Patent Publication Number: US-RE31994-E

Title: Intake system for motorcycle engines having V-shaped cylinder arrangement

Description:
The present invention relates to intake systems for motorcycle engines and more particularly to intake systems for motorcycle engines having V-shaped cylinder arrangements. 
     In a motorcycle having an engine of V-shaped cylinder arrangement, the engine is generally mounted on the frame with the crankshaft oriented transversely with respect to the longitudinal direction of the motorcycle. A space is therefore defined between the fore and aft cylinders and one or more carburetors are disposed in this space. The cylinders are formed with intake ports at the sides facing to the space so as to be connected with the carburetor or carburetors in the space. 
     In this type of motorcycle, an air filter is disposed behind the engine so that intake passages are provided around the aft cylinder. Thus, it has been quite difficult to accomplish a satisfactory intake passage arrangement. In order to avoid this problem, the air filter may be disposed above the engine. However, the arrangement is also inconvenient since an adequate space cannot be provided therefor due to the existence of a fuel tank or other components. 
     It is therefore an object of the present invention to provide an intake system for a motorcycle engine having a V-shaped cylinder arrangement, in which the intake passage arrangement is simplified and the intake efficiency can be improved. 
     Another object of the present invention is to provide an engine intake system which is effective to suppress engine intake noise. 
     According to the present invention, the above and other objects can be accomplished in combination with a motorcycle comprising a frame, an engine mounted on said frame and including at least one fore cylinder and at least one aft cylinder which are arranged in a V-shaped configuration with a space therebetween, each cylinder having intake port means formed at a side facing to the space, carburetor means disposed in said space and connected with said intake port means in the cylinders, said frame having a closed cavity with at least a portion above the engine, said frame being formed with inlet and outlet port means for the cavity, said outlet port means being connected with said carburetor means so that intake air is passed through the cavity in the frame to the carburetor means, and air filter means for passing therethrough the intake air before it is introduced into the carburetor means. 
     In a preferable aspect of the present invention, the air filter means is disposed behind the engine and of a box type configuration having a side cover and a back wall which are connected together to constitute a closed box, said back wall being provided with air inlet and outlet ports and supporting an air filter element disposed between the inlet and outlet ports so that air is passed from said inlet port through the air filter element to the outlet port. According to this arrangement, relatively clean air is introduced into the engine from the inboard side of the motocycle. In a more preferable arrangement, the inlet port of the air filter means is associated with an upwardly directed inlet pipe. This arrangement is effective to avoid induction of relatively warm air which has been heated by the engine. Alternatively, the air filter means may be located in the cavity in the frame. 
     According to a further aspect of the present invention, separate carburetors are provided respectively for the fore and aft cylinders and the carburetors are arranged in transversely aligned or a side-by-side relationship. In this instance, it is preferable to arrange the fore and aft cylinders in positions transversely offset from each other. 
    
    
     The above and other objects and features of the present invention will become apparent from the following descriptions of a preferred embodiment taking reference to the accompanying drawings, in which; 
     FIG. 1 is a partially cut-away side view of a motorcycle embodying the features of the present invention; 
     FIG. 2 is a fragmentary view as seen substantially along the line II--II in FIG. 1; 
     FIG. 3 is a sectional view taken substantially along the line III--III in FIG. 1; 
     FIG. 4 is a sectional view taken substantially along the line IV--IV in FIG. 1; 
     FIG. 5 is a view similar to FIG. 1 but showing another embodiment; and, 
     FIG. 6 is a sectional view taken along the line VI--VI in FIG. 5. 
    
    
     Referring to the drawings, particularly to FIG. 1, the motorcycle shown therein includes a frame 1 comprised of a steering head 12 and a main frame portion 14 which is of a welded structure having an inside cavity 14a therein. An engine 16 which is mounted on the frame 1 is of a V-shaped cylinder arrangement having a force cylinder 18 and an aft cylinder 20 which have a common crankshaft housed in a crankcase 22. To mount the engine 16 on the frame 1, the cylinders 18 and 20 are connected at their top portions to the main frame portion 14 and the crankcase 22 is connected at the rear end portion with a frame member 14b extending downwardly from the rear portion of the main frame portion 14. 
     Referring to FIG. 2 in addition to FIG. 1, it will be noted that the cylinders 18 and 20 have intake ports 24 and 26, respectively, which are provided at sides facing to the space between the cylinders 18 and 20. As shown in FIG. 2, the cylinders 18 and 20 are offset one from the other in transverse direction of the motorcyle. Thus, the intake ports 24 and 26 for the cylinders 18 and 20 are also transversely offset from each other. The intake ports 24 and 26 are respectively connected with carburetors 28 and 30 which are arranged in side-by-side relationship. 
     As shown in FIGS. 1 and 4, the main frame portion 14 of the frame has a side box or air filter assembly 32 mounted thereon at a side thereof in the vicinity of the rear end of the frame. The side box 32 is constituted by an outer cover 34 which is removably connected with a back wall 36 to provide a closed box. An air filter element 38 is disposed in the box and supported by the back wall 36. As shown in FIG. 4, the air filter 38 is of a cylindrical configuration and the back wall 36 is formed with an air inlet port 40 and an air outlet port 42. The inlet port 40 is located outside the cylinder of the filter element 38 and the inlet port 42 within the cylinder of the filter element 38 so that air from the inlet port 40 is passed through the filter element 38 to the outlet port 42. 
     The main frame portion 14 is formed at the rear end portion thereof with an inlet port 44 which is connected through a conduit 46 with the outlet port 42 of the air filter assembly 32. The main frame portion 14 is further formed at the bottom thereof with air outlet ports 48 and 50 so as to face to the space between the fore and aft cylinders 18 and 20. The port 48 is connected as shown in FIGS. 1 and 2 through a conduit 52 with the carburetor 28 leading to the inlet port 24 of the fore cylinder 18. The other port 50 is connected as shown in FIGS. 1, 2 and 3 through a conduit 54 with the carburetor 30 leading to the intake port 26 of the aft cylinder 20. 
     As shown in FIG. 1, the frame 1 carries a fuel tank 56 and a seat 58. A rear arm 64 is swingably connected at the front end with the crankcase 22 by means of a pivot shaft 60 and a rear wheel 62 is carried on the rear arm 64. A rear cushion 66 is provided between the main frame portion 14 and the rear arm 64. 
     According to the structures illustrated and described above, the intake air is passed from the air filter assembly 32 to the inside cavity 14a of the main frame portion 14 and then through the carburetors 28 and 30 respectively to the cylinders 18 and 20. It is preferably to have the inlet port 40 of the air filter assembly 32 connected with an upwardly directed inlet pipe 70 as shown in FIG. 4 because in this arrangement it is possible to prevent warm air heated by the cylinders from entering the engine. The intake passage arrangement can therefore be simplified and it is no longer necessary to provide intake passages around the aft cylinder. Since the cavity in the main frame portion is of a substantial volume, it is possible to attenuate the intake noise. The air filter assembly in the illustrated embodiment is further advantageous in that the side box is effectively utilized to constitute the air filter. The transverse offset arrangement of the cylinders and the side-by-side arrangement of the carburetors provide a compact layout of the components. The intake system in accordance with the present invention is further advantageous in that substantially the same or symmetrical intake passages are provided for the fore and aft cylinders so that intake flow resistances for the fore and aft cylinders become substantially the same and uniform or balanced mixture flow can be ensured for the both cylinders. 
     Referring to FIGS. 5 and 6, there is shown an alternative embodiment of the present invention. Since the basic structure of the motorcycle in this embodiment is the same as in the previous embodiment, corresponding parts are shown by the same reference numerals. In this embodiment, the main frame portion 14 has a side wall 14c wherein an inlet port 44 if formed. On the inner surface of the side wall 14b, there is mounted an air filter element 38 which surrounds the inlet port 44. At the other side of the main frame portion 14, there is formed an opening which facilitate installation of the filter element 38. A cover 70 is provided to close the opening. Thus, in this embodiment, the air filter element 38 is mounted within the cavity and intake air is passed from the inlet port 44 through the air filter element 38 as shown by arrows in the drawings. 
     The invention has thus been shown and described with reference to a specific embodiment, however, it should be noted that the invention is in no way limited to the details of the illustrated structures but changes and modifications may be made without departing from the scope of the appended claims.