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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to air supply control systems for
internal combustion engines, and more particularly to a system for
controlling air supply effected to an internal combustion engine by a
plurality of turbosuperchargers accompanying with the internal combustion
engine.
2. Description of the Prior Art
In the field of internal combustion engines employed in vehicles, there has
been proposed a so-called sequentially controlled supercharging system in
which a couple of turbosuperchargers of primary and secondary are provided
for an internal combustion engine and so controlled that only the primary
turbosupercharger works for supercharging the engine when intake air mass
flow in an intake passage of the engine is relatively small and both the
primary and the secondary turbosuperchargers work simultaneously for
supercharging the engine when the intake air mass flow is relatively
large, as disclosed in, for example, the Japanese patent applications
published before examination under publication numbers 56-41417 and
59-160022. In such a system, an exhaust cutoff valve is disposed in a
portion of an exhaust passage of the engine through which exhaust gas is
applied to a turbine of the secondary turbosupercharger and an intake air
cutoff valve is also disposed in a portion of the intake passage of the
engine through which air compressed by a compressor of the secondary
turbosupercharger is supplied to a combustion chamber of the engine, and
each of the exhaust cutoff valve and the intake cutoff valve is controlled
to be closed and open so as to cause the primary and secondary
turbosuperchargers to work in the aforementioned manner.
In connection with the control in operation of the primary and secondary
turbosuperchargers, it has been proposed to put the secondary
turbosupercharger in a condition of preliminary rotation before the
secondary turbosupercharger commences to work for supercharging the engine
for the purpose of suppressing torque shock arising on the engine due to
time lag in the starting characteristic of the secondary
turbosupercharger. In such a case, it has been usual that the preliminary
rotation of the secondary turbosupercharger is caused by such a control as
to open the exhaust cutoff valve for supplying the turbine of the
secondary turbosupercharger with the exhaust gas under a condition in
which an intake air relief valve which is provided in a bypass provided to
the intake passage for detouring the secondary turbosupercharger is
opened.
However, the preliminary rotation of the secondary turbosupercharger thus
caused in the manner proposed previously brings about a disadvantage that
the primary turbosupercharger is undesirably reduced in its speed of
rotation because the exhaust gas branches through the exhaust cutoff valve
which is opened under the condition in which the intake air relief valve
is opened and thereby the exhaust gas supplied to a turbine of the primary
turbosupercharger is reduced and this compels the preliminary rotation of
the secondary turbosupercharger to be conducted insufficiently for a
relatively short period of time just before the secondary
turbosupercharger commences to work for supercharging the engine.
Accordingly, in the case where the preliminary rotation of the secondary
turbosupercharger is conducted in the manner proposed previously, it is
difficult to put the secondary turbosupercharger in a condition of
sufficiently high preliminary rotation before the secondary
turbosupercharger commences to work for supercharging the engine, and
therefore the torque shock arising on the engine is not sufficiently
reduced when the secondary turbosupercharger commences to work for
supercharging the engine.
In view of the above, it has been also proposed to provide an exhaust
bypass valve disposed at a portion of the exhaust passage of the engine
for introducing therethrough a relatively small quantity of exhaust gas to
a portion of the exhaust passage downstream to the exhaust cutoff valve
from a portion of the exhaust passage upstream to the exhaust cutoff
valve, so that the turbine of the secondary turbosupercharger is driven to
rotate by the exhaust gas passing through the exhaust bypass valve and
thereby the secondary turbosupercharger is subjected to its preliminary
rotation under a condition in which the exhaust cutoff valve is in its
closed state. In the case where such an exhaust bypass valve as mentioned
above is used, the intake air relief valve is caused to close on or before
a time point at which the exhaust cutoff valve is opened and the
preliminary rotation of the secondary turbosupercharger continues until
the intake air relief valve is closed, and therefore the secondary
turbosupercharger is put in a condition of sufficiently high preliminary
rotation caused by the relatively small exhaust gas passing through the
exhaust bypass valve just before the exhaust cutoff valve is opened. When
the exhaust cutoff valve is opened, the intake air cutoff valve is also
opened and the secondary turbosupercharger under the sufficiently high
preliminary rotation commences to work for supercharging the engine under
a condition in which the intake air relief valve is closed. Consequently,
the torque shock arising on the engine is surely suppressed when the
second supercharger commences to work for supercharging the engine.
In the meantime, the internal combustion engine equipped with a
turbosupercharger is usually provided with a waste gate valve which is
operative to prevent compressed air pressure in an intake passage of the
engine from exceeding a predetermined value. The waste gate valve is
disposed in a bypass passage detouring a turbine of the turbosupercharger
and opened for reducing exhaust gas flowing through the turbine of the
turbosupercharger when the compressed air pressure in the intake passage
reaches the predetermined value.
In the case of an internal combustion engine to which the sequentially
controlled supercharging system wherein the primary and secondary
turbosuperchargers are provided as aforementioned and both the exhaust
bypass valve and waste gate valve are used for controlling exhaust gas
flow supplied to the primary and secondary turbosuperchargers is applied,
the exhaust gas flowing through the exhaust bypass valve dose not
contribute to increase in compressed air pressure in the intake passage
but causes the secondary turbosupercharger to be subjected to its
preliminary rotation prior to supercharging operation and therefore the
exhaust bypass valve functions substantially to limit the compressed air
pressure in the intake passage as well as the waste gate valve when only
the primary turbosupercharger works for supercharging the engine and, on
the other hand, the compressed air pressure in the intake passage is
limited by only the waste gate valve when both the primary and secondary
turbosuperchargers work simultaneously for supercharging the engine. This
results in a fear that the maximum value of the compressed air pressure in
the intake passage limited by the exhaust bypass valve is different from
the maximum value of the compressed air pressure in the intake passage
limited by the waste gate valve and therefore the compressed air pressure
in the intake passage has its maximum value which varies suddenly and
undesirably so as to hinder the engine from operating stably when the
secondary turbosupercharger commences to work for supercharging the engine
in addition to the primary turbosupercharger or the secondary
turbosupercharger ceases to work for supercharging the engine.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention is to provide an air
supply control system for an internal combustion engine, which includes a
first turbosupercharger, a second turbosupercharger operative to work in
addition to the first supercharger when intake air mass flow fed to the
engine is to be relatively large, an exhaust valve for controlling exhaust
gas flow supplied to the second turbosupercharger and a waste gate valve
for controlling exhaust gas flow supplied to both the first and second
turbosuperchargers, and avoids the foregoing disadvantages and problems
encountered with the prior art.
Another object of the present invention is to provide an air supply control
system for an internal combustion engine, which includes a first
turbosupercharger, a second turbosupercharger operative to work in
addition to the first supercharger when intake air mass flow fed to the
engine is to be relatively large, an exhaust bypass valve for controlling
exhaust gas flow supplied to the second turbosupercharger and a waste gate
valve for controlling exhaust gas flow supplied to both the first and
second turbosuperchargers, and by which intake air supplied to the engine
is compressed to have its maximum pressure which is prevented from varying
suddenly when the second turbosupercharger commences to work for
supercharging the engine in addition to the first turbosupercharger or the
second turbosupercharger ceases to work for supercharging the engine.
A further object of the present invention is to provide an air supply
control system for an internal combustion engine, which includes a first
turbosupercharger, a second turbosupercharger operative to work in
addition to the first supercharger when intake air mass flow fed to the
engine is to be relatively large, an exhaust bypass valve for controlling
exhaust gas flow supplied to the second turbosupercharger and a waste gate
valve for controlling exhaust gas flow supplied to both the first and
second turbosuperchargers, and in which each of the exhaust bypass valve
and waste gate valve operates to limit pressure of intake air applied to
the engine in such a manner that the intake air has its maximum pressure
which is prevented from varying suddenly when the second turbosupercharger
commences to work for supercharging the engine in addition to the first
turbosupercharger or the second turbosupercharger ceases to work for
supercharging the engine.
According to the present invention, there is provided an air supply control
system for an internal combustion engine comprising a first
turbosupercharger having a turbine disposed in a first separated exhaust
passage extending from the engine and a compressor disposed in a first
separated intake passage connected to the engine, a second
turbosupercharger having a turbine disposed in a second separated exhaust
passage extending from the engine and a compressor disposed in a second
separated intake passage connected to the engine, an exhaust cutoff valve
operative selectively to be open and closed respectively for opening and
closing the second separated exhaust passage in which the turbine of the
second turbosupercharger is disposed, a first valve driving device
operative to cause the exhaust cutoff valve to be closed so that the first
turbosupercharger works for supercharging the engine but the second
turbosupercharger is restrained from supercharging the engine when intake
air mass flow fed to the engine is to be relatively small and to cause the
exhaust cutoff valve to be open so that both of the first and second
turbosuperchargers work simultaneously for supercharging the engine when
the intake air mass flow fed to the engine is to be relatively large, an
exhaust bypass valve operative selectively to be open and closed
respectively for opening and closing an exhaust bypass passage provided to
the second separated exhaust passage for forming a first partial exhaust
passage detouring the exhaust cutoff valve, a second valve driving device
operative to cause the exhaust bypass valve to be open so that a
relatively small exhaust gas flow is supplied through the exhaust bypass
passage to the turbine of the second turbosupercharger when pressure of
intake air applied to the engine reaches a predetermined value under a
condition in which the intake air mass flow fed to the engine is to be
relatively small, a waste gate valve operative selectively to be open and
closed respectively for opening and closing a bypass passage provided in
common to the first and second separated exhaust passages for forming a
second partial exhaust passage detouring the turbines of the first and
second turbosuperchargers, and a third valve driving device operative to
cause the waste gate valve to be open so that a part of exhaust gas from
the engine flows through the bypass passage without passing through the
turbines of the first and second turbosuperchargers to prevent the
pressure of intake air applied to the engine from increasing when the
pressure of intake air applied to the engine reaches substantially the
predetermined value under a condition in which the intake air mass flow
fed to the engine is to be relatively large.
In the air supply control system thus constituted in accordance with the
present invention, when the intake air mass flow fed to the engine is to
be relatively small, the exhaust cutoff valve is kept closed by the first
valve driving device so that only the first turbosupercharger works for
supercharging the engine. In such a condition, when the pressure of intake
air applied to the engine reaches the predetermined value, the exhaust
bypass valve is opened by the second valve driving device and thereby the
relatively small exhaust gas flow is supplied through the exhaust bypass
passage to the turbine of the second supercharger, so that the second
turbosupercharger is subjected to its preliminary rotation before it
commences to work for supercharging the engine. During the preliminary
rotation of the second supercharger, the pressure of intake air applied to
the engine is not increased substantially. This means that the exhaust
bypass valve functions to limit the pressure of intake air applied to the
engine to the predetermined value when the intake air mass flow fed to the
engine is to be relatively small. After that, when the intake air mass
flow fed to the engine is to be relatively large, the exhaust cutoff valve
is opened by the first valve driving device so that the second
turbosupercharger, which has been put in a condition of sufficiently high
preliminary rotation, commences to work for supercharging the engine in
addition to the first turbosupercharger. Then, with the pressure of intake
air applied to the engine having substantially the predetermined value
under a condition in which the first and second turbosuperchargers work
simultaneously for supercharging the engine, the waste gate valve is
opened by the third valve driving device and thereby a part of exhaust gas
from the engine flows through the bypass passage without passing through
the turbines of the first and second turbosuperchargers to prevent the
pressure of intake air applied to the engine from increasing. That is, the
waste gate valve is operative to limit the pressure of intake air applied
to the engine to the predetermined value when the intake air mass flow fed
to the engine is to be relatively large.
In the operation described above, each of the exhaust bypass valve and
waste gate valve responds to the pressure of intake air applied to the
engine so as to limit the pressure of intake air applied to the engine to
substantially the same predetermined value and therefore the intake air
supplied to the engine is compressed to have its maximum pressure which is
prevented from varying suddenly when the second turbosupercharger
commences to work for supercharging the engine in addition to the first
turbosupercharger or the second turbosupercharger ceases to work for
supercharging the engine. Consequently, the engine is kept in its stable
operation regardless of commencement or termination of supercharging by
the second turbosupercharger.
The above, and other objects, features and advantages of the present
invention will become apparent from the following detailed description
which is to be read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the basic arrangement of an air
supply control system for an internal combustion engine according to the
present invention;
FIG. 2 is a schematic illustration showing an embodiment of air supply
control system for an internal combustion engine according to the present
invention, together with essential parts of an engine to which the
embodiment is applied;
FIG. 3 is a schematic illustration showing a pressure difference detecting
valve employed in the embodiment shown in FIG. 2;
FIGS. 4, 5 and 6 are characteristic charts used for explaining the
operation of various valves employed in the embodiment shown in FIG. 2;
FIG. 7 is a schematic illustration used for explaining in detail each of an
exhaust snifting valve and a waste gate valve employed in the embodiment
shown in FIG. 2; and
FIGS. 8-a, 8-b and 8-c show a flow chart used for explaining the operation
of the embodiment shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a functional block diagram of a system incorporating the
present invention. In the functional block diagram of FIG. 1, the system
comprises a first valve driving section B1, a second valve driving section
B2, a third valve driving section B3, an exhaust cutoff valve B4, an
exhaust bypass valve B5, a waste gate valve B6, a first turbosupercharger
B7 and a second turbosupercharger B8, and the first and second
superchargers B7 and B8 are connected with an engine B9 to which the
system is applied.
The first turbosupercharger B7 has a turbine disposed in a first separated
exhaust passage extending from the engine B9 and a compressor disposed in
a first separated intake passage connected to the engine B9 and the second
turbosupercharger B8 has a turbine disposed in a second separated exhaust
passage extending from the engine B9 and a compressor disposed in a second
separated intake passage connected to the engine B9. The exhaust cutoff
valve B4 is operative selectively to be open and closed respectively for
opening and closing the second separated exhaust passage in which the
turbine of the second turbosupercharger B8 is disposed. The exhaust bypass
valve B5 is operative selectively to be open and closed respectively for
opening and closing an exhaust bypass passage which is provided to the
second separated exhaust passage, in which the turbine of the second
turbosupercharger B8 is disposed, for forming a first partial exhaust
passage detouring the exhaust cutoff valve B4. The waste gate valve B6 is
operative selectively to be open and closed respectively for opening and
closing a second bypass passage provided in common to the first and second
separate exhaust passages, in which the turbines of the first and second
turbosuperchargers B7 and B8 are disposed respectively, for forming a
second partial exhaust passage detouring the turbines of the first and
second turbosuperchargers B7 and B8.
The first valve driving section B1 is operative to cause the exhaust cutoff
valve B4 to be closed so that the first turbosupercharger B7 works for
supercharging the engine B9 but the second turbosupercharger B8 is
restrained from supercharging the engine B9 when intake air mass flow fed
to the engine B9 is to be relatively small and to cause the exhaust cutoff
valve B4 to be open so that both of the first and second
turbosuperchargers B7 and B8 work simultaneously for supercharging the
engine B9 when the intake air mass flow fed to the engine B9 is to be
relatively large. The second valve driving section B2 is operative to
cause the exhaust bypass valve B5 to be open so that a relatively small
exhaust gas flow is supplied through the exhaust bypass passage to the
turbine of the second turbosupercharger B8 when pressure of intake air
applied to the engine B9 reaches a predetermined value under a condition
in which the intake air mass flow fed to the engine B9 is to be relatively
small. The third valve driving section B3 is operative to cause the waste
gate valve B6 to be open so that a part of exhaust gas from the engine B9
flows through the bypass passage without passing through the turbines of
the first and second turbosuperchargers B7 and B8 to prevent the pressure
of intake air applied to the engine B9 from increasing when the pressure
of intake air applied to the engine B9 reaches substantially the
predetermined value under a condition in which the intake air mass flow
fed to the engine B9 is to be relatively large.
FIG. 2 illustrates a first embodiment of air supply control system
according to the present invention, together with a part of an engine to
which the first embodiment is applied.
Referring to FIG. 2, an internal combustion engine 101, which is, for
example, a rotary engine having a couple of rotors each forming an
operating chamber having the capacity of, for example, 654 cubic
centimeters, is provided with an exhaust passage 102 for discharging
exhaust gas from the engine 101 and an intake passage 103 for supplying
the engine 101 with intake air. The exhaust passage 102 includes first and
second separated exhaust passages 102a and 102b, and the intake passage
103 includes first and second branched intake passages 103a and 103b which
are separated from each other at a location downstream to an air flow
sensor 104 provided for detecting intake air mass flow in the intake
passage 103 and merged into each other at a location upstream to an
intercooler 105 provided for cooling the intake air in the intake passage
103. A portion of the intake passage 103 downstream to the intercooler 105
is provided with a throttle valve 106, a surge chamber 107 and fuel
injectors 108.
A primary turbosupercharger 109 is provided with a turbine Tp disposed in
the first separated exhaust passage 102a to be driven to rotate by the
exhaust gas and a compressor Cp disposed in the first branched intake
passage 103a and coupled through a rotating shaft Lp with the turbine Tp.
A secondary turbosupercharger 110 is also provided with a turbine Ts
disposed in the second separated exhaust passage 102b to be driven to
rotate by the exhaust gas and a compressor Cs disposed in the second
branched intake passage 103b and coupled through a rotating shaft Ls with
the turbine Ts.
A portion of the first branched intake passage 103a upstream to the
compressor Cp and a portion of the second branched intake passage 103b
upstream to the compressor Cs are arranged in a line to form a branched
portion, so that pressure waves produced in one of the first and second
branched intake passages 103a and 103b propagates easily to the other of
the first and second branched intake passages 103a and 103b but hardly
toward the air flow sensor 104.
An exhaust cutoff valve 111 is disposed in a portion of the second
separated exhaust passage 102b upstream to the turbine Ts. This exhaust
cutoff valve 111 is operative to close the second separated exhaust
passage 102b in order to prevent the exhaust gas from being supplied to
the turbine Ts so that only the primary turbosupercharger 109 works in a
situation where intake air mass flow supplied to the engine 101 is to be
relatively small.
A portion of the second separated exhaust passage 102b upstream to the
exhaust cutoff valve 111 is connected through a connecting passage 112
with a portion of the first separated exhaust passage 102a upstream to the
turbine Tp. The connecting passage 112 is also connected with a portion of
the exhaust passage 102 downstream to the turbines Tp and Ts through a
bypass passage 118 in which a waste gate valve 117 is provided. The bypass
passage 118 forms, together with the connecting passage 112, a partial
exhaust passage detouring the turbines Tp and Ts of the primary and
secondary turbosuperchargers 109 and 110. A portion of the bypass passage
118 upstream to the waste gate valve 117 is connected with a portion of
the second separated exhaust passage 102b between the exhaust cutoff valve
111 and the turbine Ts through an exhaust bypass passage 114 in which an
exhaust bypass valve 113 is provided. The exhaust bypass passage 114
forms, together with portions of the connecting passage 112 and bypass
passage 118, a partial exhaust passage detouring the exhaust cutoff valve
111.
The waste gate valve 117 is driven by a diaphragm actuator 120 and a
pressure chamber of the diaphragm actuator 120, in which a spring for
biasing the waste gate valve 117 to be closed is contained, is coupled,
through a control pressure pipe 132, a three-way solenoid valve 133 having
its output port connected to the control pressure pipe 132 and a control
pressure pipe 115 to which one of input ports of the three-way solenoid
valve 133 is connected, with a portion of the first branched intake
passage 103a downstream to the compressor Cp. The exhaust bypass valve 113
is driven by a diaphragm actuator 116 and a pressure chamber of the
diaphragm actuator 116, in which a spring for biasing the exhaust bypass
valve 113 to be closed is contained, is coupled through the control
pressure pipe 115 with the portion of the first branched intake passage
103a downstream to the compressor Cp. The control pressure pipe 115 is
provided with an opening 145 which is controlled to be open and closed by
a solenoid valve 144.
An intake air cutoff valve 121 is disposed in a portion of the second
branched intake passage 103b downstream to the compressor Cs. The second
branched intake passage 103b is provided also with an intake air relief
passage 122 detouring the turbine Ts and having therein an intake air
relief valve 123. The intake air cutoff valve 121 is driven by a diaphragm
actuator 124, and the intake air relief valve 123 is driven by a diaphragm
actuator 125.
A control pressure pipe 126 extending from the diaphragm actuator 124 for
driving the intake air cutoff valve 121 is connected with an output port
of a three-way solenoid valve 127, and a control pressure pipe 128
extending from a diaphragm actuator 119 for driving the exhaust cutoff
valve 111 is connected with an output port of a three-way solenoid valve
129. Further, a control pressure pipe 130 extending from the diaphragm
actuator 125 for driving the intake air relief valve 123 is connected with
an output port of a three-way solenoid valve 131.
The above mentioned three-way solenoid valves 127, 129, 131 and 133 and the
solenoid valve 144 are controlled by a control unit 135 constituted by a
microcomputer.
The control unit 135 is provided with detection output signals Sa, Sn, St
and Sp1 obtained from the air flow sensor 104, an engine speed sensor 161
for detecting the engine speed, a throttle sensor 162 for detecting
opening degree of the throttle valve 106 (opening degree of throttle), and
an air pressure sensor 163 for detecting air pressure P1 at a position
downstream to the compressor Cp in the first branched intake passage 103a,
that is, compressed air pressure applied to the engine 101, respectively,
and operative to produce control signals E1 to E5 selectively based on the
detection output signals Sa, Sn, St and Sp1 and to supply the three-way
solenoid valve 127 with the control signal E1, the three-way solenoid
valve 131 with the control signal E2, the three-way solenoid valve 129
with the control signal E3, the three-way solenoid valve 133 with the
control signal E4, and the solenoid valve 144 with the control signal E5.
One of input ports of the three-way solenoid valve 129 is open to the
atmosphere and the other of the input ports is connected through a pipe
136 with a negative pressure tank 143 to which negative pressure Pn at a
portion downstream to the throttle valve 106 in the intake passage 103 is
supplied through a check valve 137. One of input ports of the three-way
solenoid valve 131 is open to the atmosphere and the other of the input
ports is connected with the negative pressure tank 143. Further, one of
input ports of the three-way solenoid valve 127 is connected through the
pipe 136 with the negative pressure tank 143 and the other of the input
ports is connected through a pipe 138 with a pressure difference detecting
valve 139.
As shown in FIG. 3, the pressure difference detecting valve 139 has a
housing 151 in which three chambers 154, 155 and 156 are formed with
diaphragms 152 and 153. The chambers 154 and 155 are provided with input
ports 154a and 155a, respectively, and the chamber 156 is provided with an
open port 158 and an output port 157 connected with the pipe 138. The
input port 154a is connected through a pipe 141 with the portion of the
first branched intake passage 103a downstream to the compressor Cp so as
to be supplied with the air pressure P1, and the input port 155a is
connected through a pipe 142 with a portion of the second branched intake
passage 103b upstream to the intake air cutoff valve 121 so as to be
supplied with air pressure ,P2 at a position upstream to the intake air
cutoff valve 121 in the second branched intake passage 103b.
The pressure difference detecting valve 139 is provided further with a
valve body 159 connected with the diaphragms 152 and 153 and biased by a
spring 159a disposed in the chamber 154. This valve body 159 is operative
to keep the output port 157 open so as to open the chamber 156 to the
atmosphere when a pressure difference between the air pressures P1 and P2
is relatively large and keep the output port 157 closed when the pressure
difference between the air pressures P1 and P2 is equal to or smaller than
a predetermined pressure value .DELTA.P. Accordingly, when the control
pressure pipe 126 is communicated with the pipe 138 through the three-way
solenoid valve 127 controlled by the control signal E1 and the pressure
difference between the air pressures P1 and P2 is larger than the
predetermined pressure value .DELTA.P, the diaphragm actuator 124 is
opened to the atmosphere and thereby the intake air cutoff valve 121 is
opened. On the other hand, when the control pressure pipe 126 is
communicated with the pipe 136 through the three-way solenoid valve 127
controlled by the control signal E1, the negative pressure is applied to
the diaphragm actuator 124 and thereby the intake air cutoff valve 121 is
closed.
When the control pressure pipe 128 is communicated with the pipe 136
through the three-way solenoid valve 129 controlled by the control signal
E3, the negative pressure is applied to the diaphragm actuator 119 and
thereby the exhaust cutoff valve 111 is closed, so that only the primary
turbosupercharger 109 is caused to work. On the other hand, when the
control pressure pipe 128 is opened to the atmosphere through the
three-way solenoid valve 129 controlled by the control signal E3, the
exhaust cutoff valve 111 is opened, so that the secondary
turbosupercharger 110 is caused to work in addition to the primary
turbosupercharger 109.
FIG. 4 is a characteristic chart showing the operating conditions of the
exhaust cutoff valve 111, exhaust bypass valve 113, waste gate valve 117,
intake air cutoff valve 121 and intake air relief valve 123. This
characteristic chart of FIG. 4 has an axis of abscissa representing engine
speed and an axis of ordinate representing engine load embodied by opening
degree of throttle, the maximum value of which is indicated by Dm, and is
stored in the form of data map in a memory contained in the control unit
135.
According to the characteristic chart of FIG. 4, the exhaust bypass valve
113 is changed to be open from closed and to be closed from open in
accordance with a line Le in common. On the other hand, the three-way
solenoid valve 131 is changed into the ON state from the OFF state for
causing the intake air relief valve 123 to be open from closed in
accordance with a line L1 which indicates the operating condition of
engine in which the engine 101 operates with intake air mass flow Q1 and
the operating condition of engine in which the engine 101 operates at
engine speed N1 and into the OFF state from the ON state for causing the
intake air relief valve 123 to be closed from open in accordance with a
line L2 which indicates the operating condition of engine in which the
engine 101 operates with intake air mass flow Q2 and the operating
condition of engine in which the engine 101 operates at engine speed N2,
the three-way solenoid valves 129 and 133 are changed into the OFF state
from the ON state for causing respectively the exhaust cutoff valve 111
and waste gate valve 117 to be closed from open in accordance with a line
L3 which indicates the operating condition of engine in which the engine
101 operates with intake air mass flow Q3 and the operating condition of
engine in which the engine 101 operates at engine speed N3 and into the ON
state from the OFF state for causing respectively the exhaust cutoff valve
111 and waste gate valve 117 to be open from closed in accordance with a
line L4 which indicates the operating condition of engine in which the
engine 101 operates with intake air mass flow Q4 and the operating
condition of engine in which the engine 101 operates at engine speed N4,
and the three-way solenoid valve 127 is changed into the OFF state from
the ON state for causing the intake air cutoff valve 121 to be closed from
open in accordance with a line L5 which indicates the operating condition
of engine in which the engine 101 operates with intake air mass flow Q5
and the operating condition of engine in which the engine 101 operates at
engine speed N5 and into the ON state from the OFF state for causing the
intake air cutoff valve 121 to be open from closed in accordance with a
line L6 which indicates the operating condition of engine in which the
engine 101 operates with intake air mass flow Q6 and the operating
condition of engine in which the engine 101 operates at engine speed N6.
On the characteristic chart of FIG. 4, an operating area having the line L4
as a lower boundary is set to correspond to the operating condition of the
engine 101 in which intake air mass flow fed to the combustion chambers
formed in the engine 101 is to be relatively large, and each of an
operating area between the lines L2 and L4, and operating area having the
line L2 as an upper boundary is set to correspond to the operating
condition of the engine 101 in which intake air mass flow fed to the
combustion chambers formed in the engine 101 is to be relatively small.
When the operating condition of the engine 101 resides in the operating
area having the line L2 as an upper boundary, the control unit 135 is
operative to keep each of the exhaust cutoff valves 111 and the intake air
cutoff valve 121 closed and, contrary, the intake air relief valve 123
open, so that only the primary turbosupercharger 109 is caused to work for
supercharging the engine 101. Then, when the intake air mass flow fed to
the engine 101 has increased to cross the line L2 and the operating
condition of the engine 101 has moved into the operating area between the
lines L2 and L4, the control unit 135 is operative to close the intake air
relief valve 123. In process of this, before the intake air relief valve
123 is closed, the exhaust bypass valve 113 is opened when the intake air
mass flow fed to the engine 101 has increased to cross the line Le and
thereby the exhaust gas is supplied slightly to the turbine Ts of the
secondary turbosupercharger 110 through the exhaust bypass passage 114
under a condition in which the intake air relief valve 123 is open. This
results in that the turbine Ts is driven to rotate by the exhaust gas
flowing through the exhaust bypass passage 114 so that the secondary
turbosupercharger 110 is subjected to its preliminary rotation before the
exhaust cutoff valve 111 is opened.
After that, when the intake air mass flow in the engine 101 has further
increased to cross the line L4 and the operating condition of the engine
101 has moved into the operating area between the lines L4 and L6, the
control unit 135 is operative to open the exhaust cutoff valve 111, and
then, when the intake air mass flow fed to the engine 101 has still
further increased to cross the line L6 and the operating condition of the
engine 101 has moved into the operating area having the line L6 as a lower
boundary, the control unit 135 is operative to open the intake air cutoff
valve 121, so that the turbine Tp of the primary turbosupercharger 109 and
the turbine Ts of the secondary turbosupercharger 110 are driven to rotate
by the exhaust gas passing through the first and second separated exhaust
passages 102a and 102b respectively and thereby both the primary and
secondary turbosuperchargers 109 and 110 are caused to work for
supercharging the engine 101.
As described above, since the secondary turbosupercharger 110 is rotated
preliminarily by the exhaust gas supplied thereto through the exhaust
bypass valve 113 under the condition in which the intake air relief valve
123 is open before it commences to work for supercharging the engine 101
and the intake air relief valve 123 is closed before the exhaust cutoff
valve 111 is opened, the secondary turbosupercharger 110 under the
sufficiently high preliminary rotation commences to work for supercharging
the engine 101, and consequently, the response in supercharging by the
secondary turbosupercharger 110 is improved and torque shock arising on
the engine 101 is surely suppressed when the secondary turbosupercharger
110 commences to work for supercharging the engine 101.
The control unit 135 is also operative to supply the three-way solenoid
valve 133 with the control signal E4 so as to cause the three-way solenoid
valve 133 to supply the diaphragm actuator 120 with the air pressure P1
obtained through the control pressure pipe 115 when the exhaust cutoff
valve 111 is opened. Therefore, under a condition in which the operating
condition of the engine 101 resides in the operating area having the line
L6 as the lower boundary and therefore both the primary and secondary
turbosuperchargers 109 and 110 work simultaneously for supercharging the
engine 101, when the air pressure P1, that is, the compressed air pressure
applied to the engine 101 reaches a predetermined value, the waste gate
valve 117 is opened by the diaphragm valve 120 to cause a part of exhaust
gas flowing through the first and second separated exhaust passages 102a
and 102b to pass through the bypass passage 118 without passing through
the turbines Tp and Ts of the primary and secondary turbosuperchargers 109
and 110 for preventing the compressed air pressure applied to the engine
101 from exceeding the predetermined value. That is, the waste gate valve
117 is operative to limit the compresses air pressure applied to the
engine 101 to the predetermined value when both the primary and secondary
turbosuperchargers 109 and 110 work for supercharging the engine 101.
On the other hand, under a condition in which only the primary
turbosupercharger 109 works for supercharging the engine 101 and therefore
the waste gate valve 117 is kept closed, when the intake air mass flow fed
to the engine 101 has increased to cross the line Le shown in FIG. 4 and
the air pressure P1 has reached the predetermined value, the exhaust
bypass valve 113 is opened to cause the secondary turbosupercharger 110 to
be subjected to its preliminary rotation. During the preliminary rotation
of the secondary turbosupercharger 110, the compressed air pressure
applied to the engine 101 is prevented from increasing substantially by
the intake air relief passage 122 and the intake air relief valve 123
operative to open and close the intake air relief passage 122. That is,
the intake air relief passage 122 and the intake air relief valve 123 work
for making supercharging by the secondary turbosupercharger 110
substantially ineffective during the preliminary rotation of the secondary
turbosupercharger 110. Accordingly, the exhaust bypass valve 113 functions
to limit the compressed air pressure applied to the engine 101 to the
predetermined value when only the primary turbosupercharger 109 works for
supercharging the engine 101.
FIG. 5 is a characteristic chart showing operations of the exhaust cutoff
valve 111, exhaust bypass valve 113 and waste gate valve 117 and
variations in exha | | |
