JPH07310573A - Fuel cut recovery time control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent generation of a shock in an acceleration initial stage by detecting a characteristic of ionic current generated in a combustion chamber after a restart of fuel supply in an internal combustion engine, in which fuel is cut under the predetermined operation condition, and reducing fuel quantity in the restart of fuel supply in the following time when the characteristic exceeds the predetermined characteristic. CONSTITUTION:When fuel supply is restarted after a fuel cut, ionic current is detected by means of an ionic current measuring circuit 25, while in an electronic controller 6, an integrated value is renewed until a lapse of time after the restart reaches the determination time. When the time exceeds the predetermined time and fuel supply is restarted under a lean air-fuel ratio condition in the recovery, in other words, when the integrated, value of the integral values of the ionic current is lowered below a transient lean determination level, unsequential injection increasing quantity is increased. Reversely, if fuel supply is restarted under a rich air-fuel ratio condition in the recovery, in other words, if the accumulation value of the integral values of the ionic current exceeds the transient lean determination level, the unsequential injection increasing quantity is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a fuel cut recovery of an internal combustion engine, which stabilizes the operating state of the internal combustion engine for automobiles after the fuel cut.

[0002]

2. Description of the Related Art Conventionally, as a fuel injection method when returning from a fuel cut, for example, as disclosed in Japanese Patent Laid-Open No. 60-65249, an accelerator pedal is depressed while a fuel cut is being performed, and a throttle valve is used. It is known that when the valve is opened from the fully closed position, the asynchronous injection is performed once and the increased synchronous injection is performed. Such asynchronous injection is performed in consideration of fuel adhesion in the intake port. The amount of fuel to be asynchronously injected or the amount of fuel to be increased is set to a predetermined value, and is constant regardless of the operating state at the time of returning from the fuel cut by opening the throttle valve.

[0003]

By the way, the state of the intake port is not always the same due to the fuel cut time, the deposit adhesion state, and the like. However, as described above, in the case of injecting a predetermined amount of fuel asynchronously after returning from the fuel cut, the same amount is injected regardless of the state of the intake port, so in some cases it may cause a shock in the initial stage of acceleration. May be.

An object of the present invention is to eliminate such a problem.

[0005]

The present application takes the following means in order to achieve such an object. That is, the fuel cut recovery control method for an internal combustion engine according to claim 1 of the present application is generated in the combustion chamber after restart in the internal combustion engine in which the fuel supply is restarted when a predetermined operation condition is satisfied in the fuel supply stop state. It is characterized in that the characteristic of the ion current is detected, it is determined that the characteristic of the detected ion current exceeds a predetermined characteristic, and the fuel amount at the next fuel supply restart is reduced based on the determination result. .

Further, according to a second aspect of the present invention, there is provided a fuel cut recovery control method for an internal combustion engine, in which fuel supply is restarted when a predetermined operating condition is satisfied in a fuel supply halt state. Characterized by detecting the characteristics of the ionic current generated in the room, determining that the characteristics of the detected ionic current exceed a predetermined characteristic, and lowering the rotation speed when fuel supply is restarted based on the determination result. And

The characteristics of the ion current in the present invention refer to the maximum value, the integrated value within a predetermined time, the position where the maximum value appears (converted to crank angle), the duration, and the like. These may use the values as they are when they are detected, or may be those that have undergone arithmetic processing such as averaging and smoothing.

[0008]

With such a structure, when the characteristic of the ion current which changes according to the actual combustion state after the recovery from the fuel supply stop is detected and the characteristic exceeds the predetermined characteristic In the first aspect of the invention, the amount of fuel is reduced, and in the second aspect of the invention, the number of revolutions is decreased, so that the fuel supply suspension region can be expanded. That is, the amount of fuel to be increased and the number of revolutions to be decreased when the supply is restarted from the fuel supply suspension are determined according to the characteristics of the ion current in the operating state at the time of restart. This is equivalent to setting the amount of fuel to be reduced and the number of revolutions to be lowered over a wide range according to the state of fuel supply suspension, and the operating state at the time of restarting fuel supply differs accordingly. It is possible to extend the operating range of fuel supply suspension. Therefore, it is possible to prevent a shock from being generated in the initial stage of acceleration due to an excess or deficiency of fuel or a decrease in rotation speed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is of a four-cylinder type for an automobile, and its intake system 1 has a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown).
Is provided, and the surge tank 3 is provided on the downstream side thereof. A fuel injection valve 5 is further provided near one end communicating with the surge tank 3, and the opening of the fuel injection valve 5 is controlled by the electronic control unit 6 based on a basic injection amount TP described later. ing. Fuel injection valve 5
Is attached to each cylinder,
It is configured to operate independently in synchronization with the intake process of each cylinder (synchronous injection) and supply fuel to each cylinder. Further, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is attached to the exhaust system 20 at a position upstream of a three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown). There is.

A spark plug 18 is attached to a position corresponding to the ceiling of the combustion chamber 10. An igniter 32 and an ignition coil 33 are electrically connected to the spark plug 18 via a diode 31. The spark plug 18, the igniter 32, and the ignition coil 33 are typically an ignition system IGS, and may include diodes 23 and 33 that prevent current from flowing around. Although only one system is shown in FIG. 1 for this ignition system IGS excluding the igniter 32, one system is connected to each cylinder. It should be noted that the engine 100 is not limited to having four cylinders, and may have three cylinders, 12 cylinders, or the like.

The electronic control unit 6 includes a central processing unit 7
And a memory device 8, an input interface 9, and an output interface 11 are mainly configured, and the input interface 9 is for detecting the pressure in the surge tank 3. Intake pressure signal a output from the intake pressure sensor 13,
A cylinder determination signal G1, a crank angle reference position signal G2, an engine speed signal b output from a cam position sensor 14 for detecting the rotational state of the engine 100, and a vehicle speed output from a vehicle speed sensor 15 for detecting a vehicle speed. Signal c, LL signal d from the idle switch 16 for detecting the opening / closing state of the throttle valve 2, water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, current from the air-fuel ratio sensor 21 described above. The signal h or the like is input. On the other hand, the output interface 11 outputs the fuel injection signal f to the fuel injection valve 5 and a plurality of signals including the ignition signal IGt to the igniter 32. Although not shown, the electronic control unit 6 includes an A / D converter that converts an analog signal into a digital signal.

A bias power source 24 for measuring an ion current and an ion current measuring circuit 25 are connected to the spark plug 18 via a high voltage diode 23 to form an ion current detecting system IDL. As the ion current measuring circuit 25 itself including the bias power source 24, various circuits known in the art can be used,
In order to detect the ion current for each cylinder, the same number as the number of cylinders, that is, one ion current detection system IDL is provided for one cylinder.

The electronic control unit 6 includes an intake pressure signal a output from the intake pressure sensor 13 and a cam position sensor 14.
The rotational speed signal b output from the engine is used as main information, and the basic injection time TP is corrected by various correction coefficients determined according to the operating state of the engine to determine the fuel injection valve opening time, that is, the injector final energization time T. Then, a program for controlling the fuel injection valve 5 according to the determined energization time and injecting fuel according to the engine load from the fuel injection valve 5 into the intake system 1 is incorporated. Further, in order to control the injection amount at the time of fuel cut recovery, the ion current of the ion current generated in the combustion chamber after the restart in the internal combustion engine where the fuel supply is restarted when a predetermined operating condition is satisfied in the fuel supply stop state is controlled. A program is stored that detects the characteristic, determines that the characteristic of the detected ion current exceeds a predetermined characteristic, and reduces the fuel amount when the fuel supply is restarted next time based on the determination result.

The outline of this fuel cut recovery control program is as shown in FIGS.

First, in step S1, it is determined whether or not the elapsed time C4FCRET after the return of the fuel cut exceeds the determination time KFCI. Step S2a (Step S
2b, step S2c) is a step of determining a cylinder by the cylinder number NTCRANK. Cylinder number NTCR
ANK of 0 is set to 1 cylinder, 3 is set to 2 cylinders, and 1 is set to 3 cylinders. Step S3a (Step S3b, Step S
3c, step S3d) adds the integrated value IONn of the ion current during the current combustion stroke to the integrated value IONn of the integrated value that is the characteristic of the ion current stored at that time, and newly stores it as the integrated value IONTn. To do. The steps up to this point are executed for each cylinder. Steps S2a and S3a are steps for one cylinder. Similarly, steps S2b to S3b are two cylinders, steps S2c to S3c are three cylinders, and step S3d.
Are steps for four cylinders.

Next, at step S4, the cycle counter NTCYC is incremented to obtain the integrated value IONTn.
Is counted once. Step S5 is
It is determined whether the cycle counter NTCYC is the initial value (= 0). Step S6 is the asynchronous injection increase value A
This is a subroutine for calculating SYIn. In this embodiment, since the fuel injection valve 5 is provided for each cylinder and the synchronous injection control is performed, the asynchronous injection increase value ASYIn is actually added to the synchronous injection time, and the asynchronous injection increase value ASYIn is asynchronous. That is, it does not refer to the increased fuel amount injected separately from the synchronous injection, but for convenience of explanation, the term “asynchronous” is used for the fuel increase amount after returning from the fuel cut. Step S7 is a cycle counter N
Reset TCYC. In step S8, integrated values IONT1, IONT2, IONT3, I
ONT4 is set to the initial value, that is, 0.

As shown in FIG. 3, in the increment value calculation subroutine, first, in step S11a (step S11b, step S11c), step S1a (step S1) is executed.
b, similarly to step S1c), the cylinder is determined. That is, in step S11a, one cylinder is determined, if it is not one cylinder, two cylinders are determined in step S11b, if it is not two cylinders, three cylinders are determined in step S11c, and if it is determined that it is not three cylinders in step S11c. , 4 left
The cylinder will be determined. In step S12a (step S12b, step S12c, step S12d), it is determined whether or not the integrated value IONTn of each cylinder exceeds the transient lean determination level LVION. The transient lean level LVION is set by the rotational speed and the intake pressure as parameters indicating the operating state of the engine,
It is stored in the storage device 8 as a two-dimensional map. Then, in detail, the interpolative calculation is performed to determine the transient lean level LVION corresponding to the operating state at that time.

In step S13a (step S13b, step S13c, step S13d), the asynchronous injection boost value ASYIn is incremented. Step S1
In 4a (step S14b, step S14c, step S14d), it is determined whether or not the asynchronous injection increase value ASYIn exceeds the injection increase upper limit value ASYIMAX. Step S15a (Step S15b, Step S
15c, step S15d), the asynchronous injection amount increase value A
The injection amount increase upper limit value ASYIMAX is set in SYIn. Step S16a (Step S16b, Step S
16c, step S16d), the asynchronous injection increase value A
Decrement SYIn. Step S17a (Step S17b, Step S17c, Step S17d)
Then, it is determined whether or not the asynchronous injection amount increase value ASYIn is not negative. In step S18a (step S18b, step S18c, step S18d), the asynchronous injection boost value ASYIn is set to zero.

FIG. 4 is a flow chart showing the outline of the asynchronous injection routine. Step S21 is
It is determined whether or not the fuel cut recovery asynchronous execution flag XASYFC is set (= 1). The fuel cut recovery asynchronous execution flag XASYFC is set when the elapsed time C4FCRET after fuel cut is within the determination time KFCI. In step S22, the fuel cut return asynchronous value TASYFC is set to the fuel cut return asynchronous initial value T.
Set ASYFCINT. In step S23a (step S23b, step S23c), the cylinder is determined. In step S24a (step S24b, step S24c, step S24d), the fuel cut return asynchronous value TASYFC is determined by adding the asynchronous injection increase value ASYn obtained in the increase value calculation routine to the fuel cut return asynchronous value TASYFC. Step S25 is an asynchronous injection execution routine, and in this embodiment, normal synchronous injection is extended.

In such a configuration, when the fuel cut is being executed, for example, when the accelerator pedal is depressed to recover from the fuel cut, or when the engine speed drops and reaches the return speed, The combustion state of each cylinder within the determination time is detected from the integrated value of the ion current, and the asynchronous injection amount at the time of the next fuel cut recovery, that is, the extension time of the synchronous injection time is determined.

The ion current is measured for each cylinder and for each ignition, and the integrated value IONn thereof is determined, for example, by the method described below. Normally, the ionic current flows from the bias power source 24 to the spark plug 18 immediately after the start of discharge.
When a bias voltage is applied to the combustion chamber 10, it flows into the combustion chamber 10 according to the degree of combustion during combustion after discharge. In the case of normal combustion, the ion current rapidly flows immediately after ignition, and then the top dead center TD.
A peak value I at which the value of the ion current becomes maximum near the crank angle at which the combustion pressure becomes maximum after decreasing at C and then increasing again
It becomes ONP (shown in FIG. 5). Therefore, the ion current is measured by A / A set according to the engine speed NE.
Top dead center TDC in D conversion cycle (unit based on crank angle)
The A / D conversion is started from, the analog current value is converted to a converted value which is digital data, and the obtained converted value is assigned a data number DTn in ascending order from the top dead center TDC to the RAM of the storage device 8. It is done by storing in. By summing the converted values within a predetermined time from the start of measurement,
The integrated value IONn of the ion current is obtained. It is also possible to obtain the maximum value, that is, the peak value, by comparing the stored converted value with the maximum value at that time in each measurement. A / D conversion is at TDC
To a predetermined time, for example, 30 ° C converted to crank angle
Do only A. As described above, by attaching the data number DTn to the converted value, it is possible to easily specify the position where the peak value has occurred (in terms of crank angle conversion).

A case where the accelerator pedal is depressed to restore the fuel cut in such a situation will be described. When the fuel cut is restored, combustion starts and the ionic current is detected. The return from the fuel cut is configured to be detected when the flag set by the execution of the fuel cut is reset. And
When the elapsed time after returning from the fuel cut does not reach the determination time KFCI, the control proceeds from step S1 to S2a (S2
b, S2c) → S3a (S3b, S3c, S3d) → S
In step 4, the integrated value IONTn is updated. On the other hand, when the elapsed time exceeds the determination time KFCI, the counter NTCYC always counts 1 or more, so the control is
Steps S1 → S5 → S6 are executed to execute the increment value calculation subroutine. Here, at the time of this return, when the fuel supply is restarted in a state where the air-fuel ratio is lean, that is, when the integrated value IONTn of the integrated value IONn of the ion current is below the transient lean determination level LVION, the control is
Step S11a (S11b, S11c) → S12a
(S12b, S12c, S12d) → S13a (S13
b, S13c, S13d), the asynchronous injection increase value A
Increase SYIn. And the asynchronous injection boost value AS
If YIn does not exceed the injection increase upper limit value ASYIMAX, {S13a (S13b, S13c, S13
d)}, this routine is terminated, and the control is step S7.
→ Proceed with S8. In this way, step S13a (S
13b, S13b, S13c, S13d), the asynchronous injection boost value ASYIn is incremented,
The next asynchronous injection amount will be increased.

On the contrary, when the fuel supply is restarted in the state where the air-fuel ratio is rich at the time of return, that is, when the integrated value IONTn of the integrated value IONn of the ion current exceeds the transient lean determination level LVION. , Control is performed in step S11a (S11b, S11c) → S12a (S
12b, S12c, S12d) → S16a (S16b,
S16c, S16d) → S17a (S17b, S17
c, S17d) → return or S18a (S18b, S
18c, S18d), and the asynchronous injection amount increase value ASYI
n is decreased. The asynchronous injection amount increase value ASYIn is
An upper limit and a lower limit are set, and when the calculated asynchronous injection boost value ASYIn exceeds the injection boost upper limit value ASYIMAX, it is set to the injection boost upper limit value ASYIMAX, and when it becomes a negative value, it is set to 0. It

As described above, the asynchronous injection amount increase value AS
When YIn is determined, when the fuel cut is resumed, the synchronous injection time is extended based on the asynchronous injection amount increase value ASYIn, and the fuel injection is executed. That is, when returning from the fuel cut, as described above, the ion current is detected and the asynchronous injection boost value ASY is detected.
While determining In, the asynchronous injection routine
The fuel injection time is extended and executed by the asynchronous injection amount increase value ASYIn. In this case, the control is step S21.
→ S22 → S23a (S23b, S23c) → S24a
(S24b, S24c, S24d) → S25, and the fuel injection time is extended by the asynchronous injection amount increase value ASYIn, that is, the fuel injection amount is increased and injected.

As described above, the increased fuel injection amount after the fuel cut is returned is determined by detecting the ion current during combustion to determine the combustion state, and based on the result, the asynchronous injection increased value ASYIn
Since the fuel injection amount is determined, it is possible to increase / decrease the fuel injection amount according to the operating state at that time each time the fuel cut is restored, and the operation after the restoration can be ensured. Therefore, it is possible to improve the fuel efficiency in the operation at the time of returning from the fuel cut and to expand the fuel cut operation region.

Although the synchronous injection type has been described in the above embodiment, the simultaneous injection type may be used. In such a simultaneous injection type, the average value of the integrated values of the integrated values of the ion current of each cylinder is adopted to grasp the combustion condition, and the average value of the integrated values is used as the integrated value IONn in the above-mentioned embodiment. Alternatively, the asynchronous injection boost value ASYIn may be determined, and the asynchronous injection may be executed at a timing different from the simultaneous injection based on the determined asynchronous injection boost value ASYIn.

Next, a second embodiment will be described. This embodiment is basically the same as the above embodiment,
Only the control program after the fuel cut recovery stored in the electronic control unit 6 is different.

The schematic structure of the control program is shown in FIG.
It is as shown in 7.

FIG. 6 shows a rotational speed control routine after returning from the fuel cut.

First, in step S211, a determination parameter for grasping the operating state when the fuel cut is restored is calculated. Typical examples of the determination parameter include the ignition timing, that is, the peak value during the 180 ° CA in terms of the crank angle, the integrated value (the integrated value of the instantaneous values), and the like. It is preferable that the specific processing of step S211 be as shown in FIG. That is, the routine shown in FIG. 7 is a routine for detecting the integrated value SION of the instantaneous value IONAD which is the characteristic of the ion current and the peak value IMAX. First, the ion current is A / D converted (step S201), the obtained converted value of the instantaneous value IONAD of the ion current is stored in the storage device 8 (step S202), and the integrated value SION is calculated (step S203). Transition. Integrated value SION
Is updated every time the instantaneous value IONAD is obtained, is calculated by the following equation, and is stored in the storage device 8.

ION = SION + IONAD When the integrated value SION is calculated, it is determined whether the instantaneous value IONAD stored at that time exceeds the ion peak value IMAX up to that point (step S2).
04), if it exceeds, the ion peak value IMAX is updated as the current instantaneous value IONAD (step S20).
5) If it is below the range, the ion peak value IMAX is not updated. This A / D conversion routine is, for example, 4 to
It is executed every 5 milliseconds.

Next, in step S212, it is determined whether or not the fuel cut is returning. If the fuel cut is returning, the process proceeds to step S213, and if not, the process proceeds to step S218. If it is at the time of returning to the fuel cut, the determination parameters stored in the storage device 8 are integrated in step S213, and the integrated parameter value SSION is obtained.
Is calculated.

SION = SSION + SION This parameter integrated value SSION is obtained by calculating the specified number M of times, and therefore step S
At 214, it is determined whether or not the accumulation of the specified number of times M is completed. If it is completed, the process proceeds to step S215, and if it is not completed, the process proceeds to step S218.
Now, assuming that the calculation of the parameter integrated value SSION has been completed a predetermined number of times, it is determined in step S215 whether or not the parameter integrated value SSION is less than the first set value K1, and if it is less than, the process proceeds to step S216. , Or more, the process proceeds to step S219. If the parameter integrated value SSION is less than the first set value K1, the return rotational speed NA is set higher by the predetermined value NT in step S216. On the other hand, the parameter integrated value SS
If ION is greater than or equal to the first set value K1, in step S219, the parameter integrated value SSION is set to the second value.
It is determined whether or not it is the set value K2 or more, and if it is the set value K2 or more, the process proceeds to step S220, and the return rotational speed NA is set lower by the predetermined value NT. On the contrary, if it is less than the second set value K2, the process proceeds to step S218.

After the return speed NA is determined, the control is
The process proceeds to step S217, and the parameter integrated value SSION
And the specified number M of times is initialized (= 0), and then step S
At 218, the integrated value SION and the ion peak value I
Initialize MAX. In this embodiment, the integrated value SION of the specified number of times M is integrated to calculate the parameter integrated value SSION that substantially determines the combustion. However, similar to the first embodiment, It is also possible to integrate until the elapsed time after returning from the fuel cut exceeds a predetermined time.

In such a configuration, after the fuel cut is returned, the integrated value SION which is the determination parameter is integrated M times for the specified number of times, and if the integrated value SSION of the parameter is below the first set value K1, then at that time point. The return rotational speed NA is increased by a predetermined value NT from the return rotational speed NA set in 1. to prevent the occurrence of things such as knocking that may cause deterioration of drivability. The control in this case is steps S211, S212, S213, S214, S215, and so on.
The process proceeds from S216 → S217 → S218. On the other hand, in an operating state in which the parameter integrated value SSION exceeds the second set value K2, there is no problem even if the return rotational speed NA is lowered, so the return rotational speed NA is lowered by the predetermined value NT. The fuel cut operation area is expanded (FIG. 8). The control in this case is step S211 → S2.
12 → S213 → S214 → S215 → S219 → S2
The process proceeds from 20 → S217 → S218.

As described above, in this embodiment, since the return rotational speed NA is raised and lowered according to the operating state after the fuel cut return, the return rotational speed is taken into consideration in the state of the engine under the worst environmental conditions. Compared to the case of setting
It is possible to improve fuel efficiency and increase the number of revolutions to be returned until just before the drivability deteriorates. This is because the combustion state after recovery is detected by the ion current to make a judgment.Therefore, when the return speed is set to a single value, there is a margin in the return speed, Even if there is no problem with setting, it is because that judgment could not be made.

The present invention is not limited to the embodiments described above. For example, although the ignition system IGS using the igniter 32 has been described in the above embodiment, a distributor may be used.

Besides, the configuration of each part is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0040]

As described above in detail, the present invention is based on the result of detecting the characteristic of the ion current and comparing the characteristic with the set characteristic. Since the injection amount at the time of restart is increased and the number of revolutions at that time is decreased in the invention of claim 2, it is possible to improve the fuel efficiency at the time of restarting the fuel supply, and to expand the operating range during the suspension of fuel supply. You can

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing a first embodiment of the invention according to claim 1 of the present application.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is a flowchart showing a control procedure of the embodiment.

FIG. 4 is a flowchart showing a control procedure of the embodiment.

FIG. 5 is a waveform diagram showing a typical ion current waveform in the example.

FIG. 6 is a flowchart showing a control procedure of a second embodiment of the invention according to claim 2 of the present application.

FIG. 7 is a flowchart showing a control procedure of the embodiment.

FIG. 8 is an explanatory view of the operation of the same embodiment.

[Explanation of symbols]

 5 ... Fuel injection valve 6 ... Electronic control device 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 10 ... Combustion chamber 11 ... Output interface 24 ... Bias power supply 25 ... Ion current measurement circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Yamamoto 2-1-1 Taoyuan, Ikeda City, Osaka Daihatsu Industry Co., Ltd.

Claims (2)

[Claims] 1. A characteristic of an ion current detected in an internal combustion engine in which fuel supply is restarted when a predetermined operation condition is satisfied in a fuel supply stop state, after which the characteristic of an ion current generated in a combustion chamber is detected. Is determined to exceed a predetermined characteristic, and the fuel amount at the time of restarting fuel supply next time is reduced based on the determination result. 2. A characteristic of an ion current generated in a combustion chamber after restarting in an internal combustion engine in which fuel supply is restarted when a predetermined operating condition is satisfied in a fuel supply stop state, and the detected ion current A fuel cut recovery control method for an internal combustion engine, comprising: determining that a characteristic exceeds a predetermined characteristic, and decreasing the rotation speed when restarting fuel supply based on the determination result.