Abstract:
A motorcycle carries a multiple cylinder overhead cam shaft V-type engine whose cylinders are inclined in the plane of longitudinal (forward) movement of the vehicle. One cylinder (preferably the forward cylinder) is laterally offset to the right, and the other is laterally offset to the left. An overhead cam shaft is provided for each cylinder, and is driven by a drive located on the respective cylinder on the outside, in the direction of offset. An ignition plug and its cord are mounted on the opposite side, whereby to be shielded from obstacles by structure associated with the neighboring cylinder.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a vehicular overhead cam shaft type V-engine which has its respective cylinders inclined in the longitudinal direction, and which is arranged to protect vulnerable parts from damage. 
     BACKGROUND OF THE INVENTION 
     An engine of V-type, in which two cylinders are inclined in the longitudinal direction, has its front and rear cylinders offset in the transverse direction. In the V-engine, more specifically, in order that the enlarged end portions of the connecting rods of the paired front and rear cylinders may be hinged to a common crank pin, the cylinder, which has its larger connecting rod end portion hinged to the righthand side of the crank pin, is offset in the rightward direction, whereas the cylinder, which has its larger connecting rod end portion hinged to the lefthand side of the crank pin, is offset as a whole to the leftward direction. The V-engine thus constructed and equipped with the overhead cam shafts has to be equipped with an overhead cam shaft driving mechanism at either the right or left side of each cylinder. Therefore an ignition plug has to be arranged to protrude from the opposite side to the corresponding overhead cam shaft driving mechanism in order that it can be mounted and demounted. The ignition plug is connected with a plug chord, and, if this plug chord excessively protrudes sideways outwardly, it may make contact with an obstacle, when the driver walks his vehicle, whereby the plug chord or the ignition plug may be broken by the obstacle. 
     The present invention has been conceived in view of the background thus far described and contemplates to provide a vehiclular ovehead cam shaft type V-engine which has its ignition plugs and plug chords placed where they are protected from being struck by obstacles. 
     In order to attain the aforementioned contemplation, the present invention is constructed such that two cylinders are inclined in the longitudinal direction of a vehicle, and overhead cam shaft driving mechanisms are arranged in the rightward and leftward offset sides of the two cylinders, and ignition plugs are arranged to protrude obliquely from the opposite sides of the two cylinders to said offset sides so as to be sheltered by the adjacent cylinder. The present invention will now be described in detail with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side elevation showing a motorcycle, on which an engine according to the present invention is installed, with a portion being omitted; 
     FIGS. 2 and 3 are sections taken along lines II--II and III--III of FIG. 1; 
     FIG. 4 is a top plan view showing the motorcycle with its portion being similarly omitted; and 
     FIG. 5 is a view taken in the direction of arrow A from FIG. 1 for showing the relative positions of front and rear cylinders. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In these Figures, reference numeral 1 indicates a frame, which is constructed by welding a pair of frame members at their circumferential edges into a drum shape and which has its front end welded to a steering head pipe 2. To this steering head pipe 2, there is attached a front fork which is used to support a not-shown front wheel. The rear portion of the frame 1 is bent downward and formed with an opening 3. In this opening 3, there is mounted a not-shown air cleaner so that atmospheric air is introduced into the frame 1 through those air cleaner and opening 3. In other words, the inside of the frame 1 forms an intake passage through which intake air is introduced from the air cleaner into later-described carburetors 26 and 27. Indicated at numeral 4 are a pair of right and left brackets (only the left one of which is shown in FIG. 1) which are fixed to the rear end of the frame 1 and to which the rear end portion of a later-described engine 20 is fixed. Indicated at numeral 5 is a rear arm having a generally triangular shape, as viewed in a side elevation, which has its front end portion hinged to the aforementioned brackets 4 and its rear end portion supporting a rear wheel in a rotatable manner. Moreover, the lefthand bottom side 5a of that rear arm 5 is formed into a pipe shape while having its rear end connected to a rear hub case 7. In this hub case 7, there is mounted a reduction gear mechanism which is composed of a bevel gear, and a propeller shaft is received to extend through the bottom side 5a so that a well known shaft drive type rear wheel driving mechanism is constructed. To the vertex 5b of the rear arm 5, there is hinged the rear end of a cushion unit 8, which has its front end received axially in a recess 9 (as shown in FIG. 4) formed in the aforementioned frame 1. 
     Numeral 20 indicates an overhead cam shaft type V-type air-cooled two-cylinder engine which has its two cylinders 21 and 22 inclined in the longitudinal direction. In this engine 20, the upper portion of the front cylinder 21 and the upper portion of the rear cylinder 22 are attached to the afore-mentioned frame 1 through elastic members (not shown) by means of brackets 23 and 24, respectively. On the other hand, the engine 20 has its crank case 25 fixed at its rear end portion to the bracket 4, as has been described hereinbefore. The respective cylinder 21 and 22 have their facing sides formed with respective intake ports which are connected with the carburetors 26 and 27 positioned in the space defined between the respective cylinders 21 and 22. The carburetors 26 and 27 have their upstream sides further connected with the aforementioned frame 1. As a result, the intake air having entered the frame 1 from the aforementioned opening 3 are introduced through the frame 1 into the carburetors 26 and 27 of the respective cylinders 21 and 22. Numerals 28 and 29 indicate exhaust pipes which are connected to the front and rear sides of the respective cylinders 21 and 22. 
     In FIG. 2, numerals 40, 41 and 42, 43 and 44 indicate a crankshaft, main and auxiliary shafts forming a part of the reduction gear mechanism, a damper shaft, and an output shaft, respectively. The rotations of the crankshaft 40 are transmitted through a well known wet type multiple disc clutch 45, which is attached to the righthand end portion of the main shaft 41, to this shaft 41, the rotations of which in turn are transmitted to the auxiliary shaft 42 after having their speed changed by reduction gear train 46 which is mounted on the main shaft 41 and the auxiliary shaft 42. The rotations of the auxiliary shaft 42 are further transmitted through a damper 47, which is arranged on the damper shaft 43, to this shaft 43, the rotations of which in turn are transmitted through a bevel gear 48 to the output shaft 44 arranged to extend in the longitudinal direction. The output shaft 44 has its rear end portion protruding backwardly of the crankcase 25 such that its protrusion is connected to the aforementioned propeller shaft (although not shown) through a universal joint. 
     Numerals 50a and 51a indicate the piston and connecting rod of the front cylinder 21, whereas numerals 50b and 51b indicate the piston and connecting rod of the rear cylinder 22. As is apparent from FIGS. 2 and 3, the enlarged end portion of the connecting rod 51a of the front cylinder 21 and the enlarged end portion of the connecting rod 51b of the rear cylinder 22 are hinged together to a crank pin 52 such that the connecting rod 51a is positioned adjacent to the righthand side of the other connecting rod 51b. As a result, the front cylinder 21 is offset in the rightward direction whereas the rear cylinder 22 is offset in the leftward direction. 
     In FIG. 2, numerals 53a and 54a indicate the cylinder block and head of the front cylinder 21, and an overhead cam shaft 55a is transversely supported in the cylinder head 54a in a rotatable manner. The righthand side of the front cylinder 21, i.e., the offset side is formed with such a chain passage 56a as provide communication between the insides of the cylinder head 54a and the cylinder block 53a. Numeral 57a indicates a shaft which is attached to the crankcase 25 such that it is positioned between the aforementioned crankshaft 40 and overhead cam shaft 55a. On this shaft 57a, there is rotatably mounted a gear 59a which is made integral with a sprocket 58a and which is in meshing engagement with a gear 60a fixed to the crankshaft 40. The sprocket 58a is positioned in a lower portion of the aforementioned chain passage 56a. To the righthand end of the aforementioned overhead cam shaft 55, on the other hand, there is fixed a sprocket 61a which is disposed in an upper portion of the chain passage 56a. A timing chain 62a is made to run of those sprockets 58a and 61a. In other words, that timing chain 62a constitutes the overhead cam driving mechanism together with the gear 59a and the sprockets 58a and 61a. By this overhead cam shaft driving mechanism, incidentally, the overhead cam shaft 55a is rotated at a half speed of the crankshaft 40 thereby to control the openings of not-shown intake and exhaust valves. 
     Numeral 65a indicates an ignition plug. Numeral 66a indicates a cooling air passage which is formed below the overhead cam shaft 55a and which is opened in the lefthand side of the front cylinder 21, i.e., the opposite side to the offset side of the same. The ignition plug 65a is attached to the lefthand side of the front cylinder 21 in a manner to protrude obliquely from the lefthand opening of that cooling air passage 66a. A plug chord 68a is connected with that ignition plug 65a by means of a plug cap 67a (as shown in FIGS. 1, 4 and 5). 
     Numeral 70a indicates an air communication passage which is formed in the cylinder block 53a such that it is interposed between the cylinder and the chain passage 56a, i.e., between the cylinder and the overhead cam shaft driving mechanism and is elongated to extend in the longitudinal direction. 
     Since the rear cylinder 22 is constructed such that it is bisymmetric to the front cylinder 21, as shown in FIG. 3, its portions corresponding to those of the front cylinder 21 are indicated by adding a letter &#34;b&#34;, for example, the overhead cam shaft of the rear cylinder 22 is indicated at 55b, so that their repeated explanations are omitted here. 
     The front cylinder 21 is not only offset rightwardly, as has been described hereinbefore, but also is equipped with the timing chain 62a at its righthand side. On the other hand, the rear cylinder 22 is not only offset leftwardly but also equipped with a timing chain 62b at its lefthand side. As a result, the rear cylinder 22 has its ignition plug 65b and plug cap 68b hidden behind the front cylinder 21, as is apparent from FIG. 5. Likewise, the ignition plug and cap 65a and 68a of the front cylinder 21 are also positioned inside of the lefthand side of the rear cylinder 22. As a result, even if there exists an obstacle when the vehicle is to be moved forward by the driver, that obstacle will hit the righthand side of the front cylinder 21 before the ignition plug or the like of the rear cylinder 22 so that the ignition plug 65b, the plug cap 67b and the plug chord 68b of the rear cylinder 22 can be effectively protected. On the other hand, since the front cylinder 21 is offset rightwardly, the position of the ignition plug 65a of the front cylinder 21 approaches the side of the frame 1 (or toward the center of the vehicular body), as is apparent from FIG. 4, so that the leftward protrusions of the ignition plug 65a, the plug cap 67a and plug chord 68a from the frame 1 are accordingly reduced. As a result, the ignition plug 65a, the plug cap 67a and the plug chord 68a of the front cylinder are reluctant to be hit by the obstacle. 
     Moreover, since the front cylinder 21 is formed with the air communication passage 70a, the coming air flow passes through that communication passage 70a until it is introduced to the ignition plug 65b of the rear cylinder 22. As a result, the cooling characteristics of the rear cylinder 22 can be improved. 
     According to the embodiment, still moreover, since the rear cylinder 22 is also formed with an air communication passage 70b, the coming air flow also hits the surroundings of the exhaust pipe 29 of the rear cylinder 22 so that the cooling characteristics can be further improved. 
     In the embodiment, incidentally, although the overhead cam shaft driving mechanism is constructed of the timing chain, it may be constructed of the toothed belt, a bevel gear or a train of a plurality of spur gears. 
     As has been described hereinbefore, according to the present invention, since the overhead cam shaft driving mechanisms are arranged at the offset sides of the front and rear cylinders and since the ignition plugs are arranged to protrude obliquely from the opposite sides of the respective cylinders to those offset sides, each of the ignition plugs is not only retracted to the vehicular body from the cylinder having the other ignition plug but also positioned closer to the center of the vehicular body. As a result, the ignition plugs, the plug chords and so on become reluctant to be attacked by an obstacle so that they can be prevented from being broken.