Resonance System. Intake system of an inline six-cylinder engine

With a resonance charge, the charge effect is generated by an oscillating container-pipe system. The periodic intake cycles of the individual cylinders cause oscillating pressure through short induction pipes in the container that increase the pressure gradient between the inlet port and combustion chamber at the beginning and end of the intake phase.

This oscillating pressure that substantially increases the air expenditure has a definite maximum when the excitation by the cylinder corresponds to the natural angular frequency of the container-pipe system. An optimum condition for exciting oscillations is when the individual intake phase is offset by a 240° crankshaft angle, i.e., by three cylinders per resonance container.

When the intake valve is open, the system vibrates similar to a Helmholtz resonator. Vibrations arise when the air column in the inlet port moves against the “rigid” air in the cylinder, and the entire system functions like a spring mass system. The air in the cylinder can be viewed as the spring, and the air column can be viewed as the mass. The natural frequency of a Helmholtz resonator can be determined as follows:

where A_Intake is the cross-sectional area of the induction pipe, and V_be is the container volume.

In transferring the Helmholtz equation (10.17) to the internal combustion engine, Engelman used the compression chamber for the volume V_BE plus the half stroke volume of a cylinder and created the following simple relationship for the resonance speed n_res in a system consisting of a cylinder with an induction pipe:

This allows the natural frequencies of the Helmholtz resonator effect to be precisely described for a cylinder with an induction pipe. If there are several cylinders, the overlapping of the waves influences the results, and the phenomenon becomes very difficult to describe.

This vibration behavior is also noticeable with closed intake valves. The manifold volume acts as the resonance volume. With this design (volume), the natural frequency of the system can be varied so that it increases the air expenditure at certain speeds when an overpressure wave arrives in the intake port briefly before IC of the intake valve.

The resonance charge is particularly important in combination with turbocharging to compensate for the low torque at low speeds. In addition, it is useful to combine ram tube charge and resonance charge for six- and twelve-cylinder engines. At low speeds, the resonance vibration in the container is exploited, while short induction pipes at higher speeds contribute to the increase in air expenditure as a ram tube system. Figure 10-37 schematically illustrates a combined ram tube and resonance charge with a six-cylinder engine.

Fig. 10-37. Intake system of an inline six-cylinder engine

Fig. 10-38. Torque characteristic of an inline six-cylinder spark-ignition engine with a resonance system

The adaptation is realized by opening or closing the resonance control valve. In the torque position, the resonance control valve is closed so that two “three-cylinder” intake systems with long pipes are active. In the output position, the resonance control valve is open, and the intake module works for all six cylinders as a ram tube system that is then fed from the entire upper manifold range with short ram tubes. The cross section and lengths can be tailored and optimized with one-dimensional calculations with these effects in mind. The air mass is controlled with the central throttle valve. The gain in torque from such a system is shown in Fig. 10-38.