Mechanical Design Consideration and Lubrication

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Mechanical Design Consideration and Lubrication

• Engine layout and Balancing
• Number of Cylinders
• Dynamic Balancing
• Lubrication
• Bearing Loading
• Piston Speeds
• Friction

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How Many Cylinders, and Where?

• Considerations
• How many cylinders to produce steady output
• Minimum swept volume per cylender (400cc?)
• Balancing considerations
• Steady torque output

• Types
• V
• Inline
• VR (Narrow)
• Flat (Boxer?)
• W
• H Type
• Max 6 for inline
• May use torque split in center of crank (12 cyl
  Pcar)

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Layouts

• Inline, V, Flat, can also be H, VR or W

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Torque Characteristics

• More cylinders, flatter output
• Make up for it with a flywheel
• Flywheel slows down acceleration

• 4 Stroke
• Minimum of 5 cylinders needed to always be
  producing power

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Balancing Considerations
Approximate rod with two point masses is good
first-order approximation

• Actual rod has center of mass and radius of
  gyration

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Model crank as Crank-Slider-Mass

• mr mass of rod

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4 cylinders out of balance on secondary mass

• This is purely BALANCING reciprocating mass.
  Note that in 4 cylinder they add.
• What happens in 6 cylinder inline? V? Flat?
• What happens in 8 cylinder V?

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Mitsubishi Balance Shaft

• Masses rotate in opposite directions and at twice
  crank speed.
• Why opposite directions?
• Where should they be placed?
• Does it work?

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Balance Shafts
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Materials

• Cast Iron
• Cheap
• Good Machining
• Good Dampening
• Low conductivity
• Hard enough for cylinder liners
• HEAVY

• Aluminum
• More expensive
• Light
• OK machining
• High conductivity
• Special treatment for cylinder liners
• Excellent Silicon alloys available

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Parts

• Cylender Heads
• Aluminum
• Needs Valve Seat
• Block
• Aluminum
• Needs cyl liners or chemical etching
• Al Si Mg alloys
• Etching allows for ceramic wear surface

• Pioneers
• Chevy Vega
• Porsche 944
• Mercedes
• Problems
• Different thermal expansion than steel
• Corrosion is an issue
• Weak

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Pistons Rings

• Cast, Billet, Forged
• Lightness is an issue
• Maybe coated to reduce heat transfer
• Rings
• Cast Iron or Steel
• Thinner is Better
• Narrower
• Better Seal
• Better for out of round
• Less friction

• Rings
• A) Seal combustion chamber
• B) Transfer heat from piston to Cylinder
• C) Control oil flow
• D) Act as bearing surface

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Pistons Rings
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Lubrication Bearings

• 2/3 of engine friction is at the pistons rings
• Losses increase with speed
• Friction most significant at part load operation,
  since it is a weak function of load and a strong
  function of RPM

• Read Info on Viscosity
• SAE 10W40 measured at 0oF and 210oF
• Beware of 10W40 and multi-grades in general
• Ratings lose meaning at high loading

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Typical Crank Lubrication
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Lubrication Modes

• Boundary bad for bearings!
• Boundary OK for cams/lifters/ rockers

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Boundary Lubrication Smoothness Matters!
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Some Oiling Systems
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911 Oiling System (Early) Dry Sump
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911 Oiling System (Late) Dry Sump
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Dry Sump Oil Pump

• Dual Pump for scavenge and feed
• Talk About Piston Squirters