Variable Induction System: Description and Operation

GF09.20-P-6002MLK Component Description For The Variable Intake Manifold
- ENGINE 113.989 in MODEL 171.473 as of Model Year 09 /Modification Year 08 model refinement package





View of the engine from the front
22 Variable intake manifold

Location
The variable intake manifold is located in the middle between the cylinder heads.

Task
The variable intake manifold optimizes the engine torque characteristic in the partial-load range, by using two different lengths of intake tract.





Body
22 Variable intake manifold
22/1 Vacuum reservoir with check valve (integrated in the variable intake manifold)
22/6 Vacuum unit for variable intake manifold
Y22/6 Variable intake manifold switchover valve

The variable intake manifold is made up of a number of magnesium pressure castings. During assembly, the individual intake manifolds for each cylinder and the air manifold collecting sections are in the center. The different parts are separated from each other by plastic seals.

The individual intake manifolds, each approx. 800 mm long, are arranged in a spiral shape around the air collecting volume. A single intake pipe is assigned to each cylinder.

At the center of each intake manifold is another opening to the air collector manifold. The opening can be opened or closed by the switchover flap, which can swivel by up to 60°.

The housing for the variable intake manifold must not be disassembled.

Function
The switchover flaps are mounted on steel spindles. One spindle is installed for each cylinder bank. The spindles are linked to each other and closed by vacuum from the variable intake manifold vacuum unit.

When the variable intake manifold switchover valve (Y22/6) is actuated, vacuum is supplied from the variable intake manifold vacuum reservoir. The reservoir capacity is sufficient for about 5 actuations before it has to be evacuated again.

When not actuated, the switchover flaps are opened by the spring in the variable intake manifold vacuum unit, and open the short intake tracts.





Sectional view from rear (at cylinder level)
22/2 Variable flap (one variable flap for each cylinder)
A Intake air when variable flap opened
B Intake air when variable flap closed
C Intake air to engine