U.S. patent application number 12/059226 was filed with the patent office on 2008-10-09 for method and apparatus for controlling engine exhaust sound for vehicles.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Kazushige Maeda, Akira Sasaki.
Application Number | 20080245605 12/059226 |
Document ID | / |
Family ID | 39500035 |
Filed Date | 2008-10-09 |
United States Patent
Application |
20080245605 |
Kind Code |
A1 |
Maeda; Kazushige ; et
al. |
October 9, 2008 |
METHOD AND APPARATUS FOR CONTROLLING ENGINE EXHAUST SOUND FOR
VEHICLES
Abstract
An exhaust sound controlling method including reducing a flow
rate of exhaust gas that passes through an exhaust path, to a first
flow rate in accordance with increase in engine speed in a first
engine speed region, and increasing the flow rate of exhaust gas to
a second flow rate in accordance with increase in engine speed in a
second engine speed region higher in engine speed than the first
engine speed region. An exhaust sound controlling apparatus
including a baffle plate and a valve that is operated to open a
communication passage that communicates upstream and downstream
sides of the baffle plate in an engine starting region, close the
communication passage in an idling region and a low engine speed
region, and open the communication passage and increase an opening
of the valve as the engine speed rises in a high engine speed
region.
Inventors: |
Maeda; Kazushige;
(Yokohama-shi, JP) ; Sasaki; Akira; (Zushi-shi,
JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
39500035 |
Appl. No.: |
12/059226 |
Filed: |
March 31, 2008 |
Current U.S.
Class: |
181/254 ;
181/264 |
Current CPC
Class: |
F01N 1/084 20130101;
F01N 1/166 20130101; F01N 1/168 20130101; F01N 2470/14 20130101;
F01N 1/089 20130101 |
Class at
Publication: |
181/254 ;
181/264 |
International
Class: |
F01N 1/00 20060101
F01N001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2007 |
JP |
2007-098526 |
Claims
1. A method for controlling exhaust sound from an engine which is
emitted through an exhaust path, the method comprising: a first
control step of reducing a flow rate of exhaust gas that passes
through the exhaust path, to a first flow rate in accordance with
increase in engine speed in a first engine speed region; and a
second control step of increasing the flow rate of exhaust gas to a
second flow rate in accordance with increase in engine speed in a
second engine speed region in which the engine speed is higher than
that in the first engine speed region.
2. The method as claimed in claim 1, further comprising a third
control step of reducing the flow rate of exhaust gas to a third
flow rate that is lower than the first flow rate and the second
flow rate in a third engine speed region between the first engine
speed region and the second engine speed region.
3. The method as claimed in claim 1, wherein the engine speed in
the first engine speed region comprises an engine speed in an
engine starting region.
4. The method as claimed in claim 1, wherein the engine speed in
the second engine speed region comprises an engine speed in a high
engine speed region.
5. The method as claimed in claim 2, wherein the engine speed in
the third engine speed region comprises an engine speed in an
idling region.
6. The method as claimed in claim 2, wherein the engine speed in
the third engine speed region comprises an engine speed in a low
engine speed region.
7. An apparatus for controlling exhaust sound from an engine which
is emitted through an exhaust path, the apparatus comprising: a
baffle plate that is disposed within the exhaust path so as to
block a flow of exhaust gas in the exhaust path, the baffle plate
being formed with an aperture; a communication passage that
communicates an upstream side of the baffle plate and a downstream
side of the baffle plate with each other; a valve that is so
disposed as to cover a part of the aperture of the baffle plate and
operated to open and close the communication passage; and wherein
the valve is operated to open the communication passage in an
engine starting region, the valve is operated to close the
communication passage in an idling region and a low engine speed
region, and the valve is operated to open the communication passage
and increase an opening of the valve as the engine speed rises in a
high engine speed region.
8. The apparatus as claimed in claim 7, further comprising a means
for cooperating with the valve to define the communication passage
during the rotational movement of the valve.
9. The apparatus as claimed in claim 7, further comprising a
biasing means for biasing the valve toward the baffle plate.
10. An apparatus for controlling exhaust sound from an engine which
is emitted through an exhaust path, the apparatus comprising: a
baffle plate that is disposed within the exhaust path so as to
block a flow of exhaust gas in the exhaust path, the baffle plate
being formed with an aperture; a valve that is so disposed as to
cover a part of the aperture of the baffle plate, the valve being
rotationally moveable relative to the baffle plate so as to be
apart from the baffle plate in a direction of the flow of exhaust
gas, a biasing means for biasing the valve toward the baffle plate;
and an enclosure member that extends from the baffle plate so as to
be opposed to the outer periphery of the valve when the valve is
moved relative to the baffle plate, wherein the valve has a contact
position in which the valve is contacted with the baffle plate and
covers the part of the aperture of the baffle plate, a small
distance position in which the valve is apart from the baffle plate
in the direction of the flow of exhaust gas with a first distance
therebetween, an intermediate distance position in which the valve
is apart from the baffle plate in the direction of the flow of
exhaust gas with a second distance therebetween which is larger
than the first distance, and a large distance position in which the
valve is apart from the baffle plate in the direction of the flow
of exhaust gas with a third distance therebetween which is larger
than the first distance and the second distance, and wherein when
the valve is placed in the contact position, the valve cooperates
with the baffle plate to define an opening between the outer
periphery of the valve and a periphery of the aperture of the
baffle plate, when the valve is placed in the small distance
position, the valve cooperates with the enclosure member to define
a first clearance between the outer periphery of the valve and an
opposing surface of the enclosure member that is opposed to the
outer periphery of the valve, when the valve is placed in the
intermediate distance position, at least a part of the outer
periphery of the valve is substantially contacted with the opposing
surface of the enclosure member, and when the valve is placed in
the large distance position, the valve cooperates with the
enclosure member to define a second clearance between the outer
periphery of the valve and the opposing surface of the enclosure
member, and the second clearance is increased as the third distance
between the valve and the baffle plate becomes larger.
11. The apparatus as claimed in claim 10, wherein the biasing means
has a biasing force that acts on the valve against a pressure of
the exhaust gas that flows in the exhaust path, the biasing force
urges the valve to move to the small distance position in an engine
starting region, the biasing force urges the valve to move to the
intermediate distance position in an idling region and a low engine
speed region, and the biasing force urges the valve to move to the
large distance position in a high engine speed region.
12. The apparatus as claimed in claim 10, wherein the valve
comprises a gas leakage inhibiting portion that prevents the
exhaust gas and the exhaust sound from leaking from a support
portion of the valve at which the valve is supported relative to
the baffle plate, toward a downstream side of the baffle plate
during the rotational movement of the valve.
13. The apparatus as claimed in claim 10, further comprising a gas
leakage inhibiting member that prevents the exhaust gas and the
exhaust sound from leaking from a support portion of the valve at
which the valve is supported relative to the baffle plate, toward a
downstream side of the baffle plate during the rotational movement
of the valve.
14. The apparatus as claimed in claim 10, further comprising a
first expansion chamber, a second expansion chamber that are
separated from the first expansion chamber by the baffle plate, a
first communication tube having one end that is connected to the
engine and the other end that is opened within the second expansion
chamber, a second communication tube having one end that is exposed
to atmospheric air and the other end that is opened within the
first expansion chamber, and a third communication tube that
extends through the baffle plate and communicates the first
expansion chamber and the second expansion chamber with each other,
wherein the first and second expansion chambers are larger in
sectional area than the first, second and third communication
tubes.
15. The apparatus as claimed in claim 10, further comprising a
first expansion chamber, a second expansion chamber that is
separated from the first expansion chamber by the baffle plate, a
third expansion chamber, a second baffle plate that separates the
third expansion chamber and the second expansion chamber from each
other, an inlet tube having one end that is connected to the engine
and the other end that is opened within the second expansion
chamber, a first tail tube having one end that is exposed to
atmospheric air and the other end that is opened within the first
expansion chamber, a second tail tube having one end that is
exposed to atmospheric air and the other end that is opened within
the second expansion chamber, a first pass-through tube that
extends through the second baffle plate and communicates the second
expansion chamber with the third expansion chamber, and a second
pass-through tube that extends through the second baffle plate and
communicates the third expansion chamber with the aperture of the
baffle plate, wherein the first, second and third expansion
chambers being larger in sectional area than the inlet tube, the
first and second tail tubes and the first and second pass-through
tubes.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to method and apparatus for
controlling engine exhaust sound that is emitted from an exhaust
system of vehicles such as an automobile.
[0002] There have been conventionally proposed engine exhaust sound
controlling apparatuses for vehicles which reduce exhaust sound in
high engine speed region as well as in low engine speed region
while reducing exhaust loss in high engine speed region.
[0003] Japanese Patent Application First Publication No. 8-109815
(corresponding to U.S. Pat. Nos. 5,614,699 and 5,739,483) indicates
engine exhaust sound controlling apparatus for vehicles which
includes a valve for conducting changeover of exhaust paths in
response to exhaust pressure, a biasing member such as a spring
which biases the valve in a closing direction of the valve against
the exhaust pressure, and a spring constant changing member that
reduces an increment of a reaction force of the biasing member when
a rotational angle of the valve exceeds a predetermined value.
SUMMARY OF THE INVENTION
[0004] Recently, it has been required to reduce back pressure and
vary a level of exhaust sound in an exhaust system in response to a
vehicle running state. Specifically, when a vehicle engine is
started, the exhaust sound would be increased to create a powerful
sound to be heard by a passenger of the vehicle. When the engine is
operated in an idling region and a low engine speed region, i.e., a
slow acceleration state, the exhaust sound would be reduced to
ensure a silence within the interior of the vehicle. Further, when
the engine is operated in a high engine speed region, i.e., a rapid
acceleration state, the exhaust sound would be increased again to
create a good acceleration sound to be heard by the passenger.
[0005] However, in the apparatus of the conventional art as
described above, when the engine is operated in the low engine
speed region, the valve is kept in the closed state by the biasing
member until a pressure in a muffler reaches a certain pressure
value in order to ensure the silence within the interior of the
vehicle. Further, in the conventional apparatus, the valve is kept
closed even in the engine starting region. Thus, the conventional
art shows the exhaust system that is constructed from a viewpoint
of reducing the exhaust sound. Therefore, the apparatus of the
conventional art fails to produce a powerful exhaust sound in the
engine starting region.
[0006] It is an object of the present invention to provide a method
and apparatus for controlling exhaust sound which is capable of
producing a powerful exhaust sound in an engine starting region and
ensuring silence in the interior of the vehicle in a low engine
speed region.
[0007] In one aspect of the present invention, there is provided a
method for controlling exhaust sound from an engine which is
emitted through an exhaust path, the method comprising:
[0008] a first control step of reducing a flow rate of exhaust gas
that passes through the exhaust path, to a first flow rate in
accordance with increase in engine speed in a first engine speed
region; and
[0009] a second control step of increasing the flow rate of exhaust
gas to a second flow rate in accordance with increase in engine
speed in a second engine speed region in which the engine speed is
higher than that in the first engine speed region.
[0010] In a further aspect of the present invention, there is
provided an apparatus for controlling exhaust sound from an engine
which is emitted through an exhaust path, the apparatus
comprising:
[0011] a baffle plate that is disposed within the exhaust path so
as to block a flow of exhaust gas in the exhaust path, the baffle
plate being formed with an aperture;
[0012] a communication passage that communicates an upstream side
of the baffle plate and a downstream side of the baffle plate with
each other;
[0013] a valve that is so disposed as to cover a part of the
aperture of the baffle plate and operated to open and close the
communication passage; and
[0014] wherein the valve is operated to open the communication
passage in an engine starting region, the valve is operated to
close the communication passage in an idling region and a low
engine speed region, and the valve is operated to open the
communication passage and increase an opening of the valve as the
engine speed rises in a high engine speed region.
[0015] In a still further aspect of the present invention, there is
provided an apparatus for controlling exhaust sound from an engine
which is emitted through an exhaust path, the apparatus
comprising:
[0016] a baffle plate that is disposed within the exhaust path so
as to block a flow of exhaust gas in the exhaust path, the baffle
plate being formed with an aperture;
[0017] a valve that is so disposed as to cover a part of the
aperture of the baffle plate, the valve being rotationally moveable
relative to the baffle plate so as to be apart from the baffle
plate in a direction of the flow of exhaust gas,
[0018] a biasing means for biasing the valve toward the baffle
plate; and
[0019] an enclosure member that extends from the baffle plate so as
to be opposed to the outer periphery of the valve when the valve is
moved relative to the baffle plate,
[0020] wherein the valve has a contact position in which the valve
is contacted with the baffle plate and covers the part of the
aperture of the baffle plate, a small distance position in which
the valve is apart from the baffle plate in the direction of the
flow of exhaust gas with a first distance therebetween, an
intermediate distance position in which the valve is apart from the
baffle plate in the direction of the flow of exhaust gas with a
second distance therebetween which is larger than the first
distance, and a large distance position in which the valve is apart
from the baffle plate in the direction of the flow of exhaust gas
with a third distance therebetween which is larger than the first
distance and the second distance, and
[0021] wherein when the valve is placed in the contact position,
the valve cooperates with the baffle plate to define an opening
between the outer periphery of the valve and a periphery of the
aperture of the baffle plate,
[0022] when the valve is placed in the small distance position, the
valve cooperates with the enclosure member to define a first
clearance between the outer periphery of the valve and an opposing
surface of the enclosure member that is opposed to the outer
periphery of the valve,
[0023] when the valve is placed in the intermediate distance
position, at least a part of the outer periphery of the valve is
substantially contacted with the opposing surface of the enclosure
member, and
[0024] when the valve is placed in the large distance position, the
valve cooperates with the enclosure member to define a second
clearance between the outer periphery of the valve and the opposing
surface of the enclosure member, and the second clearance is
increased as the third distance between the valve and the baffle
plate becomes larger.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a front view of a valve structure for use in an
exhaust sound control apparatus of an embodiment of the present
invention.
[0026] FIG. 2 is a sectional view of the valve structure, taken
along line 2-2 of FIG. 1.
[0027] FIG. 3 is an explanatory diagram illustrating an operation
of a valve of the valve structure of FIG. 1.
[0028] FIG. 4 is a sectional view of a muffler to which the exhaust
sound control apparatus of the embodiment is applied.
[0029] FIG. 5 is a diagram showing a relationship between engine
speed and opening of the valve.
[0030] FIG. 6 is a diagram showing a relationship between a flow
rate of exhaust gas and a pressure forward of the valve.
[0031] FIG. 7 is a front view of a modification of the valve
structure shown in FIG. 1.
[0032] FIG. 8 is a sectional view of the modified valve structure,
taken along line 8-8 of FIG. 7.
[0033] FIG. 9 is an explanatory diagram illustrating an operation
of the modified valve structure of FIG. 7.
[0034] FIG. 10 is a sectional view of a modification of the muffler
shown in FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Referring to FIG. 1 to FIG. 3, an exhaust sound controlling
apparatus for vehicles, according to an embodiment of the present
invention, now is explained. The exhaust sound controlling
apparatus includes a valve structure shown in FIG. 1 and FIG. 2. As
shown in FIG. 1 and FIG. 2, the valve structure includes valve 2
that is disposed on baffle plate 1. Baffle plate 1 is disposed
within a muffler as explained later which is connected to a vehicle
engine. Baffle plate 1 divides an interior of the muffler into a
plurality of expansion chambers which constitute an exhaust path
through which a flow of exhaust gas from the engine passes. Baffle
plate 1 is so arranged as to block the flow of exhaust gas in the
exhaust path.
[0036] Baffle plate 1 includes a generally rectangular-shaped
aperture la as shown in FIG. 1. Aperture la extends through baffle
plate 1. Valve 2 is disposed on a downstream side surface of baffle
plate 1 with respect to the flow of exhaust gas and so arranged as
to cover a part of aperture 1a. Specifically, a pair of supports
3a, 3b are arranged in a spaced and opposed relation to each other.
Supports 3a, 3b are fixed to baffle plate 1 by a suitable fastening
manner such as welding. Valve shaft 4 is supported at opposite end
portions thereof by supports 3a, 3b. Valve 2 is rotatably mounted
onto valve shaft 4.
[0037] Valve 2 is rotationally moveable relative to baffle plate 1
so as to be apart from baffle plate 1 in a direction of the flow of
exhaust gas. Valve 2 is operated to open and close a communication
passage which allows fluid communication between an upstream side
expansion chamber and a downstream side expansion chamber which are
disposed on an upstream side and a downstream side of baffle plate
1 with respect to the flow of exhaust gas in the exhaust path.
[0038] Specifically, valve 2 is a generally rectangular-shaped
plate member. Valve 2 includes curved end portion 2a at one end
thereof, a pair of support portions 2b disposed on opposite sides
of curved end portion 2a and planar valve body 2c connected with
curved end portion 2a. Valve 2 has end peripheral surface 2d and
two side peripheral surfaces which are disposed on an outer
periphery of valve body 2c. End peripheral surface 2d is located at
an opposite end of valve 2, namely, at a lower end of valve 2 when
viewed in FIG. 2. The side peripheral surfaces are opposed to each
other in the axial direction of valve shaft 4 and joined with end
peripheral surface 2d. Curved end portion 2a is raised up from
valve body 2c and formed into a curved shape. Support portions 2b
are spaced from each other in an axial direction of valve shaft 4
and located between supports 3a, 3b. Valve shaft 4 extends through
shaft insertion holes of support portions 2b and is supported by
support portions 2b. Valve body 2c serves as a closing member that
comes into contact and non-contact with baffle plate 1 so as close
the part of aperture 1a.
[0039] Curved end portion 2a is so curved as to have a
predetermined radius that extends from a central axis of valve
shaft 4. An outer circumferential surface of curved end portion 2a
is opposed to baffle plate 1 and substantially in slide contact
with baffle plate 1 during the rotational movement of valve 2 about
valve shaft 4.
[0040] Torsion spring 5 is mounted to valve shaft 4 and biases
valve body 2c of valve 2 toward baffle plate 1. When valve 2 is
biased by torsion spring 5 so as to be placed in a position shown
in FIG. 2, valve body 2c is contacted near curved end portion 2a
with a part of baffle plate 1 which is located along an upper
periphery of aperture 1a. Thus, a planer upstream side surface of
valve body 2c is contacted with the downstream side surface of
baffle plate 1 exclusive of aperture 1a. In other words, when valve
2 is urged to be in the position shown in FIG. 2, the upstream side
surface of valve body 2c is aligned with the downstream side
surface of baffle plate 1.
[0041] Aperture 1a is so configured as to be partially covered by
valve body 2c of valve 2. Specifically, aperture 1a extends in the
axial direction of valve shaft 4 so as to have an opening width
equal to or slightly smaller than a width of valve 2 as shown in
FIG. 1. As shown in FIG. 2, aperture 1a also extends in a direction
perpendicular to the axial direction of valve shaft 4 beyond end
peripheral surface 2d of valve 2. A part of aperture 1a which is
located on an outside of end peripheral surface 2d of valve 2,
namely, on a lower side of end peripheral surface 2d in FIG. 2,
serves as opening 10 through which an upstream side expansion
chamber and a downstream side expansion chamber disposed on an
upstream side and a downstream side of baffle plate 1 with respect
to the flow of exhaust gas in the exhaust path are communicated
with each other when valve 2 is urged to be in the position shown
in FIG. 2. Specifically, when valve 2 is biased by torsion spring 5
and placed in the position shown in FIG. 2, valve body 2c is in
contact with baffle plate 1 and aperture 1a is covered by valve
body 2c except for opening 10. Opening 10 is disposed between end
peripheral surface 2d and an aperture forming rim of baffle plate 1
which defines a periphery of the rectangular-shaped aperture la.
Opening 10 is always prevented from being covered by valve body
2c.
[0042] Valve guides 6, 7 and 8 serve as an enclosure member that
extends from baffle plate 1 so as to surround the outer periphery
of valve 2. Valve guides 6, 7 and 8 cooperate with baffle plate 1
and valve 2 to define the communication passage that allows the
fluid communication between the upstream side expansion chamber
disposed on the upstream side of baffle plate 1 and the downstream
side expansion chamber disposed on the downstream side of baffle
plate 1.
[0043] Specifically, side valve guides 6 and 7 are disposed on both
sides of valve 2 in an opposed and spaced relation thereto in the
axial direction of valve shaft 4. Side valve guides 6 and 7 are
formed into a plate shape and extend from the downstream side
surface of baffle plate 1 in the direction of the flow of exhaust
gas, namely, in a rotational direction of valve 2, so as to be
opposed to the side peripheral surfaces of valve 2 during the
rotational movement of valve 2 about valve shaft 4. End valve guide
8 is interposed between side valve guides 6 and 7 on the side of
the other end of valve 2.
[0044] End valve guide 8 is opposed to and spaced from end
peripheral surface 2d of valve 2 in the direction perpendicular to
the axial direction of valve shaft 4. End valve guide 8 uprightly
extends from the downstream side surface of baffle plate 1 and has
a predetermined height. End valve guide 8 extends along the
bottom-linear part of the generally rectangular-shaped periphery of
aperture 1a in the axial direction of valve shaft 4. End valve
guide 8 has clearance forming surface 8a and contact surface 8b on
a side of valve 2 and valve shaft 4, namely, on an upper side of
end valve guide 8 in FIG. 1 and FIG. 2. Specifically, clearance
forming surface 8a extends uprightly from the downstream side
surface of baffle plate 1. Clearance forming surface 8a cooperates
with end peripheral surface 2d of valve 2 to form the clearance
therebetween when valve 2 is rotated about valve shaft 4 and moved
from the position shown in FIG. 2 in an opening direction thereof
in which valve body 2c moves apart from baffle plate 1 to uncover
aperture 1a. Contact surface 8b is connected with upright surface
8a through a step portion between clearance forming surface 8a and
contact surface 8b. Contact surface 8b is so curved as to be
approximately close to or contacted with end peripheral surface 2d
of valve 2 during a further rotational movement of valve 2 about
valve shaft 4 subsequent to passing through above clearance forming
surface 8a. Thus, end peripheral surface 2d of valve 2 is
approximately close to or in contact with contact surface 8b of end
valve guide 8 when valve 2 is further rotated about valve shaft 4
subsequent to passing through above clearance forming surface 8a of
end valve guide 8.
[0045] Valve 2 serves as a control valve that controls the flow of
exhaust gas passing through the exhaust path. An operation of valve
2 is explained hereinafter with reference to FIG. 3. As shown in
FIG. 3, valve 2 is urged to be placed in position A by the biasing
force of torsion spring 5. In position A, valve body 2c is in
contact with baffle plate 1, and aperture 1a of baffle plate 1 is
covered with valve body 2c except for opening 10 that is disposed
on the outside of end peripheral surface 2d of valve 2. In position
A, opening 10 is prevented from being covered with valve body 2c
and there is a clearance between end peripheral surface 2d of valve
2 and clearance forming surface 8a of end valve guide 8. That is,
in position A, valve 2 is in a first open state in which there is
no distance between valve body 2c and baffle plate 1 in the
direction of the flow of exhaust gas, namely, in the rotational
direction of valve 2, and the expansion chambers on the upstream
and downstream sides of baffle plate 1 are communicated with each
other through opening 10 and the clearance between end peripheral
surface 2d and clearance forming surface 8a.
[0046] Next, as shown in FIG. 3, when an external force, i.e., an
exhaust pressure, is applied to valve 2 in the direction of the
flow of exhaust gas in which valve 2 moves apart from baffle plate
1, valve 2 is rotated about valve shaft 4 against the biasing force
of torsion spring 5 and moved from position A to a position
immediately before position B. At this time, a distance between
baffle plate 1 and valve body 2c of valve 2 in the direction of the
flow of exhaust gas is relatively small and an amount of the
rotational movement of valve 2, namely, an opening of valve 2, is
relatively small. During the rotational movement of valve 2, there
exists the clearance between end peripheral surface 2d of valve 2
and clearance forming surface 8a of end valve guide 8. The fluid
communication between the upstream side expansion chamber and the
downstream side expansion chamber which are disposed on the
upstream side and the downstream side of baffle plate 1 can be
maintained through opening 10 and the clearance. Thus, valve 2 can
be kept in the first open state while valve 2 is moved from
position A to the position immediately before position B.
[0047] When the external force that is applied to valve 2 in the
opening direction is increased, valve 2 is further rotated about
valve shaft 4 against the biasing force of torsion spring 5. Valve
2 is placed in position B and then moved from position B to
position C. At this time, the rotation amount of valve 2 becomes
intermediate and the distance between baffle plate 1 and valve body
2c in the direction of the flow of exhaust gas becomes
intermediate. During the rotational movement of valve 2 from
position B to position C, at least a part of the outer periphery of
valve 2, namely, end peripheral surface 2d of valve 2, is in
substantially contact, namely, slide contact, with contact surface
8b of end valve guide 8. Therefore, the upstream side expansion
chamber on the upstream side of baffle plate 1 can be prevented
from being communicated with the downstream side expansion chamber
on the downstream side of baffle plate 1. Thus, during the
rotational movement of valve 2 from position B to position C, valve
2 is restrained from the first open state and kept in a closing
state in which there is the intermediate distance between valve
body 2c and baffle plate 1 in the direction of the flow of exhaust
gas and the fluid communication between the upstream side expansion
chamber and the downstream side expansion chamber which are
disposed on the upstream and downstream sides of baffle plate 1 can
be substantially prevented.
[0048] When the external force is further increased, valve 2 is
further rotated about valve shaft 4 against the biasing force of
torsion spring 5 and moved from position C in the opening direction
to thereby be apart from end valve guide 8. At this time, the
rotation amount of valve 2 becomes large and the distance between
baffle plate 1 and valve body 2c in the direction of the flow of
exhaust gas becomes large. End peripheral surface 2d of valve 2 is
apart from contact surface 8b of end valve guide 8, and there is
generated a clearance between end peripheral surface 2d and contact
surface 8b. Therefore, the upstream side expansion chamber on the
upstream side of baffle plate 1 can be communicated again with the
downstream side expansion chamber on the downstream side of baffle
plate 1 through the clearance between end peripheral surface 2d and
contact surface 8b. Thus, when valve 2 is further rotationally
moved from position C in the opening direction, valve 2 is in a
second open state in which the fluid communication between the
upstream side expansion chamber and the downstream side expansion
chamber which are disposed on the upstream and downstream sides of
baffle plate 1 can be re-established through the clearance between
end peripheral surface 2d and contact surface 8b. The clearance is
increased as the distance between baffle plate 1 and valve body 2c
in the direction of the flow of exhaust gas becomes larger.
Further, in the second open state of valve 2, the opening of valve
2 and the angular position of valve 2 with respect to baffle plate
1, varies in accordance with the rotation amount of valve 2 and the
distance between baffle plate 1 and valve body 2c in the direction
of the flow of exhaust gas. That is, as the rotation amount of
valve 2 and the distance between baffle plate 1 and valve body 2c
in the direction of the flow of exhaust gas increases, the opening
of valve 2 becomes larger.
[0049] Opening 10 and the clearance between baffle plate 1, valve
body 2c and valve guides 6, 7 and 8 constitute the communication
passage between the upstream side expansion chamber disposed on the
upstream side of baffle plate 1 and the downstream side expansion
chamber disposed on the downstream side of baffle plate 1. That is,
the communication passage is formed by the aperture-forming rim of
baffle plate 1, end peripheral surface 2d of valve body 2c, opposed
surfaces of side valve guides 6 and 7 opposed in the axial
direction of valve shaft 4, and clearance forming surface 8a and
contact surface 8b of end valve guide 8.
[0050] Referring to FIG. 4, there is shown muffler 20 to which the
exhaust sound controlling apparatus of the embodiment is applied.
FIG. 4 shows a sectional view of muffler 20, taken in a direction
of the flow of exhaust gas that passes through muffler 20. Muffler
20 may have a generally elliptic-shape in cross-section taken in a
direction perpendicular to the direction of the flow of exhaust
gas. As shown in FIG. 4, baffle plate 21 is disposed within muffler
20 so as to divide an interior of muffler 20 into two expansion
chambers adjacent to each other, namely, first expansion chamber 22
and second expansion chamber 23 which are located on the left side
and the right side of FIG. 4, respectively. First expansion chamber
22 and second expansion chamber 23 are thus separated from each
other by baffle plate 21.
[0051] Inlet tube 24 extends into second expansion chamber 23
through an upstream end wall of muffler 20, first expansion chamber
22 and baffle plate 21. Inlet tube 24 has one end that outwardly
projects from the upstream end wall of muffler 20 and is connected
to the engine through an exhaust pipe, not shown. Inlet tube 24 has
the other end that is opened within second expansion chamber 23.
Inlet tube 24 serves as a first communication tube that
communicates second expansion chamber 23 with the engine. Inlet
tube 24 introduces the exhaust gas from the engine into second
expansion chamber 23. Pass-through tube 25 extends through baffle
plate 21 and communicates first expansion chamber 22 and second
expansion chamber 23 with each other. Pass-through tube 25 has one
end that is opened within second expansion chamber 23 and the other
end that is opened within first expansion chamber 22. Tail tube 26
extends from first expansion chamber 22 to an outside of muffler 20
through baffle plate 21, second expansion chamber 23 and a
downstream end wall of muffler 20. Tail tube 26 has one end that is
opened within first expansion chamber 22 and the other end that
outwardly projects from the downstream end wall of muffler 20 and
is exposed to atmospheric air. Tail tube 26 serves as a second
communication tube that communicates first expansion chamber 22
with atmospheric air. First expansion chamber 22 and second
expansion chamber 23 are larger in cross-sectional area than inlet
tube 24, pass-through tube 25 and tail tube 26.
[0052] Baffle plate 21 has generally rectangular-shaped aperture
21a that is disposed parallel with pass-through tube 25. The valve
structure described above with reference to FIG. 1 to FIG. 3 is
provided on baffle plate 21 on a side of first expansion chamber
22. That is, valve 2 is arranged on a downstream side surface of
baffle plate 21 which is exposed to first expansion chamber 22,
such that valve body 2c covers aperture 21a except for opening 10.
Valve 2, valve guides 6, 7 and 8 and baffle plate 21 cooperate with
each other to define a communication passage that allows fluid
communication between first expansion chamber 22 and second
expansion chamber 23 in parallel with pass-through tube 25. The
communication passage includes opening 10 that is disposed between
end peripheral surface 2d of valve 2 and the aperture-forming rim
of baffle plate 21 which defines the periphery of aperture 21a. The
communication passage further includes the clearance that is formed
between valve 2 and valve guides 6, 7 and 8 upon rotation of valve
2 about valve shaft 4. In the construction of muffler 20, the
exhaust path extends through inlet tube 24, pass-through tube 25,
tail tube 26, first expansion chamber 22, second expansion chamber
23 and the communication passage between first expansion chamber 22
and second expansion chamber 23.
[0053] In thus constructed muffler 20, exhaust sound generated from
the engine is controlled in accordance with an operating condition
of the engine. The exhaust sound is emitted to atmospheric air via
a first route, a second route or both of the first and second
routes in accordance with the engine operating condition. The first
route is indicated by arrow A in FIG. 4 and the second route is
indicated by arrow B in FIG. 4. The first route extends
sequentially through inlet tube 24, second expansion chamber 23,
pass-through tube 25, first expansion chamber 22 and tail tube 26.
The second route extends sequentially through inlet tube 24, the
communication passage between valve 2 and valve guides 6, 7 and 8,
first expansion chamber 22 and tail tube 26. The second route thus
bypasses pass-through tube 25.
[0054] Specifically, in an engine starting region in which a flow
of exhaust gas from the engine starts at zero and increases, the
exhaust sound from the engine is emitted from tail tube 26 to
atmospheric air via the first route indicated by arrow A in FIG. 4.
Further, in the engine starting region, valve 2 is rotationally
moved from position A to the position immediately before position B
as shown in FIG. 3. At this time, valve 2 is placed in the first
open state in which second expansion chamber 23 is communicated
with first expansion chamber 22 through the communication passage
therebetween, namely, through opening 10 and the clearance between
end peripheral surface 2d of valve 2 and clearance forming surface
8a of end valve guide 8. In this condition, the exhaust sound from
the engine is emitted from tail tube 26 to atmospheric air via the
second route in addition to the first route. Since the emission of
the exhaust sound is performed via both the first route and the
second route, the exhaust sound that is generated in the engine
starting region can be enhanced as compared to the conventional
exhaust sound controlling apparatus.
[0055] Further, when the engine speed is raised up to a
predetermined engine speed which is in the idling region, valve 2
is rotationally moved to position B shown in FIG. 3 due to an
increase in an exhaust pressure immediately forward of valve 2,
namely, an exhaust pressure within second expansion chamber 23,
which is hereinafter referred to as a valve-forward pressure. Valve
2 is placed in the closing state in which end peripheral surface 2d
is substantially contacted with contact surface 8b of end valve
guide 8. In the closing state of valve 2, the opening of valve 2
and the sectional area of the communication passage are
approximately zero. The exhaust sound from the engine is emitted to
atmospheric air substantially only via the first route. As a
result, the exhaust sound can be reduced.
[0056] When the engine speed is raised up to the low engine speed
region in which the engine speed is higher than in the idling
region, namely, when the engine is operated in a slow acceleration
state, and the engine is maintained in the low engine speed region,
the valve-forward pressure is further increased with the engine
speed raise. Due to the increase in the valve-forward pressure,
valve 2 is rotationally moved from position B to position C shown
in FIG. 3. During the rotational movement from position B to
position C, valve 2 is kept in the closing state. Therefore, the
emission of the exhaust sound substantially only via the first
route is maintained so that the exhaust sound can be reduced.
[0057] When the engine speed is further raised up to a high engine
speed region in which the engine speed is higher than in the low
engine speed region, namely, when the engine is operated in a rapid
acceleration state, the valve-forward pressure is further increased
due to an increase in the flow of exhaust gas from the engine.
Valve 2 is further rotationally moved away from position C and
placed in the second open state. In the second open state, end
peripheral surface 2d of valve 2 becomes out of contact with
contact surface 8b of end valve guide 8 so that there is generated
a clearance therebetween. Therefore, the exhaust sound from the
engine is emitted from tail tube 26 to atmospheric air via both the
first route and the second route. Thus, even when the flow of
exhaust gas is increased, increase in pressure loss can be
suppressed to thereby enhance the engine output in the high engine
speed region.
[0058] Referring FIG. 5, there is shown a relationship between the
engine speed and the opening of valve 2. As shown in FIG. 5, when
the engine speed is in the engine starting region, valve 2 is
placed in the first open state described above. Further, when the
engine speed is increased to be in the idling region or the low
engine speed region, valve 2 is brought into the closing state.
When the engine speed reaches the high engine speed region, valve 2
is brought into the second open state as described above.
[0059] That is, in the exhaust sound controlling apparatus of the
present invention, valve 2 is constructed to be operated
corresponding to the engine speed. The spring force (spring
constant) of torsion spring 5, the opening of valve 2 and the
opening area of aperture 1a, 21a may be suitably set to operate
valve 2 corresponding to the engine speed as described above.
Alternatively, the valve-forward pressure (the exhaust pressure in
second expansion chamber 23) may be suitably set to operate valve 2
corresponding to the engine speed.
[0060] FIG. 6 shows a relationship between the valve-forward
pressure and the flow rate of exhaust gas. As shown in FIG. 6, the
valve-forward pressure varies depending upon the flow rate of
exhaust gas. Further, as shown in FIG. 6, as the engine speed
becomes higher, the flow rate of exhaust gas is increased in the
order of the idling region, the low engine speed region and the
high engine speed region.
[0061] On the basis of the relationships as explained above, the
construction of the exhaust sound controlling apparatus of the
present invention is appropriately designed. For instance, the
spring constant (the biasing force) of torsion spring 5 can be set
such that valve 2 is rotationally moveable from position A to the
position immediately before position B against the valve-forward
pressure in the engine starting region, valve 2 is rotationally
moveable from position B to position C against the valve-forward
pressure in the idling region and the low engine speed region, and
valve 2 is rotationally moveable beyond and away from position C in
the high engine speed region, as shown in FIG. 3.
[0062] Owing to suitably setting the spring constant of torsion
spring 5 as described above, the rotational movement of valve 2
from position B and position C can be ensured even when the flow of
exhaust gas pulses in the idling region and the low engine speed
region and the rotational movement of valve 2 pulses along with the
pulse of the flow of exhaust gas. Valve 2, therefore, can be
prevented from coming into contact with baffle plate 1, 21. As a
result, when the engine is operated in the idling region and the
low engine speed region, it is possible to suppress occurrence of
striking noise which would be caused due to the contact of valve 2
with baffle plate 1, 21, and maintain a silence within the interior
of the vehicle.
[0063] The exhaust sound controlling apparatus of the embodiment
can perform the following function and effect. In the engine
starting region, valve 2 is placed in the first open state in which
exhaust gas emitted from the engine is permitted to pass through
the communication passage in the second route B and thereby flow in
the exhaust path via both the first route A and the second route B
as shown in FIG. 4. As a result, powerful exhaust sound can be
created. In the idling region and the low engine speed region,
valve 2 is placed in the closing state in which the flow of exhaust
gas is prevented from passing through the communication passage in
the second route B and thereby allowed to flow in the exhaust path
substantially only via the first route A. As a result, a silence
within the interior of the vehicle can be ensured. In the high
engine speed region, valve 2 is placed in the second open state in
which the flow of exhaust gas is permitted to pass through the
communication passage in the second route B and thereby flow in the
exhaust path via both the first route A and the second route B, and
the opening of valve 2 is increased as the engine speed becomes
higher. Therefore, in the high engine speed region, even when an
amount of the flow of exhaust gas is increased, increase in
pressure loss can be suppressed.
[0064] Further, with the provision of the simple valve structure as
described above, the exhaust sound control can be suitably
performed depending on the engine speed as explained above.
Further, the exhaust sound can be controlled by setting the spring
constant (the biasing force) of torsion spring 5 as explained
above.
[0065] Furthermore, curved end portion 2a of valve 2 serves as a
gas leakage inhibiting portion that prevents the exhaust gas and
the exhaust sound from leaking from curved end portion 2a toward
the downstream side of baffle plate 1 during the rotational
movement of valve 2. Valve 2 is supported at curved end portion 2a
relative to baffle plate 1, and the outer circumferential surface
of curved end portion 2a is substantially in contact (slide
contact) with baffle plate 1 during the rotational movement of
valve 2. Therefore, while valve 2 is rotationally moved, the
exhaust gas and the exhaust sound can be prevented from leaking
from curved end portion 2a toward the downstream side of baffle
plate 1.
[0066] Referring to FIG. 7 to FIG. 9, a modification of the valve
structure used in the exhaust sound controlling apparatus of the
embodiment is explained. Similar to the valve structure as
described above, the modified valve structure is constructed to
prevent the exhaust gas from leaking from the support portion of
valve 102 with respect to baffle plate 1. As shown in FIG. 7 and
FIG. 8, valve 102 is a generally rectangular-shaped plate member
and differs from valve 2 used in the embodiment in that a curved
end portion is not formed. Valve 102 includes planar valve body 2c
with one end portion 2e, and a pair of support portions 2b disposed
on opposite sides of one end portion 2e. Valve shaft 4 extends
through shaft insertion holes of support portions 2b and is
supported by support portions 2b. Each of support portions 2b has
an extension that extends around the shaft insertion hole, and is
connected at the extension with one end portion 2e.
[0067] Gas leakage inhibiting member 11 is disposed on the
downstream side surface of baffle plate 1 and located on a side of
one end portion 2e of valve body 2c. Gas leakage inhibiting member
11 extends parallel to valve shaft 4 or one end portion 2e of valve
body 2c, namely, an upper end periphery of valve 102 when viewed in
FIG. 7 and FIG. 8. Gas leakage inhibiting member 11 is a bar member
that has a generally L-shape in cross-section as shown in FIG. 8.
Gas leakage inhibiting member 11 has one strip portion 11a that is
mounted to baffle plate 1 and the other strip portion 11b that is
disposed uprightly with respect to baffle plate 1. Specifically,
the other strip portion 11b is inclined toward aperture 1a of
baffle plate 1.
[0068] As shown in FIG. 9, when valve 102 is rotationally moved
about valve shaft 4, a tip end of one end portion 2e of valve 102
is moved so as to draw a part of a circle that has a center on the
axis of valve shaft 4. At this time, the tip end of one end portion
2e is moved on an outer surface of the other strip portion 11b of
gas leakage inhibiting member 11 in contact with the outer surface
of the other strip portion 11b.
[0069] During the rotational movement of valve 102, the exhaust gas
and the exhaust sound can be prevented from leaking from one end
portion 2e of valve 102 at which valve 102 is supported relative to
baffle plate 1 through gas leakage inhibiting member 11, toward the
downstream side of baffle plate 1. In view of this effect of gas
leakage prevention, it is preferred that the other strip portion
11b of gas leakage inhibiting member 11 is curved in conformity
with a locus of the tip end of one end portion 2e of valve 102
which is drawn during the rotational movement of valve 102.
[0070] Valve 102 has the same operating positions and operating
states as those of valve 2 as shown in FIG. 3. That is, in the
engine starting region, valve 102 is moveable from position A to a
position immediately before position B as shown in FIG. 9. At this
time, valve 102 is in the first open state in which the fluid
communication between the upstream side expansion chamber on the
upstream side of baffle plate 1 and the downstream side expansion
chamber on the downstream side of baffle plate 1 through the
communication passage therebetween is established. In the idling
region and the low engine speed region, valve 102 is moved from
position B to position C as shown in FIG. 9. At this time, valve
102 is in the closing state in which the fluid communication
between the upstream side expansion chamber on the upstream side of
baffle plate 1 and the downstream side expansion chamber on the
downstream side of baffle plate 1 through the communication passage
therebetween is blocked. In the high engine speed region, valve 102
is moved away from position C in the opening direction. At this
time, valve 102 is in the second open state in which the fluid
communication between the upstream side expansion chamber on the
upstream side of baffle plate 1 and the downstream side expansion
chamber on the downstream side of baffle plate 1 through the
communication passage therebetween is re-established.
[0071] Referring to FIG. 10, a modification of muffler 20 shown in
FIG. 4 is explained. As shown in FIG. 10, modified muffler 40
includes first baffle plate 41 and second baffle plate 42 that
extend within muffler 40 in a cross-sectional direction of muffler
40, namely, in a direction perpendicular to the flow of exhaust gas
that passes through muffler 40. Baffle plates 41 and 42 are
disposed within muffler 40 so as to divide the interior of muffler
40 into three expansion chambers adjacent to each other, namely,
first expansion chamber 43, second expansion chamber 44 and third
expansion chamber 45, which are located from the left side to the
right side of muffler 40 in this order. First expansion chamber 43
and second expansion chamber 44 are separated from each other by
baffle plate 41. Second expansion chamber 44 and third expansion
chamber 45 are separated from each other by baffle plate 42. Second
expansion chamber 44 is disposed between first expansion chamber 43
and third expansion chamber 45.
[0072] Inlet tube 46 extends into second expansion chamber 44
through an upstream end wall of muffler 40, first expansion chamber
43 and first baffle plate 41. Inlet tube 46 has one end that
outwardly projects from the upstream end wall of muffler 40 and is
connected to the engine through an exhaust pipe, not shown. Inlet
tube 46 has the other end that is opened within second expansion
chamber 44. Inlet tube 46 introduces the exhaust gas from the
engine into second expansion chamber 44.
[0073] First pass-through tube 47 is disposed within muffler 40
coaxially with inlet tube 46. First pass-through tube 47 extends
from second expansion chamber 44 into third expansion chamber 45
through second baffle plate 42 and communicates second expansion
chamber 44 and third expansion chamber 45 with each other. First
pass-through tube 47 has one end that is opened within second
expansion chamber 44 and the other end that is opened within third
expansion chamber 45 with each other. Second pass-through tube 48
extends through second baffle plate 42 in parallel with first
pass-through tube 47. Second pass-through tube 48 has one end that
is opened within third expansion chamber 45 and the other end that
is connected with one side surface of first baffle plate 41 which
is exposed to second expansion chamber 44.
[0074] First baffle plate 41 has generally rectangular-shaped
aperture 41a. Second pass-through tube 48 is disposed coaxially
with aperture 41a so as to communicate third expansion chamber 45
with aperture 41a. Third expansion chamber 45 and first expansion
chamber 43 are communicated with each other through aperture 41a
and second pass-through tube 48. The valve structure shown in FIG.
1 to FIG. 3 or the modified valve structure shown in FIG. 7 to FIG.
9 is provided on an opposite side surface of first baffle plate 41
which is exposed to first expansion chamber 43. That is, valve 2 or
102 is arranged on the opposite side surface of first baffle plate
41, namely, on a downstream side surface of first baffle plate 41
with respect to the flow of exhaust gas passing through second
pass-through tube 48, such that valve body 2c covers aperture 41a
except for opening 10. Valve 2 or 102, valve guides 6, 7 and 8 and
first baffle plate 41 cooperate with each other to define a
communication passage that allows fluid communication between first
expansion chamber 43 and third expansion chamber 45 through second
pass-through tube 48. The communication passage includes opening 10
that is disposed between end peripheral surface 2d of valve 2 or
102 and an aperture-forming rim of first baffle plate 41 which
defines the periphery of aperture 41a. The communication passage
further includes the clearance that is formed between valve 2 or
102 and valve guides 6, 7 and 8 upon rotation of valve 2 or 102
about valve shaft 4.
[0075] First tail tube 49 extends from first expansion chamber 43
to an outside of muffler 40 through first baffle plate 41, second
baffle plate 42, second expansion chamber 44, third expansion
chamber 45 and a downstream end wall of muffler 40. First tail tube
49 has one end that is opened within first expansion chamber 43 and
the other end that outwardly projects from the downstream end wall
of muffler 40 and is exposed to atmospheric air. Second tail tube
50 extends from second expansion chamber 44 to the outside of
muffler 40 through second baffle plate 42, third expansion chamber
45 and the downstream end wall of muffler 40. Second tail tube 50
has one end that is opened within second expansion chamber 44 and
the other end that outwardly projects from the downstream end wall
of muffler 40 and is exposed to atmospheric air. Each of expansion
chambers 43, 44, 45 is larger in cross-sectional area than inlet
tube 46, pass-through tubes 47, 48 and tail tubes 49, 50. In the
construction of muffler 40, the exhaust path extends through first
inlet tube 46, second expansion chamber 44, second tail tube 50,
first pass-through tube 47, third expansion chamber 45, second
pass-through tube 48, first expansion chamber 43, first tail tube
49 and the communication passage between first expansion chamber 43
and third expansion chamber 45.
[0076] In thus constructed muffler 40, exhaust sound generated from
the engine is controlled depending on an operating condition of the
engine. The exhaust sound is emitted to atmospheric air via a first
route indicated by arrow A in FIG. 10, a second route indicated by
arrow B in FIG. 10 or both the first route and the second route in
accordance with the engine operating condition. The first route
extends sequentially through inlet tube 46, second expansion
chamber 44 and second tail tube 50. The second route extends
sequentially through inlet tube 46, second expansion chamber 44,
first pass-through tube 47, third expansion chamber 45, second
pass-through tube 48, the communication passage between valve 2 or
102 and valve guides 6, 7 and 8, first expansion chamber 43 and
first tail tube 49. The second route bypasses second tail tube
50.
[0077] Specifically, in the engine starting region, the exhaust
sound from the engine is emitted from second tail tube 50 to
atmospheric air via the first route indicated by arrow A in FIG.
10. Further, in the engine starting region, valve 2 or 102 is
moveable from position A to a position immediately before position
B as shown in FIG. 9. At this time, valve 2 or 102 is placed in the
first open state in which the communication passage including
opening 10 and the clearance between end peripheral surface 2d of
valve 2 or 102 and clearance forming surface 8a of end valve guide
8 is opened so that the second route indicated by arrow B in FIG.
10 is permitted. Therefore, exhaust sound from the engine is also
emitted from first tail tube 49 to atmospheric air via the second
route. Since the emission of the exhaust sound is thus performed
via both the first route and the second route, the exhaust sound in
the engine starting region can be enhanced as compared to the
conventional exhaust sound controlling apparatus.
[0078] Further, when the engine speed is raised up to the idling
region, valve 2 or 102 is rotationally moved to position B shown in
FIG. 9 due to an increase in the valve-forward pressure. Valve 2 or
102 is placed in the closing state in which end peripheral surface
2d is substantially contacted with contact surface 8b of end valve
guide 8. Therefore, the exhaust sound from the engine is prevented
from being emitted from tail tube 49 to atmospheric air via the
second route indicated by arrow B in FIG. 10 and can be emitted
from tail tube 50 to atmospheric air substantially only via the
first route indicated by arrow A in FIG. 10. As a result, the
exhaust sound that is emitted from muffler 40 to atmospheric air
can be reduced.
[0079] When the engine speed is further raised up to the low engine
speed region and maintained in the low engine speed region, the
valve-forward pressure is further increased with raising of the
engine speed. Due to the increase in the valve-forward pressure,
valve 2 or 102 is rotationally moved from position B to position C
shown in FIG. 9. During the rotational movement from position B to
position C, valve 2 or 102 is kept in the closing state. Therefore,
the emission of the exhaust sound substantially only via the first
route indicated by arrow A in FIG. 10 is maintained so that the
exhaust sound from the engine can be kept reduced.
[0080] Further, when the engine speed is raised up to the high
engine speed region, the valve-forward pressure is further
increased due to an increase in the flow of exhaust gas from the
engine. Valve 2 or 102 is further rotationally moved away from
position C shown in FIG. 9 and placed in the second open state. In
the second open state, end peripheral surface 2d of valve 2 or 102
becomes out of contact with contact surface 8b of end valve guide 8
and there is generated a clearance therebetween. Therefore, the
exhaust sound from the engine is emitted from both tail tubes 49
and 50 to atmospheric air via both the first route indicated by
arrow A in FIG. 10 and the second route indicated by arrow B in
FIG. 10. Thus, in the high engine speed region, even when the flow
of exhaust gas is increased, increase in pressure loss can be
suppressed to thereby enhance the engine output.
[0081] Next, a method for controlling exhaust sound from the engine
which is emitted through the exhaust path, of the embodiment is
explained. The method includes a first control step of reducing a
flow rate of exhaust gas that passes through the exhaust path, to a
first flow rate in accordance with increase in engine speed in a
first engine speed region, and a second control step of increasing
the flow rate of exhaust gas to a second flow rate in accordance
with increase in engine speed in a second engine speed region in
which the engine speed is higher than the engine speed in the first
engine speed region. The method further includes a third control
step of reducing the flow rate of exhaust gas to a third flow rate
that is lower than the first flow rate and the second flow rate in
a third engine speed region between the first engine speed region
and the second engine speed region. The engine speed in the first
engine speed region includes an engine speed in an engine starting
region. The engine speed in the second engine speed region includes
an engine speed in a high engine speed region. The engine speed in
the third engine speed region includes an engine speed in an idling
region and an engine speed in a low engine speed region.
[0082] The method for controlling exhaust sound can perform the
following effects. In the engine starting region, exhaust gas
emitted from the engine is permitted to pass through the exhaust
path so that powerful exhaust sound can be created. In the idling
region and the low engine speed region, the flow of exhaust gas is
reduced so that a silence within the interior of the vehicle can be
ensured. In the high engine speed region, the flow of exhaust gas
is permitted to pass through the exhaust path and the flow rate of
exhaust gas is increased as the engine speed becomes higher. As a
result, increase in pressure loss can be suppressed.
[0083] This application is based on prior Japanese Patent
Application No. 2007-098526 filed on Apr. 4, 2007. The entire
contents of the Japanese Patent Application No. 2007-098526 are
hereby incorporated by reference.
[0084] Although the invention has been described above by reference
to a certain embodiment of the invention and modifications of the
embodiment, the invention is not limited to the embodiment and the
modifications described above. Variations of the embodiment and the
modifications described above will occur to those skilled in the
art in light of the above teachings. The scope of the invention is
defined with reference to the following claims.
* * * * *