Cylinder head structure for V-type engine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a cylinder head structure for a V-type engine. 
     2. Description of the Prior Art 
     In Japanese unexamined patent publication No. 58(1983)-119929, there is disclosed a cylinder head for a V-type engine in which camshafts are rotatably supported in the respective cylinder heads of the left and right cylinder banks to project forward from the front ends of the cylinder heads, cam pulleys are mounted on the projected portions of the camshafts, a chain belt is passed around the cam pulleys and a crank pulley to drivingly connected the crank pulley and the cam pulleys and a chain casing for covering the chain belt is formed integrally with the cylinder heads. 
     In such a V-type engine, the manhour required for part control can be reduced by using identical cylinder heads for the left and right cylinder heads since the left and right cylinder heads are the same in shape. 
     However, since the left and right cylinder heads are symmetrical with respect to the center of the cylinder banks and accordingly the cylinder heads for the respective cylinder banks are reversed in back-front orientation, when the chain casing is formed integrally with the cylinder head, the chain casings are positioned on the front side in one of the cylinder banks and on the rear side in the other cylinder bank, thereby making it difficult to layout of the cam pulley driving system. 
     Further, the width of the cylinder head depends on the width of the chain casing which is generally wider than the cylinder head body, thereby adding to the overall size of the engine. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing observations and description, the primary object of the present invention is to provide a cylinder head structure for a V-type engine which enables the use of identical cylinder heads for the left and right cylinder banks. 
     In accordance with the present invention, there is provided a cylinder head structure for a V-type engine comprising a pair of cylinder head members which are the same in shape and oriented in opposite directions and which are provided in each of the front and rear end wall portions with an opening, camshafts supported for rotation in the respective cylinder head members so that the respective one ends of the camshafts project outside through the openings on the same end of the engine, a cam pulley mounted on the projecting portion of each cam shaft, a transmission belt means for transmitting the driving force of the crankshaft to the cam pulley on each camshaft, a pair of first cover members mounted on the end wall portions of the respective cylinder head members through which the camshafts project to form closed cross section spaces together with the corresponding cylinder head members for covering the transmission belt means, and second cover members mounted on the end wall portions of the respective cylinder heads opposite to the end wall portions through which the camshafts project to cover the openings therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a part of a V-type engine provided with a cylinder head structure in accordance with an embodiment of the present invention, 
     FIG. 2 is a plan view of the same, and 
     FIG. 3 is a cross-sectional view taken along line III--III in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 and 2 which show a V-type engine provided with a cylinder head structure in accordance with an embodiment of the present invention, reference numeral 1 denotes a cylinder block and reference numerals 2 and 3 respectively denote cylinder heads for left and right cylinder banks L and R provided on the cylinder block 1. Three cylinders 4 each are formed between the cylinder block 1 and the left cylinder head L and between the cylinder block 1 and the right cylinder head R. The cylinder row in the right cylinder bank R is forwardly displaced from the cylinder row in the left cylinder bank L as clearly shown in FIG. 2. The cylinder heads 2 and 3 for the left and right cylinders L and R are the same in shape but are reversed in back-front orientation. 
     An intake camshaft 5 for exclusively driving the intake valves for the cylinders 4 and an exhaust camshaft 6 for exclusively driving the exhaust valves for the cylinders 4 are provided above each of the cylinder heads 2 and 3 to extend in parallel to the cylinder row. In the upper face of each of the cylinder heads 2 and 3 are formed bearing portions 7a to 7e for supporting the camshafts 5 and 6, and in the front and rear end wall portions of each of the cylinder heads 2 and 3 are formed semi-circular openings 8 adapted to receive the camshafts 5 and 6. Each of the camshafts 5 and 6 is supported on the bearing portions 7a to 7e so that the front end portion thereof projects forward through the opening 8. As can be understood from comparison of the left and right cylinder banks in FIG. 2, the bearing portion 7a on one end of each cylinder head is retracted away from the corresponding end face and the bearing portion 7e on the other end projects beyond the corresponding end face, and the former bearing portion 7a is forwardly directed in the left cylinder bank L in which the cylinder row is rearwardly disposed with respect to that in the right cylinder bank R as described above while the latter bearing portion 7e is rearwardly directed in the right cylinder bank R. This contributes to reduction of the distance between the bearing portion and the cam pulley, thereby increasing the supporting rigidity of the camshaft. 
     Cam pulleys 9 are mounted on the front end portions 5a and 6a of the camshafts 5 and 6 projecting forward through the openings 8 in the front end wall portions of the cylinder heads. The cam pulleys 9 in each cylinder bank are drivingly connected to the crank pulley 10 by way of a chain belt 11 which is passes around the cam pulleys 9, the crank pulley 10 and a pair of chain guides 11a. 
     On the front side of each of the cylinder heads 2 and 3 is mounted a first cover member 12 to cover the chain belt 11. The first cover member 12 has an opening on the rear side and forms together with the front end portion of the cylinder head a closed cross section space 13 for accommodating therein the chain belt 11. As clearly shown in FIG. 3, the space 13 communicates with a space 13a formed on the front end of the cylinder block 1 between the front end and a cover member 1a mounted thereon, thereby forming a chain chamber for accommodating therein the chain belt 11. Bolt holes for bolts 15 for fixing the first cover member 12 to the corresponding cylinder head are formed along the edge of the opening. Seal surfaces 12a on the left and right sides of the first cover member 12 are bent inwardly behind the chain belt 11 to conform to the width of the cylinder head, and the bolt holes for the bolts 15 are disposed on the inner side of the seal surfaces 12a. 
     A service hole 16 for providing access to the bolts 15 is formed on the front face of the first cover member 12 and a service hole cover 17 is removably mounted on the front face of the first cover member 12. 
     A second cover member 14 is mounted on the rear side of each of the cylinder heads 2 and 3 to cover the rear side openings 8 in order to prevent oil flowing rearward through the spaces between the camshafts 5 and 6 from leaking out. 
     In the embodiment described above, the openings 8 through which the camshafts 5 and 6 project are formed in both the front and rear wall portions of the cylinder heads 2 and 3, the camshafts 5 and 6 are supported so that the front end portions thereof project forward through the forwardly positioned openings 8 and the cam pulleys 9 are mounted on the front end portions of the camshafts 5 and 6 in both the cylinder heads. Accordingly, the crank pulley 10 and the chain belts 11 can be positioned on the front side of the engine, and at the same time, the cylinder heads 2 and 3 may be the same in shape. 
     Further, since the first cover member 12 is separated from the cylinder heads 2 and 3, the width of the cylinder heads 2 and 3 may be smaller than the width of the first cover member 12 by forming the seal surfaces 12a to extend inwardly toward the edge of the opening in the rear face of the first cover member 12. 
     Further, by virtue of the second cover member 14 mounted on the rear ends of the cylinder heads 2 and 3, leakage of oil through the rearwardly positioned openings 8 can be prevented. 
     The bolts 15 for fixing the first cover member 12 to the cylinder head are positioned inside the seal surfaces 12a in the embodiment described above. This is advantageous in that the bolt holes in the cylinder head can be positioned close to each other, and accordingly, the width of the cylinder head can be reduced. 
     Further, maintenance of the chain belt 11, tension adjustment of the chain belt 11 and the like can be easily effected by removing the service hole cover 17.