Muffler cooling device for V-type engine

A muffler cooling device for a V-type engine which includes an engine cooling fan disposed at an end of a crankshaft. An air guide plate is provided at a part of a duct through which air sucked by the cooling fan flows, and the duct has at least one opening through which the air flows as being guided by the air guide plate. The arrangement is such that the air having flown through the opening is led, through a space surrounded by a V-bank formed by cylinder heads and an intake manifold, to an area in which a muffler and exhaust pipes extending from the cylinder heads to the muffler are arranged.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a muffler cooling device for a V-type 
engine used for working machines such as a ride-on type lawn mower or a 
combine. 
2. Description of the Prior Art 
A cooling device for cooling a muffler of a V-type engine mounted on a 
working machine is shown in, for example, Japanese Patent Unexamined 
Publication No. 62-55410. In the structure shown in this publication, a 
muffler is horizontally fixed to the front or rear end of a chassis on 
which a V-type engine is mounted. The muffler has exhaust gas inlets near 
the left and right ends thereof, and exhaust gas pipes extending from left 
and right cylinders, respectively, of the engine are connected to the 
respective exhaust gas inlets of the muffler. Further, in the structure 
described in this publication, the cooling of the muffler is effected 
solely by an air flow produced by the travel or running of the working 
machine. 
In a working machine in which a muffler thereof is cooled with the 
utilization of the air flow produced by the travel of the machine, as in 
the structure of the abovementioned publication, the cooling of the 
muffler may be made only during travel of the machine. Thus, in the case 
where the working machine is of the type travelling at low speed, or of 
the type operated in a fixed position, the muffler would not be cooled. As 
a result, there is the fear that the muffler will be abnormally hot, and 
that an after-burn phenomenon of unburnt gas may result due to heat 
remaining after the operation of the machine has been stopped. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide a muffler cooling 
device for a V-type engine which is constructed to effectively cool the 
muffler. 
It is another object of the invention to provide a muffler cooling device 
for a V-type engine which provides effective cooling of a muffler and 
exhaust pipes connected thereto even when a working machine on which the 
engine is mounted is not in motion. 
In accordance with the invention, a muffler cooling device for a V-type 
engine which includes an engine cooling fan disposed at an end of a 
crankshaft comprises: passage means for air sucked by the cooling fan, and 
means for guiding a part of the air flowing in the passage means to flow 
from the passage means, through a space surrounded by a V-bank formed by 
cylinder heads and an intake manifold, to an area in which a muffler and 
exhaust pipes extending from the cylinder heads to the muffler are 
arranged. 
Preferably, the guiding means includes an air guide plate provided in the 
passage means. The engine may be a liquid cooled engine having a radiator 
cooled by the cooling fan. Further, the passage means may include a duct, 
and in this case the air guide plate may be formed integral with the duct. 
The exhaust pipes may be conveniently arranged at a location opposite to 
the air guide plate with respect to the V-bank. Further, the exhaust pipes 
may be arranged substantially along a chassis on which the engine is 
mounted. 
According to the invention constructed as described hereinabove, a part of 
the air flowing in the passage means is led into the space surrounded by 
the V-bank and the intake manifold and is discharged to the area located 
opposite to the guiding means with respect to the space. Since a 
carburetor is located behind the intake manifold and hence the cooling air 
flow does not blow directly on the carburetor, the carburetor is prevented 
from being heated even in the case where the temperature of the cooling 
air is relatively high. The air flow having passed through the space 
between the V-bank and the intake manifold is blown against the muffler 
and the exhaust pipes. Further, the air flow which impinges on a chassis 
on which the engine is mounted is dispersed or diffused to cool the 
muffler and the exhaust pipes. 
The other objects, features and advantages of the invention will become 
more apparent from the following description with reference to the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention will now be described by way of example with reference to the 
accompanying drawings. 
FIG. 1 is a partially fragmentary, longitudinal sectional view showing an 
engine body 1, and FIG. 2 is a plan view of the engine body shown in FIG. 
1. A V-type engine is arranged horizontally as shown in FIG. 2. Cylinder 
heads 2, 2 are arranged in a V-shape, and an axis of a crankshaft 7 passes 
through or coincides with a center of a fan 3. Cylinders of the engine are 
arranged horizontally at the same level as that of a crank compartment 4, 
though the cylinders are not shown in FIG. 1. Exhaust pipes 5 extend from 
the cylinder heads 2, 2, one of which is partially fragmentary shown in 
FIG. 1, and are connected to a muffler 6. The fan 3 is arranged at an end 
of the crankshaft 7 for cooling a radiator, and air having been sucked by 
the fan 3 and having passed through the radiator 9 is discharged through a 
duct 10. An air guide plate 11 is provided at a part of the duct 10, and 
the duct 10 has at least one opening for leading therethough an air into a 
space defined between the cylinder heads 2, 2 arranged in a V-shape. An 
intake manifold 12 is arranged between the cylinder heads 2, 2 to define a 
space surrounded on three sides. A carburetor 13 is arranged behind the 
intake manifold 12 and hence air led from the duct, being guided by the 
air guide plate 11, does not blow directly on the carburetor 13. 
The operation of the thus constructed engine will now be described. The 
engine body 1 is mounted and operated on a chassis 14 indicated by a 
two-dotted broken line in FIG. 1. A working tool not shown is mounted on a 
lower end of the crankshaft 7. The fan 3 at the upper end of the 
crankshaft 7 is rotated together with the crankshaft 7 to suck air from 
the upper side of the radiator 9 to cool the latter, and the air having 
passed through the radiator 9 is discharged through the duct 10. Although 
the air flowing through the duct is heated, the temperature thereof is 
much lower than the temperature of the engine exhaust gas. Namely, the 
temperature of the engine exhaust gas in the exhaust pipes 5 is 
700.degree. to 800.degree. C., and the temperature at the outer surface of 
the exhaust pipes 5 is about 450.degree. C. The air branched from the duct 
10, being guided by the air guide plate 11, is led downwardly into the 
space surrounded by the V-bank and the intake manifold 12, and in turn to 
an area in which the exhaust pipes 5 and the muffler 6 are arranged. Thus, 
the exhaust pipes 5 and the muffler 6 are cooled by the air. The air flow 
in the vicinity of the chassis 14 is diffused or dispersed along the 
chassis 14. During travel or running of the working machine, the muffler 6 
and the exhaust pipes 5 are cooled by the air flow caused by the motion of 
the machine. According to the invention, even in the case where the 
working machine is not in motion, the muffler and the exhaust pipes are 
effectively cooled. 
As will be apparent from the foregoing description, the muffler cooling 
device according to the invention includes air guiding means which guides 
a part of the air flowing in the passage for air sucked in by the cooling 
fan to flow from the passage into the space surrounded by the intake 
manifold and the V-bank formed by the cylinder heads of the V-type engine, 
and the muffler and the exhaust pipes are cooled by the air which has 
passed through the space. Thus, the muffler and the exhaust pipes may be 
effectively cooled even when the engine is installed in working machines 
of low running speed. 
Since the muffler is prevented from being excessively heated, the 
occurrence of a disadvantageous after-burn phenomenon due to unburnt gas 
may be avoided after operation of the engine has been stopped. Further, 
since the carburetor is located behind the intake manifold and hence air 
having passed through the radiator is not led directly to the carburetor, 
the troubles such as the boiling of fuel in the carburetor may be avoided 
even when the temperature of the air which has passed through the radiator 
is relatively high.