JPH0533728A - Air-fuel ratio control device for gas engine - Google Patents

Abstract

PURPOSE:To enable succession of gas engine operation under a high load condition with a proper air-fuel ratio by determining additional supply of gas fuel from an engine speed and a throttle opening based on a memorized contant of a memory means at abnormality of an air-fuel sensor. CONSTITUTION:An engine speed Nm and a throttle opening Sm are detected with a preset interval time. A set value of an air-fuel ratio is judged. When a threshold S2 calculated under a condition that = 1.0 has a relation other than Sm<S2, the condition is judged through an O2 sensor detection signal to be rich or lead. When the O sensor outputs, for instance, a signal indicating rich, an injector duty continues going down. After a specified time, the detection signal is necessarily changed to one indicating lean. When output of one kind signal continues more than a specified time, it is judged abnormality and switching is carried out to control without the O2 sensor. Difference between the throttle opening Sm and the threshold with which switching is performed to a condition lambda=1.4. A control signal with which fuel is additionally supplied correspondingly to the previously memorized engine speed and throttle opening is calculated and output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for a gas engine, which switches the air-fuel ratio according to the load condition of the engine.

[0002]

2. Description of the Related Art A detection signal from an air-fuel ratio sensor arranged in exhaust gas is fed back to determine the rich (RICH) / lean (LEAN) state according to the oxygen concentration contained in the exhaust gas, and the engine speed is preliminarily determined. The throttle opening set in accordance with the threshold value is used as a threshold, and at the time of high load where a large output is required, a predetermined amount of gas fuel is additionally supplied from the additional gas fuel supply means to perform λ = 1.0 operation, The applicant of the present application has proposed a gas engine in which the air-fuel ratio is controlled by sometimes stopping the additional supply and performing λ = 1.4 operation with high thermal efficiency. Sho 5
9-215951) and the like. In this way, controlling the additional fuel only without controlling the entire fuel supply amount means that even in a large-sized gas engine with a large fuel supply amount, the fuel adjusting means is downsized and the responsiveness is improved. This is because the feature of becoming

However, in a gas engine which performs such control, when the air-fuel ratio sensor is deteriorated or destroyed due to some cause, the output voltage of the air-fuel ratio sensor does not accurately represent the oxygen concentration of the exhaust gas. Therefore, despite such a situation, the detection signal of the air-fuel ratio sensor is directly fed back and λ =
When 1.0 control is performed, the air-fuel ratio becomes too rich or too thin depending on the output state of the air-fuel ratio sensor, which not only deteriorates exhaust emissions but also makes it impossible to operate at high load and the engine stops. There was a possibility that a situation would occur.

[0004]

The present invention pays attention to these points and makes it possible to continue the operation of the gas engine while continuously controlling the air-fuel ratio even if an abnormality occurs in the air-fuel ratio sensor at the time of high load. It was made as an issue.

[0005]

In order to achieve the above object, in the present invention, a predetermined amount of gas fuel is preliminarily leaned from an additional fuel supply means in accordance with a detection signal from an air-fuel ratio sensor arranged in exhaust gas. The air-fuel ratio control means for controlling the air-fuel ratio at the time of high load by additionally supplying the air-fuel ratio set to, and the air-fuel ratio control with the throttle opening set in advance according to the engine speed as a threshold value. In a gas engine equipped with an air-fuel ratio switching means for switching the operation of the means,
The duration of each detection signal indicating rich or lean by the air-fuel ratio sensor is compared with a preset abnormality determination time,
Abnormality detection means that determines that the air-fuel ratio sensor is abnormal if the same detection signal continues until the abnormality determination time is reached, and additional supply of gas fuel to the engine speed and throttle opening that is applied when the air-fuel ratio sensor is abnormal The amount of additional supply of gas fuel based on the stored contents of the storage means regardless of the detection signal from the air-fuel ratio sensor when the abnormality detection means determines that the air-fuel ratio sensor has an abnormality And calculating means for outputting a control signal for controlling the additional fuel supply means, and the additional fuel supply means is configured to supply the additional fuel into the air-fuel mixture upstream of the throttle. There is.

[0006]

When the air-fuel ratio sensor is abnormal, the additional supply amount of the gas fuel is determined according to the engine speed and the throttle opening based on the stored contents of the storage means. However, the operation can be continued while controlling the air-fuel ratio. Further, the intake negative pressure largely changes in the downstream of the throttle according to the opening degree of the throttle, but in the present invention, since the additional fuel is supplied to the upstream of the throttle that is not easily affected by the fluctuation of the intake negative pressure, It is not necessary to consider the fluctuation of the intake negative pressure when determining the fuel, and the calculation of the additional supply amount of fuel becomes easy.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment shown in the drawings will be described below. 1 is a conceptual system diagram, 1 is a gas engine, 2 is a mixer,
3 is a throttle, 4 is an electronic governor, 5 is an opening detector of the throttle 3, 6 is a gas injector, 7 is an exhaust pipe, 8 is a three-way catalyst, 9 is an O ₂ sensor for detecting an air-fuel ratio, and 10 is a rotation speed. The detector 11 is a microcomputer. The mixer 2 is preset so as to maintain the air-fuel ratio at λ = 1.4, and the fuel gas 15a and the air 16 are mixed by the mixer 2 and then supplied to the engine 1 through the throttle 3 and the exhaust pipe 7 The exhaust gas 17 that has been discharged into the exhaust gas is exhausted through the three-way catalyst 8. The gas injector 6 is arranged upstream of the throttle 3, and the control of λ = 1.0 during high load is performed by additionally supplying a predetermined amount of gas fuel 15b from the injector 6.

The throttle opening is detected by an opening detector 5 which is attached to the shaft of the throttle 3 whose opening is controlled by the electronic governor 4 and which is, for example, a potentiometer, and the output is sent to the microcomputer 11. The number of revolutions of the engine 1 is detected by the number of revolutions detector 10 which is attached to the ring gear portion 18 of the engine 1 and is composed of, for example, an electromagnetic pickup, and its output is sent to the microcomputer 11.

The microcomputer 11 has a CPU 2
1, the ROM 22, the RAM 23, the I / O port 24, the system bus line 25, etc., and the analog output of the opening detector 5 is converted into a digital amount by the A / D converter 26 and input to the microcomputer 11. , O again
The detection signal of the _two sensor 9 is also input to the microcomputer 11 through the A / D converter 26. The pulse output of the rotation speed detector 10 is counted by the counter 27 and input to the microcomputer 11. ROM22
Alternatively, in the RAM 23, in addition to a program for arithmetic control, the relationship between the engine speed applied when the O ₂ sensor 9 is abnormal and the additional supply amount of gas fuel with respect to the throttle opening is stored in advance in the form of a map or a calculation formula. The abnormality determination time for determining the abnormality of the O ₂ sensor 9 is stored in advance.

When an abnormality of the O ₂ sensor 9 is detected, CP
U21 outputs a control signal in the form of a digital signal from the I / O port 24 according to the engine speed and the throttle opening detected based on the above stored contents, not depending on the detection signal of the O ₂ sensor 9. The gas injector 6 is driven at a predetermined duty by the signal amplified by the power transistor array 28.
Is driven, the gas fuel 15b is additionally supplied, and the operation is continued. In addition, the power transistor array 28
Also outputs a signal to the O ₂ sensor abnormality indicator 29. The O ₂ sensor abnormality indicator 29 emits light or sound. For example, the O ₂ sensor abnormality indicator 29 is installed in an operation control room or the like by using an LED and blinks to notify a maintenance manager of the abnormality of the O ₂ sensor 9.

Next, the operation of this apparatus will be described with reference to the flow chart of FIG. Microcomputer 11
The CPU 21 detects the engine speed Nm and the throttle opening Sm at preset interval times.
(Step 1) After the detection, the set value of λ is determined in Step 2. When λ = 1.4, the throttle opening threshold value S ₁ = f ₁ (Nm) for switching to λ = 1.0 is calculated or calculated from the map (step 3), and the following When Sm and S ₁ are compared in step 4 and Sm ≧ S ₁ , the injector 6 is operated at a constant injector duty ID = g (0) to additionally supply a predetermined amount of gas fuel. , Λ = 1.0 The control signal for switching to the operation is calculated (step 5). The set value is λ = 1.0
In step 6, the throttle opening threshold value S ₂ = f ₂ (Nm) for switching to λ = 1.4 is obtained in step 6, and the injector 6 is activated when Sm <S _{2 in} step 7. Is stopped (ID = 0) and a control signal for switching to λ = 1.4 is calculated (step 8).

If the set value of λ is 1.0 and Sm <S ₂ is not satisfied in step 7, the abnormality flag is checked in step 9. If the abnormality flag is 0, the O ₂ sensor 9 is normal. And the rich / lean is judged by feeding back the detection signal of the O ₂ sensor 9 (step 10). For example, if rich, the lean time counter CL is set to 0 and the rich time counter CR is set.
Is set to the abnormality determination count number (corresponding to the abnormality determination time) C ₀ (step 11), and a control signal for reducing the injector duty ID until CR = CL is output (step 12). If the signal is lean in step 10, the reverse operation is performed and the control signal for increasing the injector duty ID is output (steps 13 and 14).

By the way, while the O ₂ sensor 9 outputs a rich (or lean) signal, for example, the injector duty continues to decrease (or increase), so that the detection signal becomes lean (or rich) after a certain period of time. If the O ₂ sensor 9 is normal, the rich and lean detection signals may be alternately output in a certain cycle, and one of the rich and lean signals may be continuously output. I don't get it. Therefore, when one of the signals continues for a certain time or longer, it is determined that the O ₂ sensor 9 is abnormal, and the O ₂ sensor 9
The control is switched to the control not using the sensor 9, and CR = C ₀ (or CL = C ₀ ) in step 11 (or step 13).
If the rich (or lean) signal continues until the condition becomes, the error flag is set to 1 (step 15 or 1
6), control transfers from step 9 to step 17.

In step 17, the difference ΔS between the actual throttle opening Sm and the threshold value S ₂ for switching to λ = 1.4.
Is calculated, and a control signal ID = g (ΔS) for additionally supplying fuel corresponding to the engine speed and the throttle opening obtained in advance by the test is calculated, and at the same time, a signal for operating the O ₂ sensor abnormality indicator 29. Is also output (step 1
7). In this way, the control signal corresponding to each case is output to the injector 6, the fuel 15b is additionally supplied, and the air-fuel ratio is maintained at a predetermined value.
(Step 18), even if the O ₂ sensor 9 is abnormal, the operation can be continued while controlling the air-fuel ratio. It should be noted that the throttle opening functions f ₁ (Nm) and f ₂ (Nm) used as the above-mentioned λ switching threshold and the injector duty function g (Δ
S), the abnormality determination count number C _0, etc. are set by a test conducted in advance according to the model and capacity of the engine.

FIG. 3 shows that the injector duty ID is stored in the storage means such as the ROM 22 in step S17.
An example of a map or a calculation formula used for obtaining is shown in the form of a graph, and the numerical value of the throttle opening on the vertical axis is obtained by converting the detection output of the throttle opening detector 5 into a digital value. It is a dimensionless number. Further, the injector duty function g (ΔS) is set to be slightly thicker than λ = 1.0 in order to reduce exhaust emission.

In the present invention, since the injector 6 for additionally supplying the fuel is arranged upstream of the throttle 3, the map or the calculation formula illustrated in FIG. 3 becomes simple. That is, when performing air-fuel ratio control by the additional supply of fuel, conventionally, an additional fuel nozzle is arranged downstream of the throttle in order to suck the additional fuel by using the intake negative pressure. Since the amount of supply of the additional fuel fluctuates greatly depending on the degree of opening of the throttle, and the amount of the additional fuel also fluctuates considerably, the fluctuation of the intake negative pressure must be taken into consideration when calculating the additional fuel. Therefore, the stored contents are the throttle opening, the engine speed and the intake negative pressure.
Those corresponding to individual variables are required, and for example, in the case of a map, it becomes a three-dimensional map, which makes the production of the map cumbersome. Further, in the case of the calculation formula, the formula becomes complicated, the calculation takes time, and there arises a problem that a high-performance microcomputer is required.

On the other hand, in the present invention, the additional fuel is supplied upstream of the throttle 3 which is hardly affected by the negative pressure of the intake air. Therefore, the additional fuel is added in accordance with the two variables of the throttle opening and the engine speed. It suffices to determine the supply amount of Eq. 3, and in the case of a map, a two-dimensional one as shown in FIG. According to this embodiment, the abnormality of the injector 6 is also detected and displayed on the O ₂ sensor abnormality display 29. In this case, abnormalities in the operation itself cannot be prevented, but a malfunction of the injector 6 is detected early, so that appropriate measures can be promptly implemented.

[0018]

As is apparent from the above description, the present invention is effective when the air-fuel ratio sensor becomes abnormal under high load.
In such a case, based on the stored contents prepared in advance, the additional supply amount of the gas fuel is controlled according to the engine speed and the throttle opening, and the additional fuel is supplied upstream of the throttle. It was done like this. Therefore,
By supplying a predetermined amount of gas fuel to the lean mixture, the fuel adjusting means can be downsized and the response can be improved even with a large gas engine that supplies a large amount of fuel. Prevents exhaust emission from deteriorating or the engine to stop due to improper control performed by the output of the air-fuel ratio sensor in an abnormal state, and the operation of the gas engine at high load is continued at an appropriate air-fuel ratio. It is possible to do so. In addition, since the additional fuel is supplied upstream of the throttle, it is hardly affected by the intake negative pressure that fluctuates greatly depending on the opening of the throttle, and the maps and calculation formulas used during abnormalities are simple and control is easy. Of.

[Brief description of drawings]

FIG. 1 is a conceptual system diagram of an embodiment of the present invention.

FIG. 2 is a flowchart of a control procedure of the embodiment.

FIG. 3 is a diagram showing an example of a relationship between an engine duty and an injector duty with respect to a throttle opening when the O ₂ sensor is abnormal in the embodiment.

[Explanation of symbols]

1 Gas Engine 2 Mixer 3 Throttle 4 Electronic Governor 5 Opening Detector 6 Gas Injector 9 O ₂ Sensor 10 Rotation Speed Detector 11 Microcomputer 15a, 15b Fuel Gas 16 Air 21 CPU 22 ROM

Claims (1)

Claim: What is claimed is: 1. A predetermined amount of gas fuel is additionally supplied from an additional fuel supply means to an air-fuel mixture that has been set lean beforehand according to a detection signal from an air-fuel ratio sensor arranged in the exhaust gas. Thus, the air-fuel ratio control means for controlling the air-fuel ratio at the time of high load, and the air-fuel ratio switching means for switching the operation of the air-fuel ratio control means with the throttle opening set in advance according to the engine speed as a threshold value. In the equipped gas engine, the duration of each detection signal indicating rich or lean by the air-fuel ratio sensor is compared with a preset abnormality determination time,
Abnormality detection means that determines that the air-fuel ratio sensor is abnormal if the same detection signal continues until the abnormality determination time is reached, and additional supply of gas fuel to the engine speed and throttle opening that is applied when the air-fuel ratio sensor is abnormal The amount of additional supply of gas fuel based on the stored contents of the storage means regardless of the detection signal from the air-fuel ratio sensor when the abnormality detection means determines that the air-fuel ratio sensor has an abnormality And calculating means for outputting a control signal for controlling the additional fuel supply means, and the additional fuel supply means is configured to supply the additional fuel into the air-fuel mixture upstream of the throttle. An air-fuel ratio control device for a gas engine, which is characterized in that