Lecture Notes on Cylinder Head and Valves

Overview

• The cylinder head contains valves and the valve mechanism.
• Importance of intake and exhaust manifolds in engine operation.

Intake and Exhaust Manifolds

Intake Manifold

• Function: Facilitates air flow from the atmosphere into the engine cylinders.
  • Comprises pipes or flow paths.
  • Air passes through a filter to remove dust before reaching the cylinders.
• Structure: Typically designed for multi-cylinder engines (e.g., a 4-cylinder engine).

Exhaust Manifold

• Function: Facilitates removal of exhaust gases from the cylinders.
• Comprises a similar set of pipes as the intake manifold.
• Interfaces with the valves that control air intake and exhaust processes.

Valves

• Valves act as doors between the manifolds and the cylinders.
• Types of valves: Intake valves (for air) and exhaust valves (for gases).

Valve Assembly

• Construction: Uses spring return valves commonly in automotive applications.
  • Return of valves is enabled by the restoring force of springs.
• Operation:
  • When the intake valve is opened, air flows into the cylinder.
  • When closed, the spring force returns the valve to its seat.

Components of Valve Assembly

• Mushroom-Shaped Valves: Curved surface resembling a mushroom.
• Valve Stem: Projects through the thickness of the cylinder head.
• Assembly Process:
  • Insert valve stem from the bottom of the cylinder head.
  • Valve head sits on the valve seat.
  • Assembly involves spring seat, dual coil springs, and spring retainer.

Importance of Spring Seats

• Prevents lateral vibrations and ensures optimal operation of springs.

Valve Operation and Challenges

• Actuation: Valves operated through a cam connected to a rocker arm.
  • The cam's profile determines when the valve opens and closes.
• Issues:
  • Valve Train Noise: Caused by vibrations when valve mechanisms interact.
  • Valve Float: Occurs at high RPMs when the valve does not close completely before the next cycle begins.
  • Solutions include increasing spring stiffness and using shims.

Advanced Valve Mechanisms

• Tappet Valves: Used to dampen vibrations, filled with oil to reduce noise.
• Desmodromic Valves: A mechanism that eliminates valve float by using rocker arms for both opening and closing.
  • Provides more accurate control and operates without a spring.

Conclusion

• Understanding the components and mechanisms of the valve assembly is crucial for engine operation.
• Next lecture will cover additional components like the camshaft.