Method for controlling exhaust system of vehicle

There is provided a method for controlling an exhaust system of a vehicle including a controller for controlling an open-close operation of an on-off valve which is provided at an intermediate portion of one of a pair of exhaust pipes arranged in parallel and communicating with an exhaust port of an engine depending upon running condition of the vehicle. The control method includes three control patterns different from each other, i.e., a first control pattern during an accelerated running condition of the vehicle, a second control pattern during a constant-speed running of the vehicle, and a third control pattern during a decelerated running condition of the vehicle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for controlling an exhaust system 
of a vehicle by regulating area of a flow passage in an exhaust pipe 
depending upon operational condition of the vehicle. More particularly, 
the present invention relates to a method for assigning an optimum control 
pattern to an on-off valve disposed in an exhaust system for discharging 
exhaust gas from a driving engine of a vehicle depending upon running 
condition of the vehicle, thus increasing the engine output and/or 
reducing a noisy sound from the engine to a desired degree. 
2. Description of Related Art 
The volume of exhaust gas discharged from a driving engine of a vehicle 
will constantly vary depending upon an engine speed and/or running 
condition of the vehicle. If an engine is provided with an exhaust system 
the construction of which remains unchanged regardless of varying running 
condition of the vehicle, the engine would represent insufficient 
efficiency and/or a noisy sound resulting from exhaust gas from the engine 
would become louder. 
That is, if the engine is provided with an exhaust system which is 
effective enough to damp noisy sound from the engine during a relatively 
small quantity of exhaust gas is discharged from the engine, such exhaust 
system may cause a large resistance to the exhaust gas when the quantity 
of exhaust gas becomes greater, thus restricting the engine from producing 
higher output. On the contrary, and if the engine is provided with an 
exhaust system which does not cause a very high resistance to a flow of 
exhaust gas during a large quantity of exhaust gas is discharged from the 
engine, such an exhaust system would be incapable of reducing or damping a 
noisy sound to a desired level. 
Under the circumstances, an exhaust system of a variable construction which 
is designed to vary the area of an exhaust gas flow passage depending upon 
running condition of a vehicle, such as shown in Japanese Utility Model 
Public Disclosure No. 62-54210, has been proposed and is employed in some 
vehicle engines. 
Such an exhaust system of variable construction includes, as shown in FIG. 
7, a pair of exhaust pipes 1 and 2 each communicating with an exhaust port 
of an engine and arranged in parallel with each other, an on-off valve 3 
disposed at an intermediate portion of one exhaust pipe 1, and a 
controller 4 for controlling the on-off valve 3 depending running 
condition of a vehicle. 
In FIG. 7, reference numeral 5 designates an actuator which actuates to 
open or close the on-off valve 3 in accordance with a signal from the 
controller 4 and numeral 6 a silencer which receives flow of exhaust gas 
from the engine for reducingly damping components of a noisy sound 
accompanying the exhaust gas. The pair of exhaust pipes 1 and 2 are 
incorporated in the silencer 6 so as to constitute outlet conduits 
thereof. 
A signal indicative of an accelerator opening and a signal indicative of an 
engine speed are input to the controller 4. The controller 4 controls an 
open-close operation of the on-off valve 3 in accordance with the above 
two signals, as shown in FIG. 8. 
Specifically, the on-off valve 3 is opened when the engine speed is very 
high (for example, no less than 4,600 r.p.m), or when the engine speed is 
relatively high (for example no less than 2,500 r.p.m.) and at the same 
time the accelerator opening is relatively large (for example, no less 
than 40%), whereas the on-off valve 3 is closed in any other cases. 
As a result, when a large quantity of exhaust gas is discharged from the 
engine, the area of a flow passage of exhaust gas becomes greater so as to 
prevent occurrence of a large amount of resistance against the exhaust gas 
flow, whereby maintaining sufficient amount of engine output. On the 
contrary, and when a relatively small quantity of exhaust gas is 
discharged from the engine, the area of the flow passage of exhaust gas is 
restricted so as to reducingly damp noisy sound to a desired degree. 
It has been found, however, that the prior art exhaust system of variable 
construction for a vehicle having the construction and function as shown 
above is incapable of satisfactorily functioning when the engine is 
rapidly accelerated. 
That is to say, the controller 4 is designed to detect the engine speed and 
the accelerator opening so as to open the on-off valve 3 when the engine 
speed is instantaneously increased in response to a rapid acceleration 
motion. The on-off valve 3, however, will not be opened until after the 
engine speed has reached 2,500 r.p.m. even if the accelerator is fully 
opened. Thus, it is unavoidable for such a prior art exhaust system to 
represent a slight time-lag until the on-off valve 3 actually opens. 
During such a time-lag, the volume of exhaust gas discharged from the 
engine continuingly increases. The area of the flow passage of exhaust gas 
however remains narrow, thus forming a considerable amount of resistance 
to the exhaust gas flow. Accordingly, the amount of back pressure within 
the engine increases, thereby restricting the engine from producing higher 
output. 
If, on the other hand, it is intended to minimize the above time lag by 
setting a predetermined level of the engine speed to commence the opening 
operation of the on-off valve 3 at a lower point, it would be possible to 
obtain an increased output of the engine upon rapid acceleration 
operation. This may cause, however, a change in the damping 
characteristics of the silencer when the engine operates at a lower speed 
slightly higher than such a predetermined level, thus resulting in 
resonance noise due to occurrence of resonant vibration of the vehicle 
chamber by means of discharge sound and vibration of the exhaust system, 
whereby causing insufficient silencer effect at a lower engine speed. 
SUMMARY OF THE INVENTION 
The present invention is aimed at solving the above inconveniences 
experienced in prior art. 
It is therefore one object of the invention to provide a method for 
controlling an exhaust system of a vehicle which permits high engine 
output when the vehicle is rapidly accelerated. 
Another object of the invention is to provide a method for controlling an 
exhaust system of a vehicle which permits high engine output when the 
vehicle is rapidly accelerated, without specifically shortening a 
change-over time for an on-off valve. 
A still further object of the invention is to provide a method for 
controlling an exhaust system of a vehicle which permits the exhaust 
system to exert satisfactory silencing effect upon engine running at lower 
speeds. 
In order to achieve the above object, the method for controlling an exhaust 
system of a vehicle according to the present invention includes a first 
control pattern upon an accelerated running condition of the vehicle, a 
second control pattern during a constant-speed running condition of the 
vehicle, and a third control pattern upon a decelerated running condition 
of the vehicle, the first, second and third control patterns being 
different from each other. 
The change-over action between the control patterns is carried out 
instantaneously by means of a vehicle speed signal, for example. For 
example, and when the vehicle is rapidly accelerated, a control pattern 
appropriate to such a rapid acceleration mode, i.e., a control pattern 
which enlarges the area of an exhaust gas passage, will be conducted from 
the beginning before the engine attains a predetermined speed, thus 
causing the engine to produce satisfactory output. On the other hand, and 
when the vehicle is decelerated, a control pattern appropriate to such a 
deceleration mode, i.e., a control pattern which reduces the area of the 
exhaust gas passage, will be conducted from the beginning of the 
deceleration mode before the engine speed decreases to a predetermined 
level, thus facilitating satisfactory silencing effect. 
In order to achieve the above object, another method for controlling an 
exhaust system of a vehicle in accordance with the invention includes a 
fourth control pattern when the vehicle speed is no less than a 
predetermined level and no kick-down motion of an accelerator has been 
made, a fifth control pattern when the kick-down motion of the accelerator 
has been made, and a sixth control pattern when the vehicle speed is less 
than the predetermined level and no kick-down motion of the accelerator 
has been made, the fourth, fifth and sixth control patterns being 
different from each other. 
The change-over action between the control patterns is carried out 
instantaneously by means of a vehicle speed signal and a kick-down signal, 
for example. For example, and when a kick-down motion of the accelerator 
has been made so as to obtain rapid acceleration of the vehicle, a control 
pattern appropriate to such a rapid acceleration mode, i.e., a control 
pattern which enlarges the area of an exhaust gas passage, will be 
conducted from the beginning of the rapid acceleration before the engine 
attains a predetermined speed, thus causing the engine to produce 
satisfactory output. On the other hand, and when no kick-down motion has 
been made, change-over action between the control patterns is carried out 
on the basis of a predetermined level of the engine speed and a 
predetermined value of the accelerator opening which correspondingly 
define an area effective to cause engine braking at different vehicle 
speeds. Thus, the area of exhaust gas flow passage will be reduced when 
the engine speed and the accelerator opening are less than a predetermined 
value at a given vehicle speed whereby satisfactory silencing effect for 
exhaust noise can be obtained in all area in which engine braking is 
effective.

DETAILED DESCRIPTION 
Several embodiments of a control method for an exhaust system of a vehicle 
in accordance with the present invention will be explained in detail 
hereinbelow with reference to the attached drawings. 
FIG. 1 is a flow chart illustrating the first control method of the 
invention as described in claim 1. FIGS. 2 (A), (B) and (C) illustrate 
several patterns in accordance with the first control method of the 
invention, while FIG. 3 is a block diagram of a control unit for 
conducting the first control method of the invention. 
An exhaust system intended to be controlled in accordance with a control 
method of the invention includes, as shown in FIG. 7 for example, a pair 
of exhaust pipes 1 and 2 arranged in parallel with each other and each 
being adapted for communication with an exhaust port of an engine, an 
on-off valve 3 disposed at the intermediate portion of the exhaust pipe 1, 
an actuator 5 for controlling on-off operation of the on-off valve 3, and 
a controller 4 for transmitting a driving signal to the actuator 5 so as 
to open or close the on-off valve 3. 
For the purpose of conducting the control method of the invention and as 
shown in FIG. 3, the controller 4 is input by a speed signal indicative of 
a vehicle speed, a rotation signal indicative of rotation numbers of the 
engine, a first opening signal indicating the fact that the opening of an 
accelerator exceeds 50%, and a second opening signal indicating the fact 
that the opening of the accelerator exceeds 75%. The controller 4 is 
designed so as to generate a control signal based on these input signals 
for transmitting the same to the actuator 5 for driving the on-off valve 
3. 
That is to say, the controller 4 controls to vary the operational condition 
of the on-off valve 3 in three different control patterns shown in FIGS. 
(A), (B) and (C) in accordance with the above several signals. 
First, and when it is determined that the vehicle is in an accelerated 
condition based on the above signals, the controller assigns the first 
control pattern of FIG. 2 (A) to the on-off valve 3. 
Accordingly, and during an accelerated condition of the vehicle, the on-off 
valve 3 will be opened when the engine speed is equal to or above a 
predetermined value, fo in FIG. 2 (A), or when the engine speed is less 
than the predetermined value but the opening of the accelerator is 
relatively high, for example 67.5% or above. 
As a result, the on-off valve 3 always remains open to restrict built-up of 
an increased back pressure within the engine so as to maintain a desired 
engine output upon acceleration, except when the engine speed is 
relatively low and the opening of the accelerator is also relatively low. 
When the engine speed is relatively low and the opening of the accelerator 
is also relatively low, the on-off valve 3 will closed, since, in such a 
case, discharge volume of the exhaust gas is small and hence, even with a 
relatively narrow exhaust passage, build-up of a high back pressure within 
the engine is not expected. Thus, it is able to prevent occurrence of a 
noisy sound which might occur when the on-off valve 3 is opened in spite 
of a relatively small exhaust gas volume. 
When the vehicle is in a constant-speed running condition, the controller 4 
assigns the second control pattern of FIG. 2 (B) to the on-off valve 3, 
whereby the on-off valve 3 in the exhaust pipe 1 is kept closed, 
regardless of the engine speed or the accelerator opening. 
Since a very high engine output is not required during a constant-speed 
running of the vehicle, shortage of the engine output would not occur even 
if the on-off valve 3 is closed, thus achieving satisfactory silencing 
effects. 
When the vehicle is in a decelerated condition, the controller 4 assigns a 
third control pattern of FIG. 2 (C) to the on-off valve 3, whereby the 
on-off valve 3 will be opened only when the opening of the accelerator 
reaches or exceeds a predetermined value, for example 40% or more, and 
regardless of the engine speeds. 
A situation in which the opening of the accelerator is maintained at a 
relatively high degree even though the vehicle is in a decelerated 
condition might occur when a driver of the vehicle slightly releases an 
accelerator pedal during the running of the vehicle at a relatively low 
gear ratio so as to cause relatively weak engine braking force. In such a 
case, the on-off valve 3 will be opened, whereby a stream of exhaust gas 
of a relatively large quantity is distributed into the pair of the exhaust 
pipes 1 and 2 so as to reduce flow rate of the exhaust gas, thus 
maintaining desired engine output, simultaneously preventing the exhaust 
gas from causing noisy sound. 
When the vehicle is in an decelerated condition and the opening of the 
accelerator is relatively low, such as a case when it is intended to 
obtain a relatively large engine braking force, the on-off valve 3 will be 
closed so as to vary the damping characteristic, thus preventing 
occurrence of noisy sound due to the exhaust gas volume and vibration. 
FIG. 4 illustrates a flow chart of a second control method described in 
claim 2. FIGS. 5 (A), (B) and (C) show control patterns conducted in 
accordance with the second control method of the invention. FIG. 6 is a 
block diagram of a control unit for conducting the second control method 
of the invention. 
For conducting the control method of the invention, and as shown in FIG. 6 
the controller 4 is input by a speed signal indicative of a running speed 
of the vehicle, a rotational signal indicative of an engine speed, an 
opening signal indicating that the opening of the accelerator is equal to 
or above 50%, and a kick-down signal indicating that an automatic 
transmission has been changed to a lower gear ratio. The controller 4 is 
designed so as to transmit a drive signal to the actuator 5 for actuating 
the on-off valve in accordance with the above signals. 
Based on the above signals, the controller 4 actuates the on-off valve 3 in 
one of the three control patterns shown in FIGS. 5 (A), (B) and (C). 
First, and when it is determined from the above signals that the vehicle 
speed is equal to or above a predetermined value (So) and that kick-down 
of the automatic transmission has not been effected, the controller 4 
issues a fourth control pattern shown in FIG. 5 (A). 
That is to say when the vehicle speed is no less than the predetermined 
value (So) and no kick-down of the automatic transmission has been carried 
out, the on-off valve 3 will be opened if the engine speed is equal to or 
above a first threshold (Tx1) of a relatively high value, or if the engine 
speed is no more than the above first threshold but the opening of the 
accelerator is relatively high, for example no less than 50%. 
As a result, except when the engine speed is low and the opening of the 
accelerator is also relatively low, the on-off valve 3 will be opened so 
as to restrict increase of back pressure within the engine, thus 
maintaining the engine output at a sufficient value. 
When the engine speed is low and the opening of the accelerator is also 
relatively low, the on-off valve 3 will be closed, since, in such a case, 
a loud echo-sound would be generated due to the actuation of an engine 
braking. In this case, build-up of a high back pressure within the engine 
would not occur even though the exhaust gas flow passage is narrow, since 
exhaust gas volume is small. 
When it is determined that a kick-down motion has been made to the 
automatic transmission at any vehicle speeds, the controller 4 assigns a 
fifth control pattern of FIG. 5 (B) to the on-off valve 3 in the exhaust 
pipe 1, regardless of the engine speed or the opening of the accelerator, 
whereby the on-off valve 3 is kept open. 
Once a kick-down motion is made to the automatic transmission, the vehicle 
is then brought into an accelerated condition. In such a case, the exhaust 
gas passage is provided with a sufficient flow area since the on-off valve 
3 is opened, whereby satisfactory engine output can be obtained. 
When the vehicle speed is less than the predetermined value (So) and no 
kick-down motion has been made to the automatic transmission, the 
controller 4 assigns a sixth control pattern of FIG. 5 (C) to the on-off 
valve 3. Thus, the on-off valve 3 will be opened when the engine speed is 
equal to or above a second threshold (Tx2) of a relatively low value, or 
when the engine speed is less than the second threshold but the opening of 
the accelerator is relatively high, for example no less than 50%. 
As a result, the on-off valve 3 remains open except when the engine speed 
is low and the opening of the accelerator is also relatively low, thus 
restricting increase of a back pressure within the engine, whereby 
satisfactory engine output can be maintained. 
When the engine speed is low and the opening of the accelerator is also 
relatively low, the on-off valve 3 will be closed so as to prevent 
occurrence of an echo-sound resulting from the actuation of an engine 
braking. It should be noted that, in such a case, discharge volume of the 
exhaust gas will be small and hence no build-up of a high back-pressure in 
the engine might occur even if the area of flow passage of the exhaust gas 
is small. 
With the above construction of the method for controlling the exhaust 
system of a vehicle in accordance with the present invention, different 
control patterns are separately assigned to the on-off valve depending 
upon a running condition of the vehicle. It is therefore possible to 
obtain an increased output of the engine when the engine speed is very 
high and hence a large quantity of exhaust gas is discharged, while at the 
same time preventing occurrence of noisy sounds when a small quantity of 
exhaust gas is discharged.