Abstract:
A suction system for an internal combustion engine having a sub-suction path for generating a swirl of suction gases in a combustion chamber. The sub-suction path is in addition to the main suction path to be opened or closed by a suction valve. More specifically, in a multicylinder internal combustion engine, path portions for constructing the sub-suction path are formed in a cylinder head, a suction manifold and a carburetor such that the sub-suction path is automatically constituted when the carburetor is connected to the cylinder head through the suction manifold, without further connections being necessary.

Description:
This application is a continuation application of Ser. No. 302,230, Sept. 14, 1981, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a suction system for an internal combustion engine, and more particularly to a suction system of the above type, in which a sub-suction path for generating a swirl of suction gas in a combustion chamber is provided in addition to a main suction path to be opened or closed by a suction valve. 
     2. Description of the Prior Art 
     Recently, internal combustion engines for automobiles are required not only to purify the exhaust gas but also to improve the rate of fuel consumption (mileage). For these requirements, exhaust gas recirculation (EGR) and a lean combustion are frequently employed. It is known that in order to prevent the combustion fluctuations and misfiring while satisfying both the requirements for EGR and lean combustion, it is satisfactory to increase the burning velocity. 
     In order to raise this burning velocity, there have been recently proposed several systems, in which a sub-suction path provided separately from a main suction path is designed to inject a gas into a combustion chamber thereby to generate a swirl of the suction gas in the combustion chamber. 
     However, the suction system provided with the sub-suction path is still being developed. In fact, since the suction system according to the prior art uses a variety of different conduits to construct the sub-suction path, it becomes remarkably complex. Furthermore, connecting the conduits becomes troublesome. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a suction system for an internal combustion engine, in which a sub-suction path is constructed without use of any piping outside the conventionally existing parts. 
     A secondary object of the present invention is to provide a suction system for an internal combustion engine, in which a sub-suction path is automatically constituted when a carburetor is connected to a cylinder head through a suction manifold. 
     In order to attain these objects, according to the present invention, the sub-suction path is constituted by a first path portion formed in the cylinder head, a second path portion formed in the suction manifold, and a third path portion formed in the carburetor so that the sub-suction path having its inlet end opened into the flow path of the carburetor and its outlet end opened into the suction port of the cylinder head may be automatically formed when the carburetor is connected to the cylinder head through the suction manifold and so that the sub-suction path is communicated with or cut off from the combustion chamber by means of the suction valve which serves to open or close the main suction path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The accompanying drawing is a schematic view showing one embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the accompanying drawing there is shown an internal combustion engine of the present invention comprising a cylinder 1, a cylinder head 2 and a piston 3, respectively, which define a combustion chamber 4 into which a main suction path 5 is opened. This main suction path 5 is constructed into a path which leads from a suction port 6 formed in the cylinder head 2, a suction manifold 7, a two-barrel carburetor 8 acting as a fuel supply device to an air cleaner 9. 
     The outlet end of the suction port 6, i.e., the open end opened into the combustion chamber 4, is equipped with a suction valve 10, by which the suction port 6 is opened or closed. An exhaust port 11 formed in the cylinder head 2 is opened or closed by an exhaust valve 12. The valves 10 and 12 are opened or closed by the action of a control mechanism which is constructed of return springs 13 and 14, cams 16 and 16 driven by a cam shaft 15 and rocker arms 18 and 19 and so on, so that they are seated upon their respective valve seats 20 and 21 when closed. 
     The internal combustion engine of the present invention has a sub-suction path 22 which has a smaller effective opening area than that of the main suction path 5. The sub-suction path 22 is constructed of: a first path portion 22a formed in the cylinder head 2 and having an injection nozzle pipe 23 pressfitted therein; a second path portion formed in the suction manifold 7; and a third path portion 22c formed in the body 8a of the carburetor 8. The third path portion 22c is bifurcated to form two inlet ends 22d and 22e which are respectively opened into the primary flow path 8b of the carburetor 8. Both the two inlet ends 22d and 22e are spaced in the flow direction of the primary flow path 8b. Specifically, the upstream side inlet end 22d is always opened in the path 8b between the primary venturi portion 8c and the primary throttle valve 8d of the carburetor 8 whereas the downstream side inlet end 22e is opened at such a position as is closed by the primary throttle valve 8d at its closed (i.e., idling) position. 
     The injection nozzle pipe 23 substantially constructing the outlet end portion of the sub-suction path is designed to have a nozzle portion with a reduced diameter at its tip such that it is opened immediately upstream of the suction valve 10. Moreover, the injection nozzle pipe 23 is directed substantially in the tangential direction of the wall of the cylinder 1 so that a swirl of the suction gases is generated around the axis of said cylinder 1 in the combustion chamber 4. The swirling direction is determined such that the suction gases flow to the exhaust port 11 after it has swept an ignition plug (not shown). 
     The exhaust gas is recirculated from an exhaust path to either the main suction path 5 or the sub-suction path 22 via an EGR valve (not shown). The constructions of the EGR path and the EGR valve can be made similar to those of the prior art, and are therefore omitted from the drawing. 
     The first, second and third path portions 22a, 22b and 22c constituting the sub-suction path will be described in more detail. The first path portion 22a is designed to have its one end opened immediately upstream of the suction valve 10, i.e., in the port 6 and in the vicinity of the suction valve 10 and its other end opened in a joint end face 7a to be jointed to the suction manifold 7. The second path portion 22b is designed to have its one end opened in a joint end face 7a to be joined to the cylinder head 2 and its other end opened in a joint end face 7b to be joined to the carburetor 8. The third path portion 22c is designed to have its one end opened in a joint end face 8e to be joined to the suction manifold 7 and its other ends 22d and 22e opened in the flow path 8b of the carburetor 8, as has been described hereinbefore. Thus, communication is established between the first and second path portions 22a and 22b, when the suction manifold 7 is connected to the cylinder head 2. Communication is also established between the second and third path portions 22b and 22c when the suction manifold 7 and the carburetor 8 are connected to each other. By combining the cylinder head 2, the suction manifold 7 and the carburetor 8 in the aforementioned ways, the first, second and third path portions are made to communicate, thus automatically forming the sub-suction path 22. 
     In a multicylinder engine, the second path portion 22b formed in the suction manifold 7 is divided into branches equal in number to the number of cylinders of the engine, each branch being opened in the joint end face to be joined to the cylinder head 2. On the other hand, the cylinder head 2 is also provided with the first path portions of a number corresponding to the cylinder number and is connected to the suction manifold 7 such that the first path portions are respectively coincident with the open ends of the aforementioned branches of the second path portion 22b formed in the aforementioned suction manifold 7. 
     In the internal combustion engine of the present invention, during the suction stroke having the suction valve 10 opened, the combustion chamber 4 is supplied with an air-fuel mixture from the main suction path 5, whereas a gas is injected from the sub-suction path 22 into the combustion chamber 4. By the injection of the gas from the sub-suction path 22, the mixture sucked into the combustion chamber 4 is swirled around the axis of the cylinder 1 so that the burning velocity is accelerated. 
     The number and the open positions of the inlet ends of the sub-suction path are arbitrary so long as the inlet ends of the sub-suction path are opened into the flow path of the carburetor. In fact, in case the sub-suction path is provided with such two inlet ends as are indicated at 22d and 22e and as are opened at the positions according to the embodiment, the gas is introduced, during the idling operation, into the sub-suction path only from the inlet end 22d so that the gas can be injected from the sub-suction path at a relatively low rate matching the mixture supplied to the combustion chamber at a low rate during the idling operation. To the contrary, the gas can be sucked at a high rate into the sub-suction path from both the inlet ends 22d and 22e during a medium load operation in which much EGR is effected so that a stable combustion can be ensured.