JP2564846B2 - Air-fuel ratio controller for LPG engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an engine that uses liquefied petroleum gas as a fuel.

[Prior Art] Generally, an LPG engine is used as a fuel (hereinafter, simply referred to as an LPG engine) in an intake passage to have an LPG.
A normal fuel passage for supplying the main fuel to the engine is provided, and the liquefied petroleum gas discharged from the normal fuel passage is supplied mixed with intake air via a venturi formed in the intake passage. It was The opening degree of the fuel passage is fixed in advance so that the fuel-air mixture is on the fuel lean side. Furthermore, an injector for injecting fuel is provided in the intake passage on the downstream side of the venturi so that the air-fuel ratio of the LPG engine becomes the theoretical air-fuel ratio.
The amount of fuel injected was feedback-controlled based on the oxygen concentration in the exhaust gas. (See Japanese Patent Laid-Open No. 60-67756) [Problems to be Solved by the Invention] In such an LPG engine, the air-fuel ratio is controlled based on the oxygen concentration in the exhaust gas. There was a time delay, and in particular, when the intake air amount changed abruptly, it was sometimes impossible to follow the change. As a result, the air-fuel ratio fluctuates, which may deteriorate drivability and emission. In order to solve this problem, the fact that liquefied petroleum gas has good followability to changes in the intake air amount is used to change the air-fuel ratio of the fuel mixture supplied from the normal fuel passage to the theoretical air-fuel ratio from the conventional one. Close to slightly leaner than the theoretical air-fuel ratio,
In some cases, the opening of the fuel passage is fixed.

However, as described above, when the opening of the normal fuel passage is fixed so as to be slightly leaner than the stoichiometric air-fuel ratio, for example, changes in the components of liquefied petroleum gas, changes in water temperature and intake temperature, and air cleaner Due to deterioration over time due to clogging, etc., a fuel-rich mixture that was richer than the theoretical air-fuel ratio could be supplied to the LPG engine. At that time, there was a problem that the injector could not perform feedback control, resulting in deterioration of emission and fuel consumption.

[Means for Solving the Problems] As means for solving the above problems, the present invention has adopted the following configuration. That is, as shown in FIG. 1, the air-fuel ratio control apparatus for an LPG engine of the present invention uses a venturi M3 formed in an intake passage M2 of an engine M1 that uses liquefied petroleum gas as a fuel, and the fuel and the intake air. A fuel mixing means M4 for mixing with the engine M1 to supply a fuel mixture to the engine M1, and a fuel injection means M5 provided in the intake passage M2 downstream of the fuel mixing means M4 for injecting fuel into the intake passage M2. An air-fuel ratio control device for an LPG engine, comprising: controlling the amount of fuel supplied by the both means, and controlling the air-fuel ratio of the engine, the operation of detecting an operating state of the engine M1 including at least a load. State detection means M6, air-fuel ratio detection means M8 provided in the exhaust passage M7 of the engine M1 for detecting the air-fuel ratio of the engine M1 from the oxygen concentration in the exhaust gas, and mixed with intake air by the fuel mixing means M4 Fuel Is variably controlled according to the control amount set based on the detection result of the operating state detection means M6, and the air-fuel ratio of the fuel mixture is controlled to be slightly leaner than a predetermined target air-fuel ratio. Air-fuel ratio control means M9, when the air-fuel ratio detected by the air-fuel ratio detection means M8 is leaner than the target air-fuel ratio, so that the air-fuel ratio of the engine M1 becomes a predetermined target air-fuel ratio, The gist is an air-fuel ratio control device for an LPG engine, characterized by comprising: feedback control means M10 for feedback-controlling the amount of fuel supplied by the fuel injection means M5.

Here, the fuel injection means M5 is, for example, an injector that injects fuel into the intake passage M2.

Further, the operating state detected by the operating state detecting means M6 refers to an operating state including at least a load, for example, the intake pipe internal pressure, which includes the rotational speed of the LPG engine M1 and the cooling water temperature in addition to the load. Good.

The air-fuel ratio control means M9 is, for example, a venturi M3 by changing the opening degree of the fuel passage by a step motor.
It controls the amount of main fuel supplied to the part.

The feedback control means M10 is, for example, a means for feedback-controlling the amount of fuel injected by the injector based on the output of the oxygen sensor as the air-fuel ratio detection means M8 in order to supply a fuel-air mixture having a stoichiometric air-fuel ratio to the engine. Is.

[Operation] In the air-fuel ratio control device for an LPG engine of the present invention configured as described above, the fuel mixing means M4 causes the venturi M3 formed in the intake passage M2 of the engine M1 that uses liquefied petroleum gas as a fuel to flow therethrough. , Mixes fuel and intake air, and supplies the fuel mixture to the engine M1. Also, operating state detection means
The M6 detects an operating state of the engine M1 including at least the load, and the air-fuel ratio control means M9 controls the amount of fuel mixed with the intake air in the fuel mixing means M4 based on the detected operating state. Variable control according to the amount,
The air-fuel ratio of the fuel-air mixture is controlled to be slightly leaner than the target air-fuel ratio. At the same time, the air-fuel ratio detecting means M8 provided in the exhaust passage M7 of the engine M1 detects the air-fuel ratio of the engine M1 from the oxygen concentration in the exhaust gas, and the air-fuel ratio detected by this air-fuel ratio detecting means M8 is the target. If it is leaner than the air-fuel ratio, feedback control means
The M10 feedback-controls the amount of fuel supplied by the fuel injection means M5 to inject fuel into the intake passage M2 so that the air-fuel ratio of the engine M1 becomes a predetermined target air-fuel ratio. As described above, the amount of fuel supplied to the engine is controlled by the air-fuel ratio control means M9 and further controlled by the feedback control means M10, so that the air-fuel ratio of the engine can be controlled to the target air-fuel ratio. That is, in the present invention, the main fuel is supplied so that the air-fuel ratio of the fuel mixture supplied from the fuel mixing means M4 is on the lean side close to the target air-fuel ratio (for example, the theoretical air-fuel ratio), A control amount (for example, the basic step number of the step motor) is set based on the operating state including the load, and the fuel amount supplied from the fuel mixing means M4 is adjusted by this control amount. At the same time, the air-fuel ratio is detected by the air-fuel ratio detection means M8, based on the signal from this air-fuel ratio detection means M8,
By supplying the fuel by the fuel injection means M5, the fuel mixture can be feedback-controlled to the target air-fuel ratio. Therefore, even if the load suddenly changes, the main fuel amount can be immediately adjusted, and a slight fuel injection can be performed to quickly respond to the change in the load.

Also, for example, when the air-fuel ratio of the fuel mixture is set slightly leaner than the stoichiometric air-fuel ratio point, due to changes in the LPG component, changes in water temperature and intake temperature, and deterioration due to clogging of the air cleaner, etc. Although the fuel component of the fuel mixture may increase and become rich, in the present invention, since the control amount for supplying the main fuel amount can be set according to the operating state, the supplied fuel mixture is The air-fuel ratio can be controlled to a lean side close to the stoichiometric air-fuel ratio. As a result, it is possible to suitably cope with changes in LPG components, changes in water temperature and temperature, and various types of deterioration over time.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail.

FIG. 2 is a schematic configuration diagram of an engine (LPG engine) system using liquefied petroleum gas as an air-fuel ratio control device of an LPG engine which is an embodiment of the present invention.

The LPG engine 1 communicates with an air cleaner 3 via an intake manifold 2, takes in outside air from the air cleaner 3, and also communicates with a venturi 4 formed in the intake manifold 2 via a normal fuel passage 5 and an acceleration fuel passage 6 for LPG engine 1. It is configured to take in liquefied petroleum gas (LPG) from the radiator 7, explode and burn a mixture of the outside air and LPG to obtain a driving force, and then discharge the exhaust gas from the exhaust manifold 8 to the outside.

Further, the opening degree of the normal fuel passage 5 is controlled by the step motor 9 provided in the middle of the normal fuel passage 5, and the acceleration fuel passage 6 is controlled.
Is opened by a power valve 10 provided midway in the acceleration fuel passage 6 only during acceleration. On the other hand, the intake amount of the air-fuel mixture of outside air and LPG is determined by the opening degree of the throttle 11 provided in the intake manifold 2. Further, the exhaust gas discharged from the exhaust manifold 8 is purified by passing through the three-way catalyst 12, and a part of the exhaust gas is recirculated to the exhaust system by the so-called exhaust gas recirculation device 13. The swirl device 14 attached to the upper part of the LPG engine 1
The swirl flow of the air-fuel mixture is generated in the cylinder of the engine 1. Power valve 10, exhaust gas recirculation device
The swirl device 14 and the swirl device 14 are turned on and off by negative pressure switching valves 16, 17, and 18, respectively. Further, by the negative pressure switching valve 19, the slow lock valve 22 for opening and closing the slow fuel passage 21 for supplying the fuel for idle is turned on and off,
Fuel cuts during deceleration are performed. Negative pressure switching valve
The check valves 16a and 19a respectively connected to 16 and 19 prevent malfunction of the power valve 10 and the slow lock valve 22 when the negative pressure of the intake manifold 2 is reduced. Each of these negative pressure switching valves 16, 17, 18, 19 is electrically connected to an electronic control unit (hereinafter simply referred to as an ECU) 23, and its on / off timing is controlled. The ECU 23 also includes an intake air temperature sensor 24 that detects the temperature of the outside air drawn from the air cleaner 3, a water temperature sensor 25 that detects the cooling water temperature of the LPG engine 1, a pressure sensor 26 that detects the pressure in the intake manifold 2, and a throttle 11. Sensor 27 for detecting the opening of the exhaust gas, oxygen sensor 28 for detecting the oxygen concentration in the exhaust gas discharged from the exhaust manifold 8, exhaust temperature sensor 29 for detecting the temperature of the exhaust gas, and for detecting the rotational speed of the LPG engine 1. A rotation speed sensor 31 and the like attached to the distributor 30 are connected to the. The ECU 23 determines the negative pressure switching valve according to the output signal output from each of these sensors.
While controlling 16, 17, 18, and 19, the stepper motor 9, the injector 32, the distributor 30 attached to the LPG engine 1 and the like described above are preferably controlled. The injector 32 is mounted in the intake manifold 2 closer to the LPG engine 1 than the throttle 11 and is also used for controlling the air-fuel ratio of the LPG engine 1.

Next, the ECU 23 will be described. FIG. 3 is a block diagram showing the configuration of the ECU 23.

The ECU 23 is a well-known central processing unit (CPU) 51, read-only memory (ROM) 52, random access memory (RAM)
53, a backup RAM 54 for storing stored data, and the like, are configured as a logical operation circuit in which these are connected to an external input circuit 55, an external output circuit 56, etc. by a bus 57.

The intake air temperature sensor 24, the water temperature sensor 25, the pressure sensor 26, the throttle sensor 27, the oxygen sensor 28, the exhaust gas temperature sensor 29, the rotation speed sensor 31, and the like are connected to the external input circuit 55. Via 51, the CPU 51 reads the signal output from each sensor or the like as an input value. CP
U51 is based on these input values, and the step motor 9 connected to the external output circuit 57, the negative pressure switching valve 16 or
19, controlling the distributor 31, the injector 32, and the like.

Next, the air-fuel ratio control processing of the LPG engine executed by the ECU 23 described above will be described with reference to the flowcharts shown in FIG. 4, FIG. 6 and FIG.

The "step motor control routine" shown in FIG.
Of the processes executed by U23, only the process showing the control of the step motor 9 for operating the opening degree of the normal fuel passage 5 is shown, and is the process periodically executed by the hard interrupt.

First, when the processing shifts to this routine, step 100
Then, based on the rotational speed NE of the LPG engine 1 detected by the rotational speed sensor 31 and the intake pressure PM in the intake manifold 2 detected by the pressure sensor 26, it is stored in advance in the ROM 52.
The basic step number S of the step motor 9 for operating the opening degree of the normal fuel passage 5 is calculated by performing the interpolation calculation using the dimension map. The basic step number S of this three-dimensional map is set in advance so as to be on the fuel lean side. In the following step 110, the basic step number S is multiplied by the learning correction value KG, the intake temperature correction coefficient FTHA, the fuel temperature correction coefficient FTHF, and the rich correction coefficient FRICH.
Is corrected to the target step number ST of the step motor 9.
This learning correction value KG is obtained by a learning routine described later,
The rich correction coefficient FRICH is obtained by a feedback correction coefficient FAF calculation routine described later. Further, as shown in FIGS. 5A and 5B, the intake temperature correction coefficient FTHA is detected from the two-dimensional map with the intake temperature THA detected by the intake temperature sensor 24, and the fuel temperature correction coefficient FTHF is detected from the water temperature sensor 25. The cooling water temperature is used as the fuel temperature THF and is calculated by interpolation calculation from the two-dimensional map with the fuel temperature THF.

In the following step 120, the current step number SNOW representing the step number of the step motor 9 is read from the backup RAM 54, and in the following step 130, the current step number S
Compare NOW with the target step number ST. When the CPU 51 outputs a rotation command to the step motor 9 via the external output circuit 56, the current number of steps SNOW
Is the value written as the current step number SNOW. In steps 130 to 170, a process of matching the current step number SNOW, which indicates the step number of the step motor 9, with the target step number ST is performed.

(A) First, in step 130, the target number of steps S
If it is determined that T = SNOW, the current step number SNOW of the step motor 9 matches the target step number ST that is the target, so it is not necessary to drive the step motor 9 and the process returns to "RETURN" in that state. This routine ends.

(B) In step 130, the target number of steps ST> SNO
If it is determined to be W, the current step number SNOW that indicates the step number of the step motor 9 is smaller than the target step number ST, so the CPU 51 issues a forward rotation command to the external output circuit to increment the step number of the step motor 9. Output to the step motor 9 via 56 to set the step motor 9 to 1
After rotating forward by only steps (step 140) and incrementing the current step number SNOW representing the step number of the step motor 9 (step 150), the process returns to "RETURN".

(C) In step 130, the target number of steps ST / SNOW
If it is determined that the current step number SNOW representing the step number of the step motor 9 is larger than the target step number ST, the CPU 51 outputs a reverse rotation command to decrement the step number of the step motor 9 After the motor 9 is reversely rotated by one step (step 160) and the current step number SNOW is decremented (step 170),
The process ends to "RETURN" and the routine is finished.

The number of steps of the step motor 9 matches the target number of steps ST by repeatedly executing the processes (a) to (c).

Next, an "injection amount calculation routine" for calculating the injection amount of the fuel injected into the intake manifold 2 by the injector 32 in order to perform the feedback control of the air-fuel ratio will be described with reference to the flowchart of FIG.

First, in step 200, it is judged whether or not the feedback (F / B) control condition is satisfied. The case where the F / B control condition is satisfied is a case where the start time, the rich monitor control time, the catalyst heating control time and the lean control time are excluded. When it is determined that the F / B control condition is satisfied, the process proceeds to step 210. In step 210, the basic injection amount TBPSE is obtained from the three-dimensional map based on the rotational speed NE of the LPG engine 1 detected by the rotational speed sensor 31 and the intake pressure PM in the intake manifold 2 detected by the pressure sensor 26. In the following step 220, the basic injection amount TPBSE is multiplied by a feedback correction coefficient FAF described later to obtain the injection amount TAU, and this routine is ended.

On the other hand, if it is determined in step 200 that the F / B control condition is not satisfied, the process proceeds to step 230. In step 230, the injection amount TAU is set to "0" and this routine ends.

Next, the feedback correction coefficient FAF used in step 220 of the "injection amount calculation routine" will be described. 7A and 7B are flowcharts showing the "feedback correction coefficient FAF calculation routine". This "feedback correction coefficient FAF calculation routine"
Is also a subroutine that is periodically executed like the "step motor control routine".

First, in step 300, it is determined whether or not the F / B control condition is satisfied. If it is determined that the F / B control condition is satisfied, the process proceeds to step 310. In step 310,
The output signal of the oxygen sensor 28 determines whether the air-fuel ratio is rich. If it is determined to be rich, the next processing of steps 320 to 440 is executed.

In step 320, it is determined whether the air-fuel ratio was lean when the processing routine was last executed, and the flag YOX is displayed.
Is determined by If the value of the flag YOX is "0", it is assumed that the previous time was lean and the next step 330
Proceed to. That is, when the process proceeds to step 330 according to the determination in steps 310 to 320, it is determined that the air-fuel ratio has switched from lean to rich. In the following step 330, the current F / B correction coefficient FAF is added to the average F / B correction coefficient FAFAV during F / B control and the old F / B correction coefficient FAFO at the time of shifting from rich to lean the previous time. The average is obtained, and the average F / B correction coefficient FAFAV during F / B control is processed. In steps 340 to 370, which is a series of subsequent processes, the F / B correction coefficient FAF is set to the old F / B correction coefficient FAFO (step 340), and the value obtained by subtracting the skip amount a from the F / B correction coefficient FAF is changed to the new F. After setting the / B correction coefficient FAF (step 350), set the learning timing flag YKG (step 350).
360), and the value of the flag YOX is set to "1" (step 37)
0). The learning timing flag YKG will be described later,
It is used when determining the timing for learning the learning value KG, and the value of the flag YOX being "1" indicates that the air-fuel ratio is rich.

On the other hand, when it is determined in step 320 that the value of the flag YOX is "1", the process executes steps 380 to 400. Here, when the process proceeds to step 380 by the determination in steps 310 to 320, it means that the air-fuel ratio is maintained in the rich state. Step 38
At 0, it is determined whether the timer counter CNT1 is greater than or equal to the constant c. The timer counter CNT1 is incremented in a processing routine by a hardware interrupt having a shorter cycle than this routine. When the timer counter CNT1 exceeds the constant c, the constant b is subtracted from the F / B correction coefficient FAF in step 390 and then the process proceeds to step 400 to clear the value of the timer counter CNT1 to "0". On the other hand, when the timer counter CNT1 is less than the constant c in step 380, the steps 390 and 400 are skipped. That is,
In steps 380 to 400, F / B correction coefficient F
This means that the constant b is subtracted from the AF value.

After step 370 or step 400, or if a negative determination is made in step 380, the process proceeds to step 410. In step 410, it is determined whether the timer counter CNT2 is equal to or greater than the constant d. This timer counter CNT2
Indicates the duration of the rich signal, which is incremented like the timer counter CNT1. In this step 410, it is determined whether or not the duration is longer than a predetermined constant d. is there. The value of this constant d is
It is set longer than the duration of the rich signal output when the feedback control is normally performed, and is set shorter than the determination time of the rich monitor for determining the inactivity of the oxygen sensor 28 and the like. Therefore, when the constant d is exceeded, it is determined that the rich state is long, and the lean side is controlled in the step described later.

If the timer counter CNT2 is a constant d or less, "RETU
RN ”to end the present routine, and when the constant d is exceeded, the routine proceeds to step 420. In the following step 420, it is determined whether the timer counter CNT3 is equal to or greater than the constant e. The timer counter CNT3 is incremented like the timer counter CNT1. When the timer counter CNT3 exceeds the constant e, exit to "RETURN",
When this routine is finished and the timer counter CNT3 is equal to or smaller than the constant e, in step 430, the rich correction coefficient FRICH
After the constant f is subtracted from the value, the value of the timer counter CNT3 is cleared to "0", and this routine ends. That is,
In steps 420 to 440, the value of the rich correction coefficient FRICH is subtracted by the constant f every predetermined time.

The rich monitor means that when the F / B control condition is satisfied,
When the rich signal continues for a predetermined time or more, F /
This is a monitor for stopping the B control and making it open control. When the lean signal is generated after the rich signal, the oxygen sensor 28 is considered to be active and the rich monitor is released.

The above-described processing of steps 320 to 440 is processing when the air-fuel ratio is rich and is processing for reducing the F / B correction coefficient FAF and the rich correction coefficient FRICH. This F / B
In contrast to the processing for reducing the correction coefficient FAF and the rich correction coefficient FRICH, the processing of steps 450 to 580 in FIG. 7 (b) is processing when the air-fuel ratio is lean, and the F / B correction coefficient FAF and This is a process for increasing the rich correction coefficient FRICH.

First, if it is determined in step 310 that the air-fuel ratio is lean, the process proceeds to step 450. In step 450, the YOX
It is determined whether or not the value of is 1. If the value of YOX is "1", the process executes steps 460 to 580. When the process proceeds to step 460 according to the determinations of steps 310 and 450, the air-fuel ratio is switched from rich to lean. The process of steps 460 to 470 is the same as the process of steps 330 to 340, and the average F / B correction coefficient FAFAV during F / B control is calculated (step 460), and the F / B correction coefficient FAF is calculated. Value of old F / B correction factor FAFO
(Step 470). In the following step 480, the skip amount a is added to the F / B correction coefficient FAF to obtain a new F / B correction coefficient FAF, and then the learning timing flag YKG is set (step 490) and the value of the flag YOX is set to "0". To "" (step 500).

On the other hand, when it is determined in step 450 that the value of the flag YOX is "0", the processes of steps 510 to 530 are executed. Here, when the process proceeds to step 510 based on the determinations in steps 310 and 450, it means that the air-fuel ratio is maintained in the lean state. Step 510 to 5
The process of 30 is a process opposite to steps 380 to 400, and is a process of increasing the value of the F / B correction coefficient FAF by a constant b at every predetermined time.

After step 500 or step 530, or if a negative determination is made in step 510, the process proceeds to step 540. At step 540, since it is in the lean state, the value of the timer counter CNT2 indicating the duration of the rich signal is cleared to “0”, and the routine proceeds to step 550. In the following step 550,
It is determined whether or not the rich correction coefficient FRICH is "1". If the rich correction coefficient FRICH is "1", "RETUR
The process exits to "N" to end this routine, and if not "1", the process proceeds to step 560. In the following step 560, it is determined whether or not the timer counter CNT3 is greater than or equal to the constant g. When the timer counter CNT3 exceeds the constant g, the routine returns to "RETURN" and this routine is terminated. When the timer counter CNT3 is less than the constant g, at step 430, after adding the constant f to the rich correction coefficient FRICH, the timer Counter CNT3
The value is cleared to "0" and the present routine ends. That is, in steps 560 to 580, the value of the rich correction coefficient FRICH is added by the constant h every predetermined time.

The constant g is larger than the constant e, and the constant h is the constant f.
As shown in steps 420 to 440, when the value of the rich correction coefficient FRICH is decreased, the speed of the decrease is increased, while steps 560 to 580 are set.
As shown in, when increasing the rich correction coefficient FRICH, the speed of increase is decreased. This is because if the air-fuel ratio suddenly shifts to the rich side due to changes in the fuel component, etc., it may become richer than the stoichiometric air-fuel ratio without the injection of the injector 32. This is for reducing ST to reduce the amount of main fuel supply, thereby changing the air-fuel ratio to the lean side, and enabling F / B control by the injector 32. That is, when the value of the rich correction coefficient FRICH is reduced quickly so as not to affect the rich monitor, on the other hand, when the value of the rich correction coefficient FRICH is increased, it is slowly increased for learning described later. It is what makes me.

The timing chart of FIG. 8 shows the processing contents of the above steps 300 to 580. As shown in FIG. 8, with respect to the basic step number S determined based on the rotation speed NE and the intake pressure PM, the injection amount TAU injected by the injector 32 is the air-fuel ratio signal detected by the oxygen sensor 28. It is controlled so as to approach the stoichiometric air-fuel ratio.

Returning to FIG. 7A, when it is determined in step 300 that the F / B control condition is not satisfied, the values of the F / B correction coefficient FAF and the old F / B correction coefficient FAFO are each “1”. ”Is set (step 590), and the correction coefficient F at rich time is set again.
The value of RICH is set to "1" (step 600), and this routine ends.

Next, only when the value of the learning timing flag YKG set in steps 360 and 490 of the "feedback correction coefficient FAF calculation routine" is "1", in other words, the air-fuel ratio changes from rich to lean or lean to rich. The "learning routine" of FIG. 9 (a), which is executed only when the switching is performed, will be described.

First, at step 700, it is judged if the value of the learning timing flag YKG is "1". When the value of the learning timing flag YKG is not "1", the processing is step 7
The routine proceeds to 10 and resets the value of the learning timing flag YKG to "0" and exits to "RETURN] to end this routine. When it is determined that the value of the learning timing flag YKG is" 1 ", the process proceeds to step 720. In step 720, pressure sensor
It is determined whether the intake pressure PM in the intake manifold 2 detected by 26 is lower than a predetermined pressure PMG. This predetermined pressure PMG
Is determined by the "predetermined pressure PMG calculation routine" shown in FIG. 9 (b). Here, first, the predetermined pressure PMG will be described.

The predetermined pressure PMG is a pressure obtained by subtracting a certain pressure j from another predetermined pressure PMVL (step 800). The other predetermined pressure PMVL is the intake pressure PM detected by the pressure sensor 26 when the throttle opening VL detected by the throttle sensor 27 is larger than a predetermined value (50 ° in this embodiment) (step 810). Predetermined pressure PMVL (step
820). Further, when the throttle opening VL is larger than 50 °, it is considered that the intake pressure PM is almost the same value as the atmospheric pressure, so the predetermined pressure PMG (= PMLV-j) is a pressure lower than the atmospheric pressure by a certain pressure j. Becomes In step 720 of the "learning routine", the magnitude relationship between the predetermined pressure PMG and the intake pressure PM detected by the pressure sensor 26, which changes every moment, is determined.

When it is determined that the intake pressure PM is less than the predetermined pressure PMG,
The process executes the process of steps 730 to 750. In step 520, the value of the average F / B correction coefficient FAFAV determined in the “feedback correction coefficient FAF calculation routine” is determined.

(A) First, in step 730, the average F / B correction coefficient FAFAV =
When it is determined to be 1, the air-fuel ratio is considered to have reached the stoichiometric air-fuel ratio and no processing is performed.

(B) If it is determined that the average F / B correction coefficient FAFAV> 1, the process proceeds to step 740. In step 740, the learning value KG corresponding to the intake pressure PM at that time is increased by the constant i.

(C) When it is determined that the average F / B correction coefficient FAFAV <1, the process proceeds to step 750. In step 750, the learning value KG is reduced by the constant i.

The learning value KG is increased / decreased by ± i by executing the processes (A) to (C) each time lean or rich is switched, and eventually becomes the optimum value for the intake pressure PM at that time. This learning value KG is used to calculate the target number of steps ST during normal operation (correction coefficient FAF = 1 at this time) other than during acceleration (step of "step motor control routine").
110).

On the other hand, in step 720, the intake pressure PM is equal to the predetermined pressure PMG.
When it is determined that the above is the case, the learning process of steps 730 to 750 is not executed, the learning timing flag YKG is reset to "0" (step 710), and this routine ends.

As described above in detail, in the present embodiment, first, the step motor 9 is used to supply the fuel from the normal fuel passage 5 based on the learning value or the like, so that the air-fuel ratio of the air-fuel mixture is adjusted to the theoretical air-fuel ratio. Control so that the lean side is close to the fuel ratio. Then, the oxygen concentration in the exhaust gas is detected by the oxygen sensor 28, and the oxygen sensor 28 is detected by the injector 32.
The fuel mixture can be feedback-controlled to the stoichiometric air-fuel ratio by supplying the fuel based on the signal from.

That is, the basic step number S of the step motor 9 for adjusting the opening degree of the normal fuel passage 5 is set so that the air-fuel ratio of the air-fuel mixture supplied from the normal fuel passage 5 is on the lean side close to the stoichiometric air-fuel ratio. , Predetermined rotational speed NE and intake pressure PM
It is set based on the map with. In addition, LPG is a gas and has the property of following the changes in the intake air amount well. Therefore, when the intake air amount changes suddenly, the fuel mixture is rapidly increased or decreased in response to the change,
The air-fuel ratio can be adjusted to a lean side close to the stoichiometric air-fuel ratio. Furthermore, when the fuel component of the fuel mixture increases and becomes rich due to deterioration over time due to changes in the LPG component, changes in the water temperature and intake temperature, and clogging of the air cleaner, etc., the step motor 9 By reducing the target step number ST, the air-fuel ratio of the supplied fuel-air mixture can be appropriately controlled to the lean side close to the stoichiometric air-fuel ratio. Since the air-fuel ratio is controlled to the lean side close to the stoichiometric air-fuel ratio in this way, the air-fuel ratio of the LPG engine 1 can be feedback-controlled to the stoichiometric air-fuel ratio by the injector 32 based on the signal of the oxygen sensor 28. it can. That is, the step motor 9 controls the air-fuel ratio of the air-fuel mixture supplied from the normal fuel passage 5 so as to be on the lean side close to the stoichiometric air-fuel ratio, and is further feedback-controlled to the stoichiometric air-fuel ratio by the injector 32. Therefore, it is possible to quickly and suitably respond to changes in the driving state, improve emissions, and improve fuel efficiency.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and can be implemented in various modes without departing from the scope of the present invention. Of course.

[Effects of the Invention] As described in detail above, the air-fuel ratio control apparatus for an LPG engine of the present invention quickly changes the fuel supply amount so as not to become fuel rich even if the operating state suddenly changes. The air-fuel ratio can be controlled appropriately. Therefore, it is possible to prevent the emission of the vehicle and the fuel consumption from deteriorating and improve the drivability.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram of an LPG engine system as an air-fuel ratio control device for an LPG engine of one embodiment of the present invention, and FIG. 3 is its electronic control. FIG. 4 is a block diagram showing the configuration of the apparatus, FIG. 4 is a flowchart showing a step motor control routine, and FIG.
FIG. 7 is a graph showing a two-dimensional map for obtaining the intake air temperature correction coefficient FTHA and the fuel temperature correction coefficient FTHF. FIG. 6 is a flowchart showing the injection amount control routine. FIG. 7 (a) is a part of the feedback correction coefficient FAF calculation routine. FIG. 7 (b) is a flow chart showing the feedback correction coefficient FA
FIG. 8 is a flowchart showing a part of the F calculation routine, FIG. 8 is a timing chart showing the relationship between the air-fuel ratio signal and the fuel injection amount, FIG. 9 (a) is a flowchart showing the learning routine, and FIG. 9 (b) is It is a flow chart which shows a predetermined pressure PMG calculation routine. M1 …… Engine, M2 …… Intake passage M3 …… Venturi, M4 …… Fuel mixing means M5 …… Fuel injection means, M6 …… Operating state detecting means M7 …… Exhaust passage, M8 …… Air-fuel ratio detecting means M9… … Air-fuel ratio control means M10 …… Feedback control means 9 …… Step motor, 10 …… Power valve 11 …… Throttle, 23 …… Electronic control unit 24 …… Intake air temperature sensor, 25 …… Water temperature sensor 28 …… Oxygen sensor

Claims (1)

(57) [Claims] 1. A fuel mixing means for mixing a fuel and intake air through a venturi formed in an intake passage of an engine using liquefied petroleum gas as a fuel to supply a fuel mixture to the engine, and the fuel mixture. A fuel injection means for injecting fuel into the intake passage, the fuel injection means being provided in the intake passage downstream of the means, and controlling the amount of fuel supplied by both means and controlling the air-fuel ratio of the engine. An air-fuel ratio control device for detecting an operating state of the engine including at least a load; and an air-fuel ratio of the engine, which is provided in an exhaust passage of the engine and detects an air-fuel ratio of the engine from an oxygen concentration in exhaust gas. Air-fuel ratio detection means, and the amount of fuel mixed with the intake air by the fuel mixing means,
An air-fuel ratio control for variably controlling the air-fuel ratio of the fuel-air mixture to be slightly leaner than a predetermined target air-fuel ratio by performing variable control according to a control amount set based on the detection result of the operating state detection means. Means, and when the air-fuel ratio detected by the air-fuel ratio detection means is leaner than the target air-fuel ratio, the air-fuel ratio of the engine is supplied by the fuel injection means so as to reach a predetermined target air-fuel ratio. An air-fuel ratio control device for an LPG engine, comprising: feedback control means for feedback controlling the fuel amount.