Exhaust gas purification apparatus

An improvement in an exhaust gas purification apparatus wherein a detector senses the operation of a device for injecting additional intake air into the intake passage and triggers a timing unit. The timing unit produces a signal for a predetermined amount of time which holds open a control valve for introducing secondary air into the exhaust passage ahead of the catalytic converter. This structure enables the reduction of harmful components of the exhaust gas produced during a gear-change operation of the engine without greatly overheating the catalytic converter.

BACKGROUND OF THE INVENTION 
This invention relates to an exhaust gas purification apparatus in an 
internal combustion engine wherein harmful exhaust gas components such as 
CO, HC and others are decreased at the catalytic converter, by supplying 
secondary air to the exhaust passage. 
A known exhaust gas purification apparatus for an internal combustion 
engine includes a means for injecting additional intake air into the 
intake passage and a means for introducing secondary air into the exhaust 
passage. The means for injecting additional intake air includes a valve 
interposed in a passage connected to the intake passage of the engine on 
the downstream side of the throttle valve. It is arranged to open for a 
predetermined time by a rapid increase of intake negative pressure and 
inject additional intake air into the intake passage. The secondary air 
introducing means includes a control valve interposed in a passage 
connected to the exhaust passage of the engine on the upstream side of the 
catalytic converter. It is arranged to open at the time of low load 
operation of the engine and introduce secondary air into the exhaust 
passage. The injection of additional intake air prevents the air-fuel 
ratio of the intake mixture gas from being too rich at the initial period 
of engine starting, at the initial period of deceleration, at the time of 
gear changing operation or the like when the intake negative pressure is 
rapidly increased. Additionally, at the time of low load operation such as 
idling, deceleration or the like, the harmful ingredients in the exhaust 
gas are burned in the catalytic converter by the introduction of the 
secondary air to the exhaust passage. Furthermore, an excess of the 
secondary air cools the catalytic converter to prevent it from 
overheating. 
In this type of apparatus, the introduction of the secondary air to the 
exhaust passage is stopped at the time of high load operation of the 
engine. This is because in the high load operation, the amount and 
temperature of exhaust gas increases. Therefore, if the secondary air is 
introduced, overheating damage of the catalytic converter would be likely. 
Accordingly, for improving the purification of the exhaust gases at the 
time of high load operation, it is necessary that the air-fuel ratio of 
the mixture be set to be lower than the theoretical air-fuel ratio. If, 
however, the air-fuel ratio is set to become too lean the responsiveness 
and power of the engine are lowered. In order to keep the engine 
parameters satisfactory, it becomes necessary that the air-fuel ratio be 
set on the lean side near the theoretical air-fuel ratio. 
If, however, the air-fuel ratio is so set near the theoretical ratio, the 
harmful components, especially CO, are generated at the time of gear 
change operation in the midst of the high load operation. It then becomes 
necessary to remove the same in the catalytic converter by introduction of 
secondary air. It can be considered, in this case, that the introduction 
of secondary air can be carried out by utilizing the means for injecting 
additional intake air which is operated at the time of gear change 
operation, but sufficient introduction of the air for such a short time 
cannot be carried out. If, in reverse thereto, the length of time for the 
introduction of air is prolonged, overheating of the catalytic converter 
is caused in the high load operation subsequent to the gear change 
operation. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improvement in an 
exhaust gas purification apparatus that reduces harmful components in the 
exhaust gas produced during a gear change operation of the engine. 
It is a further object of the invention to enable cooling of the catalytic 
converter at the time of high load operation immediately subsequent to a 
gear change operation. 
These and other objects are attained in an improvement in an exhaust gas 
purification apparatus wherein the apparatus has certain additional 
structure. The apparatus is fitted to an internal combustion engine having 
an intake passage, a throttle valve in the intake passage, an exhaust 
passage, and a catalytic converter in the exhaust passage. The apparatus 
includes means for injecting additional intake air into the intake passage 
downstream of the throttle valve upon a rapid increase of intake negative 
pressure, and means for introducing secondary air into the exhaust passage 
upon low load operation of the engine. The secondary air introducing means 
includes an air introduction passage connected between atmosphere and the 
exhaust passage at a position upstream of the catalytic converter, and a 
control valve in the introduction passage. 
The improvement comprises detecting means for detecting the operation of 
the means for injecting and thereupon producing an operation signal, and 
control means for opening the control valve for a predetermined amount of 
time in response to the operation signal. 
The control valve can be a negative pressure operated valve. That is, upon 
an increase in negative pressure to the valve, it opens. The apparatus can 
further include a negative pressure passage connected between the intake 
passage and the valve, an electromagnetic valve in the negative pressure 
passage, and means for operating the electromagnetic valve upon low load 
operation of the engine. The detecting means can comprise an electric 
switch operatively coupled to the injection means to be closed when the 
injection means is operated. The control means can comprise a timer means 
electrically connected between the switch and the electromagnetic valve 
for generating an electric signal for the predetermined amount of time to 
the electromagnetic valve upon closing of the switch thereby holding the 
control valve open for the predetermined amount of time. A check valve can 
be provided in the negative pressure passage between the intake passage 
and the electromagnetic valve permitting flow only in the direction of the 
intake passage away from the electromagnetic valve. A negative pressure 
surge tank can be connected to the negative pressure passage between the 
check valve and the electromagnetic valve.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
One embodying example of this invention will be explained with reference to 
the accompanying drawing: 
Referring to the drawing, a main body 1 of an internal combustion engine 
has an intake passage 2 and an exhaust passage 3. The intake passage 2 is 
provided with a throttle valve 4 interposed therein and an air cleaner 5 
located on an upstream end portion thereof. The exhaust passage 3 is 
provided with a catalytic converter 6 interposed therein. 
Additionally, the intake passage 2 is provided with means 9 for injecting 
additional intake air comprising an air introducing passage 7 connected to 
the intake passage 2 at position located on a downstream side of the 
throttle valve 4, and a valve 8 interposed in the introducing passage 7. 
The exhaust passage 3 is provided with a means 12 for introducing 
secondary air comprising an air introducing passage 10 connected at its 
one end to exterior air and at its other end to the exhaust passage 3 at a 
position located on an upstream side of the catalytic converter 6, and a 
control valve 11 interposed in the introducing passage 10. 
More in detail, the injection means 9 is arranged so that a rapid increase 
in intake negative pressure in the intake passage 2 such as at the initial 
period of engine deceleration, at the initial period of engine starting 
operation, at the time of gear change operation or the like is transmitted 
through negative pressure passage 13 into a negative pressure chamber 14 
and opens the valve 8 for a predetermined amount of time to inject 
additional intake air into the intake passage 2. The additional air serves 
to prevent the mixture in the intake passage 2 from becoming too rich. A 
diaphragm 15 on the front surface of the negative pressure chamber 14 is 
provided with an orifice 16 so that the operation time of the valve 8, 
that is, the operation time of the chamber 14 (0.5-1 sec., for instance,) 
is determined by the orifice 16 and the capacity of the chamber 14. 
The foregoing injection means 9 is not especially different from a 
conventional apparatus. 
More in detail, the secondary air introducing means 12 is arranged so that 
the control valve 11 thereof is composed of a negative pressure operated 
valve arranged to be opened by having intake negative pressure applied 
thereto through a negative pressure passage 17 connected to the intake 
passage 2. An electromagnetic valve 18 interposed in the negative pressure 
passage 17 is arranged to open at the time of low load operation by an 
output signal from a control unit 19 to apply intake negative pressure in 
the intake passage 2 to negative pressure chamber of the control valve 11 
and open the valve 11. Consequently, if the valve 11 is opened, secondary 
air is introduced therethrough into the exhaust passage 3 and serves to 
decrease the harmful components in the exhaust gas in the catalytic 
converter 6 and to cool the catalytic converter 6 to prevent it from 
overheating. 
The control unit 19 comprises an engine speed switch 20 arranged to output 
an ON signal at the time of low speed operation below 1400 r.p.m., for 
instance; a negative pressure switch 21 arranged to output on ON signal at 
the time of deceleration wherein the intake negative pressure becomes 
above 550 mm Hg., for instance, an engine speed switch 22 arranged to 
output on an ON signal when the engine speed is below 3000 r.p.m., for 
instance, an engine cooling water temperature switch 23 arranged to output 
on an ON signal when a cooling water temperature is below 70.degree. C., 
for instance; an AND gate 24 arranged to output on an ON signal when both 
the engine speed switch 22 and the water temperature switch 23 output the 
respective ON signals, that is, when the engine is started in its cold 
condition; and an OR gate 25 arranged to output an ON signal when any of 
the engine speed switch 20, the negative pressure switch 21 and the AND 
gate 24 outputs an ON signal, that is, at the time of such a low load 
operation as low speed operation, the deceleration operation, cold 
starting operation or the like. 
Referring to the drawing, a detecting means 26, for detecting the operation 
of the injection means 9, and a control means 27 for opening the control 
valve 11 for a predetermined time in response to an operation signal of 
the detecting means 26 are provided. In the illustrated example, the 
detecting means 26 comprises a negative pressure operated switch 28 
arranged to be operated in conjunction with the operation of the injection 
means 9. More in detail, the foregoing passage 7 is provided with a jet 
orifice 29 therein on an upstream side of the valve 8, so that when the 
injection means 9 is operated, a negative pressure generated between the 
jet 29 and the valve 8 is applied through a negative pressure passage 30 
to the switch 28 to close the switch 28. 
The control means 27 comprises a timer unit arranged to generate an output 
by the closing, that is, the "ON" position of the switch 28 and continue 
the generation of the output for a predetermined time totalling a 
predetermined time of the ON of the switch 28 (0.5-1 sec.) and a 
predetermined time after the OFF of the switch 28 (1-4 sec., for 
instance,). The foregoing electromagnetic valve 18 is opened by the output 
thereof and accordingly the valve 11 is opened by application of the 
negative pressure to the control valve 11 through the negative pressure 
passage 17. 
In the illustrated example, a negative pressure surge tank 31 is connected 
to the negative pressure passage 17. The passage 17 is connected through a 
check valve 32 to the intake passage 2. In this manner, even when the 
intake negative pressure is lowered after a gear change operation, the 
control valve 11 can be kept in its open condition for the set time of the 
timer unit 27 by a negative pressure stored in the tank 31. 
Next, the operation of the apparatus will be explained as follows: 
During the time of operation of the engine, the secondary air introducing 
means 12 is operated at the time of low load operation of the engine, that 
is, in idling, deceleration operation or cold starting operation, to cause 
secondary air to be introduced into the exhaust passage 3, whereby the 
harmful components in the exhaust gas are decreased and the catalytic 
converter 6 is also cooled and protected. On the other hand, at the 
initial period of starting operation, at the initial period of 
deceleration operation or at the time of gear change operation, the 
additional intake air injection means 9 is operated to prevent the mixture 
in the intake passage 2 from becoming too rich. Additionally, the 
operation of the injection means 9 is detected by the closing of the 
switch 28 of the detecting means 26. The timer unit 27 operated by this 
closing serves to generate an output signal continued for a predetermined 
time, (1-4 sec., for instance) and open the electromagnetic valve 18 for a 
predetermined time. The control valve 11 opened by the operation of the 
valve 18 serves to supply secondary air into the exhaust passage 3 for a 
predetermined time. Thus, the harmful components in the exhaust gas, 
especially CO, are burned by the catalytic converter 6. Because the supply 
of secondary air to the exhaust passage 3 is short in time, the 
temperature of the catalytic converter 6 does not rise too high at the 
time of such a high load operation as the subsequent pedalling of an 
acceleration pedal. 
FIG. 2 is a diagram showing certain test results in which, when the 
air-fuel ratio of the mixture is set to be on the lean side near the 
theoretical air-fuel ratio, for instance, (A/F=15-18), and the vehicle 
speed is accelerated with two gears changed from G.sub.1 to G.sub.2, the 
amount of the harmful component (CO) in the case of this invention and 
htat in the case of the conventional apparatus lacking the means 27, 27 
are measured and plotted to obtain a dotted curve of this invention and a 
solid curve of the conventional case. It has been found therefrom that 
this invention reduces the content of the harmful component (CO) 
remarkably more than the conventional apparatus. In the case of this 
invention, the control valve 11 is operated, as shown by crosshatched 
sections in the same Figure, by being applied for 1.6 sec. with a negative 
pressure of about 400 mm Hg from the surge tank 31 of a capacity of 280 
c.c. In this test, the operation pressure of the control valve 11 is so 
set to be 300 mm Hg. 
Instead of the negative pressure operated switch 28 arranged to detect the 
operation of the injection means 9 as shown in the foregoing example, a 
switch arranged to be closed in mechanical conjunction with the opening 
operation of the valve 8 of the injection means 9 may be used for the 
detecting means 26. 
Thus, according to this invention, the operation of the injection means 
arranged to be operated by a rapid increase of the intake negative 
pressure at the time of gear change operation or the like is detected. By 
the detection, the control valve is opened for a predetermined time for 
introducing the secondary air for a predetermined time into the exhaust 
passage. In this manner, the harmful components in the exhaust gas are 
burned in the catalytic converter by the introduced secondary air. The 
catalytic converter is cooled so that no overheating occurs even at the 
time of high load operation subsequent to the gear change operation. In 
addition, the harmful components in the exhaust gas at the time of gear 
change operation are decreased remarkably, and the air-fuel ration of the 
mixture can be set near the theoretical air-fuel ratio. In this manner, 
the responsiveness and power of the engine are not lowered. Additionally, 
even if there are individual variations in driving technique which have a 
large influence on generation of the harmful components at the time of 
gear change operation of the vehicle or even if the vehicle is increased 
in weight (if the weight thereof is increased, the deceleration degree is 
increased and consequently generation of the harmful components in the 
exhaust gas is increased), the removal effect of the harmful components in 
the exhaust gas according to this invention apparatus is not obstructed 
thereby. 
It is readily apparent that the above-described improvement in exhaust gas 
purification meets all of the objects mentioned above and also has the 
advantage of wide commercial utility. It should be understood that the 
specific form of the invention hereinabove described is intended to be 
representative only, as certain modifications within the scope of these 
teachings will be apparent to those skilled in the art. 
Accordingly, reference should be made to the following claims in 
determining the full scope of the invention.