JPS61132744A - Air-fuel ratio controller of internal-conbustion engine - Google Patents

Abstract

PURPOSE:To ensure good car drivability and exhaust emission by installing a fuel increasing device to increase fuel during the accelerating driving of an engine, and a distinguishing device to detect output signals of an oxygen density detector. CONSTITUTION:A fuel increasing device 24 increases fuel during the accelerating driving of an engine. A distinguishing device 25 finds out whether the output signal of an oxygen density sensor 19 is a rich or lean signal. A supplied fuel control device 26 stops feedback control, while fuel is increasing and the oxygen density sensor 19 is emitting rich signals, and works feedback control, while fuel is not increasing, or while fuel is increasing and the oxygen density sensor 19 is emitting lean signals. Thus, this constitution can ensure good car drivability and exhaust emission.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an air-fuel ratio control device for an internal combustion engine.

Conventional technology A fuel injection valve is placed in the engine intake passage, and an oxygen concentration detector is installed in the engine exhaust passage, and feedback is provided so that the air-fuel mixture formed by the fuel injected from the fuel injection valve has the stoichiometric air-fuel ratio. An internal combustion engine is known in which the amount of fuel injected from the fuel injection valve is increased during engine acceleration operation to supply a rich mixture into the engine cylinders (Japanese Patent Laid-Open No. 59-39940). ). In this internal combustion engine, feedback control is performed even while the amount of injected fuel is being increased during acceleration operation.

Furthermore, Japanese Patent Application Laid-Open No. 58-48751 discloses that the amount of supplied fuel is reduced or increased during deceleration operation, and the amount of fuel supplied is reduced or increased during the reduction control. ．． ) describes an internal combustion engine in which feedback control is stopped during fuel increase control.

Means to Solve the Problem However, as mentioned above, if feedback control is performed even while the amount of injected fuel is being increased, the air-fuel ratio will not be adjusted because the air-fuel mixture supplied into the engine cylinders will become too rich during this period. The feedback correction coefficient gradually decreases in order to achieve the stoichiometric air-fuel ratio. Therefore, by the time the injected fuel amount increasing action is completed, the feedback correction coefficient has become considerably small. Next, when the increase in the amount of injected fuel is completed, the feedback correction coefficient has become considerably small, and the mixture supplied into the engine cylinder becomes too lean. Increase gradually. However, even during this time, the air-fuel mixture supplied into the engine cylinders becomes too lean, and the air-fuel ratio reaches the stoichiometric air-fuel ratio after a while.

If feedback am is performed while the amount of injected fuel is being increased in this way, the mixture will become too lean when the amount increasing action is completed, and the engine output will temporarily decrease, resulting in poor vehicle drivability. There is a problem in that exhaust emissions deteriorate as the temperature deteriorates.

Furthermore, in the air-fuel ratio control device described in Japanese Patent Application Laid-Open No. 58-48751, feedback control is started when the reduction control or increase control is completed, regardless of the output signal of the oxygen concentration detector. It is difficult to immediately bring the air-fuel ratio to the stoichiometric air-fuel ratio when the increase control is completed.

Means for Solving the Problems - In order to solve the above problems, according to the present invention, as shown in the configuration diagram of the invention in FIG. Oxygen concentration detector 1 in exhaust passage 23
In an internal combustion engine in which feedback control is performed so that the air-fuel ratio of the mixture formed by the fuel supply device 22 becomes the stoichiometric air-fuel ratio based on the output signal of the oxygen concentration detector 19, engine acceleration operation is performed. a fuel increasing means 24 for increasing the amount of fuel when the fuel is being increased; a determining means 25 for detecting whether the output signal of the oxygen concentration detector 19 is a rich signal or a lean signal; The supply fuel control means 26 is provided with a supply fuel control means 26 which stops the feedback control while the rich signal is being issued and performs the feedback control when the fuel is not being increased or when the fuel is being increased and the oxygen concentration detector 19 is issuing the lean signal. ing.

Referring to FIG. 2 of the embodiment, 1 is the engine body, 2 is the piston, and 3 is the engine body.
is a combustion chamber, 4 is a spark plug, 5 is an intake valve, 6 is an intake boat,
7 indicates an exhaust valve, 8 indicates an exhaust port, and the intake boat 6
is connected to a surge tank 10 via a branch pipe 9. The surge tank 1o is connected to an air cleaner (not shown) via an intake duct 11, and a throttle valve 12 connected to an accelerator pedal is disposed within the intake duct 11. A fuel injection valve 13 is installed in each branch pipe 9, and fuel is injected from the fuel injection valve 13 into the corresponding intake boat 6. Each fuel injection valve 13 has an electronic control unit 30
The fuel injection valve 13 is controlled by the output signal of the electronic control unit 30.

The electronic control unit 30 is composed of a digital computer, which is interconnected by a bidirectional bus 31, and includes ROM (read only memory) 3 each having a known function.
2, RAll (Random Access Me%l7) 33, C
It includes a PU (microprocessor) 34, an input boat 35, and an output boat 36.

The output boat 36 has drive circuits 37 , 38 , 39 , 4
0 to the corresponding fuel injection valve 13. A negative pressure sensor 20 disposed inside the surge tank 10 generates an output voltage proportional to the negative pressure inside the surge tank 10, and this negative pressure sensor 20 is connected to the input port 35 via an AD converter 41.
connected to. On the other hand, a water temperature sensor 14 that generates an output voltage proportional to the engine cooling water temperature in response to the engine cooling water temperature is attached to the engine body 1, and this water temperature sensor 14 is connected to the input port 35 via the AD converter 42. Ru. Furthermore,
A distributor 15 is attached to the engine body 1,
A TDC sensor 16 that detects the intake top dead center of any one cylinder and a crank angle sensor 17 that generates a reference pulse every time the crankshaft rotates by 30 degrees are attached to the distributor 15.

These TDC sensor 16 and crank angle sensor 17
is connected to input port 35. Further, an exhaust manifold 18 is connected to the exhaust port 8, and the exhaust manifold 18
An oxygen concentration detector 19 is inserted inside. The oxygen concentration detector 19 generates a rich signal or a lean signal depending on whether excess oxygen exists in the exhaust gas, that is, whether the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is greater than the stoichiometric air-fuel ratio. do. This oxygen concentration detector 19 is connected to the input port 35 via a comparator 43.

Next, the fuel injection control method according to the present invention will be explained with reference to the flowchart shown in FIG. 3 and the diagram shown in FIG.

Referring to FIG. 3, first, in step 50, the output signal of the negative pressure sensor 20 representing the negative pressure P and the output signal of the crank angle sensor 17 representing the engine speed N are acquired. The optimum basic fuel injection time τ0 for the negative pressure P and engine speed N is stored in the ROM 32 in the form of a predetermined map, and in step 51, the basic fuel injection time τO is determined from this map. Next, in step 52, the output signal of the oxygen concentration detector 19 is captured. The oxygen concentration detector 19 issues a rich signal when the air-fuel ratio is too rich (rich), and issues a lean signal when the air-fuel ratio is too lean (lean). Next, in step 53, a feedback correction coefficient C is calculated from the output signal of the oxygen concentration detector 19.

As shown in Fig. 4, this feedback correction coefficient C changes when the air-fuel ratio changes from lean to rich (in Fig. 4).
) Temporarily sharply decreases, that is, skips, and then gradually decreases (Fig. 4(C)). On the other hand, when the air-fuel ratio changes from rich to lean (FIG. 4(b)), it temporarily increases rapidly and then gradually increases (FIG. 4(C)). □Therefore, the feedback correction coefficient C repeatedly moves up and down around the reference value B. This reference value B is a value close to 1, and is stored in a backup RAM (not shown) as an average value obtained by learning changes in the feedback correction coefficient C over a long period of time.

Next, in step 54, the output signal of the water temperature sensor 14 representing the cooling water temperature T is acquired. Next, in step 55, it is determined whether or not it is in an accelerated operation state. If the value exceeds a certain value, it is determined that the driving is accelerated. When the vehicle is not in acceleration mode, the acceleration increase coefficient K is set to 1 in step 56, and then the process proceeds to step 57. Step 57
Then, it is calculated based on the fuel injection time using the following formula.

τ=τO−C−K+τV Here, τV is the invalid injection time.

Therefore, at this time, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio by the feedback correction coefficient C.

On the other hand, during acceleration operation, the process proceeds to step 58 and an acceleration increase coefficient is calculated. If the difference ΔP between the negative pressure P in the previous processing cycle and the negative pressure P in the current processing cycle is greater than or equal to a predetermined value, a predetermined value is sequentially added to this acceleration increase coefficient, and the difference ΔP is When the value falls below a predetermined value, a predetermined numerical value is sequentially subtracted. Therefore, if acceleration starts at time t in Figure 4, the acceleration increase coefficient changes in a triangular waveform as shown in Figure 4 (al).The acceleration increase coefficient increases as the engine cooling water temperature decreases. It is set as follows.The difference △P
The relationship between the engine cooling water temperature T and the numerical value to be added or subtracted is determined in advance and stored in the ROM 32.

Next, in step 59, the set value A is read from the ROM 32. As shown in FIG. 5, this set value A becomes smaller as the engine cooling water temperature T becomes lower. The relationship shown in FIG. 5 is previously stored in the ROM 32.Next, in step 60, it is determined whether the acceleration increase coefficient K is larger than the set value A.

If K≦A, the process advances to step 57. At this time, feedback control is performed while accelerating and increasing the amount. on the other hand,
If K>A, the process proceeds to step 61, where it is determined whether or not the oxygen concentration detector 19 is emitting a rich signal. If the oxygen concentration detector 19 is emitting a lean signal, the process proceeds to step 57, and therefore, feedback control is performed while accelerating and increasing the amount. On the other hand, if the oxygen concentration detector 19 is emitting a rich signal, step 6
2, the feedback correction coefficient C is set to the reference value B (fourth
(C)), and then the process proceeds to step 57. Therefore, at this time, since the feedback correction coefficient C is maintained at the reference value, the acceleration amount is increased, but the feedback control is stopped. In other words, it becomes an open loop.

In this way, in the present invention, the acceleration increase coefficient K is set to A during acceleration operation.
, and the oxygen concentration detector 19 is emitting a rich signal, feedback control is stopped.

Next, with reference to FIG. 4, the variation of the air-fuel ratio according to the present invention and the variation of the air-fuel ratio according to the prior art will be explained. In FIG. 4, the broken line represents the prior art, and the solid line represents the present invention. Fourth
In figure (al), acceleration operation is started at time t,
When the fuel is then increased during acceleration, the air-fuel ratio becomes rich as shown in FIG. 4(b). At this time, if feedback control is performed as in the prior art, the feedback correction coefficient C continues to decrease to reduce the fuel injection amount in order to bring the air-fuel ratio to the stoichiometric air-fuel ratio. Next, when the acceleration increase operation is completed and the air-fuel ratio becomes lean, the feedback correction coefficient C gradually increases. However, since the feedback correction coefficient C is quite small, after the acceleration increase effect is completed, the air-fuel ratio temporarily becomes quite equal as shown in FIG. 4 (kll).As a result,
Vehicle drivability deteriorates and exhaust emissions deteriorate.

On the other hand, in the present invention, if the acceleration increase coefficient K exceeds the set value A and the air-fuel ratio is rich at this time, then
1, the feedback correction coefficient C is held at the reference value B. Next, when the air-fuel ratio becomes lean, feedback control is started. At this time, the feed bank correction coefficient C increases from the reference value B, so the air-fuel ratio immediately changes to rich, thus preventing the air-fuel ratio from continuing to become lean.

When the acceleration increase coefficient K is small, that is, during slow acceleration, there is no need to increase the engine output much; rather, at this time, it is preferable to maintain the air-fuel ratio as close to the stoichiometric air-fuel ratio as possible to ensure a good exhaust emission day. - Therefore, in the present invention, when the acceleration increase coefficient K is smaller than the set value A, feedback control is performed.

Further, as the engine temperature decreases, fuel vaporization deteriorates, and therefore, in order to ensure good acceleration operation, it is necessary to increase the amount of fuel injection as the engine temperature decreases. Therefore, as described above, the fuel increase coefficient is set to increase as the engine cooling water temperature T decreases. However, even if the fuel increase coefficient K is increased in this manner, if feedback control is performed, the fuel injection amount decreases, and acceleration performance deteriorates. Therefore, in the present invention, as shown in FIG. 5, as the engine cooling water temperature T decreases, the set value A is decreased, thereby reducing the amount of decrease in injected fuel due to the feed bank control, thereby ensuring good acceleration operation when the engine temperature is low. That's what I do.

Effects of the Invention Since it is possible to prevent the air-fuel ratio from continuing to become lean after the start of accelerated driving, good vehicle drivability and good exhaust emissions can be ensured.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of the present invention, Fig. 2 is a side sectional view of the internal combustion engine, Fig. 3 is a flowchart for fuel injection control, Fig. 4 is a diagram showing changes in air-fuel ratio, etc., and Fig. 5 is a diagram showing the relationship between set value A and engine cooling water temperature T. 6... Intake boat, 10... Surge tank,
13...Fuel injection valve, 14...Water temperature sensor, 1
7... Crank angle sensor, 19... Oxygen concentration detector, 30... Electronic control unit.

Claims (1)

[Claims] A fuel supply device is disposed in the engine intake passage, and an oxygen concentration detector is disposed in the engine exhaust passage, and the air-fuel ratio of the mixture formed by the fuel supply device is determined based on the output signal of the oxygen concentration detector. In an internal combustion engine that performs feedback control to maintain a fuel ratio, a fuel increasing means increases the amount of fuel during engine acceleration operation, and a determination unit detects whether an output signal of an oxygen concentration detector is a rich signal or a lean signal. and the feedback control is stopped while the fuel is being increased and the oxygen concentration detector is emitting a rich signal, and the feedback control is not being increased or the fuel is being increased and the oxygen concentration detector is emitting a lean signal. 1. An air-fuel ratio control device for an internal combustion engine, including a supply fuel control means that sometimes performs feedback control.