V-shaped internal combustion engine

Details V-shaped internal combustion engine V-shaped internal combustion engine

1999-11-24

2001-04-10

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Camshaft drive means

C123S054400, C123S192200

Reexamination Certificate

active

06213072

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a V-shaped internal combustion engine, particularly, a V-shaped internal combustion engine having a balancer device for canceling a secondary vibromotive force thereof.
Conventionally, there have been proposed many engines each comprising a sub-chain for driving a balancer device, an oil pump, a water pump and the like in addition to a timing chain for connecting a valve cam on a cylinder head and a crankshaft so as to drive said valve cam (for instance, Japanese Unexamined Patent Publication No. Sho. 62-233423).
For instance, if a plane crank is adopted in a four-cycle V-shaped eight cylinder engine having a bank defining angle of 90 degrees (which is formed between the V-shaped banks of cylinders) in which plane crank axial centers of all crank pins are located on the same plane, operating cycles of two cylinder banks shift 180 degrees, and explosions take place in the respective cylinder banks in an alternate fashion. According to this construction, since explosions on one of the banks are timed at a regular interval, causing no exhaust interference, the plane crank configuration is advantageous in achieving a high output. On the other hand, in the V-shaped eight cylinder engine adopting the plane crank, secondary imbalance is generated by virtue of an inertia force generated in turn by the reciprocating mass of the engine. The direction of the inertia force so generated while the secondary imbalance is being generated becomes similar to that of an inertia force generated in a state in which cylinders of a conventional in-line four cylinder engine are made horizontal when the engine is viewed as a whole. The aforesaid imbalance can, therefore, be compensated for by adopting the theory of the secondary balancer for a conventional in-line four cylinder engine, and rotating in opposite directions to each other two balancer shafts disposed at symmetrical positions with respect to a horizontal plane acting as a center therebetween which bisects the bank defining angle and passes through the center of a crankshaft (refer to Japanese Unexamined Patent Publication No. Hei. 8-193648).
When trying to provide the aforesaid balancer in the V-shaped eighth cylinder engine adopting the plane crank, it is practical to provide the same at a lower portion of one of the cylinder heads so as to be driven by the sub-chain, as shown in the above Japanese Unexamined Patent Publication No. Hei.8-193648.
On the other hand, since with a V-shaped engine having a bank defining angle of 90 degrees two cylinder heads are spaced away form each other relatively wide, it is the normal practice that separate endless power transmission timing belts are provided between the crankshaft and the respective cylinder heads individually therefor. In this case, it is natural that the balancer is disposed such that it does not interfere with an endless power transmission timing belt. In addition, however, in a case where the balancer is driven by means of a chain, the driver chain also has to be disposed such that it does not interfere with the endless power transmission timing belt.
This requires the triple provision of pulleys or sprockets on the crankshaft and due to this the engine tends to be expanded in the axial direction of the crankshaft. This is a first problem in the conventional technique.
However, it is the normal practice that a guide for the valve cam driving timing chain and a guide for the sub-chain are provided separately. In this case, the chains are spaced away from each other so that they do not interfere with each other, and the chain guides have to be enlarged unnecessarily in order to secure support portions for the chain guides, these eventually leading to a problem of the engine being made larger in size and heavier in weight. This is a second problem in the conventional technique.
SUMMARY OF THE INVENTION
The present invention was made with a view to solving the problem inherent in the conventional technique.
It is an object of the present invention to provide a V-shaped internal combustion engine with a balancer device that can be miniaturized so as to be equipped on mass-production vehicles.
The above-mentioned object can be achieved by a V-shaped internal combustion engine having a balance device, the engine according to the present invention, comprising:
a crankshaft;
V-shaped cylinder banks having a bank defining angle of 90 degree;
a first endless power transmission belt for driving a first camshaft member which is provided above a cylinder head of one of the V-shaped cylinder banks;
a first gear interposed between the first endless power transmission belt and the crankshaft;
a second endless power transmission belt for driving a second camshaft member which is provided above a cylinder head of the other of the V-shaped cylinder banks;
a second gear interposed between the second endless power transmission belt and the crankshaft,
a pair of balancer shafts rotating in opposite directions to each other and extending in parallel with an axis of the crankshaft;
a pair of third gears driving the pair of balance shafts respectively; and
a third power transmission belt for connecting the crankshaft and one of the balancer shafts, the third power transmission belt being disposed at a position outside an area interfering with the first and second endless power transmission belts on a plane perpendicular to the axial direction of the crankshaft.
In the above-mentioned construction, it is preferable that the crankshaft comprises a plane crank in which axial centers of all crank pins for relative cylinders are located in a common plane, the V-shape cylinder banks comprise a cylinder block in which an upper block and a lower block thereof are separated from each other with a substantially horizontal plane passing through a center of the crankshaft, one of the pair of balancer shafts which is located in the lower block side is connected to the crankshaft through the third endless power transmission belts, and the other of the pair of balancer shafts which is located in the upper block side is connected to the one of the pair of balancer shafts by intermeshing the pair of third gears with each other in such a manner that the pair of balancer shafts rotate in opposite directions to each other.
The object above can also be attained by an V-shaped internal combustion engine, according to a first aspect of the present invention, having a balancer device with a plane crank in which centers of all crank pins are located on the same plane and having a bank defining angle of 90 degrees, wherein first and second gears
12
are interposed, respectively, between first and second endless power transmission belts (chains
15
) each for driving a camshaft of a cylinder head of each of V-shaped cylinder banks and a crankshaft
7
, wherein a pair of balancer shafts
16
a
,
16
b
are provided at symmetrical positions with respect to a separating plane acting as a center therebetween where an upper block
1
and a lower block
2
of a cylinder block are separated from each other from a horizontal plane passing through a center of the crankshaft
7
in such a manner that axes of the pair of balancer shafts
16
a
,
16
b
become parallel with the crank shaft
7
so that the balancer shafts
16
a
,
16
b
rotate in opposite directions to each other, and wherein the crankshaft
7
and the balancer shaft
16
b
on the lower block
2
side are connected to each other by means of a third endless power transmission belt (a chain
19
), and the balancer shaft
16
b
on the lower block
2
side and the balancer shaft
16
a
on the upper block side are connected to each other by means of third gears
20
a
,
20
b
, whereby the pair of balancer shafts
16
a
,
16
b
are driven to rotate in the opposite directions. According to this construction, the first and second endless power transmission belts for driving the camshafts and the third endless power transmission belt for driving the balancer shaft are prevented from overlapping each other in an axial direction of

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