Valve Train (Camshaft, Rocker arm, Pushrods) By: Hewett Sze

1
Valve Train (Camshaft, Rocker arm, Pushrods)
By Hewett Sze

• Objective
• To give an overview of how these components
  function in an engine and how their
  configurations affect engine performance.

2
Valve Train

• The valve train consists of the valves and a
  mechanism that opens and closes them. The opening
  and closing system is called a camshaft.

3
Camshaft
http//static.howstuffworks.com/gif/camshaft-ch.jp
g http//www.familycar.com/classroom/Images/Engine
_Camshaft.gif
4
Cams continued

• The camshaft uses lobes (called cams) that push
  against the valves to open them as the camshaft
  rotates
• Springs on the valves return them to their closed
  position

5
http//auto.howstuffworks.com/engine-cam2.htm
6
A pictorial representation of intake and exhaust
valves
http//www2.gsu.edu/bioasx/engine.gif
7
Rocker Arm

• Works as an intermediary between the camshaft and
  the valves
• Camshaft cam pushes up on the rocker arm (via a
  push rods) which in turn pushes down on the valves

8
Piston Engines

• Some older engine models placed the camshaft
  below the pistons
• Pushrods actuated rocker arms above the cylinder
  head to actuate the valves.
• Lifters or tappets reside in the engine block
  between the camshaft and pushrods.

9
Overhead Cam Systems

• Place the camshaft above the cylinder heads and
  drive the valves or lifters directly instead of
  using pushrods.
• This arrangement is more complex, and relies on a
  timing belt or chain, but allows for greater
  valvetrain flexibility.

10
Single Overhead Cam (SOHC)

• One Camshaft is located above the valves
• The one camshaft controls both the inlet and
  exhaust valves

11
Dual Overhead Cam (DOHC)

• Two camshafts for each bank of cylinders
• DOHC engines have separate camshafts for inlet
  valves and exhaust valves
• DOHC allow for more valves in each cylinder than
  SOHC
• More valves allow for greater intake and exhaust
  flow and greater engine power

12
Conclusion

• 3 types of engines that use different valve train
  configurations are Piston Engines, Single
  Overhead Camshaft Engines, and Dual Overhead
  Camshaft Engines
• Modern Engines use overhead camshaft
  configurations

13
Sources

• http//www.familycar.com/engine.htm
• http//auto.howstuffworks.com/camshaft3.htm
• http//en.wikipedia.org/wiki/Dual_overhead_camshaf
  t
• http//www2.gsu.edu/bioasx/engine.gif