ICE-18 — Variable Valve Lift (VVL)

ASSUMPTION — This lesson covers the general principle; no manufacturer’s proprietary implementation is discussed.

In this lesson you will learn:

• The effect of valve lift
• VVL vs VVT
• Reducing throttling losses

1. What Is Lift?

Valve lift is how far the valve opens off its seat. It directly affects how much air enters the cylinder.

FACT — In a classic engine, load is controlled by the throttle, which creates intake vacuum and “pumping loss”. VVL aims to reduce this loss by controlling load through valve lift instead.

2. VVL vs VVT

• VVT — changes valve timing (when it opens).
• VVL — changes valve lift (how much) and duration.

FACT — VVL changes valve opening so the throttle is needed less at low load; air control moves to the valve, reducing pumping losses and improving efficiency.

3. Trade-offs

INTERPRETATION — VVL systems are mechanically more complex (extra cam profiles or variable mechanisms), adding cost/complexity for a low-load efficiency and emissions benefit. Each application weighs cost vs benefit.

4. Summary

• Lift is the valve opening amount.
• VVT changes timing; VVL changes lift/duration.
• VVL reduces throttle losses, improving low-load efficiency.

5. Sources

• Bosch Automotive Handbook
• Heywood, Internal Combustion Engine Fundamentals

Next Lesson

• ICE-19 — EGR: exhaust gas recirculation.