JP3013050B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement for improving the purification performance of an air-fuel ratio control device in an internal combustion engine.

[0002]

2. Description of the Related Art As an air-fuel ratio control device for an internal combustion engine, a three-way catalyst is provided in an exhaust passage and an air-fuel ratio sensor is arranged at least upstream of the three-way catalyst. When the detection signal becomes leaner than the reference value, the air-fuel ratio of the air-fuel mixture supplied to the engine is changed to the rich side. Conversely, when the detection signal becomes richer, the air-fuel ratio of the air-fuel mixture is changed. By controlling the operation of the air-fuel ratio adjusting unit so as to change the air-fuel ratio to the lean side, the air-fuel ratio of the exhaust gas as a whole is maintained at a predetermined value, for example, a value matching the window of the three-way catalyst. General.
Such feedback control uses a detection signal of the air-fuel ratio sensor as it is, and also uses a control constant map and a control variable map (for example, Japanese Patent Application Laid-Open No.
And an air-fuel ratio sensor provided downstream of the three-way catalyst and controlled according to the detection results of the two air-fuel ratio sensors (see, for example, JP-A-61-234241). Are known.

FIG. 5 shows the basic operation of these controls. FIG. 5A shows the change of the air-fuel ratio of the exhaust gas.
(b) shows the state of change of the detection signal of the air-fuel ratio sensor, and (c) shows the operation of the air-fuel ratio adjusting unit, for example, the state of change of the opening of the fuel flow control valve. Adjustment of the air-fuel ratio is also performed by controlling the flow rate of air or controlling both fuel and air.

[0004]

When the detection signal of the air-fuel ratio sensor falls below the reference value and changes from the lean side to the rich side, or vice versa, as shown by the symbol A in FIG. The waveform may be disturbed and the signal voltage may change while cutting the reference value up and down several times. For this reason, conventionally, a change in the opening degree of the flow control valve is not inverted immediately after the detection signal first falls below the reference value, and a slight delay time is usually provided before the inversion starts. T ₂ in FIG. 5 (c) shows this delay time. However, this delay time T ₂
The purpose was to prevent malfunction, and no special consideration was given to the relationship with the purification action, and it was not considered to be an important factor in improving the purification performance. The present invention pays attention to this delay time, studies the relationship between the delay time and the emission amount of NOx, HC and CO, and succeeds in solving the problem of further reducing the emission amount of these harmful components.

[0005]

In order to achieve the above-mentioned object, in the air-fuel ratio control device according to the present invention, the air-fuel ratio adjusting unit changes the air-fuel ratio after the detection signal of the air-fuel ratio sensor falls below the reference value. Is set to (0.2 to 1.0) × (1200 / engine speed (rpm)) seconds.

[0006]

If the delay time is less than the above range, HC and C
If the amount of O emission increases and the delay time exceeds the above range, the amount of NOx emission increases. This is considered to be because if the delay time is short, the oxidation reaction in the catalyst becomes insufficient, and if it is too long, the oxidation proceeds and the temperature of the catalyst rises. On the other hand, if the delay time is within the above range,
It is considered that the amount of oxygen stored in the three-way catalyst is increased and the treatment reaction of HC and CO by oxidation is promoted, and the temperature rise of the catalyst is within a relatively small range, so that generation of NOx is considered to be reduced.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the illustrated gas fuel engine will be described below. 1 is a block diagram, FIG. 2 is a schematic configuration diagram, FIG. 3 is an operation explanatory diagram corresponding to FIG. 5, and FIG. 4 is a graph showing operation results. The present invention can be applied not only to a gas engine described below but also to other types of engines. Further, in the embodiment, the O ₂ sensor is provided on the upstream side of the three-way catalyst. However, the present invention is also applicable to other systems such as a case where the O ₂ sensor is provided on each of the upstream and downstream of the three-way catalyst. can do.

In the figure, 1 is an engine, 2 is an intake manifold, 3 is a throttle valve, 4 is a mixer, 5 is an air supply path, 6 is a main fuel supply path, 7 is a gas regulator,
The fuel 8 is supplied to the mixer 4 via the gas regulator 7 and the main fuel supply path 6, where it is mixed with the air 9 supplied from the air supply path 5. Reference numeral 11 denotes a bypass passage which branches off from the middle of the main fuel supply passage 6 and communicates between the mixer 4 and the throttle valve 3. Reference numeral 12 denotes a flow control valve for air-fuel ratio control provided in the bypass passage 11. As the flow control valve 12, for example, an actuator valve having a step motor 12a is used. Reference numeral 13 denotes a balance line for controlling the gas pressure according to the air pressure. 16 is an exhaust manifold, 17 is an exhaust pipe, 18 is a three-way catalyst, 19
Is an O ₂ sensor disposed upstream of the three-way catalyst 18;
1 is an exhaust gas, 22 is a load detection sensor for detecting a load based on intake pressure, and 23 is a rotation detection sensor.

Reference numeral 25 denotes a control unit whose main part is constituted by a microcomputer, for example, an output port 25a and a CPU.
25b, a ROM 25c, a RAM 25d, and the like.
The detection outputs of the O ₂ sensor 19, the load detection sensor 22, and the rotation detection sensor 23 pass through the input / output port 25a.
5, and the control output is output to the flow control valve 12 via the input / output port 25a. The ROM 25c of the control unit 25 appropriately stores maps, necessary programs, and the like used for various controls including air-fuel ratio control.
The rotation detection sensor 23 is a known electromagnetic pickup, and outputs a pulse corresponding to the rotation speed of the engine 1 as a detection signal.

The apparatus of the embodiment has the above-described configuration.
The detection signal of the O ₂ sensor 19 changes as shown in FIG. 3B in accordance with the change in the air-fuel ratio of the exhaust gas shown in FIG. 3A, and when the detection signal falls below the reference value L, the flow control valve 12 is opened. The degree is controlled as shown by the solid line in (c). The control variables in (c), that is, the skip amounts Su and Sd and the change rates 1 / Cu and 1 / Cd
Is selected in accordance with the detection results of the load detection sensor 22 and the rotation detection sensor 23.
In JP-A-113565, a control constant is selected from a separately set control constant map according to the load and the number of revolutions, and a control variable is selected according to the selected control constant.

The dashed line in FIG. 3 (c) shows the change in the opening degree according to the conventional example of FIG. 5 for comparison. In the prior art, the delay time has elapsed since the detection signal of the O2 sensor 19 fell below the reference value L. T
While the direction of the change in the opening degree is reversed after two, the delay time T1 of this embodiment is set longer than the conventional delay time T2. Note that the delay time when the valve opening switches in the opening direction and the delay time when switching in the closing direction can have different values as needed.

FIG. 4 shows an example of the relationship between the delay time T ₁ and the emissions of NOx, HC and CO. The unit of the horizontal axis is based on 1200 rpm, and the engine speed at that time (unit is rpm) The number divided by is shown in seconds. From this figure, it can be seen that the shorter the delay time, the higher the HC and CO emissions, and the longer the delay time, the higher the NOx emissions. Although not shown in this figure, if the delay time is long, the temperature of the three-way catalyst 18 rises and the oxidation deterioration of the catalyst proceeds.

Therefore, considering these conditions, it is considered that the range of (0.2 to 1.0) × (1200 / engine speed) seconds is appropriate as the delay time. the delay time T ₂ in the conventional device generally
Since it is selected to be about 0.1 × (1200 / engine speed) seconds, it means that the operation is performed in a region where the emission amounts of HC and CO are considerably large. That is, by selecting the delay time T ₁ within the above range, the emission of the toxic components is greatly reduced than the conventional apparatus, yet obtain an air-fuel ratio control system without reducing the life of the catalyst It becomes possible. The discharge amount of each harmful components will vary in such formats and the operating state of the engine, not observed little difference in the trend itself shown in FIG. 4, by selecting the above range as the delay time T ₁ All could be accommodated.

The above-mentioned delay time T ₁ can be set, for example, in a control program. As an example, a fixed number of pulses continuously output from the rotation detection sensor 23 is defined as one count, and the flow rate control is performed until a predetermined count elapses after the detection signal of the O ₂ sensor 19 falls below the reference value L. The direction of the change in the opening degree of the valve 12 is not reversed, but is reversed when a predetermined count is reached.
For example, if one count is 6.7 ms × (1200 / engine speed), the predetermined count is 30 to 150.
Count may be by setting the, Thus, the delay time in inverse proportion to the rotational speed at that time is stretchable automatically, always proper delay time T ₁ is thus obtained in accordance with the rotational speed. The delay time T ₁ can be changed continuously or stepwise as necessary, for example, by setting a plurality of values and selecting a desired value by an appropriate selection means. Good to put.

[0015]

As is apparent from the above description, in the air-fuel ratio control device according to the present invention, the air-fuel ratio adjusting unit switches the change of the air-fuel ratio in the reverse direction after the detection signal of the air-fuel ratio sensor falls below the reference value. The operation up to (0.2-1.0) × (120
0 / engine speed (rpm)) seconds. Therefore, not only the malfunction due to the disturbance of the signal waveform of the air-fuel ratio sensor is prevented, but also the delay time is stored in the three-way catalyst as compared with the conventional case where the delay time is about 0.1 × (1200 / engine speed) seconds. Since the amount of oxygen to be used increases and the treatment reaction of HC and CO by oxidation is promoted and good purification is performed, the amount of these emissions is greatly reduced as illustrated in FIG. Is 1.0 ×
Since (1200 / engine speed) seconds, the generation of NOx is maintained at a low level. As described above, according to the present invention, the purifying performance of the three-way catalyst can be improved, and the catalyst capacity can be reduced by that much to reduce the cost. Because of the enlargement, the period until readjustment for correcting aging of the apparatus and the like becomes longer, so that effects such as improvement in practical durability and reduction in maintenance cost can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the embodiment.

FIG. 3 is an operation explanatory diagram of the embodiment.

FIG. 4 is a graph showing an operation result of the example.

FIG. 5 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

1, the engine 4 mixer 6 main fuel supply passage 11 bypass passage 12 flow control valve 17 exhaust pipe 18 three-way catalyst 19 O ₂ sensor 21 exhaust gas 25 controller 25a CPU

Claims (1)

(57) [Claims] A three-way catalyst and an air-fuel ratio sensor are provided in an exhaust passage, and when the detection signal of the air-fuel ratio sensor becomes leaner than a reference value, the air-fuel ratio of the air-fuel mixture supplied to the engine becomes richer. In the air-fuel ratio control device for an internal combustion engine configured to change the air-fuel ratio of the air-fuel mixture to the lean side when the detection signal becomes richer, the detection signal of the air-fuel ratio sensor falls below a reference value. From (0.2 to 1.0) × (1200 / engine speed (rpm) until the air-fuel ratio adjustment unit switches the change of the air-fuel ratio in the reverse direction.
m)) An air-fuel ratio control device for an internal combustion engine, which is delayed by seconds.