Variable Valve Timing (VVT) is an automotive technology used in internal combustion engines to optimize the timing of the intake and exhaust valves. By adjusting the timing of valve opening and closing, VVT improves engine performance, fuel efficiency, and reduces emissions across a range of driving conditions. VVT allows the engine to operate more efficiently at different RPMs (revolutions per minute), enhancing both power and economy.
In a traditional internal combustion engine, the timing of the opening and closing of the intake and exhaust valves is fixed. This means that regardless of engine speed or load, the valves open and close at the same times. However, this fixed timing may not always be ideal for optimizing performance in all driving situations.
VVT systems adjust the timing of valve operation based on factors like engine speed, load, and throttle position. By doing so, VVT helps to:
Improve Engine Efficiency: Adjusting valve timing allows for better air-fuel mixture intake, combustion efficiency, and exhaust expulsion.
Increase Power Output: At higher RPMs, the system can adjust the valve timing to allow for more air and fuel to enter the engine, increasing power.
Improve Fuel Economy: At lower RPMs or during light driving conditions, VVT adjusts the timing for more efficient combustion, helping to reduce fuel consumption.
Lower Emissions: By optimizing combustion, VVT reduces unburned fuel and the production of harmful emissions.
There are various types of VVT systems used by automakers, each with slightly different methods for altering valve timing.
1. VVT-i (Variable Valve Timing with intelligence) – Toyota:
This is one of the most common VVT systems, used in many Toyota vehicles.
How it works: VVT-i adjusts the timing of the intake valves to optimize engine performance at different speeds. It uses an oil-controlled actuator that adjusts the position of the camshaft.
Benefits: Better performance, improved fuel efficiency, and reduced emissions.
2. VTEC (Variable Valve Timing and Lift Electronic Control) – Honda:
VTEC is a more complex system that not only adjusts the timing but also changes the lift of the intake valves.
How it works: VTEC uses two or more camshaft profiles and switches between them depending on engine speed. At lower RPMs, a camshaft profile with lower lift is used for better fuel economy, while at higher RPMs, a cam profile with higher lift is activated to improve power output.
Benefits: Combines the benefits of both high power and fuel efficiency across a wider range of engine speeds.
3. VANOS (Variable Nockenwellen Steuerung) – BMW:
BMW's VANOS system adjusts the timing of the intake and exhaust valves independently.
How it works: The VANOS system uses a hydraulic actuator that adjusts the camshaft position. BMW has further advanced this system with Double VANOS, which adjusts both intake and exhaust valves in real-time, optimizing the performance at both low and high RPMs.
Benefits: Improves low-end torque, high-end power, and fuel efficiency while reducing emissions.
4. CVVT (Continuously Variable Valve Timing) – Hyundai/Kia:
CVVT continuously adjusts the valve timing rather than using discrete steps.
How it works: The CVVT system is a variable camshaft timing system that provides continuous and smooth adjustment of the intake valve timing, improving fuel efficiency, and performance.
Benefits: Smooth performance changes and better fuel economy at varying engine speeds.
5. MIVEC (Mitsubishi Innovative Valve Timing Electronic Control) – Mitsubishi:
MIVEC is Mitsubishi’s version of variable valve timing, which allows for the adjustment of both valve timing and valve lift.
How it works: Similar to Honda’s VTEC, MIVEC switches between camshaft profiles for optimized performance.
Benefits: Enhances both engine performance and fuel efficiency.
Improved Fuel Efficiency:
At low engine speeds (idle or cruising), VVT adjusts the valve timing to ensure optimal fuel combustion, reducing fuel consumption.
Increased Power Output:
At higher engine speeds (during acceleration or high-load conditions), VVT adjusts the valve timing for improved airflow, allowing for more power to be generated.
Reduced Emissions:
By optimizing combustion, VVT helps reduce incomplete combustion, which lowers emissions such as unburned hydrocarbons and NOx (nitrogen oxides).
Better Engine Response:
VVT allows for faster throttle response, as the system continuously adjusts the timing to match the driving conditions, improving the overall driving experience.
Camshaft:
The camshaft controls the timing of the valve movements. In VVT systems, the camshaft position is adjustable to alter the valve timing.
Actuator:
The actuator (often hydraulic) adjusts the camshaft position based on feedback from the engine control unit (ECU). This actuator is responsible for adjusting the timing of the intake and/or exhaust valves.
Engine Control Unit (ECU):
The ECU monitors engine speed, load, and other parameters and controls the actuator to adjust the camshaft position for optimal performance.
Timing Chain or Belt:
A timing chain or belt links the camshaft to the crankshaft, allowing the actuator to make adjustments.
Oil Pressure (in some systems):
In many VVT systems, the actuator is driven by engine oil pressure, which allows for precise, variable adjustments of the camshaft position.
Complexity and Maintenance:
VVT systems add complexity to the engine, requiring more sophisticated components and sensors, which can increase maintenance costs and potential repair issues.
Cost:
The technology adds to the cost of the engine, making it more expensive to produce and repair compared to traditional, non-VVT engines.
Potential for Increased Oil Consumption:
Some VVT systems, especially those using hydraulic actuators, may lead to higher oil consumption due to the additional oil required to operate the system.