Variable intake manifold

A variable intake manifold (also variable intake manifold (VSR), engl. Variable Intake System ) shall be optimized, a device on the suction side of a gasoline engine, to the degree of filling of flammable gases in the combustion chamber at different speeds.

Switching intake manifolds are based on the principle of gas oscillations within the intake manifold and are mostly switchable oscillating intake manifolds . When the inlet valve is opened, for example, a negative pressure wave is created which runs back as an overpressure wave at the end of the intake manifold. This prevents the air that has already been drawn in in the combustion chamber from flowing back into the intake tract ( degree of delivery ) or even generates a charge due to the excess pressure wave ( air consumption ). The constant speed of the positive and negative pressure waves in the pipe corresponds to the speed of sound . However, the opening times of the valves are primarily based on the position of the crankshaft, which means that the valves are opened shorter and shorter when the engines are rotating faster. In order to be able to use the effects of the constantly fast gas waves even at different speeds, the length of the pipe must be adapted to the speed. The example shown is therefore optimally designed for two speeds. Newer models have three or four different lengths or are even fully variable in length.

The resonance effect, which can also be reinforced by the design of the exhaust manifold, is important in the design of intake manifolds: All manifold pipes are designed to be the same length for each cylinder in both speed ranges ( Variable Resonance Induction System , VRIS).

Working method using the example:

At speeds below 5400 min ⁻¹ , the flaps (1) are closed, which results in a long air path for the suction. The solenoid valve (5) is then de-energized and connects the vacuum unit (4) with the outside air.
The electrovalve (5) receives power over 5400 min ⁻¹ and connects the vacuum reservoir (2) with the vacuum unit (4), which opens the flaps via an actuator. This shortens the path of the sucked in air.
In the accumulator (2) a negative pressure is constantly generated by the suction and held by the check valve (3).

Resonance effect

The resonance effect is a term from vibration engineering and gas dynamics. A rhythm (resonance effect) is created between control times, intake strokes and gas oscillations, which leads to better cylinder filling with fresh gas. The pipe lengths are selected accordingly during construction in order to maximize the effect.

For this reason, it does not make sense to replace the original air filter box with an open air filter or something similar on models with variable intake manifolds , as such measures change the air path and thus the resonance frequency . The vibrations of the fresh gas column change, which is why incorrect measurements occur in certain operating areas due to the air mass meter . That is why the air mass meter is located close to the intake manifold, so that it can measure as close as possible to the intake valves (smaller deviation). A shift in the maximum torque and u. U. to expect a poorer response behavior in certain operating states.

literature

Richard van Basshuysen, Fred Schäfer: Handbook Internal Combustion Engine Basics, Components, Systems, Perspectives. 3rd edition, Friedrich Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden, 2005, ISBN 3-528-23933-6 .
Peter Gerigk, Detlev Bruhn, Dietmar Danner: Automotive engineering. 3rd edition, Westermann Schulbuchverlag GmbH, Braunschweig, 2000, ISBN 3-14-221500-X .