JPH01200053A - Air-fuel ratio controller for lpg engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an air-fuel ratio control device for an engine that uses liquefied petroleum gas as fuel.

[Prior Art] Conventionally, an intake passage of an engine that uses liquefied petroleum gas as fuel (hereinafter simply referred to as an LPG engine) is provided with a normal fuel passage that supplies main fuel. The liquefied petroleum gas flowing through the engine was mixed with intake air and supplied to the engine body through a venturi formed in the intake passage. Further, an injector serving as a fuel injection means is provided in the intake passage on the downstream side of the venturi, and fuel is also supplied auxiliary.

Note that the opening degree 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 closer to the stoichiometric air-fuel ratio, the injection amount of the injector is adjusted in the exhaust gas. Feedback control was performed based on the oxygen concentration of
67756).

[Problems to be Solved by the Invention] However, in such a conventional air-fuel ratio control device for an LPG engine, pulsation in the intake passage becomes large during high loads such as when the throttle valve is fully opened, and the fuel normally supplied from the fuel passage increases. The amount may vary greatly, and as a result, the air-fuel ratio of the supplied fuel may be controlled to be richer than the stoichiometric air-fuel ratio. In particular, the L
In the PG engine, the above-mentioned change in fuel amount becomes larger, so the air-fuel ratio is controlled to be richer. Therefore, even if the injector is driven in such a case, the air-fuel ratio cannot be returned to the stoichiometric air-fuel ratio, resulting in a problem of deterioration of engine output, emissions, and fuel efficiency.

The present invention has been made in view of the above-mentioned problems.
An object of the present invention is to provide an air-fuel ratio control device for an LPG engine that can prevent over-rich air-fuel ratios during high loads such as when driving, and can improve emissions, fuel efficiency, and drivability.

[Means for Solving the Problem] In order to achieve the above object, the present invention employs the configuration shown below as a means for solving the problem. That is, the air-fuel ratio control device for an LPG engine of the present invention has a first
As illustrated in the figure, fuel is mixed with intake air through a venturi M3 formed in an intake passage M2 of an engine M1 that uses liquefied petroleum gas as fuel, and a fuel mixture is supplied to the engine M1. a mixing means M4; and a fuel injection means M5 provided in the intake passage M2 on the downstream side of the fuel mixing means M4 and injecting fuel into the intake passage M2, the fuel being supplied by both the means M4 and M5. LP that controls the air-fuel ratio of the engine M1;
The air-fuel ratio control device for the G engine includes: an air-fuel ratio detection means M7 that is provided in the exhaust passage M6 of the engine M1 and detects the air-fuel ratio of the engine M1 from the oxygen concentration in the exhaust gas; a high load state determining means M8 for determining whether or not the engine M1 is in a high load state; a fuel amount control means M9 that controls the amount of fuel mixed with the intake air by the fuel mixing means M4 so that the air-fuel ratio of the air is on the lean side; and a control result of the fuel amount control means M9 that controls the engine M1. When the air-fuel ratio becomes lean, the engine M
a first feedback control means MIO that 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 so that the air-fuel ratio of 1 becomes a predetermined target air-fuel ratio; and when the high load state determining means M8 determines that the engine M1 is in a high load state, the engine M
The amount of fuel mixed with the intake air by the fuel mixing means M4 is feedback-controlled based on the air-fuel ratio detected by the air-fuel ratio detecting means M7 so that the air-fuel ratio of 1 becomes a predetermined target air-fuel ratio. Second feedback control means Ml
The gist is that it is equipped with the following.

Here, the high load state determining means M8 is for determining whether or not the engine M1 is in a high load state. There are devices that detect pressure and determine a high load state when the detected value is equal to or higher than a predetermined value.

[Function] The air-fuel ratio control device for an LPG engine of the present invention configured as described above mixes liquefied petroleum gas as a fuel and intake air using the fuel mixing means M4, and supplies the fuel mixture to the engine M1. At the same time, the fuel injection means M5 supplies fuel to the engine M1. However, when the high load state determination means M8 determines that the engine M1 is not in a high load state, the fuel amount control means M9 controls the fuel mixture. The air-fuel ratio of the fuel mixture supplied from the means M4 is set to the lean side, and the first feedback control means MIO sets the amount of fuel supplied by the fuel injection means M5 to the air-fuel ratio detected by the air-fuel ratio detection means M7. The air-fuel ratio of the engine M1 is adjusted to a predetermined target air-fuel ratio by feedback control based on the following. Moreover, when the high load state determining means M8 determines that the engine M1 is in a high load state, the second feedback control means Mll controls the amount of fuel mixed with the intake air by the fuel mixing means M4 to the air-fuel ratio detecting means M7. The air-fuel ratio of the engine M1 is set to a predetermined target air-fuel ratio through feedback control based on the air-fuel ratio detected by the air-fuel ratio, and the air-fuel ratio becomes overrich even under high loads when the pulsation in the intake passage becomes large. Not at all.

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

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

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 absorbs LPG via a normal fuel passage 5 and an acceleration fuel passage 6, which communicate with a venturi 4 formed in the intake manifold 2. Liquefied petroleum gas (LPG) from regulator 7
The exhaust gas is taken in and the mixture of outside air and LPG is exploded and burned to obtain driving force, and then the exhaust gas is discharged to the outside from the exhaust manifold 8.

Further, the opening degree of the normal fuel passage 5 is controlled by a step motor 9 provided in the middle thereof, and the opening degree of the acceleration fuel passage 6 is controlled by a power valve 10 provided in the middle of the acceleration fuel passage 6 only during acceleration. The circuit is opened. On the other hand, the intake amount of a mixture of outside air and LPG is determined by the opening degree of a 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 portion of the exhaust gas is recirculated to the exhaust system by a so-called exhaust gas recirculation device 13.

, the swirl device 14 attached to the upper part of the LPG engine 1 generates a swirling flow of the air-fuel mixture within the cylinder of the LPG engine 1. Said power valve 10
, exhaust gas recirculation device 13, and swirl device 14 are turned on and off by negative pressure switching valves 16, 17, and 18, respectively. Further, the slow lock valve 22, which opens and closes the slow fuel passage 21 that supplies fuel for idling, is turned on and off by the negative pressure switching valve 19, and performs fuel cut during deceleration, etc. Check valves 16a and 19a connected to the negative pressure switching valves 16 and 19 prevent the power valve 10 and the slow lock valve 22 from closing when the negative pressure in the intake manifold 2 decreases. These negative pressure switching valves 16, 17, 18, and 19 are each electrically connected to an electronic control f3j device (hereinafter simply referred to as ECU 6) 23, and control their on/off timing. Also,
This ECU 23 includes an intake temperature sensor 24 that detects the temperature of outside air taken in from the air cleaner 3, and an LPG engine 1.
A water temperature sensor 25 detects the cooling water temperature THW of An oxygen sensor 28 to detect, an exhaust temperature sensor 29 to detect the temperature of exhaust gas, and a rotation speed sensor 3 attached to the distributor 30 to detect the rotation speed of the LPG engine 1.
1st class is connected. The ECU 23 switches the negative pressure switching valve 1 according to the output signals output from each of these sensors.
6.17.18.19, and also suitably controls the step motor 9, the injector 32, the distributor 30 attached to the LPG engine 1, etc. mentioned above. The injector 32 is installed in the intake manifold 2 closer to the LPG engine 1 than the throttle 11, and is used to control the air-fuel ratio of the LPG engine 1.

Next, the ECU 23 will be explained. Figure 3 shows ECU2
3 is a block diagram showing the configuration of No. 3. FIG.

ECU 23 is a well-known central processing unit) (CPU) 51
, read-only memory (ROM) 52, random access memory (RAM) 53. It is configured as a logic operation circuit which mainly includes a backup RAM 54 for storing stored data, and connects these to an external input circuit 55, an external output circuit 56, etc. via a bus 57.

The external input circuit 55 includes the aforementioned intake temperature sensor 24, water temperature sensor 25, pressure sensor 26, and throttle sensor 27.
, an oxygen sensor 28, an exhaust temperature sensor 29, a rotational speed sensor 31, etc. are connected, and via this external input circuit 55, the CPU 51 reads the signals output from each sensor etc. as a human power value. Based on these human power values, the CPU 51 controls the step motor 9, the negative pressure switching valves 16 to 19, the distributor 31, the injector 32, etc. connected to the external output circuit 57.

Next, the air-fuel ratio control process of the LPG engine executed by the ECU 23 mentioned above will be explained along the flowcharts shown in FIGS. 4 to 12.

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 is periodically executed. executed.

When the process moves to this routine, first step 1
At 00, an ST calculation routine for calculating the target step number ST of the step motor 9 is executed.

In subsequent step 200, an FAF calculation routine for calculating a feedback correction coefficient FAF for feedback control is executed, and in subsequent step 300, a learning routine is executed. In a subsequent step 400, the injector 32
A TAU calculation routine for calculating the injection time TAU of is executed, and then the processing of this routine is temporarily terminated.

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

"rST calculation routine of step 100" is step 1
This is a process executed by calling a subroutine at 00, as shown in FIG. When the process starts, first, in step 110, data is stored in the ROM 52 based on the rotation speed NE of the LPG engine 1 detected by the rotation speed sensor 31 and the intake pipe pressure PM in the intake manifold 2 detected by the pressure sensor 26. By using a previously stored three-dimensional map and performing interpolation calculations, the basic number of steps S of the step motor 9 for controlling the opening of the normal fuel passage 5 is calculated. This 3
The basic step number S of the dimensional map is set in advance so as to be on the fuel lean side. In the subsequent step 120, the learning correction value KG is loaded as a correction coefficient for the basic step number S, and in the subsequent steps 130 and 140, the intake temperature correction coefficient FTHA and the water temperature correction coefficient FTHW are calculated as correction coefficients, and the process continues. In step 150, the feedback correction coefficient FAFST for the step motor 9 is
Load. The learning correction value KG is obtained by a learning routine described later, and the feedback correction coefficient FAFST for the step motor 9 is obtained by the FAF calculation routine at step 200. These are temporarily stored in the RAM 53, and It is loaded from the RAM 53.

The intake temperature correction coefficient FTHA is calculated from a two-dimensional map of the intake temperature THA detected by the intake temperature sensor 24.
THW is determined from a two-dimensional map of the cooling water temperature THW detected by the water temperature sensor 25. Next step 1
60, the learned correction value KG, the intake temperature correction coefficient FTHA, and the water temperature correction coefficient F are added to the calculated basic step number S.
The basic step number S is corrected by multiplying THW and the step motor feedback correction coefficient FAFST, and is set as the target step number ST of the step motor 9.

After executing the process of step 160, the process of this routine is temporarily terminated.

The rFAF calculation routine in step 200 is a process that is executed by calling a subroutine in step 200.
This is shown in FIGS. 6(a) and 6(b).

As shown in FIG. 6(a), first, in step 210, it is determined whether a feedback (hereinafter simply referred to as F/B) control condition is satisfied. If it is determined that the F/B control conditions are satisfied, the process proceeds to step 220, where it is determined whether the air-fuel ratio is rich based on the output signal of the oxygen sensor on the second day. Here, if it is determined that it is rich, the next process, steps 230 to 262, is executed.

In step 230, the flag YO determines whether the air-fuel ratio was lean the last time this processing routine was executed.
Judging by X. If the value of the flag YOX is "0", it is assumed that the previous time was lean, and the next step 2 is performed.
Proceed to step 32. In other words, when the process proceeds to step 232 based on the determinations made in steps 220 to 230, it is determined that the air-fuel ratio has been switched from lean to rich. In the following step 232, in order to calculate the average correction coefficient FAFAV during F/B control, the current F/B correction coefficient FAF and the old F/B correction coefficient FAFO at the time of the previous transition from rich to lean are added. Find the average and convert it to F
/B Perform processing to set the average F/B correction coefficient FAFAV during control. The following series of processing steps 234 to 2
40, the F/B correction coefficient FAF is replaced by the old F/B correction coefficient F.
AFO step 234), F/B correction coefficient FAF
After subtracting the skip amount a from the value and setting it as a new F/B correction coefficient FAF (step 236), set the learning timing flag YKG to 1 shift 1 (step 238),
Also, the flag YOx is set to the value 1 (step 24
0). The learning timing flag YKG, which will be described later, is used when determining the timing to learn the learning correction 1fiKG, and the value of the flag YOX being "1" means that the air-fuel ratio is rich. represents something.

On the other hand, in step 230, the value of the flag YOX is "1".
”, the process proceeds to steps 242 and 2.
46 processes are executed. Here, when the process proceeds to step 242 based on the determination in steps 220 to 230, this indicates that the air-fuel ratio is maintained in a rich state. In step 242, the timer counter CNTl
It is determined whether or not is greater than or equal to a constant C. This timer counter CNT1 is incremented in a conveyor interrupt routine (described later) which has a shorter period than this routine. When the timer counter CNT1 exceeds the constant C, the F/B correction coefficient FA is set in step 244.
After subtracting the constant S from F, the process proceeds to step 246, where the value of the timer counter CNT1 is cleared to "0". On the other hand, if the timer counter CNTl is less than or equal to the constant C in step 242, steps 244 and 246 are skipped. That is, in steps 242 to 246,
This means that the value of the F/B correction coefficient FAF is subtracted by a constant every predetermined time.

After executing step 240 or step 246, or if a negative determination is made in step 242, the process proceeds to step 250. In step 250, it is determined whether the injector F/B determination flag YFB INJ is the value 1 or not. This injector F/B judgment flag YFB
INJ indicates whether or not feedback control of the injector 32 should be executed, and rYFBI shown in FIG.
This is determined by the "NJ Calculation Routine". Here, the rYFBINJ calculation routine shown in FIG. 7 will be explained first.

In FIG. 7, when the process is started, first, in step 251, a predetermined constant j is subtracted from a predetermined pressure PMVL to calculate a high load determination pressure PMG. This predetermined pressure PMVL is determined by changing the intake pipe pressure PM detected by the pressure sensor 26 to a predetermined pressure when the throttle opening degree VL detected by the throttle sensor 27 is larger than a predetermined value (50 degrees in this embodiment) (step 252). PMVL (
Step 253) shows the intake pipe pressure when the throttle 11 is wide open. In the following step 254, it is determined whether the intake pipe pressure PM detected by the pressure sensor 26 is smaller than the high load determination pressure PMG calculated as described above.

If it is determined that PM<PMG, the injector F/B determination flag YFBINJ has a value of 1 because it is not in a high load state.
is set (step 255), and the timer counter CNT2, which will be described later, is cleared to zero in step 256.
), On the other hand, if it is determined that PM≧PMG, it is a high load state, so the flag YFBINJ is set to 0 (step 257). Thereafter, this routine ends once.

Returning to FIG. 6(a) again, in step 250, the flag Y
If FB I N J is determined to have a value of 1,
In order to perform feedback control of the injector 32,
Processing proceeds to step 260 where the step motor F/
The B correction coefficient FAFST is set to a value of 1.0, and in the following step 262, the F/B correction coefficient FAF for the injector is set.
The F/B correction coefficient FAF calculated up to step 246 is set in INJ. On the other hand, if it is determined that the flag YFBINJ is not 1, the process proceeds to step 26 to execute feedback control of the step motor 9.
Proceed to step 4 and set the F/B correction coefficient FAFS for the step motor.
The F/B correction coefficient FAF calculated up to step 246 is set in T, and in the following steps 266 to 269, the F/B correction coefficient FAFIN for the injector is set.
Set J to 0. In addition, in step 266, it is determined whether or not the timer counter CNT2 is smaller than the constant d. This timer counter CNT2 indicates the duration of the rich signal, and similarly to the timer counter CNT1, it is determined whether or not the timer counter CNT2 is smaller than the constant d. It is incremented by , and cleared to zero in the YFBINJ calculation routine, and when it is determined that CNT2<d at step 266,
The F/B correction coefficient FAF I N J for the injector is set to a value of 1.0 (step 268), while the CN
When it is determined that T2≧d, the value O is set to the F/B correction coefficient FAF I N J for the injector (step 269). That is, the value of FAFINJ is 1.0 until the timer counter CNT2 becomes equal to or greater than the constant d, and only when CNT2 becomes equal to or greater than d, the value 0 is set to FAF INJ. After executing step 262, step 268, or step 269, the process exits to "rRETURN" and ends at -1.

Note that the processing in steps 230 to 246 described above is as follows:
This is a process when the air-fuel ratio is rich, and is a process for decreasing the F/B correction coefficient FAF. In contrast to this process, the processes in steps 270 to 294 in FIG. 6(b) are processes when the air-fuel ratio is lean, and are processes for increasing the F/B correction coefficient FAF.

First, if the air-fuel ratio is determined to be lean in step 210, the process proceeds to step 270. In step 270, it is determined whether the value of YOX is "1". YO
If the value of X is "1", the process performs steps 272-280.

When the process proceeds to step 272 based on the determinations in steps 220 and 270, the air-fuel ratio has been switched from rich to lean. The processing in step 272 and step 274 is the same processing as the processing in steps 232 to 234 described above, in which the average F/B correction coefficient FAFAV during F/B control is calculated (step 272), F/B
The value of the correction coefficient FAF is set as the old F/B correction coefficient FAFO (step 274). In the following step 276, F/B
A new F/ is obtained by adding the skip amount a to the correction coefficient FAF.
After setting B correction coefficient FAF, learning timing flag YK
G is set (step 278), and the value of the flag YOX is reset to "0" (step 280).

On the other hand, in step 270, the value of the flag YOX is "0".
”, steps 290 to 294
Execute the process. Here, when the process proceeds to step 290, this indicates that the air-fuel ratio is maintained at a high level. The processing of steps 290 to 294 is
This process is the opposite of steps 242 to 246, and is a process in which the value of the F/B correction coefficient FAF is increased by a constant every predetermined time.

Note that after executing step 280 or step 294,
Alternatively, after a negative determination is made in step 290, the process returns to step 250 in FIG. 6(a) and proceeds to step 25.
0 and steps 260 to 269 are executed.

Steps 210 to 246 and step 27 above
The timing chart in FIG. 13 shows the processing contents of 0 to 294. As can be seen from FIG. 13, F/F/F is
The B correction coefficient FAF is increased or decreased and controlled to approach the stoichiometric air-fuel ratio. and steps 250 to 26
9, when the load is not high (YFBIN
J:1), in order to perform feedback control of the injector 32, the F/B correction coefficient FAF for the step motor is
ST has value 1. 0 is set and the F/
The F/B correction coefficient FAF is set to the B correction coefficient FAFINJ. On the other hand, when the load is high (YFBI
NJ≠1), in order to perform feedback control of the step motor 9, an F/B correction coefficient F for the step motor is set.
The F/B correction coefficient FAF is set in AFST, and after a predetermined time d after the load is switched to a high load state, the value 0 is set in the F/B correction coefficient FAF I N J for the injector.

Note that when it is determined in step 210 that the F/B control condition is not satisfied, the F/B correction coefficient FAF
and the old F/B correction coefficient FAFO are each set to "1" (step 299), and the process proceeds to step 250, where the F/B correction coefficient FAF is used to correct the F/B for the step motor. A coefficient FAFST or an F/B correction coefficient FAFINJ for the injector is determined.

Next, the "learning routine" executed in step 300 of the "main routine" will be explained. This "learning routine" is a process executed by calling a subroutine in step 300, and is shown in FIG.

First, in step 310, the learning timing flag YK
It is determined whether the value of G is "1". If the value of the learning timing flag YKG is not "1", the process proceeds to step 320, resets the value of the learning timing flag YKG to "0", exits to rRETURN], and ends this routine.

That is, the following process 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.

When the value of the learning timing flag YKG is determined to be "1", the process proceeds to step 330, and the injector F/B
Whether the determination flag YFBINJ is 1 or not, that is, the intake pipe pressure PM detected by the pressure sensor 26 is the high load determination pressure PM.
Determine whether it is larger than G. If YFBINJ=1, that is, if it is determined that there is no high load state, the process executes steps 340 to 360. Step 3
In step 20, the value of the average F/B correction coefficient FAFAV calculated in the "feedback correction coefficient FAF calculation routine" is determined.

(A) First, when it is determined in step 340 that the average F/B correction coefficient FAFAV=1, it is assumed that the air-fuel ratio has 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 decreased by a constant i.

By executing the process (A) or C) above every time lean and rich are switched, the learning correction value KG can be adjusted to ±i.
The intake pipe pressure PM will be increased or decreased by a certain amount, and will eventually reach 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 (not under high load).
Step 160 of "rST Calculation Routine").

On the other hand, if it is determined in step 330 that YFBINJ≠1, that is, it is a high load state, the process
The program proceeds to step 20, where the learning processing in steps 340 to 360 is not executed, the learning timing flag YKG is reset to "0", and this routine ends.

Next, the rTAU calculation routine executed in step 400 of the main routine will be described. This rTAU calculation routine is a process that is executed by calling a subroutine in step 400, and is shown in FIG.

First, in step 410, based on the rotational speed NE of the LPG engine 1 detected by the rotational speed sensor 31 and the intake pipe pressure PM in the intake manifold 2 detected by the pressure sensor 26, the basic injection time TAUBSE is determined from a three-dimensional map. seek. In the subsequent step 420, the injector F/B correction coefficient FAF calculated in the rFAF calculation routine is
I N J is loaded, and in the following steps 430 and 440, the intake temperature correction coefficient FTHAI and the water temperature correction coefficient FTHW are also set as correction coefficients for the injector.
Calculate I. 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 subsequent step 450, the injector F/B correction coefficient FAF I N J and the intake temperature correction coefficient F, which were also calculated, are added to the basic injection time TAUBSE.
The basic injection time TAUBSE is corrected by multiplying THAI and the water temperature correction coefficient FTHWI, and the result is set as the target valve opening time TAU of the injector 32. After executing the process of step 450, the process of this routine is temporarily ended.

The target opening degree ST of the step motor 9 and the target opening time TAU of the injector 32 obtained as described above.
How the step motor 9 and the injector 32 are driven using this will be explained below with reference to FIGS. 10 to 12.

FIG. 10 shows what is called a capture interrupt, in which it is determined whether or not it is the injection timing of the injector based on the engine rotation speed NE calculated from the detection signal from the rotation speed sensor 31 (steps 500 and 510).
, steps 520 and 530 are executed. That is, when it is determined in step 510 that it is the injector injection timing, energization is started to the injector 32 to open the injector 32 (step 52
0), the energization end time is set based on the target valve opening time TAU mentioned above (step 530).

FIG. 11 shows what is called a conveyor interrupt, which is executed at relatively short predetermined intervals.

When the process starts, it is determined whether or not it is the energization end time set in step 530 (step 600), and if it is the timing, the injector 32
energization is stopped, and the injector 32 is closed (step 610). Thereafter, it is determined whether or not the step motor control timing is determined in a process to be 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 calling a subroutine at step 630.

As shown in FIG. 12, first, the current step number 5NOW representing the number of steps of the step motor 9 is loaded (step 631), and then this current step number 5NOW is compared with the target step number ST (step 632). )
. The current step number 5NOW is a value written in the backup RAM 54 when the CPU 51 outputs a rotation command to the step motor 9 via the external output circuit 56.

In steps 633 to 637, processing is performed to match the current step number 5NOW indicating the number of steps of the step motor 9 with the target step number ST.

(a) First, in step 633, if it is determined that the target number of steps 5T=SNOW, the current number of steps 5NOW of the step motor 9 matches the target number of steps ST, so the step motor 9 is driven. There is no need to do this, and this routine ends if rRETURNJ is selected in that state.

(b) In step d33, a target step.

If it is determined that the number ST>5NOW, the current step number 5NOW representing the number of steps of the step motor 9 is smaller than the target number of steps ST, so the CPU 51 issues a forward rotation command to increment the number of steps of the step motor 9. After outputting the output to the step motor 9 via the external output circuit 56 to rotate the step motor 9 forward by one step (step 634), and incrementing the current step number 5NOW representing the number of steps of the step motor 9 (step 635), the process is performed. exits to "rRETURN".

CC') At step °633, the target stellate number S
If it is determined that T<5NOW, the step motor 9
Since the current step number 5NOW representing the number of steps 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 and reversely rotates the step motor 9 by one step in step 636. ), after decrementing the current step number 5NOW (step 637), the process is rRETURN
”, the routine ends.

By repeatedly executing the processes (a) to (c) above, the number of steps of the step motor 9 matches the target number of steps ST.

After executing the step motor control routine, the process proceeds to step 640 (FIG. 11), where the next control timing is set. This control timing is used for the determination in step 620, and is, for example, a time obtained by adding a certain amount of time. After that, the timer counter CNTl mentioned above,
Each CNT2 is incremented by 1 (step 650), and the processing of this routine is temporarily ended. In addition,
If a negative determination is made in step 620, step 6
The process from 30 to 650 is skipped and the process of this routine is temporarily ended.

As detailed above, in this embodiment, when the LPG engine 1 is not in a high load state (when the intake pipe pressure PM is smaller than the high load determination pressure PMG), first, the step motor 9 is used to control the learned value. Normal fuel passage 5 based on etc.
By supplying fuel from the injector 32, the air-fuel ratio of the fuel is controlled to be lean, and the oxygen moisture level in the exhaust gas is detected by the oxygen sensor 28.
By supplying fuel based on the signal from the oxygen sensor 28, the lean air-fuel ratio can be feedback-controlled to the stoichiometric air-fuel ratio. Furthermore, when the load is high, such as when the throttle valve is fully open (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 LP
While the air-fuel ratio of the G engine 1 shifts to the rich side as shown by the broken line in FIG. 14, it can be maintained at the stoichiometric air-fuel ratio as shown by the solid line in the same figure. Therefore, engine output is stabilized, drivability can be improved, and deterioration of emissions and fuel efficiency can be prevented.

Note that in this embodiment, the step motor 9 and the injector 3
When switching from control of both 2 and 2 to control of only the step motor 9, the injector 32 is not closed immediately, but is closed after a predetermined time d, as described below. It also has a great effect. That is,
The injector 32 is connected to the intake manifold 8 from the venturi 4.
Due to the position on the downstream side of This 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 includes
The present invention is not limited to the above-mentioned embodiments; for example, instead of the above-described embodiments in which the determination is made from the intake pipe pressure, an output signal from a high-output range detection switch of a throttle sensor is used as the high-load state determination means. It goes without saying that the invention can be implemented in various ways without departing from the gist of the invention.

[Light skin effect] As detailed 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, and properly empties the fuel to prevent over-rich conditions. The fuel ratio can be controlled. Therefore, engine output is stabilized, drivability can be improved, and deterioration of emissions and fuel efficiency can be prevented.

[Brief explanation of the drawing]

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 according to an embodiment of the present invention, and FIG.
Figure 1 is a block diagram showing the configuration of the electronic control unit, Figures 4 to 12 are flowcharts each representing the processing executed by the electronic control unit, and Figure 13 is the relationship between the air-fuel ratio signal and the feedback correction coefficient FAF. FIG. 14 is a graph showing the air-fuel ratio characteristics under high load according to this embodiment. Ml...Engine M'2...Intake passage M3
...Venturi M4...Fuel mixing means M5.
...Fuel injection means M6...Exhaust passage M7...Air-fuel ratio detection means M8...High load state determination means M9...Fuel amount control means

Claims (1)

[Claims] Mixing fuel and intake air through a bench lily formed in the intake passage of an engine that uses liquefied petroleum gas as fuel,
a fuel mixture means for supplying a fuel mixture to the engine; and a fuel injection means provided in an intake passage downstream of the fuel mixture means for injecting fuel into the intake passage; In the air-fuel ratio control device for an LPG engine, the air-fuel ratio control device controls the air-fuel ratio of the engine by controlling the amount of fuel to be used in the engine, the air-fuel ratio detection device being provided in the exhaust passage of the engine and detecting the air-fuel ratio of the engine from the oxygen concentration in the exhaust gas. means for determining whether the engine is in a high load state; and when the high load state determining means determines that the engine is not in a high load state, the fuel mixing means so that the air-fuel ratio of the supplied fuel mixture is on the lean side.
a fuel amount control means for controlling the amount of fuel mixed with intake air by the fuel mixing means; and when the air-fuel ratio of the engine becomes lean as a result of the control of the fuel amount control means, a 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 achieve 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 the intake air by the fuel mixing means is adjusted to the air-fuel ratio so that the air-fuel ratio of the engine becomes a predetermined target air-fuel ratio. An air-fuel ratio control device for an LPG engine, comprising: second feedback control means that performs feedback control based on the air-fuel ratio detected by the detection means.