JP2536014B2 - Air-fuel ratio controller for LPG engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an air-fuel ratio control system for an engine using liquefied petroleum gas as a fuel.

[Prior Art] Conventionally, a normal fuel passage for supplying main fuel is provided in an intake passage of an engine that uses liquefied petroleum gas as fuel (hereinafter simply referred to as an LPG engine). The liquefied petroleum gas flowing through was mixed with the intake air and supplied to the engine body through the venturi formed in the intake passage. Further, an injector as a fuel injection means is provided in the intake passage on the downstream side of the venturi, and the fuel is also supplied auxiliary.
The opening of the normal fuel passage is fixed in advance at a position where the air-fuel ratio is on the lean side, and when it is desired to bring the air-fuel ratio of the LPG engine close to the stoichiometric air-fuel ratio, the injection amount of the injector in the exhaust gas The feedback control is performed based on the oxygen concentration of the water (JP-A-60-6775).
"Air-fuel ratio control device for LPG vaporizer" shown in Japanese Patent No. 6).

[Problems to be Solved by the Invention] However, in such an air-fuel ratio control device for a conventional LPG engine, the pulsation of the intake passage becomes large at a high load such as when the throttle valve is fully opened, and the fuel supplied from the normal fuel passage is increased. The amount may change greatly, and for this reason, the air-fuel ratio of the supplied fuel may be controlled to be richer than the stoichiometric air-fuel ratio. In particular, LPs designed in advance to be supplied with fuel by utilizing the pulsating effect
In the G engine, the change in the fuel amount described above becomes larger, so the air-fuel ratio was controlled to the rich side.
Therefore, in such a case, even if the injector is driven, the air-fuel ratio cannot be returned to the stoichiometric air-fuel ratio, and there is a problem that engine output, emission and fuel consumption are deteriorated.

The present invention has been made in view of the above problems, and WOT
An object of the present invention is to provide an air-fuel ratio control device for an LPG engine, which can prevent air-fuel ratio overrich under heavy load such as time, and improve emission, fuel efficiency and drivability.

Configuration of the Invention [Means for Solving the Problems] In order to achieve the above object, the present invention adopts the following configurations as means for solving the above problems.
That is, the air-fuel ratio control device of the LPG engine of the present invention is the first
As illustrated in the figure, the fuel and the intake air are mixed via a venturi M3 formed in the intake passage M2 of the engine M1 using liquefied petroleum gas as the fuel, and the fuel mixture is supplied to the engine M1. Fuel mixing means M4, which is provided in the intake passage M2 downstream of the fuel mixing means M4, and which injects fuel into the intake passage M2, is provided with the fuel supplied by the both means M4, M5. In the air-fuel ratio control device of the LPG engine for controlling the air-fuel ratio of the engine M1 to control the amount, the air provided in the exhaust passage M6 of the engine M1, the air-fuel ratio of the engine M1 is detected from the oxygen concentration in the exhaust gas. Fuel ratio detection means M7, high load state determination means M8 to determine whether the engine M1 is in a high load state, when the high load state determination means M8 determines that the engine M1 is not in a high load state The fuel mixture Means
A fuel amount control means M9 for controlling the amount of fuel mixed with the intake air in the fuel mixing means M4 so that the air-fuel ratio of the fuel mixture supplied from M4 becomes lean, and the fuel amount control means M9 The engine depends on the control result
When the air-fuel ratio of M1 becomes lean, the amount of fuel supplied by the fuel injection means M5 is detected by the air-fuel ratio detection means M7 so that the air-fuel ratio of the engine M1 becomes a predetermined target air-fuel ratio. The first feedback control means M10 for performing feedback control based on the air-fuel ratio, and the high-load condition determination means M8 determines that the engine M1 is in the high-load condition, the air-fuel ratio of the engine M1 is a predetermined target. A second feedback control means M11 for feedback-controlling the amount of fuel mixed with the intake air by the fuel mixing means M4 so as to obtain an air-fuel ratio, based on the air-fuel ratio detected by the air-fuel ratio detection means M7. The main point is that.

Here, the high load state determination means M8 is for determining whether or not the engine M1 is in a high load state, for example, for detecting the fully open state of the throttle valve and determining the high load state, the intake pipe There is a device that detects a pressure and determines that the detected value is equal to or higher than a predetermined value as a high load state.

[Operation] The air-fuel ratio control device for an LPG engine of the present invention configured as described above mixes liquefied petroleum gas as fuel with intake air by the fuel mixing means M4 and supplies the fuel mixture to the engine M1. While supplying, by the fuel injection means M5,
Although the fuel is being supplied to the engine M1, when the high load condition determination means M8 determines that the engine M1 is not in the high load state, the fuel amount control means M9 causes the fuel mixture supplied from the fuel mixing means M4 to While setting the air-fuel ratio to the lean side, the first feedback control means M10 feedback-controls the amount of fuel supplied by the fuel injection means M5 based on the air-fuel ratio detected by the air-fuel ratio detection means M7, and the engine M1 The air-fuel ratio is set to a predetermined target air-fuel ratio. Moreover,
When the high load state determination means M8 determines that the engine M1 is in the high load state, the second feedback control means M11 detects the amount of fuel mixed with the intake air by the fuel mixing means M4 by the air-fuel ratio detection means M7. The air-fuel ratio of the engine M1 is set to a predetermined target air-fuel ratio by performing feedback control based on the determined air-fuel ratio, and the air-fuel ratio may become overrich even at the time of high load such that the pulsation of the intake passage becomes large. Absent.

[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 is in communication 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 an ordinary fuel passage 5 and an acceleration fuel passage 6 to an LPG engine 1. It is configured to take in liquefied petroleum gas (LPG) from the regulator 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 controls its on / off timing. 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 THW of the LPG engine 1, a pressure sensor 26 that detects the pressure in the intake manifold 2, and a throttle. A throttle sensor 27 that detects the opening degree of 11, an oxygen sensor 28 that detects the oxygen concentration in the exhaust gas discharged from the exhaust manifold 8, an exhaust temperature sensor 29 that detects the temperature of the exhaust gas, and the rotational speed of the LPG engine 1 Therefore, the rotation speed sensor 31 and the like attached to the distributor 30 are connected. The ECU 23 controls the negative pressure switching valves 16, 17, 18, 19 according to the output signals output from these sensors, and is attached to the step motor 9, the injector 32, and the LPG engine 1 described above. The distributor 30 and the like 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 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 to FIG.

The "main routine" shown in FIG. 4 represents only the processing related to the opening control of the normal fuel passage 5 and the valve opening control of the injector 32 among the processing executed by the ECU 23, and To be executed.

When the processing shifts to this routine, first, step 10
At 0, the ST calculation routine for calculating the target step number ST of the step motor 9 is executed. In the following step 200,
Feedback correction factor FA for feedback control
Execute the FAF calculation routine that calculates F, and continue to step 30.
At 0, the learning routine is executed. In the following step 400, a TAU calculation routine for calculating the injection time TAU of the injector 32 is executed, and thereafter, the processing of this routine is once ended.

Next, the processing of each step of the main routine will be described in detail below.

The "ST calculation routine" of step 100 is a process that is called by executing a subroutine in step 100 and is shown in FIG. When the processing is started, first, at step 110, the rotation speed N of the LPG engine 1 detected by the rotation speed sensor 31.
3 stored in advance in the ROM 52 based on E and the intake pipe pressure PM in the intake manifold 2 detected by the pressure sensor 26
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 120, the learning correction value KG as the correction coefficient of the basic step number S is loaded, and the following step 13
In step 0, step 140, an intake air temperature correction coefficient FTHA and a water temperature correction coefficient FTHW, which are also correction coefficients, are calculated. In step 150, a feedback correction coefficient FAFST for the step motor 9 is loaded. The learning correction value KG is obtained in the learning routine described later, and the feedback correction coefficient FAFST for the step motor 9 is obtained in the FAF calculation routine in step 200, and these are temporarily stored in the RAM 53. Loaded from RAM53. The intake air temperature correction coefficient FTHA is the intake air temperature TH detected by the intake air temperature sensor 24.
The water temperature correction coefficient FTHW is obtained from the two-dimensional map of A and the two-dimensional map of the cooling water temperature THW detected by the water temperature sensor 25. In the following step 160, the basic step number S is corrected by multiplying the calculated basic step number S by the learning correction value KG, the intake air temperature correction coefficient FTHA, the water temperature correction coefficient FTHW, and the feedback correction coefficient FAFST for the step motor. , The target number of steps ST of the step motor 9 is set. After executing the processing of step 160, the processing of this routine is once ended.

The “FAF calculation routine” in step 200 is
The process executed by the subroutine call in FIG. 6 is shown in FIGS. 6 (a) and 6 (b).

As shown in FIG. 6 (a), first, at step 210, it is judged if a feedback (hereinafter simply referred to as F / B) control condition is satisfied. If it is determined that the F / B control condition is satisfied, the process proceeds to step 220, and it is determined from the output signal of the oxygen sensor 28 whether or not the air-fuel ratio is rich. Here, if it is determined to be rich, the next processing of steps 230 to 262 is executed.

In step 230, it is determined whether the air-fuel ratio was lean when the processing routine was last executed, and whether or not the flag YOX is set.
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 232
Proceed to. That is, when the process proceeds to step 232 according to the determination in steps 220 to 230, it is determined that the air-fuel ratio has switched from lean to rich. In the following step 232, addition of the current F / B correction coefficient FAF and the old F / B correction coefficient FAFO at the time of shifting from the previous rich to lean to calculate the average correction coefficient FAFAV during F / B control. The average is obtained, and the average F / B correction coefficient FAFAV during F / B control is processed. In steps 234 to 240, which are a series of subsequent processes, the F / B correction coefficient FAF is set to the old F / B correction coefficient FAFO (step 234), 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 / B correction coefficient FAF (step 236), the learning timing flag YKG is set to the value 1 (step 238), and the flag YOX is set to the value 1 (step 240). The learning timing flag YKG is
As will be described later, it is used when determining the timing to learn the learning correction 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 230 that the value of the flag YOX is "1", the process executes steps 242 to 246. Here, when the process proceeds to step 242 by the determination in steps 220 to 230, it means that the air-fuel ratio is maintained in the rich state. Step 24
At 2, it is determined whether the timer counter CNT1 is greater than or equal to the constant c. The timer counter CNT1 is incremented by a compare interrupt routine (described later) whose cycle is shorter than that of this routine. Timer counter CNT1
Is greater than the constant c, the constant b is subtracted from the F / B correction coefficient FAF in step 244, and then the process proceeds to step 246.
Clear the value of timer counter CNT1 to "0". on the other hand,
When the timer counter CNT1 is equal to or smaller than the constant c in step 242, step 244 and step 246 are skipped. That is, in steps 242 to 246, the value of the F / B correction coefficient FAF is subtracted by the constant b every predetermined time.

After the execution of step 240 or step 246, or if a negative decision is made in step 242, step 250
Proceed to. In step 250, the injector F / B judgment flag
It is determined whether YFBINJ has a value of 1. The injector F / B determination flag YFBINJ indicates whether or not the feedback control of the injector 32 should be executed, and is determined by the "YFBINJ calculation routine" shown in FIG. Here, the “YFBINJ calculation routine” shown in FIG. 7 will be described first.

In FIG. 7, when the process is started, first, in step 251, a predetermined constant j is subtracted from the predetermined pressure PMVL to calculate the high load determination pressure PMG. This predetermined pressure PMVL
When the throttle opening VL detected by the throttle sensor 27 is larger than a predetermined value (50 degrees in this embodiment) (step 252), the intake pipe pressure PM detected by the pressure sensor 26 is set to the predetermined pressure PMVL. In step 252, the intake pipe pressure at the wide opening of the throttle 11 is shown. In the following step 254, it is determined whether or not the intake pipe pressure PM detected by the pressure sensor 26 is lower than the high load determination pressure PMG calculated as described above. If PM <PMG is determined, the value is set to 1 for the injector F / B determination flag YFBINJ because it is not in a high load state (step 255), and the timer counter CNT2 described later is cleared to zero (step 256).
On the other hand, if it is determined that PM ≧ PMG, the flag YFBINJ is set to the value 0 because the load is high (step 25).
7). Then, this routine ends once.

Returning to FIG. 6 (a) again, in step 250, the flag YFB
If it is determined that INJ has the value 1, injector 3
In order to execute the feedback control of step 2, the process is step 2
Go to 60 and set the F / B correction factor FAST for the step motor to 1.0.
Set, then in step 2622 F / for the injector
B correction factor FAFINJ F / B calculated up to step 246
Set the correction factor FAF. On the other hand, the flag YFBINJ has the value 1
If not, the process proceeds to step 264 to execute the feedback control of the step motor 9, and the F / B correction coefficient FAFST for the step motor is calculated using the F / B correction coefficient calculated up to the step 246. Set the FAF, and in the following steps 266 to 269, set F / F for the injector.
B Set the correction coefficient FAFINJ to 0. Note that step 266
Then, it is determined whether or not the timer counter CNT2 is smaller than the constant d. This timer counter CNT2 indicates the time during which the rich signal continues, and is incremented by the compare interrupt routine described later like the timer counter CNT1T. It is zero-cleared by the YFBINJ calculation routine, and when it is determined that CNT2 <d in step 266, the F / B correction coefficient FAFINJ for the injector is set to 1.0 (step 268), while CNT2 ≧ d is determined. Then, the value 0 is set to the F / B correction coefficient FAFINJ for the injector (step 269). That is, the value of FAFINJ is 1.0 until the timer counter CNT2 becomes the constant d or more, and the value 0 is set to FAFINJ for the first time when CNT2 becomes d or more. Step 26
2. After executing step 268 or step 269, the process exits to “RETURN” and ends once.

The above-described processing of steps 230 to 246 is processing when the air-fuel ratio is rich, and is processing for reducing the F / B correction coefficient FAF. In contrast to this processing, the processing of steps 270 to 294 in FIG. 6B is processing when the air-fuel ratio is lean, and is processing for increasing the F / B correction coefficient FAF.

First, if it is determined in step 210 that the air-fuel ratio is lean, the process proceeds to step 270. In step 270, the YOX
It is determined whether or not the value of is 1. If the value of YOX is "1", the process executes steps 272 to 280. When the process proceeds to step 272 according to the determinations of steps 220 and 270, it is when the air-fuel ratio is switched from rich to lean. Step 272 and Step 274
Is the same as the processing of steps 232 to 234, the average F / B correction coefficient FAFAV during F / B control is calculated (step 272), and the value of the F / B correction coefficient FAF is changed to the old F / B correction coefficient FAFV. / B correction factor
Set as FAFO (step 274). In the following Step 276, F /
After adding the skip amount a to the B correction coefficient FAF to obtain a new F / B correction coefficient FAF, the learning timing flag YKG is set (step 278) and the value of the flag YOX is reset to "0" (step 280). ).

On the other hand, if it is determined in step 270 that the value of the flag YOX is "0", the processes of steps 290 to 294 are executed. Here, when the process proceeds to step 290, it means that the air-fuel ratio is kept lean.
The processing of steps 290 to 294 is the same as steps 242 to 246.
The process is the opposite of the above process, and is a process of increasing the value of the F / B correction coefficient FAF by a constant b at every predetermined time.

After the execution of step 280 or step 294, or after the negative judgment is made in step 290, the processing is the sixth step.
Returning to step 250 of FIG. 10A, the processes of step 250 and steps 260 to 269 are executed.

The timing chart of FIG. 13 shows the processing contents of steps 210 to 246 and steps 270 to 294. As can be seen from FIG. 13, the F / B correction coefficient FAF is increased / decreased according to the air-fuel ratio signal detected by the oxygen sensor 28, and is controlled to approach the stoichiometric air-fuel ratio. Then, by the processing of steps 250 to 269, when the high load state is not established (YFBINJ = 1), the feedback control of the injector 32 is executed to execute the F / B for the step motor.
The correction factor FAFST is set to the value 1.0 and the injector
The F / B correction coefficient FAFINJ is set to the F / B correction coefficient FAF. On the other hand, when the load is high (YFBINJ ≠ 1),
In order to execute the feedback control of the step motor 9,
The F / B correction coefficient FAFST for the step motor is set to the F / B correction coefficient FAF, and after the predetermined time d when the load is switched to the high load state, the F / B correction coefficient FAFINJ for the injector is set.
Is set to the value 0.

When it is determined in step 210 that the F / B control conditions are not satisfied, the F / B correction coefficient FAF and the old F / B
The value of the B correction coefficient FAFO is set to "1" (step 299), the process proceeds to step 250, and the F / B correction coefficient FAFST for the step motor is used by using the F / B correction coefficient FAF.
Alternatively, the F / B correction coefficient FAFINJ for the injector is set.

Next, the "learning routine" executed in step 300 of the "main routine" will be described. This "learning routine" is a process that is called and executed as a subroutine in step 300, and is shown in FIG.

First, at step 310, it is judged if the value of the learning timing flag YKG is "1". Learning timing
If the value of YKG is not "1", the process proceeds to step 320, resets the value of the learning timing flag YKG to "0", exits to "RETURN", and ends this routine. That is, the following processing is executed only when the value of the learning timing flag YKG is "1", in other words, only when the air-fuel ratio is switched from rich to lean or from lean to rich.

If the value of the learning timing flag YKG is determined to be "1", the process proceeds to step 330, and whether or not the injector F / B determination flag YFBINJ has the value 1, that is, the intake pipe pressure PM detected by the pressure sensor 26 is It is judged whether it is higher than the high load judgment pressure PMG. If YFBINJ = 1, that is, if it is determined that the load is not high, the process executes steps 340 to 360. At step 320, the average F / B correction coefficient FA calculated by the "feedback correction coefficient FAF calculation routine" is calculated.
The value of FAV is judged.

(A) First, in step 340, 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) When it is determined that the average F / B correction coefficient FAFAV> 1, the process proceeds to step 350. In step 350, the learning correction value KG corresponding to the intake pipe pressure PM at that time is increased by a constant i.

(C) When it is determined that the average F / B correction coefficient FAFAV <1, the process proceeds to step 360. In step 360, the learning correction value KG is reduced by the constant i.

The learning correction value KG is ± i by executing the processing of (A) to (C) each time lean or rich is switched.
It is increased or decreased only and becomes the optimum value for the intake pipe pressure PM at that time. This learning correction value KG is used to calculate the target number of steps ST during normal operation that is not under high load (step 2160 of "ST calculation routine").

On the other hand, when YFBINJ ≠ 1 is determined in step 330, that is, when it is determined that the load is high, the process proceeds to step 320, the learning process of steps 340 to 360 is not executed, and the learning timing flag YKG is reset to “0”. Then, this routine is finished.

Next, the “TAU calculation routine” executed in step 400 of the “main routine” will be described. This "TAU calculation routine" is a process which is called by executing a subroutine in step 400 and is shown in FIG.

First, in step 410, L detected by the rotation speed sensor 31
Based on the rotational speed NE of the PG engine 1 and the intake pipe pressure PM in the intake manifold 2 detected by the pressure sensor 26, the basic injection time TAUBSE is obtained from the three-dimensional map. Subsequent steps
In 420, the injector F / B correction coefficient FAFINJ calculated in the "FAF calculation routine" is loaded, and the subsequent step 43
In step 0, step 440, the intake air temperature correction coefficient FTHAI and the water temperature correction coefficient FTHWI, which are also correction coefficients for the injector, are calculated. The intake air temperature correction coefficient FTHAI is obtained from a two-dimensional map with the intake air temperature THA detected by the intake air temperature sensor 24, and the water temperature correction coefficient FTHWI is obtained from a two-dimensional map with the cooling water temperature THW detected by the water temperature sensor 25. In the following step 450, the calculated basic injection time TAUBSE is also multiplied by the injector calculated F / B correction coefficient FAFINJ, the intake air temperature correction coefficient FTHAI and the water temperature correction coefficient FTHWI, to correct the basic injection time TAUBSE. 32 target opening time TA
U. After executing the processing of step 450, the processing of this routine is once ended.

Using the target opening degree ST of the step motor 9 and the target opening time TAU of the injector 32, which are obtained as described above, how the step motor 9 and the injector are
Whether 32 is driven will be described below with reference to FIGS. 10 to 12.

FIG. 10 is what is called a capture interrupt, and determines whether or not it is the injector injection timing based on the engine speed NE calculated from the detection signal from the speed sensor 31 (steps 500 and 510), and the step
It executes the processing of 520 and 530. That is, when it is determined in step 510 that it is the injector injection timing, energization of the injector 32 is started, the injector 32 is opened (step 520), and the energization is terminated based on the target valve opening time TAU described above. The time is set (step 530).

FIG. 11 is what is called a conveyor interrupt, and is executed at relatively short predetermined time intervals. When the process is started, it is judged whether or not it is the timing of the energization end time set in step 530 (step 600), and if it is that timing, the energization of the injector 32 is stopped,
The injector 32 is closed (step 610). Then, it is judged whether or not it is the control timing of the step motor determined by the process described later (step 620), and if it is the control timing, the step motor control routine is executed (step 630).

This step motor control routine is shown in the flowchart of FIG. 12, and is executed by a subroutine call in step 630.

As shown in FIG. 12, first, the current step number SNOW representing the step number of the step motor 9 is loaded (step
631), and subsequently, the current step number SNOW is compared with the target step number ST (step 632). 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 to. In steps 633-637,
Current step number SN indicating the step number of step motor 9
Perform processing to match OW with the target number ST of steps.

(A) First, in step 633, the target number of steps ST
If it is determined that SNOW is equal to the target step number ST, the current step number SNOW of the step motor 9 does not have to be driven, and in that state, "RETURN" is skipped. Finish the routine.

(B) In step 633, the target number of steps ST> SNOW
If it is determined that the current step number SNOW indicating the step number of the step motor 9 is smaller than the target step number ST, the CPU 51 issues a forward rotation command to the external output circuit 56 to increment the step number of the step motor 9. To the step motor 9 to rotate the step motor 9 forward by one step (step 634), and after incrementing the current step number SNOW that represents the step number of the step motor 9 (step 635), the process returns to "RETURN To exit.

(C) In step 633, 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 636) and the current step number SNOW is decremented (step 637),
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).

After executing the step motor control routine, the process proceeds to step 640 (FIG. 11) to set the next control timing. This control timing is used for the determination in step 620, and is, for example, a time added with a fixed time. Thereafter, the timer counters CNT1 and CNT2 described above are each incremented by 1 (step 650), and the processing of this routine is once terminated. If a negative decision is made in step 620, the process of steps 630 to 650 is skipped and the process of this routine is once ended.

As described above in detail, in the present embodiment, when the LPG engine 1 is not in the high load state (when the intake pipe pressure PM is lower than the high load determination pressure PMG), first, the step motor 9 is used to set the learning value. By supplying fuel from the normal fuel passage 5 on the basis of the above, the air-fuel ratio of the fuel is controlled to the lean side, and the oxygen concentration in the exhaust gas is detected by the oxygen sensor 28, and the injector 32 is used. By supplying fuel based on the signal from the oxygen sensor 28, the lean side air-fuel ratio can be feedback-controlled to the stoichiometric air-fuel ratio. Further, when the load is high such as when the throttle valve is fully opened (WOT), fuel is supplied by the step motor 9 based on the signal from the oxygen sensor 28, and the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio. Due to the pulsation in the manifold 2, the air-fuel ratio of the fuel mixture normally supplied from the fuel passage 5 becomes overrich, and the air-fuel ratio of the LPG engine 1 becomes
The portion that shifts to the rich side as shown by the broken line in FIG. 14 can be maintained at the stoichiometric air-fuel ratio as shown by the solid line in FIG. Therefore, the engine output is stable, the drivability can be improved, and the emission and the fuel consumption can be prevented from being deteriorated.

In this embodiment, the step motor 9 and the injector are
When switching from the control of both 32 and 32 to the control of only the step motor 9, the injector 32 is configured not to immediately close the valve but to delay it by a predetermined time d and close it. It also has a great effect. That is, since the injector 32 is located on the downstream side of the intake manifold 8 with respect to the venturi 4, when the control is switched as described above, a fuel delay may occur and the air-fuel ratio may become over lean. By configuring as above,
The lean phenomenon can be eliminated and the engine output can be stabilized.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and for example, as the high load state determination means, the present embodiment is replaced with the above embodiment for determining from the intake pipe pressure. As a matter of course, the present invention can be implemented in various modes such as a configuration using the output signal from the high output range detection switch of the throttle sensor without departing from the scope of the present invention.

Effects of the Invention As described in detail above, the air-fuel ratio control device for an LPG engine of the present invention changes the supply amount of the fuel mixing means even in a high load state so that the air-fuel ratio is appropriately adjusted so as not to become overrich. Control can be performed. Therefore, the engine output is stable, the drivability can be improved, and the emission and the fuel consumption can be prevented from being deteriorated.

[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 device, FIG. 4 to FIG. 12 are flow charts showing the processes executed by the electronic control device, and FIG. 13 is a timing chart showing the relationship between the air-fuel ratio signal and the feedback correction coefficient FAF. FIG. 14 is a graph showing the air-fuel ratio characteristic at high load according to this embodiment. M1 …… engine, M2 …… intake passage M3 …… Venturi, M4 …… fuel mixing means M5 …… fuel injection means, M6 …… exhaust passage M7 …… air-fuel ratio detection means M8 …… high load condition determination means M9 ... ... fuel amount control means M10 ... first feedback control means M11 ... second feedback control means 1 ... LPG engine, 2 ... intake manifold 4 ... venturi, 5 ... normal fuel passage 8 ... exhaust manifold, 9 ...... Step motor 23 ...... Electronic control unit 26 ...... Pressure sensor 28 ...... Oxygen sensor 32 ...... Injector

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, and supplying a fuel mixture to the engine, and the fuel. LPG for controlling the air-fuel ratio of the engine by controlling the amount of fuel supplied by the both means, the fuel injection means being provided in an intake passage downstream of the mixing means and injecting fuel into the intake passage. In an air-fuel ratio control device for an engine, an air-fuel ratio detection unit that 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, and determines whether the engine is in a high load state. And a high-load state determination means for performing a high-load state determination means, and when the high-load state determination means determines that the engine is not in a high-load state As but a lean side,
When the air-fuel ratio of the engine becomes lean due to the control result of the fuel amount control means, the fuel amount control means for controlling the amount of fuel mixed with the intake air by the fuel mixing means, the air-fuel ratio of the engine becomes First feedback control means for feedback-controlling the amount of fuel supplied by the fuel injection means based on the air-fuel ratio detected by the air-fuel ratio detection means so as to attain a predetermined target air-fuel ratio; and the high load state determination means. When it is determined that the engine is in a high load state, the amount of fuel mixed with intake air by the fuel mixing means is set to the air-fuel ratio so that the air-fuel ratio of the engine becomes a predetermined target air-fuel ratio. Second feedback control means for performing feedback control based on the air-fuel ratio detected by the detection means, and an air-fuel ratio control device for an LPG engine, comprising: .