Exhaust systems for multi-cylinder internal combustion engines

Details Exhaust systems for multi-cylinder internal combustion engines Exhaust systems for multi-cylinder internal combustion engines

1986-07-21

1989-03-28

Hart, Douglas

Power plants

Internal combustion engine with treatment or handling of...

Pulsed, timed, tuned or resonating exhaust

60323, F02B 2702

Patent

active

048152749

DESCRIPTION:

BRIEF SUMMARY
The invention relates to exhaust systems for multi-cylinder internal combustion engines.
It has been known for a long time that what can be called the "resonant length" of the individual exhaust channels of the respective cylinders, that is the length of any individual exhaust channel from the exhaust valve stem (or stems in the case of a four-valve cylinder) of the associated cylinder to the point at which the channel merges with one or more of the other channels has a marked influence on the shape of the engine torque curve and other engine characteristics. For example, it has been found that increasing the length of the individual channels has the effect of obtaining maximum torque at a lower RPM. More generally, the choice of a particular length or lengths for the individual channels assists :n reaching an optimum compromise between the power and torque characteristics of an engine desired for a given application. To obtain optimum results from each cylinder the individual channels should all have approximately the same resonant length.
The exhaust system chosen for most car engines for domestic or public use comprises a compact cast manifold containing individual exhaust channels leading from each exhaust port to an exit face of a flange by which the manifold is connected with one or two steel tailpipes which extend to the lower part of the engine compartment and are then directed towards the rear of the car to connect with a silencer system before discharging into the atmosphere. This system has the advantage of being compact enough to fit into the limited and congested space of the engine compartment of modern cars but restricts the length of the individual or primary exhaust channels of the system.
On a four-cylinder engine, which is the most commonly used in cars today, there are two systems which allow a good compromise to be reached. One of these is the "four-into-one" system, in which all four primary exhaust tubes or channels, constituting a manifold, merge into one tailpipe. To produce a good compromise between maximum power and maximum torque at low RPM for a touring car engine, the length of the primary exhaust tubes or channels has to be very long, of the order of one meter, which cannot be fitted into an ordinary engine compartment. When used it must be dimensioned with much shorter channels and is thus tuned for a higher RPM than would have been desirable. The other system is the "four-into-two-into-one" system, in which the primary channels from cylinders Nos. 1 and 4 are paired into a secondary channel; the primary channels from cylinders Nos. 2 and 3 are similarly paired into a separate secondary channel; and further downstream the two secondary channels are joined together into a single tailpipe which proceeds rearwards to the silencer system. Expansion of the exhaust gases occurs at each junction before final expansion at the open end of the tailpipe and silencer system. Here again for the desired low end torque for a touring car, the overall length of the primary and secondary channels has to be of the order of one meter which again is too long for a practical layout within an ordinary engine compartment.
The theory and technology relevant to these two systems is well known and examined in detail in the literature of the art, for example in "Scientific Design of Exhaust and Intake Systems" by Philip H. Smith, 1963, published by G. T. Foulis & Co. Ltd. (particularly Chapters 5 and 7) and "Gas Flow in the Internal Combustion Engine" by W. J. D. Annand and G. E. Roe, 1974, also published by G. T. Foulis & Co. Ltd. (particularly Chapter 6) and does not require further discussion here. Suffice it to say that the returning rarefaction waves from the expansion points play an important role in influencing the engine power curve, torque curve, fuel consumption and other engine characteristics, the optimisation of which depends upon the application to which the engine is to be put and can be modified significantly by appropriate selection of the length of the exhaust channels.
The invention

REFERENCES:
patent: 2423602 (1947-07-01), Magdeburger
patent: 3938330 (1976-02-01), Nakajima

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