Intake Manifold - RA1400HFM0010X(14-0010)

The length of the intake manifold has a decisive influence on the torque pattern and on the power output of the internal combustion engine.

In the induction stroke, the pistons produce a strong vacuum which sets the air contained in the intake manifold in motion when the inlet valve is opened. As a result, the inflowing air or the air/fuel mixture develops a considerable kinetic energy. When the inlet valve closes, a dynamic pressure is produced which immediately begins to expand in the opposite direction. The level of this pressure depends on the flow velocity and on the mass of the gas which is contained in the intake pipe.

If the gas column is accelerated and braked in a rapid alternating sequence, a vibration is produced, the frequency of which is dependent on the length of the intake manifold. If the engine timing is matched to the vibrations of the gas column, a certain charge effect is achieved as a result of the resonance vibrations. As the vibrations of the gas column are also dependent on engine speed, it is possible to achieve resonance vibrations with a given intake manifold length only within a certain engine speed range.

To enable this charge effect to be utilized over a greater engine speed range, these engines are equipped with a "resonance intake manifold". In the case of this intake manifold, a "resonance flap" makes it possible to utilize two different intake manifold lengths.

Fig 1: Engine Torque Graph

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Design and function 

A pneumatically operated resonance flap (22) is provided at the intake manifold.

Fig 2: Identifying Resonance Flap Provided At Intake Manifold

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The resonance intake manifold switchover valve (Y22/6) is connected to the resonance flap (22) and is actuated by the HFM control unit as follows:

Idling speed at 3900 rpm

Full load engine 104.942 3450 rpm

engine 104.992 3350 rpm

Fig 3: Identifying Intake Manifold Switchover Valve Connected To Resonance Flap

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Resonance flap closed 

The inducted air flows in the resonance intake manifold (19a) through the intake pipes which are branched downstream of the throttle valve, into the air collecting housing of the ram manifold (19b). The air collecting volume is split into two by the resonance flap (22). This results in a significant rise in the torque in the lower rpm range.

Fig 4: Identifying Intake Manifold And Ram Manifold

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Resonance flap open 

When the resonance flap is opened, the air collecting volume of the ram manifold (19b) is no longer split into two. The inducting cylinder makes use of both intake pipes of the resonance intake manifold (19a).

Fig 5: Identifying Ram Manifold Intake Pipes Of Resonance Intake Manifold

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Partial intake manifold preheating PSV (KAT only) 

4 PSV elements (R8/3 - R8/6) (PTC elements) are provided in the cylinder head in order to preheat the mixture during the warming-up phase. The relay (K3/1) is actuated by the HFM control unit with ground for heating the 4 PSV elements.

Fig 6: Identifying PSV Elements

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Operating principle 

If the engine is started at a coolant temperature <60 °C, the PSV elements are energized by the relay (K3/1).

As the temperature of the PSV elements rises, the current flow (PTC elements) is constantly reduced until the HFM control unit interrupts the ground actuation to the relay (K3/1) at a coolant temperature of about 60 °C. The maximum current consumption of a PSV element is about 6 - 10 A.

Fig 7: Identifying PSV Elements Relay

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.