Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Describe how Variable Valve Timing (VVT) systems work.
• Explain the pros and cons of VVT systems.
• Compare turbochargers and superchargers.
• Understand the basics of boost pressure and efficiency.
• Identify common faults in these advanced systems.

Lesson summary

This week, we delve into advanced engine technology and performance, focusing on cutting-edge innovations designed to maximize efficiency, reduce emissions, and enhance power output in internal combustion engines. Understanding these advancements is crucial not only for future mechanics and engineers but also for all citizens as South Africa grapples with energy efficiency, environmental concerns, and the need for sustainable transportation solutions. The skills and knowledge acquired in this module are directly applicable to the automotive industry, transportation sector, and related fields which contribute significantly to the South African economy.

Lesson notes

2.1 Variable Valve Timing (VVT) Systems Variable Valve Timing (VVT) is a technology used in internal combustion engines to improve performance, fuel economy, and emissions. Traditional engines have fixed valve timing, meaning the intake and exhaust valves open and close at the same points in the engine cycle regardless of engine speed or load. VVT systems allow the valve timing to be adjusted to optimize engine performance under different operating conditions.

Types of VVT Systems: Camshaft Phasing (Cam Phasers): This is the most common type of VVT. It involves rotating the camshaft relative to the crankshaft. By advancing or retarding the camshaft, the valve timing is shifted earlier or later in the engine cycle. This changes the valve overlap (the period when both intake and exhaust valves are open), affecting cylinder scavenging and volumetric efficiency.

Variable Valve Lift: This system alters the amount the valves open. Higher lift allows more air and fuel to enter the cylinder, increasing power at high engine speeds. Lower lift improves fuel economy and reduces emissions at low engine speeds. Mechanisms include rocker arms with varying cam followers and electrically controlled cam lobes.

Variable Valve Duration: This system changes the length of time the valves stay open. Longer duration allows more time for air and fuel to enter and exhaust gases to exit the cylinder, improving performance. Shorter duration reduces pumping losses and improves fuel economy at low engine speeds. This is often achieved in combination with variable lift systems.

Advantages of VVT Systems: Improved Fuel Efficiency: By optimizing valve timing for different engine speeds and loads, VVT systems can reduce pumping losses and improve combustion efficiency.

Increased Power Output: Adjusting valve timing to maximize airflow at high engine speeds can increase power output.

Reduced Emissions: VVT systems can reduce emissions by optimizing combustion and minimizing unburned hydrocarbons.

Better Idle Quality: Optimizing valve timing at idle can improve engine smoothness and reduce vibrations.

Disadvantages of VVT Systems: Complexity: VVT systems are more complex than traditional valve timing systems, which can increase manufacturing costs and maintenance requirements.

Cost: VVT systems add to the cost of the engine.

Potential for Failure: VVT systems have more moving parts, which increases the potential for failure.