Variable Valve Timing
TechnologieAverage price
Inclus
Variable valve timing, also known by the English acronym VVT, is an engine technology designed to optimize the internal combustion process. Its role is to dynamically adjust the opening and closing timing of the intake and/or exhaust valves according to engine speed and load. On a traditional engine, this timing is fixed, representing a compromise between high-rpm performance and low-rpm flexibility. Variable valve timing overcomes this limitation by using actuators, often hydraulic, to vary the camshaft phase. This allows the engine to 'breathe' optimally across its entire operating range. At low speeds, a low valve overlap improves stability and torque. At high speeds, a greater overlap promotes better cylinder filling, thereby increasing power. This technology has become quasi-standard on modern engines as it offers a perfect balance between power, fuel consumption, and reduction of pollutant emissions.
Benefits
- ✓Increased power and torque over a broader rpm range
- ✓Reduced fuel consumption thanks to optimized combustion
- ✓Reduction of pollutant emissions (notably nitrogen oxides, NOx)
- ✓Improved engine flexibility and idle stability
Learn more
What is variable valve timing?
Variable valve timing, often referred to as VVT, is an essential technology in modern internal combustion engines. It allows the timing of the intake and exhaust valves to be modified in real time. In a conventional engine, the moment the valves open and close is fixed, defined by the shape and position of the camshafts. This fixed setting is always a compromise: optimized either for low-end torque or high-end power, but never for both. Variable valve timing solves this dilemma by adapting the engine's breathing cycle to different driving conditions, thereby optimizing efficiency across the entire rpm range.
How does variable valve timing work?
The basic principle of most variable valve timing systems relies on modifying the angular position (or phase) of the camshaft relative to the crankshaft. This is generally accomplished using a camshaft phaser, a component located between the camshaft pulley and the camshaft itself. This phaser is most commonly actuated by engine oil pressure, controlled by a solenoid valve managed by the engine control unit (ECU).
- At low rpm: The system retards the opening of the intake valves and reduces valve overlap (the period when both intake and exhaust valves are open simultaneously). This ensures a stable idle and high torque.
- At high rpm: The system advances the opening of the intake valves and increases overlap. This maximizes the filling of the cylinders with air and fuel, resulting in maximum power.
Some more sophisticated systems, such as BMW's Valvetronic or Fiat's MultiAir, can also vary valve lift, offering even more precise control of airflow and even making the traditional throttle body unnecessary.
What are the tangible benefits?
The adoption of variable valve timing brings multiple benefits that explain its widespread use in the automotive industry.
- Improved performance: By adapting the engine's breathing, VVT technology delivers a flatter torque curve and higher power at high rpm. The engine is both more flexible in the city and higher-performing on the highway.
- Reduced fuel consumption: More complete combustion and a reduction in pumping losses at partial load significantly lower fuel consumption. The system can create an internal exhaust gas recirculation (EGR) effect, improving efficiency.
- Lower pollutant emissions: Combustion optimization and the internal EGR effect help reduce the formation of nitrogen oxides (NOx), one of the main pollutants from thermal engines.
Variable valve timing and technological synergy
Variable valve timing is particularly effective when combined with other modern engine technologies. In tandem with a turbocharger, it can help reduce turbo-lag by optimizing the flow of exhaust gas that drives the turbine. Coupled with direct injection, it allows for extremely precise control of the combustion process, maximizing power while minimizing fuel consumption. This synergy is the key to today's downsized engines, which offer the power of a large engine with the fuel economy of a small one.
In conclusion, variable valve timing is not a mere gimmick, but a fundamental innovation that has allowed engineers to reconcile once-contradictory requirements: performance, fuel efficiency, and compliance with environmental standards. Today, it is a pillar of efficiency for gasoline engines and, to a lesser extent, certain diesel engines.
Finitions équipées
1 finition(s) proposent cet équipement
Associated equipment
Gasoline engine
The gasoline engine, also known as a spark-ignition engine, is a type of internal combustion engine that has been the heart of the majority of light vehicles for over a century. Its operating principle is based on the four-stroke cycle: intake, compression, combustion-expansion, and exhaust. During this cycle, a mixture of air and fuel (gasoline) is drawn into a cylinder, compressed by a piston, and then ignited by an electric spark generated by a spark plug. The resulting explosion pushes the piston back down, creating the mechanical energy required to propel the vehicle. Modern gasoline engines have evolved considerably, incorporating advanced technologies such as direct injection, turbocharging (downsizing), or mild hybridization. These innovations aim to improve efficiency, increase power, and reduce fuel consumption as well as pollutant emissions. Appreciated for its flexibility, responsiveness, and rapid revving, the gasoline engine offers high driving pleasure, particularly suited for dynamic driving and urban trips.
Turbocharger
The turbocharger, commonly known as a 'turbo', is a forced induction system designed to increase the power and efficiency of an internal combustion engine. Its operating principle is based on utilizing the energy wasted in the exhaust gases. It consists of two main components mounted on a common shaft: a turbine and a compressor. The turbine, driven by the speed and pressure of the exhaust gases, spins the compressor. The compressor draws in ambient air, compresses it, and then sends it under pressure into the engine cylinders. By increasing the amount of intake air, the engine can burn a larger amount of fuel, thereby generating more power and torque for an equivalent displacement. This technology is at the heart of the 'downsizing' concept, which involves using smaller, turbocharged engines to achieve the performance of larger engines while reducing fuel consumption and CO2 emissions. Today, the turbocharger is ubiquitous in diesel engines and increasingly common in modern gasoline engines.
Direct injection
Direct injection is an engine technology where fuel is injected at very high pressure directly into the combustion chamber of each cylinder, rather than into the intake manifold as with indirect injection. This method allows for extremely precise control of the air-fuel mixture, both in terms of metering and injection timing. By spraying fuel directly into the cylinder, more efficient vaporization is achieved along with a cooling effect that increases the density of the intake air. This phenomenon allows for a higher compression ratio to be used without the risk of engine knock, resulting in more complete and efficient combustion. Initially popularized on diesel engines (with Common Rail technology), direct injection has become widely adopted in modern gasoline engines (GDI, FSI, THP, etc.) as part of downsizing strategies. It has become a technological pillar for manufacturers seeking to balance increasingly strict requirements regarding performance, fuel consumption, and pollutant emission reduction.
Cylinder Deactivation
Cylinder deactivation, also known by commercial names such as 'Cylinder on Demand' (COD) or 'Active Cylinder Technology' (ACT), is an advanced engine technology designed to improve the fuel efficiency of internal combustion engines, primarily gasoline engines. The principle involves temporarily interrupting the operation of a certain number of cylinders when the engine is under low load. In these driving conditions, such as at a steady highway speed or during smooth city driving, the full power of the engine is not required. The engine management system then deactivates fuel injection and valve lift for half of the cylinders (for example, 2 out of 4, or 4 out of 8). The engine thus operates like a smaller-displacement engine, reducing pumping losses and optimizing the efficiency of the remaining cylinders, which operate at a higher and therefore more efficient load. The transition between modes is managed electronically in a way that is imperceptible to the driver, ensuring optimal driving comfort without vibrations or surges. This technology represents an ingenious solution for balancing on-demand performance with controlled fuel consumption.