JPS6214700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for a multi-cylinder engine, and more particularly, to an air-fuel ratio control device for a multi-cylinder engine that controls the air-fuel ratio of the air-fuel mixture for the entire engine based on the output of an exhaust sensor consisting of an O ₂ sensor installed in an exhaust passage. This invention relates to an air-fuel ratio that is controlled to an air-fuel ratio different from the stoichiometric air-fuel ratio.

Conventionally, an exhaust sensor that detects the concentration of exhaust gas components is installed in the exhaust passage of an engine, and an air-fuel ratio correction circuit is installed that controls a fuel supply device that adjusts the air-fuel ratio of the air-fuel mixture supplied to the engine. The fuel supply system is operated and controlled by the output of the air-fuel ratio correction circuit according to the output of the sensor, and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to the set air-fuel ratio, that is, the stoichiometric air-fuel ratio (approximately 14.7). is known to do.

In such air-fuel ratio control of the air-fuel mixture, the stoichiometric air-fuel ratio is usually set as the target value, and as a result, the atmosphere in the catalyst device installed in the exhaust passage downstream of the exhaust sensor is made into a three-way atmosphere. Although efforts are being made to maintain good purification performance, engine performance, fuel efficiency, emission performance, etc.
If necessary, there is a demand for setting the target value to an air-fuel ratio different from the stoichiometric air-fuel ratio, particularly to an air-fuel ratio leaner than the stoichiometric air-fuel ratio in order to improve fuel efficiency.

However, conventionally, the above-mentioned exhaust sensor uses O ₂
As shown in Figure 4, this conventional O ₂ sensor has an output characteristic that depends on the air-fuel ratio.
Since it has characteristics that change rapidly around 14.7, accurate control is possible when controlling the air-fuel ratio to the stoichiometric air-fuel ratio, but as mentioned above, we want to control the air-fuel ratio to a leaner or richer one than the stoichiometric air-fuel ratio. In this case, there is a problem in that the deviation value from the set voltage corresponding to the target air-fuel ratio becomes small, making it impossible to accurately control the air-fuel ratio.

In view of this, the present invention divides a multi-cylinder engine into a first cylinder group and a second cylinder group, and adjusts the air-fuel ratio of the air-fuel mixture supplied to the first cylinder group and the second cylinder group. The air-fuel ratio of the supplied air-fuel mixture is set to be different in advance (that is, to be different by a certain amount when the operating condition is constant), and one of the independent exhaust passages provided independently to each of the above two cylinder groups is An exhaust sensor consisting of an O ₂ sensor is arranged in the independent exhaust passage of the first cylinder group, and the first
Feedback control is performed so that the air-fuel ratio of the mixture supplied to the second cylinder group becomes the target value (stoichiometric air-fuel ratio), and the air-fuel ratio of the mixture supplied to the second cylinder group is indirectly changed accordingly. The basic idea is to control the air-fuel ratio of the air-fuel mixture for the entire engine to a predetermined air-fuel ratio, thereby adjusting the air-fuel ratio of the air-fuel mixture supplied to the multi-cylinder engine to the stoichiometric air-fuel ratio. It is an object of the present invention to provide an air-fuel ratio control device for a multi-cylinder engine that can accurately control an air-fuel ratio different from the stoichiometric air-fuel ratio, especially an air-fuel ratio leaner than the stoichiometric air-fuel ratio.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the present invention, which is an example in which an electronically controlled fuel injection device is used as means for controlling the air-fuel ratio of an air-fuel mixture. In FIG. 1, 1 is a four-cylinder engine, and one cylinder 1 out of four cylinders 1a to 1d of the engine 1 is
cylinder a is classified into a first cylinder group, and the other three cylinders 1b to 1d are classified into a second cylinder group. 2 is an intake passage, and each intake passage 2 is divided into independent branch intake passages 2.
It communicates with each cylinder 1a-1d via a-2d. Further, 3a to 3d are independent exhaust passages provided independently to each cylinder 1a to 1d, respectively,
The independent exhaust passages 3a to 3d are assembled downstream to form a collective exhaust passage 3. 4 is an air cleaner connected upstream of the intake passage 2; 5 is a throttle valve disposed in the intake passage 2 to control the amount of intake air; and 6 is a catalyst device disposed in the collective exhaust passage 3.

In addition, 7a to 7d are the branch intake passages 2a to 7d.
2d, each of the fuel injection valves 7a to 7d includes a fuel injection valve 7a to 7d.
A control device 8 that controls the injection pulse width of d is connected, and the fuel injection valves 7a to 7d and the control device 8 control the air-fuel mixture supplied to each cylinder 1a to 1d via each branch intake passage 2a to 2d. A fuel supply device 9 is configured to adjust the air-fuel ratio of the fuel.

Further, 10 is an air flow sensor disposed in the intake passage 2 to detect the amount of intake air; 11 is a rotation speed sensor disposed in the engine 1 to detect the engine rotation speed; both sensors 10 and 11 are Both detection signals, that is, an intake air amount signal and an engine rotational speed signal, are connected to the control device 8, respectively, and input to the control device 8. Also, 1
Reference numeral 2 denotes an exhaust sensor composed of an O ₂ sensor arranged in the independent exhaust passage 3a of the first cylinder group 1a and configured to detect the concentration of exhaust gas components, and the exhaust sensor 12 is connected to the control device 8. ing.

As shown in FIG. 2, the control device 8 receives an intake air amount signal from an air flow sensor 10 and an engine rotation speed signal from a rotation speed sensor 11, and controls the amount of air per revolution according to the intake air amount and the engine rotation speed. an injection pulse width transmission circuit 13 that outputs a pulse signal with a predetermined injection pulse width; an air-fuel ratio correction circuit 14 that outputs an air-fuel ratio correction signal according to the output of the exhaust sensor 12; The pulse signal of the first cylinder group 1a and the air-fuel ratio correction signal from the air-fuel ratio correction circuit 14 are calculated.
an arithmetic circuit 15 that outputs a pulse signal with a target injection pulse width to the fuel injection valve 7a to bring the air-fuel ratio of the mixture to the target value (stoichiometric air-fuel ratio); and the arithmetic circuit 1
For example, the target pulse width of the pulse signal from 5 is set from 100% to an air-fuel ratio different from the above-mentioned target air-fuel ratio (for example, an air-fuel ratio leaner than the stoichiometric air-fuel ratio).
A pulse width correction circuit 1 that corrects the pulse width to 80% and outputs a pulse signal with the corrected pulse width to each of the fuel injection valves 7b to 7d of the second cylinder group 1b to 1d.
6, and thus constitutes a control means that performs feedback control on the fuel injection valve 7a so that the air-fuel ratio of the air-fuel mixture supplied to the first cylinder group 1a becomes a target value (the stoichiometric air-fuel ratio). At the same time, the air-fuel mixture supplied to the second cylinder group 1b to 1d is set to an air-fuel ratio that differs by a predetermined amount from the air-fuel ratio of the air-fuel mixture supplied to the first cylinder group 1a (for example, an air-fuel ratio leaner than the stoichiometric air-fuel ratio). ), that is, a changing means is configured to change the air-fuel ratio by a certain amount when the operating state is constant.

Therefore, in the first embodiment, the first
For the cylinder group 1a, a control device 8 according to the outputs of the air flow sensor 10 and the rotation speed sensor 11 is provided.
The fuel injection valve 7a for the first cylinder group 1a is operated by the output of the injection pulse width transmitting circuit 13, and the air-fuel ratio of the air-fuel mixture supplied to the first cylinder group 1a is controlled to the target value (the stoichiometric air-fuel ratio). On the other hand, the second cylinder group 1b~
1d, the injection pulse width transmitting circuit 13
The fuel injection valves 7 for the second cylinder group 1b to 1d are controlled by the output corrected by the pulse width correction circuit 16.
By operating each of b to 7d, the air-fuel ratio of the mixture supplied to the second cylinder groups 1b to 1d becomes the target air-fuel ratio (stoichiometric air-fuel ratio) of the mixture supplied to the first cylinder group 1a. What is the above pulse width correction circuit 16?
For example, the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio. Moreover, regarding the air-fuel mixture supplied to the first cylinder group 1a, the independent exhaust passage 3a of the first cylinder group 1a
In other words, the air-fuel mixture supplied to the first cylinder group 1a is controlled as fuel for the first cylinder group 1a by the correction signal of the air-fuel ratio correction circuit 14 according to the output of the exhaust sensor 12. The fuel injection amount of the injection valve 7a is corrected and feedback-controlled to the target value (stoichiometric air-fuel ratio). Along with this, the air-fuel ratio of the air-fuel mixture supplied to the second cylinder group 1b to 1d is also the same as that of the air-fuel mixture of the first cylinder group 1a.
When the operating condition is constant, indirect feedback control is performed to a different air-fuel ratio with a certain amount of difference (for example, an air-fuel ratio leaner than the stoichiometric air-fuel ratio), so that the stoichiometric air-fuel ratio of the engine 1 as a whole is controlled. It is possible to accurately perform feedback control to an air-fuel ratio different from the stoichiometric air-fuel ratio, for example, to an air-fuel ratio leaner than the stoichiometric air-fuel ratio.

For example, specifically, when the injection pulse width of the fuel injection valves 7b to 7d for the second cylinder group 1b to 1d is set to 80% with respect to the injection pulse width of the fuel injection valve 7a for the first cylinder group 1a, which is 100%. The engine as a whole will be feedback-controlled to a lean air-fuel ratio of 85% of the stoichiometric air-fuel ratio.

In addition, when performing feedback control to a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio for the entire engine,
Injection pulse width of fuel injection valve 7a for first cylinder group 1a
In contrast to 100%, the injection pulse width of the fuel injection valves 7b to 7d for the second cylinder groups 1b to 1d may be set to 120%.

FIG. 3 shows a second embodiment of the present invention, which is an example in which a carburetor 20 is used in the intake system instead of the fuel injection type intake system in the first embodiment (FIG. 1). The same parts as in FIG. 1 are denoted by the same reference numerals, and the explanation thereof will be omitted.

That is, in FIG. 3, 20 is the intake passage 2.
The carburetor 20 is provided with an actuator 21 that controls the air-fuel ratio by increasing or decreasing the air lead amount, for example, separately from the throttle valve 5'. The actuator 21 constitutes a fuel supply device 9' that adjusts the air-fuel ratio of the air-fuel mixture supplied to the engine 1 (both cylinder groups 1a to 1d) via the intake passage 2. Furthermore, 22 is an actuator 21 of the fuel supply device 9' to control the air-fuel ratio of the air-fuel mixture supplied to the engine 1 according to the output of the exhaust sensor 12 disposed in the independent exhaust passage 3a of the first cylinder group 1a.
The air-fuel ratio correction circuit 22 serves as a control means for controlling the operation of the air-fuel ratio correction circuit 22, and the exhaust sensor 12 detects the concentration of exhaust gas components to generate a signal having a correlation with the air-fuel ratio of the air-fuel mixture taken into the first cylinder group 1a. The air-fuel ratio correction circuit 22 has a comparison circuit, a proportional circuit, an integration circuit, an addition circuit, a duty ratio control circuit, etc., and outputs a correction signal according to the output of the exhaust sensor 12 to adjust the fuel supply. The actuator 21 of the device 9' is operated to feedback-control the air-fuel mixture supplied to the engine 1 to a target value (stoichiometric air-fuel ratio).

On the other hand, 23 is an auxiliary air supply passage that supplies auxiliary air to the second cylinder group 1b to 1d, and the upstream side of the auxiliary air supply passage 23 is connected to the air cleaner 4, while the downstream side is connected to three branch supply passages. 23b
23d to the branch intake passages 2b to 2d of the second cylinder groups 1b to 1d. The auxiliary air supply passage 23 is provided with an auxiliary air amount control valve 25 that is interlocked with the throttle valve 5' of the carburetor 20 via an interlocking link 24, and controls the auxiliary air amount of the auxiliary air supply passage 23 at a low load. The air-fuel mixture is controlled to be a constant proportion of the amount of air-fuel mixture in the intake passage 2 over a high load range, and is supplied to each of the branch intake passages 2b to 2d of the second cylinder group 1b to 1d. . Therefore, the air-fuel ratio is supplied to the first cylinder group 1a by the fuel supply device 9' at the target value (stoichiometric air-fuel ratio), but the air-fuel mixture is supplied to the second cylinder group 1b to 1d. On the other hand, by supplying auxiliary air, a certain amount of air-fuel mixture with a lean air-fuel ratio is supplied when the operating state is constant with respect to the target air-fuel ratio, so that the air-fuel ratio of the air-fuel mixture of the second cylinder group 1b to 1d is A changing means is configured to change the air-fuel ratio by a predetermined amount with respect to the air-fuel ratio of the first cylinder group 1a.

Therefore, also in the second embodiment, the first
The air-fuel mixture supplied to the cylinder group 1a is feedback-controlled to a target value (stoichiometric air-fuel ratio), while the air-fuel mixture supplied to the second cylinder groups 1b to 1d is the same as the air-fuel mixture supplied to the first cylinder group 1a. Since the air-fuel ratio is indirectly controlled to an air-fuel ratio that is a certain amount leaner than the air-fuel ratio (stoichiometric air-fuel ratio), the engine 1 as a whole can be accurately feedback-controlled to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.

In addition, in the second embodiment, the second cylinder group 1b to 1
By supplying auxiliary air to d, the second
Although the air-fuel mixture of the cylinder groups 1b to 1d was set to an air-fuel ratio leaner than the air-fuel ratio of the air-fuel mixture supplied to the first cylinder group 1a, the branch intake passages 2b to 2d of the second cylinder groups 1b to 1d were The same effect as described above may be achieved by changing the shape of the branch intake passage 2a of the first cylinder group 1a and changing the fuel distribution ratio.

In the above embodiment, the fuel injection method or the carburetor 2 is used as a means for adjusting the air-fuel ratio of the air-fuel mixture.
0 and the actuator 21, various other known means can be adopted as appropriate.

Further, although the above description has been made regarding a four-cylinder engine, it goes without saying that the present invention can be applied to various other multi-cylinder engines.

As explained above, according to the present invention, the air-fuel ratio of the air-fuel mixture in the first cylinder group is feedback-controlled to the stoichiometric air-fuel ratio by the O ₂ sensor, while the air-fuel ratio of the air-fuel mixture in the second cylinder group is controlled to be the stoichiometric air-fuel ratio. Since the air-fuel ratio of the group mixture is changed by a predetermined amount, a conventional O ₂ sensor can be used to accurately adjust the air-fuel ratio of a multi-cylinder engine to a lean or rich air-fuel ratio that is different from the stoichiometric air-fuel ratio. It is something that can be controlled.

[Brief explanation of the drawing]

The drawings illustrate embodiments of the invention.
The figure is a schematic diagram of the first embodiment, Figure 2 is a block circuit diagram of the control device in Figure 1, Figure 3 is a schematic diagram of the second embodiment, and Figure 4 shows the output characteristics of the O ₂ sensor. FIG. 1...Engine, 1a...1st cylinder group, 1b~
1d...Second cylinder group, 2...Intake passage, 2a-2
d... Branch intake passage, 3... Collective exhaust passage, 3a
~3d...Independent exhaust passage, 4...Air cleaner,
5, 5'... Throttle valve, 6... Catalyst device, 7a to 7d... Fuel injection valve, 8... Control device, 9, 9'... Fuel supply device, 10... Air flow sensor, 11... Rotation speed sensor, 12... Exhaust sensor, 13... Injection pulse width transmitting circuit, 14
...Air-fuel ratio correction circuit, 15...Arithmetic circuit, 16...
...pulse width correction circuit, 20... vaporizer, 21...
Actuator, 22... Air-fuel ratio correction circuit, 23
...Auxiliary air supply passage, 23b to 23d... Branch supply passage, 24... Interlocking link, 25... Auxiliary air amount control valve.

Claims (1)

[Claims] 1 a first and a second cylinder group, a fuel supply device that adjusts the air-fuel ratio of the air-fuel mixture supplied to each cylinder group, an independent exhaust passage provided independently for each of the cylinder groups, and the first and second cylinder groups; an exhaust sensor disposed in an independent exhaust passage of the first cylinder group; and the fuel supply device configured to adjust the air-fuel ratio of the air-fuel mixture supplied to the first cylinder group to a stoichiometric air-fuel ratio according to the output of the exhaust sensor. control means for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the second cylinder group with respect to the air-fuel ratio of the first cylinder group so that the overall air-fuel ratio is different from the stoichiometric air-fuel ratio; 1. An air-fuel ratio control device for a multi-cylinder engine, comprising: changing means for changing the ratio by a predetermined amount.