Engine exhaust gas cleaning system

An engine exhaust gas cleaning system including a converter section that is disposed at the rear end of the exhaust pipe and which has an outer shell that is surrounded by a further outer shell having a rearwardly disposed atmospheric air inlet and a forwardly disposed atmospheric air outlet that communicates with the inlet of the converter through a venturi section. This heats the air admitted to the converter and also insures that any exhaust sound or exhaust leakage will be disposed rearwardly.

BACKGROUND OF THE INVENTION 
This invention relates to an engine exhaust gas cleaning system and more 
particularly to an improved arrangement for introducing secondary air to 
an exhaust gas catalyzer. 
In order to control the emission of unwanted exhaust gas constituents, a 
wide variety of devices have been proposed. Frequently, catalytic 
converters are employed for treating the exhaust gases before their 
discharge to the atmosphere. As is well known, a catalytic converter must 
be operated at the appropriate temperature in order for it to effectively 
treat the exhaust gases. 
For this reason, it has been proposed to place the catalytic converter as 
close to the exhaust ports of the engine as possible. However, frequently 
a single catalytic converter is not sufficient to provide all of the 
desired exhaust gas treatment. Therefore, it has been proposed to employ 
plural catalytic converters in series along the exhaust system. 
Where this is done, the downstream catalytic converter will receive exhaust 
gases that have been previously treated. A converter in effect causes 
afterburning of the exhaust gases and this is one way in which their 
unwanted exhaust gas constituents are controlled. However, the downstream 
catalytic converter will not receive exhaust gases that are adequate to 
permit afterburning. 
It has, therefore, been proposed to add supplemental air to the exhaust 
system between the upstream and downstream converters so that the 
downstream converter can effectively treat the exhaust gases. One way in 
which this is done is to provide an atmospheric air inlet to the 
downstream catalytic converter which will introduce air to the converter 
so as to permit more effective afterburning. This has been done by 
providing a jacket around the catalytic converter with the upstream end of 
the jacket being in communication with the atmosphere and the downstream 
end being in communication with the converter. This type of system has 
been proposed for use with motorcycles. 
There are a number of disadvantages of this type of system. First, since 
the supplemental air is drawn from the atmosphere, there is a risk that 
the exhaust gases may flow back into the atmosphere through the 
supplemental air passage inlet. This problem can be particularly acute 
where the application is with a motorcycle since the air inlet is in 
proximity to rider of the motorcycle. In addition, exhaust gas sounds to 
emanate can the atmosphere through the supplemental air inlet. 
In addition to the aforenoted defects, the atmospheric air which is drawn 
into the system will be cold and this can detract from the efficiency of 
the converter. That is, the drawing of cold atmospheric air into the 
converter can lower its temperature and make the system inefficient. 
It is, therefore, a principal object to this invention to provide an 
improved engine exhaust gas cleaning system. 
It is a further object to this invention to provide an improved engine 
exhaust gas cleaning system that employs supplemental air for a catalytic 
converter but wherein the supplemental air is drawn in such a way that 
exhaust gas noises and exhaust gases cannot be discharged to the 
atmosphere at an undesirable location. 
It is a further object to this invention to provide an arrangement for 
introducing supplemental air to a catalytic converter wherein the 
supplemental air is preheated. 
It is a still further object to this invention to provide an improved 
silencing system for the supplemental air drawn for a catalytic converter. 
SUMMARY OF THE INVENTION 
This invention is adapted to be embodied in a catalytic convertor for the 
exhaust gases of an internal combustion engine having an exhaust pipe. The 
catalytic converter has a converter section that is supported by an outer 
shell. The outer shell has an inlet portion for receiving exhaust gases 
from the exhaust pipe and an outlet for discharging exhaust gases to the 
atmosphere. A supplemental air conduit is provided for adding atmospheric 
air to the exhaust gases flowing through the converter section. This 
supplemental air conduit has an inlet end that is disposed in proximity to 
the outlet end of the outer shell and a discharge end which is disposed 
upstream of the converter section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring now in detail to the drawings and first to FIG. 1, a motorcycle 
having an exhaust system constructed in accordance with an embodiment of 
the invention is identified generally by the reference numeral 11. 
Although the invention is described in conjunction with a motorcycle, it 
can be used with other types of vehicular applications for internal 
combustion engines. The invention has, however, particular utility in 
conjunction with motorcycles because of their small size and the fact that 
the operator is exposed and will be readily cognizant of exhaust gases 
escaping in his proximity and exhaust noises in his proximity. 
The motorcycle 11 is comprised of a frame assembly 12 of any known type 
which mounts a seat 13 rearwardly of a fuel tank 14. A handlebar assembly 
15 is positioned at the front of the seat 13 and is journalled by a head 
pipe 16 of the frame 12 for steering of a front wheel 17 in a well known 
manner. The motorcycle 11 also includes a rear wheel 18 that is suspended 
by a trailing arm suspension 19 from the frame 12 in a known manner. 
An internal combustion engine, indicated generally by the reference numeral 
21 and which may in an illustrated embodiment, be comprised of a single 
cylinder, two cycle internal combustion engine is mounted in the frame 12 
for driving the rear wheel 18. It is to be understood that the type of 
engine with which the invention is practiced is exemplary of only one of 
many types of applications. The invention does have particular utility 
with two cycle engines, however, due to the presence of oil in their 
exhaust gases which must be treated before it is discharged to the 
atmosphere so as to render it harmless. 
As is well know, the motorcycle engine 21 includes a crankcase in which a 
change speed transmission is provided for driving the rear wheel 18. Since 
the construction of the motorcycle as thus far described may be considered 
to be conventional, further details of the motorcycle construction are not 
believed to be necessary to understand the construction and operation of 
the invention. 
The engine 21 has a forwardly facing exhaust port 22 which delivers exhaust 
gases to an exhaust system, indicated generally by the reference numeral 
23 which is comprised of a forward expansion chamber 24 which may also 
include, if desired some sound deadened or silencing arrangement. The 
expansion chamber 24 has a discharge end 25, the constructions of which 
will be described later by reference to FIG. 2, which delivers exhaust 
gases to a combined silencer catalytic converter and secondary air 
introducing device 26. This device 26 has a tail pipe 27 from which the 
exhaust gases are discharged to the atmosphere. 
A catalytic converter 28 is provided in the expansion chamber 24 close to 
the exhaust port 22 so as to provide effective treatment of the exhaust 
gases. The catalytic converter 28 has a construction as will be described 
later by reference to FIG. 4. 
Referring now to FIGS. 2 and 3, the device 26 is comprised of a catalytic 
converter 28 which has a general construction like the catalyst bed 29 and 
which will be described later by reference to FIG. 4. This catalyst bed 29 
is contained and supported within a shell 31 that is closed at its forward 
end by a header plate 32 which, in turn, supports an exhaust gas inlet 
tube 33 that is adapted to be positioned in proximity to the discharge end 
25 of the expansion chamber 24, as previously noted. It will be seen that 
a small air gap is provided between the discharge end 25 of the expansion 
chamber 24 and the inlet tube 33 of the catalyst shell 31. The reason for 
this will be described later. 
A silencing device, indicated generally by the reference numeral 34 is 
provided at the rear end of the shell 31. The silencing device 34 is 
comprised of an inner tube which consists of the tail pipe 27 and which 
extends forwardly and is capped by a closure plug 35 with a plurality of 
circumferentially spaced exhaust inlet openings 36 being formed 
therearound. The tail pipe 27 further has a perforated section 37 that is 
surrounded by a silencing material such as glass wool or the like 38 and 
which is held in place by a tubular outer shell 39 that is closed to the 
tail pipe 27 within the shell 31 between the inlet openings 36 and a rear 
header plate 41 which completes the outer shell. 
A forward baffle plate 42 has a flange portion 43 that supports the outer 
shell 39 and an outer flange portion 44 that is affixed, as by welding, to 
the inner side of the outer shell 31. A plurality of openings 45 are 
formed in the baffle plate 42 so that the exhaust gases may communicate 
with an expansion chamber formed between the outer shells 39 and 31 and 
between the baffle plate 42 and the header plate 41 so as to further 
assist in silencing. 
In accordance with the invention, an air inlet channel for receiving 
atmospheric air is provided by means of a further other shell 46 which has 
a reversely bent rear end 47 which is spaced from the outer shell 31 so as 
to provide an annular atmospheric air inlet 48 through which atmospheric 
air may be drawn as shown by the arrows in FIG. 2. This atmospheric air 
flows forwardly in the space between the shells 31 and 46 although its 
flow path may be interrupted by a plurality of arcuate baffles 49 and 51 
that extend between the shells 31 and 46 on their lower and upper sides, 
respectively, as seen in FIG. 2 so as to provide a serpentine air flow 
path forwardly along not only the silencing device 34 but that outer 
periphery of the catalyst bed 29. As a result of this reverse flow, the 
atmospheric air that is drawn into the atmospheric air inlet 48 will be 
heated before it is introduced to the interior of the converter 26, in the 
manner now to be described. 
A forward closure plate 52 closes the forward end of the shell 46 and, in 
turn, has a flange 53 that is sealingly engaged with a tube 54 which, in 
turn, has a forward flange 55 that is affixed, as by welding, to the 
converter discharge section 25. As a result, there will be formed an air 
channel 56 around the converter inlet pipe 33. Atmospheric air may flow 
into this channel 56 through a plurality of inlet openings 57 that are 
formed in the portion of the tube 54 contained within the flange 53 of the 
header plate 52. This air then flows through an opening 58 into the 
venturi section formed by the air gap between the inlet end of the tube 33 
and the discharge end 25 of the expansion chamber 24. As a result, heated 
atmospheric air will be delivered to the converter 29 and this will 
improve the operational temperature and operating efficiency of the 
converter 29. In addition, any exhaust gases which may leak or exhaust 
pulses which may be transmitted back through this supplemental air inlet 
passage will be discharged at the opening 48 in proximity to the tail pipe 
27 and away from the rider. In addition, the noise will not be significant 
due to this rear discharge even if any leakage or sound does escape. 
The construction of the catalytic converter sections 28 and 29 will now be 
described by particular reference to FIG. 4. In the illustrated 
embodiment, the converter sections 28 and 29 are formed cylindrically in a 
generally honeycomb-like cross section by winding a flat band foil A and a 
corrugated band foil B spirally around each other. Both surfaces of either 
the flat band foil A or the corrugated band foil B are covered with a thin 
flat plate-like solder and the solder covered foil is then rolled with 
their fore and aft ends trued up and fixed together in a jig to form the 
band of honeycomb material. The rolled assembly is then heated in a 
furnace to cause the solder to bond the foils A and B to each other. After 
this, the column like member which is formed is soaked in a suspension 
mixed with the catalyst materials, such as platinum, palladium, copper, 
chromium, iron, nickel, etc. and alumina so that the catalytic substance 
may be carried on the column like member. Then the converter is completed 
by reducing and drying. Of course, the foregoing method is only one method 
in which the catalytic converters 28 and 29 may be formed. Various other 
methods can be employed in conjunction with the invention. 
It should be readily apparent from the foregoing description, that with the 
described construction that not only the front converter 28 but the rear 
converter 29 can operate at maximum efficiency. The front converter 28 
will be extremely efficient because it is in close proximity to the 
exhaust port 22 and received heated exhaust gases where further combustion 
may occur in proximity to the catalyst 28. 
Even though the converter 29 is rearwardly positioned, the secondary air 
which drawn in flows around the outer periphery of the converter 29 and 
also the silencer 34 so that it will be heated before it flows into the 
venturi section formed between the opening of the inlet tube 33 of the 
converter shell and the discharge opening 25 of the expansion chamber 24. 
Thus, the gases will not only be heated but because of their rear inlet, 
any exhaust gas leakage which may occur will not be in proximity to the 
rider and the exhaust sounds which may leak also will be remotely 
positioned and hence, effective silencing is accomplished. It is to be 
understood, of course, that the foregoing description is that of a 
preferred embodiment of the invention and that various changes and 
modifications may be made without departing from the spirit and scope of 
the invention, as defined by the appended claims.