JPS6027747A - Air-fuel ratio controlling method for gas engine - Google Patents

Abstract

PURPOSE:To attain stable operation of an engine, by preventing occurrence of cycling by stopping for a predetermined while after changing the air-fuel ratio to a lower value, and obtaining an optimum incremental threshold value by correcting the incremental threshold value reduced from the opening of a throttle valve at the time of changing the air-fuel ratio according to the difference of the engine speed before and after changing the engine speed for increasing or decreasing the same. CONSTITUTION:Opening thetan1 of an air-fuel ratio switching throttle valve meeting the engine speed is selected from a table by detecting the engine speed by a sensor 11. Then, the actual opening thetam of the throttle valve is detected by a valve opening detector 30 and it is compared with the opening thetan1. In case of thetam>=thetan1, theoretical air-fuel ratio control is executed by closing an EGR valve 17 and setting an air-fuel ratio control mechanism into operation. Thereafter, a certain interval time is taken, and after passing of waiting time, the engine speed N1 and the actual throttle valve opening thetam at the time are detected to prepare the valve opening thetan2, obtained by subtracting several steps from the valve opening thetam as a threshold value for switching the air-fuel ratio from lambda= 1.0 to lambda=1.4. Thus, since an optimum throttle valve opening meeting the engine load can be obtained regardless of the change of the load/throttle valve opening characteristics, it is enabled to prevent occurrence of cycling.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a gas engine which can prevent cycling when switching the air-fuel ratio by optimizing one threshold value of the throttle valve opening when switching the air-fuel ratio in the direction of increasing the air-fuel ratio. This invention relates to an air-fuel ratio control method.

Generally, when controlling the air-fuel ratio of a gas engine, for example, the excess air ratio λ (λ=supply air-fuel ratio/stoichiometric air-fuel ratio) is set to λ=1.
When performing air-fuel ratio control by switching between 0 (stoichiometric mixture ratio) and λ = 1.4 (lean mixture ratio), λ = 1゜4→
Threshold value θ for comparing the throttle valve opening degree when switching between λ=1°0 and λ=1.0. .

→Threshold value θn2 for comparing the throttle valve opening when switching λ=1.4 was set to a fixed value (θ
nl)θn2).

However, with this method of fixing the threshold value of the throttle valve opening when switching the air-fuel ratio, the throttle valve opening when switching the air-fuel ratio may The threshold value of the opening degree, especially the throttle valve opening degree (Jn2) serving as the threshold value, is no longer the optimal value.

That is, when the throttle valve opening degree θn2 becomes larger than the optimum value, the threshold value when switching from λ=1.0 to λ=1.4 becomes larger. Then, from λ=1.4 to λ=1
As soon as it switches to 0, the actual throttle valve opening θm falls below this threshold value (θn2).
It returns to λ=1.4 again. However, unless the load suddenly changes, the actual throttle valve opening θ at λ=1.4
Since m is greater than the throttle valve opening on1 which is the threshold value at the time of switching from λ=1°4 to λ=1.0, the switch is again made to λ=1°0. In this way, the gas engine has λ=1.0
and λ=1°4, resulting in so-called cycling, which makes stable operation impossible.

Furthermore, if the throttle valve opening θn2 becomes smaller than the optimum value, once it is switched from λ = 1°4 to λ = 1.0, it will be switched from λ = 1.0 to λ = 1.4. Because the threshold for switching is small, the load is small.
There is a drawback that even if the actual throttle valve opening θm reaches the throttle valve opening that should return to λ=1.4, it will not switch, and the gas engine 75 will not be able to operate efficiently.

An object of the present invention is to eliminate the drawbacks of the conventional air-fuel ratio control method for a gas engine, which fixes the throttle valve opening θn2 when switching from λ=1.0 to λ=1°4, and to The throttle valve opening when switching from λ=1.4 to λ=1.0 can be optimized regardless of readjustment of the air-fuel ratio in part of the mixer or changes in the engine over time, and cycling when changing the air-fuel ratio. An object of the present invention is to provide an excellent air-fuel ratio control method for a gas engine that can prevent this.

The air-fuel ratio control method for a gas engine according to the present invention that achieves the above object has an air-fuel ratio control mechanism that adds a predetermined amount of fuel to an injector, and controls the throttle valve opening determined according to the engine speed. In a gas engine that switches the air-fuel ratio by turning on and off the operation of the air-fuel ratio control mechanism, the actual throttle valve opening degree is judged using the opening degree as a threshold value, and the air-fuel ratio is switched on and off based on the result. When switching, the switching operation of the air-fuel ratio control mechanism is stopped for a predetermined period of time after the air-fuel ratio is switched, and the throttle valve opening is set to a direction that increases the air-fuel ratio by a predetermined opening smaller than the throttle valve opening at the time of the air-fuel ratio switching. Set the threshold value for air-fuel ratio switching, and
The threshold value is corrected in accordance with the difference in engine speed between the engine speed at the time of switching to the air-fuel ratio increasing direction and the engine speed at the time of switching to the air-fuel ratio decreasing direction. It is said that

An embodiment of the method of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram showing the configuration of an air-fuel ratio control mechanism of a gas engine to which the method of the present invention is applied.

A gas introduction pipe 26 is provided in the venturi 24 of the intake pipe 21 of the gas engine 20, and the gas injector 14 and the EGR pipe 18 are connected to the downstream side of the intake pipe 21 to form a mixer part 26. are doing.

A throttle valve 22 is further provided on the downstream side of the mixer portion 26, and its rotating shaft 22a connects to the governor 1 through the connecting member 16 outside the intake pipe 21.
The control lever 12a is connected to the control lever 12a. 1 is a throttle valve opening degree detector attached to the throttle valve 22.

Further, a rotation speed sensor 11 is attached to rotating parts such as the flywheel 25 of the gas engine 20, so that the actual rotation speed of the gas engine 20 can be detected. 2
7 is an intake valve, 28 is an exhaust valve, and 29 is a piston.

Further, the exhaust pipe 19 of the gas engine 20 has the EGR
The other end of the pipe 18 is connected, an 02 sensor 15 is disposed on the downstream side thereof, and a three-way catalyst 16 is disposed further downstream.

Reference numeral 17 denotes an EGR valve provided in the middle of the EGR pipe 18, which opens and closes the EGR pipe 18 in response to a signal from the control unit 10. This EGR valve 17 and the gas injector 14 are connected to an amplifier 8 of a control unit 10, which will be described later.

The control unit 10 that controls the rotation speed of the gas engine 20 configured as described above includes a CPU.
2. ROM 3. RAM 4. A microcomputer 1 consisting of an I10 port 5, and the rotation speed sensor 11
A counter 6 connects to the gas engine 20 and outputs the rotation speed of the gas engine 20 as a digital signal, an opening signal from the engine load and the throttle valve opening detector 60, and a 02 sensor 1.
In order to input the residual oxygen amount signal from 5 to the microcomputer 1, a 0 converter 7 and the like are built in to convert it into a digital signal, and these are connected to each other by a pass line 9. 8 is an amplifier, which amplifies the control signal output from the gas injector 14, E'
There are 17 GR valves in total.

In this embodiment, the gas filter 12 is an electronically controlled governor, which is controlled by, for example, a step motor 12C according to instructions from the microcomputer 1, and is controlled by the step number of the pulse signal output from the microcomputer 1. It is assumed that the throttle valve 22 is rotatable.

In the air-fuel ratio control mechanism for a gas engine configured as described above, the basic controls of speed governor control and air-fuel ratio control are conventionally performed. That is, regarding speed control control, the microcomputer 1 of controller 10 performs ax processing based on the deviation between the set rotation speed according to the heat pump load and the actual engine rotation speed, and sends a pulse signal to the step motor 12C. output and operate the throttle valve 22. Regarding air-fuel ratio control, the actual throttle valve opening is determined using the throttle valve opening corresponding to the engine speed stored in the ROM 3 of the microcomputer 1 as a threshold, and the mixer is adjusted according to the deviation. A combination of lean combustion in part 26 and EGR by opening the EGR valve 17;
The feedback signal from the 02 sensor 15 switches between stoichiometric air-fuel ratio combustion by operating the gas injector 14 and the combination of the three-way catalyst 16.

The actual throttle valve opening degree is detected using a throttle valve opening degree detector 60 attached to the throttle valve 22.

However, since cycling occurs as described above in the IT control, in this invention, when changing the air-fuel ratio, the throttle valve opening degree is adjusted separately from the self-regulating speed e control. The threshold value at the time of air-fuel ratio switching is adjusted according to the procedure shown in the flowchart of FIG.

First, when changing the excess air ratio from the lean burn system to the stoichiometric mixture ratio to the catalytic system (λ = 164 → λ = 1°O), in step The air-fuel ratio switching throttle opening degree θn1 corresponding to the rotation speed is selected from the table below in step (3). , In the air-fuel ratio switching throttle opening number table and correction number table method, the actual throttle valve opening θm is determined by the throttle valve opening detector 60 in step 2, and in step 2 this is converted to the aforementioned throttle valve opening. (Compare and judge with lnl. θm≦
If θn1 (No), return to step ■ without switching the air-fuel ratio, but if θm≧θn1 (YES),
The program moves to step (2) to close the EGR valve 17, and then to step (2), the operation of the air-fuel ratio control mechanism is turned on to perform stoichiometric air-fuel ratio control.

After this, take an interval time in step ■ and move on to step ■. Step (3) is for providing a waiting time after the air-fuel ratio switching, and is intended to prevent the air-fuel ratio switching from being performed during this waiting time. The predetermined waiting time is determined by the ROM 3 of the microcomputer 1.
As long as the waiting time has not elapsed, I) (NO),
In step (2), the process returns to before step (2) to take an interval time.

After the waiting time has elapsed (YES), move to step [phase].
Engine speed N1 and actual throttle valve opening θm at that time
I apologize. Then, the throttle valve opening θn2' obtained by subtracting a few steps from the throttle valve opening θm at this time and the reduced throttle valve opening is calculated by the microcomputer 1, and the engine speed N1. RAM
4 and store this throttle valve opening θn2' as λ=1
・Prepare as a threshold for switching the air-fuel ratio from 0 to λ=1.4. In this way, regardless of changes in the load-throttle valve opening characteristic due to readjustment of the air-fuel ratio of MIKI V-4V+26 or changes in the engine over time, the optimal throttle corresponding to the load that should return to λ = 1.4 can be set. It will return depending on the valve opening.

The reason for providing a certain waiting time after switching from λ=1°4 to λ=1.0 is to take into account the response characteristics of the governor 12, and the actual throttle valve opening θm) Step small throttle valve opening θn2″ λ=1.o→λ=
The reason for setting the threshold value at the time of switching to 1.degree. 4 is to provide hysteresis to prevent cycling.

However, when λ=1. Since the optimal throttle valve opening threshold for switching from o to λ=1.4 varies depending on the engine speed, if the engine speed for switching from λ=1° to λ=1.4 is different from the engine speed when switching from λ=1°4 to λ=1.0, the throttle valve opening θn2' will be the optimum when switching from λ=1°0 to λ=1.4. is no longer the threshold value. Therefore, in the method of the present invention, in the steps from step 0 to step [Yes], the throttle valve opening degree θn2' is corrected based on the engine rotation speed.

In other words, after taking the interval time at step 0,
Every time step 0 is passed, the engine speed Nm at that time is detected and stored in RAM4, and at step @, the above λ=1°4→
Read the engine rotation speed N1 at the time of λ=1.0 switching and the engine rotation speed Nm at this time from RAM 4, and store the correction step numbers f(N1) and f(Nm) according to the rotation speed in the ROM.
Calculate based on the deletion stored in 3. Then, the process moves to step 0'), and the CPU 2 calculates the optimal throttle valve opening degree θn2'' at that time as a threshold value based on the following formula.

on2″=θn2′ −t (N1) 10f (Nm
) As can be seen from this equation, if the engine speed N1 when switching from λ=1°4 to λ=1°0 is equal to the engine speed Nm when switching from λ=1°0 to λ=1°4, Throttle valve opening θn
2' is not subjected to correction, and Onz"=θn2'.

Then, in step [phase], the actual throttle valve opening θm at that time is determined, and in step [phase], this throttle valve opening θm is determined using the throttle valve opening θnf determined in step @ as a threshold value.

If it is determined that Onz"≦θm (No) in this step [phase], the air-fuel ratio switching from λ = 1.0 to λ = 1°4 is not performed and the process returns to before step 0, and 0m (Onz" (Y
If it is determined that ES), the process moves to step 0 in order to perform the air-fuel ratio switching from λ=1°0 to λ=1°4. Then, in step ◎ and step [phase], the EGR valve 17 is opened in the complete opposite of steps ■ and step ■, the operation of the air-fuel ratio control mechanism is turned off, the stoichiometric air-fuel ratio control is stopped, and the lean burn mode is started. . After this step [phase], the process returns to step (2) and the same control as described above is performed.

In this way, in the air-fuel ratio control method for a gas engine of the present invention,
It is possible to always perform stable air-fuel ratio switching control without causing cycling when switching the air-fuel ratio of a gas engine.

As explained above, the air-fuel ratio control method for a gas engine of the present invention has an air-fuel ratio control mechanism that adds a predetermined amount of fuel to an injector, and a throttle valve that is determined according to the engine speed. In a gas engine in which the actual throttle valve opening is determined using the opening as a threshold value, and the air-fuel ratio is switched by turning on and off the operation of the air-fuel ratio control mechanism based on the result, the air-fuel ratio is decreased. When switching the air-fuel ratio, the switching operation of the air-fuel ratio control mechanism is stopped for a predetermined period of time after the air-fuel ratio is switched, and the throttle valve opening is set in the direction of increasing the air-fuel ratio by a predetermined opening smaller than the throttle valve opening at the time of the air-fuel ratio switching. Set the threshold value for switching the air-fuel ratio to , and further set the engine speed difference between the engine speed at the time of switching to the air-fuel ratio increasing direction and the engine speed at the time of switching to the air-fuel ratio decreasing direction. By correcting the threshold value accordingly, it is possible to suppress the occurrence of cycling when switching the air-fuel ratio of the gas engine, and there is an excellent effect that hunting does not occur in the gas engine.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram of an embodiment of an air-fuel ratio control mechanism for a gas engine to which the method of the present invention is applied, and FIG. 2 is a flowchart showing the operating procedure of the air-fuel ratio control mechanism of FIG. 1. 1... Microcomputer, 2... CPIJ, 3
... ROM, 4... RAM, 5...■, snout port, 6... counter, 7... converter, 8... amplifier, 10... control unit, 11...・Rotational speed sensor, 12... Governor, 12C... Step motor, 14... Gas engine exhaust, 15... 02 sensor, 16... Three-way catalyst, 17... EGR valve, 20
...Gas engine, 22...Throttle valve, 26...
Gas introduction pipe, 25... Flywheel, 26... Part of mixer, 60... Throttle valve opening detector.

Claims (1)

[Claims] It has an air-fuel ratio control mechanism that adds a predetermined amount of fuel to the injector, and uses the throttle valve opening determined according to the engine speed as a threshold to determine the actual throttle valve opening. Depending on the result, in a gas engine in which the air-fuel ratio is switched by turning on and off the operation of the air-fuel ratio control mechanism, when switching in the direction of decreasing the air-fuel ratio, the air-fuel ratio is changed for a predetermined period of time after the air-fuel ratio is switched. stopping the switching operation of the control mechanism, and setting a throttle valve opening that is a predetermined opening smaller than the throttle valve opening at the time of air-fuel ratio switching as a threshold value for switching the air-fuel ratio in the direction of increasing the air-fuel ratio; The threshold value is corrected in accordance with the difference in engine speed between the engine speed at the time of switching to the direction of increasing the air-fuel ratio and the engine speed at the time of switching to the direction of decreasing the air-fuel ratio. Air-fuel ratio control method for gas engines.