Manifold tuning

Details Manifold tuning Manifold tuning

1991-03-11

1992-02-04

Okonsky, David A.

Internal-combustion engines

Multiple cylinder

F02M 3510

Patent

active

050851772

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to the tuning of inlet and exhaust manifold systems of internal combustion engines.
It is well known that some degree of supercharging can be achieved by selecting the length of the intake system to take advantage of the pressure waves caused by the rapid opening of the intake valve, which pressure wave propagates back and forth along the intake tract in a series of compression and rarefaction waves. By choosing the tract length such that the time taken for the compression wave to arrive back at the intake valve is approximately the same as the time interval of the intake valve opening period, the density of the intake charge as it is being trapped inside the engine cylinder can be momentarily increased thereby increasing the power output of the engine.
As the speed of sound is substantially constant (approx. 350 m/s in air), the time taken for the pressure wave to traverse an intake tract of fixed length for a fixed number of reflections is also constant. On the other hand, the duration of the intake event, if constant when expressed in terms of crankshaft angle, will vary inversely with engine speed. Thus, the time from the start of the pressure wave perturbation to the instant when the intake valve closes is not constant and progressively shortens with increased engine speed. It will be clear from this that for a fixed length of intake tract, there is only one speed at which the desired matching or tuning of the intake tract is achieved. The resulting torque curve for such an engine would exhibit a narrow high peak at the tuned engine speed and the torque would fall off rapidly on each side of this peak.
Variably tuned intake systems have attempted to achieve increased torque over a broader speed range by providing a control enabling the length of the intake tract to be varied in dependence upon engine speed in order to match the changing time delay requirements.
The tuning of engine manifolds to take advantage of pressure waves is not restricted to the intake system but can also be used in exhaust systems. In the case of exhaust manifolds, tuning is used to achieve improved scavenging, that is to say removal of residual exhaust gases from the combustion chamber. Here, a negative pulse is required at the exhaust valve as it is being closed.
Manifold tuning can furthermore be employed not only to increase engine power output but to derate an engine under part load operation. Thus, it is possible in the case of an intake system to arrange for a negative pulse to be present during intake valve closing as this reduces the mass of air without throttling, thereby reducing pumping losses.
Both the fixed length and variable length manifold systems previously proposed are passive systems in as much as the pressure wave perturbation used to alter the charge density is created by the engine itself and the various designs of the manifold systems have only been intended to optimise the phasing of a process which occurs naturally within the engine.
U.S. Pat. No. 3,254,484 proposes the use of acoustical resonators and sound generators in intake and exhaust systems to achieve effects similar to manifold tuning. However, this patent does not identify a sound generator which can produce sound waves having sufficient energy to alter the intake charge significantly and relies instead predominantly on acoustical resonance.
The present invention does share with the tuned manifold system described above the fact that a shock or sound wave is employed to vary charge density at the instant of valve closing but seeks to provide greater control over the process so as to enable regulation of the breathing efficiency to be achieved over a wide range of engine speeds.
In other known systems, such as EP-A-0194503, GB-437321 and EP-A-0141165 a secondary valve is placed in series with the inlet valve and remains closed for some length of time after the inlet valve has opened. The effect of this is to develop a drop in pressure in the cylinder, which starts a surge of air flow when the secondary valve opens

REFERENCES:
patent: 3254484 (1966-06-01), Kopper
patent: 4646689 (1987-03-01), Katsumoto et al.
patent: 4890582 (1990-01-01), Schatz et al.
patent: 5018485 (1991-05-01), Washizu et al.

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