Internal-combustion engines – Charge forming device – Multiple carburetors
Reexamination Certificate
2000-12-12
2002-05-07
Hirsch, Paul J. (Department: 3747)
Internal-combustion engines
Charge forming device
Multiple carburetors
C123S579000
Reexamination Certificate
active
06382196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a V-type two-cylinder engine suitable for being mounted on an all terrain vehicle (referred to as ATV), and a straddle-type four wheel all terrain vehicle on which the engine is mounted.
2. Description of the Related Art
Some motor cycles include V-type two cylinder engines mounted thereon. The V-type two cylinder engine has an advantage over other type engines having the same engine displacement in that a width (dimension in a longitudinal direction of a crank shaft) of the engine can be reduced because cylinders can be placed such that they are partially overlapped seen in a front view (seen from a direction orthogonal to the crank shaft). For this reason, the V-type two-cylinder engine is suitable for a straddle-type vehicle.
In the prior art, there has been proposed an all terrain vehicle on which the V-type two-cylinder engine is mounted. This all terrain vehicle has an engine in which a carburetor is provided between forward and rearward cylinders arranged in V shape and an air cleaner is provided above the carburetor and covered with a cover situated above (see Japanese Laid Open Publication No. Hei. 1-172083). However, with this configuration, the following technical problems arise.
(a) When two carburetors are provided according to placement of respective cylinders to obtain suitable performance for various operating conditions of the all terrain vehicle, it is impossible to place them on an axis parallel to the crank shaft like an inline-shaped engine, because these cylinders are arranged in V shape and placed as having positional difference between them in a direction of the crank shaft. Accordingly, each of the carburetors is independently placed for each of the cylinders at an appropriate position adapted to a position of each of the cylinders.
In this case, it is necessary to set up a throttle lever, a choke lever, and the like for each of the carburetors and provide fixing members having high rigidity and complex shapes for fixing the carburetors at predetermined positions, fixing members for the air cleaner, and a cooperating mechanism for cooperating levers of the carburetors. In this case, the entire intake equipment including the two carburetors has a complex structure and the number of parts is increased. As a consequence, man-hour of assemblies is increased and hence, a manufacturing cost is increased. Japanese Utility Model Application Publication No. Sho 60-66862 discloses such a prior art.
When the V-type two cylinder engine is configured such that the carburetors are placed in parallel on an axis orthogonal to the crank shaft, a distance between an intake port of one cylinder and a venturi bore (exit of fuel-air mixture of an carburetor) of the corresponding carburetor differs from a distance between an intake port of the other cylinder and a venturi bore of the corresponding carburetor. Accordingly, two intake manifolds each connecting the intake port and the venturi bore have different lengths and are curved at the middle thereof. Such a configuration is less preferable to engine performance and a manufacturing cost of the intake manifolds is high because of complex shapes.
(b) Since the all terrain vehicle is limited in space, the air cleaner might be placed immediately above the carburetors such that it covers the carburetors. In case of the all terrain vehicle traveling in atmosphere in which water or mud is flying in all directions, the air cleaner or the like requires any measures to prevent attachment (adherence) of the mud or water to a filter of the air cleaner.
(c) While an air bent tube for making the interior of the carburetor communicate with atmosphere and guiding an opening thereof to a desirable position might be extended below the air cleaner, it is required that a predetermined length of the air bent tube be horizontally placed below the air cleaner. With such a configuration, fuel is accumulated in the horizontally extended portion of the air vent tube and a primary function of the air bent tube for making the interior of the carburetor communicate with atmosphere is impeded. Further, the position of the opening of the air vent tube is restricted by parts around the carburetors.
SUMMARY OF THE INVENTION
The present invention has been developed for the purpose of obviating the above-described problems, and a first object of the present invention is to provide a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle that includes a compact intake equipment having a simple configuration and being manufactured at a low cost, in which a distance between an intake port of one cylinder and a venturi bore of the corresponding carburetor is equal to a distance between an intake port of the other cylinder and a venturi bore of the corresponding carburetor and connecting members and the like for connecting these parts are less curved.
A second object of the present invention is to provide a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle, comprising an air cleaner with improved maintainability and compactness that is capable of reducing attachment (adherence) of water, mud or the like contained in introduced air to a filter, with a compact configuration.
A third object of the present invention is to provide a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle comprising an air vent system of carburetors that is capable of preventing fuel from being accumulated in an air vent tube with a simple configuration and freely setting a position at which the air vent tube is opened in atmosphere and has a superior external design appearance when an air cleaner is placed above the carburetors.
A fourth object of the present invention is to provide a straddle-type four wheel all terrain vehicle on which the above-described V-type two-cylinder engine is mounted.
To achieve the first object of the present invention, there is provided a V-type two cylinder engine of the present invention comprising: cylinders arranged forward and rearward such that they are inclined in V shape; a downdraft carburetor unit placed between the cylinders and including twin venturi bores provided for the respective cylinders and an air vent system making the interior of carburetors communicate with atmosphere; intake manifolds each connecting a venturi bore of each of the carburetors to an intake port of a corresponding cylinder; and an air cleaner placed above the carburetors such that it covers the carburetors, wherein the carburetor unit is placed obliquely seen in a plan view according to positional difference between the cylinders in a direction of a crank shaft of the engine such that the venturi bore of each of the carburetors is closer to the intake port formed in a corresponding cylinder.
In the V-type two cylinder engine so configured, a distance between an intake port of one cylinder and a venturi bore (opening through which fuel-air mixture is supplied from the carburetor to the cylinder) of the corresponding carburetor can be made equal to a distance between an intake port of the other cylinder and a venturi bore of the corresponding carburetor and these distances can be made short. Besides, the intake manifolds are short and less curved. Therefore, this configuration is preferable to improvement of engine performance. Further, the carburetor unit, the air cleaner, and the like are efficiently placed in a space above the engine, which has been conventionally a dead space, and a distance from the air cleaner to the cylinder is short and connecting members for connecting these parts are less curved. Such a configuration, in addition to placement of the carburetors, realizes an efficient and compact intake equipment and a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle.
It is preferable that the carburetor unit is placed obliquely such that the venturi bore of each of the carburetors is situated on an extended line of an intake passage for
Kawamoto Yuichi
Kuji Yasuhiro
Mikasa Masao
Hirsch Paul J.
Kawasaki Jukogyo Kabushiki
Oppenheimer Wolff & Donnelly LLP
LandOfFree
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