IT 221 Power Transmission

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IT 221 Power Transmission

• Week 5
• Chapters 4 and 5

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Friction clutch

• Driving member - Disk driven by engine
• Driven member - Disk connected to output shaft
• Levers and springs to disengage/engage plates
• Energy transferred by friction
• Originally, asbestos because of heat

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Describe the operation of the friction clutch
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Friction drive

• Driven wheel is usually harder than the driver to
  minimize wear
• Only appropriate for low horsepower applications
• Similar principle to that of the friction clutch

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Explain the operation of a friction drive
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Friction Band Brake

• Applying force to the lever tightens the band
• This slows the rotation of the shaft
• Generates heat
• Often need to add water

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Drum brake

• Cylindrical working surface
• Shoes press against the drum
• Shoes outside
• Heat expansion increases friction
• Shoes inside
• Centrifugal force aids disengagement

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Disk Brake

• Pressure on both sides of a rotating disk
• Calipers hold the brake pads
• Fading may occur
• Reduction in friction coefficient with heat

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Positive clutch

• Positive engagement of two turning shafts
• Does not rely upon friction, but rather on
  compression

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Overrunning clutches - sprag, roller

• Activated by centrifugal force
• Increased speed results in loose part becoming
  wedged between inner and outer shaft

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Pneumatic, hydraulic, and electric clutches

• Energy that activates clutching may be
• Pneumatic
• Hydraulic
• Electric solenoid

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Electric Clutches

• Magnetically energize particles
• Magnetic energy is variable
• Degree of clutching can be controlled
• Controlled amount of slip can be permitted
• Used where speed changes often

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Couplings

• Device to connect two shafts
• Rotational energy transferred through the coupling

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Rigid Couplings

• Rigid used when minimal shaft mis-alignment
• Spline - similar to external gear inside an
  internal gear
• No slip
• Tapered shaft with anti rotation device
• Woodruff key
• Dowel pins

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Rigid Couplings

• Flanged

• Sleeve

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Flexible couplings

• To accommodate shaft mis-alignment
• Chain Oldham

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Flexible Coupling

• Gear Grid

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Flexible Coupling

• Elastomeric

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Universal joint

• Hookes joint
• Cardan joint
• Usually two in combination to transfer rotation
  around a corner

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Fluid coupling

• Drive shaft turns impeller (pump)
• Turbine turns output shaft
• Shape of housing helps transfer of energy
• Can control the quantity of fluid to control
  energy transfer

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Fluid coupling
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Bearing radial and thrust load
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Plain Bearings

• Friction bearing
• Journal bearings
• Contain soft material called Babbitt
• Friction at low speeds
• At high speeds held by a thin layer of oil
• Sometimes teflon or oil

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Plain Bearings

• Pillow block
• Radial Bearing

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Axial Plain Bearing

• Kingsbury

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Frictionless bearing

• Rolling contact to minimize friction
• Ball bearing
• Radial Axial

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Tapered Roller Bearing
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Spherical Bearing
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Ball screw

• Recirculating ball system
• Return channel

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Types of bearing mountings

• Pillow block
• Rod end

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Lubricants

• Reduce friction
• Remove heat
• Oil, grease, graphite
• Viscosity important
• Drop feed oilers, jet spray oilers

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Seals

• Surfaces
• Gaskets - cork, rubber
• Shaft
• O ring - rubber, elastomeric

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Flexible shafts

• Ability to transmit torque around a corner
• Usually wire wound around center core