Exhaust gas recirculation control system for engines

An exhaust gas recirculation control system employs a flow rate valve in the recirculation line. The valve is operated by suction pressure obtained from two suction ports in the engine intake passage. Suction lines from those ports contain air inlet valves which dilute the suction pressure with atmospheric air, depending upon engine operating conditions. A fuel supply increasing valve is connected to a venturi in the engine intake passage and suction operated control means control operation of that valve. The result is an improved acceleration characteristic for the engine under load without substantial increase in discharge of pollutants into the atmosphere.

This invention relates to an exhaust gas recirculation control system 
mainly for use in vehicle engines having a flow rate control valve 
provided in an exhaust gas recirculation passage. 
Exhaust gas recirculation systems are conventionally employed in engines 
which operate to return part of the exhaust gas emitted from the engine to 
the engine intake passage via an exhaust gas recirculation line during the 
operation of the engine to prevent excessive increase of the combustion 
temperature of the mixture in the engine cylinders. Lowering of the 
combustion temperature reduces the output of nitrogen oxides which are 
objectionable from the standpoint of atmospheric air contamination. 
Further, a system is also known which operates to supply the engine with a 
mixture having a high overall air-fuel ratio in order to reduce the 
concentrations of hydrocarbon, monoxide, nitrogen oxides, etc. contained 
in the exhaust gas. The above two systems can both the employed in engines 
so as to further reduce the concentration of nitrogen oxides in the 
exhaust gas. However, all the above-mentioned systems more or less have an 
unfavorable influence upon the ability of the engine to accelerate under 
load. 
The present invention has been devised in view of the above circumstances, 
and it is an object of the invention to provide a system of the 
above-mentioned type which, during acceleration of the engine, operates to 
increase the quantity of fuel being delivered from the engine carburetor 
to compensate for insufficient engine power, and at the same time increase 
the flow rate of exhaust gas being returned to the engine intake passage. 
This has the effect of limiting increase of the combustion temperature 
which would be caused by the increased fuel quantity. The new system 
thereby contributes to both enhancement of the engine power characteristic 
and prevention of air contamination.

Referring to the drawing, the automobile engine generally designated E is 
provided with an intake manifold Mi and an exhaust manifold Me. A 
carburetor C is connected to an upstream end of the intake manifold Mi 
through a heat insulating barrel B. 
The carburetor C includes a venturi 1a provided in the intake passage 1. A 
choke valve 2 is positioned upstream of the venturi 1a and a throttle 
valve 3 is positioned downstream of the venturi 1a. A fuel nozzle 4 opens 
into the venturi 1a. The intake manifold Mi and the heat insulating barrel 
B constitute the intake passage 1 of the engine. A first suction port D1 
is located in the vicinity of or downstream from the throttle valve 3, and 
a second suction port D2 opens into the venturi 1a. A third suction port 
D2 opens into the venturi 1a. A third suction port D3 is positioned at a 
location downstream of the throttle valve 3. 
A fuel passage leading to the fuel nozzle 4 comprises a main fuel passage 
5m and an auxiliary fuel passage 5s, both of which communicate with a 
float chamber, not shown, in which float chamber the passages 5m and 5s 
open below the fuel surface level. The auxiliary fuel passage 5s is 
provided with a fuel supply increasing valve 6. The valve 6 includes a 
movable valve element 7 arranged to open or close the auxiliary fuel 
passage 5s. The valve 6 also includes a diaphragm 8 connected to the valve 
element 7, and a valve spring 10 positioned within the suction pressure 
chamber 9 below the valve element 7. The spring 10 urges the valve element 
7 in the valve-opening direction. 
The suction chamber 9 of the fuel supply increasing valve 6 communicates 
with the third suction port D3 via a suction passage 11 in which a 
solenoid-type stop valve 12 is provided. This stop valve 12 operates to 
open the suction passage 11 when its solenoid is energized, and closes the 
same passage 11 and simultaneously connects the downstream side of the 
passage 11 with an air intake port 14 provided with a filter, when the 
solenoid is de-energized. Accordingly, the fuel supply increasing valve 6 
is kept open to cause an increase in the quantity of fuel being injected 
through the fuel nozzle 4 when the valve 12 is de-activated, or when the 
valve 12 is activated while the suction pressure at the third suction port 
D3 is below a predetermined value. When the suction pressure at port D3 
exceeds the predetermined value, the fuel supply increasing valve 6 is 
closed by activation of the stop valve 12 to interrupt the fuel increasing 
action. Control of the activation of the stop valve 12 is described below. 
An exhaust gas recirculation conduit 15 extends from an exhaust port of the 
engine E and communicates with the intake manifold Mi, with a flow rate 
control valve 16 provided in the conduit 15. Valve 16 includes a movable 
valve element 17 operated by a diaphragm 18. A valve spring 20 is 
positioned within the suction chamber 19 formed above the diaphragm 18 and 
acts to urge the valve element 17 toward closed position. 
The first suction line L1 extends from the suction port D1 through the 
solenoid-operated air valve 21 to the suction chamber 19 of the 
recirculation control valve 16. An orifice 24 is located downstream of the 
valve 21 in the suction line L1. A second suction line L2 extends from the 
suction port D2 to the suction chamber 19 by way of solenoid-operated air 
valve 22 and the regulating valve 28. The air valves 21 and 22 each 
operate to close the upstream side of their respective suction lines L1 
and L2, and simultaneously allow the downstream sides to communicate 
respectively with air intake ports 26 and 27 provided with filters, when 
their solenoids are energized. 
The control valve generally designated 23 includes a suction pressure 
responsive-type regulating valve 28 arranged to open or close the second 
suction line L2, and also includes an air valve 29 of the suction pressure 
responsive-type adapted to adjust the suction pressure acting upon the 
regulating valve 28. The regulating valve 28 includes a valve chamber 30 
connected to the second suction line L2 and also includes a suction 
chamber 32 separated from the valve chamber 30 by the diaphragm 31. A flat 
movable valve element 33 fixed to the diaphragm 31 opens and closes with 
respect to a valve port 48 at the open end of the line 11a extending 
between the regulating valve 28 and the recirculation control valve 16. A 
valve spring 20 urges the valve element 17 toward its closed position. 
The air valve 29 is comprised of a valve chamber 36 positioned in a third 
suction line L3 extending from the third suction port D3 and leading to an 
air intake port 35 provided with a filter. A suction chamber 38 is 
separated from the valve chamber 36 by the diaphragm 37. A movable valve 
element 39 secured on the diaphragm 37 is positioned to vary the opening 
of a valve port 49 formed at the open end of the third suction line L3. A 
valve spring 40 is arranged to urge the valve element 39 in its closing 
direction. The valve element 39 of this valve 29 has a configuration 
similar to that of the valve element 17 of the aforementioned flow rate 
control valve 16. The suction chamber 38 communicates with the first 
suction line L1 located downstream of the regulating valve 28, while the 
valve chamber 36 communicates with the pressure chamber 32 via an orifice 
41. Another orifice 42 is provided at a location between the valve chamber 
36 and the air intake port 35. 
In the present specification, the terms "upstream side" and "downstream 
side" of the suction lines mean "suction pressure supply source side" and 
"air intake port side", respectively. 
When the solenoid-type stop valves 21, 22 are de-activated, the suction 
pressure control valve 23 operates as follows: 
A suction pressure is produced in the vicinity of the throttle valve 3 or 
at a location downstream of same as the engine E operates, and is detected 
as negative pressure Pc at the first suction pressure port D1. The suction 
pressure Pc is transmitted to the chamber 38 of the air valve 29 via the 
stop valve 21 and the orifice 24, so that when the suction pressure Pc 
overcomes the setting load of the valve spring 40, it lifts the valve 
element 39 together with the diaphragm 37 to open the third suction 
pressure line L3. 
When the third suction pressure line L3 is thus opened, atmospheric air is 
introduced into the third suction line L3 via the intake port 35 and then 
into the intake passage 1 of the engine E. As a consequence, suction 
pressure P produced in the valve chamber 36 of the air valve 29 is 
transmitted to the suction chamber 32 of the regulating valve 28. When the 
difference between the suction pressure P and the suction pressure Pv, at 
the second suction port D2, overcomes the setting load of the valve spring 
34, the valve element 33 is lifted together with the diaphragm 31 to open 
the valve port 48. Part of the suction pressure Pv escapes through the 
valve port 48 to dilute or reduce the intensity of the suction pressure 
which has previously passed the orifice 24 into suction pressure Pe in 
line 11a. This suction pressure Pe serves as actuating pressure for the 
flow rate control valve 16. 
Due to the above dilution or reduction of intensity in the suction 
pressure, the suction pressure present in the chamber 38 is reduced, and 
accordingly the opening of the air valve 29 is reduced which results in a 
corresponding decrease in the suction pressure in the valve chamber 36. 
The suction pressure in the chamber 32 of the regulating valve 28 also 
decreases so that the valve element 33 closes the valve port 48. Then, the 
suction pressure Pe increases. This cycle of operation is repeated. Since 
this repetition occurs very quickly, the quantity of air travelling in the 
third suction passage L3 becomes proportional to the quantity of air being 
sucked into the engine E so that the suction pressure P has a value 
approximate to that of the suction pressure Pv. 
Thus, when the quantity of air being sucked into the engine E is small, the 
suction pressure P is higher than the suction pressure Pv and accordingly 
the valve element 33 of the regulating valve 28 is displaced in its open 
position to decrease the actuating pressure Pe for the flow rate control 
valve 28. On the other hand, when the quantity of suction air increases, 
the suction pressure Pv increases so that the valve element 33 is 
displaced into its closing position to increase the actuating pressure Pe. 
In this manner, the air valve 29 and the flow rate control valve 16 are 
actuated by the same suction pressure Pe. Further, their respective valve 
elements 39, 17 are similar in configuration to each other. Therefore, the 
quantity of air flowing in the third suction pressure passage L3, that is, 
the quantity of air being sucked into the engine E, is proportional to the 
quantity of exhaust gas being returned to the suction passage so that the 
engine E can be supplied with exhaust gas at a permanently constant return 
ratio. 
On the other hand, when the stop valve 22 is activated to block the 
upstream side of the second suction pressure line L2 and simultaneously 
allow the downstream side of same to communicate with the air intake port 
27, the regulating valve 28 has its valve chamber 30 supplied with 
atmospheric pressure which displaces the valve element 33 into its open 
position so that the actuating suction pressure Pe decreases. This reduces 
the opening of the flow rate control valve 16, resulting in a decrease in 
the flow rate of exhaust gas being recirculated. 
When the other stop valve 21 is activated to block the upstream side of the 
first suction line L1 and simultaneously allow the downstream side of same 
to communicate with the air intake port 26, the actuating suction pressure 
Pe is replaced by atmospheric pressure to bring the flow rate control 
valve 16 into its closed position, resulting in interruption of the 
recirculation of exhaust gas. 
The control system for the above-mentioned solenoid-type stop valves 12, 
21, 22 will now be described. The control system is mainly comprised of 
first and second vehicle speed sensing switches S1, S2, an engine 
temperature sensing switch St, and first and second vacuum pressure 
detecting switches Sd1, Sd2. The switch S1 closes when the vehicle speed 
is high (e.g., 45 km/h or more), the switch S2 opens when the vehicle 
speed is low (e.g., 20 km/h or less), the switch St detects the 
temperature of engine cooling water as engine temperature and closes when 
the temperature is low (e.g., 60.degree. C. or less), and the switch Sd1 
closes when the suction pressure detected by the third suction port D3 
exceeds a predetermined value (e.g., 500 mm Hg), and the switch Sd2 closes 
when said suction pressure exceeds another predetermined value (e.g., 350 
mm Hg). The suction line leading to the switch Sd2 is provided therein 
with an orifice 50 which acts to slightly delay the actuating timing of 
the switch Sd2 with respect to the actuating timing of the switch Sd1. 
The stop valves 12 and 22 have their solenoids connected in parallel to a 
power source or battery 43 via the first vehicle speed sensing switch S1. 
These solenoids are also connected to the power source 43 via the second 
vacuum pressure sensing switch Sd2. Also, the stop valve 12 has its 
solenoid connected to the power source 43 via the engine temperature 
sensing switch St and a diode 44. The stop valve 21 has its solenoid 
connected to the power source 43 via the first vehicle speed sensing 
switch S1, the first vacuum pressure sensing switch Sd1 and a diode 45, 
and also via the engine temperature sensing switch St and a diode 46. 
Reference numeral 47 designates the ignition switch of the engine. 
The operation of the control system with the above arrangement will now be 
described. 
During Cold State of the Engine 
In this state, the engine temperature sensing switch St is on to activate 
the stop valve 12 so that the fuel supply increasing valve 6 has its 
chamber 9 supplied with suction pressure from the third suction port D3. 
As this suction pressure decreases, that is, as the engine load increases, 
the valve element 7 is displaced so as to increase the quantity of fuel 
injected through the fuel nozzle 4. 
When the switch St is thus on, the stop valve 21 is also activated and 
accordingly the flow rate control valve 16 is kept in its closed position, 
and exhaust gas recirculation is not carried out, since the actuating 
suction pressure Pe is replaced by atmospheric pressure. This interruption 
of exhaust gas recirculation is effected for the reason that when the 
engine E is in a cold state, nitrogen oxides are not produced in 
appreciable quantities due to low combustion temperature of the mixture, 
even in the absence of exhaust gas recirculation. 
During Warmed-up State of the Engine (But Not During Deceleration) 
A. In low or medium vehicle speed ranges (e.g., 45 km/h or less) and when 
engine load is relatively high (e.g., vacuum pressure in the intake 
passage is below 350 mm Hg): 
In this state, the engine temperature sensing switch St, the first vehicle 
speed sensing switch S1 and the second vacuum pressure sensing switch Sd2 
are all in the off position, and accordingly the solenoid valves 12, 21 
and 22 are all de-activated. Since the suction pressure chamber 9 of the 
fuel supply increasing valve 6 is supplied with atmospheric pressure via 
the air intake port 14 during de-activation of the valve 12, as previously 
mentioned, the valve element 7 is displaced to its maximum opening 
position so that the rate at which fuel is injected through the fuel 
nozzle 4 is increased. Therefore, the engine power can be increased when 
the vehicle is operated at a low or medium speed as well as at a high 
load, thus improving acceleration. Particularly, the present system can be 
advantageously applied to an engine operating on a lean mixture. 
On the other hand, when the stop valves 21, 22 are de-activated, the first 
and second suction pressure lines L1, L2 are both held open so that, as 
previously mentioned, the flow rate control valve 16 has its opening 
regulated to a value appropriate for the quantity of suction air supplied 
to the engine. This is caused by the action of the actuating suction 
pressure Pe which is controlled by the suction pressure control valve 23, 
resulting in supply of exhaust gas into the suction passage through the 
exhaust gas recirculation passage 15 at a required and sufficient flow 
rate. Thus, the production of unwanted nitrogen oxides due to the elevated 
engine power can be effectively restrained. 
B. In a high vehicle speed range (e.g., 45 km/h or more): 
In this speed range, the first vehicle speed sensing switch S1 closes, with 
the stop valves 12 and 22 in an activated state so that the fuel 
increasing valve 6 has its suction pressure chamber 9 supplied with 
suction pressure from the third suction port D3 to weaken its fuel 
quantity increasing function. At the same time, the suction pressure 
control valve 23 acts to reduce the actuating suction pressure Pe so that 
the flow rate control valve 16 has its opening reduced to correspondingly 
reduce the flow rate of recirculating exhaust gas. In this manner, the 
fuel consumption rate can be reduced while maintaining a satisfactory 
level of engine power. 
During Deceleration of the Engine 
By the time the vehicle comes into high speed operation, the second vehicle 
speed sensing switch S2 is closed. If the vehicle in this state is 
decelerated (engine braking effect), suction pressure (e.g., 500 mm Hg) is 
produced in a zone downstream of the throttle valve 3 which is higher than 
that produced during idling. The switches Sd1 and Sd2 close in response to 
this high negative pressure. Since the stop valves 21, 22 are activated 
when the switches S2, Sd1, Sd2 are closed, the flow rate control valve 16 
is closed to interrupt the exhaust gas recirculation. This interruption is 
effected for the reason that the rate of production of nitrogen oxides is 
small during deceleration of the engine and that the quantity of unburned 
gas components in the exhaust gas should desirably be kept as small as 
possible. 
When the switch Sd2 is closed, the stop valve 12 is also activated so that 
the suction pressure chamber 9 of the fuel supply increasing valve 6 is 
supplied with high suction pressure from the third suction port D3, via 
the stop valve 12, to close the valve 6, thus interrupting the fuel 
quantity increasing action. 
Then, when the vehicle speed decreases to a predetermined low range, e.g., 
20 km/h or less, the second vehicle speed sensing switch S2 opens to 
de-activate the stop valve 21 and accordingly the flow rate control valve 
16 again opens to the proper degree. 
As set forth above, according to the present invention, first and second 
suction pressure lines are connected to a suction pressure chamber 
provided in a flow rate control valve for controlling the flow rate of 
exhaust gas being returned to the intake passage of the engine. The first 
and second suction pressure lines extend, respectively, from a first 
suction port provided in the vicinity of a throttle valve of the 
carburetor or in a zone downstream of the throttle valve, and from a 
second suction port provided at a venturi of the carburetor. A suction 
pressure control valve is provided in the second suction pressure line for 
controlling the degree of dilution of suction pressure at the first 
suction port by admixture with the suction pressure at the second suction 
port. Further, a stop valve is provided between the suction pressure 
control valve and the second suction port, for acting in response to the 
action of a control valve for regulating the fuel quantity increasing 
action of a fuel supply increasing valve provided in the carburetor. The 
effect is to overcome the suction pressure at the second suction port when 
the fuel quantity increasing action declines. 
With the above arrangement, when the fuel quantity increasing action is 
strengthened to compensate for insufficient engine power, recirculation of 
exhaust gas can be effected at a sufficient flow rate to achieve 
satisfactory enhancement of the engine power and minimize air 
contamination at the same time. Further, when the fuel quantity increasing 
action declines or ceases, the flow rate of exhaust gas being returned can 
be reduced to a moderate extent, to thereby avoid an unnecessary drop in 
the engine power. 
Having fully described our invention, it is to be understood that we are 
not to be limited to the details herein set forth but that our invention 
is of the full scope of the appended claims.