Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Describe how Variable Valve Timing (VVT) works.
• Explain the function of turbochargers and superchargers.
• Calculate boost pressure and volumetric efficiency.
• Identify advantages and disadvantages of these systems.
• Diagnose common faults in VVT and forced induction systems.

Lesson summary

This week, we delve into the fascinating world of advanced engine technology and performance, focusing specifically on variable valve timing (VVT) and forced induction systems (turbochargers and superchargers). These technologies are increasingly prevalent in modern vehicles, playing a crucial role in improving fuel efficiency, reducing emissions, and enhancing engine power. Understanding these systems is vital for any aspiring mechanic, automotive engineer, or even a car enthusiast in South Africa.

Lesson notes

2.1 Variable Valve Timing (VVT) What is VVT? Variable Valve Timing (VVT) is a technology that allows the timing and lift of an engine's valves to be altered while the engine is in operation. Traditional engines have fixed valve timing, which is a compromise designed for optimal performance at a specific engine speed. VVT systems optimize valve timing for different operating conditions, improving fuel efficiency, reducing emissions, and boosting power. Why is VVT important? At low engine speeds, a smaller valve overlap is desirable to prevent exhaust gas from flowing back into the intake manifold. At high engine speeds, a larger valve overlap is needed to improve cylinder filling and exhaust scavenging. VVT allows the engine to adjust the valve timing to suit these different conditions. How does VVT work? There are various VVT technologies, but they generally involve mechanisms that can alter the position or phasing of the camshaft relative to the crankshaft.

Some common VVT systems include: Cam Phasers: These systems use a hydraulic actuator to rotate the camshaft relative to the crankshaft, changing the valve timing. The actuator is controlled by the engine control unit (ECU) based on engine speed, load, and other parameters.

Variable Valve Lift: Some systems, like Honda's VTEC, can alter the amount the valves open (valve lift), as well as the timing. This provides even greater control over the engine's breathing.

Types of VVT: Continuous VVT (CVVT): Offers continuous adjustment of valve timing. More sophisticated and provides finer control.

Discrete VVT: Offers valve timing adjustments in steps. Simpler and less expensive than CVV

T. Example: A cam phaser system might advance the intake valve opening at higher engine speeds, increasing the duration the intake valve is open and allowing more air to enter the cylinder. This leads to improved power output.