JP2605731B2 - Air-fuel ratio control device for LPG engine - Google Patents

Description

The present invention relates to an air-fuel ratio control device for an engine that uses liquefied petroleum gas as fuel, and more particularly to a control device that is effective when cold.

2. Description of the Related Art Generally, in an engine using liquefied petroleum gas as fuel (hereinafter, simply referred to as an LPG engine), liquefied petroleum gas discharged from an LPG regulator is injected into a venturi formed in an intake passage, and The liquefied petroleum gas is mixed with the intake air to supply the mixture to the LPG engine.
In the fuel passage from the LPG regulator to the Venturi, a control valve with a variable opening (the opening is normally controlled by a step motor) is provided, based on the basic fuel amount determined by the rotation speed and load of the LPG engine. The opening degree is controlled, and further, the fuel amount is feedback-controlled based on the oxygen concentration in the exhaust gas so that the air-fuel ratio of the LPG engine becomes the target air-fuel ratio, and the opening degree is determined.

[Problems to be Solved by the Invention] However, in the air-fuel ratio control device of the conventional LPG engine, the liquefied petroleum gas may be cooled and liquefied before reaching the venturi during a cold period. As the volumetric efficiency of the fuel increases, even when the control valve in the fuel passage is opened by a predetermined amount, a larger amount of fuel is supplied than the desired amount of fuel, and the air-fuel ratio of the LPG engine becomes richer than the desired air-fuel ratio. There was a problem that became. Therefore, a vehicle surge or engine stall may occur, leading to deterioration of drivability or causing a misfire,
Unburned fuel caused unburned fuel to burn in the exhaust gas purifying catalyst, resulting in heating deterioration of the catalyst.

Particularly, in a normal LPG engine, since the liquefied petroleum gas is heated by the engine cooling water before reaching the venturi, the above problem is more remarkable at the time of a cold start.

The present invention has been made in view of the above problems, and prevents over-rich of the air-fuel ratio at the time of cold, improves drivability, and prevents overheat deterioration of the exhaust gas catalyst.
An object is to provide an air-fuel ratio control device for an LPG engine.

Configuration of the Invention [Means for Solving the Problems] In order to achieve the above object, the present invention has the following configurations as means for explaining the above problems.
That is, the air-fuel ratio control device for an LPG engine of the present invention
As illustrated in the figure, a fuel supply means M4 disposed between a venturi M3 formed in an intake passage M2 of an engine M1 using liquefied petroleum gas as a fuel and a regulator RG, and an operation state of the engine M1 is detected. Operating state detection means M5, so that the air-fuel ratio of the engine M1 becomes the target air-fuel ratio,
Target fuel amount calculating means M6 for calculating a target value of the amount of fuel supplied through the fuel supply means M4 based on the operating state detected by the operating state detecting means M5. In the fuel ratio control device, a fuel temperature detecting means M7 for detecting the temperature of the fuel, and a target fuel amount calculating means M6 corresponding to a decrease in the temperature of the fuel detected by the fuel temperature detecting means M7. And a target fuel amount correcting means M8 for reducing and correcting the target value to be set.

Here, the fuel temperature detecting means M7 may be any device that can directly or indirectly detect the temperature of the fuel, for example, a temperature sensor provided in a fuel passage,
Alternatively, this may be the case with a coolant temperature sensor or the like in those configured to heat the fuel with engine coolant before reaching the Venturi M3.

[Operation] The air-fuel ratio control device for an LPG engine according to the present invention configured as described above is provided with a target fuel amount calculating means such that the air-fuel ratio of the engine M1 using liquefied petroleum gas as fuel becomes the target air-fuel ratio.
The engine M1 detected by the operating state detecting means M5 by M6
The target value of the fuel amount to be supplied to the engine M1 is calculated based on the operating state of the engine M1, and the fuel amount corresponding to the target value is supplied into the venturi M3 formed in the intake passage M2 by the fuel supply means M4. When the temperature of the fuel detected by the fuel temperature detecting means M7 decreases, the target fuel amount correcting means M8 decreases and corrects the target value calculated by the target fuel amount calculating means M6 in accordance with the fuel temperature decrease. ing. Therefore,
Even if the temperature of the fuel decreases and the volumetric efficiency of the fuel increases,
The amount of fuel supplied to the engine M1 does not increase.

In addition, the decrease in fuel supply as described above
Since the operation is performed by the fuel supply means M4 arranged between the RG and the venturi M3, when returning from the reduced correction state to the normal state, the inflow state of the liquefied petroleum gas flowing into the regulator RG greatly changes. There is no. Therefore, when returning from the decrease correction state to the normal state, the air-fuel ratio is not greatly disturbed.

Example Next, a preferred example of the present invention will be described in detail.

FIG. 2 is a schematic configuration diagram of an engine using liquefied petroleum gas (hereinafter simply referred to as an LPG engine) as an air-fuel ratio control device of an LPG engine according to one embodiment of the present invention.

The LPG engine 1 is communicated with an air cleaner 3 via an intake manifold 2 to take in outside air from the air cleaner 3 and an LPG engine via a normal fuel passage 5 and an acceleration fuel passage 6 which communicate with a venturi 4 formed in the intake manifold 2. The liquefied petroleum gas (hereinafter simply LPG)
), The mixture of the outside air and LPG is exploded and burned to obtain a driving force, and then the exhaust gas is discharged from the exhaust manifold 8 to the outside. The normal fuel passage 5 and the accelerating fuel passage 6 are heated by the cooling water of the LPG engine 1, and the LPG flowing through these passages 5 and 6
The vaporization is promoted.

The opening degree of the normal fuel passage 5 is controlled by a step motor 9 provided in the middle thereof,
Is opened only during acceleration by a power valve 10 provided in the middle of the acceleration fuel passage 6. On the other hand, the intake amount of the mixture of the outside air and LPG is determined by the opening of the throttle 11 provided in the intake manifold 2. 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 a so-called exhaust gas recirculation device 13. The swirl device 14 attached to the upper part of the LPG engine 1
The swirling flow of the air-fuel mixture is generated in the cylinder of the engine 1. The power valve 10, the exhaust gas recirculation device
13. The swirl device 14 is turned on and off by negative pressure switching valves 16, 17, and 18, respectively. Also, by the negative pressure switching valve 19,
A slow lock valve 22 that opens and closes a slow fuel passage 21 that supplies idling fuel is turned on and off, thereby performing fuel cut or the like during deceleration. The check valves 16a and 19a connected to the negative pressure switching valves 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 decreases. Each of these negative pressure switching valves 16, 17, 18, and 19 is electrically connected to an electronic control unit (hereinafter, simply referred to as an ECU) 23, and its on / off timing is controlled. Further, the ECU 23 has an intake air temperature sensor 24 for detecting the temperature of the outside air sucked from the air cleaner 3, and an L signal from the LPG regulator 7.
Fuel temperature sensor 25 for detecting PG temperature, intake manifold 2
A pressure sensor 26 for detecting the pressure of the inner, a throttle sensor 27 for detecting the degree of opening of the throttle 11, O ₂ sensor 28 for detecting oxygen concentration in exhaust gas discharged from the exhaust manifold 8,
An exhaust gas temperature sensor 29 for detecting the temperature of the exhaust gas, a rotational speed sensor 31 attached to the distributor 30 for detecting the rotational speed of the LPG engine 1, and the like are connected. ECU2
3 controls the negative pressure switching valves 16, 17, 18, and 19 according to output signals output from these sensors, and controls the step motor 9, the injector 32, the LPG
The distributor 30 and the like attached to the engine 1 are suitably controlled. The injector 32 is mounted in the intake manifold 2 closer to the LPG engine 1 than the throttle 11 and performs fuel injection when the LPG engine 1 is started.

Next, the ECU 23 will be described. Figure 3 is E
FIG. 3 is a block diagram illustrating a configuration of a CU23.

The ECU 23 includes a well-known central processing unit (CPU) 51, a read-only memory (ROM) 52, and a random access memory (RAM).
A logic operation circuit 53 is connected to the external input circuit 55, the external output circuit 56, and the like via a bus 57, mainly a backup RAM 54 for storing stored data, and the like.

The external input circuit 55, the intake air temperature sensor 24 described above, the fuel temperature sensor 25, pressure sensor 26, a throttle sensor 27, O ₂ sensor 28, an exhaust temperature sensor 29 and speed sensor 31 or the like is not connected, the external The CPU 51 reads a signal output from each sensor or the like via the input circuit 55 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 process of the LPG engine executed by the ECU 23 will be described with reference to the flowcharts shown in FIGS. The “step motor control routine” shown in FIG. 4 represents only the processing indicating the control of the step motor 9 for operating the opening degree of the normal fuel passage 5 among the processing executed by the ECU 23, This is a process that is periodically executed by the

First, when the processing shifts to this routine, step 100
Is stored in advance in the ROM 52 based on the rotational speed NT 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.
A basic step number S of the step motor 9 for performing the opening operation of the normal fuel passage 5 is calculated from a dimensional map or the like. In the subsequent step 110, the basic step number S is multiplied by the feedback correction coefficient FAF, the learning correction value KGi, and the temperature condition correction value MSP to correct the basic step number S to obtain the target step number ST of the step motor 9. This feedback correction coefficient FA
F and the learning correction value KGi are values obtained during feedback control during acceleration, and will be described later in detail. Further, the temperature condition correction value MSP is a value obtained in a processing routine described later and is also described later.

In the following step 120, the current step number SNOW representing the number of steps of the step motor 9 is read from the backup RAM 54, and then in step 130, the current step number SNOW is read.
W is compared with the target step number ST. Current step number S
NOW is a value written as the current step number SNOW in the backup RAM 54 when the CPU 51 outputs a rotation command to the step motor 9 via the external output circuit 56. Steps
In steps 130 to 170, a process for matching the current step number SNOW indicating the step number of the step motor 9 with the target step number ST is performed.

(A) First, in step 130, the target step number ST
When it is determined that SNOW is equal to SNOW, the current step number SNOW of the step motor 9 matches the target target step number ST, so that it is not necessary to drive the step motor 9 and in that state, the process returns to “RETURN”. End the routine.

(B) In step 130, target step number ST> SNOW
If it is determined that the current step number SNOW representing the number of steps of the step motor 9 is smaller than the target step number ST, the CPU 51 outputs a forward rotation instruction to increase the number of steps of the step motor 9 to the external output circuit 56. The step motor 9 is rotated forward by one step (step 140), and the current step number SNOW representing the step number of the step motor 9 is incremented (step 150). ".

(C) In step 130, target step number 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 and outputs the step number. The motor 9 is rotated reversely by one step (step 160), and after decrementing the current step number SNOW (step 170),
The processing exits to "RETURN" and ends this routine.

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

Next, the feedback correction coefficient FAF used in step 110 of the “step motor control routine” will be described. FIG.
9 is a flowchart illustrating a “FAF calculation routine”. This “feedback correction coefficient FAF calculation routine” is a subroutine that is periodically executed similarly to the “step motor control routine”.

First, in step 200, feedback (hereinafter simply referred to as F
Call it / B. ) It is determined whether the control condition is satisfied. This F / B control condition is satisfied at the time of acceleration, and is determined by setting a flag at the time of acceleration in another processing routine. If it is determined that the F / B control condition is satisfied during acceleration, the process proceeds to step 210. Step 2
In 10, the output signal of the O ₂ sensor 28 whether the air-fuel ratio is rich or not. If it is determined that the air conditioner is rich, the processes of steps 220 to 300 as the next process are executed.

In step 220, it is determined by the flag YOX whether the air-fuel ratio was lean when this processing routine was executed last time. If the value of the flag YOX is “0”, the process proceeds to the next step 230 assuming that the previous time was lean. That is, according to the determination of steps 210 to 220, step 230
When the process proceeds to, it is determined that the air-fuel ratio has been switched from lean to rich. Next step 23
At 0, the arithmetic mean of the current F / B correction coefficient FAF and the old F / B correction coefficient FAFO at the time of the transition from rich to lean to calculate the average correction coefficient FAFAV during F / B control is calculated. , This is F
A process for setting the average O / B correction coefficient FAFAV during the / B control is performed. In steps 240 to 270, which are a series of subsequent processes, the F / B correction coefficient FAF is set to the old F / B correction coefficient FAFO (step 240).
After the value obtained by subtracting the skip amount a from the / B correction coefficient FAF is set as a new F / B correction coefficient FAF (step 250), the learning timing flag YKG is set (step 260), and the flag YOX is set.
Is set to "1" (step 270), and this routine ends. The learning timing flag YKG, which will be described later, is used when determining the timing at which the learning value KGi should be learned. The fact that the value of the flag YOX is "1" indicates that the air-fuel ratio is rich. It indicates that there is.

On the other hand, when it is determined in step 220 that the value of the flag YOX is “1”, the processing executes the processing of steps 280 to 300. Here, when the process proceeds to step 280 based on the determination in steps 210 to 220, it indicates that the air-fuel ratio is maintaining a rich state. Step 28
At 0, it is determined whether or not the timer counter CNT is equal to or greater than the constant C. This timer counter CNT is incremented in a processing routine by a hard interrupt having a shorter cycle than this routine. If the timer counter CNT is equal to or smaller than the constant C, the routine exits from the "RETURN" and ends this routine. If the timer counter CNT exceeds the constant C, the constant b is subtracted from the F / B correction coefficient FAF in step 290, and then the timer The value of the counter CNT is cleared to "0" (step 300), and this routine ends. That is, step 2
In the case of 80 to 300, the value of the F / B correction coefficient FAF is subtracted by a constant b every predetermined time.

The processing of steps 210 to 300 described above is processing for the case where the air-fuel ratio is rich, and is processing for reducing the F / B correction coefficient FAF. In contrast to the process of decreasing the F / B correction coefficient FAF, the processes of steps 320 to 400 are processes in the case where the air-fuel ratio is lean, and are processes for increasing the F / B correction factor FAF.

First, if it is determined in step 210 that the air-fuel ratio is lean, the process proceeds to step 320. In step 320, the YOX
Is determined whether or not the value of is “1”. YO
If the value of X is "1", the process proceeds to steps 330 to 37.
Execute 0. When the process proceeds to step 330 based on the determinations in steps 210 and 320, it is when the air-fuel ratio is switched from rich to lean. The processing of Steps 330 to 340 is the same processing as the processing of Steps 230 to 240, and the average F / B correction coefficient FAFA during the F / B control.
V is calculated (step 330), and the value of the F / B correction coefficient FAF is
A B correction coefficient FAFO is set (step 340). Next step 35
In the case of 0, after adding the skip amount a to the F / B correction coefficient FAF to obtain a new F / B correction coefficient FAF, the learning timing flag YK
G is set (step 360), and the value of the flag YOX is set to "0"
(Step 370), and this routine ends.

On the other hand, when it is determined in step 320 that the value of the flag YOX is “0”, the processing executes the processing of steps 380 to 400. Here, when the process proceeds to step 380 based on the determinations in steps 210 and 320, it indicates that the air-fuel ratio is maintaining a lean state. Step 380
Steps 400 to 400 are the opposite of steps 280 to 300, and the value of the F / B correction coefficient FAF is
It is processing that only increases.

FIG. 8 is a timing chart showing the processing contents of steps 200 to 400 described above. F / B correction coefficient FAF is controlled so as to approach the stoichiometric air-fuel ratio is increased or decreased in accordance with the air-fuel ratio signal to be detected of the O ₂ sensor 28 as can be seen from this Figure 8.

If it is determined in step 200 that the F / B control condition is 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 410), and this routine ends.

Next, only when the value of the learning timing flag YKG set in steps 260 and 360 of the “feedback correction coefficient FAF calculation routine” is “1”, in other words, the air-fuel ratio changes from rich to lean or from lean to rich. The “learning routine” in FIG. 6A that is executed only when switching is performed will be described.

First, in step 500, it is determined whether the value of the learning timing flag YKG is "1". If the value of the learning timing flag YKG is not “1”, the processing is performed in step 5
The program proceeds to 05, resets the value of the learning timing flag YKG to "0", exits "RETURN", and ends this routine, and when the value of the learning timing flag YKG is determined to be "1", the process proceeds to step 510. In step 510, the 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 in the "predetermined pressure PMG calculation routine" shown in FIG. 6 (B). Here, the predetermined pressure PMG will be described first.

The predetermined pressure PMG is a pressure obtained by subtracting a certain pressure e from another predetermined pressure PMVL (step 600). When the throttle opening VL detected by the throttle sensor 27 is larger than a predetermined value (50 ° in this embodiment) (step 610), the other predetermined pressure PMVL is determined by subtracting the intake pressure PM detected by the pressure sensor 26 from the predetermined pressure. PMVL (Step 62
0). When the throttle opening VL is larger than 50 °, the intake pressure is considered to be substantially equal to the atmospheric pressure. Therefore, the predetermined pressure PMG (= PMLV-e) is lower than the atmospheric pressure by a certain pressure (e). In step 510 of the “learning routine”, the magnitude relationship between the predetermined pressure PMG and the intake pressure PM detected by the pressure sensor 26 that changes every moment is determined.

When it is determined that the intake pressure PM is less than the predetermined pressure PMG,
The processing executes the processing of steps 520 to 540. 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 520, the average F / B correction coefficient FAFAV =
When it is determined to be 1, it is considered 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 processing proceeds to step 530. In step 530, the learning value KGi corresponding to the intake pressure PM at that time is increased by a constant d.

(C) When it is determined that the average F / B correction coefficient FAFAV <1, the processing proceeds to step 540. In step 540, the learning value KGi is reduced by a constant d.

The learning value KGi is increased or decreased by ± 2 by executing the above-described processes (A) to (C) every time switching between lean and rich is performed, and eventually becomes the optimal value for the intake pressure PM at that time. Using the learning value KGi, the target step number ST during normal operation (at this time, the correction coefficient FAF = 1) other than during acceleration is calculated (step 110 of the “step motor control routine”).

On the other hand, in step 510, the intake pressure PM becomes the predetermined pressure PMG
When it is determined that the above is the case, the learning process of steps 520 to 540 is not executed, the learning timing flag YKG is reset to "0" (step 505), and this routine ends. This is because when the intake pressure PM is equal to or higher than the predetermined pressure PMG and is close to the atmospheric pressure, there is a characteristic that the air-fuel ratio sharply increases due to the influence of the intake pulsation, and the learning process is prohibited at this time. .

In this embodiment, the learning value KG corresponding to the intake pressure PM
i is KG when the intake pressure PM is 200mmHg or more and less than 300mmHg
1, When the intake pressure PM is 300mmHg or more and less than 400mmHg, KG2,
KG3 when the intake pressure PM is 400 mmHg or more and less than 500 mmHg, KG4 when the intake pressure PM is 500 mmHg or more and less than 600 mmHg, and KG5 when the intake pressure PM is 600 mmHg or more and less than 700 mmHg.

Next, the temperature condition correction value MSP used in step 110 of the “step motor control routine” will be described. FIG. 7 is a flowchart showing a “temperature condition correction value MSP calculation routine”. This “temperature condition correction value MSP calculation routine” is also a subroutine that is executed periodically like the “step motor control routine”.

When the process is started, in step 700, the ROM (temperature) based on the temperature (THL) of the fuel (LPG) detected by the fuel temperature sensor 25 and the temperature THA of the intake air detected by the intake temperature sensor 24 is used.
The temperature condition correction value MSP is calculated with reference to the three-dimensional map A stored in advance in 52. The three-dimensional map A is the ninth map
As shown in the figure, the temperature condition correction value MSP decreases as the fuel temperature THL decreases, and the temperature condition correction value MSP increases as the intake air temperature THA decreases. , For example, take values as shown in FIG. Note that the calculation processing in step 700 is executed by well-known interpolation calculation using the three-dimensional map A. After executing step 700, the process exits to "RETURN" and ends the present routine.

According to the air-fuel ratio control device for an LPG engine of the present embodiment described in detail above, the lower the fuel temperature THL, the lower the temperature condition correction value MSP, and the lower the target step number ST is corrected. You. For this reason, when cold, LP
G is supplied in a liquefied state, and the air-fuel ratio of the LPG engine 1 does not become excessively rich. Therefore, it is possible to prevent vehicle surge and engine stall, improve drivability, and prevent the exhaust gas three-way catalyst 12 from being heated and deteriorated. In particular, at the time of a cold start, the LPG flowing through the normal fuel passage 5 and the acceleration fuel passage 6 is further cooled by the engine cooling water, so that the LPG is more easily liquefied. Since the decrease correction is performed, it is possible to sufficiently improve the drivability at the time of starting and prevent the three-way catalyst 12 from overheating and deteriorating.

Further, in the present embodiment, the temperature condition correction value MSP is configured to increase as the intake air temperature THA becomes smaller, so that the air temperature changes and the air density changes. It is possible to prevent the fuel ratio from becoming excessively lean, thereby further improving the drivability and preventing the three-way catalyst 12 from overheating.

In the above-described embodiment, the fuel temperature sensor 25 provided in the fuel passage is used as the fuel temperature detecting means M7. Instead, a cooling water temperature sensor for detecting the temperature of the cooling water of the LPG engine 1 is used. May be used. This is because the fuel passage is warmed by the cooling water temperature, so that the fuel temperature substantially coincides with the cooling water temperature. Even with this configuration, the same effects as those of the above embodiment can be obtained.

As mentioned above, although one Example of this invention was described in full detail, this invention is not limited to the said Example at all, and can be implemented in various aspects in the range which does not deviate from the summary of this invention. Of course it is.

Effect of the Invention As described in detail above, the air-fuel ratio control device for an LPG engine according to the present invention does not allow the LPG engine to be supplied in a liquefied state when the engine is cold so that the air-fuel ratio of the LPG engine does not become excessively rich. In addition, it is possible to prevent vehicle surges and engine stalls, improve drivability, and further prevent heat deterioration of the exhaust gas catalyst. Moreover,
Since the inflow state of liquefied petroleum gas flowing into the regulator does not change significantly when returning from the reduced correction state to the normal state, the air-fuel ratio is greatly disturbed when returning from the reduced correction state to the normal state. Nor.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a 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 of an LPG engine according to one embodiment of the present invention, and FIG. FIG. 4 is a block diagram showing the configuration of the device, FIGS. 4 to 7 are flowcharts each showing a process executed by the electronic control device, FIG. 8 is a timing chart showing the relationship between the air-fuel ratio signal and the feedback correction coefficient FAF, FIG. 9 shows fuel temperature THL, intake air temperature THA and temperature condition correction value MS.
FIG. 10 is a graph of a three-dimensional map A showing a relationship with P, and FIG. 10 is an explanatory diagram showing an example of a temperature condition correction value MSP that the three-dimensional map A can take. 1 LPG engine 2 Intake manifold 4 Venturi 5 Normal fuel passage 6 Acceleration fuel passage 7 LPG regulator 8 Exhaust manifold 9 Step motor 10 Power valve 11 Throttle 12 ...... three-way catalyst 23 ...... electronic control unit 24 ...... intake air temperature sensor 28 ...... O ₂ sensor

Claims (2)

(57) [Claims] 1. A fuel supply means disposed between a regulator and a venturi formed in an intake passage of an engine using liquefied petroleum gas as a fuel; an operating state detecting means for detecting an operating state of the engine; Target fuel amount calculation for calculating a target value of the amount of fuel supplied through the fuel supply means based on the operating state detected by the operating state detection means so that the air-fuel ratio of the engine becomes the target air-fuel ratio Means for controlling the air-fuel ratio of the LPG engine, comprising: a fuel temperature detecting means for detecting the temperature of the fuel; and the target corresponding to a decrease in the temperature of the fuel detected by the fuel temperature detecting means. An air-fuel ratio control device for an LPG engine, comprising: target fuel amount correction means for reducing and correcting the target value calculated by the fuel amount calculation means. 2. The target fuel amount correcting means determines a target value decrease correction amount by referring to a map in which a target value decreases based on a decrease in fuel temperature and a target value increases based on a decrease in intake air temperature. The LP according to claim 1 configured to determine
G engine air-fuel ratio controller.