Variable Induction System: Description and Operation

GF09.20-P-6002MLR Component Description For The Variable Intake Manifold
- ENGINE 273.965 in MODEL 230.471 as of Model Year 09 /Modification Year 08 model refinement package





View of the engine from above
12 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 curve using two different intake manifold lengths.
Furthermore, the air stream is improved through tumble flaps which can be swung in and out of the intake ports.

Design
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.

There is a total of four shafts mounted in the variable intake manifold (two tumble flap shafts and two variable length intake manifold switchover flap shafts).

When the switchover valves are actuated, the vacuum for the vacuum units is supplied from a vacuum reservoir in the variable intake manifold.
The reservoir volume is designed for several actuations without renewed evacuation.

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





View from front
12 Variable intake manifold (with integral vacuum memory)
12/1 Tumble flap shaft, left cylinder bank
12/2 Tumble flap shaft, right cylinder bank
22/6 Intake manifold switchover vacuum unit
22/9 Tumble flap switchover vacuum unit
Y22/6 Variable intake manifold switchover valve
Y22/9 Intake manifold tumble flap switchover valve

Function
Intake manifold changeover
The individual intake manifolds, each approx. 800 mm long, are arranged in a spiral shape around the air collecting volume. Each single intake manifold has a further opening to the air collecting volume somewhere in the middle. This opening can be opened or closed by rotating longitudinal switch flap shafts.
The variable length intake manifold switchover flaps for a cylinder bank are interconnected via a shaft. Both shafts (right and left) are interconnected over a linkage and are actuated by the intake manifold switchover vacuum unit.
The intake manifold switchover vacuum unit is interconnected over hose lines with the intake manifold switchover valve.

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

Tumble flap switchover
The tumble flaps can be swiveled in the variable intake manifold for partial load in every intake port. In this way the cross-section of the intake port is reduced by about 50%.
The flow rate of the intake air increases and ensures better distribution of the fuel air mixture in the combustion chamber.
The tumble flaps are carried on two spindles, which are actuated through a linkage by the tumble flap switchover vacuum unit.

When not actuated, the tumble flaps are swiveled inward by a spring in the tumble flap switchover vacuum unit, and thus open the intake ports.