FR2838162A1 - Direct injection spark ignition IC engine on automotive vehicle, uses EGR gases during the compression phase to improve cold starting - Google Patents

Abstract

In an engine which injects fuel in the combustion chamber (13), an injector (43) and which executes ignition and combustion by the spark plug (17), a unit for variable control of valves (2) is opened during cold starting, and the overlapping value of an inlet valve (23) and the exhaust valve (24) is improved in a manner to execute an introduction of Exhaust gas recirculation (EGR) gases, with the fuel being injected by the injector during the compression phase.

Description

operation.

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  TYPE SPARK IGNITION INTERNAL COMBUSTION ENGINE

  INJECTION INTO THE CYLINDER AND METHOD FOR CONTROLLING THE SAME

BACKGROUND OF THE INVENTION

  1. Field of the Invention The invention relates to a spark-ignition internal combustion engine of the type injected into the cylinder which burns fuel injected directly into a cylinder using a spark plug, and more particularly to a

  technology during a cold start of the engine.

  2. Description of the related technique

  Recently, a gasoline engine of the injection type in the cylinder which achieves combustion in lean mixture is the subject of wide use. An example of such an engine is a technology described in the Japanese patent publication available to the public N 11324 778 which states that, in order to avoid dilution of the oil and generation of smoke at the same time when '' cold start, an intake valve is set to open when a predetermined crank angle is exceeded After an exhaust valve has been closed, and fuel is caught while both valves are closed. In this way, by avoiding an overlap of an opening period of the exhaust valve and the intake valve, a certain amount of high temperature combustion gas is left inside a combustion chamber. combustion and fuel is injected into it to facilitate fuel atomization. Therefore, adhesion of the fuel to a piston head surface and a cylinder wall surface can be suppressed, and therefore both smoke generation

  and dilution of the oil can be removed.

  However, because this technology injects fuel at an initial stage of the intake time during a cold start, a dense homogeneous mixture is formed to perform homogeneous combustion and therefore a saving of

fuel gets dograde.

SUMMARY OF THE INVENTION

  It is an object of the invention to provide a spark-ignition internal combustion engine of the type injected into the cylinder and a method of controlling it with -

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  which improved fuel economy during a

cold start is obtained.

  In accordance with the invention, a spark-ignition internal combustion engine of the cylinder injection type which burns fuel injected into a cylinder using a spark plug further comprises an exhaust gas recirculation system which reintroduces the combustion gas into the cylinder for circulation and, during a cold start, the exhaust gas control system is implemented and fuel is injected into the cylinder during

compression time.

  High temperature exhaust gas is reintroduced into the cylinder through the exhaust gas recirculation system (EGR), so that the intake air inside the cylinder is heated, making it easier to spray the fuel injected. Therefore, even during a cold start, adhesion of the fuel to a wall surface inside the cylinder is suppressed, and therefore generation of smoke and dilution of the oil can be suppressed. In addition, by reintroducing the exhaust gas, the combustion temperature is lowered, thereby reducing the amount of NOx emission. In addition, even during a cold start, fuel economy is improved by injecting fuel into the cylinder during

compression time.

  I1 is preferable that the engine further comprises a means for determining a vacuum of the intake pipe, and that the exhaust gas recirculation system is implemented when the vacuum of the determined intake pipe is greater than or equal at a predetermined level. This is due to the fact that when the depression of the intake pipe is low, an introduction of EGR gas is difficult to carry out, and therefore the introduction of EGR gas would preferably be suppressed.

in such a case.

  This exhaust gas control system would preferably be a variable valve control device (VVT device) which adjusts a valve overlap value of the intake valve and the exhaust valve. An increase in the valve overlap value can help the exhaust gas inside the

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  exhaust pipe to flow into the cylinder again

  after returning to the intake pipe.

  A variable rate of change of valve overlap during a cold start would preferably be increased compared to that in other cases. In other cases, that is to say during an injection during the admission time, if the quantity of EGR gas is suddenly increased, an uneven distribution of the EGR gas takes place, and therefore a homogeneous mixture does not cannot be formed, which can eventually lead to unstable combustion. On the contrary, during an injection during the compression time, a homagenic mixture is only necessary around the spark plug. Therefore, even if an uneven distribution of EGR gas is caused due to a sudden increase in the overlap value

  valves, it is possible to perform stable combustion.

  The variable valve controller may be a mechanism which, when either the inlet valve or the exhaust valve is open, changes a lift stroke of the other valve. Such a change in the lifting stroke can be achieved, for example, by a three-dimensional cam, and therefore the amount of introduction of RGE gas can be controlled without modifying the basic setting of

intake and exhaust.

  In addition, during a cold start, the ignition timing of the spark plug can be delayed until after a piston reaches top dead center. By delaying the ignition timing, the amount of secondary combustion (combustion during the expansion stroke) is increased so as to raise the temperature of the exhaust, and therefore the temperature rise performance of a catalyst is improved, in a way to

  avoid dogradation of program performance.

  It is preferable that the operation of the exhaust gas recirculation system is controlled so that the amount of EGR gas increases as the value of the ignition delay angle is increased. When the ignition timing is delayed, the interior of the combustion chamber is cooled by the injected fuel, and the amount of fuel adherence to the cylinder wall surface and

  another increases, which can cause unstable combustion.

  Therefore, by increasing the amount of EGR gas to increase

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  the temperature in the cylinder and facilitate fuel spraying, combustion is stabilized and the generation of

  black and other fumoe is removed.

  In addition, in an area where the value of the ignition delay angle is large and where unstable combustion is expected, it is preferable that the operation of the exhaust gas recirculation system be controlled by so that the amount of EGR gas decreases as the value of the ignition delay angle is increased. If the value of the ignition delay angle is further increased, the combustion time is too short, possibly causing unstable combustion. In this case, by decreasing the amount of EGR gas, the concentration of the fuel is increased and the hardness

  combustion is ensured, thus stabilizing combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

  Figure 1 is a simplified drawing showing the structure of an internal combustion engine with spark ignition of the type ingoction in the cylinder according to the invention, Figure 2 is a graph illustrating the details of the operation of a device variable valve control in FIG. 1, FIG. 3 is a flow diagram illustrating a first control operation during the starting of an engine according to FIG. 1, FIG. 4 is a flow diagram illustrating the details of a processing intended to determine if compression time is possible or impossible, which is executed during the processing shown in Figure 3, Figure 5 is a flowchart illustrating a control for adjusting a valve lift timing executed during the processing of the Figure 3, Figure 6 is a flowchart illustrating a second control operation when starting the engine according to Figure 1, Figure 7 is a graph ill ustructing a fluctuation in the amount of intake air relative to the valve overlap value,

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  FIG. 8 is a graph illustrating a fluctuation in the amount of internal EGR recirculation with respect to the value of valve overlap, FIG. 9 is a graph illustrating the value of valve overlap established with respect to the value of angle of ignition delay, FIG. 10 is a drawing illustrating a shape of the cam head of an exhaust cam, and FIG. 11 is a drawing illustrating the details of the operating principle of a variable control device

  of valves using the cam shown in Figure 10.

  - DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

  Hereinafter, the details of the preferred embodiments according to the invention will be described with reference to the accompanying drawings. In order to facilitate the understanding of

  descriptions, the same reference numbers are used

  for the same constituent elements on each drawing as much

  as possible, and redundant descriptions are omitted.

  FIG. 1 is a simplified drawing showing the structure of a spark-ignition internal combustion engine of the type injected into the cylinder according to the invention. The internal combustion engine 1 is a gasoline engine of a type which directly injects gasoline, or fuel, into a combustion chamber 13 by a high pressure injector 43, and which performs the ignition and combustion

by a spark plug 17.

  A piston head 11 is arranged in a cylinder 10 of the engine in a manner allowing a reciprocating movement in a longitudinal direction in the drawing. The piston head 11 is connected to a crankshaft (not shown) by a connecting rod 12, and converts the reciprocating movement into rotational movement. The top (crowning surface) of the piston head 11 is provided with a cavity 11A. A space between the crowning surface of the piston head 11 and a cylinder head 14 forms

the combustion chamber 13.

  The injector 43, an intake valve 23, an exhaust valve 24 and the spark plug 17 are arranged on the edge of the cylinder head 14 with the combustion chamber 13. Among these components, the injector 43 is arranged in a direction which allows fuel to be injected towards the cavity

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  llA of the piston head 11. In addition, the spark plug 17 is disposed between the intake valve 23 and the exhaust valve 24 so as to be located near an edge portion of the cavity llA which is opposite to the injector 43. The intake valve 23 is disposed between the combustion chamber 13 and an intake pipe 15, and the exhaust valve 24 is disposed between the combustion chamber 13 and a delivery pipe 'exhaust 16. The two valves 23 and 24 are driven by cams 21 and 22, respectively. A variable valve control device 2 has the function of modifying an opening / closing phase of the intake valve 23 and

of the exhaust valve 24.

  The injector 43 is connected to a fuel tank 40 and is supplied with compressed fuel by a pump 41. On this fuel line, a fuel pressure sensor 42

  intended to detect the fuel pressure is provided.

  The operation of the internal combustion engine 1 is

  controlled by an electronic ECU 3 engine control unit.

  The outputs coming from a water temperature sensor 5 which measures a coolant temperature of the engine, from a crankshaft angle sensor 6 which measures a crankshaft angle, from a vacuum sensor 8 which detects a vacuum inside the intake pipe 15 downstream of a throttle valve 7, a fuel pressure sensor 42 and others are applied as input to the engine ECU 3. The engine ECU 3 controls the operation of the variable valve control device 2, the spark plug 17 and

the injector 43.

  Figure 2 is a drawing illustrating the details of the

  operation of the variable valve control device 2.

  By adjusting a phase of rotation of the cams 21 and 22 with respect to their respective crankshaft, an opening setting (valve levoe) of each of the intake valve 23 and exhaust valve 24 is adjusted, thus allowing adjustment a length of valve overlap during which both the intake valve 23 and the exhaust valve 24 are open. Hereinafter, an adjustment for advancing the opening of the valves 23 and 24 (equivalent to a displacement of the valve lift curve to the left in the drawing) is called adjustment towards the angle of advance side, while qu 'a setting for

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  delaying valve opening (equivalent to moving the valve lift curve to the right in the drawing) is called setting to the delay angle side. The valve overlap value can be increased by adjusting the intake valve 23 to the advance angle side, or by adjusting the exhaust valve 24 to the delay angle side, or by performing both settings. That is, it may suffice that a valve lift setting of at least one of the intake valve 23 and the exhaust valve 24

is adjustable.

  Next, the operation when the engine 1 is started will be described. Figure 3 is a flowchart illustrating a

  first control operation when starting engine 1.

  This command is. unless otherwise stated, executed by the engine ECU 3 and is repeated at a rate

  predetermined from start to stop of engine 1.

  In step S1, an evaluation is made to determine whether the engine 1 is in the starting phase. In this case, the state "in the start-up phase" is not only retained at an instant at which the engine 1 is started, but is also considered to include a period going from the start until the rise in temperature of the engine 1 is completed after a few minutes. If the evaluation is made that the motor 1 is in the starting phase in step S1, the processing goes to step S2 in which it is determined whether the current operating conditions allow injection during the compression time. A detailed flow diagram of this determination process is shown in FIG. 4. First, in step S21, a depression of the intake pipe Pi and a fuel pressure Pf are detected by reading the outputs of the vacuum sensor 8 and the fuel pressure sensor 42. In the following step S22, the depression of the intake pipe Pi and a threshold value are compared. If the depression of the intake pipe Pi is greater than the threshold value, the processing proceeds to step S23 to which the fuel pressure Pf and a threshold value are compared. If the fuel pressure Pf is greater than the threshold value 0, the processing proceeds to step S24. In step S24, it is evaluated that the injunction during the compression time is possible assuming that the fuel pressure Pf, at which

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  the fuel injection during the compression time can be effectively overridden, has been reached and the vacuum of the intake pipe Pi, at which an EGR effect can be sufficiently exerted, has been reached, and then the treatment is completed. On the other hand, it is evaluated that the depression of the intake pipe Pi is less than or equal to the threshold value in step S22, the introduction of the RGE gas is prevented, and therefore a temperature inside the chamber combustion 13 is low and fuel vaporization is prevented. As a result, in addition to the appearance of fuel stickiness on the wall surface of the cylinder 10, stable stratified combustion cannot be started. Therefore, the processing proceeds to step S25 in which it is evaluated that

  injection during the compression time is not possible.

  Furthermore, if it is judged that the fuel pressure Pf is less than or equal to the threshold value in step S23, the fuel pressure becomes insufficient and therefore the fuel injection volume required during the time of compression cannot be assured, resulting in a misfire in the worst case. Therefore, the treatment proceeds to step S25 at which it is assessed that the infection during

  compression time is not possible.

  As a result of this treatment, if it is evaluated that injection during the compression time is possible, the treatment proceeds to step S3 of the main treatment in FIG. 3, and

  a setting of the anoction is established at the compression time.

  Then, in step S4, a target value of the VVT device is established so that the overlap value becomes large, and the processing is completed. Therefore, the variable valve controller 2 adjusts the phases of the cams 21 and 22 to match the valve lift timing of the intake valve 23 and the exhaust valve 24 to the target value, thereby increasing the valve overlap value, and the injector 43 injects the fuel during the compression time. By increasing the valve overlap value, an internal EGR effect can be obtained, whereby a combustion gas which has been exhausted to the exhaust pipe 16 is reintroduced into the combustion chamber 13 during the intake time . Of

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  in this way, the amount of return of the EGR gas is increased, thereby increasing the actual compression ratio, the temperature inside the combustion chamber 13 is quickly raised by the combustion gas at high temperature, thus facilitating the vaporization of the fuel and suppressing the adherence of the fuel to the inner wall of the combustion chamber 13 and the like, and the combustion stability is improved due to lamination, thereby suppressing the emission of black smoke. Consequently, the performance of the programs is improved. As a result, stratified combustion with an air-fuel ratio of approximately 15 to 16, which is slightly leaner than the theoretical air-fuel ratio, becomes possible, and therefore a fuel saving when

  start-up and program performance is improved.

  On the contrary, if it is assessed that the ingestion during the compression time is not possible in step S2, the processing proceeds to step S5 in which the timing of the ingestion is established at the time of intake, and then the target value of the VVT device is established so that the overlap value is small in step S6. In this case, the operating conditions do not meet the requirements for effectively performing the injection during the compression time and therefore the infection during the admission time will be overridden. However, the fact that the combustion rate is slow during the ingestion during the admission time and that the increase in the overlap value at the time of the ingestion during the admission time during the start-up causes an uneven distribution EGR gas inside the combustion chamber 13, which prevents a homogeneous mixture, the combustion can become unstable. Therefore, by reducing the valve overlap value and suppressing a reflux of the EGR gas, stable combustion is bypassed, thus suppressing the degradation of the emission performance. If it is evaluated that it is not a start in step S1, the processing goes to step S7 in which the timing of the fuel injection and the target value of the VVT device

  are established in accordance with an engine load and speed.

  For example, in a low speed and low load condition, the fuel is ingested during the compression time

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  and stable combustion is performed, so as to improve fuel economy and emission performance. In a high speed and high load condition, the fuel is injected during the intake time so that a homogeneous mixture is formed and a homogeneous combustion is carried out,

  thus ensuring high output power.

  Upon actual adjustment of the valve lift timing of the intake valve 23 and the exhaust valve 24 by the variable valve control device 2, the next command will preferably be executed. FIG. 5 is a flowchart illustrating such an adjustment command and the command is executed following the command processing on

Figure 3.

  First, at step S31, an evaluation is made for

  determine if engine 1 is in a starting phase.

  If it is judged that the engine is in a starting phase in step S31, the processing proceeds to step S32 to evaluate whether the injection during the compression time is established. If it is judged that injection during the compression time is established, processing proceeds to step S33 at which a rate of variation in valve overlap is set to a high value, and an actual control value of the variable valve controller 2 is calculated in the next step S34 so that the rate of change, which is set, can be obtained. In accordance with this treatment, at the time of ingestion during the compression time, the valve overlap value quickly changed to the target value and the amount of internal EGR gas supply is increased, so as to raise the temperature in the cylinder and facilitate vaporization of the fuel, thereby stabilizing combustion. On the other hand, if the evaluation is made of the fact that the engine is not in a starting phase in step S31 or if it is evaluated in step S32 that the injection during the compression time does not is not established, i.e. injection during admission time is established, processing proceeds to step S35 at which the rate of change of valve overlap is set to a low value, and the actual control value of the variable valve controller 2 is calculated in the next step S34 so that the rate of change, which is set, can be obtained. In accordance with this treatment, in particular, a sudden change in the value of valve overlap at the time of injection during the intake time is suppressed, and therefore a sudden change in the quantity of the internal EGR gas supply is deleted. As a result, an abrupt change in combustion conditions is suppressed, thereby preventing the combustion of

become unstable.

  Next, some of the other embodiments of the operation when the engine 1 is started will be particularly described. FIG. 6 is a flowchart illustrating a second command operation when starting the engine 1. Unless otherwise indicated, this command is also executed by the ECO unit 3 of the engine and is repeated at a predetermined rate from the start until stopping

motor 1.

  The contents of the return processing from step S1 to steps S2 and S7 and of the return processing from step S2 to steps S3 and S5 are the same as for the first control operation shown in FIG. 3, so that 'a

  detailed description of these is omitted. After stalling

  of the ingestion is established at the compression time in step S3, processing proceeds to step S51 at which the value of the ignition delay angle is established. The value of the ignition delay angle can be established by referring to a prepared map based on the operating conditions of the engine 1 such as a temperature of the engine coolant measured by the temperature sensor d 5 and a vacuum inside the intake pipe 15 measured by the vacuum sensor 8. On the basis of this, a delay treatment is carried out, in which the timing of the ignition of the spark plug ignition 17 is delayed until after the piston head 11 has reached top dead center (TDC) (hereinafter simply called "after TDC") during the passage of the

  compression time at motor stroke.

  In the following step S52, the target value of the device VVT is established. The target value of the VVT device is established, for example, at the overlap value at which the quantity of intake air or internal EGR gas becomes maximum,

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  in accordance with the engine speed. Figures 7 and 8 are graphs illustrating the fluctuations in the amount of internal EGR intake and recirculation air relative to the valve overlap value. As shown in FIG. 7, under a constant engine speed, there is a valve overlap value at which the quantity of intake air becomes maximum. If this value is set as the valve overlap value, the efficiency of the load is maximized. In addition, by delaying ignition, a ratio of secondary combustion is increased, and the temperature of the exhaust is raised, so as to facilitate early activation of a catalyst. Therefore, an emission of unburnt HC can be suppressed. At the same time, with respect to the amount of internal EGR gas as shown in Figure 8, there is also a valve overlap value at which the amount of internal EGR gas becomes maximum under constant engine speed. In this case, the valve overlap value with the maximum amount of intake air and the valve overlap value with the maximum internal EGR gas quantity may coincide with each other, but normally they take different values. If the valve overlap value with the maximum internal EGR gas quantity is selected, a fuel vaporization facilitation effect and an early cylinder temperature rise effect are maximized. Therefore, the combustion stability is maintained, and at the same time a reduction effect

  Black smoke emissions can be maximized.

  On the other hand, if the injection timing is established at the admission time during start-up in step S5, the processing proceeds to step S53 in which the ignition timing is established towards the angle side beforehand. Then, in step S54, as in step S6 shown in Fig. 3, the target value of the device VVT is established so that the overlap value is small. The order in this case is the same as the first order operation. This also applies

  when ordering at a time other than start-up.

  Here, the description has been given by taking an example from the

  case in which the target value of the VVT device is established at the valve overlap value at which the quantity

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  intake air or the amount of internal RGR gas is maximized based on the current engine speed. However, the target value of the VVT device can be established based on the value of the ignition delay angle. In this case, as shown in Figure 9, the valve overlap value is maximized when the value of the ignition delay angle AI takes a certain value AIth. When the value of the ignition delay angle AI is less than the certain value AIth, the value of valve overlap can be set larger when the value of the ignition delay angle increases, while when the value of the ignition delay angle AI is greater than the certain value AIth, the value of valve overlap can be set smaller when the value of the ignition delay angle increases. The larger the value of the ignition delay angle, the more easily the fuel adherence to the surface of the cylinder wall 10 takes place. Therefore, in an area where the value of the ignition delay angle is relatively small, increasing the valve overlap value when the value of the ignition delay angle increases, the amount of Internal EGR gas is increased and the temperature in the cylinder during fuel injection is raised, thus facilitating the vaporization of the fuel. As a result, the adhesion of the fuel to the surface of the wall of the cylinder 10 is suppressed, the stability of combustion is maintained and at the same time the generation of black smoke is suppressed. On the other hand, combustion tends to become more unstable as the value of the ignition delay angle is increased. In a region where combustion is unstable, the amount of internal EGR gas is reduced so as to improve the stability of combustion. The AIth value which is a threshold value is based on experimental and other data and can be stored in the engine ECU 3. In addition, it can be established during an operation based on the combustion condition (such as an air-fuel ratio of the exhaust gas and a variation of the speed).

  In the descriptions mentioned above, such as

  shown in Figure 2, an example of variation of

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  valve overlap by moving the valve lift curve to the side of the feed angle and the side of the angle

  delay without changing the shape of the curve is explained.

  However, for example, as shown in Figure 10, the cam 22 intended to open and close the exhaust valve 24 can be shaped to have a different cam shape in an axial direction so that the cam 22 has only a single cam head 22a in a first cross section and two cam heads 22a and 22b in another transverse section, so that the exhaust valve 24 is reopened while the intake valve 23 is open, as shown in Figure 11. Likewise, using this type of valve control device, valve overlap is increased to perform internal EGR recirculation. The cam 21 for opening and closing the intake valve 23 can be shaped so as to have two cam heads, so that the intake valve 23 is also open while the exhaust valve 24 is open. With this structure, by sliding the cam 21 or 22 in an axial direction of the camshaft, the valve overlap value can be changed, thus allowing the structure of the variable valve control device 2 to be simple and further improving the reliability of the device

variable valve control 2.

  It is obvious that a recirculation system which directly returns the burnt gas from the exhaust pipe 16 to the intake hose 15 can be provided in place of the control of the

  valve overlap value.

  As described above and in accordance with the embodiments mentioned above, the vaporization of the fuel is facilitated, and the interior of the cylinder rises quickly during cold start by injecting the fuel during the compression time and by introducing the gas. RGE. As a result, combustion is stabilized, the emission of black smoke and the downgrading of emission performance are suppressed and the fuel economy is improved. In addition, by delaying the ignition timing until after TDC, the early activation of the catalyst is obtained and the temperature rise performance is improved, thus allowing the suppression of degradation of the

emission performance.

Claims (16)

REVENDI CAT IONS   1. Internal combustion engine with spark ignition of the injection type in the cylinder comprising an exhaust gas recirculation system intended to reintroduce and cause a combustion gas to be driven into the cylinder (10), characterized in that: during a cold start, the exhaust gas recirculation system is implemented and fuel is supplied   to the cylinder (10) during a compression time.   2. Internal combustion engine according to claim 1, comprising means (3, 8) for determining a depression of the intake pipe, wherein the exhaust gas recirculation system is implemented when a depression of the intake pipe   determince is greater than or equal to a predetermined level.   Internal combustion engine according to claim 1 or 2, wherein the exhaust gas recirculation system is a variable valve control device (2) which adjusts a valve overlap value of a valve.   intake (23) and an exhaust valve (24).   4. Internal combustion engine according to claim 3, in which a variable rate of variation of the valve overlap is increased during cold start compared to other cases.   5. Internal combustion engine according to claim 3 or 4, wherein when either of the intake valve (23) or the exhaust valve (24) is open, the variable control device valves (2)   changes the lift stroke of the other valve.   6. Internal combustion engine according to any one of   Claims 1 to 5, in which during cold starting, a   ignition timing of a spark plug (17) is delayed   until after a piston reaches top dead center. 17 2838162   7. An internal combustion engine according to claim 6, wherein an operation of the exhaust gas recirculation system is controlled such that an amount of a recirculation gas is increased as the value of the stall delay of ignition is increased. 8. Internal combustion engine according to claim 7, wherein in an area where the value of the ignition timing delay is large and where it is expected that the combustion becomes unstable, the operation of the exhaust gas recirculation is controlled so that the amount of recirculation gas is reduced as the   ignition timing delay value is increased.   9. Control method for a spark-ignition internal combustion engine of the type injected into the cylinder comprising an exhaust gas recirculation system intended to reintroduce and circulate a combustion gas in the cylinder (10), characterized in that: during a cold start, the exhaust gas recirculation system is used and fuel is supplied   to the cylinder (10) during a compression time.   10. The control method according to claim 9, further comprising the step of determining a vacuum of the intake pipe, in which the exhaust gas recirculation system is implemented when a vacuum of the intake pipe admission   determined is greater than or equal to a predetermined level.   11. The control method according to claim 9 or 10, wherein the exhaust gas recirculation system is a variable valve control device (2) which adjusts a valve overlap value of an intake valve   (23) and an exhaust valve (24).   12. The control method as claimed in claim 11, in which a variable speed of variation of the valve overlap is increased during cold start compared to other cases. 1 8 2838162   13. The control method according to claim 11 or 12, wherein when either of the intake valve (23) or the exhaust valve (24) is open, the variable control device of valves (2) changes a lift stroke of the other valve. 14. Ordering method according to any one of   Claims 9 to 13, in which during cold starting, a   ignition timing of a spark plug (17) is delayed   until after a piston reaches top dead center.   15. The control method according to claim 14, wherein an operation of the exhaust gas recirculation system is controlled so that an amount of a recirculation gas is increased as a value of the delay of   ignition timing is increased.   16. The control method as claimed in claim 15, in which in a zone where the value of the ignition timing delay is large and where combustion is expected to become unstable, the operation of the recirculation system of exhaust gas is controlled so that the amount of recirculation gas is reduced as