Abstract: An air/fuel ratio control system for use with an internal combustion engine, which includes a three-way catalyst arranged in the exhaust system of the engine, an electrical circuit operatively connecting an O.sub.2 sensor with fuel quantity adjusting means in a manner effecting feedback control of the air/fuel ratio of a mixture produced by the fuel quantity adjusting means and being supplied to the engine, in response to an output signal produced by the O.sub.2 sensor, and secondary air supply means for supplying atmospheric air into the exhaust system at a zone upstream of the O.sub.2 sensor. The secondary air supply means is adapted to operate only during open loop control of the air/fuel ratio.

Abstract: A motorcycle having an internal combustion engine mounted on a main frame and including suction and exhaust systems, an exhaust gas cleaning means adapted to supply secondary air to the exhaust system for cleaning an exhaust gas flowing therethrough, a carburetor provided in the suction system and provided with a throttle valve therein, and a throttle opener provided on the carburetor and adapted to open the throttle valve slightly while the internal combustion engine is decelerated. A secondary air supply passage is connected to the exhaust system, and a flow rate of the secondary air flowing through the passage is controlled by a secondary air control valve. When a vehicle speed of the motorcycle has decreased to a level not higher than a predetermined level, the secondary air control valve is closed to stop supplying the secondary air to the exhaust system, and the operation of the throttle opener is rendered ineffective simultaneously. This prevents the temperature of the exhaust gas from increasing.

Abstract: An improvement of an exhaust gas cleaning system for an internal combustion engine which is provided with a secondary air feed system connected to an exhaust port and a reed valve device opened on an exhaust pulsation pressure arising in the exhaust port to feed secondary air to the exhaust port.The secondry air feed system has an upstream side secondary air passage through to the atmosphere and a downstream side secondary air passage formed on a thick wall zone of the internal combustion engine proper and connected through to the exhaust port. The reed valve device has a valve casing installed on the circumference of the engine proper, an inflow port connected to the upstream side secondary air passage, and an efflux port connected to the downstream side secondary air passage. The valve casing is partitioned internally into an upstream chamber provided adjacently to the engine proper and a downstream chamber provided on a side away from the engine proper across the upstream chamber.

Abstract: An exhaust gas cleaning device of an internal combustion engine wherein a secondary-air supply passage is connected to an exhaust system of the engine and a reed valve means is provided in the intermediate part of the secondary-air supply passage for opening in response to the pulsation pressure of the exhaust gas in the exhaust system to supply secondary air for cleaning exhaust gas to an exhaust passage and burn the unburnt components present in the exhaust passage thereby to clean exhaust gas. A desired amount of secondary air is supplied to each of a plurality of exhaust systems so that the exhaust gas cleaning efficiency as well as the reliability and durability of the reed valve means are improved and moreover a good external appearance is obtained.

Abstract: An exhaust gas cleaning device of an internal combustion engine, comprising a secondary-air supply system connected to exhaust ports to supply the secondary air for cooling the exhaust gas, and reed valve devices installed in the secondary-air supply system and adapted to be opened and closed by the pulsating pressure generated in the exhaust ports when the engine is in operation. The reed valve devices are mounted on the side surface of the cylinder block, each of which has a reed valve chamber and a reed valve that divides the reed valve chamber into an upstream chamber and a downstream chamber and that is adapted to be opened and closed by the pulsating exhaust gas. The upstream chamber is communicated with the open air via a secondary-air intake pipe, and the downstream chamber is connected to the exhaust port via a secondary-air supply passage.

Abstract: A secondary air introducing apparatus for introducing secondary air into the exhaust manifold of an internal combustion engine. The apparatus includes a secondary air introducing passage connected between the air cleaner and the exhaust manifold of the engine, a check valve in the passage arranged to operate in response to pulsation pressure in the exhaust manifold to supply clean secondary air thereto, a first expansion chamber interposed in the passage on an upstream side of the check valve, and a second expansion chamber interposed in the passage on an upstream side of the first chamber. At least the check valve and the first chamber are fixedly mounted on the intake manifold.

Abstract: An exhaust gas cleaning system for an internal combustion engine including two cylinders arranged in V-shape and an exhaust system having exhaust ports. A secondary air supplying system is connected to the exhaust system for supply of secondary air. Reed valve devices responsive to an exhaust gas pulsation pressure are incorporated in the secondary air supplying system and are opened and closed under the action of exhaust gas pulsation developing during engine operation. The reed valve devices are disposed in a space defined between the two cylinders. The reed valve devices are connected to the exhaust ports through respective secondary air supplying pipes which form a part of the secondary air supplying system. The secondary air supplying pipes are wound so as to surround the respective cylinders.

Abstract: An exhaust gas cleaning system for an internal combustion engine having a cylinder head with a plurality of exhaust valve ports therein associated with respective exhaust valves and an exhaust passage for discharge of exhaust gases to an exhaust system. The exhaust passage is constituted by a manifold exhaust port which is connected to the exhaust system and a plurality of branch ports which branch from the manifold exhaust port and communicate with respective exhaust valve ports. A secondary air passage is directly connected to the respective branch exhaust ports for supplying secondary air thereto in immediate proximity to the exhaust valves. Each secondary air passage is composed of a manifold secondary air passage opening externally of the cylinder head and branch secondary air passages branching from the manifold secondary air passage and communicating with the branch exhaust ports.

Abstract: A secondary air supply system for an internal combustion engine having a supercharger comprises a secondary air supply valve operable in response to the pulsating flow of exhaust gases emitted from at least one of engine cylinders. The remaining engine cylinders are communicated to an exhaust gas purifying device through a supercharger so that the exhaust gases emitted therefrom can drive a turbine of the supercharger. The exhaust gases emitted from such at least one of the engine cylinders are directly supplied to the exhaust gas purifying device in admixture with a secondary air supplied by the valve to facilitate an effective and efficient purification of the exhaust gases as a whole.

Abstract: A motorcycle comprising a frame on which are mounted a fuel tank, a seat, front and rear wheels, and a multi-cylinder internal combustion engine disposed in a space defined by the fuel tank, seat and wheels. The engine has a plurality of exhaust ports open at the front of the engine connected to an exhaust system. An exhaust gas cleaning system is provided for the multi-cylinder internal combustion engine and comprises a reed valve assembly on the engine operating in response to pulsating exhaust pressure in the engine for selectively connecting an upstream secondary air passage connected to an inlet port of the reed valve assembly and a plurality of downstream secondary air passages of substantially equal length connected between outlet ports of the reed valve assembly and corresponding exhaust ports of the engine.

Abstract: An engine includes a three way catalytic converter in its exhaust system, and a carburetor whose throttle valve has a normal and an idle up idling position, selected between by an idle up device. A device for weakening the air/fuel ratio of the mixture in the engine intake system only functions when no oxygen is detected in the engine exhaust system by an oxygen sensor. A means for supplying enough secondary air into the exhaust system upstream of the oxygen sensor to make the exhaust gases leaner than stoichiometric functions according to supply of a controlling vacuum. A first vacuum take out port is provided in the throat of the carburetor at a position downstream of the throttle valve when it is in the normal idling position and upstream of it when it is opened a little from the normal idling position.

Abstract: The present invention relates to a four-cycle internal combustion engine in which a strong swirl can be generated within the combustion chamber through the directionality of the mixed gas supplied from the main suction path and the injection of a gas from the sub-suction path, and a heavier EGR than before can be carried out without detracting the engine performance, and NOx generation can be substantially reduced by EGR alone. In time of idling when a heavy EGR is needless, the gas injection from the sub-suction path is controlled to prevent a misfiring.

Abstract: In a one way non-return valve comprising a cylindrical duct, a cone in said duct with its apex pointing in the direction of flow and provided with a plurality of apertures, and a membrane lying on the downstream surface of the cone and clamped at the outer circumference, the membrane having a central aperture, the improvement which comprises employing a cone having an apex angle of about 140.degree. to 160.degree., the membrane comprising a disk of elastomeric material having a central circular aperture which engages the hollow cone under bias. Advantageously the apertures in the cone are a series of concentrically disposed, round or long-oval apertures, the hollow cone has an apex angle of about 154.degree. and the total area of the apertures in the cone is about twice as great as the area of the aperture in the membrane.

Abstract: A secondary air supply device including a reed valve arranged in a secondary air passage for supplying a secondary air into an exhaust gas passage of an engine through a secondary air cleaner which is provided separately from an intake air cleaner to shorten the secondary air passage as much as possible, comprises two expansion chambers in the secondary air cleaner defined by a cup-shaped support for a casing of the cleaner and a silencer along air cleaner elements and an outer wall of the cleaner, thereby effectively prevent noise by supplying the secondary air through the silencer, the air cleaner elements, the two expansion chambers and the reed valve.

Abstract: A device for supplying air into the exhaust gases of an internal combustion engine to promote complete combustion of carbon monoxide and hydrocarbons for the reduction of atmospheric pollution has a manually operable shut-off valve held open by a spring, which can be operated by a push-button to intercept the supply of air to an air feed pipe when making test measurements on the engine or tuning the carburettor.

Abstract: A four cylinder spark ignition internal combustion engine has an exhaust emission control system including means for admitting fresh air into the exhaust system in order to promote a further combustion of partly burnt components in the gases coming from the combustion chambers, this means include a "reed" valve connected to the exhaust ports leading from the first and fourth cylinders (numbering from one end of the engine) through internal passages within the cylinder head; the system also comprises an exhaust gas recirculating system comprising a pneumatic valve which opens, when the conditions are appropriate, to draw off a proportion of the exhaust gases from the exhaust side of the engine and admit them to the induction side of the engine taking exhaust gases from branches of the exhaust manifold carrying exhaust gases from the second and third cylinders; in addition there is a system for admitting supplementary air to the induction manifold downstream of the carburettor during engine overrun conditions e

Abstract: In an exhaust gas cleaning system wherein secondary air is supplied into the exhaust passage to re-burn the unburnt harmful component in the exhaust gases, a secondary air controlling apparatus for an internal combustion engine is provided. At deceleration of the vehicle, secondary air is interrupted from being fed into the exhaust passage, and is introduced into the intake passage to prevent after-burning in the exhaust cleaning system. When the ignition key is switched off, secondary air is fed into the intake passage to prevent the unburnt gas from flowing out into the exhaust passage. This effect is attained by using a valve operated in response to the negative pressure in the intake pipe to protect the exhaust gases cleaning system and to clean the exhaust gases.

Abstract: An exhaust emission control system for a spark ignition internal combustion engine comprises a first pressure sensitive valve for recycling a proportion of the exhaust gases from the exhaust to the induction when the engine is warm, being inhibited when the engine is cold, valves for admitting a small amount of fresh air to the exhaust manifold, a second pressure sensitive valve for admitting fresh air to the induction manifold downstream of the carburettor when the engine is warm, being closed when the engine is cold and when the starter motor is energized, a first fuel/air mixture enrichment valve in the carburettor sensitive to induction manifold pressure and de-sensitized when the engine is cold, a second fuel/air mixture enrichment valve sensitive to induction manifold pressure and de-sensitized when the engine is hot, and a vacuum advance delay which is by-passed when the engine is warm.

Abstract: An exhaust gas purifying apparatus having an exhaust pipe divided into at least two branches each connected to a different cylinder or cylinders. Each of the exhaust pipe branches is further connected to a secondary air supply tube to intermittently supply secondary air upstream of a three-way catalyst disposed in the branch thereby to vary periodically within a range the air-fuel ratio of exahust gases flowing into the three-way catalyst.

Abstract: A cylinder primary air filter element is coaxially disposed within a cylindrical shell between an air intake pipe and an outlet provided in the shell. A resilient secondary air filter element is deformably secured in an opening formed in a sidewall of the shell so as to be located outside the outer periphery of the primary air filter. The secondary filter element is secured in place by a filter element retaining plate which is arcuately shaped so as to be concentric with the primary filter element and is readily detachably attached to the shell. A sufficiently enlarged air flow passageway is thus defined between the outer periphery of the primary air filter element and the filter element retaining plate and consequently the resistance encountered by the air flowing through this passageway may be considerably reduced and the excessive bulging of the air cleaner may be avoided. A reed valve assembly is connected to the outlet of a housing which surrounds the secondary filter element.

Abstract: An exhuast gas purifying apparatus for use in an automobile multi-cylinder engine of the type which has exhaust ports communicating with engine cylinders and through which exhaust gases are emitted subsequent to combustion of an air-fuel mixture. The exhaust gas purifying apparatus comprising a reducing catalyst unit and a three-way catalyst unit which are disposed in a main exhaust manifold which is connected at one end to a first group of the exhaust ports and at the other end to the atmosphere, and an auxiliary exhaust manifold connected at one end to a second group of the exhaust ports and at the other end to a portion of the main exhaust manifold at a location downstream of the reducing catalyst unit and upstream from the three-way catalyst unit. A pressure operated valve is disposed in a secondary air supply passage for introducing a secondary air into the auxiliary exhaust manifold by the utilization of the pulsating flow of the exhaust gases through the auxiliary exhaust manifold.

Abstract: For use in an automobile multi-cylinder engine having exhaust port ducts leading from engine cylinders and through which exhaust gases are emitted subsequent to combustion of air-fuel mixture, an exhaust gas purifying apparatus which has a reducing catalyst unit and an oxidizing catalyst unit disposed in a main exhaust manifold connected on one hand to a first group of the exhaust port ducts and on the other hand to the atmosphere, and an auxiliary exhaust manifold connected on one hand to a second group of the exhaust port ducts and on the other hand to a portion of the main exhaust manifold at a position downstream of the reducing catalyst unit and upstream of the oxidizing catalyst unit. The apparatus further has a pressure operated valve disposed in a secondary air supply passage for introducing secondary air into the auxiliary exhaust manifold by the utilization of a pulsating flow of the exhaust gases through the auxiliary exhaust manifold.

Abstract: For use in an automobile multi-cylinder engine having exhaust ports leading from engine cylinders and through which exhaust gases are emitted, an exhaust gas purifying apparatus comprising a reducing catalyst unit and an oxidizing catalyst unit disposed in a main exhaust manifold communicated through exhaust ducts to a first group of the exhaust ports and, on the other hand, to the atmosphere, an auxiliary exhaust manifold communicated to a second group of the exhaust port and, on the other hand, to a portion of the main exhaust manifold at a position intermediately between the reducing and oxidizing catalyst units, a secondary air supply passage extending from a source of secondary air to the auxiliary exhaust manifold, and an additional secondary air supply passage extending from the secondary air source to any one of the collecting ducts communicated to the exhaust ports of the first group.

Abstract: An exhaust gas purifying apparatus, for use in an automobile multi-cylinder engine of the type which has exhaust port ducts leading from engine cylinders and through which exhaust gases are emitted subsequent to combustion of an air-fuel mixture, the exhaust gas purifying apparatus having a reducing catalyst unit and an oxidizing catalyst unit disposed in a main exhaust manifold which is corrected on one side, to a first group of the exhaust port ducts and, on the other side to the atmosphere, an auxiliary exhaust manifold is connected, on one side to a second group of the exhaust port ducts and on the other side to a portion of the main exhaust manifold which is downstream from the reducing catalyst unit and upstream of the oxidizing catalyst unit.

Abstract: A sufficient amount of secondary air is supplied to the exhaust gases without requiring numerous supply tubes. The supply tubes are connected to the longest branch of the exhaust manifold or the exhaust port passage to which the longest branch is connected where the inertial flow of the exhaust gases is greatest. A mass of the exhaust gases recirculated to the intake through a recirculation tube is prevented from being admixed with the secondary air. The recirculation tube is connected to the branches of the manifold exclusive of the longest branch.

Abstract: An exhaust gas purification system for internal combustion engine having a thermal reactor interposed in the exhaust passage. The thermal reactor comprises a heat insulated inner shell for defining a reaction chamber therein and a core shell provided in the core shell spaced therefrom for providing a space between the both shells. A pair of exhaust pipes communicating with the exhaust valves of the engine are inserted into the core shell through an opening of the core shell so as to form a confluence and constant swirling of the exhaust gases in the core shell to provide a high temperature zone in the center of the swirling. The opening of the core shell is narrowed for preventing high temperature zone from moving out of the reaction chamber.

Abstract: The secondary air supply system of an internal combustion engine is provided with two reed valves through which atmospheric air is induced to the exhaust system of the engine. The two reed valves are selectively maintained operable under low and high engine speed operating conditions, respectively.

Abstract: A reed valve assembly in which a gummous material coating is applied to the noise-propagating passageway of a secondary-air exhaust gas recombustion system for internal combustion engines.

Abstract: Hemispherical combustion chambers of a cross flow type cylinder head, having symmetrically disposed and synchronously sparked plugs are fed a near stoichiometric air fuel mixture containing up to 40% EGR gas which after combustion is exhausted through individual ports, mixed with secondary air supplied by a simple reed valve and oxidized in a catalytic converter.

Abstract: Disclosed is a secondary air feeding device for feeding secondary air into the exhaust passage located upstream of the catalytic converter. A diaphragm type secondary air control valve is provided for usually controlling an amount of secondary air fed into the exhaust passage. Said secondary air control valve stops the feeding operation of secondary air at the time of idling.

Abstract: An exhaust gas purifier for a four-stroke internal combustion engine has a plurality of cylinders consisting of cylinder groups, each of which has at least two cylinders, and the opening durations of the exhaust valves in any one group do not overlap. The exhaust passages of the cylinders of one of the cylinder groups are connected to the atmosphere via a common reed valve.

Abstract: An exhaust gas purification system for internal combustion engines having at least two cylinders of which the port of each exhaust valve communicates with a port passage provided in the cylinder head, and a pair of the adjacent port passages communicate with a common port passage forming a siamese port passage therewith. A secondary air intake passage having a check valve communicates with the port passages for introducing secondary air by exhaust pulsation. In order to enhance the exhaust pulsation effect, the exhaust pipe connected to the opening of the common port passage has a constant cross section of a fixed diameter. Heat insulation is provided along the siamese port passage and a portion of the exhaust pipe for good oxidation of the unburned constituents. The total volume of the exhaust passage through the siamese port passage and the heat insulated exhaust pipe portion is equal to the displacement volume of the corresponding cylinders for introduction of a sufficient amount of the secondary air.

Abstract: A catalytic exhaust cleaning device for a high-power multi-cylinder engine of the type including independent carburetors and exhaust pipes for the respective cylinders. The exhaust pipes are interconnected for fluid communication therebetween at locations upstream of the respective catalytic converters arranged therein so that the latter are evenly fed with exhaust gases of substantially the same composition and volume and with substantially equal amounts of secondary air and operate effectively with substantially the same high efficiency. The exhaust communicating pipe interconnecting two adjacent exhaust pipes is divided into two sections, which are fixed at one end to the respective exhaust pipes and held at the other end in aligned abutting relation by a radially expansible tubular joint member, which is fixed to one of the two pipe sections and clamped against the other section.

Abstract: An exhaust gas purification system for use in an internal combustion engine equipped with a dual exhaust system. The exhaust gas purification system includes a secondary air supplying port of a secondary air supplying passage opened into a selected exhaust pipe belonging to one of first and second exhaust pipe groups, while an exhaust gas deriving port of an exhaust gas recycling passage for recycling the exhaust gases to a downstream of the carburetor throttle valve is provided in another exhaust pipe belonging to the other of the first and second exhaust pipe groups for effective suppression of NO.sub.x through accurate control of the amount of exhaust gases to be recycled.

Abstract: An exhaust line including an exhaust pipe assembly, a reactor for oxidizing hydrocarbons and carbon monoxide, a main muffler and a mechanism for drawing secondary air from the atmosphere into the exhaust line upstream of the reactor based on the pulsation of the exhaust pressure, wherein a front tube of the exhaust pipe assembly for passing the exhaust gas from the engine to the reactor has a smaller cross-sectional area than a center tube connecting the reactor to the main muffler, so that the pulsation is of a great magnitude even at an engine speed where the pulsation is in an anti-resonance state.

Abstract: Disclosed is an air cleaner for use in an internal combustion engine. The air cleaner has an air filter element and a secondary air filter element therein. Secondary air is fed into the exhaust system of the engine from the air cleaner via the secondary air filter element and a reed valve for promoting the oxidation of unburned HC and CO components in the exhaust gas. A partition is disposed on the circumferential wall of the casing of the air cleaner and is arranged so as to extend along approximately half of the circumferential wall. A secondary air passage is formed between the partition and the circumferential wall. The secondary air filter element and the secondary air inlet are disposed in one end of the secondary air passage. The other end of the secondary air passage opens into the atmosphere. A plurality of holes are formed on the partition and are equiangularly arranged along the circumferential wall.

Abstract: An internal combustion engine employing a siamesed exhaust port arrangement is equipped with a secondary air supply system which is arranged to induct atmospheric air into the exhaust system of the engine in response to the pressure pulsation in the exhaust port. At least two air injection nozzles are disposed open to portions of the exhaust port where they are not affected by the interaction of the pressure pulsations caused by the strokes of two adjacent engine cylinders.

Abstract: Disclosed is an internal combustion engine provided with a charcoal canister for absorbing evaporative fuel issued from the fuel tank and/or the float chamber of the engine. A pipe is provided between the canister and the intake manifold which is always located downstream of the throttle valve of the engine, for desorbing the absorbed evaporative fuel by the flow of purge air which flow is formed in the canister under the influence of a vacuum existing in the intake manifold. Thus, the evaporative fuel can still be introduced into the engine even if the throttle valve is in its idle position.

Abstract: An exhaust pressure responsive flow control valve is disposed in a secondary air supply passageway leading from the atmosphere to engine exhaust system. The valve has a valve member of a material which is movable by influence of magnetic fields and an electromagnet means for urging the valve member toward a valve closed position upon passing of electric current therethrough. First circuit means is provided which permits a relatively large current through the electromagnet when the exhaust gas temperatures are so high as to overheat the exhaust reactor or converter closing the valve to block secondary air supply through the passageway. Second circuit means is provided which permits a relatively small current through the electromagnet at normal stable operating conditions of the engine to restrict secondary air supply. At acceleration when a relatively large amount of secondary air is required no current is permitted through the electromagnet to open the valve.

Abstract: An internal combustion engine equipped with a catalytic converter for catalytically purifying the exhaust gases discharged from the combustion chambers of the engine. The oxygen-combustibles ratio of the exhaust gases introduced to the catalytic converter is normally controlled to a predetermined level suitable for the reaction within the catalytic converter in response to the composition of the exhaust gases upstream of the catalytic converter. However, the secondary air is continuously supplied to the catalytic converter regardless of the oxygen-combustibles ratio of the exhaust gases during cold start or warmup of the engine to rapidly raise the temperature within the catalytic converter to a level over which the catalytic converter effectively functions.

Abstract: A system for introducing secondary air into gas exhausted from an internal combustion engine of the carburetor type, provided with a three-way catalytic converter in the exhaust system of the engine. The system includes a flow control valve having a diaphragm operated valve member for controlling the amount of secondary air in accordance with electric signals from a .lambda.-sensor arranged in an exhaust system of the engine so that excess air ratio .lambda. of the exhaust gas, which is introduced into the three-way catalytic converter, is controlled near 1.0. Therefore, effective cleaning operation of the three-way catalytic converter is expected.

Abstract: A system for supplying secondary air into the exhaust system of internal combustion engines having in combination two parallel systems, one feeding air depending upon exhaust gas pressure pulsation and the other feeding air depending upon intake vacuum pulsation.

Abstract: A system for supplying secondary air into the exhaust system of internal combustion engines having in combination two parallel systems, one feeding air depending upon the exhaust gas pressure pulsation and the other feeding air depending upon the delivery of an air pump driven by the output power of the engine.

Abstract: A reed valve device having two reeds capable of selectively closing and opening the corresponding openings formed in the device is snugly fitted in a casing through an elastomeric sealing member without using any other connecting means. The casing communicates with an exhaust conduit system of an internal combustion engine so that the reed valve device functions to intermittently admit air into the exhaust conduit system by the pulsations of the exhaust gas under pressure passing through the exhaust conduit system.

Abstract: Secondary air is fed into the engine exhaust gas passageway at a position upstream of an oxygen sensor to cause the electric air-fuel ratio control device and the air-fuel mixture generator to provide an air-fuel mixture having an air-fuel ratio lower than a set desired air-fuel ratio during idle and slow speed running of the engine.

Abstract: An internal combustion gasoline engine for reducing undesirable exhaust emissions, hydrocarbons, carbon monoxide and nitrogen oxides mainly by means of the design techniques for exhaust passages. The present engine comprises two determined regions extending from an exhaust valve downwards in the exhaust passage so as to pass exhaust gases therethrough in their discharging order, one region having a volume permitting self-reaction of unburned constituents of exhaust gases therein at a temperature of the exhaust gases and another having so much volume and sectional area as capable of aspirating air by itself (automatically) through a check valve into the exhaust passage.

Abstract: A non-return air flow system for supplying secondary air into the exhaust system of internal combustion engines by utilizing pulsating flow of exhaust gases in the exhaust system, wherein the critical valve opening pressure for a check valve incorporated in the non-return system is varied in accordance with intake air flow rate of the engine so that supply of secondary air is effected in proportion to air intake of the engine.

Abstract: An internal combustion gasoline engine comprises a determined region which is so formed in an exhaust passage from an exhaust valve to a thermal reactor as to pass exhaust gases therethrough in their discharging order, a secondary air passage with a check valve means communicating with the exhaust port near the exhaust valve, and means for maintaining the temperature of exhaust gases over the trigger temperature of the thermal reactor. The exhaust passage has a volume equal to or more than the displacement of the engine and less than four times the displacement volume and has a cross-sectional area less than three times the opening area of the exhaust valve.

Abstract: The valve-overlapping period of a spark ignition type, four stroke internal combustion engine extends within the range of 60.degree. to 90.degree. of crank angle with the valve overlapping period being generally equally divided to each side of the piston top dead center so that the pressure differential between the exhaust gas passage of the engine and the fuel and air intake passage causes the exhaust gas to counterflow from the exhaust gas passage to the combustion chamber and into the intake passage of the engine with the suction effect of piston descent being negligible when the piston is in the vicinity of top dead center.