In internal combustion engines, a variable-length intake manifold (VLIM),variable intake manifold (VIM), or variable intake system (VIS) is an automobile internal combustion engine manifold technology. As the name implies, VLIM/VIM/VIS can vary the length of the intake tract in order to optimise power and torque across the range of engine speed operation, as well as to help provide better fuel efficiency. This effect is often achieved by having two separate intake ports, each controlled by a valve, that open two different manifolds – one with a short path that operates at full engine load, and another with a significantly longer path that operates at lower load. The first patent issued for a variable length intake manifold was published in 1958, US Patent US2835235 by Daimler Benz AG.[1]
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Lower intake manifold on a 1999 Mazda Miata engine, showing components of a variable-length intake system.
There are two main effects of variable intake geometry:
Swirl
Variable geometry can create a beneficial air swirl pattern, or turbulence in the combustion chamber. The swirling helps distribute the fuel and form a homogeneous air-fuel mixture. This aids the initiation of the combustion process, helps minimise engine knocking, and helps facilitate complete combustion. At low revolutions per minute (rpm), the speed of the airflow is increased by directing the air through a longer path with limited capacity (i.e., cross-sectional area) and this assists in improving low engine speed torque. At high rpm, the shorter and larger path opens when the load increases, so that a greater amount of air with least resistance can enter the chamber. This helps maximise 'top-end' power. In double overhead camshaft (DOHC) designs, the air paths may sometimes be connected to separate intake valves[citation needed] so the shorter path can be excluded by de-activating the intake valve itself.
Pressurisation
A tuned intake path can have a light pressurising effect similar to a low-pressure supercharger due to Helmholtz resonance. However, this effect occurs only over a narrow engine speed band. A variable intake can create two or more pressurized "hot spots", increasing engine output. When the intake air speed is higher, the dynamic pressure pushing the air (and/or mixture) inside the engine is increased. The dynamic pressure is proportional to the square of the inlet air speed, so by making the passage narrower or longer the speed/dynamic pressure is increased.
Many automobile manufacturers use similar technology with different names. Another common term for this technology is variable resonance induction system (VRIS).
BMW — DISA (DIfferenzierte SaugAnlage – "Differential Air Intake"), two stage: M42, M44, M54, N62TU, three stage: N52; DIVA (continuously variable length runners): N62, is the world's first continuously variable length intake manifold.[2]
Citroën — XM 3,0 V6.24 (200hp) used during 1991 to 1997, ZX Coupe 2.0 16v XU10J4 engine.
Daewoo — Variable Geometry Induction System (VGIS) Lanos
Dodge / Chrysler — 3.5L V6 EGE, (1993-1997) used in Dodge Intrepid, Chrysler Concorde and LHS; 2.0 A588 - ECH (2001–2005) used in the 2001-2005 model year Dodge Neon R/T; 6.4L V8 2011-2014 Dodge Charger and Challenger, Chrysler 300, Jeep Grand Cherokee (SRT8 versions)
Ford — Dual-Stage Intake (DSI), on their Duratec 2.5 and 3.0-litre V6s, and it was also found on the Yamaha V6 in the Taurus SHO. The Ford Modular V8 engines and the V6 Cologne use either the Intake Manifold Runner Control (IMRC) for four-valve engines, or the Charge Motion Control Valve (CMCV) for three-valve engines. The SVT edition (in North America) and ST170 edition (in Europe) of the Ford Focus added IMRC to the Ford Zetec engine. A system called Split Port Induction (SPI) was used on the 2.0L CVH I4 of the 1997-2002 Escort and 2000-2004 Focus, and the 3.8L Essex V6 of the 1996-2003 Windstar and 2001-2004 Mustang.
Volvo — V-VIS[5] (Volvo Variable Induction System) Volvo B52 engine as found on the Volvo 850. Longer inlet ducts used between 1,500 and 4,100rpm at 80% load or higher.[6]
Hirschfelder, Klaus; Völkl, Werner; Kühnel, Hans-Ulrich; Sinn, Walther; Huck, Armin (March 2002). "The first continuously variable intake system in the new eight-cylinder engine from BMW". MTZ Worldwide. 63 (3): 2–6. doi:10.1007/bf03227525. ISSN2192-9114.
