Internal-combustion engines – Intake manifold – Manifold tuning – balancing or pressure regulating means
Patent
1993-12-09
1995-08-15
Okonsky, David A.
Internal-combustion engines
Intake manifold
Manifold tuning, balancing or pressure regulating means
F02M 3510
Patent
active
054410231
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a tuned engine manifold and is applicable to both intake and exhaust manifolds.
BACKGROUND OF THE INVENTION
When air flows through a manifold of an engine, the flow along the branches of the manifold results not only in a mass transfer along the length of the branch but also in the transmission of sound waves or pressure waves along the branch. By appropriate tuning of the length of the branches, the sound waves can be used to enhance the charge density at the instant that the intake valves close and to improve scavenging of the exhaust gases at the instant that the exhaust valves close, thereby improving engine output power. In other cases, tuning may be required to reduce charge density at the time the intake valves close, for example to reduce pumping losses during part load operation or to increase the pressure at the time that the exhaust valve closes, so that internal exhaust gas recirculation is increased. In other words, the tuning of the manifold can be designed to reflect a positive or a negative pressure wave to the engine port at the time that the port valve closes, to enhance engine performance in a variety of ways.
Though their advantages have been known, tuned manifolds have hitherto been bulky and difficult to incorporate within the limited amount of the space available in the engine compartment and the present invention seeks to introduce greater flexibility into the design of a tuned engine manifold and to enable a tuned manifold of smaller dimensions to be produced.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an engine manifold having a plurality of branches for connecting respective engine ports to ambient air, characterised in that each branch of the manifold is connected to pass through an acoustic coupling formed by a chamber of shallow depth having conjugate foci and defined by two closely spaced end plates and acoustically reflective side walls, the branch section of the manifold for connection to an engine port being connected to the coupling at one of its conjugate foci and the branch section leading, in use, to ambient air being connected to the coupling at a point remote from its conjugate foci, an acoustic reflector being connected to the other of the conjugate foci of the acoustic coupling such that in use sound waves propagating along the branch section leading to the engine port are reflected back towards the same engine port.
The acoustic coupling separates the mass air flow from the acoustic waves propagating along the manifold branches. When an acoustic wave created by the opening of a valve reaches the acoustic coupling chamber it does not flow along the branch section leading to ambient air but is focused by the coupling at the second of the conjugate foci. There the acoustic wave can be arranged to be reflected, with or without inversion, after following any desired path independent of the path of the mass flow thereby affording considerable flexibility in the design of the manifold.
The acoustic chamber may be generally elliptical, in which case the two conjugate foci are both real and lie on the major axis of the ellipse symmetrically about the minor axis. An ellipse can be drawn by connecting the ends of a slack piece of string to two fixed points, placing a pencil against the string and drawing the locus of the points at which the string is held taut by the pencil. The two fixed points are called conjugate foci because waves emanating from one and reflected by the elliptical boundary are always focused at the other. It is known for example that if a snooker table is formed in the shape of an ellipse, a ball struck without spin in any direction from one of the conjugate foci will always collide with another ball located at the other focus.
A complete ellipse is not however the only shape having conjugate foci. If, an ellipse is divided into halves or quarters by reflective walls lying on the minor and/or major axes, then there will still be two conjugate points of focu
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patent: 5107800 (1992-04-01), Araki et al.
No affiliations
Drouillard Jerome R.
Ford Motor Company
May Roger L.
Okonsky David A.
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