Over-head cam type V-type engine

Details Over-head cam type V-type engine Over-head cam type V-type engine

2002-03-07

2002-12-10

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Overhead camshaft

C123S090310, C123S090340, C123S1960CP, C123S1960CP, C123S054400, C184S006900

Reexamination Certificate

active

06491010

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an over-head cam type V-type engine, and more particularly to a V-twin engine comprising a lubricating oil feedback path from the head portion of a cylinder to an oil sump.
2. Description of the Related Art
FIG. 7
is a sectional view showing the structure of a conventional over-head cam type engine for an all terrain vehicle.
As shown in
FIG. 7
, the engine has a crank case
101
and a crank chamber
101
a
is formed in the crank case
101
. A cylinder
102
is provided to extend upward from the upper end of the crank case
101
such that an inner portion thereof communicates with the crank chamber
101
a
. Moreover, a crank shaft
103
is provided to penetrate through the crank chamber
101
a
in a horizontal direction and a piston
104
which reciprocates in the cylinder
102
is coupled through a connecting rod to a portion of the crank shaft
103
which is accommodated in the crank chamber
101
a
. On the other hand, a head portion
102
a
of the cylinder
102
is provided with a cam shaft
105
for driving an intake valve and an exhaust valve (not shown) through a cam (not shown). A cam chain
108
for transmitting the rotation of the crank shaft
103
to the cam shaft
105
and rotating the cam shaft
105
is co-wound on sprockets
107
and
106
provided on one end of the cam shaft
105
and a portion
103
a
of the crank shaft
103
which protrudes toward the outside of the crank chamber
101
a
, respectively. The cam chain
108
is accommodated in a cam chain tunnel
109
formed in the side portion of the cylinder
102
and a chain chamber
101
b
formed in the side portion of the crank case
101
to be connected to the cam chain tunnel
109
and separated from the crank chamber
101
a
through a wall. An oil chamber (not shown) is formed in the crank case
101
to communicate with the lower ends of the chain chamber
101
b
and the crank chamber
101
a
. An oil pump and an oil passage (not shown) are provided to supply a lubricating oil accumulated in the oil chamber to the cam shaft
105
provided in the head portion
102
a
of the cylinder
102
and the like. The reference numeral
110
denotes a belt converter provided on an end of the crank shaft
103
which penetrates through the chain chamber
101
b
and extends toward the outside thereof. The belt converter
110
serves to cause a driver to easily carry out a speed change operation of a vehicle.
In the over-head cam engine having such a structure, the cam shaft
105
or the like is lubricated by the lubricating oil supplied to the head portion
102
a
of the cylinder
102
and the lubricating oil which completes the lubrication is returned to the oil chamber through the chain tunnel
109
and the chain chamber
101
b
. Consequently, the cam shaft
105
or the like is forcibly lubricated.
If the cam shaft structure of the conventional over-head cam engine is to be applied to a engine having two cylinders inclined in opposite directions to each other, it is necessary to provide two sprockets for driving the cam shafts of the two cylinders on the crank shaft. Correspondingly, the length of the crank shaft is increased so that the width of the engine is made greater. There is a cam shaft driving structure in which the cam shafts of the two cylinders are driven through an intermediate shaft by a crank shaft. In such a cam shaft driving structure, the intermediate shaft is provided above the crank shaft to penetrate through the crank chamber and a sprocket for driving the cam shaft of each cylinder is provided in each of portions of the intermediate shaft which protrude toward outsides of the crank chamber, respectively, and only one sprocket for driving the intermediate shaft is provided on the crank shaft. As a result, one sprocket on the crank shaft is omitted, so that the width of the engine can be reduced.
In the cam shaft driving structure, however, if an oil passage extending from the chain chamber to the oil chamber is provided as in the conventional over-head cam type engine, the oil passage is to be formed in both side portions of the crank chamber. For this reason, the size of a crank case is increased, and furthermore, the size of an engine is increased. Moreover, a space in the crank case cannot be utilized effectively.
SUMMARY OF THE INVENTION
In order to solve the above-mentioned problems, it is an object of the present invention to provide an over-head cam type V-type engine which can be small-sized and can efficiently utilize a space in a crank case.
In order to attain the object, the present invention provides an over-head cam type V-type engine comprising a crank case having a crank chamber, a crank shaft provided to penetrate through the crank chamber, a first cylinder and a second cylinder provided in an upper portion of the crank chamber to be positioned on virtual lines extending like a V-shape upward from a center of the crank shaft as seen in an axial direction of the crank shaft, respectively, a cam shaft provided in a head portion of each of the first and second cylinders, an intermediate shaft provided above the crank shaft to penetrate through the crank chamber, a first transmitting means for transmitting a rotation of the crank shaft to the intermediate shaft through a chain at one of end sides of the intermediate shaft, a chain chamber formed adjacently to a side portion of the crank chamber and serving to accommodate the first transmitting means, a second transmitting means for transmitting a rotation of the intermediate shaft to the cam shaft of one of the first and second cylinders through a chain at the other end side of the intermediate shaft, a first chain tunnel for accommodating the second transmitting means, a third transmitting means for transmitting the rotation of the intermediate shaft to the cam shaft of the other cylinder through a chain at one of the end sides of the intermediate shaft, a second chain tunnel for accommodating the third transmitting means, an oil sump formed in a lower portion of the crank case and serving to accumulate a lubricating oil therein, a forcible oil supply means for supplying the lubricating oil from the oil sump to the head portion of each of the first and second cylinders such that each cam shaft is lubricated, a first lubricating oil feedback path formed such that the lubricating oil supplied to the head portion of one of the first and second cylinders flows down into the oil sump through the first chain tunnel and the crank chamber, and a second lubricating oil feedback path formed such that the lubricating oil supplied to the head portion of the other cylinder flows down into the oil sump through the second chain tunnel and the chain chamber.
In this specification, “above” also implies an obliquely upward direction as well as a just upward direction.
According to such a structure, the lubricating oil feedback path utilizes the inner space of the crank chamber, so that a space in the crank case can be saved. Consequently, the space of the crank case can be utilized efficiently. Moreover, the size of the engine can be reduced.
The cylinder may have a skirt portion, the skirt portion being provided to be inserted into the crank chamber, and an inlet hole for the lubricating oil flowing from the first chain tunnel into the crank chamber may be opened in a portion of an internal surface of the crank chamber which is opposed to a peripheral surface of the skirt portion of the cylinder.
According to such a structure, even if the lubricating oil vigorously flows into the crank chamber through the inlet hole, it hits against the skirt portion of the cylinder and is thereby prevented from advancing toward the inside of the crank chamber. Consequently, it is possible to prevent the lubricating oil from splashing on the crank shaft positioned in the crank chamber and its temperature from being raised.
A lubricating oil guide member may be provided on the internal surface of the crank chamber to guide the lubricating oil flowing into the crank chamber from the f

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