V-type engine

[0002] 1. Field of the Invention

[0003] The present invention relates to a V-type engine including a first bank and a second bank which are disposed in a V-shape on opposite sides of a vertical line passing through the center of a crankshaft carried in a crankcase, the banks being formed continuously with the crankcase, and a first piston and a second piston which are fitted in cylinder blocks of the first and second banks, respectively and which are connected to a common crank pin of the crankshaft through first and second connecting rods, respectively.

[0004] 2. Desription of the Related Art

[0005] Such V-type engines are known, as disclosed, for example, in Japanese Patent Application Laid-open No.61-291734.

[0006] Such V-type engine is effective to suppress the entire height of the engine to a low level, while permitting the number of cylinders to be increased by virtue of the inclined attitude of each of the banks, but if the lower portion of the crankcase can be formed at a small depth, the entire height of the engine can be further lowered.

[0007] However, a defined amount of oil corresponding to the capacity of the engine is generally stored in the lower portion of the crankcase. For this reason, there is a certain limit to forming the lower portion of the crankcase at a small depth. Especially, when it is desired that the surface of the oil does not contact with a large end of the connecting rod in order to eliminate the loss of power due to the agitation of the oil during rotation of the engine, it is further difficult to decrease the depth of the lower portion of the crankcase.

[0008] Accordingly, it is an object of the present invention to ensure that the defined amount of oil stored in the lower portion of the crankcase is not agitated by the large end of the connecting rod, thereby preventing the loss of power, and the lower portion of the crankcase can be formed at a small depth, thereby lowering the entire height of the engine and providing a compactness of the engine.

[0009] To achieve the above object, according to a first aspect and feature of the present invention, there is provided a V-type engine including a first bank and a second bank which are disposed in a V-shape on opposite sides of a vertical line passing through the center of a crankshaft carried in a crankcase, said banks being formed continuously with the crankcase, and a first piston and a second piston which are fitted in cylinder blocks of the first and second banks, respectively and which are connected to a common crank pin of a crankshaft through first and second connecting rods, respectively, wherein large ends of the connecting rods, which are connected to the crank pin, are formed so that their lower faces assume a substantially horizontal attitude at a most-lowered position of the crank pin, and a defined amount of oil is stored in a lower portion of the crankcase, so that the oil does not contact with the large ends of the connecting rods.

[0010] With the first feature, the large ends of the connecting rods cannot contact with the surface of the oil stored in the lower portion of the crankcase, thereby making it possible to avoid a loss of power due to the agitation of the oil and to contribute to an enhancement in power performance. Moreover, when the crank pin is brought into the most-lowered position, the distance between a horizontal plane tangent to the lowermost end points of the large ends of the connecting rods and the center of the crank pin can be minimized, and the lower portion of the crankcase for storing the defined amount of oil can be formed at a corresponding decreased depth, thereby lowering the entire height of the engine and providing a compactness of the engine.

[0011] According to a second aspect and feature of the present invention, each of the large ends is comprised of a large end half formed integrally on a connecting rod body and having a semi-circumferential bearing surface conformed to a semi-circumferential surface of the crank pin, and a cap bolted to the large end half and having a semi-circumferential bearing surface conformed to the other semi-circumferential surface of the crank pin, a joint face between the large end half and the cap being formed in parallel to the lower surface of the large end.

[0012] With the second feature, even if the joint face is inclined with respect to an axis of the rod body due to the construction of the large end of the connecting rod, the cap can be maintained in a laterally symmetric shape as in the conventional cap, and the formation and the machining thereof can be achieved easily.

[0013] The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

[0014] FIG. 1 is a cross-sectional front view of a V-type engine according to an embodiment of the present invention;

[0015] FIG. 2 is a sectional view taken along a line 2—2 in FIG. 1;

[0016] FIG. 3 is a front view of a connecting rod in the engine with a portion being sectioned vertically; and

[0017] FIG. 4 is a reference view showing the mentioned V-type engine but with conventional connecting rods assembled thereto.

[0018] The present invention will now be described by way of an embodiment with reference to the accompanying drawings.

[0019] Referring first to FIG. 1, an engine body 1 of a V-type engine is comprised of a crankcase 2, a pair of left and right cylinder blocks 3₁and 3₂integrally formed in a V-shape at an upper portion of the crankcase 2, and cylinder heads 4₁and 4₂bonded to upper ends of the cylinder blocks 3₁and 3₂. The left cylinder block 3₁and cylinder head 4₁constitute a first bank B₁, and the right cylinder block 3₂and cylinder head 4₂constitute a second bank B₂. The banks B₁and B₂are disposed to form an included angle θ of 90° therebetween, and a vertical straight line Y passing through the center of a crankshaft 5 carried in the crankcase 2 is a line bisecting the included angle θ.

[0020] Connecting rods 7₁and 7₂are connected at smaller ends 7s, 7sthereof through piston pins 10₁and 10₂to pistons 6₁and 6₂fitted in the cylinder blocks 3₁and 3₂of the first and second banks B₁and B₂, and at their larger ends 7b, 7bto a common crank pin 5aof the crankshaft 5 (see FIG. 2).

[0021] As shown in FIGS. 1 and 2, a lower portion of the crankcase 2 is formed as an oil reservoir 2ain which a defined amount of oil 11 is stored. An oil pump 15 for pumping the oil 11 to supply it to various portions of the engine E is mounted to an inner wall of the crankcase 2 and is driven through a pair of gears 16 and 17 from the crankshaft 5.

[0022] As shown in FIGS. 1 and 3, the large ends 7bof each of the connecting rods 7₁and 7₂is comprised of a large end half 7b₁integrally formed on a connecting rod body 7aand having a semi-circumferential bearing surface 9₁conformed to a semi-circumferential surface of the crank pin 5a, a cap 7b₂having a semi-circumferential bearing surface 9₂conformed to the other semi-circumferential surface of the crank pin 5a, and a pair of bolts 12, 12 for coupling the larger end half 7b₁and the cap 7b₂to each other. The pair of bolts 12, 12 are inserted through bolt bores 13, 13 in opposite ends of the cap 7b₂and threadedly fastened in threaded bores 14, 14 in opposite ends of the larger end half 7b₁, respectively, so that the pair of bolts 12, 12 are disposed in parallel to each other with the crank pin 5ainterposed therebetween. Each of end faces of heads 12a, 12aof the bolts 12, 12 forms a lower face C of the large end 7b. The lower face C is formed so that it is parallel to a joint face D between the larger end half 7b₁, and the cap 7b₂and substantially horizontal at a most-lowered position of the crank pin 5a. To ensure this, in the case of the V-type engine E, the angle α of inclination of the joint face D and the lower face C with respect to an axis A of the connecting rod body 7ais set at approximately 50°.

[0023] On the other hand, the oil reservoir has such a capacity provided that even when the oil 11 is accommodated in an amount reaching an upper limit level H, the lower face C of the larger end 7bdoes not contact with the oil surface. Reference character L designates a lowest limit level of the oil 11.

[0024] A crank web 5bof the crankshaft 5 is also formed so that it does not contact with the oil 11 in the oil reservoir 2aduring rotation of the crankshaft 5.

[0025] The operation of this embodiment will be described below.

[0026] During operation of the engine E, the oil pump 15 driven from the crankshaft 5 pumps the oil 11 in the oil reservoir 2ato supply it to various portions of the engine E and hence, these various portions can be reliably lubricated.

[0027] On the other hand, the large ends 7bof the connecting rods 7₁and 7₂and the crank web 5bdo not contact with the liquid surface of the oil 11 stored in the oil reservoir 2aand hence, it is possible to avoid the loss of power due to the agitation of the oil 11 by the large ends 7band the crank web 5b, which can contribute to an enhancement in power performance.

[0028] Moreover, the lower face C of the large end 7bof each of the connecting rods 7₁and 7₂is formed so that it is substantially horizontal at the most-lowered position of the crank pin 5a, and hence, when the crank pin 5ais brought into the most-lowered position, the distance S from a horizontal plane tangent to the lowermost end points of the large ends 7bof the connecting rods 7₁and 7₂to the center of the crank pin 5acan be minimized, and the oil reservoir 2ahaving the defined capacity can be provided correspondingly close to the crankshaft 5, i.e., the depth of the lower portion of the crankcase 2 can be decreased, thereby lowering the entire height of the engine and providing a compactness of the engine.

[0029] FIG. 4 shows the V-type engine according to the present invention, to which conventional connecting rods 07₁and 07₂are assembled with a joint face D between a large end half 07b₁and a cap 07b₂being perpendicular to an axis A of a connecting rod body 07a. As can be seen from FIG. 4, in such a case, unless the depth of the lower portion 2aof the crankcase 2 is increased, or the amount of oil 11 stored in the crankcase 2 is decreased, the large ends 07aof the connecting rods 7₁and 7₂agitate the oil 11 during rotation of the crankshaft 5, thereby bringing about a loss of power.

[0030] In addition, according to the present invention, the lower face C of the large end 7bof each of the connecting rods 07₁and 07₂is formed in parallel to the joint face D between the large end half 7b₁and the cap 7b₂constituting the large end 7b. Therefore, even if the joint face D is inclined with respect to the axis A of the connecting rod body 7aas described above, the cap 7b₂can be maintained in a laterally symmetrical shape, as in the conventional common cap and hence, the formation and machining of the cap 7b₂can be easily achieved.

[0031] Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications in design may be made without departing from the spirit and scope of the invention defined in claims. For example, the oil reservoir 2aof the crankcase 2 can be replaced by an oil pan.