torque.
  • Chain drives are a variation of gear drives.
• Sprockets (gears) are connected by a chain to eliminate slippage.
  • Driving sprocket transfers power to the driven sprocket.

Gear, Pulley, and Sprocket Ratios and Shaft Speeds

• Gear ratio is the tooth count ratio of two gears.
  • 1:1 ratio means no speed or torque change.
  • A smaller driver gear produces less speed and more torque. -Example: If a smaller driver gear with 12 teeth turns at 500 RPM, the driven gear with 24 teeth turns at 250 RPM (resulting in 600 foot-pounds of torque).
• Larger driver gear produces more speed and less torque.

Purpose of the Clutch

• The clutch connects and disconnects the engine and transmission.
• Used to gradually apply load to the power source.
• Most clutches use friction to transfer power.

Operation of a Basic Clutch

• Two disks are mounted on separate shafts with a space/clearance between the shafts.
• When the surfaces contact, friction causes them to turn together.
• Engaging positions release the clutch pedal and the clutch disk turns with the flywheel.
• Disengaging positions depress the clutch pedal, compressing springs and breaking the frictional contact between disks.

Types or Classifications of Clutches

• Disk/plate clutches, wet or dry
  • Many modern clutches use plates and disks instead of single disk units.
  • Dry clutches operate through linkages.
  • Wet clutches operate in an oil bath.
• Overrunning Clutch—only engages in one direction.
• Magnetic Clutch—uses magnetic forces to hold together/engage.

Major Ways in Which Clutches Operate

• Mechanically operated clutches use linkages and springs.
• Hydraulically operated clutches use a master and slave cylinder. Hydraulic fluid controls the clutch.
• Electrically operated clutches use electromagnetism to engage/disengage the clutch.

Final Drives

• Final drives provide a final reduction in speed and increase in torque.
  • Different types of final drives exist (pinion drives, planetary drives, chain drives).
• This reduction is vital to transmit power at lower speeds, but higher torque levels.

Torque Dividers

• Component added to power trains to divide torque to front and rear drive axles.
• Useful in vehicles with true four-wheel drive or mechanical front wheel drive.
• Used when front and rear drive tires are different sizes or for other variations in the power train system.
  • Torque divider clutch/shifting options and use for varying situations.

Power Take Off (PTO)

• PTO is an extension of the power train in tractors—connects engine power to auxiliary equipment.
  • Classifications: transmission-driven, continuous-running, and independent.
  • Includes speed and torque considerations, and safety precautions.

Transmission Features

• Mechanical transmissions use gears for various speed ratios, reverses.
  • Types of mechanical transmissions (sliding, collar, synchromesh).
• Hydraulic transmissions use hydraulic fluids for power transmission; types include hydrodynamic, and hydrostatic.
• Uses a gear and piston assembly to transmit power; this is different than power transmissions that rely on gears or chains.

Power Train Lubricants

• Gear oils, automatic transmission fluids, transmission/hydraulic fluids, lubricating greases are vital.
  • Viscosity ratings, foam inhibitors, extreme pressure, and other critical additives.
  • Manufacturers' recommendations for types and amounts differ by application, operating conditions, and equipment (i.e. tractor).
• Oil additives for safety and efficiency and prevent oxidation/damage.

Gear Oil Classifications

• SAE classification by viscosity ratings

  • Higher numbers mean higher viscosity.

• API classification by operating conditions

  • GL-1 to GL-6. Use different oils depending on engine capabilities.

• Different ratings for different functions in the power train system.

Lubricating Greases

• Grease types (calcium, sodium, lithium).
• Grease additives to handle high temperatures, moisture, and other varying conditions.