JPH04350342A - Fuel controller of engine - Google Patents

Abstract

PURPOSE:To improve exhaust emission of an engine by providing a restriction means which restricts the increase quantity control of an increase quantity control means provided for increasing a fuel supply quantity inrresponse to a required quantity of engine output for a specified period until an exhaust gas purification device is activated. CONSTITUTION:A basic fuel injection quantity calculated based on an output value of an air flow meter 2 or the like and engine speed is feedback-corrected on a basis of a deviation between a real air-fuel ratio by an oxygen sensor S1and target air-fuel ratio in an ECU 9 which controls an air-fuel ratio at the time of operating an engine. A fuel injection quantity is increasingly corrected according to an increase quantitycorrection coefficient which is set respectively at the times of start acceleration, and high load. In this case, an acceleration increase quantity value and high load increase quantity value set in response to an require quantity of the engine output become zero, during a specified period until interposed in an exhaust passage is activated, so that a three-way catalyst converter 11 the air-fuel ratio may be made lean. Consequently, an increase rate of exhaust gas temperature is increased, and activation of the converter 11 is expedited.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel control system for an engine.

0002

[Prior Art] The air-fuel ratio A/F of an engine is basically determined according to the amount of intake air determined by the throttle opening (TVO) of a throttle valve that is linked to the driver's accelerator operation. The air-fuel ratio A/F is also normally corrected arbitrarily to the rich side or lean side depending on the engine operating condition at the time, and is controlled to the air-fuel ratio that is optimal for the actual driving condition and vehicle running characteristics. be. Recently, in order to comply with strict exhaust gas regulations, many vehicles are equipped with exhaust gas purification devices that use, for example, three-way catalysts. As is well known, the three-way catalyst simultaneously oxidizes CO and HC and reduces NOx only in a very narrow region near the stoichiometric air-fuel ratio (A/F = 14.7, λ = 1), and each reduces CO2 , H2O, O2
, has the ability to render it harmless to N2. In other words,
In an exhaust gas purification device using such a three-way catalyst,
When the engine's actual air-fuel ratio A/F becomes leaner than the stoichiometric air-fuel ratio of 14.7, NOx is emitted, while when it becomes rich, CO
O, HC will be discharged.

Therefore, in order to make effective use of the three-way catalyst and to reliably and sufficiently purify the exhaust gas from the engine, the actual air-fuel ratio of the engine must be adjusted as accurately as possible depending on the operating conditions of the engine. and ensure that the stoichiometric air-fuel ratio (A/F
=14.7, λ=1).

However, as mentioned above, CO, HC, NOx
The stoichiometric air-fuel ratio window (λ
=1±a) is extremely narrow, and normal open-loop control of the air-fuel ratio cannot meet such a strict requirement.

Therefore, conventionally, an air-fuel ratio sensor such as an O2 sensor (oxygen sensor) has been used to detect the oxygen concentration in the exhaust gas with high accuracy, and the air-fuel ratio sensor has also been used to detect the oxygen concentration (A/F). Based on the value, fluctuations in the actual air-fuel ratio of the engine are equivalently determined, and the amount of fuel supplied to the engine is feedback-controlled as soon as possible according to the determined value, thereby accurately achieving the target stoichiometric air-fuel ratio (A /F
Feedback control (closed loop control) of the air-fuel ratio using an electronic control method is employed to maintain the air-fuel ratio within a window of =14.7±φ, λ=1±a). This makes it possible to achieve sufficient exhaust gas purification performance.

On the other hand, in an exhaust gas purification device using a three-way catalyst as described above, an activation temperature of a predetermined value or higher (exhaust gas temperature: for example 30
0°C or higher), and unless the exhaust gas temperature from the engine exceeds the activation temperature, sufficient exhaust gas purification function cannot be achieved even if the air-fuel ratio is close to the stoichiometric air-fuel ratio. There's a problem.

Under these circumstances, when considering exhaust gas purification performance at the time of starting an engine, generally, when starting an engine, the amount of fuel is increased during cold operation (increase in water temperature, increase in warm-up amount) to improve the air-fuel ratio. By enriching the A/F, fuel increase control is executed to improve engine startability, ensure combustion stability after startup, and warm up the engine. Therefore, since the amount of unburned fuel discharged into the exhaust system increases due to the increase in the amount of fuel, the exhaust gas is cooled by the unburned fuel, making it more difficult for the temperature of the exhaust gas to rise. As a result, there is a problem in that the above-mentioned exhaust gas purification device is particularly difficult to activate, and the exhaust gas purification performance is also lowered.

Furthermore, under such circumstances, if the engine is started as described above and starts running immediately without being warmed up sufficiently, the combustion stability requirements of the engine when cold are met. In addition to the cold fuel increase based on , the fuel increase value due to output demands such as acceleration fuel increase and high load fuel increase is added, so that the exhaust gas temperature becomes more difficult to rise.

Therefore, as a means to solve this problem, conventionally, as shown in Japanese Utility Model Application Publication No. 54-11213, secondary air can be supplied to the exhaust system. A method has been adopted in which the amount of O2 in the exhaust gas is increased by controlling the supply amount of O2, and the temperature of the exhaust gas is increased by promoting afterburning in the exhaust system, thereby activating the exhaust gas purification device.

0010

[Problems to be Solved by the Invention] However, if a secondary air supply system is adopted as in the above-mentioned prior art, a secondary air supply passage and a control device exclusively for secondary air control are required, and the structure However, there is a problem in that it is complicated and costs increase. Furthermore, it is not very effective since it is not possible to prevent the exhaust gas temperature itself from decreasing due to an increase in the amount of fuel.

[0011]

[Means for Solving the Problems] The inventions described in each of claims 1 to 4 of the present application have been made for the purpose of solving the above-mentioned problems, and are each constructed as follows.

(1) Configuration of the invention as claimed in claim 1 The fuel control device for an engine as claimed in claim 1 includes a fuel supply means for supplying fuel to the engine, and an amount of fuel supplied to the engine by the fuel supply means. a first fuel increase control means for increasing the amount of fuel according to the engine output requirement; a second fuel increase control means for increasing the fuel according to the engine combustion stability requirement; and a second fuel increase control means for purifying the engine exhaust gas. In a fuel control device for an engine comprising a catalytic exhaust gas purification device, the fuel control device restricts fuel increase control by the first fuel increase control means for a predetermined period until the exhaust gas purification device is activated. The present invention is characterized in that an increase control limiting means is provided.

(2) Configuration of the invention according to claim 2 The fuel control device for an engine according to the invention according to claim 2 comprises a fuel supply means for supplying fuel to the engine, and an amount of fuel supplied to the engine by the fuel supply means. a first fuel increase control means for increasing the amount of fuel according to the engine output requirement; a second fuel increase control means for increasing the fuel according to the engine combustion stability requirement; and a second fuel increase control means for purifying the engine exhaust gas. An engine comprising: a catalytic exhaust gas purification device; and a fuel increase control limiting means for restricting the fuel increase control by the first fuel increase control means for a predetermined period until the exhaust gas purification device is activated. The fuel control device is characterized by being provided with an increase restriction prohibiting means for prohibiting the second fuel increase control means from restricting the fuel increase control based on the combustion stability requirement when the fuel increase control restriction means is activated. It is something to do.

(3) Configuration of the invention as claimed in claim 3 The fuel control device for an engine as claimed in claim 3 includes a fuel supply means for supplying fuel to the engine, and an amount of fuel supplied to the engine by the fuel supply means. a first fuel increase control means for increasing the amount of fuel according to the engine output requirement; a second fuel increase control means for increasing the fuel according to the engine combustion stability requirement; and a second fuel increase control means for purifying the engine exhaust gas. An engine comprising: a catalytic exhaust gas purification device; and a fuel increase control limiting means for restricting the fuel increase control by the first fuel increase control means for a predetermined period until the exhaust gas purification device is activated. In the fuel control device, there is provided an octane number determining means for determining the octane number of the fuel supplied to the engine, and when the octane number of the fuel determined by the octane number determining means is higher than a predetermined value, the ignition timing of the engine is advanced. The invention is characterized in that it is provided with ignition timing control means that sets the ignition timing of the engine to the retarded side when the octane number of the same fuel is lower than a predetermined value.

(4) Structure of the invention recited in claim 4 The engine fuel control device of the invention recited in claim 4 has the basic structure of the invention recited in each of claims 1, 2, and 3 above, and has the same structure. The fuel increase restriction period by the fuel increase control limiting means is set longer as the ignition timing of the engine is set to the retarded side.

[0016]

[Function] As a result of each of the engine fuel control devices of the invention recited in claims 1 to 4 of the present application having the above-described configuration, the following functions are achieved corresponding to each of the configurations.

(1) The operation of the invention according to claim 1, that is, the engine fuel control device according to the invention according to claim 1, first includes a fuel supply means for supplying fuel to the engine, and a supply of fuel to the engine by the fuel supply means. A first fuel increase control means for increasing the supply amount according to the engine's output requirement, a second fuel increase control means for increasing the fuel according to the combustion stability requirement of the engine, and purifying the exhaust gas of the engine. a catalytic exhaust gas purification device for controlling the amount of fuel supplied by the first fuel amount increasing control means corresponding to the amount of output required from the engine side and a second one for maintaining combustion stability. At least three basic functions are realized: the effect of increasing the amount of fuel supplied by the fuel increase control means, and the effect of purifying exhaust gas by the exhaust gas purifying device.

In this case, the first fuel increase, which is one of the basic functions, is performed within a predetermined period until the exhaust gas purification device is activated. Fuel increase control limiting means is provided for limiting the first fuel increase control action performed by the control means in response to an output request from the engine side, and is configured to increase the temperature of the exhaust gas purification device (exhaust gas temperature). At least until the activation temperature is reached, the amount of fuel is not increased based on the output request from the engine (therefore, slight deterioration in acceleration performance, etc. is ignored), and priority is given to promoting activation of the exhaust gas purification device. .

As a result, for example, the exhaust gas purification device is activated more quickly after the engine is started, and the exhaust emission performance of the engine can be improved.

(2) Effects of the invention claimed in claim 2 The engine fuel control device of the invention claimed in claim 2 has the same three basic functions as the device of the invention claimed in claim 1 by its basic components, and In addition to the action of promoting the activation of the exhaust gas purification device, there is also an increase restriction prohibiting means for prohibiting the first fuel increase control means from restricting the fuel increase control based on the combustion stability requirement when the fuel increase restriction means is activated. is provided to ensure fuel increase control for maintaining the minimum combustion stability of the engine, such as water temperature increase control and warm-up increase control when starting the engine. Therefore, the activation of the exhaust gas purification device can be promoted, and the basic running performance of the vehicle itself can be sufficiently ensured.

(3) Effect of the invention claimed in claim 3 The fuel control device for an engine according to the invention claimed in claim 3 has the same features as the fuel control device for an engine according to the invention claimed in claim 1 based on its basic components. In addition to the three basic actions and the action of promoting activation of the exhaust gas purification device, the unique structure of the invention of claim 3 includes an octane number determining means for determining the octane number of the fuel supplied to the engine, and an octane number determining means that determines the octane number of the fuel supplied to the engine. When the determined octane number of the fuel is higher than a predetermined value, the ignition timing of the engine is set to the advanced side, while on the other hand, when the octane number of the same fuel is lower than the predetermined value, the ignition timing of the engine is set to the retarded side. Since the ignition timing control means is provided, the reduction in output due to the fuel increase control means limiting the fuel increase by the first fuel increase control means corresponding to the engine output request is prevented by the ignition timing. This can be compensated for through control. Therefore, the driving performance of the vehicle becomes better.

Moreover, since the ignition timing is controlled within a range that does not cause knocking in accordance with the octane number of the fuel used, the driving performance of the vehicle is not deteriorated in this respect as well.

(4) Effect of the invention according to claim 4 The engine fuel control device according to the invention according to claim 4 has the same effect corresponding to the structure of the invention according to each of claims 1, 2, and 3 described above. In addition, in particular, the period for restricting fuel increase by the fuel increase control limiting means is set longer as the engine's ignition timing is set to the retarded side. Can increase the amount of combustion,
This makes it possible to increase the temperature of the exhaust gas and to activate the exhaust gas purification device earlier.

[0024]

Therefore, according to the engine fuel control device of the present invention, while maintaining the combustion stability of the engine and the driving performance of the vehicle, the exhaust gas purification device can be effectively activated, and the exhaust gas purification can be performed well. performance can be achieved.

[0025]

[Example] The following is an example of the present invention shown in FIG. 2 of the drawings.
This will be explained in detail with reference to FIG.

This embodiment is an example in which the present invention is applied to, for example, an in-line four-cylinder engine for automobiles.

First, FIG. 2 shows the overall system configuration of an engine fuel control device according to an embodiment of the present invention.

First, the outline of the fuel control system according to the embodiment of the present invention will be explained with reference to FIG. 2, and then the control of the main parts will be explained.

In FIG. 2, reference numeral 1 denotes an engine body, and intake air is sucked in from the outside via an air cleaner 30, and then supplied to each cylinder via an air flow meter 2 and a throttle chamber 3. Further, fuel is supplied from the fuel tank 12 to the engine side by the fuel pump 13 and is injected by the fuel injector 5. The amount of air taken into the cylinder when the accelerator pedal is operated, such as when the vehicle is running, is controlled by a throttle valve 6 provided in the throttle chamber 3. The throttle valve is operated in conjunction with the accelerator pedal, and is maintained at the minimum opening state during deceleration running and idling. And the minimum (
Fully closed) In the open state, the idle switch ID/SW is O.
Become N.

The throttle chamber 3 is provided with a bypass intake passage 7 that bypasses the throttle valve 6, and the bypass intake passage 7 is provided with a bypass intake passage 7 for controlling the engine speed at idle and when dashpot air is supplied. A current-controlled solenoid valve (ISC) is used as a means for adjusting the intake air amount.
valve) 8 is provided. Therefore, in the idling operation state and the dashpot air supply state, the intake air that has passed through the air flow meter 2 is supplied to each cylinder via the bypass intake passage 7, and the supply amount is adjusted by the solenoid valve 8. be done. The opening/closing state of this electromagnetic valve 8 is controlled by a duty ratio D of a control signal supplied from an engine control unit (hereinafter abbreviated as ECU) 9.

Further, reference numeral 10 indicates a three-way catalytic converter (catalyst converter) 11 in the middle of the exhaust passage, for example.
This shows an exhaust pipe with an exhaust gas purification function. An O2 sensor S1 is provided in the exhaust pipe 10 upstream of the three-way catalytic converter 11 to detect the oxygen concentration (air-fuel ratio A/F) in the exhaust gas. Further, the engine body 1 is provided with a knock sensor (not shown).

[0032] Then, the air-fuel ratio (A/F
) is an air-fuel ratio control system on the electronic fuel injection control device side of the ECU 9, which first determines the basic fuel injection amount Tp based on, for example, the output value of the air flow meter 2, etc. and the engine rotation speed Ne, and then further determines the basic fuel injection amount Tp based on the output value of the air flow meter 2, etc. The above setting is always maintained by detecting the actual engine air fuel ratio (A/F) using sensor S1 and feedback correcting the basic fuel injection amount Tp according to the deviation between the detected value and the set target air fuel ratio. Air-fuel ratio (generally stoichiometric air-fuel ratio A
A system is adopted that maintains the value near /F=14.7).

Therefore, the general formula for calculating the final fuel injection amount To in the air-fuel ratio control system is as follows.

To=Tp・CFB・(1+KTW+KAS+KA
I+KMR+CACC+Cer-CRE
C)+Ts
...(1) However, Tp: Basic fuel injection amount CFB: Air-fuel ratio feedback correction coefficient based on O2 output KTW: Water temperature correction coefficient KAS: Starting correction coefficient KAI: After idling increase correction coefficient KMR:
Air-fuel ratio (mixture ratio) increase correction coefficient CACC: Acceleration increase correction coefficient Cer: High load increase correction coefficient CREC: Reduction correction coefficient (deceleration fuel cut correction coefficient) T
s: Voltage correction coefficient On the other hand, reference numeral 14 denotes a spark plug provided in the cylinder head of the engine body 1;
A predetermined ignition voltage is applied to the ignition voltage via the distributor 17 and the igniter 18, and the application timing, that is, the ignition timing, is determined by the ignition timing control signal θIg supplied from the ECU 9 to the igniter 18.
controlled by t. Furthermore, reference numeral S2 is a boost pressure sensor, which detects an engine boost pressure B corresponding to the engine load and inputs it to the ECU 9.

The ECU 9 is centered around a microcomputer (CPU) which is, for example, an arithmetic unit, and controls the amount of intake air,
It is comprised of various control circuits for fuel injection amount, ignition timing, etc., a fuel octane number determination circuit, memory (ROM and RAM), interface (I/O) circuit, etc. In addition to the above-mentioned detection signals, the interface circuit of the ECU 9 also receives, for example, an engine start signal (ECU trigger) from a starter switch (not shown), an engine rotation speed detection signal Ne from an engine rotation speed sensor 15, and a water temperature thermistor 16. Detection signal Tw of engine cooling water temperature detected by , for example, throttle opening detection signal TVO detected by throttle opening sensor 4, intake air amount detection signal Q detected by air flow meter 2, etc. necessary for engine control. Various detection signals are respectively inputted.

The ECU 9 is configured to control the fuel injection amount depending on the operating state as shown in FIG. 3, and to control the ignition timing depending on the type of fuel as shown in FIG. 4, for example.

First, control of the fuel injection amount according to the operating state shown in the flowchart of FIG. 3 will be explained.

That is, first, in step S1, various detected data necessary for the following fuel injection amount control, such as engine rotational speed Ne, intake air amount Q, crank angle θc, starter switch ON/OFF, etc. are read.

Then, in step S2, it is determined whether or not the engine is currently starting, and if it is starting (YES), the process proceeds to step S3, where a starting increase pulse (fixed value) KAS is set according to the water temperature characteristics. do.

The starting increase pulse KAS is set such that the increase value becomes larger as the engine water temperature Tw at that time is lower.

Next, when the setting of the starting increase pulse KAS is completed, the process proceeds to step S4, where a fuel cut is performed to promote three-way catalyst activation, which is determined according to the octane number of the currently used fuel. After setting the time T (initial value) (timer setting), finally step S
In step S5, the final fuel injection amount is calculated, and then in step S6, the fuel injector 5 is driven to inject fuel. The fuel cut time T for activating the three-way catalyst is, for example, as shown in FIG. 4, the higher the octane number of the fuel used (the higher the octane number, the less likely it is that knocking will occur).
It is set with the characteristic that it becomes longer (high-octane gasoline > regular gasoline).

On the other hand, as a result of the start/non-start determination in step S2, NO is determined to be in the start completion state rather than in the start state.
When the determination is made, proceed to step S7,
The basic fuel injection amount Tp is calculated from the engine speed Ne and the intake air amount Q at that time, and then the process proceeds to step S8, where the fuel cut time T set in step S4 is determined.
Determine whether or not has not yet elapsed.

[0043] If YES (T>0), the set time has not elapsed, the process proceeds to step S9, where the set time T is decremented (counted down) by one cycle, and then the acceleration is increased in the following steps S10 and S11. The value of CACC is CA
CC=0 and the high load increase value Cer is set to Cer=0 (in other words, increase fuel cut), and then the final fuel injection amount is calculated as described above (step S5), and the fuel injector drive operation ( Proceed to step S6).

As a result, according to the configuration of steps S1 to S11, while the engine is started and sufficient warm-up is not completed (therefore, the temperature of the three-way catalyst has not reached the activation temperature)
When the vehicle starts running, the acceleration increase value CACC and high load increase value Cer are cut as described above, the engine air-fuel ratio A/F becomes lean, and the rate of increase in exhaust gas temperature increases. , the activation of the three-way catalyst is promoted. Therefore, the exhaust purification performance can be improved as much as possible.

On the other hand, when the fuel cut time T has elapsed (when the warm-up is completed) and the result of the "T>0?" determination in step S8 is NO, the process moves to step S12 and the engine is actually accelerated. After determining whether or not there is, YES (when accelerating)
If so, proceed to step S13 and set the original acceleration increase value CAC.
After setting C, the process proceeds to high load determination in step S15, while if the other result is NO (at the time of non-acceleration), the process proceeds to step S14, where the acceleration increase value CACC is processed to be unset (CACC=0), and then further steps are performed. Proceed to high load determination in S15.

[0046] If it is determined in step S15 that the load is high (YES), first step S16 is performed.
After setting the value of the air-fuel ratio feedback correction coefficient CFB to 0, that is, switching the control system from a closed loop to an open loop, the process proceeds to step S17, and a high load increase value Cer is set. On the other hand, if NO judgment is made that the load is not high, the process proceeds to step S18, where the air-fuel ratio feedback correction coefficient CFB is set based on the deviation between the detected value of the O2 sensor S1 and the target air-fuel ratio, while the high-load increase is performed in step S19. Set the value Cer to Cer=0.

[0047] Thereafter, the process proceeds to step S5 to calculate the final fuel injection amount based on the above-mentioned calculation formula (1), and based on the calculated value, the fuel injector is driven in step S6 to inject fuel. .

In the above case, the ignition timing is also controlled according to the type of fuel, as shown in the flowchart of FIG. It has been subjected.

That is, first, in step S1, various detection signals necessary for the following ignition timing control are read.

[0050] As in the above case, in step S2 it is determined whether the engine is started or not, and Y
In the case of ES, the process proceeds to step S3 where the advance angle is set to a constant fixed advance angle, and then ignition timing control is executed in step S4.

On the other hand, if the answer is NO, which is when the engine is not started, the process proceeds to step S5, where it is determined whether the type of fuel used is high-octane gasoline or regular gasoline.

As a result, when the determination is YES that it is high octane gasoline, the process proceeds to step S8, and the basic advance value is changed to the advance angle value corresponding to high octane gasoline (from regular gasoline) based on the characteristics shown in FIG. is also advanced by a predetermined amount), then further calculates a corrected lead angle value Igc according to the driving condition, corrects the basic lead angle value Igh based on the corrected lead angle value Igc, and then steps Ignition timing control is finally executed in S4. As a result, when the fuel is high-octane gasoline and the octane number is high and knocking is less likely to occur, the ignition timing can be advanced as much as possible to improve output. Therefore, the above-mentioned power loss can be covered.

On the other hand, if the fuel used is regular gasoline, which is determined to be NO in step S5, step S5 is performed.
After moving to Step 7 and setting the basic advance value of the ignition timing control to the basic advance value Igr that corresponds to the octane number of regular gasoline and is slightly retarded than that of high-octane gasoline, the steps S8, S9, and S4 described above are performed. Executes ignition timing control.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a control system of an engine fuel control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the fuel control operation of the device.

FIG. 3 is a flowchart showing the ignition timing control operation of the device.

FIG. 4 is a control characteristic diagram used in the control of FIG. 2;

FIG. 5 is a control characteristic diagram used in the control of FIG. 3;

[Explanation of symbols]

1 is an engine body, 2 is an air flow meter, 5 is a fuel injector, and 9 is an engine control unit.

Claims (4)

[Claims] 1. A fuel supply means for supplying fuel to an engine, a first fuel increase control means for increasing the amount of fuel supplied to the engine by the fuel supply means according to an output requirement of the engine, and a first fuel increase control means for increasing the amount of fuel supplied to the engine by the fuel supply means, An engine fuel control device comprising a second fuel increase control means for increasing the amount of fuel according to stability requirements, and a catalytic exhaust gas purification device for purifying engine exhaust gas. A fuel control device for an engine, characterized in that a fuel increase control limiting means is provided for limiting fuel increase control by the first fuel increase control means for a predetermined period until the device is activated. 2. A fuel supply means for supplying fuel to the engine, a first fuel increase control means for increasing the amount of fuel supplied to the engine by the fuel supply means according to an output requirement of the engine, and a first fuel increase control means for increasing the amount of fuel supplied to the engine by the fuel supply means, a second fuel increase control means for increasing the amount of fuel according to stability requirements; a catalytic exhaust gas purification device for purifying engine exhaust gas; and a predetermined period of time until the exhaust gas purification device is activated. and a fuel increase control limiting means for limiting the fuel increase control by the first fuel increase control means, wherein the first fuel increase control means controls the fuel increase control based on the combustion stability requirement when the fuel increase limit means is activated. 1. A fuel control device for an engine, comprising a fuel increase restriction prohibiting means for prohibiting the fuel increase control by the fuel increase control means of item 2. 3. A fuel supply means for supplying fuel to the engine, a first fuel increase control means for increasing the amount of fuel supplied to the engine by the fuel supply means in accordance with an output requirement of the engine, and a first fuel increase control means for increasing the amount of fuel supplied to the engine by the fuel supply means; a second fuel increase control means for increasing the amount of fuel according to stability requirements; a catalytic exhaust gas purification device for purifying engine exhaust gas; and a predetermined period of time until the exhaust gas purification device is activated. A fuel control device for an engine comprising: fuel increase control limiting means for limiting fuel increase control by the first fuel increase control means; octane number determining means for determining the octane number of fuel supplied to the engine; When the octane number of the fuel determined by the octane number determining means is higher than a predetermined value, the ignition timing of the engine is set to the advanced side, while on the other hand, when the octane number of the same fuel is lower than the predetermined value, the ignition timing of the engine is retarded. 1. A fuel control device for an engine, comprising: ignition timing control means set on a corner side. 4. Claim 1, wherein the limit period for fuel increase by the fuel increase control limiting means is set longer as the ignition timing of the engine is set to the retarded side. Or the fuel control device for an engine according to 2 or 3.