JPH1130141A - Air-fuel ratio control device for gas engine - Google Patents

Abstract

(57) [Object] To provide an air-fuel ratio control device for a gas engine capable of performing combustion at a target air-fuel ratio and reliably purifying exhaust gas by an exhaust purification catalyst. A three-way catalyst is provided in an exhaust pipe of an engine, and an O ₂ sensor is disposed upstream of the three-way catalyst. The O ₂ sensor 11 has an element 12, and an atmosphere-side electrode 15 is formed on the inner surface of the element 12, and an exhaust gas-side electrode 14 is formed on the outer surface. The exhaust gas side electrode 14 is covered with a catalyst layer 17 for removing hydrogen by a catalytic reaction. ECU
Controlling the fuel supply amount of the gas injector in order to reduce a deviation between the air-fuel ratio and the target air-fuel ratio according to O ₂ sensor 11 by using the feedback correction coefficient FAF based on the output of the O ₂ sensor 11.

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 vehicle or power generation gas engine mainly composed of natural gas.

[0002]

2. Description of the Related Art In recent years, from the viewpoints of environmental protection and air quality improvement, exhaust emissions (HC, CO, NO
_X , CO ₂ ) has been increasingly demanded, and as a means for responding to this demand, automobiles and cogeneration engines using natural gas as fuel have been developed.

[0003]

However, in a natural gas engine, an O ₂ sensor (rich / lean sensor) is used.
The point at which the electromotive force suddenly changes is shifted to a region leaner than the stoichiometric state, so that the control air-fuel ratio (A / F) becomes lean and deviates from the window of the three-way catalyst. Therefore, NO
There is a problem that _X emission increases.

It is an object of the present invention to provide an air-fuel ratio control device for a gas engine that can perform combustion at a target air-fuel ratio and reliably purify exhaust gas by an exhaust gas purifying catalyst. .

[0005]

As also described in SAE872165 and internal combustion engine 28 Vol 12 No., etc. SUMMARY OF THE INVENTION Natural gas engines are H ₂ in the exhaust gas than gasoline is discharged approximately twice as much. Therefore, the present inventors consider that the reason why the air-fuel ratio becomes lean is that the diffusion rate of H ₂ in the exhaust gas is higher than that of O _2, so that the concentration of the component at the reaction interface of the sensor differs from the actual concentration of the component of the exhaust gas. I think that it may be the cause.

[0006] Against this background, the air-fuel ratio control apparatus for a gas engine according to the first aspect of the present invention prevents hydrogen intrusion in the exhaust gas from entering the surface of the exhaust gas side electrode in the air-fuel ratio sensor. It is characterized in that means are provided.

Therefore, the intrusion of hydrogen into the surface of the exhaust gas side electrode is prevented by the hydrogen intrusion prevention means. By removing H _2, which is a cause of the sensor output deviation, from the reaction interface of the sensor (the surface of the exhaust gas side electrode) in this manner,
The output deviation of the sensor can be prevented, and appropriate air-fuel ratio control can be performed.

Further, the air-fuel ratio control device for a gas engine according to the present invention is characterized in that the exhaust gas side electrode of the air-fuel ratio sensor is coated with a catalyst layer for removing hydrogen by a catalytic reaction.

Accordingly, since the exhaust gas side electrode of the air-fuel ratio sensor is covered with the catalyst layer, H ₂ is removed by the catalytic reaction. In this way it is possible to remove and H ₂ as the output deviation factor of the sensor from the reaction interface of the sensor (the surface of the exhaust gas side electrode). As a result, the output deviation of the sensor can be prevented and appropriate air-fuel ratio control can be performed.

According to a third aspect of the present invention, there is provided an air-fuel ratio control device for a gas engine, wherein a heater is provided in the air-fuel ratio sensor, and the surface of the exhaust gas side electrode is maintained at 600 ° C. or higher by the heater. .

Therefore, since the surface of the exhaust gas side electrode is maintained at 600 ° C. or higher by the heater, H ₂ is spontaneously combusted and removed. In this way, H _2, which is a cause of sensor output deviation, is transferred to the reaction interface of the sensor (the surface of the exhaust gas side electrode).
Can be removed from As a result, the output deviation of the sensor can be prevented and appropriate air-fuel ratio control can be performed.

An air-fuel ratio control device for a gas engine according to a fourth aspect is characterized in that a correction means for correcting the air-fuel ratio by the air-fuel ratio sensor to the rich side is provided. Therefore,
Even if the air-fuel ratio sensor deviates to the lean side, the deviation is expected,
By setting the air-fuel ratio control target value based on the air-fuel ratio sensor to the rich side, it is possible to perform optimal air-fuel ratio control.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described.
An embodiment will be described with reference to the drawings.

FIG. 1 shows an overall configuration diagram of an air-fuel ratio control device for a gas engine according to this embodiment. In the engine 1, a piston 3 is arranged in a cylinder 2.
An intake pipe 4 is connected to the engine 1,
An intake valve 5 is provided at the intake port. A gas injector 6 is arranged in the intake pipe 4. And
Air is sucked through the intake pipe 4 and the intake valve 5, and a fuel mainly composed of natural gas is supplied from the gas injector 6, and a mixture of air and natural gas is supplied into the cylinder 2 of the engine.

The engine 1 is provided with a spark plug 7,
The air-fuel mixture in the cylinder 2 is ignited by an ignition plug 7.
An exhaust pipe 8 for forming an exhaust path is connected to the engine 1, and an exhaust port is provided with an exhaust valve 9. Exhaust gas is exhausted to the atmosphere through the exhaust valve 9 and the exhaust pipe 8. A three-way catalyst 10 as an exhaust gas purifying catalyst is provided in the exhaust pipe 8. Further, an O ₂ sensor 11 as an air-fuel ratio sensor is provided upstream of the three-way catalyst 10 in the exhaust pipe 8.

FIG. 2 is a sectional view of the O ₂ sensor 11.
In FIG. 2, a sensor mounting hole 8a is formed in the exhaust pipe 8, and a cup-shaped element 12 made of a solid electrolyte is inserted into the sensor mounting hole 8a. The element 12 is made of zirconia and has a bottomed cylindrical shape. An outer electrode 14 made of Pt is attached to an outer peripheral surface of the element (solid electrolyte tube) 12, and an inner electrode 15 made of Pt is attached to an inner peripheral surface of the element 12. As described above, the O ₂ sensor 11 has the element 12 made of the solid electrolyte, the inner electrode 15 is formed on the inner surface (one side surface) as the atmosphere side electrode, and the outer surface (other side surface) is formed as the exhaust gas side electrode. An outer electrode 14 is formed.

The outer electrode 14 is covered with a coating film 16 for protecting the electrode.
Is coated (applied) with a catalyst layer 17. The catalyst layer 17 is obtained by mixing a catalyst metal such as platinum rhodium with a material such as alumina in an amount of 3 to 5 wt%. Further, the catalyst layer 17 has a protective layer (alumina) 1 for protecting the catalyst layer.
8 covered.

Between the outer electrode 14 and the inner electrode 15,
An electromotive force corresponding to the oxygen concentration in the exhaust gas is generated through the element (solid electrolyte tube) 12, and this is measured by the electromotive force detector 19. FIG. 3A shows the output of the O ₂ sensor 11.

On the other hand, the fuel supply system to the gas injector 6 shown in FIG. 1 has cylinders 20a and 20b, a fuel cutoff valve 21 and a regulator 22, and the cylinders 20a and 20b compress natural gas to about 200 atm. I'm saving. The natural gas in the cylinders 20a and 20b is sent to the regulator 22 through the fuel cutoff valve 21, and the regulator 22 reduces the internal pressure of the cylinder from 200 atm to 3 to 8 atm and supplies the gas to the gas injector 6. The gas pressure between the fuel cutoff valve 21 and the regulator 22 (inside cylinder pressure)
Is measured by the pressure sensor 23 and the fuel meter 2
At 4, the remaining fuel in the cylinder is displayed.

Electronic control unit (hereinafter referred to as ECU)
Reference numeral 25 mainly includes a microcomputer. The ECU 25 receives a signal from the engine speed sensor, a signal from the intake pressure sensor, and a signal from the engine water temperature sensor, and detects the engine speed Ne, the intake pressure PM, the engine water temperature Tw, and the like. Further, the ECU 25 receives the output signal of the O ₂ sensor 11 shown in FIG. 3A, compares it with the comparison voltage Vref, and sets the L level if the sensor signal is smaller than the comparison voltage Vref.
If it is larger, it is set to the H level. According to this comparison result,
The ECU 25 calculates an air-fuel ratio feedback correction coefficient FAF shown in FIG. Furthermore, E
The CU 25 controls the driving of the gas injector 6 to generate O ₂
The injection amount is feedback-controlled using the feedback correction coefficient FAF so that the sensor 11 becomes stoichiometric, and the three-way catalyst 10 is controlled to have the highest purification performance.

Next, the operation of the air-fuel ratio control device for a gas engine configured as described above will be described. FIG.
5 shows a routine for calculating a feedback correction coefficient FAF according to FIG. That is, a routine for calculating the feedback correction coefficient FAF shown in FIG.

In FIG. 4, the ECU 25 determines in step 10
At step 1, it is determined whether or not inversion has occurred due to the output signal of the O ₂ sensor 11 crossing the comparison voltage Vref. If no inversion has occurred, the process proceeds to step 102 to determine whether or not the output is at the H level. If it is at the H level, the ECU 25 proceeds to step 103
Then, the proportional coefficient KIL is subtracted from the feedback correction coefficient FAF at that time. By this process, the feedback correction coefficient FAF gradually decreases at the slope KIL as shown in FIG. Meanwhile, ECU 25 an output signal of the O ₂ sensor 11 in step 102 is at the L level, adds the proportional coefficient KIR to the feedback correction coefficient FAF at that time in step 104. By this processing, the feedback correction coefficient FAF gradually increases with the slope KIR as shown in FIG.

Further, ECU 25 is from the inverted or, alternatively H level of the O ₂ when the output signal of the sensor 11 crosses the reference voltage Vref inversion occurs shifts to its inverted to step 105 from L level in step 101 to the H level It is determined whether the inversion is to the L level. If it is the inversion from the L level to the H level, the ECU 25 sets the delay time TDR in step 106. Also, the ECU 25
If it is the inversion from the level to the L level, step 107
Sets the delay time TDL.

Then, the ECU 25 executes step 108,
At 109, it is determined whether or not the delay times TDR, TDL have elapsed. When the delay time TDR has elapsed since the inversion, at step 110, the feedback correction coefficient FAF at that time is determined.
, The skip amount SL is subtracted. On the other hand, when the delay time TDL has elapsed since the reversal, the ECU 25 executes step 1.
In step 11, the skip amount SR is added to the feedback correction coefficient FAF at that time. By this processing, (the predetermined amount S
L, SR), the feedback correction coefficient F
AF changes greatly (skip) as shown in FIG.
I do.

As described above, the ECU 25 controls the O ₂ sensor 1
1 is compared with the reference level Vref, and when the result is inverted, the feedback correction coefficient FAF is set to a predetermined value S.
By adding or subtracting only R and SL, and not inverting, the feedback correction coefficient FAF is gradually increased or decreased. Then, the fuel amount is calculated using the feedback correction coefficient FAF as described below.

FIG. 5 shows a fuel injection control routine performed by the ECU 25. In FIG. 5, the ECU 25 takes in the engine speed Ne and the intake pressure PM in step 201,
In step 202, a basic injection amount Tp corresponding to the engine speed Ne and the intake pressure PM is calculated using a map prepared in advance. Then, the ECU 25 determines in step 203
It is determined whether or not the air-fuel ratio feedback control condition (the temperature Tw of the engine cooling water is equal to or higher than a predetermined temperature) is satisfied. If the condition is satisfied, the process proceeds to step 204, where the feedback correction coefficient FAF is multiplied by the basic injection amount Tp. Calculate the final injection amount.

The driving of the gas injector 6 is controlled so as to attain the final injection amount. As described above, the ECU 25 as the air-fuel ratio control means controls the amount of fuel supplied by the gas injector 6 so as to reduce the deviation between the air-fuel ratio detected by the O ₂ sensor 11 and the target air-fuel ratio.

Next, as shown in FIG.
The difference between the case where the catalyst layer 17 is provided and the case where the catalyst layer 17 is not provided will be described. FIGS. 6 and 7 show the mechanism of occurrence of sensor output deviation when the catalyst layer 17 is not provided.
This will be described with reference to FIG. In FIG. 6, when there is no catalyst layer 17, O ₂ and H ₂ pass through the coating layer 16 and cause an oxidation reaction at the outer electrode 14 made of Pt. At this time, since the fast H ₂ of the gas diffusion rate than O ₂ are to be spread more than O _2, the exhaust gas component be stoichiometric, will with H ₂ rich near the electrode, the output of the O ₂ sensor 11, the exhaust gas If the ingredients are not leaner than stoichiometric, they will not change suddenly. for that reason,
As shown in FIG. 7, the relationship between the excess air ratio λ and the sensor output shifts to the lean side.

On the other hand, when the catalyst layer 17 is provided as shown in FIG. 8, O ₂ and H ₂ react in the catalyst layer 17 and Pt is used as an equilibrium gas (post-reaction gas; H ₂ O gas). Since the light reaches the outer electrode 14, the shift of the sensor output can be suppressed as shown by the solid line in FIG.

[0030] Figure 26, HC amount of exhaust gas after passing through the three-way catalyst 10, CO amount, which shows the amount of NO _x,
“O” indicates that there is no catalyst layer 17, and “▲” indicates that there is a catalyst layer 17. As can be seen, by providing the catalyst layer 17, HC, CO, NO _x is reduced both can suppress emissions after the three-way catalyst.

As described above, the present embodiment has the following features.
Have. (B) O_TwoThe outer electrode 14 of the sensor 11 is
In addition, it was covered with a catalyst layer 17 for removing hydrogen. Yo
The catalyst is carried on the surface of the outer electrode 14 on the exhaust gas side.
The H_TwoIs removed. Toes
The catalyst layer 17 _TwoOuter electrode 1 in sensor 11
4 prevents hydrogen in the exhaust gas from entering the surface
It functions as an entry prevention means. In this way, the sensor output
H that causes force deviation_TwoThe reaction interface of the sensor (of the outer electrode
Surface). As a result, the sensor
Output deviation can be prevented and appropriate air-fuel ratio control can be performed. (Second Embodiment) Next, a second embodiment will be described with reference to the first embodiment.
The following description focuses on the differences from this embodiment.

In this embodiment, a wide-range air-fuel ratio sensor (linear sensor) 26 shown in FIG. 10 is used in place of the rich / lean sensor (O ₂ sensor) 11. The outside of the outer electrode 14 of the element (solid electrolyte tube) 12 is covered with a catalyst layer 27 for removing hydrogen by a catalytic reaction.

That is, the structure of the wide-range air-fuel ratio sensor is basically the same as that of the O ₂ sensor shown in FIG. 2, except that a coating film 27 for controlling the diffusion of gas is provided instead of the coating layer 16 of FIG. I have. The coating film 27 is coated with a catalyst layer 28. Further, the catalyst layer 2
The surface 8 is covered with a protective layer (alumina) 33. Further, a power supply 29 is connected between the electrodes 14 and 15, and an alumina heater 30 is arranged in the element (solid electrolyte tube) 12. The alumina heater 30 receives power from the power supply 31 and heats the element (solid electrolyte tube) 12. Also,
The current flowing between the electrodes 14 and 15 is detected by a current detector 32.

FIGS. 11 to 13 show the principle of the wide area air-fuel ratio sensor.
This will be described with reference to FIG. As shown in FIG. 12, an electromotive force generated at λ = 1 in the zirconia element (solid electrolyte tube) 12 is 0.5.
A volt is applied in the opposite direction of the electromotive force as shown in FIG.
The air-fuel ratio is detected by the current IG between the electrodes.

At the time of stoichiometry, as shown in FIG. 13B, the electromotive force of the element 12 is balanced with the applied voltage, so that the current IG becomes "0". At the time of leaning, as shown in FIG. 13 (c), the electromotive force of the element 12 becomes 0 volt, so that O ^2- moves from the outer electrode 14 to the inner electrode 15 due to the applied voltage, and the positive current IG Is generated. In addition, when rich, as shown in FIG. 13A, the electromotive force of the element 12 is 1 volt, so that O ^2- moves from the inner electrode 15 to the outer electrode 14 due to a difference from the applied power, and A negative current is generated as IG. The current IG flowing at this time is
At the time of leaning, O passing through the coating film (porous layer) 27
₂ amount, since determined that the rich during coating film (porous layer) HC through 27, CO amount, like natural gas engine, when the H ₂ increases in the exhaust, varies the current value for the same air-fuel ratio .

FIG. 14 shows a case where a general wide-range air-fuel ratio sensor without the catalyst layer 28 of FIG. 10 is provided before (upstream) and after (downstream) the three-way catalyst 10 in a natural gas engine. And the relationship between the excess air ratio λ and the sensor current. In other words, before the three-way catalyst 10, there is an exhaust gas atmosphere containing hydrogen, and after the three-way catalyst 10, there is an exhaust gas atmosphere containing no hydrogen. The measurement results of the output characteristics when the sensor is arranged in each atmosphere Is shown. As shown in FIG. 15, in the stoichiometric to rich region, the H ₂ concentration in the exhaust gas rapidly increases, and thus becomes H ₂ rich near the active surface (the surface of the outer electrode 14) of the sensor, as shown in FIG. , The sensor output shifts to the rich side.

By providing the air-fuel ratio sensor with the catalyst layer 28 shown in FIG. 10, the output deviation can be suppressed as shown in FIG. (Third Embodiment) Next, a third embodiment will be described with reference to the first embodiment.
The following description focuses on the differences from this embodiment.

FIG. 17 is a structural view of the O ₂ sensor according to the present embodiment. Zirconia element 12, inner electrode 1
5, the outer electrode 14 and the coating layer 16 are the same as the structure shown in FIG. 2, but in the present embodiment, a rod-shaped alumina heater 40 is inserted inside the cup-type element (solid electrolyte tube) 12. . The heater-equipped sensor is the same as that used for the purpose of activating the sensor early in a general gasoline engine. In FIG. 17, a power supply 41 is connected to an alumina heater 40 via a switching element 42. Then, the duty control (on / off control) of the switching element 42 is performed by the ECU 25. By adjusting the duty ratio during this control, the amount of power supply to the heater 40 can be adjusted. That is, when the duty ratio (ON time) is increased, the power supply amount is increased.

The heater 40 is controlled such that the engine speed and the intake pipe pressure are adjusted so that the surface side temperature of the outer electrode 14 of the sensor becomes 600 ° C. or higher in a region Z1 where the exhaust temperature is 600 ° C. or lower shown in FIG. The power supply is determined based on the dimensional map. That is, the power supply characteristic lines L1 to L8 are provided in the region Z1 at the exhaust temperature of 600 ° C. or lower, and the power supply amount of L2 is larger than that of the power supply characteristic line L1, and similarly, L3, L4, L5, L6 , L7, and L8 are determined so that the power supply amount increases in this order. Then, characteristic lines L1 to L8 corresponding to the engine state (engine speed and intake pipe pressure) at that time are selected, and the power supply amount corresponding to the selected characteristic line is supplied.

More specifically, the heater control is performed so that the surface side temperature of the outer electrode 14 of the sensor is in the range of 600 to 700 ° C. By setting the temperature to 700 ° C. or lower, the durability of the heater can be secured. The surface side temperature of the outer electrode 14 of the sensor may be 600 ° C. or more.

Referring to FIGS. 19 and 20, the effect of suppressing output deviation during heater control will be described. In general, H ₂ is known to spontaneously burn at 600 ° C. or higher in an oxidizing atmosphere, and as shown in FIG.
By maintaining the temperature at 0 ° C. or higher, H ₂ and O ₂ react on the surface side of the outer electrode 14, and the equilibrium gas (reacted gas; H ₂ O gas) passes through the coating layer 16. Therefore, the output shift can be suppressed as shown by the solid line in FIG.

In FIG. 26, "△" indicates that the heater 40 of FIG. 17 is installed and maintained at 700.degree. As can be seen, by providing the heater 40 and maintaining the temperature at 700 ° C., both HC, CO, and NO _x are reduced, and the amount of exhaust after the three-way catalyst can be suppressed.

As described above, this embodiment has the following features. (A) The heater 40 is provided in the O ₂ sensor, and the outside of the outer electrode 14 is maintained at 600 ° C. or higher by controlling the energization of the heater 40 by the ECU 25. Therefore, the heater 40
Since the temperature outside of the outer electrode 14 is maintained at 600 ° C. or higher, H ₂ is spontaneously combusted and removed. That is, the heater 40 and the ECU 25 function as hydrogen intrusion prevention means for preventing intrusion of hydrogen in the exhaust gas into the surface of the outer electrode 14 in the O ₂ sensor. In this way it is possible to remove and H ₂ as the output deviation factor of the sensor from the reaction interface of the sensor (the surface of the outer electrode). As a result, the output deviation of the sensor can be prevented and appropriate air-fuel ratio control can be performed. (Fourth Embodiment) Next, a fourth embodiment will be described with reference to the first embodiment.
The following description focuses on the differences from this embodiment.

In this embodiment, the comparison voltage (reference level) Vref of FIG. 3 is used without using the catalyst layer 17 of FIG. 2 so that the ECU 25 of FIG. 1 moves the control center of the air-fuel ratio feedback control to the rich side. Proportional coefficients (gradual change values without inversion) KIL, KIR, delay times (time from inversion to addition or subtraction of correction coefficient) TDR, TDL,
At least one of the skip amounts (addition value and subtraction value at the time of inversion) SL and SR is adjusted, and the value is stored in the memory.

That is, the air-fuel ratio feedback control of the system shown in FIG. 4 is performed by a method in which the output of the O ₂ sensor is compared with the comparison voltage Vref by the ECU 25 to increase or decrease the feedback correction coefficient FAF. As control constants at this time, Vref, SL, SR, KIL, K in FIG.
IR, TDR, and TDL are used, and the control air-fuel ratio is controlled to be richer than stoichiometric by adjusting these constants (changing the ratio of the constants).

For example, with respect to the general FAF calculation system shown in FIG. 21, TDL or KIL is reduced, TDR or KIR is increased, or Vre
By increasing f, the rich time ratio in the air-fuel ratio feedback cycle is increased, and the control center of the air-fuel ratio feedback control is moved to the rich side.

Specifically, for example, the sensor output is shown in FIG.
As shown in FIG. 22, the comparison voltage Vref is 0.45 volts, and this is set to be equal to or greater than the comparison voltage Vref = 0.70 volts as shown in FIG.
0.8 for 2). That is, a value equal to or greater than 70% of the width (1 volt) of the sensor output voltage is set as the comparison voltage Vref.

Alternatively, as shown in FIG.
Normally, the proportional coefficient KIR is set to the same value (1 time) as compared to IL, but this is set to the proportional coefficient KIL as shown in FIG.
Is set to a value three times as large as

Alternatively, as shown in FIG. 21, the delay time TDR is usually set to be about 10 times as long as the delay time TDL, but as shown in FIG. 24, the delay time TDR is set to be 20 times as large as the delay time TDL. Set to the value of.

As described above, in the case of a natural gas engine, O ₂
Since the output of the sensor shifts to the lean side, the control target can be set to the rich side by adjusting the ratio of the constant, and the actual control A / F can be stoichiometric, and the catalyst purification performance can be improved. Is obtained.

In FIG. 26, "□" shows a constant changed. As can be seen, by changing the constants, HC, CO, NO _x is reduced both can suppress emissions after the three-way catalyst. Specifically, KIR = 6% / sec and KIL = 5% / s before the measures
ec was changed to KIR = 10% /
When sec and KIL are set to 2% / sec, the emission amount after the three-way catalyst can be suppressed as described above.

As described above, this embodiment has the following features. (A) The ECU 25 as the correction means is the O ₂ sensor 11
Has a correction function of correcting the air-fuel ratio to the rich side.
That is, Vref, SL, and
At least one of SR, KIL, KIR, TDR, and TDL was adjusted. Therefore, even if the O ₂ sensor 11 shifts to the lean side, it is possible to anticipate the shift, set the A / F control target value based on the O ₂ sensor 11 to the rich side, and perform optimal air-fuel ratio control. Therefore, HC, CO,
Both NO _X and the emission amount after the three-way catalyst can be suppressed. (Fifth Embodiment) Next, a fifth embodiment will be described with reference to FIG.
The following mainly describes differences from the third embodiment.

In this embodiment, in the system shown in FIG. 1, when a sensor with a catalyst layer is used as in the first embodiment or a sensor with a heater is used as in the third embodiment, depending on the engine, high rotation, in a low load region, when the increasingly cold gas flow, H ₂ removal capacity of the sensor in some cases not sufficiently obtained. In this embodiment,
We are working on that.

As shown in FIG. 25, constants (Vref, SL, SR, KI in FIG. 3) for air-fuel ratio feedback are stored in the ECU 25 according to the engine speed and the intake pipe pressure.
L, KIR, TDR, and TDL) are determined, and the degree of enrichment of the control target is increased in a high-speed and low-load region.

That is, the characteristic line L
L1 to L9, the rich amount of L2 is larger than that of the characteristic line L1, and similarly, L3, L4, L5, L6, L7, L
The rich amount is determined to increase in the order of 8, L9. Then, characteristic lines L1 to L9 according to the engine state (engine speed and intake pipe pressure) at that time are selected, and a correction coefficient and the like are selected so as to have a rich amount corresponding to the selected characteristic line.

As a result, the H ₂ removal capability is reduced at the high rotation speed and low load side, and the lean displacement of the sensor is easily caused. However, the lean displacement of the control A / F can be suppressed.

In addition to those described above, the first, third, and fourth embodiments may be implemented in combination. That is, the catalyst layer 17 shown in FIG. 2 and the heater 40 shown in FIG. 17 are provided, and constants (Vref, SL, SR, KIL, KIR, TDR, TD in FIG. 3) for the air-fuel ratio feedback are provided.
L) may be changed. In this way, as shown by “x” in FIG. 26, both HC, CO, and NO _x are significantly reduced, and the emission after the three-way catalyst can be suppressed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an air-fuel ratio control device for a gas engine according to a first embodiment.

FIG. 2 is a sectional view of the O ₂ sensor.

FIG. 3 is an explanatory diagram of an output signal and an FAF of an O ₂ sensor.

FIG. 4 is a flowchart illustrating an FAF calculation processing routine;

FIG. 5 is a flowchart showing an air-fuel ratio control processing routine.

FIG. 6 is a schematic diagram of an O ₂ sensor without a catalyst layer.

FIG. 7 is a sensor output characteristic diagram when there is no catalyst layer.

FIG. 8 is a schematic diagram of an O ₂ sensor when a catalyst layer is provided.

FIG. 9 is a sensor output characteristic diagram when a catalyst layer is present.

FIG. 10 is a sectional view of a wide-range air-fuel ratio sensor according to a second embodiment.

FIG. 11 is a schematic diagram showing the principle of a wide area air-fuel ratio sensor.

FIG. 12 is an output characteristic diagram of a wide area air-fuel ratio sensor.

FIG. 13 is a schematic diagram showing the principle of a wide area air-fuel ratio sensor.

FIG. 14 is an output characteristic diagram when there is no catalyst layer.

FIG. 15: Excess air ratio of natural gas engine and H in exhaust gas
_The figure which shows the relationship of ₂ quantity.

FIG. 16 is an output characteristic diagram when there is a catalyst layer.

FIG. 17 is a sectional view of an O ₂ sensor according to a third embodiment.

FIG. 18 is a two-dimensional map used in the third embodiment.

FIG. 19 is a schematic diagram of an O ₂ sensor according to a third embodiment.

FIG. 20 is an output characteristic diagram of the O ₂ sensor.

FIG. 21 is a control diagram of a general FAF.

FIG. 22 is a control diagram of the FAF according to the fourth embodiment.

FIG. 23 is a control diagram of the FAF according to the fourth embodiment.

FIG. 24 is a control diagram of the FAF according to the fourth embodiment.

FIG. 25 is a two-dimensional map used in the fifth embodiment.

FIG. 26 is a view showing a measurement result of LA mode emission.

[Explanation of symbols]

6 gas injector, 8 exhaust pipe, 10 three-way catalyst,
11 ... O ₂ sensor, 12 ... device, 15 ... inner electrode, 14
... outer electrode, 17 ... catalyst layer, 25 ... ECU, 40 ... heater.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G01N 27/409 G01N 27/58 B (72) Inventor Motomasa Iizuka 14 Iwatani, Shimowasumimachi, Nishio-shi, Aichi Japan Automotive Parts Co., Ltd. Within the Research Institute (72) Inventor Takeshi Mizobuchi 14 Iwatani, Shimowasumi-machi, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute, Inc. (72) Inventor Hidetaka Hayashi 1-1-1, Showa-cho, Kariya-shi, Aichi, Japan Denso Corporation (72) Inventor Yoshihiko Kuroda 1-1-1, Showa-cho, Kariya-shi, Aichi prefecture, Denso Corporation

Claims (5)

[Claims] 1. An exhaust purification catalyst provided in an exhaust passage of an engine, and an exhaust gas catalyst is disposed on one side of the exhaust passage and disposed on an upstream side of the exhaust purification catalyst of the exhaust passage. An air-fuel ratio sensor having an element made of a solid electrolyte on which a side electrode is formed; a gas injector for supplying fuel mainly composed of natural gas to the engine; and a deviation between an air-fuel ratio and a target air-fuel ratio by the air-fuel ratio sensor. Air-fuel ratio control means for controlling the amount of fuel supplied by the gas injector in order to reduce the air-fuel ratio. An air-fuel ratio control device for a gas engine, comprising a hydrogen intrusion prevention means for preventing intrusion of hydrogen. 2. An exhaust gas purification catalyst provided in an exhaust path of an engine, and an exhaust gas catalyst is disposed on one side of the exhaust path and disposed on an upstream side of the exhaust purification catalyst of the exhaust path. An air-fuel ratio sensor having an element made of a solid electrolyte on which a side electrode is formed; a gas injector for supplying fuel mainly composed of natural gas to the engine; and a deviation between an air-fuel ratio and a target air-fuel ratio by the air-fuel ratio sensor. An air-fuel ratio control device for a gas engine, comprising: an air-fuel ratio control unit that controls the amount of fuel supplied by the gas injector to reduce the fuel consumption. An air-fuel ratio control device for a gas engine, wherein the device is coated with a catalytic layer. 3. An exhaust gas purification catalyst provided in an exhaust path of an engine; and an exhaust electrode disposed on one side and an exhaust gas disposed on the other side, disposed on the upstream side of the exhaust purification catalyst on the exhaust path. An air-fuel ratio sensor having an element made of a solid electrolyte on which a side electrode is formed; a gas injector for supplying fuel mainly composed of natural gas to the engine; and a deviation between an air-fuel ratio and a target air-fuel ratio by the air-fuel ratio sensor. Air-fuel ratio control means for controlling the amount of fuel supplied by the gas injector in order to reduce the air-fuel ratio. A heater is provided for the air-fuel ratio sensor, and the exhaust gas side electrode is provided by the heater. An air-fuel ratio control device for a gas engine, wherein a surface of the gas engine is maintained at 600 ° C. or higher. 4. An exhaust gas purification catalyst provided in an exhaust path of an engine; and an exhaust gas catalyst disposed on an upstream side of the exhaust gas purification catalyst of the exhaust path and having an atmosphere-side electrode formed on one side surface and an exhaust gas on another side surface. An air-fuel ratio sensor having an element made of a solid electrolyte on which a side electrode is formed; a gas injector for supplying fuel mainly composed of natural gas to the engine; and a correction for correcting an air-fuel ratio by the air-fuel ratio sensor to a rich side. And an air-fuel ratio control means for controlling a fuel supply amount by the gas injector so as to reduce a deviation between an air-fuel ratio and a target air-fuel ratio by the correction means. apparatus. 5. The air-fuel ratio sensor detects an electromotive force due to a difference in oxygen concentration between one side surface and the other side surface of the element at an atmosphere side electrode and an exhaust gas side electrode. When the output signal of the sensor is compared with the reference level and the result is inverted, the correction coefficient is added or subtracted by a predetermined value. Otherwise, the correction coefficient is gradually increased or decreased. 5. The method according to claim 4, wherein at least one of the subtraction value, the gradual change value when not inverted, and the time from inversion to addition or subtraction of the correction coefficient is adjusted so that the air-fuel ratio is on the rich side. Air-fuel ratio control device for gas engine.