Heat insulating device for an engine exhaust system

A plurality of parallel slanted fins like a louver are formed at a bottom wall of a heat insulating panel located under a catalytic converters with an exhaust pipe for attachment to an engine exhaust system.

BACKGROUND OF THE INVENTION 
This invention relates generally to catalytic converters having exhaust 
pipe attachments for attachment to an internal combustion engine and in 
particular to an improved heat insulating device for such catalytic 
converters. 
During running of an engine driven vehicle, heat developed at an exhaust 
system, particularly at a catalytic converter unit exposed to a high 
operating temperature, amounts to such a degree that dry grass and like 
inflammable materials on a road occasionally burns upon contact with the 
exhaust system. One conventional solution to this is to mount a heat 
insulating element beneath the underside of a converter casing or exhaust 
pipe of the exhaust system, or to enclose those elements in a jacket type 
heat insulating element. 
Such structure however involves several drawbacks: the heat insulating 
element prevents heat from being dissipated to the outside, therefore the 
element itself is heated to an elevated temperature; Since the panel 
directly adjoins to the road surface, water is splashed into a clearance 
between the outer casing wall of the exhaust system and the heat 
insulating element rusting their metal parts, and stones or pebbles are 
liable to be thrown into that clearance causing offensive rattling noises. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention is to provide an improved heat 
insulating element for a catalytic converter of an exhaust system which is 
free from the aforementioned drawbacks and inconveniences. 
Another object of this invention is to provide a heat insulating element of 
the nature described above which enables efficient dissipation of the heat 
transferred from the exhaust system and ventilation of fresh cooling air, 
while preventing water or pebbles or the like from entering the clearance 
between the a catalytic converter and the element and facilitating 
expelling such disturbant substances, if entered, from that clearance. 
According to one important feature of this invention, a heat insulating 
element for a catalytic converter of the nature described above has at its 
wall facing the road a plurality of parallel slanted fins which define an 
opening between the adjacent two of them.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustratively shows the embodiment in which a catalytic converter 
unit 12 located intermediary of an exhaust system 10 is enclosed by an 
envelope-like heat insulating element 20. The element 20 is separated into 
an upper member 21 and a lower member 22 which are both of shallow box 
shape, the latter having a flat bottom wall 23, two side walls 24 and two 
end walls 25 with apertures (no numeral) through which exhaust pipe 13 
extends outwardly. 
With reference to FIGS. 2 to 4, the bottom wall 23 of the lower member 22 
forms a plurality of parallel slanted fins 30 like a louver, which are 
arranged on either side of the converter unit 2 in a row along the side 
walls 24. FIG. 4 particularly shows that each fin is raised toward the 
converter unit 12 forming a horizontal surface 30a parallel with the 
bottom wall 23 and an oblique surface 30b between the horizontal surface 
30a and the bottom wall 23. 
As best seen in FIG. 3, an opening 32 is defined between the horizontal 
surface 30a of any one fin and the part of the bottom wall 23 forming 
another, directly adjoining fin so that the plane containing the opening 
32 is vertical or at least oblique to the road surface. Several or 
preferably half of the openings 32 face to the front of the exhaust system 
10, while the rest of the openings to the rear, the two groups of the 
openings being devided substantially at a center cross line of the 
converter unit. 
Also, the plane containing the openings 32 are not perpendicular to the 
side wall 24 but are slanted by an angle .theta., for instance, 30.degree. 
to 45.degree. with respect to the side wall 24, as shown in FIG. 2. 
Although the directions in which the openings are slanted are different 
and opposite across the center cross line of the converter unit, the same 
slanting direction may be all right. The angle .theta. is suitably 
determined in dependence on a relative position of the openings 32 and the 
side wall 24. 
The afore-described embodiment of this invention offers a number of 
excellent features and advantages, a few of which are mentioned below. 
As already mentioned, the plane containing the opening 32 is vertical or 
oblique to the road surface. This results in that various disturbant 
substances on the road such as water, mud, dry grass and pebbels are 
prevented from entering the space between the exhaust system and the heat 
insulating element. On the other hand, such substances, if already 
entered, are relatively easily expelled out by a high-velocity air flow 
around the heat insulating element inspired by running of the vehicle. 
Since the directions in which the openings are directed are different, 
driving out the heat air to the outside and drawing fresh air into the 
inside both easily take place, effectively cooling the heat insulating 
element. 
Also, the fact that the openings are slanted by an acute angle with respect 
to the side wall yields a significant ventilating effect, because air, hot 
or cool, flowing along the side wall easily enters and is emitted from the 
slanted openings. 
All these features permit the heat insulating element to enjoy an elongated 
service life. 
It may also be noted that in this example, the fins are raised toward the 
exhaust system so that a restricted road clearance of modern automobiles 
is not influenced by provision of the fins. 
According to FIGS. 5 to 7, this preferred embodiment shows a heat 
insulating element 10 of semicylindrical shape which is particularly 
suited for use with an exhaust pipe 13. In practical use, the element 40 
is mounted to enclose a lower part of the exhaust pipe as shown in FIG. 8. 
The cylindrical bottom wall 41 of the element 40 has several pairs of 
step-like slanted fins, each pair consisting of a raised fin 42 and a 
lowered fin 43. Each of the fins forms a horizontal surface 42a and 43a 
and an oblique surface 42b and 43b between the horizontal surface 42a or 
43a and the bottom wall 41 as in the first embodiment. As best seen in 
FIGS. 6 and 7, the horizontal surface 42a of the raised fin is 
substantially laid over the horizontal surface 43a of the lowered fin 43, 
defining an opening 44 therebetween. Formed at the both ends of the 
opening 44 are circular apertures 45 for preventing a mechanical stress 
from being concentrically applied to a narrow area of the edges of the 
opening. 
Formation of the circular apertures is further advantageous in that the 
distance between the horizontal surface and the bottom wall lying one over 
another, that is, the effective area of the opening 44 can be enlarged by 
the radius of curvature of the circular apertures. Besides, the circular 
shape of the apertures is least vulnerable to a crack-shaped breakage at 
the both ends of the opening. 
As is already apparent from FIG. 8, the heat insulating element is 
preferably so mounted to the exhaust pipe that the lateral distance h 
between the element and the exhaust pipe is substantially smaller than the 
vertical distance H between the same. Removal of pebbeles and the like 
through the openings will be further facilitated by this way of mounting. 
It would be readily understood that the basic objects, features and 
advantages previously described in connection with the first embodiment 
can be achieved also by the aforementioned second embodiment. In 
particular, the effect of preventing entrance of pebbles and the like is 
ensured in this embodiment by partially laying the raised and lowered fins 
one over another.