Multiple cylinder engine having air-fuel ratio control means in accordance with a signal from an exhaust gas sensor

A multiple cylinder engine including a first group of cylinders having a first intake passage which is provided with a air-fuel mixture of a predetermined ratio in accordance with the signal from an exhaust gas sensor provided in the exhaust passage from the first group of cylinders. The engine further includes a second group of cylinders having a second intake passage which is provided with a mixture having an air-fuel ratio which is of a predetermined relationship with respect to the air-fuel ratio of the mixture provided to the first group of cylinders, the predetermined relationship being determined in accordance the engine operating condition. Check valves are provided in the intake passages to prevent the mixture in the first intake passage from being mixed with that in the second intake passage so that accurate control can be ensured.

The present invention relates to internal combustion engines and more 
particularly to means for controlling the air-fuel ratio in a multiple 
cylinder engine. More specifically, the present invention pertains to 
air-fuel ratio control means for a multiple cylinder engine in which the 
air-fuel ratio is controlled in accordance with a signal from an exhaust 
gas sensing means. 
In internal combustion engines, it has been known to control air-fuel ratio 
of the intake mixture by means of an exhaust gas sensor which detects the 
concentration of a specific constituent of the exhaust gas to produce an 
output signal so that the fuel control system is controlled in accordance 
with the output signal of the exhaust gas sensor to establish a desired 
air-fuel ratio of the intake mixture. This type of control system is 
usually designed so as to accomplish an air-fuel ratio at or close to the 
stoichiometric value, which is approximately 14.7 in case of gasoline, and 
the exhaust system is provided with a ternary catalytic device to 
eliminate noxious constituents in the exhaust gas. 
Usually, the exhaust gas sensor is a so-called O.sub.2 sensor which is 
known as having an output that significantly changes in the vicinity of 
the air-fuel ratio of 14.7. The O.sub.2 sensor is therefore very 
convenient to perform accurate control when it is desired to obtain an 
air-fuel ratio at or close to the stoichiometric value. However, it is 
very often desirable to obtain a richer or leaner mixture, depending on 
the engine operating conditions. For example, a richer mixture is 
desirable under a light load or heavy load operation or under a low 
temperature condition in order to obtain stable engine operation. Further, 
a leaner mixture may be desirable under steady engine operation for the 
purpose of obtaining improved fuel economy. The O.sub.2 sensor usually 
adopted as the exhaust gas sensor is however inconvenient for such control 
because the change in the output of the sensor for a change in the 
air-fuel ratio becomes small under a richer or leaner air-fuel ratio. 
In order to solve the aforementioned problems in the air-fuel ratio control 
system using an O.sub.2 sensor, there is proposed in Japanese Patent 
Publication No. 54-35258 to control, in a multiple cylinder engine, the 
air-fuel ratio for one cylinder in accordance with the output of the 
exhaust gas sensor and the air-fuel ratio for the other cylinders with 
respect to the air-fuel ratio for the one cylinder so that the air-fuel 
ratio can be changed as a whole with respect to the stoichiometric value. 
The present invention has as an object to provide an air-fuel ratio control 
device for a multiple cylinder engine in which accurate control of 
air-fuel ratio can be ensured. 
Another object of the present invention is to provide an air-fuel ratio 
control device for a multiple cylinder engine in which accurate control to 
any desired value of air-fuel ratio can be performed. 
According to the present invention, the above and other objects can be 
accomplished by a multiple cylinder internal combustion engine including 
first group of cylinder means, second group of cylinder means, an intake 
system comprising main intake passage means, first intake passage means 
branched from said main intake passage means and leading to said first 
group of cylinder means and, second intake passage means branched from 
said main intake passage means and leading to said second group of 
cylinder means, first fuel supply means for providing a supply of fuel to 
said first intake passage means, second fuel supply means for providing a 
supply of fuel to said second intake passage means, first exhaust passage 
means leading from said first group of cylinder means for passing exhaust 
gas therefrom, exhaust gas sensing means disposed in said first exhaust 
passage means for providing an output signal in accordance with the 
concentration of a constituent in the exhaust gas, first air-fuel ratio 
control means for controlling the first fuel supply means in accordance 
with the output of the exhaust gas sensing means so as to provide a first 
intake mixture of a first predetermined air-fuel ratio, second air-fuel 
ratio control means for controlling the second fuel supply means in 
accordance with the first predetermined air-fuel ratio to provide a second 
intake mixture of a second air-fuel ratio which is a predetermined 
relationship with respect to the first air-fuel ratio and, mixing 
preventing means provided in said intake system for preventing said first 
and second intake mixtures from being mixed with each other due to 
pulsations in said intake system. The mixing preventing means may be in 
the form of check valve means which may be of a reed type. Alternatively, 
it may be provided by expansion chamber means. 
The second air-fuel ratio control means may include detecting means for 
detecting an engine operating condition and adjusting means for 
determining a compensation ratio which is the ratio of the second 
predetermined air-fuel ratio to the first predetermined air-fuel ratio in 
accordance with the engine operating condition. In one aspect of the 
present invention, the engine operating condition is the engine 
temperature and the second intake mixture is enriched under cold engine 
operation. In another aspect, the engine operating condition is the engine 
load so that the second intake mixture is enriched under light load or 
heavy load engine operation. 
The first and second groups of cylinder means may have the same number of 
cylinders, respectively, and each of said first and second intake passage 
means may include a manifold passage and branch passages leading from said 
manifold passage and communicating with the respective ones of the 
cylinders, said mixing preventing means being provided in said manifold 
passage. The first and second fuel supply means may include fuel injection 
valve means and the first and second air-fuel ratio control means may 
include circuit means which control duration of fuel injection in 
accordance with the engine operating condition and the output of the 
exhaust gas sensing means. 
The second group of cylinder means may have second exhaust passage means 
which is merged with said first exhaust passage means, at least said first 
exhaust passage means having back flow preventing means downstream of said 
exhaust gas sensing means.

Referring now to the drawings, particularly to FIG. 1, there is shown a 
four cylinder engine 1 having cylinders 1a, 1b, 1c and 1d. The engine has 
an intake system including a main intake passage 2 which is branched into 
intake passages 2a and 2b. The intake passage 2a is connected through 
branch passages 102a with the cylinders 1b and 1c, whereas the intake 
passage 2b is connected through branch passages 102b with the cylinders 1a 
and 1d. The cylinders 1b and 1c are not adjacent to each other in respect 
of the order of combustion and the cylinders 1a and 1d are not adjacent to 
each other in respect of the order of combustion. The engine further has 
an exhaust system including an exhaust passage 3a leading from the 
cylinders 1b and 1c and an exhaust passage 3b leading from the cylinders 
1a and 1d. The exhaust passages 3a and 3b are merged into an exhaust 
manifold 3 which has a catalytic converter 7 disposed therein. 
The main intake passage 2 is provided at the upstream end with an air 
cleaner 4. A throttle valve 6 is provided in the main intake passage 2 to 
control the air flow into the cylinders. The engine is equipped with a 
fuel supply system 8 which includes fuel injection valves 9a, 9b, 9c and 
9d which are associated respectively with the branch intake passages. An 
air flowmeter 5 is provided in the main intake passage 2 between the air 
cleaner 4 and the throttle valve 6 and produces an air flow signal to an 
oscillator 11. An engine speed sensor 10 is provided to detect the engine 
speed and applies an engine speed signal to the oscillator 11. The 
oscillator 11 produces a pulsating output of which pulse width is 
determined in accordance with the air flow signal and the engine speed 
signal to control the amount of fuel supply in one operating cycle. The 
output pulse of the oscillator 11 is applied to a processing circuit 12. 
The exhaust passage 3a is provided with an exhaust gas sensor 18 such as an 
O.sub.2 sensor which applies an output to an air-fuel ratio adjusting 
circuit 19 which produces an adjusting signal to apply it to the 
processing circuit 12. The processing circuit 12 produces an output pulse 
of which pulse width is determined in accordance with the pulse width of 
the output from the oscillator 11 and the signal from the circuit 19. The 
output of the circuit 12 is applied to the fuel injection valves 9b and 9c 
which are provided in the branch intake passages 102a to control the 
duration of fuel injection through these valves. It should be noted that 
the fuel injection valves 9b and 9c constitute a first fuel supply device 
8a and the control through the processing circuit 12 of the first fuel 
supply device 8a produces an air-fuel mixture having mixing ratio at or 
close to the stoichiometric value. 
The output of the processing circuit 12 is also applied to a pulse 
modifying circuit 13 which produces an output for controlling a second 
fuel supply device 8b constituted by the fuel injection valves 9a and 9d. 
There are provided an engine temperature sensor 16 and an intake suction 
pressure sensor 17 which produce output signals to be applied to a 
modifying oscillator 15 which constitutes an air-fuel ratio modifying 
device 14. The output from the engine speed sensor 10 is also applied to 
the oscillator 15. The oscillator 15 produces a modifying signal in 
accordance with the engine operating conditions which is judged by the 
signals from the sensors 10, 16 and 17. The modifying signal is applied to 
the pulse modifying circuit 13 to modify the width of the pulse from the 
processing circuit 12 in accordance with the engine operating condition. 
Thus, the fuel ratio modifying device 14 functions to enrich the mixture 
supplied to the cylinders 1a and 1d under cold engine operation or under a 
light load or heavy load operation to ensure stable engine operation 
whereas a mixture of the stoichiometric ratio is supplied to the cylinders 
1a and 1d under a medium load operation. Further, a leaner mixture may be 
supplied to the cylinders 1a and 1d under steady engine operation. 
The intake system is further provided with an exhaust gas recirculation 
system 22 including a recirculation passage 23 extending from the exhaust 
manifold 3. The passage 23 opens into branch passages 23a and 23b, 
respectively, with the intake passages 2a and 2b. In the passages 23a and 
23b, there are respectively provided control valves 24a and 24b which may 
be proportional solenoid valves of which the openings are propositioned 
with electric current applied thereto. In order to control the current to 
the valves 24a and 24b, there is provided a valve driving circuit 25 which 
receives the output signal from the air flow sensor 5 and produces an 
output signal for determining the amount of recirculation gas to be 
introduced into the cylinders 1b and 1c. The signal from the driving 
circuit 25 is therefore directly applied to the control valve 24a. The 
output from the driving circuit 25 is further applied to a modifying 
circuit 26 which also receives the signal from the oscillator 15 to 
produce a modified signal for energizing the control valve 24b. The 
exhaust gas recirculation system 22 therefore functions to control the 
amount of recirculation gas in accordance with the air-fuel ratio so that 
a larger amount of gas is recirculated when a richer mixture is being 
supplied. 
In the intake system, there is also provided a mixing preventing device 20 
which comprises, in this embodiment, a first and second check valves 20a 
and 20b respectively located in the intake passages 2a and 2b. As shown in 
FIG. 2, the check valve 20a is of a reed type including a valve body 120 
formed with openings 121 and valve members 122 adapted to close the 
openings 121. Stoppers 123 are provided to limit the open positions of the 
valve members 122. The check valve 20b has the same structure as the check 
valve 20a. 
In the exhaust passage 3a, there is formed downstream of the exhaust gas 
sensor 18 an expansion chamber 21 which serves to prevent back flow of the 
exhaust gas into the exhaust passage 3a. 
In the arrangement described above, the mixture to be supplied to the 
cylinders 1b and 1c is maintained substantially at a predetermined 
air-fuel ratio, for example at the stoichiometric ratio, due to the 
feedback control using the signal from the exhaust gas sensor 18. The 
mixture to the cylinders 1a and 1d is modified in accordance with the 
engine operating condition to adjust the air-fuel ratio as a whole. 
The chech valves 20a and 20b provided in the intake passages 2a and 2b 
function to prevent the mixtures in the passages 2a and 2b from being 
mixed with each other due to pulsations in the intake passages. Thus, it 
is possible to maintain the air-fuel ratio of the mixture to be supplied 
to the cylinders 1b and 1c accurately at the predetermined value and at 
the same time to control the air-fuel ratio of the mixture to the 
cylinders 1a and 1d at a desired value. In the illustrated embodiment, the 
branch intake passages 102a and 102b are connected with the main intake 
passage 2 through the intake passages 2a and 2b, respectively. However, 
the passages 102a and 102b may be connected directly with the main intake 
passage 2. In that case, the check valves are located in the branch 
passages 102a and 102b. 
Referring now to FIG. 3, there is shown another embodiment of the present 
invention. In this embodiment, corresponding parts are shown by the same 
reference numerals as in the previous embodiment. In this embodiment, the 
main intake passage 2 is connected through an intake passage 2a with a 
first cylinder 1a and through an intake passsge 2b and branch passages 102 
with the other cylinders 1b, 1c, and 1d. In the intake passage 2a, there 
is formed an expansion chamber 220 which functions to absorb pulsations in 
the intake system to thereby prevent the mixture in the passage 2a from 
being mixed with that in the passage 2b. 
The invention has thus been shown and described with reference to specific 
embodiments, however, it should be noted that the invention is in no way 
limited to the details of the illustrated arrangements, but changes and 
modifications may be made without departing from the scope of the appended 
claims.