Crankshafts%20and%20Fluid%20Bearings

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Crankshafts and Fluid Bearings

• Anthony Manistre

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Objective

• To explain the functions of a crankshaft and
  fluid bearings in the automotive system.

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4-Cylinder Engine
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Four-Stroke Combustion

• Intake Stroke
• Compression Stroke
• Combustion Stroke
• Exhaust Stroke

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Intake Stroke

• The piston starts at the top, the intake valve
  opens, and the piston moves down to let the
  engine take in a cylinder-full of air and
  gasoline. This is the intake stroke. Only the
  tiniest drop of gasoline needs to be mixed into
  the air for this to work.

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Compression Stroke

• Then the piston moves back up to compress this
  fuel/air mixture. Compression makes the explosion
  more powerful.

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Combustion Stroke

• When the piston reaches the top of its stroke,
  the spark plug emits a spark to ignite the
  gasoline. The gasoline charge in the cylinder
  explodes, driving the piston down.

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Exhaust Stroke

• Once the piston hits the bottom of its stroke,
  the exhaust valve opens and the exhaust leaves
  the cylinder to go out the tail pipe.

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Job of the Crankshaft

• The crank shaft turns the piston's up and down
  motion into circular motion just like a crank on
  a jack-in-the-box does.

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Journal Bearing
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Automotive Journal Bearings

• Journal bearings in gasoline (petrol) and diesel
  engines pump oil at low pressure in to a
  large-gap area of the bearing. As the bearing
  rotates, oil is carried in to the working part of
  the bearing, where it is compressed, with oil
  viscosity preventing the oil's escape. As a
  result, the bearing hydroplanes" on a layer of
  oil.

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Draw Backs

• This bearing type is an example of a hydrodynamic
  bearing which does not use a secondary bearing
  for start/stop. In this application, a large part
  of the bearing wear occurs during startup and
  shutdown, though in engine use, substantial wear
  is also caused by hard combustion contaminants
  that bridge the oil film.

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Sources

• http//en.wikipedia.org
• http//auto.howstuffworks.com
• www.efunda.com