JP4572827B2 - Combustion control device for internal combustion engine - Google Patents

Description

  The present invention relates to a combustion control device for an internal combustion engine.

  In an internal combustion engine equipped with an exhaust purification catalyst for purifying exhaust gas discharged from the combustion chamber in the exhaust passage, when the temperature of the exhaust purification catalyst has not reached its activation temperature, the temperature of the exhaust purification catalyst is raised to the activation temperature The technique to make is described in patent document 1. FIG. According to the technique described in Patent Document 1, in a spark ignition internal combustion engine having a fuel injection valve that directly injects fuel into a combustion chamber, fuel is injected twice from the fuel injection valve during one engine cycle. The lean fuel mixture is uniformly formed in the entire combustion chamber by the previous fuel injection, and the rich mixture is locally formed around the spark plug by the subsequent fuel injection, and the rich mixture is ignited.

  According to this, immediately after ignition, the rich air-fuel mixture formed around the spark plug burns at a time to obtain output from the internal combustion engine, and then the lean air-fuel mixture uniformly formed in the entire combustion chamber burns slowly. By doing so, the temperature of the gas in the combustion chamber is raised. The gas thus heated is discharged as exhaust gas from the combustion chamber and flows into the exhaust purification catalyst, so that the temperature of the exhaust purification catalyst is raised.

JP 2003-214235 A Japanese Patent Laid-Open No. 2004-28031 JP 2004-28046 A

  By the way, as described in Patent Document 1, when the temperature of the exhaust purification catalyst is raised by raising the temperature of the exhaust gas discharged from the combustion chamber and flowing this exhaust gas into the exhaust purification catalyst, If the amount of air sucked into the room (hereinafter referred to as “intake amount”) is increased and the amount of fuel injected into the combustion chamber (hereinafter referred to as “fuel injection amount”) is increased, the exhaust discharged from the combustion chamber Since the gas temperature can be further increased, the temperature of the exhaust purification catalyst can be increased to its activation temperature more quickly.

  However, simply increasing the intake air amount and increasing the fuel injection amount in an attempt to raise the temperature of the exhaust purification catalyst to its activation temperature earlier cannot satisfactorily meet other requirements for the internal combustion engine. There is a case. For example, if the fuel burns at once and the combustion temperature rises, the amount of nitrogen oxide (NOx) generated increases, and the engine speed cannot be kept constant due to excessive output. Here, if the timing of igniting the fuel is delayed, the output can be reduced, but in order to generate a constant output within a short combustion period, the peak of the combustion temperature must be increased, so the generation of NOx is suppressed. It is not possible.

  In any case, when increasing the intake air amount and increasing the fuel injection amount in order to raise the temperature of the exhaust purification catalyst to the activation temperature earlier, in order to satisfy various requirements for the internal combustion engine as well as possible, Special measures are required for the fuel injection form from the injection valve and the fuel combustion form. Also, when the intake air amount is increased and the fuel injection amount is increased to increase the temperature of the exhaust gas discharged from the combustion chamber for the purpose other than raising the temperature of the exhaust purification catalyst to the activation temperature earlier. In order to satisfy various requirements for the internal combustion engine as well as possible, special measures are required.

  An object of the present invention is to satisfy the requirements for an internal combustion engine as well as possible when increasing the intake air amount and increasing the fuel injection amount in order to increase the temperature of the exhaust gas discharged from the combustion chamber.

In order to solve the above problems, in the first invention, in an internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and an ignition plug that ignites the fuel, a temperature increase of the exhaust gas is required. During one engine cycle, fuel injection for engine output is performed such that fuel is injected from a fuel injection valve mainly to obtain output from an internal combustion engine, and the injected fuel is ignited by a spark plug to burn the fuel. In addition to performing combustion control, it is also used for raising the temperature of the exhaust gas that injects fuel from a fuel injection valve and burns the injected fuel in order to raise the temperature of the exhaust gas after execution of the fuel injection combustion control for engine output The fuel injection combustion control is performed immediately before the first fuel injection combustion control for raising the temperature of the exhaust gas, in which fuel is injected from a fuel injection valve and the injected fuel is ignited by a spark plug to burn the fuel. Fuel injection combustion control At least one of at least one of the fuel injection combustion control for raising the temperature of the second exhaust gas and injecting the fuel from the fuel injection valve at the timing of being ignited by the combustion heat of the burned fuel and burning the injected fuel. In a combustion control device that performs revolving, when the exhaust gas temperature rise is required , even if the amount of depression of the accelerator pedal is constant, the intake amount is increased by increasing the opening of the throttle valve, and the intake amount depending on, it increases the amount of fuel the total for injecting for heating the exhaust gas during the expansion stroke by increasing the number of times of the exhaust fuel injection combustion control for raising the temperature during the expansion stroke.

  In the second invention, in the first invention, the fuel injection timing in the exhaust gas temperature increase fuel injection combustion control increases as the amount of fuel injected per one time of the exhaust gas temperature increase fuel injection combustion control increases. Retard.

In the third aspect, in the first or second invention, the timing for injecting the fuel in the fuel injection combustion control for the exhaust gas Atsushi Nobori is a timing in the expansion stroke.

  In the fourth invention, in any one of the first to third inventions, the timing at which fuel is injected in the fuel injection fuel control for engine output is the timing during the compression stroke.

In the fifth aspect of the invention, in any one of the first to fourth aspects of the invention, when the fuel injection combustion control for raising the second exhaust gas temperature is performed, the fuel injection combustion control for raising the second exhaust gas temperature is performed. at substantially the same time the fuel if the timing for injecting fuel which fuel is injected is slower timing than the timing to start burning in.

  In a sixth aspect of the invention, in any one of the first to fifth aspects of the invention, when the fuel injection combustion control for increasing the temperature of the exhaust gas is performed a plurality of times during one engine cycle, the exhaust gas temperature rising performed sequentially in sequence. The amount of fuel injected in the fuel injection combustion control is increased.

7th In the invention, in any one of 1 to 6 th invention, the fuel injection combustion for the exhaust KiNoboru temperature by increasing the fuel injection number in the upper Symbol exhaust fuel injection combustion control once for heating The total amount of fuel injected per control is increased.

  In the eighth invention, in any one of the first to seventh inventions, the fuel injection valve is configured such that a part of the fuel injected from the fuel injection valve directly reaches the ignition electrode of the spark plug. .

  In a ninth invention, in any one of the first to eighth inventions, a catalyst for purifying exhaust gas is arranged in the exhaust passage.

  According to the present invention, when the intake air amount is increased and the fuel injection amount is increased to increase the temperature of the exhaust gas discharged from the combustion chamber, the demand for the stability of combustion in the internal combustion engine and the output of the internal combustion engine are increased. It is possible to satisfactorily satisfy the demands for the internal combustion engine, such as the demand for the amount of NOx (nitrogen oxide) generated in the internal combustion engine.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an internal combustion engine provided with the combustion control device of the present invention. In FIG. 1, 1 is a body of an internal combustion engine, 2 is a cylinder head, 3 is a cylinder block, 4 is a piston, 5 is a combustion chamber, 6 is a fuel injection valve, 7 is a spark plug, 8 is an intake valve, and 9 is an intake port. Reference numeral 10 denotes an exhaust valve, and 11 denotes an exhaust port. The fuel injection valve 6 directly supplies fuel to the combustion chamber 5 by directly injecting fuel into the combustion chamber 5.

  The intake port 9 is connected to the surge tank 13 via the intake pipe 12. The surge tank 13 is connected to an air cleaner 15 via an intake pipe 14. A throttle valve 16 for controlling the amount of air taken into the combustion chamber 5 is disposed in the intake pipe 14. The opening degree of the throttle valve 16 is controlled by the step motor 17. On the other hand, an exhaust pipe 18 is connected to the exhaust port 11. The exhaust pipe 18 is connected to a casing 20 that houses a three-way catalyst 19.

  The three-way catalyst 19 can purify carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in the exhaust gas when the temperature is higher than the activation temperature, When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is in the vicinity of the stoichiometric air-fuel ratio, CO, HC, and NOx can be simultaneously purified with a high purification rate.

  Incidentally, the fuel injected from the fuel injection valve 6 moves from the fuel injection valve 6 into the fuel chamber 5 along the conical wall surface 2a, as shown in FIG. That is, the fuel F injected from the fuel injection valve 6 forms a fuel spray that spreads in a hollow cone shape along a conical surface extending from the fuel injection valve 6. A part of the fuel spray injected from the fuel injection valve 6 directly reaches the ignition electrode 7 a of the spark plug 7. That is, the fuel injection valve 6 injects the fuel so that the ridgeline of the fuel spray spreading in a hollow conical shape overlaps the ignition electrode 7a. That is, before the fuel spray injected from the fuel injection valve 6 collides with the upper wall surface of the piston 4 or the cylinder bore wall defining the combustion chamber 5 or diffuses relatively uniformly into the fuel chamber 5, It reaches the ignition electrode 7a.

  When it is desired to ignite the fuel that has directly reached the ignition electrode 7a of the spark plug 7 from the fuel injection valve 6 and burn the fuel, the fuel is injected from the fuel injection valve 6 during the compression process or the expansion stroke. The fuel may be ignited by operating the spark plug 7 at the timing when the fuel injected from the valve 6 reaches the ignition electrode 7a (the combustion at this time can be said to be so-called stratified combustion). On the other hand, when it is desired to ignite the fuel injected from the fuel injection valve 6 and uniformly diffused into the combustion chamber 5 to burn the fuel, the fuel is injected from the fuel injection valve 6 during the intake stroke, and near the compression top dead center. The ignition plug 7 may be operated at the timing to ignite the fuel (combustion at this time can be said to be so-called homogeneous combustion).

  When the fuel directly reaching the ignition electrode 7a of the spark plug 7 is ignited from the fuel injection valve 6, the flame generated by the combustion of a part of the fuel reaching the ignition electrode 7a propagates to the remaining fuel. The entire fuel is burned.

  By the way, immediately after the internal combustion engine is started, in many cases, the temperature of the three-way catalyst 19 is lower than its activation temperature. In this case, the three-way catalyst 19 cannot purify CO, HC, and NOx with a high purification rate even if the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 19 is the stoichiometric air-fuel ratio. Therefore, in order for the three-way catalyst to purify these CO, HC, and NOx with a high purification rate, the temperature of the three-way catalyst needs to reach its activation temperature at an early stage. Therefore, in the present embodiment, after the internal combustion engine is started, the temperature of the exhaust gas discharged from the combustion chamber 5 is increased as follows, so that the temperature of the three-way catalyst is quickly brought to its activation temperature. To reach.

  That is, in this embodiment, after starting the internal combustion engine, during one engine cycle, the fuel is injected from the fuel injection valve 6 immediately before the compression top dead center in order to obtain output mainly from the internal combustion engine. In addition to performing control (hereinafter referred to as “main injection combustion control”) of igniting the fuel by activating the spark plug at the timing when it reaches the ignition electrode 7a of the spark plug 7 (hereinafter referred to as “main injection combustion control”), During the expansion stroke after execution, control is performed to inject fuel from the fuel injection valve in order to raise the temperature of the exhaust gas and burn the injected fuel (hereinafter referred to as “sub-injection combustion control”). According to this, since the temperature of the exhaust gas is raised by the sub-injection combustion control, the temperature of the three-way catalyst is forcibly raised, and as a result, the temperature of the three-way catalyst reaches its activation temperature early. It will be.

  By the way, the temperature of the exhaust gas increases as the total amount of fuel combusted by the sub-injection combustion control described above increases. Therefore, in order to make the temperature of the three-way catalyst 19 reach its activation temperature faster, it is preferable to increase the total amount of fuel burned by the sub-injection combustion control. And in order to burn more fuel, more air is required. Therefore, in the present embodiment, when the main injection combustion control and the sub injection combustion control are performed in one engine cycle after the internal combustion engine is started, the opening degree of the throttle valve 16 is maintained even if the accelerator pedal depression amount is constant. By gradually increasing (hereinafter referred to as “throttle opening”), the amount of air taken into the combustion chamber (hereinafter referred to as “intake amount”) is gradually increased, and during one engine cycle according to the intake amount. Gradually increase the total amount of fuel burned by the sub-injection combustion control. According to this, the temperature of the exhaust gas is further increased by the sub-injection combustion control, so that the temperature of the three-way catalyst reaches its activation temperature earlier.

  By the way, various means can be considered as means for increasing the total amount of fuel burned by the sub-injection combustion control during one engine cycle. In the present embodiment, either of the following two means is adopted. That is, the first means is to increase the number of times of performing the sub-injection combustion control during one engine cycle as the intake air amount increases. In this case, the amount of fuel injected in each sub-injection combustion control performed during one engine cycle may be the same or different, but in any case, the sub-injection combustion control is performed during one engine cycle. The fuel amount to be injected in each sub-injection combustion control is set so that the total fuel amount combusted by the sub-injection combustion control during one engine cycle increases as the number of times of performing is increased.

  In general, the more the fuel is burned at a timing near the compression top dead center, the greater the proportion of the combustion that contributes to the output of the internal combustion engine, and the smaller the proportion that the combustion contributes to the temperature rise of the exhaust gas. . Therefore, from the viewpoint of increasing the rate at which combustion contributes to the temperature rise of the exhaust gas as much as possible, it is preferable to reduce the amount of fuel to be burned as the sub-injection combustion control is performed at a timing close to the compression top dead center. Therefore, from this point of view, when the amount of fuel injected in each sub-injection combustion control during one engine cycle is set to a different amount, it is preferable to increase the amount of fuel injected in order in the subsequent sub-injection combustion control. .

  On the other hand, the second means for increasing the total amount of fuel burned by the sub-injection combustion control during one engine cycle is a single sub-injection combustion control performed during one engine cycle. This is to increase the amount of fuel injected in the injection combustion control. As described above, the more the fuel is burned at the timing close to the compression top dead center, the smaller the proportion of the combustion contributing to the temperature rise of the exhaust gas. It is preferable to delay the fuel injection timing as the amount of fuel injected in the control increases.

  In this second means, in order to increase the amount of fuel to be injected, it is only necessary to lengthen the time for opening the fuel injection valve. Instead, a plurality of fuel injections are performed within a very short time. By performing this, the number of fuel injections per unit time in one sub-injection combustion control may be increased.

  In the present embodiment, either of the following two means is employed as the means for burning the fuel by each sub-injection combustion control. That is, the first means operates the ignition plug when the fuel injected in each sub-injection combustion control reaches the ignition electrode 7a of the ignition plug 7, and ignites the fuel by the ignition electrode to burn the fuel. That's it. The second means is the timing at which the fuel is injected in each sub-injection combustion control, the timing at which the fuel is ignited by the combustion heat of the fuel burned by the main injection combustion control or the sub-injection combustion control performed immediately before. It is means that.

  In the second means, it is preferable that the timing at which the fuel is injected in each sub-injection combustion control is set to be a timing that is later than the timing at which the fuel starts to burn almost simultaneously with the fuel being injected. According to this, since the combustion of the fuel is performed relatively slowly, the combustion temperature (particularly its peak temperature) is suppressed to a relatively low level, so that the generation of NOx (nitrogen oxide) in the combustion chamber is suppressed. The Further, since the fuel is burned relatively slowly, the generation of noise due to the combustion is suppressed.

  FIG. 3 shows a case in which, in order to raise the temperature of the exhaust gas, in addition to performing the main injection combustion control during one engine cycle, the sub injection combustion control is performed a plurality of times from the fuel injection valve in each sub injection combustion control. An example is shown in which means for operating the ignition plug when the injected fuel reaches the ignition electrode of the ignition plug and igniting the fuel by the ignition electrode to burn the fuel is shown.

  In FIG. 3, (A) to (D) respectively indicate injection combustion control during one engine cycle, and each engine cycle is performed in order from (A) to (D). In FIG. 3, TDC indicates a compression top dead center, BDC1 indicates an intake bottom dead center, and BDC2 indicates an expansion bottom dead center.

  In the first engine cycle shown in FIG. 3A, fuel is injected immediately before the compression top dead center in order to obtain the output of the internal combustion engine (Fm in the figure), and the injected fuel is a spark plug. When the ignition electrode is reached, the ignition plug is operated (Im in the figure) to perform main injection combustion control for burning the fuel. Then, in the next engine cycle shown in FIG. 3B, the same main injection combustion control as above is performed, and fuel is injected to raise the temperature of the exhaust gas during the subsequent expansion stroke (in the figure). , Fs), and when the injected fuel reaches the ignition electrode of the spark plug, the spark plug is operated (Is in the figure) to perform the sub-injection combustion control for burning the fuel once. In the further next engine cycle shown in FIG. 3C, the same main injection combustion control as above is performed, and the same sub injection combustion control as above is performed twice during the subsequent expansion stroke. In the further next engine cycle shown in FIG. 3D, the same main injection combustion control as above is performed, and the same sub injection combustion control as above is performed three times during the subsequent expansion stroke.

  FIG. 4 shows the fuel injection in each sub-injection combustion control when the sub-injection combustion control is performed once in addition to performing the main injection combustion control during one engine cycle in order to raise the temperature of the exhaust gas. An example is shown in which means for operating the ignition plug when the fuel injected from the valve reaches the ignition electrode of the ignition plug and igniting the fuel by the ignition electrode to burn the fuel is shown.

  Also in FIG. 4, (A) to (D) respectively show injection combustion control in one engine cycle, and each engine cycle is performed in order from (A) to (D), and (A) In FIG. 3, TDC indicates compression top dead center, BDC1 indicates intake bottom dead center, and BDC2 indicates expansion bottom dead center. .

  In the first engine cycle shown in FIG. 4A, in order to obtain the output of the internal combustion engine, fuel is injected immediately before the compression top dead center (Fm in the figure), and the injected fuel is a spark plug. When the ignition electrode is reached, the ignition plug is operated (Im in the figure) to perform main injection combustion control for burning the fuel. In the next engine cycle shown in FIG. 4B, the same main injection combustion control as above is performed, and the exhaust gas at a predetermined timing (hereinafter referred to as “first timing”) during the subsequent expansion stroke. A predetermined amount (hereinafter referred to as “first amount”) of fuel is injected (Fs in the figure) to increase the temperature of the spark plug, and when the injected fuel reaches the ignition electrode of the spark plug, The sub-injection combustion control is performed once (Is in the figure) to burn the fuel. In the further next engine cycle shown in FIG. 4C, the same main injection combustion control as above is performed, and the timing is later than the first timing (hereinafter referred to as “second timing”). The same sub-injection combustion control as the above is performed once except that the fuel of the amount larger than the first amount (hereinafter referred to as “second amount”) is injected. In the further next engine cycle shown in FIG. 4D, the same main injection combustion control as above is performed, and the amount of fuel larger than the second amount at a timing later than the second timing. The same sub-injection combustion control as above is performed except for injecting.

  FIG. 5 shows the fuel injection in each sub-injection combustion control when the sub-injection combustion control is performed a plurality of times in addition to performing the main injection combustion control during one engine cycle in order to raise the temperature of the exhaust gas. The fuel is burned in the sub-injection combustion control by setting the timing of injecting the fuel from the valve to the timing of being ignited by the combustion heat of the fuel burned by the main injection combustion control or the sub-injection combustion control performed immediately before. The example which employ | adopted the means is shown.

  In FIG. 5, (A) to (D) respectively indicate injection combustion control in one engine cycle, and each engine cycle is performed in order from (A) to (D). In FIG. 3, TDC indicates a compression top dead center, BDC1 indicates an intake bottom dead center, and BDC2 indicates an expansion bottom dead center.

  In the first engine cycle shown in FIG. 5 (A), fuel is injected immediately before the compression top dead center in order to obtain the output of the internal combustion engine (Fm in the figure), and the injected fuel is a spark plug. When the ignition electrode is reached, the ignition plug is operated (Im in the figure) to perform main injection combustion control for burning the fuel. Then, in the next engine cycle shown in FIG. 5B, the same main injection combustion control as above is performed, and during the subsequent expansion stroke, the fuel is burned by the combustion heat of the fuel burned by the main injection combustion control. Sub-injection combustion control is performed once by injecting fuel at the timing when is ignited (Fs in the figure). In the next engine cycle shown in FIG. 5 (C), the same main injection combustion control as above is performed, and during the subsequent expansion stroke, the same sub injection combustion control as above is performed. The sub-injection combustion control is performed by injecting the fuel at the timing when the fuel is ignited by the combustion heat of the fuel combusted by the injection combustion control (Fs in the figure). In the next engine cycle shown in FIG. 5 (D), the same main injection combustion control as above is performed, and during the subsequent expansion stroke, the same two sub-injection combustion controls as above are performed. Then, the fuel is injected at the timing when the fuel is ignited by the combustion heat of the fuel burned by the final sub-injection combustion control (Fs in the figure), and the sub-injection combustion control is performed.

  FIG. 6 shows the fuel injection in each sub-injection combustion control when the sub-injection combustion control is performed once in addition to performing the main injection combustion control in one engine cycle in order to raise the temperature of the exhaust gas. The fuel is burned in the sub-injection combustion control by setting the timing of injecting the fuel from the valve to the timing of being ignited by the combustion heat of the fuel burned by the main injection combustion control or the sub-injection combustion control performed immediately before. The example which employ | adopted the means is shown.

  In FIG. 6, (A) to (D) respectively show injection combustion control during one engine cycle, and each engine cycle is performed in order from (A) to (D). In FIG. 6, TDC indicates a compression top dead center, BDC 1 indicates an intake bottom dead center, and BDC 2 indicates an expansion bottom dead center.

  In the first engine cycle shown in FIG. 6A, fuel is injected immediately before the compression top dead center in order to obtain the output of the internal combustion engine (Fm in the figure), and the injected fuel is a spark plug. When the ignition electrode is reached, the ignition plug is operated (Im in the figure) to perform main injection combustion control for burning the fuel. Then, in the next engine cycle shown in FIG. 6 (B), the same main injection combustion control as above is performed, and during the subsequent expansion stroke, the fuel is burned by the combustion heat of the fuel burned by the main injection combustion control. Is injected at a timing (hereinafter referred to as “first timing”) to inject a predetermined amount of fuel (hereinafter referred to as “first amount”) to increase the temperature of exhaust gas (Fs in the figure). Combustion control is performed once. In the next engine cycle shown in FIG. 6 (C), the same main injection combustion control as above is performed, and during the subsequent expansion stroke, the combustion heat of the fuel burned by the main injection combustion control is used. In order to raise the temperature of the exhaust gas at a timing when the fuel is ignited and later than the first timing (hereinafter referred to as “second timing”), an amount larger than the first amount (hereinafter referred to as “the second timing”). Sub-injection combustion control is performed once (in the figure, Fs). In the next engine cycle shown in FIG. 6D, the same main injection combustion control as above is performed, and during the subsequent expansion stroke, the combustion heat of the fuel burned by the main injection combustion control is used. Sub-injection combustion control for injecting a larger amount of fuel than the second amount is performed once at a timing when the fuel is ignited and later than the second timing.

  Further, in the example shown in FIG. 3, so-called pilot injection may be performed in which a small amount of fuel is injected before performing main injection combustion control in each engine cycle. An example of this is shown in FIG. In FIG. 7, the injection indicated by the symbol Fp is pilot injection.

  FIG. 8 shows a time chart showing a time transition such as the throttle opening when the temperature of the exhaust gas is raised according to the present invention after the internal combustion engine is started. In FIG. 8, (A) shows the throttle opening, (B) shows the intake air amount, (C) shows the fuel amount (main injection amount) injected in the main injection combustion control, and (D) shows sub-injection. The total fuel amount (sub injection amount) injected in the combustion control is shown, and (E) shows the engine speed.

  In the example shown in FIG. 8, time T0 is the time when the internal combustion engine is started. When trying to start the internal combustion engine at time T0, the throttle valve is opened and a certain amount of air is sucked into the combustion chamber, the main injection combustion control is performed, the sub injection combustion control is performed, and the engine speed is increased. To rise. Then, after the main injection amount is once reduced at time T1, the throttle opening is gradually increased and the intake air amount is gradually increased from time T2. As the intake air amount increases, the auxiliary injection amount is increased.

  At time T3, when the throttle opening is constant and the intake air amount is constant, the sub-injection amount is also constant.

  In addition, according to this invention, the following advantages are also acquired. That is, conventionally, as a method for raising the temperature of exhaust gas, there is known a method for retarding (retarding) the timing of igniting the fuel supplied to the combustion chamber in order to drive the internal combustion engine. As a result, the combustion of the fuel becomes unstable, and the output of the internal combustion engine becomes smaller than the required value. However, according to the present invention, it is not necessary to retard the timing for igniting the fuel supplied to the combustion chamber in order to obtain output from the internal combustion engine when trying to raise the temperature of the exhaust gas. The combustion of the engine does not become unstable, and the output of the internal combustion engine does not become smaller than the required value.

  Further, in the past, when retarding the timing for igniting the fuel, if the intake air amount is increased and the amount of fuel supplied to the combustion chamber is increased in order to make the output of the internal combustion engine the required value, FIG. ), A state in which the pressure in the combustion chamber (hereinafter referred to as “in-cylinder pressure”) Pc is very high occurs after the compression top dead center TDC. For this reason, as indicated by the symbol Y in FIG. 9B, the temperature in the combustion chamber (hereinafter referred to as “in-cylinder temperature”) Tc may generate a large amount of NOx (nitrogen oxide) in the combustion chamber. There is a problem in that the amount of NOx (nitrogen oxide) generated in the combustion chamber increases beyond a certain temperature Tnox.

However, according to the present invention, even if the intake air amount is increased and the amount of fuel injected into the combustion chamber is increased, the fuel is injected in a plurality of times , so as shown in FIG. Therefore, the in-cylinder pressure Pc is not very high. Therefore, as shown in FIG. 9D, the in-cylinder temperature Tc is a temperature Tnox at which a large amount of NOx may be generated in the combustion chamber. It will not exceed.

  In the above-described embodiment, in the main injection combustion control, the timing for injecting the fuel is set immediately before the compression top dead center, and the timing for igniting the fuel is the timing at which the injected fuel reaches the ignition electrode 7a of the spark plug 7 However, the fuel injection timing may be set as the timing during the intake stroke, and the fuel ignition timing may be set near the compression top dead center.

  Further, in the above description, the embodiment in which the present invention is applied when the temperature of the exhaust gas is increased in order to increase the temperature of the three-way catalyst after the internal combustion engine is started is described. However, the temperature of the three-way catalyst is increased. In addition to this, the present invention can be applied to the case where the temperature of the exhaust gas is raised.

  In the above description, the present invention has been described by taking as an example the case where the temperature of the three-way catalyst reaches the activation temperature early after the internal combustion engine is started, but the temperature of the three-way catalyst is not required after the internal combustion engine is started. The present invention can also be applied to the case where the temperature of the three-way catalyst is raised to the activation temperature when the temperature does not reach the activation temperature.

  Further, in the above description, the present invention has been described by taking as an example the case where the temperature of the three-way catalyst reaches the activation temperature early, but not only for the purpose of causing the temperature of the three-way catalyst to reach the activation temperature early. The present invention can also be used to raise the temperature of the exhaust gas for the purpose.

It is a figure which shows the internal combustion engine provided with the control apparatus of this invention. It is a figure which shows the structure around the fuel injection valve of the internal combustion engine shown in FIG. It is a figure which shows an example of the injection combustion control according to this invention. It is a figure which shows another example of the injection combustion control according to this invention. It is a figure which shows another example of the injection combustion control according to this invention. It is a figure which shows another example of the injection combustion control according to this invention. It is a figure which shows another example of the injection combustion control according to this invention. It is a figure which shows a time chart of an example of time transitions, such as throttle opening, when injection combustion control is performed according to this invention. It is a figure which shows the in-cylinder pressure and in-cylinder temperature when the conventional injection combustion control is performed, and the in-cylinder pressure and the in-cylinder temperature when the injection combustion control is performed according to the present invention.

Explanation of symbols

5 Combustion chamber 6 Fuel injection valve 7 Spark plug 7a Ignition electrode 19 Three-way catalyst

Claims (9)

In an internal combustion engine having a fuel injection valve for directly injecting fuel into a cylinder and an ignition plug for igniting the fuel, when temperature rise of the exhaust gas is required, it is mainly output from the internal combustion engine during one engine cycle In addition to performing fuel injection combustion control for engine output in which fuel is injected from a fuel injection valve and the injected fuel is ignited by a spark plug to burn the fuel, fuel injection for engine output As fuel injection combustion control for raising the temperature of exhaust gas, fuel is injected from the fuel injection valve to increase the temperature of the exhaust gas after the combustion control is performed, and the fuel is injected from the fuel injection valve. The first fuel injection combustion control for raising the temperature of the exhaust gas in which the injected fuel is ignited by the spark plug and combusted, and the combustion heat of the fuel combusted by the fuel injection combustion control performed immediately before Ignited by In a combustion control device that performs at least one of fuel injection combustion control for increasing the temperature of a second exhaust gas by injecting fuel from a fuel injection valve at a desired timing and combusting the injected fuel, Even when the amount of depression of the accelerator pedal is constant when temperature rise is required , the intake amount is increased by increasing the opening of the throttle valve , and the exhaust gas is increased during the expansion stroke according to the intake amount. combustion control device comprising a Turkey to increase the amount of fuel the total for injecting for heating the exhaust gas during the expansion stroke by increasing the number of times of performing fuel injection combustion control for temperature.   2. The timing for injecting fuel in the fuel injection combustion control for exhaust gas temperature increase is retarded as the amount of fuel injected per one time of the fuel injection combustion control for exhaust gas temperature increase increases. The combustion control apparatus described in 1. The combustion control device according to claim 1 or 2 , wherein the timing of injecting fuel in the fuel injection combustion control for raising the temperature of the exhaust gas is a timing during an expansion stroke.   The combustion control device according to any one of claims 1 to 3, wherein the timing of injecting fuel in the fuel injection fuel control for engine output is a timing during a compression stroke. At substantially the same time the fuel if the timing for injecting the fuel in the fuel injection combustion control for exhaust gas Atsushi Nobori of said second fuel is injected when the fuel injection combustion control of the second exhaust Atsushi Nobori is carried out The combustion control device according to any one of claims 1 to 4, wherein the timing is later than a timing at which combustion starts.   When the fuel injection combustion control for raising the temperature of the exhaust gas is performed a plurality of times during one engine cycle, the amount of fuel injected in the fuel injection combustion control for raising the temperature of the exhaust gas is increased in sequence. The combustion control device according to any one of claims 1 to 5. Characterized by increasing the fuel quantity total which injects per fuel injection combustion control once for exhaust KiNoboru temperature by increasing the fuel injection number in the upper Symbol exhaust fuel injection combustion control once for heating The combustion control device according to any one of claims 1 to 6.   The combustion according to any one of claims 1 to 7, wherein the fuel injection valve is configured such that a part of the fuel injected from the fuel injection valve directly reaches the ignition electrode of the spark plug. Control device.   The combustion control apparatus according to any one of claims 1 to 8, wherein a catalyst for purifying exhaust gas is disposed in the exhaust passage.

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