BACKGROUND OF THE INVENTION
This invention concerns internal combustion engines and more particularly
noise reduction systems and methods for engine intake and exhaust systems. Engines
commonly employed for automotive use have intake and exhaust valves which are rapidly
opened and closed at timed intervals during the engine cycle.
Much development effort has been exerted to produce quieter running
passenger vehicles, and specifically to eliminating engine noise.
Exhaust muffler systems have long been employed and more recently
resonators and expansion chambers on the air intake systems. Such devices are bulky
since the exhaust gases and air flows must be expanded to large volumes to reduce
the noise levels.
A more exotic approach has been active noise attenuation systems involving
the use of microphones, amplifiers, and speakers to generate cancellation sound
waves 180° out-of-phase with detected noise sound waves. This approach requires
significant electrical power and considerable equipment to execute.
The major source of noise in the exhaust and air induction passages
is generated by the sudden opening and closing of the exhaust and intake valves
during the engine cycle to enable the intake, compression, power, and exhaust engine
phases in each cylinder to proceed in the well known manner. The sudden opening
and closing of the valves create acoustic waves due to the inertia of the gas streams
in the connected passages. That is, the arrested exhaust gas flow into an exhaust
passage by the exhaust valve suddenly closing creates a rarefaction zone near the
exhaust valve as the downstream exhaust flow persists as a result of the inertia
of the exhaust gas. A compression zone near the exhaust valve is created as the
exhaust flow is initiated in a stationary volume of exhaust gas downstream from
a suddenly opening exhaust valve. The arrested intake air flow from an intake passage
by the intake valve suddenly closing creates a compression zone near the intake
valve as the upstream intake air flow persists as a result of the inertia of the
intake air. A rarefaction zone near the intake valve is created as the intake flow
is initiated in a stationary volume of intake gas upstream from a rarefaction zone
near the exhaust valve as the downstream exhaust flow persists as a result of the
inertia of the exhaust gas. A compression zone near the exhaust valve is created
as the exhaust flow is initiated in a stationary volume of exhaust gas downstream
from a suddenly opening exhaust valve. The arrested intake air flow from an intake
passage by the intake valve suddenly closing creates a compression zone near the
intake valve as the upstream intake air flow persists as a result of the inertia
of the intake air. A rarefaction zone near the intake valve is created as the intake
flow is initiated in a stationary volume of intake gas upstream from a suddenly
opening intake valve.
These compression and rarefaction zones propagate as acoustic waves
travelling at the speed of sound through the manifold passages in either the intake
or exhaust systems and finally emanate from the air intake in the induction system
or the exhaust tailpipe in the exhaust system.
A number of Japanese documents describe placing an exhaust and an
intake manifold runner in communication with each other and additionally include
means to dampen sound waves propagating from the exhaust and intake valves. JP-A-04
027 753 suggests using a valve for that purpose, JP-A-05 106 420 has a variable
expansion chamber, JP-A-02 040 014 adjusts the length of respective passages and
JP-A-05 098 928 uses an actuator exciting a diaphragm.
It is the object of the present invention to attenuate noise generated
in this fashion in an internal combustion engine without using bulky mufflers,
expansion chambers, resonators and the like, and without expending electrical power
and necessitating complex equipment.
SUMMARY OF THE INVENTION
The above objects are achieved in a multicylinder engine having intake
and exhaust valves of different cylinders opening and closing at substantially
the same time.
A connecting cross passage creates fluid communication between respective
manifold locations adjacent the exhaust and the intake valves of different cylinders
opening at the same time so as to cause the
- Figures 1A-1C are diagrams of the valve system of a representative four cylinder
engine depicting the acoustic waves generated by opening and closing of the intake
and exhaust valves.
- Figure 2 is a table showing the relationship between the cycles of each cylinder
in a four cylinder engine having a 1-3-4-2 firing order.
- Figure 3 is a table showing the cross passage connections according to the
concept of the present invention.
- Figure 4 is a diagram of a four cylinder engine showing the connections according
to the chart in Figure 3.
- Figure 5 is a sectional view taken through a representative cross passage,
together with fragmentary portions of associated intake and exhaust manifold runners.
In the following detailed description, certain specific terminology
will be employed for the sake of clarity and a particular embodiment described
in accordance with the requirements of 35 USC 112, but it is to be understood that
the same is not intended to be limiting and should not be so construed inasmuch
as the invention is capable of taking many forms and variations within the scope
of the appended claims.
Referring to Figure 1A, the first plot 10 shows the lift of the exhaust
valve (in hidden lines) and the lift of the intake valve (in solid lines) over
two crankshaft revolutions, the exhaust lift mainly taking place between 180°-360°
of crankshaft rotation, the intake valve lift executed approximately 180° later
in the cycle.
Plot 12 shows a trace for each corresponding acoustic wave generation
produced by opening and closing of the exhaust valve. As the exhaust valve opens,
fluid inertia causes a compression sound wave 14 to be generated, while closing
of the valve causes a corresponding rarefaction wave 16 to be generated, as a result
of fluid inertia, both propagated at the speed of sound through the associated
exhaust manifold runner.
Plot 18 shows the same thing for the intake valve, in which opening
of the intake valve creates a rarefaction wave 20 to be generated and upon closing
a compression wave 22.
It can be understood that these sound waves are substantially inversions
of each other, such that combining them would achieve substantially complete cancellation
of each other.
The chart of Figure 2 shows the phase relationship between the engine
cycles of each cylinder of a four cylinder engine and degrees of crankshaft rotation
for a 1-3-4-2 firing order.
Since the engine cycles of each cylinder are out of phase with each
other, there is generation of these inverted sound waves in certain cylinders at
the same time.
According to the concept of the present invention, cross passages
are provided between exhaust and intake manifold runners associated with the exhaust
and intake valves of the cylinders in which these waves are simultaneously generated.
Figure 3 is a chart showing the cross connection for the four cylinder
That is, the exhaust runner of cylinder 1(E1) is placed
in communication with the intake of the cylinder 2(I2), E2
with I4, E3 with I1, and E4 with I3.
This is illustrated diagrammatically in Figure 4 for a four cylinder
engine 23 having an exhaust manifold 24 and intake manifold 26 connected respectively
with an exhaust system 28 and air induction system 30.
Four cross passages 32, 34, 36, 38 extend between exhaust and intake
manifold runners to establish fluid communication as described. Thus, as reverse
sound waves propagated in the cross passages 32-38 reach each other, they will
largely cancel each other.
The diameter and length of each cross passage should be selected to
tune the passages to achieve the interference or cancellation of the sound waves
by application of known acoustic design principles.
Since the intermixing of highly pressurized pressure exhaust gases
into the intake air will result in overheating of the intake manifold, a separation
diaphragm arrangement is provided as shown in Figure 5, which includes a low mass
flexible diaphragm 40 constructed of a durable material able to withstand exposure
to exhaust gases, the diaphragm 40 mounted to extend across and partition each
respective cross passage 32, 34, 36 and 38 (cross passage 32 shown as representative
The cross passage 32 is connected to an exhaust manifold runner 42
at one end and an intake manifold 43 at the other end.
The flexible diaphragm 40 allows transmission of the sound waves with
only slight losses in order to achieve cancellation while preventing intermixing
of the intake air and exhaust gases.
Since a large static pressure difference will typically occur, the
diaphragm 40 must be supported to resist excessive stretching This is accomplished
by porous plugs 44, 46 closely positioned on either side of the diaphragm 40.
Damping porous plugs 48 and 50 are also provided to further protect
the diaphragm from the hot exhaust gases.
The porous plugs 44, 46, 48, and 50 are preferably constructed of
a sintered ceramic material.
It has been established that a porosity of at least 20% will allow
free transmission of low frequencies sound, i.e., will be acoustically transparent.
The acoustic transmission loss for the thin flexible diaphragm is
given by the "mass law":
Transmission loss (db) = 20 log (fρs)-48
- f = frequency (Hz)
- ρs = surface mass density (kg/m2)
Note that surface mass density is simply the product of the material
density and the wall thickness, i.e.,
- ρ = material density (kg/m3)
- t = wall thickness (m)
Thus, the porous plugs 44, 46, 48, 50 and diaphragm 40 can be designed
for low transmission losses while effectively protecting against the effects of
high temperature exhaust gases flowing out of the exhaust manifold.
It may be advantageous to provide some openings in the diaphragm 40
to allow limited flow of exhaust gas into the intake air flow.
Accordingly, a low volume noise cancellation system is effected without
requiring a powered, active cancellation components to achieve the object of the