Intake Manifold

Intake Manifold




The N62 engine is equipped with a Variable Intake Manifold making it possible to reach a generous torque curve even at low engine speeds, without incurring losses in engine output at higher speeds. It ensures that the engine exhibits optimum volumetric efficiency through the entire range of speeds.

The new feature is the Variable Intake Manifold intake pipe length can be adjusted depending on the engine speed to provide efficient cylinder tilling and scavenging. This is determined by the optimal matching of the intake pipe dimensions, the exhaust system and the valve timing.

The intake manifold is located in the engine "V" and is mounted on the cylinder head intake ports.

Function

In order to understand how engine speed relates to volumetric efficiency, the physical processes within the intake pipe must be taken into consideration.

To ensure that there is good airflow to the engine cylinders, the intake pressure in front of the intake valve should ideally be high. This means that good airflow (high gas molecule density) in front of the intake valve is necessary.

This is only possible if the intake valve is closed and the mass inertia causes the intake air to flow in front of the closed intake valve. The air is compressed, the pressure and the air flow increase.

Intake air flows in front of the closed intake valve.




As soon as the intake valve is opened, the pressurized intake air flows into the cylinder, expands and draws the air molecules which follow into the cylinder. The suction waves form in the intake pipe (moving at sonic speed) in the opposite direction to the intake air.

These suction waves are reflected in the intake manifold and create pressure waves which then move once more at sonic speed in the direction of the intake valve.

Movement of the intake air with the intake valve open.




The intake pipe is at the optimum length when the pressure waves are at the intake valve shortly before it is closed. The increase in pressure in front of the intake valve results in increased air flow to the cylinders once more. This process is described as recharge effect.

The opening angle of the intake valve remains unchanged as the engine speed increases. The opening time, however, is reduced proportionately (with conventional, non-Valvetronic engines).

Since the suction waves and pressure waves expand at sonic speed, the suction path length must be adapted depending on the engine speed to ensure that the tip of the pressure wave reaches the intake valve before it is closed.




Each cylinder has its own intake pipe (1) which is connected to the manifold volume (6) via a rotor (3). The rotors are supported by one shaft (4) per cylinder bank.

The second shaft, from which the rotor for the opposite cylinder bank is adjusted, is turned by spur gears (5) in the opposite direction from the driven shaft.

The intake air flows via the manifold volume through the funnel (2) and on to the cylinders. The intake path length is set as the rotor turns,

The intake path length can be adjusted according to the engine speed. Adjustment from the long to short intake path begins at 3,500 rpm. If the engine speed increases, the intake path length is progressively reduced, up to 6,200 rpm.

The intake path length is determined by the funnel position. If the engine speed is less than 3,500 rpm, the funnel is in the longer intake path length position.

This means that the intake air must cover a longer path to reach the cylinders.

- Intake manifold set to longer intake path.




When an engine speed of 6,200 rpm is reached, the rotor is adjusted to the shorter intake path position. The intake path to the cylinders is now short.

The funnel can be progressively adjusted to any point between the long/short intake path positions.

- Intake manifold set to short intake path.




Funnel adjustment is carried out by the drive unit, which is located on the rear of the intake manifold housing. The drive motor adjusts the drive shaft with funnels (cylinder bank 1-4). The second shaft with funnels for cylinder bank 5-8 is synchronously adjusted by the spur gears.




The drive motor is controlled by the ECM and provides feedback about the funnel position via an integral potentiometer.