Supercharged internal combustion engine

A supercharged internal combustion engine is provided with a turbo supercharger mounted on an intake pipe and driven by engine exhaust gases to produce a pressurized intake air to be fed into the engine. A bypass intake pipe branches out of the intake pipe upstream of the supercharger and merges into the intake pipe at a point downstream of the supercharger. A first valve member is disposed in the intake pipe adjacent to the merging point to control the communication between the intake pipe and the bypass intake pipe and the communication between the upstream part of the intake pipe and the downstream part of the intake pipe. A first and second air release ports are formed in the intake pipe, one of which is disposed between the supercharger and the merging point and the other is disposed downstream of the merging point. Second and third valve members are provided to open and close the first and second air release ports, respectively. The first and second valve members are pneumatically actuated in accordance with the variation in the engine intake manifold pressure, whereas the third valve member is moved to its open position when the pressure in the intake pipe downstream of the merging point exceeds a predetermined level.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a supercharged internal combustion engine 
and, more particularly, to an internal combustion engine equipped with a 
super-charger which is controlled in accordance with the operating 
conditions of the engine. 
2. Description of the Prior Art 
Engine superchargers include those of a mechanically driven type and 
exhaust gas pressure type. A supercharger of the second type is so-called 
"turbo supercharger". The conventional supercharged internal combustion 
engine is so designed as to be supercharged over the entire operational 
range from throttle part-open to full-open engine operating conditions. 
The engine is provided with either a bypass exhaust passage or a bypass 
intake passage to avoid unduly high supercharging pressure so that an 
increased engine output is obtained in the throttle full-open engine 
operating condition only. 
Japanese Patent Laid-Open Publication No. 52-18517 laid-open on Feb. 12, 
1977 for public inspection discloses a supercharged internal combustion 
engine which is so designed as to be supercharged not in 
throttle-part-open engine operating condition but in throttle-full-open 
engine operating condition. In the throttle-part-open engine operating 
condition, an intake passage is closed by a control valve so that 
pressurized air from a supercharger is released into the atmosphere 
through a release valve, while the engine is charged with the atmospheric 
pressure through an atmospheric air passage. In the throttle-full-open 
engine operating condition, however, the control valve closes the 
atmospheric air passage and opens the intake passage so that the 
pressurized air produced by the supercharger is introduced into the 
engine. The release valve is closed at this time. The valves are 
controlled by signals representative of air pressure in the intake 
manifold of the engine. 
However, these conventional superchargers have various problems and 
shortcomings. 
More specifically, the first-mentioned way of supercharging, i.e. the 
supercharging over the entire range of engine operation, is not 
advantageous in that the intake air is restricted or throttled by the 
throttle valve during the throttle-part-open engine operation to render 
the supercharging itself meaningless. In addition, especially in the 
exhaust-pressure type supercharging in which the exhaust gas is made to 
pass through a turbine, the exhaust pressure is increased to lower the 
intake efficiency of the engine, resulting in a reduced engine output. 
Further, the supercharging over entire range of engine operation forces 
the supercharger, exhaust system and the intake system to work under a 
permanent additional load. This is quite inconvenient from the view point 
of durability of these systems and the supercharger. 
Turning now to the second-mentioned supercharging system as disclosed in 
the Japanese Patent Laid-open Publication No. 52-18517, the following 
disadvantage is pointed out. As stated before, the relief valve for 
allowing the compressed air to be released into the atmosphere is 
controlled to open and close solely dependent on the intake pressure, i.e. 
the discharge pressure of the blower of the supercharger. In other words, 
the relief valve is made to open at the same intake pressure irrespective 
of the operating condition of the engine. To explain in more detail, the 
intake pressure at which the compressed air is released during the 
throttle-part-open engine operation is equal to that at which the 
excessive supercharging pressure is released during the throttle-full-open 
engine operation. For instance, if the maximum allowable supercharging 
pressure in the throttle-full-open engine operating condition is 
predetermined to be +180 mmHg (gauge pressure), the relief valve starts 
release of air when the pressure in the supercharging intake air passage 
reaches +180 mmHg (gauge pressure). This will mean that the relief valve 
is kept closed, even in the throttle-part-open engine operating condition, 
until the pressure of air compressed by the blower of the supercharger 
reaches +180 mmHg (gauge pressure), with a result that a surging of the 
gas turbine occurs. The surging would be avoided by allowing the relief 
valve to open at a lower supercharging intake pressure, i.e., +50 mmHg 
(gauge pressure). However, this relief valve setting will inconveniently 
limit the maximum supercharging pressure in the throttle-full-open engine 
operating condition to a level as low as +50 mmHg (gauge pressure). Thus, 
the second-mentioned known supercharging system falls short of achieving 
such a control as to allow the release of compressed air at a low pressure 
during the throttle-part-open engine operation and to raise the 
supercharging air pressure in the throttle-full-open engine operation. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved 
supercharged internal combustion engine in which all the air pressurized 
by a supercharger is released into the atmosphere at an engine operating 
condition where a throttle valve is opened to its part-open position or 
less than that, in which all the pressurized air from the supercharger is 
introduced into the engine at an engine operating condition where the 
throttle valve is fully open but the supercharging intake pressure is 
lower than a predetermined level, and in which a part of the pressurized 
air from the supercharger is released into the atmosphere to keep the 
intake pressure at the predetermined level at an engine operating 
condition where the throttle valve is fully open and the supercharging 
intake pressure tends to exceed the predetermined level, whereby the 
engine output drop which would otherwise occur due to the provision of the 
supercharger is avoided, engine knocking which would otherwise occur due 
to an excessive supercharging at a heavy load engine operating condition, 
and the supercharger itself, the engine body, intake system the exhaust 
system are all prevented from being damaged. 
According to the present invention, there is provided a supercharged 
internal combustion engine comprising: 
an intake system including an intake pipe; 
a turbo supercharger mounted on said intake pipe and driven by the engine 
exhaust gases to produce a pressurized intake air to be fed into the 
engine; 
said intake system further including a bypass intake pipe merging with said 
intake pipe at a point downstream of said supercharger; 
first and second air release ports formed in said intake pipe downstream of 
said supercharger; 
said merging point being located between said first and second air release 
ports; 
a first valve means disposed in said intake system at said merging point 
for selectively pneumatically connecting said bypass intake pipe to said 
intake pipe downstream of said merging point to interrupt the 
communication between said intake pipe upstream of said merging point and 
said intake pipe downstream of said merging point, and pneumatically 
disconnecting said bypas intake pipe from said intake pipe downstream of 
said merging point to pneumatically connect said intake pipe upstream of 
said point to said intake pipe downstream of said point; 
second and third valve means mounted on said intake pipe upstream and 
downstream of said merging point, respectively, for opening and closing 
said first and second air release ports, respectively; 
said first and second valve means being operative in response to changes of 
the engine operating conditions, and said third valve means being 
operative in response to the variation in the pressure of the supercharged 
intake air. 
The above and other objects, features and advantages of the present 
invention will be made apparent by the following description with 
reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring first to FIG. 1, a supercharged internal combustion engine 
designated by reference numeral 1 has an intake pipe 3 through which air 
from an air cleaner 2 is introduced through a supercharger 11, to be 
described later, to the engine 1. An intake bypass pipe 4 extends in 
bypassing relationship to the supercharger 11 and has upstream and 
downstream ends connected to the intake pipe 3 upstream and downstream of 
the supercharger 11, respectively, to cause the air from the air cleaner 2 
to bypass the supercharger 11 to the engine 1. A sensor 5 for detecting 
the intake air flow rate is mounted on the intake pipe 3 at a portion 
thereof downstream of the point at which the bypass pipe 4 merges with the 
intake pipe 3. A throttle valve 6 is disposed in the intake pipe 3 
downstream of the sensor 5 and is operatively connected to an accelerator 
pedal 7. Reference numerals 8, 9 and 10 denote, respectively, an intake 
manifold, an exhaust manifold and an exhaust pipe. 
An exhaust-pressure type supercharger (or so-called "turbo supercharger") 
11 has a gas turbine which is disposed in the exhaust pipe 10 so as to be 
driven by the energy possessed by the exhaust gas flow. The gas turbine 
drives a blower of the supercharger which is disposed at an intermediate 
portion of the intake pipe 3 thereby to supercharge the engine. 
An intake control valve generally designated by 12 has a first valve member 
120 adapted to selectively open and close the intake pipe 3 and the bypass 
intake pipe 4, a second valve member 121 for opening and closing a first 
relief port 3a formed in the intake pipe 3, a valve rod 122 carrying the 
first and the second valve members 120 and 121, a diaphragm 123 connected 
to the valve rod 122, a spring 124 adapted to bias the diaphragm 123 in a 
direction to cause the intake bypass pipe 4 and the relief port 3a to be 
closed by the first and the second valve members 120 and 121, 
respectively, and first and second chambers 125 and 126 separated from 
each other by the diaphragm 123. The first chamber 125 is vented to the 
atmosphere, while the second chamber 126, in which the spring 124 is 
disposed, communicates with the intake manifold 8 through a 
pressure-transmitting passage 13. 
An intake relief valve generally denoted by numeral 14 has a third valve 
member 140 adapted to selectively open and close a second relief port 3b 
formed in the intake pipe 3, a valve rod 141 on which the third valve 
member 140 is mounted, a spring 142 adapted to normally bias the third 
valve member 140 in a direction to close the second relief port 3b, and a 
casing 143 adapted to guide the valve rod 141. 
The fuel circuit of the engine includes a fuel tank 15, a fuel filter 16, a 
fuel pump 17 for delivering the fuel, a fuel-pressure regulator 18 adapted 
to regulate the pressure of the fuel delivered from the fuel pump 17, a 
fuel conduit 19 and fuel injectors 20. A computer 21 is provided for 
controlling the rate of fuel injection by the fuel inectors 20, in 
response to a signal from the sensor 5 for detecting the intake air flow 
rate. The computer 21 emits a control signal which is transmitted to the 
fuel injectors 20 through a conductor 22. 
In operation, the intake air flow rate is determined by the opening degree 
of the throttle valve 6 during the running of the engine and is metered by 
the flow rate detecting sensor 5. Upon receipt of the signal 
representative of the intake air flow rate delivered from the sensor 5, 
the computer 21 determines the optimum rate of fuel injection in relation 
to the intake air flow rate, and emits an output signal to the fuel 
injectors 20 so as to cause them to perform a fuel injection at the rate 
determined by the computer 21. 
The fuel is continuously pumped up by the fuel pump from the fuel tank 15 
through the filter 16 and is delivered to the fuel injectors 20 through 
the fuel conduit 19 at a constant pressure regulated by the regulator 18. 
The intake air flow is throttle by the throttle valve 6 when the latter is 
opened to part-open position or less than that, so that a vacuum is 
produced in the intake manifold 8. This vacuum is transmitted through the 
pressure-transmitting passage 13 to the second chamber 126 of the intake 
control valve 12. Consequently, the diaphragm 123 is displaced to the 
right, as shown in FIG. 1, against the biasing force exerted by the spring 
124, so that the bypass intake pipe 4 is fully opened and the intake pipe 
3 is fully closed by the first valve member 120. At the same time, the 
second valve member 121 fully opens the first relief port 3a. 
Consequently, the atmospheric air is taken into the engine 1 through the 
bypass intake pipe 4. On the other hand, the air discharged from the 
supercharger 11 is released into the atmosphere through the first relief 
valve 3a, without establishing a substantial pressure in the intake pipe 3 
upstream of the valve member 120. Meanwhile, the third valve member 140 of 
the intake relief valve 14 keeps the second relief port 3b closed since 
the pressure in the intake pipe 3 downstream of the valve member 120 is as 
low as the atmospheric pressure. 
It will be seen that the gas turbine is relieved from the load which would 
be applied to the turbine if the intake air pressure were high. 
Consequently, the increase of the exhaust pressure of the engine 1 is 
restrained to diminish the decrease of intake efficiency which would 
otherwise be caused by the provision of the supercharger 11, thereby to 
minimize the reduction of the engine output. 
In the full throttle-opening operation including an abrupt acceleration of 
the engine, if the supercharging pressure is in a lower range, e.g. 
between -20 and +180 mmHg (gauge pressure), a small vacuum or a positive 
pressure is introduced into the second chamber 126 of the valve 12, so 
that the diaphragm 123 is displaced to the left almost solely by the 
biasing force of the spring 124. Consequently, the first valve member 120 
is moved to close the bypass intake pipe 4 and to allow the intake pipe 3 
to fully open. At this time, the second valve member is moved to close the 
first relief port 3a. The supercharging pressure in the low pressure range 
referred to above is insufficient to force the third valve member 140 of 
the intake relief valve 14 to open the second relief port 3b. 
Consequently, the whole parts of the air compressed and discharged by the 
supercharger 11 are forced into the engine 1 to contribute to an increase 
in the engine output. 
As the supercharging intake pressure grows larger, e.g. up to +180 mmHg or 
higher during the throttle-full-open engine operation, the third valve 
member 140 of the intake relief valve 14 is moved against the spring 142 
by the increased supercharging intake pressure to allow the second relief 
port 3b to open, although the intake control valve 12 functions in the 
same manner as in the foregoing operation with lower supercharging intake 
pressure. Consequently, a part of the intake air is released from the 
intake pipe 3 to maintain a predetermined supercharging intake pressure in 
the intake pipe 3 downstream of the valve member 120, i.e., to preclude 
excessively high supercharging intake pressure. 
It will be appreciated that, because the supercharger 11 functions 
substantially only when a large engine output is needed and because the 
supercharging pressure is always lower than a predetermined level, not 
only the supercharger 11 itself but also the exhaust system and even the 
intake system of the engine are saved from being subjected to continuous 
loads, with resultant increase in the durability. 
FIG. 2 shows a modification of the described embodiment, wherein the second 
valve member 121 of the intake control valve 12 of the described 
embodiment is replaced by an independently operable second valve member 
121a. More specifically, the second valve member 121a is incorporated into 
an air release valve 23 which includes a valve rod 230 carrying at its one 
end the second valve member 121a, a diaphragm 231 connected to the other 
end of the valve rod 230, a spring 232 adapted to bias the diaphragm 231 
in a direction to move the second valve member 121a to close the first 
relief port 3a, and first and second chambers 233 and 234 separated by the 
diaphragm 231 from each other. 
The first chamber 233, in which the spring 232 is disposed, is connected 
through a pressure-transmitting passage 24 to the pressure-transmitting 
passage 13, while the second chamber 234 is opened to the atmosphere. 
The intake control valve 12 and the relief valve 14 remain unchanged. 
The air release valve 23 will be described in more detail. When the 
throttle valve 6 is opened to its part-open position or less than that, a 
vacuum is produced in the intake manifold 8 and transmitted to the first 
chamber 233 of the air release valve 23 through the pressure-transmitting 
passages 13 and 24. The force exerted by the vacuum to the diaphragm 231 
is strong enough to overcome the biasing force of the spring 232 and thus 
move the second valve member 121a to open the first relief port 3a. 
During a throttle-full-open engine operation, including an abrupt engine 
acceleration, if the super-charging intake pressure is in a relatively low 
range of, for example, from -20 mmHg to +180 mmHg, a small vacuum or 
positive pressure is applied to the first chamber 233, so that the 
diaphragm 231 is deflected leftwards, as viewed in FIG. 2, by the force of 
the spring 232. Consequently, the second valve member 121a closes the 
first relief port 3a. When the supercharging intake pressure is increased 
to, for example, +180 mmHg (gauge pressure) or higher than that during the 
throttle-full-open engine operation, the increased intake pressure is 
introduced into the first chamber 233. Consequently, the diaphragm 231 is 
kept deflected leftwards, as viewed in FIG. 2, by the combined force 
produced by the increased air pressure and the spring 232 to keep the 
first relief port 3a closed by the second valve member 121a. 
It will be seen that the operation of the second valve member 121a is 
similar to that of the second valve member 121 of the embodiment described 
with reference to FIG. 1. 
In the described embodiment and the modification thereof, the first and the 
second valve members are pneumatically actuated in accordance with the 
pressure in the intake manifold 8 of the engine 1. The first and second 
valve members, however, may alternatively be mechanically connected to the 
throttle valve 6 so as to be directly operated thereby. Further 
alternatively, the valve members may be driven by solenoids which are 
energized and deenergized in accordance with the degree of opening of the 
throttle valve 6. 
As having been described, according to the present invention, all parts of 
the air compressed by supercharger are released into the atmosphere at an 
engine operating condition where the throttle valve is opened to its 
part-open position or less than that. Consequently, the pressure in the 
intake system downstream of the supercharger is maintained as low as the 
atmospheric pressure, so that the surging of the supercharger does not 
occur. In addition, since the turbine of the supercharger is relieved from 
unduly high load, the exhaust pressure is restrained from being increased, 
whereby the reduction of the engine output which would otherwise occure 
due to the provision of the supercharger is minimized. 
When the throttle valve is fully open but the supercharging air pressure is 
lower than a predetermined pressure level, all the compressed air from the 
supercharger is fed into the engine to efficiently increase the engine 
output. When the supercharging air pressure rises beyond the predetermined 
pressure level at the throttle-full-open engine operating condition, a 
part of the supercharging air pressure is released into the atmosphere to 
the intake air pressure at the predetermined constant level to 
advantageously avoid engine knocking which would otherside be caused by an 
excessively high supercharging pressure, and to highly improve the 
durability of the supercharger itself, the engine body and the exhaust and 
intake systems of the engine as well.