02-10-2017, 10:48 AM
In internal combustion engines, a variable length intake manifold (VLIM), a variable intake manifold (VIM) or a variable intake system (VIS) is a manifold technology of the car's internal combustion engine. As the name implies, VLIM / VIM / VIS can vary the length of the intake section - in order to optimize power and torque over the full range of engine speed, as well as help provide better efficiency gas. This effect is often achieved by having two separate intake ports, each controlled by a valve, which opens two different manifolds - one with a short trajectory that runs at full load of the engine and one with a significantly longer trajectory that runs at lower load. The first patent issued for a variable length intake manifold was published in 1958, U.S. Pat. US2835235 to Daimler Benz AG.
There are two main effects of variable intake geometry:
Swirl
Variable geometry can create a whirling pattern of beneficial air, or turbulence in the combustion chamber. The whirlpool helps distribute the fuel and form a homogeneous mixture of air and fuel, which helps start the combustion process, helps minimize engine stroke and helps to facilitate complete combustion. At low revolutions per minute (rpm), airflow velocity is increased by directing air through a longer trajectory with limited capacity (i.e., cross-sectional area) and this helps to improve low-speed torque . At high speeds, the shortest and largest path opens when the load increases, so that more air with less resistance can enter the chamber, which helps to maximize "high-end" power. In double overhead camshaft (DOHC) designs, air paths can sometimes be connected to separate intake valves so that the shortest path can be excluded by deactivating the intake valve itself.
Pressurisation
A tuned input path may have a light pressurising effect similar to a low pressure supercharger - due to Helmholtz resonance. However, this effect only occurs on a narrow engine speed band. Variable fuel consumption can create two or more pressurized "hot spots", which increases engine power. When the intake air velocity is greater, the dynamic pressure that pushes the air (and / or the mixture) inside the engine increases. The dynamic pressure is proportional to the square of the velocity of the incoming air, so when making the passage narrower or longer the dynamic velocity / pressure increases.
There are two main effects of variable intake geometry:
Swirl
Variable geometry can create a whirling pattern of beneficial air, or turbulence in the combustion chamber. The whirlpool helps distribute the fuel and form a homogeneous mixture of air and fuel, which helps start the combustion process, helps minimize engine stroke and helps to facilitate complete combustion. At low revolutions per minute (rpm), airflow velocity is increased by directing air through a longer trajectory with limited capacity (i.e., cross-sectional area) and this helps to improve low-speed torque . At high speeds, the shortest and largest path opens when the load increases, so that more air with less resistance can enter the chamber, which helps to maximize "high-end" power. In double overhead camshaft (DOHC) designs, air paths can sometimes be connected to separate intake valves so that the shortest path can be excluded by deactivating the intake valve itself.
Pressurisation
A tuned input path may have a light pressurising effect similar to a low pressure supercharger - due to Helmholtz resonance. However, this effect only occurs on a narrow engine speed band. Variable fuel consumption can create two or more pressurized "hot spots", which increases engine power. When the intake air velocity is greater, the dynamic pressure that pushes the air (and / or the mixture) inside the engine increases. The dynamic pressure is proportional to the square of the velocity of the incoming air, so when making the passage narrower or longer the dynamic velocity / pressure increases.