Intake air system for multi cylinder internal combustion engine

Abstract: An air intake system for an internal combustion engine 206 including an air cleaner chamber 201, a surge tank 204, a throttle valve 203, an air flow meter and independent air conduits 205, preferably of variable effective length, to the engine cylinders. The system may also incorporate one or more of the following: fuel injector valves and fuel supply lines, auxiliary air lines 210 to each cylinder to create a swirl in the cylinders to enhance combustion of a lean mixture, and EGR gas passages 214, in which at least some of the components are preferably formed in one or more integral resin mouldings. An associated engine control unit 222 to optimise engine operation by adjusting the richness or leanness of the fuel/air mix and the EGR supply is provided.

Description: Background of the Invention 1. Field of the Invention The present invention relates to an air intake system for a multi-cylinder internal combustion engine having a compact size, a light weight and an unproved throttle valve mechanism. 2. Description of Related Art JP-A-62-48927 (1987), for example, discloses a conventional air intake arrangement for performing a fuel lean air/fuel ratio operation wherein in an engine with two air intake valves there are provided two separate passages leading to the respective air intake valves. An intake air control valve is provided in one of the passages, so that, in a straight port, during a low engine load the intake air control valve is closed so as to increase flow velocity of the intake air flowing into the combustion chamber. In the other passage a swirl port or helical port, which is used during such low engine load condition, is bent so as to follow along the inner wall face of the combustion chamber. As a result, a swirl is caused in the combustion chamber thereby combusting speed of the mixture gas is increased and a stable combustion is obtained even with a fuel lean mixture gas. During an idling operation of an engine, it is usually necessary to feed in a good response a small amount of air to the engine for realizing a smooth engine operation. Further, such measure is known that when auxiliary devices such as an air conditioner are rendered operative an amount of air is increased to compensate a torque consumed in the auxiliary devices in order to prevent a variation of the engine operating condition. However, in order to achieve a smooth engine operation it is desirable to be able to supply air for a torque-up use immediately when the auxiliary devices are turned on and a necessity of a torque-up occurs. Namely, it is desirable that air for torque-up use shows a good response. Further, when a so called EGR operation is intended to be performed which improves fuel economy and cleans up the exhaust gas by reducing combustion temperature through the exhaust gas recirculation during a partial engine load, it is well known to introduce EGR gas into a collector which is a collecting portion of air intake conduits. Further, an EGR with about 0 ∼ 20% EGR gas is recommended as a proper range for fuel economy improvement, therefore it is preferable to perform an EGR with a possible large % of EGR gas within the above range. In the conventional air intake arrangement which is designed to generate a swirl, there is provided an intake air control valve in a main air passage near an air inlet valve, therefore there arises a problem that the intake air control valve constitutes a resistance to the intake air during an engine full load operation and effects to reduce the engine output. Further, when the air intake valve is closed, fuel deposits onto the air intake valve and causes a problem which reduces an acceleration response of fuel supply. Still further, a fuel injection valve, the mounting portion, fuel piping and air piping for fuel atomization for the fuel injection valve, and the air intake conduits conventionally were separately designed and assembled, the fuel injection valve is placed far remote from the center axis of the air intake conduit, as a result, an angle formed by the atomizing axis of the fuel injection valve and the center axis of the air intake conduit is increased which allows easy deposition of the fuel on the inner wall of the air intake conduits even when the air intake valve is opened, and causes a problem of reducing an acceleration response of fuel supply. Further, since the direction of intake air is determined by the main air passage itself, it is difficult to effectively induce a swirling. Still further, in case of the two air intake valve type engine, either a minimum flow passage cross sectional area of the swirl port has to be selected at about 1/2 of the main passage or the swirl port has to be more restricted than the straight port. In both cases, an adjustable range of the swirling strength depending on operating conditions of the engine is limited, and there arised a problem that an obtained swirl is sometimes weaker and sometimes stronger than that required depending on the engine rpm. On the other hand, when the intake air control valve is opened, the air intake passage is narrowed by the existence of the swirl port and the air intake characteristic of the passage including the straight port and the swirl port is deteriorated, namely which caused a problem of reducing the maximum engine output. Further, when air for an engine idling and for a torque-up operation is introduced into the collector which is a collecting portion of the air intake conduits, there arose a problem of deteriorating a response characteristic of intake air due to the large volume of the collector. When EGR gas is introduced into the collector, the EGR gas interfers with the combustion, in particular, when it is required to accelerate combustion by means of swirling it is difficult to uniformly introduce the EGR gas to the respective cylinders of the engine. Further, during a transient engine operation a response of EGR gas supply delays and the combination of the mixture gas is extremely interfered with depending on the engine operating condition which created a problem of impeding a large amount of EGR gas introduction. The EP 0 523 027 A2 shows an intake system for internal combustion engines incorporating a filter housing with an air intake opening, a filter element and at least one air outlet tube, which communicates with the engine inlet manifold. The top part of the inlet manifold is designed to form the lowermost border of the filter housing and to provide a support for the filter element. The EP 0 523 027 A2 is only relevant according to Art. 54(3) EPC. The document EP 0 384 359 A2 shows an integrated tuned induction system providing a plenum support surrounded by runners that spiral around the plenum side wall and around each other to the entrances of the engine cylinders. The circumferential extent of each runner exceeds 360 degrees about a longitudinal axis of the plenum. An object of the present invention is to provide an intake air system having a compact size, a light weight and an improved throttle valve mechanism. The object is solved according to the features of the independent claims. The dependent claims show advantageous embodiments of the invention. Brief Description of the Drawings Fig. 1 is a schematic fluidic system diagram of an example of air intake arrangements for an internal combustion engine; Fig. 2(a) and Fig. 2(b) are examples of maps used for controlling the air intake arrangements for an internal combustion engine. Fig. 2(a) is a map for determining an air/fuel ratio and an amount of EGR for an engine based on an engine operating condition represented by an engine rpm and engine load; and Fig. 2(b) is a map for determining an opening degree of an intake air control valve in engine operating regions I and II in Fig. 2(a) based on an engine operating condition represented by an engine rpm and engine load; Fig. 3 is the schematic fluidic system diagram shown in Fig. 1 for explaining the operating condition thereof under engine operating region I in Fig. 2(a); Fig. 4 is the schematic fluidic system diagram shown in Fig. 1 for explaining the operating condition thereof under engine operating region II in Fig. 2(a); Fig. 5 is the schematic fluidic system diagram shown in Fig. 1 for explaining the operating condition thereof under engine operating region III in Fig. 2(a); Fig. 6 is the schematic fluidic system diagram shown in Fig. 1 for explaining the operating condition thereof under engine operating region IV or V in Fig. 2(a); Fig. 7 is a schematic structural example of an auxiliary gas passage outlet port opened into a main air passage near a gas intake valve for an engine cylinder which is included in the air intake arrangements; Fig. 8 is another schematic structural example of an auxiliary gas passage outlet port opened into a main air passage near a gas intake valve for an engine cylinder which is included in the air intake arrangements; Fig. 9 is a still another schematic structural example of an auxiliary gas passage outlet port opened into a main air passage near a gas intake valve for an engine cylinder which is included in the air intake arrangements; Fig. 10 is a further schematic structural example of an auxiliary gas passage outlet port opened into a main air passage near a gas intake valve for an engine cylinder which is included in the air intake arrangements; Fig. 11 is a schematic fluidic system diagram of air intake arrangements for an internal combustion engine; Fig. 12 is a schematic fluidic system diagram of air intake arrangements for an internal combustion engine; Fig. 13 is a schematic fluidic system diagram of air intake arrangements for an internal combustion engine; Fig. 14 is a structural embodiment of a main air passage at a portion where a fuel injection valve is mounted which is included in the air intake arrangements; Fig. 15 is a similar schematic fluidic system diagram to the example shown in Fig. 1 when applied to a four cylinder internal combustion engine; Fig. 16(a) is a similar schematic fluidic system diagram to the example shown in Fig. 12 when applied to a four cylinder internal combustion engine; Fig. 16(b) is a graph illustrating a variation in intake air amount into an engine cylinder and opening degrees of an auxiliary intake air control valve 313 and of a throttle valve 314 in Fig. 16(a) depending on an opening degree of an acceleration pedal 315; Fig. 17 is a schematic fluidic system diagram of air intake arrangements for an internal combustion engine; Fig. 18(a) illustrates a change of an engine operating condition from region III to region II on the map shown in Fig. 2(a); Fig. 18(b) illustrates variations of an angle of the acceleration pedal, an amount of fuel injected, an amount of air supplied via the main air passage and an amount of air supplied via the auxiliary gas passage with respect to time in one of the examples of the air intake arrangements in response to the change illustrated in Fig. 18(a); Fig. 19(a) is a flow chart illustrating a control sequence performed in one of the examples of the air intake arrangements immediately after detecting the change as illustrated in Fig. 18(a); Fig. 19(b) is a flow chart illustrating a control sequence performed in one of the examples of the air intake arrangements after the control sequence shown in Fig. 19(a) has terminated; Fig. 20 is a flow chart illustrating a modified control sequence of that shown in Fig. 19(b); Fig. 21 is a flow chart illustrating another modified control sequence using an engine roughness signal of that shown in Fig. 19(b); Fig. 22 is a flow chart illustrating a modified control sequence incorporating a learning function of a swirl solenoid opening degree of that shown in Fig. 21; Fig. 23(a) illustrates a change of an engine operating condition within region II on the map shown in Fig. 2(a); Fig. 23(b) illustrates variations of an angle of the acceleration pedal, an amount of fuel injected, an amount of air supplied via the main air passage and an amount of air supplied via the auxiliary gas passage with respect to time in one of the examples of the air intake arrangements in response to the change illustrated in Fig. 23(a); Fig. 24 is a flow chart illustrating a control sequence performed in one of the examples of the air intake arrangements immediately after detecting the change as illustrated in Fig. 23(a); Fig. 25(a) illustrates a change of an engine operating condition from region II to region III on the map shown in Fig. 2(a); Fig. 25(b) illustrates variations of an angle of the acceleration pedal, an amount of fuel injected, an amount of air supplied via the main air passage and an amount of air supplied via the auxiliary gas passage with respect to time in one of the examples of the air intake arrangements in response to the change illustrated in Fig. 25(a); Fig. 26 is a flow chart illustrating a control sequence performed in one of the examples of the air intake arrangements immediately after detecting the change as illustrated in Fig. 25(a); Fig. 27 is a top plane view of one structural embodiment of air intake arrangements according to the present invention which is realized based on one of the embodiments illustrated by the schematic fluidic system diagrams in Fig. 1, Fig. 11, Fig. 12, Fig. 13, Fig. 15, Fig. 16(a) and Fig. 17; Fig. 28 is a cross sectional view taken along the line A-A in Fig. 27; Fig. 29 is a cross sectional view taken along the line B-B in Fig. 27; Fig. 30 is a cross sectional view taken along the line C-C in Fig. 27; Fig. 31 is a top plane view of another structural embodiment of air intake arrangements according to the present invention which is realized based on one of the embodiments illustrated by the schematic fluidic system diagrams in Fig. 1, Fig. 11, Fig. 12, Fig. 13, Fig. 15, Fig. 16(a) and Fig. 17; Fig. 32 is a cross sectional view taken along the line A-A in Fig. 27; Fig. 33 is a cross sectional view taken along the line B-B in Fig. 27; and Fig. 34 is a cross sectional view taken along the line C-C in Fig. 27. Detailed Description of the Embodiments Fig. 1 shows that inlet air is introduced from an air cleaner 201, and the flow rate thereof is measured by an air flow meter 208. An amount of air passing through a main passage 202 is adjusted by a throttle valve 203 and then distributed for respective engine cylinders from a collector 204 and thereafter introduced into an engine 206 via respective independent air intake conduits 205. In the present embodiment, an auxiliary gas passage 210 is provided in parallel with the respective independent air intake conduits 205. Air flow rate passing through example the auxiliary gas passage 210 is adjusted through a control of an intake air control valve 211 by a computer 222 based on a signal from an acceleration pedal opening degree detecting means 221, an ON/OFF signal from engine accessories 220, a signal from an engine rpm detecting means 223 and an intake air amount signal from the air flow meter 208. In addition to the above, EGR gas is supplied to the auxiliary gas passage 210 from an engine exhaust gas conduit 207 via an EGR gas passage 214 and an EGR valve 212. An outlet port 213 of the auxiliary gas passage 210 opens into the independent air intake conduit 205 at the vicinity of an air intake valve (not shown) of the engine 206. At this moment, the flow velocity of the intake air flowing into the engine 206 is determined based on the flow rate of the auxiliary air and the opening cross sectional area of the auxiliary gas passage outlet port 213. When the opening cross sectional area of the auxiliary gas passage outlet port 213 is determined smaller than that of the independent air intake conduit 205, flow velocity of the intake air is raised and further, when the outlet port 213 is disposed eccentrically with respect to the circumference of the intake air conduit 205, a swirling can be induced in a combustion chamber (not shown) of the engine 206. Fig.3 through Fig.6 show diagrams for explaining operating conditions of the Fig.1 example depending upon engine operating regions as illustrated in Fig.2(a). Fig.2(a) and Fig.2(b) are examples of maps used for controlling the air intake arrangements for an internal combustion engine, Fig.2(a) is a map for determining an air/fuel ratio and an amount of EGR for an engine based on an engine operating condition represented by an engine rpm and engine load, and Fig.2(b) is a map for determining an opening degree of an intake air control valve in engine operating regions I and II in Fig.2(a) based on an engine operating condition represent by an engine rpm and engine load. Judgement under which region of Fig.2(a) the present engine operating condition comes is determined by the computer 222 based on a signal from the engine rpm detecting sensor 223 and a signal from the acceleration pedal opening degree detecting sensor 221. Depending on the judgement, the intake gas control valve 211 and the EGR valve 212 are controlled so as to perform a control meeting the respective operating regions. Controls corresponding to the respective operating regions are illustrated in Fig.3 through Fig.6. Fig.3 shows an operating state under the region I wherein an engine rpm is low and no substantial load is applied. The throttle valve 203 and the EGR valve 212 are closed and the inlet air is adjusted by the intake air control valve 211. Namely, air 231 is supplied via the auxiliary gas passage 210 so as to maintain the air/fuel ratio at the stoichiometric air/fuel ratio. Under this condition, when the engine load is varied due to turn on or turn off the engine accessories 220 or when the engine rpm varies due to a small internal condition change of the engine 206, a proper amount of intake air has to be immediately supplied in response to these changes in order to maintain a smooth engine operation. In the present example the entire inner volume of the auxiliary gas passage 210 is determined smaller than the total volume of the main passage 202 including the collector 204 and the independent air intake conduits 205 for the respective engine cylinders, for example, less than 80% of the total volume, the response charactristic with respect to a required air amount change is improved in comparison with the conventional arrangement wherein the intake air supply is performed via the main passage 202. Accordingly, with the present example, air for idling operation can be supplied with a good response charactristic to meet an engine rpm variation, and an engine rpm stability is enhanced. Fig.4 shows an operating state under the region II wherein the engine rpm is higher than that under region I and the engine load extends from a low to an intermediate region. The throttle valve 203 slightly opens dependent upon the engine load and engine rpm. The EGR valve 212 remains in closed state. In the region II, the air/fuel ratio is controlled at a fuel lean air/fuel ratio, for example, of 22∼23, such that when the engine operating condition moves to other regions, an adjustment of the air/fuel ratio is necessitated. In the present example, when the engine operating condition moves into the region II, the opening degree of the intake air control valve 211 is opened wider than those in other regions to increase inlet air amount. In addition thereto, the flow rate of the air 231 which flows into the engine 206 via the auxiliary gas passage inlet port 213 is increased, and the intake gas flow velocity is raised such that a swirling is induced in the combustion chamber (not shown) of the engine and the combustion speed of the mixture gas is increased, thereby a desirable combustion is obtained even with a fuel lean mixture gas. In this instance, by determining a proper cross sectional area of the auxiliary gas passage outlet port 213 the strength of the swirling is optimized. Namely, when it is required to increase the strength of the swirling, the cross sectional area of the passage outlet port 213 is set small, on the other hand, when it is required to decrease the strength, the cross sectional area thereof is set large. Further, for the air/fuel ratio control, a measure to vary the fuel amount supplied from the fuel injection valve (not shown) to the engine 206 can be used in parallel. With the present example, in both cases one in which the engine operating condition moves into the region II from other adjacent regions and the other in which the engine operating condition moves from the region II to other adjacent regions, the amount of inlet air 231 can be increased or decreased with a good response. Fig.5 shows an operating state under the region III wherein either the engine rpm is extremely low and the engine load is larger than that under idling condition or the engine load is higher than that in the region II or the engine rpm is higher than that in the region II. Under this region the air/fuel ratio is set at the stoichiometric air/fuel ratio for obtaining a higher torque. The throttle valve 203 opens in response to the engine load or the engine rpm. The amount of EGR gas is adjusted by the EGR valve 212 depending on engine operating conditions, thereby the combustion temperature is lowered and fuel economy is improved through a pumping loss reduction. The intake air control valve 211 is at this moment closed so as to prevent a reverse flow of the EGR gas. At this instance, the EGR gas 232 of a high velocity is supplied from the auxiliary gas passage outlet port 213 and is uniformly mixed with the air 231 passing through the main passage 202, thereby the distribution of the EGR gas to the respective cylinders of the engine is improved in comparison with the conventional arrangement wherein the EGR gas is supplied to the collector portion 204, as a result a limit of EGR amount can be expanded. Further, by orienting the auxiliary gas passage outlet port 213 to the direction along the wall face of the combustion chamber (not shown) of the engine, a swirling is induced in the combustion chamber to thereby improve combustion as well as to form a layer of the EGR gas 232 near the wall face thereof which reduces thermal loss through the wall face and achieves a fuel economy improvement. Further, when the inner volume of the EGR gas passage 214 is determined smaller than the totaled volume of the main passage 202 including the collector 204 and the independent gas intake conduits 205 for the respective engine cylinders, the EGR gas can be supplied to the engine with a good response. Fig.6 shows an operating state under the region IV and the region V wherein the engine rpm is further higher than under the region III or the engine load is further larger than under the region III. In these regions, the air/fuel ratio is set at the stoichiometric air/fuel ratio or at a fuel rich air/fuel ratio wherein an importance is placed on an engine operation for obtaining a necessary torque. The EGR valve 212 is closed, however the inlet air control valve 211 can take both conditions, that is, both open and close conditions. The throttle valve 203 in the main passage 202 is fully opened at a high engine load side, and at a high engine rpm side the opening degree of the throttle valve 203 is controlled depending upon a required torque. At this instance, different from the conventional arrangement, the elements in the independent gas intake conduits 205 such as an intake air control valve and a throttle for the air intake conduits which constitute a resistance for the intake air are eliminated to thereby prevent an engine output reduction. Fig.7 through Fig.10 show structural examples of the auxiliary gas passage outlet ports 213. Fig.7 is an example wherein the auxiliary gas passage outlet port 213 is disposed eccentrically toward the right side or the left side of the independent air intake conduit 205. With this structure, the auxiliary gas passes through the air intake valve 241 and flows along the circumference of an engine cylinder wall to thereby induce a strong swirling in a plane parallel with the piston top plane. When air is introduced as the auxiliary gas, excess air is supplied with respect to fuel and a condition of a fuel lean air/fuel ratio is generated, however, with the inducement of the swirling the combustion speed is increased and a desirable combustion is realized. Further, when EGR gas is introduced as the auxiliary gas, a uniform mixing of the EGR gas and air is achieved by making use of the swirling which lowers the combustion temperature and reduces a thermal loss effected via the engine cylinder wall as well as suppresses emission of nitrogen oxides. Further, through the introduction of air or EGR gas from the auxiliary gas passage outlet port 213 to the engine cylinder wall face 242, a layer of air or EGR gas is formed along the circumference and a combustion is effected near the center portion of the combustion chamber 244 where an ignition plug 243 is disposed, thereby a thermal loss through the engine cylinder wall face 242 is reduced by means of adiabatic effect of air or EGR gas. Fig.8 is another example wherein the auxiliary gas passage outlet port 213 is disposed eccentrically toward the upper side of the independent air intake conduit 205. With this structure, the auxiliary gas passes through the air intake valve 241 and induces a vertical swiling (tumbling). At this instance, when fuel is injected from a fuel injection valve (not shown) only toward one of the two air intake valves 241, a mixture gas is formed only in a partial region of the combustion chamber 244 covered by the one air intake valve 241 located at one side. Thereby a stratification of the mixture gas in the combustion chamber 244 is achieved and a sufficiently combustible fuel lean mixture gas is obtained. Further, in an engine compression stroke the tumbles are collapsed and a multiplicity of small turbulences are generated such that a combustion speed is improved even with the fuel lean mixture gas. Fig.9 is a still another example wherein the auxiliary gas passage outlet port 213 is disposed eccentrically toward the lower side of the independent air intake conduit 205. With this structure, the auxiliary gas passes the air intake valve 241 and induces a tumble moving in an opposite direction to that of Fig.8. At this instance, when fuel is injected from a fuel injection valve (not shown) only toward one of the two air intake valves 241, a mixture gas is formed only in a partial region of the combustion chamber 244 covered by the one air intake valve 241 located at one side. Thereby a stratification of the mixture gas in the combustion chamber 244 is achieved and a sufficiently combustible fuel lean mixture gas is obtained. Further, in an engine compression stroke the tumbles are collapsed and a multiplicity of small turbulences are generated such that a combustion speed is improved even with the fuel lean mixture gas. Fig.10 is a further example wherein a pair of auxiliary gas passage outlet ports 213 are provided on the right and left sides of the independent air intake conduit 205 near the end thereof. The respective passage outlet ports 213 are directed toward the center of the combustion chamber 244. Further, the atomized fuel from the fuel injection valve 245 is adapted to collide with the gas flow from the auxiliary gas passage outlet ports 213. With this structure, an easily ignitable fuel rich mixture gas is formed at the center portion of the combustion chamber 244, therefore, when the ignition plug 243 is disposed at such region a desiarable ignition and combustion are achieved even when a mixture gas of a fuel lean air/fuel ratio as a whole is charged into the combustion chamber 244. Further, if the atomized fuel 246 from the fuel injection valve 245 can be concentrated at the center of the combustion chamber 244, the auxiliary gas passage outlet ports 213 are not necessarily provided on both sides of the independent air intake conduit 205, instead only a single auxiliary gas passage outlet port 213 can be disposed eccentrically toward upper side or lower side of the independent air intake conduit 205 for obtaining substantially the same advantages as above. Fig.11 through Fig.13 show further examples having modified auxiliary gas passage structures. In Fig.11 example inlet air is introduced through an air cleaner 201, and after being measured the flow rate thereof by an air flow meter 208, the amount of the inlet air is adjusted by a throttle valve 203 and the dividing ratio of the inlet air for a main passage 202 and an auxiliary gas passage 210 is adjusted by an intake air control valve 251. The intake air control valve 251 is designed either to open in synchronism with the throttle valve 203 but with a predetermined delay or to open when the intake air negative pressure reaches to a predetermined value near the atomospheric pressure to thereby adjust a swirling strength. With such structure, amount of air passing through an auxiliary air control valve 252 for an idling operation and for a torque-up operation for driving engine accessories can be reduced, thereby manufacturing cost of the arrangement is reduced. Further, since the intake air control valve 251 is disposed upstream the collector 204, it is not necessary to provide many intake air control valves corresponding to the number of engine cylinders as in the conventional arrangement, but only one intake air control valve 251 is satisfactory. Accordingly, manufacturing cost of the arrangement is again reduced. With the present embodiment, since the inner volume of the auxiliary gas passage 210 is also designed small in comparison with the total volume of the main gas passage 202 including the collector 204 and the independent air intake conduits for the respective engine cylinders, an improvement of the response characteristic - of the auxiliary gas and an inducement of a gas swirl having a necessary strength are of course obtained. Fig.12 is an example wherein an auxiliary throttle valve 253 is provided in the auxiliary gas passage 210 so as to bypass the intake air control valve 211. In the present example, the intake air control valve 211 is used for controlling air amount for an idling operation and for a torque-up operation and the auxiliary throttle valve 253 is used for adjusting the flow rate of air used for inducing a gas swirl in a fuel lean air/fuel ratio operating region, thereby the capacity of the intake air control valve 211 can be reduced and the manufacturing cost of the arrangement is lowered. Likely, with the present structure, an improvement of the response characteristic and an inducement of the gas swirl of a necessary strength can also be obtained. Fig.13 is an example wherein a throttle nozzle 254 is provided at the auxiliary gas passage outlet port 213, and the fundamental structure and the operation thereof are substantially the same as those explained in connection with Fig.1 through Fig.6. In the present example, when an opening degree of the throttle valve 203 is small and a flow rate of the auxiliary air is small such as in an idling region, the auxiliary gas passage outlet port 213 is restricted by the throttle nozzle 254 to thereby increase a flow velocity of the auxiliary air and to increase the gas swirl strength, as a result, a stable combustion is achieved even when the combustion is effected with a fuel lean air/fuel mixture gas. Likely, in the present example , since the inner volume of the auxiliary gas passage 210 is determined smaller than the totaled volume of the main air passage 202 including the collector 204 and the independent intake air conduits 205 for the respective engine cylinders, an improved response characteristic of the auxiliary gas is of course obtained. Fig.14 shows a structural example of the idependent intake air conduit 205 with an integrated fuel injection valve fitting arrangement. All of a mounting portion 262, a fuel piping 263 and an air piping 264 for fuel atomization for the fuel injection valve are structurally integrated with the independent air intake conduit 205. The fuel injection valve 261 is secured to the independent air intake conduit 205 via a stopper 262. Through the integration of the mounting portion 262, the fuel piping 263 and the air piping 264 for fuel atomization for the fuel injection valve with the independent air intake conduit 205, the fuel injection valve 261 can be located near the center axis of the air intake conduit 205 in comparison with the conventional arrangement wherein the four parts are separately manufactured so that an angle α formed by the fuel atomization axis and the center axis of the intake air conduit 205 can be decreased. Further, the air intake conduit 205 can be optimally designed so as to meet a spreading configuration of the atomized fuel and to reduce a deposition rate of the atomized fuel injected from the fuel injection valve 261 on the inner wall of the air intake conduit 205. As a result, the fuel deposition on the air intake conduit 205 is reduced. Fig.15 shows a further example similar to Fig.1 example. Air is taken-in into a collector 304 via an air cleaner 301, an air flow rate sensor 302 and a throttle valve 303, further the air passes through independent air intake conduits 305 for the respective engine cylinders and is taken-in into the respective combustion chambers of the engine 307 via air intake valves 306. A passage 308 bypassing the throttle valve 303 is provided through which air is supplied to a gas intake port 309 of the respective independent air intake conduits 305. The flow velocity of the air bypassing the throttle valve 303 is higher than the main air flowing through the independent air intake conduits 305. The outlet of the bypass passage 308 is opened so as to provide a drift current for the air flow in the gas intake port 309. The upstream inlet of the bypass passage 308 opens at the upstream of the throttle valve 303. Further, another bypass passage 310 branching from the bypass passage 308 is provided. The passage 310 is used for supplying air for fuel atomization to a fuel injection portion 312 of a fuel injection valve 311. The outlets of the bypass passage 308 open to the independent gas intake ports 309 for the respective engine cylinders. A flow rate control valve 313 is provided in the bypass passages 308 and 310 and is designed to control the amount of air flowing therethrough depending on engine operating conditions. The flow rate control valve 313 is actuated by an electrical signal. As indicated above, since the outlet portion of the bypass passage 308 is arranged eccentrically with respect to the gas intake port 309, a drift current is caused in the air flow. As a result, a gas swirl is formed in the combustion chamber and the combustion during a fuel lean air/fuel ratio operation is stabilized. Further, since air for an idle speed control and for a fast idle control is also supplied via the control valve 313, the combustion during an idling operation and a starting-up operation is improved and an amount of emission of unburnt hydrocarbon is reduced. Still further, an air/fuel ratio during an idling operation and a starting-up operation can be set at a fuel lean air/fuel ratio, which is effective for the reduction of fuel cost and for the reduction of unburnt hydrocarbon emission. Fig.16(a) shows a still another example similar to Fig.12 example, wherein two throttle valves 313 and 314 are provided, and are constituted respectively for supplying air for the bypass passage 308 which is designed to supply air to the gas intake port 309 and for the bypass passage 310 which is designed to supply air for atomizing fuel injected from the fuel injection valve 311. The inlet port of the bypass passage 310 opens at the upstream of the throttle valve 314. The respective throttle valves 313 and 314 are mechanically linked with an acceleration pedal 315. The throttle valve 313 is at first opened in response to depression of the acceleration pedal 315. After the throttle valve 313 is fully opened, the throttle valve 314 begins to open, which operation sequence is illustrated in Fig.16(b) wherein curve a shows an opening degree of the throttle valve 313 and curve b of the throttle valve 314. During a fuel lean air/fuel ratio operation, air is taken in through the throttle valve 313 and the bypass passage 308. Accordingly, a swirling is induced in the intake gas and the combustion is stabilized. When the acceleration pedal 315 is depressed beyond a predetermined degree, air passing through the throttle valve 314 is also taken-in. Although under such condition, combustion with a fuel lean air/fuel mixture gas is possible because air flowing at a high velocity is supplied via the bypass passage 308. However, in response to opening operation of the throttle valve 314 the operation at a fuel lean air/fuel ratio can be returned to the operation at a normal air/fuel ratio. With the present example, the supply of a high velocity gas is controlled via a mechanical actuating operation. A control valve 316 for an idle speed control is arranged so as to bypass the throttle valve 313 or 314. However, in order to improve combustion during an idling operation it is preferable to arrange the control valve 316 for the idle speed control so as to bypass the throttle valve 313. Further, it is also preferable to arrange a control valve 317 for a fast idle control so as to bypass the throttle valve 313. With thus constituted arrangement, the combustion during starting-up and idling operations is improved and emission amount of unburnt hydrocarbon is reduced. According to the present example, since air flows through the passage 308 until an opening degree of the acceleration pedal 315 reaches the predetermined degree, an operation at a fuel lean air/fuel ratio is possible. Fig.17 shows a still another example, wherein a collector 318 having a larger passage area than the bypass passage 308 is provided in the bypass passage 308 connected to the throttle valve 313. With such constitution, an intake air inertia effect is induced in the bypass passage 308 and torque at a low engine rpm is increased. Further, air passing throuth the throttle valve 314 is introduced into a conventional collector 319. For the air passing through the throttle valve 314, an intake air inertia effect is likely induced by means of the collector 319. The map illustrating air/fuel ratio settings shown in Fig.2(a) is again explained. During idling operation in region I an air/fuel ratio, namely excess air ratio λ is set near 1. Further, under a light load condition in region II, the air excess rate is set at λ >1.0 i.e. a fuel lean air/fuel ratio. Outside this region, since an importance is placed on an engine output, the air/fuel ratio is set at λ =1 i.e. stoichiometric air/fuel ratio. A further outer region constitutes a powering range wherein the air/fuel ratio is set at λ <1.0 i.e. a fuel rich air/fuel ratio. Air for inducing a gas swirl in the combustion chamber is introduced in an operating condition in region II wherein an air/fuel ratio is set at λ >1.0 i.e. a fuel lean air/fuel ratio. As indicated above, since even during an idling operation air bypassing the throttle valve is introduced as an idle speed control (ISC) use into the gas intake port, the combustion during a starting-up operation and idling operation is improved. In Fig.2(a), the air/fuel ratio in the region I corrsponding to the idling operation is set at λ =1, however, by means of the above combustion improving effect the air/fuel ratio can be set at λ >1.0 i.e. a fuel lean air/fuel ratio. Fig.2(b) shows an example of maps of opening degree of the control valves for the bypassing air in regions I and II. Under an idling operation region I, amount of air is controlled by making use of a control valve for ISC. Further; under a light load operation region II, amount of bypassing air is controlled by making use of a separate air control valve wherein the opening degree of the control valve is varied depending on a required air amount of the engine. Although, the map of Fig.2(b) shows a use of the separate control valves for region I and region II, a common control valve can be used for both regions I and II as illustrated in Fig.1 example. Fig.18 (a) and Fig.18(b) are views for explaining an operation of the control valve 313. Fig.18(a) is a diagram illustrating a change of engine operating condition from point A to point B wherein the acceleration pedal is depressed and the engine operating region is moved into the region II corresponding to a fuel lean air/fuel ratio. Fig.18(b) shows changes of control variables with respect to time in response to the engine operating condition change.  ac designates a depression angle of the acceleration pedal and in the drawing the depression angle is increased which represents an acceleration condition. Immediately after the operating condition moves into the region II operating at a fuel lean air/fuel ratio, the base fuel injection amount is fixed to the previous value. However, since the air/fuel ratio is set at a fuel lean air/fuel ratio, amount of bypassing air is increased to settle at the set air/fuel ratio. In the drawing, Qm and Qs respectively represent the main air amount and the bypassing air amount flowing through the respective air intake passages at this moment. Immediately after the engine operating condition moves into the region II of a fuel lean air/fuel ratio, the bypassing air amount Qs is increased to shift the air/fuel ratio into a fuel lean air/fuel ratio. The main air amount Qm is increased in response to the depression angle of the acceleration pedal. The bypassing air amount Qs can be understood to be an air amount necessary for shifting the air/fuel ratio into a fuel lean air/fuel ratio. When assuming that Qf represents a fuel amount with which the stoichiometric air/fuel ratio will result in with respect to the air amount immediately before the acceleration pedal is depressed, the increasing portion in Qs corresponds to an air amount used for shifting the air/fuel ratio from the stoichiometric air/fuel ratio to the fuel lean air/fuel ratio. With such measure a shifting of engine operating condition from the stoichiometric air/fuel ratio operation to a fuel lean air/fuel ratio operation is smoothly performed. Fig.19(a) shows a control flow chart of the above explained control sequence. First, it is judged whether the engine operating condition moved into a fuel lean air/fuel ratio region. When it is judged that the condition moved into a region permitting a fuel lean air/fuel ratio operation, the fuel amount is temporarily held unchanged. Subsequently, an opening degree of the control valve (hereinafter called as swirl solenoid) 313 is retrieved on a map and the swirl solenoid is actuated according to the map retrieved opening degree, and after completing the above operation, the fuel amount holding is canceled. Thereafter, the process moves to another operation flow in a fuel lean air/fuel ratio operating region as shown in Fig.19(b), wherein at first it is judged whether the engine operating condition still stays in the fuel lean air/fuel ratio operating region and when it is judged that the condition stays under the fuel lean air/fuel ratio operating region, the swirl solenoid opening degree map is retrieved and the retrieved value is output. Thereafter, it is judged whether the air/fuel ratio reaches a target air/fuel ratio and if the actual air/fuel ratio is in a fuel lean side with respect to the target air/fuel ratio, the fuel amount is increased, and if the actual air/fuel ratio is in a fuel rich side with respect to the target air/fuel ratio, the fuel amount is decreased. Namely, after the swirl solenoid has been opened to a target opening degree, the air/fuel ratio control is performed by increasing or decreasing the fuel amount. Fig.20 shows a modified control sequence of air/fuel ratio of that shown in Fig.19(b). When it is judged that the engine operating condition is in a fuel lean air/fuel ratio operating region, a fuel injection amount is map-retrieved and the map-retrieved fuel amount is injected from the fuel injection valve. Thereafter, it is judged whether the actual air/fuel ratio reaches to a target air/fuel ratio, and if actual air/fuel ratio is determined in fuel lean side with respect to the target air/fuel ratio, the swirl solenoid is closed to move the air/fuel ratio toward fuel rich side, and further, if the actual air/fuel ratio is determined in fuel rich side with respect to the target air/fuel ratio, the swirl solenoid is opened to move the air/fuel ratio toward fuel lean side. Namely, in the present control method, the air/fuel ratio is adjusted by varying air amount via the opening degree control of the swirl solenoid. An example of judging methods whether the actual air/fuel ratio reaches to a target air/fuel ratio used in the methods exemplified in Fig.19(b) and Fig.20 is one in which the judgement is made based on a detected value from an air/fuel ratio sensor detecting exhaust gas. Other than the air/fuel ratio sensor detecting exhaust gas, a sensor for detecting engine roughness can be used for determining air/fuel ratio. The engine roughness can be determined either based on a combustion pressure variation detected by a combustion pressure sensor attached to the combustion chamber, based on an engine rpm variation detected by such as a crank angle sensor attached to the cam shaft and a ring gear sensor, or based on a knock magnitude detected by a knock sensor attached to an engine block. Fig.21 shows a further air/fuel ratio control sequence which makes use of an engine roughness sensor. When it is determined that the engine operating condition is in a fuel lean air/fuel ratio operating region, a detected value of engine roughness degree is read. The engine roughness is determined by making use of one of the above methods and when the detected engine roughness is larger than a target value, it is judged that the present air/fuel ratio reaches a limit of fuel lean air/fuel ratio and the swirl solenoid is closed and the air/fuel ratio is shifted toward fuel rich side. Contrary, when the detected engine roughness is smaller than the target value, the swirl solenoid is opened and the air/fuel ratio is shifted toward fuel lean side. Thus operating the swirl solenoid in dependence upon the engine roughness, the engine is allowed to operate always at a fuel lean limit of air/fuel ratio. Fig.22 shows a further modified air/fuel ratio control sequence incorporating a learning function of a swirl solenoid opening degree. After detecting an engine roughness, the detected engine roughness is judged smaller than a target value, the opening degree of the swirl solenoid is increased and the engine roughness is again judged. At this instance, when the detected engine roughness exceeds the target value, the opening degree of the swirl solenoid is slightly decreased and the opening degree of the swirl solenoid at that moment is rewritten on a map and stored. Namely, the newly stored opening degree of the swirl solenoid represents an air/fuel ratio close to the fuel lean limit of air/fuel ratio at this moment. With this method, the map is always maintained to represent an opening degree limit even when motor vehicle components such as the engine have suffered a secular change. Fig.23(a) shows a diagram illustrating a change of engine operating condition from point C and to point D when the acceleration pedal is depressed during an engine operating condition at a fuel lean air/fuel ratio operating region II. In this instance, the fuel amount Qf also increases according to an increase of acceleration pedal angle  ac as illustrated in Fig.23(b). The increasing tendency of air amount at this moment is also illustrated by the air amount Qm of the main intake gas conduit and the air amount Qs of the auxiliary air passage 308 in Fig.23(b). Both air amounts Qm and Qs are designed to increase at a predetermined rate in accordance with the increase of acceleration pedal angle  ac. With such control, a gas swirl having a predetermined strength is always obtained. Alternatively, the flow rate of Qm and Qs can be varied depending on engine rpm. In both cases, the control can be performed by storing optimum opening degrees of the swirl solenoid on the map having parameters of engine rpm and engine load as illustrated in Fig.2(b). Fig.24 shows a flow chart of the control sequence as explained above. At first, it is determined whether the engine is accelerated in a fuel lean air/fuel ratio operating region, and when the answer is yes, the swirl solenoid opening degree map is retrieved and the swirl solenoid is opened based on the retrieved opening degree, and an amount of fuel corresponding to the sum of Qm and Qs is injected, however at this moment the air/fuel ratio is set at fuel lean side, the amount of fuel injected corresponds to one at the set fuel lean air/fuel ratio. Fig.25(a) shows a diagram illustrating a change of engine operating condition from point E to point F, in that, when an engine operating condition changes from a fuel lean air/fuel ratio operating region to another air/fuel ratio operating region. As illustrated in Fig.25(b), immediately after the engine operating condition moves out from a fuel lean air/fuel ratio operating region in response to an increase of acceleration pedal angle  ac, the fuel amount Qf is held unchanged. In this instance, a change of air/fuel ratio is performed by varying the air amount passing through the air passage 308. Namely, the air/fuel ratio is controlled by varying Qs while maintaining Qm substantially constant. A flow chart of the control sequence at this instance is illustrated in Fig.26. At first, it is judged whether the engine operating condition has moved out from the fuel lean air/fuel operating region II, and when the answer is yes, the fuel injection amount is temporarily held unchanged. Thereafter, the opening degree of the swirl solenoid is decreased. After completing the above operation, the fuel injection amount holding is canceled. Thus the control is performed only by varying the air amount without varying the fuel amount, thereby a torque shock which may be caused during transition to another air/fuel ratio operating condition is reduced. Fig.27 is an upper view illustrating one structural embodiment of the present invention, Fig.28 is a cross sectional view taken along the line A-A of Fig.27, Fig.29 is another cross sectional view taken along the line B-B of Fig.27 and Fig.30 is a further cross sectional view taken along the line C-C in Fig.27. In these drawings, numeral 101 is an air cleaner, 102 a measuring portion of inlet air flow rate, 103 a throttle valve, 104 a surge tank or a main collector chamber, 105 independent branching air intake conduits, 106 a control unit, 107 fuel injectors, 108 a pressure regulator, 109 an auxiliary air control valve, 110 an EGR valve, 111 a conduit length variable type intake air valve (wherein the valve opened position is illustrated by the solid line and the valve closed position by the broken line), 112 an actuator for opening and closing the conduit length variable type intake air valve, 113 an auxiliary air intake passage, and 150 an engine main body. Further, the arrows in the drawings indicate the flow direction of the inlet air in the arrangement, and the arrows indicated by broken lines indicate the inlet air flow direction when the conduit length variable type intake air valve 111 is closed. The air to be taken-in into the engine is introduced into the air cleaner 101 via the inlet port thereof and is filtered via an air filter 101a provided therein and is led via the air flow rate measuring portion 102 toward the throttle valve 103 which is operated to open or close in accordance with intentions of the motor vehicle driver. An inlet air flow is controlled by an opening area determined by the throttle valve 103. The air passing through the throttle valve 103 is distributed from the surge tank 104 to the respective engine cylinders via the independent branching intake air conduits 105. In the respective independent branching intake air conduits 105, the conduit length variable type intake air valve 111 is provided of which opening and closing operations are controlled by the actuator 112. Other than via the above air passage, the inlet air which bypasses the throttle valve 103 at the downstream of the air flow rate measuring portion 102 is further supplied to the engine via the auxiliary intake air passage 113 after the inlet air amount is controlled by the auxiliary air control valve 109. The fuel to be supplied to the engine of which pressure in the fuel piping is maintained constant by the pressure regulator 108, is injected into the respective engine cylinders from the fuel injectors 107 which are actuated based on a signal value calculated in the control unit 106 by making use of signals such as from the air measuring portion 102. In the present embodiment, the elements indicated above as well as the EGR valve 112 for supplying a part of the exhaust gas to the engine are structured into an integral body. Some of the elements can be removed from the integral body and additional elements can be added thereto if required, the elements integrated into the integral body are not limited to those indicated above. With the above structure, a duct connecting the air cleaner or the intake air flow meter accommodating portion with the throttle valve accommodating portion provided in a conventional air intake arrangement is eliminated, and the air cleaner and the air flow meter accommodating portion can be mounted on the engine portion. Further, in the present embodiment, since the throttle valve 103 is located between the independent branching intake air conduits 105, the volume of the surge tank 104 can be increased, while keeping the length of the independent branching intake air conduits 105 for multi-cylinders substantially identical each other in the limited space. Accordingly, the space for the air intake arrangement can be reduced as well as the entirety of the air intake arrangement can be treated as a unitary body, thereby the lay-out design thereof in an engine room of a motor vehicle is facilitated and a standardization thereof is enabled. Further, the number of steps for the assembly work thereof is reduced, and an engine performance test on the respective actual products in an engine production line is enabled. Still further, since the air intake arrangement itself is formed into an integral body, a performance test on the respective actual products is enabled, thereby the performance of the entire air intake arrangement can be controlled at the moment of their productions. Still further, as a general tendency, the output signal of the air flow meter is likely to oscillate due to engine intake air ripple and the oscillation is maximized when the engine rpm coincides with the natural oscillation frequency in the air intake conduit. Since the length of the conduit portion wherein the air flow meter is disposed substantially corresponds to the length from the air cleaner to the surge tank, in the conventional arrangement wherein the conduit length was extended because of the provision of the duct, the natural oscillation frequency of the conduit showed a frequency in a low frequency range which likely caused a disturbance in the air flow meter output signal during actual use thereof, however, in the present embodiment, the conduit length is shortened thereby the natural oscillation frequency in the conduit is improved to show a frequency in a high frequency range (five times higher frequency than that of the conventional arrangement, for example, from 25Hz to 125Hz) and the conventional disturbance caused in the air flow meter output signal is reduced. Further, a torque increase during a low engine rpm is effected by elongating the length of the respective independent branching intake air conduits. In the present embodiment, the elongation of the respective independent branching air intake conduits is realized in a limited space by disposing the respective independent branching air intake conduits 105 around the circumference of the surge tank 104 and by commonly using a part of the outer wall face of the surge tank 104. Contrary, a torque increase during a high engine rpm is effected by shortening the length of the respective independent branching intake air conduits which is a totally opposite requirement for that during a low engine rpm. In the present embodiment, independent branching air intake conduits resolving the above opposing requirements are easily realized by incorporating the conduit length variable type intake air valve 111 as illustrated clearly in Fig.29. In the present embodiment, the conduit length variable type intake air valve 111 is controlled to open the valve during a high engine rpm and to close the valve during a low engine rpm by a diaphragm mechanism of the actuator 112. However, the control method of the valve is not specifically limited to that explained above, the valve, for example, can be controlled linearly by making use of an electric motor. Further, the control unit 106 which controls engine operating conditions is mounted on the outer wall of the air cleaner 101. Accordingly, the control unit 106 is cooled by the inlet air and a thermal effect thereon from the engine 150 is reduced. Further, the replacement work of the control unit 106 in service stations is facilitated and the serviceability of the motor vehicle is further improved. Still further, the auxiliary air intake passage 113 accommodating the auxiliary air control valve 109 is also integrated in the air intake arrangement of the present embodiment, piping lines such as by rubber hoses are eliminated and the production cost of the arrangement is reduced. Still further, although the above air intake arrangement can be constituted by combining respective separately manufactured functional elements, preferably as many as possible are manufactured by one-piece molding such as with a synthetic resin, so that the manufacturing cost thereof is further reduced. Fig.31 through Fig.34 show another structural embodiment. These figures correspond respectively to Fig.27 through Fig.30 of the previous structural embodiment and the same reference numerals are used as in the previous structural embodiment for designating the same or equivalent elements. In the present embodiment, the throttle valve 103 is located outside the respective independent branching air intake conduits 105. With this structure, the volume of the air filter 101a is increased and the resistance for the intake air flow is decreased, thereby the engine output can be raised. Further, the one-piece molding of the respective functional elements is further facilitated. Further, the control unit 106 is mounted on the inside of the air cleaner 101. With this structure, the control unit 106 is further forcedly cooled by the inlet air, moreover since the control unit 106 is located downstream of the air filter 101a the control unit 106 is hardly subjected to such as water splashes and dusts, thereby the reliability of the control unit 106 is further enhanced. Further the replacement work of the control unit in the service station is made easier like that for the air filter 101a. Further, in the above two structural embodiments, when the air intake arrangement is combined with the engine after completing the same as one sub-assembly unit, the efficiency of the assembling work is further improved. Through the provision of the auxiliary gas passage through which a plurality of gases are introduced other than the main passage of the air intake conduit and of the outlet port thereof near the air intake valve, the direction of the auxiliary gas passage with respect to the main air intake passage can be freely set, and the amount of auxiliary gas can be controlled by the control valve even during the engine operation, thereby the strength of the induced gas swirl can be freely varied in a wide range in comparision with the conventional arrangement. Since the gas swirl inducing means of the present invention requires no intake air control valve and helical port provided in the main air passage as required in the conventional arrangement, namely, elements constituting a resistance to the intake air flow in the main air passage during the engine full load operation are eliminated, a reduction of engine output is suppressed. Since the inner volume of the auxiliary gas passage is determined smaller than that of the main air passage, a required amount of gas can be supplied promptly to the engine, thereby an engine stability during an idling operation is enhanced and a response characteristic during an idling operation, a torque-up operation and an EGR operation is improved. Since the EGR gas can be introduced uniformly into the respective engine cylinders or can be introduced in the direction so as not to adversely affect the combustion therein, the engine can operates stably under an EGR operation with a large amount of EGR gas. Since the mounting portion, the fuel piping and the air piping for fuel atomization for the fuel injection valve are integrally formed with the air intake conduit, the fuel injection valve can be located near the central axis of the air intake conduit, and the angle formed by the axis of atomized fuel and the central axis of the air intake conduit can be reduced. Further, the air intake conduit can be designed optimally in accordance with the spreading configuration of the atomized fuel so as to reduce the deposition rate on the inner wall of the air intake conduit of the atomized fuel injected from the fuel injection valve. As a result, fuel deposition on the air intake conduit is reduced and the air intake arrangement having a good acceleration response characteristic of fuel is obtained.

Claims: An intake air system for a multi-cylinder internal combustion engine, comprising: an air cleaner housing (101) having an air filter (101a) in an interior portion for purifying the air flowing to a throttle chamber; a surge tank (104) having plural air outlets corresponding to respective cylinders of the engine and having an air inlet; said throttle chamber having a throttle valve (103) and a valve shaft, said valve shaft is projected from an outer wall face of said throttle chamber so that, in use, said throttle valve shaft projects into an engine room; plural independent branching air intake conduits (105) for passing air from the surge tank (104) to the respective engine cylinders; and a valve shaft driving element for driving said valve shaft of said throttle valve (103) and being connected to one end of said valve shaft; wherein said plural independent branching air intake conduits (105) are commonly using a part of an outer wall of said surge tank (104) and form with said surge tank (104) an air intake module, in a central portion in a longitudinal direction of said air intake module, an air outlet port of said air cleaner housing (101) and an air inlet of said air intake module are connected by a straight conduit member disposed perpendicularly to said longitudinal direction of said air intake module, wherein an outer periphery of said straight conduit member is exposed to said engine room; to said straight conduit member said throttle valve (103) and said throttle shaft are installed, wherein with this construction said straight conduit member forms said throttle chamber, and further to one end of said throttle shaft said valve shaft driving element is installed; and wherein said air intake module, said straight conduit member being said throttle chamber and said air cleaner housing (101) are formed independently and are assembled. An intake air system for a multi-cylinder internal combustion engine, comprising: an air cleaner housing (101) having an air filter (101a) in an interior portion for purifying the air flowing to a throttle chamber; a surge tank (104) having plural air outlets corresponding to respective cylinders of the engine and having an air inlet; said throttle chamber having a throttle valve (103) and a valve shaft, the throttle valve (103) is supported rotatively by said valve shaft, said valve shaft is projected from an outer wall face of the throttle chamber, so that, in use, said throttle valve shaft projects into an engine room; plural independent branching air intake conduits (105) for passing air from the surge tank (104) to the respective engine cylinders; and a valve shaft driving element for driving the valve shaft of the throttle valve (103) and connected to one end of said valve shaft; wherein said throttle chamber is connected directly to said at least one air inlet of the surge tank (104); the plural independent branching air intake conduits (105) are mounted integrally on the surge tank (104) around a circumference of the surge tank (104) as an air intake module and are commonly using a part of the outer wall face of the surge tank (104); an upper portion of said air intake module forms an outer wall thereof and is a part of an inner wall of said air cleaner housing (101); said air inlet of said air intake module is positioned at an end portion in a longitudinal direction of said air intake module and is formed to an outer wall portion of the air intake module to which an inner wall portion of the air cleaner housing (101) is formed, wherein said air outlet of said air cleaner housing (101) is formed at a position being opposed to said air inlet of said air intake module, wherein a straight conduit member disposed perpendicularly to said longitudinal direction of said air intake module connects said air outlet portion of said air cleaner housing (101) and said air inlet of said surge tank (104), wherein an outer periphery of said straight conduit member is exposed to said engine room; to said straight conduit member the throttle valve (103) and said throttle shaft are installed, wherein with this construction, said straight conduit member forms said throttle chamber, and further to one end of said throttle shaft said valve shaft driving element is installed; and wherein said air intake module including a part of said air cleaner housing (101), said straight conduit member forming said throttle chamber and a remainder of said air cleaning housing (101) are formed independently and are assembled. The system according to claim 1 or 2, wherein the air intake conduits (105) are provided for elongating the length of the air intake path in order to increase engine torque during a low engine revolution speed. The system according to claims 1 to 3, wherein an intake air valve (111) is provided in the air intake conduits (105). The system according to claim 4, wherein the intake air valve (111) is opened during a high engine revolution speed and is closed during a low engine revolution speed.

Inventors: FUJIEDA MAMORU, KEMMA SHIGEYUKI, KURIHARA NOBUO, NOGI TOSHIHARU, OHSUGA MINORU, OHYAMA YOSHISHIGE, YAMADA HIROYUKI, YAMAGUCHI JUN ICHI, FUJIEDA, MAMORU, KEMMA, SHIGEYUKI, KURIHARA, NOBUO, NOGI, TOSHIHARU, OHSUGA, MINORU, YAMAGUCHI, JUN'ICHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1993
Main classification: F02M35
IPC codes: F02B31, F02B27, F02M25, F02M35, F02F1, F02D21