Internal-combustion engines – Intake manifold – For in-line engine
Patent
1993-12-09
1995-01-10
Cross, E. Rollins
Internal-combustion engines
Intake manifold
For in-line engine
F02M 2506
Patent
active
053797353
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to the tuning of the intake system of an internal combustion engine.
BACKGROUND OF THE INVENTION
Conventionally the intake tracts of a multi-cylinder engine are brought together to a common plenum chamber, each tract opening into the plenum chamber at a point which is designed to experience the minimum flow interference from the other tracts. The tracts function as tuned lengths for which there is one engine speed where the torque is enhanced because of resonance of the pressure wave excitations within the intake system. More specifically, when the inlet valve starts to open, at the beginning of a four stroke cycle, the combustion chamber is still under pressure from the exhaust stroke of the previous cycle and a pressure wave passes out of the intake port and propagates at the speed of sound along the intake tract. This wave travels the entire length of the intake tract until it reaches the plenum chamber at which point it is reflected with opposite phase. A further three traverses of the entire length of the intake tract and two reflections at the open and closed ends of the tract are necessary before the wave again reaches the intake port as a positive pressure wave.
Thus, with a fixed length tract, there are engine speeds at which the reflected pressure wave increases the charge density at the instant when the inlet valve closes so as to improve volumetric efficiency but other speeds when the wave arrives as a negative pressure tending to reduce volumetric efficiency.
To obtain an improvement at low engine speeds, a long tract length is required but this has the disadvantage of increasing the package size and the resistance to flow at high engine speeds.
Variable length manifolds have been proposed to avoid the performance degradation at certain engine speeds but these do not provide the solution to the packaging problems in designing a manifold which will resonate at low engine speeds.
OBJECT OF THE INVENTION
The invention therefore seeks to provide a longer tuned length without increasing the size of the intake system and to avoid performance degradation from reflected waves having a negative pressure.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an intake system for an internal combustion engine having a plurality of intake tracts of equal length connected in use to extend from individual engine intake ports to a common plenum chamber, and a common passage opening into the plenum chamber for supplying air to all the intake ports, wherein the tracts are arranged to open into the plenum chamber in pairs associated with intake ports of which the intake valve events do not overlap, characterised in that the ends of each pair of tracts disposed within the plenum chamber are arranged directly facing one another and are separated by a gap which is narrower than the diameter of the tracts, the gap being sufficiently wide to permit mass air flow between the respective tracts and the common passage but being sufficiently narrow to couple most of any pressure wave energy emanating from one tract directly into the other tract.
PREFERRED FEATURES OF THE INVENTION
Preferably, the gap between the ends of the tracts within the plenum chamber should be between one quarter and one half of the diameter of the tracts.
This arrangement permits mass air flow to enter freely into either one of the intake tracts yet at the same time a pressure wave coming from either tract is transmitted across to the opposite tract which now functions as a resonance column with a closed end. By ensuring good coupling of the pressure wave across the facing pipes, the effective tuned length is made equal to the combined length of the two tracts and the pressure wave can propagate several times along its length with closed-end reflections at both ends. Because both ends of the resonating column are closed, the pressure wave suffers no pressure inversion as would be the case in a conventional tract.
Because no reflection is inverted, there are twice as
REFERENCES:
patent: 3845746 (1974-11-01), Elsbett
patent: 4228769 (1980-10-01), Gartner et al.
patent: 4318371 (1982-03-01), McFarland
patent: 4409934 (1983-10-01), Kaindl
patent: 4497287 (1985-02-01), Schleiermacher et al.
patent: 5094210 (1992-03-01), Endres et al.
Cross E. Rollins
Drouillard Jerome R.
Ford Motor Company
Macy M.
May Roger L.
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