In recent years, automobile engines have higher requirements for fuel efficiency and exhaust emissions. Early engine valves only had fixed opening and closing times, making it difficult to achieve optimal intake and exhaust according to engine speed.
Therefore, variable valve timing (VVT) has become the mainstream.
Contents
What is VVT?
The engine variable valve timing system adjusts the phase of the cam so that the time of valve opening and closing changes with the engine speed, adjusts the amount of intake (exhaust), and the valve opening and closing time and angle.
This optimizes the amount of air entering and improves the engine combustion efficiency.
What does Variable Valve Timing Do?
Variable cam phase technology controlled by hydraulic pressure has become mainstream due to its high cost-effectiveness and reliability.
A cam phase adjuster that can rotate back and forth within a certain angle is installed at the front end of the camshaft.
The engine lubrication system is connected to the phase adjuster.
The engine ECU collects information through the crankshaft phase sensor and the cam phase sensor.
An electromagnetic oil control valve (OCV) is set in the engine oil circuit, which adjusts the flow and direction of the oil of the phase adjuster through electrical signals to achieve control of the rotation angle of the phase adjuster.
VVT usually controls the opening and closing of the valve by changing the position of the camshaft. This is usually done with the help of a hydraulic actuator.
At low speeds: The VVT system allows the valve to open and close earlier, providing better fuel efficiency and smooth idling.
At high speeds: It delays the valve opening, allowing the engine to breathe better, thereby improving performance and power output.
Variable Valve Timing System: Key Components
The Variable Valve Timing system includes a cam phase adjuster, oil control valve, sensors, and ECU to control valve timing.
Hydraulically controlled variable cam phase technology has become a mainstream solution due to its cost-effectiveness and reliability. The technology operates on the following principles:
Cam Phase Adjuster: A cam phase adjuster is mounted at the front of the camshaft, which can rotate within a certain angle. This adjuster is responsible for altering the camshaft’s position, thereby adjusting the valve timing.
The Engine Control Unit (ECU) monitors the crankshaft and camshaft positions through sensors (crankshaft phase sensor and cam phase sensor). This data provides real-time feedback on the engine’s performance.
An oil control valve is positioned in the engine’s oil circuit. This valve is responsible for regulating the oil flow and its direction, based on signals from the ECU. By adjusting the oil flow, the OCV controls the rotation of the cam phase adjuster, thus fine-tuning the camshaft’s position.
The rotation angle of the phase adjuster determines the timing of the intake and exhaust valves. By adjusting this angle, the system optimizes engine performance across different operating conditions, enhancing fuel efficiency, power output, and emissions.
VVT system provides a smoother and more responsive engine performance by continuously adjusting the valve timing based on real-time driving conditions. It’s a highly efficient method for balancing engine power, fuel economy, and emissions.
Advantages of Variable Valve Timing
Improved Fuel Efficiency
VVT improves fuel efficiency by adjusting valve timing to suit different engine loads and speeds.
Enhanced Performance
At high rpm, VVT allows more air and fuel to enter the combustion chamber, increasing the engine’s maximum power.
Reduced Emissions
VVT helps the engine burn fuel more efficiently. This reduces harmful emissions such as nitrogen oxides and carbon monoxide.
Smooth Operation
By adjusting valve timing for low-speed driving conditions, VVT reduces engine vibration and improves smoothness, improving driver experience and comfort.
Powder Metallurgy Applications in VVT
Compared to traditional metal manufacturing processes, powder metallurgy (PM) is recognized as a green manufacturing process with a material utilization rate of over 95% and lower energy consumption.
PM uses metal powder as raw material and produces the final product through compacting and sintering. What’s more, powder metallurgy can achieve tight dimensional tolerances and is cost-effective for mass production.
Some variable valve timing sprockets in variable valve timing systems are manufactured through powder metallurgy. Through PM, VVT sprockets can achieve both lightweight and high precision.
Variable Valve Timing Systems by Major Auto Manufacturers
Auto manufacturers have introduced their own variable valve technology. The following table shows the names of their variable valve timing (VVT) systems.
| Manufacturer | Variable Valve Timing System |
|---|---|
| Honda | VTEC, i-VTEC, VTEC-E |
| Toyota | VVT-i, VVTL-i, VVT-iE |
| Nissan | N-VCT |
| Mazda | S-VT |
| Suzuki | VVT |
| Mitsubishi | MIVEC |
| Mercedes-Benz | Camtronic |
| BMW | VANOS |
| Audi | Valvelift |
| Volkswagen | VVT |
| Porsche | VarioCam |
BLUE is a dedicated powder metallurgy supplier, ISO 9001:2015 certified with 20 years of industry experience. We provide a wide range of standard parts with no tooling fees. Our VVT sprockets & rotors feature tight tolerances and competitive pricing. Free to contact us if you have any questions
FAQ
1. What are the Disadvantages of VVT?
Here are the main disadvantages of VVT.
Complexity:
VVT systems are more complex than conventional engines. Components such as cam phasers, oil control valves, solenoids, and sensors must work in precise coordination under real-time engine conditions. This complex setup makes the system design, calibration, and diagnosis more challenging
Higher Costs:
The integration of VVT technology increases the overall production cost of the engine. Compared with fixed timing engines, VVT-equipped engines involve more parts and are manufactured to tighter tolerances, which drives up costs.
Maintenance Costs:
VVT systems are highly sensitive to oil quality and cleanliness because they rely on oil pressure to operate the camshaft phasers and actuators. Poor quality oil or infrequent oil changes may cause sludge buildup, clogged passages, and increased wear on internal components, raising maintenance costs.
2. What Happens when Variable Valve Timing Fails?
When Variable Valve Timing fails, engine performance may decline noticeably. Common symptoms include rough idling, reduced power, increased fuel consumption, poor acceleration, and higher emissions.
3. What is the Ddifference between VVT and VVT-i?
VVT is a general system that changes camshaft timing based on engine speed and load. VVT-i (Variable Valve Timing-intelligent) is Toyota’s version that uses electronic control to adjust timing more precisely for better fuel efficiency, power, and lower emissions.
